Bulkfill Resin Composite Polymerization Efficiency by Monowave vs. Polywave Light Curing Units: A Systematic Review of In Vitro Studies

Featured Application

Polywave light curing units (LCUs) do not seem to present a significant advantage in polymerization of bulk fill resin composites, compared to monowave LCUs, when cured up to a depth of 4 mm. Therefore, the use of a monowave LCU with a power of at least 1000 mW/cm² can adequately cure Bulk Fill resin composites.

Abstract

Objective: This systematic review aimed to analyze if polywave light curing units can polymerize Bulk Fill resin composites better than monowave. Materials and methods: Inclusion criteria were in vitro studies that evaluated the polymerization of Bulk Fill resin composites by monowave and/or polywave light curing units. Selection of studies, data extraction, and risk-of-bias analysis were performed. Data from selected studies were qualitatively analyzed. A systematic search was performed in May 2025 using PubMed/Medline, EBSCO/Medline, Scopus, and ISI Web of Science databases and grey literature in English, and 788 studies were found. Results: A total of 65 studies were included in the qualitative analysis. Seventeen of them were investigating both monowave and polywave light-curing units for the polymerization of Bulk Fill resin composites. The evidence was graded as medium quality due to the medium risk of bias for most studies. Polywave LED LCUs improved the microhardness ratio, or DC, of Bulk Fill resin composite compared to monowave in 3 of the included studies, while 3 studies revealed that monowave LED LCUs demonstrated a favorable microhardness ratio, or DC, compared to polywave, and the rest of the 11 studies presented material-dependent results. Due to the heterogeneity of the studies included, a meta-analysis was not performed. Conclusion: The existing studies, with their limitations, revealed that polywave light curing units do not seem to have an advantage over monowave in the polymerization of Bulk Fill resin composites.

1. Introduction

Resin composites have been effectively used in esthetic restoration of anterior and posterior teeth for many decades. Historically, 1,7,7-trimethylbicyclo-[2.2.1]-hepta-2,3-dione and a tertiary amine, known as camphorquinone (CQ), have been the primary photoinitiator system used in light-cured resin composites, with CQ exhibiting an absorption peak around 460 nm in the blue light spectrum. However, CQs yellow color limits its use in highly aesthetic applications, prompting the introduction of alternative systems based on Norrish type I initiators such as acyl phosphonates, acylphosphine oxides, and bisacylphosphine oxides, namely the 1-phenyl-1,2-propanedione or phenylpropanedione (PPD), bisacylphosphine oxide (BAPO), monoacylphosphine oxide (MAPO), ethyl 4-dimethylaminobenzoate, diphenyl(2,4,6-trimethylbenzoyl)-phosphine or Lucirin-TPO (TPO), and Bis(4-methoxybenzoyl)diethylgermanium (Ivocerin), which absorb light in the violet or ultraviolet B (UVB) range. Ivocerin is excited in a broader spectrum from violet (390 nm) up to 445 nm with a peak at 418 nm. Ivocerin is a more efficient photoinitiator and does not need a co-initiator in order to be excited. While halogen and plasma arc LCUs, which emit a broad spectrum of light between 375 nm and 510 nm, can effectively cure resins containing these photoinitiators, they present drawbacks such as decreased irradiance over time, heat generation, and short bulb lifespan. To address these issues, light-emitting diode (LED) LCUs were developed, offering narrow-spectrum emission in the blue region (theoretically 450–470 nm, but usually in a broader spectrum of 420–540 nm) with high radiant power, effectively polymerizing resin composites containing CQ as the sole photoinitiator. However, the efficacy of single-peak LED LCUs is limited for resin composites with additional photoinitiators like PPD, TPO, and dibenzoyl germanium derivative or Ivocerin, as they require broader spectrum light for activation. Unfortunately, manufacturers often provide limited information on the photoinitiators used in their composite formulations, complicating the choice of optimal curing light [1].

Mechanical properties, as well as biocompatibility of resin composites depend on ex-tent of polymerization. In order to evaluate resin composite polymerization, direct and in-direct methods are employed. Direct techniques (FTIR, Raman spectroscopy) measure the amount of double bond bonds elimination, due to reaction among macromolecules, lead-ing to higher crosslinking, and investigate are investigating characteristic absorbance bands [2]. On indirect methods include the other hand, measurement of the bottom to top microhardness ratio, or depth of cure according to ISO 4049 [3]. Microhardness ratio gives an insight into of the mechanical property of hardness in top and bottom surfaces, and there-by characterizes the materials tested according to the elimination of this mechanical property at the bottom of the irradiated specimens [2]. Raman spectroscopy is a near-Depth of cure according to ISO 4049 [3] is performed by scraping away the uncured and inadequately cured material at the bottom of the specimen and then dividing the remaining cured depth by two. Raman spectroscopy is near infrared spectroscopy method, while FTIR is a mid-infrared spectroscopy method [2]. These methods can directly provide the concentration of reactive groups associated with a polymerization process [2]. The FTIR technique relies on light absorption, and contains several fundamental absorbance bands associated with the carbon–carbon double bond in methacrylate monomers [2]. Raman analyses involve wavelength-dependent light scattering, and evaluate evaluates changes in the wavelength of the incident light as a result of its interaction with the rotational and vibrational energy levels in molecules, including vinyl groups, as well as other reactive functionality in monomers [2].

The advent of polywave LED LCUs aimed to overcome these limitations by emitting both blue light and violet/UVB light to activate multiple photoinitiators. In the systematic review of Francis et al. [4], it was concluded that high light intensity can enhance the hardness of resin composites. From the systematic review by Correa et al. [5], it was postulated that polywave LED devices improve the degree of conversion (DC) of resin composites compared to monowave LED LCUs. Lima et al. [6], in a systematic review, reported that polywave light-emitting diodes maximize activation, resulting in a higher degree of double-bond conversion and microhardness of resin composites containing alternative photoinitiators.

Bulk fill resin composites represent a significant advancement, allowing placement in thicker increments (up to 4 mm) without compromising DC, polymerization shrinkage, or marginal adaptation. Bulk fill composites can be adequately cured up to 4 mm due to the reduction in percentage of filler by volume, the incorporation of larger fillers [7], and a reduction in color pigments in order to become more translucent [8], which leads to a higher depth of cure by increasing translucency. As a result, older products displayed an unpleasant grayish shade. Newer materials demonstrate lower translucency attributed to the addition of a more efficient germanium-based photoinitiator [9] or to a different polymerization mechanism, the reversible addition-fragmentation chain transfer polymerization that is less dependent on diminished translucency [10]. Veloso et al. [11] reported that bulk-fill restorations exhibit failure rates of 5.57%, compared to 3.32% for regular composite resins in a meta-analysis of controlled clinical trials over a period of up to 6 years, and most prevalent reason for failure was material fracture. From another meta-analysis of clinical trials of up to 5 years by Loguercio et al., bulk-fill restorations exhibited similar performance to those placed with the incremental filling [12]. Recently, new bulk-fill materials have been introduced that follow the universal chromatic concept, and therefore, the shade selection can be skipped.

From two systematic reviews [13,14], it is demonstrated that most bulk-fill composites can be adequately cured up to a depth of 4 mm and that flowable bulk-fill composites perform better than high-viscosity ones. Newer Bulk Fill resin composites have been introduced, containing CQ and Ivocerin but not TPO, and therefore a new systematic review may lead to a different conclusion than the previous [6].

The aim of this systematic review was to determine the potential advantage of the use of polywave light-curing compared to monowave light-curing units in the mechanical properties of bulk-fill composite resins by means of depth of cure or degree of conversion.

2. Materials and Methods

A systematic review was conducted according to the PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) [15,16] and the Cochrane Handbook for Systematic Reviews [17]. The research question (intervention) according to the PICO for the development of the study was, “Does the use of polywave light curing units improve the physical mechanical properties (degree of conversion and microhardness) of bulk fill resin composites?” Bulk fill resin composites were the population, monowave LCUs are the comparison (control), and the degree of conversion or depth of cure was the outcome. A full protocol was previously registered on OSF (Open Science Framework Protocols.io, Washington, DC, USA), receiving the protocol number, which can be found at https://osf.io/6z498/overview (accessed on 20 October 2025).

2.1. Sources and Search Strategy

MEDLINE PubMed, ISI Web of Science, Scopus, and EBSCO/Medline electronic databases were searched to identify studies that could be considered. The Cochrane Library was not searched because in this database, controlled clinical trials are mainly found, while this review was focused on laboratory studies. In the PubMed database, the following search strategy was employed. ((((((composite resin [MeSH Terms]) AND (Bulk Fill)) OR (Bulk Fill)) AND (light curing unit)) AND (polymerization)) AND (monowave)) OR (polywave). Filters used, was English language, and the publication dates 2012–2025 May In Web of Science database text words “ bulk fill composite,” “bulk-fill (All Fields) or bulk fill composite,” “(All Fields) and polywave light curing units,” “(All Fields) and poly wave light curing units,” “(All Fields) or polywave light curing,” “(All Fields) or poly wave light curing,” “(All Fields) or multi wave light cur-ing (All Fields) or multiwave light curing,” “multiwave light curing,” or “multi-peak light curing” were used. In the Web of Science database, text words: (All Fields) and depth of cure (All Fields) and degree of conversion (All Fields) and Dentistry Oral Surgery Medi-cine (Web of Science Categories) and Dentistry Oral Surgery Medicine (Web of Science Categories) bulk fill resin composite (All Fields) or bulkfill resin composite (All Fields) and polywave light curing units (All Fields) and poly wave light curing units (All Fields) or polywave light curing (All Fields) or poly wave light curing (All Fields) or multiwave light curing (All Fields) or multiwave light curing (All Fields) and Article (Document Types) and Dentistry Oral Surgery Medicine (Web of Science Categories). In the Scopus database, the following text words were used: (ALL (bulk AND fill AND composite) AND ALL (polywave AND light AND curing)). In the EBSCO database, text, bulk-fill composites, and LED light were used. No filter or limits were used.

In all databases, the search was performed in all fields in order to detect potential “grey literature”, which is often used to refer to reports published outside of traditional commercial publishing, such as dissertations and conference abstracts. Hand searches were also performed in the reference lists of the included studies.

Additionally, a search was performed for theses retrieval from the following web pages: Grey.cda-amc.ca, oatd.org (Open access theses and dissertations) and the EBSCOhost opendissertations.org. The search was limited to 5 last years. English language and the department of Materials Science and Engineering were selected.

The search was performed until May 2025. Duplicate records from the four databases were then eliminated with the use of Zotero 6 software (Zotero.org).

2.2. Selection, Inclusion, and Exclusion Criteria

Initially, titles and abstracts were reviewed independently by two authors (ST and KM) and selected, according to their consensus, for further assessment considering the following inclusion criteria: In vitro studies of bulk fill resin composites light cured by monowave or polywave LCUs, evaluating the depth of cure by microhardness or degree of conversion at the 4 mm depth. If consensus was not reached, the abstract was set aside for further evaluation. The references of all selected studies were manually searched for further relevant studies that could fulfill the inclusion criteria. The full texts of all studies that fulfilled the inclusion criteria for eligible papers were then reviewed independently by two authors (ST and KM) considering the exclusion criteria. In vitro studies evaluating the polymerization efficiency of bulk fill resin composites by means of direct measurement (Fourier transform infrared spectroscopy or micro-Raman spectroscopy) of the degree of conversion of double bonds (DC) of the bottom 4 mm-depth surface of composite resins or indirect measurement of the bottom-to-top microhardness ratio (Knoop or Vickers Hardness), up to the depth of 4 mm from the irradiation surface, were selected. Thereby at the title and abstract screening, clinical trials, studies referring to heat development, dentine bonding agents, composites other than Bulk Fill, studies on light transmission through material such as ceramic, marginal adaptation, cytotoxicity, water sorption, solubility, case reports, reviews, and systematic reviews, and conference papers, were excluded. At the full text screening, studies that evaluated top surface DC, or microhardness only in top or bottom surfaces, were excluded. Studies investigating the polymerization immediately after curing, or 24 h later or more, considering post-curing, were included. The irradiation time and LCU radiant exitance should comply with manufacturers’ instructions, and thereby studies that evaluated the polymerization of bulk fill resin composites with the use of a monowave or polywave LCU and a radiant exitance of around 1000 mw/cm², as well as 10 s, 20 s, or more, were included. Studies with high-power LCUs were included only if the radiant exposure was homogenized in terms of irradiance multiplied by time. Studies evaluating polymerization from a distance between the polymerization tip and the composite surface were excluded. Studies that did not evaluate bulk fill composites or evaluated properties other than depth of cure by microhardness or degree of conversion at the 4 mm depth were excluded. Studies evaluating depth of cure exclusively by ISO 4049 [3] were excluded. Studies investigating other mechanical properties than degree of cure or bottom/top microhardness evaluation; reports evaluating materials other than bulk fill; studies in which the time of irradiance was not reported or with incomplete descriptions of LCU characteristics, depth of cure less than 4 mm, or distance from the LCU tip more than 0 mm; studies considering only high irradiance for a very short time; and studies without exact descriptions of means but only depicted in figures were excluded. Any disagreements in the eligibility criteria were solved by discussion and consensus with a third reviewer (EP). The eligibility of studies between the authors showed a substantial agreement between the authors, with a kappa score of 0.84.

2.3. Data Extraction

Two authors (ST and KM) performed the data extraction by means of a standardized sheet in Microsoft Office Excel 2013 (Microsoft Corporation, Redmond, WA, USA). A protocol for data extraction was defined: the authors categorized similar information into groups according to the main outcomes of interest. For each paper, the following data were systematically extracted: First author last name, publication year, DC evaluation method, light curing protocol (including LED curing units, total energy or irradiance, and curing time), number of specimens per experimental group, resin composite description, and a brief statement on the results. The mean values of DC, or the bottom/top microhardness ratio, and the standard deviation for each material were listed. Wherever bottom-to-top microhardness ratios were not reported, but only the bottom and top microhardness values were, the ratio was computed and listed. When DC or microhardness ratios were not explicitly reported in the text or tables but only in charts, the values were approximately listed according to the corresponding charts. When standard deviation values were not reported but instead were depicted in figures, certainty of confidence in the body of evidence was adversely affected. Possible causes of heterogeneity among study results were the difference in time of measurement of DC, or microhardness ratio (immediately after specimen preparation or 24 h later, in order to register post-curing), as well as the media stored (dry and dark, tap water, deionized water, or artificial saliva. Funding of each study was also reported. When the necessary data for quantitative analysis were not clearly provided (number of specimens per group or DC values), an e-mail was sent to the corresponding author, and if an answer was not received, they were not included in the study. Sensitivity analysis in order to assess robustness of the study was performed, by excluding high risk of bias studies. Another method was also implemented, and studies reporting inadequately cured Bulk Fill resin composites, were analyzed in conjunction to the type of LCU used.

2.4. Risk of Bias Assessment

Two authors (ST and KM) independently evaluated the risk of bias of each included study, according to the Quin tool for in vitro studies, as described, and evaluated by Sheth et al. [18]. The following parameters were evaluated in each study: clearly stated aims/objectives, detailed explanation of sample size calculation, detailed explanation of sampling technique, details of comparison group (the use of control), detailed explanation of methodology, operator details, randomization, method of measurement of outcome, outcome assessor details, blinding, statistical analysis, and presentation of results.

The studies included in this systematic review were studies that evaluated either the degree of conversion through FTIR or Raman spectroscopy or the bottom-to-top hardness ratio. Therefore, the criteria, detailed explanation of sampling technique, and outcome assessor details did not apply for risk of bias assessment. On the contrary, benchtop studies including specimens, which are composed of extracted teeth, along with the materials aimed to be investigated, should assess the aforementioned criteria. According to the Quin tool, 10 criteria were evaluated as adequately specified = 2 points, inadequately specified = 1 point, not specified = 0 points, and not applicable = exclude criteria from calculation. Thus, the scores obtained were used to grade the in vitro study as high, medium, or low risk of bias (>70% = low risk, 50% to 70% = medium risk, and <50% = high risk).

3. Results

3.1. Search and Selection

The Prisma flow diagram is presented in Figure 1. After the database screening in the Pubmed Database (n = 75), Scopus Database (n = 231), Web of Science Database (n = 414), and EBSCO Database (n = 68), 788 records were found, and after the removal of duplicates, 561 studies were identified (Figure 1). During the screening process, 372 reports were excluded after reading the title (n = 305) and abstract (n = 67) because they were clinical trials, studies referring to heat development, dentine bonding agents, resin composites other than bulk fill, studies on light transmission through material such as ceramic, marginal adaptation, cytotoxicity, water sorption, solubility, case reports, reviews, and systematic reviews, studies on specimens bonded to extracted teeth, and conference papers. Then, the authors tried to download the full texts of 189 potentially eligible studies, but 37 full manuscripts were unavailable. Their authors were contacted via e-mail but did not respond. Thus, 152 studies were read in detail. Ninety-eight (98) studies were excluded according to the following criteria: studies on other mechanical properties (n = 26), studies evaluating materials other than bulk fill (n = 12), studies with time of irradiance not reported (n = 3), studies with depth of cure less than 4 mm (n = 8), studies without microhardness bottom/top evaluation (n = 7), distance from the LCU tip more than 0 mm (n = 11), studies on high irradiance for very short time (n = 12), depth of cure based on ISO 4049 [3] (n = 5), studies without exact description of means but only from figures (n = 7), and studies with incomplete description of LCU characteristics (n = 5). Therefore, 54 studies were retrieved. After reading the reference lists from the included studies, 12 potentially eligible studies were identified, but one was not retrieved. Thus, 65 studies were considered eligible for the qualitative synthesis of this systematic review.

3.2. Descriptive Analysis

The characteristics of the 65 studies selected are listed in Table 1. The following characteristics were presented: name of the first author and year of publication, Bulk Fill resin composites used, Light Curing Unit used, monowave or polywave, their irradiance, time of polymerization, polymerization investigation method, number of specimens, results, and statistical significance of the difference in polymerization efficiency when both monowave and polywave LCUs were used.

Among the 65 studies included, 17 investigated both monowave and polywave light curing units for the polymerization of Bulk Fill resin composites [19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35].

The polymerization of bulk fill resin composites was evaluated by direct methods or indirect methods. Direct methods investigate the degree of conversion either by means of Fourier-transform infrared spectroscopy (FTIR), used in 23 studies [19,20,21,22,24,27,29,32,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54], or by Micro-Raman spectroscopy measurements used in 8 studies [34,55,56,57,58,59,60,61]. The indirect methods evaluate the polymerization through bottom to top microhardness measurements, with the use of a Vickers indenter (VHN) used in 25 studies [25,28,33,45,46,48,49,52,54,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77], or a Knoop indenter (KHN) used in 10 studies [23,31,50,51,66,78,79,80,81,82]. Eight studies used both direct (FTIR), and indirect (VHN) techniques in order to study bulk fill composite resin polymerizarion [36,45,46,49,50,51,52,54].

The most commonly used bulk fill resin composites were Tetric EvoCeram [19,20,21,22,23,25,26,28,29,31,32,33,35,36,37,39,40,45,47,48,49,50,51,54,55,56,58,59,60,63,69,71,74,75,76,78,80,81,82], followed by Filtek bulk fill [22,25,26,28,31,32,39,40,43,45,53,54,55,56,58,59,61,64,71,73,75,76,80], SDR [22,23,25,27,30,32,33,34,38,40,41,42,44,45,47,52,53,54,58,59,60,63,70,79,80,82], X-tra Fil [28,30,36,40,47,62,63,69,71,72,74,78,80], SonicFill [29,33,36,40,41,42,45,47,48,50,51,52,64,69,71,72,73,75,76,78,79,81], Venus bulk fill [33,38,39,40,41,54,59,64,70,71,79], X-tra Base [33,47,54,59,64,70,71,80], and Filtek bulk fill Posterior [25,48,60,71,75,80].

The newer addition–fragmentation chain transfer (AFCT) and the reversible addition-fragmentation chain transfer (RAFT) reactions agents are incorporated in bulk fill resin composites in order to deduce polymerization contraction. The AFCT Bulk Fill resin composite One Filtek bulk fill, was evaluated in 15 studies [19,20,27,43,50,51,57,61,62,63,65,66,67,75,77], and the RAFT bulk fill resin composites Tetric Power Fill and Tetric Power Flow in 9 studies [19,27,37,43,46,49,57,68,83], and another 8 studies [19,27,30,43,46,49,68,83] respectively.

Table 1. Main methodological data and results from included studies.

First Author Year of Publication	Bulk Fill Resin Composite	LCU Monowave Irradiance (mW/cm2)	Exposure Time (s)	LCU Polywave Irradiance (mW/cm2)	Exposure Time (s)	Methodology	Number of Specimens	Results	Polywave-Monowave Difference
Abdelwahed 2022 [62]	PALFIQUE BULK FLOW X-tra fil (Voco) Filtek™ One Bulk Fill (3M/ESPE)			Dr’s light AT CL-AT24 1400	5 s	VHN	10	All materials >80% B/T VHN	_
Aldhafyan 2025 [63]	STARK bulk fill Composite (President) Filtek One bulk fill restorative (3M/ESPE) SDR Plus bulkfill flowable (Dentsply) Tetric N-Cerambulk fill (Ivoclar) X-tra fil (Voco) BEAUTIFIL-Bulk Restorative (Shofu)	Elipar S10 (3M/ESPE) 1200	20 s			VHN Immediate/24 h	5	58.31/61.97 32.08/48.51 18.75/29.28 38.19/46.94 64.03/72.06 45.09/49.50
Algamaiah 2024 [19]	Filtek One Bulkfill (3M/ESPE) Tetric EvoCeram Bulk Fill (Ivoclar) Tetric Power Fill (Ivoclar) Tetric EvoFlow Bulk Fill (Ivoclar) Tetric Power Flow (Ivoclar) Estelite bulkfill (Kuraray)	Elipar S (3M/ESPE) 1200	20 s	BluePhase Powercure (Ivoclar) 1200	10 s 3 s	DC (FTIR)	5	EliparS > Bluephase Power cure All material >50% except for Tetric PowerFlow and Filtek One Bulkfill	_
Alrahlah 2014 [64]	Tetric Evo Ceram Bulk Fill (Ivoclar) X-tra Base (Voco) Venus Bulk Fill (Heraeus) Filtek Bulk Fill (3M) Sonicfill (Kerr)	Elipar-S (3M/ESPE) 1200	20 s			VHN	3	All > 80%	_
Alzahrani 2023 [65]	Bulk Fill One Bulk Fill (3M/ESPE)			Blue phase G2 1200	20 s 40 s	VHN	20	4.1 mm (20 s) 5 mm (40 s)	_
ALShaafi 2016 [78]	SDR (Dentsply) x-Trafil (Voco) Tetric Bulk Fill (Ivoclar) SonicFill (Kerr)			Bluephase 20i (Ivoclar) 1402	20 s	KHN	5	80% 88% 70% 70%	_
Altınok Uygun 2021 [36]	SonicFill (Kerr) Tetric EvoCeram Bul kFill (Ivoclar) X-trafil (Voco)			Valo (Ultradent) 1000 1400 3200	20 s 12 s 6 s	DC (FTIR) VHN	10	Peculiar method >80% Filtek76–79	_
Arafa 2025 [37]	Tetric Power Fill (Ivoclar) Tetric N-Ceram Bulk Fill (Ivoclar)			Guilin (Woodpecker Medical Instrument) 900	20 s	DC (FTIR)	5	55.3 (5.47) 61.6 (6.60)
Cardoso 2022 [20]	Filtek One Bulk Fill (3M/ESPE) Aura Bulk Fill (SDI) Tetric Bulk Fill (Ivoclar)	Radii Xpert (SDI) 1575	20 s	Valo (Ivoclar) 1103	20 s	DC (FTIR)	10	~50% Significantly higher differrences Valo Tetric bulkfill	Material dependent Polywave
Conteras 2021 [21]	Tetric N-Ceram Bulkfill (Ivoclar)	3M/ESPE 2nd generation LED 1181.2	20 s	BluePhase N 1145.3	20 s	DC (FTIR)	5	No significant difference	No significant defference
Czasch 2013 [38]	Surefil SDR Flow (Dentsply) Venus bulk fill (Heraeus Kulzer)	Elipar Freelight 2 (3 M ESPE) 1226	10 s 20 s 40 s			FTIR	6	58.3 (1.7) 62.9 (2.3) 59.7 (1.7) 66.1 (2.8) 61.2(2.1) 67.92 (1.6)
Daugherty 2018 [39]	Beautifil-Bulk, (SHOFU) Filtek-Bulk-Fill, (3 M ESPE) Tetric-EvoCeram-Bulk-Fill (Ivoclar) Sonic-Fill-2(Kerr) Venus-Bulk-Fill (Kulzer)	FlashMax P3 (CMS Dental) 2378 Paradigm (3M ESPE 1226 SPEC 3 (Coltene) 1827 3001	3 s, 9 s 10 s, 20 s 5 s 20 s			DC (FTIR)	1	standard irradiance& exposure did significantly outperform the other two combinations Venus-Bulk-Fill best	_
Derchi 2018 [22]	Filtek Bulk Fill (3M/ESPE) Surefil SDR (Dentsply) Tetric Evo Ceram Bulk Fill (Ivoclar)	Bluephase style M8 800	20 s	Bluephase style 1200 Valo 1000	20 s 20 s	DC (FTIR)	3	>50% except Filtek Bulkfill with monowave, which was lower	Polywave
Elhejazi 2024 [66]	Any-Com™ Bulk (Mediclus) Opus Bulk Fill Flow APS (FGM) Filtek™ One Bulk Fill Restorative (3M/ESPE) Opus Bulk Fill APS (FGM)			BluePhase	manufacturer’s instructions	VHN KHN	5	>80% except Opus Bulk and Opus Flow	_
Fronza 2017 [84]	Filtek Bulk Fill (3M ESPE) Tetric Evo Ceram Bulk Fill (Ivoclar)			Valo (Ultradent) 995	20 s	DC Raman	5	46.2 (1.0) 61.0 (1.5)
Gan 2018 [23]	Tetric N-Ceram Bulk Fill (Ivoclar) SDR Posterior Bulk Fill Flowable Base (Dentsply)	Bluephase N monowave 800 QHL-5 550	15 s 21.8 s	Bluephase N polywave 1200 650	10 s 18.5 s	KHN	6	Monowave significantly higher Both < 80%	Monowave
Garcia 2014 [79]	SureFil SDR flow (Dentsply) Venus Bulk Fill (Kulzer) Sonic Fill (Kerr)	SmartLite iQ2 (Dentsply) 800	20 s			KHN	10	All materials < 70% B/T KHN at 4 mm	_
Garoushi 2016 [40]	X-trafil (Voco) Venus bulk fill (Heraeus) TetricEvoCeram Bulk Fill (Ivoclar) SDR (Dentsply) Filtek Bulk Fill (3M) SonicFill (Kerr)	Elipar Freelight 2 (3M) 1000	40 s			DC (FTIR)	3	All >55% except for Tetric Evo Ceram Bulk Fill	_
Georgiev 2021 [67]	Filtek One Bulk Fill Restorative (3M/ESPE)			LED LCU Curing Pen (Eighteeth, China) 600 1000 1500	20 s 40 s 60 s	VHN	3	600 × 20 > 78% >80%	_
Gomes de Araújo-Neto 2021 [56]	Filtek Bulk Fill (3M/ESPE) Tetric N-Ceram Bulk Fill (Ivoclar)			Valo 1680	10 s	DC (micro-Raman)	10	FB88% TC 83%	_
Goncalves 2018 [41]	Filtek bulk fill (3M/ESPE) Filtek bulk fill flow (3M/ESPE) SonicFill (Kerr) Venus bulk fill flow (Kulzer)	Radii (SDI) 800	25 s			DC (FTIR)	5	All above 55%, except Filtek bulk fill flow	_
Goracci 2014 [42]	SonicFill (Kerr) SDR (Dentsply)	Demi Led (Orange) 1100	20 s			DC (FTIR)	5	SonidFill > 55% SDR > 50%	_
Gonzales Guarneri 2025 [42]	Tetric PowerFill (Ivoclar) Tetric PowerFlow (Ivoclar) Filtek One Bulk Fill Restorative (3M/ESPE) Filtek Bulk Fill Flowable (3M/ESPE) Tetric plus Fill (Ivoclar) Tetric plus Flow (Ivoclar)			Bluephase PowerCure (Ivoclar) 1226	10 s	DC (FTIR)	3	42.8 56.1 45.6 45.4 45.8 52.9
Jakupovic 2023 [68]	Tetric Power Fill (Ivoclar) Tetric Power Flow (Ivoclar)			Bluephase PowerCure (Ivoclar) 3440 1340	3 s 10 s	VHN	8	All bulkfil > 80%	_
Jakupovic 2025 [83]	Tetric PlusFill (Ivoclar) Tetric PowerFill (Ivoclar) Tetric PlusFlow (Ivoclar) Tetric PowerFlow (Ivoclar)			Bluephase PowerCure (Ivoclar) 1200	10 s	VHN	7	88 87 89 87
Javed 2025 [44]	(SDR)-Universal shade (Dentsply Caulk) Beautifi Bulk Restorative universal shade (Shofu Inc)			Bluephase N (Ivoclar) 1120	20 s	DC (FTIR) VHN	7	70.65 (1.37) 46.48 (1.07) 94% 86% VHN > 80% all
Ilie Stark 2014 [69]	High viscosity Tetric Evo Ceram Bulk Fill (Ivoclar0 X-tra Fil (Voco) SonicFill (Kerr)			Valo (Ultradent) 1272	20 s 40 s	VHN	5	80% B/T VHN 6 mm 5.6 mm (20 s) 6 mm (40 s) 4.3 mm (20 s) 5.4 mm (40 s)	_
Ilie Stark 2015 [70]	Low Viscosity Venus Bulk Fill (Kulzer) Surefil SDR (Dentsply) X-tra base (Voco) Filtek Bulk Fill (3M/ESPE)			Valo (Ultradent) 1272	20 s 40 s	VHN	5	80% B/T VHN All > 6 mm	_
Karacolak 2018 [71]	Aura (Kuraray) Filtek Bulk Fill Posterior (3M) SonicFill (Kerr) X-tra Fill (Voco) Tetric EvoCeram Bulk Fill (Ivoclar Filtek Bulk Fill Flowable (3M/ESPE) SDR (Dentsply) X-tra Base (Voco) Venus Bulk Fill	SmartLite Focus (Dentsply)	20 s			VHN	5	>80% Except Sonicfill and Tetric EvoCeraqm Bulk Fill	_
Kaya 2018 [24]	Beautifil Bulk Restorative (Shofu)	Optima 10 1100 Demi Ultra 1100–1330	20 s 10 s	Valo (Ultradent) 3200	3 s	DC (FTIR)	5	Demi Ultra> Optima> Valo	Monowave
Lempel 2023 [57]	Tetric PowerFill (Ivoclar) Filtek One Bulk Fill Restorative (3M/ESPE)			Bluephase PowerCure (Ivoclar) 3150 1180 1950	3 s 5 s 10 s, 20 s	DC (Micro-Raman spectroscopy)	5	20 s Tetric 50.8 Filtek 48.9	_
Li 2015 [58]	Filtek Bulk Fill Flowable (3M/ESPE) Tetric EvoCeram Bulk Fil (Ivoclar) SDR (Dentsply)			Bluephase 20i (Ivoclar Vivadent)	20 s	DC Micro-Raman mapping	3	Properly cured	_
Maghaireh 2019 [25]	X-tra fill (Voco) Filtek-Bulk Fill flowable (3M/ESPE) Tetric Evo-Ceram Bulk Fill (Ivoclar) SDR posterior Bulk Fill Flowable (Dentsply) Filtek Bulk Fill posterior (3M/ESPE)	Elipar S10 (3M) 1200	10 s	Bluephase Style (Ivoclar) 1000	10 s	VHN	5	4 mm B/T VHN above 80% except Tetric EvoCeram Bulkfill and Filtek Bulk Fill Flowable X-tra fill polywave and Filtek Bulk Fill posterior Monowave	Material dependent
Makhdoom 2020 [26]	Tetric EvoCeram Bulk Fill (Ivoclar) Filtek Bulk Fill (3M/ESPE)	Satelec	10 s 20 s	BluePhase Style	10 s 20 s	4049	5	No statistically significant differences Inadequate depth	No significant difference
Marovic 2025 [27]	Filtek One Bulk Fill (3M ESPE) Tetric PowerFill (Ivoclar) Tetric PowerFlow (Ivoclar) SDR flow(Dentsply Sirona)	Translux Wave (Kulzer) 1000 1000	10 s 20 s	VALO Cordless (Ultradent) 3000 1000 1000 Bluephase PowerCure (Ivoclar) 3000 1000 1000	3 s 10 s 20 s 3 s 10 s 20 s	DC (FTIR)	5	20 s > higher conversion Power Flow and SDR > 50% Monowave Polywave no significant difference	No significant difference
Miletic 2017 [45]	Filtek Bulk Fill Flowable (3M/ESPE) SDR, Smart Dentin Replacement (Dentsply) SonicFill (Kerr) Xenius Base (Xenius) Tetric EvoCeram Bulk Fill (Ivoclar)			Bluephase 20i (Ivoclar)	10 s 20 s	DC (FTIR) VHN ISO 4049 [3]	6 6 6	DC SDR: >60% at 6 mm Filtek > 60% at 4 mm Rest < 50% B/T VHN At 10 s well above 80% SDR and Filtek Bulkill flowable At 20 s all Bulk Fills ISO > 4 mm except For SonicFill >5 mm: SDR, Filtek, Xenius	_
Moharam 2017 [72]	X-tra Fill (Voco) Sonic Fill (Kerr)	Elipar S10, (3M ESPE) 1000	20 s			VHN	10	97.6 (0.6) 90.4 (1.5)
Ozciftci 2025 [46]	PowerFill (Ivoclar) PowerFlow (Ivoclar) Omnichroma Flow Bulk (Tokuyama)			Bluephase PowerCure 1100	10 s/20 s	DC (FTIR) VHN		61.71/57.38 77.9/66.49 47.34/51.78 80.31%(5)/81.05%(4) 80.96%/(4)/79.87%(3) 75.09%(5)/86.97%(5)
Özdemir 2025 [73]	GrandioSO Heavy Flow (Voco) Filtek Bulk Fill (3M/ESPE) SonicFill 2 (Kerr)			Valo (Ultradent) 1000	20 s	VHN	5	4.8–5.1 mm Depth of cure 80%	_
Papadogiannis 2015 [47]	SDR (Dentsply) SonicFill (Kerr) Tetric Evo Ceram Bulk Fill (Ivoclar) X-tra Base (Voco) X-tra Fill (Voco)			Bluphase G2 1200	30 s	DC (FTIR)	5	Venus, SDR > 55% Material dependent	_
Par 2015 [59]	Tetric EvoCeram BulkFill (Ivocalr) Quixfil (Dell Denral) X-tra fil (Voco) Venus Bulk Fill (Kulzer) X-tra Base (Voco) SDR (Dentsply) Filtek Bulk Fill (3M/ESPE)			Bluephase G2 (Ivoclar) 1090	20 s	DC (Raman Spectroscopy)	5	Adequate polymerizarion 59.1–71.8%	_
Par 2019 [28]	TetricEvoCeramBulkFill (Ivoclar) FiltekBulkFill (3M/ESPE) X-trafil (Voco)	BluePhasreStyle M8 (Ivoclar)648	30 s	BluePhase Style (Ivoclar) 924	30 s	VHN	5	No benefit for Bf containing alternative Photonitiators All BF > 80%	No significant difference
Parasher 2020 [74]	X-tra fil Tetric EvoCeram Bulk Fill (Ivoclar) Beautiful Bulk restorative (Shofu)			Bluephase G2	manufacturer’s recommenda tions	VHN	19	X-tra Fil > 80%	_
Renzai 2019 [48]	Filtek Bulk Fill Posterior (3M/ESPE) Sonic Fill 2(Kerr) Tetric N-Ceram Bulk Fill (Ivoclar) X-tra fil (Voco)			Bluepase N 1200	30 s	VHN DC (FTIR)	6 3	B/T VHN > 85% DC > 60%	_
Rizzante 2019 [80]	Admira Xtra Fusion (Voco) Filtek Bulk Fill Posterior (3M/ESPE) Tetric Evo Ceram Bulk Fill (Ivoclar) X-tra Fil (Voco) Filtek Bulk Fill Flowable (3M/ESPE) Surefil SDR flow (Dentsply) X-tra Base	LED Blue Star 3 (Microdont) 1550	20 s			KHN	8	All Bulkfill CR Adequate 80% DoC up to 4.5 mm	_
Rocha 2017 [29]	Sonic Fill 2(Kerr) Tetric EvoCeram Bulk Fill (Ivoclar)	Smartllite Focus (Dentsply) 1000	20 s	Valo (Ultradent) 954	21 s	DC (FT-NIR)	3	Inhomegeinity Polywave more effective in the superficial 2 mm of the material containing alternative photoinitiators 4 mm: no significant difference	No significant difference
Rocha 2022 [30]	Surefil SDR (Dentsply) Tetric Power Flow (Ivoclar) X-tra-Fil (Voco)	SmartLite Pro (Dentsply/Sirona) 1200 Monet (AMD Lasers) 2000–2400	10 s 20 s 1 s, 3 s	Valo Grand (Ultradent) 900	10 s 20 s	ISO 4049 [3]	10	DOC > 4 mm Monowave no significant differences, SDR monowave higher Monowave 10 s higher	No significant difference
Sampaio 2024 [49]	Tetric EvoCeram Bulk Fill (Ivoclar) Tetric EvoFlow Bulk Fill (Ivoclar) Tetric PowerFill (Ivoclar) Tetric PowerFlow (Ivoclar)			Bluephase Style 20i 1200 Bluephase Powercure 3050	20 s 3 s	DC (FTIR) VHN	5	Bottom DC Only Tetric Evo Ceram Bulk Fill 53.3% TetricPower Flow 61.2% B/T VHN all > 80%	_
Shimokawa 2018 [31]	Filtek Bulk Fill posterior Restorative (3M/ESPE) Tetric EvoCeram Bulk Fill (Ivoclar)	Elipar DeepCure-S (3M) 1470 Celalux 3 (Voco) 1300		Bluephase 20i (Ivoclar) 1200 Valo Grand (Ultradent) 1000		KHN	5	All ~70% Polywave Wide light tip> homogeneous distribution of irradiance and wave lengths	Monowave
Siagian 2020 [32]	Filtek Bulk-Fill (3M/ESPE) Tetric N-Ceram Bulk-Fill (Ivoclar) SDR flow (Dentsply)	SmartLite Focus (Dentsply Sirona)	20 s	Bluephase style (Ivoclar)	40 s	DC (FTIR) Pulverized samples	5	DC > 50% Filtek and Tetric with both LCUs SDR < 50% No significant differences	No significant difference
Skrinjaric 2025 [75]	Tetric EvoCeram Bulk Fill (Ivoclar) Filtek Bulk Fill Posterior (3M/ESPE) Filtek One Bulk Fill(3M/ESPE) SonicFill 2 (Kerr) Admira Fusion X-tra (Voco) Admira Fusion X-tra (Voco)			D-Light Duo (RF-Pharmaceuticals Sarl) 1200–1300	20 s	VHN 4 mm/ 6 mm	3	91/87 90/90 96/90 95/94 98/96 98/97
Son 2017 [76]	Filtek Bulk Fill (3M), SureFil SDR (Dentsply) Venus Bulk Fill (Heraeus) SonicFill (Kerr) Tetric N-Ceram Bulk Fill (Ivoclar)	LE Demetron (Kerr) 900	40 s			VHN	12	SDR, Venus > 80%	_
Soto-Montero 2020 [81]	Sonic Fill (Kerr) Tetric EvoCeram Bulk Fill (Ivoclar)			Bluephase Style, Ivoclar Regular tip 935 homogenizer tip 850	SF 20 s TECBF 10 s	KHN	10	Below 80% 78% with HT and 70% with RT	_
Strini 2022 [50]	Filtek One Bulk Fill (3M/ESPE) Tetric N-Ceram Bulk-Fill (Ivoclar) SonicFill 2 (Kerr)			Valo (Ultradent) 1000	20 s	DC (FTIR) KHN	15	DC SonicFill2: 63.67% Rest below 50% B/T KHN all below 80%	_
Terada 2024 [60]	Filtek Bulk-Fill Flowable (3M/ESPE) Beautifil Bulk Flowable (Shofu) Surefill SDR Flow (Dentsply) Filtek Bulk-Fill Restorative (3M/ESPE) Beautifil-Bulk Restorative (Shofu) Tetric EvoCeram Bulk Fill			Valo (Ultradent) 1001	20 s	DC (Raman spectroscopy) 3–4 mm depth	5	Between 82.2% and 90.9%	_
Thomaidis 2024 [33]	VenusBulkFill (Kulzer) X-traBase (Voco) SDR (Dentsply) Tetric EvoCeram BulkFill (IvocalR0 SonicFill (Kerr) FiltekBulkFill flowable restorative (3M/ESPE)	Demi Ultra 1100	20 s	Bluephase Style 1100 Valo 1000	20 s 20 s	VHN	10	Material dependent	Material dependent
Torres 2024 [51]	Filtek One bulk fill restorative (3M/ESPE) Tetric N Ceram bulk fill (Ivoclar) SonicFill (Kerr) VisCalor (Kuraray)	Demi (Kerr) 1000	10 s 20 s 40 s			KHN DC (FTIR)	5 5	B/T KH > 80% only 40 s	_
Tsuzuki 2020 [34]	SDR (Dentsply)	Raddi Plus (SDI) 1300 Emitter.D (Schuster) 1250 Biolux Plus (Bioart) 880 Woodpecker (Guilin Woodpecker) 520	20 s 40 s	Valo Cordless (Ultradent) 1010	20 s 40 s	DC (confocal Raman spectroscopy)	10	All LCUs above 50% at 20 s and 40 s Valo significantly higher than Radii plus and Biolux at 20 s	Polywave
Varshney 2022 [35]	Wonder Bulk Fill (Wizden) (CQ) Tetric N-Ceram (Ivoclar) (CQ + TPO + Ivocerin)	Waldent ECO Plus (Waldent)	10 s	Bluephase N LED (Ivoclar)	10 s	DC (FTIR) Of pulverized samples	20	BluePhase Tetric DC 59% Wonder < 50% Waldent(CQ) no significantly higher DC in Tetric(ivocerin)	Polywave
Wang 2021 [61]	Filtek Bul Fill Flowable (3M/ESPE) Filtek One Bulk Fill (3M/ESPE)	Elipar S10 (3M ESPE) 1200	20 s 40 s			DC (Micro-Raman spectroscopy) at 5 mm depth	25	Filtek Bulkfill Flowable >55% at 20 s and 40 s	_
Yap 2016 [82]	Beautifil Bulk Restorative (Shofu) Beautifil Bulk Flowable (Shofu) SDR Posterior Bulk-Fill Flowable Base (Dentsply) EverX Posterior (GC) Tetric N-Ceram Bulk-Fill (Ivoclar)	Blue Shor LED (Shofu) 700	20 s			KHN ISO4049	5	80% B/T KHN 3 mm, except for EverX Posterior Tetric N-Ceram Bulk-Fil at 2.5 mm ISO 4049 [3] overestimated	_
Yeo 2021 [77]	Filtek One Bulk Fill Restorative (3M/ESPE)	Elipar LED light cure 1200	20 s 40 s			VHN	1	B/T VHN 40 s > 96.8% 20 s > 85%	_
Yıldırım 2023 [52]	SDR Plus (Dentsply) SonicFill 2 (Kerr) ACTIVA BioActive Restorative (Pulpdent)	Elipar FreeLight 2 (3M/ESPE) 1000	Manufacturer’s instructions 20 s SDR 40 s			DC (FTIR) VHN	6 10	Inadequate polymerization In all materials	_
Yokesh 2017 [53]	Surefil SDR bulk fill f lowable composite (Kerr) Filtek bulk fill flowable composite (3M/ESPE)	LEDition (Ivoclar) 600	20 s			DC(FTIR) Of pulverized coronal and pulpal half ISO 4049 [3]	10	DC < 50% ISO 4049 [3] Surefil: 3.89 Filtek: 3.54	_
Zorzin 2015 [54]	Filtek Bulk Fill Flowable (3M/ESPE) SDR Surefil (Dentsply) Tetric Evo Ceram Bulk Fill (Ivoclar) Venus Bulk Fill (Heraeus) X-tra Base (Voco)			Bluephase 20i (Ivoclar) 1200	Manufacturer’s instructions 30 s	DC (FTIR) VHN	5	30 s all Manufacturer’s instructions all except SDR and X-tra Base	_

Table 1. Main methodological data and results from included studies.

First Author Year of Publication	Bulk Fill Resin Composite	LCU Monowave Irradiance (mW/cm2)	Exposure Time (s)	LCU Polywave Irradiance (mW/cm2)	Exposure Time (s)	Methodology	Number of Specimens	Results	Polywave-Monowave Difference
Abdelwahed 2022 [62]	PALFIQUE BULK FLOW X-tra fil (Voco) Filtek™ One Bulk Fill (3M/ESPE)			Dr’s light AT CL-AT24 1400	5 s	VHN	10	All materials >80% B/T VHN	_
Aldhafyan 2025 [63]	STARK bulk fill Composite (President) Filtek One bulk fill restorative (3M/ESPE) SDR Plus bulkfill flowable (Dentsply) Tetric N-Cerambulk fill (Ivoclar) X-tra fil (Voco) BEAUTIFIL-Bulk Restorative (Shofu)	Elipar S10 (3M/ESPE) 1200	20 s			VHN Immediate/24 h	5	58.31/61.97 32.08/48.51 18.75/29.28 38.19/46.94 64.03/72.06 45.09/49.50
Algamaiah 2024 [19]	Filtek One Bulkfill (3M/ESPE) Tetric EvoCeram Bulk Fill (Ivoclar) Tetric Power Fill (Ivoclar) Tetric EvoFlow Bulk Fill (Ivoclar) Tetric Power Flow (Ivoclar) Estelite bulkfill (Kuraray)	Elipar S (3M/ESPE) 1200	20 s	BluePhase Powercure (Ivoclar) 1200	10 s 3 s	DC (FTIR)	5	EliparS > Bluephase Power cure All material >50% except for Tetric PowerFlow and Filtek One Bulkfill	_
Alrahlah 2014 [64]	Tetric Evo Ceram Bulk Fill (Ivoclar) X-tra Base (Voco) Venus Bulk Fill (Heraeus) Filtek Bulk Fill (3M) Sonicfill (Kerr)	Elipar-S (3M/ESPE) 1200	20 s			VHN	3	All > 80%	_
Alzahrani 2023 [65]	Bulk Fill One Bulk Fill (3M/ESPE)			Blue phase G2 1200	20 s 40 s	VHN	20	4.1 mm (20 s) 5 mm (40 s)	_
ALShaafi 2016 [78]	SDR (Dentsply) x-Trafil (Voco) Tetric Bulk Fill (Ivoclar) SonicFill (Kerr)			Bluephase 20i (Ivoclar) 1402	20 s	KHN	5	80% 88% 70% 70%	_
Altınok Uygun 2021 [36]	SonicFill (Kerr) Tetric EvoCeram Bul kFill (Ivoclar) X-trafil (Voco)			Valo (Ultradent) 1000 1400 3200	20 s 12 s 6 s	DC (FTIR) VHN	10	Peculiar method >80% Filtek76–79	_
Arafa 2025 [37]	Tetric Power Fill (Ivoclar) Tetric N-Ceram Bulk Fill (Ivoclar)			Guilin (Woodpecker Medical Instrument) 900	20 s	DC (FTIR)	5	55.3 (5.47) 61.6 (6.60)
Cardoso 2022 [20]	Filtek One Bulk Fill (3M/ESPE) Aura Bulk Fill (SDI) Tetric Bulk Fill (Ivoclar)	Radii Xpert (SDI) 1575	20 s	Valo (Ivoclar) 1103	20 s	DC (FTIR)	10	~50% Significantly higher differrences Valo Tetric bulkfill	Material dependent Polywave
Conteras 2021 [21]	Tetric N-Ceram Bulkfill (Ivoclar)	3M/ESPE 2nd generation LED 1181.2	20 s	BluePhase N 1145.3	20 s	DC (FTIR)	5	No significant difference	No significant defference
Czasch 2013 [38]	Surefil SDR Flow (Dentsply) Venus bulk fill (Heraeus Kulzer)	Elipar Freelight 2 (3 M ESPE) 1226	10 s 20 s 40 s			FTIR	6	58.3 (1.7) 62.9 (2.3) 59.7 (1.7) 66.1 (2.8) 61.2(2.1) 67.92 (1.6)
Daugherty 2018 [39]	Beautifil-Bulk, (SHOFU) Filtek-Bulk-Fill, (3 M ESPE) Tetric-EvoCeram-Bulk-Fill (Ivoclar) Sonic-Fill-2(Kerr) Venus-Bulk-Fill (Kulzer)	FlashMax P3 (CMS Dental) 2378 Paradigm (3M ESPE 1226 SPEC 3 (Coltene) 1827 3001	3 s, 9 s 10 s, 20 s 5 s 20 s			DC (FTIR)	1	standard irradiance& exposure did significantly outperform the other two combinations Venus-Bulk-Fill best	_
Derchi 2018 [22]	Filtek Bulk Fill (3M/ESPE) Surefil SDR (Dentsply) Tetric Evo Ceram Bulk Fill (Ivoclar)	Bluephase style M8 800	20 s	Bluephase style 1200 Valo 1000	20 s 20 s	DC (FTIR)	3	>50% except Filtek Bulkfill with monowave, which was lower	Polywave
Elhejazi 2024 [66]	Any-Com™ Bulk (Mediclus) Opus Bulk Fill Flow APS (FGM) Filtek™ One Bulk Fill Restorative (3M/ESPE) Opus Bulk Fill APS (FGM)			BluePhase	manufacturer’s instructions	VHN KHN	5	>80% except Opus Bulk and Opus Flow	_
Fronza 2017 [84]	Filtek Bulk Fill (3M ESPE) Tetric Evo Ceram Bulk Fill (Ivoclar)			Valo (Ultradent) 995	20 s	DC Raman	5	46.2 (1.0) 61.0 (1.5)
Gan 2018 [23]	Tetric N-Ceram Bulk Fill (Ivoclar) SDR Posterior Bulk Fill Flowable Base (Dentsply)	Bluephase N monowave 800 QHL-5 550	15 s 21.8 s	Bluephase N polywave 1200 650	10 s 18.5 s	KHN	6	Monowave significantly higher Both < 80%	Monowave
Garcia 2014 [79]	SureFil SDR flow (Dentsply) Venus Bulk Fill (Kulzer) Sonic Fill (Kerr)	SmartLite iQ2 (Dentsply) 800	20 s			KHN	10	All materials < 70% B/T KHN at 4 mm	_
Garoushi 2016 [40]	X-trafil (Voco) Venus bulk fill (Heraeus) TetricEvoCeram Bulk Fill (Ivoclar) SDR (Dentsply) Filtek Bulk Fill (3M) SonicFill (Kerr)	Elipar Freelight 2 (3M) 1000	40 s			DC (FTIR)	3	All >55% except for Tetric Evo Ceram Bulk Fill	_
Georgiev 2021 [67]	Filtek One Bulk Fill Restorative (3M/ESPE)			LED LCU Curing Pen (Eighteeth, China) 600 1000 1500	20 s 40 s 60 s	VHN	3	600 × 20 > 78% >80%	_
Gomes de Araújo-Neto 2021 [56]	Filtek Bulk Fill (3M/ESPE) Tetric N-Ceram Bulk Fill (Ivoclar)			Valo 1680	10 s	DC (micro-Raman)	10	FB88% TC 83%	_
Goncalves 2018 [41]	Filtek bulk fill (3M/ESPE) Filtek bulk fill flow (3M/ESPE) SonicFill (Kerr) Venus bulk fill flow (Kulzer)	Radii (SDI) 800	25 s			DC (FTIR)	5	All above 55%, except Filtek bulk fill flow	_
Goracci 2014 [42]	SonicFill (Kerr) SDR (Dentsply)	Demi Led (Orange) 1100	20 s			DC (FTIR)	5	SonidFill > 55% SDR > 50%	_
Gonzales Guarneri 2025 [42]	Tetric PowerFill (Ivoclar) Tetric PowerFlow (Ivoclar) Filtek One Bulk Fill Restorative (3M/ESPE) Filtek Bulk Fill Flowable (3M/ESPE) Tetric plus Fill (Ivoclar) Tetric plus Flow (Ivoclar)			Bluephase PowerCure (Ivoclar) 1226	10 s	DC (FTIR)	3	42.8 56.1 45.6 45.4 45.8 52.9
Jakupovic 2023 [68]	Tetric Power Fill (Ivoclar) Tetric Power Flow (Ivoclar)			Bluephase PowerCure (Ivoclar) 3440 1340	3 s 10 s	VHN	8	All bulkfil > 80%	_
Jakupovic 2025 [83]	Tetric PlusFill (Ivoclar) Tetric PowerFill (Ivoclar) Tetric PlusFlow (Ivoclar) Tetric PowerFlow (Ivoclar)			Bluephase PowerCure (Ivoclar) 1200	10 s	VHN	7	88 87 89 87
Javed 2025 [44]	(SDR)-Universal shade (Dentsply Caulk) Beautifi Bulk Restorative universal shade (Shofu Inc)			Bluephase N (Ivoclar) 1120	20 s	DC (FTIR) VHN	7	70.65 (1.37) 46.48 (1.07) 94% 86% VHN > 80% all
Ilie Stark 2014 [69]	High viscosity Tetric Evo Ceram Bulk Fill (Ivoclar0 X-tra Fil (Voco) SonicFill (Kerr)			Valo (Ultradent) 1272	20 s 40 s	VHN	5	80% B/T VHN 6 mm 5.6 mm (20 s) 6 mm (40 s) 4.3 mm (20 s) 5.4 mm (40 s)	_
Ilie Stark 2015 [70]	Low Viscosity Venus Bulk Fill (Kulzer) Surefil SDR (Dentsply) X-tra base (Voco) Filtek Bulk Fill (3M/ESPE)			Valo (Ultradent) 1272	20 s 40 s	VHN	5	80% B/T VHN All > 6 mm	_
Karacolak 2018 [71]	Aura (Kuraray) Filtek Bulk Fill Posterior (3M) SonicFill (Kerr) X-tra Fill (Voco) Tetric EvoCeram Bulk Fill (Ivoclar Filtek Bulk Fill Flowable (3M/ESPE) SDR (Dentsply) X-tra Base (Voco) Venus Bulk Fill	SmartLite Focus (Dentsply)	20 s			VHN	5	>80% Except Sonicfill and Tetric EvoCeraqm Bulk Fill	_
Kaya 2018 [24]	Beautifil Bulk Restorative (Shofu)	Optima 10 1100 Demi Ultra 1100–1330	20 s 10 s	Valo (Ultradent) 3200	3 s	DC (FTIR)	5	Demi Ultra> Optima> Valo	Monowave
Lempel 2023 [57]	Tetric PowerFill (Ivoclar) Filtek One Bulk Fill Restorative (3M/ESPE)			Bluephase PowerCure (Ivoclar) 3150 1180 1950	3 s 5 s 10 s, 20 s	DC (Micro-Raman spectroscopy)	5	20 s Tetric 50.8 Filtek 48.9	_
Li 2015 [58]	Filtek Bulk Fill Flowable (3M/ESPE) Tetric EvoCeram Bulk Fil (Ivoclar) SDR (Dentsply)			Bluephase 20i (Ivoclar Vivadent)	20 s	DC Micro-Raman mapping	3	Properly cured	_
Maghaireh 2019 [25]	X-tra fill (Voco) Filtek-Bulk Fill flowable (3M/ESPE) Tetric Evo-Ceram Bulk Fill (Ivoclar) SDR posterior Bulk Fill Flowable (Dentsply) Filtek Bulk Fill posterior (3M/ESPE)	Elipar S10 (3M) 1200	10 s	Bluephase Style (Ivoclar) 1000	10 s	VHN	5	4 mm B/T VHN above 80% except Tetric EvoCeram Bulkfill and Filtek Bulk Fill Flowable X-tra fill polywave and Filtek Bulk Fill posterior Monowave	Material dependent
Makhdoom 2020 [26]	Tetric EvoCeram Bulk Fill (Ivoclar) Filtek Bulk Fill (3M/ESPE)	Satelec	10 s 20 s	BluePhase Style	10 s 20 s	4049	5	No statistically significant differences Inadequate depth	No significant difference
Marovic 2025 [27]	Filtek One Bulk Fill (3M ESPE) Tetric PowerFill (Ivoclar) Tetric PowerFlow (Ivoclar) SDR flow(Dentsply Sirona)	Translux Wave (Kulzer) 1000 1000	10 s 20 s	VALO Cordless (Ultradent) 3000 1000 1000 Bluephase PowerCure (Ivoclar) 3000 1000 1000	3 s 10 s 20 s 3 s 10 s 20 s	DC (FTIR)	5	20 s > higher conversion Power Flow and SDR > 50% Monowave Polywave no significant difference	No significant difference
Miletic 2017 [45]	Filtek Bulk Fill Flowable (3M/ESPE) SDR, Smart Dentin Replacement (Dentsply) SonicFill (Kerr) Xenius Base (Xenius) Tetric EvoCeram Bulk Fill (Ivoclar)			Bluephase 20i (Ivoclar)	10 s 20 s	DC (FTIR) VHN ISO 4049 [3]	6 6 6	DC SDR: >60% at 6 mm Filtek > 60% at 4 mm Rest < 50% B/T VHN At 10 s well above 80% SDR and Filtek Bulkill flowable At 20 s all Bulk Fills ISO > 4 mm except For SonicFill >5 mm: SDR, Filtek, Xenius	_
Moharam 2017 [72]	X-tra Fill (Voco) Sonic Fill (Kerr)	Elipar S10, (3M ESPE) 1000	20 s			VHN	10	97.6 (0.6) 90.4 (1.5)
Ozciftci 2025 [46]	PowerFill (Ivoclar) PowerFlow (Ivoclar) Omnichroma Flow Bulk (Tokuyama)			Bluephase PowerCure 1100	10 s/20 s	DC (FTIR) VHN		61.71/57.38 77.9/66.49 47.34/51.78 80.31%(5)/81.05%(4) 80.96%/(4)/79.87%(3) 75.09%(5)/86.97%(5)
Özdemir 2025 [73]	GrandioSO Heavy Flow (Voco) Filtek Bulk Fill (3M/ESPE) SonicFill 2 (Kerr)			Valo (Ultradent) 1000	20 s	VHN	5	4.8–5.1 mm Depth of cure 80%	_
Papadogiannis 2015 [47]	SDR (Dentsply) SonicFill (Kerr) Tetric Evo Ceram Bulk Fill (Ivoclar) X-tra Base (Voco) X-tra Fill (Voco)			Bluphase G2 1200	30 s	DC (FTIR)	5	Venus, SDR > 55% Material dependent	_
Par 2015 [59]	Tetric EvoCeram BulkFill (Ivocalr) Quixfil (Dell Denral) X-tra fil (Voco) Venus Bulk Fill (Kulzer) X-tra Base (Voco) SDR (Dentsply) Filtek Bulk Fill (3M/ESPE)			Bluephase G2 (Ivoclar) 1090	20 s	DC (Raman Spectroscopy)	5	Adequate polymerizarion 59.1–71.8%	_
Par 2019 [28]	TetricEvoCeramBulkFill (Ivoclar) FiltekBulkFill (3M/ESPE) X-trafil (Voco)	BluePhasreStyle M8 (Ivoclar)648	30 s	BluePhase Style (Ivoclar) 924	30 s	VHN	5	No benefit for Bf containing alternative Photonitiators All BF > 80%	No significant difference
Parasher 2020 [74]	X-tra fil Tetric EvoCeram Bulk Fill (Ivoclar) Beautiful Bulk restorative (Shofu)			Bluephase G2	manufacturer’s recommenda tions	VHN	19	X-tra Fil > 80%	_
Renzai 2019 [48]	Filtek Bulk Fill Posterior (3M/ESPE) Sonic Fill 2(Kerr) Tetric N-Ceram Bulk Fill (Ivoclar) X-tra fil (Voco)			Bluepase N 1200	30 s	VHN DC (FTIR)	6 3	B/T VHN > 85% DC > 60%	_
Rizzante 2019 [80]	Admira Xtra Fusion (Voco) Filtek Bulk Fill Posterior (3M/ESPE) Tetric Evo Ceram Bulk Fill (Ivoclar) X-tra Fil (Voco) Filtek Bulk Fill Flowable (3M/ESPE) Surefil SDR flow (Dentsply) X-tra Base	LED Blue Star 3 (Microdont) 1550	20 s			KHN	8	All Bulkfill CR Adequate 80% DoC up to 4.5 mm	_
Rocha 2017 [29]	Sonic Fill 2(Kerr) Tetric EvoCeram Bulk Fill (Ivoclar)	Smartllite Focus (Dentsply) 1000	20 s	Valo (Ultradent) 954	21 s	DC (FT-NIR)	3	Inhomegeinity Polywave more effective in the superficial 2 mm of the material containing alternative photoinitiators 4 mm: no significant difference	No significant difference
Rocha 2022 [30]	Surefil SDR (Dentsply) Tetric Power Flow (Ivoclar) X-tra-Fil (Voco)	SmartLite Pro (Dentsply/Sirona) 1200 Monet (AMD Lasers) 2000–2400	10 s 20 s 1 s, 3 s	Valo Grand (Ultradent) 900	10 s 20 s	ISO 4049 [3]	10	DOC > 4 mm Monowave no significant differences, SDR monowave higher Monowave 10 s higher	No significant difference
Sampaio 2024 [49]	Tetric EvoCeram Bulk Fill (Ivoclar) Tetric EvoFlow Bulk Fill (Ivoclar) Tetric PowerFill (Ivoclar) Tetric PowerFlow (Ivoclar)			Bluephase Style 20i 1200 Bluephase Powercure 3050	20 s 3 s	DC (FTIR) VHN	5	Bottom DC Only Tetric Evo Ceram Bulk Fill 53.3% TetricPower Flow 61.2% B/T VHN all > 80%	_
Shimokawa 2018 [31]	Filtek Bulk Fill posterior Restorative (3M/ESPE) Tetric EvoCeram Bulk Fill (Ivoclar)	Elipar DeepCure-S (3M) 1470 Celalux 3 (Voco) 1300		Bluephase 20i (Ivoclar) 1200 Valo Grand (Ultradent) 1000		KHN	5	All ~70% Polywave Wide light tip> homogeneous distribution of irradiance and wave lengths	Monowave
Siagian 2020 [32]	Filtek Bulk-Fill (3M/ESPE) Tetric N-Ceram Bulk-Fill (Ivoclar) SDR flow (Dentsply)	SmartLite Focus (Dentsply Sirona)	20 s	Bluephase style (Ivoclar)	40 s	DC (FTIR) Pulverized samples	5	DC > 50% Filtek and Tetric with both LCUs SDR < 50% No significant differences	No significant difference
Skrinjaric 2025 [75]	Tetric EvoCeram Bulk Fill (Ivoclar) Filtek Bulk Fill Posterior (3M/ESPE) Filtek One Bulk Fill(3M/ESPE) SonicFill 2 (Kerr) Admira Fusion X-tra (Voco) Admira Fusion X-tra (Voco)			D-Light Duo (RF-Pharmaceuticals Sarl) 1200–1300	20 s	VHN 4 mm/ 6 mm	3	91/87 90/90 96/90 95/94 98/96 98/97
Son 2017 [76]	Filtek Bulk Fill (3M), SureFil SDR (Dentsply) Venus Bulk Fill (Heraeus) SonicFill (Kerr) Tetric N-Ceram Bulk Fill (Ivoclar)	LE Demetron (Kerr) 900	40 s			VHN	12	SDR, Venus > 80%	_
Soto-Montero 2020 [81]	Sonic Fill (Kerr) Tetric EvoCeram Bulk Fill (Ivoclar)			Bluephase Style, Ivoclar Regular tip 935 homogenizer tip 850	SF 20 s TECBF 10 s	KHN	10	Below 80% 78% with HT and 70% with RT	_
Strini 2022 [50]	Filtek One Bulk Fill (3M/ESPE) Tetric N-Ceram Bulk-Fill (Ivoclar) SonicFill 2 (Kerr)			Valo (Ultradent) 1000	20 s	DC (FTIR) KHN	15	DC SonicFill2: 63.67% Rest below 50% B/T KHN all below 80%	_
Terada 2024 [60]	Filtek Bulk-Fill Flowable (3M/ESPE) Beautifil Bulk Flowable (Shofu) Surefill SDR Flow (Dentsply) Filtek Bulk-Fill Restorative (3M/ESPE) Beautifil-Bulk Restorative (Shofu) Tetric EvoCeram Bulk Fill			Valo (Ultradent) 1001	20 s	DC (Raman spectroscopy) 3–4 mm depth	5	Between 82.2% and 90.9%	_
Thomaidis 2024 [33]	VenusBulkFill (Kulzer) X-traBase (Voco) SDR (Dentsply) Tetric EvoCeram BulkFill (IvocalR0 SonicFill (Kerr) FiltekBulkFill flowable restorative (3M/ESPE)	Demi Ultra 1100	20 s	Bluephase Style 1100 Valo 1000	20 s 20 s	VHN	10	Material dependent	Material dependent
Torres 2024 [51]	Filtek One bulk fill restorative (3M/ESPE) Tetric N Ceram bulk fill (Ivoclar) SonicFill (Kerr) VisCalor (Kuraray)	Demi (Kerr) 1000	10 s 20 s 40 s			KHN DC (FTIR)	5 5	B/T KH > 80% only 40 s	_
Tsuzuki 2020 [34]	SDR (Dentsply)	Raddi Plus (SDI) 1300 Emitter.D (Schuster) 1250 Biolux Plus (Bioart) 880 Woodpecker (Guilin Woodpecker) 520	20 s 40 s	Valo Cordless (Ultradent) 1010	20 s 40 s	DC (confocal Raman spectroscopy)	10	All LCUs above 50% at 20 s and 40 s Valo significantly higher than Radii plus and Biolux at 20 s	Polywave
Varshney 2022 [35]	Wonder Bulk Fill (Wizden) (CQ) Tetric N-Ceram (Ivoclar) (CQ + TPO + Ivocerin)	Waldent ECO Plus (Waldent)	10 s	Bluephase N LED (Ivoclar)	10 s	DC (FTIR) Of pulverized samples	20	BluePhase Tetric DC 59% Wonder < 50% Waldent(CQ) no significantly higher DC in Tetric(ivocerin)	Polywave
Wang 2021 [61]	Filtek Bul Fill Flowable (3M/ESPE) Filtek One Bulk Fill (3M/ESPE)	Elipar S10 (3M ESPE) 1200	20 s 40 s			DC (Micro-Raman spectroscopy) at 5 mm depth	25	Filtek Bulkfill Flowable >55% at 20 s and 40 s	_
Yap 2016 [82]	Beautifil Bulk Restorative (Shofu) Beautifil Bulk Flowable (Shofu) SDR Posterior Bulk-Fill Flowable Base (Dentsply) EverX Posterior (GC) Tetric N-Ceram Bulk-Fill (Ivoclar)	Blue Shor LED (Shofu) 700	20 s			KHN ISO4049	5	80% B/T KHN 3 mm, except for EverX Posterior Tetric N-Ceram Bulk-Fil at 2.5 mm ISO 4049 [3] overestimated	_
Yeo 2021 [77]	Filtek One Bulk Fill Restorative (3M/ESPE)	Elipar LED light cure 1200	20 s 40 s			VHN	1	B/T VHN 40 s > 96.8% 20 s > 85%	_
Yıldırım 2023 [52]	SDR Plus (Dentsply) SonicFill 2 (Kerr) ACTIVA BioActive Restorative (Pulpdent)	Elipar FreeLight 2 (3M/ESPE) 1000	Manufacturer’s instructions 20 s SDR 40 s			DC (FTIR) VHN	6 10	Inadequate polymerization In all materials	_
Yokesh 2017 [53]	Surefil SDR bulk fill f lowable composite (Kerr) Filtek bulk fill flowable composite (3M/ESPE)	LEDition (Ivoclar) 600	20 s			DC(FTIR) Of pulverized coronal and pulpal half ISO 4049 [3]	10	DC < 50% ISO 4049 [3] Surefil: 3.89 Filtek: 3.54	_
Zorzin 2015 [54]	Filtek Bulk Fill Flowable (3M/ESPE) SDR Surefil (Dentsply) Tetric Evo Ceram Bulk Fill (Ivoclar) Venus Bulk Fill (Heraeus) X-tra Base (Voco)			Bluephase 20i (Ivoclar) 1200	Manufacturer’s instructions 30 s	DC (FTIR) VHN	5	30 s all Manufacturer’s instructions all except SDR and X-tra Base	_

The most frequently used light curing unit was Bluephase (Ivoclar), used in 29 studies [19,21,22,23,25,26,28,31,32,33,35,43,44,45,47,48,49,54,57,58,59,65,66,68,74,78,81,83], followed by Valo (Ultradent) in 16 studies [20,24,27,29,30,31,33,34,36,50,55,56,60,69,70,73]. The light curing unit Radii Plus was used in 3 studies [20,34,41], Elipar S in 9 studies [19,38,40,52,61,63,64,72,77], Elipar Freelight in 2 studies [40,52], Elipar Deep Cure S in one study [31], and DEMI (Kerr) in 4 studies [24,33,42,51].

Some studies received national/State funding [20,21,27,29,31,34,41,45,50,56,57,59,60,65,68,79,80,81], University funding [23,25,26,30,48,52,73,78,82], or both [73]. Some other studies declared no funding [28,33,35,40,51,53,61,62,74,76,77], and some did not mention anything on this issue [19,22,24,32,36,39,43,47,54,55,64,66,67,69,70,71]. No study whatsoever was funded by bulk fill resin composite, or LCU manufacturer companies, which could potentially imply conflict of interest.

A possible cause of heterogeneity among study results was the difference in time of measurement of DC or microhardness ratio. Measurements were performed immediately after specimen preparation in some studies [19,21,24,27,39,40,41,42,43,49,53,55,56,61,78,80,82], and in others 24 h later [20,22,23,25,26,28,29,31,32,33,34,35,36,39,44,45,48,50,51,52,54,55,57,59,60,62,64,65,66,67,68,69,70,71,73,74,75,76,77,79,81,83] or 48 h later [47]. The 24 h measurement can register post-curing. In some reports, specimens were stored in a dry and dark environment at 37 °C [33,34,35,43,45,47,48,50,51,52,60,62,64,65,67,73,76,79,81], tap water at 37 °C [54,77], distilled water at 37 °C [36,57,69,70,71] or artificial saliva at 37 °C [74]. In order to assure robustness of the reports, sensitivity testing was implemented by means of stating the funding of each study. Some studies received national/state funding [20,21,27,29,30,31,41,45,50,56,57,59,60,65,68,79,80,81], university funding [23,25,26,30,48,52,73,78,82], or both [49]. Some other studies declared no funding [28,33,35,40,51,53,61,62,74,76,77], and some did not mention anything on this issue [19,22,24,32,36,39,43,47,54,64,66,67,69,70,71].

3.3. Risk of Bias (Quality Assessment)

The risk of bias evaluation is presented in

Table 2. The risk of bias assessment of the reports included, according to the Quin tool [17].

Author	Clearly Stated Aims/Objectives	Randomization	Detailed Explanation of Sample Size Calculation	Details of Compa- rison Group	Detailed Expla- nation of Methodology	Operator Details	Method of Measurement of Outcome	Proper Statistical Analysis	Presenta- tion of Results	Blinding	Risk of Bias
Abdelwahed [62]	2	1	2	2	2	0	2	2	2	0	Low
Aldhafyan [63]	2	0	0	1	2	0	2	2	2	0	Medium
Algamaiah [19]	2	0	0	1	2	0	2	2	2	0	Medium
Alrahlah [64]	2	0	0	1	2	0	2	2	2	0	Medium
ALShaafi [78]	2	0	0	1	2	0	2	2	2	0	Medium
Altınok Uygun [36]	2	0	2	2	2	0	2	2	2	0	Low
Alzahrani [65]	2	0	2	2	2	0	2	2	2	0	Low
Arafa [37]	2	0	0	1	2	0	2	2	2	0	Medium
Conteras [21]	2	0	0	1	2	0	2	2	2	0	Medium
Cardoso [20]	2	0	0	2	2	0	2	2	2	0	Medium
Szalma [57]	2	0	0	1	2	0	2	2	2	0	Medium
Daugherty [39]	2	0	0	2	2	0	2	2	2	0	Medium
Derchi [22]	2	0	0	1	2	0	2	2	2	0	Medium
Elhejazi [66]	2	0	0	2	2	0	2	2	1	0	Medium
Fronza [55]	2	0	0	2	2	0	2	2	2	0	Medium
Gan [23]	2	0	0	2	2	0	2	2	2	0	Medium
Garcia [79]	2	0	0	2	2	0	2	2	2	0	Medium
Garoushi [40]	2	0	0	1	2	0	2	2	2	0	Medium
Georgiev [67]	2	0	0	2	2	0	2	0	1	0	High
Gomes de Araújo-Neto [56]	2	0	0	2	2	0	2	2	2	0	Medium
Goncalves [41]	2	0	0	1	2	0	2	2	2	0	Medium
Gorrachi [43]	2	0	0	1	2	0	2	2	2	0	Medium
Gonzales Guarneri [42]	2	0	0	1	2	0	2	2	1	0	Medium
Jakupovic (2023) [68]	2	0	0	2	2	0	2	2	2	0	Medium
Jakupovic (2025) [83]	2	0	0	1	2	0	2	2	2	0	Medium
Javed [44]	2	0	2	2	2	0	2	2	2	0	Low
Ilie Stark 2014 [69]	2	0	0	1	2	0	2	2	2	0	Medium
Ilie Stark 2015 [70]	2	0	0	1	2	0	2	2	2	0	Medium
Karacolak [71]	2	0	0	1	1	0	2	1	1	0	High
Kaya [24]	2	0	0	1	2	0	2	2	2	0	Medium
Lempel [57]	2	0	0	1	2	0	2	2	2	0	Medium
Li [58]	2	0	0	2	2	0	2	2	2	0	Medium
Maigaireh [25]	2	0	0	2	2	0	2	2	2	0	Medium
Makhdoom [26]	2	0	0	2	2	0	1	2	2	0	Medium
Marovic [27]	2	0	0	2	2	0	2	2	2	0	Medium
Miletic [45]	2	0	0	2	1	0	2	2	1	0	Medium
Moharam [72]	2	0	0	2	2	0	2	2	2	0	Medium
Ozciftci [46]	2	0	2	1	2	0	2	2	2	0	Medium
Özdemir [73]	2	0	0	2	2	0	2	2	2	0	Medium
Papadogiannis [47]	2	0	0	2	2	0	2	2	2	0	Medium
Par 2015 [59]	2	0	0	2	2	0	2	2	2	0	Medium
Par 2019 [28]	2	0	0	2	2	0	2	2	1	0	Medium
Parasher [74]	2	0	0	1	2	0	2	2	2	0
Renzai [48]	2	0	2	2	2	0	2	2	1	0	Medium
Rizzante [80]	2	0	0	2	2	0	2	2	2	0	Medium
Rocha (2017) [29]	2	0	0	1	2	0	2	2	1	0	Medium
Rocha (2022) [30]	2	2	0	2	2	2	2	2	2	2	Low
Sampaio [49]	2	0	0	1	2	0	2	2	2	0	Medium
Shimokawa [31]	2	0	2	2	2	0	2	2	2	0	Medium
Siagian [32]	2	0	0	1	2	0	1	2	1	0	Medium
Skrinjaric [75]	2	0	0	1	2	0	2	2	2	0	Medium
Son [76]	2	0	0	2	2	0	1	2	1	0	Medium
Soto-Montero [81]	2	0	0	2	2	0	2	2	2	0	Medium
Strini [50]	2	0	0	2	2	0	2	2	1	0	Medium
Terada [60]	2	0	0	2	2	0	2	2	2	0	Medium
Thomaidis [33]	2	0	0	2	2	0	2	2	2	0	Medium
Torres [51]	2	0	0	1	2	0	2	2	2	0	Medium
Tsuzuki [34]	2	0	0	2	2	0	2	2	2	0	Medium
Varshney [35]	2	0	2	2	2	0	1	2	1	0	Medium
Wang [61]	2	0	2	2	2	0	2	2	2	0	Medium
Yap [82]	2	0	0	2	2	0	2	2	2	0	Medium
Yeo [77]	2	0	0	2	2	0	2	0	2	0	Medium
Yıldırım [52]	2	0	0	2	2	0	2	2	2	0	Medium
Yokesh [53]	2	0	0	1	2	0	2	2	2	0	Medium
Zorzin [54]	2	0	0	2	2	0	2	2	2	0	Medium

2: Criterion fully met. Low risk of bias for that specific item (clear, detailed, and appropriate information provided). 1: Criterion partially met. Moderate risk of bias. (some information provided but incomplete or unclear). 0: Criterion not met or not reported. High risk of bias. (missing or inadequate methodological information).

. According to the Quin tool for in vitro studies risk of bias criteria [18], 5 studies [30,36,44,62,78] presented low risk of bias, 2 studies presented high risk of bias [67,71], and all the rest, 58 studies, presented medium risk of bias. None of the studies reported operator details or blinding. Abdelwahed et al. [62] and Rocha et al. [30] performed randomization, while Abdelwahed et al. [62], Alzahrani et al. [65], Altinok Uygun et al. [36], Javed et al. [44], Ozciftci et al. [46], Renzai et al. [48], Shimokawa et al. [31], Varshney et al. [35], and Wang and Wang [61] performed sample size calculation. Control groups were included, but just a few studies reported it explicitly [20,23,25,26,27,28,30,31,33,34,35,36,39,44,45,48,50,52,54,55,56,58,59,60,61,62,65,66,67,68,72,73,77,79,81,82].

4. Discussion

According to the Quin tool for in vitro studies risk of bias criteria [18], the studies by Abdelhawed et al. [62], Alzahrani et al. [65], Altinok Uygun et al. [36], Javed et al. [44], and Rocha et al. [30] presented low risk of bias; Georgiev et al. [67] and Karacolak et al. [71] presented high risk of bias; and all the rest presented medium risk of bias. According to the Quin tool for in vitro studies [18], the criteria seem to present a higher sensitivity to the risk of bias compared to previously used techniques [17] and lead to quite different rankings.

The 80% or higher bottom-to-top microhardness ratio is considered adequate for the prompt polymerization of composite resins [85]. Previous literature suggests composites placed in load-bearing areas require a DC% of at least 50–55% [86,87]. DC can be assessed by direct methods, such as infrared spectroscopy [88], or indirect methods, such as the scrape back length technique [89] and microhardness testing [90,91,92]. Bouschlicher, Rueggeberg, and Wilson [93] demonstrated that the 0.80 B/T-KHN ratio corresponds to 0.90 B/T-DC of posterior hybrid resin composites and that at the 2 mm depth, the B/T-KHN ratio was less than 0.80 (r = 0.97). However, although a good correlation exists between the decrease in hardness and the decrease in DC, raw microhardness values cannot be used to directly compare composites with different inorganic matrices or filler sizes and loadings. It is found that with an increase in depth from the irradiation surface, DC exhibits a more rapid decrease compared to hardness [87]. Microhardness comparisons of a resin composite are a mechanical property that can depict the degree of conversion (DC) of light-cured resin composites in comparisons of the same material. Miletic et al. [45] found a positive linear correlation for bottom DC and VH in bulk fill CRs. An average DC ratio of 0.9 corresponded to a bottom-to-top VH ratio of 0.8. This was confirmed by Ferracane for unfilled composite resins [91]. Bouschlicher et al. [93] postulated that as a measure of completeness of conversion, B/T-KHN was approximately 2.5 times more sensitive than the B/T-DC ratio for posterior hybrid resin composites.

From the 65 studies included, 17 were investigating both monowave and polywave light-curing units for the effectiveness of polymerization of bulk fill resin composites [19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35].

Table 3. The effectiveness of monowave and polywave LCUs.

Author	Monowave	Polywave	Material Dependent	No Statistical Signify
Algamiah [19]			X
Cardoso [20]			X
Conteras [21]				X
Derci [22]		X
Gan [23]	X
Kaya [24]	X
Maghaireh [25]			X
Makhdoom [26]				X
Marovic [27]				X
Par [28]				X
Rocha [29]				X
Rocha [30]				X
Shimokawa [31]	X
Siagian [32]				X
Thomaidis [33]			X
Tsuzuki [34]		X
Varshney [35]		X

depicts the effectiveness of monowave and polywave LCUs in the aforementioned studies. The studies by Conteras et al. [21], Derchi et al. [22], Maigaireh et al. [25], Makdoom et al. [26], Marovic et al. [27], Par et al. [28], Rocha et al. [29], Rocha et al. [30], and Thomaidis et al. [33] reported that there is no statistically significant difference in polymerization efficiency between monowave and polywave LCUs and that it is material dependent. The studies by Gan et al. [23], Kaya et al. [24], and Shimokawa et al. [31] postulated that a significantly higher polymerization efficiency of bulk fill resin composites, when cured with monowave light curing units, was found. The polywave LCUs demonstrate a benefit against monowave in curing bulk fill resin composites up to 4 mm in the studies by Cardoso et al. [20], Tsuzuki et al. [34], and Varshey et al. [35]. Derchi et al. [22] found that Bluephase Style did not demonstrate a significant difference in DC of Tetric Evo Ceram Bulkfill (CQ, TPO, Ivocerin) and Filtek BulkFill (CQ) compared to the monowave LCU Bluephase M8, but the polywave LCU Valo did. They also reported that Bulkfill SDR (CQ) presented a lower DC when cured with Valo compared to the monowave and Bluephase styles, which did not show a statistically significant difference. Tsuzuki et al. [34] reported that the polywave LCU Valo showed statistically significant differences in DC compared to two (Radii Plus and Biolux Plus) of the four monowave LCUs used for 20 s, but no significant differences with the other two monowave LCUs (Emitter D and Woodpecker), at the depth of 4 mm, when polymerizing the BulkFill SDR, which contains just the CQ photoinitiator. Varshney et al. [35] reported that the bulk fill containing only CQ did not demonstrate statistically significant differences when cured with monowave or polywave LCUs. While the BulkFill containing CQ, TPO, and Ivocerin showed statistically significant higher DC when cured with Polywave LCU, the monowave LCU was not able to polymerize to an acceptable degree.

Alrahlah et al. [64], Goncalves et al. [41], Goracci et al. [43], Jakupovic et al. [68], Ilie and Stark [69,70], Kaya et al. [24], Lempel et al. [57], Li et al. [58], Renzai et al. [48], Rizzante et al. [80], Son et al. [76], Yap et al. [82], and Yeo et al. [77] confirmed that bulk fill resin composites can be adequately cured by means of 80% or higher bottom-to-top microhardness or DC above 50% using monowave LCUs. Abdelwahed et al. [62], Alzahrani et al. [65], ALShaafi et al. [78], Altınok Uygun et al. [36], Elhejazi et al. [66], Gomes de Araújo-Neto et al. [56], Jakupovic et al. [68], Ilie and Stark [69,70], Lempel et al. [57], Li et al. [58], Özdemir et al. [73], Par et al. [28,59], Parasher et al. [74], Soto-Montero et al. [81], and Terada et al. [60] confirmed that bulk fill resin composites can be adequately cured by means of 80% or higher bottom-to-top microhardness or DC above 50% using polywave LCUs. Conteras et al. [21], Kaya et al. [24], Makhdoom et al. [26], Marovic et al. [27], Rocha et al. [29,30], Siagian et al. [32], Tsuzuki et al. [34], Varshney et al. [35], and Wang et al. [61] confirmed that bulk fill resin composites can be adequately cured by means of 80% or higher bottom-to-top microhardness or DC above 50% using both types of LCUs. Studies evaluating depth of cure by ISO 4049 [3] were not included, because they overestimate depth of cure [85]. Only one study [30], evaluating depth of cure by ISO 4049 [3], was included, because it investigated the efficiency of both monowave and polywave LCUs in bulk fill resin composites, and therefore results were comparable between the LCUs tested.

To evaluate robustness of the reports, sensitivity testing can be implemented by means excluding studies according to risk of bias. Studies by Georgiev et al. [67] and by Karakolak et al. [71] presented high risk of bias. If studies with high risk of were excluded, the conclusions would not be be altered Studies by Abdelwahed et al. [62], Alzahrani et al. [65], Altinok Uygun et al. [36], Javed et al. [44], and Rocha et al. [30] presented low risk of bias. If only studies with low risk of bias were used in order to evaluate robustness of the study, there would be very few studies left, in order to draw conclusions. Another way to investigate robustness would be to exclude studies with limited sample size. A different approach was selected. Studies reporting inadequate DC or microhardness ratio of the Bulk Fill resin composites tested, were investigated, by addressing the inadequately cured materials in relation to the respective LCU.

Table 4. Studies reporting inadequately cured bulk fill resin composites.

Author	Monowave	Polywave	CQ	CQ + Ivocerin + TPO	CQ + Ivocerin
Aldhafyan [63]	Y	-	Filtek One Bulk Fill SDR	Ok	-
Algamaiah [19]	Y	Y	Filtek One Bulk Fill	-	Power Flow
Al Shaafi [78]	-	Y	SonicFill	Tetric BulkFill
Daugherty [39]	Y	-	SonicFill Beautiful Filtek Bulk Fill	Tetric Evo Ceram Bulk Fill
Derci [22]	Y	Y	Filtek Bulk Fill	-	-
Fronza [55]		Y	Filtek Bulk Fill	-	-
Elhejazi [66]	-	Y	Opus Bulk Fill	-	-
Gan [23]	Y	Y	All materials	All materials	-
Garcia [79]	Y	-	All materials	All materials	-
Georgiev [67]	-	Y	Filtek One Bulk Fill	-	-
Gonzales Guarneri [42]	-	Y	Filtek One Bulk Fill Filtek Bulk Fill flowable	-	Tetric PowerFill Tetric Powerflow
Kaya [24]	Y	Y	Beautiful	-	-
Lempel [57]	-	Y	Filtek One Bulk Fill	-	-
Maghaireh [25]	Y	Y	Filtek Bulk Fill X-tra Fill	Tetric Evo Ceram Bulk Fill	-
Makhdoom [26]	Y	Y	All materials	All materials	-
Ozciftci [46]	-	Y	Omnichroma flow Bulk Fill	-	-
Papadogiannis [47]	-	Y	X-tra Base X-tra Fill	Tetric Evo Ceram Bulk Fill	-
Parasher [74]	-	Y	Beautiful	Tetric Evo Ceram Bulk Fill	-
Shimokawa [31]	Y	Y	-	Tetric Evo Ceram Bulk Fill	-
Soto Montero [81]	-	Y	SonicFill	Tetric Evo Ceram Bulk Fill	-
Strini [50]	-	Y	Filtek One Bulk Fill	Tetric Evo Ceram Bulk Fill

demonstrates these inadequately cured materials in conjunction to the LCU used, in different studies. These studies show that both types of LCUs were not able to polymerize properly, both types of materials, those including only CQ, as well as materials with additional photoinitiators. All the rest studies reported acceptable polymerization of all bulk fill resin composites.

Garcia et al. [79] and Yildirim et al. [52], using monowave light-curing units, and Gan et al. [23] and Shimokawa et al. [31], using both monowave and polywave light-curing units, reported that bulk-fill resin composites were not adequately cured by means of less than 80% of bottom-to-top microhardness when the manufacturer’s instructions were followed.

Studies by Daugherty et al. [39], Garoushi et al. [40], Karacolak et al. [71], Torres et al. [51], and Yap et al. [82], using monowave light curing units, and Miletic et al. [45], Papadogiannis et al. [47], Sampaio et al. [49], Strini et al. [50], Thomaidis et al. [33], and Zorzin et al. [54], using polywave light curing units, concluded that not all bulk fill resin composites could be adequately cured by means of less than 50% degree of conversion, or less than 80% of bottom-to-top microhardness, and that was material dependent.

Magairegh et al. [25], using a spectrophotometer, monitored in real time the transmitted irradiance and radiant exposure reaching the bottom of bulk fill resin composite specimens of a monowave and a polywave LCU. It was reported that there were not significant differences in the total amount of light transmitted through the Bulk Fill RC used between the monowave and polywave LCU, with similar microhardness depth of cure results.

The most commonly used low-viscosity materials were SDR, Venus Bulk Fill, Filtek Bulk Fill, Xtra Base, and Tetric Evo Bulk Fill Flow. The Bulk Fill resin composite SDR contains UDMA and TEGDMA monomers, Xtra Base Bis GMA and UDMA, Venus BulkFill UDMA and EBADMA, and Filtek BulkFill BisGMA, BisEMA, UDMA, and TEGDMA.

The most commonly used high-viscosity materials were Tetric Evo Ceram BulkFill, SonicFill, Xtra Fill, Xenius Base, and Filtek Bulk Fill Posterior. Tetric Evo Ceram Bulk Fill contains BisGMA, BisEMA, and UDMA; SonicFill contains BisGMA, BisEMA, and TEGDMA; and XtraFill contains BisGMA, BisEMA, and TEGDMA. According to Zorzin et al. [54], UDMA is found in SDR, Tetric Evo Ceram, Venus Bulk Fill, X-tra Fill, and X-tra Flow. The monomer UDMA was shown to reach higher DC values than Bis-GMA, despite its relatively high molecular weight. Co-polymerization of Bis-GMA with UDMA or TEGDMA is usually utilized to increase conversion and create a highly cross-linked, dense, and stiff matrix [94,95]. Elastic modulus is increased with filler fraction [92] and BisGMA concentration in the organic matrix [95]. An increased amount of filler particles is an obstacle for polymeric chain propagation [96], and BisGMA, due to its high viscosity, has decreased mobility [97]. Both factors result in reduced DC. It was also reported that all bulk fills, light-cured for 30 s, showed lower %DC at the top surface when compared to depths of 2 and 4 mm [54]. This was attributed to the contraction towards the center of the specimen in non-bonded resin composite or to a higher polymerization due to the insulation of the exothermal reaction by the overlying material [54,69,70]. The DC of different monomer systems increases in the following order: bisGMA < bis-EMA < UDMA < TEGDMA [97]. Papadogiannis et al. [47] also reported that the highest degree of conversion was found in bulk-fill composite resins containing UDMA and TEGMA without Bis-GMA. This happens because UDMA has a lower viscosity than Bis-GMA. Resin composites containing UDMA possess extensive H-bonds through -NH₂ components, which are not as strong as covalent bonds but contribute to higher crosslinking and a denser matrix.

Highly filled bulk fill resin composites present lower degrees of polymerization or top-to-bottom microhardness ratios [58]. The low-viscosity bulk-fill resin composites demonstrate higher bottom-to-top depth of cure, through microhardness measurements, compared to high-viscosity bulk-fill RC [19,69,70], attributed to the presence of UDMA monomers, which can increase the degree of conversion compared to Bis-GMA-containing high-viscosity resin composites. Bulk fill materials, such as SDR, composed of UDMA monomers and larger fillers (approx. 20 µm), allow increased polymerization as a consequence of smaller filler surface area for light scattering and higher light transmittance [7,19,25,84,98,99]. Bulk fill resin composites, characterized by the increased refractive index mismatch between the polymer matrix and fillers, such as Filtek Bulk Fill, show lower light penetration and lower bottom-to-top microhardness ratios [84,98,99,100,101].

The newer AFCT bulk fill resin composites, Filtek One Bulk Fill, and the RAFT Tetric Power Fill and Tetric Power Flow, contain special monomers in order to decrease polymerization shrinkage [57] and are able to be polymerized with very short light exposure time (3 s) with high radiant exitance (>3000 mW/cm²) without adverse consequences [101,102]. Filtek One Bulk Fill contains AUDMA, UDMA, and AFM; Tetric Power Fill contains Bis-GMA, BisEMA, and β-ally sulfone AFCT AFM; and Tetric Power Flow contains Bis-GMA, BisEMA, and UDMA. Lempel et al. [57] reported that Filtek One Bulk Fill, as well as Tetric PowerFill, is comprised of monomers that are not specified by the manufacturers. They detected Bis-GMA in Filtek One Bulk Fill and TEGDMA in Tetric PowerFill through reversed-phase high-performance liquid chromatography.

Any higher polymerization time, such as 20 s or more, with a regular radiant exitance of around 1000 mW/cm² resulted in a higher % DC [19,57]. The application of 20 J/cm² was beneficial for all bulk fill resin composites [69,70].

Tetric EvoCeram Bulk Fill contains alternative photoinitiators TPO and Ivocerin, except for CQ, while Filtek Bulk Fill and SonicFill contain only CQ. The absorption peak of CQ is around 460 nm, in the blue spectrum. The absorption peak of Ivocerin is set in the violet spectrum (380–420 nm) and slightly extends to the blue spectrum range (420–455 nm), where almost 50% of its peak absorbance occurs at 440 nm. Ivocerin is a photoinitiator with higher photopolymerization reactivity [21]. Ivocerin has a broad absorption spectrum, and it is possible to activate it to a certain extent with blue wavelengths with the use of monowave or quartz-tungsten-halogen lights (QTH) LCUs, which may emit light up to a range of 420–540 nm. Some studies reported [32,60] that Filtek seems to be polymerized to a higher degree than Tetric Evo Ceram BulkFill when Polywave LEDs are used. Rocha et al. [103] found that the combination of CQ-amine and TPO increases the polymerization shrinkage stress and does not improve the depth of cure of bulk-fill composites. Therefore, some newer bulk fill composites with additional photoinitiators, such as Tetric Power Fill and Tetric Power Flow, do not contain TPO but only Ivocerin. Many studies using a monowave LCU [19,21,23,24,26,28,29,30,31,32,33,34,35,39,51,54,64,71,80] demonstrated that Tetric Evo Ceram, containing CQ, TPO, and Ivocerin, was properly cured. The study by Marovic et al. [27] using monowave LCU properly cured PowerFill, containing CQ and Ivocerin.

Newer bulk fill resin composites, such as Filtek Bulk Fill One and Tetric Power Fill, are highly filled (76% and 79% Wt, respectively), incorporate additional fragmentation chain reaction monomers, and demonstrate higher depth of cure and lower polymerization shrinkage strain [99,102]. Filtek Bulk Fill One’s monomer matrix includes a long-chain UDMA (AUDMA), which slows down the polymerization reaction rate [19,27], while Tetric Power Fill forms short polymer chains. Both materials are intended for achieving relatively high DC with the high-intensity 3-stack cure polymerization protocol [19,27,49]. From the bulk-fill resin [32,60] composites intended for a high-irradiation protocol, the flowable bulk-fill PowerFlow exhibited higher DC and light transmission. The high irradiance protocol (3 s protocol) showed faster polymerization, especially for flowable BF. Bulkfill One, containing addition–fragmentation chain transfer (AFCT) agents, exhibited lower DC compared to Lucirin TPO boosted composites when cured with all protocols (monowave 20 s, polywave 10 s, high irradiance 3 s) [19,57]. Extended curing times with moderate irradiance (1 W/cm²) were beneficial for all tested materials [19,27,30,34,49,50,51,57,77], as confirmed by Alzahrani et al. [65] and Altinok Uygen et al. [36], for longer employed curing times.

Jakupovic et al. [68] reported that both addition fragmentation monomer composites, Tetric PowerFill and Tetric PowerFlow, presented higher than 80% bottom-to-top microhardness, both with the 10 s low-power LCUs and with the 3 s high-power LCUs, but the irradiance was homogenized by extending light curing time in order to apply equal excitation energy to the specimens. Abdelwahed et al. [62] confirmed these results with a 5 s light-curing time.

The deeper polymerization of bulk fill resin composites is mainly due to their ability to enable higher light transmission. The amount of light transmission through the composite resin depends on the amount of reflected, scattered, and absorbed light, which varies depending on the composition of the resin composite [84]. An increase in the amount of filler causes translucency to decrease due to higher light refraction at the filler-resin interface. On the contrary, the translucency increases as filler size increases [84]. Filler size, radiopacity, translucency, and pigments affect the light transmission through the material and the curing depth [100,104]. Nano-filled bulk-fill resin composites, such as Filtek Bulk Fill and SonicFill contain fillers smaller than the visible light wavelength (390 to 750 nm). As a consequence, nanoparticles cannot scatter or absorb visible light, with a significant effect on the curing and translucency of resin composites [105]. The translucency of a resin composite is influenced to a great extent by the difference in the refractive indices between the fillers and the resin matrix, with an effect on light scattering within a material [105,106]. Monomer BisGMA and silica fillers present similar refractive indices, and thus, they improve translucency [107,108].

Strini et al. [50] reported that lower values of DC at the bottom of the samples do not necessarily imply unacceptable clinical performance since the degree of cross-linking cannot always be measured by FTIR double bond conversion [108]. The degree of crosslinking of a composite resin is affected by other monomers incorporated in its composition, such as the additional fragmentation monomer (AFM), which can form other cross bonds, and the imino groups (-NH-) in the UDMA monomer, which provide an alternative path for the polymerization. The monomer TEGDMA has two functional terminal methacrylate groups similar to BisGMA, but due to the aliphatic chain between the groups, it presents lower viscosity, yielding higher conversion degree values. The lower viscosity may reduce the composite resin’s mechanical properties, which could further explain the KHN and DC findings. Nonetheless, the low viscosity of this monomer is yielding towards higher conversion degree values [50]. Bottom-to-top microhardness measurements could be more sensitive than bottom-to-top DC, as bottom-to-top microhardness indirectly considers the matrix network crosslinking, while bottom-to-top DC only reveals the amount of remaining carbon double bonds [109].

Violet spectra of light (wavelengths below 420 nm), emitted from the polywave LED LCUs, were not able to penetrate all the way to the 4 mm depth but only up to 2.5 mm depth, especially in viscous composites, despite their high light translucency [28,29,31,98,103,110,111]. Nevertheless, QTH and monowave LED LCUs, emitting light in a broad spectrum, may adequately cure bulk-fill composites with additional photoinitiators. Moreover, blue light emitted by QTH and monowave LED seems able to penetrate all the way to the depth of 4 mm, and even deeper, and is able to adequately cure the Tetric EvoCeram Bulkfill. The QTH used (Elipar Trilight) delivers a small amount of energy, about 10%, in the 350–420 nm (violet), while the Bluephase G2 and Valo deliver 14–24% and 17–19% in this region, respectively [28,98]. Therefore, lower energy is emitted by the specific LED LCU in the blue spectrum, which is useful for the excitation of camphoroquinone. Thus, when the Elipar Trilight QTH with an irradiance of 750 mW/cm² emits 675 mW/cm² in the blue spectrum and 75 mW/cm² in the violet spectrum, the Bluephase G2, with an irradiance of 1200 mW/cm², emits 936 mW/cm² in the blue spectrum and 264 mW/cm² in the violet spectrum [31]. The low penetration of the violet spectrum through the bulk fill resin composites is also confirmed by Maghairel et al. [25], Marovic et al. [27], and Par et al. [28]. The two reasons mentioned above can explain why polywave LCUs do not seem to have an advantage over monowave LCUs in light-curing bulk-fill resin composites. Par et al. [28] reported that the potentially beneficial effect of polywave LCUs may be due to the presence of an additional violet spectrum light emission and a precise blue spectrum light, which was more effective in activating the conventional camphorquinone/amine photoinitiator system. Shimokawa et al. [110] studied the effect of monowave and polywave LCUs, placed 2 mm from the specimen, through top and bottom microhardness, emission spectrum, and light beam profile, and reported that approximately 10% of the radiant power delivered to the top reached the bottom of the specimen, and almost no violet light passed through 4 mm of either bulk fill resin composite. This happened because the lower wavelengths of violet light are more highly scattered within the bulk fill resin composite compared to the longer wavelengths of blue light. There was also found a significant difference in the irradiance homogeneity of the light emitted by all LCUs, and higher irradiance was recorded in the central area of the curing tip, and higher microhardness was recorded in the central area of the specimens. They also reported that the use of multiple-peak LCUs resulted in lower hardness values at the bottom of the bulk-fill resin composites compared to the microhardness when they were photoactivated with single-peak blue LCUs for the same exposure time. Therefore, the light in the violet spectrum was not able to penetrate all the way to the depth of 4 mm, and this is the main reason that suggests the use of polywave LCUs does not seem to offer an advantage over monowave LCUs in the polymerization of BulkFill resin composites. The findings of a systematic review by Lima et al. [6] are somewhat different when talking about conventional resin composites in 2 mm increments, concluding that polywave LCUs can more adequately cure them.

Rocha et al. [29] reported that polywave light curing units emitted non-homogeneous light profiles, but the non-homogeneity of the light beam did not affect the homogeneity of the DC of the bulk fill resin composites tested. The emission spectrum across the light tip of the polywave Bluephase Style with the original non-homogenizer light guide was not uniform [112], resulting in nonuniform nanohardness across the top and bottom surfaces [113]. On the contrary, Rocha et al. [29] found that monowave and polywave LEDs emitted nonhomogeneous light beams, but this did not affect the DC homogeneity of bulk fill composites, according to the regions under the influence of blue and/or violet emission at the same depth. The use of a homogenizer tip with the use of a polywave LCU did not show any effect on the beam profile or microhardness measurements in the specimen’s bottom surface [81]. They also suggest that the homogenizer light guide resulted in significantly increased microhardness at the top; in resin composites containing alternative photoinitiators, however, that effect was not observed at the bottom surfaces [76].

Materials react differently to the supplied irradiance. An exposure time of 20 s at moderate irradiance of about 1000 mW/cm² is recommended for all materials [19,57,69,70]. The highest mechanical properties were reached not at the specimens’ surface, but in deeper layers [70]. Ilie and Stark [69,70] and Zorzin et al. [54] showed that increasing the irradiation duration had a positive impact on DC of bulk-fill resin composites, so extending the irradiation duration was suggested by researchers for the application of resin composites into deep cavities [32]. Regarding the different curing times, the extended curing time (20 s) significantly increased the depth of cure (DOC) for all composites and for both light-curing units [26]. Rapid curing protocol should be reserved exclusively for materials specifically designed for this and is not recommended for use with other materials [27,30,112]. Extended curing times with moderate irradiance (1 W/cm²) were beneficial for all tested materials. High-irradiance rapid 3 s curing of AFCT-modified RBCs resulted in inferior results for the degree of polymerization [27,57]. A longer exposure time is recommended in a clinical situation [19,27,57]. It can also be concluded that LCUs with regular intensity (around 1000 mW/cm²) used for 20 s perform better than high-intensity LCUs for a lower time [24,26,63]. Par et al. [28] advocated the extension of curing time of bulk fill composites to 30 s with the use of an LCU of 1000 mW/cm² in order to adequately cure them with an 80% or higher bottom-to-top microhardness ratio.

The relatively large number of studies were excluded due to the lack of access to the full text, is a limitation of the systematic review study, due to the potential impact on the completeness and robustness of the review. Heterogeneity in the studies included can be considered a limitation of the present systematic review. Heterogeneity was detected among the included studies, with the difference in time of measurement of DC or microhardness ratio, as well as storage media. Measurements were performed immediately after specimen preparation [19,21,24,27,39,40,41,42,43,49,53,55,56,61,78,80,82] and are expected to present lower values of DC or microhardness ratio compared to the ones registered 24 h later [20,22,23,25,26,28,29,31,32,33,34,35,36,39,44,45,48,50,51,52,54,55,57,59,60,62,64,65,66,67,68,69,70,71,73,74,75,76,77,79,81,83] or 48 h later [47]. The 24 h measurement can register post-curing, but the restorations are loaded intraorally immediately after placement. Therefore, the immediate values of DC, or microhardness ratio, are preferable. Specimens were stored in a dry and dark environment at 37 °C [33,34,35,45,47,48,50,51,52,60,62,64,65,67,68,73,76,79,81], tap water at 37 °C [54,77], distilled water at 37 °C [36,57,69,70,71], or artificial saliva at 37 °C [74], which could possibly affect the recorded properties. Due to the heterogeneity of the studies included, a meta-analysis was not performed.

Another reason for heterogeneity in DC computation via FTIR or Raman spectroscopy is that newer bulk fill resin composites comprise mainly, or to a great extent, UDMA monomers. In Bis-GMA composite resins, the aromatic C-C bond adsorption spectra of 1605 cm⁻¹ is used as a reference for the DC calculation by FTIR. The formulation of composite resins, in the present time, comprises UDMA as well as Bis-GMA monomers. UDMA monomers do not contain aromatic C-C bonds, and in order to establish the DC of UDMA-containing composite resins, it is advisable to use a different normalization reference peak for FTIR DC analysis, and according to Guerra et al. [114], this could be the secondary amide adsorption at 1537 cm⁻¹. This could result in differences in DC computation in UDMA-containing composite resins.

Dynamic mechanical analysis (DMA) is a technology that measures the mechanical properties of materials by applying an oscillating force to a sample and measuring its response. The technique allows for the determination of the material’s stiffness and damping properties, which are expressed as the storage modulus (elastic response) and loss modulus (viscous response), respectively [115]. It is referred to as nanoindentation and can be used in studying the viscoelastic behavior of polymers, composites, and other viscoelastic materials.

Nanoindentation is a technique that, compared to micro-indentation implemented by Vickers or Knoop indenters, can give insight on the elastic as well as the plastic deformation of composite resins [115,116], given the limitation of adequate quasistatic load applied in order to promptly characterize the modulus of elasticity of the combined material and not just the mechanical properties of the fillers or matrix [117]. Therefore, future studies may use nanoindentation for the bottom-to-top hardness ratio. Future research could be focused mainly on immediate DC investigation in order to acknowledge the material properties as soon as the restoration is completed and subjected to masticatory forces. Additionally, delayed (24 h) measurements can give the optimum properties of the material tested. Future studies evaluating DC of materials comprising mainly UDMA should use the secondary amide adsorption at 1537 cm⁻¹ as a reference bandwidth in FTIR spectroscopy.

5. Conclusions

Within the limitations of this systematic review, polywave LCUs do not seem to offer a significant advantage over monowave LCUs in the effective polymerization of bulk fill resin composites. The emission of 20 J, by use of a regular exitance of 1000 mW/cm² for 20 s, can adequately cure most bulk fill resin composites, and an extension of time to 30 s or 40 s can be beneficial in terms of depth of cure.