Bond Strength of Impression Materials to Conventional and Additively Manufactured Custom Tray Materials: A Systematic Review

Abstract

Purpose: We aimed to systematically review the current literature on the bond strength between custom tray materials and impression materials, including the various parameters affecting the strength. Methods: Four electronic databases were used: Ovid, Web of Science, PubMed, and Scopus. Relevant studies were chosen based on their eligibility, determined through inclusion and exclusion criteria. This review followed the PRISMA strategy. A risk of bias assessment was produced to evaluate the validity of each study. Results: There were 173 initial relevant studies identified, and after the screening process, this was reduced to seven. Two additional studies were also included from hand searching, resulting in total nine studies to be included in the review. Four of the nine evaluated studies concerned additively manufactured (AM) materials, including acrylonitrile butadiene styrene (ABS), polyethylene terephthalate glycol polyester (PETG), high-impact polystyrene (HIPS), and polylactic acid (PLA). Five studies evaluated an auto-polymerizing resin and one a thermoplastic material. All studies used polyvinyl siloxane impression materials and an adhesive selection following manufacturers’ recommendations. Three studies used scanning electron microscopy (SEM) to analyze their specimens. All studies reported a low risk of bias. Conclusions: Surface roughening was shown to reduce the strength of the bonding interface, whereas combining chemical and mechanical retention was shown to increase the bond strength. Inconsistent results exist in determining if AMed (3D-printed) tray materials are comparable or perform better than the conventional tray materials, highlighting the need for further study. Clinical Significance: The bond strength of the custom tray to the dental impression material is critical as it affects the model produced and therefore the final prosthesis. It is therefore invaluable to use materials with high bond strength for the construction of custom trays.

1. Introduction

Accurate impressions of the teeth and surrounding structures are crucial in dentistry and can be captured using either stock or custom trays. Stock trays are commonly used for primary impressions, whilst custom trays are customized to individual patients from a primary model and used for secondary impressions [1,2]. Custom trays could be made from polymethyl methacrylate (PMMA) and offer benefits like moisture resistance and stability. They enhance accuracy but require more time and expense than stock trays due to the need for them to be constructed indirectly in a laboratory setting [1,2]. Advances in digital technologies have seen the advent of construction techniques that employ additive manufacturing (AM; also known as 3D-printing), these can be utilized with designs directly from an intra oral scan, scan of a preliminary impression or a model [3]. Despite the increase in direct optical scanning techniques the use of custom trays in many clinical scenarios is still required [4]. When producing indirect restoration, the precision of the custom tray is one of several important elements influencing the final product [5]. The digital manufacturing of custom trays has shown to be quicker, simpler, more accurate while fitting with less human errors [6].

Common impression materials include irreversible hydrocolloid and polyvinyl siloxane [7]. The bond of the selected impression material to a custom tray is critical to the success of restorations as it will affect the accuracy of the secondary model [8,9]. Furthering the importance of bond strength is its’ need to resist the stresses that develop within the impression material, adhesive, and tray during removal. Therefore, bond strength testing is crucial for comparing properties, predicting performance parameters, and ensuring quality [10]. Various testing methods exist to evaluate the bond strength including shear, chevron notch, flexural, tensile, and peel-off tests [10,11,12,13,14].

Shear tests apply force via a blade from a universal testing machine to a resin composite cylinder adhered to a substrate disk [12]. The chevron notch test employs a three-to-four-point flexure setup, yielding fracture energy release toughness and flexural bond strength. The strength indicates the maximum force before chevron-shaped bonding area fractures [14,15]. Flexural strength tests the force required for a beam to catastrophically fail under three-point loading conditions. The specimen is balanced over two supports where the load is then applied at the midpoint from a bearer of force until the specimen fails [11]. Tensile and peel-off tests are widely used to assess bond strength between dental custom trays and impression materials. Tensile tests measure the resistance of a material to breaking under tension, helping understand its behavior under axial stretching load [10]. Higher tensile strength indicates greater resistance to tension-induced failure. Peel tests are designed for flexible materials, gauging resistance to localized stresses and bonded surface quality. They quantify peel strength, the average force needed to separate bonded materials [16]. These tests are crucial in defining impression material to tray adhesion as it impacts master model accuracy, subsequently affecting the final restoration outcome.

Currently, there is a growing need for insights into AM materials due to their increasing relevance and utilization in dentistry. Yet, information on AM custom tray materials is notably scarce, resulting in most studies focusing on the traditional materials used in tray fabrication. A custom tray is a small part of a bigger treatment plan [17,18]. Many dental practitioners are looking to AM to reduce their time investment per appliance/restoration, where bond strength remains a critical consideration [18]. Common applications include the use of resin through digital light processing (DLP), and filament through fused filament fabrication (FFF). This study aimed to systematically review studies that investigate the bond strength of custom tray materials to various impression materials and influencing factors.

2. Methods

This search strategy was conducted to answer the following question: “Which variables contribute the most the highest bond strength of custom tray materials to various impression materials?” The Preferred Reporting Items for Systematic Reviews and Meta-Analysis Protocol (PRISMA-P) and methods outlined by Moher et al. (2015) were followed [19]. This review protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO Registration ID: CRD420251089824).

2.1. Eligibility Criteria

The inclusion and exclusion criteria are listed in

Table 1. Eligibility Criteria.

Eligibility Criteria
Inclusion criteria	Exclusion criteria
Full study available published in peer reviewed pub lication. Studies that evaluated dental tray and impression material interface. In vitro, comparative, and cross-sectional studies.	Review articles, clinical trials, case studies, case reports, and letters to the author. Studies published in a language other than English. Studies that only have the abstract available. In vivo studies.

. Studies were included if the full text was available and if it evaluated the bond strength of impression material to a tray material. It was also included if it was an in vitro, comparative, or cross-sectional study. Studies were excluded if they were reviewed articles, clinical trials, case studies, reports, or letters to the author. If the study was published in any language other than English, only had the abstract available or was an in vivo study, it was also excluded.

2.2. Search Strategy

Electronic searches were carried out using Ovid, Web of Science, PubMed, and Scopus databases. The following search strategy was adapted to each database: (Alginate* OR “Dental Impression Technique” OR “Dental Alginate” OR “Dental Impression Material” OR Silicon* OR “Silicone Elastom*”) AND (“Bond Strength” OR “Surface Properties” OR “Dental Adhesion” OR “Shear Strength” OR “Tensile Strength” OR “Dental Stress Analysis”) AND (“Custom Tray*” OR “Stock Tray*” OR “Impression Tray*”) AND (Human*) AND (Computer-Aided Design/ OR (“computer aided design*” or “computer assisted design*” or “computer aided manufactur*” or “computer assisted manufactur*” or “additive manufactur*” or print* or “rapid prototyp*” or stereolithography or “digital light projection”). There was no restriction placed on the date of publication for the search. Furthermore, the reference lists of the identified studies were reviewed, and hand searching was conducted to identify any additional relevant published studies that may have been overlooked during the initial database searches. All studies were screened utilizing EndNote software (version 20.2, Clarivate), and any duplicates removed. The titles of all studies were screened and those that met the eligibility criteria were transferred to the next stage where the abstracts were evaluated for inclusion and omitted if they were found not to meet the eligibility criteria. Finally, the remaining studies were assessed in full text to decide upon their final eligibility. This process was carried out by two reviewers (P.C. and J.C.) independently. Any disagreements between the reviewers would be mediated by a third reviewer (A.C.).

2.3. Data Extraction

The following information was extracted from each of the final studies: titles, authors, objectives, testing methods, testing machines used, speeds of machines, attachment methods to the machines, evaluation techniques, statistical analysis methods, materials used for the custom/stock tray, impression materials, and adhesive materials. The impression material setting time and other variables identified in the studies were recorded. The number of specimens was recorded, the size details, and the specimens drying time. Finally, the key findings from each study were extracted and the highest bond strength from their testing. Inter-rater reliability between the authors was evaluated using PRISM V10 using Cohen’s Kappa Coefficient, which met the satisfactory threshold before a risk of bias assessment was conducted.

2.4. Risk of Bias

The risk of bias of included studies was assessed according to a modified version of the QUIN Tool from Sheth et al. [20]. Only relevant items criteria from the QUIN Tool were employed, totaling seven descriptors. Each criterion was assigned a score of 2 points for being adequately specified, 1 point for being inadequately specified, and 0 points for not being specified. The total score achieved categorized the selected study as high, medium, or low risk: above 70% indicates low bias risk, 50% to 70% represents medium risk, and below 50% reflects high risk of bias.

3. Results

3.1. Study Selection

One hundred seventry-three studies were initially identified from the four databases (Figure 1). After the removal of 81 duplicates, 92 studies remained. According to the eligibility criteria, they were screened by titles, and 77 further studies were excluded. The remaining 15 studies were screened by abstracts, and eight studies were excluded. This left seven studies to be screened by their full texts. Two additional studies were excluded via manual searching. Therefore, nine studies were included in this systematic review. Both reviewers were in agreement with the final selected publication, so no mediation was required (An inter-assessor reliability value (Cohen’s kappa) of 0.99).

3.2. Risk of Bias Assessment

As reported in

Table 2. A table reporting the bias of each individual study (Note: Adequately specified = 2 points, Inadequately specified = 1 point, Not specified = 0 point).

Criteria	Selected Studies
	Abdullah et al. (2003) [23]	Dixon et al. (1993) [21]	Maruo et al. (2007) [24]	Patil et al. (2021) [26]	Payne et al. (1995) [22]	Xu et al. (2018) [25]	Xu et al. (2020) [13]	Priyadarshini et al. (2023) [27]	Naidu et al. (2025) [28]
1. Clearly stated aims/objectives	2	2	2	2	2	2	2	2	2
2. Detailed explanation of sample size calculation	0	0	0	0	0	0	0	0	0
3. Details of comparison group	2	2	2	2	2	2	2	2	2
4. Detailed explanation of methodology	2	2	2	2	2	2	2	2	2
5. Method of measurement of outcome	1	1	1	2	2	2	2	1	1
6. Statistical analysis	1	1	1	2	1	1	1	1	1
7. Presentation of results	2	2	2	2	2	2	2	2	2
Final score	71%	71%	71%	86%	79%	79%	79%	71%	71%
Overall risk of bias	LOW	LOW	LOW	LOW	LOW	LOW	LOW	LOW	LOW

, all studies were found to have an overall low risk of bias [13,21,22,23,24,25,26,27,28]. All seven studies contained detailed statements and explanations of the studies’ objectives, methodologies and results but none explained how they determined the sample size. Many studies did not provide adequate details to describe the methods of measurement [21,23,24,27,28] and statistical analysis [13,21,22,23,24,25,27,28].

3.3. Study Characteristics

Of the seven studies that investigated traditional materials, five used an auto-polymerising acrylic resin [21,22,23,24,26,28]. Payne et al. [22] was the only study to use a thermo-plastic material (

Table 3. Table summarizing selected studies adjectives, testing method and evaluation.

Author	Objective	Testing Method	Machine Used	Speed	Method of Attachment to Machine	Post-Analysis of Debonded Surfaces (e.g., SEM)
Abdullah et al. (2003) [23]	To evaluate the tensile bond strengths of two impression material systems to two custom tray materials.	Tensile Loading	Instron universal machine (Norwood, MA, USA)	500 kg load cell at 0.5 cm/min	Metal chains attached to the brass hooks of the assembly.	No
Dixon et al. (1993) [21]	To evaluate the tensile bond strength of impression material adhesive to different custom tray materials and, the effect of different surface treatments was evaluated for each of the materials.	Tensile Loading	Instron universal machine (Norwood, USA)	500 kg load cell at 0.5 cm/min	A T-nut was incorporated into the holder so that an eyebolt could be threaded into it.	No
Maruo et al. (2007) [24]	To evaluate how to achieve sufficient and stable adhesive strength between impression material and a tray.	Tensile Loading	Universal testing machine; Autograph DSC-2000, Shimazu Co., (Kyoto, Japan)	0.5 cm/min	Not specified.	Yes
Patil et al. (2021) [26]	To evaluate the bond strength of addition silicone with different tray materials using different retentive methods.	Tensile Loading	Universal testing machine (Norwood, USA)	0.5 cm/min	A hook was screwed into the resin center of the specimen.	No
Payne et al. (1995) [22]	To evaluate the tensile bond strength of impression materials bonded to tray materials and, the effects of surface roughening.	Tensile Loading	Universal testing machine (model DCS5000, Shimadzu, Tokyo, Japan)	500 kg load cell at 1 cm/min	The specimens were placed between the grips with the long axis of the specimen coinciding with the direction of the applied load.	No
Xu et al. (2018) [25]	To evaluate the retention of FDM tray materials to a silicone impression/adhesive system before and after GB.	Peel-off strength test through tensile loading.	Universal testing machine (Z010, Zwick, Ulm, Germany)	0.3 cm/min	Hook that fitted into the hole in the specimen.	Yes
Xu et al. (2020) [13]	To evaluate the bonding between 3D printed custom tray materials and elastomeric impression/adhesive systems.	Peel-off strength test through tensile loading.	Universal testing machine (Z010, Zwick, Ulm, Germany)	0.3 cm/min	Hook that fitted into the hole in the specimen.	Yes
Priyadarshini et al. (2023) [27]	To evaluate the dimensional stability and retention strength of impressions to custom impression trays fabricated using conventional method and additive technology.	Peel-off strength test through tensile loading.	Universal testing machine (Norwood, USA)	1 mm/min	One fixture held the impression tray and the other part hold the impression material.	No
Naidu et al. (2025) [28]	To evaluate the tensile bond strength of addition silicone impression material when used with custom trays featuring grooves and perforations, made from self-cure acrylic resin, visible light-cure resin and 3D printed resin materials.	Tensile Loading	Digital Instron tensile testing machine (Hounsfield, Swindon, UK computerized model ISO 9001:2020)	1 mm/min	Lower plate of the tray was secured to a clamp and upper member was fixed using a hook.	No

). Xu et al. [25] investigated four types of materials, including acrylonitrile butadiene styrene (ABS), polyethylene terephthalate glycol polyester (PETG), high-impact polystyrene (HIPS), and conventional light-curing resin. Xu et al. [13] varied the tested materials and used Dental LT (Freeprint, Detax GmbH, Germany), an acrylate-based photopolymer, Polylactic acid (PLA), and Zeta Tray LC (methacrylate based). There were four included studies that investigated AM materials [13,25,27,28]. Among them, Xu et al. [25] printed at a layer thickness of 50 microns, and Xu et al. [13] printed at a thickness of 100 microns; however, the other two studies did not specify this printing parameter [27,28].

Except for the bond strength between the trays and the impression materials, Dixon et al. [21], Payne et al. [22], Abdullah et al. [23], Maruo et al. [24], Xu et al. [25], Patil et al. [26], and Naidu et al. [28] also explored the effect that other variables can have on the bond strength (

Table 4. Table summarizing materials, variables, and specimen details of selected studies.

Author	Custom Tray Materials	Impression Materials (Brand/Type)	Impression Setting Time	Adhesive Materials and Dry Time	Other Variables	Number of Specimens	Specimen Details	Specimen Dry Time
Abdullah et al. (2003) [23]	1. Fastray (autopolymerising acrylic resin) 2. Triad (visible light-cured polymerising resin)	1. Permlastic (polysulphide) 2. President (polyvinyl siloxane)	Not specified.	- Not specified. - 15 min.	- The use of wax and tinfoil against the tray and impression materials	30 per group, =120 total	2 cm2 of testing surface and 1.5 cm thick.	24 h.
Dixon et al. (1993) [21]	1. Fastray (autopolymerising) 2. Triad (light polymerising) 3. Exoral (light polymerising)	1. Reprosil Heavy Body Impression Material	10 min.	- Caulk Tray Adhesive - 10 min.	- Using alcohol or no alcohol with Fastray and Triad. - Using an air barrier or no air barrier with Extraoral.	18 per group, =54 total	Flat square surface that measured 3.81 cm2.	24 h.
Maruo et al. (2007) [24]	1. Ostron ll (autopolymerising)	1. Imprint ll Penta Heavy body (vinyl polysiloxane) 2. Exaimplant (vinyl polysiloxane) 3. Reprosil Heavy Body (vinyl polysiloxane) 4. Polyether (impregum enta)	6 min.	1. VPS tray adhesive 2. Exaimplant adhesive 3. Cauld tray adhesive 4. Polyether adhesive. Not specified.	- Effect of tray storage time; 1, 2, 4, 7, and 10 days. - Effect of tray adhesive drying time; 0, 1, 5, 10, 15 min. - Effect of tray surface roughness; air abrasion, bur, no treatment.	10 per group, =130 total	Columns 2.5 cm in diameter × 2.2 cm in height.	Not specified.
Patil et al. (2021) [26]	1. Tray acrylic resin samples 2. Repair resin samples (DPI RR Cold Cure) 3. Visible light cure resin samples (Plaque Photo, WP Dental)	1. Monophase polyvinyl siloxane aka medium body addition silicone.	Not specified.	- Manufacturer recommendation. - Not specified.	- Chemical retention. - Mechanical retention. - Chemical and Mechanical retention.	30 per group, =90 total	30 mm2 testing surface area with 2 mm depth and 10 mm2 borders. The cover tray is 40 mm2. Perforated die with holes of 2 mm diameter and 5 mm in depth 5 mm away.	24 h.
Payne et al. (1995) [22]	Thermoplastic resin tray materials. 1. Hydro Tray, Tak Systems 2. Tray Dough, Hygenic Corp.	Non-Aqueous elastomeric impression materials/adhesive combinations 1. Hydrosil, dentsply 2. Permadyne	Not specified.	- Manufacturer recommendation. - Not specified.	- Surface roughening.	10 per group, =30 total	Contact area of the tray material was 380 × 10−6 mm2.	Not specified.
Xu et al. (2018) [25]	1. Acrylonitrile butadiene styrene (ABS) 2. Polyethylene terephthalate glycol polyester (PETG) 3. High impact polystyrene (HIPS) 4. Conventional light-curing resin	Silicone impression material Xantopren L blue, Hereus Kulzer, Hanau, Germany, and the activator Universal Play, Heraeus Kulzer, Hanua, Germany.	3 min.	- Sili fluid, DETAX, Ettlingen - Manufacturer recommendation.	- Grit blasting.	11 per group, =44 total	A cuboid base was designed with a dimension of 25.4 mm × 25.4 mm × 6 mm, and a cuboid handle was added onto its top at an angle. Layer thickness = 0.35 mm	Not specified.
Xu et al. (2020) [13]	1. Dental LT (methacrylate based) 2. FREE PRINT tray (methacrylate based) 3. PLA 4. Zeta Tray LC (reference block, (methacrylate based)	1. Identium Heavy; vinylsiloxanether (VSXE) 2. Flexitime Heavy Tray Dynamix; vinyl polysiloxane (VPS) 3. Impregnum Penta Heavy Duo Soft polyether (PE)	1. 4.30 min. 2. 4.30 min. 3. 6 min.	The adhesives used were recommended with the impression materials used. Drying times: 1. 5 min 2. 2 min 3. 1 min	- N/A	36 per group, =144 total	A cuboid handle with dimensions of 25.4 mm × 13 mm× 7 mm was connected at 45 degrees to the edge of a cuboid base with dimensions of 25.4 mm × 25.4 mm× 6 mm. A 0.5 mm diameter hole was designed at the center of the handle. Layer thickness = 0.1 mm	Not stated.
Priyadarshini et al. (2023) [27]	1. Conventional light-curing resin 2. Polylactic acid (PLA) by digital light processing (DLP) technology 3. PLA by fused deposition Modeling (FDM) technology	Dentsply Aquasil LV (polyvinyl siloxane)	Not specified.	- VPS tray adhesive - 15 min	- N/A	12 per group = 36 total	2 mm thickness and 0.15–2 mm relief	Not specified.
Naidu et al. (2025) [28]	1. Self-cure acrylic resin 2. Visible light-cure resin 3. 3D-printed resin (PLA)	Dentsply Aquasil Ultra (polyvinyl siloxane)	Not specified.	- Dentsply Caulk tray adhesive - Manufacturer recommendation.	- Different surface treatments (grooved or perforated)	12 per group = 36 total	5 cm × 5 cm with a depth of 5 mm	24 h.

). Four of them evaluated the effect of different surface treatments [21,22,25,28]. Abdullah et al. [23] investigated the effect of wax and tinfoil against tray materials when it was polymerizing. Maruo et al. [24] investigated the effect of tray storage time, tray adhesive drying time, and the tray surface roughness. Xu et al. [13] and Priyadarshini et al. [27] did not investigate the effect of any variables outside of bond strength. Patil et al. [26] evaluated the different means of retentive methods being chemical and mechanical retention. There was a wide variety in the number of test specimens across the seven studies, with Payne et al. [22] having the minimum amount of test specimens from the evaluated studies at 30 total and Xu et al. [13] having the maximum of the evaluated studies at 144 total test specimens (Table 4). Conversely, the sample size per group ranged from 10 to 36.

Three of the seven studies used an auto-polymerizing acrylic resin for their control test specimens [21,23,24]. Maruo et al. [24] concluded that surface treatments should be adapted to the specific impression material for better bond strength. They also suggested that 15 min was the optimum adhesive drying time for all materials tested. In four studies, light-cured resin achieved the highest bond strength to the corresponding impression/adhesive material [22,23,26,28] (

Table 5. Table summarizing the results of selected studies.

Author	Key Findings	Results (If Possible, Data Was Converted to MPa)
Abdullah et al. (2003) [23]	Autopolymerising acrylic resin and VLC (Visible Light Curing) tray materials polymerised against tinfoil exhibited higher tensile bond strengths to polysulphide and polyvinyl siloxane impression materials than to the tray materials processed directly over wax spacer.	Wax/Polyvinyl Siloxane Acrylic/Wax = 0.35 Acrylic/Tinfoil = 0.41 VLC/Wwax = 0.47 VLC/Tinfoil = 0.55 * Converted from N/m2
Dixon et al. (1993) [21]	No significant difference in impression material adhesive means tensile bond strengths were exhibited for any of the materials as the result of variations in the surface treatment.	Triad/A = 0.50 Triad/NA = 0.43 Extoral/NAB = 0.31 Extoral/AB = 0.30 Fastray/A = 0.23 Fastray/NA = 0.21 * Converted from kg/cm3
Maruo et al. (2007) [24]	All materials reported their highest kPa after 7/10 days storage time (apart from Impregnum Penta = 4 days). 15 min adhesive dry time achieves the highest kPa in all specimens. Burr roughness achieved the highest kPa in all, but Impregnum Penta, which had highest kPa in air abrasion. It was concluded that surface treatment of custom trays should be adapted to the type of impression material used to achieve optimum bond strength.	DAY 4 I2PHB (Implant II Penta Heavy Body) = 0.21 E (Exaimplant) = 0.23 RHB (Reprosil Heavy Body) = 0.19 IP (Impregum Penta) = 0.22 * Converted from kPa
Patil et al. (2021) [26]	VLC resin showed the highest bond strength in chemical mechanical methods, followed by repair resin material. Tray resin material showed poor bond strength in all three retentive methods. The mechanical method was the least retentive of all three resin materials. The best performing method is to use both mechanical perforations and adhesive applications.	ATM (Acrylic Tray Material) = 0.30 ARM (Acrylic Repair Material) = 0.33 VLCM (Visible Light Cure Material) = 0.41 * Converted from N/m2
Payne et al. (1995) [22]	Hydrosil and Permadyne impression materials exhibited a significantly greater bond strength to Hydrotray thermoplastic resin than to Hygenic tray dough resin. Surface roughening of Hydrotray thermoplastic resin specimens resulted in a significant reduction in bonding strength to the monophasic addition silicone impression material (Hydrosil) but an increase in bonding strength to the medium-body polyether impression material (Permadyne). Bond strengths of Hydrosil and Permadyne impression materials to unaltered Hygienic tray dough resin specimens were lower than reported bond strengths to other types of custom tray materials.	H-S/H (Hydrotray Smooth) = 0.80 H-R/H (Hydrotray Rough) = 0.63 HTD-S/H (Hygenic traydough) = 0.38 H-S/P = 0.63 H-R/P = 0.78 HTD-S/P = 0.43 * Converted from kPa
Xu et al. (2018) [25]	The results indicated ABS, HIPS, and PETG could provide sufficient adhesion to the adhesive as the conventional light-curing resin, and GB could reduce the roughness generated by FDM and weaken the bonding between the adhesive and the silicone impression.	Before GB ABS ≈ 550 HIPS ≈ 630 PETG ≈ 600 REF ≈ 660 * Given in N/m
Xu et al. (2020) [13]	The four tray materials featured different surface topography. The peel bond strength was not significantly different with VSXE and PE, but PLA and the reference showed higher peel bond strength with VPS than the Dental LT and FREE PRINT tray (p < 0.05).	VSXE/D (Dental LT) = 1809.73 VSXE/F (Freeprint Tray) = 1835.51 VSXE/P (PLA) =1911.82 VSXE/R (Reference) = 1880.79 * Given in N/m VSXE (Vinylsioloxanether)
Priyadarshini et al. (2023) [27]	FDM (Fusion Deposition Manufacturing), DLP (Digital light processing) and Light cure trays are all clinically acceptable in terms of retention strength. The mean retention strength between impression and tray seen in descending order was FDM trays, followed by DLP and Light cure trays.	Light Cure = 510.53 DLP = 696.16 FDM = 808.56 * Given in N
Naidu et al. (2025) [28]	Light-cured acrylic trays demonstrated significantly superior bond strength with impression materials and adhesives, followed by 3D-printed trays, with self-cure acrylic trays showing the lowest tensile strength. Trays featuring indentations showed greater tensile bond strength compared to those with grooves across all groups.	SC (Self-curing) grooved = 15.61 SC perforated = 27.30 VLC (Visible Light Curing) grooved = 48.05 VLC perforated = 57.74 3D grooved = 38.02 3D perforated = 39.41 * Given in N

).

Eight of the studies included attached a hook, screw, or fixture to the specimens/trays to connect the universal testing machine [13,21,22,23,25,26,27,28] but only the study from Maruo et al. [24] did not specify the method of attachment. All studies used a polyvinyl siloxane impression material and an adhesive selection that followed the manufacturers’ recommendations. Xu et al. [25], Xu et al. [13], and Priyadarshini et al. [27] used the peel-test method, whereas the other six studies used a tensile loading test to evaluate the strength of the tray/impression interface. Maruo et al. [24], Xu et al. [25], and Xu et al. [13] used SEM observation to analyze their specimens post testing. In the study conducted by Xu et al. [25], a 200× magnification at 10 kV acceleration voltage was used, whereas Xu et al. [13] had 100× and 500× magnification at 10 kV acceleration voltage. The highest bond strength was found in the study by Payne et al. [22], which was 0.80 MPa for the Hydrotray resin material (smooth) with the Hydrosil impression material. However, four studies presented their results in units of either N/m [13,25] or N [27,28], and there was insufficient information to convert them to MPa for direct comparison with other studies.

4. Discussion

This study systematically reviewed the bond strength of custom tray materials to impression materials and explored the variables influencing the bond strength. When selecting a custom tray material, bond strength is an important issue to consider for the success of the final restoration. Most of the studies included in this systematic review explored the interface of traditional/conventional materials with impression materials. However, there is minimal information to be found on this topic, particularly regarding the bond to AM products. There is a need for information on the bond strength to AM materials with their increased use as a manufacturing method.

Among the nine studies, trends emerged in the selection of tray materials. Five studies employed auto-polymerizing acrylic resin [21,22,23,24,26,28], while six adopted visible light-cure (VLC) materials [21,23,25,26,27,28]. Notably, VLC materials gained popularity after rigorous testing in the late 1990s [29]. Auto-polymerizing resin also found favor at this time [23]. Cold-cure and thermoplastic acrylics were less prevalent, with Payne et al. [22] using thermoplastic, due to the nascent state of VLC research at that time. These studies, although old, are still ever so relevant to the progression of dental technology today and the future of research in the field.

Among the relevant studies, only four studies employed AM materials [13,25,27,28]. The inclusion of two studies by the same first authors raise concerns about potential bias, risking skewed results and compromised objectivity [13,25]. In the study by Xu et al. [25], ‘fused filament fabrication’ (FFF) was used to print all specimens, except for the reference block, which yielded comparable results to those of conventional material, due to the intrinsic surface roughness produced through additive manufacturing. To draw a more definitive outcome of the bond strength of 3D printed materials to impression materials, further studies should be carried out. In another study by Xu et al. [13], various AM materials were utilized for distinct fabrication methods and compared for their bond strength. Despite differing surface topographies among the four materials, no standout performer emerged, implying similar performance. It was found that custom trays printed via FFF possess intrinsic surface roughness features which enhance their bonding capabilities [25]. The surface of printed custom tray will vary depending on the layer thickness and the print orientation. This could be a future area of investigation to see if changes to this variable have any effect on the bond strength.

Recommendations for clinical implementation require additional research on diverse AM materials. There is currently limited literature available on the bond strength of AM tray materials, which emphasizes a need for further research. However, based on the findings from existing literature from Xu et al. [25] and Xu et al. [13], AM tray materials have comparable or better adhesion to the impression materials than the standard acrylic tray materials.

The validity of the methods utilized are paramount to translating the results to clinical practice. Katona [30] underscores the direct impact of having various testing methods on outcome validity, suggesting caution in comparing discrepant studies. Among the seven assessed studies, five employed the tensile loading method, while two adopted the peel-off test [13,25]. This imbalance could be due to the high prevalence of studies available on tensile testing and the lack thereof of peel testing. For tensile bond testing, Rasmussen [31] highlighted that the strength observed in one configuration could predict approximate failure loads in other configurations. However, Xu et al. [13] noted a disadvantage with this method, where retracting the tray perpendicular to its center induced tensile stress centrally and generated shear stress between tray walls and the impression material.

The tray is withdrawn by applying a prying force to the handle once the impression sets. In cases of inadequate impression-to-tray bond strength, the impression may detach from the tray during this process. Two studies by Xu et al. [13,25] designed a test block to simulate this real-life scenario. Rasmussen [31] found shear bond tests often led to adhesive failure due to tensile stresses, which was a drawback in peel-off testing. However, they noted shear bond methods were less sensitive to alignment and have simpler specimen preparation. Therefore, for further studies, it is recommended that a peel-off strength test is adopted due to its profound clinical significance, as it closely emulates real-life practical scenarios.

The three studies that used SEM observation commented on the surface textures and compared the microstructures between specimens and varied materials. SEM analysis aids microstructural comparison and understanding, offering detailed perspectives on study findings [32]. In the two studies by Xu et al. [13,25], SEM images provided a closer look at the printing layer thickness and how this intrinsic surface roughness can aid in the bonding to an impression material. These studies both printed their specimen in only one print orientation so differences could not be observed here; however, this could be a topical area of investigation for future studies.

The study from Bindra and Heat [33] emphasized the need for strong and compatible adhesive bonds between impression materials and trays for optimal clinical performance. In contrast, Samman and Fletcher [34] explored interchanging adhesives, deviating from manufacturer recommendations, and noted that adhesion strength depends on tray materials. Notably, the latter study’s relevance may diminish due to its age, being nearly 40 years old. Among the reviewed studies, all followed the instructions of the manufacturers’ recommendation for adhesives and drying time, except Maruo et al. [24], who investigated adhesive drying time. This controlled approach isolates variables for more applicable and clinically significant outcomes.

Patil et al. [28] examined retentive methods (chemical, mechanical, and a combination) on bond strength, revealing the highest strength with combined chemical and mechanical methods. Mechanical retention yielded the lowest strength. Similar findings were reported, emphasizing the effectiveness of combining chemical and mechanical retention [35]. For polyvinyl siloxane impression materials, chemical retention involves a reaction between specific reactive polyvinyl siloxane and ethyl silicate, forming bonds and hydrated silicate [8]. Combining this with mechanical retention, like perforations, specimens were found to yield optimal bond strength for superior impression results.

The highest bond strength recorded was 0.80 MPa, with the Hydrotray tray resin material and no surface roughening [22]. Xu et al. [25] reported similar findings with grit blasting reducing bond strength, causing lower impression material retention. They also found FFF’s wave pattern enhanced layer retention and strength. A study on build angle and layer thickness interaction is suggested for further insight into bond strength improvement. Additionally, assessing the correlation between build angles and tray sections post-printing is important for clinical application. In the studies by Xu et al. [13,25], no information was available on the exact values of bond strength. Although there were some graphs, the results must be derived through estimation. These factors, when combined, make it exceedingly difficult to compare the results with those of other studies and to draw an accurate conclusion regarding the biomechanical properties of AM materials. As clinicians are already using AM custom trays and their prevalence is only growing, it is important that there are reliable studies and data. Therefore, further investigation should be performed.

There were clear limitations identified in this review, with limited information directly investigating the bond strength of the various materials used to construct custom trays and impression materials. Predominantly, studies focused on the bond strength of conventional materials. In addition, there was limited clarity on the best bond strength test method, due to non-standardized methodologies and multiple variables being adopted among the various studies. As dentistry trends toward digital manufacturing techniques, including AM, studies investigating the bond strength of impression materials to AM materials could provide valuable insights, establishing consistency in results and better recommendations for clinical use.

5. Conclusions

Within the limitations of this systematic review the following conclusions are made:

• Grit blasting reduces the tray–impression material bond strength as it smooths or removes intrinsic surface roughness that otherwise aids in mechanical retention.
• Combining chemical and mechanical retention (adhesive and perforations) reported the highest bond strength, with perforations alone providing some benefit but less than the combined approach.
• Based on the existing literature, it cannot be deduced whether AM tray materials have comparable or better bond strength to the impression materials than the standard acrylic tray materials due to inconsistent reporting and study designs.
• Clinically, material–tray combinations should be selected according to the impression materials’ intended clinical indication; combinations showing higher bond strength may be preferred for full-arch impressions.
• Differences in methodology, test parameters, and outcome measures limit direct comparisons and must be considered when interpreting results. Standardized protocols are needed for future studies to guide more definitive clinical recommendations.