A Scoping Review on Accuracy and Acceptance of 3D-Printed Removable Partial Dentures

Abstract

This scoping review aims to provide comprehensive evidence on methods used to assess the accuracy and acceptance of three-dimensional (3D)-printed removable partial dentures (RPDs). An electronic search of English language literature from January 2014 to 2024 was performed on five databases, PubMed, Scopus, Web of Science, EMBASE, and Google Scholar, using MesH terms. The parameter of interest was extracted and presented in tabular form. Of 1025 retrieved studies, 35 studies were included in the final analysis. Most studies were laboratory-based, and clinical trials were conducted between 2018 and 2022 without a control group. The studies included the use of the stone model or duplication model as a reference, as well as the direct 3D printing method and polished frame for detecting the accuracy of fit. The assessment method was divided into two categories: (1) qualitative (visual and tactile method) and (2) quantitative assessment, which includes optical and computerized methods for assessing the accuracy of fit. Dentist perception and patient-related outcomes were evaluated to measure the acceptance of 3D-printed RPDs. In conclusion, patients’ satisfaction and dentists’ acceptance of digitally printed RPDs were greater than those of conventional ones. The quantitative method (mainly computerized) provides a more accurate and precise assessment to evaluate the accuracy of fit. It allows clinicians to detect minute changes that cannot be inspected with visual and optical methods.

1. Introduction

Removable partial denture (RPD) adaptation is critical in evaluating the success rate. Ill-fitting RPD is the most common complaint of denture wearers. Components like clasps, rest, and connectors play a crucial role in enhancing the functionality of RPDs. These components help to maintain the stability of RPDs and maintain periodontal health. Studies have reported that conventionally designed cobalt chromium RPDs are ill-fitting dentures and cause oral health issues such as periodontal pockets, caries, denture stomatitis, temporomandibular disorder, and ulcers [1,2]. Another cause of ill-fitting dentures is dimensional changes during fabrication, mainly during the casting process [3,4]. Studies have reported that around 76% of patients wearing a conventionally prepared RPD report dissatisfaction [2,5]. A well-fitted RPD reduces the chances of oral health damage and improves patient-related outcomes.

In this era of digital dentistry, the fabrication of RPDs from conventional to digital fabrication has evolved rapidly. Theoretically, combining additive (3D printing) and subtractive (computer-aided design and computer-aided manufacturing, CAD/CAM) technology surpasses the fabrication outcome of conventional techniques. Moreover, digital fabrication requires fewer steps and reduces the chances for errors during fabrication [6,7,8,9]. Previous studies reporting the accuracy of RPDs fabricated by CAD/CAM milling and three-dimensional (3D) printing resulted in comparable and clinically accepted findings [8,10,11]. Furthermore, 3D printing requires less fabrication time and material wastage than conventional and milling techniques [12,13,14]. With the advancement in 3D printing technologies, the utilization of biocompatible materials like resins and metals has become possible [15]. Since the fabrication of digitally printed RPDs has recently increased, it is vital to understand the accuracy of fit and acceptance of these dentures.

Various methods have been reported in the literature to assess the accuracy and fit of digitally printed RPDs. The most conventional and clinically used assessment methods are visual and tactile, and a mouth mirror and dental explorer are used [1]. For the extraoral evaluation of fit, the accuracy of a denture on the master cast is considered a successful adaptation [16]. Although these assessments are acceptable in clinical settings, they also have several limitations. Researchers are concerned about the clinically acceptable gap between the material and the corresponding tissue. Several studies have been reported in the literature to assess the gaps, and they have reported that a range between 50 μm and 310 μm is considered clinically acceptable. Gaps of more than 310 μm are considered misfits [17,18,19,20]. A study evaluated the internal fit of conventionally prepared RPDs and reported that around 78% of RPDs do not have optimal contact with the rest seat [4]. This chair-side assessment for internal fit is only acceptable with conventionally prepared RPDs [21]; however, this assessment is inconsistent and does not provide a three-dimensional evaluation.

In the 3D printing technology, the trueness is referred to as the closest resemblance of a 3D-printed model to the reference model, indicating the accuracy of design [1]. Furthermore, the trueness of the 3D printing model is an essential parameter to evaluate the model’s accuracy. It also indicates the deviation from a 3D-printed model to originally designed data that cannot be assessed with visual assessment [14,22,23,24].

In the last decade, numerous studies have been published on the clinical and laboratory evaluation of the accuracy of 3D-printed RPD models [11,14,15,16,18,19,22,25,26,27,28]. All these studies have varied findings, where few studies suggest 3D-printed RPDs are more accurate than conventional and CAD/CAM-milled. In contrast, other studies found no significant difference in the fit of 3D-printed and CAD/CAM-milled prostheses. A few reviews have also been published to check the accuracy of the fit of 3D-printed RPDs, and conflicting findings have been reported [2,29].

With the advent of technologies, it is essential to understand the views and challenges dental practitioners face in adopting 3D-printed prostheses. In their comparative studies, Chobe et al. [30] and Urumova [31] provided an insight into the global perspective of adopting 3D printing technologies. These researchers marked various parameters, such as awareness levels, integration of technology in the curriculum, and comparative perspective, to acknowledge the implementation of 3D printing technology. Multiple studies have focused on patient-related outcomes and experience with digital technology, such as reduced chair-side time, fewer patient appointments, and cost effectiveness [3,32,33]. Understanding the impact of 3D printer RPDs on patient satisfaction and treatment efficacy is a need at this time.

Literature suggests a lack of studies focusing on the methods utilized to check the fit accuracy of 3D-printed RPDs, the treatment efficacy, and patients’ satisfaction with this novel technique. Therefore, this scoping review aims to summarize the current methods utilized to assess the fit of 3D-printed RPDs, treatment efficacy, and dentist perception of this new technique. The main objective of this scoping review is to identify and extract evidence on techniques utilized to evaluate the fit of 3D-printed RPDs. The second objective is to systematically assess dentists’ perception of 3D printing techniques and barriers associated with the implementation.

2. Materials and Methods

The author conducted this review in compliance with PRISMA-ScR [34] (preferred reporting items for systematic review and meta-analysis extension for scoping review) (Supplementary Materials Table S1) to answer the following question: “What is known in the existing literature about the accuracy and acceptance of 3D-printed removable partial dentures?” The PCC format for this research question was P (population) patients wearing RPDs constructed by 3D printer; C (content) clinical and laboratory methods to check the accuracy of fit for RPDs and dentists’ perception; and C (context) clinical setting. Protocol for this scoping review has been register with open science framework with DOI: https://doi.org/10.17605/OSF.IO/6RQMS.

2.1. Search Strategy

The author searched five electronic databases for publications between January 2014 and January 2024: Web of Science, Medline/PubMed, Google Scholar, EMBASE, and SCOPUS. The following relevant key terms used were “3D-printed RPD”, “Rapid prototyping”, “Three-dimensional printing”, “Additive manufacturing”, “Dental polymers”, “Dental framework”, “Removable partial denture”, “PEEK denture”, “PMMA denture”, “Dentists’ perception”, and “Laboratory studies”. The complete list of MesH terms and accessed date are noted in Supplementary Materials Table S1.

The reviewer retrieved data, entered it into the Endnote file, and removed duplicates, followed by data analysis and synthesis. Furthermore, full texts of potential articles were downloaded for further screening.

2.2. Inclusion and Exclusion Criteria

The articles included in this scoping review followed strict inclusion criteria like in vitro studies (experimental, laboratory-based); in vivo studies, clinical trials, and comparative studies of 3D-printed removable partial dentures; clinical case reports, dentists’ perception of acceptance; articles published in English language and in peer-reviewed journals in past ten years. Studies on subtractive and conventional techniques for RPD fabrication, review articles, conference proceedings, and editorials were excluded.

2.3. Data Extraction and Clinical Outcomes

The parameter of interest was extracted from each study and entered into an Excel sheet. These parameters were as follows: author, country, year of study, study design, Kennedy’s classification of edentulism, control group, 3D printer utilized, source of reference for RPD design, and primary outcome. Additionally, in the second table, the parameters analyzed were the type and the method of assessment, the area of measurement, and the materials utilized for RPD fabrication. The primary outcome for each study was presented to analyze the accuracy of the RPD fabricated by 3D printing. Finally, in the third table, the parameters measured were the perception of dentists and prosthodontists on clinical performance and long-term prognosis on acceptance of 3D-printed RPDs.

3. Results

A total of 1025 articles were retrieved from an initial search on the five electronic databases. Of these, 829 were excluded as duplicates, yielding 196 articles screened with the abstract and titles. One hundred forty-two articles were excluded as irrelevant, two reports could not be retrieved, and fifty-two were extracted and included for full-text screening. During the full-text screening, nineteen articles were excluded for reasons such as non-English language, year of publication, not evaluating accuracy and acceptance of 3D-printed RPDs, and studies on crowns and veneers. A manual search of the bibliography included two articles. Finally, 35 articles were included in this scoping review and proceeded with qualitative analysis (Figure 1). Litmaps were evaluated to determine the relationship between the included studies and to thoroughly examine the literature related to the review question (Figure 2).

The results of the study were divided into three parts: (1) basic characteristics of the included studies, (2) comparison of methods utilized for assessment of accuracy of fit of 3D-printed RPDs, and (3) dentists’ perception of acceptance of 3D-printed RPDs. The themes and sub-themes were developed and analyzed in the result sections and are discussed in further sections.

3.1. Characteristics of Included Studies

Table 1 and Table 2 demonstrate the basic characteristics of the included studies. Among the 35 included studies, the maximum was published in 2019, followed by 2018, and only one was published in 2016. This trend shows the importance of 3D printing technologies in dentistry after 2017. Of the included studies, 12 were qualitative (without control), and 21 were quantitative (with control). Seventeen studies were of laboratory design [6,10,11,13,24,32,35,36,37,38,39,40], nine were clinical case reports [17,18,19,25,26,41,42,43,44], three were randomized control trials [28,45,46], and two were experimental studies [47,48] concentrating on the accuracy and acceptance of 3D-printed RPDs in dentistry. Only two studies were cross-sectional and demonstrated dental clinicians’ knowledge, attitude, and awareness regarding the acceptance of 3D-printed dentures [30,31]. Twenty-six studies utilized Kennedy’s classification for edentulism, with a dominance of Kennedy’s class I followed by classes II and III, with or without modifications. However, three studies used simulation of the first molar [27,28,39], while one study utilized the dentate model [45], and two studies did not mention any classification [19,36].

Twelve studies included conventional RPDs; four studies used the stone model [22,32,40,48]; one study used replica models as a control group [19]; and three studies used intraoral scanners [17,44,49]. In comparison, the remaining twelve studies assessed accuracy without a control group.

Regarding the types of printing, twenty studies utilized direct printing techniques like stereolithography, digital light prototyping, selective laser melting, etc. Three studies used indirect printing [28,50,51], including direct printing of metal or resin framework and casting pattern in conventional techniques, and three studies used both direct and indirect printing techniques [14,27,38]. As the primary outcome of this scoping review, almost all included studies demonstrated the accuracy of 3D-printed RPDs. Twelve studies without a control group reported better accuracy and fit of digitally manufactured RPDs, while one stated no significant difference [28]. However, four studies with the control group (lost wax technique) reported better accuracy with 3D-printed RPDs [6,10,47,52]. In comparison, three studies reported a lesser fit for 3D-printed RPDs than the conventional technique, but the authors suggested a clinically acceptable fit for 3D-printed RPDs [17,26,53].

Table 1. Basic characteristics of the included studies (quantitative studies).

Sr No.	Author/Year/Country	Study Design	Kennedy’s Classification	Control Group	Type of 3D Printer	Outcome
1	Anan and Saadi 2015 [47]; Syria	In vitro study (Experimental)	Mandibular class III modification 1	Traditional technique	Light curing model technique	Fit accuracy of 3D-printed RPDs was better than traditional
2	Lee et al., 2017 [19]; South Korea	Clinical report	Maxillary and mandibular class I	Replica technique	Digital light projection (DLP)	The RPD constructed with the replica technique has varied results
3	Ye et al., 2017 [46]; China	Randomized control trial	Mandibular class I modification 1	Lost wax- technique	Stereolithography (SLA)	The single design RPD prepared with a 3D printer was more accurately fit than those with the traditional technique
4	Arnold et al., 2018 [6]; Germany	Laboratory study	Maxillary class III modification 2	Lost wax technique	Direct and indirect 3D printing techniques	The 3D-printed RPD has less fit
5	Soltanzadeh et al., 2018 [50]; USA	Laboratory study	Maxillary class III modification 1	Lost wax technique	Indirect printing	The conventional RPD was more accurate
6	Torii et al., 2018 [28]; Japan	Experimental study	First molar simulation	Lost wax technique	indirect printing (CAD)	No significant difference was reported in the accuracy of fit within both techniques
7	Bajunaid et al., 2019 [10]; Saudi Arabia	Laboratory study	Mandibular class III	Lost wax technique	Direct CAD printers	3D-printed RPDs are more accurate
8	Chen et al., 2019 [35]; China	Laboratory study	All classes	Lost wax technique	Direct CAD printing technique	3D-printed RPDs are less fitting but clinically acceptable
9	Negm, Aboutaleb, and Alam-Eldein 2019 [22]; Egypt	Laboratory study	Maxillary class I	Stone cast model	Stereolithography (SLA)	RPDs prepared by 3D printers have less accuracy
10	Carneiro Pereira et al., 2019 [49]; Brazil	Clinical report	Mandibular class III modification 1	Intra-oral scanner (Patients mouth)	Direct and indirect printing techniques	The 3D-printed RPDs have an acceptable clinical fit
11	Tregemen et al., 2019 [48]; South Carolina	Clinical trial	Mandibular and maxillary class I, II, and III	Stone cast model	Selective laser melting	3D-printed RPDs have a better fit
12	Hayama et al., 2019 [17]; China	Clinical report	Mandibular class I	Intraoral scanners	Direct digital technique	3D-printed RPD have an acceptable fit
13	Oka et al., 2019 [13]; Japan	Laboratory study	Mandibular and maxillary class I, II, and III	Lost wax technique	Direct CAD printing technique	3D-printed RPD have an acceptable fit
14	Wu et al., 2020 [44]; China	Clinical report	Mandibular class I modification 1	Intraoral scanners	Selective laser melting	3D-printed RPD have an acceptable fit
15	Xie et al., 2020 [39]; China	Laboratory study	First molar simulation	Lost wax technique	Direct CAD printing	3D-printed RPDs have better fit
16	Yoon et al., 2021 [40]; China	Laboratory study	Maxillary class I	Stone cast	Direct 3D printing	Acceptable fit
17	Hussein and Hussein 2022 [11]; Saudi Arabia	Laboratory study	Maxillary class III and Mandibular class 1	Lost wax technique	Digital light processing	No effect on the accuracy of fit
18	Saadaldin et al., 2022 [36]; Egypt	Laboratory Study	Not mentioned	Lost wax technique	Selective laser melting technique	Better accuracy fit of SLM-prepared RPDs
19	Rokshad et al., 2022 [24]; Germany	Laboratory study	Maxillary class III modification 1	Convectional technique	Digital light processing	Acceptable fit
20	Peng et al., 2022 [14]; China	Laboratory study	Mandibular class II modification 2	Lost wax technique	Direct and indirect 3D printing	3D-printed RPDs have a better fit
21	Grymak et al., 2023 [32]; New Zealand	Laboratory study	Maxillary class III modification 1	Stone cast	Selective laser melting	3D-printed RPDs have better acceptance

Table 1. Basic characteristics of the included studies (quantitative studies).

Sr No.	Author/Year/Country	Study Design	Kennedy’s Classification	Control Group	Type of 3D Printer	Outcome
1	Anan and Saadi 2015 [47]; Syria	In vitro study (Experimental)	Mandibular class III modification 1	Traditional technique	Light curing model technique	Fit accuracy of 3D-printed RPDs was better than traditional
2	Lee et al., 2017 [19]; South Korea	Clinical report	Maxillary and mandibular class I	Replica technique	Digital light projection (DLP)	The RPD constructed with the replica technique has varied results
3	Ye et al., 2017 [46]; China	Randomized control trial	Mandibular class I modification 1	Lost wax- technique	Stereolithography (SLA)	The single design RPD prepared with a 3D printer was more accurately fit than those with the traditional technique
4	Arnold et al., 2018 [6]; Germany	Laboratory study	Maxillary class III modification 2	Lost wax technique	Direct and indirect 3D printing techniques	The 3D-printed RPD has less fit
5	Soltanzadeh et al., 2018 [50]; USA	Laboratory study	Maxillary class III modification 1	Lost wax technique	Indirect printing	The conventional RPD was more accurate
6	Torii et al., 2018 [28]; Japan	Experimental study	First molar simulation	Lost wax technique	indirect printing (CAD)	No significant difference was reported in the accuracy of fit within both techniques
7	Bajunaid et al., 2019 [10]; Saudi Arabia	Laboratory study	Mandibular class III	Lost wax technique	Direct CAD printers	3D-printed RPDs are more accurate
8	Chen et al., 2019 [35]; China	Laboratory study	All classes	Lost wax technique	Direct CAD printing technique	3D-printed RPDs are less fitting but clinically acceptable
9	Negm, Aboutaleb, and Alam-Eldein 2019 [22]; Egypt	Laboratory study	Maxillary class I	Stone cast model	Stereolithography (SLA)	RPDs prepared by 3D printers have less accuracy
10	Carneiro Pereira et al., 2019 [49]; Brazil	Clinical report	Mandibular class III modification 1	Intra-oral scanner (Patients mouth)	Direct and indirect printing techniques	The 3D-printed RPDs have an acceptable clinical fit
11	Tregemen et al., 2019 [48]; South Carolina	Clinical trial	Mandibular and maxillary class I, II, and III	Stone cast model	Selective laser melting	3D-printed RPDs have a better fit
12	Hayama et al., 2019 [17]; China	Clinical report	Mandibular class I	Intraoral scanners	Direct digital technique	3D-printed RPD have an acceptable fit
13	Oka et al., 2019 [13]; Japan	Laboratory study	Mandibular and maxillary class I, II, and III	Lost wax technique	Direct CAD printing technique	3D-printed RPD have an acceptable fit
14	Wu et al., 2020 [44]; China	Clinical report	Mandibular class I modification 1	Intraoral scanners	Selective laser melting	3D-printed RPD have an acceptable fit
15	Xie et al., 2020 [39]; China	Laboratory study	First molar simulation	Lost wax technique	Direct CAD printing	3D-printed RPDs have better fit
16	Yoon et al., 2021 [40]; China	Laboratory study	Maxillary class I	Stone cast	Direct 3D printing	Acceptable fit
17	Hussein and Hussein 2022 [11]; Saudi Arabia	Laboratory study	Maxillary class III and Mandibular class 1	Lost wax technique	Digital light processing	No effect on the accuracy of fit
18	Saadaldin et al., 2022 [36]; Egypt	Laboratory Study	Not mentioned	Lost wax technique	Selective laser melting technique	Better accuracy fit of SLM-prepared RPDs
19	Rokshad et al., 2022 [24]; Germany	Laboratory study	Maxillary class III modification 1	Convectional technique	Digital light processing	Acceptable fit
20	Peng et al., 2022 [14]; China	Laboratory study	Mandibular class II modification 2	Lost wax technique	Direct and indirect 3D printing	3D-printed RPDs have a better fit
21	Grymak et al., 2023 [32]; New Zealand	Laboratory study	Maxillary class III modification 1	Stone cast	Selective laser melting	3D-printed RPDs have better acceptance

Table 2. Basic characteristics of included studies (qualitative studies).

Sr No.	Author/Year/Country	Study Design	Kennedy’s Classification	Type of 3D Printer	Outcome
1.	Kattadiyil et al., 2014 [26]; USA	Clinical report	Maxillary class III	Stereolithographic	The finished prosthesis was successfully placed and used by the patient
2.	Husain Omran 2014 [54]; Saudi Arabia	Case report	Maxillary class I	Digital light prototyping	Well-fitted silicone framework
3.	Lee and Lee 2015 [18]; South Korea	Case report	Maxillary class I	Stereolithographic	Fit accuracy is satisfactory
4.	Mansour et al., 2016 [43]; USA	Clinical report	Maxillary class I modification 1	Stereolithography (SLA)	Fit of RPD prepared by rapid prototyping was highly satisfactory
5.	Batalha and Araújo 2017 [41]; Brazil	Clinical report	Mandibular class I modification 1	Digital light projection(DLP)	The accuracy of fit was satisfactory
6.	Hu, Pei, and Wen 2017 [42]; China	Clinical report	Maxillary class I	Stereolithography (SLA)	The 3D-printed RPD is the best alternative to conservative RPD, and the accuracy of fit is acceptable
7.	Gan et al., 2018 [45]; China	Randomized control trials	Dentate	Selective laser melting (SLM)	RPDs designed with 3D printers have an acceptable fit
8.	Katreva et al., 2018 [25]; Bulgaria	Clinical case report	Mandibular class I	Stereolithography (SLA)	3D-printed RPD appears to be more precise and accurate
9.	Tasaka et al., 2019 [51]; Japan	Laboratory study	Mandibular class II modification 1	Indirect printing	RPD fabricated by 3D printer has an acceptable fit
10.	Takahashi et al., 2020 [38]; USA	Laboratory study	First molar simulation	Direct and indirect printing	Acceptable fit
11.	Tasaka et al., 2020 [27]; Japan	Laboratory study	Mandibular class II modification 2	Direct and indirect printing	3D-printed RPDs have a better fit
12.	Cabrita et al., 2021 [55]; USA	Clinical report	Mandibular class I	Selective laser melting	3D-printed RPD have an acceptable fit

Table 2. Basic characteristics of included studies (qualitative studies).

Sr No.	Author/Year/Country	Study Design	Kennedy’s Classification	Type of 3D Printer	Outcome
1.	Kattadiyil et al., 2014 [26]; USA	Clinical report	Maxillary class III	Stereolithographic	The finished prosthesis was successfully placed and used by the patient
2.	Husain Omran 2014 [54]; Saudi Arabia	Case report	Maxillary class I	Digital light prototyping	Well-fitted silicone framework
3.	Lee and Lee 2015 [18]; South Korea	Case report	Maxillary class I	Stereolithographic	Fit accuracy is satisfactory
4.	Mansour et al., 2016 [43]; USA	Clinical report	Maxillary class I modification 1	Stereolithography (SLA)	Fit of RPD prepared by rapid prototyping was highly satisfactory
5.	Batalha and Araújo 2017 [41]; Brazil	Clinical report	Mandibular class I modification 1	Digital light projection(DLP)	The accuracy of fit was satisfactory
6.	Hu, Pei, and Wen 2017 [42]; China	Clinical report	Maxillary class I	Stereolithography (SLA)	The 3D-printed RPD is the best alternative to conservative RPD, and the accuracy of fit is acceptable
7.	Gan et al., 2018 [45]; China	Randomized control trials	Dentate	Selective laser melting (SLM)	RPDs designed with 3D printers have an acceptable fit
8.	Katreva et al., 2018 [25]; Bulgaria	Clinical case report	Mandibular class I	Stereolithography (SLA)	3D-printed RPD appears to be more precise and accurate
9.	Tasaka et al., 2019 [51]; Japan	Laboratory study	Mandibular class II modification 1	Indirect printing	RPD fabricated by 3D printer has an acceptable fit
10.	Takahashi et al., 2020 [38]; USA	Laboratory study	First molar simulation	Direct and indirect printing	Acceptable fit
11.	Tasaka et al., 2020 [27]; Japan	Laboratory study	Mandibular class II modification 2	Direct and indirect printing	3D-printed RPDs have a better fit
12.	Cabrita et al., 2021 [55]; USA	Clinical report	Mandibular class I	Selective laser melting	3D-printed RPD have an acceptable fit

3.2. Comparison of the Method Utilized for Assessment of Fit of 3D-Printed RPDs

The method of assessment is divided into two categories: qualitative and quantitative. The qualitative method for detecting the accuracy of fit is visual inspection, which is usually done in clinical settings and does not require any numerical data. At the same time, the quantitative assessment for analyzing the accuracy is divided into two categories: optical inspection (microscopes) and computer software (

Table 3. Method of assessment for checking the accuracy of fit.

Author	Method of Assessment	Type of Measurement	Area of Measurement
Kattadiyil et al., 2014 [26]	Visual inspection (mouth mirror and probe)	Adaptation	Overall
Hussain Orman et al., 2014 [54]	Optical (Microscope)	Accuracy and adaptation	Overall
Batalha and Araújo 2017 [41]	Visual inspection (mouth mirror and probe)	Adaptation	Overall
Hu, Pei, and Wen 2017 [42]	Visual inspection (mouth mirror and probe)	Adaptation	Overall
Lee et al., 2017 [19]	Optical (Stereomicroscope)	Internal discrepancy	All components
Ye et al., 2017 [46]	Visual inspection (mouth mirror and probe)	Adaptation	Overall
Batalha and Araújo 2017 [26]	Optical (Stereomicroscope)	Gap distance	Different sections
Arnold et al., 2018 [6]	Optical (Light microscope)	Gap distance	Clasp
Gan et al., 2018 [45]	Optical (Stereomicroscope)	Gap distance	All components
Soltanzadeh et al., 2018 [50]	Computerized (Geomagic)	Gap distance	All components
Torii et al., 2018 [28]	Optical (Profile projector)	Gap distance	Rest, 3-point clasp
Bajunaid et al., 2019 [10]	Optical (Digital microscope)	Gap distances	Rest
Chen et al., 2019 [35]	Computerized (Geomagic NX image)	Gap distance	Overall
Negm, Aboutaleb, and Alam-Eldein 2019 [22]	Computerized (Geomagic)	Gap distance	Overall
Oka et al., 2019 [13]	Computerized	Adaptation	Overall
Soltanzadeh et al., 2018 [35]	Computerized (Geomagic)	Trueness	All components
Carneiro Pereira et al., 2019 [49]	Visual inspection (mouth mirror and probe)	Adaptation	Overall
Tasaka et al., 2019 [51]	Computerized (GOM Inspect)	Average deviation	All components
Tregemen et al., 2019 [48]	Visual inspection (mouth mirror and probe)	Adaptation	Overall
Takahashi et al., 2020 [38]	Optical (Profile projector)	Gap distance	Clasp
Tasaka et al., 2020 [27]	Computerized (GOM Inspect)	Average deviation	Clasp
Wu et al., 2020 [44]	Visual inspection (mouth mirror and probe)	Adaptation	Overall
Xie et al., 2020 [39]	Optical (Stereomicroscope)	Gap distance	3-point clasp
Cabrita et al., 2021 [55]	Visual inspection (mouth mirror and probe)	Adaptation	Overall
Peng et al., 2022 [14]	Computerized (Geomagic)	Trueness	Overall
Rokshad et al., 2022 [24]	Computerized (Geomagic Control X)	Adaptation and Gap measurement	All areas
Grymak et al., 2023 [32]	Computerized (Geomagic Control X)	Adaptation	Overall
Hussain and Hussain 2022 [11]	Computerized (Geomagic Control X)	Trueness	Overall

). Quantitative methods usually require the control group to confirm the findings, while qualitative methods involve dentist experience and perception. A comparison between these two assessment methods and their sub-themes will be discussed further.

3.3. Qualitative Assessment Method (Visual Method)

The qualitative assessment method involves dentists’ perception and experience and relies on materials, manufacturing techniques, and gap registration. Eight studies utilized qualitative methods, such as direct inspection (naked eyes, mouth mirror, and probe) or tactile sensation, to determine the overall adaptation of 3D-printed RPDs [26,41,42,44,46,48,49,55]. Of these, three studies demonstrated both qualitative and quantitative methods to check the accuracy of fit of 3D-printed RPDs [40,43,46].

Seven studies used silicon material as a registration material to fill the gap between the fitting surfaces of RPDs and the cast model for measuring the accuracy of fit [6,19,32,38,41,42,43]. Some studies used silicone to demonstrate the accuracy of fit of RPD clasps prepared by 3D printers and conventional RPDs. Two studies used polyvinyl siloxane as a registration material to assess the accuracy of fit of RPD prepared by 3D printers [36,55]. These studies used dial calipers to measure the gaps between the clasp assembly and rest seats. The method to analyze the accuracy of fit with the help of a caliper is most used in clinics. However, using this method, it is not easy to measure the thickness accurately due to the elasticity of the silicone materials. Secondly, placing the material has a chance for distortion, resulting in inaccurate findings. Therefore, the results of the studies utilizing silicone material to register the gap could be erroneous. The same points apply to the studies that evaluated visual and tactile sensation to evaluate the accuracy of fit.

3.4. Quantitative Assessment Method (Computerized and Optical)

This method is divided into two categories: optical and computerized. In the optical method, the accuracy of fit was measured in two dimensions, mainly vertical and horizontal. This method demonstrates the accuracy of fit by analyzing gaps between the RPD components and internal discrepancies between the underlying tissue. Eight studies used optical methods to demonstrate the accuracy of fit [11,22,27,35,39,40,43,44], while one study used both visual and optical methods [28]. Of these, five studies utilized a stereomicroscope [18,19,27,45,46], two studies used profile projectors [28,51], and one study used a light microscope [6]. In the optical method, various components of RPDs are studied, like clasps, proximal plates, and major connectors, to check the accuracy of fit. Optical measurement is performed with or without the help of the registration method. Among the studies included, four studies utilized light-bodied polyvinyl siloxane (PVS) [6,10,35,44], three studies used fit and bite checkers [17,53,55], while two studies did not use any registration materials [39,46].

A study used a light microscope at 560 magnification to determine the accuracy of fit of RPDs prepared by different CAD/CAM systems and compared them to conventionally prepared RPDs [6]. The RPDs produced by various CAD/CAM techniques were indirect prototyping with the lost wax technique, indirect milling (wax milling with the conventional method), and direct milling with resin polymers. These prepared models were placed on the clasp model, and the accuracy of 12 prepared canine clasps of each group was determined at three vertical and three horizontal areas. This study determined that vertical and horizontal distances are essential concepts in measuring accuracy [6]. Using a digital microscope at 15X in micrometers, another study compared the accuracy of fit of 15 RPDs fabricated using the stereolithography technique to 15 RPDs fabricated by the conventional method using light-bodied polyvinyl siloxane (PVS) [32]. Silicone registration materials measured the fit in this study, and a total of 348 images were used to evaluate the accuracy of fit [32].

Furthermore, one study compared 30 RPDs fabricated by the conventional method and the light-curing method from three different angles and concluded that there were clinically acceptable marginal gaps in both methods. The authors of this study also commented that the framework’s accuracy could differ according to the time required for fabrication and the material utilized [44]. In another study with 24 machine-milled casts, it was reported that the accuracy of fit was better for the maxillary major connector than the mandibular connector or control group [46].

The computerized assessment method mainly depends on standard tessellation language files (STL files) for the reference and development of the output of RPD. Eleven studies used the computerized method for assessment. The measurement of accuracy was performed in three dimensions, including the gap distance (n = 4), average deviation (n = 2), trueness (n = 3), and adaptation (n = 3). A study by Rokshad et al. used two measurement types (adaptation and gap distance) [24]. All the studies used different software to assess the accuracy of fit; for example, eight studies used Geomagic software, two used GOM Inspect [27,51], and one did not mention the name of the software [13]. Additionally, a conceptual map was developed from the qualitative and quantitative assessments (Figure 3).

Dentist’s Perception of Acceptance of 3D-Printed RPDs

Since 3D-printed RPDs are most used in modern dentistry, there are limited data available on dentists’ perceptions of the acceptance of 3D-printed RPDs. Only two studies (

Table 4. Perception of dentists on acceptance of 3D-printed RPDs.

Authors	Study Design	Dentist Perception	Long-Term Prognosis
Urumova et al., 2021 [30]; Bulgaria	Questionnaire	Cost effective and reduces chair-side timing	More clinical studies are required for the analysis of long-term prognosis
Chobe et al., 2023 [31]; India	Questionnaire	Cost effective and easily acceptable	Not mentioned

) have been published to check dentists’ perception [30,31], of which only one study has checked long-term prognosis [31]. Dentists who participated in both studies suggested that patients accept 3D-printed RPDs well and that they are cost effective. However, dentists believe there is a considerable gap in the knowledge of using 3D-printed RPDs, and this topic should be incorporated in the dental curriculum. Regarding patients’ satisfaction, both studies mentioned that due to less chair-side time and proper retention, the 3D RPDs were accepted by the patients.

4. Discussion

This scoping review aimed to provide comprehensive evidence on methods used to assess the accuracy and acceptance of 3D-printed RPDs in clinical practice. Three primary criteria were checked for accessing the accuracy of RPD: (1) all the rest should be adequately seated on their rest seats, (2) all the rigid elements should touch the teeth, and (3) major connectors should not impinge the underlining soft tissue or palate and the visible space should not exceed 1 mm. Initially, visual and tactile examinations were used in the clinical setting. This technique solely depends on clinicians’ experience, which may vary accordingly. Unfortunately, a visual inspection will not provide a proper quantitative assessment. Moreover, adequate dentist training and RPD calibration are required to obtain accurate and acceptable results.

The optical assessment method employs optical instruments such as light microscopes or stereomicroscopes to achieve more precise fit measurements than visual inspection. This assessment can be conducted with or without registration materials that capture the gap between the removable partial denture (RPD) framework and the opposing surface. Various materials have been utilized, including polyvinyl siloxane (PVS) [10,45,46], Fit & Bite Checker [19,27,28], and radiopaque fit testing material [13]. However, optical assessment has certain limitations, such as the challenge of precisely identifying measurement sites and the inability to comprehensively evaluate the framework’s overall fit. Additionally, the accuracy of the space measured by assessing the thickness of the silicone registration materials may be compromised due to potential distortion or tearing of the material upon removal from the mouth [56]. Some studies have combined visual and optical methods for accurate assessment results.

The advent of digital technology has led to the development of computer-based software that improves the accuracy of accessing RPD fitting by optimizing the alignment of the RPD framework with the opposing surface at various sites. This technology generates a virtual color map, where different colors represent varying degrees of fit. The use of color mapping allows clinicians to detect over-pressed or misfit areas across more than 500 points [10,21,35]. This method significantly increases the number of comparison points compared to traditional optical and visual methods [56,57,58]. Additionally, the superimposition of a 3D-fabricated RPD with the original CAD data provides both qualitative and quantitative insights into dimensional discrepancies, trueness, and the accuracy of the printing process.

For evaluation of the overall accuracy of 3D-printed RPDs, it is advisable to use virtual superimposition of the original CAD design with the 3D-printed RPD via specialized surface-matching software, recording the average deviation. This deviation can be quantified as minimum, maximum, and average values. Notably, only one study [48] utilized the root mean square (RMS) to assess the trueness of 3D-printed RPDs. RMS is an effective metric for comparing prediction errors within different models or configurations of a particular variable. However, it cannot be used to compare different variables due to its scale dependence [17]. Most studies in this review reported low average deviation, indicating high trueness in 3D-printed RPDs, suggesting that the accuracy of these devices is promising and clinically acceptable. The high trueness of 3D-printed RPDs may be attributed to reduced laboratory errors and decreased inter-operator variability [10,14,27]. Data from recent studies indicate that over the past three years, software-based methods for assessing RPD fit have produced more accurate and reliable results, both in laboratory settings and clinically. Oka et al. (2016) introduced a novel method for testing dental prostheses by combining the silicone replica technique with micro-computed tomography (μCT) [13]. This approach can be used during the try-in stage, as it provides non-invasive and accurate fit evaluation. Despite its potential, this method has not been employed in the included studies for assessing RPD framework fit, likely due to the high cost of CT scans.

The studies in this scoping review present mixed results regarding the fit and accuracy of RPDs fabricated using 3D printing techniques. While some studies report promising outcomes, others indicate poorer fit and more significant dimensional discrepancies in 3D-printed frameworks. These varying results may be due to the different protocols employed during the 3D-printing process, including variations in light intensity, printing direction, layer thickness, and number, the amount of supporting material used, and post-processing heat treatments [39,45].

Differences in polishing procedures may also influence the outcomes [10]. It has been reported that the polishing procedure can significantly impact fit accuracy, particularly on the intaglio surface of the framework’s rest component [57]. Al Motardi (2020) suggested meticulous finishing and polishing may enhance fit precision, while excessive finishing could lead to unnecessary metal removal from the internal surface [2]. Brudvik and Reimers (1992) observed an average metal loss of 127 μm from the surface of a Co-Cr framework after finishing and polishing [59]. Careful sandblasting and polishing are essential to minimize their effects on the intimate fit of the RPD framework [57]. The findings of this review revealed inconsistent results regarding the fit of 3D-printed RPDs when different finishing and polishing protocols were applied. No study has identified the optimal polishing protocol for 3D-printed RPD frameworks. Therefore, further research is needed to evaluate the impact of polishing on the dimensional accuracy of digitally fabricated frameworks.

The current scoping review has also focused on dentists’ perceptions and patient-reported outcomes for assessing the long-term prognosis of digitally fabricated RPDs. Only two cross-sectional studies have been conducted to report the perception of dentists. These studies have shown that dentists and patients were highly satisfied with digitally fabricated dentures over conventional ones [30,31]. The main reason for this could be better fit and retention, less chair-side time, and a lighter framework than conventional ones. Further clinical studies are required to evaluate dentist perception of acceptance of 3D-printed RPDs.

One of the strengths of this scoping review is the high quality of the included studies, mainly clinical trials and crossover studies. These designs are advantageous as they require a small sample size and complex statistics. Hence, they provide accurate results when compared with other study designs. This scoping review also summarized dentist’s perceptions and patient-reported outcomes for digitally fabricated RPDs.

This scoping review has a few limitations; the articles included were in English and could not reach a definitive conclusion due to the restriction of published resources. Even though the accuracy of fit yielded a mixed result among the included studies, almost all reported a clinically acceptable range. However, further studies with a larger sample size and randomized control trials are required to support the findings of this review.

5. Conclusions

Based on the findings of this scoping review, evidence suggests that digitally fabricated RPDs are more acceptable and accurate than conventional ones. However, due to the scarcity of articles on this topic, the generalization of the result is not possible. Visual, optical, and computerized methods perform the accuracy of fit of digitally fabricated RPDs. This review reported that the automated method is more reliable than optical and visual. It can detect minute misfit and dimensional changes and can provide precise measurements.