Comparison of Conventional Methods and Laser-Assisted Rapid Prototyping for Manufacturing Fixed Dental Prostheses: An In Vitro Study

Impact of different CAD software programs on marginal and internal fit of provisional crowns: An in vitro study

Statement of the problem

Different CAD software programs used for designing crowns show variations in marginal and internal fit. Marginal and internal discrepancies may cause poorly fitting crowns.

Purpose

The aim of this study was to compare the marginal and internal fit of single crown temporary restorations designed using three different CAD software programs.

Materials and methods

Dentbird, Exocad and Inlab 20 were used to design temporary single crowns using the same cement gap. Three experimental groups (n = 10/group) were formed based on the CAD software used. Geomagic Control X three-dimensional analysis software was used to compare the marginal and internal fit among the groups. Measurements were obtained at nine different thickness points. IBM SPSS Statistics, version 22 was used for all statistical analyses.

Results

Among the CAD software programs tested, Dentbird produced the best internal fit on the buccal surface and the best marginal fit on both buccal and mesial surfaces. Exocad achieved the best values on the distal surface for both internal and marginal fit, while Inlab showed the best values on the mesial surface for internal fit and on the palatal surface for marginal fit.

Conclusions

The Dentbird CAD software program provided the most accurate fit values that closely matched the design. The marginal and internal fit oftemporary crowns may vary depending on the CAD software used.

Evaluating the Marginal and Internal Discrepancy of Nickel-Chrome Copings Made on Fixed Partial Denture Implants with Conventional and 3D Printing Techniques

AIM

This study aimed to evaluate the marginal and internal discrepancy of nickel-chrome (Ni-Cr) copings made on implant bridges with conventional and 3D printing techniques.

MATERIALS AND METHODS

30 three-unit Ni-Cr FDPs (60 copings) were made by 3D-printing technique (PolyJet group), lost-wax method with die spacer technique (die spacer group), and lost-wax method with burn-out the cap (burn-out cap group). Then, the frames obtained from the three methods were checked to examine the marginal discrepancy by stereomicroscope after preparation and polishing. The silicon replica method was used to investigate the internal discrepancy at 6 points (buccal portion of occlusal surface, lingual portion of occlusal surface, middle area of the axial surface in the lingual, middle area of the axial surface in the buccal, cervico-buccal area, and cervico-lingual area). Kolmogorov-Smirnov test was performed first to estimate the normality of data distribution. A one-way ANOVA and post hoc Tukey test were done for comparing marginal and internal discrepancies between groups. The significant level was considered p < 0.05.

RESULTS

The mean ± standard deviation of marginal discrepancy in the PolyJet group, die spacer group, and burn-out cap group was 37.9 ± 15, 68.8 ± 31.8 and 42.7 ± 3.6 µm for buccal margins and 40.4 ± 12.3, 64 ± 21.7, and 42.4 ± 2.1 µm for lingual margins, respectively. The means of buccal and lingual marginal discrepancy in the burn-out cap group and PolyJet group were significantly lower than the die spacer group (p < 0.001). Marginal discrepancy was not statistically different between the burn-out cap group and the PolyJet group. The mean ± standard deviation of overall internal discrepancy in the PolyJet group, die spacer group, and burn-out cap group was 64.6 ± 3.7, 72 ± 22.2, and 58.7 ± 2 µm, respectively. There was a significant difference between the mean of internal discrepancy between three groups (p = 0.001). The mean of internal discrepancy of the burn-out cap group was significantly lower than the die spacer group (p = 0.001) and PolyJet group (p = 0.005). Internal discrepancy was not significantly different between the PolyJet group and the die spacer group (p = 0.168).

CONCLUSION

The marginal and internal gap rates of the three groups were within clinically acceptable limits. The 3D printing technique and lost-wax method with burn-out the cap had the lowest buccal and lingual marginal discrepancies. The burn-out cap method had better fitness and less internal discrepancy than 3D printing and die spacer groups.

CLINICAL SIGNIFICANCE

Lower marginal discrepancy of copings fabricated by using 3D printed patterns may improve clinical success of implant restoration. How to cite this article: Ziaei M, Bajoghli F, Sabouhi M, et al. Evaluating the Marginal and Internal Discrepancy of Nickel-Chrome Copings Made on Fixed Partial Denture Implants with Conventional and 3D Printing Techniques. J Contemp Dent Pract 2023;24(11):826-833.

The state of additive manufacturing in dental research - A systematic scoping review of 2012-2022

Background/purpose

Additive manufacturing (AM), also known as 3D printing, has the potential to transform the industry. While there have been advancements in using AM for dental restorations, there is still a need for further research to develop functional biomedical and dental materials. It's crucial to understand the current status of AM technology and research trends to advance dental research in this field. The aim of this study is to reveal the current status of international scientific publications in the field of dental research related to AM technologies.

Materials and methods

In this study, a systematic scoping review was conducted using appropriate keywords within the scope of international scientific publishing databases (PubMed and Web of Science). The review included related clinical and laboratory research, including both human and animal studies, case reports, review articles, and questionnaire studies. A total of 187 research studies were evaluated for quantitative synthesis in this review.

Results

The findings highlighted a rising trend in research numbers over the years (From 2012 to 2022). The most publications were produced in 2020 and 2021, with annual percentage increases of 25.7% and 26.2%, respectively. The majority of AM-related publications in dentistry research originate from Korea. The pioneer dental sub-fields with the ost publications in its category are prosthodontics and implantology, respectively.

Conclusion

The final review result clearly stated an expectation for the future that the research in dentistry would concentrate on AM technologies in order to increase the new product and process development in dental materials, tools, implants and new generation modelling strategy related to AM. The results of this work can be used as indicators of trends related to AM research in dentistry and/or as prospects for future publication expectations in this field.

Accuracy of marginal fit of an implant-supported framework fabricated by 3D printing versus subtractive manufacturing technique: A systematic review and meta-analysis

STATEMENT OF PROBLEM

Evidence comparing additive 3-dimensional printing (3DP) with subtractive milling for implant-supported frameworks is lacking.

PURPOSE

The purpose of this systematic review and meta-analysis was to compare the marginal fit and accuracy of complete arch implant-supported frameworks (CA), implant-retained fixed partial dentures (IRFPDs), single implant crowns (SICs), and interim implant-retained restorations (IIRRs) by using additive manufacturing (AM) and subtractive manufacturing (SM) methods.

MATERIAL AND METHODS

An electronic search was performed in PubMed, ScienceDirect, Google Scholar, and the Cochrane Library for articles published up to August 2020. The authors acquired the data and evaluated the articles, and the final selection of articles was made according to the inclusion and exclusion criteria. The Methodological Index for Non-Randomized Studies (MINORS) scale was used to evaluate the quality of the included studies. Heterogeneity was evaluated, and meta-analyses with subgroup analyses were performed in the selected studies.

RESULTS

The database search resulted in 960 articles. After removing duplicate articles (410 studies), the titles and abstracts were screened in detail, and 10 in vitro studies were selected for qualitative analysis and 9 for quantitative analysis according to the eligibility criteria. Subgroup analyses were performed to compare the 3DP versus the SM technique for different types of implant-supported frameworks (IRFPDs, SICs, IIRRs, and CA). In the IRFPDs analysis, the marginal fit accuracy of the 3DP systems was higher than that with the subtractive manufacturing method (P<.001). In the subgroup analysis of SIC frameworks (P=.55) and CA (P=.67) frameworks, no significant difference was observed in the assessed techniques.

CONCLUSIONS

The marginal fit of implant-supported frameworks manufactured by AM or SM methods is in the clinically acceptable range.

Micro-CT analysis of 3D printed provisional crowns fitting

BACKGROUND

The provisional crowns (PR) play an important role during the course of fixed prosthesis treatment. The fitting of PR varies and depends on various factors.

OBJECTIVE

The aim of the study was to evaluate the marginal and internal fit of PR produced by three-dimensional (3D) printing technique and to compare those with PR made by the milling technique by using micro computed tomography (μCT) on three commonly used finish line designs.

METHOD

Ninety study models were made using metal die of #14 tooth (i.e. maxillary 1st premolar molar) prepared for full veneer crown with three different finish line chamfer (C), rounded shoulder (RS) and rounded shoulder with bevel (RSB). PR was fabricated on each study model, using milling (MiL group, n= 45), and 3D printing technique (3D-P group, n= 45). Marginal and internal fit of each study model was measured by micro computed tomography, at 7 Zones Pr-1- Pr-7 on each finish line. Recorded data were statistically analysed by one-way analysis of variance (ANOVA) and using Dunnett t-Test (p> 0.05).

RESULTS

The mean gap at margins was minimum for provisional crowns in 3D-P group in any finish line with minimum in rounded shoulder with bevel at zone Pr-1 30.9 ± 5.3 and at zone Pr-7 32.7 ± 5.3. In the axial region, i.e. zone Pr-2, the smallest gap was recorded in the 3D-P group and in the occlusal region, for zone Pr-3, 4 and 5, the maximum gap was recorded in the MiL group.

CONCLUSION

The provisional crowns fabricated by 3D printed technique have better marginal and internal fit than the provisional crowns made by milling technique.

Effects of Post-Curing Light Intensity on the Mechanical Properties and Three-Dimensional Printing Accuracy of Interim Dental Material

This study evaluated the effects of the light intensity of curing and the post-curing duration on the mechanical properties and accuracy of the interim dental material. After designing the specimen, 3D printing was performed, and the light intensity was divided into groups G20, G60, G80, and G120 (corresponding to 1.4−1.6, 2.2−3.0, 3.8−4.4, and 6.4−7.0 mW/cm2, respectively), with no post-curing or 5, 10, or 20 min of post-curing being performed. The flexural properties, Vickers microhardness, degree of conversion (DC), and 3D accuracy were then evaluated. The flexural properties and Vickers microhardness showed a sharp increase at the beginning of the post-curing and then tended to increase gradually as the light intensity and post-curing time increased (p < 0.001). On the other hand, there was no significant difference between groups in the accuracy analysis of a 3D-printed three-unit bridge. These results indicate that the light intensity of the post-curing equipment influences the final mechanical properties of 3D-printed resin and that post-curing can be made more efficient by optimizing the light intensity and post-curing time.

[Metal 3D printing in dentistry]

The article describes the use of 3D printing in dentistry, the principle of operation of 3D printers for metals, a review of comparative data on the quality and accuracy of the final product of 3D metal printing is carried out. Possibilities and prospects of using 3D metal printing in dentistry are indicated.

Bone mineralization and immediate function of six dental implants in patients with Klinefelter syndrome

Patients with Klinefelter syndrome face many challenges in oral treatment and bone mineralization due to multiple systemic dysfunctions. This case report follows the geometrical treatment with immediate implant loading of an adult male patient with Klinefelter syndrome. Satisfactory results were demonstrated in clinical follow-up.

Marginal and internal fit of provisional crowns fabricated using 3D printing technology

BACKGROUND

Clinicians routinely provide provisional crowns following teeth preparation. Three-dimensional (3D) printing technology could be used over conventional methods for better fit as lack of adequate fit would result in plaque accumulation, micro-leakage, teeth sensitivity, caries and periodontal diseases.

OBJECTIVE

The aim of the study was to evaluate the marginal and internal fit of provisional crowns fabricated using 3D printing technology and to compare it with that of compression molding and milling methods.

METHODS

Ninety study models were fabricated by duplicating metal master models of the maxillary first premolar molar with three different finish line chamfer, rounded shoulder and rounded shoulder with bevel. On each study model, provisional crowns were fabricated using compression molding (Mo. group, n= 30 - by over impression technique), milling (Mi. group, n= 30 - by 5-axis dental milling machine), and 3D printing method (3D-P. group, n= 30 - by 3D printer). Marginal and internal fit of the samples were evaluated by measuring gap using a scanning electron microscope with a magnification of 27 ×, at 7 zones A-G on different finish line models. The data were statistically analysed using one-way analysis of variance (ANOVA) at the 0.05 significance level. The p-values were calculated using Dunnett's test.

RESULTS

The marginal gap was minimal for the 3D-P. group for each finish line with lowest for rounded shoulder with bevel at zone A 30.6 ± 5.3 and at zone G 32.8 ± 5.4. In axial area, i.e. zones B and F, the minimum gap was noticed for the Mo. group and in Occlusal area (cusp and fossa), for zones C-E maximum gap was determined in Mi. group followed by Mo. and 3D-P. groups.

CONCLUSIONS

3D printed provisional crowns have better marginal and internal fit compared to milled and molded provisional crowns.

Comparison of marginal and internal fit of three-unit implant-supported fixed prosthetic substructures fabricated using CAD/CAM systems

OBJECTIVE

This study compared the marginal and internal fit of implant-supported fixed dentures fabricated using CAD/CAM systems.

MATERIALS AND METHODS

A lower jaw model representing partial edentulism was produced. Two dental implants were inserted in the area of teeth 35 and 37, onto which cemented abutments were screwed. The model was scanned using a laboratory scanner and transferred to a design software program for substructure fabrication. Sixty substructures were fabricated out of each group for six substructure types (n = 10), cast Co-Cr (control), milling Co-Cr, laser sintering Co-Cr, titanium (Ti), zirconium, and polyetheretherketone (PEEK) substructures. The marginal and internal fit was evaluated using a silicone replica viewed under a stereomicroscope. The data were analyzed using the statistical package program for social sciences (SPSS, Chicago, IL, USA, v. 17) at a significance level of 0.05. Marginal and internal gaps were compared using the one-way ANOVA test and Tukey's post hoc test. The differences between abutment teeth were determined using the independent sample t-test.

RESULTS

There was a significant difference in the marginal gap between PEEK and Ti groups (p < 0.05) but no difference between other groups (p > 0.05). There was a significant difference in the internal gap between PEEK, laser sintering Co-Cr, and milling Co-Cr groups (p < 0.05) but no difference between other groups (p > 0.05). The PEEK group had a higher marginal gap than the Ti group and a higher internal gap than the DMLS Co-Cr group (p < 0.05).

CONCLUSION

All substructures have a marginal and internal fit within acceptable clinical limits.

CLINICAL RELEVANCE

This in vitro study suggests that materials and techniques used in CAD/CAM systems improve the fitting accuracy of implant-supported fixed restorations.

A Review of 3D Printing in Dentistry: Technologies, Affecting Factors, and Applications

Three-dimensional (3D) printing technologies are advanced manufacturing technologies based on computer-aided design digital models to create personalized 3D objects automatically. They have been widely used in the industry, design, engineering, and manufacturing fields for nearly 30 years. Three-dimensional printing has many advantages in process engineering, with applications in dentistry ranging from the field of prosthodontics, oral and maxillofacial surgery, and oral implantology to orthodontics, endodontics, and periodontology. This review provides a practical and scientific overview of 3D printing technologies. First, it introduces current 3D printing technologies, including powder bed fusion, photopolymerization molding, and fused deposition modeling. Additionally, it introduces various factors affecting 3D printing metrics, such as mechanical properties and accuracy. The final section presents a summary of the clinical applications of 3D printing in dentistry, including manufacturing working models and main applications in the fields of prosthodontics, oral and maxillofacial surgery, and oral implantology. The 3D printing technologies have the advantages of high material utilization and the ability to manufacture a single complex geometry; nevertheless, they have the disadvantages of high cost and time-consuming postprocessing. The development of new materials and technologies will be the future trend of 3D printing in dentistry, and there is no denying that 3D printing will have a bright future.

Reliability of Metal 3D Printing with Respect to the Marginal Fit of Fixed Dental Prostheses: A Systematic Review and Meta-Analysis

Three-dimensional (3D) printing technologies have been widely used to manufacture crowns and frameworks for fixed dental prostheses. This systematic review and meta-analysis aimed to assess the reliability of the marginal fit of 3D-printed cobalt-chromium-based fixed dental prostheses in comparison to conventional casting methods. Articles published until 25 June 2020, reporting the marginal fit of fixed prostheses fabricated with metal 3D printing, were searched using electronic literature databases. After the screening and quality assessment, 21 eligible peer-reviewed articles were selected. Meta-analysis revealed that the marginal gap of the prostheses manufactured using 3D printing was significantly smaller compared to that manufactured using casting methods (standard mean difference (95% CI): -0.92 (-1.45, -0.38); Z = -3.37; p = 0.0008). The estimated difference between the single and multi-unit types did not differ significantly (p = 0.3573). In the subgroup analysis for the measurement methods, the tendency of marginal discrepancy between the 3D printing and casting groups was significantly different between articles that used direct observation and those that used the silicone replica technique (p < 0.001). Metal 3D printing technologies appear reliable as an alternative to casting methods in terms of the fit of the fixed dental prostheses. In order to analyze the factors influencing manufacturing and confirm the results of this review, further controlled laboratory and clinical studies are required.

Adaptability Evaluation of Metal-Ceramic Crowns Obtained by Additive and Subtractive Technologies

(1) Background: Traditional metal-ceramic restorations are considered as a standard in the evaluation of new technologies. A critical factor in their longevity is represented by their adaptability; The purpose of this study was to evaluate the marginal and internal gap of ceramic-fused to metal crowns with frameworks obtained by additive manufacturing (AM) technologies and the influence of veneering process on their fit; (2) Methods: Metal-ceramic crowns have been produced by conventional lost-wax technology (T), digital milling (F), selective laser sintering (SLS) and selective laser melting (SLM). The adaptability was assessed using silicone replicas before and after ceramic veneering; (3) Results: The best values were obtained for the milled group followed closely by SLM and SLS, and a significantly higher gap for casted copings. The veneering process did not significantly influence the adaptability of the crowns, regardless of the manufacturing process used for frameworks. The present study promotes additive technologies (AT) as a fast, efficient, and cost-effective alternative to traditional technology. There are fewer steps in which errors can occur when digital technologies are used and the risk of distortion is diminished. (4) Conclusions: CAD/CAM technologies, both additive and subtractive, represent an excellent option to produce time-effective, precise metal-ceramic crowns with excellent adaptation.

Effect of repetitive firing on passive fit of metal substructure produced by the laser sintering in implant-supported fixed prosthesis

PURPOSE

The aim of the present study was to investigate the passive fit of metal substructure after repetitive firing processes in implant-supposed prosthesis.

MATERIALS AND METHODS

Five implants (4 mm diameter and 10 mm length) were placed into the resin-based mandibular model and 1-piece of screw-retained metal substructure was produced with the direct metal laser sintering (DMSL) method using Co-Cr compound (n = 10). The distance between the marked points on the multiunit supports and the marginal end of the substructure was measured using a scanning electron microscope (SEM) at each stage (metal, opaque, dentin, and glaze). 15 measurements were taken from each prosthesis, and 150 measurements from 10 samples were obtained. In total, 600 measurements were carried out at 4 stages. One-way ANOVA test was used for statistical evaluation of the data.

RESULTS

When the obtained marginal range values were examined, differences between groups were found to be statistically significant (P<.001). The lowest values were found in the metal stage (172.4 ± 76.5 µm) and the highest values (238.03 ± 118.92 µm) were determined after glaze application. When the interval values for groups are compared with pairs, the differences between metal with dentin, metal with glaze, opaque with dentin, opaque with glaze, and dentin with glaze were found to be significant (P<.05), whereas the difference between opaque with metal was found to be insignificant (P=.992).

CONCLUSION

Passive fit of 1-piece designed implant-retained fixed prosthesis that is supported by multiple implants is negatively affected by repetitive firing processes.

Influence of the CAD-CAM Systems on the Marginal Accuracy and Mechanical Properties of Dental Restorations

The aim of this study was to compare the quality of different computer-assisted-design and computer assisted manufacturing systems (CAD-CAM) generated by only one scanner, focusing on vertical fit discrepancies and the mechanical properties. A master model was obtained from a real clinical situation: the replacement of an absent (pontic) tooth, with the construction of a fixed partial denture on natural abutments with three elements. Nine scans were performed by each tested and 36 copies were designed using a dental CAD-CAM software (Exocad). The frameworks were manufactured using three-axis and five-axis, with the same batch of the chrome-cobalt (CrCo) alloy. The frameworks were not cemented. A focus ion beam-high resolution scanning electron microscope (FIB-HRSEM) allowed us to obtain the vertical gap measurements in five points for each specimen. Roughness parameters were measured using white light interferometry (WLI). The samples were mechanically characterized by means of flexural tests. A servo-hydraulic testing machine was used with a cross-head rate of 1 mm/min. One-way ANOVA statistical analysis was performed to determine whether the vertical discrepancies and mechanical properties were significantly different between each group (significance level p < 0.05). The overall mean marginal gap values ranged: from 92.38 ± 19.24 µm to 19.46 ± 10.20 µm, for the samples produced by three-axis and five-axis machines, respectively. Roughness was lower in the five-axis machine than the three-axis one, and as a consequence, the surface quality was better when the five-axis machine was used. These results revealed a statistically significant difference (p < 0.005) in the mean marginal gap between the CAD-CAM systems studied. The flexural strength for these restorations range from 6500 to 7000 N, and does not present any statistical differences’ significance between two CAD-CAM systems studied. This contribution suggests that the number of axes improves vertical fit and surface quality due to the lower roughness. These claims show some discrepancies with other studies.

Influence of Manufacturing Methods of Implant-Supported Crowns on External and Internal Marginal Fit: A Micro-CT Analysis

Aim

To evaluate the influence of different manufacturing methods of single implant-supported metallic crowns on the internal and external marginal fit through computed microtomography.

Methods

Forty external hexagon implants were divided into 4 groups (n = 8), according to the manufacturing method: GC, conventional casting; GI, induction casting; GP, plasma casting; and GCAD, CAD/CAM machining. The crowns were attached to the implants with insertion torque of 30 N·cm. The external (vertical and horizontal) marginal fit and internal fit were assessed through computed microtomography. Internal and external marginal fit data (μm) were submitted to a one-way ANOVA and Tukey's test (α = .05). Qualitative evaluation of the images was conducted by using micro-CT.

Results

The statistical analysis revealed no significant difference between the groups for vertical misfit (P = 0.721). There was no significant difference (P > 0.05) for the internal and horizontal marginal misfit in the groups GC, GI, and GP, but it was found for the group GCAD (P ≤ 0.05). Qualitative analysis revealed that most of the samples of cast groups exhibited crowns underextension while the group GCAD showed overextension.

Conclusions

The manufacturing method of the crowns influenced the accuracy of marginal fit between the prosthesis and implant. The best results were found for the crowns fabricated through CAD/CAM machining.

Fit of interim crowns fabricated using photopolymer-jetting 3D printing

STATEMENT OF PROBLEM

The fit of interim crowns fabricated using 3-dimensional (3D) printing is unknown.

PURPOSE

The purpose of this in vitro study was to evaluate the fit of interim crowns fabricated using photopolymer-jetting 3D printing and to compare it with that of milling and compression molding methods.

MATERIAL AND METHODS

Twelve study models were fabricated by making an impression of a metal master model of the mandibular first molar. On each study model, interim crowns (N=36) were fabricated using compression molding (molding group, n=12), milling (milling group, n=12), and 3D polymer-jetting methods. The crowns were prepared as follows: molding group, overimpression technique; milling group, a 5-axis dental milling machine; and polymer-jetting group using a 3D printer. The fit of interim crowns was evaluated in the proximal, marginal, internal axial, and internal occlusal regions by using the image-superimposition and silicone-replica techniques. The Mann-Whitney U test and Kruskal-Wallis tests were used to compare the results among groups (α=.05).

RESULTS

Compared with the molding group, the milling and polymer-jetting groups showed more accurate results in the proximal and marginal regions (P<.001). In the axial regions, even though the mean discrepancy was smallest in the molding group, the data showed large deviations. In the occlusal region, the polymer-jetting group was the most accurate, and compared with the other groups, the milling group showed larger internal discrepancies (P<.001).

CONCLUSIONS

Polymer-jet 3D printing significantly enhanced the fit of interim crowns, particularly in the occlusal region.