Evaluation of the fit of metal copings fabricated using stereolithography

Accuracy of CAD-CAM milling versus conventional lost-wax casting for single metal copings: A systematic review and meta-analysis

STATEMENT OF PROBLEM

Information comparing the marginal and internal adaptation of single metal copings fabricated via computer-aided design and computer-aided manufacturing (CAD-CAM) milling and lost-wax casting is insufficient.

PURPOSE

The purpose of this systematic review and meta-analysis was to compare the adaptation of single metal copings fabricated via CAD-CAM milling to that of copings fabricated via lost-wax casting and to identify factors that influenced their accuracy.

MATERIAL AND METHODS

Following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines, Elsevier ScienceDirect, PubMed, Cochrane Library, SpringerLink, and Wiley online databases were searched to select qualified articles, which were assessed by the methodological items for nonrandomized studies (MINORS) criteria. The data on the mean absolute marginal gap, marginal gap, axial gap, occlusal gap, and internal gap values of single metal copings fabricated via CAD-CAM milling and lost-wax casting were extracted, and meta-analysis and meta-regression were used with R software (α=.05) and random-effects models to estimate differences and homogeneity between the 2 methods.

RESULTS

For the single metal copings, lost-wax casting and CAD-CAM milling led to similar marginal and internal accuracies, but lost-wax casting led to better absolute marginal gap values. For the cast copings, Ni-Cr alloy (92.8 μm) and noble alloy (51.5 μm) led to the largest and smallest marginal gaps, respectively, (P=.005). For milled copings, the noble alloy led to the smallest marginal gap (19.1 μm), and Co-Cr alloy to the largest (76.2 μm) (P=.012). Soft milling led to a more accurate marginal gap (41.4 μm) than hard milling (66.1 μm) (P=.04).

CONCLUSIONS

When CAD-CAM milling was used to fabricate single metal copings, no advantage in precision was found compared with lost-wax casting, and single metal copings cast from handmade conventional wax patterns had better marginal adaptation than those fabricated via CAD-CAM milling. Noble metal copings had improved marginal accuracy than base metal copings for both the casting and milling methods. Single copings fabricated via soft milling from unsintered metal blocks had more accurate marginal adaption than copings fabricated via hard milling.

Effect of lamination layer thickness and abutment preparation on the fit of Co-Cr multi-unit prostheses fabricated by additive manufacturing: An in vitro study

STATEMENT OF PROBLEM

Selective laser melting has been increasingly used in the fabrication of metal-ceramic prostheses. The lamination layer thickness may influence the fit of the restoration. However, data regarding its impact remain scarce.

PURPOSE

The purpose of this in vitro study was to evaluate the marginal and internal fit of cobalt-chromium (Co-Cr) 3-unit frameworks fabricated by additive manufacturing with different melting layer thicknesses on different abutments.

MATERIAL AND METHODS

The first right maxillary premolar and molar from a typodont were prepared with a circumferential 1.2-mm chamfer, 2-mm occlusal reduction, and total taper of 8 degrees to receive 3-unit fixed partial dentures. After framework design, the data were sent to a laser machine, and 30 specimens were fabricated from Co-Cr metal powder (Mediloy S-Co) by selective laser melting. Specimens were assigned to 3 groups (n=10) with different lamination layer thicknesses of 25 (L25), 50 (L50), and 100 (L100) μm. Marginal fit and internal fit were evaluated. Results were compared among layer thickness groups and abutments. Data were compared by using the Levene test, t test, and ANOVA (α=.05).

RESULTS

A statistical difference was found between different layer thickness groups (P=.016), but not between abutments (P=.429). On the abutment level, significant difference was found in the gap values for the molars (P=.049) between layer thickness groups, but not for the premolars (P=.126). Group L25 reported the smallest mean discrepancy values, and group L100 reported the highest, with statistical difference found between group L100 and groups L25 (P<.001) and L50 (P<.025), but not between groups L25 and L50 (P=.094).

CONCLUSIONS

The lamination layer thickness affected the adaptation of the metal frameworks. Framework fit did not significantly differ between abutments.

An assessment of the passivity of the fit of multiunit screw-retained implant frameworks manufactured by using additive and subtractive technologies

STATEMENT OF PROBLEM

The lack of passive fit in implant-supported restorations can lead to mechanical and biological complications and compromise the longevity of the prosthesis. The manufacturing technique and evaluation site are factors that may affect the passive fit of multiunit screw-retained implant frameworks. However, scientific information regarding this issue is lacking.

PURPOSE

The purpose of this in vitro study was to investigate the effect of manufacturing technique and evaluation site on the passive fit of multiunit screw-retained implant frameworks.

MATERIAL AND METHODS

Two multiunit implant analogs were placed into the right second premolar and second molar sites of a mandibular typodont model. A total of 50 3-unit Co-Cr frameworks were fabricated with 3 indirect (conventional technique, polymethyl methacrylate milling, stereolithography) and 2 direct techniques (selective laser melting and soft alloy milling). The patterns obtained by indirect techniques were subsequently cast. The Sheffield test was used for the assessment. Digital images of the sites were obtained by using a stereomicroscope at ×40 magnification, and the measurement points (n=10 for each site) were examined to record the vertical marginal discrepancy values (μm) with the aid of a measuring software program. The collected data were subjected to the 2-way ANOVA and Tukey honestly significant difference test (α=.05).

RESULTS

The influence of the manufacturing technique (variable 1) on the vertical marginal discrepancy values was statistically significant (P<.001). However, the evaluation site (variable 2) (P=.097) and the interaction of the variables (P=.960) were not statistically significant. The lowest misfit values were observed for selective laser melting (74.2 ±20.5 μm) followed by stereolithography (92.8 ±23.9 μm), soft alloy milling (108.4 ±12.0 μm), polymethyl methacrylate milling (116.7 ±17.0 μm), and conventional technique (137.5 ±18.9 μm). The vertical marginal discrepancy values of the selective laser melting group were significantly lower than those of all other groups (P<.05).

CONCLUSIONS

The manufacturing technique significantly affected the passive fit. selective laser melting-fabricated frameworks demonstrated superior fitting accuracy. Among the indirect techniques, stereolithography-fabricated frameworks revealed the lowest misfit values. The vertical marginal discrepancy values of all manufacturing groups were within the range of clinical acceptability (<150 μm).

Effect of different finish line preparations on the marginal and internal adaptation of cobalt-chromium metal alloy copings fabricated by using CAD-CAM technology: A systematic review and meta-analysis

STATEMENT OF PROBLEM

The marginal and internal adaptation of a fixed dental prosthesis depends on a variety of factors, finish line designs being one of them. A clear consensus as to which finish line design can provide a better marginal and internal adaptation with respect to cobalt-chromium metal alloy copings fabricated by using computer-aided design and computer-aided manufacturing (CAD-CAM) technology is lacking.

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the effect of different finish line preparations on the marginal and internal adaptation of cobalt-chromium metal alloy copings fabricated by using CAD-CAM technology.

MATERIAL AND METHODS

Electronic (PubMed, Cochrane, EBSCOhost, and Google Scholar) and manual searches were conducted for articles published from January 2010 to December 2020 to identify relevant studies evaluating the effect of different finish line preparations (chamfer, deep chamfer, shoulder, rounded shoulder) on the marginal and internal adaptation of cobalt-chromium metal alloy copings fabricated by using CAD-CAM technology.

RESULTS

A total of 573 articles were obtained via electronic search, and 10 articles were obtained through manual search, of which 24 in vitro studies were selected after title, abstract, and full-text screening and were included for both qualitative and quantitative analyses. The marginal adaptation was evaluated under the parameters of marginal gap, absolute marginal discrepancy, and vertical marginal discrepancy, whereas internal adaptation was evaluated under the parameters of internal gap, cervical discrepancy, axial discrepancy, and occlusal discrepancy. The methods of CAD-CAM fabrication (direct metal laser sintering, hard milling, and soft milling) were considered under the subgroup analysis.

CONCLUSIONS

An overall better marginal and internal adaptation was observed with shoulder and rounded shoulder finish line designs when CAD-CAM methods were used for coping fabrication. Marginal and internal adaptation in chamfer and deep chamfer finish line designs showed better results with soft milling and direct metal laser sintering methods, whereas shoulder finish line showed better results with hard milling.

Marginal and internal fit of feldspathic ceramic CAD/CAM crowns fabricated via different extraoral digitization methods: a micro-computed tomography analysis

The aim of this study was to compare the fit of feldspathic ceramic crowns fabricated via 3 different extraoral digitizing methods. Twelve maxillary first premolars were prepared and 36 single crowns were fabricated via 3 extraoral digitizing methods using a laboratory scanner (n = 12): (1) scanning the typodont (ST [control] group); (2) scanning the impression (SI group); (3) scanning the stone cast (SC group). Micro-computed tomography was used to calculate two-dimensional marginal-internal gap and the three-dimensional volumetric gap between the crowns and their corresponding dies. The measured gaps were divided into 6 location categories as follows: marginal gap (MG), finish line gap (FLG), axial wall gap (AWG), cuspal gap (CG), proximal transition gap (PTG), and central fossa gap (CFG). The correlation between each of the 3 extraoral digitizing methods and the adaptation status of the crown margins were also evaluated. The Wilcoxon signed-rank test, Spearman's rank test, and Chi-square test were used for data analysis (α = 0.05). The marginal gaps in the ST, SI, and SC groups differed significantly (24, 198 and 117.6 µm, respectively) (p < 0.05). Significant differences were found between the groups with regard to internal gap measurements, with SI representing higher gap measurements at FLG, PTG and CFG locations (p < 0.05). 3D volumetric gap measurements did not differ significantly (p > 0.05). Under-extended margins observed in the SI and SC groups were correlated with the digitizing method (Cramer's V-square: 0.14). When performing extraoral digitalization, clinicians should choose to scan the stone cast as scanning the stone cast resulted in better internal and marginal fit compared to scanning the impression.

Variables affecting the fit of zirconia fixed partial dentures: A systematic review

STATEMENT OF PROBLEM

Different parameters affect the marginal and internal fit of zirconia fixed partial dentures (FPDs) on natural teeth. Determining a way to optimize these restorations is essential.

PURPOSE

The purpose of this systematic review was to determine the variables affecting the marginal fit and internal accuracy of zirconia FPDs on natural teeth.

MATERIAL AND METHODS

An electronic search was conducted by 2 independent reviewers by using the MEDLINE, Cochrane, Web of Science, and Scopus databases, as well as Google Scholar, for studies published up to July 2018, and a manual search was conducted from the reference lists of related articles. Eligibility criteria included articles in English published in peer-reviewed journals that assessed the marginal and/or internal adaptation of zirconia FPDs on teeth with 3 or more units, with at least 1 of the experimental groups being frameworks or FPDs fabricated from zirconia. Risk of bias was assessed with the aid of the Cochrane Handbook for Systematic Reviews of Interventions.

RESULTS

The search provided 418 records, with 41 fulfilling the inclusion criteria. The selected studies showed considerable heterogeneity regarding materials, state of sintering, manufacturer and computer-aided design and computer-aided manufacturing (CAD-CAM) system, experimental methodology, sample size, and span length. Of the included articles, 36 were in vitro studies and 5 were clinical studies, most of which exhibited high-performance and detection biases. CAD-CAM systems provided more precise marginal and internal fit than CAM systems. An increase of framework span length to 6 or more units decreased both marginal and internal fit. The reported marginal gap tended to increase after the veneering process. The introduction of a conventional impression into an otherwise digital workflow seems to have a negative effect on the marginal fit.

CONCLUSIONS

The accuracy of zirconia FPDs or frameworks is considerably influenced by the processing procedure used and the choice of CAD-CAM system.

Evaluation of marginal adaptation of Co-Cr-Mo metal crowns fabricated by traditional method and computer-aided technologies

Background/purpose

The purpose of this study was to evaluate the marginal gaps of dental restorations manufactured using conventional loss wax and casting, computer-aided design/computer-aided manufacturing (CAD/CAM), and 3D printing methods.

Materials and methods

A zirconia master die model with an upper right first molar resin crown was prepared as a standardized model. A total of 30 resin master die models were duplicated from this standard model. Simultaneously, 10 Co—Cr—Mo metal crowns were individually obtained using the conventional loss wax and casting method (Group A), selective laser sintering (Group B), and CAD/CAM (Group C), respectively. The marginal gaps between the crowns fabricated conventional and digital methods with master die models were calculated using a 3D replica and mapping technique.

Results

Statistical analyses revealed there were significant differences in the marginal gaps in the group A with group B and C (p < 0.05). The mean marginal gaps between dental crowns with die models were 76 ± 61 μm, 116 ± 92 μm, and 121 ± 98 μm for groups A, B, and C, respectively.

Conclusion

Within the limitations of this study, the marginal gaps were clinical acceptable in conventional and digital techniques.