Evaluation of the marginal and internal gaps of partially crystallized versus fully crystallized zirconia-reinforced lithium silicate CAD-CAM crowns: An in vitro comparison of the silicone replica technique, direct view, and 3-dimensional superimposition analysis

Marginal gap measurement of ceramic single crowns before cementation: A systematic review

STATEMENT OF PROBLEM

Different instruments have been used to measure the marginal gaps of crowns in vitro. However, a comprehensive systematic review is lacking.

PURPOSE

The purpose of this systematic review was to evaluate the existing literature on the instruments used for the in vitro marginal gap measurement of ceramic single crowns before cementation and to determine whether the crown material and method of fabrication influenced the marginal gap.

MATERIAL AND METHODS

The search was conducted in 2024 across the EBSCO Host, Scopus, PubMed, and Web of Science databases by following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and predefined eligibility criteria. Eligible articles were screened to evaluate 6 instruments for measuring crown marginal gaps: direct view microscopy, scanning electron microscopy, impression replica, cross-sectioning, microcomputed tomography, and 3-dimensional (3D) superimposition. The normality of the data was assessed by using the Kolmogorov-Smirnov test, and the differences in mean marginal gap were statistically evaluated using the Welch ANOVA (α=.05).

RESULTS

Ninety-two articles were included, with 77 documenting single measurement instruments and 15 using a combination of 2 or more measurement instruments. Direct view microscopy was the most used instrument and appeared in 31 (40%) of the studies. No significant differences in mean marginal gap (F=2.09, P=.077) were found across the 6 measurement instruments. Across all studies, excluding those using 3D superimposition, the mean ±standard deviation number of marginal gap measurements per crown was 34.3 ±50.6. Among the 77 studies using a single measurement instrument, 64 used computer-aided design and computer-aided manufacturing (CAD-CAM) technology to fabricate the crowns. CAD-CAM crowns had a mean ±standard deviation marginal gap of 78.9 ±28.6 µm (n=64) compared with 71.6 ±29.5 µm (n=13) for crowns manufactured using conventional methods. Zirconia and lithium disilicate were the most researched materials. Zirconia crowns recorded a mean ±standard deviation marginal gap of 69.4 ±34.2 µm for 972 crowns, which was significantly different (P=.045) from lithium disilicate with a mean ±standard deviation marginal gap of 92.2 ±42.5 µm for 602 crowns.

CONCLUSIONS

Direct view microscopy was the most used marginal gap measurement instrument for ceramic single crowns before cementation, and CAD-CAM was the most used crown fabrication method. No significant differences in mean marginal gap were found among the 6 marginal gap measurement instruments.

Evaluation of the marginal and internal gaps of partially crystallized versus fully crystallized lithium disilicate CAD-CAM crowns

This in vitro study aimed to evaluate the internal and marginal adaptation of crowns produced from partially crystallized and fully crystallized lithium disilicate CAD-CAM blocks using direct view and the silicone replica method. The mandibular first molar was used as an abutment. A total of twenty crowns (n = 10) were produced using milling CAD-CAM. The direct viewing technique was used to measure the marginal gap. The measurement of internal adaptation was conducted using the silicone replica technique. Following the subsequent glazing procedure, all crowns underwent another round of measurements. The paired samples t-test was used to compare two related continuous variables. The study revealed that the mean value of the marginal gap of the partially crystallized block is significantly higher than the fully crystallized block both before and after the glazing process. A statistically significant difference was found before and after glazing of the partially crystallized block in the marginal gap values. The fully crystallized crowns showed better marginal gap values than the partially crystallized ones. No change was observed before and after the glaze in the fully crystallized block. The recommended limit of 120 µm for the marginal gap of lithium disilicate CAD-CAM crowns was never exceeded.

Influence of repeated porcelain firing cycles on the microstructure, marginal and internal fit of implant-cemented Co-Cr frameworks

This study investigated the effect of porcelain firing cycles and fabrication techniques on the microstructure, marginal, and internal fit of implant-cemented cobalt-chromium alloys (Co-Cr) frameworks. Two groups of Co-Cr specimens were prepared: one using selective laser melting (SLM) and the other through the lost wax-casting technique (C). Each group was further divided into two subgroups: as-manufactured and porcelain-fired specimens. The microstructure was analyzed using x-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM/EDX). Ten Co-Cr frameworks per manufacturing technique were fabricated, with marginal and internal discrepancies measured using micro-CT before and after the firing cycles. The results were analyzed by two-way ANOVA and Tukey multiple-comparison tests. The results showed a mixed microstructure of γ-fcc and ε-hcp cobalt-based phases, with porcelain firings increasing ε-Co content, especially in group C. The C specimens exhibited distribution of small pores, while no pores/defects were found in the SLM group. The SLM group, although not at a statistically significant level, showed reduced marginal and internal discrepancy values after firings. In the same behavior pattern, the C group exhibited statistically significantly lower discrepancy values. Ultimately, all subgroups demonstrated clinically acceptable marginal adaptation, but the SLM frameworks exhibited superior marginal and internal fit which remained unaffected by the firing cycles.

Marginal adaptation analysis of CAD/CAM resin crown with non-invasive methods

OBJECTIVES

This study compared the silicone replica method with swept-source optical coherence tomography (SS-OCT) to analyze marginal adaptation and investigated the effect of the light incidence angle of SS-OCT on measurement precision.

MATERIALS AND METHODS

A typodont-prepared mandibular right first molar was scanned using an intraoral scanner (Trios 3). Fourteen crowns were fabricated from CAD/CAM resin blocks (Katana Avencia P) using a 5-axis milling machine (DWX-50). Marginal adaptation at the buccal, lingual, mesial, and distal points was assessed using the silicone replica method and SS-OCT at light incidence angles of 60°, 75°, and 90°. Statistical comparisons were performed using two-way analysis of variance (ANOVA) and t-tests with Bonferroni correction, and t-tests at a significance level of 0.05.

RESULTS

At 60°, SS-OCT showed significantly larger marginal discrepancies than the silicone replica method at the buccal, lingual, and mesial points (p < 0.05). At 75°, only the lingual point showed a significantly larger value than the silicone replica method (p < 0.05). At 90°, no significant differences were observed between the SS-OCT and silicone replica methods (p > 0.05). Marginal discrepancy values increased as the angle changed from 90° to 75° to 60°, with significant differences between 60° and 75° and between 60° and 90° at the buccal and lingual points (p < 0.05).

CONCLUSIONS

SS-OCT is a viable alternative to the silicone replica method for assessing marginal adaptation at an incidence angle of 90 °.

CLINICAL RELEVANCE

SS-OCT, a non-invasive method, has the potential to be applied clinically for evaluating marginal fit in indirect restorations in vivo.

Effect of machining method and margin design on the accuracy and margin quality of monolithic zirconia crowns

STATEMENT OF PROBLEM

The machining accuracy and marginal integrity of monolithic zirconia crowns with minimal invasive preparations may impact the long-term survival rate of tooth and periodontal health, but studies on the effect of machining method are lacking.

PURPOSE

The purpose of this in vitro study was to digitally evaluate the machining accuracy and margin quality of monolithic zirconia crowns fabricated using gel deposition and conventional soft milling processes by comparing 2 different margin types.

MATERIAL AND METHODS

A total of 40 monolithic zirconia crowns were produced using gel deposition (Self-glazed Zirconia Group, SGG, n=20) and soft milling (Milled Zirconia Group, MG, n=20). Each group was further divided into 2 subgroups with different margin designs (chamfer and feather-edge). The trueness and fit of crowns were compared using root mean square (RMS) values. Furthermore, the margin quality was examined before and after final sintering with a scanning electron microscope (SEM). The Scheirer-Ray-Hare and 2-way ANOVA test analysis nonparametric and parametric data, respectively (α=.05).

RESULTS

The trueness analysis revealed that SGG had significantly lower RMS values for both the cameo and intaglio areas compared with MG (P<.001). In addition, crowns with a feather-edge margin exhibited significantly lower marginal RMS values than those with a chamfer margin (P<.01) according to the fit assessment. Followed by milling processes, SGG exhibited a constantly homogeneous microstructure compared with MG. Marginal defects were detected in both groups except for the SGG with the chamfer margin.

CONCLUSIONS

SGG exhibited better accuracy associated with ductile-regime machining than MG, and SGG with chamfer margins displayed flaw-free margin areas. Moreover, the feather-edge margin showed improved marginal fit compared with the chamfer margin.

Comparison of fit and trueness of single-unit and short-span fixed dental restorations fabricated by additive and subtractive manufacturing-A systematic review and meta-analysis

OBJECTIVES

Numerous studies have been conducted on the adaptation of dental restorations fabricated by additive (AM) and subtractive manufacturing (SM); however, the results are conflicting. This systematic review and meta-analysis aimed to evaluate the fit and trueness of fixed restorations made by AM compared to SM.

DATA

Studies investigating internal fit, marginal fit, and trueness of fixed prostheses were involved.

SOURCES

The protocol was registered in PROSPERO (registration number CRD42022323090). An electronic search was performed with a predefined search query across four medical databases on the 6th of September 2023.

STUDY SELECTION

A total of 57 eligible studies were included and sub-grouped by material type (metals, ceramics, acrylic resins, composites). The outcomes were specified as internal fit, marginal fit, and trueness expressed in micrometer (µm). Further subgrouping was based on measurement area: axial, occlusal, and marginal. When we analyzed marginal fit, there were no statistically significant differences between the two techniques in any of the subgroups. The measurement of internal fit metal and ceramic restorations provided no significant differences. However, milled acrylic resin restorations showed a significantly higher occlusal gap compared to 3D printed prostheses with 39.12 µm (95 % CI: 12.44; 65.79). In the case of trueness, a statistically significant difference was observed between ceramic AM and SM restorations with -47.76 µm (95 % CI: -95.51; -0.00). QUIN and GRADE Pro tools were used to evaluate the risk of bias and certainty of evidence.

CONCLUSION

Fixed restorations manufactured with additive manufacturing are valid alternatives to subtractive manufacturing in the digital workflow.

CLINICAL SIGNIFICANCE

Additive manufacturing is an accurate and cost-effective manufacturing method of digital workflow, especially for metal and resin fixed restorations. Once the challenges in ceramics manufacturing are addressed, AM will show more significant promise in the field.

Effect of crystallization and finish line curvature on the marginal integrity of lithium disilicate crowns

PURPOSE

This study aimed to investigate the effect of crystallization and finish line curvature on the integrity of lithium disilicate crowns fabricated by using partially crystallized (P) and fully crystallized (F) blocks.

MATERIALS AND METHODS

Forty-eight lithium disilicate crowns were fabricated based on the designated lithium disilicate blocks and finish line curvatures. The specimens were divided into four groups (n = 12 each): P block with a curved finish line (PC), P block with a straight finish line (PS), F block with a curved finish line (FC), and F block with a straight finish line (FS). Using the silicone replica technique and triple scan method, the absolute marginal discrepancy was measured at four surfaces. Using the triple scan method, five sections were segmented for each surface. Global deviation was measured by using a best fit alignment. Three-way mixed analysis of variance followed by Fisher least significant difference test and the Kruskal-Wallis test were used for statistical analyses (α = 0.05).

RESULTS

The block crystallization had a significant impact on the marginal integrity in the triple scan method, showing a greater marginal discrepancy in the F block crowns (p < 0.001). The finish line curvature significantly influenced the marginal integrity in both measurement methods, with curved finish line crowns exhibiting a greater marginal discrepancy (p < 0.05). However, the areas with the greatest marginal discrepancies differed depending on the analytical method used.

CONCLUSIONS

The marginal discrepancies of the crowns differed according to the fabricated blocks and finish line curvature.

Accuracy, fit, and marginal quality of advanced additively manufactured and milled zirconia 3-unit fixed dental prostheses

STATEMENT OF PROBLEM

Advanced additive manufacturing (AM) of zirconia is an emerging technology that can explore the limitations of traditional computer-aided design and computer-aided manufacturing (CAD-CAM) milling techniques. However, a comprehensive evaluation of their differences in producing zirconia restorations, especially multi-unit restorations, is lacking.

PURPOSE

The purpose of this in vitro study was to compare the accuracy, fit, marginal quality, and surface roughness of zirconia 3-unit fixed dental prostheses (FDPs) by using advanced AM and 2 CAD-CAM milling materials.

MATERIAL AND METHODS

Based on the same CAD model, 30 3-unit posterior FDPs (n=10) were manufactured by using AM and 2 CAD-CAM milling materials (VT and UP). The accuracies of the total, intaglio, occlusal, axial, and marginal regions were calculated separately by comparing the scanned model with the design model by using 3-dimensional (3D) deviation analysis. The silicone layer was scanned to evaluate the marginal and intaglio fit in 3 dimensions. A 3D laser microscope was used for surface roughness detection, marginal quality assessment, and marginal defect measurement. The data were analyzed using ANOVA and the Tukey post hoc test (α=.05).

RESULTS

Compared with CAD-CAM milling, the AM group had higher accuracy and smaller positive deviations on the axial and intaglio regions (P<.001). Different manufacturing methods showed no statistically significant effect on the mean intaglio fit (P>.05), and all were within the clinically acceptable range (<100 µm). The intaglio gap was significantly higher than the target parameter in the occlusal regions. AM-fabricated FDPs had significantly higher surface roughness than milled ones, yet showed better margin quality with fewer marginal defects CONCLUSIONS: Compared with CAD-CAM milling, the advanced additively manufactured zirconia 3-unit FDPs provided better accuracy, improved margin quality, and clinically acceptable fit, but higher surface roughness, and may be a promising alternative for clinical applications.

Effects of Different Crystallization Protocols on Marginal Gap of Lithium Disilicate Single Crowns: SEM Analysis

Objective: In everyday dentistry, lithium disilicate is a valid option for single-fix partial dentures, and this material crystallization process is available with two protocols: long and short. This study's aim was to assess the effects of these two different crystallization protocols, long and short, on the marginal gap of lithium disilicate single crowns. Methods: A total of 24 abutment plastic teeth were scanned using an intra-oral scanner. For each plastic tooth, an identical pair of lithium disilicate crowns was milled (a total of 48 crowns) by a four-axis machine. Each paired sample was categorized into two groups: long crystallization (24 crowns) and short crystallization (24 crowns). To assess precision, each unit's marginal gap (including abutments and crowns) was meticulously measured at four specified regions using a scanning electron microscope. A Kolmogorov-Smirnov test performed on the study variables indicated a normal distribution (p > 0.05), and it was followed by independent t-tests (α = 0.05). Results: For the long crystallization group, the mean total marginal gap values were 42.91 ± 9.67 μm, and for the short crystallization group, the values were 43.25 ± 8.14 μm, with no significant difference between the groups (p = 0.894). In addition, no significant differences were found between the groups regarding the mean marginal gap measurements for all four surfaces (distal (p = 0.310), mesial (p = 0.732), palatal (p = 0.655), and buccal (p = 0.535)). Conclusions: Both the long and short crystallization methods used for lithium disilicate single crowns demonstrated marginal gap values of less than 120 μm, which are within the clinically acceptable range, with no significant differences across any parameters between the two groups. Regarding the marginal gap value, it is recommended to use the short crystallization protocol as it is more time-efficient.

Advantages and drawbacks of different methods to measure marginal gaps in fixed dental prostheses: A scoping review

OBJECTIVES

This review aimed to compare traditional and digital methods to assess marginal gaps in fixed dental prostheses. Each method's characteristics, advantages, and limitations were identified and discussed, also addressing the knowledge gaps in the current scientific literature.

DATA

Studies comparing currently available techniques for marginal gap examination were investigated. The main techniques analyzed were the Cross-Sectional Method (CSM), Direct View (DV), Silicone Replica Technique (SRT), Dual-Scan Method (DSM), Triple-Scan Method (TSM), Optical Coherence Tomography (OCT), and Micro-Computed Tomography (MCT).

SOURCES

Two experienced independent reviewers screened online databases (MEDLINE via PubMed and Scopus) to identify studies published in English up to March 2024. References from primary studies and the main peer-reviewed scientific journals were manually searched.

STUDY SELECTION

From an initial pool of 8126 articles, the reviewers meticulously selected 25 in vitro studies on objective comparisons between two or more methods for assessing marginal gaps in fixed dental prostheses on natural teeth. Publications that assessed marginal gaps in implant-supported fixed dental prostheses were excluded.

CONCLUSIONS

This study highlights that while traditional methods like CSM and SRT are widely used and validated, they have limitations in comprehensive gap assessment, often neglecting recommended measurement points. The DV technique, focusing solely on external gaps, may be less relevant for modern assessments. Conversely, three-dimensional techniques like TSM, DSM, OCT, and MCT offer a more thorough evaluation of dental restoration fit. Moreover, digital methods such as TSM and DSM have a significant potential for future clinical application.

CLINICAL SIGNIFICANCE

This review examined methods for evaluating marginal gaps in fixed dental prostheses. The review aids dental professionals and researchers in choosing the most suitable technique for clinical in vivo or laboratory assessment of the marginal adaptation of dental restorations. This study also indicates the need for an established and standardized assessment protocol for the marginal fit.

Accuracy and adaptation of one-piece endodontic crowns fabricated through 3D printing and milling

STATEMENT OF PROBLEM

High-level evidence regarding the accuracy and adaptation of 1-piece endodontic crowns fabricated by using 3-dimensional (3D) printing technology is lacking.

PURPOSE

The purpose of this in vitro study was to compare the accuracy and adaptation of 1-piece endodontic crowns produced through 3D printing and computer-numerical-control milling technology and to explore the influence of trueness on 1-piece endodontic crown adaptation.

MATERIAL AND METHODS

One-piece endodontic crowns were prepared for a typodont right mandibular first molar, scanned with a 3Shape E3 scanner, and designed with a computer-aided design software program. Two types of 1-piece endodontic crowns were fabricated: 3D printed by using resin and zirconia slurry and milled from Grandio and zirconia blocks. A reverse engineering software program was used to superimpose 4 groups of crowns with the reference crowns used for accuracy analysis. Microcomputed tomography was used to measure 1-piece endodontic crown adaptation. The correlation between trueness and adaptation was evaluated through the Spearman correlation test (α=.05).

RESULTS

Milled resin-based 1-piece endodontic crowns demonstrated better trueness on marginal and occlusal surfaces compared with 3D printed ones (P<.001). However, no significant difference was observed in the trueness of intaglio surfaces between the 2 groups (P>.05). The milled group exhibited better adaptations than the printed one (P<.05). For zirconia 1-piece endodontic crowns, no significant differences were found in trueness or adaptation between the milled and printed groups (P>.05). Notably, the trueness of the axial wall had the greatest impact on overall crown adaptation, with its adaptation closely linked to the trueness of each area, particularly the axial wall.

CONCLUSIONS

Milled resin-based 1-piece endodontic crowns exhibited higher levels of trueness and adaptation compared with 3D printed ones, while 3D printed zirconia 1-piece endodontic crowns were comparable with milled ones.

The Impact of Open versus Closed Computer-Aided Design/Computer-Aided Manufacturing Systems on the Marginal Gap of Zirconia-Reinforced Lithium Silicate Single Crowns Evaluated by Scanning Electron Microscopy: A Comparative In Vitro Study

This study aimed to compare the impact of CAD/CAM closed systems and open systems on the marginal gap of monolithic zirconia-reinforced lithium silicate (ZLS) ceramic crowns, as both systems are used in everyday dentistry, both chair-side and laboratory. For the closed system, 20 plastic teeth were scanned by a Primescan intra-oral scanner (IOS), and for the open system, the same number of plastic teeth were scanned by Trios 4 IOS. For the closed system, CEREC software was used, and for the open system, EXOCAD software was used. All 40 ZLS crowns were grinded by the same four-axis machine and cemented with Temp-bond, followed by self-adhesive resin cement. For each type of cement, an evaluation of the marginal gap was conducted by scanning electron microscopy (SEM). Before comparisons between the groups, a Kolmogorov-Smirnov test was performed on the study variables showing a normal distribution (p > 0.05). Independent T tests (α = 0.05) and paired-sample T tests (α = 0.05) were used. The independent T test found no significant mean marginal gap differences in the zirconia-reinforced lithium silicate crowns bonded with Temp-bond and scanned by Primescan (28.09 μm ± 3.06) compared to Trios 4 (28.94 μm ± 3.30) (p = 0.401), and there was no significant mean marginal gap differences in zirconia-reinforced lithium silicate crowns bonded with self-adhesive resin cement (Gcem ONE) and scanned by Primescan (46.70 μm ± 3.80) compared to Trios 4 (47.79 μm ± 2.59) (p = 0.295). Paired-sample T tests showed significantly higher mean marginal gaps with Gcem ONE compared to Temp-bond for the total mean marginal gap when scanning with Primescan (p = 0.0005) or Trios 4 (p = 0.0005). In everyday dentistry, both closed systems (Primescan with Cerec) and open systems (Trios 4 with Exocad) can be used to achieve an acceptable (<120 µm) marginal gap for ZLS CELTRA® DUO single crowns. There is a significant difference between cementation with Temp-bond and Gcem ONE self-adhesive resin cement (p < 0.05).

SEM Evaluation of the Marginal Gap of Zirconia-Reinforced Lithium Silicate Full Crowns and the Effect of Post Crystallization: An In Vitro Study

BACKGROUND

This study compared the influence of crystallization on marginal gap adaptation by using computer-aided design and manufacturing (CAD-CAM) for producing monolithic zirconia-reinforced lithium silicate (ZLS) ceramic crowns.

METHODS

A total of 25 plastic teeth were scanned using a Primescan intra-oral scanner (IOS), and ZLS crowns were ground. For each unit (abutment and crown), the marginal gap was evaluated pre crystallization and post crystallization at four regions of interest through the use of a scanning electron microscope (SEM). To compare the marginal gap between the two groups, a Kolmogorov-Smirnov test performed on the study variables indicated a normal distribution (p > 0.05) followed by paired samples T-tests (α = 0.0005).

RESULTS

After crystallization, there were significantly higher circumferential marginal gaps (CMGs) for all four surfaces (distal (p = 0.0005), mesial (p = 0.0005), palatal (p = 0.0005), and buccal (p = 0.0005)). The total mean marginal gap (MMG) revealed a significantly higher result for the post-crystallization group (79.82 ± 7.86 μm) compared to the pre-crystallization group (24.25 ± 5.49 μm).

CONCLUSIONS

The post-crystallization group showed a significantly higher marginal gap compared to the pre-crystallization group in all parameters, but both groups were in the clinically accepted threshold (<120 microns). In terms of the marginal gap, it is arguable whether to carry out post-crystallization for CELTRA® DUO crowns and achieve better mechanical properties but significantly increase the marginal gap.

Marginal and internal fit of five-unit zirconia-based fixed dental prostheses fabricated with digital scans and conventional impressions: A comparative in vitro study

PURPOSE

This study aimed to compare the marginal and internal fit of five-unit zirconia-based fixed dental prostheses (FDPs) fabricated using digital scans and conventional impressions.

MATERIALS AND METHODS

Nine master models with three zirconia abutments were scanned with an intraoral scanner (test group), and nine conventional impressions (control group) of these same models were also made. The stone casts from these impressions were scanned with a laboratory extraoral scanner (D700, 3Shape, Copenhagen, Denmark). A total of 18 five-unit zirconia-based FDP frameworks (test group, n = 9; control group, n = 9) were manufactured. Marginal and internal fit (in μm) were evaluated using the replica method under micro-computed tomography. Analysis of variance (one-way ANOVA) and Kruskal-Wallis tests were used to compare continuous variables across two groups. A level of p < 0.05 was accepted as statistically significant.

RESULTS

The mean ± standard deviation of the marginal fit was 95.03 ± 12.74 μm in the test group and 106.02 ± 14.51 μm in the control group. The lowest marginal mean value was observed in the test group, with a statistically significant difference compared to the control group (F = 14.56, p < 0.05). The mean ± standard deviation of the internal fit was 103.61 ± 9.32 and 106.38 ± 7.64 μm, respectively, in the test and control groups, with no statistically significant difference (F = 1.56, p > 0.05). The mean values of both groups were clinically acceptable.

CONCLUSIONS

The five-unit zirconia-based FDPs fabricated with digital scans showed better fit than those in the conventional impression group. Within the limitations of this study, these results are encouraging, and continued progress in the digital field should allow for more accurate long-span restorations.

Influence of the Crystallization Firing Process on Marginal and Internal Adaptation of Silicate-based Glass-ceramic Inlays Fabricated With a CAD/CAM Chairside System

OBJECTIVE

Computer-aided design/computer-aided manufacturing (CAD/CAM) systems are widely used in dental treatment. Clinicians can use chairside CAD/CAM technology, which has the advantage of being able to fabricate inlays on the same day. We aimed to evaluate the effects of crystallization firing processes, fabrication methods (one-step and two-step), and materials on marginal and internal adaptations of silicate-based glass-ceramic all-ceramic inlays fabricated with CAD/CAM chairside systems.

METHODS

Ten artificial mandibular left first molars were prepared with standardized ceramic class II mesialocclusal (MO) inlay cavities. Optical impressions were obtained using CEREC Omnicam Ban. IPS e-max CAD (IE), (Ivoclar Vivadent, Schaan, Liechtenstein), Initial LiSi Block (LS) (Hongo, Bunkyoku, Tokyo, Japan), VITA Suprinity (SP), (Vita Zahnfabrick, Bad Säckingen, Germany), and Celtra Duo (CD) (Ivoclar Vivadent, Schaan, Liechtenstein) (n=10) were milled using CEREC MC XL (Bensheim, Germany). IE and SP were crystallization-fired using CEREC Speed Fire. The silicone replica technique was used for the measurement of internal (axial and pulpal walls) and marginal (cervical and occlusal edge) adaptations. The adaptations were measured using a thin layer of light-body polyvinyl siloxane impression material placed between the master tooth inlay preparation and restoration. Marginal and internal adaptations of IE, LS, SP, and CD were measured using a stereomicroscope (500×). For IE and SP, marginal and internal adaptations were measured before and after the crystallization firing process. Data analyses were conducted using one-way ANOVA and the Tukey test. For IE and SP, marginal and internal adaptations before and after the crystallization firing process were analyzed using the t-test. The significance level was set at α=0.05.

RESULTS

One-way ANOVA revealed statistically significant differences in occlusal and cervical edge marginal adaptations among the material groups (p<0.001). The Tukey HSD test revealed a significant difference in marginal occlusal and cervical edge adaptations between LS and CD groups and IE and SP groups (p≤0.05). For IE and SP inlays, the t-test revealed a significant difference between occlusal and cervical edge adaptations before the crystallization firing process and those after the crystallization firing process, with the latter group showing a more significant discrepancy in adaptation than the former group (p≤0.05).

CONCLUSIONS

Fabrication methods (one- and two-step) affected the marginal adaptation compatibility but not internal compatibility of MO inlays. The crystallization firing process affected the marginal adaptation of inlays using lithium silicate or lithium disilicate glass-ceramics. However, adaptation to the cavity was considered clinically acceptable for all materials.

Internal Adaptation and Marginal Accuracy of Two Different Techniques-based Poly (ether ether ketone) Single Crowns: An In Vitro Study

PURPOSE

The goal of this study was to evaluate how different fabrication techniques affected the marginal accuracy and internal adaptability of poly (ether ether ketone) (PEEK) molar single crowns.

MATERIALS AND METHODS

Twenty PEEK crowns were constructed using two different fabrication techniques, and they were divided into two main groups (PEEK-CAD and PEEK-pressed). PEEK-CAD crowns were numbered from 1 to 10. PEEK-pressed crowns were numbered from 11 to 20. Each group had 10 PEEK crowns, and both were constructed over a master die. For internal fit measurements, silicone replica bodies were built and cut into two halves buccolingually. Marginal accuracy was measured using three evenly spaced landmarks along the specimen's cervical circumference on each surface using a Leica L2 APO* microscope.

RESULTS

In terms of marginal accuracy, the Press group had a statistically significant greater mean marginal gap value than the computer aided-designing (CAD) group. While in terms of internal fit, there was no statistically significant difference in internal fit between the CAD and Press groups. At a significance level of two-tailed p-value = 0.21 (p > 0.05).

CONCLUSION

PEEK-CAD crowns demonstrated higher marginal accuracy and nearly similar internal fit when compared to PEEK-pressed crowns.

CLINICAL SIGNIFICANCE

PEEK material could be used as a substitute for zirconia for a full coverage posterior restoration.

Evaluation of the Marginal Fit of Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) Zirconia Bridges Fabricated With Different Firing Cycles of Veneering Porcelain: An In Vitro Study

Introduction Zirconia provides adequate mechanical strength to be used as a framework for all ceramic prostheses. Such prostheses must be covered with suitable porcelain to obtain good aesthetic results. The aim To study the effect of the firing cycle numbers of veneering ceramics (one cycle, two cycles, and three cycles) on the marginal fit of computer-aided design (CAD) and computer-aided manufacturing (CAM) zirconia bridges. Materials and methods The sample consisted of 30 full ceramic zirconia bridges, designed by CAD/CAM on a metal bridge model that was designed for this purpose. The sample was divided into three groups (N = 10); group A underwent a single firing cycle, group B underwent two cycles, and group C underwent three cycles. The copper model of the bridge was prepared to be a three-unit bridge, and the impressions of the metal models were taken to make zirconia cores. After that, the veneering ceramic layer and the micro-marginal gap were measured (in microns) on both the buccal and lingual surfaces of each bridge in the sample using the replica technique. A one-way ANOVA test was used to detect statistically significant differences between the groups. Results There were no significant differences between the studied groups in binary comparison; however, the arithmetic mean values of the marginal gap in group C were greater than all the studied groups. Conclusion Within the limitations of the current work, we found that increasing the number of firing cycles of zirconia cores affects the marginal fit; thus, it is recommended to follow the two firing cycle protocol for better adaptation of the CAD/CAM zirconia bridges.

Evaluation of the marginal and internal fit of CAD/CAM crowns designed using three different dental CAD programs: a 3-dimensional digital analysis study

OBJECTIVES

The purpose of this in vitro study was to assess and compare the marginal and internal fit of machine-milled crowns designed using three different CAD software programs.

MATERIALS AND METHODS

Digital impressions of the master zirconia casts containing the prepared molar were obtained using an intraoral scanner. The obtained standard tessellation language (STL) files were imported into three CAD software programs (Multi-CAD, Blue-Sky CAD, and InLab), and crown designs were generated. Crown design digital STL files were used to mill crowns with a five-axis dental milling machine. The internal and marginal fits of the fabricated crowns over the master-prepared tooth were assessed using the triple-scan protocol and digital analysis techniques. The 3D marginal and internal fit values of the fabricated crowns from the designs generated by the three CAD programs were evaluated and statistically compared using one-way analysis of variance (ANOVA) and post hoc Tukey's tests (α = 0.05).

RESULTS

There were no significant differences in the internal fit of the crowns designed by the three CAD programs (p > 0.05). However, there were significant differences in the mean marginal fit (p = 0.009) of the crowns. The marginal fit values for the InLab-designed crowns were significantly better than those for Multi-CAD (p = 0.03) and Blue-Sky CAD (p = 0.012) groups.

CONCLUSIONS

All three CAD programs can design clinically acceptable crowns in terms of internal and marginal fit. InLab crowns outperformed the Multi-CAD and Blue-Sky CAD programs in terms of marginal fit.

CLINICAL RELEVANCE

It is critical to test the ability of newly released CAD programs to design acceptable virtual crowns that can be transformed into actual crowns with optimal marginal and internal fit to existing clinical tooth preparations/conditions to ensure the high technical quality and long-term success of fabricated crowns.

Indirect restorative systems-A narrative review

OBJECTIVE

The background and clinical understanding of the properties of currently available indirect restorative systems and fabrication methods is, along with manufacturer and evidence-based literature, an important starting point to guide the clinical selection of materials for tooth and/or implant supported reconstructions. Therefore, this review explores most indirect restorative systems available in the market, especially all-ceramic, along with aspects of manufacturing process, clinical survival rates, and esthetic outcomes.

OVERVIEW

Progressive incorporation of new technologies in the dental field and advancements in materials science have enabled the development/improvement of indirect restorative systems and treatment concepts in oral rehabilitation, resulting in reliable and predictable workflows and successful esthetic and functional outcomes. Indirect restorative systems have evolved from metal ceramics and polymers to glass ceramics, polycrystalline ceramics, and resin-matrix ceramics, aiming to improve not only biological and mechanical properties, but especially the optical properties and esthetic quality of the reconstructions, in attempt to mimic natural teeth.

CONCLUSIONS

Based on several clinical research, materials, and patient-related parameters, a decision tree for the selection of indirect restorative materials was suggested to guide clinicians in the rehabilitation process.

CLINICAL SIGNIFICANCE

The pace of materials development is faster than that of clinical research aimed to support their use. Since no single material provides an ideal solution to every case, professionals must continuously seek information from well designed, long-term clinical trials in order to incorporate or not new materials and technological advancements.

Effect of virtual cement space and restorative materials on the adaptation of CAD-CAM endocrowns

BACKGROUND

This study aimed to evaluate the effect of virtual cement space and restorative materials on the fit of computer-aided design and computer-aided manufacturing (CAD-CAM) endocrowns.

METHODS

A mandibular first molar tooth model received a butt joint margin endocrown preparation with a 2-mm occlusal thickness. Then, using a 3D-printing system, 120 copies of this prepared die were printed and assigned equally to three groups with different cement space settings (30, 60, and 120 μm) during the chairside CAD design. In the milling process, CAD-based models with a particular space setting were subdivided into four groups (n = 10) and fabricated from different CAD-CAM materials: Vita Suprinity (VS), Celtra Duo (CD), Lava Ultimate (LU), and Grandio blocs (GR). Finally, the endocrowns were stabilized over their corresponding models with siloxane and subjected to micro-computed tomography to measure the fit.

RESULTS

The cement space that was predesigned at 30 μm generated the largest marginal discrepancy (from 144.68 ± 22.43 μm to 174.36 ± 22.78 μm), which was significantly different from those at 60 μm and 120 μm (p < 0.001). The combination of VS or CD with a pre-setting cement space of 60 μm and the combination of LU or GR with a cement space of 120 μm showed better agreement between the predesigned and actual measured marginal gap widths. For internal adaptation, only the cement space set to 30 μm exceeded the clinically acceptable threshold (200 μm).

CONCLUSIONS

The setting of the cement space and restorative material significantly affected the marginal adaptation of CAD-CAM endocrown restorations. Considering the discrepancy between design and reality, different virtual cement spaces should be applied to ceramic and resin composite materials.