Clinical outcomes of single crown and 3-unit bi-layered zirconia-based fixed dental prostheses: An upto 6- year retrospective clinical study: Clinical outcomes of zirconia FDPs

Comparison of clinical outcomes between single metal-ceramic and zirconia crowns

STATEMENT OF PROBLEM

Evidence comparing the survival of zirconia crowns with metal-ceramic crowns is sparse. Knowledge of their survival and a comparison of their clinical outcomes would improve clinical decision making.

PURPOSE

The purpose of this university-based study was to compare the survival, failures, biological and technical complications encountered with zirconia and metal-ceramic crowns restored and followed up over a similar period.

MATERIAL AND METHODS

This retrospective chart review consisted of 403 patients treated at the University of Toronto, Faculty of Dentistry, predoctoral dental clinic in whom zirconia (n=209) and metal-ceramic (n=306) crowns were inserted between September 2015 and July 2016 and followed for up to 7 years. Outcome measures included failure, causes for failure, and complications associated with survival. Inferential statistical analysis included the chi-squared test, t test, Mann-Whitney test, Bonferroni-adjusted z-test, Kaplan-Meier survival test, and logistic regression to examine differences between crown types and explore crown failures (α=.05).

RESULTS

The mean follow-up period was 3.00 years (median 2.58 years). Forty-one (8.0%) crowns had no follow-up, with no difference in follow-up between crown type: metal-ceramic n=23(7.5%), zirconia n=18(8.6%), χ²(1)=0.20, P=.652). Excluding those with no follow-up, the follow-up time between metal-ceramic (mean=3.07, median=2.58) and zirconia (mean=3.54, median=3.32) crowns was statistically similar (P=.052). There were 62 anterior crowns (12.0%) and 453 posterior crowns (88.0%), χ²(1)=22.40, P<.001, with no difference between groups. Overall, 44 crowns (8.5%) failed, 30 (9.8%) metal-ceramic and 14 (6.7%) zirconia, with no statistical difference in proportion of failed crowns between groups (χ²(1)=1.53, P=.216). There were 35 crowns with biological failures (6.8%), 26 (8.5%) in the metal-ceramic and 9 (4.4%) in the zirconia group, with no statistical difference between groups (χ²(1)=3.33, P=.068). Nine crowns had technical failures (1.7%), 4 (1.4%) in the metal-ceramic group and 5 (2.5%) in the zirconia group, with no statistical difference between groups (χ²(1)=0.73, P=.394). Biological (79.5%) rather than technical complications were found to be the most frequent cause of failure, goodness-of-fit χ²(1)=15.36, P<.001. Tooth fracture (50.0%) specifically was found to be the most frequent cause of failure, χ²(3)=21.27, P<.001. The total number of crowns that survived was 471 (91.5%); 276 (90.1%) were metal-ceramic and 195(93.3%) zirconia. The survival time (years) for metal-ceramic was mean=6.26, 95% CI [6.01-6.51] and for zirconia crowns mean=6.54, 95% CI [6.31-6.77]. Of the crowns that survived, 370 (78.6%) had no clinical complications, and 101 (21.4%) crowns demonstrated similar clinical complications, with no statistical differences between groups.

CONCLUSIONS

Within the study follow-up time, the survival of monolithic zirconia and metal-ceramic crowns was 91.5%, with similar clinical complications between groups. Biological complications, especially tooth fracture, were a significantly more frequent complication with both types of crowns.

Shear bond strength of vat photopolymerization additive-manufactured zirconia to veneering ceramic

PURPOSE

To evaluate the shear bond strength (SBS) of stereolithography (SLA), digital light processing (DLP) manufactured, and computer numerical control (CNC) milled zirconia to veneering ceramic.

MATERIALS AND METHODS

Rectangular shaped zirconia substrates (10 × 5 × 5 mm3) were manufactured through SLA, DLP, and CNC technology separately. Their surface roughness was measured and the surface topography was analyzed by atomic force microscope (AFM). Then the veneering ceramic (5 × 5 × 5 mm3) was applied to carry out the SBS test. Failure modes were examined by a scanning electron microscope (SEM). The data of SBS and roughness were statistically analyzed with one-way ANOVA followed by S-N-K post hoc comparisons (a = 0.05).

RESULTS

The surface roughness of the SLA group (0.38 ± 0.03 µm) and the DLP group (0.37 ± 0.04 µm) were both significantly higher than the CNC group (0.16 ± 0.00 µm) (p < 0.001). AFM results revealed irregular surface of SLA and DLP zirconia. No significant difference was found in SBS value of the three groups (p = 0.253). SEM image showed different failure modes including cohesive, adhesive, and mixed failure.

CONCLUSION

The bonding ability of SLA and DLP zirconia to veneering ceramic were comparable with that of CNC zirconia.

Minimally Invasive Fixed Prosthodontics: A Narrative Review

OBJECTIVE

Minimally invasive dentistry is being widely practiced. The center stone is to be as conservative as possible to minimize unnecessary removal of healthy tooth structure. In prosthodontics the patients have generalized and combined nature of diseases. This narrative literature review analyzed available evidence on minimally invasive treatment protocols in fixed prosthodontics and raised awareness on the importance of longevity of treatments and secondary prevention.

OVERVIEW

The long-term clinical survival of ceramic and resin composite materials was reviewed. Loss of tooth vitality after prosthodontic treatment was also explored. And finally, treatment options for patients with severe wear were examined. The search of the literature resulted in evidence of superior survival of ceramic restorations over resin composites. The literature is also clear that ceramic partial coverage inlay and onlay restorations have excellent long-term clinical performance in posterior dentition. Glass ceramic lithium disilicate showed to be an adequate material not only for anterior but also for posterior dentition, including the patients with severe wear.

CONCLUSIONS

Minimally invasive dentistry as applied in fixed prosthodontics needs updates in its concepts to account for secondary prevention and longevity of chosen treatment techniques.

CLINICAL SIGNIFICANCE

This narrative review article critically reviews available evidence on long-term clinical performance of minimally invasive and traditional treatment concepts and materials in fixed prosthodontics. Awareness is raised for secondary prevention and longevity of chosen treatments.

Edge Chipping Resistance and Flexural Strength of CAD-CAM Ceramics Before and After Thermomechanical Aging

OBJECTIVES

To evaluate the complementary mechanical properties of dental ceramics using edge chipping resistance (Rea) and flexural strength before and after thermomechanical aging.

MATERIAL AND METHODS

Computer-aided design and computer-aided manufacturing of ceramic materials, including zirconia (ZR), lithium disilicate (LS2), and resin nanoceramics (RNC), were evaluated. Specimens for flexural strength testing were fabricated with dimensions of 3 × 4 × 25 mm, with 30 specimens per group. For the edge chipping test (ECT), specimens were fabricated with dimensions of 3 × 4 × 12 mm, with 48 specimens per group. Half of the specimens for both tests were subjected to thermomechanical aging for 200,000 cycles at 50 N. A Weibull analysis was performed to determine flexural strength. Fractographic analysis was performed before and after thermomechanical aging during the ECT. X-ray diffractometry (XRD) was performed on the ZR specimens before and after thermomechanical aging. Flexural strength was analyzed using a two-way repeated analysis of variance (ANOVA) with a t-test, and Rea was analyzed using Pearson correlation and a two-way repeated ANOVA.

RESULTS

The flexural strength and Rea differed according to the material (p = 0.001), whereas they were similar before and after thermomechanical aging (p > 0.05). The Weibull modulus of the flexural strength decreased after thermomechanical aging. In the fractographic analysis of the ECT, more than two fracture origins were identified after thermomechanical aging. The XRD analysis of ZR showed an increased monoclinic phase after thermomechanical aging.

CONCLUSION

All the materials met the ISO 6872 standards for bending test. However, LS2 and RNC show low edge chipping resistance within the range of the occlusal force. The thermomechanical aging did not significantly alter the mechanical properties of the materials. However, the Weibull coefficients of the flexural strength decreased, and an additional origin of fracture appeared after thermomechanical aging.

SIGNIFICANCE

Flexural strength and Rea differed depending on the material used. The probability of the material fracture increased after thermomechanical aging. To understand ceramic fractures, two mechanical tests and thermomechanical aging must be performed together.

Comparison of the clinical outcomes of resin-modified glass ionomer and self-adhesive resin cementations for full-coverage zirconia restorations

OBJECTIVES

Both resin-modified glass ionomer cement (RMGIC) and self-adhesive resin cement (SAC) may be suitable for cementation of full-coverage zirconia restorations. This retrospective study aimed to investigate the clinical outcomes of zirconia-based restorations cemented with RMGIC and compare them with those cemented with SAC.

METHODS

Cases of full-coverage zirconia-based restorations cemented with either RMGIC or SAC between March 2016 and February 2019 were evaluated in this study. The clinical outcomes of the restorations were analyzed according to the type of cement used. In addition, cumulative success and survival rates were evaluated according to the cement and abutment types. Non-inferiority, Kaplan-Meier, and Cox hazard tests were conducted (α=.05).

RESULTS

A total of 288 full-coverage zirconia-based restorations (natural teeth, 157; implant restorations, 131) were analyzed. Loss of retention occurred in only one case; a single-unit implant crown cemented with RMGIC, which decemented 4.25 years post-restoration. RMGIC was non-inferior to SAC in terms of loss of retention (<5%). For single-unit natural tooth restorations, the four-year success rates in the RMGIC and SAC groups were 100% and 95.65%, respectively (p=.122). For single-unit implant restorations, the four-year success rates in the RMGIC and SAC groups were 95.66% and 100%, respectively (p=.365). The hazard ratios of all the predictor variables, including cement type, were not significant (p>.05).

CONCLUSIONS

Cementation of full-coverage zirconia restorations of both natural teeth and implants using RMGIC and SAC yields satisfactory clinical outcomes. Furthermore, RMGIC is non-inferior to SAC in terms of cementation success.

CLINICAL SIGNIFICANCE

Cementation with RMGIC or SAC for full-coverage zirconia restorations has favorable clinical outcomes in both natural teeth and implants. Both RMGIC and SAC have advantages in the cementation of full-coverage zirconia restorations to abutments with favorable geometries.