Effect of firing and fabrication technique on the marginal fit of heat-pressed lithium disilicate veneers

Marginal and internal fit of porcelain laminate veneers: A systematic review and meta-analysis

STATEMENT OF PROBLEM

Marginal integrity and internal adaptation are key to the long-term success of porcelain laminate veneers. Evidence for their marginal and internal fit is unclear, and the factors affecting such fit have not been identified.

PURPOSE

The purpose of this systematic review and meta-analysis was to summarize the scientific literature assessing the effects of various parameters on the marginal and internal fit of porcelain laminate veneers.

MATERIAL AND METHODS

An electronic search was conducted to identify all relevant published articles on the fit accuracy of ceramic veneers between January 2000 and June 2021 in the PubMed-MEDLINE, Scopus, Embase, Google Scholar, and Web of Science databases. Information, including the study outcomes, in terms of the mean marginal gap, internal gap, and absolute marginal discrepancies of porcelain laminate veneers, was extracted from the selected studies. The inverse-variance random effects model was used to analyze the pooled results and estimate the overall effect based on the heterogeneity of studies (α=.05).

RESULTS

Twenty-one studies were selected for analysis, 2 clinical and 19 in vitro. The risk of bias was "medium" for most studies (19 of 21), and only 2 studies were classified as "high risk." A mean difference of -4.53 μm (95% CI: -21.46 to 12.41) was found, with no statistically significant difference in marginal gap between the pressed and milled fabrication modes (P=.600). As for the internal gap, significant differences were found (mean difference=-40.56 μm; 95% CI: -76.54 to -4.58), with pressed veneers performing better (P=.030). Butt joint preparation design produced significantly (P=.002) lower marginal gaps than the palatal chamfer (mean difference=-14.02 μm; 95% CI: -23.07 to -4.98).

CONCLUSIONS

No significant differences were found between the pressed and milled porcelain laminate veneers for marginal gap, but for the internal gap, the differences were significantly in favor of the pressed type. The butt joint veneer preparation design was significantly better than the palatal chamfer design in terms of marginal fit.

Load-bearing capacity of pressable lithium disilicates applied as ultra-thin occlusal veneers on molars

PURPOSE

The aim was to investigate the load bearing capacity of different pressable lithium disilicates cemented as occlusal veneers on molars.

MATERIALS AND METHODS

One control group and six test groups were formed consisting of 20 specimens each (n = 20). The six test groups differed in the utilizing pressable lithium disilicate to fabricate occlusal veneers. As a control group, "group Lis", the lithium disilicate with the highest reported flexural strength was used (initial LiSi Press, GC Europe; Leuven, Belgium / flexural strength: 508 MPa). The test groups consisted of other pressable lithium disilicates with lower flexural strength values: "Ema" (IPS e.max press), "Vit" (VITA Ambria), "Liv" (Livento Press), "Amb" (Amber Press), "Mas" (Amber Press Master) and "Ros" (Rosetta SP)". After the preparation of 140 extracted human molars, which included the removal of the central enamel, the specimens were scanned using a desktop scanner. With the aid of a design software, the occlusal veneers were designed in a standardized thickness of 0.5 mm. To fabricate the restorations, all tested materials were processed using heat-pressing technique. All restorations were adhesively cemented. Afterwards, the specimens underwent cyclic fatigue during an aging procedure in a chewing simulator (1'200'000 chewing-cycles, 49 N force, 5-55°C temperature changes). Subsequently, the specimens were statically loaded and the load which was necessary to fracture the specimen (F_max) were measured. Differences between the groups were compared applying the Kruskal-Wallis (KW) test and the Wilcoxon-Mann-Whitney-Test (WMW: p < 0.05). The two-parameter Weibull distribution values were calculated.

RESULTS

The fatigue resistance was 100% for the groups Lis, Vit, Liv, Amb, Mas and Ros, whereas the group Ema showed a fatigue resistance of 95%. The control group Lis showed median F_max values of 2'328 N. The median F_max values for the test groups ranged between 1'753 N (Vit) and 2'490 N (Ros). Statistically significant difference was observed among the groups Lis (control) and Vit (KW: p < 0.001). Weibull distribution presented the highest shape values for the group Ros (12.83) and the lowest values for the group Ema (4.71).

CONCLUSION

Regarding their load-bearing capacity different pressable lithium disilicates can be recommended to fabricate ultra-thin occlusal veneers on molars when restoring occlusal tooth wear.