Influence of Conventional Versus Digital Workflow on Marginal Fit and Fracture Resistance of Different Pressable Occlusal Veneers After Thermomechanical Fatigue Loading

Abstract

Objectives: The aim of the present study was to evaluate the marginal fit and the fracture resistance after thermomechanical fatigue of lithium disilicate occlusal veneers compared to zirconia lithium silicate occlusal veneers constructed using two techniques for wax pattern fabrication. Methods: Thirty-two recently extracted non-carious maxillary molars were used in this study. The roots of all teeth were inserted with their long axes into epoxy resin moulds. All the teeth were prepared to receive all ceramic occlusal veneers. The non-retentive full-coverage circumferential design was chosen for the preparation of all selected teeth. All the prepared teeth were randomly divided into two equal groups(n=16) according to the material used for fabrication of the occlusal veneer: Group I (e-max): Teeth received pressable lithium disilicate glass ceramic occlusal veneers. Group II (Celtra): Teeth received pressable zirconia-reinforced lithium silicate glass ceramic occlusal veneers. Each group was further subdivided into two equal subgroups (n=8) according to the technique of construction of the wax pattern: Subgroup A (CAD/CAM): The wax pattern was constructed using CAD/CAM technique. Subgroup B (Conventional): The wax pattern was constructed by the manual conventional technique. CAD/CAM and conventional wax pattern were constructed according to manufacturer’s instructions. The wax patterns of all groups and subgroups were sprued, invested and heat pressed to produce pressable lithium disilicate glass ceramic occlusal veneers for group I and pressable zirconia-reinforced lithium silicate glass ceramic occlusal veneers for group II. All occlusal veneers were cemented to their corresponding teeth using dual-polymerizing adhesive resin cement. Thermomechanical aging was performed on all the cemented occlusal veneers. Vertical marginal gap distance measurement was performed using USB Digital microscope. Fracture resistance testing was done using computer controlled Instron testing machine.Results: The results of this study revealed that e.max processed by conventional wax technique recorded the highest vertical marginal gap mean values followed by Celtra processed by conventional wax technique then Celtra processed by CAD wax technique while e.max processed by CAD wax technique recorded the lowest mean values. The difference between subgroups was statistically non-significant as demonstrated by one-way ANOVA. Regarding the fracture resistance testing, It was found that e.max processed by conventional wax technique recorded the highest fracture resistance mean values followed by Celtra processed by conventional wax technique then e.max processed by CAD wax technique while Celtra processed by CAD wax technique recorded the lowest mean values. The difference between subgroups was statistically significant as demonstrated by one-way ANOVA (P=<0.0001<0.05). Tukey’s post-hoc test showed non-significant (p>0.05) difference between ceramic groups processed by CAD or conventional wax technique. Conclusions: Within the limitations of this study, it was concluded that: CAD/CAM constructed wax pattern presents a viable alternative option to conventional wax pattern fabrication for heat- pressing restorations. Vertical marginal gap distance values of all groups were within the clinically acceptable range. The fracture resistance values of both tested materials used showed comparable results. The newly launched Celtra Press all-ceramic material revealed promising results in comparison to the gold standard e-max press all-ceramic material. KEYWORDS: Pressable ceramics, Celtra press, IPS e-max press, Conventional wax pattern, CAD/CAM wax pattern, Thermomechanical aging, Marginal gap distance, Fracture resistance.