الفهرس 
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Abstract
This study was conducted to study the effect of short fiber-reinforced composite as a base for direct occlusal veneers on premolars. One maxillary premolar was digitally scanned and virtually prepared for an occlusal veneer. By performing a 2-mm anatomical occlusal reduction with a butt joint marginal design. The prepared model was printed into duplicates of resin dies (Tough 1500 Resin). In total, (n=48) resin dies were printed and assigned into three groups (n=16) according to the base of the occlusal veneers; mono-structured without a SFRC base, a high viscosity SFRC base (EverX Posterior) and a low viscosity SFRC base (EverX Flow). Each group was re-divided into two subgroups (n=8) according to the veneering composite resin; packable nanohybrid composite resin (G-aenial A’CHORD) and injectable nanohybrid composite resin (G-aenial injectable).
Designing the occlusal veneer was performed using dental CAD software (Exocad Dental CAD) to ensure an accurate design of a 2-mm occlusal veneer with a 1-mm base. Both the veneer and base designs were printed into resin models (Grey Resin V5). Transparent silicone (Exaclear) was used to fabricate indices for each model. And using these indices, each design was accurately reproduced on the resin dies using the base and veneering materials mentioned. Each specimen was then tested for fracture strength using a universal testing machine (Instron 3365) along with failure mode inspection.
For each specimen, the mean and standard deviation of fracture strength was calculated. Comparison between veneering materials and base materials was performed using independent t test (P ≤ 0.05) and one way ANOVA followed by tukey’s post hoc test (Pa ≤ 0.0166) when appropriate. Which showed that the presence of a SFRC base significantly increased the fracture strength of all specimens. Additionally, there wasn’t a significant difference between the fracture strength of high viscosity SFRC (EverX Posterior) and low viscosity SFRC (EverX Flow). Moreover, injectable composite resin (G-aenial injectable) had superior fracture strength than packable composite resin (G-aenial A’CHORD). Interactions between all subgroups was tested using Two-way ANOVA & one way ANOVA was used to compare all subgroups followed by tukey’s post hoc test (Pa ≤ 0.0033) and all tests were two tailed. This showed that interaction of the veneering material with the base material had no statistically significant effect. Failure analysis was described as frequency and percentage. Intergroup comparison between failure modes was performed using chi square test (Pa ≤ 0.0033). A weak correlation was observed between the mode of failure and fracture strength.
Conclusions:
Under the limitations of this study, it can be concluded that:
1. Fracture strength of direct occlusal veneers is greatly enhanced when supported by a short fiber-reinforced composite base.
2. High viscosity short fiber-reinforced composite (EverX Posterior) and low viscosity short fiber-reinforced composite (EverX Flow) function similarly as supportive bases for direct occlusal veneers.
3. Injectable nanohybrid composite resin (G-aenial injectable) is stronger than packable nanohybrid composite resin (G-aenial A’CHORD) as a veneering material of direct occlusal veneers.
4. Fracture strength is weakly correlated to the mode of failure of direct occlusal veneers.