Bonding interface affects the load-bearing capacity of bilayered composites.

This study evaluated the effect of material type, thickness and composite-composite interfacial adhesion on the load-bearing capacity of the bilayered composite structures. Bilayered cylindrical specimens (diameter=7 mm, height=5 mm) were prepared having three surface-layer thicknesses (1, 1.5, 2 mm) of Gænial Posterior to overlay base-composites [everX Posterior or Smart Dentin Replacement (SDR)]. Adhesion between surface and base composite-layers was based on an O2-inhibited layer for optimal-adhesion (OA) or polished surface for deteriorated-adhesion (DA). Specimens (n=10) were light-cured before static-loading with a steel-ball until fracture. Stress distribution in the same designs of mechanical test was calculated by finite element analysis (FEA). Static-loading demonstrated that in both base materials, thickness and adhesion had an effect on load-bearing capacity (p<0.05). FEA showed less strain distribution for everX groups than SDR.With OA, everX Posterior demonstrated higher load-bearing capacity even with thin surface-composite layer. DA made the load-bearing capacity more sensitive to surface-layer thickness.

Effect of interface surface design on the fracture behavior of bilayered composites.

This study aimed to evaluate the effect of different interface designs on the load-bearing capacity of bilayered composite structures (BLS). Cylindrical specimens of BLS were prepared from base composite of 3.5 mm thickness and surface composite of 1.5 mm thickness (n = 80). Two different base composites - flowable bulk-fill (FBF) [smart dentin replacement (SDR)] and short fiber-reinforced (FRC) (everX Posterior) - were evaluated, and conventional composite (G-aenial Posterior) was used as the surface layer. Four different interface designs were used: (i) pyramidal; (ii) mesh; (iii) linear grooves; and (iv) flat surface (control). Three-dimensional printed molds were fabricated to standardize the interface design between the surface and the base composites. The specimens were then statically loaded with a steel ball until fracture using a universal testing machine. Fracture types were classified into catastrophic, complete, and partial bulk. ANOVA revealed that both the material and the interface design had a statistically significant effect on the load-bearing capacity. Flowable bulk-fill showed lower mean load-bearing capacity than FRC in all the interface designs tested, except for the flat surface design. Fracture analysis showed that FRC demonstrated up to 100% partial bulk fractures with the pyramid interface design, but no incidence of catastrophic bulk fracture. By contrast, FBF demonstrated up to 84.6% and 40% catastrophic bulk fractures with the flat interface design but no incidence of partial bulk fracture. Consequently, the interface designs studied enhanced the fracture behavior of BLS.

The effect of rubber dam on atmospheric bacterial aerosols during restorative dentistry.

Rotatory dental instruments generate atmospheric aerosols that settle on various surfaces, including the dentist's head. The aim of this study was to quantitatively assess bacterial contamination of the dentist's head and to evaluate whether it is affected by using a rubber dam. Senior dental students (n=52) were asked to wear autoclaved headscarves as collection media while performing restorative dental treatment with and without a rubber dam. Four points from each headscarf were swabbed for bacterial culture after 30min of operative work. Bacterial contamination was quantified by counting the colony-forming units. Regardless of the collection point, using a rubber dam was associated with more bacterial colony-forming units than not using a rubber dam (P=0.009). Despite its clinical value, the rubber dam seems to result in significantly higher aerosol levels on various areas of the dentist's head, requiring that dentists cover their heads with suitable protective wear.

Influence of increment thickness on dentin bond strength and light transmission of composite base materials.

OBJECTIVES: Bulk-fill resin composites (BFCs) are gaining popularity in restorative dentistry due to the reduced chair time and ease of application. This study aimed to evaluate the influence of increment thickness on dentin bond strength and light transmission of different BFCs and a new discontinuous fiber-reinforced composite. MATERIALS AND METHODS: One hundred eighty extracted sound human molars were prepared for a shear bond strength (SBS) test. The teeth were divided into four groups (n = 45) according to the resin composite used: regular particulate filler resin composite: (1) G-ænial Anterior [GA] (control); bulk-fill resin composites: (2) Tetric EvoCeram Bulk Fill [TEBF] and (3) SDR; and discontinuous fiber-reinforced composite: (4) everX Posterior [EXP]. Each group was subdivided according to increment thickness (2, 4, and 6 mm). The irradiance power through the material of all groups/subgroups was quantified (MARC® Resin Calibrator; BlueLight Analytics Inc.). Data were analyzed using two-way ANOVA followed by Tukey's post hoc test. RESULTS: SBS and light irradiance decreased as the increment's height increased (p < 0.05), regardless of the type of resin composite used. EXP presented the highest SBS in 2- and 4-mm-thick increments when compared to other composites, although the differences were not statistically significant (p > 0.05). Light irradiance mean values arranged in descending order were (p < 0.05) EXP, SDR, TEBF, and GA. CONCLUSIONS: As increment thickness increased, the light transmission decreased for all tested resin composites. Discontinuous fiber-reinforced composite showed the highest value of curing light transmission, which was also seen in improved bonding strength to the underlying dentin surface. CLINICAL RELEVANCE: Discontinuous fiber-reinforced composite can be applied safely in bulks of 4-mm increments same as other bulk-fill composites, although, in 2-mm thickness, the investigated composites showed better performance.