Repair potentiality of CAD/CAM composite block and hybrid ceramic block by direct resin composite restoration with and without surface treatment

Objective: to evaluate microshear bond strength of CAD/CAM composite block and hybrid ceramic block repaired by direct resin composite restoration with and without surface treatment.
Materials and Methods: Two different CAD/CAM restorative materials were tested in the present study: hybrid ceramic blocks (Vita Enamic) and resin composite blocks (Grandio). Six sections were prepared from each CAD/CAM blocks. The sections from each block type were randomly divided into three groups according to the surface treatment performed. Control group: the specimens were ground with a grinding machine. Etching gel Group: 37% phosphoric acid etching gel was applied occlusally on the surface of the section and CoJet Group. the surface of all groups were then silanized using Bis-Silane then bonding agent Futura bond DC was applied. A polyethylene micro tubes were prepared that were held in place with a tweezer on the uncured then light cured for 10 seconds Resin composite (Grandioso X-tra) was packed inside the microtubes and light cured. All specimens were prepared by the same operator at 22.0–22.5 ˚C (room temperature) and relative humidity of 50%. The specimens were further divided into two groups according to storage conditions. Half of the specimens were thermocycled in distilled water for 5000 cycles in a 5–55˚C water bath with a dwell time of 30 seconds and a transfer time of 5 seconds. The other specimens were stored in distilled water for 2 days. Microshear bond strength was performed and fractographic analysis to determine the failure mode. Statistical analysis was then performed using a commercially available software program (SPSS 19; SPSS, Chicago, IL, USA). As data were not normally distributed, significance of the difference between different groups within the same surface pretreatment was evaluated using Kruskall Wallis test. Mann Whitney U test was used for pairwise comparisons and to study the effect of surface pre-treatment. The interaction of restoration and type of pretreatment variables was evaluated using 3 ways ANOVA. The level of significance was set at P < 0.05.
Results: Three ways ANOVA test revealed that each of the material type (composite/hybrid ceramic), the subgroup type group (control/etching/Cojet) and the thermocycling (Yes/No) variables resulted in a statistically significant difference (p=0.00, p=0.00, p=0.003 respectively). Interaction of the subgroup (control/etching/Cojet) variable with the thermocycling (Yes/No) variable and the material (composite/hybrid ceramic) variable showed a statistically significant difference (P=0.023, p=0.001 respectively). Moreover, interaction of thermocycling and material variable resulted in a significant difference (p=0.034). However, interaction of the 3 study variables (material, subgroup, thermocycling) was not statistically significant (p=0.165). The failure mode of the tested specimens analyzed using Scanning Electron Microscope at magnification 80X was commonly mixed type of failure (adhesive failure between resin composite restoration and CAD/CAM blocks with cohesive failure within resin composite restoration).
Conclusions: Grandio composite blocks is very promising materials and their optimum long lasting repair potentiality that offers to the clinicians great chance to easily repair the defective restoration with safety. Surface treatment using Phosphoric acid or Cojet system greatly improve the bond strength between composite repair system and hybrid ceramic or composite blocks. The bond performance of repaired composite blocks was much more greater than than that of repaired hybrid ceramic. Thermocycling affect the bond durability of repaired hybrid ceramic blocks and composite blocks.Further investigations focusing on the effect of different surface treatments to yield results that lead to concrete clinical recommendations are needed to evaluate the long term durability of new CAD/CAM materials.