الفهرس 
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Abstract
Bonding of indirect esthetic restorations to the tooth structure remains a challenging matter, as the bonding interfaces are increased with the indirect restorative procedure. It is essential to improve the bond strength between the indirect restorative materials and cements, since they are the principal factors in the success of resin-bonded fixed dental prosthesis.
The present study was designed to assess and evaluate the effect of aging on the μTBS of resin cement to two recent CAD/CAM hybrid esthetic materials which are zirconia-reinforced lithium silicate ceramic (Celtra TM Duo) and hybrid resin nano-ceramic (Cerasmart TM) using 2 surface treatment protocols; hydrofluoric acid etching and sandblasting, both were followed by silanization.
Plates were cut from each ceramic material block. Then, the Celtra TM Duo plates were placed inside the ceramic furnace for further maturation. Then, one surface of each ceramic plate was polished using (400, 600) grit SiC paper followed by ultrasonic cleaning in distilled water for 5 minutes. A plate from each material was treated with HF-acid etching and the other plate was sandblasted according to the manufacturer’s recommendations. Then, SEM examination was carried out. Finally, all the plates received a silane coupling agent application.
A Teflon mold of dimensions similar to the cut ceramic plates was fabricated to prepare the composite plates. Another Teflon mold of 6.1 mm thickness was fabricated where the treated ceramic plate was placed inside it, followed by generous application of adhesive resin cement on the ceramic plate then the composite plate was placed above the resin cement, and finally a fixed load (500 gm) was positioned and was light cured using Blue-phase LED unit from each side to ensure optimal polymerization. The resin-ceramic blocks were stored in distilled water for 24 hours. Then, the blocks were fixed on epoxy resin cylinders.
Each resin-ceramic block was vertically sectioned into serial slabs. Then, it was rotated 90◦ to make additional vertical cuts so that the resin-ceramic block has perpendicular cuts in order to obtain a thin long micro-beam using Isomet 4000. Twenty micro-beams were obtained from each block excluding the use of the peripheral slices to avoid slices with an excess or a deficient amount of resin cement at the interface. Half of the micro-beams from each subgroup (n=10) was tested after 24 hours storage in distilled water, and the other half (n=10) was tested after being subjected to 5000 cycles of thermocycling between 5 and 55 °C with dwell time of 20 seconds in each bath. After that, all the specimens were subjected to a tensile load in the universal testing machine to gather data about the μTBS before and after aging. Finally, data were statistically analyzed.
The results showed that aging (thermocycling) dramatically affected the mean μTBS of both ceramic materials. There was a statistically significant decrease in mean μTBS after aging. Using either Celtra Duo TM or Cerasmart TM, whether with hydrofluoric acid or sandblasting, there was a statistically significant decrease in mean micro-tensile bond strength after aging. But hydrofluoric acid showed higher mean μTBS than sandblasting after aging.
Regarding the effect of surface treatment, Hydrofluoric acid showed statistically significant higher mean μTBS than sandblasting. Using Celtra Duo TM before aging, there was no statistically significant difference between mean μTBS values of the two surface treatments. After aging, Hydrofluoric acid showed statistically significant higher mean μTBS than sandblasting. Using Cerasmart TM whether before or after aging, Hydrofluoric acid showed statistically significant higher mean μTBS than sandblasting.
Regarding the effect of the type of the ceramic material, Celtra TM Duo showed statistically significant lower mean micro-tensile bond strength than Cerasmart TM before aging. After aging, there was no statistically significant difference between the two ceramic types.