الفهرس 
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Abstract
This study evaluated the effect of three different surface treatments on the retention strength of resin nano ceramics (RNC) and Polyetheretherketon (PEEK) ceramic materials luted to self-adhesive resin cement (RelyX U200) after artificial aging using crown pull-off test. It also studied the mode of failure occurred between the tested ceramic materials and the resin luting agent.
Forty freshly extracted sound human upper central incisors were collected, cleaned then stored in 0.10 g/mL Thymol at room temperature. Retention holes with a depth of approximately 1 mm were prepared in the roots of teeth. Cylindrical Teflon split molds and rings were used for production of acrylic molds. Teeth were placed into the centers of the molds. After polymerization of acrylic resin, each tooth with its acrylic base was removed from the split mold. The resultant acrylic molds were coded; group (L) for Lava Ultimate specimens and group (B) for Bio HPP specimens, each group’s specimens were numbered from 1 to 20 and subgroup name of each specimen were crafted on its mold base.
A silicon index was made for each tooth prior to any preparation to assure a uniform reduction. Preparation of 5-6° taper, 1.5 mm axial reduction, 1.5 mm incisal reduction and a 1 mm thick shoulder finish line was done by the same operator according to the manufacturer’s instructions. Then teeth were stored in water at room temperature till cementation.
Prepared teeth were scanned with a Cerec 3D camera and each crown was designed with two arms at the incisal third to act as a retentive mean for the universal testing machine wire. Forty-crown specimens were constructed; twenty of each tested material. Specimens were divided into two main groups; group (L) for Lava Ultimate specimens and group (B) for Bio HPP specimens. Each group was randomly subdivided into 4 subgroups according to the applied surface treatment. (n=5):
- Subgroups (L1 & B1): Control groups without any surface treatment.
- Subgroups (L2 & B2): Air abrasion with 50 µm Al2O3.
- Subgroups (L3 & B3): Air abrasion with 110 µm Al2O3.
- Subgroups (L4 & B4): Acid etching using 5% HF acid gel for 20 sec.
Surface treatments were applied to specimens’ intaglio surfaces then each specimen was cemented to its corresponding tooth according to manufacturer’s instructions under constant static load using RelyX U200 then stored in 37 °C water for 60 days. After that, all specimens were artificially aged using 5000 thermocycles. Crown specimens underwent crown pull-off test using a universal testing machine with a crosshead speed of 0.5 mm/minute until failure took place. Data were collected, tabulated and statistically analyzed using SPSS. Failure modes were evaluated using scanning electron microscope.
Statistical analysis revealed that there is no statistical significant difference between both tested materials at P value ≤ 0.05. Two-way Anova revealed that there was no statistical significant difference between mean values of maximum pull out load (N) of the Lava Ultimate and Bio HPP among the eight tested subgroups at P ≤ 0.05 level. The highest mean values of maximum pull out load (N) were recorded for subgroups (B2) (219.81), followed by (L2) (213.52), (B4) (204.10), (L3) (195.92), and then (B3) (168.04) and that subgroup (L1 recorded the lowest mean values of maximum pull out load (N) (105.17).
Tukey’s post hoc test showed that specimens of both tested materials that were air-abraded using 50 µm Al2O3 (subgroups L2 & B2) recorded the highest mean values of maximum pull out load (N) followed by HF acid-etched specimens (subgroups L4 & B4) then air-abraded specimens with 110 μm Al2O3 (subgroups L3 & B3). Whereas, control subgroup (L1 & B1) recorded the lowest mean values of pull off testing. Pairwise comparison showed that there was a statistical significant difference between the mean values of both (L1 & B1) & (L2 & B2) subgroups and all other tested subgroups.
Lava Ultimate control subgroup (L1) showed adhesive failure at cement-porcelain interphase and Bio HPP control subgroup (B1) showed mixed and cohesive within the cement failures. However, treated specimens of both tested materials showed adhesive failures at the cement-dentin interphase and cohesive failure in porcelain except for Bio HPP acid-etched subgroup (B4) which showed mixed failure.
Conclusions:
Within the limitations of this study, the following could be concluded:
1- Bio HPP crowns are more retentive than Lava Ultimate RNC ones.
2- Air abrasion using 50 µm Al2O3 particles recorded higher retentive strength than the other tested surface treatments for both tested materials.
3- Non-treated Specimens recorded the lowest retention strength for both tested materials.
4- Adhesive failure mode at the cement-dentin interphase and cohesive within the ceramic material denoted adequate bonding between the tested materials and luting agent.
Recommendation:
It is recommended to run a clinical trial with a controlled standardized study design to evaluate the clinical long-term performance of the tested materials. As this in-vitro study cannot replicate the intraoral conditions with all individual variations exactly, yet, it provides some hints for the retention strength of two CAD/CAM materials.