Influence of Clinical-treatments to Abutment-surface on Bond-strength of CAD/CAM-ceramic-crown-restoration

Objectives: The purpose of this study was to examine the influence of clinical-treatments to abutment-surface on bond-strength of CAD/CAM-ceramic-crown-restoration.
Methods: Standardized CAD/CAM-ceramic-crown abutment was prepared in 60 extracted human mandibular-premolars. Prepared-specimens were divided into two groups; resin-coating group(C+) and non-coating group(C-). Exposed dentin-surfaces of C+ specimens were coated with an all-in-one adhesive system and a flowable resin-composite(CLEARFIL Universal Bond Quick and CLEARFIL Majesty ES Flow, Kuraray Noritake Dental). All specimens were scanned by CEREC AC Omnicam(SW4.3, Dentsply Sirona) and then CAD/CAM-crown was individually fabricated from VITABLOCS Mark II(VITA) by CEREC MC XL. Regardless of coating mode, a half number of specimens(T+) were restored with individual temporary-crown(Protemp⁴ Temporization Material, 3M ESPE) and non-eugenol zinc-oxide cement(Temp-Bond NE, Kerr), and then stored in 37°C water. The other specimens were not restored with temporary-crowns(T-). The temporary-crowns of T+ group were removed after one-week storage, the abutment surfaces were cleaned up using a low-speed-rotated polishing-brush. Each fabricated CAD/CAM-crown was cemented to individual specimen with an adhesive-resin-cement(PANAVIA V5, Kuraray Noritake Dental). All restored-specimens were subjected to cyclic-loading at 118N for 90cycles/min, 3×10⁵cycles in total, in 37°C water. Two slabs 1.0mm thick were obtained from each specimen, and were trimmed into a standardized-dumbbell-shaped-specimen that contained bonded interface on the occlusal-wall(O) or axial-wall(A). The micro-tensile bond-strength(µ-TBS) to O/A walls under four experimental-conditions were measured(n=15). The statistics analysis was performed using two-way ANOVA and Tukey’s test.
Results: The mean µ-TBS(SD) in MPa to O/A were C-T-:3.2(1.2)/4.4(1.5), C-T+:3.5(1.5)/4.1(2.4), C+T-:5.5(1.4)/5.1(2.3), C+T+:4.3(1.3)/4.6(2.5). Temporary-crown restoration did not influence the intra-crown µ-TBS. Resin-coating significantly affected the µ-TBS, especially the O-value of C+T- group was significantly greater than those of C-T- and C-T+ groups at p<0.05.
Conclusions: The bond-strength of CAD/CAM-ceramic-crown-restoration was enhanced by the resin-coating, but the temporary-crown application did not influence the bonding.