The effect of immediate dentin sealing procedure using different adhesive systems on the bond strength of monolithic zirconia to dentin

The aim of this thesis study is to evaluate the effect of immediate dentin sealing (IDS) procedure using different adhesive systems on microtensile bond strength of monolithic zirconia-based CAD/CAM blocks with differerent surface pretreatment methods. 32 intact human lower molar teeth were used. The occlusal coronal 1/3 crown was removed, parallel to the ground, with a model trimmer device (MT3 Wet trimmer, Germany). The dentin surfaces of the teeth were exposed. Then, they were randomly allocated into 8 groups according to the presence of the IDS procedure (with/without IDS), the type of universal adhesive systems used for IDS procedure (Single Bond Universal, Clearfil Quick Bond, Optibond Universal) and surface pretreatment methods for the monolithic zirconia-based CAD/CAM blocks (tribochemical silica coating method/CoJet and sandblasting/SB): 1) Group CJ: CoJet+no IDS, 2) Group CJ+SBU: CoJet+Single Bond Universal, 3) Group CJ+CUQ: CoJet+Clearfil Universal Bond Quick, 4) Group CJ+ OBU : CoJet+Optibond Universal, 5) Group SB: sandblasting+no IDS, 6) Group SB+ SBU: sandblasting+ Single Bond Universal, 7) Group SB+CUQ: sandblasting+Clearfil Universal Bond Quick, 8) Group SB+OBU: sandblasting+ Optibond Universal. Universal adhesive systems were applied in self-etch mode to the exposed dentin surfaces according to the manufacturer's instructions for IDS procedure. Specimens of 4 mm thickness, 10 mm width and 10 mm length were obtained from a monolithic zirconia-based CAD/CAM block (3M Lava Plus, 3M ESPE, USA). Before luting, the surfaces of CAD/CAM specimen were pretreated with 30 µm silica-coated aluminium oxide (Al2O3) particles (CoJet Sand, 3M ESPE, USA) at 2.8 bar pressure for CoJet method and 50 µm Al2O3 particles at 3 bar pressure for SB method, from a distance of 10 mm and 10s. They were luted to the dentin surfaces with a self-adhesive dual-cure resin cement (Rely X U200, 3M ESPE, USA) according to the manufacturer's instructions. All specimen were kept in distilled water at 37°C for 24 h and then subjected to 10.000 thermocycles (5ºC-55ºC) with a thermocycle device (SD Mechatronic Thermocycler, Germany). Specimen were vertically sectioned to obtain zirconia-dentin bars (2x2x8 mm) with a micro cutting device (Isomet 1000, Buehler Ltd., Lake Bluff IL, USA). They were subjected to microtensile bond strength test with a universal test machine (Microtensile Tester, Bisco Inc, USA) at a crosshead speed of 1 mm/min until failure. Failure types were analyzed using a stereomicroscope (Leica MZ 21, Leica Microsystems, Türkiye) under 15x magnification. After surface pretreatment methods, surface roughness (Ra,µm) of CAD/CAM blocks were measured using a contact profilometer (Mahr GmbH, Mahrsurf PS1, Göttingen, Germany). Besides, one specimen from each pretreatment methods were analyzed for surface morphology with scanning electron microscopy (SEM) (Evo LS10, Zeiss, Oberkochen, Germany). Semi-quantitative chemical microanalysis were performed with energy dispersive x-ray spectroscopy (EDS). The zirconia-dentin interfaces of all groups were observed with SEM for the morphological analysis. Two-way ANOVA and Bonferroni tests were used for statistical analyses (p<0.05). Regarding the presence of IDS, Group CJ+OBU showed statistically higher mean microtensile bond strength than Group CJ (p<0.05); while Group CJ+SBU and Group CJ+CUQ exhibited statistically similar mean microtensile bond strength to Group CJ (p>0.05). Group SB+SBU, Group SB+CUQ and Group SB+OBU showed statistically similar mean microtensile bond strength to Group SB (p>0.05). When comparing the IDS procedure applied groups; respectively, Group CJ+OBU and Group SB+OBU showed statistically higher mean microtensile bond strength than Group CJ+CUQ and Group SB+CUQ, respectively (p<0.05). Regarding the surface pretreatment methods, no significant differences in mean microtensile bond strength were detected among all groups (p>0.05). After the surface pretreatment methods, according to the contact profilometry measurements, no significant differences in mean surface roughness were found between both pretreatment methods (p>0.05). A rougher and more irregular appearance was observed for CoJet treated specimen than SB treated one, with SEM analysis of surface morphology. According to EDS analysis, for SB treated specimen, higher amount of Al content was detected; while for CoJet treated one, the amount of Si content was higher. SEM analysis of the zirconia-dentin interfaces revealed that a thick and intact hybrid layer with long resin tag formations were observed for Group CJ+OBU and Group SB+OBU. Besides, gap formations in hybrid layer were detected for Group CJ. The predominant mode of failure was mixed type for most groups except Group CJ. After CoJet surface pretreatment, bond strength of monolithic zirconia-based CAD/CAM blocks to dentin for IDS procedure applied group with Optibond Universal was found significantly higher than the ones for no IDS procedure applied group. After both surface pretreatment methods, IDS procedure with Optibond Universal resulted in significantly higher bond strength compared to with IDS procedure with Clearfil Universal Bond Quick. Keywords: immediate dentin sealing, CAD/CAM, zirconia, sandblasting, tribochemical silica coating, bond strength.