MICRO SHEAR BOND STRENGTH EVALUATION FOR IMMEDIATELY SEALED DENTINE WITH HYBRID CERAMICS AFTER DIFFERENT PROVISIONALIZATION PERIODS: IN VITRO STUDY

Statement of the problem: CAD/CAM restorations can be immediately cemented after tooth preparation, however, a delay between final impression and restoration delivery is sometimes unavoidable, thus provisionalization period becomes necessary. There are concerns whether this delay would affect the dentin bond strength when bonding to immediately sealed dentin.
Purpose: to study the effect of different provisionalization periods (1 and 3 weeks) on the bond strength of immediately sealed dentin to two types of hybrid ceramics
Materials and Methods: A total of sixty ceramic discs were fabricated in this study from CAD/CAM blocks. The discs were divided into two groups; Group 1: Thirty discs were constructed from polymer-infiltrated-ceramic-network material (VITA Enamic) and Group 2: Thirty discs constructed from resin nanoceramic (CERASMART). Each of the previous groups were further subdivided into three equal subgroups according to the provisionalization period as follows; Subgroup 1: Ten discs were cemented to immediately sealed dentin without any provisionalization period, Subgroup 2: Ten discs were cemented to immediately sealed dentin after 1 week of provisionalization and Subgroup 3: Ten discs were cemented to immediately sealed dentin after 3 weeks of provisionalization. Teeth were trimmed to have a flat, midcoronal dentin surfaces. This was followed by immediate dentin sealing of the exposed dentin. Ceramic samples were then obtained by slicing the CAD/CAM blocks with standardized dimensions. For subgroup 1, adhesive cementation was immediately done for the ceramic samples to immediately sealed dentin. For subgroup 2 and 3, the sealed surfaces were coated with a layer of petroleum gel followed by application of a provisional restoration for 1 and 3 weeks respectively. The samples were then immersed in saline solution until the end of the provisionalization period. At the end of these various periods, the provisional restoration was removed and the sealed dentin was cleaned by pumice and water followed by roughening with a coarse diamond stone. This was followed by adhesive cementation of the discs. Micro shear bond strength test was then performed to debond the specimens in a universal testing machine (Lloyd Instruments Ltd, Hampshire, UK) with a crosshead speed of 0.5 mm/s. The maximum load at failure was recorded in Newtons (N) unit and was divided over the bonded area (mm2) to convert to MPa unit. Data was then collected, tabulated and statistically analyzed.
Results: For CERASMART group: It was found that the highest shear bond strength mean±SD values were recorded with no provisionalization subgroup (9.37±0.35MPa) followed by 1 week provisionalization subgroup (8.4±0.12MPa) while the lowest shear bond strength mean±SD values were after 3 weeks provisionalization subgroup (4.48±0.23MPa). The difference between provisionalization subgroups was statistically significant (p=<.0001<0.05) as indicated by one way ANOVA test. Pair-wise Tukey’s post-hoc tests showed no significant difference (p>0.05) between (no- provisionalization and 1 week provisionalization) subgroups. For Vita Enamic group: It was found that the highest shear bond strength mean±SD values were recorded with 3 weeks provisionalization subgroup (7.3±0.67MPa) followed by no provisionalization subgroup (7.08±1MPa) while the lowest shear bond strength mean±SD values were after 1 week provisionalization subgroup (5.59±0.71MPa). The difference between all subgroups was statistically non-significant (p=0.2192 >0.05) as indicated by one way ANOVA test. Effect of ceramic: With no provisionalization; it was found that CERASMART group recorded statistically non-significant higher shear bond strength mean value (9.37±0.35 MPa) than Vita Enamic group (7.08 ±1 MPa) as indicated by t-test (p=0.0598>0.05). After 1 week provisionalization; it was found that CERASMART group recorded statistically non-significant higher shear bond strength mean value (8.4 ± 0.12 MPa) than Vita Enamic group (5.59±0.71 MPa) as indicated by t-test (p=.0540 >0.05). After 3 weeks provisionalization it was found that Vita Enamic group recorded statistically significant higher shear bond strength mean value (7.3±0.67 MPa) than CERASMART group (4.48±0.23 MPa) as indicated by t-test (p=.0089<0.05).
Conclusions: 1) The effect of provisionalization period on microshear bond strength of immediately sealed dentin with indirect restorations is ceramic type dependant. 2) When it is inevitable to cement the final restoration within 3 weeks, Vita Enamic ceramic would be a preferred choice compared to CERASMART as it provided higher bond strength when IDS protocol is used. 3) When final restoration cementation is planned immediately or within 1 week of IDS, both ceramics can be used as the difference between them was insignificant.