PURPOSEThe objective of this study was to determine the effect of the color of a background substructure on the overall color of a zirconia-based all-ceramic crown.MATERIALS AND METHODSTwenty one posterior zirconia crowns were made for twenty subjects. Seven premolar crowns and six molar crowns were cemented onto abutments with metal post and core in the first and second group. In the third group, eight molar crowns were cemented onto abutments with a prefabricated post and composite core build-up. The color measurements of all-ceramic crowns were made before try-in, before and after cementation. A repeated measure ANOVA was used for a statistical analysis of a color change of all-ceramic crowns at α=.05. Twenty four zirconia specimens, with different core thicknesses (0.4-1 mm) were also prepared to obtain the contrast ratio of zirconia materials after veneering.RESULTSL*, a*, and b* values of all-ceramic crowns cemented either on a metal cast post and core or on a prefabricated post did not show significant changes (P>.05). However, the slight color changes of zirconia crowns were detected and represented by ΔE*ab values, ranging from 1.2 to 3.1. The contrast ratios of zirconia specimens were 0.92-0.95 after veneering.CONCLUSIONNo significant differences were observed between the L*, a*, and b* values of zirconia crowns cemented either on a metal cast post and core or a prefabricated post and composite core. However, the color of a background substructure could affect the overall color of posterior zirconia restorations with clinically recommended core thickness according to ΔE*ab values.

Objectives-The objectives of this study were to characterize the clinical performance and wear characteristics of lithia-disilicate-based ceramic crowns.Methods-Thirty posterior crowns were made using the heat-pressing technique and lithiadisilicate-based core ceramic. Subjects were recalled annually. The quality of crowns and adjacent gingival tissues were examined using nine criteria for acceptability. All crowns were examined and ranked from 4 (Excellent) to 1 (Unacceptable) for each criterion. Impressions were made for replica models at each appointment. Wear characteristics of dental ceramic and enamel were obtained by comparing the surface of the original model with the follow-up model using a laser scanner.Results-Twenty nine subjects returned for the one-year recall examination. The maximum clenching force for the 30 subjects ranged from 125 to 815 N. All clinical criteria were ranked good to excellent at the one-year recall exam and no fractures were observed. The mean occlusal wear volumes for the ceramic crowns after one year were 0.19 (0.065) mm 3 for premolar sites and 0.34 (0.08) mm 3 for molar sites. The mean occlusal wear volumes of opposing enamel after one year were 0.21 (0.06) mm 3 for premolar teeth and 0.50 (0.22) mm 3 for molar teeth. The mean occlusal wear volume of ceramic molar crowns was significantly lower than the volume of enamel wear of the opposing teeth (p≤0.05).Conclusions-The quality of the overall prostheses and the gingival tissues were acceptable after one year. The mean occlusal wear volume of ceramic molar crowns was significantly lower than the enamel wear volume of the opposing teeth.

The thickness and brands had significant effects on the contrast ratio of six zirconia dental ceramics. The mean contrast ratio values of inCoris TZI, Lava™, and Lava™ Plus High Translucency were significantly lower than those of Cercon® Base, Zeno®, and ZENO® Translucent at all thicknesses.

PURPOSEThe objective of this study was to investigate the effect of surface treatments on microtensile bond strengths (MTBSs) of two types of indirect resin composites bonded to a conventional direct resin composite.MATERIALS AND METHODSIndirect resin composite blocks of Ceramage and SR Nexco were prepared in a plastic mold having a dimension of 10 × 10 × 4 mm. These composite blocks were divided into three groups according to their surface treatments: Group1: Sandblast (SB); Group2: Sandblast and ultrasonically clean (SB+UL); Group3: Sandblast plus silane (SB+SI). After bonding with direct resin composite, indirect-direct resin composite blocks were kept in distilled water for 24 hours at 37℃ and cut into microbars with the dimension of 1 × 1 × 8 mm. Microbar specimens (n = 40 per group) were loaded using a universal testing machine. Failure modes and compositions were evaluated by SEM. The statistical analyses of MTBS were performed by two-way ANOVA and Dunnett's test at α = .05.RESULTSSurface treatments and brands had effects on the MTBS without an interaction between these two factors. For SR Nexco, the MTBSs of SB and SB+SI group were significantly higher than that of SB+UL. For Ceramage, the MTBSs of SB and SB+SI were significantly higher than that of SB+UL. The mean MTBS of the Ceramage specimens was significantly higher than that of SR Nexco for all surface treatments.CONCLUSIONSandblasting with or without silane application could improve the bond strengths of repaired indirect resin composites to a conventional direct resin composite.

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