ABSTRACT
MATERIALS AND METHODS: The electronic search was conducted in the MEDLINE/PubMed, Cochrane, and Google Scholar databases until November 2020, regardless of language limitations. The inclusion criterion was as follows: S/M-R regarding prosthetic restorations in endodontically treated teeth. Three qualified researchers evaluated the inclusion criteria and bias risk. The fourth investigator was referred to when facing any doubtfulness. RESULTS: From 43 achieved S/M-R, 14 studies were selected for this inquiry. Primary extracted information included success rate, survival rate, and postendodontic failure rate. Five S/M-R had a moderate risk of bias, and nine S/M-R had a low risk of bias and were considered strong clinical evidence in this examination. According to the low-risk reports, the success rate of fiber posts was higher than that of metal posts; the rate of root fracture in metallic and fiber posts was alike; the failure rate for fiber posts was comparable to fixed partial dentures or single crowns; the construction of endocrowns was likely to perform better than intracanal posts, composite resin, or inlay/onlay restorations. CONCLUSION: It appears that with practice and experience, deciding which type of restoration to choose changes. In dental restorations associated with root canal therapy, the single crowns are likely to be a proper option. Nevertheless, due to the heterogeneity of the studies, more clinical assessments are required to achieve more specific findings in this field.
ABSTRACT
STATEMENT OF PROBLEM: How multiple firing cycles may affect the oxide layer and, consequently, the shear bond strength of metal-ceramic restorations is unclear. PURPOSE: The purpose of this in vitro study was to determine the effect of multiple firings on the shear bond strength of porcelain to cobalt-chromium (Co-Cr) alloy. MATERIAL AND METHODS: Forty cylinders (Ø6.8×9 mm) of a representative presintered Co-Cr alloy (Ceramill Sintron) were prepared with computer-aided design and computer-aided manufacturing (CAD-CAM) technology. After airborne-particle abrasion and polishing, the specimens were ultrasonically cleaned of surface contaminants. A circular surface (Ø4×2 mm) was veneered on each specimen with porcelain (VM13) after 3 firings (wash opaque, opaque, and dentin). The specimens were then randomly divided into 4 groups (n=10). The normal group underwent 3 firings. The other groups underwent an additional porcelain firing: the one-plus firing group underwent 4 firings, the two-plus firing group underwent 5 firings, and the three-plus firing group underwent 6 firings. Next, the specimens were mounted in autopolymerized acrylic resin and tested in a universal testing machine and loaded at a crosshead speed of 0.5 mm/min at the metal-ceramic interface until fracture occurred. The average shear bond strength (MPa) was calculated by dividing the maximum fracture force (N) by the bonded surface of the specimens (mm2). The fracture patterns were observed microscopically and classified as adhesive, cohesive, or mixed. One-way ANOVA was used to determine differences between groups (α=.05). RESULTS: No significant differences were found among the shear bond strengths of specimens after 3, 4, 5, and 6 porcelain firings (P>.05). The mean bond strength of all groups ranged from 30 to 34 MPa. The fracture pattern of all specimens was mixed, indicating that multiple firings had no significant effect on the failure pattern. CONCLUSIONS: Multiple porcelain firings under controlled conditions had no significant effect on the fracture pattern or shear bond strength of porcelain to a presintered Co-Cr alloy.
