ABSTRACT
Background & Objectives: Color matching between ceramic restorations and natural teeth has been a major challenge in dentistry. Faults may occur during shade matching procedure in the dental clinic or in the laboratory at the time of fabrication of restoration. This study assessed the effect of porcelain thickness and repeated firing on the color of metal-ceramic restorations. Method: Thirty 12mm square samples of nickel chromium alloy were prepared and divided into three groups of 10 samples each. All samples were fired with opaque porcelain followed by dentin porcelain maintaining the dentin thickness to 1mm, 2mm and 3mm with silicon molds. The color of all the samples was measured with a spectrophotometer after 1st firing. Samples were subjected to repeated firing and color was again measured after 4th firing, 7th firing, 10th firing and 13th firing. The data was subjected to statistical analysis. Results: The results showed that increasing the thickness of porcelain resulted in significant increase in the Lightness (L*) and decrease in the Chroma (C*) of the samples. It also demonstrated that repeated firing did not cause significant color change (ΔE) on repeated firing of 1mm and 2mm, however, repeated firing of 3mm samples showed substantial color changes (ΔE) on repeated firing but this change was within acceptable limits of oral environment. Interpretation and Conclusion: The results of the study suggest that increased thickness of the dentin porcelain increases the Lightness (L*) thereby reducing the graying effect of the opaque layer. Therefore, maximum tooth reduction should be encouraged without violating the pulp integrity to provide enough space for the bulk of porcelain for better esthetic results. The results also show that repeated firing does not affect the color stability of the porcelain samples tested although significant color changes were seen with 3mm samples which were within acceptable limits of oral conditions. So, it can be inferred that repeated firing of the porcelain can be done to achieve correct contours and shape of the restorations.
ABSTRACT
Aims: The aim of this study was to evaluate the number of intracanal bacteria extruded apically during root canal preparation using rotary ProTaper, K3XF, twisted, and hand K‑file system. Subjects and Methods: Seventy extracted single‑rooted human mandibular premolar teeth were used. Access cavities were prepared and the teeth were mounted in glass vials. Root canals were then contaminated with a pure culture of Enterococcus faecalis (ATCC 29212) and incubated at 37°C for 24 h. The contaminated roots were divided into four experimental groups of 15 teeth each and one control group of 10 teeth. Group 1: ProTaper; Group 2: K3XF; Group 3: Twisted file; Group 4: Hand K‑file; Group 5: Control group. Bacteria extruded from the apical foramen during instrumentation were collected into vials. The microbiological samples were incubated in culture media for 24 h. Colonies of bacteria were counted and the results were given as number of colony‑forming units (CFU)/ml. Statistical Analysis Used: The obtained data were analyzed using the Kruskal–Wallis one‑way analysis of variance and Mann–Whitney U‑tests. Results: There was a significant difference between the rotary and hand instrumentation system related to the apically extruded intracanal bacteria. Conclusions: Both the rotary and hand instrumentation systems extruded intracanal bacteria through the apical foramen. K3XF file system showed least bacterial extrusion amongst all instrumentation groups.