Browsing School of Dentistry by Subject "lithium disilicate"
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The Effect of CAMBRA Recommended Anti-Caries Agents on Surface Roughness of Lithium Disilicate CeramicsPurpose: The purpose of this study was to explore the clinical importance of the effect of Prevident and chlorhexidine on the surface roughness of three commonly utilized lithium disilicate ceramics: pressed (Press), milled (CAD), milled and veneered with fluorapatite (CAD/CERAM). Methods and Materials: Seventy-six rectangular specimens in each group of Press, CAD, and CAD/CERAM were fabricated. A profilometer was used to measure the surface roughness prior to and after soaking. The samples were immersed in the assigned anti-caries solution in an airtight plastic container. For the simulation of 2 years use the samples were soaked in chlorhexidine for 3 hours, Prevident, 6% alcohol and distilled water for 12 hours. Statistical analysis was completed using a two-way ANOVA followed by Tukey's HSD test. A p value ≤.05 was considered significant. Results: The results demonstrated that Press samples became significantly rougher. In addition to that, the surface roughness of CAD and CAD/CERAM was significantly decreased. However, CAD was significantly less rough than CAD/CERAM. Water did not significantly change the surface roughness of ceramics, while 6% alcohol, Prevident, and chlorhexidine significantly decreased the roughness of the ceramics. There was no significant difference in the increase of surface smoothness among the three solutions. A significant interaction was found only with water, the control. Conclusion: Within the limitations of this study, it can be concluded that Prevident and chlorhexidine can change the surface roughness of lithium disilicate ceramics when used for a period of 2 years. The surface roughness of Press increased, while that of CAD and CAD/CERAM decreased.
Radiographic Evaluation of All Ceramic Crown MarginsStatement of Problem: Radiographs aid in clinical determination of crown fit, specifically interproximal margins where tactile and visual methods can fail us. With the use of all ceramic materials surpassing ceramometal, it is beneficial to understand what limitations are present with this method to determine the correct marginal adaptation. Purpose: The purpose of this study was to assess if we can accurately identify crown margin closure via radiographs for all ceramic and ceramometal crown margins, and if not, to understand where the error lies. Materials and Methods: Individual IPS e.max, ZirPress, and ceramometal crowns were fabricated using a single prepared maxillary premolar and measured with light microscopy to ensure fit at the margin to below 20μm. The crowns were set up on a margin opening jig, and radiographs were made at 20μm increments starting at 0μm and finishing at 180μm for a total of 10 marginal adaptations. The threshold for closed versus open was >80μm. 80° and 90° radiographs were also made for each discrepancy to account for clinician variation in radiograph making. The 60 radiographs were then randomized and evaluated by prosthodontists and general dentists. Results: Individual evaluation accuracy of marginal adaptation was 48.8% for ceramometal crowns, 72.1% for e.max, and 76.9% for ZirPress. The scientific hypotheses were found to be true. When incorrectly evaluated, ceramometal crowns were significantly more likely to be evaluated acceptable when open margins were present, or as false positives. E.max and ZirPress were found to be more likely evaluated unacceptable with closed margins present. No significant difference was seen between general dentists and prosthodontists or between 80° and 90° variations except for ceramometal crowns which were more accurate for 90°. Conclusions: Within the limitations of this in vitro study, accuracy of marginal adaptation evaluations without clinical examination is not as high as would be expected. Ceramometal crowns tend to be incorrectly evaluated closed. Ceramic crowns (IPS e.max lithium disilicate and ZirPress) tend to be incorrectly evaluated open. No difference between prosthodontists and general dentists was evident in this study with relation to accuracy of evaluations. The goal of this study was to provide information to aid in marginal closure determination when evaluating crowns radiographically and guidance when examining crowns of different radiopacities with relation to the common inaccuracies found in the study.
Streptococcus mutans Bacterial Adherence on Lithium Disilicate Porcelain SpecimensStreptococcus mutans as it pertains to dental and oral health is significant for its role as the primary etiologic factor of caries. While primary caries results from initiation of lesions in virgin tooth structure, secondary caries is a significant contributing factor to the replacement of dental restorations. Caries formation is directly related to plaque accumulation, which is mediated by bacteria adhesion to intraoral surfaces. In the case of the restored tooth, bacteria must adhere to the restorative material, particularly along margins in order to cause recurrent pathology. A material that has recently come into much favor is lithium disilicate, a glass based system with fillers in a homogenous glass. Lithium disilicate restorations can be either (1) pressed or (2) milled to fabricate inlays, onlays, veneers or single unit crowns. These restorations can be full-contour, or may be cut back and subsequently modified with (3) veneering fluorapatite, or (4) glazed. With respect to bacterial adhesion to restorative surfaces, the overwhelming factor is surface roughness. The threshold for this effect has previously been found to be 0.2 µm Ra value, above which there was a positive correlation between surface roughness and plaque retention. Specimens were fabricated for each of the four preparation types per manufacturer's recommendations and incubated with S. mutans UA159 wild-type. Biofilms adherent to specimens were then sonicated, redispersed, and plated for quantification. Results were tested with an analysis of variance (ANOVA). Significant differences that were found were further analyzed by Tukey's Honestly Significant Difference (HSD) test. Pearson's r was also be used to evaluate the relationship between surface roughness and biofilm accumulation. A p-value of ≤ 0.05 was considered significant. Surface roughness, as quantified by Ra values, indicated that Press and CAD groups were not significantly different from one another, but were significantly lower than that of ZirPress/Ceram, which was lower than surface roughness of the Ceram Glaze group (F = 513.898, p ≤ 0.0005). Similarly, CFUs/ml for the CAD and Press groups were significantly lower than the ZirPress/Ceram group, which were also significantly lower than those of the Ceram Glaze group (F = 201.721, p ≤ 0.0005). A strong positive association was also seen between surface roughness and biofilm accumulation (r = .95). Many factors, such as caries risk, presence of other restorations, and individual patient hygiene, influence whether these differences in surface roughness and biofilm accumulation become clinically relevant to the formation of caries. The present study has demonstrated that different preparations vary in their surface roughness and biofilm accumulation measurements, and that these differences in surface quality are associated with bacterial adherence.