Digital evaluation of absolute marginal discrepancy: A comparison of ceramic crowns fabricated with conventional and digital techniques.

STATEMENT OF PROBLEM: Marginal discrepancy is key to evaluating the accuracy of fixed dental prostheses. An improved method of evaluating marginal discrepancy is needed. PURPOSE: The purpose of this in vitro study was to evaluate the absolute marginal discrepancy of ceramic crowns fabricated using conventional and digital methods with a digital method for the quantitative evaluation of absolute marginal discrepancy. The novel method was based on 3-dimensional scanning, iterative closest point registration techniques, and reverse engineering theory. MATERIAL AND METHODS: Six standard tooth preparations for the right maxillary central incisor, right maxillary second premolar, right maxillary second molar, left mandibular lateral incisor, left mandibular first premolar, and left mandibular first molar were selected. Ten conventional ceramic crowns and 10 CEREC crowns were fabricated for each tooth preparation. A dental cast scanner was used to obtain 3-dimensional data of the preparations and ceramic crowns, and the data were compared with the "virtual seating" iterative closest point technique. Reverse engineering software used edge sharpening and other functional modules to extract the margins of the preparations and crowns. Finally, quantitative evaluation of the absolute marginal discrepancy of the ceramic crowns was obtained from the 2-dimensional cross-sectional straight-line distance between points on the margin of the ceramic crowns and the standard preparations based on the circumferential function module along the long axis. RESULTS: The absolute marginal discrepancy of the ceramic crowns fabricated using conventional methods was 115 ±15.2 µm, and 110 ±14.3 µm for those fabricated using the digital technique was. ANOVA showed no statistical difference between the 2 methods or among ceramic crowns for different teeth (P>.05). CONCLUSIONS: The digital quantitative evaluation method for the absolute marginal discrepancy of ceramic crowns was established. The evaluations determined that the absolute marginal discrepancies were within a clinically acceptable range. This method is acceptable for the digital evaluation of the accuracy of complete crowns.

[Correlation between periodontitis and metabolic syndrome of the middle-aged and aged population in Shijingshan community of Beijing].

OBJECTIVE: To survey the metabolic status of the middle-aged and aged population with periodontitis in Shijingshan community of Beijing, and investigate the relationship between periodontitis and metabolic syndrome (MS). METHODS: The middle-aged and aged population in the community were investigated by questionnaires, periodontal clinical examinations and blood biochemical tests in 2005. A total of 903 subjects were enrolled, who were divided into two groups by severity of periodontitis. Their waist circumferences, values of high-density lipoprotein cholesterol (HDL-C), systolic blood pressure, fasting glucose, MS and its individual components (central obesity, insulin resistance, hypertriglyceridemia, low HDL-C and hypertension) were compared between the two groups. The Logistic regression model was set to analyze the relationship between periodontitis and MS. RESULTS: There was a significantly higher mean of systolic blood pressure, fasting glucose in the subjects with moderate-severe periodontitis than that with no-mild periodontitis. With severity of periodontitis increasing, the prevalence of MS, high blood glucose and low HDL-C increased significantly. After adjustment for gender, age, and smoking, the subjects with moderate-severe periodontitis were 1.524, 1.527 and 2.349 times more likely to suffer from MS, high blood glucose and low HDL-C than those with no-mild periodontitis, respectively. CONCLUSION: With severity of periodontitis increasing, the prevalence of MS, high blood glucose and low HDL-C increased significantly in the middle-aged and aged population of the community in Beijing. Severity of periodontitis is associated with MS, high blood glucose and low HDL-C.