Accuracy of silicone impressions and stone models using two laboratory scanners: a 3D evaluation.

PURPOSE: To evaluate the in vitro accuracy of impressions obtained with two silicone and corresponding stone models using two laboratory scanners. MATERIAL AND METHODS: A master model with synthetic resin teeth with two single-unit crown preparations was created and scanned using a 12-MP scanner. Five conventional impressions of the physical model were prepared with different silicone impression systems (Zhermack and Coltene) using the double-mix technique and poured with gypsum. The impressions and stone models obtained were scanned by two extraoral scanning systems (Identica T500 Medit and S600 ARTI Zirkonzahn). All best-fit superimpositions of the teeth areas were conducted between the master model and the scans of the impressions and models obtained with the two scanners. A P < .05 significance level was considered. RESULTS: The Identica T500 Medit scanner showed an accuracy of 102.34 (89.67, 115.01) µm for Coltene silicone and 79.51 (67.82, 91.21) µm for Zhermack silicone, while the S600 ARTI Zirkonzhan scanner presented 110.79 (98.24, 123.33) µm and 91.91 (81.29, 102.54) µm, respectively, with significant differences between scanners for Zhermack silicone (P = .008) and for the corresponding stone models (P = .002). Zhermack silicone presented overall discrepancies lower than Coltene silicone, with statistically significant differences in both scanners analyzed (P < .001; P = .017). However, the discrepancies found were within clinically acceptable values. With the Zirkonzahn scanner, discrepancies found in the Zhermack impressions were lower than in the corresponding stone models (P < .001). CONCLUSION: The direct digitalization of silicone impressions by laboratory scanners presented comparable results to conventional techniques with stone models.

IL1 gene polymorphisms and unsuccessful dental implants.

OBJECTIVES: This study aimed to analyse the association between polymorphisms in the IL1 gene cluster and failure of dental implants in a Portuguese population. MATERIAL AND METHODS: A total of 155 Caucasian Portuguese subjects were divided into two groups: 100 with successful dental implants and 55 with unsuccessful dental implants. DNA was obtained through an oral mucosa scraping. PCR was used to identify the polymorphisms: single nucleotide changes in positions -889 of IL1A gene and +3953 of IL1B gene. RESULTS: The prevalence of the polymorphisms -889IL1A gene and +3953IL1B gene, determined by the positive result of TGP (Genetic Test for Periodontitis; CGC, Genetics, Portugal), in the studied population rehabilitated with dental implants was of 33.50%. Allele 1 of the IL1B gene was the most prevalent (62.20%), followed by allele 1 of the IL1A gene (54.80%) and the least frequent was allele 2 of IL1B gene (37.40%). Success of dental implants was mainly associated with a negative TGP result, whereas no success was found to be related to a positive result. There were no statistically significant differences between the alleles 1 and 2 of the genes IL1A and IL1B and the tobacco and alcohol consumption for the success or no success of the dental implants. CONCLUSIONS: The alleles 1 and 2 of IL1A gene and the alleles 1 and 2 of IL1B gene were statistically associated with the success or no success of the dental implants. Tobacco habit and alcohol consumption showed no statistically significant association with success or no success of the dental implants.

Noise levels in dental schools.

OBJECTIVE: To measure and analyse noise levels in the learning-teaching activities at the Dental School of the University of Porto (Portugal). MATERIALS AND METHODS: Sound levels were measured in five different practice areas and laboratories, selected as representative of a variety of learning-teaching activities. The noise levels were determined using a precision sound level meter that was positioned at ear level and at 1 m distance from the operator. RESULTS: The noise levels registered vary between 60 and 99 dB(A) and are similar to the data of other international studies. The results recorded differences in sound levels when the equipment was merely turned on and during cutting operations. Differences between brand new and used equipment were also noted. It appears that hearing damage risk may be lesser amongst dentists who use brand new equipment. CONCLUSION: The noise levels detected in this study are considered to be close to the limit of risk of hearing loss.