Evandro Afonso Sartori

Effect of microwave disinfection on denture base adaptation and resin surface roughness

This study evaluated the effect of disinfection methods [chemical disinfection (immersion in 100 ppm chloride solution) or microwave disinfection (690 W for 6 min)] on the internal adaptation of denture bases and resin surface roughness. For the adaptation test, 18 maxillary denture bases were obtained from stone casts duplicated from a metallic master model and submitted to the following treatments: 1) control (no disinfection), 2) chemical disinfection or 3) microwave disinfection. Disinfection procedures were performed twice (T1, T2) with a 7-day interval between them. Internal adaptation was measured at baseline (T0) and after T1 and T2 by weighing a vinyl polysiloxane film reproducing the gap between the resin base and the master model. For surface roughness measurement, 60 rectangular (5x10x40 mm) resin specimens were either mechanically or chemically polished and then submitted to the disinfection treatments. Surface roughness (Ra) was recorded after polishing (T0) and after T1 and T2. Data were analyzed by ANOVA GLM for repeated measures and Bonferroni correction at 5% significance level. Bases submitted to microwave disinfection had gradual increase of misfit, while bases immersed in chloride solution did not differ from the control group. Surface roughness increased in the mechanical polishing groups with microwave disinfection and decreased in the chemical polishing groups.

Reliability of a digital image method for measuring medial mandibular flexure in dentate subjects

UNLABELLED Medial mandibular flexure (MMF) is the functional approximation of hemi-mandibles in jaw opening and protrusion, which may affect conventional or implant-supported arch prostheses. OBJECTIVE This study evaluated the intra- and inter-rater reliability of a digital image method for linear measurement of MMF in dentate subjects. MATERIAL AND METHODS Mandibular occlusal impressions in vinyl polysiloxane during rest and maximum opening were obtained from seven adult volunteers. Each impression and the Mitutoyo digital calipers with a 10mm opening were scanned at a 200% magnification. The images were processed using Adobe Photoshop software to get reference points on contralateral first molars. Linear intermolar measurements were taken using the Image Tool software (UTHSCSA), which was calibrated with the standard opening of the digital calipers. Intermolar distance was measured in triplicate for each image by two independent examiners. MMF was calculated by subtracting the intermolar distance in maximum opening (or protrusion) from the distance in rest position. Data were analyzed by intraclass correlation (ICC) tests for estimating intra- and inter-rater reliability. RESULTS MMF values ranged from -0.21 to 0.44mm. Intra-rater ICCs were 0.982 and 0.993, and inter-rater ICC was 0.696. CONCLUSION The present results show excellent intra-rater and good inter-rater reliability of this digital image method for measuring MMF in dentate subjects.

Three-dimensional finite element analysis of mandibular overdentures with different implant positions and attachment types

OBJECTIVE: This 3-D FEA study compared the stress distribution in two-implant mandibular overdentures as a function of implant position and attachment system (LA: locator attachment vs. BA: ball attachment). METHODS: Four models of mandibular overdentures were tested: M1-LA – with implants at the canine regions (standard implant position) and LA; M2-LA – with implants placed at the first premolar regions (distalized implant position) and LA; M1-BA – with standard implant position and BA; and M2-BA – with distalized implant position and BA. The geometric models were converted into finite element models. A 100 N axial load was applied at the first molar region. The von-Mises stress distribution was compared in selected points. RESULTS: The models with BA had pattern of stress distribution was more uniform along the implant axis than the ones with LA, although the stress magnitude was larger. The largest area of von Mises stresses on the alveolar ridge was in the models with standard implant distribution. CONCLUSION: The findings showed that the models with BA had better biomechanical behavior than the ones with LA. For both types of attachment, the models with increased inter-implant distance presented a smaller area of stress distribution in the perimplant cortical bone tissue than the standard implant position.