T he objective of this research was to evaluate, by three-dimensional (3D) finite element analysis (FEA), the stress distribution in three different fiveimplant mandibular protocol prosthesis models, when these three undergo a simulated occlusal load of 100 N in the area of the cantilever: (1) model A, temporary all-acrylic resin; (2) model B, metal-acrylic; and (3) model C, metal-ceramic. Materials and Methods Modeling of the External and Internal Portions of the MandibleThe external 3D modeling of the mandible was acquired from the laser digitization of a natural edentulous mandible in the sagittal, horizontal, and frontal planes (0.01mm precision) using Digimil 3D (Technodrill). The first 3D model was created using Geomatic Studio version 7.0, and then a continuous model was obtained using Rhynoceros 3D version 3.0.A tomographic image (70 transversal vertical slices, 1-mm thickness) of the same edentulous mandible was obtained using Helicoidal Tomographic Hispeed CTI System Series 6.3 (GE Healthcare). This image was superimposed over the external mandible model to develop the internal model (Rhynoceros 3D version 3.0). Modeling of Implants and Prosthetic ComponentsThe 3D shapes of implant and prosthetic components were obtained by manual measurements (eg, length, diameter, thread pitch) with magnifying lens and a digital caliper. These dimensions were used for generating digital surfaces (Rhynoceros 3D version 3.0), and then solid shapes were obtained (SolidWorks 2012, SolidWorks).

Objectives: This experimental laboratory study aimed to compare the effect of four external irrigation protocols on bone tissue heating during guided implant drilling. Methods: Forty perforations were made in ten bovine rib specimens using customized surgical templates. Four experimental groups (n=10/group) were tested: Control group = 10-ml syringe with 25°C saline solution, Group 1 = 10-ml syringe with 10°C saline solution, Group 2 = combined external irrigation using a handpiece and a 10-ml syringe with 25°C saline solution, and Group 3 = combined external irrigation using a handpiece and a 10-ml syringe with 10°C saline solution. The temperature was measured at cervical and apical points using K-type thermocouples, a digital thermometer, and a video recorder. Data were analyzed by ANOVA and Pearson’s correlation coefficients (alpha=0.05). Results: The maximum temperature was 42°C (cervical) and 44°C (apical). No difference in temperature changes was found among groups, but the difference between bone specimens was statistically significant. Temperature and time were positively associated for most groups, mainly in the cervical region. Conclusions: All irrigation methods were equally effective in controlling the bone temperature in cervical and apical regions. However, longer drilling times caused a greater increase in temperature.

Objectives: This nonlinear three-dimensional finite element analysis (FEA) study evaluated the effect of the number of implants, distal implant inclination, and use of angled abutments on stress magnitude and distribution in cortical bone (CB), abutment screw (AS), and prosthetic screw (PS) of implant-supported fixed complete dentures. Methods: Nonlinear 3D FEA models of mandibular fixed complete dentures were created with five, four, or three parallel straight implants (5S, 4S, 3S) and with tilted distal implants (5T, 4T, 3T). In addition, the 5T model was tested using angled abutments over the tilted distal implants to re-align the implant inclination. A 100-N axial load was applied over the first molar region (cantilever) to analyze the von Mises stresses in selected points (CB, AS, and PS). Results: The implant adjacent to the load showed the highest stresses in CB, AS, and PS. The model with three implants showed higher stresses than the ones with four and five implants. Peak stresses in the AS increased 40% from five to four implants and 100% from five to three implants. Tilting the distal implants increased stresses in CB. Peak stress in the PS increased 150% from 5S to 5T models and 100% from 4S to 4T models. Angled abutments generated lower stresses on CB and AS but higher stresses on PS. Conclusions: The results suggest that stresses in the cortical bone, abutment screw, and prosthetic screw increase when tilting the posterior implants and reducing the number of implants. The use of angled abutments decreased stresses at the bone-implant interface and in abutment screws but increased stresses on prosthetic screws.

No abstract

No abstract