Influence of Different Implants on the Biomechanical Behavior of a Tooth-Implant Fixed Partial Dentures: A Three-Dimensional Finite Element Analysis.

This study analyzed the biomechanical behavior of rigid and nonrigid tooth-implant supported fixed partial dentures. Different implants were used to observe the load distribution over teeth, implants, and adjacent bone using three-dimensional finite element analysis. A simulation of tooth loss of the first and second right molars was created with an implant placed in the second right molar and a prepared tooth with simulated periodontal ligament (PDL) in the second right premolar. Configurations of two types of implants and their respective abutments-external hexagon (EX) and Morse taper (MT)-were transformed into a 3D format. Metal-ceramic fixed partial dentures were constructed with rigid and nonrigid connections. Mesh generation and data processing were performed on the 3D finite element analysis (FEA) results. Static loading of 50 N (premolar) and 100 N (implant) were applied. When an EX implant was used, with a rigid or nonrigid connection, there was intrusion of the tooth in the distal direction with flexion of the periodontal ligament. Tooth intrusion did not occur when the MT implant was used independent of a rigid or nonrigid connection. The rigid or nonrigid connection resulted in a higher incidence of compressive forces at the cortical bone as well as stress in the abutment/pontic area, regardless of whether EX or MT implants were used. MT implants have a superior biomechanical performance in tooth-implant supported fixed partial dentures. This prevents intrusion of the tooth independent of the connection. Both types of implants studied caused a greater tendency of compressive forces at the crestal area.

Photoelastic comparison of as-cast and laser-welded implant frameworks.

STATEMENT OF PROBLEM: A misfit between the implant and metal framework can produce biomechanical problems. PURPOSE: The purpose of this in vitro study was to evaluate the vertical misfit, passivity, and biomechanical behavior of a prosthetic protocol-shaped I-beam framework, varying the number and inclination of implants before and after laser welding. MATERIAL AND METHODS: Two metal models with 4 or 5 implants were used. The I-beam framework for 4 or 5 implants was fabricated with cobalt-chromium alloy. The vertical misfit and passivity were evaluated with a stereomicroscope at ×80 magnification, with frameworks screwed into the respective model. The biomechanical behavior was analyzed with photoelastic studies. These analyses were performed before and after welding to observe the influence of the laser welding. RESULTS: The misfit was not significantly different among the groups studied; laser welding did not influence the vertical misfit. However, when the groups were compared for passivity, the 5 implants before welding group were statistically different (P=.025). CONCLUSIONS: Laser welding generated more passivity, less vertical misfit, and favorable stress distribution to the I-beam framework supported by 4 implants. To the I-beam framework supported by 5 implants laser welding did not influence the misfit or stress distribution, but there was an improvement in passivity.

Tensile bond strength of cast commercially pure titanium dowel and cores cemented with three luting agents.

PURPOSE: The purpose of this study was to compare the tensile strength of commercially pure titanium dowels and cores cemented with zinc phosphate or resin cements. METHODS: Twenty-one extracted human canines were endodontically treated. The root preparations were accomplished using Largo reamers (10mm in depth and 1.7 mm in diameter). Acrylic resin patterns for the dowel and cores were made, and specimens were cast in commercially pure titanium (n=7) and divided in three groups: TZ-CP Ti dowels luted with zinc phosphate luting agent, TP-CP Ti dowels luted with Panavia F and TR-CP Ti dowels luted with RelyX U100. Tensile strengths were measured in a universal testing machine at a crosshead speed of 0.5mm/min. The results (N) were statistically analyzed by ANOVA and Tukey tests (α=0.01). RESULTS: The ANOVA indicated that there were significant differences among the groups tested. A Tukey multiple comparison procedure was performed and revealed statistically significant higher retention values for the dowel luted with RelyX U100 when compared with zinc phosphate or Panavia F. CONCLUSION: Cast commercially pure titanium dowels and cores fixed with RelyX U100 cement presented superior bond strength retention when compared to zinc phosphate and Panavia F.