The importance of correct implants positioning and masticatory load direction on a fixed prosthesis

Abstract

BackgroundThrough the biomechanical study of dental implants, it is possible to understand the dissipation effects of masticatory loads in different situations and prevent the longevity of osseointegration. Aims: To evaluate the microstrains generated around external hexagon implants, using axial and non-axial loads in a fixed four-element prosthesis with straight implants and implants inclined at 17°.Material and MethodsThree implants were modeled using CAD software following the manufacturer’s measurements. Then, implants were duplicated and divided into two groups: one with straight implants and respective abutments, and the other with angled implants at 17° and respective abutments. Both groups were arranged inside a block simulating bone tissue. A simplified fixed prosthesis was installed on both groups and the geometries were exported to CAE software. Five loads of 300N were performed at axial and non-axial points on the fixed prosthesis. Stress on the implants and strain on the block were both analyzed. An in vitro experiment was performed following all structures made in FEA in order to validate the model. In each experimental block, 4 strain gauges were linearly placed between the implants and the same loads were repeated with a loading applicator device.ResultsThe deformations computed by the gauges were correlated with the FEA results, showing that the group with inclined implants had more damaging biomechanical behavior and was significantly different from the group with straight implants (P<0.005).ConclusionsThe mathematical model used is valid and inclined implants can induce unwanted bone remodeling. Key words:Finite Element Analysis, Dental Implants, Fixed Prosthesis.

Does the prosthesis weight matter? 3D finite element analysis of a fixed implant-supported prosthesis at different weights and implant numbers

“…This probably occurs because of the shape of the maxillary arch, which has a thinner anterior region than the posterior region, and also because the distribution of 4 implants is not exactly equidistant from the distribution of 8 implants. This theory reinforces the need to use three-dimensional anatomical models in numerical simulations of implant prosthesis, since simplified geometric models such as blocks 14 or cylinders 17 may propagate a symmetry force distribution in the bone tissue.…”

“…An indirect rehabilitation of 14 adult teeth supported by implants was simulated herein, and no microstrain values which could be harmful for any of the bone tissue were calculated. 13,14 Thus, dentists and technicians can choose the design and material which are advantageous for dissipating the masticatory load, not simply considering light or heavy materials.…”

“…The main novelty of this study over other reports in the literature is the simulation of tensile forces in the prosthesis, representing the effect generated by the structural weight in the bone tissue. Although the load exerted during mastication is simulated in several previous studies, 5,7,14,16,19,35,37,45 which seek to study the instant of maximum average force capable to generate mechanical problems in the prosthesis/ bone, this simulation included a momentary load. The effect of gravity on the prosthesis is present throughout the patient's life, especially during the rest position where there is no contact between the antagonist tooth.…”

“…The external hexagon was extruded 0.7 mm high and attached to the previously created cylindrical body. 14 One of the evaluated factors was the number of implants (3 levels) used on the simulated surgical approach: 4, 6, or 8 equidistant implants. A mini conical abutment indicated for the screw retained prosthesis was modeled for each implant.…”

“…As bone strain around osseointegrated implants can induce unwanted bone remodeling with consequent loss of osseointegration, 13 it is necessary that all the choices during the surgical and prosthetic planning should be considered to optimize the biomechanical response to occlusal loads. 14 What is unknown is whether the prosthesis weight itself is already capable of causing some damage or benefit to the bone tissue around the implants. According to Wolff 's law, the bone tissue may be encouraged to stay in position, depending on the magnitude of the generated strain.…”