REHABILITATION OF THE EDENTULOUS HEMIMANDIBLE

A study carried out by the Department of Mechanics, Turin Politecnico
Ing. Cristina Bignardi e Ing. Pertusio
Preface

The basis for this study is the clinical observation of the presence of morphological alterations to the perimplant osseous neck that occur when occlusal forces are applied. This typically cone-shaped anatomic variation is characteristic of implants that are allowed to work individually, as a functional and mechanical entity. To counter this problem, given that nothing more could be achieved with hidden or emerging techniques, to the extent that it has even been described as physiological, the technique of intraoral solidification was introduced using electrowelding by sincrystallisation.
The different behaviour of the resulting implant structure avoids the occurrence of this alteration. This is further demonstrated by the fact that spontaneous remission occurs when implants with first and second degree mobility are solidified using this method.
Biomechanics applied to the orthopedic field has clearly shown that when means of synthesis are fixed, the resorption process is started in the subcortical zone around the first thread of the screw. An analysis of this district was carried out for this reason to evaluate the tensional status using the system of “finished elements”.
As can be seen from this study, there is a marked prevalence of reduced cortical perimplant tension in welded implants which do not show the typical cone-shaped degeneration of individual elements.
The need for long-term reconstructive surgery is a clinical demonstration of vulnerability to loads that are not well absorbed and which contribute to the formation of the well-known clinical syndrome known as perimplantitis. This should be not regarded as a primary septic episode, but rather a secondary pathology of bone destruction caused by the inability to sustain the action of occlusal forces acting on the implants.


dr. Giorgio Lorenzon

Introduction

The aim of this research project was to analyse the tensional status occurring in some conditions of constraint and loading in a biomechanical system consisting of a partially edentulous hemimandible in which the insertion of various kinds of implant is simulated in numerical terms.
A model was realised for this purpose with the following finished hemimandible elements:A compact volume of cortical bone with Young’s modulus equal to 11000MPa (shown in red in Figure 1) A compact volume of cortical bone with Young’s modulus equal to 11000MPa (shown in purple) containing a volume of cancellous bone with Young’s modulus equal to 300MPa (shown in blue)
The values of Young’s modulus were taken from the literature.
The hemimandible was constrained so as to allow only a vertical physiological shift.
Figures 2 and 3 show two examples of the hemimandible model containing two different types of implant.
The visible filiform elements in Figures 2 and 3 were used to simulate the behaviour of the muscles involved in centric occlusion