Three Dimensional Finite Element Analysis of Stress Distribution around Implant with Straight and Angled Abutments in Different Bone Qualities

Abstract

INTRODUCTION: Dental implants have been proven to be an effective way of restoring the masticatory ability of completely or partially edentulous patients. The desired position of the artificial teethis determined by esthetic and functional requirements. Sufficient amount of bone for implant placement is an essential pre requisite for the long term success in oral implant therapy. The quantity of alveolar bone decreases after periodontal disease or after extraction, causing bone loss in both horizontal and vertical direction. Lack of horizontal bone volume always result in exposure of implant surface, decreased bone- implant interface and finally implant failure. Lack of bone volume is more common in the anterior maxilla. The long term prognosis for implants in the maxilla is less secure than that of edentulous mandible. Following tooth extraction in the anterior part of the maxilla horizontal bone resorption is almost twice as pronounced as vertical resorption. This can be managed either by surgical correction or by positioning the implant in the area with the greatest available bone with the intention of correcting the implant alignment at the time of implant restoration. This is made possible, in carefully planned cases, using angled implant abutments. Eger et al and Sethi et al concluded that angled abutments may be considered a suitable restorative option when implants are not placed in ideal axial positions. The successful osseo integration of implant depends not only on the bone quantity but also on the bone quality. The classification scheme for bone quality proposed by Lekholm and Zarb has been accepted by clinicians and investigators as standard in evaluating patients for implant placement. In this system, the sites are categorized in 1 to 4 groups on the basis of jawbone quality. In Type 1 (D1) bone quality, the entire jaw is comprised of homogenous compact bone. In Type 2 (D2) bone quality, a thick layer (2 mm) of compact bone surrounds a core of dense trabecular bone. In Type 3 (D3) bone quality, a thin layer (1 mm) of cortical bone surrounds a core of dense trabecular bone of favorable strength. In Type 4 (D4) bone quality, a thin layer (1 mm) of cortical bone surrounds a core of low-density trabecular bone. Implant manufacturers have introduced preangled abutments as a prosthetic option for dentitions that are otherwise difficult to restore because of implant locationor angulation. The angulation of these abutments varies from 15° to 35°. Clinical comparative studies of implant with straight abutments and angled abutments showed that the bone loss or the survival rate of angled abutments were not significantly different from straight abutment. However the Strain gauge measurements and Photoelasticmodels of Brosh et al. and the finite element analyses of Canay et al. and Clell and et al revealed that angled abutment were subjected to higher stress values around the cervical region than those observed for straight abutment. Few investigators have studied the unavoidable situation of placing and loading implants at an angulation in the anterior maxilla, but they did not consider the variation in bone qualities which may influence the stress distribution around the implant with angled abutments. The purpose of the present studyis to compare the stress distribution in various bone qualities of D1, D2, D3 and D4 with straight and angled abutments using three dimensional finite element analysis. AIM OF THE STUDY: The aim of this study was to compare the stress distribution in different bone qualities of D1, D2, D3 & D4 with straight and angled abutments using Three Dimensional Finite Element analysis. MATERIALS AND METHODS: A three dimensional finite element model of the premaxilla region and a solid 4.3 x 10 mm implant with a straight abutment (M1) and an angled abutment (M2) was done. Four distinctly different bone qualities of D1, D2, D3 & D4 were made. Simulated occlusal load of 178 N was applied at the centre of incisal edge along the long axis of each abutment. The maximum equivalent von Misses stress values around the implants were recorded. RESULTS: The distribution of stresses changed considerably with abutment angulation. As angulation increased from 00 to 150 the concentration of von Mises stress shifted to the cortical layer of bone on the facial side of the fixture. In D1, D2, D3 & D4 bone qualities the highest von Mises stress values were obtained at the crestal region of implant. The maximum von Mises stress of 20.832 was recorded in D4 cortical bone on the buccal side of angled abutment. CONCLUSION: The high stresses induced through preangled abutments at the cervical zone of the implant due to forces and moments could be a dominant factor that may aggravate the peri implant bone loss or may change the existing periimplantitis direction