Abstract Today implant dentistry has made great inroads into the treatment modalities that are available in treating an edentulous patient. Popularity of a two implant retained overdenture has created a necessity to examine the various attachment systems being used and the stresses that are transmitted to the alveolar bone. Hence a Three dimen- sional Finite Element Analysis was done to analyze the stress distribution in the mandibular bone with implant- supported overdenture having Ball/O-ring and Magnet attachments of different diameters. A segment of the anterior region of the mandible was modeled with implant and the overdenture. Four different models were generated having Ball/O-Ring and Magnet  Attachments.  Forces of 10 N, 35 N and 70 N were applied from the horizontal, vertical and oblique directions respectively and the stress distribution studied. It was concluded that the greatest stress concentrations were seen at the crest of the cortical bone and could be reduced by using smaller sized attach- ments for implant supported-overdenture.71224

Keywords    Implant · Overdenture  ·Finite element analysis ·  Mandibular

Introduction As life spans lengthen, a significant number of people outlive their teeth. Treating older patients, especially  those

with disabilities, may be a demanding challenge. The ultimate goal of treating such cases is to restore the patient to a level of satisfactory esthetics, physiological functions of speech, deglutition and mastication. The  chief reason that complete mandibular dentures pose functional prob- lems is because of poor retention. Also bone resorption is significantly greater in the mandible  than  in the  maxilla of edentulous people. Since  complete  dentures  rely  on the residual alveolar  ridge  for  support  and  retention,  it is the mandibular dentures that suffer the most from this natural process [1]. Overdentures can be used as a treat- ment modality for the compromised completely edentulous patients especially in the mandibular arches. Retention for an overdenture is obtained by the implant supporting either retentive studs or magnet attachments similar to those used in natural tooth abutments [2]. The use of a minimal number of implants that is adequate for prosthodontic support and retention is also of economic benefit to the patient [3].

Various methods for evaluation of stress around dental implant system include Photoelastic Study, Finite Element Analysis and Strain Measurement on bone surface. The finite element method offers several advantages, including accurate representation of complex geometries, easy model modification and representation of the internal state of stress and other mechanical qualities  [4].

In this study, a Three Dimensional Finite Element Model of a section of the mandible with an osseointe- grated implant and overdenture is modeled having two types of attachment systems namely the Ball/O-ring and the Magnet system. The diameters of  the  attachments were varied and the stress distribution to the bone around the implant was studied. The loads were applied in the horizontal, vertical, and the oblique directions on the simulated overdenture.

Methodology

Four different finite element models, having an implant, mandibular bone section and overdenture were created for the study. The variables that were changed were the over- denture attachments as shown in (Table 1). A segment of bone around the implant with a length of 20 mm, height  of

Table 1   Model designation and type of  attachment

Attachment type Attachment diameter (mm)

B1 BALL/O-RING 2.5

B2 BALL/O-RING 4.0