日補綴会誌 Ann Jpn Prosthodont Soc 1 : 000-000, 2009 77 Abstract: Purpose: The aim of this research was to evaluate and compare the maximum stabilizing force and sta- bilizing energy of mandibular overdentures with sev- eral attachments during anterior, lateral, and poste- rior dislodgement before and after wear simulation. Changes in the maximum retentive force and maxi- mum stabilizing force of each attachment during vari- ous levels of wear simulation were also examined. Methods: Ten samples, each of 8 different overden- ture attachments, were sequentially embedded in mandibular overdentures in pairs. Maximum sta- bilizing force and stabilizing energy were measured during anterior, lateral, and posterior dislodgement by a universal testing machine before and after wear simulation. A total of 5000 insertion-removal cycles were performed. The maximum retentive force of each sample was measured during various levels of wear simulation by a micro material testing machine. Results: The mean maximum stabilizing force ranged from 1.94N to 28.6N, and the mean stabilizing energy ranged from 1.9N•mm to 30.24N•mm before wear simulation. After wear simulation, the values ranged from 1.03N to 20.49N for maximum stabilizing force and from 1.9N•mm to 21.51N•mm for stabilizing en- ergy. This study revealed a decrease (4.13-84.46 %) and an increase (1.23-41.8 %) in maximum stabiliz- ing force. A decrease (6.5-85.42%) and increase (5.35- 23.55%) were also seen for stabilizing energy. Conclusions: Maximum stabilizing force and stabiliz- ing energy can each be used to evaluate the stability of overdentures. Both parameters were different during anterior, lateral, and posterior dislodgement after and before wear simulation. The changes in the maximum retentive force for each attachment during wear simu- lation were different. Among the attachments tested, Hyperslim 4013 was the least sensitive to wear simu- lation. Key words: stabilizing force, retentive force, wear simulation, overdenture Introduction The treatment concepts that underlie root- and implant-supported overdentures are similar. 1 These treatment concepts offer a better likelihood of desirable results than a complete denture, es- pecially in the mandible. Overdentures provide reduced residual ridge resorption and improved denture stability, retention, masticatory perfor- mance, and patient satisfaction. 2-5 For edentulous patients, implant-retained overdentures have become more popular than fxed implant-supported prostheses because of the reduced number of implants, easier surgical procedures and an easier dental technique due to the application of prefabricated parts, and simi- lar effcacy. 6-8 Consistent pre-treatment and post-recon- structive follow-up or regular periodic servicing is very important for long-term prosthodontic success. 9,10 Adequate overdenture design for the individual case is also a signifcant part of the treatment strategy. Many different attachments are available for use with a root- or implant-sup- ported overdenture. Therefore, the stability and changes in stability of an overdenture due to wear of the attachment are important factors in the selection of an appropriate attachment. Functional and nonfunctional stresses can dis- place a dental prosthesis. During such displace- ment, some amount of energy is transferred by force, i.e., mechanical work is done. ORIGINAL ARTICLE Stability of Mandibular Overdentures Before and After Attachment Wear. An in vitro Study Bazar Amarsanaa, DDS, a Hiroshi Mizutani, DDS, PhD, a Hidekazu Takahashi, DDS, PhD, b and Yoshimasa Igarashi, DDS, PhD a a Department of Removable Partial Prosthodontics, Masticatory Function Rehabilitation, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan b Department of Advanced Biomaterials, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan Corresponding to: Dr Hiroshi Mizutani Removable Prosthodontics, Masticatory Function Rehabili- tation, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan Tel: +81-3-5803-5513, Fax: +81-3-5803-5513, E-mail: mztn.rpro@tmd.ac.jp Received on August 19, 2008/Accepted on September 17, 2008 Ann Jpn Prosthodont Soc 1 : 000-000, 2009 Ann Jpn Prosthodont Soc 1 : 77-84, 2009