Background and Objectives. A key factor for the long-term function of a dental implant is the manner in which stresses are transferred to the surrounding bone. The effect of adding a stiffener to the tissue side of the Hader bar helps to reduce the transmission of the stresses to the alveolar bone. But the ideal thickness of the stiffener to be attached to the bar is a subject of much debate. This study aims to analyze the force transfer and stress distribution of an implant-supported overdenture with a Hader bar attachment. The stiffener of the bar attachments was varied and the stress distribution to the bone around the implant was studied. Methods. A CT scan of edentulous mandible was used and three models with 1, 2, and 3？mm thick stiffeners were created and subjected to loads of emulating the masticatory forces. These different models were analyzed by the Finite Element Software (Ansys, Version 8.0) using von Mises stress analysis. Results. The results showed that the maximum stress concentration was seen in the neck of the implant for models A and B. In model C the maximum stress concentration was in the bar attachment making it the model with the best stress distribution, as far as implant failures are concerned. Conclusion. The implant with Hader bar attachment with a 3？mm stiffener is the best in terms of stress distribution, where the stress is concentrated at the bar and stiffener regions. 1. 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. Lack of retention and stability is one of the major complaints of edentulous patients [1]. The introduction of osseointegrated implants into dentistry has provided new alternatives for the rehabilitation of edentulous patients. Mandibular implant retained overdentures can provide an effective treatment modality for these patients and, in particular, those who have persistent problems with a conventional mandibular prosthesis [2, 3]. Implant-supported overdentures have gained acceptance over the complete denture because of its relative simplicity, increased comfort and chewing efficiency, greater satisfaction, preservation of residual ridge, retention, stability, and improved patient quality of life [1–4]. Retention for the mandibular implant-supported overdentures is commonly achieved by ball attachments, clip on bar connecting the implants, or magnetic attachments [4]. These retentive attachments generate forces and stresses that differ from those seen with natural teeth
References
[1]
W. G. Assun？ao, V. A. R. Barao, L. F. Tabata, E. A. C. de Sousa, E. A. Gomes, and J. A. Delben, “Comparison between complete denture and implant-retained overdenture: effect of different mucosa thickness and resiliency on stress distribution,” Gerodontology, vol. 26, no. 4, pp. 273–281, 2009.
[2]
G. Celik and B. Uludag, “Photoelastic stress analysis of various retention mechanisms on 3-implant-retained mandibular overdentures,” Journal of Prosthetic Dentistry, vol. 97, no. 4, pp. 229–235, 2007.
[3]
R. Mericske-Stern, “Treatment outcomes with implant-supported overdentures: clinical considerations,” Journal of Prosthetic Dentistry, vol. 79, no. 1, pp. 66–73, 1998.
[4]
M. Tokuhisa, Y. Matsushita, and K. Koyano, “In vitro study of a mandibular implant overdenture retained with ball, magnet, or bar attachments: comparison of load transfer and denture stability,” International Journal of Prosthodontics, vol. 16, no. 2, pp. 128–134, 2003.
[5]
P. S. Wright, R. M. Watson, and M. R. Heath, “The effects of prefabricated bar design on the success of overdentures stabilized by implants,” The International Journal of Oral & Maxillofacial Implants, vol. 10, no. 1, pp. 79–87, 1995.
[6]
H. J. A. Meijer, F. J. M. Starmans, W. H. A. Steen, and F. Bosman, “A three-dimensional, finite-element analysis of bone around dental implants in an edentulous human mandible,” Archives of Oral Biology, vol. 38, no. 6, pp. 491–496, 1993.
[7]
G. Menicucci, M. Lorenzetti, P. Pera, and G. Preti, “Mandibular implant-retained overdenture: finite element analysis of two anchorage systems,” International Journal of Oral and Maxillofacial Implants, vol. 13, no. 3, pp. 369–376, 1998.
[8]
H. J. A. Meijer, F. J. M. Starmans, W. H. A. Steen, and F. Bosman, “Loading conditions of endosseous implants in an edentulous human mandible: a three-dimensional, finite-element study,” Journal of Oral Rehabilitation, vol. 23, no. 11, pp. 757–763, 1996.
[9]
D. Vollmer, U. Meyer, U. Joos, A. Vègh, and J. Piffkò, “Experimental and finite element study of a human mandible,” Journal of Cranio-Maxillofacial Surgery, vol. 28, no. 2, pp. 91–96, 2000.
[10]
F. van Kampen, M. Cune, A. van der Bilt, and F. Bosman, “Retention and postinsertion maintenance of bar-clip, ball and magnet attachments in mandibular implant overdenture treatment: an in vivo comparison after 3 months of function,” Clinical Oral Implants Research, vol. 14, no. 6, pp. 720–726, 2003.
[11]
M. Cruz, T. Wassall, E. M. Toledo, L. P. da Silva Barra, and A. C. de Castro Lemonge, “Three-dimensional finite element stress analysis of a cuneiform-geometry implant,” International Journal of Oral and Maxillofacial Implants, vol. 18, no. 5, pp. 675–684, 2003.
[12]
M. R. Rieger, M. Mayberry, and M. O. Brose, “Finite element analysis of six endosseous implants,” The Journal of Prosthetic Dentistry, vol. 63, no. 6, pp. 671–676, 1990.
[13]
E. Carl, Misch Contemporary Implant Dentistry, Mosby, Philadelphia, Pa, USA, 2nd edition, 1999.
[14]
A. M. Weinstein, J. J. Klawitter, S. C. Anand, and R. Schuessler, “Stress analysis of porous rooted dental implants,” Journal of Dental Research, vol. 55, no. 5, pp. 772–777, 1976.
[15]
K. Kordatzis, P. S. Wright, and H. J. A. Meijer, “Posterior mandibular residual ridge resorption in patients with conventional dentures and implant overdentures,” International Journal of Oral and Maxillofacial Implants, vol. 18, no. 3, pp. 447–452, 2003.
[16]
H. J. Meijer, F. J. Starmans, W. H. Steen, and F. Bosman, “A comparison of three finite element models of an edentulous mandible provided with implants,” Journal of Oral Rehabilitation, vol. 20, no. 2, pp. 147–157, 1993.
[17]
L. Borchers and P. Reichart, “Three dimensional stress distribution around an implant at different stages of interface development,” Journal of Dental Research, vol. 62, no. 2, pp. 155–159, 1983.
[18]
S. D. Cook, J. J. Klawitter, and A. M. Weinstein, “A model for the implant-bone interface characteristics of porous dental implants,” Journal of Dental Research, vol. 61, no. 8, pp. 1006–1009, 1982.
[19]
S. D. Cook, A. M. Weinstein, and J. J. Klawitter, “A three-dimensional finite element analysis of a porous rooted Co-Cr-Mo alloy dental implant,” Journal of Dental Research, vol. 61, no. 1, pp. 25–29, 1982.
[20]
A. M. O'Mahony and J. L. Williams, “Anisotropic elastic properties of cancellous bone from a human edentulous mandible,” Clinical Oral Implants Research, vol. 11, pp. 415–421, 2000.
[21]
E. R. Teixeira, Y. Sato, Y. Akagawa, and N. Shindoi, “A comparative evaluation of mandibular finite element models with different lengths and elements for implant biomechanics,” Journal of Oral Rehabilitation, vol. 25, no. 4, pp. 299–303, 1998.
[22]
S. Tada, R. Stegaroiu, E. Kitamura, O. Miyakawa, and H. Kusakari, “Influence of implant design and bone quality on stress/strain distribution in bone around implants: a 3-dimensional finite element analysis,” International Journal of Oral and Maxillofacial Implants, vol. 18, no. 3, pp. 357–368, 2003.
[23]
F. A. Fontijn-Tekamp, A. P. Slagter, M. A. van't Hof, M. E. Geertman, and W. Kalk, “Bite forces with mandibular implant-retained overdentures,” Journal of Dental Research, vol. 77, no. 10, pp. 1832–1839, 1998.
[24]
J. H. Koolstra, T. M. G. J. van Eijden, W. A. Weijs, and M. Naeije, “A three-dimensional mathematical model of the human masticatory system predicting maximum possible bite forces,” Journal of Biomechanics, vol. 21, no. 7, pp. 563–576, 1988.
[25]
F. M. C. van Kampen, A. van der Bilt, M. S. Cune, and F. Bosman, “The influence of various attachment types in mandibular implant-retained overdentures on maximum bite force and EMG,” Journal of Dental Research, vol. 81, no. 3, pp. 170–173, 2002.
[26]
J.-P. A. Geng, K. B. C. Tan, and G.-R. Liu, “Application of finite element analysis in implant dentistry: a review of the literature,” Journal of Prosthetic Dentistry, vol. 85, no. 6, pp. 585–598, 2001.
[27]
G. Eskitascioglu, A. Usumez, M. Sevimay, E. Soykan, and E. Unsal, “The influence of occlusal loading location on stresses transferred to implant-supported prostheses and supporting bone: a three-dimensional finite element study,” Journal of Prosthetic Dentistry, vol. 91, no. 2, pp. 144–150, 2004.
[28]
W. G. Assun？？o, L. F. Tabata, V. A. R. Bar？o, and E. P. Rocha, “Comparison of stress distribution between complete denture and implant-retained overdenture-2D FEA,” Journal of Oral Rehabilitation, vol. 35, no. 10, pp. 766–774, 2008.
[29]
T. Haraldson, T. Jemt, P. A. St？lblad, and U. Lekholm, “Oral function in subjects with overdentures supported by osseointegrated implants,” Scandinavian Journal of Dental Research, vol. 96, no. 3, pp. 235–242, 1988.
[30]
D. Levy, D. A. Deporter, P. A. Watson, and R. M. Pilliar, “Periodontal parameters around porous-coated dental implants after 3 to 4 years supporting overdentures,” Journal of Clinical Periodontology, vol. 23, no. 6, pp. 517–522, 1996.
[31]
G. Papavasiliou, P. Kamposiora, S. C. Bayne, and D. A. Felton, “Three-dimensional finite element analysis of stress-distribution around single tooth implants as a function of bony support, prosthesis type, and loading during function,” Journal of Prosthetic Dentistry, vol. 76, no. 6, pp. 633–640, 1996.
[32]
S. Yokoyama, N. Wakabayashi, M. Shiota, and T. Ohyama, “Stress analysis in edentulous mandibular bone supporting implant-retained 1-piece or multiple superstructures,” International Journal of Oral and Maxillofacial Implants, vol. 20, no. 4, pp. 578–583, 2005.
[33]
O. L. Koca, G. Eskitascioglu, and A. Usumez, “Three-dimensional finite-element analysis of functional stresses in different bone locations produced by implants placed in the maxillary posterior region of the sinus floor,” Journal of Prosthetic Dentistry, vol. 93, no. 1, pp. 38–44, 2005.
[34]
R. Chowdhary, K. Lekha, and N. P. Patil, “Two-dimensional finite element analysis of stresses developed in the supporting tissues under complete dentures using teeth with different cusp angulations,” Gerodontology, vol. 25, no. 3, pp. 155–161, 2008.
