Biomechanical Modeling of the Mandible and Teeth

Sinan Muftu

Associate Professor Department of Mechanical and Industrial Engineering
Northeastern University, Boston, MA

Background and Goals

The primary goal of this collaboration is to advance image-based finite element (FE) biomechanical analysis for better treatment of dental implant systems. Specifically, Prof. Muftu investigating therapeutically beneficial ideas for dental implant systems by modeling and simulation of the biomechanics of mastication, bone loading and adaptive bone remodeling. The project relies on anatomically correct and patient specific CT image data. Dental implant systems are used in patients with full or partial edentulism to provide anchoring support for full or partial dental prosthesis. While dental implant systems have been proven clinically successful, various clinical conditions have less than ideal prognosis, including implant treatments in low density bone and in the the maxillary molar region, and implant treatments for patients with bruxism habits. Moreover, from a therapeutic point of view, immediate loading of dental implant systems would be desirable. Understanding the biomechanical components of osseointegration is critical in improving the outcome of such treatments.

Wolff's law states that "every change in the function of the bone is followed by certain definite changes in internal architecture and external conformation in accordance with mathematical laws." In reality, in addition to mechanical stimuli, hormonal and genetic factors contribute a great extent to the bone regeneration process. Mathematical models of various complexities have been developed for predicting bone regeneration over the last century. In particular, the Frost,¹ and Carter² models have been widely cited.^3,4 Good correlation between model predictions and experiments has been observed for orthopedic implants.

The finite element method can be combined with bone adaptation algorithms to predict long-term tissue reactions around implants. Iterative computations can be used to predict the time course of peri-implant tissue response, including bone adaptation and tissue differentiation. Recent work on the simulation of bone remodeling around various implant systems in Dr. Muftu's group showed that external screw threads and/or fins on the implants make a significant contribution to bone remodeling response, and long term loading has a strong influence on bone remodeling. This work also showed that the specific conditions of the bone, and the particular anatomy of the patient, played a significant role in the homeostatic strain levels around teeth and dental implants.

However there is a need to seamlessly incorporate high density CT images into this group's finite element modeling studies. Currently, image analysis places a significant overhead on the biomechanical analyses of the dental implant systems. Having some or all of the following capabilities at hand, would significantly improve the time spent for analyzing the masticatory loading conditions of specific patients:

The capability to identify the bone, the teeth and muscles from CT scans, in a customizable but user friendly manner,
The capability to identify bone density distribution in close vicinity of the implant system
The cpability to determine the relative material properties using pixel densities (Honsfield scale),
The capability to create a finite element mesh with hexahedral or tetrahedral, linear or quadratic elements, and
The capability to output the mesh and the material properties in a flexible format that can be identified by different finite element packages.

These capabilities would enable Prof. Muftu and his students to develop a finite element approach that can be used to carry out the investigations of the biomechanical component of bone remodeling around dental implants systems. The anatomically correct models can then be used to test the effect of different implant designs on osseointegration, with a reduced need for animal studies.

In addition Prof. Muftu has begun a collaboration with Prof. Brooks and Prof. Paul Canavan of Northeastern's Physical Therapy Department on image-based modeling of temporo-mandibular disease that would benefit from much of the same technological interaction. Prof. Muftu and two of his graduate students attended the CIBC Workshp at Northeastern in January and, with the release of BioMesh3D and with our DBP collaboration with Prof. Weiss, this collaboration is well-poised for success.

Collaborator Publications

D. Bozkaya, S. Muftu, and A. Muftu. "Evaluation of load transfer characteristics of five different implants in compact bone at different load levels by finite element analysis". Journal of Prosthetic Dentistry, 92(6):523–530, 2004.

D. Bozkaya and S. Muftu. "Efficiency considerations for the purely tapered interference fit (tif) abutments used in dental implants". Journal of Biomechanical Engineering, Trans ASME, 126:393–401, 2004.

D. Bozkaya and S. Muftu. "Mechanics of the taper integrated screwed-in (tis) abutments used in dental implants". Journal of Biomechanics, 38:87–97, 2005.

D. Bozkaya and S. Muftu. "Mechanics of the tapered interference fit in dental implants". Journal of Biomechanics, 36(11):1649–1658, Nov 2005.

H-Y Chou, J.J. Jagodnik, and S. Muftu. "Predictions of bone remodeling around dental implant systems". fJournal of Biomechanics, 41(6):1365–1373, 2008.

Cited References

H.M. Frost. "Skeletal structural adaptations to mechanical usage (SATMU): 1. redefining wollf's law: the bone modeling problem". Anat. Rec., 22(4):403–413, 1990.
D.R. Carter and GS. Beaupre. "Skeletal function and form". Cambridge, Cambridge, England, 2001n.
R.T. Hart. S.C. Cowin, chapter "Bone Modeling and Remodeling: Theories and Computation". CRC Press, Boca Raton, FL, 2nd edition, 2001.
P.J. Prendergast. "Bone prostheses and implants". In S.C. Cowin, editor, Bone Mechanics Handbook. CRC Press, Boca Raton, FL, 2nd edition, 2001.