MASTICATORY FORCE MEASUREMENT IN NATURAL DENTITION

L. Himmlova1, T. Goldmann2 and S. Konvickova2 1Institute of Dental Research 1st Medical Faculty of Charles University and General Medical Hospital, Vinohradska 48, 120 21

Prague 2, Czech Republic, 2Czech technical University in Prague, Laboratory of Biomechanics, Technicka 4, 166 67 Prague, Czech Republic; email:

himmlova@seznam.cz, web: www.vus.cz

INTRODUCTION Clinical observations and mathematical models show that the loading influences natural teeth as well as dental implants. Teeth/implants are loaded during masticating, phonation and even in quiescent condition (breathing, swallowing). The masticatory force reaches the highest values of all, so its magnitude and direction is determinative for choice and usage of dental materials and prosthetic treatment planning. The magnitude of masticatory force acting on each single tooth is likely very individual and dependent on extensive number of variables varying during the life (number of occluding teeth, size of contact surface, type of the food). Therefore it is very important to determine not only masticatory force but especially its direction and frequency when acting. These factors can be responsible for possible overloading of teeth, abutments or implants. The aim of the proposed project was the experimental detection of physical quantities, which will result in chewing forces magnitude computation. METHOD Measurement of masticatory force from the biomechanical point of view was realized by measurement of crownwork strain occurring during loading. All measurements were performed using individually custom-built crownworks of first lower molars, because these are most mechanically loaded teeth in the natural dentition. The crownwork was pipe shaped with the physiological adjustment of upper relief, the lower part geometrically responded to an upper surface of the molar stub. Three measuring and one compensating strain gauges were placed in the central part of the crownwork made from light curing composite material. The strain measured by strain gauges and point of the occlusal contact of the first lower molar crownwork with antagonist was detected during experiment. Spider 8 multi-channel electronic measurement unit realized measurements. The magnitude and direction of loading force was computed from strain gauges measurement, location of occlusion and from known crownwork profile. Subjects were asked to chew with maximal and ordinary force. RESULTS AND DISCUSSION The strains measured of 5 subjects with natural dentition were recorded. Approximated value of ordinary chewing force reached 135 N. Resultant values computed in this pilot study suggest, that chewing forces are markedly individual and depending on chewing habits of each subject. The knowledge of mastication biomechanics may facilitate prosthetics work articulation, may permit usage of current

prosthetic and filling materials for presently marginal indications and may result in their further modifications. Also the innovation of occlusal surface morphology adjustment can influence the susceptibility to fracture of treated teeth crowns, fractures or abrasion of dentures and implant stress distribution. CONCLUSIONS The information obtained in this pilot study indicate, that magnitude of the chewing force vary by individual. The results of this study can be used to plan treatment and to reconstruct defective dentition from a masticatory point of view, as well as to validate treatment procedures. Results can also affect the design and the usage of materials for the dental implants, their position in jaws and the shape of the occlusal surface of bridgeworks and dentures. The implementation of measured quantities into mathematical models is very important from the technical viewpoint. The boundary condition for FEM models of tooth-bone or dental implant-bone interface may be developed following masticatory force measurement. REFERENCES 1. Takada K, Miyawaki S, Tatsuta M. The effects of food

consistency on jaw movement and posterior temporalis and inferior orbicularis oris muscle activities during chewing in children. Arch Oral Biol. 39(9), 793-805, 1994.

2. Mericske-Stern R., Venetz E., Fahrländer F., Bürgin W. In vivo force measurements on maxillary implants supporting a fixed prosthesis or an overdenture: A pilot study. J Prosth Dent, 84 (5), 535-547, 2002.

3. Koolstra, J.H., van Eijden, T.M.G.J. Three-dimensional dynamical capabilities of the human masticatory muscles. J Biomech 32, 145-152, 1999.

4. Zatsiorsky, V.M. Kinematics of Human Motion. Human Kinetics, Champaign, IL, 1998.

5. Bhatka R., Throckmorton G.S., Wintergerst A.M., Hutchins B., Buschang P.H. Bolus size and unilateral chewing cycle kinematics. Arch Oral Biol. 49, 559–566, 2004.

6. van der Helm F. C. T. , Veenbaas R. Modeling the mechanical effect of muscles with large attachment sites: application to the shoulder mechanism. J Biomech 24, 1151–1163, 1991.

ACKNOWLEDGEMENTS This work was funded by the Czech Ministry of Education project No. MSM 6840770012 and by the Grant Agency of the Czech Republic under project No. 106/06/0849.