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Measurement of human masticatory biomechanics—preliminary study of chewing kinematics
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Track 7. Dental Biomechanics References [1] C. Sanctuary, H.W.A. Wiskott, J. Justiz, J. Botsis, U.C. Belser. In vitro timedependent response of periodontal ligament to mechanical loading. Journal of Applied Physiology 2005; 99: 2369-2378. [2] A. Kawarizadeh, C. Bourauel, A. J~ger. Experimental and numerical determination of initial tooth mobility and material properties of the periodontal ligament in rat molar specimens. European Journal of Orthodontics 2003; 25: 569-578.
4739 We-Th, no. 8 (P62) Enamel canine surface wear evolution in bruxism E.B. Las Casas 1, F. de Souza Bastos 1, A. Batista Meireles 2, T.RM. Cornacchia 2, G.C. Dur~es de Godoy 1, V.T. Lopes Buono 1. 1School of Engineering, Federal University of Minas Gerais, Belo Horizonte, Brazil, 2School of Dentistry, Federal University of Minas Gerais, Belo Horizonte, Brazil. This work proposes a methodology to investigate the evolution of wear caused by bruxism, aiming at surface characterization and improving the understanding of wear mechanisms in teeth. Impressions were made four times, with 3 month intervals, of six worn surfaces of four canines of two bruxer men. Replicas of the teeth were prepared to obtain, through 3D contact profilometry, surface parameters, to allow following the progression of wear during a one year period. The selected parameters for the analysis were peak, nucleos and valley zone amplitudes (Sk, Spk and Svk), the hybrid parameters, surface slope (Sdq), peak curvature (Ssc) and interfacial surface (Sdr) and the peak density spatial parameter (Sds). Five of the six surfaces showed a clear pattern of reduction of the hybrid parameters. As for the amplitude parameters, while in one patient there was a tendency to reduction, in the second individual this trend was not consistent, with an increase observed in one of the surfaces in the last period. The analysis of the density parameter was not conclusive. The acting wear mechanisms were different, as expected, due to the fact that the surfaces were located at different regions of the teeth, and also due to the different level of bruxism for the two patients. Nevertheless, the analysis suggests a common trend in the evolution of canine enamel wear, more related to the form than to the amplitude of the irregularities. The obtained geometric data will be used later to validate numerical models for simplified wear prediction in teeth. 4991 Measurement of human masticatory biomechanics of chewing kinematics T. Goldmann 1, S. Konvi~kov~ 1, S. Hol~ 1, L. Himmlov~ 2. University in Prague, Prague, Czech Republic, 2Institute Prague, Czech Republic
We-Th, no. 9 (P62) preliminary study
1Czech Technical of Dental Research,
The knowledge of the human masticatory biomechanics (the direction and the magnitude of the masticatory force, kinematics of mastication) is described in the literature inconsistently; the specifications of the direction of the masticatory force were not yet published. The measurement of the masticatory force and its direction is in our case performed using an individually produced crownworks of first lower molars, because these are most mechanically loaded teeth in the natural dentition. The crownwork is the pipe shaped with the physiological adjustment of the upper relief. The crownwork is rigidly connected to the dental stub and three strain gauges are placed in the inner part of the crownwork. The magnitude and the direction of the loading force are then computed from the measured strains and the location of the occlusal contact. The masticatory force acting on each single tooth is very individual and dependent on the extensive number of variables (number of occluding teeth, type of the food, frequency of the mastication ...), so the research of the human chewing kinematics, which is the main aim of this work, is important as well. The trajectory, the ratio of amplitudes in three main anatomical directions and duration of the human mastication were registered during the processing of hard and soft aliment by use of the motion analysis method. Totally 50 patients participated in this study and all measured data were statistically evaluated. The results of this pilot study suggest that the mastication is a very individual process which can be separated up to parts of the bolus chopping, crushing and final grinding. Also aliment character influence the trajectory of jaw movements. Acknowledgement: This work was supported by the Ministry of Education project No. MSM 6840770012 and the Grant Agency of Sciences of the Czech Republic under project No. 106/06/0849 5780 We-Th, no. 10 (P62) Kinematic analysis of the chewing cycle of horses before and after dental treatment M. Niederl, C. Anen, H. Simhofer, C. Peham. University ef Veterinary Medicine, Department V, Vienna, Austria The first aim of the study was to document the masticatory cycle of the horse with aid of a kinematic system. The second intent was to evaluate the
effect of routine dental procedures, reduction of sharp enamel overgrowths and balancing of the cheek teeth, on the chewing pattern of horses. Materials and Methods: The study was performed in 5 horses of different breeds. The horses were between 8 and 20 years of age. Minor pathological changes were well tolerated. Prior to kinematic analysis, 9 spherical markers were glued to the skin of the head at defined anatomical landmarks: rostral edge of the facial crest, temporal bone in close proximity to the temporo-mandibular joint, midline on the frontal bone and on the nasal bone at the level of the Incisura nasoincisiva, Incisura vasorum and the Sutura intermandibularis. Measurements were performed using the kinematic system with 6 cameras (Motion Analysis Corp.). In order to exclude any external influences, three measurements were performed before and after dental correction in the same location under standardised conditions. Each horse was fed a standardised ration of high quality hay. A minimum of fifteen masticatory cycles was recorded and analysed. The data was transformed in a segmental coordinate system on the head. Chewing cycles were separated and normalized to 100%. The initial point of the masticatory cycle was defined at the maximum opening of the mouth via the sutura intermandibularis marker. Results: The mean maximum lateral excursion of the Sutura intermandibularis marker was 5.8cm (SD 0.9). The mean maximum vertical excursion (opening) of the Sutura intermandibularis marker was 4.3cm (SD 0.03). The mean Duration of the Chewing Cycle (DCC) changed significantly (p < 0.05) after dental correction from 0.69 s (SD 0.03) to 0.66 s (SD 0.03). Conclusion: We showed that a kinematic system is suitable to document the chewing motion in detail. Clinical relevance: In further studies we intend to test the motion analysis system as an additional diagnostic- and therapy control method in equine dental patients. 6538 We-Th, no. 11 (P62) A computational study on NiTi rotary endodontic instruments S. Necchi 1, L. Petrini 1, S. Taschieri 2, G. Dubini 1. 1LABS - Laboratory of Biological Structure Mechanics, Department of Structural Engineering, Politecnico di Milano, Milan, Italy, 2Department of Odontology, Galeazzi Institute, University of Milan, Italy Introduction: In the late 1980s, the Nickel-Titanium alloy (NiTi) was introduced in endodontics: its ability of undergoing great strains (up to 10-15%) in loading cycles without showing a permanent deformation (the well known "superelasticity") suggested to employ NiTi to produce instruments for the treatment of the tooth root canal. Indeed the NiTi files show a higher flexibility than the stainless steel ones. Notwithstanding the use of NiTi instruments is considered the main novelty in the recent evolution of the root canal shaping strategies, up to now a very limited number of numerical and experimental tests has been performed to investigate deeply their performances and drawbacks. The aim of this study is the computational analysis of the mechanical behaviour of superelastic NiTi rotary endodontic instruments. Materials and methods: 3D models of different types of instruments (i.e. ProTaper and SystemGT ®) were created using the software Rhinoceros 2.0. The models were meshed into tetrahedral elements using the software Gambit 2.1.3. The commercial code ABAQUS/Standard version 6.5-1 was chosen to perform the numerical simulations. Some working conditions of the instruments were simulated: both rotational and translational movements into a conical and angulated canal were imposed to the files. Contact and friction between the instruments and the dentinal walls were considered. Comparative analyses were performed considering two different constitutive models for the instruments: the NiTi alloy model, developed by the authors, and the ABAQUS stainless steel model. Results and Conclusions: The performed computational analyses have highlighted the expected superiority of NiTi alloy with respect to stainless steel in terms of flexibility and recovery of the undeformed shape as well as the important role of the geometry in determining the stresses distribution in the body and in the cutting edges area. These results are intended preliminary to the design of a new high performance instrument.
Track 7. Dental Biomechanics References [1] C. Sanctuary, H.W.A. Wiskott, J. Justiz, J. Botsis, U.C. Belser. In vitro timedependent response of periodontal ligament to mechanical loading. Journal of Applied Physiology 2005; 99: 2369-2378. [2] A. Kawarizadeh, C. Bourauel, A. J~ger. Experimental and numerical determination of initial tooth mobility and material properties of the periodontal ligament in rat molar specimens. European Journal of Orthodontics 2003; 25: 569-578.
4739 We-Th, no. 8 (P62) Enamel canine surface wear evolution in bruxism E.B. Las Casas 1, F. de Souza Bastos 1, A. Batista Meireles 2, T.RM. Cornacchia 2, G.C. Dur~es de Godoy 1, V.T. Lopes Buono 1. 1School of Engineering, Federal University of Minas Gerais, Belo Horizonte, Brazil, 2School of Dentistry, Federal University of Minas Gerais, Belo Horizonte, Brazil. This work proposes a methodology to investigate the evolution of wear caused by bruxism, aiming at surface characterization and improving the understanding of wear mechanisms in teeth. Impressions were made four times, with 3 month intervals, of six worn surfaces of four canines of two bruxer men. Replicas of the teeth were prepared to obtain, through 3D contact profilometry, surface parameters, to allow following the progression of wear during a one year period. The selected parameters for the analysis were peak, nucleos and valley zone amplitudes (Sk, Spk and Svk), the hybrid parameters, surface slope (Sdq), peak curvature (Ssc) and interfacial surface (Sdr) and the peak density spatial parameter (Sds). Five of the six surfaces showed a clear pattern of reduction of the hybrid parameters. As for the amplitude parameters, while in one patient there was a tendency to reduction, in the second individual this trend was not consistent, with an increase observed in one of the surfaces in the last period. The analysis of the density parameter was not conclusive. The acting wear mechanisms were different, as expected, due to the fact that the surfaces were located at different regions of the teeth, and also due to the different level of bruxism for the two patients. Nevertheless, the analysis suggests a common trend in the evolution of canine enamel wear, more related to the form than to the amplitude of the irregularities. The obtained geometric data will be used later to validate numerical models for simplified wear prediction in teeth. 4991 Measurement of human masticatory biomechanics of chewing kinematics T. Goldmann 1, S. Konvi~kov~ 1, S. Hol~ 1, L. Himmlov~ 2. University in Prague, Prague, Czech Republic, 2Institute Prague, Czech Republic
We-Th, no. 9 (P62) preliminary study
1Czech Technical of Dental Research,
The knowledge of the human masticatory biomechanics (the direction and the magnitude of the masticatory force, kinematics of mastication) is described in the literature inconsistently; the specifications of the direction of the masticatory force were not yet published. The measurement of the masticatory force and its direction is in our case performed using an individually produced crownworks of first lower molars, because these are most mechanically loaded teeth in the natural dentition. The crownwork is the pipe shaped with the physiological adjustment of the upper relief. The crownwork is rigidly connected to the dental stub and three strain gauges are placed in the inner part of the crownwork. The magnitude and the direction of the loading force are then computed from the measured strains and the location of the occlusal contact. The masticatory force acting on each single tooth is very individual and dependent on the extensive number of variables (number of occluding teeth, type of the food, frequency of the mastication ...), so the research of the human chewing kinematics, which is the main aim of this work, is important as well. The trajectory, the ratio of amplitudes in three main anatomical directions and duration of the human mastication were registered during the processing of hard and soft aliment by use of the motion analysis method. Totally 50 patients participated in this study and all measured data were statistically evaluated. The results of this pilot study suggest that the mastication is a very individual process which can be separated up to parts of the bolus chopping, crushing and final grinding. Also aliment character influence the trajectory of jaw movements. Acknowledgement: This work was supported by the Ministry of Education project No. MSM 6840770012 and the Grant Agency of Sciences of the Czech Republic under project No. 106/06/0849 5780 We-Th, no. 10 (P62) Kinematic analysis of the chewing cycle of horses before and after dental treatment M. Niederl, C. Anen, H. Simhofer, C. Peham. University ef Veterinary Medicine, Department V, Vienna, Austria The first aim of the study was to document the masticatory cycle of the horse with aid of a kinematic system. The second intent was to evaluate the
effect of routine dental procedures, reduction of sharp enamel overgrowths and balancing of the cheek teeth, on the chewing pattern of horses. Materials and Methods: The study was performed in 5 horses of different breeds. The horses were between 8 and 20 years of age. Minor pathological changes were well tolerated. Prior to kinematic analysis, 9 spherical markers were glued to the skin of the head at defined anatomical landmarks: rostral edge of the facial crest, temporal bone in close proximity to the temporo-mandibular joint, midline on the frontal bone and on the nasal bone at the level of the Incisura nasoincisiva, Incisura vasorum and the Sutura intermandibularis. Measurements were performed using the kinematic system with 6 cameras (Motion Analysis Corp.). In order to exclude any external influences, three measurements were performed before and after dental correction in the same location under standardised conditions. Each horse was fed a standardised ration of high quality hay. A minimum of fifteen masticatory cycles was recorded and analysed. The data was transformed in a segmental coordinate system on the head. Chewing cycles were separated and normalized to 100%. The initial point of the masticatory cycle was defined at the maximum opening of the mouth via the sutura intermandibularis marker. Results: The mean maximum lateral excursion of the Sutura intermandibularis marker was 5.8cm (SD 0.9). The mean maximum vertical excursion (opening) of the Sutura intermandibularis marker was 4.3cm (SD 0.03). The mean Duration of the Chewing Cycle (DCC) changed significantly (p < 0.05) after dental correction from 0.69 s (SD 0.03) to 0.66 s (SD 0.03). Conclusion: We showed that a kinematic system is suitable to document the chewing motion in detail. Clinical relevance: In further studies we intend to test the motion analysis system as an additional diagnostic- and therapy control method in equine dental patients. 6538 We-Th, no. 11 (P62) A computational study on NiTi rotary endodontic instruments S. Necchi 1, L. Petrini 1, S. Taschieri 2, G. Dubini 1. 1LABS - Laboratory of Biological Structure Mechanics, Department of Structural Engineering, Politecnico di Milano, Milan, Italy, 2Department of Odontology, Galeazzi Institute, University of Milan, Italy Introduction: In the late 1980s, the Nickel-Titanium alloy (NiTi) was introduced in endodontics: its ability of undergoing great strains (up to 10-15%) in loading cycles without showing a permanent deformation (the well known "superelasticity") suggested to employ NiTi to produce instruments for the treatment of the tooth root canal. Indeed the NiTi files show a higher flexibility than the stainless steel ones. Notwithstanding the use of NiTi instruments is considered the main novelty in the recent evolution of the root canal shaping strategies, up to now a very limited number of numerical and experimental tests has been performed to investigate deeply their performances and drawbacks. The aim of this study is the computational analysis of the mechanical behaviour of superelastic NiTi rotary endodontic instruments. Materials and methods: 3D models of different types of instruments (i.e. ProTaper and SystemGT ®) were created using the software Rhinoceros 2.0. The models were meshed into tetrahedral elements using the software Gambit 2.1.3. The commercial code ABAQUS/Standard version 6.5-1 was chosen to perform the numerical simulations. Some working conditions of the instruments were simulated: both rotational and translational movements into a conical and angulated canal were imposed to the files. Contact and friction between the instruments and the dentinal walls were considered. Comparative analyses were performed considering two different constitutive models for the instruments: the NiTi alloy model, developed by the authors, and the ABAQUS stainless steel model. Results and Conclusions: The performed computational analyses have highlighted the expected superiority of NiTi alloy with respect to stainless steel in terms of flexibility and recovery of the undeformed shape as well as the important role of the geometry in determining the stresses distribution in the body and in the cutting edges area. These results are intended preliminary to the design of a new high performance instrument.