Analysis For Mastication Process Based On Numerical Simulation

Oral processing is both a physiological process controlled by central nerve systemand a physical process modulated by mechanical and geometrical properties of thefood. Study on mastication process assists in understanding mastication mechanism,interpreting enjoyment and standards when consuming food, evaluating texture toprovide a useful knowledge to food industries, and developing high-quality foods tomeet consumers appeal, particularly for some specific consumers groups such asjunior, senior citizens and denture wearers. Due to complexity of mastication andchanges of mechanical properties of food during chewing, there is still difficult instudying interaction between human mastication process and food fracture. A newtechnology for researching mastication process should have been necessarilydiscussed, because previous hardware and software techniques can’t completelyanalyze all mechanical behaviors like food bending, breaking, blending andtransforming in mouth. Main purpose of this study was to evaluate food texture,improve mastication efficiency, and reveal the relationships between food propertiesand mastication process, by constructing simulation models of mastication andanalyzing dynamical process of food particles and the effects of mastication styles onresults. Meanwhile, flowing process of food was simulated in oral in order to underpinmechanisim design of chewing simulator. The main contents in this paper are asfollowing:(1)Bionic identer was developped by simulating properties of human masticatorymuscles. Bionic identers originated from the first upper and lower molars weredeveloped and created using reverse engineering technology, after scanning structruesof maxillary, mandible and dentition of a heathy man through Computed TomographyScanner. Meanwhile, electromyographies(EMG) of human masticatory musclesduring chewing different foods were captured, changing laws of myoelectricitysignals were analyzed, and then eigenvalue were extracted. Based on data obtainedbefore, a correlation analysis was performed between variable characteristics ofmasticatory activations and food texture properties from bionic identers, showing thataverage osculation degree which exsited among texture properties from bionicidenters and laws of masticatory activations was9.3%higher than universal indenter.Thus, it is indicated that bionic identers can reflect texture properties of food better. (2) Effects of mandible motion during mastication on crushing of food materialswere studied by Finite Elements Methods(FEM). Masticatory motions, based ontemporomandibular articulation movement theory and modern occlusion theory, couldbe classified into3simplified modes: cutting mode, compressiong mode and grindingmode. Under conditions in which mandible had been assumed as a rigid body andmaxillary as reference substance, mandible motions could be divided into uniformmotion and3different variable motions. Furthermore, mastication process were,separately, simulated in different motion laws in3modes where incisors were set asboundary for cutting mode, and first molars for both compressing and grinding modes.Stress distribution on marterials surface after chewing was studied by joint strengththeory. It was shown that grinding mode generated greater shear stress and Misesstress, and achieved better crushing effects in elastic and tough foods, comparing withthe other2modes. The greatest primary stress existed in cutting mode and wassuitable for biting brittle foods, while the bigger chewing rate in griding mode was,the better the crushing of food realised. Besides, shear stress and Mises stress wouldbe generated much greater when acceleration varied stably, however variation ofacceleration affected mastication comparatively weak. Simulation results had beenverified by effects of variaration in speed of bionic identers on materials crushing.(3) Mastication broken model was created by discrete elements method (DEM),and used to simulate dynamic mastication process and analyze changes in morphologyand mechanical behaviors of food during chewing. Phenomenon of crushing ofspherical foods during mastication was simulated by bonding model selected fromDEM, which assumed micro-paticles with the same semidiameters to form a sphericalbolus to replace spherical food particles. In assumed spherical bolus, bonding keyexists among any adjacent micro-particles. It is needed to set corresponding bondingparameters such as bonding semidiameter, normal stiffness, shear stiffness, criticalnormal stress and critical shear stress for analyzing fracture happening betweenparticles. When food is sufferred from force of chewing boundary (identers), fracturehappened to food if both of normal stress and shear tress between particles are morethan the critical values set before and bonding key is disrupted by force. Locationinformation of every micro-particle in bolus should be caculated ahead: formationprocess of bolus by pressing was simulated by DEM in order to obtain accuratecoordinate data. After that, crushing process can be simulated by mastication brokenmodel including dynamic link library files (DLL files) into which all information ofparticles location is added as a data files. Results of mastication broken model were verified by crush trial of bionic identers. Degree of correlation between simulationforce of materials and experimental values was tested by linear regression model, andthe coefficient of determination were all above87%, implying that it was DEM thatcan be use to analyze mastication process. Samples were ranked by texture usingsimulation and sensory evaluation, and it showed simulation results of masticationbroken model were the same as sensory evaluation results, implying that sensoryevaluation can be replaced by mastication broken model to evaluate food texture.(4) Influences of the geometric on food texture properties were studied byconstructing food bolus model with different geometrical shapes and by simulatingmastication broken process for the same food with different shapes. Masticationbroken model was applied to crush the simulated bolus which was formed by pressingthrough different boundaries in DEM software and in which location information ofeach micro-particle had been obtained before. By DEM analysis it was shown that thebigger size of the food with the same section but different thickness was, the higherthe hardness, springiness and fracture energy were. Besides, hardness, resilience,cohesiveness, springiness, and fracture energy varied significantly in food with thesame thickness and volumn but different shapes, and cylinder were minimum infracture energy and easy to be disrupted. A texture measurement experiment wasperformed by assembling bionic identers on texture analyzer to verify simulationresults from DEM, and it was discovered that simulation values were in line with trialresults, providing a new theory for selecting shapes when evaluating texture.(5) A bionic tongue block was designed for chewing simulator. Gradient ofbionic tongue block was opitimized through DEM by simulating the dynamicprocesing in which materials slipped out of tongue surface. Based on models ofdentition, maxillary and mandible that were created by reverse engineering, thetongue model was designed to be suitable for dentition: symmetry slope with highpoint and low root. The dynamic process that materials slipped from point to molaralong tongue was simulated by changing gradient and an optimal tongue model wasdeveloped with better slipping efficiency and to be produced as an entity. The optimaltongue entity, with horizontal tilt angle10°and vertical tilt angle20°, was used inchewing simulator, enhancing the work efficiency of the chewing simulator.Overall, it provides a further understanding of relationship between masticationprocess and mechanical properties of foods, based on study about mastication process.Both of FEM and DEM can be used in researching mastication process, while, FEM isused for analyzing deformation process before food fracturing, and DEM for broken process. Association of both methods realizes and quantizes simulation of dynamicchewing process of food in mouth, provides theory for mastication mechanism,connects texture evaluation, mechanics and fracture properties together, and presents anovel evaluation method for food texture.