Masticatory Movements Research Articles

Effects of nasal obstruction on prefrontal cortex activities during chewing

ABSTRACT Purpose: This study was conducted to clarify the effects of experimentally induced nasal obstruction (NO) on prefrontal activation and jaw movement activities, as well as feelings of discomfort and dyspnoea during chewing. Methods and materials: Eighteen healthy volunteers were enrolled as subjects. The levels of awareness of discomfort and sense of dyspnoea with nasal breathing (NB) and NO were determined using a visual analogue scale (VAS) following chewing and imagery tasks. Masticatory movements were analysed for masticatory path width, cycle duration, masticatory velocity, number of masticatory cycles, and duration of pre-swallowing phase during mastication in the subjects with establishment of NO and NB. An FNIRS device (Hb131S, astem Inc., Japan) was used to measure prefrontal cortex activities. Results: Discomfort and feelings of dyspnoea under the NO condition were significantly increased as compared with NB. Also, cycle duration with NO was significantly increased as well as the number of masticatory cycles, whereas those in the pre-swallowing phase were significantly decreased as compared to NB. Furthermore, prefrontal activities during chewing with NO were significantly decreased as compared to NB. Conclusion: These results indicate that nasal obstruction during chewing may induce a decline in prefrontal activities, accompanied with deterioration comfort and dyspnoea, and modulated jaw movement activities.

Distinguish fatty acids impact survival, differentiation and cellular function of periodontal ligament fibroblasts

Alveolar bone (AB) remodeling is necessary for the adaption to mechanical stimuli occurring during mastication and orthodontic tooth movement (OTM). Thereby, bone degradation and assembly are strongly regulated processes that can be altered in obese patients. Further, increased fatty acids (FA) serum levels affect bone remodeling cells and we, therefore, investigated whether they also influence the function of periodontal ligament fibroblast (PdLF). PdLF are a major cell type regulating the differentiation and function of osteoblasts and osteoclasts localized in the AB. We stimulated human PdLF (HPdLF) in vitro with palmitic (PA) or oleic acid (OA) and analyzed their metabolic activity, growth, survival and expression of osteogenic markers and calcium deposits. Our results emphasize that PA increased cell death of HPdLF, whereas OA induced their osteoblastic differentiation. Moreover, quantitative expression analysis of OPG and RANKL revealed altered levels in mechanically stimulated PA-treated HPdLF. Furthermore, osteoclasts stimulated with culture medium of mechanical stressed FA-treated HPdLF revealed significant changes in cell differentiation upon FA-treatment. For the first time, our results highlight a potential role of specific FA in the function of HPdLF-modulated AB remodeling and help to elucidate the complex interplay of bone metabolism, mechanical stimulation and obesity-induced alterations.

咀嚼の自動運動が保持されたFoix-Chavany-Marie症候群による嚥下障害の1 例

咀嚼の自動運動が保持されたFoix-Chavany-Marie症候群による嚥下障害の1 例

Effect of mandibular advancement device on the stomatognathic system in patients with mild-to-moderate obstructive sleep apnoea-hypopnoea syndrome.

ObjectiveThis study was conducted to evaluate the changes of temporomandibular joints (TMJs) through magnetic resonance imaging (MRI) scanning and the electrical changes in mandibular movement and masticatory muscle surface of mild‐to‐moderate obstructive sleep apnoea‐hypopnoea syndrome (OSAHS) patients before and after treatment with mandibular advancement device (MAD).MethodsThis was a single‐centre, prospective study recruiting OSAHS patients undergoing treatment with MAD in Department of Stomatology, Yannan Hospital, Kunming, China. Patients were recruited from February 2015 to October 2015, and TMJ changes were observed in MRI scanning before and after 18 months of treatment with MAD in cohort 1. The second cohort of the patients were recruited from January 2014 to September 2015 and electrical changes in mandibular movement and masticatory muscle surface of patients before and after 6 months of treatment with MAD.ResultsIn the cohort 1, TMJ changes analysed through MRI scanning, before and after 18‐month treatment with MAD, there was no significant deviation in the angle of joint disc position. A minor change in the position relationship between condylar process, articular disc and articular fossa but not significant was observed. There was no significant difference in the shape and magnitude of mandibular incision edge movement, percussion movement, masticatory movement and condylar central trajectory among the recruited OSAHS patients, before and after 6 months of MAD treatment as analysed through electromyography.ConclusionIn this study, from the results it was evident that the effect of MAD on the stomatognathic system of OSAHS patients is minimal.

Short communication: Detection of mastication speed during rumination in cattle using 3-axis, neck-mounted accelerometers and fast Fourier transfer algorithm

There have been limited reports on mastication speed during cattle rumination. The objective of this study was to establish a method to detect mastication speed based on data obtained during rumination through the use of a 3-axis accelerometer attached to the neck. A 3-axis accelerometer was attached to 6 dry Holstein cattle. When rumination behavior was observed, the accelerometer and the high-speed camera simultaneously recorded acceleration at the neck and moving image of the head movement. Based on the number of mastication movements recorded on video, mastication speed A was calculated. Data obtained from the 3-axis accelerometer were analyzed with fast Fourier transfer algorithm and identified as mastication speed B. The vibration of the neck recorded in the accelerometer during rumination was considered as mastication movement. Using Bland-Altman plot analysis, the mean difference between mastication speed A and mastication speed B was 0.041 s/bite, and the 95% limits of agreement ranged from -0.080 to 0.161. Since mastication movement occurred periodically, it was possible to detect the movement using spectrum analysis, as mastication speed B. Although there were some differences between calculated speeds and speeds obtained from spectrum analysis, there was clinical compatibility between mastication speed A and B. This study showed the feasibility of establishing a detection method for mastication speed during rumination, which might provide a basic procedure for studying the purpose of mastication and the variable factors involved.

Symmetry of mandibular movements: A 3D electromagnetic articulography technique applied on asymptomatic participants

Statement of problemAsymmetries in mandibular movements (MMs) can be found in patients with some temporomandibular joint disorders, condylar fracture, or after orthognathic or orthodontic surgery. Quality and symmetry of the MMs should be recorded and analyzed. However, methods for this purpose are limited. PurposeThe purpose of this clinical study was to determine the symmetry of MMs on asymptomatic participants by applying an innovative technique based on 3D electromagnetic articulography. Material and methodsThe symmetry of MMs was studied in 16 fully dentate participants (8 men and 8 women). A 3D electromagnetic articulograph was used to register MM by placing a sensor on the interincisal midline of the mandible. The border movements related to the frontal (FP), sagittal (SP), and horizontal (HP) polygons of the Posselt envelope of motion were recorded, as well as masticatory movements. Digital data processing was applied to calculate the trajectory and ranges of mandible displacement, area of the right and left sectors of FP and HP, similarity index between the right and left sectors of FP and HP, and orientation of the individualized masticatory cycles. The Shapiro-Wilk statistical test was used to determine the normality of the sample. To compare the characteristics of the right and left sectors of the polygons, a paired-samples t test (normal distributions) and Wilcoxon test for paired samples (non-normal distributions) were applied (α=.05). ResultsNo statistically significant differences were found between the right and left sectors of the frontal and horizontal polygons in terms of trajectory (FP, P=.408; HP, P=.417), ranges of movement (FP, P=.736; HP, P=.650), areas (FP, P=.736; HP, P=.233), or orientation of the cycles (P=.506). The similarity index between the morphology of the right and left sectors of the polygons was 68 ±12% for the FP and 67 ±11% for the HP. The areas, trajectories, and ranges had similar values, but they had a different morphology on each side of the polygons. Regarding masticatory cycles, a balanced distribution was observed in terms of their orientation. ConclusionsThe technique used allowed the assessment of symmetry of MM on asymptomatic participants. The evaluated parameters maintain similar values at both left and right sides; however, a different morphology of the trajectories and areas was observed.

In vitro wear characteristics of a nano-hydroxyapatite filled dental resin composite under two-body wear condition

The aim of this work is to fabricate and characterize the Bis-GMA-based nano-hydroxyapatite (n-HAP) filled dental resin composites (DRCs) which comply with oral tribological behavior. The seven series (i.e., 0, 4, 8, and 12 wt%) of each MPTS ((3-methacryloxypropyl) trimethoxysilane)- and APTES (3-aminopropyl)-treated n-HAP-filled composites were prepared. These DRCs were characterized for void contents, vickers microhardness, and volumetric wear under dynamic working conditions (normal load, speed, and temperature) in artificial saliva medium. In order to perform the volumetric wear experiment, the masticatory movement was simulated by using a dental wear simulator in eight profile motion. The wear tests were conducted as per steady-state and Taguchi (L16) orthogonal array; further, ANOVA analysis was employed to define the contribution of each considered process parameter. The findings of the experiment and ANOVA result reveal that n-HAP filler content has a greater contribution (95%) in improving the wear resistance ability of DRCs. In concerned with the unfilled dental material, 12 wt% of MPTS- and APTES-modified n-HAP-filled DRCs shows maximum microhardness [i.e., 34.10 Hv (39.52% improvement) for DRCs-12M and 33.32 Hv (36.33% improvement) for DRCs-12A] and minimum volumetric wear in the artificial saliva medium. According to the orthogonal setting of the design of the experiment, volumetric wear of dental composite was improved by 15.164% for DRCs-12M (i.e., A4B2C3D1) and 17.647% for DRCs-12A (i.e., A4B3C2D4) under two-body wear condition (artificial saliva medium). The W-SEM analysis after 20,000 mastication cycles in artificial saliva medium indicates that wear surfaces of DRCs were predominantly affected by the abrasion and adhesion phenomenon.

Study on the correlation between the mandibular masticatory muscle movement and sleep tooth wear

To investigate the correlation between the clinical diagnostic criteria of sleep bruxism and the frequency of mandibular movements during sleep. Video polysomnography was used to record 20 healthy adults with at least one of the following clinical symptoms and signs: 1) report of frequent tooth grinding; 2) tooth wear and dentin exposure with at least three occlusal surfaces; 3) masticatory muscle symptoms in the morning; 4) masseter muscle hypertrophy. The rhythmic masticatory muscle activity (RMMA) and isolated tonic activity were scored to compare the correlations with clinical symptoms and signs. Finally, the incidence of temporomandibular disorders (TMD) was investigated in patients with isolated tonic and RMMA subjects. Among the 20 subjects, RMMA events were observed (5.8±3.1) times·h⁻¹ and isolated tonic episodes were observed (2.1±0.9) times·h⁻¹. The frequency of RMMA events was significantly greater in the patients with acoustic molars than in those without (P<0.05). Similarly, the frequency of RMMA events was significantly greater in the patients with tooth attrition than in those without (P<0.05). However, no difference was observed between the occurrence of RMMA and the symptoms of masticatory muscles or masseter hypertrophy in the morning. The incidence of TMD was significantly higher in the patients with RMMA than in the isolated tonic patients. The clinical symptoms and signs often used to diagnose sleep bruxism are different clinical and physiological mandibular movements during sleep. RMMA during sleep can reflect the occurrence of tooth attrition and the high risk of TMD.

A reassessment of the genus Groeberia Patterson, 1952 (Mammalia, Metatheria): functional and phylogenetic implications

With two recognized species, the extinct (late Eocene) Groeberia is periodically at the centre of systematic disputes. On the basis of its best-preserved specimen, we describe in detail the dental and functional morphology of the masticatory apparatus of Groeberia minoprioi. A review of its dental anatomy indicates that Groeberia has a tribosphenic molar pattern which confirms its therian affinities. Its dental formula of I2/1; C1/1; P3/1; M4/4 is compatible with the usual metatherian set of three premolars and four molars in the upper dentition, and with the common ‘pseudodiprotodont’ lower postcanine formula of one premolar (p3) and four molars. A cladistic analysis resulted in the inclusion of Groeberia among australidelphian metatherians, clustering with vombatiform diprotodontians in the strict consensus tree; however, these affinities require further testing. The functional morphology of the masticatory apparatus suggests distinct incisive and chewing phases. The incisive stroke was followed by a power stroke with a combination of proal and ectental motion of the jaw. Integrating the results of masticatory movements, occlusal tooth wear, infraorbital foramen size, and body mass estimations (90.2 g for G. pattersoni and 216.3 g for G. minoprioi), we suggest an omnivorous diet with a preference for plant material, like that characterizing living potoroids.

Two mastication tests used in children with down syndrome: A feasibility study.

Children with Down syndrome can have problems with chewing and swallowing. However, no objective tests are available that give information about the efficiency and endurance of mastication. In this study, the feasibility of two mastication tests is studied by answering two research questions: are the Test of Mastication and Swallowing of Solids and the 6-min mastication test feasible to use in children with Down syndrome? Do these tests give information about the mastication efficiency and endurance in these children? A total of 24 (4-18years) children with Down syndrome participated. The collected variables in the Test of Mastication and Swallowing of Solids were masticatory time, discrete bites, masticatory cycles and number of swallows per cracker. The inter-rater reliability of these variables was tested. Collected variables in the 6-min mastication test were total masticatory cycles and percentage difference between minutes 1 and 6. Qualitative ratings of masticatory movements were made. In both tests, a comparison with a typically developing group was made. In both tests, a total of 87.5% of the children completed the test. Both tests are feasible for children with Down syndrome with language comprehension skills of 3years and over. The tests give information about the function and endurance during mastication in children with Down syndrome. The results showed that children with Down syndrome do not have endurance problems during mastication, but there is a lack of efficiency in mastication.

Cervical spine range of motion, posture and electromyographic activity of masticatory muscles in temporomandibular disorders

Abstract Introduction: Temporomandibular joint disorders (TMD or TMJD) involve clinical problems and symptoms affecting the temporomandibular joint (TMJ) and associated structures. The temporomandibular joints are anatomically connected to the cervical region, where cervical spine movements occur simultaneously to masticatory muscle activation and jaw movements. Objective: Our study sought to assess the relationship between the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD), surface electromyography (sEMG) of the masticatory muscles, posture and cervical flexibility in women with TMD. Method: Fifty women with an average age of 27.0 ± 6.37 years, diagnosed with TMD according to RDC/TMD, were assessed for craniocervical posture, cervical flexibility and sEMG of the masticatory muscles. Results: There were no differences in jaw function limitations, depression, pain level and its interference in work ability and daily activities, posture and sEMG between TMD diagnoses or between muscle classification (p &gt; 0.05). Depression scores were higher among participants with biarticular dysfunction (p = 0.023). The group with bruxism exhibited a higher pain level at assessment (p = 0.001) and a greater reduction in work ability (p = 0.039). Subjects with muscular and mixed TMD showed less cervical rotation to the right when compared with those with articular TMD. Conclusion: There was no difference in posture or sEMG values for TMD diagnoses, joint and muscle dysfunctions and the presence of bruxism. Muscle dysfunction is associated with reduced cervical rotation to the right. Jaw function limitations did not interfere in posture or sEMG and depression was associated with pain.

Systematic review of chewing simulators: Reality and reproducibility of in vitro studies.

BackgroundThe aim of this systematic review was to analyze the types of human chewing simulator described in scientific literature. Material and MethodsAn electronic search was conducted in the databases PubMed, Embase and Scopus. The search strategy included 10 search terms: “in vitro”; “dental materials”; “shear strength”; “fatigue fracture”; “bite force”; “prosthetic materials”; “chewing simulator”; “chewing machine”; “simulated mastication”; and “dental wear simulator.” Two researchers worked independently to assess the titles and abstracts of the articles. The quality of the in vitro trials selected was evaluated by means of the Consolidated Standards of Reporting Trials scale. ResultsThe electronic search identified 80 articles related to the topic of interest. After reading the full texts, ten works were selected. The articles focused mainly on the design of chewing simulators. Most of them were considered of moderate quality. Regarding the characteristics that an ideal chewing simulator should encompass, the devices described in articles varied greatly in terms of movement, periodontal ligament simulation, force sensors, and the materials tested. ConclusionsNo chewing simulator offers all the characteristics necessary to reproduce human masticatory movements and forces under the humidity and pH conditions of the oral cavity. A simulator that encompasses all these characteristics would make it possible to standardize trials involving simulated mastication. Key words:In vitro, dental materials, dental wear simulator.

КЛІНІЧНИЙ СТАН КОРІВ МОЛОЧНОГО НАПРЯМУ ПРОДУКТИВНОСТІ ЗА ТЕПЛОВОГО СТРЕСУ

Abstract. Cows with high dairy productivity differ from other animals by the excess heat generation during food fermentation in the rumen and during milk production and the milk giving. In hot weather, heat output in dairy cows is insufficient, leading to the development of heat stress. At the average daily ambient temperature of 24.75 ± 1.30 °C the tunnel ventilation in the cowshed copes with its functions and provides optimal sanitary and hygienic parameters. This allows to provide comfort zone for cows (THI 68 to 71), without not to impairing their production figures and receive extra-class milk. At an average daily ambient temperature of 28.5 ± 0.47 - 29.6 ± 0.30 °C the tunnel ventilation in the cowshed does not cope with its functions and cows are in a state of moderate or severe heat stress. The clinical condition of cows under such conditions is characterized by a significant increase in pulse and respiratory votes, prolongation of the period of standing on their feet, the reduction of cud chewing period, masticatory movements and slowing down of the cud chewing process. At the demonstrate average daily ambient temperature of 29.6 ± 0.30 °C milk quality indicators a pronounced decreasing tendency compared to those that are obtained from cows subjected to moderate thermal overheating and which are significantly lower than control data (cows in the comfort period). In almost half of the cows under severe heat stress the milk fat content is 3.05 % and protein content is 3.60 %; the number of somatic cells in the milk from these cows, increase by 10 % compared to the vote in the milk from cows subjected to the moderate heat stress and by 42 % (P ≤ 0.001) in the milk of cows that are kept under comfortable conditions. Keywords: chewing, masticatory period, masticatory movements, body temperature, pulse, respiration, somatic cell count (CSC), high-yielding dairy cows, heat stress, temperature and humidity index, thermoregulation, cardiovascular failure

Architecture and design of a robotic mastication simulator for interactive load testing of dental implants and the mandible

Statement of problemDetermination of interactive loading between a dental prosthesis and the host mandible is essential for implant prosthodontics and to preserve bone. PurposeThe purpose of this study was to develop and evaluate a robotic mastication simulator to replicate the human mastication force cycle to record the required interactive loading using specifically designed force sensors. Material and methodsThis robotic mastication simulator incorporated a Stewart parallel kinematic mechanism (PKM) controlled in the force-control loop. The hydraulically operated PKM executed the wrench operation, which consisted of the combined effect of forces and moments exhibited by the mastication process. Principal design features of this robotic simulator included PKM kinematic modeling, static force analysis to realize the masticatory wrench characteristics, and the architecture of its hydraulic system. Additionally, the design of a load-sensing element for the mandible and implant interaction was also incorporated. This element facilitated the quantification of the load distribution between implants and the host bone during the masticatory operation produced by the PKM. These loading tests were patient-specific and required separate artificial mandibular models for each patient. ResultsThe simulation results demonstrated that the robotic PKM could replicate human mastication. These results validated the hydraulic system modeling for the required range of masticatory movements and effective forces of the PKM end-effector. The overall structural design of the robotic mastication simulator presented the integration of the PKM and its hydraulic system with the premeditated load-recording mechanism. ConclusionsThe developed system facilitated the teeth-replacement procedure. The PKM accomplished the execution of mastication cycle involving 6 degrees of freedom, enabling any translation and rotation in sagittal, horizontal, and vertical planes. The mechanism can simulate the human mastication cycle and has a force application range of up to 2000 N. The designed load-sensing element can record interactive forces within the range of 200 N to 2000 N with fast response and high sensitivity to produce a robotic mastication simulator with custom-made modules.

Relation of dietary preference to masticatory movement and masticatory exercises in Japanese children

ObjectiveModern Japanese children have decreased masticatory function, which can be explained by the dietary change to soft foods. In earlier studies involving children with mixed dentition, masticatory exercises were shown to improve masticatory function and modify dental arch growth. Grinding type of mastication with a wide path reportedly increases lateral growth of the dental arch. This study aimed to assess the relationship between masticatory movements and dietary preference, and how masticatory exercises affected masticatory movement during Hellman’s dental stages IIA to IIC (period of first molar eruption). DesignIn 64 Japanese pre-school children, we measured masticatory movements with foods of five different levels of hardness and investigated the dietary preference for hard foods through a questionnaire. Participants were also required to perform masticatory exercises. Masticatory movements and dietary preference for hard foods were assessed at the start (T1), conclusion (T2), and after six months of exercises (T3). Participants were allocated to Wide and Narrow groups at T1 based on their masticatory path width. ResultsBaguettes and bananas resulted in the widest and narrowest masticatory paths, respectively, at T1. Results of questionnaire indicated that those eating hard foods had a broad grinding type of masticatory path. Masticatory exercises significantly widened the masticatory path in the Narrow group demonstrating that masticatory exercises help children learn to chew with grinding strokes. Moreover, the masticatory path remained stable on assessment at T3 (six-month follow-up). ConclusionsMasticatory exercises are effective in children who are unable to grind hard foods, affecting their dietary preferences.

Heart rate changes associated with rhythmic masticatory muscle activities and limb movements in sleep bruxers: Preliminary findings

ABSTRACT Objective: To investigate the relationship of rhythmic masticatory muscle activities (RMMAs) and limb movements (LMs) with heart rate (HR) acceleration. Methods: The amplitude and duration of HR increases, the time to reach peak HR associated with RMMAs/LMs during sleep, duration of movement events, and their relationships with cortical arousal levels were determined in 9 sleep bruxers and 10 normal controls. Results: A total of 48.15% and 49.44% HR increased before the onset of RMMAs/LMs in the sleep bruxers and controls, respectively. All of the parameters of HR increases were significantly different between the sleep bruxers and the controls (p < 0.05–0.001) and between different cortical arousal levels (p < 0.01), and the duration of RMMAs/LMs was positively correlated with the parameters (Sleep bruxers: r2 = 0.18–0.88, p < 0.0001; Controls: r2 = 0.16–0.78, p < 0.0001). Discussion: These data suggest the HR increases are associated with the movement events and changes in cortical arousal levels in the sleep bruxers and controls. Abbreviations: LMs: Limb movements; HR: Heart rate; RMMAs: Rhythmic masticatory muscle activities; SB: Sleep bruxism; PSG: Polysomnographic; EEG: Electroencephalographic; PLMS: Periodic leg movements; SSRIs: Selective serotonin reuptake inhibitors; ECG: Electrocardiographic; EOG: Electrooculographic; EMG: Electromyographic; SD: Standard deviation; Fig: Figure; SEM: Standard error of mean; N1: Non-rapid eye movement sleep stage 1; N2: Non-rapid eye movement sleep stage 2; N3: Non-rapid eye movement sleep stage 3; REM: Rapid eye movement ; NA: No arousal; mAR: Microarousal; AW: Awakening

First description of an outbreak of cattle intoxication by cyanobacteria (blue-green algae) in the South of Portugal

A herd of 53 Angus x Charolais crossbred cows and 1 herd bull grazing a stubble field broke through an electric fence, and gained access to stagnant water from a small river (Ribeira de Oeiras). In less than 19 hours, 20 cows died and 5 were sick with clinical signs of ataxia, recumbence, abdominal distension, opisthotonus, paddling and masticatory movements, frothing at the mouth, and bloody diarrhea. The 5 sick cows later died, and the remaining 29 animals remained healthy. Clinical and pathological findings revealed the presence of hepatic and renal necrosis. In the water samples, several cyanobacterial species were identified, predominantly belonging to the toxic genera Microcystis. Altogether, these observations led to a tentative diagnosis of acute hepatoxicity caused by cyanotoxins. The diagnosis was confirmed by detection of microcystin-LR in the kidney from 1 animal. To our knowledge, this is the first report of microcystin-LR animal poisoning in Portugal.

Effect of denture treatment on masticatory movement in patients with complete dentures

PurposeTo clarify the effect of denture treatment on masticatory movement in patients with complete dentures. MethodsForty eight patients who required new complete dentures and 20 patients who were satisfied with their original complete dentures (control: C group) participated in this study. Subjects were asked to chew a gummy jelly on their habitual chewing side. The movement of mandibular incisal point was recorded using a mandibular kinesiograph. First, average path and overlap of the movement path were displayed for the ten cycles between the fifth cycle and the fourteenth cycle. The movement path was classified into one of seven patterns and the frequency of each pattern was calculated and investigated the relationship between treatment and masticatory path pattern. Next, opening distance and masticatory width (spatial parameter) and cycle time (temporal parameter) were calculated and compared between the before treatment group (BT group) and after treatment group (AT group), and between the AT and C groups. ResultsThe BT group showed various patterns of masticatory path, whereas the majority of subjects in the AT and C groups showed path patterns that were representative of healthy dentate subjects. The opening distance and masticatory width increased, and the cycle time was shortened after wearing new complete denture, and there were no statistically significant differences between AT group and C group. ConclusionsFrom these results it was suggested that the masticatory movement of patients with complete dentures improved greatly after wearing new denture.

Energy Storage and Dissipation of Human Periodontal Ligament during Mastication Movement.

As a layer of soft fibrous tissue, the periodontal ligament (PDL) protects against mechanical shock when transmitting mastication force from tooth to its surrounding alveolar bone. Currently, no quantitative method is available to estimate the shock resistance ability of the PDL. To solve this problem, in the present study we developed a finite element (FE) model of the tooth-PDL-bone complex and analyzed the energy storage and dissipation during the mastication movements. Displacement and Mises stress of tooth-PDL-bone complex show that the PDL is able to protect the alveolar bone from mechanical shock by shielding the transfer of deformation and stress. During mastication, the energy of the PDL is stored up to ∼161.5 J/mm3 at the period of loading and dissipated about one-tenth of the stored energy when unloading. The energy storage is displacement-dependent but time-independent because of the hyperelasticity of PDL. However, the energy dissipation is time- and displacement-dependent because of the viscoelasticity of PDL. The present study helps to understand the periodontal potential and the origin of dental diseases such as tooth concussion and occlusal trauma from the view of energy conversion.

Relationship between Frontal/Lateral Mandibular Translations and Masticatory Movement Based on Evaluation of Occlusal Surface Motion

Objective: This study aimed to clarify whether crown restorations with adjusted occlusal surfaces that were formed using frontal/lateral mandibular translations, functioned without interference during mastication. Materials and Methods: In 10 adult volunteers who had healthy normal dentition, frontal and lateral border movement was measured during unilateral mastication and free mastication, using an ultrasound digital mandibular measuring system (ARCUS digma2). Additionally, precise impressions of the upper and lower dental arch were taken, and dental casts were made. These casts were measured using a CAD/CAM scanning system (ARCTICA). For the fabrication of crown restorations, the functionally generated path technique (FGP technique) was used on the monitor for the lower first and second molar. The movement of the opposite teeth on the occlusal surface during frontal and lateral border movement, during unilateral mastication, and during free mastication was considered the functional occlusal surface. The data of the functional occlusal surface generated by frontal/lateral mandibular translations and that of each of the masticatory functional occlusal surfaces were superimposed using three-dimensional data evaluation software (GOM). The difference between these surfaces was evaluated to determine the interference area, maximum interference difference, and average interference difference. Results: Interference was present for all functional occlusal surfaces created by mastication as well as those determined by frontal/lateral mandibular translations. The average interference values, in order of free masticatory movement, habitual masticatory side, and non-habitual masticatory side, were as follows. Interference area: 167.5±20.8 mm2, 121.9±28.5 mm2, 144.6±28.0 mm2; maximum interference distance: 345.0±43.1 μm, 189.0±39.9 μm, 309.0 ± 46.8 μm; average interference distance: 130.0±15.7 μm, 64.0±10.6 μm, 130.0±21.9 μm. Statistically significant differences were found for the maximum interference distance and average interference distance (both p<0.05). Conclusions: The functional occlusal surfaces for each form of mastication demonstrated interference with the functional surface of frontal/lateral mandibular translations. Thus, crown restorations of which the occlusal surfaces were adjusted and formed by frontal/lateral mandibular translations may interfere with mastication.