Chewing-side preference is one of the risk factors for temporomandibular disorders (TMD), and people with chewing-side preference is more prone to have short and displaced condyles, increased articular eminence inclination and glenoid fossa depth. The proportion of TMD patients with chewing-side preference is often higher than that of the normal subjects. Clinical studies have shown a strong correlation between chewing-side preference and TMD symptoms and signs; and animal studies have shown that chewing-side preference can affect the growth, development, damage and repair of the mandible. After long-term unilateral mastication, changes in the stress within the joint cause the imbalance of temporomandibular joint (TMJ) structural reconstruction, the transformation and even destruction of the fiber structure of masticatory muscle, resulting in uncoordinated movement of bilateral muscles. The joint neurogenic diseases caused by the increase of neuropeptide substance P and calcitonin-gene-related-peptide (CGRP) released locally by TMJ may be the mechanism of TMD. This article reviews the research progress of the influence of chewing-side preference on the structure of TMJ, the relationship between chewing-side preference and TMD, and the related mechanisms.
Humans ; Mastication/physiology* ; Temporomandibular Joint/physiology* ; Temporomandibular Joint Disorders/etiology* ; Mandible/physiology*

As a representative part of the oral system and masticatory robot system, the modeling method of the dental model is an important factor influencing the accuracy of the multi-body dynamic model. Taking the right first molars of the masticatory robot as the research object, an equivalent model, point-contact higher kinematic pair composed of v-shaped surface and sphere surface, was proposed. Firstly, the finite element method was used to analyze the occlusal dynamics of the original model in three static contact cases (intrusive contact, centric occlusion, and extrusive contact) and one dynamic chewing case, and the expected bite force was obtained. Secondly, the Hertz contact model was adopted to establish the analytical expression of the bite force of the equivalent model in three static contact cases. The normal vectors and contact stiffness in the expression were designed according to the expected bite force. Finally, the bite force performance of the equivalent model in three static contact cases and one dynamic chewing case was evaluated. The results showed that the equivalent model could achieve the equivalent bite force of 8 expected items in the static contact cases. Meanwhile, the bite force in the early and late stages of the dynamic chewing case coincides well with the original model. In the middle stage, a certain degree of impact is introduced, but it can be weakened by subsequent trajectory planning. The equivalent modeling scheme of the dental model proposed in this paper further improves the accuracy of the dynamic model of the multi-body system. It provides a new idea for the dynamic modeling of other complex human contacts.
Biomechanical Phenomena ; Bite Force ; Humans ; Mastication ; Molar

OBJECTIVE: To study the effect of functional chewing training (FuCT) on masticatory function, the severity of tongue thrust, and the severity and frequency of drooling in children with cerebral palsy. METHODS: A prospective study was performed for 48 children who were diagnosed with oral motor dysfunction from January 2019 to January 2020, and they were randomly divided into an FuCT group and an oral motor training group, with 24 children in each group. Both groups received FuCT or oral motor training for 12 weeks, and then they were evaluated in terms of the changes in the masticatory function, the severity of tongue thrust, and the severity and frequency of drooling. RESULTS: There were no significant differences between the two groups in the masticatory function, the severity of tongue thrust, and the severity and frequency of drooling before treatment (P>0.05). After the 12-week training, the FuCT group showed significant improvements in the masticatory function and the severity of tongue thrust and drooling (P<0.05), but with no improvement in the frequency of drooling (P>0.05), while the oral motor training group had no improvements in the masticatory function, the severity of tongue thrust, and the severity and frequency of drooling (P>0.05). After the 12-week training, the FuCT group had more significantly improvements in the severity of tongue thrust and the severity and frequency of drooling than the oral motor training group (P<0.05). CONCLUSIONS FuCT can effectively improve the masticatory function, the severity of tongue thrust, and the severity and frequency of drooling in children with cerebral palsy.
Cerebral Palsy ; Child ; Humans ; Mastication ; Prospective Studies ; Sialorrhea

PURPOSE: To investigate the influence of crown material (lithium-disilicate, 3Y-TZP zirconia) and abutment type (rigid implant, resin tooth with artificial periodontium) on wear performance of their antagonist teeth and adjacent teeth.MATERIALS AND METHODS: A mandibular left first molar (#36) with adjacent human teeth (mandibular left second premolar: #35, mandibular left second molar: #37) and antagonistic human teeth (maxillary left second premolar: #25, maxillary left first molar: #26, maxillary left second molar: #27) was prepared simulating a section of the jaw. Samples were made with extracted human molars (Reference), crowned implants (Implant), or crowned resin tooth analogues (Tooth). Crowns (tooth #36; n = 16/material) were milled from lithium-disilicate (Li, IPS e.max CAD) or 3Y-TZP zirconia (Zr, IPS e.max ZirCAD, both Ivoclar Vivadent). Thermal cycling and mechanical loading (TCML) in the chewing simulator were applied simulating 15 years of clinical service. Wear traces were analyzed (frequency [n], depth [µm]) and evaluated using scanning electron pictures. Wear results were compared by one-way-ANOVA and post-hoc-Bonferroni (α = 0.05).RESULTS: After TCML, no visible wear traces were found on Zr. Li showed more wear traces (n = 30–31) than the reference (n = 21). Antagonistic teeth #26 showed more wear traces in contact to both ceramics (n = 27–29) than to the reference (n = 21). Strong wear traces (> 350 µm) on antagonists and their adjacent teeth were found only in crowned groups. Abutment type influenced number and depth of wear facets on the antagonistic and adjacent teeth.CONCLUSION: The clinically relevant model with human antagonistic and adjacent teeth allowed for a limited comparison of the wear situation. The total number of wear traces and strong wear on crowns, antagonistic and adjacent teeth were influenced by crown material.
Bicuspid ; Ceramics ; Crowns ; Humans ; Jaw ; Lithium ; Mastication ; Molar ; Tooth

The loss of posterior support and the abnormal jaw relation can cause pathologic findings. If deep bite patients with multiple missing teeth, can not have the stable posterior contact, the mandible moves posteriorly, and consequently the overjet and overbite get worse. And when the mandibular irregular occlusal plane is corrected, it is easier to have the bilateral balanced occlusion with the maxilla. So the treatment goal is to give proper posetrior support and establish appropriate anterior guidance, and ultimately provide improved mastication and esthetics recovery. In this case, a 68 year old man, having deep bite without posterior support was evaluated by the vertical dimesion decision flow-chart. An available prosthetic height, anterior occlusal relation such as overjet, overbite and the esthetic part such as facial height and the cephalometric analysis are the factors to be considered.
Dental Occlusion ; Esthetics ; Humans ; Jaw ; Mandible ; Mastication ; Maxilla ; Mouth Rehabilitation ; Mouth ; Overbite ; Tooth ; Vertical Dimension

In patients with fully edentulous jaw, treatment of complete dentures should be carried out in many stages when following the conventional methods. Therefore there were disadvantages such as multiple visits to dental clinic is inevitable. In addition, errors caused by polymerization shrinkage, which happens during the fabrication of denture, and difficulties in reproduction of damaged or lost denture were considered as disadvantages. But nowadays, computer-aided design and computer-aided manufacturing (CAD/CAM) system is widely used in dentistry and it has begun to expand its spectrum in manufacturing complete dentures. Using CAD/CAM system to fabricate complete dentures can reduce the number of patient's visit and clinical chair time, since taking impression, recording jaw relation, and selection of artificial teeth are performed at the same time during the first visit, and delivering of dentures during the second visit is possible. In addition, because 3D-Printing technology is used, errors by polymerization shrinkage can be reduced. Among the companies that fabricate complete dentures using CAD/CAM system, DENTCA CAD/CAM denture (DENTCA Inc., Los Angeles, CA, USA) is the most commercialized company. In this case, we treated patients of complete dentures using conventional complete denture method and DENTCA CAD/CAM denture system in the same patient. We would like to report this case because we have achieved good results not only in functional aspects of pronunciation, chewing, and swallowing but also in aesthetic aspects.
Computer-Aided Design ; Deglutition ; Dental Clinics ; Dentistry ; Denture, Complete ; Dentures ; Humans ; Jaw ; Jaw, Edentulous ; Mastication ; Methods ; Polymerization ; Polymers ; Reproduction ; Tooth, Artificial

Patients with collapsed occlusal support and unilateral chewing show parafunctional mandibular movements, which can be complicated in older patients. Gothic arch tracing and split cast technique are used to confirm the deviation between centric relation and anterior habitual bite in patient who has oral dyskinesia and collapsed occlusion. Temporary denture as occlusal stabilization appliance was provided for stable occlusion and reproducible mandibular movement. Definitive denture was fabricated by lingualized occlusion concept.
Centric Relation ; Dentures ; Humans ; Mandible ; Mastication ; Mouth Rehabilitation ; Mouth ; Movement Disorders ; Prostheses and Implants

OBJECTIVE: To investigate the oral cancer awareness, its related knowledge among residents in Beijing. METHODS: A questionnaire survey was conducted among Beijing residents (non-medical related personnel) on the knowledge of oral cancer and its prevention and treatment. RESULTS: A total of 1 483 questionnaires were completed, including 663 males (44.6%) and 820 females (55.3%), ranging from 15 to 91 years. Lung cancer was the most mentioned as heard of (94.3%), followed by liver cancer (92.5%) and gastric cancer (92.4%), while oral cancer was the least heard of (47.7%). Family account (P=0.015), residence (P=0.028), income (P=0.024), frequency of brushing teeth (P<0.001), frequency of mouth self-examination (P<0.001) and chew betel nut chewing (P=0.015) were significantly associated with oral cancer awareness. Most respondents learned about oral cancer from TV programs (24.3%), phone news (22.0%), WeChat (11.3%) and chatting with friends or people around (14.6%). Only 34.9% knew that smoking was a risk factor of oral cancer, and this knowledge was associated with age (P=0.011), education level (P=0.007), frequency of brushing teeth (P<0.001), and frequency of mouth self-examination (P=0.002). Only 23.5% knew that drinking was a risk factor of oral cancer, and this knowledge was associated with education level (P=0.002), residence (P=0.022), frequency of brushing teeth (P=0.009), and frequency of mouth self-examination (P=0.005). Only 35.1% knew that betel nut chewing was a risk factor for oral cancer, and this knowledge was associated with age (P=0.040), education level (P=0.002), family account (P=0.002), income (P=0.005), frequency of brushing teeth (P=0.001), frequency of mouth self-examination (P<0.001), and betel nut chewing (P=0.002). Only 35.7%, 21.6% and 16.9%, respectively, knew that long-term unhealed ulcers, white plaques and red plaques in the mouth were the early signs of oral cancer. CONCLUSION This survey demonstrates a general lack of public awareness and knowledge about signs and symptoms of oral cancer, and its risk factors and treatment. Some residents have not formed good oral hygiene habits. Specific measures should be taken to improve the public awareness of oral cancer and related knowledge about prevention and treatment, such as the use of various new media for the public to promote their oral health knowledge, in order to reduce the incidence of oral cancer, improve early attendance rates and the patients' survival rates.
Adolescent ; Adult ; Aged ; Aged, 80 and over ; Areca ; Beijing ; Female ; Humans ; Male ; Mastication ; Middle Aged ; Mouth Neoplasms ; Risk Factors ; Smoking ; Young Adult

PURPOSE: This study examined dietary and health characteristics of the young-old and the old-old by food security status. METHODS: The study used data from the 6th (2013 ~ 2015) Korea National Health and Nutrition Examination Survey. The study subjects consisted of 3,948 subjects, of whom 2,445 were the young-old (aged 65 to 74 years) and 1,503 were the old-old (aged 75 years and over). Food security status was evaluated using an 18-item questionnaire. Energy intake, nutrient densities, and prevalence of insufficient nutrient intake were assessed. Food intake was evaluated in terms of the number of food group servings. Dietary behaviors and health status were also assessed. RESULTS: The prevalence of food insecurity among the young-old and the old-old was 10.0% and 11.6%, respectively. Among the young-old, the food insecure group had a significantly higher level of prevalence of insufficient intake for all the nutrients (protein, vitamin A, thiamin, riboflavin, niacin, vitamin C, calcium, phosphorous, and iron) assessed in this study compared with the food secure group. In case of the old-old, significant differences were found only for four nutrients (protein, riboflavin, niacin, and phosphorus) in the prevalence of insufficient nutrient intake between the food secure and the food insecure groups. Kinds of food groups with significantly different numbers of servings by food security status were dissimilar between the two age groups. In both the age groups, the food insecure group consumed a significantly lower number of servings in meat·fish·eggs·legumes and fruits than the food secure group; grains and vegetables intake in the young-old and oils·sweets intake in the old-old differed in the number of servings by food security status. Among the young-old, the prevalence of chewing difficulties in the food insecure group was significantly higher than that of the food secure group, while among the old-old, no significant differences were found by food security status. CONCLUSION: Dietary and health characteristics of the young-old and the old-old differed by food security status. Such differences were more apparent in the young-old than the old-old. Therefore, it is suggested that food and nutrition assistant programs should be designed with consideration of the differences.
Ascorbic Acid ; Calcium ; Diet ; Eating ; Energy Intake ; Food Supply ; Fruit ; Humans ; Korea ; Mastication ; Niacin ; Nutrition Surveys ; Prevalence ; Riboflavin ; Vegetables ; Vitamin A

PURPOSE: This study was to evaluate the wear resistance of 3D printed, milled, and conventionally cured provisional resin materials. MATERIALS AND METHODS: Four types of resin materials made with different methods were examined: Stereolithography apparatus (SLA) 3D printed resin (S3P), digital light processing (DLP) 3D printed resin (D3P), milled resin (MIL), conventionally self-cured resin (CON). In the 3D printed resin specimens, the build orientation and layer thickness were set to 0° and 100 µm, respectively. The specimens were tested in a 2-axis chewing simulator with the steatite as the antagonist under thermocycling condition (5 kg, 30,000 cycles, 0.8 Hz, 5℃/55℃). Wear losses of the specimens were calculated using CAD software and scanning electron microscope (SEM) was used to investigate wear surface of the specimens. Statistical significance was determined using One-way ANOVA and Dunnett T3 analysis (α = .05). RESULTS: Wear losses of the S3P, D3P, and MIL groups significantly smaller than those of the CON group (P < .05). There was no significant difference among S3P, D3P, and MIL group (P > .05). In the SEM observations, in the S3P and D3P groups, vertical cracks were observed in the sliding direction of the antagonist. In the MIL group, there was an overall uniform wear surface, whereas in the CON group, a distinct wear track and numerous bubbles were observed. CONCLUSION: Within the limits of this study, provisional resin materials made with 3D printing show adequate wear resistance for applications in dentistry.
Clothing ; Dentistry ; In Vitro Techniques ; Mastication ; Methods ; Printing, Three-Dimensional