Tooth wear and compensatory modification of the anterior dentoalveolar complex in humans

In populations living in environments where teeth wear severely, some compensatory modification of the dentoalveolar complex is thought to occur during life whereby functional occlusion is maintained as tooth substance is lost by wear. This study investigates one aspect of this modification process: Changes in the anterior dentoalveolar complex that are accompanied with wear were examined in a series of Japanese skeletal samples. In the prehistoric Japanese hunter-gatherer population heavy wear occurs over the entire dentition. The following changes were demonstrated to have occurred in the anterior segment of the dentition accompanied by wear on the anterior teeth: The anterior teeth tip lingually with wear up to a nearly upright position to fill in interproximal spaces that would have been generated by wear, and to maintain contact relations between adjacent teeth. At the same time, the anterior surface of the maxillary alveolar process also inclines lingually to a certain extent. The amount of lingual tipping is greater in the maxillary anterior teeth than in their mandibular antagonists. It is because of this discrepancy that, with age, the horizontal component of the overlap between maxillary and mandibular anterior teeth decreases, and their bite form changes from scissor bite to edge-to-edge bite. Lesser degrees of lingual tipping of the anterior teeth were also detected in the prehistoric agriculturists and historic Japanese populations. The variation in the degree of lingual tipping observed among the samples is explained by inter-population variation in severity and pattern of tooth wear. This and other evidence suggests that mechanisms that compensate for wear in the anterior dentition may be characteristic of all living human populations, independently of the degree of wear severity endured in their environments.     

Masticatory performance in 80-year-old individuals

Objective: To evaluate the masticatory performance of elderly people at the age of 80 years. Subjects: A total of 283 individuals of 80 years of age took part in a general and dental health survey. Main outcome measures: A dental examination including the number of remaining teeth, occlusion, prostheses, bite force recording, and a questionnaire regarding masticatory performance were recorded. Setting: Five municipalities (Okazaki city, Tokoname city, Tahara town, Atsumi town and Minami‐chita town) in Aichi prefecture, Japan. Results: There were 20 or more teeth in 7.4% subjects, and 44.5% were edentulous. Subjects with no occlusion accounted for 77.4% of the total. Subjects with prostheses accounted for 90.8%. Maximum bite force and masticatory ability score for patients with 20 or more teeth or not wearing prostheses were higher than other groups. The non‐wearing prostheses group had a low masticatory ability score. Conclusion: Most of the 80‐year‐old individuals recovered their masticatory ability with the assistance of prostheses. Several individuals with 20 or more remaining teeth or without removable dentures present in both jaws had a high score for bite forces and masticatory abilities.     

Craniomandibular System and Postural Balance after 3-Day Dry Immersion

The objective of the study was to determine the influence of simulated microgravity by exposure to dry immersion on the craniomandibular system. Twelve healthy male volunteers participated in a 3-day dry immersion study. Before and immediately after exposure we measured maximal bite force using piezoresistive sensors. The mechanical properties of the jaw and cervical muscles were evaluated before, during, and after dry immersion using MyotonPRO. Because recent studies reported the effects of jaw motor activity on the postural stability of humans, stabilometric measurements of center of pressure were performed before and after dry immersion in two mandibular positions: rest position without jaw clenching, and intercuspidal position during voluntary teeth clenching. Results revealed no significant changes of maximal bite force after dry immersion. All postural parameters were significantly altered by dry immersion. There were however no significant differences in stabilometric data according to mandibular position. Moreover the masseter tonicity increased immediately after the end of dry immersion period. Dry immersion could be used as a valid model for studying the effects of microgravity on human subjects. However, 3 days appear insufficient in duration to evaluate the effects of weightlessness on maximal bite force. Our research suggests a link between postural disturbance after dry immersion and masseter tonicity.     

In vivo bone strain in the mandible of Galago crassicaudatus.

Single element foil strain gages were bonded to mandibular cortical bone in eight specimens of Galago crassicaudatus. The gage was bonded below the Pm4 or M2 adjacent to the lower border of the mandible. The bonded strain gage was connected to form one arm of a Wheatstone bridge. Following recovery from the general anesthetic, the restrained Galago bit either a piece of wood, a food object, or a bite force transducer. During these biting episodes, mandibular bone strain deformed the strain gage and the resulting change in electrical resistance of the gage caused voltage changes across the Wheatstone bridge. These changes, directly proportional to the amount of bone strain along the gage site, were recovered by a strip chart recorder. Bone strain was measured on both the working and balancing sides of the jaws. Maximum values of bone strain and bite force were 435 microstrain (compression) and 8.2 kilograms respectively. During bending of the mandible, the correlation between bone strain (tension or compression) and bite force ranged from -0.893 (tension) to 0.997 (compression). The experiments reported here demonstrate that only a small percentage of the Galago bite force is due to balancing side muscle force during isometric unilateral molar biting. In addition, these experiments demonstrate that the Galago mandible is bent in a predictable manner during biting. The amount of apparent mandibular bone strain is dependent on (1) the magnitude of the bite force and (2) the position of the bite point.     

A clinical and anatomical study of the location of the mental foramen in adult Chinese mandibles

One hundred mandibles of adult Chinese cadavers of both sexes without missing teeth, alveolar bone resorption and malposition of teeth were studied. The anatomical location of each mandibular mental foramen was measured by using a combination of three previous methods. Our results showed that the location of the mental foramen below the apex of the lower second premolar (relation IV: 58.98%) was the most common. On average, the distance between the most anterior portion of the anterior border of the mental foramen and the mandibular symphysis was 28.06 mm, between the most anterior portion of the anterior border of the mental foramen and the posterior border of the ramus 74.14 mm, between the inferior border of the mental foramen and the lower border of the mandibular body 14.70 mm, between the superior border of the mental foramen and the bottom of the lower second premolar socket 2.50 mm. The distance across the mental foramen between the alveolar crest and the lower border of the mandibular body was 30.29 mm. Our results were compared with those of other investigators. The significance of identifying the anatomical location of the mental foramen in dental practice is discussed.     

Bite force in subjects with complete dentition

Bite force is the condition, expression and measure of the masticatory function. The purpose of this study was to examine, by means of a newly constructed electronic gnathodynamometer, the values of maximal bite forces in subjects with complete dentition, the time in which they express 50% and 75% respectively of the total forces value, and the shape of the bite curve during testing. The obtained data was statistically analyzed with respect to gender and age. Analysis of the variance confirmed the finding that there was no statistically significant correlation between the values of forces and subjects' age, but there was a statistically significant difference between males and females in the values of the bite forces in the front segment, as well as between the values of the force on anterior and posterior teeth. The correlation between the time T1 posterior right and T1 posterior left, and between T1 and T2 for anterior teeth are statistically significant. Analysis of the bite curves suggests that males "bite" shorter than females with a sharper peak of the curve. Numerical values and bite curves should be a diagnostic factor in the further follow-up of subjects or in the choice of prosthodontic therapy.     

Dental developmental status of southern Chinese girls in Hong Kong

Dental developmental status of the permanent canines, premolars and second molars were studied in one hundred and two twelve-year-old Southern Chinese girls born and brought up in Hong Kong. Eruption of these teeth were defined as gingival emergence during the clinical examination while the root development was assessed from orthopantomographs. Root resorption pattern of the primary canines and molars were also studied with the aid of the orthopantomographs. Two-thirds of girls presented with permanent dentition stage. The root resorption patterns of the primary teeth were different from their order of exfoliation. The mandibular permanent teeth were in advanced in both eruption and root development than the corresponding maxillary teeth, except the first premolars.     

Chewing pattern and muscular activation in open bite patients

Different studies have indicated, in open bite patients, that masticatory muscles tend to generate a small maximum bite force and to show a reduced cross-sectional area with a lower EMG activity. The aim of this study was to evaluate the kinematics parameters of the chewing cycles and the activation of masseters and anterior temporalis muscles of patients with anterior dental open bite malocclusion. There have been no previous reports evaluating both kinematic values and EMG activity of patients with anterior open bite during chewing. Fifty-two young patients (23 boys and 29 girls; mean age±SD 11.5±1.2 and 10.2±1.6years, respectively) with anterior open bite malocclusion and 21 subjects with normal occlusion were selected for the study. Kinematics parameters and surface electromyography (EMG) were simultaneously recorded during chewing a hard bolus with a kinesiograph K7-I Myotronics-Usa. The results showed a statistically significant difference between the open bite patients and the control group for a narrower chewing pattern, a shorter total and closing duration of the chewing pattern, a lower peak of both the anterior temporalis and the masseter of the bolus side. In this study, it has been observed that open bite patients, lacking the inputs from the anterior guidance, that are considered important information for establishing the motor scheme of the chewing pattern, show narrower chewing pattern, shorter lasting chewing cycles and lower muscular activation with respect to the control group.     

Influence of sex on children's body measurements and indices of biological age (findings from a study of twins of different sexes)

By antropometry and roentgenography methods in 52 twin pairs of different sex, body dimensions, the third metacarpal bone and the phalange of the third right hand finger, as well as the terms of permanent teeth eruption were studied. The investigation revealed no timely coincident periods in growth activity between girls and boys. During the first period (6,5--10 years), predominance of some dimentions is observed in boys, during the second (8,5--14 years)--in girls, and during the third (11--17 years)--in boys again. Somewhat different terms for permanent teeth eruption make it possible to distinguish two periods: 7 years when the boys surpass the girls in the number of permanent teeth (two teeth in average) and 8--14 years when the boys lag behind the girls in the number of permanent teeth.     

Characteristics of the topographic anatomical correlations of the chorda tympani, auriculotemporal nerve and anterior tympanic artery with the temporomandibular joint

The aim of the investigation was to reveal the possibility to draw into the pathological process known as the "Costen syndrome" the formations mentioned in the title. The investigation performed by means of the craniometry method on 150 mature person skulls, that are rather evenly distributed according to their sex, age and form, and simultaneous investigation of 70 heads of corpses of persons of both sex, gave the data denying the possibility of mechanical damage of the chorda tympani, when the mandibular head is shifted backward or medially. This phenomenon can be observed at a loss of teeth and lowered bite. When the mandibular head is shifted backward, it does not involve the chorda tympani, since the nerve gets out of the osseous canal more medially to the spine of the sphenoid bone. The medial shift of the mandibular head also cannot damage the chorda tympani, since the nerve is separated from the joint by a marked osseous protrusion. At the same time the data are obtained on variations in topography of the chorda tympani at various form of the intratemporal fossa. It has been stated that when a pathological process occurs around the temporomandibular joint, the auriculotemporal nerve and the anterior tympanic artery can be involved into this process. This can produce appearance of the "Costen syndrome" components.     

Circulatory and respiratory responses to muscular exercise in Czech and Norwegian children

This paper presents a comparison between Czech and Norwegian rural healthy children with regard to the functional characteristics of the circulatory and respiratory system based upon work physiological variables and measurements of some pulmonary volumes. The study included randomised samples of boys and girls at the age of 8, 12 and 16 years, 66 Czech boys and 63 girls, 54 Norwegian boys and 57 girls. At the age of 8 years the maximal aerobic power was closely similar in both countries, but in the older age groups the Norwegian children exhibited lower physical fitness. The maximal heart rate was close to 200 min-1 on the average without any sex, age or ethnic differences. In agreement with the higher maximal aerobic power the 12 and 16 year old Czech children had lower submaximal heart rates for the same oxygen uptake than the Norwegian children. The forced vital capacity and forced expiratory volume in one second was significantly higher on the average in Czech than in Norwegian children but the latter, expressed in percent age of the former, averaged 87 to 91% without any sex, age or ethnic differences. The maximal ventilation volumes during muscular exercise reached higher values in Czech than in Norwegian children of the same age, but the mean maximal respiratory rate was close to 60 min-1, being independent of age, sex and cultural differences. During heavy exercise only 40 to 50% of the vital capacity and 45 to 55% of the forced expiratory volume were taken into account and this index of pulmonary function did not differ with sex, age or ethnic differences.     

Measurements of tooth wear among Australian Aborigines: I. Serial loss of the enamel crown

The dental casts made from Aboriginal children during the course of a longitudinal growth study in Central Australia provided material for analyzing tooth wear under known environmental conditions. The wear facets produced on the occlusal surfaces were clearly preserved on the dental stone casts and recorded the progress of enamel attrition from ages 6 to 18. These casts were photographed and traced by electronic planimetric methods that automatically recorded the location and size of wear facets on the first and second permanent molars. These areas of worn tooth surface were compared to the total tooth surface. The worn surface was regressed on age to calculate wear rates of each tooth. Discriminant analyses were also performed to determine the significance of dental attrition differences between the sexes at each age group. The total wear on each tooth was highly correlated with age as expected but females wore their teeth at a significantly higher rate than males. The mandibular molars wore more rapidly than maxillary teeth in both sexes. The discriminant analysis successfully grouped 91% of the cases according to age and sex. Pattern of wear, the location, and size of wear facets also differed between age groups and sex. The questions of why there is a difference between male and female wear or why there is greater wear on one arch or arch region have no ready answers. The differing rates and pattern of dental wear do suggest that arch shape and growth rates may be the answer though it has yet to be tested. However, the occlusal surface wear is useful for age estimation in a population and provides a record of shifting masticatory forces during growth.     

Eight-year mortality associated with dental occlusion and denture use in community-dwelling elderly persons

Objective: To evaluate the influence of dental occlusion, with or without the use of dentures, on mortality in community‐dwelling elderly persons. Subjects: A total of 1030 randomly selected healthy independent elderly aged 65 and over were surveyed in 1995. For the study reported here, subjects were classified into three groups according to the presence or absence of maxillo‐mandibular tooth contacts. Subjects with no maxillo‐mandibular tooth contacts were further subdivided into those with and without dentures. Methods: Data on mortality were obtained from Kure City Council in September 2003. Cox regression models were used in analysing the risk for death with gender and age as covariates. Results: Individuals whose teeth had contact in at least the bilateral premolar regions at baseline had 0.78 times (95% CI: 0.60–0.99) smaller risk for death during the succeeding 8 years than those who had no occlusion. Among those who had no occlusion with their own teeth, the risk for mortality among denture non‐users was 1.52 times (95% CI: 1.25–1.83) higher than the risk for denture users. Conclusion: These results may support the view that, in the elderly, poor dental occlusion is associated with an increased risk for mortality and that, in the edentulous, the use of dentures is associated with a decreased risk for mortality.     

Sexual dimorphism in mandibular growth of French-Canadian children 6 to 10 years of age

Polynomial regression is used to model the mandibular growth of 28 girls and 26 boys who were followed longitudinally from 6 to 10 years of age. The pooled-within individual designs indicate that ramus height follows a linear pattern of size increase; corpus and total mandibular lengths display curvilineal, decelerating, patterns of growth over the age range. Multivariate analyses of variance reveal significant sex differences in size, favoring boys, for the two length measures at 6 years of age. Growth velocity for corpus length is also significantly greater in boys than in girls. Sexual dimorphism in the growth of total mandibular length is more complex, including differences in velocity and deceleration. Ramus height shows no significant pattern of variation between boys and girls for either size or growth velocity.     

A cinefluorographic study of mandibular movement during feeding in the rat (Rattus norvegicus)

The anatomy of the masticatory apparatus, and particularly of the mandibular joints, has led to the view that mandibular movement in the Rodentia is predominantly propalinal, or forwards and backwards in direction. As part of an investigation into the mechanism of function of the mandibular joints in these animals, the feeding behaviour of "August" strain and "Wistar" rats was examined by cinephotography and cinefluorography. The rats were trained to feed on barium sulphate impregnated biscuit and animal cake and to drink radio-opaque liquids. Cinefluorographic recordings of ingestion, mastication, deglutition and of drinking were taken in both the lateral and dorso-ventral projections.
Analysis of the recordings has shown a fundamental separation of ingestive and masticatory activity in the rat, which can be attributed to the morphology of the jaws and particularly to the disparity in the lengths of the mandibular and maxillary diastemas. To bring the incisor teeth into occlusion for ingestion, the mandible is brought forward through the rest position and the condyle into articulation with the anterior part of the fossa. In mastication the condyle is moved backwards to bring the molar teeth into occlusion and the condyle into articulation with the posterior articular facet on the fossa. Once the mandible has been moved into the appropriate position for either ingestion or mastication and deglutition, the movements involved in the separation or chewing of the food are cyclical with combined horizontal and transverse movements as well as the fundamental vertical movement acting to open and close the mouth. The basic movement of ingestion carries the mandibular incisors upwards and forwards across the lingual surfaces of the maxillary incisors, so separating the bite. The grinding stroke of mastication is a horizontal movement carrying the mandibular molars anteriorly across the maxillary.     

The growth of the skull and jaw muscles and its functional consequences in the New Zealand rabbit (Oryctolagus cuniculus)

Between weaning and adulthood, the length and height of the facial skull of the New Zealand rabbit (Oryctolagus cuniculus) double, whereas much less growth occurs in the width of the face and in the neurocranium. There is a five-fold increase in mass of the masticatory muscles, caused mainly by growth in cross-sectional area. The share of the superficial masseter in the total mass increases at the cost of the jaw openers. There are changes in the direction of the working lines of a few muscles. A 3-dimensional mechanical model was used to predict bite forces at different mandibular positions. It shows that young rabbits are able to generate large bite forces at a wider range of mandibular positions than adults and that the forces are directed more vertically. In young and adult animals, the masticatory muscles differ from each other with respect to the degree of gape at which optimum sarcomere length is reached. Consequently, bite force can be maintained over a range of gapes, larger than predicted on basis of individual length-tension curves. Despite the considerable changes in skull shape and concurrent changes in the jaw muscles, the direction of the resultant force of the closing muscles and its mechanical advantage remain stable during growth. Observed phenomena suggest that during development the possibilities for generation of large bite forces are increased at the cost of a restriction of the range of jaw excursion.     

Permanent tooth emergence in Gujjars of Punjab, India.

Patterns of permanent tooth emergence in Gujjars were studied in a cross-sectional sample of 483 children ranging in age from 6 to 13 years. Females were markedly advanced in permanent tooth emergence times over males, but no such sex differences were observed in sequence of emergence. Differences between median emergence times of right and left side antimers were significant for only 4 of 28 instances (14.29%), namely central incisors, mandibular first molars in males and lateral maxillary incisors in females. In general mandibular teeth except premolars tended to emerge earlier than their maxillary counterparts. The quiescent period between first and second tooth emergence stages was longer in males than in females. Mandibular depth and morphological facial length were very significantly correlated (p < 0.01) with the number of permanent teeth present in the oral cavity.     

牛河梁红山文化人群龋齿的统计与分析

本文通过对牛河梁遗址出土的31例红山文化时期人类牙齿龋病的统计与分析, 获知: 1)牛河梁遗址男女两性的患龋率、龋齿率没有明显的性别差异; 2)他们的患龋率和龋齿率有随年龄增长逐步增高的趋势; 3)上颌的龋齿罹患率高于下颌; 4)龋齿的发生主要集中在臼齿,且以咬合面部位为主; 5)他们的患龋率和龋齿率均较低。牛河梁红山文化人群相对偏低的龋齿率可能暗示出他们的经济生活方式还处在以采集狩猎为主体的模式中, 农耕经济可能处于较低层次的状态。     

Age-related variability in occlusal wear planes

Investigation of two populations of 136 individuals shows several patterns of occlusal wear plane change which are positively correlated with age. For individuals up to the age of 18, there is a characteristic pattern in which the occlusal wear planes of the mandibular teeth are lingually sloped and those of the maxillary dentition buccally sloped, with the exception of the maxillary premolars, which are also lingually sloped. The long axes of the mandibular teeth give them a lingual orientation relative to the maxillary teeth, and the long axes of the maxillary molars, by contrast, are buccally oriented. In the 18-30 age range for all sexes, the mandibular M1 becomes buccally sloped on its occlusal surface while the occlusal wear plane on the maxillary M1 becomes lingually sloped. Later age changes indicate a trend for the mandibular premolars to become buccally sloped, while the wear planes of the maxillary premolars remain lingually sloped. There is a corresponding tendency for the maxillary and mandibular second molars to undergo changes in the initial orientation of the occlusal wear planes.     

Loss of molar occlusion and mandibular morphology in adults in an ancient human population consuming a coarse diet

The purpose of the study is to investigate the link between number of molar teeth retained in occlusion and mandibular morphology in adults in an ancient, high dental wear human population. The study material comprises skeletons from Mediaeval Wharram Percy, England (N = 50 female, 69 male adults). It was hypothesized that adults retaining fewer occluding molars would show reduction in mandibular dimensions, particularly in the ascending ramus and gonial regions where the main muscles of mastication have their insertions. Molar occlusal status is assessed using the concept of functional units. Mandibular morphology is assessed using a suite of ten linear measurements plus the mandibular angle. Results show no evidence for any association between number of molars retained in occlusion and mandibular angle. There was an association between mandibular size and number of molars retained in occlusion, with smaller mandibular dimensions in those retaining fewer occluding molars. Some measurements were affected more than others so that there was also some shape alteration. Alteration of mandibular dimensions was more clearly demonstrable in females than in males. Only in females could significant reduction in the ascending ramus and gonial regions be demonstrated. Reasons for the apparent difference in response to loss of molar occlusion between male and female mandibles are unclear, but sex differences in bony metabolism mediated by hormonal factors may be implicated. Results suggest that care should be exercised when including mandibles from individuals showing loss of molar occlusion in morphological studies. Am J Phys Anthropol 152:383–392, 2013. © 2013 Wiley Periodicals, Inc.