Normal Dentition Research Articles

天然歯列中の歯頚円錐と辺縁歯肉についての角度分析

There are no reports on numerical investigation of suitable shapes of restoration. This study examines the relationship between gingival cone and marginal gingiva in natural dentition, and discusses the standard angles for giving a suitable shape at the gingival cone of restoration. Twenty dental casts of healthy subjects with normal dentition were examined. The angles between gingival cone and marginal gingiva (CG angle), and the angles between gingival cone and the long axis of the tooth crown (CA angle) were measured. The mean CG angles of each site were measured between 96.7 degrees (palatal surface of the upper first molar) and 123.9 degrees (labial surface of the lower central incisor). Within the same kind of teeth, lower significant differences were observed among upper and lower, or buccal and lingual surfaces. The CG angles of anterior teeth were 9.5 to 19.2 degrees larger than those of posterior teeth. The CA angles of anterior teeth were negative, and the apex of gingival cone of anterior teeth was directed toward the incisal edge. Conversely, the CA angles of posterior teeth were positive, and the apex was directed toward the root apex. Significant negative correlation was found between CA angle and CG angle (p<0.001). These results suggested that the relationship between gingival cone and marginal gingiva is fairly constant throughout their angles, and that the cervical shape could affect the shape of marginal gingiva.

A morphological study on the classification of maxillary dental arches.

To evaluate the morphology of dental arches, 62 (male: 36, female: 26) paired casts having normal dentitions and occlusion were selected from 396 (age: 18 to 26 years old; male: 257, female: 139) sets of dental study models. The maxillary dentitions were preliminarily classified as square, round-square, round and round V-shaped arches based on the conventional morphological descriptions. Midpoints of the incisor edge (I1(R), I1(L), I2(R), & I2(L), summits of the cuspids (CR & CL), buccal cusps of the premolars (P1(R), P1(L), P2(R), & P2L), mesial buccal cusps of the first and second molars (M1(R), M1(L), M2(R), & M2(L)), and the midpoint (A) of line I1(R)-I1(L) were designated as reference points. From A, let a vertical line intersected line M2(R)-M2(L) at reference point B. The line A-B intersected C(R)-C(L) at reference point E. We evaluated 1) the protrusion of the cuspids by (1) angle I2(R)-C(R)-P1(R) (angle R) + angle I2(L)-C(L)-P1(L) (angle L); 2) the curvature of the anterior teeth by (2) A-B/C(R)-C(L), (3) 180 degrees - angle C(R)-A-C(L), and (4) A-E/C(R)-C(L); 3) the length to width ratio of the dental arch by (5) A-B/M2(R)-M2(L); 4) the degree of roundness of the maxillary arch by estimation of (6) (rtheta5 - rtheta4)R + (rtheta5 - rtheta4)L; and 5) an item (7) for the differentiation of type I and type II round-square arches by relating the bilateral contour and position of break line P1-P2-M1-M2 (i) to line P1-M2 (ii). The data of items (1), (2), (3), (4), (5), and (6) were further standardized and summarized into three essential principal components: 1) the curvature of the anterior teeth, 2) the curvilinear contour of the dental arch, and 3) the length-to-width ratio of the dental arch. The results indicated that: 1) 60% of the maxillary dentitions were round-square arches which showed no prominent principal component; 2) square maxillary arches distinctly showed a small (1) angle R + angle L; 3) round arches were characteristic by small (6) (rtheta5 - rtheta4)R + (rtheta5 - rtheta4)L values; and 4) round V-shaped arches had large (1), (3) and (4) values.

Approche morphologique de l'esthétique faciale : une étude tunisienne

Over the course of time, an esthetic standard, molded by a certain number of rules, recognized virtually universally, has gained widespread recognition. Orthodontics, like the rest of the world, accepts this rule. So, we all try in our treatment objectives to conform to a set of standardized "norms" of facial and cephalometric esthetics. Still, one question must be asked: can these norms be the same throughout the four corners of the globe? Having pondered this matter carefully, we attempted to find an answer by undertaking a study of 53 patients with "normal dentitions", all students of dental medicine. On profile cephalograms and profile photographs of these patients, we carried out a variety of esthetic analyses. We then compared the results obtained with orthodontic averages and found that they differed in many points. Should this finding impel us to adopt different esthetic criteria? However, this question may be answered, we retain our essential conviction that we should endeavor to preserve the goal of achieving facial harmony for our patients and that we should know what its criteria are.

Computational models of oral and craniofacial development, growth, and repair.

This paper illustrates how biological and clinical problems stimulate research in biomedical informatics and how such research contributes to their solution. The computational models described use techniques from Logic Programming, Machine Learning, Computer Vision, and Biomathematics. They address problems in the development, growth, and repair of oral and craniofacial tissues arising in cell biology, clinical genetics, and dentistry. At the micro-level, the dynamic interaction of cells in the oral epithelium is modeled. At the macro-level, models are constructed of either the craniofacial shape of an individual or the craniofacial shape differences within and between healthy and congenitally abnormal populations. In between, in terms of scale, there are models of normal dentition and the use of computerized expert knowledge to guide the design of dental prostheses used to restore function in partially edentulous patients.

A new method for evaluating the threshold of periodontal ligament mechanoreceptor by slow speed mechanical stimulation.

This study aimed to establish a reliable method for detecting the threshold for perception of force applied to tooth and to report the basic properties of force threshold in the normal dentition subjects. The perception of mechanical stimulation exerted to tooth is formed by input from periodontal ligament mechanoreceptors and intradental mechanoreceptors. Periodontal ligament mechanoreceptors respond to a wide range speed of stimulus, whereas intradental mechanoreceptors are activated only by a rapid stimulation. Reliable properties of perception have not been reported because of the difficulties to regulate velocity and degree of the stimulus. Eighteen healthy subjects were observed in this study (mean age: 27.2 +/- 5.7 years). A loading device to generate slow speed loading was fabricated and measured as follows: (i) the fluctuation of the force threshold within a day, (ii) day-to-day fluctuation, (iii) changes in the force threshold by a transient mechanical loading. In the normal dentition, it was observed that the fluctuation within a day and day to day of the pressure sense showed no significant differences; however, a transient mechanical loading caused the sensitivity of the periodontal ligament to decrease significantly. The device examining the force threshold resulted from periodontal ligament mechanoreceptors was useful in evaluating the sensitivity of the periodontal ligament.

Novel mutation in the paired box sequence of PAX9 gene in a sporadic form of oligodontia.

Tooth development is regulated through a series of reciprocal interactions between the dental epithelium and mesenchyme and requires protein products of a number of genes. It has been reported that selective tooth agenesis is associated with mutations in human MSX and PAX9 genes. Mutational analysis of the two genes was performed in 25 individuals with familial or sporadic form of permanent tooth agenesis. Single-stranded conformational polymorphism analysis revealed no mutations in the entire coding sequence of the MSX1 gene. In PAX9, a novel, heterozygous G151A transition in the sequence encoding the paired domain of the PAX9 protein was detected in a patient with agenesis of third molars, second premolars and incisors, but not in her parents, the remaining patients or 162 individuals with normal dentition. This is the first de novo mutation described in PAX9. Our results support the view that mutations in PAX9 could constitute a causative factor of oligodontia. We hypothesize that the G151A transition in PAX9 might be responsible for the sporadic form of tooth agenesis in this patient.

Periimplant probing: positives and negatives.

Periodontium in normal dentition is not as it is surrounding an implant area. Thus, periodontal probing with normal dentition is not similar to periimplant probing. The periimplant probing protocol should be different from periodontal probing because of inherent anatomical differences. The aim of this paper is to review the topics related to periimplant probing and to draw inferences to develop a periimplant probing protocol.

Histological analysis of human tooth development in NOD/scid mice.

An increasing number of elderly people suffer from the loss of teeth due to periodontitis or dental caries. Currently accepted functional prosthetic rehabilitation includes removable or fixed prostheses, with or without osseointegrated dental implants. All of them, however, are foreign bodies for the organism. In this regard, the ideal materials are natural teeth, which do not stimulate inflammatory responses. Tissue engineering has made great progress in regenerating a variety of cell types, such as bone cells. Regenerated tooth would be of great use and importance as a material for novel dental implants. However, clear mechanisms of tooth formation have not yet been elucidated. We describe here an experimental model where normal human tooth morphogenesis and dentition occur in NOD/scid mice subcutaneous tissues. Our system would contribute not only to developing, but also understanding the process of human tooth development.

A case of upper second premolar and lower first molar guided to normal dentition position by traction

A case of upper second premolar and lower first molar guided to normal dentition position by traction

Electromyographic analysis of fatigue in temporalis and masseter muscles during continuous chewing.

The aim of this study was to evaluate the electromyographic changes in the anterior temporalis and masseter muscles after fatigue induced by continuous chewing. Surface electrodes were placed bilaterally over the anterior temporalis and masseter muscles of 31 subjects with normal dentition. Recordings were taken every minute from the beginning of chewing to the exact moment the volunteer reported subjective sensation of fatigue in the jaw muscles. The length of endurance period (fatigue threshold) was measured to each subject, as well as the average amplitude and duration of activation phase and duration of relaxation phase through electromyographic recording of each muscle. The average endurance period was about 500 s. No significant change occurred on the average amplitude of activation phase meanwhile the duration of both the activation and relaxation phase diminished after fatigue.

The effect of altering jaw position on the transmission of vibration between the skull and teeth in humans

The forces that develop in the human temporomandibular joint during function have never been directly measured, yet many patients exhibit excessive localized wear and tear of the joint, suggesting that at times these forces exceed tissue tolerance. The purpose here was to gain insight into vibration transmission between the cranium and mandible in healthy humans during variations of jaw position. In 13 normal healthy adult men (age 25–40 years) with normal dentitions, vibration (around 400 Hz, sine wave) was applied to the skull vertex and changes in the intensity of the vibration signal were measured using several small linear accelerometers cemented to the buccal surfaces of mandibular first molars and the labial surfaces of maxillary central incisors. The jaw was opened, protruded and moved laterally by the individual participant and vibration signal intensities were tested (lower first molar signal/upper incisor signal) for change at each mandibular position by ANOVA. The results showed the vibration signal changed significantly with opening and less so on protrusion and laterotrusion. The vibration signal during opening could be categorized into three types: (1) signal increased continuously with increased opening; (2) signal increased, then reached a plateau during last third of opening; (3) signal increased, then decreased when the individual moved from 40 mm to maximum opening. These findings show that as the jaw moves laterally, and especially as it opens, the magnitude of the vibration signal increases substantially compared with the near-closed position.

The Occlusal Force Distribution in Normal Deciduous Dentition

The Occlusal Force Distribution in Normal Deciduous Dentition

Cherubism: a 36-year long-term follow-up of 2 generations in different families and review of the literature.

To clarify the relationships between the varying clinical or radiographic features of cherubism. Nonparametric statistics were used in a long-term follow-up of 18 patients through 2 generations from 6 Danish families. The radiographic grade of cherubism was significantly related to sex, maximal buccal bone expansion, course of cherubism, and number of aplasia or ectopic impacted teeth, but it was not related to families. Normal dentition in nonaffected regions was present or was obtained in 14 of 14 patients (age, >14 years). Surgical treatment did not provoke growth of lesional tissue in 22 of 22 cases. Radiographically, the bone structure in the lesional areas was related to age in all grades of cherubism: new bone formation in radiolucent areas (age, >20 years), normal bone structure with multilocular sketches (age, 32 to 39 years), and completely normal bone structure (age, >41 years), also found in 7 of 7 carriers of cherubism (age, >32 years). This group analysis verifies the knowledge of cherubism previously based on cumulative reviews of findings in single-family and case reports.

Influence of clenching level on intercuspal contact area in various regions of the dental arch

The purpose of this study was to evaluate the relationship between the clenching level and the intercuspal contact area in different regions of the dental arch. Twenty-five healthy subjects with natural normal dentitions and good occlusal support performed clenching tasks in the intercuspal position at four different levels (10, 30, 70 and 100% levels of maximum voluntary contraction) through EMG visual feedback from bilateral masseter and anterior temporal muscles. Simultaneously, the occlusal contacts were recorded with a silicone occlusal contact checking material (Black Silicone, GC Dental Industrial Corp., Tokyo, Japan). The occlusal records were analysed by an image analyser. Every area of the thickness less than 50 microm was determined to be an occlusal contact area. The occlusal contact areas on the anterior teeth (incisors and canines), the premolars (first and second premolars) and the molars (first and second molars) were calculated separately. The posterior occlusal contact area increased with an increase in the clenching levels but that of the anterior did not. The results of this study indicate that the increase in clenching forces affects the anterior and posterior occlusal contact areas differently.

Mutation of PAX9 is associated with oligodontia

We identified a frameshift mutation in the paired domain of PAX9 following genome-wide analysis of a family segregating autosomal dominant oligodontia. Affected members have normal primary dentition but lacked most permanent molars.

Calvarial Doughnut Lesions Associated with High-Turnover Osteoporosis Presenting in Childhood

Osteogenesis imperfecta and juvenile osteoporosis are two well-described syndromes of osteoporosis presenting in childhood. There are also several references in the radiology literature to calvarial doughnut lesions (CDLs), areas of radiolucency surrounded by a dense and well-defined area of sclerotic bone, either as an incidental finding or associated with childhood fracture. We have characterized the metabolic abnormalities in a 13-yr-old boy with CDLs and multiple fractures and followed him during his progression through puberty. The patient's paternal grandmother; father; and paternal aunt, uncle, and first cousin were similarly affected, and a mandibular lesion in the uncle was pathologically described as fibrous dysplasia. The subject's physical examination was significant for bony protuberances of the skull and normal hearing, sclearal hue, dentition, and joint flexibility. Radiographs revealed calvarial CDLs and osteopenia which was confirmed by bone mineral density (BMD) testing. Biochemical markers of bone formation and resorption were elevated compared to normal adult and a transiliac crest bone biopsy confirmed high-turnover osteoporosis. Over 6 yr, with no specific therapy, BMD gradually normalized, but the CDLs increased in size, bone turnover remained elevated by biochemical markers, and he continued to fracture. The subject's affected father and maternal grandmother had normal BMD and no history of adult fracture. CDLs with high-turnover osteoporosis should be considered in the differential diagnosis of pediatric osteoporosis. During puberty the BMD normalizes but the high-turnover state persists, and the propensity to fracture eventually decreases in older affected adults. The CDLs may be a variant of fibrous dysplasia, and further study is necessary in order to elucidate the stimulus for increased bone turnover and the familial nature of this syndrome.

顎顔面形態がこう合力およびそしゃく筋筋放電活動に及ぼす影響について ＶＩＩＩ‐２． 総義歯装着者の側貌顎顔面形態とこう合力の方向との関連性

To determine the relationship between the lateral dentoskeletal forms of complete denture wearers and the direction of bite force, the lateral dentoskeletal forms of eight subjects in the normal face group were examined by cephalography. The directions of bite force during vertical clenching in various maxillomandibular relations were measured and correlated with the craniofacial forms.The results revealed that the lateral dentoskeletal forms and the direction of bite force in complete dental wearers had a closer relationship than that in subjects with normal occlusion and dentition. The direction ofbite force for complete denture wearers inclined more towards the front than in subjects with normal occlusionand dentition, and more so as the vertical maxillomandibular relation increased. The results suggested theextreme importance of setting a suitable occlusal plane and vertical maxillomandibular relationship.

Occlusal contacts in maximum intercuspation in normal dentitions

summary A cross‐sectional study of the contacts in maximum intercuspation was undertaken using a method to identify occlusal contacts, which is indicated as satisfactory by modern research. The aims were to describe in subjects with normal dentitions and normally functioning masticatory systems: (a) the general distribution of contacts; (b) the numbers in the various classes and types of occlusal contacts; (c) the numbers of teeth without contact. A randomized sample of 18 women and 20 men was used. Classical theoretical proposals for the numbers, distribution and nature of occlusal contacts were not supported. Wide variability was evident and asymmetry of distribution on the right and left sides of individual subjects was common. Contacts with stabilizing tendencies involved the mandibular supporting cusps in 79% of occurrences. Overall, the difference in the number of contacts with stabilizing effects was not significantly different from the number with unstabilizing tendencies. Contacts with mechanically unstabilizing effects did not produce clinically discernible, unfavourable sequelae in the dentitions. Because of the sparse number of stabilizing contacts, interventions involving the occlusal surfaces should maintain or improve on the number of such contacts in maximum intercuspation.

Sex difference of electromyogram of masticatory muscles and mandibular movement during chewing of food

The aim of this study was to investigate whether there were sex differences in the electromyograms (EMG) of the masticatory muscles and in the mandibular movement of young adults when chewing food. Twenty subjects with normal dentitions were selected. The 11 test foods selected were all easily available in Japan. The results showed firstly that although there were no significant differences of chewing frequency between males and females, females chew food more slowly with less masticatory force and narrower mouth opening width than males; and secondly it appears that the chewing function in females is lower than in males.

Three-dimensional Analysis of Masticatory Orofacial Movements in Adults with Normal Dentition

Three-dimensional Analysis of Masticatory Orofacial Movements in Adults with Normal Dentition