Eisaku Kanazawa

Three-dimensional Measurements of the Occlusal Surfaces of Upper Molars in a Dutch Population

The occlusal surfaces of the first upper molars of a Dutch population were measured three-dimensionally by moire contourography. Cusps and ridges were higher than those of a Japanese population, but distances between cuspal tips were smaller. Differences in occlusal form may influence jaw movements in the two populations.

Root canal morphology of mandibular permanent molars at different ages.

AIM To investigate differences in the root canal morphology of permanent mandibular molar teeth at various ages. METHODOLOGY Four hundred and eighty permanent mandibular first and second molars were examined. First and second molars were divided into six and five groups, respectively, according to the age of the patient at the time of extraction. Root canal morphology was studied using a clearing technique. The canal morphology of the mesial root was classified into three stages depending on its developmental pattern. When the root canal system was completely differentiated, the canal classification and the number of lateral canals and inter-canal communications were recorded. Vertuccis classification was taken as the main reference. Canal morphology was compared amongst age groups. RESULTS In both first and second molars, developmental stages of canal morphology amongst age groups were significantly different (P < 0.0001). The prevalence of inter-canal communications was highly significantly different in the first (P < 0.0001) and less significant in the second molar (P < 0.05). After completion of the canal differentiation, the mesial roots of first molars had type IV and II canal forms. The majority of the mesial roots of second molars had type I and III canals. C-shaped canals were found in 3% of second molars. CONCLUSIONS Mesial roots of first and second molars mostly had one large canal until 11 and 15 years of age, respectively. In both molars, the canal system was completely defined at 30-40 years. The prevalence of inter-canal communications was low at young and old ages but high at intermediate ages.

Three-Dimensional Measurements of the Occlusal Surface of Upper First Molars in a Modern Japanese Population

Moiré photographs of the occlusal surface of first molars of Japanese children were taken by means of a specially designed moiré contourograph apparatus. They were then used for three-dimensional measurements. The heights of 4 cusps and some other points were measured by counting contour lines. Distances and angles between them were also measured. Sex differences of these measurements are found mainly around the metacone and hypocone. There is no clear correlation of the four cuspidal heights to the distances between them.

Relationship Between Attachment of the Superficial Masseter Muscle and Craniofacial Morphology in Dentate and Edentulous Humans

Previous studies have described the importance of the interaction between the masticatory muscles and the craniofacial skeleton in the control of craniofacial growth. This study describes the attachment and orientation of the superficial masseter muscle and its relationship -with craniof acial morphology in dentate and edentulous subjects. Data were obtained from lateral cephalometric radiographs of a total of 31 cadavers in which the superficial masseter muscle had been defined with liquid barium. The results provide evidence that the morphology of the superficial masseter muscle in the gonion region differed significantly between dentate and edentulous subjects, with the masseter being 2.7 mm wider and the gonion-anterior muscle border distance being 4.0 mm greater in dentate subjects. The complex relationship between craniofacial morphology and the dimensions and inclination of the superficial masseter muscle were most clearly evident in dentate subjects where the position of the anterior border was related to ramus dimensions and mandibular and occlusal plane angles. The association is much less clear in edentulous subjects where normal function was disturbed. In general, age was not a significant determinant of variation in superficial masseter muscle dimensions and orientation.

Root and canal morphology of permanent mandibular molars in a Sri Lankan population.

The main purpose of this study was to investigate the root and canal morphology of Sri Lankan mandibular molars and to determine the affinities of these morphological variations to those of people of European and Asian origin. Two hundred mandibular first and second molars were examined. The number of roots and the prevalence of C-shaped (gutter-shaped) roots in mandibular second molars were recorded. Root canal morphology was studied using a clearing technique. The examination of root canal systems of the teeth was based on Vertuccis classification. Among mandibular first molars, only 3% had three roots. Mesial roots of the first molar typically presented with two canals and two apical foramina with type IV, V, or VI canal configuration. Most distal roots of the first molar presented with a type I canal configuration. The remainder were distributed mainly between types III and V. Among mandibular second molars, 6% had single C-shaped roots, while C-shaped canals were found in only 2%. The majority of mesial roots of the second molar showed one or two canals, with one apical foramen with type I, II, or III canal morphology. In addition, the distal root commonly showed type I canal configuration. Intercanal communications and lateral canals were more frequently seen in the first molar than in the second. The root canal morphology in mandibular molars varies among population groups. Mandibular root and canal morphology of Sri Lankan people has closer affinities with that of people of European than of East Asian origin.

Principal component analysis of intercusp distances on the lower first molars of three human populations

The distances between the five main cusps of lower first molars were measured on moiré photographs of casts obtained from Japanese, Dutch and Australian Aboriginal children. Principal component analysis of the intercusp distances, log transformed and standardized so that average tooth size was held constant, revealed three sources of shape variation in cusp topography. All populations were similar for scores on component 1 which was concerned with variations in the position of the hypoconulid. The Dutch had lowest scores on component 2 indicating small buccolingual distances compared with mesiodistal, whereas the Australian Aboriginals had the lowest mean score on component 3, expressing the distances between metaconid, entoconid and hypoconulid.

Interspecific allometry of the mandible, dental arch, and molar area in anthropoid primates: Functional morphology of masticatory components

Allometric equations relating the lengths and widths of the mandible and dental arch, and of molar area, were obtained in a wide range of anthropoid primates grouped into four subsets, pongids, cercopithecids, nonmarmoset platyrrhines, and marmosets. Mandibular width is negatively allometric against length across anthropoids but cercopithecids had relatively wider mandibles than nonmarmosets of the same size class. Mandibular length relative to dental arch length was isometric within and between the four groups but dental arch width scaled negatively against all the other dimensions examined in this study, indicating a functional dissociation between the dental arcade and the bony mandible. Molar area showed various scaling patterns relative to mandibular length (isometry) and width (positive). There were no parameters that scaled positively against body weight across groups, except for molar area in cercopithecids (strongly) and nonmarmoset (moderately). Notable functional specializations include relatively long dental arches in cercopithecoids, related to large, elongate bilophodont molars, and the tendency to increase relative jaw length across the range of anthropoid sizes, reflecting negative allometry of the brain (cranial bicondylar width). We caution that various allometry and functional patterns may be masked by generalizing from broad taxonomic comparison involving a large sweep of adaptative patterns.

Evaluation of facial osteotomy with the aid of moiré contourography

The Moiré method, a new technique for recording contour lines on the body surface, was applied to the evaluation of facial osteotomy in patients with oro-facial disharmony. The advantages of the methods are three-dimensional, with no contact. Small changes of the facial profile after osteotomies were measured three-dimensionally and the prediction of probable facial contour changes by osteotomies is discussed.

Study of the Cuspal Ridges of the Upper First Molars in a Modern Japanese Population

Materials used were dental casts of the upper first molars of modern Japanese subjects, comprising 29 males and 25 females. Their molar occlusal surfaces were photographed by moiré contourography using the standard trigonal plane. The ridges of a cusp, comprising a central ridge and mesial and distal accessory ridges, were identified from the patterns of the moiré fringes. The central ridge was observed in all cusps except for the hypocone in both sexes. Frequencies of the mesial and distal accessory ridges of trigonal cusps were over 90% except for the distal accessory ridge of the metacone, and those of the hypocone were under 25% in both sexes. These values were generally higher in males than in females, especially for the distal accessory ridge of the metacone. The running pattern of the cuspal ridges showed little difference between sexes. The oblique ridge which was higher than the central groove formed a saddle-like structure. This ridge was observed in all materials, but its heights and structural components varied remarkably. In this study, the distal accessory ridge of the metacone was found to be incorporated into the oblique ridge in about 13% of cases. Variability in the running pattern of the ridges within a single cusp was highest in the hypocone and lowest in both the paracone and protocone. The results obtained are considered to represent the stability or reductive tendency of cusps in the upper first molars.

Mandibular permanent second molar with four roots and root canals: a case report

Although four-rooted mandibular first molars have been observed on a few occasions in the literature, to the best of our knowledge, four-rooted second molars have not been reported. Here, we describe a mandibular second molar with four roots and canals: two mesial and two distal. Mesial roots were separated in the cervical one-third near the cervical margin, while distal roots were divided at a lower level in the middle one-third of the root. We discuss the possibility of different root and canal variations of the mandibular second molar from a developmental point of view.