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. Vertucci's 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.

Sexual dimorphism in the Japanese cranial base: a Fourier-wavelet representation.

An approach, computational shape analysis (CSA), is presented here which utilizes a Fourier-wavelet representation to numerically describe shape features of biological forms. Two elements are involved: 1) elliptical Fourier functions (EFFs), to provide estimates of global aspects, and 2) continuous wavelet transforms (CWTs) to generate an objective estimate of localized features. EFFs are computed, using a set of pseudohomologous points, to create a precise analog of the boundary. This computed contour is then normalized by scaling and rotated in two-dimensional space to insure a representation that is invariant with respect to starting point, size, and orientation. The predicted point coordinates derived from the EFFs are submitted to CWT for further processing. Wavelet coefficients are then computed to identify localized features, localization being a subjective process with EFFs. The advantage of wavelets is that they eliminate the inevitable subjectivity inherent in the choice of measurements. To test the usefulness of CSA, a sample of cranial base (CB) lateral radiographic outlines was available. Five archaeological periods, Yayoi, Kofun, Kamakura, Edo, and Modern, were utilized (n = 297). Statistically significant differences in sex and archaeological age were found. Although archaeological age differences were present, they were small and random in character, suggesting stability in the CB structures. In contrast, sexually dimorphic differences were present in every group from the Yayoi to the Modern period. This presence of sexually dimorphic differences in shape was consistent with earlier studies of M. nemestrina, G. gorilla, and P. troglodytes. Consequently, it is suggested that the pattern of sexual dimorphism documented in the Japanese CB is a primate pattern with an ancient evolutionary history. The results demonstrate, both visually and numerically, that CSA is a powerful approach for describing both global and localized features of craniofacial structures such as the CB.

Irritancy of scrubbing up for surgery with or without a brush.

Hand washing is an indispensable procedure for surgical nurses. Although scrubbing up with a brush is preferable to prevent infections, it is not clear how irritating to the skin scrubbing with a brush is compared with hand washing without a brush. TEWL, high frequency conductance and pH were measured on the hand skin of the same group of nurses before and after daily hand washing for 11 days in different seasons, which were chosen as favourable and unfavourable periods for the condition of hand skin, namely the early summer and autumn. Additionally, we compared the antimicrobial effects on the skin of scrubbing up, using a palm stamp method. TEWL showed significantly higher values with brush washing than with simple hand washing only in the autumn. There was no significant difference in the measurement of high frequency conductance, pH or in the antimicrobial effects between the two washing techniques. Results showed the deleterious effects on the skin of hand washing, particularly that of using a brush in the cold season.

Morphological variation of the frontal sinus in Melanesian (Fiji) and Polynesian (Western Samoa) populations.

The aims of this study were to investigate gender differences in frontal sinus morphology and to estimate differences between Fijian and Western Samoan populations. Cephalograms of 118 Fijians (59 male, 59 female), 80 W. Samoans (33 male, 47 female) and 89 Japanese (60 male, 29 female) were used in this study. The thickness of the frontal sinus and the convexity of glabella in males were found to be larger than those of females in each population. The angle of Sg-N-G in the Fijians was larger than that of the Western Samoans and Japanese. In order to compare the frontal sinus morphology among populations, Mahalanobis' generalized distances were calculated on the basis of the five distance diameters. The results indicate that gender is separated by the first axis which indicates the overall size. Japanese samples were separated from South Pacific samples by the second axis which indicates the shape factor. In populational discrimination, there was a higher percentage of correct discriminations of the females of the males. In conclusion, gender difference was recognized in the size of the frontal sinus, and the populational differences were shown in the shape factor between Melanesian and Polynesian populations, and also between South Pacific and Japanese populations.

Relationship between maxillofacial morphology and morphological characteristics of vertical sections of the mandible obtained by CT scanning.

A study was conducted to evaluate the relationship between morphological characteristics of vertical sections of the mandibular body and dentopfacial morphology. Cortical bone thickness, tooth inclination and bone inclination of the mandible were investigated. Among skeletal components, ANSMe distance was associated with the buccal cortical bone thickness of the P2 (second premolar) section. Gonial angle, SN to mandibular angle, and palatal to mandibular angle were negatively correlated with the buccal cortical bone thickness of P2 and M1 (first molar) sections. SNA and SNB which indicated the protrusion of the upper and lower jaws were positively correlated with the buccal cortical bone thickness of the M1 section. Among denture components, lower and upper incisor positions showed a significant negative correlation with the buccal cortical bone thickness of the P2 section. The interincisal angle was associated with the basal cortical bone thickness of the M2 (second molar) section. In summary, there were significant and complex relationships between the structures of the mandibular body and maxillofacial morphology. Facial types which relate to masticatory function are associated with the cortical bone thickness of the mandibular body.

Cephalometric analysis of masseter muscle and dentoskeletal morphology in dentate and edentulous humans.

A study was done to clarify the attachment position of the superficial masseter muscle and its relationship with craniofacial morphology in dentate and edentulous subjects. Data were obtained from lateral cephalometric radiographs of a total of 39 cadavers in which the superficial masseter muscle had been defined with colloidal barium. Principal component analysis provided evidence that the lower masseter muscle width was associated with the size of the ramus, and related to the position of the anterior margin of the muscle. Linear discriminant function data suggested that ramus width, coronoid height and the distance between the anterior margin of the masseter muscle and the mandibular notch contributed most to the observed difference between dentate and edentulous subjects. The derived function correctly assigned 100% of dentate and 95% of edentulous subjects. The results of this study indicated that a reduction of masticatory function was associated with the position of the anterior border of the masseter muscle insertion and also with differences in ramus dimension, the most significant of which were differences in the coronoid process and gonial angle. In general, age was not a significant determinant of variation in superficial masseter muscle dimensions or orientation.

Dental arch form in three Pacific populations: a comparison with Japanese and Australian aboriginal samples.

The purpose of this study was to provide information about arch shape variations among South Pacific populations. The application of Fourier transforms, Y(phi i) = ao/2 + sigma (aicos phi i + bisin phi i) was used to separate two components of variation; size and shape. Dental arch size can be described by one coefficient (ao), while the shape can be summarized by the first three harmonics (amp1-3) in the Fourier series. The materials used in this study were dental casts of South Pacific populations (Fiji, Western Samoa and Kiribati), Australian Aboriginals and Japanese. Fijians, Western Samoans and Kiribati people have larger upper and lower dental arches than that of Japanese. These populations were separated by the arch size and first Fourier amplitudes which showed the arch depth/width ratio. The Fijian upper and lower dental arches were significantly larger than those found in other populations and was characterized by a wide posterior arch breadth. The Western Samoan and Kiribati arch shape was more similar to the Japanese arch shape than the Fijian. Distribution patterns of arch shape characteristics in these populations showed the same tendencies in the upper and lower arches.

Lip form responses to changes in maxillary incisor position.

A study was conducted to assess the measurement accuracy of a laser three-dimensional measurement system for measuring facial profile and to investigate the changes in lower facial morphology caused by experimental protrusion of the upper incisors, and also to examine the relationship between the changes in lip form and lip thickness. The study subjects were 24 Japanese male dental students attending Nihon University School of Dentistry at Matsudo, who had normal overbite, overjet, and normal occlusion, and a good facial profile. The mean age was 23.2 years with a range of 21.5 to 25.8 years. Three-dimensional measurements obtained by a computerized 3D laser scanning system were used to evaluate facial morphology. The measurement error of this system was less than 0.5 mm in any three-dimensional linear measurements. The stability and reproducibility of the recording procedure were evaluated. The changes in facial morphology caused by orthodontic treatment and orthognathic surgery were visualized in any direction by this three-dimensional graphic system. Lip thickness was not associated with changes in lip form. However, a relationship between the right and left corners of lip and lip thickness was noted. With regard to the ratio of changes in hard tissue and lips, the value of the original position for a 4 mm protrusion was not the same as that for a 4-8 mm protrusion. Also, the correlation of the changes in both groups was very low. The changes in lip thickness were associated with changes in stomion position, which in turn were related to the vertical change in the upper lip.

Relationship between cranial base and maxillofacial morphology.

The aims of this study were to investigate the relationships between the cranial base and maxillofacial morphology in Japanese crania, and to examine the differences between Class I and Class II samples. Data were obtained from 46 male Japanese crania from the collection of the Jikei University School of Medicine (Tokyo). The sample represents populations which would have lived during the last 100 years. A principal component analysis of linear and angular measurements showed that the anterior and posterior cranial base, and the cranial base angle were associated in different ways with different aspects of maxillofacial morphology. Variation in the anterior cranial base was associated with differences in facial height, lower facial height, bicondylar breadth, ramal height, and ramal width, while posterior cranial base length was correlated with bizygomatic breadth. The cranial base angle was negatively correlated with SNA (r = -0.46) and SNB (r = -0.59), and positively correlated with the palatal and occlusal plane angles. There were significant differences between Class I and Class II specimens in palatal width, SNA, ANB, and the palatal plane angle, but no significant difference in cranial base length or angle. The evidence suggested that cranial base shape and size was related to facial length, inclination of the maxilla, and both maxillary and mandibular prognathism.

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 craniofacial 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.

A principal component analysis of morphogenetic field in the root of Japanese dentition.

Teeth extracted from Japanese male cadavers were analyzed from the morphogenetic point of view. Variables were buccolingual crown diameter, mesiodistal crown diameter, crown height, root length and total length. Each dimension was analyzed separately by means of principal component analysis with varimax rotation. Components extracted from crown dimensions and total length showed 3 or 4 of 5 underlying components for morphogenetic field, anterior group, molar, premolar, canine and incisor. However, for crown height and root length, the components were less distinct.

[Correlation between morphologies of mandibular vertical sections and linear measurements of the skull].

The purpose of this study is to evaluate the relationships between the sectional forms of the mandible and the craniofacial morphology. Vertical sections were made at the symphysis (SY) and at the second molar region (M2R). Materials were dried human skulls which were measured in three dimensional co-ordinate system. The correlation matrix of 24 measurements was examined in the male and the female. The difference of these measurements between the low angle group and the high angle group of gonial angle was also examined. Results obtained were as follows: 1. Gonial angle was negatively correlated with the height, width, breadth of ramus and the breadth of second molars. SY form was related to the facial height and size of the mandible. On the other hand, M2R form was related to the height, width and breadth of ramus. 2. The differences of measurements between the low angle group and the high angle group of gonial angle were as follows: 1) The ramal height, ramal width, bicondylar width and breadth of second molars in the low angle group were significantly larger than those in the high angle group. 2) The measurements of SY in the high angle group and the low angle group showed no significant difference. 3) The height and area of M2R in the low angle group were significantly larger than those in the high angle group. This study demonstrated that SY form might relate to vertical factors of the face (facial height), the size of mandible and the types of occlusions. On the other hand, M2R form being nearer to the attachment of masseter and medial pterygoid muscles than SY was related to the form of ramus and the gonial angle.

A quantitative investigation of irregular cuspules in human maxillary permanent molars.

The frequency of occurrence of anomalous cusps or tubercles on human upper first molars was investigated in seven racial populations using moiré contourography, which permits the three-dimensional measurement of minute cusps. Tubercles on the mesial marginal ridge were more frequently found in Mongoloid populations (Japanese and Eskimo) than in others. The frequency of the protoconule was high in Eskimos and Negroids (Bantu and San). The lingual paracone tubercle (mesial cusp) showed a particularly high frequency in Australian aborigines. The metaconule was rare or absent in all of the populations. Caucasoid groups (Dutch White and Asiatic Indian) showed generally low frequencies of all these abnormal tubercles, especially the distal accessory cusp (C5). Racial differences in the frequencies of occurrence may offer a key to understanding the adaptive significance of these traits and human microevolution. Confusion in nomenclature for upper molar tubercles is also discussed.

Quantitative investigation on irregular cusps in lower permanent molars.

The frequency of occurrence of anomalous cusps or tubercles on human lower first molars was investigated in three racial populations: Japanese, Australian Aboriginals and Dutch white. The technique used was moire contourography, which permits the three-dimensional measurement of minute cusps. Four tubercles investigated were 6th cusp, 7th cusp, deflecting wrinkle and transverse ridge. The frequencies of four traits were all highest in Australian Aboriginals among three, especially those of 6th cusp and deflecting wrinkle were significantly higher than other two populations. Japanese and Dutch showed comparatively low frequencies of four traits, but the 6th cusp in the former occurred significantly higher than that in the latter. There was no significant differences of the frequency in all the traits between sexes. It was suggested that high frequency of these traits in Australian Aboriginals demonstrates the primitive morphology of the lower molar of this population.

[Three-dimensional measurement of the maxillary first molar in Australian whites].

The occlusal surfaces of upper first molars of Australian Whites were measured in three dimensions with the aid of moiré contourography. The dental casts had been collected from Australian White twins who were considered to be of European stock and the casts housed in the Department of Dentistry, The University of Adelaide, South Australia. In the present study, our first aim was to describe the three-dimensional features of occlusal surfaces of molars in Australian whites. One cast was selected from each monozygotic twin pair at random. A total of 24 males and 15 females were photographed. The results obtained in the present study were compared with those of other human populations previously reported. Cusp height of Australian Whites showed intermediate mean values among 8 populations, but mean intercuspal distances were smaller. This feature, such as small size of occlusal surface but relatively high cusps, also found in Dutch and Asiatic Indian. Mean cusp heights in this population of showed similar values between sexes. Mean differences were insignificant as in Asiatic Indian, Australian Aboriginals, and Bantu unlike the Mongoloid, Japanese and Eskimo populations, where there were significant sex differences in cusp heights. This sexual dimorphism in cusp height among human populations is discussed phylogenetically and functionally.

[Metrical study on teeth and mandible in Macaca fuscata fuscata. 2. Principal component analysis].

Metrical investigation on teeth and mandible together was performed to understand the morphological relationship between these two components in Macaca fuscata fuscata. Measurements are 9 items from the mandible, 2 items from dental arch, and 8 mesiodistal diameters from teeth. Correlation matrix composed of 19 items, in total, was examined in males and females, respectively. Significant correlation coefficients were frequently seen among mandibular measurements and also among tooth measurements, but rarely seen between mandibular and tooth measurements. The only exception was a mesiodistal diameter of P3 which has a few significant correlations with mandibular measurements. Principal component analysis was also carried out based on the correlation matrix of 19 measurements. The first component was a size factor in which factor loadings were all positive. The second component was thought to be a factor of the mandibular size in which factor loadings were highly positive on the mandibular measurements and contrarily low on the dental measurements. It is concluded that there is no obvious correlation between general sizes of the mandible and the teeth in Macaca fuscata fuscata.

[TMJ clicking sounds and changes in masking level].

It is known that the peak distribution of the power spectrum seen in the clicking sounds of the temporomandibular joints appears in the vicinity of 1 KHz in a high rate. Based on the findings that this marginal zone corresponds to speech range, the authors have performed masking experiment by narrow band noise on 20 ears in 10 normal persons and 27 ears in 19 patients with noise as subjects to assess the influence exerted by mechanical stimulation on the condition of hearing ability in speech range. The results in normal persons were 14.8dB (S.D. 13.7) at 500Hz. 27.0dB (S.D. 11.1) at 1,000Hz and 21.3dB (S.D. 10.4) at 2,000Hz. The results in abnormal persons were 12.2dB (S.D. 9.9) at 500Hz, 20.6dB (S.D. 6.6) at 1,000Hz and 15.9dB (S.D. 4.4) at 2,000Hz. A significant difference was observed in the masking level between the two groups at 1,000Hz band with a risk rate of 5%. From the above, it was suggested that the sound constituent of TMJ clicking sound exerts influence on the specific auditory level in the patients with noise.

Three-dimensional analysis of the maxillary first molar crowns of Canadian Inuit.

The maxillary first molar crowns of 48 male and 38 female Canadian Inuit (Eskimos) were analyzed three-dimensionally by using moiré contourography methods. Cusp heights were significantly higher in males while the mesial and distal marginal ridges were more proximally placed in males. The metacone and the oblique ridge appeared to be better developed in the males. Comparison of the present results with published results for Dutch and Japanese indicated that the Japanese and Inuit had lower cusps that were more widely spaced than the Dutch. Correlation coefficients suggest that height measurements were positively correlated as were linear measurements. However, there were few significant correlations between height and linear determinations, suggesting that the development of the "width" of a crown is nearly independent of the development of the height of the cusps and crown.

Cusp height relationships between the upper and lower molars in Japanese subjects.

Relationships of cusp height between the upper and lower first molars and between the deciduous second molars in Japanese subjects were analyzed with the aid of moiré contourography. In permanent molars, the height of the hypoconid had a mean value similar to that of the upper trigonal cusps, indicating that upper and lower functional cusps of the same height occlude with each other. In deciduous second molars, however, hypoconid heights were significantly smaller than trigonal cusp heights. Such differences in cusp height between permanent and deciduous dentition may be related to the function and phylogeny of tooth or jaw movements.