Morphological Study Of Permanent Teeth Of Han Nationality In Guanzhong Area

As an integral part of oral science, tooth morphology is the basis of clinical treatment. Many previous studies show that tooth morphology varies in different times, nationalities and areas. So it is of great significance to understand exactly the interior and exterior tooth morphology. So far systematic study of tooth morphology in different areas and nationalities is scarce in our country.The objects of this study were the 1000 integrated teeth collected in Guanzhong area of Shanxi province. Firstly, the exterior morphology data such as the the crown length, the root length, the whole tooth length, the cervix length, the mesiodistal length, the buccolingual length and the furcation length were measured by digital vernier. Secondly, radiographs of the teeth were taken both from mesiodistal and buccolingual directions by parallel projection technique. Then, curvature of the root, curve length and position of the curve were measured according to improved Schneider method. At last, ink were infused into pulp cavities from the apical foramen by high pressure oxygen technique. After decalcification and dehydration in series of alcohol solutions, the teeth were finally fixed in methysalicylate and made into transparent specimen. The root canal system was observed.Results:1. Based on Professor Wang Huiyun's method, more exact measurement standard of exterior tooth morphology was established, which was combined with special anatomical points. The standard was practical and repeatable. The results showed that the whole length of human permanent teeth of Han nationality, except the third molar, was 18.72-24.58mm. Maxillary canine was the longest (24.58±1.77mm), and the second maxillary molar was the shortest (18.72±2.04mm). The morphology of maxillary teeth is larger than their peer mandibular teeth. The morphology of mandibular central incisor was the smallest (8.23±1.56mm). The crown length of maxillary canine was the longest (10.04±0.12mm). The ratio of crown length to root length in maxillary central incisor was the biggest (0.91±0.22).The crown length had significant relation with the root length, the cervix length, the mesiodistal length and the buccolingual length (P<0.05), but no obvious relation with the whole tooth length(P>0.05).The study showed that the root furcation was usually 12-14mm to the crown for maxillary premolars, and 9-10mm for maxillary molars, 12mm for mandibular first premolars, 8-9mm for mandibular molars. The incidence of apical foramen mismatching with anatomical apical foramen was 19.6%-45.7%. The length between the apical foramen and the anatomical apical foramen was about 0.4-0.6mm, while about 0.3mm for the maxillary anterior teeth.2. In anterior teeth and premolars, most of root canals were I-typed. The incidence was high( 44.9%-82.3%) in both mesiodistal and buccolingual direction. The incidence of root curve and curve angle were not equal in both directions. Curvature of anterior teeth and premolars mainly existed in the apical third of the root, but curvatures could exist in the cervical third of root of few anterior teeth. Most of curve angle were between 5°and 20°. In anterior teeth and premolars, the average length of root curve was between 2.72 mm and 4.07mm. The biggest length of root curve was 11.63mm in maxillary canine. The incidence of root curve and curve angle in premolars were bigger than that in anterior teeth.3. The root canal in maxillary anterior teeth was simpler than that in mandibular anterior teeth. Maxillary incisor root and palatine root of maxillary molar belonged to the simple canal type, and the incidence of 1-1 canal type was above 90%. The canal type of other teeth was diverse and the incidence of 1-1 canal type was about 50%-90%. The incidence of tri-canal type was low (2.2%) and so was the C-type canal which appeared only in mandibular second molar (13.8%) and maxillary third molar (21.1%). The incidence of lateral root canal was about 12.9%-77.3%. The incidence of accessory root canal was lower than 10% except the fused root in maxillary third molar. The incidence of apical ramification and apical furcation was 4.1%-52% and they appeared in nearly all tooth position especially in maxillary first molar and mandibular first molar.Conclusions:1. Based on previous experiments, the measurement method for exterior tooth morphology established in this experiment could measure exterior tooth morphology exactly. Furthermore, it is practical and repeatable. Combined with radiology and computer-assisted measurement, the degree of root curve can also be measured simply. With the help of high pressure oxygen technique, our transparent teeth specimen can reveal the whole root canal system. These methods are of great significance for the further research of other nationalities and larger range of research work on tooth morphology.2. The permanent teeth morphology of Han nationality varies in different areas. In Guanzhong area, there was obvious relation between the crown length and the root length, but no obvious relation between the crown (root) length and the whole length. The crown length had obvious relation with age and gender.3. In anterior teeth and premolars, the incidence of root curve is high in both mesiodistal and buccolingual direction. The incidence of root curve and curve angle were not equal in both directions.4. The incidence of root curve and curve angle in premolars were bigger than that in anterior teeth.5. The morphology of root canal of Han nationality is complex in Guanzhong area, and the incidence of multi-root canal is high. The morphology of maxillary root canal was simpler than that of mandibular root canal. The incidence of root canal variation was high. Root canal of mandibular incisor was the most complex among the anterior teeth. The complex of the root canal usually can't be known exactly through radiograph in clinic.