| During the long-term human evolution, the change of dietary structure andthe improvements of labor tools have weaken the masticatory organ function,and led to degeneration of masticatory organs and prevalence of certain dentaldiseases (eg. dental caries, periodontal disease). The human tooth form, and thestatus of tooth wear and third molars also changed accordingly. Tolongitudinally observe evolution of the teeth, we studied teeth morphology ofthe ancient people, and explored the pattern of occurrence and development..Given the old age and the damages of the samples, as well as thelimitations of the research methods, few scholars have studied internal tooth rootcanal of ancient people. Previouly, sequence cutting method, transparentspecimen method and X-ray technique were the main methods to study the rootand canal system. However, the former two methods are destructive and canintroduce artifacts of the specimens; and the traditional radiographic methodcould only provide2D image and a lot of3D morphological information wouldbe lost. In recent years, Micro-CT (micro-computed tomography) becomes themain tool for investigation of tooth morphology because of its high resolution.Many3D reconstruction softwares, measurement and image analysis softwareshave been developed, and the ondontometric study becomes more convenient and more accurate.In this study, we carried out precise measurements of root canals in theteeth of people living3000years ago excavated in Xi’an, by using micro-CTscanning.In the first part of the study, sixty-serven anterior teeth and25mandibularsecond premolars unearthed from cemetery of Western Zhou Dynasty in Xi’anChangan District were scanned by a Micro-CT, and root canal curvatures weremeasured by Schneider method. The results showed that:(1) there were morecanal curvatures in the buccolingual (BL) direction than in the mesiodistal (MD)direction.(2) the root canal always curved lingually in BL and distally in MD;all maxillary anterior teeth present a type1-1root canal. In a canine, apicalramification was observed.(3) The rate of straight canal was high for the type1-1canals.19.04%of maxillary lateral incisors has a S-shaped canal; and19.04%of the lateral incisor and12.50%of canine presented curvature both inthe MD and in the BL planes.(4) the proportion of severe curvature issignificantly (P <0.05) higher in BL than in MD.(5) the proportion of straightcanal is large in the mandibular second premolars. In BL, the rates of themoderate and severe curvatures were20%and12%,respectively. In MD, therate of moderate curvature was16%, and no severe curvature was observed.In the second part of the study,25mandibular second premolars unearthedfrom cemetery of Western Zhou Dynasty were scanned by Micro-CT scan. Thenthe root canal taper and root canal wall thickness were measured by the software.The results showed, in BL, the root canal tapers of coronal middle and apicalthird were0.248±0.197,0.353±0.110and0.138±0.115, respectively; and in MD,the values were0.069±0.073,0.083±0.056and0.074±0.048, respectively. InBL, the middle third had the largest taper,, followed by the coronal and the apical thirds. The difference has statistics significance (P <0.05).In MD, themean value of the root canal taper was also the highest in the middle third level,whereas the difference between three levels has no statistics significance (P <0.05).The wall thicknesses of the coronal third at the mesial, distal, buccal, and lingualsides were2.07±0.32mm,2.08±0.24mm,2.14±0.57mm and2±0.69mm,respectively; of the middle third, the values were1.66±0.32mm,1.45±0.26mm,1.68±0.56mm and1.52±0.63mm, respectively; and of the apical third, were1.30±0.39mm,1.18±0.31mm,1.25±0.56mm and1.34±0.65mm, respectively.The differences among four sides has no statistical significance (P <0.05). |
PDF Full Text Request