The Preliminary 3-dimensional Morphological Study For The Crown Tissues And Peridental Membranes Of The Human Mandibular First Molars

Mandibular first molar, the first permanent tooth that human beings generate, plays a very important role in the whole stomatognathic system.So it is in a dire need to have a understanding of the three-dimensional delicate state of the tooth and its periodontal tissue, which is extremely helpful in directing the surgery therapy. The researches on the external state of the mandibular first molar are sufficient from the existing literature, such as the clear index description of its dental diameter and near-far middle diameter. However, fewer researches describe the internal state and structure of mandibular first molar. The prevalent method (physical section cutting) to measure mandibular first molar is destructive which can only measure some linear index of a certain two-dimensional cross section enamel and dentinee thickness of its dental corona. Moreover, it can not tell the whole three-dimensional delicate state let alone the measurement of three-dimensional index of enamel and dentinee area and volume. Meanwhile there is no literature report on three-dimensional state and changes periodontal membrane of mandibular first molar in the physiological condition (stressed condition or unstressed physiological condition). With the wide application of digital technology in the stomatology, Micro CT scanning has been used considerably to three-dimensional measurement. As the present most advanced cross section scanning technology, Micro CT resolving capability is able to reach 1μm at most, finish the three-dimensional reconstruction of skeleton and teeth without the damage of the specimen, and measure the area, volume and distance of the specimen precisely. Although there are some researches from the domestic and foreign literature about the application of Micro CT scanning to the study of infra-human molar dental corona structure and the study of little mouse periodontal membrane changes in the condition of mechanics loading, literature reports on mandibular first molar are rare at present.Study objective and method:The study objective of this paper consists of 2 parts. In the first part it aims at exploring the internal structure state and some laws of mandibular first molar through its digital scanning, reconstructing, and measuring as well as the analysis the enamel cap, dentinee core and pulp chamber of the three-dimensional reconstruction model. The detailed steps are as follows:At first,30 specimen are supposed to be selected. And then after Micro CT scanning of the selected specimen there is a reconstruction of sub-model of the enamel cap, dentinee core and pulp chamber. Next step is to measure precisely the linear distance index between every pulp angle in pulp chamber and its corresponding dentinee cusp and the teeth cusp surface through reverse engineering software. Finally it comes the measurement parameter of the area and volume of the enamel cap, dentinee core and dental pulp. In the second part the aim is at detecting the jaw bone varied state and changes under the stressed and unstressed condition of periodontal membrane of mandibular first molar. First of all, periodontal membrane stressed device should be designed by oneself which imitates the normal condition of maxillmandibular occluding and conducts mechanics loading on mandibular first molar. In addition, comes the selection of 2 the jaw bone sets of maxillmandibular as specimen conducting 3 times mechanics loading((0 bite force,50% bite force,100% bite force). At last there is a three-dimensional reconstruction of periodontal membrane of mandibular first molar and a precise three-dimensional measurement analysis of the changes of periodontal membrane area, volume and thickness in terms of different mechanics loading.Study findings:1. It is the first time that a three-dimensional delicate model of mandibular first molar which includes the sub-models of the enamel cap, dentinee core and pulp chamber has been successfully constructed.2. The results of the experiment shows that the enamel cap volume of mandibular first molar is 202.93±21.58mm3 and its area is 494.38+38.60mm2. The pearson correlated test shows the enamel cap volume and area has no obvious relation with statistics.3. The results of the experiment shows that the dentinee core volume of mandibular first molar is 367.09+35.76mm3 and its area is 192.19±11.46mm2.The pearson correlated test shows the dentinee core volume and area has relation with statistics(p< 0.01). Meanwhile, it is found the linear distance maximum is the dentinee cusp of distal lingual dentine cusp through measurement of the distance between every pulp angel and its corresponding dentinee cusp. The following order is:distal lingual dentine cusp, distal buccal dentine cusp, distal dentine cusp> mesial lingual dentine cusp> mesial buccal dentine cusp. By comparison far-tongue dentinee cusp, far-cheek dentinee cusp and far-middle dentinee cusp with mesial dentinee cusp near-cheek dentinee cusp, the difference is statistically significant(P< 0.05).4. The results of the experiment shows that the pulp chamber volume is 35.55±5.32mm3 and its area is 142.01+21.75mm2.The pearson correlated test shows its volume and area has relation with statistics(p< 0.01). At the same time it is found the linear distance maximum is the istal lingual dental cusp through measurement of the distance between every pulp angel and its corresponding dentinee cusp. The following order is:distal lingual dental cusp> mesial lingual distal dental cusp> distal dental cusp> distal buccal dental cusp> mesial buccal dental cusp.The difference is statistically significant(P< 0.05) by comparison the pairs.5. A periodontal membrane device conducting mechanics loading is made.The mechanics loading scope of the device is 0-1000N and the precise degree is 0.1N. Through the practical test the device is able to conduct force loading on the target teeth according to designing requirement randomly and to be placed in Micro CT to make the force loading perpetuate. 6. The experiment has something to do with the measurement of the volume, area and thickness of 1 pairs or 2 human beings’mandibular first molar periodontal membrane and the periodontal membrane thickness of the crotch of mandibular first molar root, near middle root and far middle root under the condition of unstressed and 50% maximized occluding power and 100%maximized occluding power. The thickness measurement results is shown in the following tables:ConclusionThe experiment succeeds in making a three-dimensional delicate model of mandibular first molar which includes the sub-models of the enamel cap, dentinee core and pulp chamber and finding and inducing the internal three-dimensional state law so as to provide a new method and conception for the dental research. Moreover it is the first time a periodontal membrane three-dimensional model of mandibular first molar has been reconstructed and the three-dimensional index of its volume, area and thickness has been measured and analyzed. The preliminary study shows the changes of periodontal membrane of mandibular first molar before occluding and after occluding. So above all the paper presents a new and feasible way for human periodontal membrane study.