| Maxillary central incisors affect pronunciation and facial appearance; however, they are highly vulnerable to caries and trauma. For clinical treatment purposes, it is important to recognize the three-dimensional morphology of maxillary central incisor. The measurement of maxillary central incisors is limited to manual measurement or two-dimensional observations such as teeth grinding and X-ray radiograph etc. These methods will damage the samples and produce unnecessary errors, which cannot satisfy the needs of three-dimensional measurement of the crown. Micro CT is considered the most advanced 3D tomographic measurement method with resolution of down to 1 ?m, and can perform three-dimensional imaging and measure the distance between two spots on different sections without damage to samples such as tooth and bone.Scanning electron microscope is the most advanced equipment to observe the microstructure of the object. However, three-dimensional measurement of maxillary central incisor crown has not been reported. Meanwhile there is no literature report on three-dimensional state and changes periodontal membrane of Maxillary central incisors in the physiological condition The purpose of this study was to perform 3D scanning of maxillary central incisors with Micro CT, and to reconstruct 3D models of enamel cap and dentine core with reverse engineering software. Then the thickness of two spots on different sections of enamel cap and dentine core could be successfully measured in order to reveal the inherent law and to provide a reference for clinical restoration of the maxillary central incisors. In this study, we would explore the three-dimensional fine morphology of human maxillary central incisors and periodontal membranes from the following two aspects.Study objective and method:This research consisted of two parts. The first part of the experiment was to study the three-dimensional scanning, reconstruction and measurement of human maxillary central incisors, and to analyze 3D models of enamel cap, dentine core and pulp chamber,and to reveal the internal rules of maxillary central incisors crown.At first, 30 specimens were supposed to be selected for performing 3D scanning of maxillary central incisors with Micro CT, and to reconstruct 3D models of enamel cap and dentine core with reverse engineering software. Next step was to measure the thickness of different sites of the sub-models.The second part of the research was to explore the morphological changes of the periodontal membrane of the maxillary central incisors under different mechanical loading. First of all, periodontal membrane stressed device was modified from weight and size. In addition, fifteen pairs of specimens were selected for mechanical loading of maxillary central incisors. At the same time, the specimens were performed 3D scanning with Micro CT and SEM, and were reconstructed 3D models of periodontal membrane with reverse engineering software for exploring the morphological changes of periodontal membrane.Study findings:1. It was the first time that a three-dimensional delicate model of maxillary central incisors which included the sub-models of the enamel cap, dentine core and pulp chamber had been successfully constructed.2. The thickness of the different sites of the enamel cap were 0.47 ± 0.12 to 1.08 ± 0.19 mm for labial enamel, 0.71±0.11 mm for mesial adjacent surface, 0.88±0.12 mm for distal adjacent surface. There was no significant difference in lingual enamel thickness(P?0.05). Pearson correlation analysis showed that there was a statistically significant correlation of between mesial adjacent surface and distal adjacent surface(P?0.05).3. The thickness order,which was from low to high, of the dentine core was as follows: D<G<A<B<E<H<C<I<F(Fig. 4).4. The vertical distances between pulp chamber and enamel surface were shown. The length from mesial medullary angle to incisal edge, from distal medullary angle to incisal edge, from mesial medullary angle to mesial adjacent surface and from distal medullary angle to distal adjacent surface was 4.24 ± 1.04, 4.71 ± 0.98, 2.09 ± 0.26, and 2.53 ± 0.30 mm, respectively(P<0.05). Pearson correlation analysis showed that there was a statistically significant correlation of the distances between the pulp chamber and enamel surface.5. The periodontal membrane stressed device was improved successfully. And the mechanics loading scope of the device was 0-1000 N and the precise degree was 0.1N. When the device was applied to the measured object, the pressure could be continuously and stably applied to the teeth. Then the device was put into the Micro CT and SEM for scanning.6. The three-dimensional delicate model of periodontal membranes had been successfully constructed. The results of the experiment showed that the total area of periodontal membranes was 342.91±4.18mm2,the root area of periodontal membranes was 151.68±3.27mm2,the alveolar bone area of periodontal membranes was 183.38±4.24mm2,the alveolar ridge crest area of periodontal membranes was 7.85±1.36mm2, and the total volume of periodontal membranes was 27.11±2.47mm3. Pearson correlation analysis showed that there was a statistically significant correlation between the area and the volume of the periodontal membranes(P<0.05).7. The area and volume of the periodontal membrane of human maxillary central incisors were measured under the condition of 50% maximal bite force and 100% maximal bite force. The two 3D models of the periodontal membrane were fitted. And the distribution of periodontal ligament was observed by scanning electron microscope.Conclusion A fine 3D model of human maxillary central incisors was successfully obtained for the first time. It consisted of sub-models of the enamel cap, dentine core and pulp chamber.It enabled not only the observation of the 3D structure, but also the establishment of a biomechanical model of human maxillary central incisors. In addition, the three-dimensional model of the periodontal membrane of maxillary central incisors was reconstructed. And the volume and area of maxillary central incisors were measured under different loading conditions. The distribution of periodontal ligament was observed under stress condition. In summary, it provided a good biological model for revealing the inherent law. |
PDF Full Text Request