A Study On Tooth Wear Measurement With Three-dimensional Computer Assistance

Tooth wear is a common phenomenon in dentistry that occurs in mastication and non- mastication movement. Abrasion between occlusions of tooth and artificial tooth, and between occlusions and foodstuff results in loss of tooth structure and artificial tooth occlusion. In oral environment, it is not a single process, but affected by mechanical .thermal, chemical and electricity factors, etc. The overall processes, which seldom act in isolation, may include erosive, mechanical abrasion, masticatory abrasion and other minor types of wear. The serious tooth wear can take injure to tooth, periodontium, muscle tissue of stomatoganthic system and temporomandibular joint. It shows in clinic as tooth sensitivity, pulpitis,periodontitis,food impaction ,deformation of basifacial caused of loss of occlusal height, temporomandibular disorder syndrome, etc. The wear property of artificial tooth material will lead a direct effect to restoration result, when it exists in oral environment. It will cause tooth enamel loss too much in a very short period, if the wear property of artificial tooth superior to tooth enamel; but if it is inferior to tooth enamel, serious wear will occur on restoration occlusions, which will lead to loss of bite functions and even decrease of occlusal vertical dimension, disorder of bite functions, etc. Therefore, it is important to artificialtooth material not only it's biotic compatibility, mechanical function, chemistry property but also it's wear property. And the measurement of wear rate is always the one of excellent index to evaluate wear property of tooth and artificial tooth.As an important means to study wear, tooth wear measurement is always the focus. But the complexity of oral environment brings difficulties to the wear research. Although extra oral measurement can imitate some oral condition, but the diversified mastication movement and complex environment make it impossible to fulfill all functions. Confined by the operation condition, intra-oral measurement can't make a precise result of tooth wear in a period. Recently, the development of computer three-dimensional technology gives a new approach to tooth wear research.To observe the tooth change in wearing process and then make an exact evaluation in clinical tooth wear, a pilot study in development and application of computer assistant three-dimension measure system was been done in this test. ?Data of tooth surface before and after wear were both obtained through laser scan system. The images were then reconstructed by SURFACER software. (2) C language program used of improved iterative closest point (TCP) algorithms was developed to registrate imagines before and after wear. Standard plan was defined to the overlapped imagines after registration, then wear quantity was measured. ￤ear was imitated by tooth brush machine which was made by STOMATOLOGY COLLEGE FORTH MILITARY MEDICAL UNIVERSITY. The densities of test sampleswere got by water loss method, and electronic scale was used to get chances of test samples. The volumes then can be obtained by this traditional method. The losses of wear quantity were also measured by computer assistant three-dimension measure system. Results between traditional method and new computer assistant measure system were compared. Results indicate that:1. The data of tooth surface scanned by three-dimension laser scan device can be preferably reconstructed through SURFACER converse engineering software.2. It can accomplished imagine registration of tooth surface before and after wear by improved iterative closest point (ICP) algorithms. The new method which adds weight value to the surface data can obviously descent the reconstruct error and value noises. Multi-resolution processor is used to reduce the quantity of calculation, so to quicken the speed of registration and the precision can also reach a certain degree.3. the loss volumes got by 3-d computer assistant measure system is close to which obtained by traditional me...