Comparative Study Of The Intraoral Scanning Accuracy Of Occlusal Contacts Of Mandibular First Molar For Difference Degree Of Tooth Wear

Objective:Contrast study of the scanning accuracy difference of Cerec system towards occlusal contact of mandibular first molar with mild and moderate wear, and investigating the regional distribution of occlusal contact of the mandibular first molar with mild and moderate wear. To provide the oretical basis for the improvement of occlusal contact precision of the restorations produced by the Cerec chairside system and the clinical occlusal adjustment.Methods:From May 2015 to December 2015, we selected patients who came to our hospital for treatment or oral counseling and then after informed consent, these patients were classified according to the mandibular first molar occlusal surface abrasion degree, which was assessed by the Knight Smith abration index standard.According to the inclusion and exclusion criteria, 84 tooth of 42 patients were selected as the study objects, Through the image capture system of Cerec Omnicam,we performed the oral optical impression for the subjects, and then obtained the virtual occlusion images of mandibular first molar occlusal contact distribution. The contact occlustion of intercuspal position(ICP) was carried out in the mouth with 40?m Bausch occluding paper and then collected the surface imprinted images of the mandibular first molar occlusion using the Canon EOS 600 D digital SLR camera.Photoshop CS6 Adobe image software was used to analyze the distribution of the occlusal contact areas in ICP of mandibular first molar, and to evaluated the scanning accuracy of Cerec system by calculating the overlap rate of the occlusal contact areas.Results:1. The occlusal contact areas of mild abrasion group in ICP are broadly distributed in the distal cusp and the proximal and distal lingual triangular ridge,distal buccal cusp and the mesial and distal lingual triangular ridge, mesial buccal cusp and the mesial and distal tongue triangular ridg and the distal marginal ridge of occlusal surface of mandibular first molar; The occlusal contact areas of moderateabrasion group in ICP are located in the distal cusp, mesial and distal lingual inclined surface, distal buccal cusp and the mesial and distal lingual inclined surface, mesial buccal cusp and the mesial and distal lingual inclined surface, central fossa and the proximal and distal marginal ridge of tooth occlusal surface of mandibular first molar;The difference of occlusion contact distribution between the two groups has a statistical significance(P < 0.05).2. The average occlusal contact area overlap rate of mild abraion group in ICP is86.68 ± 1.41; The average occlusal contact area overlap rate of moderate abraion group is 87.60 ± 2.06. the occlusal contact precision of moderate abrasion group is significantly higher than that of the mild abrasion group(P < 0.05).Conclusion:1. The occlusal contact areas of mild abrasion group of mandibular first molar in ICP is distributed in the function cusp and its triangular ridge and distal marginal ridge of occlusalsurface, along with the deepening of abrasion, the distribution of occlusal contacts is expanded, The occlusal contact areas of moderate wear group of mandibular first molar in ICP increases the central fossa and the proximal marginal ridge area of occlusalsurface;2. Cerec chairside system have higher scanning precision in moderate wear group of mandibular first molar than mild wear group.