| Research background:Implantology is currently the fastest growing, most popular and influential branch in stomatology. The key to implantology success is the enough osseointegration and to avoid the damages to the adjacent organs and tissues. The selection of the implant in appropriate diameter and height is a prerequisite for successful implantation, so it is very important to judge bone mass accurately before surgery. Panoramic radiography is the most useful diagnostic tool and the most common method for bone mass detection, and also plays an important role in the treatment of orthodontics and oral and maxillofacial surgery at present. The principle is to place the subject between the x-ray machine and film. X-ray machine and film made by the subject of the curvature of the opposite direction, there by recordinglayer of Maxill of acialtomography imaging curved surfaces. Panoramic radiography can show entire views of the jaw bone in low cost and simple way, but also exist image distortion and other defects. Although scholars at home and abroad have studied distortion of panoramic radiography, this technique still remains controversial at the evaluation of distortion in clinical research. In addition, there are no research reports on distortion of each teeth of different height. Objectives:Through the retrospective analysis of panoramic radiography in the cases which have been successfully implanted,we can evaluate the feasibility of previous calculation methods,analyze the vertical distortion and the horizontal distortion of each teeth on posterior segment, find out the height and appearance situation of inferior alveolar canal on different tooth position. This study might provide the basis for clinical evaluation of bone mass in posterior segment.Methods:122 implant-surgery cases and 240 tooth positions were collected, and the following parameters were determined:the height and the top width of each dental implant, ITI dental implants diameter at the alveolar ridge crest area and 5.0mm and 8.0mm below alveolar ridge crest in physical part, the mental foramen, and theappearing situation of the inferior alveolar canal and its diameter below each teeth.The calculated method of distortion:Distortion rate= (measured value -actual value)/actual value×100%. Measurement results were analyzed using SPSS17.0 software with a 0.05 significance level test.Results:1. The mean ratios of the horizontal and vertical distortion of maxillary first premolar area were -5.00% and 0.02%; The mean ratios of the horizontal and vertical distortion of maxillary second premolar area were -5.09% and -0.39%; The mean ratios of the horizontal and vertical distortion of maxillary first mola area were -3.95% and 0.15%; The mean ratios of the horizontal and vertical distortion of maxillary second molar area were -4.05% and -1.28%; The mean ratios of the horizontal and vertical distortion of mandibular first premolar area were -2.97% and -1.98%; The mean ratios of the horizontal and vertical distortion of mandibular second premolar area were-3.79% and-0.64%; The mean ratios of the horizontal and vertical distortion of mandibular first molar area were-3.13% and -0.66%; The mean ratios of the horizontal and vertical distortion of mandibular second molar area were-3.45% and-0.41%; The horizontal distortion between each teeth, P> 0.05, no statistically significance.The vertical distortion of maxillary first premolar group and the mandibular first premolar group P=0.05,the mandibular first molar group and the maxillary first molar group P<0.05, with statistically significance.2. The distortions of two panoramic radiographies at the same patient have no statistically significance (P> 0.05).3. The distortions for the same person to the same panoramic radiography after 2 weeks have no statistically significance (P> 0.05).4. The distortions evaluated by balls before surgery and evaluted by dental implants comparison, P> 0.05, no statistically significance.5. The horizontal distortions comparison of dental implants at the alveolar ridge crest area,5.0mm and 8.0mm below alveolar ridge crest. The horizontal distortion at 5.0mm and 8mm below alveolar ridge crest have enlarging trend compared with the alveolar crest area at the maxillary first premolar and second premolar area, P<0.05, The horizontal distortion at 5.0mm and 8.0mm below alveolar ridge crest have reducing trend compared with the alveolar crest area at the mandibular first molar and second molar area, P<0.05, with statistical significance.6. The position and appearance rate of mental foramen at panoramic radiography.The appearance rate of right mental foramen at panoramic radiography is 91/122×100%= 74.59%,20.88% mental foramen located between the second premolar and first molar,46.15% located below the second premolar,29.67% located between the first premolar and second premolar, only 3.30% located below the first premolar.7. Appearance rate and the diameter of the inferior alveolar canal. Appearance rate of the inferior alveolar canal decreased from the back to the front at panoramic radiographies. Appearance probability of the inferior alveolar canal in both upper and lower wall at third molar, second molar, first molar, second premolar were:70.59%, 58.82%,39.50%,10.08%.The diameter of inferior alveolar canal at the third molar, second molar, first molar, second premolar were:3.20±0.46,2.96±0.40,2.79±0.38,2.67±0.32(unit:mm). The diameter at the third molar and second molar, third molar and first molar, third molar and second premolar, second molar and the first molar were compared, P<0.05, with statistically significance; Second premolar and first molar, second premolar and second molar were compared,P>0.05, no statistically significance.Conclusions:1.The horizontal distortion at posterior teeth was constant, showing a reduced trend; there are large differences between mandibular first premolar and maxillary first molar,maxillary first premolar in vertical distortion, but the vertical distortion is smaller than the horizontal distortion.2. The use of metal balls could accurately correct the vertical distortion and the horizontal distortion at the top of alveolar.3. In the area 5.0 mm and 8.0 mm below alveolar crest at the maxillary first premolar and maxillary second premolar, the horizontal distortion showed amplified trend compared with alveolar crest. In the area 5.0 mm and 8.0 mm below alveolar crest at the mandibular first molar and mandibular second molar, the horizontal distortion demonstrated reduced trend compared with alveolar crest. Therefore, we can not simply correct the distortion by the metal balls in these areas.4. Mental foramen was located below the second premolar at most, following between the first premolar and second premolar, and between the second premolar and first molar. The least was at the bottom of the first premolar. 5. The appearance rate and the diameter of inferior alveolar canal became smaller from the back to the front, but the trend was not obvious near the second premolar. With this feature, we can reckon the upper wall of the alveolar canal if it is not clear enough, to avoid the damage of nerves. |
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