| Objectives This study is determined to provide an anatomical map of the interradicular space between the second premolars and the first molars in the maxilla and mandible and the bone density around the circumference of miniscrews.The purpose of this study is to assist the clinicians in miniscrew placement in a safe location where better implant stability is also obtained.Materials and methods CBCT images from 38 Chinese patients were selected from Renkang Dentistry Centre,Macao.Three dimensional images were reconstructed by the Ezlmplant software.The sagittal plane in the software was defined as the buccolingual plane.The separate reference planes for the maxilla and mandible were defined as their own planes that included the midpoint of the mesio-incisal angles of incisors and both mesial cusps of the first molars.For each subject,on the median sagittal planes of the interradicular spaces between the first molars and the second premolars in both the maxilla and mandible,the buccolingual bone thickness was measured by postulating that the miniscrews would be inserted at 4 different levels of 10.0mm,12.0mm,14.0mm,16.0mm from the reference planes and 4 angles of 30°,45°,60°,90°.The danger rate representing for implantation sites where buccolingual bone thickness was less than 6.0mm was calculated.The density of the bone around the entire circumference of each miniscrew was also measured.Results①For the maxilla,there is a positive correlation between the insertion levels and danger rates(r_s=0.90).There's no statistical significance of the coefficient between the insertion angles and danger rates(P＞0.05).In the 16.0mm,14.0mm and 12.0mm levels,the highest density among four angles appears at the 30°(P＜0.05). ②There is a positive correlation between the density around the miniscrews and the danger rates.According to the density and danger rates,the K-clustering result shows that the implantation sites could be divided into three groups.Group 2,including the 16.0mm level in 30°and 16.0mm level in 45°,has the greatest danger rate and bone density.Group 1,including the 10.0mm level at 30°,10.0mm level at 45°,10.0mm level at 60°,10.0mm level at 90°,12.0mm level at 90°,14.0mm level at 90°and 16.0mm level at 90°,has the lowest danger rate and bone density.Group 3,including the rest,has the moderate danger rate and bone density.③In the mandible,there's no statistical significance of coeffecient between the danger rates and insertion levels or insertion angles(P＞0.05).For each insertion level,the highest density is found in the 30°among four insertion angles(P＜0.05).There's significant difference in bone density between each two different levels(P＜0.05).There's significant difference in bone density between each two different angles(P＜0.05).Among all implantation sites, the 16.0mm level at 30°and the 14.0mm level at 30°have the highest bone density.Conclusions①In the maxilla,higher danger rates appear in higher insertion levels. Miniscrew insertion safety insured,in order to obtain better implant stability,the insertion angle of 30°is suggested when the 12.0mm level,14.0mm level and 16.0mm level are chosen.②If the insertion safety is uncertain,the group 1 which shows the best safety is suggested,including the 10.0mm level at 30°,45°,60°or 90°,the 12.0mm level,the 14.0mm level and the 16.0mm level at 90°.③The insertion of miniscrew in the mandible can hardly injury the mandibular canal.In order to obtain better implant stability,inserting at 30°is suggested as the best choice for different insertion levels,followed by inserting at 45°. |
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