| Facial soft tissue analysis in three dimensions is very useful and uttermost imperative for pre-orthodontic planning, post-orthodontic evaluation, or for the assessment of maxillofacial development and growth. With scores of tools for facial soft tissue scanning, three-dimensional(3D) laser scanners are increasingly being used by orthodontists for its high accuracy, short scanning time, small capacity, no radiation and relatively inexpensive.Previous studies have focused on the accuracy of linear measurements on 3D soft tissue surface model made with laser scanner compared with direct caliper measurements and the precision of the repeated landmarks location on 3D images, while few discussed the repeatability and reliability of 3D laser scanners or the comparison of accuracy of different superimposition methods.As our team had completed the research of the accuracy of the laser scanner and the consistency and accuracy of landmarks’ location, the following study fell into three parts.Part 1: Reliability of capturing facial soft tissue images using a 3-dimensional laser scannerObjective: The purpose of this study was to evaluate the reliability of a 3-dimensional facial scanning technique for the assessment of facial soft tissue. Materials and Methods: Ten adult subjects, mean age 25.4 years, participated in this trial. Three dimensional images were captured at baseline(T0), three minutes later(T1) and three days later(T2) by using Minolta Vivid 9i(Osaka, Japan) laser scanner. The pictures were superimposed to assess the whole deviation between the two faces at T0 and T1, and T0 and T2. The registration was performed twice by 2 observers to investigate the inter-observer error.Results: The mean whole deviations were 0.417±0.141 mm for T0-T1 and 0.476±0.083 mm for T0-T2 conducted by observer A. And for observer B, the mean whole deviations were 0.448±0.079 mm for T0-T1 and 0.454±0.061 mm for T0-T2. Paired t-tests revealed that the difference of whole deviation at different stages and by different observer was statistically insignificant(P>0.05).Mesh deviation facial maps of the merged scans showed that when a tolerance of 0.8 mm was imposed on the aligned faces the 90% of images were reproducible.Conclusion: The three-dimensional(3D) laser scanner is an accurate tool to capture 3D images of the same individual at different times.Part 2: Comparison of two different superimposition methodsObjective: The purpose of this study was to compare the accuracy of different superimposition methods and explore their reliability.Materials and Methods: Two different superimposition methods(semi-surface superimposition and point + region composite registration) were used to register the images acquired at T0 and T2, which performed twice by two observers.Results: The mean register error of semi-surface superimposition and point + region composite registration were 0.448±0.074 and 0.516±0.094 mm respectively and there was significant difference between them, thus the semi-surface superimposition was more precise than the other one.Conclusion: According to the high accuracy and reliability of semi-surface superimposition, we consider that it will be a better method to evaluate the treatment effects.Part 3: The assessment of facial soft tissue changes of three dimensions using Invisalign technique in adultsObjective: To evaluate the changes of facial soft tissue in three dimensions among adult patients of Invisalign.Materials and Methods: Twenty adult patients, mean age 28.14 years, participated in this trial. Three dimensional images were captured at pre-treatment and post-treatment by using Minolta Vivid 9i(Osaka, Japan) laser scanner. The pictures of pre-treatment and post-treatment were superimposed using point + region composite registration to assess the whole deviation between the two faces. The lower part of their faces were incised into six regions consisting in right upper cheek(R1), right lower cheek(R2), upper lip(UL), lower lip(LL),left upper cheek(L1) and left lower cheek(L2),and the whole deviations of every region were computed. The changes of three dimensions of five landmarks including Superior labrale(Ls), Inferior labrale(Li), Left cheilion(LCh), Right cheilion(RCh), B′ were calculated.Results: The whole deviations of six regions and the changes of five landmarks in three dimensions are smaller than the tolerance level(0.8mm).Conclusion: Few changes of facial soft tissue in three dimensions occur among adult patients using Invisalign technique without extraction... |
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