Abstract:

Objective

To evaluate the reproducibility and accuracy of 3D digital model measurements for the American Board of Orthodontics objective grading system by comparing with the traditional plaster model measurements.

Methods

Thirty conventional orthodontic posttreatment plaster models were included in this study. The plaster models were scanned by 3Shape D810 laser scanner to produce corresponding digital models for 3D digital model measurements with computer software. Then they were trimmed to be standard plaster models for traditional plaster model measurements. Seven criteria （tooth alignment，marginal ridges，buccolingual inclination，occlusal contacts，occlusal relationship，overjet， and interproximal contacts） of the ABO objective grading system were measured. All the measurements were performed by the author. Digital model measurements were performed twice at 2 weeks interval. When finished after 2 weeks， plaster model measurements were also performed twice at 2 weeks interval. After the completion of the measurement，each criterion score and total score were calculated and the results were recorded. Wilcoxon test was used to analyz the easurement results and compare the reproducibility of two methods.

Results

For the reproducibility of two methods， the ABOOGS total score and each criterion score were no significance in two measurements performed at different time （P＞0.05）. Comparing the reproducibility of the two methods， 3D digital model measurements showed lower score difference in tooth alignment（Z=-3.158，P=0.002）， buccolingual inclination（Z=-2.555， P=0.011）， occlusal contacts （Z=-3.150， P=0.002） and total （Z=-2.217， P=0.027）. By comparison of the measurements of two methods， 3D digital model measurements showed higher score in tooth alignment （Z=-3.105，P=0.002）， occlusal contacts （Z=-2.415，P=0.016）， overjet（Z=-2.818，P=0.005） and total （Z=-4.149，P＜0.001）.

Conclusions

Three-dimensional digital model measurements have better reproducibility and accuracy for the American Board of Orthodontics objective grading system than traditional plaster model measurements.

Key words: Digital model, Objective grading system, Reproducibility, Accuracy