A Prospective Comparative Study between the Software Models and Clinical Models of Clear Aligner Treatment

Introduction: The purpose of this prospective clinical study was to compare the three dimensional predicted software models with the stage clinical STL models and to evaluate the efficacy of tooth movement with clear aligners. Materials & Method: The sample size included 10 cases with mild anterior crowding treated with aligner therapy. The virtual model of the predicted tooth position was superimposed on the virtual model of the achieved tooth position at various stages over their stationary posterior teeth by using MeshLab software. The amount of tooth movement predicted was compared with the amount of tooth movement achieved. Result: The results of this study have shown that when a comparison was made on the basis of irregularity scores in both the groups, it was seen that the irregularity score was more in Clinical STL group at each stage such as 2.55 at T4, 1.65 at T6 and 1.0 at T8 whereas 2.0 at T4. 0.90 at T6 and 0.25 at T8 in the Software model group. Also, On comparing mean accuracy these three stages, the analysis of data showed the mean accuracy at T4 is 62.5%, mean accuracy at T6 is 68.8% and the mean accuracy at T8 is 78.1%. Conclusion: The predicted software models do not accurately reflect the patient’s tooth position .There is an overestimation by predicted software as compared to actual clinically achieved tooth position. There is a need of overcorrection to be built in the treatment planning stage itself and execution of the anticipated end result.


INTRODUCTION
Movement of teeth without the use of bands, brackets or wires was described as early as 1945 by Dr H. D. Kesling. 1 He reported the use of a flexible tooth positioning appliance. Later, Nahoum 2 and others wrote about various types of overlay appliances such as invisible retainers.
Minor tooth movements have also been achieved with a technique developed by Raintree Essix (New Orleans, LA). This technique used clear aligners formed on plaster models of the teeth. This type of appliance was effective in correcting mild discrepancies in the alignment of teeth. [3][4][5] However, movements are limited to 2 -3 mm 4 and beyond this range, another impression and a new appliance were advocated.
Today in this modern world of orthodontics, various new techniques have been developed to make the treatment more comfortable and esthetic for the patient. The patient has a plethora of options to choose from based on factors such as cost, treatment time, esthetics, comfort and so on. Owing to these factors, increasing numbers of adult patients have sought orthodontic treatment and demand for aesthetic appliances has increased in recent years. 6 With further advancement in orthodontic technology, Align Technology introduced Invisalign TM in 1998, a series of removable polyurethane aligners, as an esthetic alternative to fixed labial appliances. Usually scanned images are converted to physical models by using different stereolithography techniques to fabricate series of aligners that sequentially reposition the teeth. 7,8 Stereolithographic models are constructed at every stage. 9 Each aligner is programmed to move a tooth or a small group of teeth 0.25 to 0.33 mm every 14 days. 10 Since there can be many variables that could affect tooth movement, 6   The tray used for treatment should not be altered with  Once 2 models are superimposed, software will perform an efficacy analysis report which will show quantitative measurements for predicted and achieved movements.

MATERIALS AND METHOD
The percentage of accurate tooth movement will be determined by the following equation:

RESULT
This study was done to assess the difference between the stage clinical outcome and the predicted outcome of clear aligners and also percentage of accuracy.

Data was entered into Microsoft Excel spreadsheet
and was checked for any discrepancies. Summarized data was presented using Tables and Graphs. The data was analysed by SPSS (21.0 version) and Epi-info version 3.0. Shapiro Wilk test was used to check which In this study the mean change from T0 to T4, T0 to T6 and T0 to T8 was compared from Clinical models and Software models and it was seen that the mean change was more in the Software models at each stage respectively. The mean accuracy of the clear aligners was around 78% at T8.
The mean change from T0 to T4 was compared     The results of this study shows that mean change from T0 to T4, T0 to T6 and T0 to T8 comparing both the groups was significantly more in software models in comparison to clinical models.
The result gave an inference that the clinical models showed resolution of crowding when it is assessed Also, the evaluation of the mean accuracy of clear aligners in clinical models at T4 was found to be 62.5, 68.83 at T6 and 78.12 at T8 (Figure 11) (table 4).
Moreover, the comparative evaluation of the irregularity score of Clinical and Software models has been depicted at T0 which is 3.25,3.25 respectively, at T4 2.55,2.00 respectively, at T6 1.60,0.90 and at T8 stage which is 1.00,0.25 respectively( Figure 12) (table 5).

CONCLUSION
The study concluded that the software models overestimated the alignment and the resolution of crowding in comparison with the actual clinical models.
There are variables or biological restrains that alter the accuracy of the clear aligner treatment Hence, there is a need of overcorrection to be built in the treatment planning stage itself and execution of the anticipated end result so as to achieve the desired correction as seen in software models.