Experimental Study On The Effect Of Orthodontic Tooth Movement With Double-foil Clear Aligners Of Different Loading Time

Objective: Clear aligner therapy is an emerging innovative industry combined with numerous subjects like contemporary orthodontics,digital image acquisition and processing,visual simulation software,3 dimensional printing and thermo-compression molding.A series of sequential thermoplastic high polymer materials are manufactured according to the designed orthodontic treatment plan,which generates force through the bias between the configuration of aligner and tooth model to achieve the designed tooth movement.The thickness and loading time of thermoplastic materials are the relatively important factors.Until now,there is still lack of the associated experiment about the effect of tooth movement with clear aligners combining different thickness and loading time.This study intends to move teeth with the combination of thin foil and thick foil.Change the loading time of thin foil and compare the differentiation of tooth movement effect and histologic appearance to investigate the relationship between effect of tooth movement and the loading time.Materials and Methods: This study selected 8 New Zealand white rabbits which were randomly assigned into 3 groups: 4 in experimental group A,3 in control group B and 1 in blank control group C.Then use clear aligners to move lower centrals distalized to produce space.The experimental group wore 0.625 mm foil for 1day and 0.75 mm foil for 2 days per step.Every step lasted for 3 days and 4 steps were designed for them with 12 days in total.While the control group wore 0.625 mm and 0.75 mm foil for 2 days per step.Every step lasted for 4 days and 3 steps were designed for them with 12 days in total.The blank control group received no treatment.Measure the specific data of tooth movement after per step and 1 rabbit was sacrificed for histologic observation.Results:(1)The clear aligners can achieve the effective tooth movement with statistical significance;(2)Compared with the control group,the experimental group has higher tooth movement rate but fewer tooth movement for per step and lower accuracy;(3)AB groups were tipping with clear aligners with no significant differences in tipping level;(4)Compared with the blank control group,AB groups were more active in osteogenesis and osteolysis,but there was no differences between A and B in histologic appearance.Conclusions:(1)Shorten the loading time of thin foil showed improvement the rate of tooth movement effectively but decrease in accuracy statistically which shows no significance clinically;(2)Shorten the loading time of thin foil showed no significance in histology.The bone remodeling and resorption maintained at a range of physiological condition with no pathological change;(3)Clinicians can shorten the loading time of thin foil properly to increase the tooth movement rate so as to shorten the period of treatment and provide better subjective feelings for patients,especially for tipping movement cases.