الفهرس 
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Abstract
This study was carried to evaluate the force delivery of different aligner systems in an in vitro setting. Force delivery of aligners is one of the most important characteristics that contribute to the efficiency of the aligner system. Many factors associated with the thermoplastic properties of clear aligners can influence their force delivery capacity.
Polyethylene Terephthalate Glycol modified (PET-G) Duran aligners were investigated in this study with different variables to evaluate the difference in force delivery. The study was carried out in the digital center of the Orthodontic Department, Faculty of Dentistry, Ain Shams University.
In order to measure the force delivered by different aligners, an electrical resistance measurement set up was incorporated for this study. A thin-film, single-force sensor was used to determine the force changes of different aligners.
Force measurements were achieved by sandwiching the sensor on a single tooth between the aligner and the resin model. Pressure applied by the aligner was received by the sensor which was connected to a circuit board. These values were then transmitted through the board to the software where an equation was integrated to convert these pressure values into force values. Force values were then displayed on the computer screen and recorded for each sample in the study.
The three main variables that were investigated in this study were the thickness of the aligner (group 1), amount of tooth activation (group 2) and method of aligner fabrication (group 3). These factors were assumed to potentially affect the force delivery capacity of clear aligners.
Force Delivery of all available Duran aligner thicknesses were evaluated with constant tooth activation and method of fabrication for group 1. For group 2, the influence of different tooth activation increments on force delivery was measured using constant aligner thickness from Duran thermoformed using the same method of fabrication.
For group 3, the force delivery of aligners thermoformed by negative pressure versus aligners thermoformed using positive pressure were compared. All the samples in both comparison groups were of made from constant thickness and thermoformed on the same tooth activation.
For each group, the force values were collected, tabulated and statistically analyzed using IBM SPSS Statistics Version 20 for Windows.
The results obtained from this study led to the following conclusions:
1) The thickness of the aligner, the amount of tooth activation and method of fabrication of the aligner are factors that substantially affect the magnitude of generated orthodontic forces.
2) As the aligner thickness increases, there is a statistically highly significant increase on the amount of generated orthodontic forces.
3) Thinner aligner thicknesses (< 0.75mm) generate forces that lie within the optimum orthodontic forces needed for uncontrolled palatal tipping of a central incisor. When considering stress relaxation experienced by aligners and viscoelasticity of the PDL, less than optimum forces delivered by thinner aligners can potentially be inefficient in a clinical situation.
4) The 0.75mm aligner was the most effective in achieving uncontrolled palatal tipping in an invitro setting. It was only aligner thickness that delivered slightly higher than optimum biologic forces.
5) The 0.75mm aligner can potentially be used during the initial stages of clear aligner treatment to achieve simple tooth movements. Thinner aligners can be used when lower forces are required during other types of tooth movement such as intrusion.
6) In an invitro setting, the 0.4mm aligner showed considerable deformation compared to the thicker aligners during experimental handling, potentially making it the most unsuitable for clinical application.
7) Greater tooth activations will lead to a statistically highly significant increase in forces delivered by the same thickness aligner.
8) The smallest tooth activation (0.1mm) with the 0.75mm aligner delivers high enough forces for uncontrolled palatal tipping. Increasing tooth activations (0.3mm and 0.4mm) can lead to up to four times more than optimum forces with the 0.75mm aligner.
9) The method of aligner fabrication affects the forces delivered by the aligner. Using positive thermoforming pressure increases aligner fit and adaptation on the resin model leading to a statistically highly significant increase in force delivery. While using negative pressure will deliver forces that lie within the biologic force range for uncontrolled tipping, however, these forces are in the lower bound of the range.
10) In summary, the 0.75mm aligner thickness paired with small activations that range between 0.1-0.2mm thermoformed with positive air pressure was found to be the best invitro combination for the Clear-Aligner System as it produces adequate orthodontic forces that lie within the biologic range.