The Effect Of Attachment To Retention Force Of Clear Removable Orthodontic Appliances And Development Of A3-dimensional Measuring System Of Teeth Movement

ObjectivePart1:To investigate the retention force of China-made removable clear orthodonticappliances with different thickness and attachment design and provide a reference forattachments design.Part2: To establish a soft ware tool to superimpose and analyze three-demensionaldigital dental models used in China-made clear removable orthodontic appliances.We canuse it to measure the efficacy of teeth movement MethodsPart1: Four models of lower arch and removable clear orthodontic appliances withdifferent design are producted. According to different thickness of material, the appliancesare divided into4groups:(1) thickness1.0mm appliance without attachment（;2）thickness0.75mm appliance without attachment;（3）thickness1.0mm appliance with attachment;（4）thickness0.75mm appliance with attachment.According to different shapes ofattachment the appliances are divided into4groups:(1) vertical-rectangle attachment（2）vertical-ellipsoid attachmen（t3）horizontal-rectangle attachment（4）horizontal-ellipsoidattachment. A repeated placement and removal test on the7different points of applianceswas performed using the universal testing machine,then record the force measurementresults and statistical evaluation.Part2: We use industrial CT to digitalized the models by layer-scanning method,combining with the CAD technique to superimpose the digital models from patients whoare treated with China-made clear removable orthodontic appliances. Then the matchingdegree of the two models will be examined by color gradation method.The dentalmovements could be measured in three dimensional directions through the coordinate ofpreselected points on teeth crown.ResultsPart1: The attachment apply great retention force to appliances. The thickness0.75mm group with attachment has greater retention force than0.75mm group withoutattachment. The thickness1.0mm group has greater retention force than0.75mm groups.There was a significant statistics difference among the4attachment shapes groups. Thehorizontal-rectangle attachment apply great retention force to appliances. There have nosignificant statistics differences between other three groups. The retention forces atremoving-points of lingual of first molar and buccal of second molar are smaller thanother points，at cuspid buccal point are maximum.Part2: Two methods have been development to model superimposition: Hausdorffdistance method and Barycentric coordinates method. This system can superimpose and analyze digital models in three dimensional directions.and we can use it to measure theefficacy of teeth movement.ConclusionsPart1:The thickness1.0mm China-made clear removable orthodontic applianceapply greater retention force than thickness0.75mm.The attachments add the retentionforce of clear removable orthodontic appliances greatly.Horizontal-rectangle attachmentapply great retention force to appliance.It’s easier to remove appliance with labially placedattachment at first premolar vertically from lingual of first molar and buccal of secondmolar.Part2: A China-made analysis system for three-dimensional digital models used inclear removable orthodontic appliances was preliminary established and we can use it tomeasure the efficacy of teeth movement.