CATEGORY 58 AUSTRALASIAN DENTIST LINICAL Effect of attachments in clear aligner system Rotation: As described in the literature, one of the most difficult movements to perform with an aligner is the derotation of a cylindric tooth, as thermoplastic appliances tend to lose anchorage and slip off due to the presence of few undercuts and a round tooth shape. Intrusion: u To facilitate anterior intrusion, attachments on the premolars for anchorage while an active intrusive force is placed on the incisors as well as building bite ramps on the lingual of the upper anterior teeth serving as a bite plane. To improve the accuracy of vertical movement, the use of horizontal attachments (conventional) on premolars for retention or optimized attachments for extrusion and retention, bite ramps or vertical elastics, is recommended. Besides, additional aligners or overbite overcorrection should be used to achieve accurate results. Arch expansion: Crossbite elastics may be used to obtain a better transverse tooth relationship. Overcorrection of maxillary arch expansion is recommended to be prescribed into the digital plan for predictable bodily movement, especially in the posterior region. Moreover, appropriate attachments for buccal root torque is important for bodily movement control during arch expansion. Molar distalization: According to Ravera et al (2016), using Class II elastics and attachments, upper first molars could be distalized 2.25 mm without tipping. Class II elastics were recommended as anchorage preservation during distalization to prevent anterior tooth proclination. Rectangular and vertical attachments were needed on the buccal surface of distalizing molars to create moment resisting undesirable tipping movements Advantages of attachments u Optimized attachments for certain movements, such as extrusion, are needed to generate enough vertical force to perform extrusion effectively. When there is no surface conducive to force application from the aligner, a surface must be created on the tooth for the appropriate force to be applied by the aligner using attachments. u Aligner retention when clinical crowns are short or lack sufficient undercuts. u To improve the ability of aligners to intrude teeth by the use of adjacent or more distant teeth for anchorage. u Active control of tooth movement where crowding can be corrected and bodily movements can be achieved. u Attachment shapes and positions are determined by the tooth movement required in the treatment plan. The shape of the aligner is also able to selectively change to control the force system applied to the tooth. Clinical issues with attachments 1. Tracking issue can be due to two reasons; u Fit of aligner: If the attachment and the aligner are not completely coupled, then the result is an unwanted force system and unpredictable tooth movements Patient should be advised to bite on aligner ‘chewies’ especially for the off-tracked areas. Also for u According to Simon et al, (2014), the mean accuracy for premolar derotation was 42.4% without and 37.5% with the support of an attachment. The lower efficacy with an attachment was mainly due to poor patient compliance, which significantly reduced the treatment efficacy. u It seems that if the aligner fitting is reduced but there is no attachment on the tooth’s surface, the rotational force transfer just decreases, whereas with an attachment, counter-moments can occur, leading to tooth movement in the opposite direction. Extrusion: u The attachments for extrusion can be placed on a single tooth or group of teeth when multiple extrusions are required. Beveled attachments are most often used when extruding a tooth. They can be 3, 4, or 5mm wide, 2mm high, and 0.25 to 1.25mm thick. u It is then necessary to use attachments that have a so-called active flat surface, on which the aligner can exert force. u The active part is the essential element of the attachment since it is the part that is engaged by the aligner. The rest of the attachment serves as a bond and a reinforcement. These attachments should be beveled on the gum side. u In open bite cases requiring absolute extrusion of the incisors, the optimized extrusion attachments are automatically placed on the incisors by the software when a pure extrusion of 0.5mm or more is detected. u Molar intrusion does no need attachments because the occlusal surfaces are adequate for delivering the axial load. However, the adjacent premolars do need attachments to resist the resulting extrusive loads. Therefore, the attachments on the premolar can be conventional for retention or optimized attachments for extrusion and retention. Premolar extraction site: Distal crown tipping of the first molars with attachments should be prescribed to maintain the normal angulation and bodily tooth movement. Posterior anchorage can be improved by increasing the number of attachments bonded on the posterior teeth, optimized and rectangular horizontal attachments have shown the best results. Power ridges, attachments, and greater labial crown torque should be planned in aligner fabrication software to obtain the optimal clinical incisal torque at the end. Anterior retraction with controlled root movement of canines into the extraction site is of primary importance.
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