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ePaper created 2017-09-06, 09:11:22 | version 1.38.0
case report maxillary molar distalisation with aligners Maxillary molar distalisation with aligners and cyclic forces Author: Dr Tommaso Castroflorio, Italy Introduction In the last decade, clear aligner therapy (CAT) has become a well-known treatment option in ortho- dontics, mainly owing to patients’ preferences for aesthetic appliances. With respect to conven- tional fixed appliances, aesthetics is not the only advantage of CAT. Several papers have concluded that aligners provide better comfort and, being metal-free, avoid irritation of the cheek and gin- gival tissue; facilitate better oral hygiene, allow- ing the patient to remove the aligner while eating and to brush and floss the teeth after eating; and results in less pain compared with conventional brackets. In clear aligner-based orthodontics, an intentional mismatch between the aligner and the teeth is programmed based on the desired tooth position. Through this process, a force system is transmitted to the teeth. However, CAT has shown some limitations regarding the gen- eration of complex force systems for achieving extrusion, rotation, bodily tooth movements and root movement control. In order to overcome these limitations, auxiliaries such as power ridges and composite attachments were designed and engineered to improve CAT biomechanics, en- abling the expression of more complex force sys- tems. Even so, orthodontics is not only a matter of applied mechanics, since the biological response of the patient plays a determining role. Aligners are capable of producing the same biological re- sponse as fixed appliances do.1 Stimulation of the bone cells is mediated by several factors, such as a member of the tumour necrosis factor ligand and receptor superfamilies, including the receptor activator of nuclear factor kappa B ligand, the receptor activator of nuclear factor kappa B, and osteoprotegerin.2 Osteopon- tin is another protein that has been linked to bone resorption via promotion of osteoclast adhesion to the osseous matrix.3 Research has demonstrated that the use of cyclic forces increases the rate of bone remodel- ling compared with static forces.4 A force prop- agating through biological tissue, such as alveolar bone and the periodontal ligament, is transduced as a tissue-borne and cell-borne mechanical stress that in turn induces interstitial flow.5 Although liquid flow is a current focus of the mechano- transduction pathways, its anabolic and catabolic efects rely upon deformation of extracellular matrix molecules, transmembrane channels, the cytoskeleton and intranuclear structures.6 Cells are known to respond more readily to rapid oscil- lation in force magnitude (i.e. to cyclic forces) than to constant forces.7 However, randomised clinical trials testing the efect of a commercial device generating cyclic forces during orthodontic treat- ment produced contrasting results.8 Biases in both the cited studies prevented the drawing of a definite conclusion. In a real clinical setting, the same device has been reported to be reliable.9 The tested device is AcceleDent (OrthoAccel Tech- nologies). The device has a mouthpiece similar to a sport mouthpiece, which the patient bites on to during use. The mouthpiece portion is connected to an activator that stays outside the mouth. The activator houses the components that generate the cyclic forces (vibration). The activator includes a battery, motor, rotating weights and micropro- cessor for storing usage data. The patient con- nects the mouthpiece to the activator and uses the device once daily for 20 min. The applied force from the device is 0.25 N (25 g). This low force is 26 ortho 2/2017