A Three Dimensional Comparative Evaluation of Distal Movement of Entire Maxillary Dentition Using Infrazygomatic Crest Miniscrews and Zygomatic Miniplates: A Randomized Clinical Trial

Premolar extraction treatment with multibracketed system and reinforced anchorage has been a common modality for correcting maxillary incisor crowding or class II malocclusion due to maxillary protrusion in nongrowing patients. Treatment of class II malocclusion without extraction frequently requires distalization of maxillary molars into class I relation by means of extraoral or intraoral forces.

Extra oral headgear traction is the oldest and most commonly used method to correct class II buccal segment relationship by restricting the forward growth of maxilla and /or distalizing the maxillary molars. This distalizes not only 1st molar but also maxillary 1st and 2nd premolars via transseptal fibers. Headgear is seldom an option in adults due to aesthetics and compliance concerns. The disadvantages of extra-oral appliances have motivated many investigators to develop the mechanics of intraoral molar distalization.

Various intraoral non-compliance appliances like magnets, distal jet, jones jig, pendulum appliance etc. have been used to distalize the maxillary molars. However, in these appliances, anchorage loss characterized by protrusion of maxillary incisors and an increase in overjet is seen. Also, considerable amount of relapse occured when the distalized molars were used as anchorage for the retraction of anteriors and premolar teeth.

Absolute skeletal anchorage available 24 hours a day is an alternative method for molar distalization. It provides stationary anchorage for various tooth movements without the need for active patient compliance and with no undesirable side effects. Inter radicular miniscrews placed between the roots limit the amount of distalization possible as they come in contact with surrounding roots during tooth movement. Also, proximity of miniscrews to the roots may lead to failure of screw anchorage.

Infrazygomatic crest is a site for miniscrew placement. It has been used successfully to provide skeletal anchorage for en-masse anterior retraction, canine retraction, and intrusion of maxillary posterior teeth. Anatomically, it is a pillar of cortical bone at the zygomatic process of maxilla. It has two cortical plates - sinus floor and buccal cortical plate. This allows for bicortical fixation and contributes to better primary stability of miniscrew. A thicker bone allows greater miniscrew biting depth and more osseous contact . A new method for maxillary dentition distalization with miniscrews implanted in the infrazygomatic crest (IZC) region was proposed by Lin. There is no interference with tooth movement by miniscrews placed here and the technique is easy to master .