TIMING FOR EFFECTIVE APPLICATION OF ANTERIORLY DIRECTED ORTHOPEDIC FORCE TO THE MAXILLA

Class III malocclusion with retrusive maxilla can be orthopedically co rrected in the deciduous and mixed dentition, with reverse-pull headge ar in combination with rapid palatal expansion. The literature recomme nds this procedure be carried out before the patient is 8 years old to obtain the optimal orthopedic result. This statement, however, has no t been supported by scientific data, The current study examined the tr eatment effects of patients younger than 8 years old (5 to 8 years) an d patients older than 8 years old (9 to 12 years). Thirty patients tre ated with maxillary protraction and expansion in the Department of Chi ldren's Dentistry and Orthodontics, University of Hong Kong were inclu ded in this study, Cephalometric radiographs were taken 6 months befor e the initiation of treatment (T-0), at the initiation of treatment (T -1), and after 6 months of treatment (T-2). In this way, (T-2-T-1) rep resented cephalometric changes during the treatment period and (T-1-T- 0) represented 6 months of growth changes without treatment. Experimen tal subjects served as their own control in this study, A grid system consisting of maxillary occlusal plane (OL) and a line perpendicular t o OL through sella (OLp) was used for linear measurements, A total of 15 linear and 3 angular cephalometric measurements were made, A multiv ariate analysis of variance (MANOVA), which used age and treatment tim e as its factors, was used to determine effect of age and/or treatment on each cephalometric parameter. Results indicated strikingly similar therapeutic response between the younger and older age groups. These data suggest that similar skeletal response can be obtained when maxil lary protraction was started either before age 8 (5 to 8 years) or aft er age 8 years (8 to 12 years).