THE VALIDITY OF MAXILLARY EXPANSION INDEXES

Numerous indices have been proposed to help the clinician decide how m uch maxillary expansion will be required to alleviate crowding. The pu rpose of this investigation was to examine the validity of Pont's inde x, Schwarz's analysis and McNamara's rule of thumb. Records of 40 pati ents (20 females and 20 males) were selected from 155 consecutive pret reatment records. The discrepancy between actual intermolar/interpremo lar widths and the index-generated widths were correlated against meas ures of crowding, and linear regressions were computed. Statistical an alysis revealed that (1) males had more significant correlations betwe en arch width and crowding than females, (2) interpremolar widths were more strongly correlated than intermolarwidths, (3) Pont's index and McNamara's rule of thumb overestimated required arch width by 2.5 mm t o 4.7 mm and 2.7 mm to 3.7 mm respectively, and (4) Schwarz's analysis overestimated interpremolar width by 2.5 mm to 4.3 mm but was reasona bly accurate for intermolar width in males. The results suggest that t hese indices potentially overestimate the arch expansion required to a lleviate crowding.