Tanaka and Johnston Space Analysis: Does It Apply to All Populations?

Objectives: An accurate analysis is considered a crucial factor that enables the clinician to select the appropriate treatment plan which may include serial extractions, guiding of eruption, maintenance of space or regaining it, or just intervallic patient observation during this period. This study aims to test the applicability of the Tanaka and Johnston prediction equations on Iraqi population. Materials and Methods: One hundred pairs of stone models belonged to 100 Iraqi adult individuals with normal occlusal relationship were utilized in this study. The greatest crown diameters of all teeth except the maxillary incisors and molars in both jaws were measured using digital calipers. The Tanaka and Johnston prediction equations were applied and modification for these equations was developed for Iraqis. Results: The original Tanaka and Johnston method of prediction tends to overestimate the mesiodistal widths of the canine and premolars among Iraqis. Novel regression equations (modified Tanaka and Johnston method) were formulated for Iraqi population and seem to be more accurate than the original one. Conclusions: The original Tanaka and Johnston method cannot be applied for Iraqi population; hence, new equations were developed for both genders and in both dental arches to accurately predict the mesiodistal widths of the unerupted canine and premolars.