The graphical analysis of tooth width discrepancy

The standard tooth width ratio tables currently do not provide an overall indication of the final interdigitation of teeth. To provide a comprehensive analysis of inter-arch tooth width discrepancy, this study has developed a combination of cumulative percentage tooth width ratios and a method to visually determine the harmony between maxillary and mandibular tooth widths. Mesiodistal tooth widths from the first permanent molar to the corresponding first permanent molar were measured from 60 sets of pretreatment study models which were selected consecutively. Cumulative percentage ratios relating mandibular teeth to maxillary teeth were calculated utilising the mesiodistal tooth width measurements. The 13 mean cumulative percentage ratios developed in this study were plotted on graph paper showing plus and minus two standard deviations from the mean. These ratios provide a standard from which cumulative percentage ratios obtained from any new case may be compared graphically. Deviations from the mean cumulative percentage ratios are immediately recognised. No simple graphical method of assessment on the final interdigitation of anterior and posterior teeth has previously been devised. The graphical analysis of tooth width discrepancy is invaluable as an aid in localising any tooth width discrepancy and ensuring that incompatible maxillary-to-mandibular tooth widths are recognised prior to orthodontic treatment.