Tanaka and Johnston Method for Space Analysis of Cambodian Adolescents

Objective: Tanaka and Johnston method is a simple and easy method to estimate the severity of crowding by measurements of teeth on dental casts. Tanaka and Johnston produced a formula using north-western European population in their study. This is a pilot project to evaluate the suitability of the Tanaka and Johnston method for Cambodian adolescents. Methods: Measurements of teeth were made from dental casts of Cambodian males and females (n=42, mean age=15.36 SD years) using a digital caliper to two decimal points. The dentitions are required to be free of any signs of dental pathology, anomalies, and proximal damage or restorations on either side of the teeth. Tanaka and Johnston’s formula for predicting the ∑ M-D width of maxillary canine and premolars is Y=11+0.5X and ∑ M-D width of mandibular canine and premolars is Y=10.5+0.5X where X is ∑ M-D width of four mandibular incisors. Reliability of measurement was confirmed by repeated measurements after an interval of 2 weeks by the same examiner. The data were analyzed using SPSS version 20. Results: The study showed that the actual ∑ measurements of M-D width of maxillary canine and premolar is 22.91±0.61mm and the actual ∑ measurements M-D width of mandibular canine and premolar is 22.00±0.92mm. By using the Tanaka and Johnston method, the predicted ∑ M-D width of maxillary canine and premolar is 22.65±0.73mm which is less than the ∑ measured width on casts while the predicted ∑ M-D width of mandibular canine and premolar is 22.15±0.73mm which is more than the ∑ measured widths in the casts. Conclusion: Tanaka and Johnston method under-estimate the ∑ M-D width of maxillary canine and premolars while it over-estimates the ∑ M-D width of mandibular canine and premolars.