Establishing a Standard Transverse Maxillary Dimension on Study Casts Using the Intermolar-to-Intercanine Width Ratio: A Pan-India Study.

Background: Evaluation of maxillary width holds significant clinical importance in identifying developmental abnormalities, aiding in orthodontic diagnosis and treatment planning, providing ethnicity-specific data, and supporting forensic applications. Still, research on maxillary growth in transverse dimension is limited due to a lack of standardized diagnostic criteria and methods for defining normalcy. Addressing these gaps, this study aimed to establish a standard transverse maxillary dimension using the intermolar (IMW)-to-intercanine (ICW) width ratio determined on a large, homogeneous sample of dental Class I well-aligned arches with Little's irregularity index 1 or 2 across India.

Methods: A pan-India, cross-sectional, model-based study of 1575 maxillary arch models with normal occlusion was conducted to define the transverse dimension of the maxillary arch. The IMW and the ICW linear dimensions and their ratio were measured and statistically analyzed. These parameters were also compared for sex-based differences.

Results: The results revealed a mean IMW and ICW of 36.87mm and 35.44 mm, respectively. The mean ratio of IMW to ICW was 1.04. Sexual differentiation revealed a significantly higher mean values of IMW (37.54) and ICW (36.10) in males compared to females for IMW (35.84) and ICW (34.92), respectively, at p=0.000.

Conclusion: In normal and well-aligned dentition, the ratio between IMW and ICW in the transverse dimension is 1.04:1. It provides a clinically easy visual evaluation chairside method to identify normal arches, even without radiographs. This norm can be further explored in diverse ethnic populations and explored for applications in orthodontic diagnosis and treatment planning, forensic odontology, and anthropological studies.