Proposal of a formula mouth opening reduction assessment, for forensic purposes.

Objectives: To propose a formula for determining reduced mouth opening due to oral and maxillofacial trauma, based on the normal standard of the Brazilian population.

Materials and methods: First, the maximum mouth opening was established, in millimeters, using a digital pachymeter, in patients between 22 and 60 years of age. The opening was measured from the upper to the lower incisor, at maximum amplitude, without pain and overbite. Second, the facial profile type and height were determined. A formula was developed to calculate the percentage of reduced mouth opening based on the normal average.

Results: The average mouth opening was found to be 51.71 mm in men and 47.94 mm in women, thus establishing a statistically significant difference in mouth opening between sexes. However, there was no statistically significant difference between age and profile type with mouth opening. The following formulas were developed to calculate the reduced mouth opening, based on the averages found, by using RA= [100-(A.1.93)].0.3 for males and RA= [100-(A.2,08)] .0.3 for female patients.

Conclusion: Considering that mouth opening tends to be larger in men than in women, valid formulas can be used to determine the correct percentage of reduced mouth opening.