Establishing a normal range for mouth opening: its use in screening for oral submucous fibrosis

The maximal mouth opening of 700 healthy Nepalese adults, age range of 18-68 years, measured by paraclinical workers was determined as there are no data available for an Asian population. The mean value of the inter-incisal distance was 47.1 mm (range 33.7-60.4 mm) and 98% of the population surveyed fell within this range. The minimum limit of normal oral opening was determined to be 34 mm. Ten out of 13 patients with histologically confirmed oral submucous fibrosis (OSF) had a maximal oral opening of less than 34 mm. It was concluded that reduced oral opening measured by paraclinical workers as a single screening test for oral submucous fibrosis, has a sensitivity of only 77% and will detect only advanced cases. However, each of the 3 subjects from the healthy population found to have restricted mandibular opening and who agreed to be examined further had significant oral conditions, namely oral submucous fibrosis (2) and pericoronitis (1). The study confirms the value of this measurement as a screening procedure for significant oral disease by paraclinical staff particularly in developing countries where trained dental and medical personnel are scarce. Because of its limited sensitivity, measurement of mouth opening is unsatisfactory as a single screening test for OSF, as it will not detect early stages of the disease.