Fibre type proportions of the buccinator muscle in clinically normal adult dogs.

In order to provide normal morphological data and reference values for fibre type proportions, against which changes due to facial nerve paralysis or primary facial muscle myopathies can be compared, a histological and histochemical study was carried out on the buccinator muscle of clinically normal adult dogs. Using myosin adenosine triphosphatase under acidic pre-incubation (pH 4.3) conditions, three histochemical fibre types--1, 2A and 2C were recognised. There was no significant difference in mean diameter between left- and right-sided buccinator muscle samples for type 1 versus 2. Mean diameters of fibre types were: type 1, 27.02 +/- 6.61 microns and type 2, 29.05 +/- 7.75 microns. The histographical distribution of fibre type diameters was unimodal. The buccinator muscle had a type 2 fibre predominance with a mean type 1 to type 2 ratio of 32:68. The number of fibres with internal nuclei was less than or equal to 1 per cent, atrophy-hypertrophy factors typically were less than or equal to 200, and variability coefficients approximated 250. Muscle spindles were not observed in any muscle sample.