Effect of location of parotid duct orifice on salivary clearance

Objectives: To determine the location of the parotid duct orifice in relation to the maxillary molars and its effects on salivary clearance on the buccal surfaces of the maxillary molars.

Methods: A 2-mm hole was made at the centre of an adhesive therapeutic agent for aphthous stomatitis and the agent was placed on the mucosa so that the hole matched the parotid duct orifice. To locate the orifice, an impression of the buccal tooth surfaces and mucosa around the agent was taken with the teeth in centric occlusion. To evaluate the salivary clearance rate, 12 subjects who displayed the parotid duct orifice within 1 SD of the mean values obtained from the original 35 subjects were selected. 1% agar containing 1 mol/l potassium chloride was placed into 3 cylinders positioned horizontally, 6 mm apart, in an acrylic holder centred over the mean duct location. The diffusion chambers were taken from the mouth at selected time intervals and the gel transferred quantitatively to flasks containing 300 ml of 100 ppm NaCl, which was assayed for potassium by atomic absorption spectrophotometry. Half-times for clearance were calculated.

Results: The mean location of the parotid duct orifice was 0.36 mm (range –7.5 to +6.1 mm) mesial to the contact surface between the maxillary first and second molars and 7.21 mm (range +3.8 to +10.4mm) above a line touching the buccal cusps of the upper molars. The half time clearance values among the three cylinders were all significantly different, the central cylinder showing the most rapid clearance.

Conclusion: The degree of undividual variation in the location of the parotid duct orifice is great and its exact location will markedly affect salivary clearance at different positions on the buccal surfaces of the upper molars.