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Condom use during oral sex although recommended is not routinely practised and this together with the low reported incidence of oral transmission of HIV tends to indicate that a healthy mouth is likely to be a fairly effective barrier. Yet oral transmission has been reported and gay male patients frequently ask dentists about potential risk factors which to date have not been clearly identified. Oral barriers to transmission include a mucous membrane where the mucosal cells display a lack of CD4 receptors and Langerhans cells are located in the basal layers suggestion that although viral DNA can be isolated in oral mucosa the cellular infection occurs from the basal rather then superficial layers. Saliva acts as a dilutant and lubricant and as well contains numerous viral inhibiting factors including salivary leucocyte protease inhibitor (SLPI), lactoperoxidase, proline rich proteins and mucins. Both saliva and crevicular fluid also play a key role in humoral and antibody mediated immune responses. Salivary concentration of HIV is very low and therefore is not considered a viable transmission medium in adults. The risk of oral transmission increases significantly with a break in the mucosal barrier from ulceration trauma or gum disease. Inflammation of the periodontal attachment in gingivitis and periodontitis causes structural changes increasing the permeability of the mucosal attachment as wen as areas of ulceration and necrosis. The surface area involved will vary but could be as much as 20 cm2 in moderate disease leaving a significant oral wound. This is probably the most significant risk factor in oral transmission of HIV as over 70% of the population have some degree of inflammatory gum disease. Clearly safer oral sex advice must strongly emphasise the importance of good oral hygiene and regular dental care to eliminate this significant risk factor.

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