Indirect porcelain onlays have been used as cosmetic restoration of posterior teeth but there is little information on the incidence of post-operative sensitivity following their placement. An investigation on the incidence of post-operative sensitivity was carried out by bonding 27 onlays using Panavia and Flexo-Ceram cementing agents onto the posterior teeth of 12 patients aged 16 to 36 years. Analysis of the incidence revealed that 14 out of the 22 previously healthy teeth developed sensitivity symptoms; an incidence of 63.6 per cent. This preliminary investigation also showed that teeth lined with a glass ionomer material over the exposed dentine did not produce symptoms.