Effect of venting on cement expressed at the crown-abutment margin

Objective: This laboratory study was carried out to investigate the effect of placement, location and diameter of a vent hole on the amount of cement being expressed at the margin of an anterior implant abutment retained crown. Methods: Three implant crown copings were fabricated to fit on the same custom abutment. Three different vent diameters (0.75mm, 1.25mm and 1.65mm) as well as three different locations on the palatal surface of the coping - cervico-palatally (away from the margin), mid-palatally (just above the cingulum), and inciso-palatally (away from the incisal edge) were chosen for vent hole placement. For each test, the coping was cemented onto the abutment under standardised conditions. A thin coating of pre-weighed amount of cement was applied to the fit surface of the coping. The amount of cement expressed at the margin and vent hole was measured by weight. This was calculated as a proportion of the amount of cement placed in the coping before seating. The results were statistically analysed using an independent samples t-test, univariate analysis of variance and Bonferroni's test. Results: (1) The presence of a vent hole influenced the proportion of cement expressed at the coping margin (p<0.05). (2) The location of a vent hole influenced the proportion of cement expressed at the coping margin (p<0.05), with the exception of the mid-palatal and inciso-palatal positioning where there was no significant difference (p=0.61). (3) The diameter of the vent hole did not significantly influence the proportion of cement expressed at the coping margin (p=0.096). Conclusion: When using anterior cement-retained implant crowns, the use of a 0.75mm mid-palatal or inciso-palatal vent hole to minimise the amount of cement expressed at the margin during cementation could be considered.