Luting of vented and etched crowns.

Introduction A frictional fitting crown is in intimate contact with the tooth whereas a passive fitting crown has more spaces and does not resist a vertical withdrawing force. The space between the tooth and the crown has been termed the precementation space.' lt is the size of this precementation space and the technique of creating iP5 that greatly influence the seating of a crown during cementation. I t has been shown that it is advantageous to have an increased precementation space as crowns made using die relief methods have approximately 25 per cent' more retention following cementation than crowns constructed on the same unrelieved die. However, it must be noted when increasing the precementation space that retention diminishes approximately one-third as the final cement thickness increases from 20 p n to 140 p n . 6 Venting,'-'o of crowns to allow improved seating and marginal fit of a crown on cementation has been used by many researchers to show consistently improved marginal fit over those non-vented crowns. However, not all research" has proved the need for venting. Vented crowns have been compared to non-vented crowns with an increased precementation space and showed an ~