Conventional cavity designs are coming under increased scrutiny because of an increased emphasis on preservation of tooth substance. The tunnel restoration when used with glass ionomer, may overcome some of the disadvantages of conventional cavity preparations. Justification for the use of the tunnel restoration is from a limited number of short-term clinical observations and destructive laboratory testing of marginal ridge strength. The technique is not without shortcomings. Long-term clinical and nondestructive laboratory trials examining the strength of teeth with tunnel restorations should be undertaken prior to its acceptance as a replacement for techniques in which the marginal ridge is removed.