Figure 4 A similar modification has been carried out on the buccal cusp but the amount of protection is less. Now a standard tapered fissure bur is being used to develop retention in under the buccal cusp. This produces a groove in the dentine which turns inwards slightly at its base to tuck the restoration in under the cusp and lock it into place. A similar groove is placed under the lingual cusp and the two grooves are joined across the gingival floor. In the long run this means that the restoration is locked on to the remaining central core of dentine and will not be lost when the ultimate crown restoration is designed at a later date.