preparation. Subsequently, a diagnostic wax up can be provided to help the patient visualise the final prosthesis and to construct a silicone index. This index can be used to make a temporary prosthesis. Selection and evaluation of abutment teeth Multiple factors influence the selection of appropriate abutment teeth. These include the size of potential abutment tooth, with larger teeth having an increased surface area preferable for retention, using teeth with a stable periodontal status, favourable tooth angulation, favourable tooth position, and an adequate crown-root ratio. Careful abutment selection is critical for the success of bridgework. The prosthesis must be capable of tolerating occlusal forces, which would normally be received by the missing tooth as well as its normal occlusal loading. These forces are transmitted to the abutment(s) via the prosthesis. Vital teeth are preferred to endodontically treated ones for bridge abutments. Endodontically treated teeth have lost a large amount of tooth structure, weakening them and making them less able to tolerate additional occlusal loading. Post crowns have been shown in some studies to have a higher failure rate. For resin bonded bridges abutment teeth should ideally be unrestored and have enough enamel to support the metal wing retainer. Additionally there must be sufficient space to accommodate the minimum connector width of 0.7mm and 2mm connector height. It is acceptable for the abutment to be minimally restored with small composite restorations provided they are sound. It is advised to replace old composite restorations prior to cementation to provide optimum bond strength via the oxide layer. Teeth with active disease such as caries or periodontal disease should not be used as abutments until the disease has been stabilised. Once stable periodontally compromised teeth may be used as abutments, depending on the crown to root ratio described below. Ante's law, states that the roots of abutment teeth must have a combined periodontal surface area in three dimensions that is more than that of the missing root structures of the teeth replaced with a bridge, is used in bridgework design. This law remains controversial in terms of supporting clinical evidence. Crown to root ratio is the distance from the occlusal/incisal surface of the tooth to the alveolar crest in relation to the length of root within the bone. The minimum ratio of crown to root is considered to be 1:1, although the most favourable is a crown:root of 2:3. As the proportion of tooth