Establish a good resistance and retention form
(1) resistance: resistance means repair after repair body and teeth in exercising the functions are able to resist the forces without breaking or cracking. (2) retention form: retention refers to restorations in the exercise of functions, can withstand the forces without capacity to wobbles or falls off. Retention of dental defect restoration, which rely on friction and adhesion. ① friction: friction is more touching and forces produced by the relative motion between the objects. Measures to increase friction: a. restoration and preparation body or cavity surface contact. B. maximize restorations and tooth contact area. C. preparation of walls should be parallel to the body axis. But clinically to make restoration easier in place of shaft-wall with 2 ° ~4 ° to the aggregation point. D. cavity floor flat, point, line, angle clearly. Measures to prevent the repair of lateral displacement: a. formation of kilted retention form. Kilted can be formed along the fissure shape, the isthmus is generally the width of l/3/~1/2. B. forming Groove retention form. C. form nail retention form. Nail hole depth, through the enamel dentine junction of dentin, is generally 2mm diameter for the LMM, its position can be selected according to the anatomical shape of the dental pulp, avoiding Medullary angle or easily damaged parts of the pulp. All nail holes to stay parallel and the path of insertion of the prosthesis. ② adhesive force: from adhesive bond strength. Bonded forces associated with the following factors: a. kinds of bonded materials. There is a new type of glass ionomer cements is more ideal. B. bond area. Bond strength is proportional to the area of the restoration. C. bonding surface condition. Bonding adhesive helps the strength of rough, 0.1~0 surface roughness control. 25mm is advisable. D. cement mixing operation. Instructions for use should be strictly enforced, too thin or too thick, it will reduce the bond strength of bonded materials.