Minimal intervention: advanced lesions.

Minimal intervention techniques are generally considered in relation to initial carious lesions. However, it appears logical to apply the same principles to extensive cavities as well as to the replacement of failed existing restorations. As the cavity becomes larger, there is an increasing need to consider protection of remaining cusps because they become seriously weakened by loss of the central core of the crown and therefore become subject to the development of splits at the base. However, it is possible to develop a protective cavity design without undue sacrifice of remaining tooth structure, at the same time that maintenance of occlusal anatomy and correct contact with the opposing arch are ensured. For larger cavities, special consideration needs to be given to the strength of the restorative material. Glass ionomer is relatively brittle and should not be exposed to undue occlusal load. Resin composites cannot be regarded as universal in their physical properties, and placement is time-consuming. A lamination technique is often useful, combining the advantages of both glass ionomer and resin composite. Amalgam should not be entirely discarded as an option because it has greater strength than both glass ionomer and resin composite and is still useful for the restoration of extensive cavities and for protection and retention of weakened cusps. Minimal intervention principles, designed to limit the loss of natural tooth structure, should be applied to all restorative dentistry. None of the available restorative materials is entirely satisfactory in the long term.