RESTORATION MATERIAL SELECTION
This is generally considered to be the most satisfactory extracoronal restorative material. It has a hardness similar to enamel, and occlusal and axial contours can easily be built up in the wax prior to casting. Cast gold alloy restorations include single and multiple surface inlays. The latter may include partial or complete coverage (onlays) of the occlusal surface. Extracoronal gold restorations include full veneer crowns and three-quarter crowns, in which only one surface of the tooth (usually the buccal) is left uncovered . Gold can be used in thin sections but it is not aesthetic. One millimetre of tooth reduction is required occlusally, with the exception of the functional cusp bevel where 1.5 mm is necessary. The choice of restoration and preparation design will depend upon the exact details of each clinical situation.
Indications for use
• In situations of severe occlusal stress • Following endodontic treatment of posterior teeth • Full or partial coverage of posterior teeth where there has been significant loss of coronal dentine • In situations where other materials are not suitable for establishing proper proximal and/or occlusal contacts • For restoration of adjacent and/or opposing teeth to avoid problems arising from use of dissimilar metals.
• Evidence of active caries/periodontal disease • Economic and social factors • Aesthetics • Where patient management requires short visits and simple procedures.
This is a brittle material which is liable to fracture in thin section unless appropriate fit surface treatment is performed (etching and silanisation) and the restoration is adhesively luted with a resin-based cement (porcelain veneers and dentine-bonded ceramic crowns). A minimum margin reduction of 0.8 mm is required with 1.5–2.0 mm incisally/occlusally. Crown margins are prepared just below the gingival margin (intracrevicularly) if aesthetics dictates that this is necessary (Fig. 10.12). Adequate retention for non-adhesive ceramic crowns depends on near-parallelism of opposing walls, particularly in the gingival third of the preparation. Porcelain crowns are relatively weak restorations and are restricted to anterior teeth unless a high-strength ceramic (Inceram, Procera, or Empress II) is used.
Indications for use
• Large inadequate restorations on anterior teeth, provided there is enough tooth substance for a strong preparation
• Severely discoloured anterior teeth
• Over an existing post and core substructure.
• Teeth which do not allow ideal preparation form to support the porcelain
• Teeth with short clinical crowns
• Edge-to-edge occlusion
• When opposing teeth occlude on the cervical fifth of the palatal surface.
Porcelain jacket crowns are finished to a shoulder or butt joint margin design unless the preparation is to be bonded (dentine-bonded crowns). All-ceramic crowns are preferred to metal ceramic crowns on post-crowned teeth where there is a risk of trauma. In this case, the weaker porcelain jacket crown fractures rather than the stress being transferred via the post core leading to root fracture.
Laboratory composites with improved strength and wear resistance are now commercially available and are increasing in popularity. Coupled with improvements in resinbased luting cements and dentine bonding systems, indirect composite restorations (with or without fibre reinforcement) may be considered appropriate for single unit inlays, onlays and crowns (Fig. 10.13).Laboratory composites are generally preferred to porcelain restorations for inlays, whereas the latter offer more permanent form stability in onlay and crown situations. Some prefer a material which is less wear-resistant and as such is sacrificial in nature to a highly wear-resistant ceramic restoration which may ultimately cause excessive wear of the opposing dentition.
Metal ceramic crown restorations offer a combination of strength and good aesthetics. Additional tooth preparation (1.5 mm) is required to allow for both the metal substructure and metal overlay. These crowns are frequently overcontoured due to inadequate tooth reduction. Heavy tooth preparation to achieve adequate thickness for both materials may result in an increased incidence of pulp death. If this is a risk then a bevelled shoulder or cervical chamfer may be preferred to the conventional full 1.5 mm axial reduction in cases where the tooth preparation has to be extended down onto root surface or where there is a large pulp. Metal occlusal coverage is generally preferred to maximise retention and resistance form and to minimise tooth reduction. Metal occlusal contacts are easier to create and adjust. Porcelain occlusal surfaces are more aesthetic but demand additional tooth reduction and create the risk of excessive occlusal wear of opposing tooth surfaces.
Indications for use
• Anterior teeth where there is insufficient space for an all-ceramic restoration
• Repeated failure of porcelain jacket crowns (identify reason first)
• Posterior crowns where aesthetics is important and full or partial veneer gold crowns are contraindicated on this basis.
• Where excessive wear of teeth opposing porcelain occlusal surfaces may be expected. Either a sacrificial indirect composite approach is preferred or permanent night-time protection with a Michigan splint may be indicated
• Where pulpal damage risk is high, particularly in a young patient. Dentine-bonded ceramic crowns have provided a more conservative viable option in many of these cases.