- ■ Definition
- ■ History and Clinical Results
- ■ Advantages
- ■ Disadvantages
- ■ Indications
- ■ Contraindications
- ■ Factors Affecting the Final Results
DEFINITION
The provision of porcelain laminate veneer is a conservative aesthetic restorative technique using laboratory-fabricated thin “wafers” of porcelain bonded onto the prepared facial surfaces of mainly the anterior permanent teeth.
HISTORY AND CLINICAL RESULTS
As early as 1937, Pincus attached thin labial porcelain veneers temporarily with denture adhesive powder to enhance the appearance of Hollywood actors for close-up photographs. This reversible technique provided an alternative for those persons who wanted their smile improved without the need to have more destructive full crown preparations.1,2
To make the restorative materials more retentive, Buonocore introduced the acid-etch technique to increase the adhesion of acrylic filling material to enamel.3 Three years later, Bowen had developed a silica-resin direct filling material.4 These persons not only laid the foundation for direct placement of resin composite restorations but also for the bonding of porcelain laminate veneers with resin composite.
Before porcelain veneers were being used to cover the entire labial tooth surface as a routine procedure in aesthetic dentistry, Rochette had already mentioned the use of a silane coupling agent with porcelain laminate veneers for repairing fractured incisors.5 The use of silane was possibly a consequence of its success in porcelain repairs for porcelain or porcelain-fused-to-metal crowns.
In addition to porcelain, acrylic resin has also been used for preformed laminate veneers by Faunce and Myers.6 These hollowed-out denture tooth veneers were treated with ethyl acetate, methylene chloride or methyl methacrylate, and then a filled resin cement was used to lute the veneers to etched teeth. Unfortunately, the failure rate was very high, because the composite-to-acrylic bonding was weak and the material was subject to wear and looked unattractive.7,82
Horn introduced the platinum foil technique9 and Calamia reported the refractory die technique10 for porcelain laminate veneer fabrication in the laboratory. Simonsen and Calamia,11,12 demonstrated good bond strengths for resin composite to hydrofluoric acid-etched porcelain, and that the use of a silane coupling agent could further increase the bond strength of resin composite to etched porcelain. Other methods such as a pressed (e.g. IPS Empress) or a castable ceramic (e.g. Dicor), and CAD/CAM (e.g. Cerec) or copy milling techniques (e.g. Celay) have also been used for veneer fabrication.
Recent clinical studies have shown very good long-term results following the placement of anterior porcelain veneers. In one 5-year study, 83 per cent of 315 veneers were rated as being satisfactory,13 while in an 8-year study, 95 to 97 per cent of the veneers were successful.14 Over 7–10 years, of 115 veneers, 7 per cent fractured,15 while Touati reported mechanical and biological failures of only 5.4 per cent over 10 years.16
Porcelain laminate veneers are an ingenious integration of available techniques and materials to solve many types of aesthetic dental problems.
ADVANTAGES
With improved dental awareness, good oral hygiene and a low incidence of dental caries, porcelain laminate veneers are now regarded as a viable conservative technique when compared with the removal of a greater amount of sound tooth substance that is required for full crowns. The risk of pulpal involvement from tooth preparation is reduced, and the remaining tooth substance is strengthened by the resin-bonded restorations. The gingival tissues are also less affected,17 and anterior tooth guidance may be largely unaltered.
Porcelain laminate veneers are biocompatible, wear and solvent resistant, very colour stable, and have a coefficient of thermal expansion similar to enamel. A life-like vital appearance and subtle surface texture effects can be produced by experienced ceramists (Fig. 1.1). Although they are fragile before placement, porcelain veneers have superior reliable bonding strengths after hydrofluoric acid etching and silane coupling agent application, when compared with resin composite and acrylic resin veneers. Because porcelain itself has a similar coefficient of thermal expansion to tooth structure, the stresses induced by temperature changes in the mouth will not produce high stresses at the tooth-veneer interface. The glazed restorations are also more wear resistant, less porous and less water-absorbent than resin composite and acrylic resin materials. These and other physical properties give rise to a dimensionally stable and strong material, which can also create a biologically sound environment, as porcelain can be less plaque retentive than enamel.3
Good periodontal health can be maintained since it is possible to place transparent and almost invisible supragingival margins if there is no underlying tooth discolouration to be masked.18
DISADVANTAGES
Despite porcelain laminate veneers having many advantages, they still have a number of shortcomings. For example, the tooth preparation, and the fabrication and handling of the veneers for cementation are highly technique-sensitive procedures, because the amount of tooth reduction is minimal and the veneers are fragile before their cementation. Due to the conservative nature of the restorations, the thickness of the porcelain limits the ability to treat satisfactorily, those teeth with severe underlying discolouration. The veneers may fracture if subjected to heavy stresses (Fig. 1.2), and any subsequent repairs are also usually less than ideal.19 Divesting the veneers from refractory die materials should be very precise since it is difficult to repair inadvertently removed margins. Patients also have to attend the dental office at least twice and the cost of treatment is high. Once cemented, any further colour modifications are also difficult to achieve.
The provision of porcelain veneers is not always a routine procedure, and problems can also arise following their cementation. These include poor appearance and marginal fit, fracture, gingivitis, debonding and tooth sensitivity.20
INDICATIONS
Porcelain laminate veneers can be used for patients who wish to have their anterior dental aesthetic problems corrected in terms of tooth shade, morphology and alignment.4
Fig. 1.2: Debonding and fracture of a veneer. The heavily-stained teeth and use of opaquer have led to a monochromatic appearance of the veneers
Clinical applications are expanding because porcelain and dentine bonding systems show continuous improvements, and porcelain laminate veneers will be used more widely in future.
If there is sufficient tooth substance for bonding and support, then veneers can be used almost routinely for correcting many tetracycline stained teeth,21,22 stained non-vital teeth,23 unattractive restorations, enamel fluorosis, enamel hypoplasia, chipped and slightly worn anterior teeth, microdontia,24 minor tooth malalignments,9,25 closure of anterior tooth diastemas with or without orthodontics,26 modifying anterior guidance, and providing undercut zones for removable prostheses27 (Figs 1.3 to 1.6).
Fig. 1.3: Veneers can be used to improve the shade of the tetra-cycline-stained teeth and the non-vital central and to improve the position of the vital central incisor
Furthermore, there are some workers who are optimistic in prescribing these restorations in adverse clinical situations such as for lingual erosion,28,29 for fractured and grossly worn anterior teeth,9,30 and as part of a complete oral rehabilitation as substitutes for porcelain and metal crowns, especially for mandibular teeth.31,32 When appropriate, veneers have also been bonded to primary teeth.33,34
CONTRAINDICATIONS
The prescription of porcelain laminate veneers would be ill-advised if there is an insufficient amount of enamel for bonding (despite improved dentine bonding systems), for example, with extensive caries and tooth fractures, heavily restored teeth, severe enamel hypoplasia and short clinical crowns,13 or if excessive forces are acting on the teeth as with active bruxism and object-biting habits.6
Fig. 1.6: Minimal incisal fractures and moderate tetracycline staining can also be treated, but the final shade may not be optimal
In some instances, darkly stained teeth (especially for single veneers), malocclusions, extensive periodontal bone loss and large diastemas preclude being able to place attractive veneers19,35 (Figs 1.7 to 1.10). Other less conservative options may be used instead.36
Mild tetracycline staining or enamel fluorosis of otherwise intact teeth may not require veneers if bleaching is feasible.
Fig. 1.7: If much dentine is exposed cervically then the long-term prognosis for the veneers may be in doubt
Fig. 1.9: Wide diastemas cannot be treated satisfactorily with veneers, although orthodontic treatment provided first may resolve such problem
FACTORS AFFECTING THE FINAL RESULTS
For bonded porcelain restorations, the colour of the underlying tooth substance, the luting cement, and the porcelain laminate veneer can all affect the final aesthetic result of the treatment.37,38 If the substructure is discoloured, it is generally accepted that more tooth substance should be removed to give more space for the porcelain build-up, in order to mask the discolouration and to avoid veneer overcontouring. However, the long-term reliability of current dentine bonding systems is not known and dentine exposure should be minimal.8
The long-term effects of vital bleaching before or after tooth preparation on the final treatment outcomes have also not been reported. The use of an opaquer, together with an increased porcelain thickness, has been advocated to modify the colour of the veneer and for masking discolouration, but it can also lead to an opaque and monochromatic appearance.39 Many dental porcelain manufacturers are now marketing powders with more intensive colours for veneer build-ups. The complementary colour technique,38 in addition to the traditional use of opaque porcelain for masking, has been used to produce restorations which are more harmonious with the underlying tooth discolouration.
It is often very difficult to colour-match a single veneer, especially for a central incisor tooth, and it is sometimes preferable to place veneers on both central incisors. To avoid an obvious shade difference between veneered anterior teeth and natural posterior teeth, it is often necessary to also veneer the premolar teeth. The shades of the most distal veneers should blend anteriorly with the other veneers, and posteriorly with the natural teeth. Vital tooth bleaching can assist with this shade transition.