Ceramic inlays nowadays are essentially divided into two components: the ceramic material and the attachment.
The ceramic material is essentially the filling, and the attachment (fixing composite, adhesive and similar substances) fixes it in place in the tooth.
Ceramic components are supplied and prepared by dental laboratories (e.g. feldspar and glass ceramics) or prefabricated industrially (industrial ceramics) and are later ground into their final shape. Ceramics are medical products according to German and European law and are therefore subject to specific guidelines with regard to effectiveness and safety. The biological and technical specifications of these materials are generally good even if various products with greater hardness in comparison to enamel can cause abrasion in the opposing tooth.
The industrial ceramics available on the market are scientifically approved as they are supported by clinical studies of over 3 to 5 years. The same applies to certain feldspar and glass ceramics. Individual products can only be recommended when positive results in studies with a duration of at least 3 to 5 years exist. The necessary safety measures applicable in the preparation of dental ceramics are also to be observed by the producers.
Ceramics must always be fixed by means of an adhesive technique to the tooth. This includes the enamel joint (etching technique), the ceramic joint (etching technique and silanising) and a dentine seal (pre-treatment, adhesive impregnation); the connection is established with a composite fixative. The required materials (composite fixative, adhesive and the appropriate aids) are also medical products according to European law. They must have the CE mark which is proof that they meet the essential requirements regarding safety and effectiveness according to the law.
It is to be kept in mind that through the use of highly viscous composite fixatives the negative after-effects that may occur due to leaching out from the cemented joint may be reduced by the choice of appropriate composite fixatives. One has to be careful to ensure sufficient polymerisation (for example 60 seconds polymerisation time at sufficient light intensity).
Ceramic inlays are indicated if the cavity – the damage to the tooth – is easily accessible on all sides. For areas adjoining dentine (up to approximately cervical step depth) there are acceptable clinical results with careful use of adhesive techniques. The thickness of the material of the inlays should not be less than 1.5mm as a rule; this means that perhaps the pulp tissue (the dental nerve) could be traumatised during the preparation, especially in the case of young patients). They are less worth recommending in the case of restoration of larger areas of the chewing surfaces where procedures in which the occlusal area in the mouth must be shaped after their being set in place.
As with all adhesive restorations, an essential requirement for ceramic inlays is first-class oral hygiene, not least because bacteria tend to cling to the composite adhesive and multiply there. The use of a coffer dam with adhesive procedures is absolutely recommended. Appropriate protection of the pulpa is necessary; if there are areas of dentine exposed the application of a dentine adhesive is recommended.
Forcing the composite fixative into the gingival sulcus is to be avoided and any overfilling is to be carefully removed. The treatment of a tooth by means of a ceramic restoration is a thus a complicated procedure. There are a whole range of studies which describe clinical experiences over a long period of time and restorative treatment of the side teeth with ceramic inlays can now be seen as a routine procedure.
By ceramic veneers, we mean shells or covers made from ceramic materials which are attached to the enamel by means of adhesive techniques. The required materials and techniques are generally on a par with those used in ceramic inlay treatments. In essence the indication for veneers arises in front areas, to treat discolouration, anomalies, gaps or specific damage from caries. Aesthetically satisfactory results are most likely when the veneer is completely in contact with enamel. In order to ensure the best possible micro-mechanical retention with the help of enamel-etching techniques and the least possible irritation of the pulpa as little dentine as possible should be exposed at the preparation stage.
Long-term clinical studies have been published which allow a serious evaluation of restoration by means of veneers, above all with regard to the duration of the improved appearance, the average retention time in the mouth or in relation to local side effects (long-lasting reactions of the pulpa and the marginal periodontium, secondary caries and so on). Today the covering of teeth with a ceramic veneer can therefore definitely be described as a scientifically recognised form of treatment.
Ceramic Partial Crowns
In comparison with ceramic inlays and veneers, results with partial crowns of the same material have not been as good. Published data in clinical studies suggest that with modern ceramics survival rates of up to 7 years can be achieved in 81% of cases. In comparison, results with gold show a survival rate of 86% after 10 years. The use of ceramic partial crowns for patients with abnormal jaw function, such as grinding of the teeth, is debatable.