Gold inlays (synonyms: gold cast inlays, gold cast fillings) are dental fillings made indirectly (outside the mouth) in the dental laboratory and inserted with luting cement into the tooth previously prepared (ground) using a specific technique. A gold inlay is used to treat cavities (holes) in the posterior teeth and extends spatially over the fissures (pits in the occlusal relief of the posterior teeth) of the occlusal surfaces (chewing surfaces) and usually into one or both approximal spaces (interdental spaces) of the tooth to be treated. Due to its material properties, in particular its insufficient hardness, pure gold is not considered as a material here; instead, alloys with a high gold content are cast, which may contain other metals such as platinum, palladium, silver, copper, iridium and others. In particular, the alloy portion from the group of platinum metals provides the necessary strength to be able to bear masticatory forces. At the same time, the lifelong physiological abrasion (natural wear) of the teeth is not negatively affected by the material. Allergic reactions to gold and high gold alloys are extremely rare. Because of this great biocompatibility (biological compatibility), they are among the preferred dental materials.
Indications (areas of application)
The indication for a gold inlay is determined by the degree of destruction of the tooth to be restored, its position in the mouth, and the oral hygiene situation: only if the patient can be expected to maintain a permanently good cleaning technique should he or she be advised to undergo technically complex and thus expensive gold casting restorations. Gold alloys have proven their worth for decades, which is one of the reasons why they are referred to as the “gold standard” against which all newer materials and restoration techniques must be measured. The greatest shortcoming of a gold cast restoration is its inadequate esthetics, which results in restrictions in the visible area of the dentition. The areas of application are thus as follows:
- Proven amalgam intolerance;
- Proven intolerance to materials used to secure tooth-colored ceramic or resin inlays;
- Cavities on the molars (posterior molars) in the upper jaw;
- Cavities on the premolars (anterior molars) in the upper jaw, where the extension to buccal (towards the cheek) can lead to aesthetic limitations;
- Cavities on the molars and premolars in the lower jaw, whereby localized gold inlays there are more visually striking than in the upper jaw;
- Cavities that extend into the root dentin in the proximal space and for which adhesive cementation techniques for ceramic and resin inlays are no longer feasible;
- As bridge anchors in the posterior region;
- Dental defects with large buccolingual extension (from the cheek to the tongue), which can no longer be treated with direct filling technique.
Contraindications
- Inadequate oral hygiene;
- Circular decalcification (surrounding the tooth in a band): this is where the indication for the crown arises;
- The residual tooth substance no longer offers the possibility of retentive preparation technique, e.g. in the absence of a cavity wall buccal or oral;
- On a very short clinical crown (tooth crown portion protruding from the gingiva), a sufficiently retentive primary fit cannot be produced by preparation technique either;
- Proven allergy to one of the alloy components.
The procedure
In contrast to direct filling therapy, the restoration with an indirectly fabricated inlay is divided into two treatment sessions. 1st treatment session:
- Excavation (caries removal);
- Preparation (grinding):
- In principle, each preparation technique must be as tooth tissue gentle as possible, ie: sufficient water cooling (at least 50 ml/min), rounded preparation shapes, no excessive roughness depths, the least possible substance removal and protection of neighboring teeth;
- Preparation angle: slightly divergent (6°-10°) in the direction of extraction, as the inlay must be placed on the tooth without jamming or leaving undercuts unprovided; however, as little divergent as possible, as this results in friction (friction; primary fit without luting cement) and retention (holding on) of the inlay; the luting cement increases this additionally.
- Occlusal preparation (in the occlusal surface area): Layer thickness at least 2 mm;
- Feather margin: a gold casting preparation receives a maximum 1 mm wide feather margin occlusally at an angle of 15° to the enamel surface, which serves to protect the enamel prisms in the marginal area of the preparation and minimizes the distance between the casting object and the tooth.
- Proximal preparation (in the interdental area): slightly diverging box-shaped, surrounded by a defined bevel in the sense of the feather edge technique (chamfer preparation); here, the use of sonic preparation instruments instead of rotating instruments makes sense. The proximal box contributes decisively to the retention of the inlay.
- Proximal contact (contact with the adjacent tooth): should not be in the tooth substance area, the inlay margins should extend to buccal and oral to be easily accessible for tooth brushing technique.
- Finishing: all areas of the preparation are reworked with ultra-fine grit diamond burs to minimize roughness depths.
- Impression: serves the dental laboratory to produce a working model from plaster in dimensions true to the original;
- Temporary (transitional) restoration to protect the tooth and prevent tooth migration until the inlay is cemented.
Working steps in the dental laboratory:
- Pouring the impression with special plaster;
- Preparation of the plaster model and the working die with the inlay preparation;
- Wax modeling of the inlay on the die;
- Embedding of the wax model in investment material, from which the wax is burned out after heating; a hollow mold is created;
- Casting the gold alloy into the hollow mold;
- Bedding out of the casting object;
- Finishing and polishing of the inlay.
2nd treatment session:
- Removal of the temporary restoration;
- Application of rubber dam (tension rubber), if the preparation margins permit, to protect against saliva ingress during cementing and against swallowing or aspiration (inhalation) of the inlay;
- Cleaning of the cavity (the milled defect);
- Try-in of the inlay, if necessary with the help of thin flowing silicone or colored spray, to find the places that hinder the internal fit;
- Checking occlusion and articulation (the final bite and chewing movements);
- Disinfection of the cavity, e.g. with chlorhexidine digluconate;
- Placement of the inlay with luting cement, e.g. zinc phosphate, glass ionomer or carboxylate.
- Removal of excess cement after curing and.
- Finishing: the feather edges of gold are driven to the enamel with the finest Arkansas stones and rubber polishers to minimize the cement gap.
Possible complications
These arise from the large number of intermediate steps that must be carefully performed, as well as from problems caused by the tooth structure that is still available:
- Loss of the inlay due to insufficient friction (primary fit) or
- Insufficient retention due to incorrectly mixed luting cement;
- Edge breakage in the area of the spring edges;
- Tooth sensitivities or pulpitides (pulpitis) e.g. due to close proximity of the cavity to the pulp (tooth pulp) or preparation trauma;
- Marginal caries due to insufficient application of luting cement in the marginal areas;
- Marginal caries due to poor cleaning technique on the part of the patient;
- Fracture of the buccal or oral limiting cavity wall when the friction of the inlay is too strong or the wall thickness is no longer sufficiently stable for restoration with a gold inlay.
