A galvano inlay is a ceramic filling produced in a dental laboratory, in which the surfaces facing the tooth structure and a delicate margin extending beyond the ceramic are made of a thin layer of fine gold. Thus, the electroformed inlay occupies an intermediate position between gold and all-ceramic inlays. The technique aims to combine the aesthetic advantages of a ceramic inlay with the key advantage of cast gold inlays, which is that it can be used with conventional luting cements such as phosphate cement. In this way, it is possible to bypass the dentin-adhesive (micro-mechanically adhering to the dentin) composite-based (resin-based) luting materials for ceramic inlays, to which a few patients show intolerance. In addition, a galvano inlay has excellent accuracy of fit, which may well exceed that of a cast gold inlay. With the advent of tooth-colored zirconia as an inlay material, which can also be incorporated with conventional cements, it is expected that the electroformed inlay, which in any case claims only a very small percentage of all inlays manufactured, will be used very rarely in the future.
Indications (areas of application)
As with all inlay restorations, the indications result from the degree of destruction of the tooth to be restored and the patient’s oral hygiene situation: only if the patient can be expected to maintain good brushing technique and caries stability over the long term should he or she be advised to undergo technically complex and thus expensive restorations. The greatest shortcoming of a cast gold inlay, its inadequate esthetics, is largely reduced with the electroformed inlay, since only a narrow circumferential margin is visible of the fine gold portion of the restoration. The ceramic itself promises the highest level of esthetics, although one must accept the limitation that, in contrast to the all-ceramic inlay, a chameleon effect as a color-matching effect to the restored tooth cannot be expected due to the gold substructure. The following indications (possible applications) are possible:
- Amalgam intolerance
- Incompatibility of composites (plastics) and thus also dentin-adhesive luting cements for ceramic inlays
- Incompatibility against one of the components of a gold casting alloy for a gold inlay.
- So if the requirement of an extremely high biocompatibility (biological compatibility) must be met by the material.
- Cavity margins in the approximal space area (interdental space area), which are located in the dentin and can not be absolutely drained for the adhesive cementation technique of a ceramic inlay;
- Cavity supply with very good oral hygiene.
- Medium-sized cavity encompassing the fissure area of the tooth as well as one or both approximal surfaces (interdental surfaces)
Contraindications
- Insufficient oral hygiene
- An – extremely rare – allergy to gold
- The patient rejects the restoration because of the limited aesthetics due to the fine gold margin; in this case, there is the possibility of a zirconia inlay in case of intolerance to dentin adhesive luting materials.
The procedure
Two to three treatment sessions in the dental office and one to two laboratory runs are required before an electroformed inlay can be placed. 1st treatment session:
- Excavation (caries removal).
- If necessary, placement of a subfilling, e.g., of phosphate or carboxylate cement for substance compensation of undercropping tooth areas
- Preparation (grinding): box-shaped with rounded edges and a 6° diverging angle of the cavity walls; the ablation in the fissure area (area of the valleys of the occlusal surface) must be at least 2 mm deep and 2 mm wide; the preparation should extend in the interdental space area to buccal (to the cheek) for aesthetic reasons only very sparingly; unlike the gold inlay, no feather edge is prepared
- Impression: serves the dental laboratory to produce a working model from plaster in dimensions that are true to the original
- Temporary (transitional) care to protect the tooth and prevent tooth migration until the cementation of the inlay.
1st phase in the laboratory:
- Pouring the impression with special plaster.
- Preparation of the plaster model and the working die on which the inlay will be made
- Electroplating: the surface of the working die corresponding to the preparation (the milled tooth area) is made electrically conductive so that it is covered with a gold layer by galvanic means in an electrolysis bath. The result is an inlay substructure made of fine gold, which reproduces the surface structure of the preparation extremely accurately. It is a maximum of 0.2 mm thin and therefore quite unstable.
- Provided that a framework try-in is to take place, which is usually not the case, the substructure is temporarily filled with plastic for stabilization.
2nd treatment session (optional)
- Removal of the temporary restoration
- Framework try-in of the inlay substructure to check the internal fit; corrections are possible at best with a very sharp milling cutter and only to a minimal extent due to the low layer thickness
- Renewed temporary restoration
2nd phase in the laboratory:
- The inlay framework first receives a bonder firing, then a tooth-colored opaquer opaque, which prevents the gold from shining through.
- Then the ceramic veneer is fired on; the material must be incised lengthwise before the first firing, as the ceramic shrinks during the firing process. The length notch thus counteracts shrinkage-related fit deficiencies
- Before firing again, the missing mass is supplemented
- Glaze firing
3rd treatment session:
- Removal of the temporary restoration and cleaning of the cavity.
- If necessary, application of rubber dam, provided that the preparation margins permit this
- Try-in of the inlay
- Control of occlusion and articulation (final bite and chewing movements);
- Cementing for example with phosphate or carboxylate cement.
- Working the fine gold margin to the tooth by hand, e.g. with a ball tamper during cement curing: in this way, the cement gap in the marginal area is minimized
