Resin inlays are dental fillings that are preferably manufactured indirectly (outside the mouth) and inserted into the tooth that has been previously prepared (ground) using a specific technique with special luting materials adapted to the resin material. The spatial extent of the preparation in the case of the inlay is limited occlusally (on the occlusal surface) to the area of the fissures (dimples in the occlusal relief of the posterior teeth); rather rarely, however, it occupies only the occlusal surface, as a rule it also includes one or both approximal space surfaces (interdental space surfaces). The transition to the onlay, which extends to the cusp tips of the occlusal surfaces, is considered to be fluid. With regard to the material properties, the term resin inlay is used in a simplified manner; as a rule, composite resins based on methyl methacrylate or its chemical derivatives which have been further developed to improve the material properties are used. Furthermore, fillers are embedded in the base material. The good mechanical properties of fine-grain hybrid composites have led to their acceptance for the manufacture of resin inlays. Chemical curing of the base material can be initiated both chemically and by light by adding appropriate initiators (triggers of the chemical reaction). Composites are also widely used in the direct filling technique; however, the finishing possibilities for the material are better under laboratory conditions. These include a higher degree of polymerization and thus a lower content of residual monomers (monomers: individual components from which the larger macromolecular compounds, the polymers, are formed by agglomeration). This results in the clearly superior material properties of the plastic inlay compared to the directly produced plastic filling. The resin inlay should be viewed in direct comparison with the ceramic inlay. Except for a few indications, the latter is used more frequently because ceramics are biologically inert (do not trigger reactions from the organism) and are therefore the material with the greatest biocompatibility.
Indications (areas of application)
The indication for resin inlay results from:
- On the one hand, from the patient’s desire for tooth-colored esthetics,
- On the other hand, from the degree of destruction of the tooth to be treated. While for small to medium defects the use of the direct filling technique is useful to work tooth substance sparing, for medium to large defects the treatment with an inlay is the means of choice, whereby an inlay treatment involves a greater expenditure of time and considerable additional financial costs for the patient and therefore sometimes compromises must be made in favor of a direct filling therapy.
From these basic and other considerations, the following indications can be derived:
- Tooth substance defects of medium to large extent in the occlusal and proximal surfaces (masticatory and interdental surfaces) without cusp involvement;
- Larger lesions that are difficult to treat with the direct filling technique;
- Desire for aesthetic color-stable tooth-colored restoration;
- As an alternative to the tooth-colored ceramic inlay, whereby this has a greater micro-hardness and is therefore less antagonist gentle in terms of abrasion (the abrasion) (less gentle on the teeth of the opposing jaw coming into contact); in the case of bruxism (involuntary grinding and pressing) is therefore a plastic inlay rather than a ceramic inlay to consider.
- For the treatment of patients who are concerned in advance that they may be sensitive to ceramic material to its harder bite;
- Slight cost savings in the dental field compared to the ceramic inlay;
- Very rare proven gold intolerance;
- Proven amalgam intolerance.
Contraindications
- The required layer thickness in the occlusal area may lead to inflammatory reactions of the pulp (tooth pulp) in adolescent patients;
- Lack of dental hygiene at home, because bacteria have a certain affinity for the luting composite and thus grow in the area around the luting joint;
- Circular decalcification (surrounding the tooth in a ring) as a result of poor oral hygiene; in this case, a crown is indicated;
- allergic intolerance reactions to the unavoidable residual monomer in both the inlay and the luting material; this should be ruled out by the allergist in advance of treatment if suspected;
- The adhesive cementation technique enforces adequate draining, which reliably prevents the penetration of saliva and blood into the cavity prepared for inlay cementation; if this is impossible due to the approximal preparation depth (trimmed tooth margin in the interdental space), a conventionally cemented gold restoration must be used;
- Endodontically treated (root-treated) teeth should tend to be treated with a partial crown due to the greater risk of marginal gap formation despite otherwise given indication for inlay.
The procedure
Unlike direct filling therapy, restorations with indirectly (outside the mouth) fabricated fillings are divided into two treatment sessions, unless they are one-time chairside (at the dental chair) ceramic restorations milled with the CAD-CAM method. Resin inlays made according to this procedure are not widely used in Europe. 1st session:
- Excavation (caries removal) and, if necessary, placement of a build-up filling for substance compensation;
- Preparation (grinding of the tooth):
- Any preparation must be carried out in principle as tooth tissue sparing as possible with sufficient water cooling and the least possible substance removal;
- The preparation angles must be selected in such a way that the future inlay can be removed from or pushed onto the tooth without jamming or leaving undercut areas unprovided. This is achieved by a slightly diverging preparation angle in the removal direction.
- Occlusal substance removal (in the occlusal surface area): at least 2 mm;
- Proximal preparation (in the interdental area): slightly diverging box-shaped; sonic preparation approaches are also used here instead of rotating instruments;
- The proximal contact (contact with the adjacent tooth) must be in the area of the inlay, not in the tooth substance area;
- Impression; it is used by the dental laboratory to produce a working model in dimensions true to the original;
- Eugenol-free temporary restoration (transitional restoration fixed with clove oil-free cement) used to protect the preparation margins and prevent tooth migration. Eugenol (clove oil) inhibits (prevents) the curing of the final adhesive cement.
2nd session:
- Control of the inlay made in the dental laboratory;
- Rubber dam system to protect against saliva ingress and against swallowing or aspiration (inhalation) of the inlay;
- Cleaning of the cavity (the ground defect);
- Try-in of the inlay, if necessary with the help of thin-flowing silicone to find areas that interfere with the internal fit;
- Control of the proximal contact;
- Preparation of the tooth for adhesive cementation: Conditioning of the enamel margins for 30-60 sec with 35% phosphoric acid gel; dentin etching for 15 sec, then application of a dentin bonding agent to the dentin, which has only been carefully dried – not dried out!
- Preparation of the inlay: cleaning and silanizing of the lower surface;
- Placement of the inlay using an adhesive technique with a preferably dual-curing (both light-initiated and chemically curing) and high-viscosity luting composite; excess cement removal before light curing! A sufficient polymerization time of, for example, 60 sec. must be observed.
- Control and correction of occlusion and articulation (final bite and chewing movements);
- Finishing the margins with ultra-fine grit polishing diamonds and rubber polishers;
- Fluoridation.
Possible complications
Difficulties may arise due to the large number of intermediate steps in the process, such as:
- In the preparation of the slightly divergent trigger angle for accessibility reasons such as mouth opening or space restrictions at the posterior molars buccally (towards the cheek);
- In juvenile teeth due to the limited possibility of hard substance removal due to the still large expansion of the pulp (the dental pulp);
- Inlay fracture (fracture) due to too sparingly chosen occlusal material thickness or occlusion control before cementation;
- lack of drainage during luting, resulting in marginal leaks with subsequent painful sensations and marginal caries in the medium term.
