Inlays and Onlays are indirect dental restorations that reinforce an existing tooth that is too damaged to support a filling, but not damaged enough to require a crown. An inlay is placed on the chewing surface between the cusps of the tooth. It is an intracoronal preparation. Whereas an onlay is an indirect restoration which is partly intracoronal and partly extra coronal that covers all cusps of posterior teeth. The main advantage of inlays and onlays is that the tooth structure is saved and it is more economical as compared to the crowns. The dental office time and the numbers of visits required to dentist office are also less. The composite inlays take less time and are more economical than the ceramic inlays and onlays but the ceramic inlays and onlays are more durable as they are stronger than the composite inlays. Both the inlays and onlays are esthetic restorations which can replace the metallic restorations.
Various materials can be used for preparing inlays and onlays. These can be
Cast metal
Gold
Composite
Porcelain
Gold Inlays
A gold inlay is indicated when there is extensive caries affecting the tooth that a satisfactory restoration cannot be fabricated using silver amalgam. Specific indications are:
1. When the cavity width does not exceed 1/3rd the intercuspal distance.
2. In case of extensive proximal caries involving the buccal and lingual line angles of the tooth.
3. In situations where the proximal margins are extending subgingivally. This is because well polished gold alloys are compatible with the periodontium.
4. Whenever there is need to establish ideal contact, contours and embrasures. The mesiodistal dimension of cast gold inlays can be extended to establish good contact.
5. In a grossly carious tooth where one or more but not all cusps need coverage.
6. In patients with good oral hygiene and low caries incidence.
7. When there are other gold castings present in the mouth.
Contraindications for Gold Inlays
1. Gold inlays are used as an abutment for a fixed or a removable prosthesis. In these situations the gold inlays are not strong enough retainer.
2. They are contraindicated in post endodontic restorations as they can wedge and fracture the remaining tooth structure.
3. In young permanent tooth gold inlays are avoided as there are increased chances of iatrogenic pulp exposure.
4. in patients with high plaque and caries incidence. Gold inlays should be avoided as there may be a greater tendency for recurrent caries.
5. When the adjacent or opposing teeth have dissimilar metallic restorations cast gold inlays should be avoided in order to prevent galvanism.
6. When cost is major factor for the patient, gold inlays are not indicated.
7. Gold inlays are not preferred in case of grossly destroyed teeth with weak cusps.
Tooth coloured inlays and onlays
Tooth colored inlays and onlays have certain advantage over direct resin composite and bonded ceramic restorations. These advantages are:
Highly esthetic.
Can be fabricated intraorally or on a cast.
Highly successful in larger restorations.
Have many materials and techniques.
Various tooth colored materials are given as under
Composite resin inlays and onlays
Compared with direct composite resin restoration
Contours and contacts can be developed outside of the mouth. If contact is inadequate, it can be easily corrected prior to cementation.
Polymerization shrinkage should be less because they are polymerized before cementation.
Less micro leakage.
Greater strength and hardness.
Less post-operative sensitivity.
Compared with ceramic
Less abrasive to opposing tooth structure.
Repairable.
Cheaper.
Advantages of composite inlays:
High esthetics.
Better control of the contact areas.
Excellent marginal adaptation.
Reduced or no laboratory fee if done in office.
Ready reparability of material intraorally.
Compensation for complete polymerization shrinkage by curing the material outside the mouth.
Increased composite resin strength because of the heat curing process.
Disadvantage of composite inlays
1. Wear faster.
2. Less stable.
3. Higher cost time.
4. Difficult to modify extrinsic color chair side.
5. More tooth reduction to create path of insertion.
Indication of composite inlay
Replacement of large amalgam restorations.
Replacement of direct resin composite restorations in premolar and molar.
Large caries.
Esthetics.
Contraindication of composite inlay
Heavy occlusal forces.
Inability to maintain dry operative field.
Deep subgingival preparations.
Porcelain inlay and onlay
Advantages:
1. Highly esthetic.
2. Acceptable marginal fit.
3. Conservation of tooth structure.
4. Less occlusal wear.
5. Highly technique sensitive.
6. Low thermal conductivity.
7. Low coefficient of thermal expansion.
8. Biocompatibility.
Disadvantages:
1. High cost.
2. Need for special and laboratory equipment.
3. Fabrication and cementation processes are highly technique sensitive.
4. Ceramic inlays are brittle and can fracture during try in or cementation.
5. The increased hardness of ceramics can wear the opposing teeth.
Indications:
1. High esthetic demands.
2. Replace moderate to large existing restoration.
3. Fractured tooth/restoration.
4. Moderate to large primary caries.
5. Patients with good oral hygiene.
6. When there is no excessive attrition.
7. Where access and isolation are easy.
8. When there is no excessive undercuts in the preparation.
Contraindications:
1. Unable to isolate the field.
2. Parafunctional habits like clenching, bruxism, excessive wear.
3. Patients with poor oral hygiene.
4. In case with minimal tooth loss.
5. When there is inadequate enamel left for bonding.
6. When there are marked undercuts in the cavity preparation.
