Inlays and onlays
When an inlay is used, the tooth-to-restoration margin may be finished and polished to a very fine line of contact to minimize recurrent decay.
While inlays might be ten times the price of direct restorations, it is often expected that inlays are superior in terms of resistance to occlusal forces, protection against recurrent decay, precision of fabrication, marginal integrity, proper contouring for gingival (tissue) health, and ease of cleansing offers.
Another study detected an increased survival time of composite resin inlays but it was rated to not necessarily justify their bigger effort and price.
The onlay allows for conservation of tooth structure when the only alternative is to totally eliminate cusps and perimeter walls for restoration with a crown.
Inlays and onlays may also be fabricated out of porcelain and delivered the same day utilizing techniques and technologies relating to CAD/CAM dentistry.
[17][7] It is also indicated when placement of direct restoration may be challenging to achieve satisfactory parameters (shape, margin, occlusion).
[citation needed] A Parafunctional habit refers to abnormal functioning of oral structures and associated muscles, for example patients who clench or grind their teeth.
Evidence (Fuzzi and Rapelli) has shown greater failure of Onlays and Inlays in molars than premolars over an 11.5 year period.
When preparing a cavity to retain an indirect restoration there is a risk of damage to the nerve supply of a vital tooth.
Young children may be unable to cope with invasive dental treatment and long procedures, therefore it is advantageous to wait until they are fully cooperative.
Digital impressions enable production of highly accurate models whilst eliminating patient discomfort.
Inlays require elimination of undercuts, therefore direct restorations may preserve tooth structure whilst also avoiding unwanted laboratory costs.
[20] For inlay and onlay preparations that are going to be completed with all-ceramic then these cavity shapes can be slightly over-tapered as most of the retention is gained from the cement lute.
The best instrument to use for this is a high-speed diamond fissure bur and the reduction should follow the inclination of the cusps and grooves as this will allow the preservation of more tooth tissue.
A high-speed tapered diamond bur has the most convenient shape to prepare the buccal, lingual and proximal reduction of the tooth.
There are two ways this can be done, either by blocking the undercuts out with an adhesive restorative material or by removing tooth tissue to create the divergent cavity needed.
The milling process uses pre-fabricated blocks of restorative material, e.g. lithium disilicate or composite reinforced ceramic, to produce the end product.
[28] Inlay wax is chosen due to its brittleness – it breaks upon removal from undercut of a cavity, either on the die or in the mouth.
The investment material must produce enough expansion to compensate for shrinkage of the metal on solidification and should be slightly porous to allow for dissipation of released gases.
The container, or casting cylinder, is then placed in a furnace to burn out the wax and what is left is a hollow shape ready for molten metal to be poured into.
Once cast a layer of oxides are present on the surface, these can be removed by placing the restoration in an ultrasonic bath for 10 minutes.
Inlays and onlays made from ceramic or metal alloy require laboratory work and therefore can only be fabricated using indirect restorative techniques as mentioned in the previous section.
[31] A study done by Rippe et al. has shown that ceramic inlays produced by the different methods, via indirect restorative techniques aforementioned, have similar longevity.
Gold has many advantages as a restorative material, including high strength and ductility, making it ideal to withstand the masticatory forces put upon the teeth.
Due to the more in-depth curing method, using heat, pressure or strong light, this can have a lower polymerisation shrinkage.
[33] However, using this indirect laboratory method demands more skill and time, and is more destructive as tooth preparation is needed prior to taking an impression.
[39] Zirconia, a high-performance ceramic material, has gained popularity in dental restorations due to its superior mechanical properties and biocompatibility.
The exceptional strength and wear resistance of zirconia make them particularly well-suited for posterior teeth subjected to high masticatory forces.
[42] With a low modulus; the cement will absorb deformations under loading and limit the pressure transmitted to surrounding tooth structures.
[41] Preparation of inlays are with close to parallel walls and a key on the occlusal surface- this is sometimes sufficient for retention purposes so adhesive resin luting cements may not be needed.
