When the biting surface of a back tooth needs a restoration, the best choice is often an Inlay or Onlay made of resin. The resin material is a mixture of acrylic resin and microscopic particles that are shaped and curved for strength.
We may recommend an inlay and Onlay depending on how much tooth structure has been lost. An inlay fits within the grooves of a tooth, spying surface like a filling. While an Onlay also covers one or more cusps of the tooth.
Both restorations are precision-crafted in a dental laboratory, so it may take two or more appointments to restore your tooth. With a resin inlay or online on your first visit, we numb the area to make you comfortable. We may also use a rubber dam to protect our mouths while we work. Then we remove any decay and shape the tooth with a handpiece.
Next, we’ll take an impression of your teeth. The lab uses the image to make a model of your mouth. They’ll use the model to create a final restoration that fits your tooth and bite. In the meantime, we often place a temporary restoration. On your next visit, we will remove the temporary and try in your final resin Inlay or Onlay. We check the fit and when everything looks good.
We bond the final restoration in place. A resin restoration has several advantages it protects the tooth. The resin material expands and contracts like a natural tooth structure. It’s gentle on the opposing teeth when you chew, and it’s natural-looking. When a back tooth needs a restoration a resin Inlay or Onlay is a natural-looking choice.
The cost of the materials and fabrication are higher than that of amalgam or composite. Laboratory costs contribute to the overall cost and vary depending on the restoration.
The procedure requires at least two appointments. This also contributes to the cost as it’s twice the amount of infection control items.
Also, consider the patient’s situation. If the patient leaves the country the next day, an Onlay may not be the best treatment. This is possibly the most extreme example, but these situations arise and must be considered. What else do we feel when determining if this is the correct restoration for the patient? Oral hygiene, caries rate, and patient age tend to go hand-in-hand.
A patient with a high caries rate and a high caries risk would be needing a replacement restoration long before he or she would need a replacement restoration if they had a low risk for caries. So for economic sake, if the patient needs repairs every six months, I would select the amalgam restoration.
Otherwise, the patient buys the gold; it is fabricated and cemented then recurrent caries necessitate its replacement. So then we cut it out and replace it- doubling the cost to someone. Insurance has a time frame where they will not cover the replacement of any direct restoration.
Introduction to Inlay and Onlay
Introduction to inlays/onlays
The aesthetic Inlay and gold Onlay. The terms Inlay and Onlay will be used interchangeably. The definition of when an inlay technically becomes an Onlay depends on the reference.
A direct restoration is placed directly into the cavity preparation chairside. The material then hardens within a retentive preparation and the restoration is completed with shaping and polishing.
An indirect restoration is made outside of the mouth and then cemented to the prepared tooth. Typically this requires at least two appointments. There is at least one method that allows for a single appointment indirect restoration but the restoration is still fabricated outside of the mouth.
We have direct and indirect restorations. There is another way to classify restorations, intracoronary and extra coronal.
Intra means inside, extra means outside. So we have restorations that are more or less within or inside the crown of the tooth and then those restorations that cover the outside of the tooth-Intracoronal.
Restorations are the operative preparations such as the Class 1 through 5. Veneers and crowns are extra coronals since they cover the outside rather than being down in the internal aspect of the tooth. Other terms to know from this lecture are flare, vent, and draw. These will be defined and described throughout the lecture. Typical materials used to fabricate indirect restorations are gold, composite, and various ceramics.
Ceramic and composite are both tooth-coloured materials. Since ceramics tend to last much longer than indirect resins, ceramics tend to be used more often.
Onlay
An indirect restoration that restores one or more cusps and the adjoining occlusal surfaces or the entire occlusal surface.
When do we use an indirect restoration?
We consider the size of the restoration and the amount of remaining tooth structure. Large restorations are very dependent on the strength of the restorative material. CAD-CAM ceramics and gold have that necessary strength.
Another issue with large restorations can be obtaining contours with direct restorations. With indirect, the contours and contacts are controlled during fabrication. The length of service of indirect restorations is generally superior to that of amalgam or direct composite. Other deciding factors include the time and cost for an Inlay or Onlay.
How Long Can on Inlay or Onlay Last?
There are gold Onlays that have been in service for over 50 years!
A more common length of time is 20 to 30 years. So they far outlive an amalgam which tends to last 15 to 20 years. CAD-CAM ceramic materials are expected to be as good.
Without having CAD-CAM for 50 years yet, we don’t have this knowledge yet.
One more note on the longevity of any restoration. The longevity is dependent upon the restoration and how well it was executed and the longevity depends upon the patient oral hygiene, diet, saliva, those factors which contribute to caries risk.
If fracture lines are noted on the tooth to be restored, a crown is more likely the restoration to select. Likewise, if Class 5 caries exist on the facial or the lingual, a crown is typically best.
Why does an indirect restoration restore the MOD defect and then restore the Class 5 with composite or amalgam? A crown covers all surfaces of the tooth, so a crown is typically best if either a Class 5 lesion or previous restoration exists.
The inlay preparation is sometimes used for a type of bridge that is bonded to the retainers. Typical bridges will encompass the entire adjacent tooth with a crown, however, there is an occasional need for a bridge of this type. The resin bonded bridge can be considered when the adjacent teeth have minimal or no caries or restorations, when the occlusion is not heavy, and when the teeth do not have short clinical crowns. The amount of divergence has a name.
This is the VENT. When divergence is excessive the preparation is said to have excessive vents or perhaps only one wall has an excessive vent. Likewise, a wall needing more divergence will thus be said to need more vent. Another term that closely follows the vent is the path of insertion.
The path of insertion is that pathway which the restoration will follow when it is either being placed in the mouth or tooth or when it is being removed. The inlay for the drawing would have to follow the blue arrow to be inserted or removed. As with other preparations the head of the handpiece should be held parallel to the occlusal table of the tooth being prepared so that the bur is then parallel to the long axis of the tooth or perpendicular to the occlusal table.
When this is accomplished for indirect preparations the path of insertion will then be parallel to the long axis of the tooth. The concept of vent leads us to the draw of the preparation. For a solid piece of material to fit down into the preparation, there must be no undercuts. All vertical walls must be able to be seen at one time.
Dental Inlay and Onlay
One of the available techniques to restore a damaged tooth is the realization of an Inlay/Onlay. Firstly, the tooth is prepared to eliminate damaged structures. After that, an impression of the preparation is taken, on which the Inlay/Onlay will be fabricated using different materials.
Once the Inlay/Onlay is done, the adjustment and occlusion with the opposing teeth are checked in the mouth, releasing any excessive contact on it.
Finally, the Contact points are checked and the surface polished.
What Is CAD-CAM?
It is a method of obtaining an optical impression. The impression is a digital image of the prepared tooth and then the computer is used to help design and cut the restoration out of a solid block of restorative material.
The drawings in yellow on the left depict various lines which can be machined by the computer systems. The six drawings on the right are of the computer monitor on the CAD-CAM system.
The system allows the operator to make a digital impression of the preparation and create a virtual restoration seen in the bottom row of pictures.
