Our goal at Atlanta Dental Spa is to be as conservative as possible when restoring posterior teeth (molars and premolars). Being conservative is important to us because it will increase the life of your teeth. We use the best restoration material available for the various conditions a tooth presents. Numerous studies have illustrated both how and why restorations are predictable, and with this knowledge we have been able to choose what restorations will be the most successful. In this post we will focus on tooth colored restorations; specifically, white fillings and all ceramic Inlay/Onlay Restorations used to restore posterior teeth.
What are white fillings?
White fillings are considered direct restoration because the dentist directly fabricates and places the restoration. The materials for white fillings we use are call composites. Composite materials have to be cured from a soft to a hard material. This process can cause shrinkage and can place tension on the bond interface, affecting its longevity. This outcome is particularly likely if the dentist is replacing a lot of tooth structure.
Why do we care so much about the bond?
Research has shown us that the stress of the biting force on the tooth of a cavity-free, healthy tooth will go down the root, which is good. When a tooth has a cavity and the tooth structure is not intact and held together, the stress of the biting force causes the cusps of a tooth to bend. Ultimately, this can lead to fracturing of teeth. When we restore the tooth by bonding, we see that the stress travels down the root just as it did before the tooth had a cavity. When the bond breaks down, the stress starts bending the cusps because the tooth structure is no longer intact, and fracture chances increase. Therefore, having the best bond with the best duration is very important in determining the predictability of the success of a restoration.
When are White fillings predictable to use?
Composite restorations (white fillings) have been proven to be predictable restorations under certain circumstances. The smaller the filling, the more successful they are. Our gauge to measure the size of the filling is the width between the cusps of a tooth. We get predictable results with composites when less than half the width between the cusps are being restored and if we have a lot of the natural tooth structure to support the bite. The biting force is 8 to 9 times more in the posterior teeth than in the anterior teeth. The wider the filling gets the more likely the filling will support the bite; thus, more likely for the bond on the filling to fail. This failure typically results in getting a new cavity, and possibly even the tooth fracturing. This is when we need a stronger material that has a better bond to reinforce that tooth structure. These type of restorations are called Inlays/Onlays.
What are inlay/onlay restorations and what’s the difference between the two?
Inlays/Onlays are indirect ceramic restorations that are fabricated by a laboratory. After preparing the tooth the dentist takes an impression of the tooth for the lab. These restorations are one solid piece of ceramic that are cemented and bonded into the tooth. See the video here. They are made out of the same material as a crown, lithium disilicate, with the strength of 300Mpa. The strength of the restoration and bond to the tooth are superior then a composite filling; thus, can they can predictably reinforce more tooth structure.
Inlays are used when half the tooth structure is missing and the cusps are still well supported with tooth structure. Onlay restorations are used when one or more cusps are not well supported and need to be replaced. The main benefit for onlays is being able to onlay or replace/cover a tooth cusp while being conservative by keeping the healthy tooth structure. Therefore, dentists don’t have to unnecessarily remove healthy tooth structure for a crown.
When and why is it necessary to replace a cusp?
Replacing a cusp is necessary when there are cracks on a cusp and when a dentist sees that the cusp is not well supported by dentin/tooth structure. Cracks are signs that the tooth cusps are bending and that a fracture of tooth structure is likely to occur. In addition, a cusp that is not well supported by dentin is likely to fracture. By onlaying cusps we are providing a restoration that contains/holds the pieces together. Replacing the cusp prevents that cusp from bending. It is now the strength of the onlay material that will determine if the tooth splits, not the bond. This will significantly decrease the chance of a fracture and restore the strength of the tooth back to where it started.
What about Silver fillings?
Let’s flow into a quick chat about silver/mercury fillings. We do not offer them in our practice for many reasons, including: they are unaesthetic, carry potential health consequences, and we have superior products available. The United Nations even has a goal to eliminate all products on the market that contain mercury by the year 2020. See the dangers on our holistic dentistry page. Silver fillings simply fill in the space of the cavity with no bonding to tooth structure. This is why we commonly see stress fracture lines in a tooth with a silver filling. The cusps on these teeth are bending and likely to fracture or cause the cracks to extend to the nerve, which would require root canal therapy. This is why being proactive and replacing these failing restorations with inlays and onlays are so important.