It is routine to see patients with lower incisal edges that are worn into the dentin. The wear can be from attrition or from erosion, and is often a combination of the two. When dentin is exposed and the wear is progressing at a rate that is not age appropriate I want to do something to protect these teeth and slow the progression of the damage. When I think about possible restorative options I want to do what is appropriate, stay conservative if possible and manage the restorative challenges that are present with lower incisors due to their size and shape. These factors combined with the fabulous properties of our new composites have me using direct composite more and more in these situations.
Often when I lecture on composite dentistry I get asked about improving the final surface texture, polish and sculptability when doing anterior teeth. In a previous blog I looked at the categories of composites and understanding their physical and handling properties based on composition. Microfill composites are an older material formulation that is still on the market for precisely the reason of it’s esthetic qualities. These materials have a lower filler percentage which means there are compromises in the areas of material strength, wear and durability under load. However, microfills to date still have the highest polishability of any composites. Not only are the easy and beautiful to polish in your office, but they maintain that polish over time due to normal hygiene with a toothbrush.
Earlier posts have discussed the difference in light and color properties between natural tooth structure (enamel & dentin) and their corresponding composite replacements. The difference in translucency, opacity and how the thickness of each layer impacts these properties and others like chroma and value become a challenge chairside when we try and replicate nature. One of the ways to understand and maximize the properties of the composite you are using is a simple bench top exercise. First create a silicone lingual matrix from a model of a patients upper anterior teeth. Next using the current composite that you would employ for a class four or anterior veneer you simply need to create a few teeth and play with the layers and their relative thicknesses.
All composite materials are a mix of organic resin matrix, filler particles and a coupling agent. The challenges we experience with composites like consistency and stickiness as well as characteristics like polymerization shrinkage, flexural strength and polishability are a result of the type and quantity of filler particles in relationship to the resin matrix. As the proportion of filler particles increase the physical properties of the material improves, but handling properties can be compromised. In a quest to create better composites with optimal physical properties and handling characteristics new advances have been made in filler particle science. As new categories of composites have come on the market some of the older types have continued to find applications and been preferred by some practitioners. With all the different types of composites on the market what should you use when, and do we have a universal material?
One of the techniques we master when doing indirect restorations is matching the tooth reduction to the thickness of the layers of ceramic the technician needs to give us our final requested esthetics. The concept is identical when completing a direct composite veneer. We will utilize multiple layers of composite, each has a different set of light properties that create opacity, hue, chroma and value. It is the combination of these layers of differing light properties that result in the final esthetics. This thickness of material must be added to the existing tooth structure and create a tooth that is correct in position, contour and proportion. Therefore, unless we are always working on undersized teeth we will need to prepare the natural tooth to create space for the correct amount of composite.
A common question that I get from patients is how long it will take for the color of a new composite filling to change. The answer to this has changed over time as our materials have evolved. Modern composites are at less risk of yellowing or darkening over time than some of the original materials, but there are still some factors that cause color instability. Studies have shown that composite resin materials due undergo a yellowing process as they age, and this is true despite the chemical composition.
I have spent the last two days at the ADA Annual Session teaching on topics from occlusion to provisionals. One conversation kept coming up over and over, so I thought it is a perfect topic for a post. I was amazed at how many times I found myself discussing using a brownie, silicone polishing point, in a high-speed handpiece in my office. So first, as a caveat, you can not run a brownie point at full speed in a high-speed handpiece, it will turn into a silicone grenade. I work with electric handpieces, so I dial them down to half speed. If you are using air driven, simply press lightly on the rheostat so you do not get full power.
In yesterday’s post I discussed the factors that impact wear resistance in modern composite materials. The great news is that we only have to think about the wear resistance of composite in areas of direct occlusal contact. The second piece of good news is that very few composite restorations are replaced because of excessive wear. The majority of restorations succumb to marginal breakdown and leakage, secondary caries or other forms of bond failure. Now, the bad news is that bond failure and bond degradation is accelerated under extreme occlusal load. With all of this in mind it makes sense to manage excessive forces and material selection to increase longevity of our restorations.
This week I have been preparing for a lecture at the USC Restorative Symposium called “Occlusal Considerations of Modern Composites”. I have been using direct composite as a restorative material and an adjunct when I equilibrate or organize a patient’s occlusion for many years. Now I have the scientific research to support what I have seen clinically. The challenge of wear is quantifying it. We see wear occur clinically , but do not have a reliable way to measure or quantify it. In the laboratory instruments that replicate the action of teeth and cause attrition and abrasion can be used and precise measurements obtained about the loss of structure that occurs as well as the surface roughness created. This allows us to look at our clinical applications and experiences and have a greater understanding of it when it comes to wear.
In yesterday’s post I looked at the light and color properties of composite and natural teeth. The combination of layers of composite with varying light and color properties is a key step in obtaining natural looking esthetics. As with a tooth, we want to have enamel layers on the lingual and facial with the layers of dentin in between. This multi-layer approach has many variations, but is the essential ingredient in a great result. The layering process begins on the lingual. Using a silicone matrix we create the lingual wall of enamel composite. This first layer should be between >5 and 1mm in thickness from the junction with the prep to the incisal edge. I prefer to capture the incisal edge int he matrix and build it in this first layer of enamel composite to capture the length and thickness of the tooth.