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.
All restorative materials have wear properties. We need to understand both how they wear and survive in the oral environment and how they impact opposing natural teeth. The wear of enamel is the basis for comparison. Despite what we sometimes see clinically enamel is highly resistant to wear (attrition and abrasion), with average annual wear rates of 30-40 microns. The range is from as low as 15 microns to as high as 100+ microns, and there is variability depending on the tooth position in the arch. Unlike enamel, that basically all has the same structure and properties, composites come in many different formulas. The chemical and physical properties of the material have a direct impact on its wear resistance and impact on other teeth. Some examples of this include:
- Size, Shape and Hardness of Filler particles
- Quality of the bond between filler particles and polymer matrix
- Polymerization Dynamics of the polymer
These same properties affect the other physical and handling properties of the material and have to be balanced to create a composite that works clinically. Creating improvements in the physical properties of composites has eliminated the high degree of wear in non-contact areas we witnessed years ago. The loss of restorative material gave the appearance of fillings losing the shape and contour. Today our primary concern is in areas of direct occlusal contact. One approach might be to avoid using composite that has direct occlusal contact. I would say this is not only not practical but not necessary. We have a variety of materials available today, with a range of handling and physical properties, and wear rates that are between 30-200 microns a year. We need to choose a composite based on things like wear versus polishability, anterior versus posterior, and the properties of the particular material we are using.. In addition we can manage the occlusion to maximize the success of the natural teeth as well as the composite.
Interesting topic. All I can say is equilibration is so important in every case, with or without orthodontic treatment. Thank you for your great work!
Can you recommend so resources (online or off) I should study to improve my knowledge on occlusion and helping my patients with excessive wear?
David, There are lots of great options. I have 2 online courses a year on occlusion and next year will be offering a hands on course. I am also teaching a course on occlusal and wear in Feb at The Pankey Institute (https://www.pankey.org/course/restoring-the-occlusally-challenged-patient). You can also think about The Pankey Institute, Spear Education, The Dawson Center or John Kois as great educational opportunities in Occlusion.
You said, “We have a variety of materials available today, with a range of handling and physical properties, and wear rates that are between 30-200 microns a year. We need to choose a composite based on things like wear versus polishability, anterior versus posterior, and the properties of the particular material we are using.. ”
I must have stopped paying close attention to what is in the marketplace, because in my mind there are 2 types of composite: microfill and ‘universal’. The highly polishable microfills are for the outer layer of anterior restorations that are facial to the contact areas and the anterior/posterior ‘universal’ composites for everything else. Among the anterior/posterior universal composites, some kits have each shade with both a dentin paste and an enamel paste for opacity and translucence control, while most kits have just 1 all-purpose universal composite per shade. Some universal and microfill composites can be found that are specifically “opaque” or “transparent”. None of the ‘universal’ composites polish as nice as microfills, but all the universals are indicated for strength and wear resistence in function. So universal composite is for posterior fillings and the lingual portion of anterior fillings and lingual aspect of incisal edge restorations. Microfills are for any part of an anterior interproximal filling that comes around to the facial and for veneering the facials of any teeth.
Is there more to it?
Spencer,
We do still have microfill, microhybrid, packable, nanofill, nanohydrid and now bulk fill type composites, and some of the manufacturers still make several different variations of composites with different [properties. Also, across the manufacturers not all nanofill, microfill and nanohybrid have the same properties as the quantity and type of filler is everything when it comes to the physical properties including wear. Whether you are choosing for the anterior, mostly based on esthetic and sculptability properties, or int he posterior for wear resistance and shrinkage stress I do not think there is one try universal composite that has the nest of all the properties.
Lee
I guess I am too trusting when a company says “universal” (meaning can be used in anterior or posterior)… I know they are never polishable enough for the outer layer on the facial, but I wasn’t paying attention to other variables. I get a little confused because I believe my patients’ teeth are like your patients’ teeth and they are like all of our patients’ teeth on this planet… so I don’t quite understand the variety of choices other than how they are manipulated or delivered (eg. sonicfill or packable or compule, etc) or in optic properties for enhanced esthetics (different opacity for ‘dentin’ vs ‘enamel’ or opaque to block dark dentin or metal). In the end, I am expecting that a material for posteriors shouldn’t be available on the market today if they are inferior in wear or shrinkage or absorption, etc. It doesn’t seem right that reputable companies market inferior materials and make us figure out today which ones won’t come back to bite us in the ass down the road later.