Ask the Expert: An Interview with Nate Lawson, DMD, MA, PhD on Composite Polishers
Q: What are some tricks to achieve a smooth composite restoration?
When I first learned to place composite restorations, I had issues achieving a smooth, porous-free surface that blended with my tooth preparation. Perhaps the most important tip to achieve this outcome is to maintain a smooth surface throughout the entire process of placing and layering the composite. In other words, I used to place composite in increments that would not have perfect adaptation and then plan to smooth the surface during my finishing and polishing steps. These imperfectly adapted layers would lead to lines and pores on the surface of my composite restoration. My current approach is to apply the final layer of composite in a single increment and adapt it to the tooth with a brush containing a blending resin (such as ResinBlend LV, Clinician's Choice). (FIG. 1) Blending resins applied with a brush have several advantages, including the production of a smooth surface, adapting composite to the preparation without the pull-back of a dry instrument, and thinning the composite at the bevel area of the preparation. If the final layer of the composite starts off smooth, then the finishing and polishing steps can be used to add the final texture and luster to the tooth.
Q: How do you achieve a final shape of composite?
Even after applying a smooth layer of composite, the final shape of the restoration may not match the contours of the adjacent teeth. A simple way to improve the shape of a restoration is to draw the line angles of the tooth on the contralateral or neighboring tooth and then draw the desired line angles on the restoration. A simple way to imagine the line angles on an incisor is that there are 2 line angles that run near the mesial and distal aspects of the tooth and then there are three planes that run horizontally on the facial surface of the tooth. Therefore, the tooth can be divided into a 3 x 3 grid with the pencil marks. The use of a finishing disc, such as the Contours Finishing & Polishing Discs (Clinician's Choice) is a great tool for defining line angles drawn with pencil to reshape the tooth. The finishing disc is placed parallel with the facial plane on one side of the pencil mark. On the other side of the pencil mark, the finishing disc is angled to be parallel with the interproximal plane. The use of finishing discs to shape a tooth is superior to the use of diamond burs as they tend to leave an irregular or flat outline. Finishing discs are flexible so they will inherently produce a smooth outline. (FIG. 2)
Q: Why is it important to polish composites?
Polishing anterior composites is performed for both esthetic and biologic reasons. Polishing allows composite to match the natural gloss of the surrounding enamel. It also helps to prevent the composite from undergoing excess surface staining. In a recent study in my laboratory, we performed a test that looked at coffee staining of composite after different manipulation techniques, including adaption with a silicone instrument, mylar strip, and blending resin on a brush. All of the adaptation techniques produced considerably more stain than polishing the composite with a polisher. Therefore, even if a composite appears smooth after adapting with an instrument or mylar strip, it is still beneficial to polish the restoration. Composite polishing also has beneficial biologic effects, including reduced plaque accumulation and patient comfort.
Q: What is the difference between the different steps of a composite polishing system?
Many polishing systems will include multiple steps. There is no exact definition of what constitutes a pre-polisher and what constitutes a high shine polisher; however, I think of the pre-polishers as instruments that remove large scratches caused by burs, diamonds, or coarse polishing discs, and high shine polishers as instruments, which further smooth a surface to allow for a high gloss. Clinically, the pre-polishers are helpful to use to remove any irregularities, scratches, sharp points, or edges out of a composite restoration. The high shine polisher can take a dull looking restoration to a high degree of gloss.
In general, a polisher is composed of abrasive particles embedded into a binder that is held to a mandrel. Polishers can smooth a surface more than a diamond rotary instrument with similar sized abrasives because the abrasives are less rigidly bound. The initial steps of polishing contain larger size abrasives and the later steps of a polisher contain smaller size abrasives. The larger abrasives produce larger scratches and the smaller abrasives produce extremely fine scratches. Therefore, it is important for the clinician to use the polishers in the correct order. Also, the abrasives in a polisher may be composed of diamonds, alumina, or silicon carbide. Generally, diamond is the hardest abrasive and should allow the most efficient polish.
The binder used for polishers also varies. Some polishers contain resin-based binders and others contain rubber-based binders. Resin-based binders will wear away over time exposing new abrasive. This can allow polishers with resin-based binders to remove material more efficiently; however, it will limit the lifetime of the polisher. The rubber-based binder used for composite polishers can also vary in firmness. Stiffer polishers are more aggressive.
Q: What is special about the A.S.A.P. Polisher?
The A.S.A.P. Polishers are 2-step composite polishers. The first step contains 44 micron diamond abrasives and the second step contains 3–6 micron abrasives. The A.S.A.P. Polishers are innovative in their design in that they are spiral wheels rather than points, cups, or discs. (FIG. 3) The spiral wheel allows these polishers to access not only flat areas of the restoration, but also difficult to reach areas, such as the embrasure areas and between proximal line angles. The binder used for this system contains sufficient thickness such that the pre-polisher is effective at smoothing a composite. The high shine polisher produces a very high polish as demonstrated in our laboratory testing.
Q: What research have you completed with A.S.A.P. Polishers?
In our laboratory, we measured the gloss produced by the A.S.A.P. Polishers using a gloss meter. Blocks of Evanesce composite (Clinician's Choice®) were produced in molds and cured with a dental curing light. The surface of the blocks of composite were standardized by using 320 grit sandpaper. The specimens were then polished with two different polishing systems: discs of Enhance and PoGo (Dentsply Sirona) and A.S.A.P. Polishers (Clinician’s Choice). Each specimen was wet polished by hand with an electric handpiece at 10,000 rpms. A new polisher was used for each specimen. Specimens were polished in 15-second increments for a total of 45 seconds per step. The data presented in the graph below demonstrated that A.S.A.P. Polishers achieved a high gloss even within 15 seconds of polishing. (FIG. 4)
About the Author
DMD, MA, PhD
Nate Lawson DMD, MA, PhD is the Director of the Division of Biomaterials at the University of Alabama at Birmingham School of Dentistry and the program director of the Biomaterials residency program. He graduated from UAB School of Dentistry in 2011 and obtained his PhD in Biomedical Engineering in 2012. His research interests are the mechanical, optical, and biologic properties of dental materials and clinical evaluation of new dental materials. He was the 2016 recipient of the Stanford New Investigator Award and the 2017 3M Innovative Research Fellowship both from the American Dental Association. He served on the American Dental Association Council of Scientific Affairs and is on the editorial board of The Journal of Adhesive Dentistry and Compendium. He has lectured nationally and internationally on the subject of dental materials. He also works as a general dentist in the UAB Faculty Practice.
This article was originally published in the Clinical Life™ magazine: Spring 2023 edition
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