POLISHING RESTORATIONS

Today’s dentistry is all about aesthetics. There is an assortment of material choices and techniques that can be employed by the clinician to create extremely lifelike restorations. However, over time, it is often the postoperative care of these restorations that poses a challenge. The dental team, particularly the dental hygienist, plays an invaluable role in the success and longevity of aesthetic restorations, whether it is a single tooth restoration, or an 8- to 10-unit smile design.

POLISHING TRIAGE
First of all, it is imperative that the dental hygienist makes an evaluation regarding the polishing environment and situation, ie, conduct a polishing triage determining exactly why you are polishing any particular restoration. Polishing to smooth down a rough surface? Smoothing down a margin? Removing plaque? Removing extrinsic stain on the restoration? Restoring shine and luster to a dull surface? Is there a true “reason” to polish? You may wish to consider selective polishing as a viable option.¹

RESTORATIVE MATERIALS
Not only is determining why you are polishing important, it is also important to know what dental material you are polishing. Quite simply, different polishing pastes will have a different effect on different materials. Aesthetic indirect all-ceramic materials fall into 2 general categories: composite or porcelain (ceramic).
Composite, or resin-based materials, are mechanically polished to a shine. Also, the filler particle size of the composite is directly related to the optimal surface luster. Normal particle size can range from 0.04 to 1 µm, affecting the material’s potential to achieve a high shine. Fillers may be made of resin, glass, or silica; or a combination of these. Composite resin materials require regular care to maximize their longevity simply because they are not as strong in comparison to the strength that porcelain materials possess. Composites are also a viable direct restorative choice in the dental office.²

With porcelain materials, an enamel glaze is baked on the surface of the restoration to provide a smooth glossy/shiny surface. Advances in dental technology offer more ceramic/nonmetallic options. The use of computer-aided design/computer-aided manufacturing systems has enhanced the availability of aesthetic choices, whether restorations are fabricated in the office or in the dental laboratory. For example, in the laboratory, copings can be milled out of zirconium oxide, and porcelain can be pressed (or layered) onto the substructure. Options for crowns and veneers include layered/stackable feldspar-based porcelains or pressed-ceramic utilizing the lost wax technique. Pressed ceramic can include materials such as leucite glass-ceramic and lithium disilicate glass-ceramic. Strength is gained once the porcelain restorations are bonded to the tooth structure.³ It is important for the hygienist to be aware of the interface between the tooth structure and the restoration, as it can stain and abrade more readily. Also, it is pertinent for the hygienist to help maintain a smooth glasslike surface to the restorations. Any roughness will attract bacteria and stain, contributing to a less aesthetic appearance, and possibly compromising the integrity of the restoration itself.^4,5

RELATIVE DENTIN ABRASION VALUE
Once you have determined the aesthetic material and the purpose of polishing, the polishing agent itself should be evaluated for its main abrasive ingredient. The relative dentin abrasion orradioactive dentin abrasivity (RDA) should be reviewed and assessed (Table 1). This value indicates the abrasivity of a material in relation to dentin. The relative enamel abrasion (REA) value can be taken into consideration as well, but the RDA value relates better to the sensitivity of dentin. Abrasives are based on the hardness, particle size, and quantity of the abrasive. The ADA has adopted a standardized test to determine the RDA and REA value of a product. Basically, to determine RDA value, extracted human teeth are irradiated with mild neutrons, stripped of enamel, and subjected to simulated tooth cleaning procedures. The rinse water is then measured for its radioactivity and recorded. Thus, after a few calculations (taking into consideration speed of rotation of the prophy cup, time, and the pressure applied, etc), a score or index is given to the product being tested (Table 1). Any value over 100 is considered to be abrasive.⁶ The ADA recommended limit is 250, whereas the FDA limit is 200. (Note: Toothpastes are also given a RDA value for FDA approval, but often are not published for marketing purposes). As for the hardness, abrasives are ranked on the Mohs scale of mineral hardness. The hardness is based upon 10 readily available minerals, on a scale of 1 to 10.