Polishing Techniques for Beauty and Longevity

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.

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.

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.

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 or radioactive 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. 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. Diamonds are assigned a 10 since it is the hardest mineral, and talc, the softest, is assigned a 1.0.7 (Tables 2 and 3).

NOT ALL POLISHING PASTES ARE CREATED EQUAL
Determining the proper polishing agents indicated specifically for aesthetic restorations can be challenging, as there are a plethora of pastes on the market. Not all abrasives are created equal, and not all of them are appropriate for aesthetic restorations. General prophylaxis pastes may compromise the surface integrity of restorations making them dull, and create microscratches that can attract plaque and stain. There is a difference between a polishing paste and a cleaning paste. A polishing paste will re­move plaque and provide luster, but will not remove stain. This is because it either does not contain an abrasive, or it has very minimal abrasive in the product. A cleaning paste will remove plaque and debris, and remove stain, as it may have various grits of an abrasive present.

In order for a surface to be polished smooth and shiny, the abrasive itself needs to be harder than the surface being polished. Grit refers to the particle size. A finer abrasive produces fewer scratches on the restorative/tooth surface, thus creating a smoother and glossy finish. The larger the particle size, the more abrasive the product will be to the surface being polished.

Common abrasives found in pastes include materials such as aluminum oxide, pumice, silica, silicon dioxide, tin oxide, and diamond particles. Pastes that contain aluminum oxide are safe for both composites and porcelains for plaque removal and general polishing. Aluminum oxide is safe to use on stain-free surfaces. However, if the porcelain restorations need to be polished to improve the shine or luster, a product that contains diamond particles should be utilized, then polished with a fine aesthetic polishing paste to restore lost luster (Table 4).

POLISHING PROTOCOL
Other variables that affect the abrasive properties of a product include quantity of the paste applied, the rotation speed of the hand piece applying the paste, how much pressure is applied to the surface being polished, and how much time is spent polishing per surface.

Keep in mind that friction and heat generation are other factors to consider. Slight modifications of current polishing techniques are re­quired even when polishing aesthetic restorations with the properly indicated paste. Handpieces should be operated below 3,000 rpm. Adaptation of a soft cup is preferred with the lip of the cup flared slightly against the surface as seen in Figures 1 and 2. Figures 3 and 4 illustrate adapting the cup to the bicuspids with medium or coarse prophy paste to remove interproximal staining. Afterward, the restorations are polished with a fine paste to restore a smooth glasslike surface as seen in Figure 5. If additional polishing is required to re-establish surface integrity, a diamond polish may be utilized.

The cup should be adequately filled (not overfilled) with paste, as shown in Figure 6, and held at a 90° angle against the tooth. Utilizing intermittent pressure strokes on the tooth, and keeping sufficient paste in the cup, will help avoid any frictional heat. Too much external pressure can contribute to increased abrasion against the surface being polished. A limited number of teeth (2 to 3) should be treated at a time. Time spent on each surface should be approximately 5 seconds. Following the complete manufacturer’s recommendations regarding the specific polishing agent will ensure proper results and success of the product.

In an ideal situation, if a restoration does not have stain present, it is an option to selectively polish. This technique is supported by the American Dental Hygienists’ Association.1,9 However, many patients feel that the “cleaning” is not complete without having their teeth and/or restorations polished, in some sort of fashion. This is where the hygienist can triage the polishing protocol specific for each patient. It may be just selecting a polishing paste that is needed to satisfy the patient’s desires. Several polishing pastes are on the market specific to aesthetic restorations.

CONCLUSION
If the assessment of the potential polish of a restoration is beyond a paste’s indications and the hygienist’s capabilities, it may be an option for the dentist to utilize porcelain polishing kits that use various grits of abrasives in the form of wheels, points, and cups, in order to reach the definitive treatment goals (Table 5).

In general, be cautious about the products used to maintain the restored aesthetic smile. The goal is to maintain and protect the longevity of the restorations for the patient. It is important to do your homework so that you do not inadvertently compromise the aesthetically-restored smile by using an inappropriate product.