Polishing Basics

Until 2012, prominent dental hygiene textbooks^1,2 and the American Dental Hygienists’ Association (ADHA) purported that the only indication for polishing was stain removal. Because of new evidence, the ADHA is reconsidering its position³ and the latest Wilkins textbook includes revised recommendations for polishing.⁴ With perspectives on polishing in flux, taking another look at the research surrounding this staple of dental hygiene practice and its clinical applications is appropriate. Polishing for biofilm removal as a stand-alone dental hygiene intervention does not prevent periodontal diseases.⁵ However, rubber-cup polishing as part of a dental prophylaxis can remove soft deposits and extrinsic stain, while creating smooth tooth surfaces that minimize biofilm retention.

On the other hand, the beneficial results of polishing do not justify indiscriminate use. Two important factors to keep in mind when considering polishing are the degree of surface roughness created and the amount of tooth structure removed. The risks vs benefits of any procedure that removes a clinically significant amount of tooth structure should be carefully weighed. The surface roughness of teeth and restorations is directly related to plaque retention because bacteria attach more readily to rough surfaces. Polishing smooths naturally-occurring rough surfaces, as well as those created by scaling. Dental hygienists need to critically evaluate the effects of procedures when providing care, including potential cumulative outcomes over time, and make ethical decisions based on the available data.

FUNDAMENTAL PRINCIPLES

A general definition of polishing is the production of a smooth, glossy surface through the use of abrasive particles.⁴ The abrasive must be harder than the surface being polished in order to abrade and produce a smooth surface. Several scales can be used to rate hardness. The Mohs Scale of Hardness is easy to apply to dental polishing, with the softest materials, such as resin, at the low end and the hardest materials, eg, diamond, at the high end (Table 1).⁶ If a surface is already smooth, polishing can be performed with a material of lower value on the Mohs scale to cleanse without abrasion.

Several factors affect the rate of abrasion, including the abrasive’s size (grit), hardness, and particle count (such as a thick paste compared to a thin, watery paste), as well as the rotation rate, pressure, and duration of action. An increase in any of these factors results in a higher rate of abrasion and more frictional heat. Generating heat should be avoided because it can harm the tooth pulp. This is particularly important for teeth with large pulp chambers such as deciduous teeth and newly erupted permanent teeth. Conservative polishing technique results in the least amount of abrasion necessary to produce the desired result. In general, a pulsating application with light pressure and low rotational speed is recommended to limit heat and prevent unwarranted abrasion. The least abrasive particle that will accomplish the task should be chosen. If a coarse paste is needed for stain removal, a second polishing pass with a fine paste can reduce resultant surface roughness.⁷ Any time a finer paste is used after a coarser paste, the rubber cup should be changed or thoroughly rinsed to remove any remaining large particles.

EFFECT ON TOOTH STRUCTURE

Sound enamel is more resistant to abrasion than other dental tissues because it is harder than dentin and cementum. Under simulated clinical conditions, polishing with coarse prophy paste removes very small amounts of enamel.^8–11 In general, more enamel is lost as pressure, time, and rotation increase. When light pressure, short duration, and low rotational speed are used, enamel loss appears negligible.^8,12 Demineralized enamel, such as a white spot lesion, is very susceptible to abrasion. Polishing white spot lesions results in three times the enamel loss than occurs when polishing sound enamel.¹²

Abrasion of cementum and dentin is different than enamel. A recent study⁸ demonstrated obvious root abrasion over time, even with light pressure, low rotational speed, and inadvertent exposure time, just from the rubber cup slipping off of the enamel and onto the root surface. Another study showed that increasing rotational speed from 3,000 rpm to 4,000 rpm nearly tripled root abrasion.¹³ This evidence demonstrates that root structure can be abraded by rubber cup polishing.

Surface roughness is also affected by polishing. Use of a rubber cup with an abrasive can roughen the tooth surface. Surface roughness is measured in micrometers. Values higher than 0.2 ?m are associated with increased bacterial adhesion.¹⁴ Ideally, polishing creates a surface with less than < 0.2 ?m of roughness. Surface roughness values for unpolished enamel range from 0.79 ?m to 2.30 ?m.^15–17 Some studies demonstrate a general increase in enamel roughness following rubber-cup polishing with pumice flour, however these studies pretreat enamel to obtain an unnaturally smooth surface.^7,18,19 Studies with no pretreatment demonstrate a decrease or no change in surface roughness after polishing with pumice or prophy paste.^16,20,21

CONCLUSION

A conservative polishing technique should be employed, using the lowest speed, lightest pressure, and shortest duration that will achieve the desired goal. To minimize surface roughness, the lowest grit paste that will be effective should be chosen. When only biofilm removal is necessary, a fine grit prophy paste or nonabrasive cleaning paste is appropriate. If a coarse grit is required, the surfaces should be repolished using a fine paste with a new prophy cup to decrease surface roughness. Despite the common use of rubber cup polishing, current, clinically-relevant research is still sparse. More research is needed to increase scientific data for providing evidence-based care and to ensure that more treatment options are available.

REFERENCES

1. Wilkins EM. Clinical practice of the dental hygienist. 10th ed. Philadelphia: Lippincott Williams & Wilkins; 2009:728.
2. Darby ML, Walsh MM. Dental hygiene theory and practice. 2nd ed. Philadelphia: Saunders; 2010: 515.
3. American Dental Hygienists’ Association. Association Position Paper on the Oral Prophylaxis. Available at: www.adha.org/resources-docs/7115_Prophylaxis_Postion_Paper.pdf Accessed February 20, 2013.
4. Wilkins EM. Clinical practice of the dental hygienist. 11th ed. Philadelphia: Lippincott Williams & Wilkins;2013:689-695.
5. Azarpazhooh A, Main PA. Efficacy of dental prophylaxis (rubber cup) for the prevention of caries and gingivitis: a systematic review of literature. Br Dent J. 2009;207:328–329.
6. Anusavice KJ. Phillips’ science of dental materials. 11th ed. St. Louis, MO: Saunders; 2003:362,370–372.
7. Roulet JF, Roulet-Mehrens TK. The surface roughness of restorative materials and dental tissues after polishing with prophylaxis and polishing pastes. J Periodontol. 1982;53:257–266.
8. Pence SD, Chambers DA, van Tets IG, Wolf RC, Pfeiffer DC. Repetitive coronal polishing yields minimal enamel loss. J Dent Hyg. 2011;85:348–57.
9. Christensen RP, Bangerter VW. Immediate and long-term in vivo effects of polishing on enamel and dentin. J Prosthet Dent. 1987;57:150–160.
10. Thompson RE, Way DC. Enamel loss due to prophylaxis and multiple bonding/debonding of orthodontic attachments. Am J Orthod. 1981;79:282–295.
11. Stookey GK. In vitro estimates of enamel and dentin abrasion associated with a prophylaxis. J Dent Res. 1978;57:36.
12. Zuniga M, Caldwell, RC. Pastes on normal and “white-spot” enamel. The effect of fluoride-containing prophylaxis. J Dent Child. 1969;36:345
13. Swan RW. Dimensional changes in a tooth root incident to various polishing and root planing procedures. Dent Hyg (Chic). 1979;53:17–19.
14. Weitman RT, Eames WB. Plaque accumulation on composite surfaces after various finishing procedures. J Am Dent Assoc. 1975;91:101–106.
15. Mathias J, Kavitha S, Mahalaxmi S. A comparison of surface roughness after micro abrasion of enamel with and without using CPP-ACP: An in vitro study. J Conserv Dent. 2009;12:22–25.
16. Castanho GM, Arana-Chavez VE, Fava M. Roughness of human enamel surface submitted to different prophylaxis methods. J Clin Pediatr Dent. 2008;32:299–303.
17. Cobankara FK, Unlü N, Altinöz HC, Füsun O. Effect of home bleaching agents on the roughness and surface morphology of human enamel and dentine. Int Dent J. 2004;54:211–218.
18. Covey DA, Barnes C, Watanabe H, Johnson WW. Effects of a paste-free prophylaxis polishing cup and various prophylaxis polishing pastes on tooth enamel and restorative materials. Gen Dent. 2011;59:466–473.
19. Bollen CM, Lambrechts P, Quirynen M. Comparison of surface roughness of oral hard materials to the threshold surface roughness for bacterial plaque retention: a review of the literature. Dent Mater. 1997;13:258–269.
20. Winston AE, Charig A, Patel V, McHale WA, Malerman R. Effect of prophy pastes on surface of tooth enamel. J Dent Res. 2005;84(Suppl):0966.
21. Salami D, Luz MA. Effect of prophylactic treatments on the superficial roughness of dental tissues and of two esthetic restorative materials. Pesqui Odontol Bras. 2003;17:63–68.

From Dimensions of Dental Hygiene. March 2013; 11(3): 26, 28.