Polishing Esthetic Materials

With the explosion of consumer demand for whiter, brighter smiles, oral health care professionals — and dental hygienists, especially — need to be well versed in the materials used in esthetic dentistry in order to successfully maintain the surface integrity of esthetic restorations. These materials have become so advanced they are almost undetectable. And while clinicians can choose from a wealth of materials, this article will concentrate on three of the most common types of restorations seen in practice: porcelain, composites and glass-ionomer cements.

Dental materials undergo polishing procedures on a routine basis in dental hygiene practice.1–4,5 Dental hygienists cannot ignore the unique polishing requirements of esthetic materials and use the same polishing pastes that are used on the teeth.1,2,5,6 Unfortunately, esthetic restorative materials are not exempt from the practice of using coarse-grit polishing paste to remove heavy stain.5 To ensure the successful maintenance of these artfully created restorations, it’s beneficial for clinicians to have a basic understanding of these three common restorative materials.

PORCELAIN

Used for crowns and veneers, porcelain has a natural, tooth-like appearance. This material has great translucency because it transmits as much light as enamel. While it is an extremely hard esthetic material, porcelain also has a brittle nature and is subject to fracture and roughness — which can cause excessive wear on opposing natural tooth structure. When porcelain is used for crowns, it can be applied over metal substructures (or copings) to increase the strength of the crown. These porcelain-fused-to-metal (or PFM) restorations are still subject to fracture, however.

Porcelain can be glazed or polished. Porcelain restorations are glazed at dental labs, while unglazed porcelain is typically found when the restoration has required adjustment during placement. When the occlusal surface or margins require adjustment, the glaze may be unavoidably removed. Unglazed porcelain can be polished and made as smooth as glazed porcelain to the extent that they are difficult to distinguish. This is important because unglazed and unpolished porcelain will stain much more readily than glazed or polished porcelain.

COMPOSITE MATERIALS

Composite resins are the most widely used esthetic restorative materials. There are several types, most of which are classified by the size and/or type of filler particle — such as microfilled, hybrid or macrofilled composites. Based on the Mohs scale, most composite restorations have a lower (i.e., softer) hardness rating than tooth enamel. This makes them more susceptible to scratching by prophylaxis polishing pastes that can contain abrasives up to 10 times harder than the composite itself.1–3,5

If used improperly, prophylaxis polishing pastes can increase the surface roughness of composite materials to the extent that the rough surface can retain bacteria. As seen in figures 1 and 2, these particular applications of a commonly used prophylaxis polishing paste7 have scratched and roughened the composite restorative material to the extent that it will readily retain stain — and may eventually be compromised.

 

Figure 1: This scanning electron micrograph shows a composite restorative material that has been polished with a popular fine-grit polishing paste. Note the scratches created by the paste’s abrasives and the clinician’s rubber polishing cup.

Figure 2: Polished with a leading brand of coarse-grit prophy paste, this composite surface also shows scratches that may encourage bacterial colonization and staining. Clinicians must tailor polishing techniques to suit specific esthetic materials.

GLASS-IONOMER CEMENTS

Compared to composites, glass-ionomer cements are not as widely used as a restorative material.8 And while more esthetically pleasing than metallic restorations, these tooth-colored products have few properties in common with composites. Although both are used for Class V esthetic restorations and other anterior and posterior procedures, glass ionomers do not have comparable shade matching. They also can’t match the strength and wear resistance found in composite resins — which make them useful for temporary and intermediate restorations.9

The glass filler particles in glass-ionomer cements range from 1 to 4.5 on the Mohs scale,10 which means they are generally softer than enamel or composites. Glass-ionomer-cement restorations are also more opaque and brittle, and have a rougher surface than composite resin restorations.11

Glass-ionomer cements are made of a calcium strontium aluminosilicate glass powder (base) combined with a water-soluble polymer (acid).8,9,11 They also contain fluoride ions, so they can be useful when treating patients with a high risk of caries.

FINISHING AND POLISHING

When discussing the subject of polishing esthetic restorations with your clients, it’s important to note the distinction between “finishing and polishing” and “polishing.” The term “finishing and polishing” refers to removing a restoration’s marginal irregularities, defining anatomic contours, and smoothing away any surface roughness.12 The polishing procedure further enhances the restoration by removing scratches from the surface to produce a smooth, light-reflecting luster.

Finishing-and-polishing procedures are typically performed in three to four steps.12,13 Finishing and polishing are critical to the esthetics of tooth-colored restorations, and can have a substantial effect on their biocompatibility with tissues, longevity and long-term success.3,14,15

POLISHING

Polishing refers to maintaining the surface characteristics of esthetic restorations by recreating a surface luster. This is done by using a succession of finer abrasives so the clinician creates smaller and smaller scratches on the surface — with the eventual result that the smallest scratches are smaller than the wavelength of visible light, which is less than 0.5?m.11.

The polishing of esthetic restorative materials incorporates both two-body and three-body abrasion.4 In two-body abrasive polishing, the bound particles are solidly fixed to a substrate — such as a rubber finisher embedded with diamond particles. In three-body abrasion, loose abrasives (polishing paste abrasive particles) move in the interface between the surface being polished and the polishing application device. An example of three-body abrasion is the use of a polishing paste and a rubber polishing cup.

When determining the optimal approach to polishing these esthetic restorative materials, your clinical clients will take the following factors into account:12

  • The structural and mechanical properties of the esthetic restorative material
  • Hardness of the material
  • Abrasive hardness of the prophylaxis polishing paste or other polishing medium
  • Physical properties of the material used to carry and apply the prophy paste or other polishing medium (which can vary from a paste to an abrasive-embedded prophylaxis cup or abrasive-embedded polishing discs of various shapes, including flame, conical, round or diamond finishers)

Decisions about polishing esthetic restorative materials should be based on patients’ needs, just as they are when polishing natural teeth. That said, the process should also be predicated on a manufacturer’s recommendations for its particular type of esthetic restorative material.

 

ESSENTIAL SELECTIVE POLISHING

Without question, the most significant change in the therapeutic approach to polishing teeth, or what clinicians call prophylaxis, is the evolution from selective polishing to the current standard of care — essential selective polishing.

The concept of selective polishing, which came out in the 1970s, states that only stained teeth require polishing, and that prophylaxis for the purpose of plaque removal is unnecessary because patients can be coached to perform this function themselves. With advances in research and clinical knowledge, we now know that polishing the entire dentition produces a smooth surface on teeth and restorations that reduces the adherence of plaque and stains.

Essential selective polishing asserts that cleaning or polishing agents should be selected according to the patient’s needs. Following an oral exam to assess factors such as whether a patient has stained teeth, esthetic restorations or stained restorations — as well as any conditions that might contraindicate polishing — the clinician should then select the most appropriate agent to use.

The change to essential selective polishing is key information for dental sales professionals, who must remain aware of the latest standards of care so they can make intelligent product recommendations.

POLISHING PORCELAIN

Glazed or Polished Porcelain: Porcelain restorations can stain in the same manner as tooth enamel — however, glazed and/or polished porcelain surfaces are significantly more stain resistant than unglazed porcelain. Unless given different instructions by the dentist, dental hygienists can polish porcelain with a diamond paste (the diamond paste should be used dry) and Robinson brush.16 Some diamond polishing pastes are offered in three grits: coarse, medium and fine. The use of each of these grits should follow the manufacturers’ directions, but if coarse grit is required, it should be followed by the use of medium grit and finished with the fine grit.

In order to achieve the smoothest surface and highest luster, each grit should be applied with a separate applicator. Some rubber polishing instruments, however, will remove stain and create a highly polished surface all in one step. Rubber polishing instruments can also be followed with a diamond paste if necessary.

Unglazed Porcelain: If unglazed porcelain is rough when felt with an explorer, it should be smoothed prior to polishing. A smooth, polished surface can be restored to unglazed porcelain with diamond paste (used dry).16 It should be applied with a felt wheel or Robinson brush, as a regular rubber polishing cup and diamond paste will not produce the same result.16 If only stain is present, however, a rubber polishing cup and diamond paste can prove effective.

Porcelain-Cement Interface: Especially on less-than-perfect margins of bonded porcelain restorations, the resin cement used for luting (i.e., sealing) may become stained. Unfortunately, resin cements used as luting agents readily absorb stain.16 Great attention should be paid to polishing the cement interface because it is softer than the porcelain. If too much cement is removed during polishing, ditching at the margin can occur, which can leave the patient susceptible to leaking margins, plaque retention and dental caries.

The resin cement should be polished in the same manner as an esthetic composite restoration16 — but, again, always in accordance with the procedure recommended by the composite manufacturer. Additionally, several polishing paste products are available that are safe and effective for resin cements. If plaque needs to be removed but no staining is present, a cleaning agent containing feldspar can be applied with a rubber polishing cup.4

POLISHING COMPOSITES

Many composite manufacturers either sell polishing materials or offer recommendations about polishing products suited for use on their materials. If these are not available, the products manufactured specifically for use on esthetic restorative materials can be used. A cleaning agent will remove dental plaque but not scratch composites — however, it will not polish or remove stain on an esthetic composite restoration.4

Your dental hygiene customers should be able to identify the difference between small-particle composites, hybrid composites and microfilled composites. Small-particle composites are fairly obsolete (although older patients may still have some small-particle composites). They are rougher than the hybrid or microfilled composites — for example, when an explorer is drawn across the surface, it will create a black line.16 A highly polished surface may be impossible to achieve on a small-particle composite, therefore, rubber finishers and rubber polishers can be used, followed by a composite polishing paste.

Microfilled composites can be quickly polished with a rubber polisher. Again, this can be followed by the use of a composite polishing paste — either the type recommended by the composite manufacturer or one specifically manufactured for dental hygienists. Hybrid composites are harder to polish than microfilled composites. Hybrids should be polished with an aluminum oxide polishing paste recommended for composite restorations. The paste should be applied with a rubber polishing cup that has been filled with water. If the restoration becomes dry during the procedure, it should be remoistened with water.16 An extra-fine aluminum oxide paste should be used as the final polish for a hybrid composite.

Finally, a cleaning agent can be used on any type of esthetic composite restorative material since it cleans but does not scratch.4

POLISHING GLASS IONOMERS

As noted, glass ionomers typically have a rougher surface than esthetic composite materials, and should be polished using light pressure at a slow speed.16 If a polishing product indicated for use on glass ionomers does not remove stain, a fine-grit finishing disc or rubber polisher can be used. Glass-ionomer restorations desiccate — which can lead to cracking and premature deterioration of the restoration — and should be lubricated with a petroleum jelly or water prior to polishing.16M Throughout the procedure, it’s important to keep in mind that glass ionomers will never have the shiny, smooth, nondetectable surface that can be achieved with a polished esthetic composite.

CHART FOR SUCCESS

When esthetic dental restorations are encountered during charting, this information should be included when planning the polishing procedure. If the brand and type of esthetic restoration are known through the patient’s chart, the polishing procedures and products used should be those recommended by the manufacturer. If this is not possible, alternative polishing procedures should be used. And as a failsafe, a cleaning agent containing feldspar and rubber polishing cup can be used on all esthetic restorative materials with no danger of damage to the surface characterization.

The principles for polishing esthetic restorations are the same as for natural teeth. If the polishing agent chosen offers more than one size grit, clinicians should start with the least abrasive grit that will render the desired initial outcome, followed by each successively smaller grit. For best results, each grit should be applied with a fresh rubber cup or applicator to avoid the possibility of contamination with the previoussize grit. This is important because a mix of abrasive particle sizes will not produce the desired shiny surface. In addition, the polishing paste should be frequently renewed in the polishing cup because the paste may dry as the binders are expressed during use, which will make the paste more abrasive.

Keeping esthetic restorative materials looking like they were just placed is a service highly valued by patients. And anything that knowledgeable sales representatives can do to assist their clients in achieving successful polishing outcomes will be equally valued by clinicians.

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  2. Barnes, CM, Covey DA, Walker MP, Johnson WW. Essential selective polishing: the maintenance of aesthetic restorations. Journal of Practical Hygiene. 2003;12:18–24.
  3. Neme AL, Frazier KB, Roeder LB, Debner TL. Effect of prophylactic polishing protocols on the surface roughness of esthetic restorative materials. Oper Dent. 2002;27:50–58.
  4. Barnes CM. The science of polishing. Dimensions of Dental Hygiene. 2009; 7(11):18–22.
  5. Barnes CM. Care and maintenance of esthetic restorations. Journal of Practical Hygiene. 2004;14:19–22.
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  7. Strategic Data Marketing. Available at: www.sdmdata.com. Accessed January 9, 2013.
  8. Saito S, Tosaki S, Hirota K. Characteristic of glass-ionomer cements. In: Davidson CL, Mjör IA. Advances in Glass-Ionomer Cements. Chicago: Quintessence Publishing Co Inc; 1999:15.
  9. Roberson TH, Heymann HO, Swift EJ. Sturdevant’s Art and Science of Operative Dentistry. St. Louis: Mosby; 2003:218–219, 502–593.
  10. United States Patent Number 4,695,251. Orthodontic bracket adhesive and abrasive for removal thereof. Available at: www.google.com/patents/US4695251. Accessed January 9, 2013.
  11. Gladwin M, Bagby M. Clinical Aspects of Dental Materials, Theory, Practice and Cases. Baltimore: Lippincott, Williams & Wilkins; 2004:65–77, 209, 268.
  12. Jeffries SR. Abrasive finishing and polishing in restorative dentistry: a stateof- the-art review. Dent Clin N Am. 2007;51:379–397.
  13. Yap AU, Lye KW, Sau CW. Surface characteristics of tooth-colored restoratives polished utilizing different polishing systems. Oper Dent. 1997;22:260–265.
  14. Goldstein RE. Finishing of composites and laminates. Dent Clin N Am. 1989;33:305–318.
  15. Goldstein RE, Garber DA. Maintaining esthetic restorations—a shared responsibility. J Esth Dent. 1995;7:187.
  16. Miller MB, ed. REALITY The Techniques, Volume I. Houston, Tex: REALITY Publishing Co; 2003:604–605.
MENTOR February 2013, 4(2): 20–23.

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