by Caren M. Barnes, RDH, MS, David A. Covey, DDS, MS, and Mary P. Walker, DDS, MS, PhD
Decades ago, the only restorations dental hygienists concentrated on for polishing were amalgam and gold restorations. Dentists placed and most often polished their restorations and dental hygienists had little to worry about regarding the polishing of amalgam or gold during recall appointments. About the worst damage a hygienist could do to an amalgam restoration was to take off too much of the restoration with a bur during the initial phases of the polishing procedure or put a matte finish on a highly polished gold restoration.
But how things have changed! The evolution of porcelain and composite resin restorations — coupled with the demand for esthetics by patients — has placed a great deal of responsibility on the dental hygienist.
No longer can the hygienist utilize a "one-size-fits all" prophylaxis paste for the teeth and whatever types of restorations happen to be in the patient's mouth. Ultimately, the esthetics of tooth-colored restorations is strongly influenced by the final surface polish and those polishing procedures performed during recall procedures.
The most important reasons for providing continuing care for dental restorations are to:
• Contribute to the longevity of the restoration, by minimizing the effects of surface corrosion
• Maintain the esthetic appearance of the restoration, which is accomplished by keeping the surface characterization of the restoration smooth thereby lessening the potential for retention of stains
• Maintain the smooth surface characterization contributing to gingival health by lessening the potential for plaque retention
Certainly, it is important to care for amalgam and gold restorations with the kind of care you would the esthetic tooth-colored restorative materials. However, the metal restorations do not present the vulnerability to polishing procedures that the hybrid and microfilled composite resins and glass ionomer cement restorative materials do.
The first step in the process of polishing restorations is to identify all existing esthetic restorations prior to an oral prophylaxis, using the patient's chart and examining the patient's mouth, which includes a tactile examination. The development of tooth-colored materials began with cements, followed by unfilled resins, silicates, and finally filled resins that are currently used.
The composition of materials used in some older existing tooth-colored restorations may not be determinable. However, contemporary esthetic restorations will include hybrid composites and microfilled composite resins, conventional and resin-modified glass ionomer cements, and compomers, as well as laboratory-fabricated composite resin and porcelain restorations.
It certainly behooves the dental hygienist to be familiar with the types of restorations being utilized within her/his practice and within the surrounding community. For example, microfilled composites will polish to a higher shine than hybrid composites, and glass ionomer cements may have a smooth surface but little shine.
A brief review of the composition of the currently utilized esthetic tooth-colored restorative materials is warranted. Composite resins in general are mixtures of a photoactivated polymers and silica/quartz filler particles. Hybrid composites are a mixture of minifill and microfill particles and can be used in anterior and posterior restorations. Microfilled composite resins provide excellent anterior esthetic restorations due to their highly polishable nature.
Glass ionomer restorative materials are cements composed of aluminosilicate filler particles surrounded by a polyacrylic matrix. Recently introduced glass ionomer materials incorporate photoactivated resins that improve their surface finish. While glass ionomer cement restorations provide the benefit of fluoride release, their mechanical properties limit their use to restorations subject to low stress or surface abrasion.
Compomers, which are a combination of glass ionomers and composite systems, may provide benefit from a limited fluoride release mechanism.
Compomers are smoother than glass ionomer cements, but again, do not produce the smooth surfaces that can be accomplished with composite resin materials. Figure 1 is a diagram by Berg that concisely demonstrates the continuum of esthetic restorative materials.
A review of the polishing process is also equally warranted to better understand the appropriateness of various techniques for maintaining esthetic restorations. The purpose of polishing is to create the smoothest surface possible, whether it is on the restoration or the tooth surface. Polishing is accomplished by a progressive abrasion process. The surface to be polished is approached with a series of finer and finer abrasives, until the scratches are smaller than the wavelength of visible light, which is 0.5 um. When scratches are created this size, the surface appears smooth and shiny. The smaller the scratches the more shiny the surface, which places a large emphasis on the size (grit) of the polishing agent particle selected.
Again, it can't be over emphasized — one prophylaxis polishing paste is not appropriate for all tooth and esthetic restorative materials. In fact, some prophylaxis polishing pastes are contraindicated on esthetic restorative materials. The polishing of esthetic materials must be a part of the treatment plan and be given as much emphasis and consideration as whether to use hand instruments vs. ultrasonic instruments for calculus removal.
Yet another aspect of polishing that must be given staid consideration is the hardness of the abrasive particles in the polishing agent. The hardness of the particle must exceed the hardness of the surface being polished, otherwise the particle would wear down and the surface to be polished would not be polished. Abrasive particles utilized in polishing pastes include diamond particles, aluminum oxide, silicates, pumice and calcium carbonate.
Finally, there are principles of polishing that include speed, pressure, and shape of the abrasive agent that play a major role in polishing. The speed refers to the rate at which the polishing device (rubber cup, disk, etc.) is rotating. Speed and pressure will increase the rate of abrasion and the creation of heat, and should be kept to a minimum. The shape of the abrasive particle also affects the rate of abrasion. Round or spherically shaped particles will abrade more slowly than sharp, irregularly shaped particles.
The effects of the use of a coarse prophylaxis paste, a fine prophylaxis paste, a Sof-Lex™ Disc (3M ESPE) and Lustre Paste™ (Kerr Dental) on a microfilled composite resin (Durafil™, Heraeus Kulzer Lab Products) can be seen in Figures 2-5.
As can be seen in Figures 2-3, the prophylaxis paste created deep, circular scratches, leaving a surface susceptible to the adherence of stain and plaque. Somewhat shallower scratches have been created by the Sof-Lex Disc (Figure 4), and, finally, no scratches can be seen (Figure 5) after polishing the composite surface with the Lustre paste, which is not a prophylaxis paste, but a paste created for composite resin restorations and included for comparison.
Having established that prophylaxis pastes were never created for the purpose of polishing esthetic restorations, exactly what recommendations can be made for polishing esthetic restorative materials?
The first and most important recommendation is to follow the esthetic restorative material manufacturer's recommendations regarding polishing. Also, many manufacturers will recommend their own products for polishing their restorative materials. However, if this information is not available, Table 1 consists of recommendations for specific products and polishing techniques that can be used for esthetic materials with instructions on their use. It is a matter of interest that recently Dentsply Caulk introduced a product, PoGo™ Polishing Discs (diamond micropolishing discs), that produces a very smooth surface and high shine on hybrid and microfilled composites as well as glass ionomers. Figures 6-8 are SEM photomicrographs that illustrate a hybrid composite (EsthetX™, Dentsply Caulk), a microfilled composite (Filtek™ A1-10, 3M ESPE) and a glass ionomer (Fugi II LC™, GC Corporation) that have been polished with the PoGo Discs. As can be seen in these photomicrographs, no irregular scratches can be detected and the clinical result was a high shine.
In the 1970s, a novel air polishing device, the Prophy-Jet™, was introduced for stain removal that was revolutionary in that it removed heavy stains and plaque in scant amounts of time without damage to enamel, cementum, or dentin. The Prophy-Jet utilizes sodium bicarbonate in a jet stream of water and approximately 43-58 psi of air pressure. The sodium bicarbonate is less abrasive than conventional prophylaxis pastes and is not to be confused with air abrasion used for dental restorative procedures, which utilizes aluminum oxide particles under 80-160 psi of air pressure.
While the Prophy-Jet is expedient for stain and plaque removal, exhaustive research has produced evidence that it must be used carefully in the presence of esthetic restorations. Even though a matte finish is produced clinically on gold and amalgam by the Prophy-Jet, SEM photomicrographs reveal no alteration in the surface integrity of either restorative material. However, as with esthetic restorative materials, the cements used for porcelain and gold are rapidly removed, therefore requiring avoidance of use of the Prophy-Jet around the margins of these materials (see Figures 9 and 10, SEM photomicrographs of gold margins demonstrating the removal of cement by the Prophy-Jet and sodium bicarbonate powder).
The Prophy-Jet is contraindicated on composite resins and glass ionomer cement restorations due to the fact these softer polymeric materials have the potential to be removed in considerable amounts and thus compromise the integrity of the restoration. Figures 11-13 illustrate composite materials treated with the Prophy-Jet and the volumetric loss of the restorative materials is readily observed.
As noted previously, the abrasive agent used in the Prophy-Jet to date has been a specially treated sodium bicarbonate. This specially treated sodium bicarbonate is food grade and is readily biocompatible except for patients who are on physician-directed, sodium-restricted diets or for some patients who find the salty taste of the sodium bicarbonate objectionable.
Dentsply has introduced a new alternative to the sodium bicarbonate polishing agent, a product called Jet-Fresh™. The abrasive particle in Jet-Fresh is aluminum trihydroxide that has a particle size that is similar to that of the specially treated sodium bicarbonate particles and with a similar Moh's hardness number. The Moh's hardness number for sodium bicarbonate is 2.5, while the range for the Moh's hardness number for aluminum trihydroxide is 2.2-3.5.
How does this differ from the agents used for air abrasion? The particles in Jet-Fresh are specially processed and are not utilized under the strong air pressure utilized in cavity-preparation air abrasion.
In a recent in-vitro research project, Jet-Fresh was utilized on several types of restorations (that had been placed according to manufacturer's directions) that included gold, porcelain, hybrid composite and microfill composite, and glass ionomer cement. Half of each restoration was covered with tape for a control surface and then each restoration was treated with the Jet-Fresh powder in the Prophy-Jet for five seconds (the tip of the nozzle was kept 4 mm from the restoration surface and in a constant circular motion). Following treatment, an impression of each restoration was made utilizing a hydrophilic vinyl polysiloxane impression material (Examinix, GC America) and poured with epoxy resin, creating a replica of the restoration. Each replica was sputter coated with gold palladium and viewed using scanning electron microscopy.
This research on the effects of Jet-Fresh reveal that it does not alter the surface integrity of enamel or porcelain. Yet, this agent should be avoided on restorative materials, including amalgam, gold, porcelain, composites, and glass ionomer cements (see Figures 14-19). Table 2 summarizes the comparison of the use of aluminum trihydroxide and sodium bicarbonate particles in the Prophy-Jet and their compatibility with dental restorative materials.
When investigating the maintenance of esthetic restorations, certainly implants need to be considered as they play a vital role in dental esthetics. Unfortunately, it is not known at this time what effects Jet-Fresh has on titanium implants. However, research evidence reveals that the use of the Prophy-Jet with the sodium bicarbonate powder is safe for dental implants. Notably, research has recommended the use of the Prophy Jet with the sodium bicarbonate powder due to the fact that it can remove 100 percent of bacteria from the implant surface without harm to the surface characterization of the titanium implant, which is especially important in the presence of peri-implantitis. Figures 20-25 illustrate implant surfaces treated with the Prophy Jet and sodium bicarbonate and, as can be seen, produced no alteration in surface characterization of the implants.
Clearly, the demand for esthetic restorations has never been greater and with that comes the responsibility of the dental hygienist to possess the skills to identify the types of materials used for these restorations and to use the correct products and agents for maintaining these restorations. Maintenance of esthetic restorations requires time and planning — but the result is one that will be appreciated by both dental professionals and patients alike.
References available upon request.
Caren M. Barnes, RDH, MS, and David A. Covey, DDS, MS, are affiliated with the College of Dentistry at the University of Nebraska Medical Center. Barnes is coordinator of clinical research, while Dr. Covey is an associate professor. Mary P. Walker, DDS, MS, PhD, is affiliated with the department of restorative dentistry at the University of Missouri-Kansas City School of Dentistry.