11: Polishing

Chapter 11 Polishing

Section A Current Technology and Clinical Approaches to Polishing of Dental Restorations

Brief History of Clinical Development and Evolution of the Procedure

Finishing and polishing procedures have existed since the beginning of modern restorative procedures. Diamond burs were used before tungsten carbide burs; their applications in margination, finishing, and polishing were integral. As demands for surface smoothness and esthetics have increased, loose-abrasive slurries and pastes have also evolved. Concurrent with loose-abrasive pastes, bonded abrasives consisting of rubberized abrasives were developed for both the finishing and the polishing steps. Coated abrasive disks, with very low abrasive particle sizes, are also effective for final polishing steps. Various grits of sandpaper on paper disks were initially used, but over the last three or four decades, coated abrasive disks bonded to Mylar or other thin-film plastic or polymer substrates have become available.

Most dental finishing and polishing devices operate in the two-body mode, a harder material abrading a softer material. Nevertheless, dentist, hygienists, and laboratory technicians often use loose abrasives, that is, the “three-body abrasive mode,” in the form of prophy or polishing pastes. A three-body abrasive wear situation exists when loose particles move in the interface between the specimen surface and the polishing application device. Such a situation occurs when abrasives are intentionally deposited to roll on the surface of the polishing substrate. A three-body mode may also occur when small pieces of material are detached from the specimen to be polished and become trapped, or circulate, within the contact between the two first bodies. Figure 11-1 further illustrates how the various dental finishing and polishing procedures fall within these two basic tribologic mechanisms.

Clinical Considerations

Material Options

Coated Abrasive Finishing and Polishing Disks and Strips

Coated abrasive disks and strips are made by bonding abrasive particles into a thin polymer or plastic backing. Finishing and polishing disks are used for gross reduction, contouring, finishing, and polishing restorations. The thin layer of abrasive present on these disks remains effective for a limited period of clinical use, making these disks single use and disposable. Most are coated with an aluminum oxide abrasive, but silicon carbide, garnet, emery, and quartz (cuttle) abrasives are also used. A sequence of grits is applied, starting with a coarser grit and finishing with a superfine grit. Coated abrasive disks and strips are especially useful on flat or convex surfaces. They work well especially on anterior restorations, such as the incisal edges and embrasures, and to a limited extent on posterior composites, especially on interproximal and some buccal and lingual areas. Coated finishing and polishing disks have limited utility on posterior occlusal and concave anterior lingual areas. These areas are better addressed with bonded-abrasive points and cups, including the newer abrasive-impregnated brushes.

A number of studies have documented the effectiveness of coated abrasive disk systems. The particle size distributions for coated abrasive disks vary from 100 to 55 µm for coarse-grade finishing disks to 7 to 8 µm for the ultra- or super-fine grade of finishing disk. Coated abrasive disks can finish and provide pre-polishing and polishing action for a wide range of restorative materials. Some studies indicate that coated abrasive disks are particularly effective for finishing traditional microfill composite resin materials.

Coated abrasive disks are available from a number of manufacturers. Some of these products include the EP Esthetic Polishing System (Brasseler USA, Savannah, Georgia), FlexiDisc (Cosmedent, Inc., Chicago, Illinois), Moore-Flex polishing system and Moore silicon carbide disks (E.C. Moore, Dearborn, Michigan), OptiDisc, (Kerr Corporation, Orange, California), Sof-Lex Finishing and Polishing System (3M ESPE, St Paul, Minnesota), and Super-Snap system (Shofu Dental Corporation, San Marcos, California).

Rubber Wheels, Cups, and Points

Rubber polishing instruments are used to finish, smooth, and/or polish composites. These finishing and polishing instruments are abrasive instruments based on fine or ultra-fine hard, abrasive particles dispersed and held in a softer, elastic matrix. The various configurations of these flexible or rubber finishers and polishers complement the access limitations of the coated abrasive disks for areas such as anterior lingual and posterior occlusal surfaces. Shapes, with varying sizes and dimensions, include disks, wheels, cups, and points. Figure 11-3 depicts the wide range of different types of bonded and elastomeric finishers and polishers available. They are often sold as kits with a variety of shapes and grits to accommodate the differing tooth dimensions and contours seen in clinical practice. Flexible, bonded-abrasive devices are made by molding abrasive particles, of varying particle size and size distribution, in an elastomeric matrix. The elastomeric matrix can be a natural or synthetic rubber, silicone, or other synthetic elastic polymer. One system uses a “urethane” elastic polymer in which a wide range of abrasive particles can be dispersed, including aluminum oxide and diamond.

Molded or bonded elastomeric abrasives come in a variety of grits, sizes, shapes, and firmnesses. These elastomeric, bonded abrasives are usually molded to a latch-type mandrel for slow-speed handpieces. The mandrels are constructed from both stainless steel and high-strength plastic. Some of these products are fabricated to be reusable after sterilization. The abrasives used within these instruments usually comprise silicon carbide, aluminum oxide, diamond, silicon dioxide, and zirconium oxide. The particle size distributions typically range from about 40 µm for an elastomeric aluminum oxide finishing device to 6 µm for elastomeric “rubber” diamond polishing instruments.

Some of these instruments may be useful in intermediate finishing and in anatomic contouring, as well as pre-polishing. Recent studies have evaluated the efficacy of various bonded, elastomeric abrasive finishers and polishers. Some of the commercial finishing and pre-polishing devices (including complete finishing-polishing systems) evaluated include Astropol (Ivoclar Vivadent, Amherst, New York); Comprepol and Composhine (Diatech, Dental Inc., Charleston, South Carolina); Enhance system (DENTSPLY Caulk, Milford, Delaware); FlexiCups (Cosmedent Inc.); Identoflex Points (Identoflex AG, Buchs, Switzerland); Identoflex (Kerr Corporation); Silicone Points C type (Shofu Dental Coporation).

Other diamond-containing elastomeric or rubber-like rotary devices have been introduced more recently for use in finer pre-polishing or final polishing. There appears to be a range of effectiveness in the ability to produce smooth surfaces on direct restorative materials. Diamond-impregnated polishers are particularly effective, with many one- and two-step polishing device systems reaching surface smoothness comparable to that of multi-step, coated-abrasive disk systems. Such diamond one-step polishers include CompoMaster (Shofu Dental Coporation) and PoGo (DENTSPLY Caulk).

Diamond-containing polishing devices produce more frictional heat than other bonded-abrasive devices; heavy pressure must be avoided to minimize the surface temperature rise. A significant increase in temperature can potentially be deleterious to the restoration as well as the tooth itself.

Loose-Abrasive Polishing Pastes and Rotary Applicator Devices for Loose Abrasives

Loose-abrasive polishing pastes are used extensively in industrial and scientific applications. In the three-body, loose-abrasive polishing process, the loose-abrasive wear induces cutting and plowing on a micrometer and nanometer scale. Following the example from other industrial and scientific disciplines, dentists have used loose-abrasive finishing and polishing compositions for several decades. Loose-abrasive polishing pastes, used in dental applications, are predominantly based on dispersed and suspended ultra-fine aluminum oxide or diamond particles. Aluminum oxide polishing pastes are usually glycerin based, with a mean particle size distribution of 1 µm or less. Diamond polishing pastes also use a glycerin-based material but with a larger mean particle distribution—10 µm to less than 1 µm. Two diamond polishing pastes contain mean sizes of diamond particles on the order of 4 to 6 µm and less than 1 µm. In a study examining the surface morphology and smoothness of the transition from a glass-ceramic insert to a bonded composite resin interface, samples finished with a sequence of progressively smoother diamond abrasive finishing burs (45 µm, 25 µm, and 10 µm), followed by polishing with first a 4- to 6-µm–grit diamond polishing paste and then a sub-micron diamond polishing paste, exhibited the smoothest transition from composite resin to insert. Of perhaps equal importance, studies and research findings have indicated that the mode of application and the structure and the composition of the applicator device can be as important as the composition of the paste used in the polishing procedure. Although the commonly used method for applying polishing paste is the flexible rubber prophy cup, surface roughness data strongly suggest that such a mode of application results in increased surface roughness, or at best no improvement in surface smoothness. On the other hand, use of soft foam or felt applicators can significantly improve the efficacy of loose-abrasive polishing paste, especially those pastes containing aluminum oxide as the abrasive agent. Surface roughness decreased by 50% when a 1-µm aluminum oxide polishing paste was applied with a porous synthetic foam cup (Ra ≅ 0.10),* as compared with application of the same paste with a conventional rubber prophy cup (Ra ≅ 0.20).

Figure 11-4 depicts visually the wide range of types and sizes of both felt and foam polishing paste applicators that are best for loose-abrasive polishing of dental restorations. These applicators can be used with both aluminum oxide–based and diamond-based polishing pastes.

The technique or mode of application of the polishing paste is also critical. Based on polishing applications in the scientific and industrial fields, it is recommended to frequently renew the pad (with fresh polishing paste) and to keep it always wet in order to avoid crystallization of the colloidal contaminants (such as silica), which can produce scratches. In fact, polishing pastes can probably act both in a more aggressive, pre-polishing or finishing mode when applied in a dry, anhydrous condition and in a polishing mode with the addition of water, facilitating finer abrasive action at nanometer levels on the treated surface. In this mode, polishing pastes tend to produce greater specular reflectance, which in turn produces a higher visual surface gloss.

With respect to the comparative efficacy of polishing pastes as a method for final polishing of composite resins, several investigations report favorable results in producing highly smooth, light-reflective surfaces. These studies involved the use of both conventional diamond-stylus contact profilometry and non-contact, three-dimensional surface profile analysis. A differential benefit of polishing paste on various restorative materials has also been noted, with optimal benefits on a sub-micron, highly filled hybrid material and surface smoothness equivalent to several commercially available bonded-abrasive diamond polishing instruments (without the use of polishing paste). The benefit of using a loose-abrasive, aluminum oxide polishing paste after using sequential, aluminum oxide–coated abrasive disks for finishing and pre-polishing has also been noted. One investigation has demonstrated that sequentially applied aluminum oxide polishing pastes produce a visually smooth and light-reflective surface on microfill and small-particle hybrid composites, directly after the sequential use of 12- and 30- to 40-fluted carbide finishing burs. With very careful technique, a finishing-polishing sequence from multi-fluted carbide burs to sequential polishing pastes is feasible. It is advisable to introduce intermediate finishing and pre-polishing devices (coated disks; rubber-like, bonded abrasives) between high-speed contouring-finishing burs and diamonds before applying polishing pastes for both composite and porcelain restorative materials.

Treatment Considerations

Procedure

Always consult literature references and review articles. Finishing and polishing procedures involve an orderly sequence of steps that progressively refine and smooth scratches and defects introduced during the initial gross reduction step. With respect to gross reduction of composite resin materials, it is now generally accepted that fine and extra-fine finishing diamonds are used first, followed by carbide multi-fluted finishing burs. The next step of intermediate finishing is a critical bridge between gross reduction and final polishing. Commonly used intermediate finishing and pre-polishing devices include rubber-like, elastomeric bonded abrasive, in cup, disk, and point configurations. Medium, fine, and extra-fine coated abrasive disks from various manufacturers also provide intermediate finishing options, especially for facial and interproximal embrasure locations. After use of one to three of these various intermediate finishing devices, the next step is final polishing of the restoration. The specific steps and procedure for final polishing will be considered in the case presentation later. Nevertheless, the practitioner needs to experiment at the bench with various finishing and polishing devices and the composite resin and ceramic restorative materials used in routine clinical practice. It is advisable to practice with various devices on cured samples of various restorative materials to work out the efficient used and sequence of these devices and products.

Controversies

Although finishing and polishing are not commonly thought as an area of significant controversies, there are several issues in this area that provide for debate and discussion. Some of these questions under debate on this topic are as follows:

Near-Future Developments

Recent New Technology in the Realm of Dental Finishing and Polishing

Although most new products in the dental finishing and polishing area are incremental improvements in existing products, new designs or abrasive compositions periodically appear.

Abrasive-Impregnated Brushes and Felt Devices

Abrasive-impregnated, latch-type polishing brushes were introduced to the profession in the late 1990s. These polishing brushes are provided in several shapes (pointed; cup shaped), with various types of polymer “bristles” impregnated with different abrasive polishing particles. The brushes are intended to reach into the grooves, fissures, and interproximal areas of ceramic and resin composite restorations, areas that cannot be reached with other finishing or polishing devices without unintentionally removing anatomic grooves, fissures, and contours. Several of these brushes are depicted in Figure 11-5. Aschmann and colleagues (U.S. Patent 6,312,257) describe a “brush for surface treatments in restorative dentistry [that] comprises one or several lamellar abrasive elements.” Dubbe and colleagues (U.S. Patent 6,554,614) describe “a brush for a dental handpiece … wherein at least some of the bristles comprise an elastomeric material and a number of abrasive particles distributed throughout the elastomeric material.” The particulate abrasive used in the Sof-Lex Brush (3M ESPE, St Paul, Minnesota) is aluminum oxide.

A precursor to this specific abrasive-impregnated brush technology was the diamond-impregnated felt wheel for polishing hybrid composite resin. These wheels effectively smooth the surface of a hybrid composite resin after initial finishing with various sequences of high-speed diamond burs, tungsten carbide finishing burs, or combinations of diamond and carbide finishing burs. An early report on these new polishing devices described a new polishing brush composed of rigid polycarbonate fibers impregnated with silicon carbide abrasive particles (Occlubrush, Hawe-Neos; now Kerr Corporation, Orange, California). The investigators found that the silicon carbide–impregnated bristle polishing brush maintained surface texture during the polishing procedure, produced a composite surface smoothness somewhere between that created by a 25-µm finishing diamond and an extra-fine coated abrasive disk, achieved a surface luster subjectively greater than an extra-fine coated abrasive disk (on both composite resin and enamel), could be reused with autoclaving up to 15 to 19 times, and was no more deleterious to enamel surface quality or restoration marginal quality than a 25-µm finishing diamond.

More recently, a few in vitro evaluations have assessed the polishing efficacy of these abrasive-impregnated polishing brushes. Yap and co-workers evaluated the residual surface roughness after using the Sof-Lex Brush and found that it produced a smooth, polished surface comparable to that achieved with a rubber or bonded-abrasive diamond polishing device. Venturini and colleagues evaluated a silicon carbide–impregnated polishing brush (Jiffy Polishing Brush, Ultradent Products, South Jordan, Utah) after finishing and pre-polishing with sequential rubber polishing cups (FlexiCups, Cosmedent, Inc.). They found a high level of surface smoothness in both microfilm and hybrid composite resins after polishing with this impregnated brush using both the immediate and the delayed polishing technique. This polishing device design is interesting in its approach to providing improved “micro-access” for bonded-abrasive polishing. Further laboratory and clinical evaluations are needed.

Rotary Resin-Matrix Stain, Cement, and Composite Removing Devices

Several rotary devices based on a polymer or composite resin binder or matrix, with apparent “controlled” abrasivity, have recently been introduced to selectively remove surface-adherent restorative materials, including composite resin and residual cement (Figure 11-6). Among this new class of abrasive devices is Flashbuster (Danville Materials, San Ramon, California), a latch-type, rotary composite fiber bur that is claimed to remove residual composite with no damage to either enamel or porcelain. It can also remove residual orthodontic adhesive and stains from areas with limited access and can be used in periodontal root planing. The structure of the rod bur consists of fibers and particles embedded in a resin matrix. This yields a working surface that has continuous abrasive power.

It can be used for cleaning and polishing the surface of teeth and/or composite materials of dental fillings. The embedded fibers are made from a glass enriched with zirconium oxide, making the instrument highly resistant to alkaline and acidic agents and detectable by electromagnetic radiation.

OptiClean (Kerr Corporation) is a latch-type rotary bur composed of aromatic polyamide containing 40-µm aluminum oxide. OptiClean is intended for the removal of temporary cement and debris on tooth preparations before final cementation. Therefore it replaces other methods of preparation surface cleaning, such as a rubber cup and pumice or the use of hand instruments.

Both of these products await further independent studies and evaluations before their performance can be fully understood.

Clinical Techniques

Clinical Step by Step

Step 1 (not shown): Using fine and micro-fine finishing diamonds and multi-fluted carbide, gross excess of the composite resin is removed, avoiding excessive contact with or damage to the enamel portion of the restoration margin. The marginal areas (and selected occlusal areas) of the class I composite restoration are carefully trimmed and finished using an aluminum oxide–containing bonded-abrasive finishing point or cup. The occlusion is checked and adjusted with fine and extra-fine diamonds, multi-fluted finishing burs, and the elastic bonded-abrasive finishing cups, points, and/or disks.

Step 2: Figure 11-7, A, illustrates an appropriate device for the optimal application of aluminum oxide polishing pastes—namely, a porous synthetic foam cup in a low-speed handpiece.

Step 3: Figure 11-7, B, illustrates the initial application of the 1-micron aluminum oxide polishing paste (Prisma Gloss, DENTSPLY Caulk). Note that the porous surface of the synthetic foam polishing cup eliminates the need to carry excess paste; the paste is carried in the surface porosities of the foam cup.

Step 4: Figure 11-7, C, illustrates the flexibility of the synthetic foam polishing cup to adapt to the contour of the occlusal surface during the application of the loose-abrasive polishing paste. A critical element in the polishing paste procedure is the rotary application of the polishing paste dry (without water) in a continuous motion over the surface of the restoration. Application times of 30 to 60 seconds ar/>

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Jan 3, 2015 | Posted by in Esthetic Dentristry | Comments Off on 11: Polishing
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