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Written by Howard E. Strassler, DMD, FADM, FAGD and Judith Porter, DDS, EdD Tuesday, 01 April 2003 00:00
The aesthetic appearance of a composite resin restoration depends upon shape, color, and gloss of the restoration achieved by finishing and polishing. When composite resins were first introduced in the late 1950s and early 1960s, they were self-cured and macrofilled with particles in the 25 to 50 µm range. In most cases, the filler particles were quartz. These composite resins, once contoured, had little surface gloss, and the patient sensed roughness when their tongue touched the restoration.
The introduction in the late 1970s of visible light-cured composite resins with smaller diameter filler particles of synthetic, softer glasses made composites more polishable. These materials allowed the clinician to provide patients with more natural and aesthetic tooth-like restorations in the anterior region of the mouth. As a result of changes in the polymerization chemistry, visible-light cured composite resins demonstrated improved color stability. Light activation was generally initiated when a blue light with a wavelength of 460 to 470 nm was absorbed by a photo-initiator, usually camphoroquinone (CQ). The use of CQ combined with an organic amine resulted in a chemical reaction so the composite resin hardened. This light-activated reaction eliminated the need for the tertiary amines that were present in the early self-cured resins. The tertiary amines contributed to unaesthetic color changes that characterized these restorative materials.
In the last 15 years, manufacturers have introduced a wide variety of composite resins with varied applications in both the anterior and posterior regions (see Table 1). For anterior restorations, microfilled composites and hybrid composite resins have become accepted standards. Microfilled composites offer high polishability with tooth-like translucency, but unfortunately are radiolucent. The microfilled composites are polishable and maintain their luster as a result of the inclusion of 0.04-µm colloidal silica particles within the polymer matrix (homogenous microfill) or mixed with the polymer matrix, light cured, and then crushed to make a prepolymer filler that is an organic filler within the microfilled composite (heterogenous microfill). The small fillers and resin-rich surface promote high polishability. Microfilled composites are generally loaded 32% to 50% by volume and have greater polymerization shrinkage, higher water sorption, and a higher coefficient of thermal expansion and contraction than hybrid composites.1
Hybrid composite resins combine microfiller particles (0.04-µm fumed silica) with microfine glass fillers with an average particle size diameter of less than 2 µm. Typically these composites are loaded 58% to 75% by volume and are radiopaque. This mixture of fillers accounts for the excellent physical properties, including high polishability, as compared to macrofilled composites.2 An important problem associated with hybrid composite resins is their inability to maintain a gloss when exposed to toothbrushing with toothpaste or application of prophylaxis pastes.3-6
Although microfilled composites maintain their gloss, these composites are susceptible to fracture in high-stress-bearing areas.7 Consequently, a highly polishable composite resin with optimal physical properties was needed for anterior and posterior restorations.
NEW GENERATION COMPOSITE RESIN
Recently, a new generation of hybrid composite resin has been introduced. These materials have been categorized as nanofilled, with filler particles with a diameter in the 0.005- to 0.1-µm range (Table 2). The nanofilled composites have physical properties equivalent to the original hybrid composite resins, good handling characteristics, and greater polishability.8,9 These nanofilled composites offer an excellent alternative to microfilled composites because they can be polished to a toothlike translucency.10 For anterior restorations, both microfill and nanofilled hybrid resins can be expected to provide good color stability, resistance to stain, low wear, and good polishability.2,8
While the new nanofilled composites are supplied with basic shades, they also have incisal, enamel, and dentin shades. With the introduction of these composites, manufacturers have provided specialized shade guides that help the clinician select the mix of shades to be used in specialized circumstances, such as building on class IV incisal edge fractures from the inside out and stratified building of completed facial veneers for aesthetic bonded restorations. Examples include Filtek Supreme (3M ESPE), which provides a comprehensive shade selection wheel that is used once the basic shade has been selected from a Vitapan (Vident) classical shade guide, and Esthet-X (DENTSPLY/Caulk), which provides a comprehensive, expanded shade guide that matches bleached teeth and includes some darker shades than the traditional Vitapan guide. These advanced composite resins have been formulated to be more sculptable and easily placed, with minimal slump and very little tackiness.
THE IMPORTANCE OF FINISHING AND POLISHING
The final aesthetic appearance of any composite resin is dependent upon the artistic abilities of the clinician in (1) choosing the correct shade or shades of composite resin to mimic the color and appearance of the teeth, and (2) shaping and contouring of the restoration. The restoration’s ability to imitate the appearance of the tooth and/or adjacent teeth also depends upon the proper finish and polish of the restorative to its highest luster.11,12 Research has shown that the technique for polishing composite resins to their optimal smoothness and gloss is specific to the type of composite resin and the product.10-17
Barkmeier and Cooley18 evaluated the ease of polish and surface finish of 4 heterogenous microfills and 1 homogenous microfill. They found all 5 microfills had no difference in ease of finish, but the homogenous microfill produced the smoothest surface. Hoelscher and coworkers19 compared 3 different finishing systems employed with 4 aesthetic materials (including glass ionomers and a hybrid and a microfill composite resin). Their findings indicate that a finishing bur left the roughest surface, while abrasive disks, when used from coarse to fine, yielded the smoothest finish of all materials tested. Setcos, Traim and Suzuki20 compared several disk systems used to polish hybrid and microfilled composites. Regardless of composite type, the sequential use of disks from coarsest to finest produced the smoothest surfaces.
The principles governing the polishing of composite resins are similar to those used to polish dental metals. Unlike metals that have a homogenous alloyed surface and a uniform hardness, however, composite resins are composed of resin matrix and filler particles. In some cases, the resin matrix and fillers have different hardnesses. While composite resin finishing systems can be used on metals, metal finishing and polishing systems should not be used for composites in order to avoid undesirable staining and discoloration. The abrasive particles used to polish composites are material specific. Similar to metal polishing, the sequence of polishing for composite resin progresses from coarsest abrasive to finest.
Finishing and polishing devices and instruments can be classified as...
(1) coated abrasives; eg, abrasive finishing disks and strips;
(2) rotary cutting devices, eg, carbide finishing burs;
(3) rotary submicron particle diamond finishing abrasives;
(4) reciprocating abrasive tips; eg, laminated abrasive flat paddles;
(5) rubberized embedded abrasives; eg, rubber or silicone rotary points;
(6) hand instruments, and;
(7) abrasives suspended in a polishing paste.
No matter which abrasives are selected, the rule of coarsest to finest must be followed. Table 3 has a partial listing of instruments, devices, and materials for polishing composite resins.
The goal when placing a composite resin is minimal finishing and polishing. While this is not difficult with routine anterior restorations (class III and class V), for larger, more involved restorations (class IV and complete facial veneering, especially for multiple teeth), significantly more contouring and finishing is usually required. Typically, for these larger restorations the sequence for finishing and polishing involves gross contouring, shaping with finishing burs and submicron finishing diamonds with a high-speed handpiece, followed by additional finishing with abrasive discs and/or rubber points. For long incisal-gingival restorations, narrow, long finishing burs or diamonds with safe-tipped ends allow the establishment of aesthetic curved surfaces. While finishing burs and diamonds can be used either wet or dry, the authors prefer using them dry with light pressure, with the dental assistant suctioning the composite “dust” during the procedure. Working with a dry field provides better visualization of shape and contour of the composite resin surface.
Judicious use of coarse and medium grit finishing disks using only small sections of the disk allows the same level of control. Today, most disks have a small metal hub to reduce the chance of accidentally hitting the composite with the hub. Some manufacturers (Shofu and Brasseler) have placed their disks on silicone sheaths that slip over the metal mandrel, thereby eliminating the potential to mar the composite resin surface. Additional finishing of facial and lingual surfaces can be accomplished with specialized rubberized polishers in flame, disk, and cup shapes. These shapes provide access to the different tooth contours. These are used on a latch-type contra-angle handpiece. It is important whenever using abrasive systems that the surface of the composite resin be physically debrided of composite and abrasive debris with a damp cotton roll or gauze. If only an air-water spray is used, some of the debris will remain on the surface and interfere with polishing when sequentially using the next finest abrasive grit.
Interproximal finishing and polishing are accomplished with gapped finishing and polishing strips covered with aluminum oxide abrasive particles, or with metal strips covered with submicron diamond particles. Occasionally, even with the use of a matrix strip, the restoration may bond to the adjacent teeth, literally splinting the teeth together. In these cases, there are specialized accessories that allow the clinician to separate the teeth without damaging the restoration. Included here is an ultra-thin stainless steel saw blade mounted in a handle (Cerisaw, Den-Mat). This mini-hacksaw and handle allows for total control of the instrument while gently sawing through the interproximal resin. When using a saw, a gingival wooden wedge should be placed between the teeth to protect the gingival papilla. Den-Mat also places diamond strips in the CeriSaw handle to finish interproximal surfaces of resin restorations and ceramic veneers. In addition, Axis Dental combines a gapped diamond-containing metal finishing strip with saw teeth on the strip.
Another useful device to help separate interproximal contacts for placement of matrix strips or gapped finishing strips is the Contact Disc (Centrix). This thin, rigid disk can be inserted from the incisal, occlusal, or facial directions to force the teeth apart. If excess composite resin is present, the disk will create space to allow a matrix strip to be placed without bleeding, as may occur when using a gingival wooden wedge to accomplish the same task. In the presence of excess interproximal composite resin, the disk will break away excess resin without damaging the restoration. Premier Dental Products has developed a diamond-impregnated thin disk (CompDisk) that not only creates space with rapid separation, but can also be used for interproximal finishing or cleaning interproximal surfaces before bonding.
Occasionally, after placement of the composite restoration, finishing the margin is best accomplished with a hand instrument or by using a specialized reciprocating handpiece with a flat abrasive paddle. Carbide-tipped hand instruments (Brasseler; Den-Mat), restorative knives (Hu-Friedy), or scalpel blades with shapes that allow access to the margin of the restoration will allow the clinician to remove excess restorative material in a more controlled manner than with rotary burs or diamonds.12,21 Carbide carvers are especially useful for marginating composite resin restorations when only minimal excess is present. In inaccessible areas such as the gingival margin of an interproximal surface, specialized instruments and devices such as a reciprocating handpiece (Profin, Dentatus) with a flat Lamineer abrasive tip can be used.21,22 Lamineer tips come in a variety of submicron abrasives for finishing and polishing the cervical margin of the restoration. The flat tips can also be used to finish and shape facial surfaces and incisal embrasures.
Final polish of the composite resin surface to its most lustrous finish can be accomplished using disks with the finest aluminum oxide abrasive. Using a disk will not only smooth the resin surface, but will also heat the surface, creating a high luster. This heating is sufficient to allow the polymer matrix to reach its glass transition temperature. This phenomenon gives the composite resin a glassy appearance. Also, a composite resin can be polished with specialized composite resin polishing pastes that contain either very fine aluminum oxide abrasive particles or diamond particles. This is best accomplished with foam cups, felt-mounted disks, or fine goat-hair brushes. If the surface of the restoration is generally smooth, disks work well. For surfaces that have anatomic variations such as lobular forms or striations, composite polishing pastes work best.
|Figure 1a. Facial view of the maxillary anterior teeth. The central incisors are lingually positioned and the lateral incisors are rotated distally.||Figure 1b. Palatal view showing the misalignment of the incisors.|
During the restorative treatment consultation, the patient was presented with 3 options—ceramic crowns, porcelain veneers, or direct placement composite resin. Adhesive bonding with composite resin and ceramic veneers are alternative treatments for aesthetic correction of tooth malposition in the anterior area.23,24 Because of financial considerations, the patient chose direct placement composite resin restorations.
|Figure 2a. Palatal view of cast demonstrating malaligned incisors.||Figure 2b. Stone has been removed from the cast to simulate tooth preparation.|
|Figure 3a. Diagnostic buildup with composite resin.||Figure 3b. Palatal view of the buildup.|
During the treatment planning phase, study casts were used to further evaluate tooth position. The maxillary incisors were reduced on the casts to determine how much tooth preparation would be needed to allow for adequate composite resin to align the incisors (Figures 2a and 2b). A diagnostic buildup with composite resin was performed to assess tooth shape, proportions, and widths, and for patient acceptance (Figures 3a and 3b). When the patient accepted the proposed treatment, he was scheduled for restoration with a direct placement, nanofilled hybrid composite resin (Point 4, Kerr).
Before tooth isolation, a shade was selected with a Vitapan shade guide (Vident). This selection was checked by placing an increment of composite resin most closely matching the shade of the maxillary canine on the lateral incisor and light curing that increment. Like many of the new generation of nanofilled composite resins, Point 4 offers regular shades, opaque shades, translucent shades, and bleaching shades. Although Point 4 has very little color change when light cured, some composite resins change shade when light cured because of removal of the orange-yellow photoinitiator (camphoroquinone) during the polymerization process. Accurate shade selection is a critical step when placing anterior composite restorations.
|Figure 4. Preparation of maxillary incisors.|
The teeth were isolated using a split rubber dam. Split rubber dam involves punching holes for rubber dam placement and then cutting through the septa between holes with a scissor. A bite block was placed. Use of the rubber dam combined with a bite block improves patient comfort and affords better access when preparing and restoring anterior teeth with direct bonded composite resin. Here, the teeth were prepared with a thin, medium-grit flame-shaped diamond (Revelation 653-016, SS White Burs) on a high-speed handpiece with water spray (Figure 4).
Before acid etching, dead soft stainless steel metal matrix, 0.001-inch thick, was placed distal to the maxillary central incisors. A piece of Tofflemire stainless steel rigid matrix (0.002-inch thick) was cut into a small rectangular strip and was placed between the central incisors. This more rigid strip holds the correct orientation of the midline.
|Figure 5. Etched facial surfaces of maxillary incisors.||Figure 6. Application of adhesive to etched tooth surfaces.|
The tooth surfaces were etched for 15 seconds with a 32% phosphoric acid etchant and then rinsed with an air-water spray for 15 seconds. The etched tooth surfaces were dried, leaving a slightly frosty appearance to the enamel, and the dentin was moistened, leaving a glossy appearance (Figure 5). An enamel/dentin adhesive (Optibond Solo Plus, Kerr) was applied to the facial surface of the etched enamel (Figure 6), and then light cured for 20 seconds with an Optilux 501 (Demetron/Kerr) curing light. The nanofilled composite resin hybrid (Point 4, Kerr) was placed on the facial surfaces of both central incisors and sculpted with a thin, broad plastic filling instrument (PFIAB1, HuFriedy). This instrument allows for smooth shaping of the broad facial areas of incisors. The instrument was lightly wetted with a coating of adhesive resin to prevent the composite resin from sticking to the instrument and pulling away from the enamel surface. The composite resin was light cured for 20 seconds using a wide-angle light probe tip so that the entire facial surface could be polymerized. After placement of the composite resin on the central incisors, the lateral incisors were restored using the same protocol.
FINISHING AND POLISHING
Many manufacturers provide kits containing finishing burs, diamond abrasives, rubberized abrasives, and disks that give the clinician an orderly sequence of finishing and polishing instruments. There is no one approach to the finishing and polishing of composite resins, but a general rule is to proceed from coarse to fine grit size.
|Figure 7. Long, thin composite resin finishing bur trimming the facial surface.||Figure 8. Shaping of the gingival margin with a thin needle shaped finishing bur.|
|Figure 9. Fine diamond finishing bur for contouring the gingival margin.|
In this case, the facial surfaces were contoured using a long, narrow, safe-ended, multifluted finishing bur (7204, SS White Burs) (Figure 7), but a submicron diamond abrasive with a similar shape could also have been used. The gingival margin was contoured and marginated with a shorter, thin-needle shaped finishing bur (CFT 2, SS White Burs) (Figure 8). Another popular choice for shaping facial surfaces of veneers and class IV restorations is the ET series of finishing burs and diamonds (Brasseler USA). The choice of finishing bur and diamond abrasive is usually made by the practitioner based upon experience. Finishing burs can have as few as 8 or 12 blades for gross reduction. For finer finishing, 16- or 30-bladed burs are available. Diamond composite finishing abrasives usually have a diamond particle size of approximately 30 µm for fine grit, 15 µm for extra-fine grit, and 8 µm for ultra-fine grit. Note that a thin, new finishing bur can cut aggressively into a facial surface. A composite resin finishing bur dulls to the ideal after 2 sequences of autoclaving. To further finish the gingival margin, a flame-shaped fine finishing diamond (862-016, SS White Burs) (Figure 9) was used as it allows better access to the gingival margin without nicking the root surface. After the fine diamond was used, the composite surface was further finished with a flame-shaped extra-fine bur and then a flame-shaped ultra-fine diamond.
|Figure 10. Coarse disk shaping the incisal edge.||Figure 11. Disk shaping the facial and incisal embrasures.|
The incisal edge was shaped and the length determined using a coarse disk (Soflex XT disk No. 2381C, 3M ESPE) (Figure 10). The best technique for shaping the incisal edge is to have the patient seated in an upright position that mimics how the incisal edges are visualized. The disk should be oriented with a slight lingual inclination following the chisel shape of the incisal edge of an intact incisor. The incisal embrasures and facial embrasures were established using a thin, flexible diamond disk (Vision Flex Disc, Brasseler USA) (Figure 11). These areas can also be shaped with a reciprocating handpiece (Profin) and an “S” series knife edge lamineer tip. Once shaped, the areas were finished using successively smoother disks, from a medium to fine to finest grit.
|Figure 12. Safe-sided Lamineer tip on reciprocating handpiece shaping the gingival interproximal embrasure.|
One of the most difficult areas to access when finishing any aesthetic restoration is the gingival margin of an interproximal surface. Finishing strips do not work well because of difficulty in accessing this area. In this case, the Profin with a Lamineer tip was used in the gingival interproximal areas because the reciprocating handpiece, with its back and forth motion, provides the control needed to safely finish and polish the root surfaces without notching (Figure 12). Finishing burs on a high-speed handpiece, if not used correctly, can easily notch the root surface. Even the thinnest finishing burs or submicron diamond abrasives are rounded and can notch a root surface. The Lamineer tips are safe-sided and are available in decreasing diamond abrasive grits to allow finishing and then polishing of the gingivoproximal area.
There are times when a rotary instrument or even a reciprocating instrument does not have complete access to the interproximal surface. For these special situations, a hand instrument allows for fine control, precision placement, and effective removal of excess composite resin. Hand instruments for this purpose include carbide-tipped composite instruments (with specialized shapes to access different tooth surfaces), composite carving knives, and a No. 12 scalpel blade.21
The finishing and polishing of the interproximal surfaces of composite resin restorations require the same attention given to accessible surfaces. Care should be taken not to remove excessive composite resin, resulting in an open proximal contact. Interproximal strips can be used to shape and contour the interproximal contact area, thus maintaining the contact. When using finishing strips, always proceed from medium abrasive grit, to fine grit, to the finest grit. Gapped finishing strips work best as they allow ease of placement between the teeth. If difficulty is encountered introducing the strip through the contact, a plastic filling instrument can be used to rapidly separate the teeth, and then the finishing strip is slid below the interproximal contact area. If a diamond abrasive-gapped strip (eg, Gateway Strip, Brasseler) is used, additional care must be taken to not remove tooth structure when finishing the interproximal areas. These diamond-impregnated strips also work well for removing stain on interproximal tooth surfaces before the bonding procedure.
|Figure 13. Finishing cup smoothing the facial surface of the composite resin.||Figure 14. Egg-shaped 12-bladed finishing bur completing the margin and shaping the lingual surface of the composite restoration.|
|Figure 15. Flame-shaped finishing point polishing the lingual surface of the composite restoration.|
Intermediate finishing of the facial surface was accomplished with a cup-shaped rubber finisher (Astropol, Ivoclar Vivadent) (Fig 13). The cup shape allows access to the gingival facial margin and also contours the facial surface. If lobular facial form is desired in the restoration, this can be accomplished once the facial surface has been smoothed by using a disk-shaped rubberized abrasive. The lingual surface was finished with an egg-shaped finishing bur (7406, SS White Burs) (Figure 14). The surface was then smoothed with a flame-shaped point (Astropol, Ivoclar Vivadent) (Figure 15). The occlusion was then checked just prior to final polishing.
|Figure 16a. Completed restoration, facial view.||Figure 16b. Aesthetic alignment has been achieved with direct composite resin bonding.|
The final polish was accomplished with a composite resin polishing paste (Extra Smooth Composite Polishing Paste, Den-Mat) on a foam cup attached to a screw-in metal mandrel (Luminescence, Premier Dental Products). Either a foam cup polisher or felt-covered disk will bring the polishing paste in contact with the anatomic areas created on the facial and lingual surfaces. Another technique for attaining a smooth, high luster is using the finest grit aluminum oxide disk available or the finest grit of rubber polishing point. Using the finest abrasive disk or rubber point at greater than 18,000 rpm creates a highly lustrous surface. This is because of both the polishing effect of the disk and heating of the resin surface; a glassy appearance is the result. Interproxmal areas can be further polished with small-width gapped fine abrasive finishing strips or composite resin polishing paste on a Lamineer plastic polishing tip on a reciprocating handpiece. The final result is seen in Figures 16a and 16b.
The clinical success of finishing and polishing techniques can best be observed over time. While the current generation of composite resins are highly polishable, highly polished surfaces of resin-rich microfills are still prone to staining.25 The staining of composite resin surfaces is directly related to patient variables, including diet (coffee, tea, wine, etc), as well as other habits (smoking, spit tobacco, and the use of alcohol-containing mouthrinses). The stain
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