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J Am Dent Assoc, Vol 131, No 3, 375-383.
© 2000 American Dental Association | ![]() |
COSMETIC AND ESTHETIC DENTISTRY |
A SIMPLIFIED PLACEMENT TECHNIQUE
| ABSTRACT |
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Methods. The authors describe an incremental layering technique that takes advantage of the improved handling characteristics and proposed reduced shrinkage and greater depth of cure.
Clinical Implications. When this new technique is used with one-bottle adhesives and improved instrumentation, posterior heavy-body composites can be placed faster, easier and possibly more predictably than when medium-body resins and previous techniques are used.
The composite resins were first introduced in the 1960s with product names such as Adaptic (Johnson & Johnson) and Concise (3M Dental Products). They were chemically cured and their use was indicated for Class III, IV and V cavity preparations. The filler particles were large and the filler content was low. They were not polishable and tended to discolor over time. For these indications, they were durable, with some restorations lasting up to 10 years. However, high wear rates and marginal leakage made such composites unacceptable for long-term restoration of posterior occlusal surfaces.1
A major step in composite technology occurred in the 1970s with the introduction of light-cured composite resins such as Nuva-Fil (DENTSPLY/L.D. Caulk). (Although it is more accurate to call these composite resins light-initiated, the popular term light-cured will be used in this article.) Studies have demonstrated that light-cured composite resins are more wear-resistant and more color-stable than the self-cured composite resins.2,3 The improved wear resistance was the result of using smaller filler particles (mean diameter, 5 to 8 micrometers) and because less air was incorporated in placement of the restoration compared with hand-mixed autocured resins. Increased air causes inhibition of the polymerization process and creates voids that accelerate wear.4
In the early 1980s, resins specifically for posterior use appeared with the introduction of such products as P-10 (autocured; 3M Dental Products), followed by P-30 (light-cured; 3M Dental Products). They were also relatively wear-resistant because of reduced particle size and increased filler loading.5
By reducing the particle size even further, to 0.04 µm, manufacturers were able to introduce microfill products around this time. This new generation of composite resins had high polishability, high wear-resistance and good color stability. However, because of lower strength in flexion and tension, these composite resins were prohibited for Class II restorations.6 The sole exception has been Heliomolar (Ivoclar-Vivadent), which was developed in 1986 and remains popular for posterior restorations.
In the mid-1980s, significantly improved light-cured composite resins, such as Herculite (SDS Kerr), APH (which stands for all-purpose hybrid) (DENTSPLY/L.D. Caulk) and P-50 (3M Dental Products) became the standards for restorative resins. They were intended for universal use (that is, for both anterior and posterior restorations). They were called hybrids because they had a mixture of particle sizes (from 0.04 to 3 mm). The mean particle size was approximately 1 µm.
Further refinements in these materials led to the term micro-hybrid being used to describe resins with mean particle sizes in the 0.6- to 0.7-µm range. Generally, the particles in these composite resins also were more uniform in size. These materials (such as TPH, DENTSPLY/L.D. Caulk; Herculite XRV, SDS Kerr; Charisma, Heraeus/Kulzer; Tetric Ceram, Ivoclar-Vivadent; and Renamel Hybrid, Cosmedent) have excellent physical properties, are relatively nonsticky, and finish and polish well; however, they do not hold a high polish.7
Although successful techniques for posterior resin placement have been developed with these universal microhybrid materials, they present many challenges when clinicians attempt to place morphologically correct and functional Class II restorations.815 Many hybrid composites are difficult to manipulate because of inherent stickiness and slumping. Stickiness can result in voids and porosity as materials are manipulated. Slumping increases the difficulty of creating proper anatomical form during incremental placement of the material.
Another problematic physical property inherent to all composite resins is shrinkage during polymerization.16 Shrinkage can present numerous challenges during placement. It has commonly been assumed that resins shrink toward the light; however, recent investigators have disputed this.17,18 They propose that the material shrinks toward the fixed boundaries and there is not much difference in vector patterns between autocured and light-cured composite resins. Either way, the bonded interface is stressed. If the preparation is bulk-filled or if a single increment connects opposing walls in Class I or II posterior restorations, the resulting high C-factor ratio (that is, the ratio of the bonded to unbonded walls in a restoration) can further increase shrinkage stress.19 This, in turn, can lead to marginal gaps and microleakage at gingival margins. Such leakage can cause postoperative sensitivity and possibly lead to secondary caries.20
Dental practitioners generally accept that one of the most difficult challenges when placing a direct Class II composite resin restoration is the formation of a high-quality, predictable contact. Composite resins cannot be condensed like amalgam. Allowances must be made for this fact during matricing and placement.
When all factors are taken into consideration, placing posterior Class II resins is much more demanding and technique-sensitive than placing amalgams. In addition, the adhesive process must be followed with precision and accuracy. Failure to do so can result in postoperative sensitivity, and even failure of the restoration.12
Finally, the time needed to place a high-quality posterior composite resin restoration can be considerably more than that needed to place an amalgam restoration. The increased time requires an increased fee, which is often resisted by patients and third-party payers who may not fully understand all of the benefits of an adhesive restoration beyond esthetics.
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NEW MATERIALS
TOP
ABSTRACT
NEW MATERIALS
INSTRUMENTATION
PLACEMENT TECHNIQUE
DISCUSSION
CONCLUSION
REFERENCES
New terminology.
New composite resins specifically developed for posterior use have recently been introduced (Table 1
). Some manufacturers are marketing these products as condensable. (The dictionary defines condensable as able to be compacted or made denser by reducing volume.) Unlike amalgam, composite resins cannot be compacted (or condensed). However, it is not necessary for composite resins to demonstrate this property to be used expediently and successfully for posterior restorations.
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A great deal of confusion exists when differentiating the various classes of composite resins in the marketplace today. Some of this is due to the various adjectives, such as condensable, packable or compactable, used by manufacturers to market their new resin products. A better way to describe these new posterior composites might be to use the common terms used to describe impression materials. Just as those materials are available in light-body, medium-body and heavy-body forms, so too are contemporary composite resins.
Light-body composite resins are the flowable materials that have a low viscosity. Medium-body composites are composed of the microfill, hybrid and microhybrid universal resins currently used for anterior and posterior restorations. In general, they have a medium viscosity, which allows them to be placed and contoured with different degrees of ease or difficulty depending on cavity configuration. The stickiness and slumping of each of these products varies. The new packable posterior composite resins can be accurately termed heavy-body. The change in composition of heavy-body composite resins compared with their medium-body predecessors is the result of increasing the volume of filler particles, varying the size and type of the particles, altering the chemistry of the resin matrix or a combination of any of the above.2123 Manufacturers are claiming that these changes result in less shrinkage during polymerization as well as in improvements in workability, depth of cure, wear resistance and color stability.
Because these materials do not slump, the entire occlusal increment can be placed and sculpted to the final anatomy at once, thereby greatly reducing the amount of final adjusting and finishing.
Characteristics. The desirable properties and handling characteristics in a composite resin used to restore posterior teeth are different from those in a material used to restore anterior teeth.24 For posterior teeth, the material will have the following desirable qualities:
Even though a dentin opacity and an enamel translucency are still required for esthetic reasons, the wide range of shades required to restore anterior teeth is generally not necessary to restore posterior teeth.
The manufacturers of the heavy-body composites currently in use claim that their products have all of the aforementioned desirable physical characteristics.2123 Because these materials do not slump, the entire occlusal increment can be placed and sculpted to the final anatomy at once, thereby greatly reducing the amount of final adjusting and finishing.
Controversy exists over whether a single increment (that is, bulk placement) should be placed against opposing walls simultaneously before light-curing.25 The concern is that polymerization shrinkage may cause the cusps to bend toward each other.26,27 This stress can be detrimental to the tooth and the marginal integrity over time. Manufacturers claim that, for the most part, because of their high density, the heavy-body resins result in less volumetric shrinkage than standard restorative resins.2123 This property, combined with a greater depth of cure (most manufacturers are claiming up to 5.0 millimeters2123), enables the clinician in many instances to place and sculpt the entire dentin replacement in one increment. If the dentin replacement is greater than 5.0 mm (that is, in a cavity with a deep proximal box), a second increment is required. In these instances, the clinician needs to sculpt only the second increment to contour.
The clinician replaces the enamel with a more translucent shade of resin than what was used to replace the dentin, and sculpts it to contour with pits, fissures, marginal ridges, triangular ridges and secondary fissures as needed to mimic the natural occlusal anatomy. More than esthetics is involved, because proper occlusal morphology affects function significantly. The last increment of resin is placed with minimal excess flash at the occlusal margins. A slight excess helps to ensure a gap-free restoration. Because the flash is minimal, the restoration may be finished quickly (Figures 1
and 2
).
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| INSTRUMENTATION |
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The Microband (Dental Innovations) is a new micromachined matrix band developed specifically for Class II posterior composite resin restorations. The contact area of a normal 0.0015-inch-thick matrix band has been thinned to 0.0006 inches (12 µm).32 A wedge is used to adapt the band to the gingival margin of the proximal box. Enough wedging force is needed to retain the wedge; however, excessive wedging to separate the teeth is not required. The thin contact area is burnished against the adjacent tooth in the ideal location and proper size. Because the band is so thin, the heavy-body composite resin is placed virtually in contact with the adjacent tooth. The manufacturer also supplies these bands as sectional matrices called Microstrips (Dental Innovations).
Contact-forming instruments are sometimes useful for Class II composite resin restorations. Most of the instruments operate by distending or stretching the matrix band while the proximal composite is light-cured. Although these instruments are not necessary in all situations, they are particularly helpful when restoring malaligned teeth or rotated teeth or when a wider-than-normal intertooth distance exists. When a contact-forming instrument is needed, we believe that the Contact Pro 2 B (C.E.J. Dental) provides a consistent contact of the correct size and location.
The combination of the new materials, matrices and contact-forming instruments has made it possible to achieve predictable, high-quality contacts in Class II direct composite resin restorations. In addition, the results are achieved faster, easier and more predictably than they were before.
| PLACEMENT TECHNIQUE |
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Clinical factors. Evaluate the clinical factors to determine if placement of a Class II direct resin is appropriate. These restorations generally are appropriate for smaller cavities where the isthmus width is one-third or less the buccolingual width of the tooth and the restoration is not subject to heavy occlusal forces.33
Shade. Before placing the rubber dam, the clinician should use an adjacent nonrestored tooth as a guide for selecting the base restoration shade. Currently, a limited number of shades are available for the heavy-body composites.
Isolation.
Administer the anesthetic to the patient and place the rubber dam. The use of a rubber dam is mandatory for adhesive posterior restorations, since isolation by other means usually is not adequate.34 Use waxed floss to ligate the teeth to be restored (Figure 3
).
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Perioprobe.
Use a perio-probe to measure the depth of the preparation in both the occlusal and proximal areas. Most manufacturers of heavy-body resins recommend bulk filling in increments no larger than 5 mm. In the placement technique shown (Figures 1
and 2
), the maximum bulk of composite cured at once is approximately 3.0 to 3.5 mm. Until more clinical studies are conducted, it may not be prudent (and it is not usually necessary) to bulk-cure 5 mm of material (Figure 5
).
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Light-body composite resin. Apply a 0.5- to 1.0-mm layer of flowable light-body composite resin in the proximal box at the gingival margin and across the entire pulpal floor and light-cure the resin. The flowable resin is an intermediate restorative material placed between the dentin hybrid layer and the heavy-body composite. Many researchers believe that flowable composite resins may partially compensate for the stress caused by polymerization shrinkage because of their low modulus elastomeric properties.37,38
Heavy-body restorative.
Place the heavy-body restorative material in 3.0- to 3.5-mm increments. The dentist builds the composite resin to contour and light-cures. The occlusal margin of the material should be just shy of the dentoenamel junction. This should leave approximately 1.0 to 1.5 mm of space for placement of the translucent enamel shade. (Because these composite resins do not slump, the primary anatomy can be easily sculpted at one time over the entire surface.) If the teeth are malaligned or if achieving proper contact seems doubtful, the dentist should use the contact-forming instrument before curing (Figure 6
). After curing, tints can be placed to mimic a natural appearance if desired (Figure 7
).
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The dentist then uses aluminum oxide finishing discs to remove flash at the proximal boxes, to contour occlusal embrasures, and to create proper marginal ridge contour.
The rubber dam is removed and the occlusion is checked with articulating paper; the occlusion and marginal excess are then adjusted with carbide finishing burs. It is best to use the bur in a high-speed hand-piece without water and use short light strokes while the assistant blows air on the tooth for good visibility. Minimal finishing should be necessary if the composite resin was sculpted to the correct contour. Excessive finishing can jeopardize marginal integrity and resin longevity (Figure 9
).39,40 Final finishing and polishing are achieved with impregnated rubber instruments used in a slow-speed handpiece.
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| DISCUSSION |
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Direct resins are by their nature conservative. Only the existing restoration (if any) and diseased tooth structure are removed. The remaining healthy tooth structure remains intact. Extension for prevention or retention is no longer necessary. The restoration is made to fit the requirements of the tooth, instead of the tooth being made to fit the requirements of the restoration.
Conservation of healthy tooth structure is a significant benefit to patients. Because people are living longer and keeping their teeth, it is more important than ever to conserve tooth structure if future treatment becomes necessary. Should part of the remaining tooth structure become fractured or diseased at a later time, the tooth usually can be restored without preparing the entire tooth again. Better materials and techniques can be expected in the future. By conserving as much tooth structure as possible now, patients will have improved options available whenand ifthey ever need to undergo treatment again.
Tooth reinforcement is another benefit of posterior bonded composite resin restorations. Proper adhesive techniques, combined with proper composite resin placement, strengthen the remaining healthy tooth structure.4244 This property, along with a coefficient of thermal expansion of resins that is closer to that of tooth structure than the thermal expansion of metals is to that of teeth, should reduce the potential for cusp fracture.
When done properly, adhesively sealed enamel margins have consistently shown resistance to microleakage.45 Although a complete seal of dentin margins has been shown to occur on an inconsistent basis, microleakage is still significantly reduced in these restorations when compared with nonadhesive restorations.46 Furthermore, thoroughly hybridized dentin can reduce postoperative sensitivity and, should marginal breakdown eventually occur, possibly provide a barrier to bacteria-caused pulpal inflammation and secondary caries over the long term.47
Although they have been in use for only a short time compared with amalgam restorations, composite resin restorations have demonstrated similar clinical longevity.4850 This is in spite of the fact that the earlier composite resins and adhesives as well as the placement techniques are considered historical by todays standards. Even better results can be predicted for currently used materials.
Finally, the most obvious benefit of posterior composite resins is esthetics. In fact, much of the current trend toward the use of posterior composite resins has been driven by patient demands for increased esthetics in all areas of the mouth.
| CONCLUSION |
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years, information about clinical performance is lacking. These materials do not have a definitive track record. Clinical trials are under way with some of them, but little information has been published.51 At least one report somewhat contradicts some of the manufacturers claims.52 On the other hand, because some of these materials do not differ significantly from their medium-body predecessors, it may be possible to extrapolate predicted clinical performance. If clinical trials demonstrate physical properties and performance that are as good asor better thanthose of current universal medium-body composite resins, then these new heavy-body composite resins will likely dominate the posterior resin market.
In our opinion, the better handling characteristics that allow a shorter, simplified placement technique will be the reason dentists will use these new heavy-body resins. Finally, because dentists who use amalgam will find the transition to this composite resin placement technique easier, the downward trend in amalgam use will undoubtedly accelerate.
| FOOTNOTES |
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| REFERENCES |
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