USING COMPOSITE RESIN AS A
KARL F. LEINFELDER, D.D.S., M.S.
^^ om posite resins have been available to the dental profession for nearly 25 years.1Since their introduction in the middle ’60s, their physical and mechanical characteristics have been improved. By decreasing the average particle size and increasing the filler loading, they have been made considerably more wear resistant. Current formulations are 10 to 15 times more resistant to occlusal stresses than the original products.23 In fact, some of the newest formulations are almost as wear resistant as amalgam. Perhaps the greatest problem associated with posterior composite resins is technique sensitivity. Unless exacting procedures are used when placing
the material, failure is almost certain. One of the more serious byproducts of this condition is secondary caries. This unfortunate situation has discouraged many clinicians from using composite resins in posterior teeth. This paper discusses the conditions under which posterior composite resin can be used successfully for proximal-occlusal restorations. It also provides guidelines for selecting material(s), using appropriate techniques and treating the restored tooth over long periods. SELECTION CRITERIA
One of the most important factors in considering a tooth for restoration with a composite resin is the location of the centric
holding area. In general, the inclusion of strong centric stops on the occlusal surface of the proposed restoration must be avoided. Failure to comply with this important consideration may lead to serious problems. To begin with, the wear rate is appreciably higher when the antagonistic cusp rests firmly on the surface of the composite resin restoration. In addition, some of the composite resins are prone to bulk failure when subjected to concentrated occlusal stresses. Sometimes the occlusal contact maybe shifted slightly up the incline plane onto the enamel surface without interfering with the functional occlusion. This procedure can be accomplished by careful enamelplasty in conjunction with conventional articulating paper with the teeth in centric contact. Another important considera tion is the anticipated depth of the gingival floor on the approximal surface. The deeper the box portion of the cavity preparation, the thinner the enamel wall in cross section. As the enamel becomes thinner, the potential for adequately bonding the composite resin decreases. Because the proximal aspect of the Class II composite restoration is the Achilles’ heel, this is a most important consideration. Although many of the newer dentin bonding agents are appreciably superior to their predecessors, none has the potential for bonding to dentin as well as they do to etched enamel. Therefore, the sound enamel must be preserved as much as possible. One more important consideration in the decision to place a posterior composite resin is the location and size of the restorations. In general, the more distally located the restoration, the greater the rate of wear. As compared with the mandibular JADA, Vol. 122, April 1991
65
first prem olar, all other locations tend to result in a higher rate of wear. As a general rule, posterior com posite resins in molars commonly w ear away approxim ately twice as fast as those in premolars. The buccal-lingual width of the restorations is also an im portant consideration. The greater the dim ension of the isthmus, the faster the rate of wear. The reason, of course, is related to the am ount of m asticatory stress applied to the surface. The clinician can choose from m any commercially available posterior composite resins. Handling characteristics, surface texture and even more im portantly, long-term resistance to w ear differ greatly among m aterials. These differences have been determ ined by extended clinical studies conducted under well-defined and controlled conditions. Such information, unfortunately, cannot come from the laboratory but only from in vivo investigations following a rigid protocol. However, progress is being m ade in this area of research. Not only are the brands of composite resin num erous but so also are the types. Perhaps the best way to classify these m aterials is according to the size of the filler particle. In general, there are four basic groups. The size of the filler particle ranges from 0.04 to nearly 50 m icrons (Table). This classification system is interesting because each category is larger or sm aller than the adjacent group by a factor of ten. Currently, only three of these categories are widely used by the clinician. In m ost practices, Adaptic (J&J) and Concise (3M) are not used widely as restorative m aterials because of the relative roughness of the finished surface. 66
JADA, Vol. 122, April 1991
TABLE 1
CLASSIFICATION OF COMPOSITE RESINS ACCORDING TO PARITE SIZE CATEGORY
AVERAGE P A R T IC L E S IZ E
Traditional
30-50
Interm ediate
1-5
Fine
0.5-1.0
Microfil
0.04-0.06
(m i c r o n s )
EXAM PLES
Adaptic Concise P-10 P-50 Adaptic II Occlusin Bis Fil P Visiomolar RO Ful Fil Post Com II Herculite XR Charisma Dentin Prisma APH Heliomolar RO *Durafill *Silux Plus *Helioprogress
J&J 3M Co. 3M Co. 3M Co. J&J ICI/COE Bisco ESPE L.D. Caulk Pentron Kerr Kulzer Coltene L.D. Caulk Vivadent Kulzer 3M Co. Vivadent
*Used prim arily for an terio r restorations. Inform ation about the m anufacturers of the products m entioned in this article m aybe available from the authors. N either the authors nor the A m erican D ental Association has any com m ercial interests in the products m entioned.
Although m ost of the current composite resins belong to the interm ediate group, a growing num ber are becoming members of the group identified as “fine.” The advantage to the latter group is th at the surface of the finished restoration can be polished to a high state of luster. Finally, one more group of composite resins may be classified according to particle size. Identified as hybrids, this group of m aterials has two different sizes of filler particles, one of which is a microfill or colloidal silica, the other a larger sized filler. Because nearly all composite resins on the m arket contain varying percen tages of microfill, it makes it difficult to determ ine which are hybrids. In general, if the total microfill content ranges between 15 percent and 20 percent, then
the m aterial may be classified as a hybrid. Material selection should be based prim arily on the results of long-term clinical studies. Unfortunately, as stated before, no laboratory test will predict the relative perform ance of any posterior composite resin. Compressive or tensile strength, volum etric shrinkage, modulus of elasticity or even hardness will not tell the clinician anything about how m uch one m aterial will perform better than another. Because standardized criteria can be used to evaluate objectively the clinical perform ance of any restorative material, more and more clinical studies are being published. The dentist should select from only those materials that have been subjected to wellcontrolled and independently
conducted studies. As a rule, the m anufacturer will supply reprints of all clinical studies related to their particular material. C A V IT Y P R E P A R A T IO N
Before initiating the operative procedure, the clinician m ust achieve adequate m oisture control. Failure to m aintain a dry field during the restorative procedure invariably will result in clinical failure. The m ost critical aspect of the restorative process concerns the acid etching process as well as the insertion and polymerization of the composite resin. Realistically, the only way th at complete m oisture control can be achieved is with a properly placed rubber dam. Protection from salivary contam ination as well as from the fluids in the gingival crevice is needed. To control m oisture contam ination by m eans other than the rubber dam, a new system has been developed th at stem s the flow of salivary fluids from the parotid duct. Capable of absorbing large am ounts of fluid, the adhesive patches m aintain a
relatively dry m outh for at least an hour. Unfortunately, they don’t prevent possible contam ination by crevicular fluids. In general, the cavity preparation should be as conservative as possible. The basic reason, of course, is th at wear resistance of the restorations is strongly related to size of the preparation. Although no long term studies have dealt with the ideal cavity preparation, it is suggested that the preparation should be patterned after that commonly used with the amalgam preparation. All the internal line angles should be rounded and the occlusal cavosurface should not be beveled. Perhaps the rationale for this kind of cavity preparation is related to the fact th at in the majority of cases, the clinician is replacing an existing amalgam restoration. In the past, beveling of the occlusal cavosurface margin was thought to increase the surface area of the enamel for bonding, thereby reducing microleakage. Furtherm ore, it was suggested that beveling would expose the ends of
Concentrated occlusal stress may cause a bulk fracture in the com posite resin.
the enamel rods rather than the sides, enhancing composite resin bonding to the etched enamel. At least one clinical study, however, has shown that beveling does not enhance the restoration perfor mance.4In fact, a trend over a twoyear period suggested that beveling may result in an increase in wear. One of the major problems associated with beveling is th at the process increases the w idth of the cavity preparation. This in turn increases the probability of including the centric holding areas. Finally, it may be more difficult to establish the actual margin between the restoration and the cavity preparation when beveling is used. Beveling should be restricted to the gingival m argin to increase the potential for bonding since it is im portant to retain as m uch enam el as possible. R E S T O R A T IV E PROCEDURES
Before matrixing, it is im portant to place a thin layer of glass ionom er over all of the dentinal surfaces. The m aterial should be extended all the way to the dentinal enam el junction. Deep excavations should first be covered w ith a thin layer of calcium hydroxide. Although either the conventional form of glass ionom er or the photocured variety is acceptable, the latter sets faster. Furtherm ore, some photocured systems bond better to the dentinal surfaces th an those that set conventionally. Glass ionomers have many advantages w hen used as liners under the composite resin, particularly in posterior teeth. First, the glass ionom er effectively releases fluoride ions th at diffuse into the underlying dentin to an average depth of 35-50 microns.57 Because posterior composite resins are considerably more prone to JADA, Vol. 122, April 1991
67
developing secondary caries than are amalgams, the appropriate use of a glass ionom er is important. A nother im portant advantage of glass ionom ers is th at they tend to reduce microleakage8,9because the coefficient of therm al expansion of these m aterials is very similar to tooth structure, particularly dentin.10The closer the coefficients of therm al expansion between two m aterials, the less likely that micro leakage will occur. Recent studies have also shown th at microbial activity is considerably reduced in the presence of fluoride ions. Finally, the use of glass ionom ers as liners under posterior composite resins tends to reduce the potential for postoperative sensitivity. Although the exact reason has not been documented, it may be related to the fact that using a liner reduces the volume of com posite resin needed to fill the preparation. There is a relationship betw een volum etric shrinkage and the potential for postoperative sensitivity. It generally is not necessary to etch the glass ionom er before applying the bonding agent.11As a rule, the bond strength of the overlying composite resin is relatively the same w hether the surface is etched or not. In both cases the tensile bond strength betw een the two m aterials is approxim ately 500 pounds per square inch or about three megapascals. Furtherm ore, because all of the m argins of the preparation consist of enamel, the overall retention of the restoration is not dependent on its retention to the glass ionomer. It is possible, however, th at etching and subsequent washing of the enamel surface will result in some of the diluted phosphoric acid contacting and etching the surface of the glass ionomer. After acid etching the enamel, 68
JADA, Vol. 122, April 1991
the bonding agent is applied. At this point, a properly wedged and contoured matrix band is applied. The composite resin is placed in small increm ents (a m aximum of two m illimeters), each followed by a 20- to 40-second exposure from the light-curing unit. While the num ber of segments depends on the size of the cavity preparation, m ost conventionally sized cavity preparations should be restored with no less than three increm ents. R ecent studies have shown that the volum etric shrinkage that accompanies the polymerization process is of great clinical significance. As the composite resin begins to contract, it actually pulls various components of the tooth toward the long axis of the tooth.12As the lingual and buccal cusps are draw n toward one another, pressure is placed on the restoration. This causes stresses to be transferred in a pulpal direction, resulting in pressure on the odontoblastic process. This then causes pain commonly referred to as “postoperative” sensitivity. The greater the volum etric shrinkage of a material,
the greater the potential for this problem. The best way of avoiding this undesirable effect is to insert the composite resin in multiple segm ents or layers. Incidentally, the postoperative sensitivity or pain associated with this phenom enon is characterized by two classic symptoms: sensitivity to cold tem peratures and pain on a given tooth during m astication. Under these two conditions, the pain can be elim inated by a simple procedure. W ithout the aid of an anesthetic, a small groove is developed through the central fissure all the way to the base of the restoration. The groove should be extended to but not include the marginal ridges. Pressure on the restoration at this point will no longer generate sensitivity because the cutting operation allows the buccal and lingual cusps to return to their original positions. The defect generated by the small diam eter bur (no. 245/225) can then be restored with the same type of composite resin using standard procedures. Although the added composite resin will also undergo polymerization
Wear Rates of Several Posterior Composite Resins at Three Years
Amai CI.FP P-50 Helio P-30 AD-2 Here Bis-F OCC F-FII P -10
Composite The wear rates of composite resins are compared.
The marginal integrity of a composite resin without the surface penetrating sealant (A) is less intact than one with sealant (B).
shrinkage, it is generally of no clinical significance. Because the volume of the com posite resin is relatively minor, th e small am ount of accompanying shrinkage is apparently insufficient to regenerate postoperative sensitivity. Shrinkage is directed toward the light source, w here the initial polym erization occurs. The next im portant consideration in restoring the prepared cavity relates to the m atrix band. There are two major types: conventional stainless m atrixes and those m ade of clear celluloid resin. The latter can be used in conjunction w ith a special type of wedge which transm its the curing light through it and onto the proximal surface of the restoration. Because of the light source, the direction in which curing shrinkage occurs can be controlled. Such a technique better assures optim um bonding to the enamel surface in the proximal region. Regardless of the m ethod used for m atrixing the prepared tooth, it is im portant th at the inside surface of the m atrix band be wedged tightly against the gingival margin. Failure to do so invariably will result in penetration of the bonding agent and the composite resin into the space, w hich then
will serve as an overhang. Such a condition is difficult to rectify and m ight cause irritation to the periodontal tissue and possibly secondary caries. As already discussed, the unpolymerized resin should be inserted in segments. While each portion should be light cured for 20 seconds, the final segm ent should be cured for no less than one m inute to substantially increase the resistance to wear.13 F IN IS H IN G
The effect of surfacing and finishing on the w ear resistance of posterior composite resins is quite pronounced. In m ost cases, the process is traum atizing to the surface. The finishing process readily creates m icrostructural defects that decrease the wear resistance appreciably. The energy from the finishing instrum ent readily creates num erous microcracks th at extend across and below the surface. Several microns in diam eter, these defects may extend below the surface for 20 m icrons or more. It is im por tant, therefore, to minimize the traum a during the finishing pro cess. This commonly can be accomplished by addressing the surface w ith a finishing bur at moderately high speeds, low pres
sure and copious am ounts of water. Based on the results of a long term clinical study, a new m aterial has been m arketed that will correct this problem. When properly applied to the finished surface, the w ear rate of the composite will decrease by as m uch as 50 percent. In effect, this m aterial is a surface penetrating sealant. This m aterial (Fortify, Bisco), readily flows across the surface and then penetrates into all the m icrostructural defects, where it is polymerized for 20 seconds, which causes a resolidification or refortification of the defective surface. It is not a glaze or a sealant in a conventional sense. Because of its extrem ely low viscosity and w etting ability, it penetrates below the surface of the composite resin m uch like w ater on the surface of a cloth fabric. Not only does this agent reduce the wear rate of the composite resin appreciably, it also can elim inate marginal defects. D IS C U S S IO N
Undoubtedly, the posterior composite resin plays a vital role in the restoration of teeth. Its success or failure as a restorative m aterial depends on the clinician’s ability to understand its JADA, Vol. 122, April 1991
69
limitations as well as how to use the material. Furtherm ore, posterior composite resins differ significantly with respect to wear resistance as well as handling characteristics. Before the clinician makes a decision to use a posterior composite resin, it is im portant to consider m any factors. One consideration is the location of the centric holding area. Strong occlusal contacts of the surface of the composite resin not only accelerate the process of w ear but also, with some materials, may result in bulk fracture. After a decision has been made regarding the suitability of placing the composite, it is im portant to educate the patient about the shortcomings of : Dr. Leinfelder is ; aium ni/Volker this material. | professor o f clinical : dentistry, director, First of all, it : biom aterials clinical should be : research, and acting explained th at : chairman, : D ep artm ent of composite : Biom aterials and resins do not : Restorative : Dentistry, School of have the : Dentistry, University established : of Alabam a a t track record of : Birmingham, amalgams. They : Birmingham 3 5 2 9 4 . | Address requests for are considerably : reprints to th e more difficult to : author. insert and also they take appreciably longer to place. As a result, the restorative process costs more. Secondly, the patient should be advised that annual appointm ents are im portant. Defective restorations m ust be corrected immediately. SUMM ARY
Composite resins have been improved dramatically over the last few years. Some of the newest formulations are nearly as wear
70
JADA, Vol. 122, April 1991
resistant as amalgam. Under the appropriate conditions, they may be used to restore Class I and Class II cavity preparations. Their use, however, m ust be in accordance with the conditions described in this paper. The following conditions should be followed: «" The selection of a posterior composite resin should be based on well-documented clinical data, not physical and m echanical properties. " Complete m oisture control is essential for the successful restoration of posterior teeth with composite resin. Always use a glass ionom er as a liner. The m aterial should cover all the dentin. ■" Cavity preparations should be minimal in dimension. Avoid unnecessary removal of tooth structure. » Do not bevel the occlusal cavosurface margin. ■» Insert the composite in increm ents. ■■ Minimize introduction of traum a during the finishing procedure. “ Use a surface penetrating sealant to reduce wear rate and to enhance margin integrity. “ Evaluate carefully the clinical perform ance of the restored tooth at least once a year. ■■ Discuss possible limitations of posterior composite resins as compared with amalgam restorations. ■ Inform ation about the m anufacturers of the products m entioned in this article m ay be available from the authors. N either the authors
nor the American D ental Association has any com m ercial in terests in the products mentioned. Publication of nam es of products does n ot imply endorsem ent by the A m erican D ental Association. 1. Bowen RL. Synthesis of a silica-resin filling material: progress report. J D ent Res 1958;37:90. 2. Leinfelder KF. C urrent developm ents in restorative m aterials and techniques. Jpn J Conserv D ent 1989;32:1505-11. 3. Gerbo LR, Leinfelder KF, M ueninghoff LA. Use of optical standards for determ ining w ear of posterior com posite resins. J Esthetic D ent 1990;2:148-52. 4. Isenberg BP, Leinfelder KF. Efficacy of beveling posterior composite resin preparations. J Esthetic D ent 1990;2:70-3. 5. T hornton JB, R etief DH, Bradley EL. Fluoride release from and tensile bond strength of KetacFil and Ketac-Silver to d entin and enam el. D ent Mater 1986;2:241-5. 6. Tysowsky G, Jenson ME, Sheth J. A nticariogenic potential of fluoride releasing dental restorative m aterials. J D ent Res 1988;67:145 (A bstract no. 257). 7. Retief DH, Bradley EL, D enton JC, Switzer P. Enam el and cem entum fluoride uptake from a glass ionom er cem ent. C aries Res 1984;18:250-7. 8. M aldonado A, Swartz ML, Phillips RW. An invitro study of certain properties of a glass ionom er cem ent. JADA 1978;96:785-91. 9. Leary RM, Kilgus GC, Leinfelder KF. In-vitro microleakage of glass ionom ers and dentin bonding agents. J D ent Res 1989;68:187 (Abstract no. 44). 10. Bullard RH, Leinfelder KF, Russell CM. Effect of coefficient of therm al expansion on microleakage. JADA 1988;116:871-4. 11. Sheth JJ. Effect of etching glass ionomer cem ents on bond strength to composite resin. J D ent Res 1989;68:1082-7. 12. Jensen ME, C han DCN. Polym erization shrinkage and microleakage. In: Vanherle G, Sm ith DC, eds. Posterior composite resin dental restorative m aterials. N etherlands: Peter Szule;1985:243-62. 13. Glasspoole EA, Erickson RL. Effect of fininishing a n d degree of cure or composite wear. J D ent Res 1990;68:127 (A bstract no. 145). 14. Dickinson GL, Leinfelder KF, Mazer RB, Russell CM. Effect of surface penetrating sealant on w ear rate of posterior com posite resins. JADA 1990;121:251-5.
KARL F. LEINFELDER, D.D.S., M.S.
^^ om posite resins have been available to the dental profession for nearly 25 years.1Since their introduction in the middle ’60s, their physical and mechanical characteristics have been improved. By decreasing the average particle size and increasing the filler loading, they have been made considerably more wear resistant. Current formulations are 10 to 15 times more resistant to occlusal stresses than the original products.23 In fact, some of the newest formulations are almost as wear resistant as amalgam. Perhaps the greatest problem associated with posterior composite resins is technique sensitivity. Unless exacting procedures are used when placing
the material, failure is almost certain. One of the more serious byproducts of this condition is secondary caries. This unfortunate situation has discouraged many clinicians from using composite resins in posterior teeth. This paper discusses the conditions under which posterior composite resin can be used successfully for proximal-occlusal restorations. It also provides guidelines for selecting material(s), using appropriate techniques and treating the restored tooth over long periods. SELECTION CRITERIA
One of the most important factors in considering a tooth for restoration with a composite resin is the location of the centric
holding area. In general, the inclusion of strong centric stops on the occlusal surface of the proposed restoration must be avoided. Failure to comply with this important consideration may lead to serious problems. To begin with, the wear rate is appreciably higher when the antagonistic cusp rests firmly on the surface of the composite resin restoration. In addition, some of the composite resins are prone to bulk failure when subjected to concentrated occlusal stresses. Sometimes the occlusal contact maybe shifted slightly up the incline plane onto the enamel surface without interfering with the functional occlusion. This procedure can be accomplished by careful enamelplasty in conjunction with conventional articulating paper with the teeth in centric contact. Another important considera tion is the anticipated depth of the gingival floor on the approximal surface. The deeper the box portion of the cavity preparation, the thinner the enamel wall in cross section. As the enamel becomes thinner, the potential for adequately bonding the composite resin decreases. Because the proximal aspect of the Class II composite restoration is the Achilles’ heel, this is a most important consideration. Although many of the newer dentin bonding agents are appreciably superior to their predecessors, none has the potential for bonding to dentin as well as they do to etched enamel. Therefore, the sound enamel must be preserved as much as possible. One more important consideration in the decision to place a posterior composite resin is the location and size of the restorations. In general, the more distally located the restoration, the greater the rate of wear. As compared with the mandibular JADA, Vol. 122, April 1991
65
first prem olar, all other locations tend to result in a higher rate of wear. As a general rule, posterior com posite resins in molars commonly w ear away approxim ately twice as fast as those in premolars. The buccal-lingual width of the restorations is also an im portant consideration. The greater the dim ension of the isthmus, the faster the rate of wear. The reason, of course, is related to the am ount of m asticatory stress applied to the surface. The clinician can choose from m any commercially available posterior composite resins. Handling characteristics, surface texture and even more im portantly, long-term resistance to w ear differ greatly among m aterials. These differences have been determ ined by extended clinical studies conducted under well-defined and controlled conditions. Such information, unfortunately, cannot come from the laboratory but only from in vivo investigations following a rigid protocol. However, progress is being m ade in this area of research. Not only are the brands of composite resin num erous but so also are the types. Perhaps the best way to classify these m aterials is according to the size of the filler particle. In general, there are four basic groups. The size of the filler particle ranges from 0.04 to nearly 50 m icrons (Table). This classification system is interesting because each category is larger or sm aller than the adjacent group by a factor of ten. Currently, only three of these categories are widely used by the clinician. In m ost practices, Adaptic (J&J) and Concise (3M) are not used widely as restorative m aterials because of the relative roughness of the finished surface. 66
JADA, Vol. 122, April 1991
TABLE 1
CLASSIFICATION OF COMPOSITE RESINS ACCORDING TO PARITE SIZE CATEGORY
AVERAGE P A R T IC L E S IZ E
Traditional
30-50
Interm ediate
1-5
Fine
0.5-1.0
Microfil
0.04-0.06
(m i c r o n s )
EXAM PLES
Adaptic Concise P-10 P-50 Adaptic II Occlusin Bis Fil P Visiomolar RO Ful Fil Post Com II Herculite XR Charisma Dentin Prisma APH Heliomolar RO *Durafill *Silux Plus *Helioprogress
J&J 3M Co. 3M Co. 3M Co. J&J ICI/COE Bisco ESPE L.D. Caulk Pentron Kerr Kulzer Coltene L.D. Caulk Vivadent Kulzer 3M Co. Vivadent
*Used prim arily for an terio r restorations. Inform ation about the m anufacturers of the products m entioned in this article m aybe available from the authors. N either the authors nor the A m erican D ental Association has any com m ercial interests in the products m entioned.
Although m ost of the current composite resins belong to the interm ediate group, a growing num ber are becoming members of the group identified as “fine.” The advantage to the latter group is th at the surface of the finished restoration can be polished to a high state of luster. Finally, one more group of composite resins may be classified according to particle size. Identified as hybrids, this group of m aterials has two different sizes of filler particles, one of which is a microfill or colloidal silica, the other a larger sized filler. Because nearly all composite resins on the m arket contain varying percen tages of microfill, it makes it difficult to determ ine which are hybrids. In general, if the total microfill content ranges between 15 percent and 20 percent, then
the m aterial may be classified as a hybrid. Material selection should be based prim arily on the results of long-term clinical studies. Unfortunately, as stated before, no laboratory test will predict the relative perform ance of any posterior composite resin. Compressive or tensile strength, volum etric shrinkage, modulus of elasticity or even hardness will not tell the clinician anything about how m uch one m aterial will perform better than another. Because standardized criteria can be used to evaluate objectively the clinical perform ance of any restorative material, more and more clinical studies are being published. The dentist should select from only those materials that have been subjected to wellcontrolled and independently
conducted studies. As a rule, the m anufacturer will supply reprints of all clinical studies related to their particular material. C A V IT Y P R E P A R A T IO N
Before initiating the operative procedure, the clinician m ust achieve adequate m oisture control. Failure to m aintain a dry field during the restorative procedure invariably will result in clinical failure. The m ost critical aspect of the restorative process concerns the acid etching process as well as the insertion and polymerization of the composite resin. Realistically, the only way th at complete m oisture control can be achieved is with a properly placed rubber dam. Protection from salivary contam ination as well as from the fluids in the gingival crevice is needed. To control m oisture contam ination by m eans other than the rubber dam, a new system has been developed th at stem s the flow of salivary fluids from the parotid duct. Capable of absorbing large am ounts of fluid, the adhesive patches m aintain a
relatively dry m outh for at least an hour. Unfortunately, they don’t prevent possible contam ination by crevicular fluids. In general, the cavity preparation should be as conservative as possible. The basic reason, of course, is th at wear resistance of the restorations is strongly related to size of the preparation. Although no long term studies have dealt with the ideal cavity preparation, it is suggested that the preparation should be patterned after that commonly used with the amalgam preparation. All the internal line angles should be rounded and the occlusal cavosurface should not be beveled. Perhaps the rationale for this kind of cavity preparation is related to the fact th at in the majority of cases, the clinician is replacing an existing amalgam restoration. In the past, beveling of the occlusal cavosurface margin was thought to increase the surface area of the enamel for bonding, thereby reducing microleakage. Furtherm ore, it was suggested that beveling would expose the ends of
Concentrated occlusal stress may cause a bulk fracture in the com posite resin.
the enamel rods rather than the sides, enhancing composite resin bonding to the etched enamel. At least one clinical study, however, has shown that beveling does not enhance the restoration perfor mance.4In fact, a trend over a twoyear period suggested that beveling may result in an increase in wear. One of the major problems associated with beveling is th at the process increases the w idth of the cavity preparation. This in turn increases the probability of including the centric holding areas. Finally, it may be more difficult to establish the actual margin between the restoration and the cavity preparation when beveling is used. Beveling should be restricted to the gingival m argin to increase the potential for bonding since it is im portant to retain as m uch enam el as possible. R E S T O R A T IV E PROCEDURES
Before matrixing, it is im portant to place a thin layer of glass ionom er over all of the dentinal surfaces. The m aterial should be extended all the way to the dentinal enam el junction. Deep excavations should first be covered w ith a thin layer of calcium hydroxide. Although either the conventional form of glass ionom er or the photocured variety is acceptable, the latter sets faster. Furtherm ore, some photocured systems bond better to the dentinal surfaces th an those that set conventionally. Glass ionomers have many advantages w hen used as liners under the composite resin, particularly in posterior teeth. First, the glass ionom er effectively releases fluoride ions th at diffuse into the underlying dentin to an average depth of 35-50 microns.57 Because posterior composite resins are considerably more prone to JADA, Vol. 122, April 1991
67
developing secondary caries than are amalgams, the appropriate use of a glass ionom er is important. A nother im portant advantage of glass ionom ers is th at they tend to reduce microleakage8,9because the coefficient of therm al expansion of these m aterials is very similar to tooth structure, particularly dentin.10The closer the coefficients of therm al expansion between two m aterials, the less likely that micro leakage will occur. Recent studies have also shown th at microbial activity is considerably reduced in the presence of fluoride ions. Finally, the use of glass ionom ers as liners under posterior composite resins tends to reduce the potential for postoperative sensitivity. Although the exact reason has not been documented, it may be related to the fact that using a liner reduces the volume of com posite resin needed to fill the preparation. There is a relationship betw een volum etric shrinkage and the potential for postoperative sensitivity. It generally is not necessary to etch the glass ionom er before applying the bonding agent.11As a rule, the bond strength of the overlying composite resin is relatively the same w hether the surface is etched or not. In both cases the tensile bond strength betw een the two m aterials is approxim ately 500 pounds per square inch or about three megapascals. Furtherm ore, because all of the m argins of the preparation consist of enamel, the overall retention of the restoration is not dependent on its retention to the glass ionomer. It is possible, however, th at etching and subsequent washing of the enamel surface will result in some of the diluted phosphoric acid contacting and etching the surface of the glass ionomer. After acid etching the enamel, 68
JADA, Vol. 122, April 1991
the bonding agent is applied. At this point, a properly wedged and contoured matrix band is applied. The composite resin is placed in small increm ents (a m aximum of two m illimeters), each followed by a 20- to 40-second exposure from the light-curing unit. While the num ber of segments depends on the size of the cavity preparation, m ost conventionally sized cavity preparations should be restored with no less than three increm ents. R ecent studies have shown that the volum etric shrinkage that accompanies the polymerization process is of great clinical significance. As the composite resin begins to contract, it actually pulls various components of the tooth toward the long axis of the tooth.12As the lingual and buccal cusps are draw n toward one another, pressure is placed on the restoration. This causes stresses to be transferred in a pulpal direction, resulting in pressure on the odontoblastic process. This then causes pain commonly referred to as “postoperative” sensitivity. The greater the volum etric shrinkage of a material,
the greater the potential for this problem. The best way of avoiding this undesirable effect is to insert the composite resin in multiple segm ents or layers. Incidentally, the postoperative sensitivity or pain associated with this phenom enon is characterized by two classic symptoms: sensitivity to cold tem peratures and pain on a given tooth during m astication. Under these two conditions, the pain can be elim inated by a simple procedure. W ithout the aid of an anesthetic, a small groove is developed through the central fissure all the way to the base of the restoration. The groove should be extended to but not include the marginal ridges. Pressure on the restoration at this point will no longer generate sensitivity because the cutting operation allows the buccal and lingual cusps to return to their original positions. The defect generated by the small diam eter bur (no. 245/225) can then be restored with the same type of composite resin using standard procedures. Although the added composite resin will also undergo polymerization
Wear Rates of Several Posterior Composite Resins at Three Years
Amai CI.FP P-50 Helio P-30 AD-2 Here Bis-F OCC F-FII P -10
Composite The wear rates of composite resins are compared.
The marginal integrity of a composite resin without the surface penetrating sealant (A) is less intact than one with sealant (B).
shrinkage, it is generally of no clinical significance. Because the volume of the com posite resin is relatively minor, th e small am ount of accompanying shrinkage is apparently insufficient to regenerate postoperative sensitivity. Shrinkage is directed toward the light source, w here the initial polym erization occurs. The next im portant consideration in restoring the prepared cavity relates to the m atrix band. There are two major types: conventional stainless m atrixes and those m ade of clear celluloid resin. The latter can be used in conjunction w ith a special type of wedge which transm its the curing light through it and onto the proximal surface of the restoration. Because of the light source, the direction in which curing shrinkage occurs can be controlled. Such a technique better assures optim um bonding to the enamel surface in the proximal region. Regardless of the m ethod used for m atrixing the prepared tooth, it is im portant th at the inside surface of the m atrix band be wedged tightly against the gingival margin. Failure to do so invariably will result in penetration of the bonding agent and the composite resin into the space, w hich then
will serve as an overhang. Such a condition is difficult to rectify and m ight cause irritation to the periodontal tissue and possibly secondary caries. As already discussed, the unpolymerized resin should be inserted in segments. While each portion should be light cured for 20 seconds, the final segm ent should be cured for no less than one m inute to substantially increase the resistance to wear.13 F IN IS H IN G
The effect of surfacing and finishing on the w ear resistance of posterior composite resins is quite pronounced. In m ost cases, the process is traum atizing to the surface. The finishing process readily creates m icrostructural defects that decrease the wear resistance appreciably. The energy from the finishing instrum ent readily creates num erous microcracks th at extend across and below the surface. Several microns in diam eter, these defects may extend below the surface for 20 m icrons or more. It is im por tant, therefore, to minimize the traum a during the finishing pro cess. This commonly can be accomplished by addressing the surface w ith a finishing bur at moderately high speeds, low pres
sure and copious am ounts of water. Based on the results of a long term clinical study, a new m aterial has been m arketed that will correct this problem. When properly applied to the finished surface, the w ear rate of the composite will decrease by as m uch as 50 percent. In effect, this m aterial is a surface penetrating sealant. This m aterial (Fortify, Bisco), readily flows across the surface and then penetrates into all the m icrostructural defects, where it is polymerized for 20 seconds, which causes a resolidification or refortification of the defective surface. It is not a glaze or a sealant in a conventional sense. Because of its extrem ely low viscosity and w etting ability, it penetrates below the surface of the composite resin m uch like w ater on the surface of a cloth fabric. Not only does this agent reduce the wear rate of the composite resin appreciably, it also can elim inate marginal defects. D IS C U S S IO N
Undoubtedly, the posterior composite resin plays a vital role in the restoration of teeth. Its success or failure as a restorative m aterial depends on the clinician’s ability to understand its JADA, Vol. 122, April 1991
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limitations as well as how to use the material. Furtherm ore, posterior composite resins differ significantly with respect to wear resistance as well as handling characteristics. Before the clinician makes a decision to use a posterior composite resin, it is im portant to consider m any factors. One consideration is the location of the centric holding area. Strong occlusal contacts of the surface of the composite resin not only accelerate the process of w ear but also, with some materials, may result in bulk fracture. After a decision has been made regarding the suitability of placing the composite, it is im portant to educate the patient about the shortcomings of : Dr. Leinfelder is ; aium ni/Volker this material. | professor o f clinical : dentistry, director, First of all, it : biom aterials clinical should be : research, and acting explained th at : chairman, : D ep artm ent of composite : Biom aterials and resins do not : Restorative : Dentistry, School of have the : Dentistry, University established : of Alabam a a t track record of : Birmingham, amalgams. They : Birmingham 3 5 2 9 4 . | Address requests for are considerably : reprints to th e more difficult to : author. insert and also they take appreciably longer to place. As a result, the restorative process costs more. Secondly, the patient should be advised that annual appointm ents are im portant. Defective restorations m ust be corrected immediately. SUMM ARY
Composite resins have been improved dramatically over the last few years. Some of the newest formulations are nearly as wear
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JADA, Vol. 122, April 1991
resistant as amalgam. Under the appropriate conditions, they may be used to restore Class I and Class II cavity preparations. Their use, however, m ust be in accordance with the conditions described in this paper. The following conditions should be followed: «" The selection of a posterior composite resin should be based on well-documented clinical data, not physical and m echanical properties. " Complete m oisture control is essential for the successful restoration of posterior teeth with composite resin. Always use a glass ionom er as a liner. The m aterial should cover all the dentin. ■" Cavity preparations should be minimal in dimension. Avoid unnecessary removal of tooth structure. » Do not bevel the occlusal cavosurface margin. ■» Insert the composite in increm ents. ■■ Minimize introduction of traum a during the finishing procedure. “ Use a surface penetrating sealant to reduce wear rate and to enhance margin integrity. “ Evaluate carefully the clinical perform ance of the restored tooth at least once a year. ■■ Discuss possible limitations of posterior composite resins as compared with amalgam restorations. ■ Inform ation about the m anufacturers of the products m entioned in this article m ay be available from the authors. N either the authors
nor the American D ental Association has any com m ercial in terests in the products mentioned. Publication of nam es of products does n ot imply endorsem ent by the A m erican D ental Association. 1. Bowen RL. Synthesis of a silica-resin filling material: progress report. J D ent Res 1958;37:90. 2. Leinfelder KF. C urrent developm ents in restorative m aterials and techniques. Jpn J Conserv D ent 1989;32:1505-11. 3. Gerbo LR, Leinfelder KF, M ueninghoff LA. Use of optical standards for determ ining w ear of posterior com posite resins. J Esthetic D ent 1990;2:148-52. 4. Isenberg BP, Leinfelder KF. Efficacy of beveling posterior composite resin preparations. J Esthetic D ent 1990;2:70-3. 5. T hornton JB, R etief DH, Bradley EL. Fluoride release from and tensile bond strength of KetacFil and Ketac-Silver to d entin and enam el. D ent Mater 1986;2:241-5. 6. Tysowsky G, Jenson ME, Sheth J. A nticariogenic potential of fluoride releasing dental restorative m aterials. J D ent Res 1988;67:145 (A bstract no. 257). 7. Retief DH, Bradley EL, D enton JC, Switzer P. Enam el and cem entum fluoride uptake from a glass ionom er cem ent. C aries Res 1984;18:250-7. 8. M aldonado A, Swartz ML, Phillips RW. An invitro study of certain properties of a glass ionom er cem ent. JADA 1978;96:785-91. 9. Leary RM, Kilgus GC, Leinfelder KF. In-vitro microleakage of glass ionom ers and dentin bonding agents. J D ent Res 1989;68:187 (Abstract no. 44). 10. Bullard RH, Leinfelder KF, Russell CM. Effect of coefficient of therm al expansion on microleakage. JADA 1988;116:871-4. 11. Sheth JJ. Effect of etching glass ionomer cem ents on bond strength to composite resin. J D ent Res 1989;68:1082-7. 12. Jensen ME, C han DCN. Polym erization shrinkage and microleakage. In: Vanherle G, Sm ith DC, eds. Posterior composite resin dental restorative m aterials. N etherlands: Peter Szule;1985:243-62. 13. Glasspoole EA, Erickson RL. Effect of fininishing a n d degree of cure or composite wear. J D ent Res 1990;68:127 (A bstract no. 145). 14. Dickinson GL, Leinfelder KF, Mazer RB, Russell CM. Effect of surface penetrating sealant on w ear rate of posterior com posite resins. JADA 1990;121:251-5.
