Dentinal Bonding Agents Versus Glass-Ionomer Cements

Restorative Dentistry

Dentinal bonding agents versus glass-ionomer cements

John W. McLean*

Aiistract The long-term bonding of dental materiais to dentin remains an area of great controversy and the results of in vitro testing do not always reflect those found in vivo. T¡ie clinician is faced with a large number of dentinal bonding agents that have had limited testing in vivo and are frequently replaced before any long-term clinical testing has been completed. Glass-ionomer cements, although having a longer history of good adhesion to dentin, are not suitable for use in high-stress- bearing areas. The selection of materials for specific clinical situations has become more and more difficult. This paper gives a personal view ofthe history and evolution of both resin bonding agents and glass-ionomer cements and their potential in clinical use. (Quintessence Int ¡996:27:659-667,)

Clinical relevance glycerophosphoric acid dimethacrylate, was used to bond an autocuring acrylic resin, Sevriton, to dentin. Glass-ionomer cements should be useti to utilize Work at the Eastman Dental Hospital, London, their main advantages of fluoride release and showed that glycerophosphoric acid dimethacrylate Iong-ierm adhesion to tooth structure. Dentinal increased adhesion to dentin by penetrating the surface bonding agents provide excellent serace when used and forming an intermediate layer, now called the in small cavities. Because they exhibit lower me- hybrid zone. This was detected because the dentin chanical strength than do the currently available exhibited an intense affinity for hematoxylin staitiitig, dual-cured resin cements, polyacid-modifted resin and the zone of altered dentin had affinities similar to composite cetncnts and resin-mo dined glass- those of calcified dentin in an exaggerated form,^ It is ionomer cements should only be used for conven- interesting to note that, despite the use of a methyl tional cementation. methacrylate resin as the restorative material, the pulpal reaction to Sevriton plus cavity seal was similar in intensity to that recorded for other autocured resins.^ Although Sevriton was capable of causing an acute inflammatory reaction when placed in moder- History of dentinai bonding ately deep, unlined cavities, the usual outcome of this The first attempt to develop an adhesive system for reaction was resolution, bonding to dentin was made by Hagger,' a Swiss Buonocore and Quigley'' used giycerophosphoric chemist working for the Amalgamated Dental Com- acid dimethacrylate in their early experiments and pany in London and Zürich in 1951, The first conciuded that the phosphate groups in SevHton cavity commercial product (Sevriton Cavity Seal), based on seal seemed ideally suited for chemical combination with constituents ofthe dentin, and they confirmed the earlier findings of Kramer and McLean,- Although * Honnrao' Senior Research Fdlow, Eastman Dental Institute, London, this work appeared to usher in a new era in dentinal England, bonding, the idea lay dormant for a long period Reprint requests: Dr John W, McLean, tO Witdwood Road, London because the restorative materials used in the 1950s NWIl 6TB, England, were all based on methyl methacrylates of relatively Based on a paper presented to the Ameriean Academy of Resioiative high viscosity that contained free monomers and Dentistry, Chicago, 19 Feb 1994,

Quintessence International Volume 27, Number tO/1996 659 exhibited high shrinkage during polymerization, prop- cal bonding could further enhance the bond, but. at the erties that were less than ideal for securing long-term present time, there is evidence that even^^wlien bonding to denlin. Subsequent clinical trials showed established, the bond is of a transitory nature. that the phosphate bonds, supposedly formed with A number of excellent reviews trace the history of calcium ions of the dentinal surface, were not of a dentinal bonding through the various generations of lasting nature and were hydrolytically unstable, a resin bonding agents.'^"'^ A comprehensive artide problem that can still arise with the current resin comparing glass-ionomer cement and resin composite bonding agents. systems has recently helped to clarify this controversial It was not until 1958 that the first low-shrinkage area.''^ It is generally agreed that the major difference resin was produced by Schmidt and Purrmann in between the success of enamel bonding and that of Germany; the material was based on their novel dentinal bonding lies in the substrate surface. Enamel development of the low-viscosity epimine resins and is composed largely of hydroxyapatite and has a very marketed under the trade name, P-Cadurit.^ In 1959, low water content." By contrast, dentin varies con- Bowen'' filed his first patent in the United States on his siderably and may be very dense, with only 1% of the now-famous bis-GMA resin and produced a dental surface at the dentinoenamel junction consisting of restorative material containing vinyl s il ane-treated tubules, or very porous at the pulpal floor, where as fused silica. More recently, the urethane dimethacry- much as 22% of the total surface area may consist of lates (ICI Dental) were developed by Knight et al' for dentinal tubules. Dentin is permeated by fluids trans- industrial use. Subsequently, Forster and Walker, ported from the pulp, and there is both loosely and working at the Amalgamated Dental Company, made a tightly bound water even in enamel. urethane dimethacrylate resin for use in resin compos- However, because enamel is an ion exchanger and ite dental materials.^'^ These new resins have the dentin is a living material subject to change, one is advantage of higher molecular weight, lower viscosity, trying to bond to sfufting sand rather than to solid and a certain degree of toughness in the urethane rock. Under such conditions, the adhesive bond must moiety, together with less staining than bis-GMA. have a dynamic character too. It will be broken as the Further work by ICI resulted in the introduction of the substrate changes and must be capable of being fyst visible light-curing systems, which started a new re-formed. Once broken, covalent chemical bonds era in restorative dentistry and made possible the cannot be re-formed. Dentinal adhesives may fail for modem methods of dentinal bonding with low- this very reason. In contrast, the ionic and polar bonds viscosity photocured resins,'" that attach the glass-ionomer cement to the substrate can be reestablished; this, together with the multi- Modern dentinal bonding agents plicity of the adhesive bonds and setting stress characteristics of the cement,'^•^' may account for this The principal barrier to effective adhesion to denta] material's unique property of long-term adhesion tissue is water. Water will compete with a potential under oral conditions. adhesive for the surlace of a substrate and can also Although measurements of hond strengths reveal hydrolyze adhesive bonds. Modern dentinal bonding much lower values for glass-ionomer cements than for agents have evolved from the original concept of dentinal bonding agents used with resin composites, increasing dentinal permeability and wettability and when these two materials were first used for the promoting bonding to the smear layer, as in the case of restoration of erosion/abrasion lesions without cavity the early Sevriton ca\nty seal, to the partial removal of preparation, the glass-ionomer materials had better the smear layer, and fmally to the use of stronger long-term retention rates.'^"-- It is thought that etchants to modify or remove the smear layer and glass-ionomer materials are not affected by sclerotic obtain some form of micromechanical retention (Fig dentin as much as are some dentinal bonding agents. 1). Nakabayashi et al" have described monomers, Also, the setting stress characteristics favor the glass- based on 4-methacryioxyethy] trimelhtate anhydride, ionomer materials. '^•-' Davidson^' considered that the that contain both hydiophilic and hydrophobic chemi- ability of glass-ionomer cements to withstand stress cal groups that can penetrate etched dentin and can be explained by an internal fracture mechanism by polymerize in situ. This resin impregnation creates a which material can easily reshape to enforced new transitional layer that is neither resin nor tooth, but a forms.-' hybrid of the two (Fig 2). Sevriton cavity seal was the It seems logical that the ideal method of clitiically first commercial material to use this approach. Chemi- testing the retention of bonded resin composite and

660 Quintessence International Volume 27, Number io/iqqR Fig 1 Evolution of dentinal bonding, from fhe early Fig 2 Formation of fhe hybrid layer in intertubular dentin. attempts fo bond to the smear iayer to fotal removal by acid etching and bonding to infertubular dentin.

Fig 3 Failure of wetfing by resin primers in ffie denfinal Fig 4 Penetration of denfinal bonding agents to form tags tubules. in fhe dentinal tubules. Ttie primer should wet the surface of the tubule prior fo the application of fhe bonding agenf.

glass-ionomer restorations should be in Class V adhesive resin system,^^ The dentinal surface and the erosion lesions without cavity preparation over a smear layer after tooth preparation show many varia- period of at least 3 years,-^ Unfortunately, clinical tions, with the result that short-term in vitro studies of trials are difficult and take years to complete, so that the strength of dentinal bonds cannot always give the each generation of dentinal bonding agents tends to be clinician an accurate picture of the future clinical superseded before long-term clinical trials can be situation, Paul and Schärer-'' believed that there has ttndertaken and produce meaningful results. Therefore been a discrepancy between the results of laboratory the profession has had to rely mainly on short-term in testing and the in vivo performance of the dentinal vitro testing of bond strengths as a measure of a bonding systems; they attributed the difference to material's success. dentinal fluid, that under pressure, leaked out of Modem dentinal banding agents used with acid- numerous cut tubules and changed the conditions of etching procedures produce high bond strength yal- the chemical reaction of the adhesive resin to the ues, but these figtires should not be confijsed with dentin (Fig 3), The interlocking ofthe bonding agent long-term resistance to microleakage, which has been with the collagen network of the intertubular dentin shown to occur even in the absence of gaps under a (see Fig 2), and not the tag formation into the tubuli resin composite placed in Class V cavities with an (Fig 4), was considered to be the main substrate that

Quintessence Intemafional Volume 27, Number 10/1996 661 The use of a single bonding agent and restorative material that can be attached to the tooth in one procedure appeals to the hard-pressed clinician but, as with most dental materials and techniques, a price has to be paid. Enamel and dentin are very different substrates; to achieve long-term adhesion, the clinician must recognize this fact and not lightly dismiss techniques that may take more time but take account of these differences. The clinician is faced with innumer- able bonding systems, and making a correct choice for each clinical case has become more and more difficult as the manufacturers move from one generation of bonding agents to the next. Fig 5 Glass-ionomer cement used as a dentin subsf itute in a Class lil preparation.

Dentinal bonding agents Considerable support is emerging, both in the clinical and research fields, for the use of mild acid etchants, such as maleic acid, to demineralize the intertubular yields high bond stretigths to dentin. It is now dentin, allowing hydrophilic primers to infiltrate the generally agreed that where the area of iiitertubular collagen network and form a thin hybrid layer or zone dentin is maximal, as in outer dentin, better bond of resin-impregnated dentin,""'-^ The only question strength figures can be obtained. that still remains unanswered is how long this seal will Glass-ionomer cements, being water-based materials, last when placed under stress and subjected to are not as affected by dentinal fluids, and, although long-term exposure to oral fluids. As previously they exhibit lower tensiie bond strengths than do the described. Sano et al^' have performed experiments resin bonding agents, the bond area generally shows a using a cryo-scanning electron microscope and a silver cohesive fracture that reflects the low tensile strength ion penetration method, Microleakage was observed, ofthe cement and not the actual strength ofthe bond. even in the absence of gaps, under a composite placed Until a much stronger cement is produced, it will not in Class V cavities with an adhesive resin system. They be possible to measure the true strength of this bond. suggested that the bonding monomer was not fully able For this reason, current use of glass-ionomer cements to penetrate the demineralized dentin after phosphoric as restorative materials should be confined to low- acid etching, thus leaving a porous zone as a pathway stress-bearing areas; their greatest value lies in bonding for microleakage beneath the resin-impregnated to dentin. In cavities where peripheral enamel bonding layer,^^ The resistance ofthe restoration to long-term can be achieved, the resin composite restoration used microleakage should be the main consideration when with a resin bonding agent is superior in strength, techniques and materials are selected for adhesive surface integrity, and esthetics. bonding. There is general agreement that the larger the bulk of Clinical use the resin composite restoration, the greater the effect of stresses produced by polymerization shrinkage.'''^' There are two schools of thought with regard to the In the large posterior restoration, bonding to cervical clinical use of dentinal bonding agents and glass- dentin involves greater risks of microleakage because ionomer cement linings and bases. One group advo- inner dentin has less intertubular dentin and because cates the exclusive use of photocured resin bonding there is an increase in dynamic occlusal stresses. agents to form a hybrid layer in the dentinal surface,-' Whenever possible, the clinician should retain an while the proponents of glass-ionomer materials rec- enamel margin, particularly at the cervical area. At ommend, for the deeper cavity, placement of glass- present, the use of composites placed on dentinal ionomer bases as a dentinal substitute to which com- margins is better confined to small cavities and posite or other restorative materials can be attached-^ low-stress-bearitig areas. (Fig 5). However, the use of resin bonding agents to seal

662 Quintessence International Volume 27, Number McLean

dentin under porcelain, gold, or amalgam restorations ations, resistance to microleakage. The efficacy of is enjoying greater success, although as yet much of the cavity sealing by glass-ionomer bases has had a long evidence for this is anecdotal. Pashley et al-' con- history of success and has been confirmed in numerous sidered the method worthy of further investigation and clinical studies.'""-'-'" In addition, because the glass- examined the ability of six différent dentinal bonding ionomer cements liberate fluoride, they possess some agents to seal the dentin of crown preparations of cariostatic properties.'*'^" Provided that these cements human teeth in vitro. They concluded that, although are placed on a clean dentinal surface, their long-term the bonding agents tend to accumulate on chamfers, resistance to microleakage has been proven over thereby increasing their thickness to 200 to 300 um, periods of more than 15 years. ^° the method cotUd be a simple way to protect the pulp A fiirther advantage is that, when these cements are from the consequences of microleakage. used as dentin substitutes in the so-called sandwich More recently, photocured resin bonding agents technique (see Fig 5 ), they reduce the bulk of overlying based on glass-ionomer technology have been devel- composite and subsequent polymerization shrinkage. oped (Scotchbond Multipurpose, 3M Dental; Pertac In the case of the Class II! restoration, a glass-ionomer Universal Bond. ESPE); carboxylic acid groups that base can ofteti improve esthetics because the cement's become available for attachment to dentin are incor- transmission of iight is ciose to that of dentin, porated. In addition, these materials are useful for preventing the halo effect sometimes observed with the attaching resin composites to glass-ionomer cement more translucent microfilled composites. surfaces. This line of chemistry may have a promising Criticism is still leveled, however, at the laminate, or future, because the introduction of carboxylic acid sandwich, technique and some in vitro studies appear groups could faciiitate some chemical bonding. These to show leakage around glass-ionomer bases where an new bonding agents could be classified as glass- acid-etched composite has been inserted.^'•^- It is ¡onomer bonding agents, because they have a dual role postulated that the polymerization shrinkage of the in bonding to both dentin and glass-ionomer cement. composite restoration breaks the seal of the glass- Swift and Triólo,'^ in an in vitro study on Scotch- ionomer cement to dentin. However, a recent study bond Multipurpose Universal Dental Adhesive, found found no loss of seal in vital teeth, and microleakage that dentin and even enamel bond strengths are was more related to the atmosphere in which the improved when the adhesive is applied to slightly restoration was placed.^^ In this in vivo test, the moist surfaces, a finding that mirrors the ideal surface partially humid environment favored the application for glass-ionomer bonding. They found that improved process and, as previously discussed, the stress relief bond strengths are obtained on enamel when the exhibited by glass-ionomer cements may contribute to stronger 35% to 40% phosphoric acid is used instead this result.'^-' The use of glass-ionomer bases has of the 10% maleic acid advocated by the manufacturer. enjoyed considerable clinical success over the iast 20 The manufacturer has started to recommend this years in countries such as the United Kingdom and procedure, which, as previously discussed, iiiustrates Australia, and this anecdotal evidence should not be the difficulty of using one material or etchant to lightly distnissed. condition enamel and dentin. In the pursuit of In the shallow cavity, loss of seal in the sandwich universality, maximal physical properties are often technique is often related to the strength and thickness sacrificed on the altar of speed. The clinician is dealing of the base used, and thin linings of less than 1.0 mm with two very different surfaces, and dentin is a vital are not aiways satisfactory. Essentially, glass-ionomer tissue that is better treated with mild etchants or cement should be used as a dentinal substitute to sur&ce conditioners.^" protect the dentin from any acid penetration during insertion of the composite. The cement itself should be Glass-ionotner cetnents protected with a glass-ionomer bonding agent, as previously described, prior to acid etching (Fig 6). In The use of glass-ionomer cement as a base or dentin the shallow cavity, the clinician should continue to use substitute for attaching composite restorations to tooth direct dentinal bonding. structure was ftrst described by McLean and Wilson-' in 1977. The main question today is whether cement Resin-modißed glass-ionotner cements bases are obsolete and have any value in operative dentistry. To answer this question it is necessary to The introduction of resin-mcdiñed glass-ionomer again consider the basic requirement of ail restor- cements that can be photocured has created great

Quintessence International Volume 27, Number 10/1996 663 McLean

Clinical use of resin-modijied and regular glass- ionomer cements With the introduction of the photocured resin-modified glass-ionomer cements, it might be thought that the regular glass-ionomer cements that set by an acid-base reaction could become obsolete. However, certain properties of the photocured materials need close examination. The clinical implications for the swelling in water ofthe resin-modified materials have yet to be established,^^ and their use as a base or core for inlays or crowns could resuit in a misftt if the cement absorbs water and swells after the impression is Fig 6 Glass-ionomer cement protected with a glass- taken. In the case of bases under resin composite or ionomer bonding agent prior to the insertion of the resin amalgam alloy restorations, the amount of swelling is composite. The bonding agent wiil act as a separator and unlikely to affect the stability of the restoration, prevent slicking ol the appiicator during insertion of the cement. provided that the resin-modified glass-ionomer cement that is selected has a significant glass-ionomer acid-base reaction and will still cure rapitíly in the

has described a method of overcoming the stresses placed on glass-ionomer bases by the polymer- interest. Their advantages are ease of placement, ization shrinkage of composites: the resin-modified setting on command, and early resistance to moisture glass-ionomer base and resin composite are cured contamination. It is not possible to photocure a regular simultaneously. He postulated that the resin composite glass-ionomer cement, and it is necessary to modify the cures before the resin-modified glass-ionomer material polyacid by grafting methacryiate groups onto the and that shrinkage stresses could be absorbed by the poly (acrylic acid) chain. Because the modified more plastic glass-ionomer base. This is an interesting poly (acrylic acid) is less soluble in water than its approach and deserves fUnher study, particularly whert parent, hydroxyethyl methacrylate (HEMA) is added conventional glass-ionomer bases are used. as a cosoivent. When this hydrophilie species is If the resin-modified materials are used as a total included, the set cement will act. to some extent, like a restorative in Class III and Class V cavities, the hydrogel, swelling in water and becoming weaker.'''"^^ implications of the water uptake must be taken into In general, the greater the amount of HEMA in- account, with regard to not only marginal adaptation corporated, the greater the swelling and reduction in but also color stability. The formation of hydrogels in strength, the resin-modified glass-ionomer cements and sub- A proposed classification for these new cements has sequent swelling in water may result iti discoloration attempted io differentiate between the true glass- over time, and the results of long-term clinical trials are ionomer cement and the newer hybrid varieties": stili awaited. It is for this reason that research aimed at 1, The unqualified term glass-ionomer cement should producing faster-setting and stronger regular glass- be reserved exciusively for a material consisting of ionomer cements that set by an acid-base reaction an acid-decomposable glass and a water-soluble should be continued, together with attempts to intro- acid that sets by a neutralization reaction, duce alternatives to HEMA in the resin-modified 2, Materials that retain a significant acid-base reac- materials. tion as part of their overali curing process, ie, they The polyacid-modlfied composite materials also will cure in the dark, are classified as resin-modified require longer-tenn clinical trials, because although glass-ionomer materials. they are stronger than either glass-ionomer or resin- 3, Materials that contain either or both ofthe essential modified materials, they are still significantly weaker components of a glass-ionomer cement but at levels than regular hybrid or microfilled composites. They insufficient to promote the acid-base curing reac- also do not cure in the dark, which indicates the tion in the dark should be referred to as polyacid- absence of any significant degree of acid-base reaction. modified resin composites. A clinical question still remains as to their perform-

664 Quintessence International Volume 27, Number IO/199R McLean

anee compared with that of the hybrid or small-particle toration may exhibit superior color in the early years, composites, particularly in posterior restorations. In the standard glass-ionomer cements can maintain addition, there seems to be little evidence that these greater color stability because of their chemical stabil- materials can adhere to dentin by chemical bonding, as ity.20,29..10 However, poor finishing techniques can occurs vflth the glass-ionomer acid-base reaction produce rough surfaces that stain, and preservation of cements, and they still require an acid-etching pro- the original gel surface should be the clinician's prime cedure, as used for conventional dentinal bonding objective, as described by McLean and Wilson^^ in agents, to obtain high bonding strengths. 1977. Provided that this goal is achieved, glass- ionomer cements are very durable in cervical restora- Properties of polyacid-modified resin composite and tions and compete with the composites, particularly resin-modified iiiting cements where bonding to cervical dentin is required. Sclerosed dentin remains the greatest obstacle to obtaining good The introduction of these new cements has aroused bonding with dentinal bonding agents, and failure at considerable interest, because both materials are the cervical margin as a result of microleakage is not stronger and are claimed to have better resistance to always easily detected. early solution than the glass-iononner luting cements, Class V cavities may also be restored with glass- although no results have yet been published on their ionomer cements, but esthetic considerations take actual loss of cement-forming ions or organic con- priority when more extensive facial areas are involved, stituents when exposed to moisture. The physical and the srttall-particle or microfilled composites are properties of both types of material appear to indicate superior. The sandwich technique is only practical in that they could make a useful contribntion to im- the deeper cavity and should be the first choice where proving the retention of crowns and inlays when caries control is a priority for the older patient. conventional cementation tecliniques are used, and Shallow cavities are better restored with direct dentin- they are worthy of further clinical study bonded composites, but again the area of cervical However, a warning should be given where direct dentin involved will influence the lotigevity of the bondirtg of porcelain inlays or crowns is contemplated. restoration. An alternative is to place a conventional Even in the case of the polyacid-modified composite glass-ionomer restoration, which can later be cut back cements, their mechanical properties are itiferior to and overlaid with an acid-etched composite. those of the current dual-cured or autocured resin cements. The prevention of crack propagation or Class II restorations debonding of porcelain restorations is dependent on the strength of the bond between the porcelain surface Direct bonding of composites to dentin in the pos- and the tooth. Therefore, the strength of the bonding terior restoration is generally regarded as the most resin plays a vita] part in securing long-term resistance challenging operation by the clinician. He or she has to to fracture or debondirtg of the restoration. At this contend not only with moisture control but also with stage, more clinical evidence is needed before either dentinal surfaces that are not as receptive to hybridiza- resin-modified glass-ionomer or polyacid-modilied tion. In addition, as described previously, the bulk of reshi composite cements are used for purposes other the restoration will determine the amount of polymeri- than for conventional cementation. zation shrinkage and subsequent distribution of stress. Unless the entire restoration can be bonded to peripheral enamel, a strong case can be made for using Class V restorations and erosion/abrasion lesions a glass-ionomer base (conventional, cermet-based,^^ The retention rate of glass-ionomer cements in the or resin-modified) to act as a biologic seal and offer erosion/abrasion lesion solely involving dentin is protection to the surrounding tooth struettire through generally better than that of dentin-bonded composite the release of fluoride. The glass-ionomer base also restorations. "•^"•^^ For this reason, other questions of avoids the risk of damage by acid etching in the deeper choice vWU depend on esthetic demands and the cavity, postoperative sensitivity is reduced, and hulk maintetiance of polished surfaces. Modem composite shritikage of the composite restoration is lessened. restorations have great esthetic appeal, but both the The sandwich technique has been misapphed to this standard and resin-modified glass-ionomer materials type of restoration. Attempts to use glass-ionomer have been considerably improved with regard to cement as a base, so that the cement is extended to the translucency and color. Although the composite res- surface at the cervical margin, may result in dissolution

Quintessence International Volume 27, Number 10/1996 665 MoLean ofthe cement, Glass-ionomer cements should only be In high-stress-bearing areas or when thin sections used as internal bases. However, in a recent 3-year of material are required, glass-ionomer cements lack clinical study comparing direct composite inlays with strength and are easily damaged during function or by conventional restorations, Wassell et al'^ observed that early finishing procedures and contamination with there was no evidence of dissolution of a cermet base, moisture. The modern hybrid and microfiHed compos- even when it extended to the cervical margin, in either ites are superior in esthetics, strength, and retention of type of restoration, and no secondary caries was surface polish where large areas of facial enamel are diagnosed. It is possible that the fluoride release and involved. better abrasion resistance of this material may have Dentinal bonding agents have been firmly estab- contributed to this result. lished for bonding anterior resin composites, porcelaiti The imperfections of the large mesio-occlusodistal veneers, inlays, and some metal restorations to tooth composite restoration are well known, and, despite structure. They possess higher bond strengths than do current attempts to ban amalgam alloy restorations, the glass-ionomer cements but require greater attention to public must be made aware of these deficiencies. the preparation of surfaces for bonding. Modem Composites can provide good service in small Class I techniques are employing weaker acids, such as maleic and Class II preparations with minimal direct stress, add, to prevent damage to the pulp in the deeper because occiusal contact is generally confined to the cavity, and these etchants facilitate the fonnation of a tooth enamel""' and the restoration is to some extent hybrid layer. The success of dentinal bonding is still protected. However, despite improvements in the dependent on the morphology ofthe dentin, and in chetnistry and particle-size distribution ofthe fillers, areas lacking a high percentage of intertubular dentin, the hydrolytic stability of the filler-matrix interface still problems can arise. remains questionable and may result in loss of material Judgments on the merits of using glass-ionomer in ñinctional occlusion, where occlusal stability is so cement bases or resin dentinal bonding agents that are vital. Wear in the contact area also remains a prob- based on short-term in vitro testing on extracted teeth lem,"" Government health departments should be are contradictory. Long-term clinical trials are still warned that compulsory replacement of amalgam alloy needed to establish the veracity of this testing. restorations with tooth-colored materials could prove Future research on dentina! bonding agents em- an expensive exercise in public health care. ploying glass-ionomer technology could provide some chemical bonding as well as materials with increased fracture toughness, negligible setting shrinkage, and Summary thermal expansion similar to that of tooth structure. Long-term stability at the enamel-dentin interface can Dentinal bonding agents and glass-ionomer cements only be achieved with restorative materials that have have a usefijl role in adhesive dentistry, and neither these properties. system has a monopoly on clinical success. It is important to recognize the optimal properties of each material when it is being selected for clinical use, Acknowledgment Glass-ionomer cements, because of their ability to [ am indebted to my daughter Dee McLean for the ¡lltjsuation. renew broken bonds, have better cavity-sealing properties and resistance to microleakage over long References periods. In addition, because of their ability to leach 1, HageerO, Swss patent 278946; Briüsh patent 687299, 1951. fluoride, they possess some cariostatic properties. 2, Kratner IRH, McLean JW, Alterations ¡n the staining reaction of They are particularly suited to the restoration of dentine resulting ftom a constituent of a new self-polymerising resin. erosion/abrasion lesions and as dentinal substitutes BtDentJ 1952i93:l50-15.T, 3, McLean JW, Kramer IRH, A clinical and pathological evaluation of when resin composite or other restorations are placed a sulphinic acid activated resin for use in restorative dentistr>', Br and iong-term resistance to microleakage is a priority, Dent J 195:Í93Í355-269, 291-293 Theh- excellent clinical performance has considerable 4, BuonocoreMG, Quigley M, Bonding ofasjnlhetic resin materialto human dentin: Preliminary study ofthe bond area J Am Dent Assoc clinical and scientific backing if confined to low- 1958;;7,-807-8]2, stress-bearing areas, and postoperative sensitivity is 5, McLean JW, Some physical properties ofa new cross-linked plastic reduced particularly where stronger acid etching is Tilling material. Br Dem J 1961^10:375-378, employed or faults in the dentinal bonding technique 6, Bowcn RL, Denial filling materials comprising vinyl.silane treated occur. iliscd siiica and a binder consisting of the reaction product of bispheno! and glycidyl methacrylate. US patent 3,066,112, 1962

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7, Knight MH, Milcliel B, Ratcliffe MI. Vmyl urethane resins, British 26. McLean JW, Prosser HJ, Wilson AD, The use of glass-ionomer patent 135:O6J, 1971, cements in bonding composite resins to dentine. Br Denl J S, Forster I, Walker RJ. Dental filling materials. British patent 198i;158:410-414. 1,401.505, 1975. 27. Pasbtey EL, Comer RW, Simpson MD, Horner JA, Pashtey DH, 9, Forster J, Dental filling materials, British patent 1,430,303, t976, Caiigbman WF, Dentin permeability: Seating the deniin in crown 10, Dan EC, NemcQck J, Ptiotopolymerisable composiliün having as preparations. Oper Dent 1992;17:t3-2O, catalyst alpha-dikelone and a reducing agenl, e.g. DMAEM, British 28. SwiflEI, Triólo PT, Bond strengths of Scotehbund Multi-Purpose to patent 408,265, 1971, moist dentin and enamel. Am J Dent I992;5:3IS-32O, tl, Nakabayashi N, Nakamura M, Yasuda N. Hybrid layer as a dentin-bond ing mechanism, J Esthet Dent 1991^3:13.1-138, 29. McLean JW, Wilson AD, The clinical development ofthe glass- ionomer cement, II, Some clinical applications, Aust Denl J t2, Asmussen E, Miinksgaard EC, Adtiesion of restorative resins to 1977;22;12O-I27, dentinat tissues, tn: Vanherle G, Smith ElC (eds). Proceedings of an Intemalional Symposium on Poslerior Composile Resin Denta! 30. Mount GJ. An Atlas of Glass-ionomer Cements, ed 2. London: Restorative Materials. Si Paul, MN: 3M, 1985:217-238. Martin Dunitz, 1994:1-31, 13, Walts A, Paterson RC, A review of current proprietary bonding 31. Dietschi D, De Siebenthal G, Neveu-Rosen stand L, Hoiz J. systems. Rest Dent 1991;7:56-61, Inflticncc of the reslorative technique and new adhesives on the 14, Eiek JD, Cobb CM. Ctiappell RP, Spencer P, Robinson SJ, The dentin maiginal seal and adaptation of resin composite Class II dentinal surface: Its influence on denlinal adhesion. Pan I. restorations: An in vitro evatuation. Quintessence Int 1995i26:7t7- Quintessence Inl t99t;22:967-977, 727, 15, Walson TF, Bartlett DW. Adhesive systems: Composites, dentine 32. Wieczkowski G, Joynt RB, Davis EL, Yu XY, Cleary K., Leakage bonding agents and glass ionomers. Br DentJ t994it75:227-231. patterns associated with gtass-ionomer-based resin restorations, 16, Pashley DH, Pashley EL, Dentin permtabitity and restorative Oper Denl t992;17 21-25. dentislri: A status reportfor the American Journal of Dentistry, Am JDenl t991;4:5-9. 33. Mason PN, Ferrari M. In vivo evaluation of glass-ionomer cement adhesion to deniin. Quintessence Int I994;25:499-5O7. 17, Pashley DH, The effects of acid etching on the pulpodentin complex, Buonoeore Memonal Lecture. Oper Dent t992;17:2;9-24;, 34. Nicholson JW. Anstice HM. McLean JW, A preliminary report on 18, Johnson GH, Powell LV Gordon GE, Dentin bonding systems. A the effect of storage in water on the properties of commercial review of current products and techniques, J Am Dent Assoc light-cured glass-ionomer cements, BrDentJ 1992:173:98-101. t99t;122:34-41. 35. Anstice HM, Nicholson JW. Studies on the structure of light-cured 19, Erickson R, Giasspoole EA. Bonding to tooth siructure; A glass-ionomer cements J Maler Science Mater Med I992;3:447- comparison of glass-ionomer and composite resin systems, J Esthel 455. Dent 1994;6:227-244. 36. Wilson AD, McLean JW, Heller]. J Am Dent Assoc 1994; 20, Wilson AD, McLean JW, Glass-ionomer Cement, Chicago; Quint- 125:1046-1048, essence, 1988:83-99, 107-115. 21 Davidson CL. Glass-ionomer bases under posterior composites, J 37. McLean JW, Nicholson JW, \Wlson AD. Proposed nomenclature for Esthel Dent 1994:6:223-226, glass-ionomer denial cemenls and related materials, Quititessence Inl 1994:25:587-589, 22, Beech DR, Bonding of restorative resins to dentine. In: Vanherle G, Smith DC (eds). Proceedings of an Intemalional Symposium on 38. Knight GM, The co-cured light-activated glass-ionomer cement- Posterior Composite Resin Dental Restorative Matenals, Si Paul, composite resin restoration. Quintessence Int 1994^25:97-100, MN: 3M, 1985:231-238, ¡9. WassellRW.WallsAWG, McCabe JF, Direct composile inlays versus 23. Sano H, Shona T, Takatsu T. Hosoda H, Microporous dentin ione conventional composite restoraliuni: Three-year clinical results. Br henealh resin impregnated layer, Oper Dent 1994; 19:59-64. DentJ 1995;l79:343-349, 24. Paut SJ, Schârer P. Factors in dentin bonding. Part I. A review ofthe morphology and physiology of human dentin, J Esthet Dent 40. Bayne SC, Heymann HQ, Swift EJ, Update on dental composite 1993i5:5-8, restorations, J Am Dent Assoc 1994:125:687-701. 25, Cox CF, Suzuki S, Reevalualing ptjip protection: Catcium hydrox- 41, ZiemieckiTL.WendtSL,LeinfelderKF. Methodology for proximal ide liners vs, cohesive hybridization. J Am Dent Assoc 1994; wear evaluation in posterior resin composites. Am J Dent 1992; 125:823-831. 5:202-207, O

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