When practitioners fu lly understand the nature o f the glass ionom er m aterials a n d use them w ith in their lim itations, their use can im prove the q u a lity o f restorative dental care for young patients. The m aterials fo r you n g patien ts can be classified as luting cements, dentin replacem ent liners a n d bases, and glass ionom er dentin an d enam el restorative m aterial. Future research efforts should be directed tow ard im p ro vin g the glass ionom er cem ent by increasing fracture toughness and wear resistance, decreasing hardening tim e, an d sim plifyin g the sensitive handling technique.
Glass ionomers for infants, children, and adolescents Theodore P. Croll, DDS
lass ionomers for use in dentistry for infants, children, and teenag ers are invaluable. If a dentist understands how the various glass ion o mer materials work, how they should be handled, and, m ost importantly, their lim itations, their use can greatly improve the quality of restorative dental care for young patients. Advantages of glass ionomer restora tives, luting cement, and dentin replace ment liners and bases include: —T he materials bond chemically to enamel and dentin with insignificant heat formation or shrinkage of material during the hardening reaction. —T he coefficient of thermal expansion is similar to that of tooth structure and the materials are biocompatible. —Certain predosed encapsulated sys tems—albeit more expensive—save time, are convenient, and elim inate handling inconsistencies. —Fluoride ions are released to sur rounding tooth structure with no effect on the integrity of the glass ionomer mass. —Materials are tooth colored (except for the metallic glass ionomff mixtures). —The material is syringe-injectable for easy application. —Hardened glass ionomer material is virtually insoluble in oral fluids. —Certain dentin replacement liners and bases have high compressive strength and are unyielding when compressed by an
overlying restorative mass such as silver am algam or bonded com p osite resin material. —Hardened material when used as a dentin replacement can form an excellent micromechanical bonded attachment with overlaid com posite resin restorative mate rials. Such stratification type of restora tions capitalize on the advantages of all materials concerned and minimize disad vantages of each. —A new, visible light-hardened glass ionomer liner/base (Vitrabond, 3M Dental Products) greatly sim plifies and improves dentin replacement. Much operating time is saved w ith convenient “on com m and” hardening, by the visible light beam. T he disadvantages of glass ionomers for use in young patients are few, but critical. These include: —The hardened glass ionomer surface has low wear resistance. —The hardened glass ionomer mass has poor fracture toughness. —Materials are extremely sensitive to moisture during the application process and to dehydration during the hardening reaction. —Even though the restoratives are tooth colored, they have yet to equal the esthetic result that can be obtained with certain bonded com posite resin materials. —With the exception of the liner/base system that hardens by application of a concentrated v isib le lig h t beam , the
quickest hardening materials still take 4 to 6 minutes for initial hardening. Materials for children Materials used for children can be cate gorized in three general types: lu ting cements; dentin replacement liners and bases; and glass ionom er dentin and enamel restorative material. Glass io n o mers as enamel pit and fissure sealants are classified with the restorative materials. Luting materials As a luting material, glass ionomer cement offers no particular advantage over polycarboxylate cement for secure placement of stain less steel crow n restorations. However, lu tin g cem ent can be used successfully for this purpose. Some prac titioners use glass ionom er cement for securing orth o d o n tic bands. R elative insolubility in oral fluids and fluoride ion release to enamel adjacent to stainless steel band margins are important advantages in using such cement to lute orthodontic bands. In addition, some bonding exists between the stainless steel and glass ionomer material. However, glass ionomer cements are much more technique sensi tive and subject to dissolution by moisture contam ination during and immediately after band cem en tation . O rth odon tic colleagues report that after using glass JA DA, Vol. 120, Ja n u a ry 1990 ■ 65
J A D A ionomer cements and comparing them with traditional types of orthodontic band cements, they generally use the glass ionomers for patients especially at risk of caries. T he fluoride-release advantage of glass ionom ers is im portant in such patients. Liners and bases Glass ionomer liners and bases used to replace dentin in carious or fractured teeth have become indispensable for treating children. Liners and bases can be used: —as an unyielding chemically bonded base under a silver amalgam restoration; —as the dentin replacement com ponent in a stratified glass ionomer-composite resin bonded restoration; —for immediate treatment of patients who have suffered traumatic dental frac tures, as a means to rapidly reinsulate exposed dentin for a short time (Fig 1); —as a biocom patible, easily m anipu lated material for immediate reattachment of a large tooth segment fractured by trauma.1 T h is use must be followed by com posite resin bonding over the fractured margins to secure the fractured segment in place. Vitrabond, a visible light-hardened liner and base, is excellen t for emergency treatment of fractured teeth. It rapidly covers freshly exposed dentin tubules and reinsulates exposed microbial access to the dental pulp. T he material also works well as a rapidly setting luting agent for rapid reattachment of fractured enamel segments (Fig 2-5). T he material hardens completely in less than 1 m inute from the visible light exposure, which provides excellent time savings for the practitioner. Vitrabond is also being used as a rapid, convenient
Fig 1 ■ Visible light-cured glass ionom er liner was bonded to reinsulate and protect dentin exposed after traum atic fracture of the central incisors. Treatm ent was rapid, caused no discom fort, and the glass ionom er “ bandages” served their purpose until the teeth were restored with bonded composite resin restorations.
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Fig 2 ■ Vitrabond light-cured glass ionomer liner was placed to lute the fractured and completely detached crown segment back into place in this injured 12 year old. A strip of utility wax was used to facilitate m anipulation of the enamel fragment.
Fig 3 ■ T he glass ionomer was hardened w ith 30second exposure to the light beam from the labial aspect and an additional 30-second exposure from the lingual aspect.
Fig 4 ■ Labial and lingual enamel veneer prep arations were cut with a water-cooled diam ond bur, in p re p a ra tio n for restoration w ith bonded composite resin.1
Fig 5 ■ T he left central incisor is shown, 1 year after glass ionomer-composite resin repair.
restorative material for smooth surface lesions of primary teeth in which perfect color m a tc h in g is n ot im portan t. A lthough there is concern about wear resistance to toothbrush abrasion in such restorations, results after 12 months have been encouraging. Restorative materials A unique type of glass ionomer restorative material was introduced in 1984. KetacSilver (ESPE) is a glass ionomer silver “cerm et” restorative m aterial.2-3 T h is restorative material consists of particles of pure silver, which is sintered to ionleachable calcium -alum inum fluorosilicate glass powder. T he glass and silver particles com bine in the high-heat reac tion, in a similar manner to which dental porcelain fuses to certain gold alloys. The resultant bulk of material is ground into powder, and when combined with an aqueous mixture of copolymer of acrylic acid, and m aleic acid and tartaric acid, the material hardens. Hardened silver cermet restorative material has all the advantages of the glass ionomers; in addition, it has rad iop acity sim ilar to that of silver amalgam and resistance to wear greater
than other glass ionomer materials. After almost 5 years of frequent use in young dental patients, an observed disadvantage of the material is the light gray color, which makes silver cermet material unsuit able for esthetically prominent regions of the m outh. Another disadvantage is low fracture toughness, w hich makes the material of limited value in regions subject to occlusal stresses. Another advantage of silver cermet material is that Ketac-Silver contains no mercury. Although dentists know there is no known health threat to most people from mercury in silver amalgam, some parents insist that restorations containing mercury not be used for their children. With the silver cermet cement, the new wear-resistant visible light-cured resins, and the stainless steel crown restorations for primary molars, the no mercury request is sim ple to comply with. It should be noted that a glass ionomer material which contains a silver amalgam alloy powder, called “Miracle M ix” (G C International), is on the market. T his material is discussed in depth by Dr. Joe Simm ons in another article in this issue.) Silver cermet restorative material has also been successful for nonstress-bearing
Fig 7 ■ T his 11-year-old girl has a typical occlusal Ketac-Silver restoration of the primary second m olar, 4% years after placement. The prim ary first m o lar has a silver am algam resto ratio n of unknow n origin or duration.
Fig 8 ■ A large disto-occlusal cermet restoration was used to restore this m axillary second primary m olar after pulpotom y treatment. T his 2-year postoperative view demonstrates how Class II Ketac-Silver restorations in primary molars m ust be of great bulk and have no occlusal contact, to avoid fracture of the material.
restoration of permanent first and second molars, especially when such teeth are carious and partially erupted. In this respect, Ketac-Silver can be viewed as an ideal interim restoration. At this time, we do not know how long “interim ” can be in permanent teeth, but 4-year results in my own practice are prom ising (Fig 6). When Dr. Ralph P hillip s and I first described the use of Ketac-Silver for infants, children, and adolescents,3 we stated that if the material proved capable of lasting 4 to 7 years in the m outh, then it lasts as long as an analogous silver
Fig 9 ■ After extensive long-term efforts in oral hygiene instruction and persistent noncom pliance w ith brushing, flossing, and home application of fluoride solutions, this teenager required removal of his orthodontic brackets for restoration of carious and decalcified enamel.
Fig 10 ■ An encapsulated glass ionom er restor ative material was used to repair the lesions for the d u ratio n of orthodontic treatm ent. After syringe injection, the m aterial was compressed into the cavity preparations.
Fig 11 ■ T he teeth restored with glass ionomer m aterial are ready for resum ption of orthodontic treatment. Fluoride ion release from glass iono mers is especially valuable in patients such as this
fracture. At this time, glass ionomers can be viewed as our best dentin replacement and polishable wear-resistant composite resins the best direct application enamel replacement material. However, toothcolored glass ionomer restoratives, espe cially the encapsulated systems, can be used in adolescents and young adults with cervical erosion lesions7and in cariesprone patients with lesions requiring restora tions not subject to forces of occlusion (Fig 9-11).
Croll : GLASS IONOMERS FOR YOUNG PATIENTS ■ 67
Fig 6 ■ A glass ionom er silver cermet buccal restoration is shown, 4 years after placement.
amalgam restoration, m aking the cermet cement an attractive alternative to silver amalgam in young patients. Except for use in Class II restorations, after 5 years, KetacSilver so far has passed the test impres sively (Fig 7, 8). T he only advantage of silver am algam when compared with Ketac-Silver in Class II restorations of primary teeth is that the cermet fractures easily unless the restoration is kept out of occlu sion and the material is placed in great bulk. I currently use KetacS ilver for C lass II cariou s le sio n s on ly in cases in w h ich the finished restoration abuts against an adjacent permanent tooth surface, in hopes that sufficient fluoride ion exchange w ill occur from tooth to tooth across the proximal contact. Such restorations are made to be of great bulk and not subjected to occlusal contact. Glass ionomers including Ketac-Silver have been recommended as pit and fissure sealants because of their fluoride leaching property. I have used glass ionomers and the cermet for that purpose with little success. Impact forces and abrasion rapidly wear or fracture away glass ionom er sealants and, in my experience, no glass ionomer is available to match micromechanically bonded resin sealants. H ow ever, this could change with improved materials. There has been a revival of interest in the “tunnel preparation” as use of glass ionomer materials has increased.4'6 Since first described by Jinks6 in 1962, the tunnel preparation has intrigued dentists who desire to conserve as much tooth structure as possible during cavity preparation and subsequent tooth restoration. (Tunnel restorations are reviewed by Dr. Peter H unt in another article in this issue.) In young patients, I have found that silver cermet is ideal for tunnel restorations because of its great radiopacity, injectability, and convenience of the encapsulated system. Also, the dentist m ust assure that a sufficient mass of the marginal ridge rem ains after tu n n el p rep aration in primary molars. T h is ensures that the weakened marginal ridge w on’t fracture after placement of a tunnel restoration. In questionable cases, it is better to perform a traditional Class II type restoration, or if tooth structure loss is sufficient, a stainless steel crown restoration can be used. Tooth-colored glass ionomer restorative material cannot currently compete with m icrom echanically bonded com posite resin for young patients either to restore enamel lost from caries or from tooth
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Various glass ionom er materials have dramatically changed restorative dentistry for infants, children, and adolescents. When practitioners fully understand the nature of glass ionomer materials and use them w ithin their lim itations, they are extrem ely valuable for use in you ng patients. Research efforts should now be directed in im proving glass ionomers for use in young patients in the areas of: greatly increased fracture toughness and strength; better wear resistance; decreasing hardening time, or possibly manufactur
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ing a visible light-hardening glass iono mer in an encapsulated, predosed form; and sim plifying the sensitive technique of handling materials. ---------------------- J'A\D)A ----------------------Dr. Croll is in private practice, pediatric dentistry in Doylestown, PA. He is clinical associate professor, departm ent of pediatric dentistry, U niversity of Pennsylvania School of Dental Medicine; he is also adjunct clinical professor, department of pediatric dentistry, University of Texas Health Science Center at Houston (Dental Branch). Address reprint requests to Dr. Croll, East St 8c N Main St, Doylestown, PA 19801-3897. 1. Croll T P. Repair of severe crown fracture with
glass ionomer and composite resin bonding. Q uin tessence 1988;19:649-654. 2. McLean JW, Gasser O. Glass-cermet cements. Quintessence 1985;16:333-43. 3. Croll T P, Phillips RW. Glass ionomer-silver cermet restorations for primary teeth. Quintessence 1986;17:607-615. 4. Croll TP. Glass ionomer-silver cermet class II tunnel-restoradons for primary molars. ASDC J Dent Child 1988;55:177-82. 5. Croll T P. Glass ionomer-silver cermet bonded composite resin class II tunnel restorations. Quintes sence 1988;19:533-9. 6. Jinks GM. Fluoride-im pregnated cements and their effect on the activity of interproxim al caries. J Dent Child 1963;30:87-92. 7. Croll TP. Conservation restoration of a sensitive cervical root lesion. J Esthetic Dent 1988;1:73-7.