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Glass Ionomers and Esthetic Dentistry: What the New Properties Mean to Dentistry
GLASS I0N0HEHS AND
ESTHETIC DENTISTRY:
W H A T THE N E W P R O P E R T IE S M E A N TO D E N TIS TR Y T H E O D O R E P. C R O LL , D .D .S .
ABSTRACT
In g e n u ity in r ese a rc h an d d ev elo p m en t o f g la ss io n o m er sy stem s h as slo w ly b u t su rely im p roved th eir h a n d lin g p ro p erties and ap p ea ran ce. T he au th or r ev ie w s th e la te st d ev elo p m en ts in rela tio n to e sth e tic d entistry.
0 u rre n t glass ionomer cem ents cannot m atch m odern composite resins in w ear resistance or fracture toughness. W hen used w ithin th eir lim itations, however, the glass ionomers possess properties th a t m ake them perhaps the m ost ideal class of direct application restorative m aterials available. Glass ionomers: ■» form a chelation bond to dentin and enamel; ■* are biocompatible with cut dentin and the underlying dental pulp; ■■ have the powder component m ade of acid-soluble calcium fluoroalum inosilicate glass which, w hen combined w ith the aqueous polyacid solution, hardens and subsequently leaches fluoride ions to adjacent tooth structure. The fluoride ion release does not degrade the hardened cement m ass, b u t renders adjacent tooth structure significantly more caries resistant; ■■ undergo the hardening reaction with insignificant h e a t form ation or dim ensional change so th a t the set cem ent has a coefficient of therm al expansion sim ilar to th a t of tooth structure; ™ once hardened, are virtually insoluble in oral fluids a t intraoral tem peratures; ■■ are syringe injectible for easy application; ■■ are not affected by a slightly moist tooth surface during application because the polyacid component is an aqueous solution; “ have a high compressive strength and are unyielding w hen used in sufficient thickness as a dentin replacem ent liner or base; ■* form an excellent micromechanical bond w ith overlaid composite resin in a glass ionom er/resin layering or “stratification” technique1,2; ■* have recently been introduced w ith the hardening reaction accelerated by initial setting using a visible light beam. The new light-hardened glass ionomers contain a visible light polymerized resin component th a t perm its “on-command” hardening followed by the longer duration glass ionomer setting reaction. These new system s can save five to seven m inutes of tre a tm e n t tim e for each restoration. Glass ionomers have an essential role in esthetic dentistry procedures. For example, certain form ulations of glass ionomer JADA, Vol. 123, May 1992
51
cem ents are used to lute fixed prostheses, individual precision cast or stainless steel crown restorations or orthodontic bands. O ther form ulations are used for bonded dentin replacem ent to reinsulate and protect dentin exposed by preparation or traum atic fracture as shown in Figures 1 and 2.3'4 Even though glass ionomer restoratives do not have the w ear resistance, fracture toughness or quite the shadem atching ability of the latest generation of composite resins, there are proven uses for glass ionomer restorative cem ents to replace dentin and enamel. They can restore combined root/crown lesions a t the cem entoenam el junction of tee th w ith prom inent faciocervical exposure. Such lesions have long been attrib u ted to abrasion caused by toothbrushing habits, or erosion from influences in the m outh. Recently, however, an in te rest ing argum ent proposes th a t “biomechanical loading forces” cause “flexure and ultim ate fatigue of enam el and dentin a t a location away from the point of loading.” 5,6
Grippo term ed such tooth alm ost as sure as with structure breakdown as composite resins. In addition, “abfractions” derived from the the glass component of glass Latin, ab m eaning “aw ay” and ionomer restoratives tends to fractio, “breaking.”5 Regardless take on optical qualities of of their cause, lesions as shown surrounding tooth structure as in Figure 3 can often be a result of reflection and restored w ithout any rotary dispersion of incident light— preparation of the dentin or particularly w hen glass ionomer enam el.7 The glass ionomerrestorations are hydrated by dentin/enam el bond, albeit saliva, which is th eir usual weak, is strong enough to retain state. the cement for m any years. Since we know th a t the glass Glass ionomer restorative ionomer/tooth structure bond is cem ent can repair smooth relatively weak, we include a surface lesions in people w ith m echanical interlocking high incidence of and suscept retention form in bur-cut ibility to caries. The cem ent’s preparations. Only those glass fluoride-releasing potential ionomer restorations th a t do especially benefits such patients not undergo occlusal loading (Figure 4). We’ve used glass ionomer restorative m aterial to repair smoothsurface lesions in prim ary teeth (Figure 5).8 The self hardening m aterials have improved to Figure 1. Glass ionomer cement can serve as a the point th a t short-term, biocompatible, rapidly applied insulating shade “bandage” restoration for carious or traumatically m atching is fractured teeth.
Figure 2a. This patient suffered an extensive enamel and dentin through-and-through fracture of the permanent canine, in a fall.
52
JADA, Vol. 123, May 1992
Figure 2b. The fractured segment was reunited using glass ionomer cement followed by labial and lingual direct application composite resin veneer restoration, for coronal support. M
Figure 3a. The cervical “abfraction” lesion of this first premolar was extremely sensitive to thermal insult.
Figure 3b. The premolar is seen four years after restoration with direct application of glass ionomer restorative material with no bur cut preparation.7 The cement is barely perceptible.
prim ary teeth w ith the idea of decreasing treatm en t tim e by using light beam hardening.9 After four years of extensive use of the lightFigure 4. After chronic non-compliance with home hardened liner care and fluoride regimens, this teenager underwent base for such removal of all orthodontic brackets and bands for restorations, repair of décalcification and carious lesions. Glass ionomer restorative cement was ideal in this case we have found because of the benefits of fluoride ion leaching. no surface degradation or m arginal breakdow n.9 Using forces can reliably be retained th is m aterial for small Class I w ithout bur-cut interlocking. Chemical bonding of glass restorations completely encircled by sound enam el has ionomers to dentin and enam el also given excellent results in is more im portant for m inim iz the last 2V2 years. ing m arginal m icroleakage and In any glass ionomer restor prom oting fluoride leaching ation th a t includes the occlusal th a n for restoration retention. surface, centric occlusal holding The disadvantage to self regions should not be positioned hardening glass ionomers is the in the cement; place occlusal five to 10 m inutes required to support on the cuspal enam el or achieve sufficient initial setting m arginal ridges. In the prim ary so the cement can be finished dentition, such occlusal rela and polished. tionships are easily achieved by Light-hardened glass slightly reducing opposing ionomer liner/base (Vitrebond, enam el contacts. 3M Dental Products) h as been A m ajor advancem ent in used as a dentin/enam el glass ionomer technology was restorative m aterial in nonintroduced commercially to the stress-bearing regions of
profession in early 1992. A light-cured glass ionomer restorative cem ent (Fuji II LC, GC America) has a resin component th a t gives the set cem ent greater wear resistance and reportedly better fracture toughness compared to Dr. Croll is in private practice, pediatric the lightdentistry, George hardened town Commons, Suite 2, 708 Shady liners and Retreat Rd., bases. If the Doylestown, Pa., 18901-3897, and new lightassociate hardened glass clinical professor, Depart ionomer has ment of Pediatric Dentistry, University durability and of Pennsylvania longevity School of Dental Medicine, and approaching adjunct professor, th a t of glass Department of ionomer-silver Pediatric Dentistry, University of Texas cerm et Health Science cem ent,10the Center at Houston. Address reprints new m aterial requests to the could change author at his restorative practice. dentistry dram atically in both the prim ary dentition and in conservative applications in the perm anent dentition. I have used this restorative m aterial frequently in my own practice since J a n u a ry 1992 for Class I, II, III and V JADA, Vol. 123, M ay 1992
53
Figure 5a. This child has a three-year-old glass ionomer-silver cermet restoration of the primary first molar and a carious lesion of the canine.'0
Figure 5b. A light-hardened restoration of the canine one year after placement.*
m onths, we found th a t restorative m argins are virtually im perceptible in hydrated restorations w ith good color m atch (Figure 6). We are now investigating Figure 6. Light-hardened occlusal and occluso-lin its use in small guai restorations in this primary second molar are Class I lesions barely perceptible after two months in the mouth of a 3-year-old boy. Light-hardened glass ionomer res in perm anent torative materials with improved physical properties tee th as an are beginning to change modern concepts of restorative dentistry. alternative to “preventive restorations. We apply the resin” restorations.11 m aterial w ith syringe injection O ther major dental m aterial after removing the sm ear layer m anufacturers are currently w ith polyacrylic acid. We use introducing or developing lightthe visible light beam in two 30hardened glass ionomer second exposures, the first after restorative cements. Long-term injection of the cem ent and the durability, color stability, second after finishing. resistance to w ear and fracture Im m ediately after placem ent are unknown a t this time. and light-hardening, the C O N C L U S IO N S restorative surfaces of these restorations can be slightly Since th eir introduction, glass indented w ith a hand ionomers have improved in instrum ent. handling properties, After 24 hours, however, the appearance of the hardened cem ent surface feels as h ard as m aterial, decreased setting tim e set am algam , fully polymerized through visible light beam composite resin or longstanding initial hardening and toughness hardened cerm et cement. At 3V2 of the hardened cem ent m ass. 54
JADA, Vol. 123, May 1992
The im provem ents offer dentists new treatm en t options for posterior and anterior teeth. W hen m anufacturers of glass ionomer m aterials finally pro duce a light-hardened cement th a t can rival composite resin in shade m atching and surface smoothness, and dental am al gam in w ear resistance and fracture toughness, traditional concepts of direct application restorative dentistry will change radically. P erhaps the change has begun. ■ N either th e author nor th e A m erican D ental Association has any commercial in terest in the products m entioned in this paper. 1. M cLean JW , Wilson AD. The clinical developm ent of th e glass ionom er cem ents. II. Some clinical applications. A ust D ent J 1977; 22:120-7. 2. Croll TP. Replacem ent of defective class I am algam restoration w ith stratified glass ionomercomposite resin m aterials. Q uintessence In t 1989; 20:711-6. 3. Croll TP. Repair of severe crown fractu re with glass ionom er and composite resin bonding. Q uintessence In t 1988; 19:649-54. 4. Croll TP. Rapid reattach m en t of fractu re crown segment: a n update. J Esthetic D ent 1990; 2:1-5. 5. Grippo JO. Abfractions: a new classification of h ard tissue lesions of teeth. J Esthetic D ent 1991; 3:14-9. 6. Grippo JO , Masi JV. Role of biodental engineering factors (BEF) in th e etiology of root caries. J E sth etic D ent 1991; 2:71-6. 7. Croll TP. Conservative restoration of a sensitive cervical root lesion. J Esthetic D ent 1989; 1:74-7. 8. Killian CM, Croll TP. Smooth surface glass ionom er resto ratio n for prim ary teeth. J Esthetic D ent 1991; 3:37-40. 9. Croll TP. Visible light-hardened glass-ionom er cem ent base/liner as an interim restorative m aterial. Q uintessence In t 1991; 22:137-41. 10. Croll TP, Phillips RW. Six years experience w ith glass ionomer-silver cerm et cement. Q uintessence In t 1991; 22:783-93. 11. Sim onsen RJ. Preventive resin restorations. In: Clinical applications of the acid etch technique. Chicago: Q uintessence Publishing; 1978: 89-101.
ESTHETIC DENTISTRY:
W H A T THE N E W P R O P E R T IE S M E A N TO D E N TIS TR Y T H E O D O R E P. C R O LL , D .D .S .
ABSTRACT
In g e n u ity in r ese a rc h an d d ev elo p m en t o f g la ss io n o m er sy stem s h as slo w ly b u t su rely im p roved th eir h a n d lin g p ro p erties and ap p ea ran ce. T he au th or r ev ie w s th e la te st d ev elo p m en ts in rela tio n to e sth e tic d entistry.
0 u rre n t glass ionomer cem ents cannot m atch m odern composite resins in w ear resistance or fracture toughness. W hen used w ithin th eir lim itations, however, the glass ionomers possess properties th a t m ake them perhaps the m ost ideal class of direct application restorative m aterials available. Glass ionomers: ■» form a chelation bond to dentin and enamel; ■* are biocompatible with cut dentin and the underlying dental pulp; ■■ have the powder component m ade of acid-soluble calcium fluoroalum inosilicate glass which, w hen combined w ith the aqueous polyacid solution, hardens and subsequently leaches fluoride ions to adjacent tooth structure. The fluoride ion release does not degrade the hardened cement m ass, b u t renders adjacent tooth structure significantly more caries resistant; ■■ undergo the hardening reaction with insignificant h e a t form ation or dim ensional change so th a t the set cem ent has a coefficient of therm al expansion sim ilar to th a t of tooth structure; ™ once hardened, are virtually insoluble in oral fluids a t intraoral tem peratures; ■■ are syringe injectible for easy application; ■■ are not affected by a slightly moist tooth surface during application because the polyacid component is an aqueous solution; “ have a high compressive strength and are unyielding w hen used in sufficient thickness as a dentin replacem ent liner or base; ■* form an excellent micromechanical bond w ith overlaid composite resin in a glass ionom er/resin layering or “stratification” technique1,2; ■* have recently been introduced w ith the hardening reaction accelerated by initial setting using a visible light beam. The new light-hardened glass ionomers contain a visible light polymerized resin component th a t perm its “on-command” hardening followed by the longer duration glass ionomer setting reaction. These new system s can save five to seven m inutes of tre a tm e n t tim e for each restoration. Glass ionomers have an essential role in esthetic dentistry procedures. For example, certain form ulations of glass ionomer JADA, Vol. 123, May 1992
51
cem ents are used to lute fixed prostheses, individual precision cast or stainless steel crown restorations or orthodontic bands. O ther form ulations are used for bonded dentin replacem ent to reinsulate and protect dentin exposed by preparation or traum atic fracture as shown in Figures 1 and 2.3'4 Even though glass ionomer restoratives do not have the w ear resistance, fracture toughness or quite the shadem atching ability of the latest generation of composite resins, there are proven uses for glass ionomer restorative cem ents to replace dentin and enamel. They can restore combined root/crown lesions a t the cem entoenam el junction of tee th w ith prom inent faciocervical exposure. Such lesions have long been attrib u ted to abrasion caused by toothbrushing habits, or erosion from influences in the m outh. Recently, however, an in te rest ing argum ent proposes th a t “biomechanical loading forces” cause “flexure and ultim ate fatigue of enam el and dentin a t a location away from the point of loading.” 5,6
Grippo term ed such tooth alm ost as sure as with structure breakdown as composite resins. In addition, “abfractions” derived from the the glass component of glass Latin, ab m eaning “aw ay” and ionomer restoratives tends to fractio, “breaking.”5 Regardless take on optical qualities of of their cause, lesions as shown surrounding tooth structure as in Figure 3 can often be a result of reflection and restored w ithout any rotary dispersion of incident light— preparation of the dentin or particularly w hen glass ionomer enam el.7 The glass ionomerrestorations are hydrated by dentin/enam el bond, albeit saliva, which is th eir usual weak, is strong enough to retain state. the cement for m any years. Since we know th a t the glass Glass ionomer restorative ionomer/tooth structure bond is cem ent can repair smooth relatively weak, we include a surface lesions in people w ith m echanical interlocking high incidence of and suscept retention form in bur-cut ibility to caries. The cem ent’s preparations. Only those glass fluoride-releasing potential ionomer restorations th a t do especially benefits such patients not undergo occlusal loading (Figure 4). We’ve used glass ionomer restorative m aterial to repair smoothsurface lesions in prim ary teeth (Figure 5).8 The self hardening m aterials have improved to Figure 1. Glass ionomer cement can serve as a the point th a t short-term, biocompatible, rapidly applied insulating shade “bandage” restoration for carious or traumatically m atching is fractured teeth.
Figure 2a. This patient suffered an extensive enamel and dentin through-and-through fracture of the permanent canine, in a fall.
52
JADA, Vol. 123, May 1992
Figure 2b. The fractured segment was reunited using glass ionomer cement followed by labial and lingual direct application composite resin veneer restoration, for coronal support. M
Figure 3a. The cervical “abfraction” lesion of this first premolar was extremely sensitive to thermal insult.
Figure 3b. The premolar is seen four years after restoration with direct application of glass ionomer restorative material with no bur cut preparation.7 The cement is barely perceptible.
prim ary teeth w ith the idea of decreasing treatm en t tim e by using light beam hardening.9 After four years of extensive use of the lightFigure 4. After chronic non-compliance with home hardened liner care and fluoride regimens, this teenager underwent base for such removal of all orthodontic brackets and bands for restorations, repair of décalcification and carious lesions. Glass ionomer restorative cement was ideal in this case we have found because of the benefits of fluoride ion leaching. no surface degradation or m arginal breakdow n.9 Using forces can reliably be retained th is m aterial for small Class I w ithout bur-cut interlocking. Chemical bonding of glass restorations completely encircled by sound enam el has ionomers to dentin and enam el also given excellent results in is more im portant for m inim iz the last 2V2 years. ing m arginal m icroleakage and In any glass ionomer restor prom oting fluoride leaching ation th a t includes the occlusal th a n for restoration retention. surface, centric occlusal holding The disadvantage to self regions should not be positioned hardening glass ionomers is the in the cement; place occlusal five to 10 m inutes required to support on the cuspal enam el or achieve sufficient initial setting m arginal ridges. In the prim ary so the cement can be finished dentition, such occlusal rela and polished. tionships are easily achieved by Light-hardened glass slightly reducing opposing ionomer liner/base (Vitrebond, enam el contacts. 3M Dental Products) h as been A m ajor advancem ent in used as a dentin/enam el glass ionomer technology was restorative m aterial in nonintroduced commercially to the stress-bearing regions of
profession in early 1992. A light-cured glass ionomer restorative cem ent (Fuji II LC, GC America) has a resin component th a t gives the set cem ent greater wear resistance and reportedly better fracture toughness compared to Dr. Croll is in private practice, pediatric the lightdentistry, George hardened town Commons, Suite 2, 708 Shady liners and Retreat Rd., bases. If the Doylestown, Pa., 18901-3897, and new lightassociate hardened glass clinical professor, Depart ionomer has ment of Pediatric Dentistry, University durability and of Pennsylvania longevity School of Dental Medicine, and approaching adjunct professor, th a t of glass Department of ionomer-silver Pediatric Dentistry, University of Texas cerm et Health Science cem ent,10the Center at Houston. Address reprints new m aterial requests to the could change author at his restorative practice. dentistry dram atically in both the prim ary dentition and in conservative applications in the perm anent dentition. I have used this restorative m aterial frequently in my own practice since J a n u a ry 1992 for Class I, II, III and V JADA, Vol. 123, M ay 1992
53
Figure 5a. This child has a three-year-old glass ionomer-silver cermet restoration of the primary first molar and a carious lesion of the canine.'0
Figure 5b. A light-hardened restoration of the canine one year after placement.*
m onths, we found th a t restorative m argins are virtually im perceptible in hydrated restorations w ith good color m atch (Figure 6). We are now investigating Figure 6. Light-hardened occlusal and occluso-lin its use in small guai restorations in this primary second molar are Class I lesions barely perceptible after two months in the mouth of a 3-year-old boy. Light-hardened glass ionomer res in perm anent torative materials with improved physical properties tee th as an are beginning to change modern concepts of restorative dentistry. alternative to “preventive restorations. We apply the resin” restorations.11 m aterial w ith syringe injection O ther major dental m aterial after removing the sm ear layer m anufacturers are currently w ith polyacrylic acid. We use introducing or developing lightthe visible light beam in two 30hardened glass ionomer second exposures, the first after restorative cements. Long-term injection of the cem ent and the durability, color stability, second after finishing. resistance to w ear and fracture Im m ediately after placem ent are unknown a t this time. and light-hardening, the C O N C L U S IO N S restorative surfaces of these restorations can be slightly Since th eir introduction, glass indented w ith a hand ionomers have improved in instrum ent. handling properties, After 24 hours, however, the appearance of the hardened cem ent surface feels as h ard as m aterial, decreased setting tim e set am algam , fully polymerized through visible light beam composite resin or longstanding initial hardening and toughness hardened cerm et cement. At 3V2 of the hardened cem ent m ass. 54
JADA, Vol. 123, May 1992
The im provem ents offer dentists new treatm en t options for posterior and anterior teeth. W hen m anufacturers of glass ionomer m aterials finally pro duce a light-hardened cement th a t can rival composite resin in shade m atching and surface smoothness, and dental am al gam in w ear resistance and fracture toughness, traditional concepts of direct application restorative dentistry will change radically. P erhaps the change has begun. ■ N either th e author nor th e A m erican D ental Association has any commercial in terest in the products m entioned in this paper. 1. M cLean JW , Wilson AD. The clinical developm ent of th e glass ionom er cem ents. II. Some clinical applications. A ust D ent J 1977; 22:120-7. 2. Croll TP. Replacem ent of defective class I am algam restoration w ith stratified glass ionomercomposite resin m aterials. Q uintessence In t 1989; 20:711-6. 3. Croll TP. Repair of severe crown fractu re with glass ionom er and composite resin bonding. Q uintessence In t 1988; 19:649-54. 4. Croll TP. Rapid reattach m en t of fractu re crown segment: a n update. J Esthetic D ent 1990; 2:1-5. 5. Grippo JO. Abfractions: a new classification of h ard tissue lesions of teeth. J Esthetic D ent 1991; 3:14-9. 6. Grippo JO , Masi JV. Role of biodental engineering factors (BEF) in th e etiology of root caries. J E sth etic D ent 1991; 2:71-6. 7. Croll TP. Conservative restoration of a sensitive cervical root lesion. J Esthetic D ent 1989; 1:74-7. 8. Killian CM, Croll TP. Smooth surface glass ionom er resto ratio n for prim ary teeth. J Esthetic D ent 1991; 3:37-40. 9. Croll TP. Visible light-hardened glass-ionom er cem ent base/liner as an interim restorative m aterial. Q uintessence In t 1991; 22:137-41. 10. Croll TP, Phillips RW. Six years experience w ith glass ionomer-silver cerm et cement. Q uintessence In t 1991; 22:783-93. 11. Sim onsen RJ. Preventive resin restorations. In: Clinical applications of the acid etch technique. Chicago: Q uintessence Publishing; 1978: 89-101.