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Why is Glass Ionomer Cement so Popular?
G o r d o n
J .
C h r is t e n s e n ,
d
. d . s .,
m
.s . d .,
p h
.d .
WHY IS GLASS I0N0MER CEMENT SO POPULAR? 0 ver the p ast 20 years, the use of glass ionomer has had a slow b u t positive evolution to the extent th a t it is now the m ost widely used luting agent worldwide. O ther cem ents still in popular use are polycarboxylate and zinc phosphate, and resin cem ents are gaining in popularity. Are d entists satisfied with the cem ents available today? Could these products be better? Are they as adequate as other categories of m aterials in dentistry? C urrently, dental cem ents do not satisfy m ost dentists. These m aterials could be significantly better, and they are among the w orst categories of dental m a terials relative to physical and working characteristics. The dental profession has not been able to advance the con cept of cem entation significant ly. Zinc phosphate, one of the first successful cements, was developed in th e early 1800s, and it is still in relatively common use today. The problem s encountered when trying to obtain adhesion to a w et substance such as dentin are well-known. These problems are often used as an excuse for lack of developm ent in cements. Is glass ionomer cem ent better th a n zinc phosphate or polycarboxylate cement? Should we be satisfied w ith it? I will adm it th a t as a m ature practitioner, w ith the exper ience of accomplishing over 30,000 u n its of fixed prosthodontics over my career, I still
find m yself fru stra ted on nearly every cem entation in determ ining which of the cu rre n t group of less-thanperfect cem ents I will use. The following inform ation will define the cem ent character istics dentists need and the acceptability of glass ionomer cem ents to m eet these needs. IS G L A S S IO N O M E R T H E PERFECT CEM ENT?
E a sy m ix in g . A simple mixing process th a t can be easily understood by all dental staff is m andatory. W ith the exception of some relatively expensive tritu rato r-activ ated glass ionomers, m ost current cements are difficult to mix and sensitive to im proper mixing. T riturator-activated glass ionomers, Fuji I (G.C. America, Inc.) and Ketac-Cem (ESPEPrem ier Sales Co.), are suggest ed to overcome th is variable. E asy clin ica l u se. It would be wonderful to be able to place crowns into the m outh without worrying about saliva contacting the u nset cement. All current cem ents are influenced negativ ely by moisture contact before setting, with glass ionomer showing the worst degeneration. D ental assistan ts m ust know the significance of m oisture contam ination during seating procedures. M oisture m ust be kept away from newly cemented crowns for a t least three to five m inutes a fter seating w ith glass ionomer. A ssigning a dental assistan t to stay w ith the patien t during
this critical cem ent-setting stage is recommended. The a ssista n t should keep m oisture away from the u n set cement, while placing heavy finger force on th e crown(s) to assure optim um seating. Glass ionomer is difficult to use, and requires close observation while working, b u t h as n ear optim um setting tim e. L ack o f to o th s e n s itiz a tio n . The single m ost perplex ing problem encountered w ith traditional cem ents today is postoperative tooth sensitivity. Both zinc phosphate and glass ionomer have dem onstrated significant postoperative sen sitivity. W hen using e ith er of these cem ents, th ere are several im portant considerations neces sary to help prevent sensitivity. M ost im portant is preventing tooth preparation dehydration im m ediately before cemen tation. Tooth preparations should be cleaned w ith w et pumice on a rubber cup and allowed to rem ain w et w ith w ater until im m ediately before cem entation. Only a t th a t tim e is an a ir blast of two or three seconds applied directly in line w ith the long axis of the tooth. The tooth should not be overdried or dehydrated. This tech nique, combined w ith close control of m oisture after cemen tation, prevents m ost post operative sensitivity w ith zinc phosphate or glass ionomer. C urrently, there is growing use of “desensitizing” tech niques before using zinc phosphate or glass ionom er.1 JADA, Vol. 125, September 1994
1257
CHRISTENSEN
Various m aterials, including All-Bond 2 (Bisco D ental Products) or GLUMA 3-Step (Miles Inc., D ental Products) have been shown to reduce postoperative tooth sensitivity. Although popular techniques, in-depth supportive research is still lacking on these. An older procedure of “disin fecting” tooth preparations with q u atern ary am m onium com pounds (Tubulicid, Global D ental Products Co., Inc. Phone: (516)221-8844) has been promoted by some clinicians. Chlorhexidine, a more potent anti-microbiologic agent, has been prom oted by others as a precem entation medication (Concepsis, U ltrad en t Products, Inc.). Again, in-depth research is still necessary. Conscientious practitioners who keep tee th hydrated during precem entation procedures and prevent postoperative contam ination have had only m inim al postoperative tooth sensitivity w ith zinc phosphate or glass ionomer cem ents. Techniques for desensitizing or disinfecting tooth prep arations may be helpful, but they should be used with caution until more research is accomplished. Dr. Christensen is co-founder and Despite pre currently senior cautions, glass consultant of ionomer cement Clinical Research Associates, 3707 N. occasionally Canyon Rd., Suite causes unex no. 6, Provo, Utah, 84604, and is a plainable tooth member o f JADA’ s sensitivity. editorial board. He A d h esion has a m aster’s degree in restorative to tooth. dentistry and a During the life doctorate in education and of a crown, psychology. He is adhesion is an board c e rtified in im portant prosthodontics. 1258
JADA, Vol. 125, September 1994
characteristic. B ut w hen a crown needs to be replaced after 10-30 years of service, adhesion is a problem, m aking th e crown extrem ely difficult to remove. P erhaps m oderate adhesive properties, such as those observed w ith glass ionomer, are ideal. More powerful adhesive cem ents m ay be disadvantageous. Cem ents w ith no adhesive properties, such as zinc phosphate, simply “lu te ” restorations into place, depending on undercuts and irregularities in tooth and restorations for retention. Glass ionomer has about the correct level of adhesiveness. H igh -flow c h a r a c te r istic s. Some cem ents, such as polycarboxylate, feel like rubber when cem enting, while others, such as glass ionomer, have high flow and excellent seating ease. High flow is an excellent characteristic of glass ionomer. C a rio sta tic. As life expect ancy continues to increase, the cariostatic properties of ce m ents should sim ilarly expand to provide long-lasting service to patients. N on-cariostatic ce m ents are less acceptable. Glass ionomer is the m ost cariostatic m aterial among current cements. In so lu b ility in m ou th flu id s. C urrently, only resin cem ents, such as C & B-Metabond (Parkell) or P anavia 21 (J. M orita USA, Inc.) are insoluble in m outh fluids. Glass ionomer is m oderately soluble, providing release of fluoride ion as a posi tive offshoot of this negative characteristic. P erhaps some solubility is necessary for opti m um preventive characteristics. Tim e an d m on ey. C urrent cem ents cost from a few cents per mix to several dollars. Also, tim e required to use the various
cem ents varies from one to three m inutes, which is the most significant cost. Glass ionomer requires m inim al mixing time. S tren gth . This character istic varies from far below tooth structure strength w ith zinc phosphate, polycarboxylate or glass ionomer to nearly tooth stru ctu re stren g th for various resin cements. It appears th a t the stren g th properties of tooth structure would be optim um for cement. SUMM ARY
Glass ionomer cem ents are popular today because they satisfy m any of the character istics of an ideal cement. They can be mixed easily by hand or tritu rato r. They bond to teeth m oderately, have optim um flow properties allowing easy seating, are cariostatic and are relatively inexpensive. On the downside, however, they are not easy to use prop erly, can cause significant post operative tooth sensitivity, are m oderately soluble in m outh fluids and have slightly less th an optim um stren g th char acteristics. Resin modifications of glass ionomer cem ents, to be introduced soon, m ay overcome m any of the negatives associ ated w ith cu rren t glass ionomer cement. There will be fu rth er discussion of these as soon as they are available. ■ Information about glass ionomer techniques is available from Dr. Christensen The opinions expressed or implied are strictly those of the author and do not necessarily reflect the opinion or official policies of the American Dental Association. 1. Christensen GJ, Christensen RP. Tooth desensitization before crown cementation. CRA Newsletter 1993;17(8):2.
J .
C h r is t e n s e n ,
d
. d . s .,
m
.s . d .,
p h
.d .
WHY IS GLASS I0N0MER CEMENT SO POPULAR? 0 ver the p ast 20 years, the use of glass ionomer has had a slow b u t positive evolution to the extent th a t it is now the m ost widely used luting agent worldwide. O ther cem ents still in popular use are polycarboxylate and zinc phosphate, and resin cem ents are gaining in popularity. Are d entists satisfied with the cem ents available today? Could these products be better? Are they as adequate as other categories of m aterials in dentistry? C urrently, dental cem ents do not satisfy m ost dentists. These m aterials could be significantly better, and they are among the w orst categories of dental m a terials relative to physical and working characteristics. The dental profession has not been able to advance the con cept of cem entation significant ly. Zinc phosphate, one of the first successful cements, was developed in th e early 1800s, and it is still in relatively common use today. The problem s encountered when trying to obtain adhesion to a w et substance such as dentin are well-known. These problems are often used as an excuse for lack of developm ent in cements. Is glass ionomer cem ent better th a n zinc phosphate or polycarboxylate cement? Should we be satisfied w ith it? I will adm it th a t as a m ature practitioner, w ith the exper ience of accomplishing over 30,000 u n its of fixed prosthodontics over my career, I still
find m yself fru stra ted on nearly every cem entation in determ ining which of the cu rre n t group of less-thanperfect cem ents I will use. The following inform ation will define the cem ent character istics dentists need and the acceptability of glass ionomer cem ents to m eet these needs. IS G L A S S IO N O M E R T H E PERFECT CEM ENT?
E a sy m ix in g . A simple mixing process th a t can be easily understood by all dental staff is m andatory. W ith the exception of some relatively expensive tritu rato r-activ ated glass ionomers, m ost current cements are difficult to mix and sensitive to im proper mixing. T riturator-activated glass ionomers, Fuji I (G.C. America, Inc.) and Ketac-Cem (ESPEPrem ier Sales Co.), are suggest ed to overcome th is variable. E asy clin ica l u se. It would be wonderful to be able to place crowns into the m outh without worrying about saliva contacting the u nset cement. All current cem ents are influenced negativ ely by moisture contact before setting, with glass ionomer showing the worst degeneration. D ental assistan ts m ust know the significance of m oisture contam ination during seating procedures. M oisture m ust be kept away from newly cemented crowns for a t least three to five m inutes a fter seating w ith glass ionomer. A ssigning a dental assistan t to stay w ith the patien t during
this critical cem ent-setting stage is recommended. The a ssista n t should keep m oisture away from the u n set cement, while placing heavy finger force on th e crown(s) to assure optim um seating. Glass ionomer is difficult to use, and requires close observation while working, b u t h as n ear optim um setting tim e. L ack o f to o th s e n s itiz a tio n . The single m ost perplex ing problem encountered w ith traditional cem ents today is postoperative tooth sensitivity. Both zinc phosphate and glass ionomer have dem onstrated significant postoperative sen sitivity. W hen using e ith er of these cem ents, th ere are several im portant considerations neces sary to help prevent sensitivity. M ost im portant is preventing tooth preparation dehydration im m ediately before cemen tation. Tooth preparations should be cleaned w ith w et pumice on a rubber cup and allowed to rem ain w et w ith w ater until im m ediately before cem entation. Only a t th a t tim e is an a ir blast of two or three seconds applied directly in line w ith the long axis of the tooth. The tooth should not be overdried or dehydrated. This tech nique, combined w ith close control of m oisture after cemen tation, prevents m ost post operative sensitivity w ith zinc phosphate or glass ionomer. C urrently, there is growing use of “desensitizing” tech niques before using zinc phosphate or glass ionom er.1 JADA, Vol. 125, September 1994
1257
CHRISTENSEN
Various m aterials, including All-Bond 2 (Bisco D ental Products) or GLUMA 3-Step (Miles Inc., D ental Products) have been shown to reduce postoperative tooth sensitivity. Although popular techniques, in-depth supportive research is still lacking on these. An older procedure of “disin fecting” tooth preparations with q u atern ary am m onium com pounds (Tubulicid, Global D ental Products Co., Inc. Phone: (516)221-8844) has been promoted by some clinicians. Chlorhexidine, a more potent anti-microbiologic agent, has been prom oted by others as a precem entation medication (Concepsis, U ltrad en t Products, Inc.). Again, in-depth research is still necessary. Conscientious practitioners who keep tee th hydrated during precem entation procedures and prevent postoperative contam ination have had only m inim al postoperative tooth sensitivity w ith zinc phosphate or glass ionomer cem ents. Techniques for desensitizing or disinfecting tooth prep arations may be helpful, but they should be used with caution until more research is accomplished. Dr. Christensen is co-founder and Despite pre currently senior cautions, glass consultant of ionomer cement Clinical Research Associates, 3707 N. occasionally Canyon Rd., Suite causes unex no. 6, Provo, Utah, 84604, and is a plainable tooth member o f JADA’ s sensitivity. editorial board. He A d h esion has a m aster’s degree in restorative to tooth. dentistry and a During the life doctorate in education and of a crown, psychology. He is adhesion is an board c e rtified in im portant prosthodontics. 1258
JADA, Vol. 125, September 1994
characteristic. B ut w hen a crown needs to be replaced after 10-30 years of service, adhesion is a problem, m aking th e crown extrem ely difficult to remove. P erhaps m oderate adhesive properties, such as those observed w ith glass ionomer, are ideal. More powerful adhesive cem ents m ay be disadvantageous. Cem ents w ith no adhesive properties, such as zinc phosphate, simply “lu te ” restorations into place, depending on undercuts and irregularities in tooth and restorations for retention. Glass ionomer has about the correct level of adhesiveness. H igh -flow c h a r a c te r istic s. Some cem ents, such as polycarboxylate, feel like rubber when cem enting, while others, such as glass ionomer, have high flow and excellent seating ease. High flow is an excellent characteristic of glass ionomer. C a rio sta tic. As life expect ancy continues to increase, the cariostatic properties of ce m ents should sim ilarly expand to provide long-lasting service to patients. N on-cariostatic ce m ents are less acceptable. Glass ionomer is the m ost cariostatic m aterial among current cements. In so lu b ility in m ou th flu id s. C urrently, only resin cem ents, such as C & B-Metabond (Parkell) or P anavia 21 (J. M orita USA, Inc.) are insoluble in m outh fluids. Glass ionomer is m oderately soluble, providing release of fluoride ion as a posi tive offshoot of this negative characteristic. P erhaps some solubility is necessary for opti m um preventive characteristics. Tim e an d m on ey. C urrent cem ents cost from a few cents per mix to several dollars. Also, tim e required to use the various
cem ents varies from one to three m inutes, which is the most significant cost. Glass ionomer requires m inim al mixing time. S tren gth . This character istic varies from far below tooth structure strength w ith zinc phosphate, polycarboxylate or glass ionomer to nearly tooth stru ctu re stren g th for various resin cements. It appears th a t the stren g th properties of tooth structure would be optim um for cement. SUMM ARY
Glass ionomer cem ents are popular today because they satisfy m any of the character istics of an ideal cement. They can be mixed easily by hand or tritu rato r. They bond to teeth m oderately, have optim um flow properties allowing easy seating, are cariostatic and are relatively inexpensive. On the downside, however, they are not easy to use prop erly, can cause significant post operative tooth sensitivity, are m oderately soluble in m outh fluids and have slightly less th an optim um stren g th char acteristics. Resin modifications of glass ionomer cem ents, to be introduced soon, m ay overcome m any of the negatives associ ated w ith cu rren t glass ionomer cement. There will be fu rth er discussion of these as soon as they are available. ■ Information about glass ionomer techniques is available from Dr. Christensen The opinions expressed or implied are strictly those of the author and do not necessarily reflect the opinion or official policies of the American Dental Association. 1. Christensen GJ, Christensen RP. Tooth desensitization before crown cementation. CRA Newsletter 1993;17(8):2.