Comparison ionomers Robert
of manually
L. Cooley,
DMD,
MS,s
and
and mechanically Terri
E. Train,
mixed
glass
BAb
University of Texas Health Science Center, Dental School, San Antonio, Texas Two mechanically mixed glass ionomer restorative materials (Ketac-Fil and Fuji Cap II) were compared with two manually mixed products (Chelon-Fil and Fuji Type II). One manually mixed material was substantially weaker than the others in bond strength tests. No sign&ant differences in microleakage were found among the materials. (J PROSTHET DENT 1991;66:773-6.)
G lass
ionomer
restorative
materials
were intro-
duced by Wilson and Kent in 1971,’ and the uses for these materials have dramatically increased. A survey in Dental Products Report revealed that glass ionomers were used by 71% of dentists as a luting cement, by 50 % as a base and core material, by 61% as a liner, and by 57 % as a restorative material.2 A survey in 1988 confirmed that 86.4% of dentists had used some form of this cement.3 Glass ionomers are integral to a family of adhesive restorative materials because they adhere to both enamel and dentin, although the bond to enamel is stronger than to dentin.4-6 Nevertheless, because of this dentinal adhesion, glass ionomer has been advocated as a direct restorative material, particularly for class V preparations.7-g Glass ionomer cements have also been suggested for class V erosion and abrasion lesions, and clinical studies have indicated that they are highly successfulg-l’ Because of the increasing popularity of these materials, manufacturers have packaged a variety of glass ionomer direct restoratives. Two major manufacturers of glass ionomers market the direct restoratives in either a manual or mechanical mix format, providing the dentist more diversity in mixing style and cost. The introduction of versatile products raises questions concerning variation and effectiveness. This study evaluated the bond strength and microleakage ofthe manual and the mechanical mix of two glass ionomer cements. MATERIAL
AND
METHODS
A manual mix and a mechanical mix glass ionomer direct restorative from two manufacturers were evaluated: KetacFil (mechanical), Chelon-Fil (manual) (ESPE-Premier, Norristown, Pa.); and Fuji Type II (manual), and Fuji Cap II (mechanical) (GC International Corp., Scottsdale, Ariz.). The bond strength and microleakage were examined independently and are described separately.
aAssociate Professor, Department of General Practice. bFourth year dental student.
JOURNAL
Shear
OF
PROSTHETIC
DENTISTRY
bond
strength
Ten human molar teeth stored in 10% buffered formalin were prepared for each of the four materials in the first part of the study. The buccal enamel was removed and the dentin was ground flat to 600&t with water-cooled abrasive belts and strips (Surfmet and Handimet, Buehler Ltd., Evanston, Ill.) The teeth were vertically mounted in PVC rings with self-curing poly(methy1 methacrylate) resin to provide a base for testing. A surveyor was used to parallel the flat dentinal surface to the vertical plane. The dentinal surfaces were treated with a dentin conditioner (G.C. Dentin Conditioner or Ketac Conditioner) for 10 seconds before the glass ionomer materials were applied.
Each of the materials was mixed according to the manufacturer’s
10/l/31369
THE
Fig. 1. Scoring categories for rating microleakage.
instructions
and applied to the treated dentinal
773
COOLEY
Fig.
TRAIN
2. Bond strengths of mechanically and manually mixed glass ionomers.
surface in a cylindrical-shaped matrix 3.68 m m in diameand approximately 3 m m in length. The bond-test specimens were coated with a varnish or glaze from their commercial kits and stored in 37” C distilled water for 24 hours before testing. After the designated storage, the specimens were inserted in an Instron universal testing machine (Instron Corp., Canton, Mass.) so that the crosshead force was parallel to the prepared tooth surface. The glass ionomer cylinders were positioned under continuous loading at 0.5 mm/min until fracture, and the shear bond strength was recorded in newtons (N) and calculated in megapascals (MPa).
Ter
M icroleakage Twelve test specimens were prepared for each of the four mat,erials in the second part of the study. A rectangularshaped cavity was prepared on the buccal surface of each tooth with a 330 bur and high-speed handpiece with water coolant. All margins were prepared on enamel, and the ap-
77:
AND
proximate dimensions of the preparations were 4 m m by 3 m m and 2 m m deep. Each material was applied to the cavity preparation according to recommendations of the manufacturer after the dentinal surfaces were treated with a dentin conditioner. The materials were coated with a glaze or varnish from their respective kits, and finishing was accomplished with Sof-Lex disks (3M Dental Products, St. Paul, Minn.) as recommended (24 hours for Fuji; 15 minutes for Ketac and Chelon). The teeth in each group were then thermal cycled for 800 cycles (approximately 24 hours) between water baths of 6’ C (5 2’) and 60” C ( + 2’) with an immersion time of 30 seconds. After thermal cycling, the root and occlusal surfaces were coated with sticky wax, and the entire tooth, except the restoration and one surrounding millimeter, was then covered with nail polish. The restorations were evaluated for microleakage by immersion in 5 % methylene blue dye for 4 hours, removed from the dye solution, rinsed in tap water, and the teeth
DECEMBER
1991
VOLUME
66
NUMBER
6
EFFECTS
Table
OF MIXING
I.
METHODS
COMPARED
Mean shear bond strength
Table
II.
Occlusal microleakage scores Scores
Shear strength Glass ionomer
MPa SD
Fuji Cap II Fuji Type II Ketac-Fil Chelon-Fil
5.10 0.78 3.28 0.86 4.39 1.4 5.20 1.9
Kg/q
c m SD
52.0 7.9 33.5 a.7 44.7 14.7 53.0 20.1
Glass ionomer
0
1
2
3
Fuji Cap II Fuji Type II Ketac-Fil Chelon-Fil
5 0 4 3
5 10 7 4
2 1 10 5
0 1
Table
were sectioned longitudinally through the center of the restoration with a diamond blade (Isomet, Buehler Ltd., Evanston, Ill.). The microleakage was determined by the penetration of the blue dye from the enamel margins along the walls of the cavity preparation with the following scoring criteria (Fig. 1): O-No marginal leakage l-Subsurface to half the distance to the pulpal wall Z-Greater than half of the distance to the pulpal wall ~--TO the pulpal wall and along the pulpal wall for any distance The specimens were examined under a stereobinocular microscope (X 10) by two examiners focusing separately on the occlusal and gingival walls for microleakage. The sectioned halves were scored according to the consensus criteria established by the two examiners. The half exhibiting the greatest leakage was recorded for statistical analysis.
RESULTS The results were divided into two categories: bond strength and microleakage.
Bond strength The mean bond strengths (MPa) for the 10 samples of each group are presented in Table I and Fig. 2. There was considerable variation within groups of materials and between groups. The mean bond strengths were as follows: Fuji Cap II, 5.1 MPa; Fuji Type II, 3.28 MPa; Ketac-Fil, 4.39 MPa; and Chelon-Fil, 5.2 MPa. When the bond strength data were evaluated by analysis of variance (ANOVA), a significant difference in bond strengths was evident among groups (p < 0.01). When the groups were analyzed by using the Student-NewmanKeuls procedure, Fuji Type II was found to be significantly weaker than the other materials (p < 0.05) and no other differences between groups were revealed.
M icroleakage Microleakage was evaluated separately for the occlusal and gingival surfaces of the restoration (Tables II and III). When the occlusal wall leakage scores were added for each material, the two mechanically mixed materials had lower
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
III.
0
sum of leakage scores
Median score
9 15 9 14
1 1 1 1
Gingival microleakage scores Scores
Glass ionomer
0
1
2
3
Fuji Cap II Fuji Type II Ketac-Fil Chelon-Fil
1 0 1 0
6 9 6 7
4 3 5 4
1 0 0 1
sum of leakage scores
17 15 16 18
Median score
1 1 1 1
leakage scores (Fuji Cap II, 9; Ketac-Fil, 9; Fuji Type II, 15; and Chelon-Fil, 14). The sum of gingival microleakage scores for the four groups were closer and generally higher (Fuji Cap II, 17; Fuji Type II, 15; Ketac-Fil, 16; and Chelon-Fil, 18). When these data were subjected to a Kruskal-Wallis test, no significant difference in microleakage was found between the materials for the occlusal or gingival surfaces. An evaluation of the microleakage data with a W ilcoxon signed ranks test revealed no significant difference between the occlusal and gingival surfaces within the groups.
DISCUSSION Bond strength testing demonstrated that Fuji Type II (manual mix) formed significantly weaker bonds to dentin than the other materials. There was no significant difference among Chelon-Fil (manual mix), Ketac-Fil (mechanical mix), or Fuji Cap II (mechanical mix). The bond strengths of this study were similar to those in a recent study comparing the bond of Ketac-Fil and Fuji Type II materials to recently extracted versus “aged” extracted teeth.* In that study, Fuji Type II material recorded a bond strength of 3.9 MPa to aged extracted teeth compared with 4.8 MPa to recently extracted teeth. Fuji Type II material exhibited a significantly higher bond strength applied to recently extracted teeth, whereas Ketac-Fil material had a bond strength of approximately 5.2 MPa on both groups of teeth. However, the bond strength of glass ionomers is modest when compared with composite resin bonded to etched enamel. The enamel-composite resin bond is approximately 16 to 20 MPa and is a clinically durable procedure.ls
*Al-Munif
H, Cooley RL, Hicks J. Unpublished data.
775
COOLEY
The m icfolq
,phaaein&-d that these glass ionomeir ~a~v~,~e subs to mic~obakage alon$ the enamei mar&ns~ -hntthew was no significant difhrrence in mi&&ea~e among the four materials. After the microleakege of eachgroup was examined, the two mechanically-mixed (Fuji Cap II and Ketac-Fil) cements appeared to have recorded less microleakage, but this difference was not statistically significant. A previous study of glass ionomer cements also confirmed microleakage. l3 Class V cavity preparations were prepared with one enamel margin and one margin in dentin. All four glass ionomers (Ketac-Fil, Ketac-Silver, Fuji Miracle Mix, and Fuji Type II) exhibited leakage at both the enamel and the dentinal margins, but the microleakage was appreciably greater at the dentinal margin than the enamel margin, except for Fuji Type II material with greater leakage at the enamel margins. Although glass ionomers have exhibited microleakage in several studies, it may not be clinically significant. Microleakage precipitates recurrent caries, postoperative sensitivity, and discoloration, but because these materials release fluoridesimilar to silicates, caries has not been a problem ~ulith glass ionomer restorations.r* Also, restoration failure-has been studied in two clinical investigations. A l-year evaluation9 revealed that 5 % of the restorations were lost, a&a f&year evaluation disclosed a loss rate of 7 % .ls Although glass ionomer restorations have displayed microleakage in the laboratory, the long-term clinical effects are unknown.
Two mechenieally mixed (Fuji Cap II and Ketac-Fil) glass ionomer-restoratives were compared with two manually mixed materials (Fuji Type II and CheIon-Fil) for
AND
TRAIN
dentin bond strength and microleakage. One manually mixed mat&&l (Fuji Type II) recorded a substantially weaker bond strength, but no significant differences in microleakage were observed between the manually mixed and mechanically mixed materials. REFERENCES 1. Wilson AD, Kent BE. A new translucent cement for dentistry. Br Dent
J 1972;132:133-5. 2. Matson J, ed. Multipurpose glass ionomer materials gain in acceptance by general practitioners. Dental Producte Report 1986;20:11. 3. Charbeneau G, Klausner L, Brandau H. Glass ionomer cements in dental practice: a national survey [Abstract]. J Dent Res 198&67:283. 4. Craig RC. Restorative dental materials. 7th ed. St Louis: CV Mosby Co, 1985;249. 5. Fan PL, Cobb EN. Council on Dental Materials, Instruments, and Equipment, American Dental Association. Dentin bonding systems: an update. J A m Dent Assoc 1987;114:91-4. 6. Swift EJ. Glass ionomers: a review for the clinical dentist. Gen Dent 1986;34:468-71. 7. McLean JW. Alternatives to amalgam alloys. Br Dent J 1984:157:432-3. 8. McLean JW. New concepts in cosmetic dentistry using glass-ionomer cements and composites. Calif Dent J 198&X20-5. 9. Ngo H, Earl M, Mount G. Glassionomer cements: a 12-month evahration. J PROSTHET DENT 1986,55:203-5. 10. Mount GJ- Longevity of glass ionomer cements. J FWSTHET DENT 1986;55:682-5.
11. Knibbs P, Plant CA. A clinical assessmentof a rapid setting glass ionomer cement. Br Dent J 1986,161:323-6. 12. Craig RG. Restorative dental materials. 8th ed. St Louis: CV Moshy Co, 1989;262. 13. Cooley RL, Robbins JW. Glass ionomer microleakage in Class V restorations. Gan Dent 1988,37:113-5. 14. Swartz ML, Phillips RW, Clark HE. Long term F release from glass ionomer cements. J Dent Res 19&1:63:158. Reprint requests to: DR. ROBERT L. COOLEY GENERAL PRACTICE-UTHSC 7703 FLOYD CURL DR. SAN ANTONIO, TX 78284-7914
DECEMBER
1991
VOLUME
66
NUMBER
6
of manually
L. Cooley,
DMD,
MS,s
and
and mechanically Terri
E. Train,
mixed
glass
BAb
University of Texas Health Science Center, Dental School, San Antonio, Texas Two mechanically mixed glass ionomer restorative materials (Ketac-Fil and Fuji Cap II) were compared with two manually mixed products (Chelon-Fil and Fuji Type II). One manually mixed material was substantially weaker than the others in bond strength tests. No sign&ant differences in microleakage were found among the materials. (J PROSTHET DENT 1991;66:773-6.)
G lass
ionomer
restorative
materials
were intro-
duced by Wilson and Kent in 1971,’ and the uses for these materials have dramatically increased. A survey in Dental Products Report revealed that glass ionomers were used by 71% of dentists as a luting cement, by 50 % as a base and core material, by 61% as a liner, and by 57 % as a restorative material.2 A survey in 1988 confirmed that 86.4% of dentists had used some form of this cement.3 Glass ionomers are integral to a family of adhesive restorative materials because they adhere to both enamel and dentin, although the bond to enamel is stronger than to dentin.4-6 Nevertheless, because of this dentinal adhesion, glass ionomer has been advocated as a direct restorative material, particularly for class V preparations.7-g Glass ionomer cements have also been suggested for class V erosion and abrasion lesions, and clinical studies have indicated that they are highly successfulg-l’ Because of the increasing popularity of these materials, manufacturers have packaged a variety of glass ionomer direct restoratives. Two major manufacturers of glass ionomers market the direct restoratives in either a manual or mechanical mix format, providing the dentist more diversity in mixing style and cost. The introduction of versatile products raises questions concerning variation and effectiveness. This study evaluated the bond strength and microleakage ofthe manual and the mechanical mix of two glass ionomer cements. MATERIAL
AND
METHODS
A manual mix and a mechanical mix glass ionomer direct restorative from two manufacturers were evaluated: KetacFil (mechanical), Chelon-Fil (manual) (ESPE-Premier, Norristown, Pa.); and Fuji Type II (manual), and Fuji Cap II (mechanical) (GC International Corp., Scottsdale, Ariz.). The bond strength and microleakage were examined independently and are described separately.
aAssociate Professor, Department of General Practice. bFourth year dental student.
JOURNAL
Shear
OF
PROSTHETIC
DENTISTRY
bond
strength
Ten human molar teeth stored in 10% buffered formalin were prepared for each of the four materials in the first part of the study. The buccal enamel was removed and the dentin was ground flat to 600&t with water-cooled abrasive belts and strips (Surfmet and Handimet, Buehler Ltd., Evanston, Ill.) The teeth were vertically mounted in PVC rings with self-curing poly(methy1 methacrylate) resin to provide a base for testing. A surveyor was used to parallel the flat dentinal surface to the vertical plane. The dentinal surfaces were treated with a dentin conditioner (G.C. Dentin Conditioner or Ketac Conditioner) for 10 seconds before the glass ionomer materials were applied.
Each of the materials was mixed according to the manufacturer’s
10/l/31369
THE
Fig. 1. Scoring categories for rating microleakage.
instructions
and applied to the treated dentinal
773
COOLEY
Fig.
TRAIN
2. Bond strengths of mechanically and manually mixed glass ionomers.
surface in a cylindrical-shaped matrix 3.68 m m in diameand approximately 3 m m in length. The bond-test specimens were coated with a varnish or glaze from their commercial kits and stored in 37” C distilled water for 24 hours before testing. After the designated storage, the specimens were inserted in an Instron universal testing machine (Instron Corp., Canton, Mass.) so that the crosshead force was parallel to the prepared tooth surface. The glass ionomer cylinders were positioned under continuous loading at 0.5 mm/min until fracture, and the shear bond strength was recorded in newtons (N) and calculated in megapascals (MPa).
Ter
M icroleakage Twelve test specimens were prepared for each of the four mat,erials in the second part of the study. A rectangularshaped cavity was prepared on the buccal surface of each tooth with a 330 bur and high-speed handpiece with water coolant. All margins were prepared on enamel, and the ap-
77:
AND
proximate dimensions of the preparations were 4 m m by 3 m m and 2 m m deep. Each material was applied to the cavity preparation according to recommendations of the manufacturer after the dentinal surfaces were treated with a dentin conditioner. The materials were coated with a glaze or varnish from their respective kits, and finishing was accomplished with Sof-Lex disks (3M Dental Products, St. Paul, Minn.) as recommended (24 hours for Fuji; 15 minutes for Ketac and Chelon). The teeth in each group were then thermal cycled for 800 cycles (approximately 24 hours) between water baths of 6’ C (5 2’) and 60” C ( + 2’) with an immersion time of 30 seconds. After thermal cycling, the root and occlusal surfaces were coated with sticky wax, and the entire tooth, except the restoration and one surrounding millimeter, was then covered with nail polish. The restorations were evaluated for microleakage by immersion in 5 % methylene blue dye for 4 hours, removed from the dye solution, rinsed in tap water, and the teeth
DECEMBER
1991
VOLUME
66
NUMBER
6
EFFECTS
Table
OF MIXING
I.
METHODS
COMPARED
Mean shear bond strength
Table
II.
Occlusal microleakage scores Scores
Shear strength Glass ionomer
MPa SD
Fuji Cap II Fuji Type II Ketac-Fil Chelon-Fil
5.10 0.78 3.28 0.86 4.39 1.4 5.20 1.9
Kg/q
c m SD
52.0 7.9 33.5 a.7 44.7 14.7 53.0 20.1
Glass ionomer
0
1
2
3
Fuji Cap II Fuji Type II Ketac-Fil Chelon-Fil
5 0 4 3
5 10 7 4
2 1 10 5
0 1
Table
were sectioned longitudinally through the center of the restoration with a diamond blade (Isomet, Buehler Ltd., Evanston, Ill.). The microleakage was determined by the penetration of the blue dye from the enamel margins along the walls of the cavity preparation with the following scoring criteria (Fig. 1): O-No marginal leakage l-Subsurface to half the distance to the pulpal wall Z-Greater than half of the distance to the pulpal wall ~--TO the pulpal wall and along the pulpal wall for any distance The specimens were examined under a stereobinocular microscope (X 10) by two examiners focusing separately on the occlusal and gingival walls for microleakage. The sectioned halves were scored according to the consensus criteria established by the two examiners. The half exhibiting the greatest leakage was recorded for statistical analysis.
RESULTS The results were divided into two categories: bond strength and microleakage.
Bond strength The mean bond strengths (MPa) for the 10 samples of each group are presented in Table I and Fig. 2. There was considerable variation within groups of materials and between groups. The mean bond strengths were as follows: Fuji Cap II, 5.1 MPa; Fuji Type II, 3.28 MPa; Ketac-Fil, 4.39 MPa; and Chelon-Fil, 5.2 MPa. When the bond strength data were evaluated by analysis of variance (ANOVA), a significant difference in bond strengths was evident among groups (p < 0.01). When the groups were analyzed by using the Student-NewmanKeuls procedure, Fuji Type II was found to be significantly weaker than the other materials (p < 0.05) and no other differences between groups were revealed.
M icroleakage Microleakage was evaluated separately for the occlusal and gingival surfaces of the restoration (Tables II and III). When the occlusal wall leakage scores were added for each material, the two mechanically mixed materials had lower
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
III.
0
sum of leakage scores
Median score
9 15 9 14
1 1 1 1
Gingival microleakage scores Scores
Glass ionomer
0
1
2
3
Fuji Cap II Fuji Type II Ketac-Fil Chelon-Fil
1 0 1 0
6 9 6 7
4 3 5 4
1 0 0 1
sum of leakage scores
17 15 16 18
Median score
1 1 1 1
leakage scores (Fuji Cap II, 9; Ketac-Fil, 9; Fuji Type II, 15; and Chelon-Fil, 14). The sum of gingival microleakage scores for the four groups were closer and generally higher (Fuji Cap II, 17; Fuji Type II, 15; Ketac-Fil, 16; and Chelon-Fil, 18). When these data were subjected to a Kruskal-Wallis test, no significant difference in microleakage was found between the materials for the occlusal or gingival surfaces. An evaluation of the microleakage data with a W ilcoxon signed ranks test revealed no significant difference between the occlusal and gingival surfaces within the groups.
DISCUSSION Bond strength testing demonstrated that Fuji Type II (manual mix) formed significantly weaker bonds to dentin than the other materials. There was no significant difference among Chelon-Fil (manual mix), Ketac-Fil (mechanical mix), or Fuji Cap II (mechanical mix). The bond strengths of this study were similar to those in a recent study comparing the bond of Ketac-Fil and Fuji Type II materials to recently extracted versus “aged” extracted teeth.* In that study, Fuji Type II material recorded a bond strength of 3.9 MPa to aged extracted teeth compared with 4.8 MPa to recently extracted teeth. Fuji Type II material exhibited a significantly higher bond strength applied to recently extracted teeth, whereas Ketac-Fil material had a bond strength of approximately 5.2 MPa on both groups of teeth. However, the bond strength of glass ionomers is modest when compared with composite resin bonded to etched enamel. The enamel-composite resin bond is approximately 16 to 20 MPa and is a clinically durable procedure.ls
*Al-Munif
H, Cooley RL, Hicks J. Unpublished data.
775
COOLEY
The m icfolq
,phaaein&-d that these glass ionomeir ~a~v~,~e subs to mic~obakage alon$ the enamei mar&ns~ -hntthew was no significant difhrrence in mi&&ea~e among the four materials. After the microleakege of eachgroup was examined, the two mechanically-mixed (Fuji Cap II and Ketac-Fil) cements appeared to have recorded less microleakage, but this difference was not statistically significant. A previous study of glass ionomer cements also confirmed microleakage. l3 Class V cavity preparations were prepared with one enamel margin and one margin in dentin. All four glass ionomers (Ketac-Fil, Ketac-Silver, Fuji Miracle Mix, and Fuji Type II) exhibited leakage at both the enamel and the dentinal margins, but the microleakage was appreciably greater at the dentinal margin than the enamel margin, except for Fuji Type II material with greater leakage at the enamel margins. Although glass ionomers have exhibited microleakage in several studies, it may not be clinically significant. Microleakage precipitates recurrent caries, postoperative sensitivity, and discoloration, but because these materials release fluoridesimilar to silicates, caries has not been a problem ~ulith glass ionomer restorations.r* Also, restoration failure-has been studied in two clinical investigations. A l-year evaluation9 revealed that 5 % of the restorations were lost, a&a f&year evaluation disclosed a loss rate of 7 % .ls Although glass ionomer restorations have displayed microleakage in the laboratory, the long-term clinical effects are unknown.
Two mechenieally mixed (Fuji Cap II and Ketac-Fil) glass ionomer-restoratives were compared with two manually mixed materials (Fuji Type II and CheIon-Fil) for
AND
TRAIN
dentin bond strength and microleakage. One manually mixed mat&&l (Fuji Type II) recorded a substantially weaker bond strength, but no significant differences in microleakage were observed between the manually mixed and mechanically mixed materials. REFERENCES 1. Wilson AD, Kent BE. A new translucent cement for dentistry. Br Dent
J 1972;132:133-5. 2. Matson J, ed. Multipurpose glass ionomer materials gain in acceptance by general practitioners. Dental Producte Report 1986;20:11. 3. Charbeneau G, Klausner L, Brandau H. Glass ionomer cements in dental practice: a national survey [Abstract]. J Dent Res 198&67:283. 4. Craig RC. Restorative dental materials. 7th ed. St Louis: CV Mosby Co, 1985;249. 5. Fan PL, Cobb EN. Council on Dental Materials, Instruments, and Equipment, American Dental Association. Dentin bonding systems: an update. J A m Dent Assoc 1987;114:91-4. 6. Swift EJ. Glass ionomers: a review for the clinical dentist. Gen Dent 1986;34:468-71. 7. McLean JW. Alternatives to amalgam alloys. Br Dent J 1984:157:432-3. 8. McLean JW. New concepts in cosmetic dentistry using glass-ionomer cements and composites. Calif Dent J 198&X20-5. 9. Ngo H, Earl M, Mount G. Glassionomer cements: a 12-month evahration. J PROSTHET DENT 1986,55:203-5. 10. Mount GJ- Longevity of glass ionomer cements. J FWSTHET DENT 1986;55:682-5.
11. Knibbs P, Plant CA. A clinical assessmentof a rapid setting glass ionomer cement. Br Dent J 1986,161:323-6. 12. Craig RG. Restorative dental materials. 8th ed. St Louis: CV Moshy Co, 1989;262. 13. Cooley RL, Robbins JW. Glass ionomer microleakage in Class V restorations. Gan Dent 1988,37:113-5. 14. Swartz ML, Phillips RW, Clark HE. Long term F release from glass ionomer cements. J Dent Res 19&1:63:158. Reprint requests to: DR. ROBERT L. COOLEY GENERAL PRACTICE-UTHSC 7703 FLOYD CURL DR. SAN ANTONIO, TX 78284-7914
DECEMBER
1991
VOLUME
66
NUMBER
6
