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Dimensional stability of glass ionomer used as a core material
Dimensional material
stability
Robert L. Cooley, D.M.D., Sean Barnwell, B.S.** University
of glass ionomer
M.S.,* James W. Robbins,
used as a core
D.D.S., M.A.,* and
of Texas Health Science Center, School of Dentistry, San Antonio, Texas
This laboratory study evaluated the dimensional stability of two reinforced glass ionomers (Ketac-Silver and Fuji Miracle Mix) in comparison with amalgam. Ten core build-ups were prepared with each material on extracted human teeth. Four Minim pins were placed in each tooth for retention. A gold casting was made for each core build-up. The specimens were placed in a distilled water and the distance between the casting and the tooth was measured at 1 hour, 6 hours, and then every 24 hours for 7 days. After 7 days, the measured changes were small, ranging from 1 to 63 pm. The reinforced glass ionomers were found to be dimensionally stable in moisture over a period of 7 days. (J PROSTHET DENT 1990;64:661-3.)
S
everal materials have been used for core build-ups in teeth with severe destruction. In recent years, glass ionomers have experienced a significant increase in use. A recent survey in the Journal of Dental Research1 revealed that 92.6% of dentists questioned were currently using glass ionomer in some form. Another survey by Dental Products Reports in August 19862 found that 50% of the dentists surveyed were using a glass ionomer as a core build-up material. However, the dimensional stability of reinforced glass ionomer as a build-up material in a wet environment has not been studied. The dimensional stability of a composite resin used as a core material has been investigated. Oliva and Lowe3 studied the effects of water sorption on Concise (3M Dental Products, St. Paul, Minn.) composite resin as it related to marginal seating of cast restorations. This study found that composite resin cores were not dimensionally stable when exposed to moisture. Marginal seating of crowns constructed over these composite resin cores was affected by the instability of the core material. These results are consistent with the reported water sorption of composite. Craig4 states that the range of water sorption for conventional composite resins is 0.3 to 0.7 mg/cm2. Pearson5 found that composite resin demonstrated rapid fluid uptake during the first 2 weeks in the wet environment and then approached an equilibrium. In contrast, Vermilyea et a1.6reported opposite results. They found that the dimensional change associated with composite resin cores in a wet environment did not significantly alter the fit of cast restorations when compared with natural teeth. This study evaluated the dimensional stability of reinforced glass ionomer in the same manner as the study of Oliva and Lowe.3
*Associate Professor, Department of General Practice. **Resident, Advanced Education in General Dentistry.
10/l/22126
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
MATERIAL
AND
METHODS
Two reinforced glass ionomers were evaluated for dimensional stability and were compared to amalgam. The glass ionomers were Ketac Silver (Espe-Premier, Norristown, Pa.) and Fuji Miracle Mix (GC International, Scottsdale, Ariz.). The amalgam control was a spherical alloy (Tytin, Sybron/Kerr, Romulus, Mich.). Thirty extracted human molar teeth previously stored in 10% formalin were mounted in polyvinylchloride (PVC) rings with poly(methy1 methacrylate), were placed in a lathe, and the crowns were removed 3 mm above the cementoenamel junction (CEJ), producing a flat dentin surface. The remaining tooth structure was then machined to a round configuration (7.2 it 0.5 mm diameter). A light shoulder was placed 1 mm below this round preparation. Four Minim pins (Whaledent International, New York, N.Y.) were placed in each tooth 1 mm from the outer surface of the preparation, at a 2 mm depth into the dentin, and were cut off projecting 2 mm out of the tooth. The prepared teeth were divided into three groups of 10 so that each material would be used as a build-up material in 10 specimens. A copper band matrix was placed over each specimen and was stabilized with compound. The dentin surface of each of the specimens to receive the glass ionomer materials was dried and conditioned with 10% polyacrylic acid (GC Dentin Conditioner, GC International) for 20 seconds. The Miracle Mix glass ionomer was mixed using a 32 powder/liquid ratio and was inserted with a Mark III C-R syringe (Centrix Inc, Milford, Conn.). The other materials were mixed and inserted according to the manufacturer’s instructions. All of the glass ionomer specimens were coated with Ketac varnish. The specimens were allowed to set undisturbed at room temperature for 24 hours and were then returned to the lathe and machined to produce a core build-up 4 mm in height with a combined taper of 10 degrees. Each core build-up had one seating groove placed with a 170 bur (Fig. 1).
651
COOLEY,
Fig. 1. Each core build-up was machined to dimensions and taper depicted.
ROBBINS,
AND
BARNWELL
Fig. 2. Measuring mark was placed on each casting (A) and on corresponding tooth (B).
Fig. 3. Casting seating jig applied constant uniform pressure during measurements.
An impression was made of each core build-up with Impregum (Espe-Premier) material and a master die was produced with Velmix (Sybron/Kerr) material. A gold casting was made for each core build-up by wax-up on the die. The castings were fitted first on the dies and were then fitted on the core build-ups. In order to detect change in dimensional stability of the cores, a measuring mark (X) was placed on the gold casting and the tooth (Fig. 2). Two additional measuring marks 652
were placed on the opposite side of the specimens to allow two measurements for each core build-up. A seating jig was made to hold each casting on the core build-up with a uniform pressure (Fig. 3). This springloaded device applied a constant uniform seating pressure of 2.5 kg on the casting while measurements were recorded. The spring-loading force of the jig was verified initially by a dead weight of 2.5 kg and by an electronic strain gauge. The distance between the measuring marks (Fig. 2) was
DECEMBER
1900
VOLUME
64
NUMBER
6
GLASS
Table
IONOMER
I.
STABILITY
Mean change in measurements (in microns) Amalgam Site
1 Hour 6 Hours 24 Hours 2 Days 3 Days 4 Days 5 Days 6 Days 7 Days
1
Ketac Site
11 4 13 10 -41 5
6 -7 13 -9 -31 10
-5 -1
-8 -3 -9
7
2
measured with a measuring microscope after fitting the gold castings and this distance was used as a baseline. The specimens were then placed in distilled water and the distances between the measuring marks (Fig. 2) were measured at 1 hour, 6 hours, and then every 24 hours for 7 days.
RESULTS The mean change (increase or decrease) in measurement is listed in Table I. These mean values represent changes from baseline. At all time periods, a small change was noted from the baseline measurement. The range of measurements for all the materials ranged from a low of 1 pm to a high of 63 Mm. At 7 days, the changes measured at both sites were small, with the following changes from baseline: amalgam: 7 pm and -9 pm; Ketac Silver: 13 and -1 Km; and Miracle Mix: 33 and 63 pm. The data obtained from measurement differences were subjected to an analysis of variance (ANOVA) for site 1 and site 2. The analysis did not show any statistical difference between groups (amalgam, Ketac Silver, Miracle Mix) or change over time for site 1. At site 2, no significant differences were found between groups, but there was a statistically significant change over time (p < 0.01). However, given the small changes measured, this change was not felt to be clinically significant.
Site
1
Miracle Site
-55 -33 22 -10 23 25 5 -5 13
2
Site
1
Mix Site
-10 17 55 10 16 27
12 27 31 31 13 22
25 55 48 52 44 71
-13
18 19 33
17 57 63
3 -1
2
of seating the castings precisely for each measurement time period, no difference in measurement was demonstrated for the three build-up materials over all time periods. In contrast with these results, Oliva and Lowe3 demonstrated a progressively increasing marginal gap when composite resin was used as the core build-up material. The maximum marginal gap with composite resin was 258 pm, which was measured at 6 days.
CONCLUSIONS The dimensional a build-up material der the conditions was dimensionally days.
stability of reinforced glass ionomer as in a wet environment was studied. Unof this study, reinforced glass ionomer stable in moisture over a period of 7
REFERENCES 1. Charbeneau
2. 3. 4. 5. 6.
DISCUSSION
Silver
G, Klausner L, Brandau H. Glass ionomer cements in dental practice: a national survey [Abstract]. J Dent Res 1988;67:283. Matson J, ed. Multipurpose glass ionomer materials gain in acceptance by general practitioners. Dent Products Rep 1986;20:40. Oliva RA, Lowe JA. Dimensional stability of composite used as a core material. J PROSTHET DENT 1986,56:554-61. Craig RG. Restorative dental materials. 7th ed. St Louis: CV Mosby Co, 1985:232. Pearson GJ. Long-term water sorption and solubility of composite materials. J Dent 1979;7:64-8. Vermilyea S, Gardner F, Moergeli J. Composite dowels and cores: effect of moisture on the fit of cast restorations. J PROSTHET DENT 1987;58:429-
31.
A pilot study was performed to develop the technique and precision necessary to achieve accurate measurements. However, as demonstrated by the measurements of the amalgam controls in Table I, the same casting would seat slightly more than the baseline value at one time and slightly less at another time. Given the measurement error
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Reprint requests to: DR. ROBERT L. C~~LEY DENTAL SCHOOL UNIVERSITY OF TEXAS HEALTH 7703 FLOYD CURL DR. SAN ANTONIO, TX 78284-7914
SCIENCE CENTER
653
stability
Robert L. Cooley, D.M.D., Sean Barnwell, B.S.** University
of glass ionomer
M.S.,* James W. Robbins,
used as a core
D.D.S., M.A.,* and
of Texas Health Science Center, School of Dentistry, San Antonio, Texas
This laboratory study evaluated the dimensional stability of two reinforced glass ionomers (Ketac-Silver and Fuji Miracle Mix) in comparison with amalgam. Ten core build-ups were prepared with each material on extracted human teeth. Four Minim pins were placed in each tooth for retention. A gold casting was made for each core build-up. The specimens were placed in a distilled water and the distance between the casting and the tooth was measured at 1 hour, 6 hours, and then every 24 hours for 7 days. After 7 days, the measured changes were small, ranging from 1 to 63 pm. The reinforced glass ionomers were found to be dimensionally stable in moisture over a period of 7 days. (J PROSTHET DENT 1990;64:661-3.)
S
everal materials have been used for core build-ups in teeth with severe destruction. In recent years, glass ionomers have experienced a significant increase in use. A recent survey in the Journal of Dental Research1 revealed that 92.6% of dentists questioned were currently using glass ionomer in some form. Another survey by Dental Products Reports in August 19862 found that 50% of the dentists surveyed were using a glass ionomer as a core build-up material. However, the dimensional stability of reinforced glass ionomer as a build-up material in a wet environment has not been studied. The dimensional stability of a composite resin used as a core material has been investigated. Oliva and Lowe3 studied the effects of water sorption on Concise (3M Dental Products, St. Paul, Minn.) composite resin as it related to marginal seating of cast restorations. This study found that composite resin cores were not dimensionally stable when exposed to moisture. Marginal seating of crowns constructed over these composite resin cores was affected by the instability of the core material. These results are consistent with the reported water sorption of composite. Craig4 states that the range of water sorption for conventional composite resins is 0.3 to 0.7 mg/cm2. Pearson5 found that composite resin demonstrated rapid fluid uptake during the first 2 weeks in the wet environment and then approached an equilibrium. In contrast, Vermilyea et a1.6reported opposite results. They found that the dimensional change associated with composite resin cores in a wet environment did not significantly alter the fit of cast restorations when compared with natural teeth. This study evaluated the dimensional stability of reinforced glass ionomer in the same manner as the study of Oliva and Lowe.3
*Associate Professor, Department of General Practice. **Resident, Advanced Education in General Dentistry.
10/l/22126
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
MATERIAL
AND
METHODS
Two reinforced glass ionomers were evaluated for dimensional stability and were compared to amalgam. The glass ionomers were Ketac Silver (Espe-Premier, Norristown, Pa.) and Fuji Miracle Mix (GC International, Scottsdale, Ariz.). The amalgam control was a spherical alloy (Tytin, Sybron/Kerr, Romulus, Mich.). Thirty extracted human molar teeth previously stored in 10% formalin were mounted in polyvinylchloride (PVC) rings with poly(methy1 methacrylate), were placed in a lathe, and the crowns were removed 3 mm above the cementoenamel junction (CEJ), producing a flat dentin surface. The remaining tooth structure was then machined to a round configuration (7.2 it 0.5 mm diameter). A light shoulder was placed 1 mm below this round preparation. Four Minim pins (Whaledent International, New York, N.Y.) were placed in each tooth 1 mm from the outer surface of the preparation, at a 2 mm depth into the dentin, and were cut off projecting 2 mm out of the tooth. The prepared teeth were divided into three groups of 10 so that each material would be used as a build-up material in 10 specimens. A copper band matrix was placed over each specimen and was stabilized with compound. The dentin surface of each of the specimens to receive the glass ionomer materials was dried and conditioned with 10% polyacrylic acid (GC Dentin Conditioner, GC International) for 20 seconds. The Miracle Mix glass ionomer was mixed using a 32 powder/liquid ratio and was inserted with a Mark III C-R syringe (Centrix Inc, Milford, Conn.). The other materials were mixed and inserted according to the manufacturer’s instructions. All of the glass ionomer specimens were coated with Ketac varnish. The specimens were allowed to set undisturbed at room temperature for 24 hours and were then returned to the lathe and machined to produce a core build-up 4 mm in height with a combined taper of 10 degrees. Each core build-up had one seating groove placed with a 170 bur (Fig. 1).
651
COOLEY,
Fig. 1. Each core build-up was machined to dimensions and taper depicted.
ROBBINS,
AND
BARNWELL
Fig. 2. Measuring mark was placed on each casting (A) and on corresponding tooth (B).
Fig. 3. Casting seating jig applied constant uniform pressure during measurements.
An impression was made of each core build-up with Impregum (Espe-Premier) material and a master die was produced with Velmix (Sybron/Kerr) material. A gold casting was made for each core build-up by wax-up on the die. The castings were fitted first on the dies and were then fitted on the core build-ups. In order to detect change in dimensional stability of the cores, a measuring mark (X) was placed on the gold casting and the tooth (Fig. 2). Two additional measuring marks 652
were placed on the opposite side of the specimens to allow two measurements for each core build-up. A seating jig was made to hold each casting on the core build-up with a uniform pressure (Fig. 3). This springloaded device applied a constant uniform seating pressure of 2.5 kg on the casting while measurements were recorded. The spring-loading force of the jig was verified initially by a dead weight of 2.5 kg and by an electronic strain gauge. The distance between the measuring marks (Fig. 2) was
DECEMBER
1900
VOLUME
64
NUMBER
6
GLASS
Table
IONOMER
I.
STABILITY
Mean change in measurements (in microns) Amalgam Site
1 Hour 6 Hours 24 Hours 2 Days 3 Days 4 Days 5 Days 6 Days 7 Days
1
Ketac Site
11 4 13 10 -41 5
6 -7 13 -9 -31 10
-5 -1
-8 -3 -9
7
2
measured with a measuring microscope after fitting the gold castings and this distance was used as a baseline. The specimens were then placed in distilled water and the distances between the measuring marks (Fig. 2) were measured at 1 hour, 6 hours, and then every 24 hours for 7 days.
RESULTS The mean change (increase or decrease) in measurement is listed in Table I. These mean values represent changes from baseline. At all time periods, a small change was noted from the baseline measurement. The range of measurements for all the materials ranged from a low of 1 pm to a high of 63 Mm. At 7 days, the changes measured at both sites were small, with the following changes from baseline: amalgam: 7 pm and -9 pm; Ketac Silver: 13 and -1 Km; and Miracle Mix: 33 and 63 pm. The data obtained from measurement differences were subjected to an analysis of variance (ANOVA) for site 1 and site 2. The analysis did not show any statistical difference between groups (amalgam, Ketac Silver, Miracle Mix) or change over time for site 1. At site 2, no significant differences were found between groups, but there was a statistically significant change over time (p < 0.01). However, given the small changes measured, this change was not felt to be clinically significant.
Site
1
Miracle Site
-55 -33 22 -10 23 25 5 -5 13
2
Site
1
Mix Site
-10 17 55 10 16 27
12 27 31 31 13 22
25 55 48 52 44 71
-13
18 19 33
17 57 63
3 -1
2
of seating the castings precisely for each measurement time period, no difference in measurement was demonstrated for the three build-up materials over all time periods. In contrast with these results, Oliva and Lowe3 demonstrated a progressively increasing marginal gap when composite resin was used as the core build-up material. The maximum marginal gap with composite resin was 258 pm, which was measured at 6 days.
CONCLUSIONS The dimensional a build-up material der the conditions was dimensionally days.
stability of reinforced glass ionomer as in a wet environment was studied. Unof this study, reinforced glass ionomer stable in moisture over a period of 7
REFERENCES 1. Charbeneau
2. 3. 4. 5. 6.
DISCUSSION
Silver
G, Klausner L, Brandau H. Glass ionomer cements in dental practice: a national survey [Abstract]. J Dent Res 1988;67:283. Matson J, ed. Multipurpose glass ionomer materials gain in acceptance by general practitioners. Dent Products Rep 1986;20:40. Oliva RA, Lowe JA. Dimensional stability of composite used as a core material. J PROSTHET DENT 1986,56:554-61. Craig RG. Restorative dental materials. 7th ed. St Louis: CV Mosby Co, 1985:232. Pearson GJ. Long-term water sorption and solubility of composite materials. J Dent 1979;7:64-8. Vermilyea S, Gardner F, Moergeli J. Composite dowels and cores: effect of moisture on the fit of cast restorations. J PROSTHET DENT 1987;58:429-
31.
A pilot study was performed to develop the technique and precision necessary to achieve accurate measurements. However, as demonstrated by the measurements of the amalgam controls in Table I, the same casting would seat slightly more than the baseline value at one time and slightly less at another time. Given the measurement error
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Reprint requests to: DR. ROBERT L. C~~LEY DENTAL SCHOOL UNIVERSITY OF TEXAS HEALTH 7703 FLOYD CURL DR. SAN ANTONIO, TX 78284-7914
SCIENCE CENTER
653