to measure the polymerization red composites Aaron
D.
University
Puckett, of Mississippi,
PhD,a School
and
Rebecca
of Dentistry,
Smith, Jackson,
shrinkage
of
BSb Miss.
The polymerization shrinkage of light-cured dental composite resins has been reported to cause a marginal gap between the cavity wall and the restoration, leading to the premature and/or tensile stress failure of the composite restoration. This study measured the volumetric shrinkage of six light-cured posterior composites by measuring specific gravity differences between uncured and cured composite test specimens, using a modified version of ASTM method D792 “Specific Gravity and Density of Plastics by Displacement.” The measured volumetric shrinkage ranged from 1.35% to 3.22%. (J PROSTHET QENT 1992;68:56-8.)
olymerization shrinkage may have a significant impact on the longevity of composite resin restorations and the sensitivity of the vital tooth. Studies have shown that marginal gaps for initial polymerization shrinkage are not overcome by acid etching ok by volumetric expansion due to water uptake.l, 2 In addition, internal stresses are formed in the restorative material during polymerization that may accelerate degradative reactions such as wear. A number of methods have been proposed for measuring the contraction of dental materials during polymerization. Most methods are based on measuring volumetric changes by using dilatometry. 3-5 Other investigators have measured linear dimensional changes.6, 7 This article describes a simple method to measure volumetric polymerization shrinkage of light-activated composite materials by using a modified version of ASTM
Partially supported aAssistant Professor, bD3 Student. lQ/1/35796
Table
I.
Materials Material
Ful-Fil Herculite Occlusin P-30 P-50 Visio-Molar
56
by NIH/NIDR Department
grant No. 63877. of Restorative Dentistry.
method D792 “Specific Displacement.”
Gravity
MATERIAL
METHODS
AND
and Density of Plastics by
Six commercial light-cured posterior composite resins were used in this study (Table I). Approximately 0.5 gm of composite resin was extruded onto plastic wrap and shaped into a disk approximately 1.5 cm in diameter and 2.0 mm thick. An excavator was used to produce a small hole at the edge of the cylindrical specimen for attachment to the balance. A small gauge stainless wire was hung from the balance and weighed to the nearest 0.1 mg. The composite disk was removed from the wrap and attached to the wire and weighed. The operator wore polyethylene gloves to facilitate transfer of the disk for weighing without contamination. An immersion vessel containing distilled water was placed in the balance and the wire was weighed while it was immersed in the water. The composite disk was weighed in water to the same depth as the previous measurement with care that no air was trapped on the surface of the samples. Five different samples were similarly measured for each composite resin, and
used Manufacturer
Caulk/Dentsply York, Pa. Sybron/Kerr Romulus, Mich. Coe Laboratories Chicago, Ill. 3M St. Paul, Minn. 3M ESPE Lake Worth, Fla.
Batch
No.
Packaging
051288006
Compule
53291
Syringe
50-040186
Syringe
6R3
Syringe
8FIP 0002
Syringe Syringe
JULY
1992
VOLUME
68
NUMBER
1
POLYMERIZATION
Table
SHRINKAGE
Tabulated
II.
results Specific gravity uncured
Material
Specific gravity cured
x
SD
x
SD
x
SD
Ful-Fil
2.105
0.007
2.175
0.006
I 3.22
Occlusin Herculite
2.381
0.006
2.442
0.005
1 2.50
0.14
2.114
0.008
2.167
0.005
2.45
0.19
P-50
2.197
0.001
2.251
0.003
2.40
0.06
P-30
2.237
0.005
2.286
0.006
2.19
0.15
Visio-Molar
2.420
0.003
2.453
0.003
I 1.35
0.08
Lines
connect
groups
not significantly
different
using
the Newman-Keul
method
the measurements were used to calculate the specific gravity of the uncured composite resin. The temperature of the water was 23’ f 0.5’ C for all measurements. Additional sample disks were prepared and cured under plastic wrap for 90 seconds on each side with a Command (Sybron Kerr, Romulus, Mich.) curing light. The cured disks were weighed in air and water as described immediately after preparation. Preliminary studies showed that the composite resins (polymerized or unpolymerized) under investigation did not gain or lose weight during the 2-minute water immersion necessary for testing.
RESULTS Specific gravities lationship:
were calculated
SPgr=L
where
using the following
re-
a+w-b
a = weight of the disk in air b = weight of the disk and wire in water w = weight of the wire in water
The volume shrinkage relationship:
was calcul.ated using the following
xloo
The calculated results are given in Table II. A grouped standard deviation is reported for t,he percentage shrinkage values. The group standard deviation was calculated by using the deviations of the specific gravity measurements and the relationship given below. A3
where
C2 D2
Group standard deviation = 5B2 - + __5B4 A = Standard deviation of uncured specific gravity measurement B = mean specific gravity of cured samples C = mean specific gravity of uncured samples D = standard deviation of cured specific gravity measurements
The Newman-Keuls
JOURNAL
I
0.19
(01 = 0.05).
search for significant age values.
differences
between
the mean shrink-
DISCUSSION The method described provides a precise measure of polymerization shrinkage without the use of sophisticated instrumentation. The equipment required is an analytical balance capable of measuring to the nearest 0.1 mg. The values measured agree well with the range of values (1% 6 % ) previously reported.8 The amount of polymerization shrinkage is related to the filler loading, amount of monomer, type of monomer, and the degree of cure. Because the exact compositions of these materials are proprietary, no attempt was made to relate the measured shrinkages to reactivity or degree of cure. However, this method can be used to monitor changes in degree of cure of a particular material as a function of time or other experimental variables. The density of cured samples was measured immediately after preparation; therefore any shrinkage associated with postcure was not measured.
CONCLUSION
% Shrinkage = 1 - SPSp grgr (uncured) (cured)
THE
% Shrinkage
procedure
OF PROSTHETIC
(01 = 0.05) was used to
DENTISTRY
The method described provides a convenient way to measure polymerization shrinkage of light cured dental composite resins. Visio-Molar material exhibited less shrinkage than the other products tested. In contrast, the volume change measured for Ful-Fil was larger than the other materials tested. No significant difference in polymerization shrinkage was measured for Herculite, Occlusin, P-30 or P-50 materials. No relationship between the polymerization shrinkage and reactivity or clinical acceptability can be inferred from this study. Materials for this study were graciously donated by the manufacturers listed in Table I. REFERENCES 1. Goldman 11. Polymerization shrinkage terials. Aust Dent J 1983;28:156-161.
of resin-based
restorative
ma-
57
PUCKETT
2. Hansen EK. Visible light-cured composite resins: polymerization contraction, contraction patterns and hygroscopic expansion. Stand J Dent Res 1982;90:329-35. 3. Bausch JR, Lange K, Davidson CL, Peters A, de Gee AJ. Clinical significance of polymerization shrinkage of composite resins. J PROSTHET DENT
19&2;48:59-67.
4. de Gee AJ, Davidson CL, Smith A. A modified dilatometer for continuous recording of volumetric polymerization shrinkage of composite restorative materials. J Dent 1981;9(1):36-42. 5. Bandyopadhyay S. A study of the volumetric shrinkage of some dental materials. J Biomed Mater Res 1982;16:135-44. 6. Lee HL, Swartz MC, Smith FF. Physical properties of four thermosetting dental restorative resins. J Dent Res 1969;48:526.
Bound
volumes
available
AND
SMITH
7. Wilson HJ. Properties of radiation cured restorative resins. International Symposium on Fotofil Dental Restorative Proceedings. London: Johnson &Johnson, 1978, 11-36. 8. Jensen ME, Chan PC. Polymerization shrinkage and microleakage. In: Vanherle G, Smith DC, eds. Posterior composite resin dental restorative materials. Utrecht, Netherlands: Peter Szalc, 243. Reprint requests to: DR. AARON D. PUCKETT DEPARTMENT OF RESTORATIVE UNIVERSITY OF MISSISSIPPI SCHOOL OF DENTISTRY JACKSON, MS 39216
DENTISTRY
to subscribers
Bound volumes of THE JOURNAL OF PROSTHETIC DENTISTRY are available to subscribers (only) for the 1992 issues from the publisher at a cost of $55.00 ($68.00 international) for Vol. 67 (January-June) and Vol. 68 (July-December). Shipping charges are included. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Volumes 65 and 66 are also available. Payment must accompany all orders. Contact Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, USA; phone (800) 325-4177, ext. 4351, or (314)453-4351. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular JOURNAL subscription.
58
JULY
1992
VOLUME
68
NUMBER
1
D.
University
Puckett, of Mississippi,
PhD,a School
and
Rebecca
of Dentistry,
Smith, Jackson,
shrinkage
of
BSb Miss.
The polymerization shrinkage of light-cured dental composite resins has been reported to cause a marginal gap between the cavity wall and the restoration, leading to the premature and/or tensile stress failure of the composite restoration. This study measured the volumetric shrinkage of six light-cured posterior composites by measuring specific gravity differences between uncured and cured composite test specimens, using a modified version of ASTM method D792 “Specific Gravity and Density of Plastics by Displacement.” The measured volumetric shrinkage ranged from 1.35% to 3.22%. (J PROSTHET QENT 1992;68:56-8.)
olymerization shrinkage may have a significant impact on the longevity of composite resin restorations and the sensitivity of the vital tooth. Studies have shown that marginal gaps for initial polymerization shrinkage are not overcome by acid etching ok by volumetric expansion due to water uptake.l, 2 In addition, internal stresses are formed in the restorative material during polymerization that may accelerate degradative reactions such as wear. A number of methods have been proposed for measuring the contraction of dental materials during polymerization. Most methods are based on measuring volumetric changes by using dilatometry. 3-5 Other investigators have measured linear dimensional changes.6, 7 This article describes a simple method to measure volumetric polymerization shrinkage of light-activated composite materials by using a modified version of ASTM
Partially supported aAssistant Professor, bD3 Student. lQ/1/35796
Table
I.
Materials Material
Ful-Fil Herculite Occlusin P-30 P-50 Visio-Molar
56
by NIH/NIDR Department
grant No. 63877. of Restorative Dentistry.
method D792 “Specific Displacement.”
Gravity
MATERIAL
METHODS
AND
and Density of Plastics by
Six commercial light-cured posterior composite resins were used in this study (Table I). Approximately 0.5 gm of composite resin was extruded onto plastic wrap and shaped into a disk approximately 1.5 cm in diameter and 2.0 mm thick. An excavator was used to produce a small hole at the edge of the cylindrical specimen for attachment to the balance. A small gauge stainless wire was hung from the balance and weighed to the nearest 0.1 mg. The composite disk was removed from the wrap and attached to the wire and weighed. The operator wore polyethylene gloves to facilitate transfer of the disk for weighing without contamination. An immersion vessel containing distilled water was placed in the balance and the wire was weighed while it was immersed in the water. The composite disk was weighed in water to the same depth as the previous measurement with care that no air was trapped on the surface of the samples. Five different samples were similarly measured for each composite resin, and
used Manufacturer
Caulk/Dentsply York, Pa. Sybron/Kerr Romulus, Mich. Coe Laboratories Chicago, Ill. 3M St. Paul, Minn. 3M ESPE Lake Worth, Fla.
Batch
No.
Packaging
051288006
Compule
53291
Syringe
50-040186
Syringe
6R3
Syringe
8FIP 0002
Syringe Syringe
JULY
1992
VOLUME
68
NUMBER
1
POLYMERIZATION
Table
SHRINKAGE
Tabulated
II.
results Specific gravity uncured
Material
Specific gravity cured
x
SD
x
SD
x
SD
Ful-Fil
2.105
0.007
2.175
0.006
I 3.22
Occlusin Herculite
2.381
0.006
2.442
0.005
1 2.50
0.14
2.114
0.008
2.167
0.005
2.45
0.19
P-50
2.197
0.001
2.251
0.003
2.40
0.06
P-30
2.237
0.005
2.286
0.006
2.19
0.15
Visio-Molar
2.420
0.003
2.453
0.003
I 1.35
0.08
Lines
connect
groups
not significantly
different
using
the Newman-Keul
method
the measurements were used to calculate the specific gravity of the uncured composite resin. The temperature of the water was 23’ f 0.5’ C for all measurements. Additional sample disks were prepared and cured under plastic wrap for 90 seconds on each side with a Command (Sybron Kerr, Romulus, Mich.) curing light. The cured disks were weighed in air and water as described immediately after preparation. Preliminary studies showed that the composite resins (polymerized or unpolymerized) under investigation did not gain or lose weight during the 2-minute water immersion necessary for testing.
RESULTS Specific gravities lationship:
were calculated
SPgr=L
where
using the following
re-
a+w-b
a = weight of the disk in air b = weight of the disk and wire in water w = weight of the wire in water
The volume shrinkage relationship:
was calcul.ated using the following
xloo
The calculated results are given in Table II. A grouped standard deviation is reported for t,he percentage shrinkage values. The group standard deviation was calculated by using the deviations of the specific gravity measurements and the relationship given below. A3
where
C2 D2
Group standard deviation = 5B2 - + __5B4 A = Standard deviation of uncured specific gravity measurement B = mean specific gravity of cured samples C = mean specific gravity of uncured samples D = standard deviation of cured specific gravity measurements
The Newman-Keuls
JOURNAL
I
0.19
(01 = 0.05).
search for significant age values.
differences
between
the mean shrink-
DISCUSSION The method described provides a precise measure of polymerization shrinkage without the use of sophisticated instrumentation. The equipment required is an analytical balance capable of measuring to the nearest 0.1 mg. The values measured agree well with the range of values (1% 6 % ) previously reported.8 The amount of polymerization shrinkage is related to the filler loading, amount of monomer, type of monomer, and the degree of cure. Because the exact compositions of these materials are proprietary, no attempt was made to relate the measured shrinkages to reactivity or degree of cure. However, this method can be used to monitor changes in degree of cure of a particular material as a function of time or other experimental variables. The density of cured samples was measured immediately after preparation; therefore any shrinkage associated with postcure was not measured.
CONCLUSION
% Shrinkage = 1 - SPSp grgr (uncured) (cured)
THE
% Shrinkage
procedure
OF PROSTHETIC
(01 = 0.05) was used to
DENTISTRY
The method described provides a convenient way to measure polymerization shrinkage of light cured dental composite resins. Visio-Molar material exhibited less shrinkage than the other products tested. In contrast, the volume change measured for Ful-Fil was larger than the other materials tested. No significant difference in polymerization shrinkage was measured for Herculite, Occlusin, P-30 or P-50 materials. No relationship between the polymerization shrinkage and reactivity or clinical acceptability can be inferred from this study. Materials for this study were graciously donated by the manufacturers listed in Table I. REFERENCES 1. Goldman 11. Polymerization shrinkage terials. Aust Dent J 1983;28:156-161.
of resin-based
restorative
ma-
57
PUCKETT
2. Hansen EK. Visible light-cured composite resins: polymerization contraction, contraction patterns and hygroscopic expansion. Stand J Dent Res 1982;90:329-35. 3. Bausch JR, Lange K, Davidson CL, Peters A, de Gee AJ. Clinical significance of polymerization shrinkage of composite resins. J PROSTHET DENT
19&2;48:59-67.
4. de Gee AJ, Davidson CL, Smith A. A modified dilatometer for continuous recording of volumetric polymerization shrinkage of composite restorative materials. J Dent 1981;9(1):36-42. 5. Bandyopadhyay S. A study of the volumetric shrinkage of some dental materials. J Biomed Mater Res 1982;16:135-44. 6. Lee HL, Swartz MC, Smith FF. Physical properties of four thermosetting dental restorative resins. J Dent Res 1969;48:526.
Bound
volumes
available
AND
SMITH
7. Wilson HJ. Properties of radiation cured restorative resins. International Symposium on Fotofil Dental Restorative Proceedings. London: Johnson &Johnson, 1978, 11-36. 8. Jensen ME, Chan PC. Polymerization shrinkage and microleakage. In: Vanherle G, Smith DC, eds. Posterior composite resin dental restorative materials. Utrecht, Netherlands: Peter Szalc, 243. Reprint requests to: DR. AARON D. PUCKETT DEPARTMENT OF RESTORATIVE UNIVERSITY OF MISSISSIPPI SCHOOL OF DENTISTRY JACKSON, MS 39216
DENTISTRY
to subscribers
Bound volumes of THE JOURNAL OF PROSTHETIC DENTISTRY are available to subscribers (only) for the 1992 issues from the publisher at a cost of $55.00 ($68.00 international) for Vol. 67 (January-June) and Vol. 68 (July-December). Shipping charges are included. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Volumes 65 and 66 are also available. Payment must accompany all orders. Contact Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, USA; phone (800) 325-4177, ext. 4351, or (314)453-4351. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular JOURNAL subscription.
58
JULY
1992
VOLUME
68
NUMBER
1
