Marginal capacity Chantal
integrity related to bond strength and strain of composite resin restorative systems M. Kemp-Scholte,
D.D.S.,*
and
Care1
L. Davidson,
Ph.D.**
ACTA, Amsterdam, The Netherlands The shear strength of composite resin restorative systems bonded to dentin was measured and marginal integrity of class V restorations was assessed. A correlation between bond strength and marginal adaptation could not be demonstrated. The application of an intermediate layer of unfilled resin or the use of low-stiffness composite resins to improve the strain capacity of the restoration significantly influenced the quality of the marginal integrity. (J PROSTEIET DENT 1990;64:658-64.)
V
arious adhesive restorative systems have been tested in class V restorations.1*3 Although the methods of investigation were not mutually comparable, none of the available systems prevented marginal gap formation cervically.4 To enhance marginal integrity of composite resin restorations, bonding agents are used. Often the quality of such agents is expressed in terms of 24-hour bond strength. Improved bond strength is being proposed as the solution to the problem of marginal leakage of composite resin restorations.5-7 However, the marginal integrity of a composite resin restoration also depends on the configuration of the cavity,s-g the insertion technique,lO and the development of material properties during setting.‘l In this respect, curing shrinkage, l2 stiffness or strain capacity in terms of Young’s module,4 flow capacity,13 and water sorption14 of both the restorative and the bonding agent determine the marginal integrity of the restoration. Apart from possible insufficient wetting of the cavity walls by the adhesive composite resin system, polymerization shrinkage is often mentioned as an early-appearing cause of marginal gap formation. As the shrinkage develops with time during curing, the development of bond strength with time is of interest because the bond has to withstand the contraction forces. This study tested the effects of a series of bonding agents and restorative resins in cervical restorations on marginal adaptation and the relationship with bond strength during setting.
MATERIAL
AND
METHODS
Cylindrical butt-joint cavities 4 mm-wide and 2 mm deep were prepared in the cervical region of freshly extracted bovine teeth with the outline incisally located in enamel
*Research Associate,Department of Dental Materials Science; general practitioner. **Professor and Chairman, Department of Dental Materials Science.
658
Fig. 1. Schematic representation of the design of class V restorations and locations of cross sectioning and examination (bevel in enamel has not been drawn). Arrow represents direction from which photographs of Fig. 2 are taken.
and cervically in root dentin (Fig. 1). The enamel outline was beveled and acid etched. The examined bonding systems (restorative and bonding agent) and their batchnumbers are given in Table I. If the resin systems were compatible, not all bonding agents were investigated with the composite resin of the same brand. The materials were handled according to the manufacturers’ instructions. The cavities were restored by use of the material combinations listed in Table II. Ten restorations were made for each test group. Five of each group were thermocycled (600 cycles, 15’ to 60’ C). After at least 24 hours’ storage in room temperature water, the samples were cross sectioned and replicated for scanning electron microscopy (SEM) (Int Scientific Instruments Type SS40, Akashi, Wetzlar, West Germany). Each sample was classified on four locations incisally and cervically on (0) perfect marginal integrity or (1)
DECEMBER
1990
VOLUME
64
NUMBER
6
MARGINAL
INTEGRITY
OF RESTORATIVE
SYSTEMS
Fig. 2. Cross section (replica) of (A), Silux resin restoration with a marginal gap (test group 11) and (B), Silux resin restoration with an intermediate unfilled resin layer without marginal gap (test group 12). S, Silux; D, dentin. Marker represents 100 pm.
Table
I.
Products
investigated
in study
Product
Bondlite
Batch
TM
Herculite condensable Durafill Scotchbond light-curing
adhesive 1
Scotchbond light-curing
adhesive 2
Silux Enamel Bond system Silar Silux P-10 P-30 Tenure Bond
No.
Manufacturer
R 54291 A 53231 U 51346 150/30689
L
R 7BP L 7BEl P 8H5P A 8H4P 6L A 7ACl B 7CDl IA1 A 7AEl B 7AEl
L
Kerr Mfg. Co. Romulus, Mich. Kerr Mfg. Co. Kulzer & Co. GmbH Bad Hamburg, W. Germany 3M Co., St. Paul, Minn.
L
3M Co.
L S
3M Co. 3M Co.
L S
3M Co. 3M Co.
7x3
L S S L S/L
3M Co. Den-Mat Co. Santa Maria, Calif. Den-Mat Bayer Dental AG. Leverkussen, FRG
A 1142/1144 B 1143/1144 3806/139084 190287
Visar Seal Gluma Dentin Bond
S/L
L L
S, Self-cured; L, light-cured.
presence of a marginal gap (Fig. 2). Six test groups were made twice and intraexaminer scoring reliability was assessed. The results were statistically analyzed using Statistical Analysis System (General Linear Models, SAS
Inst., Cary, N.C.). Each observation was treated as independent measurement. Tests of significance on treatment method, thermocycling, and location (incisal or cervical margin) were performed by use of the Student t-test.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Shear bond strengths were measured with the device described by Krabbendam et ~1.‘~Dentin samples were prepared from the cervical region of freshly extracted bovine teeth, mounted in the sample holders, and ground with abrasive No. 240 paper grit. After the dentin was dried with a tissue, the test materials were applied according to the manufacturer’s instructions. Shear bond strength was measured in a tensilometer (Zwick 1463, Ulm, Einsingen,
659
KEMP-SCHOLTE
AND
DAVIDSON
0.25
0.35 0.13 0.30
"0
IO
20
30 40 Time (mln)
50
60
Fig. 3. Development of shear bond strength and fraction of samples showing cervical gap (at right hand side of figure) for Silux resin combined with different bonding agents (test groups 11, 13, 14, and 15).
II. Combinations of bonding systems and composite resins investigated
Table
Test group
Dentin
pretreatment
1 2 3 5 6 7 8 9 10
Gluma Bond Tenure Bond
Procedures were carried out as indicated *Self-curing
from
Intermediate
layer
Restorative
Silux Enamel Bond Silux Enamel Bond Silux Enamel Bond Silux Enamel Bond Silux Enamel Bond Silux Enamel Bond
Herculite Herculite p-10* p-10* P-30 P-30 Durafill Durafill Silar* Silar* Silux Silux Silux Silux Silux
left to right.
material.
W. Germany) with loading speed 0.1 mm/min, at 5,15, and 60 minutes and at 24 hours after initiation of the curing. For each test group six measurements were carried out. The curves in Fig. 3 were obtained with a hyperbolic function fitting. RESULTS Significant differences in marginal integrity resulted from different treatment methods and from location (p < 0.0001). Most incisal margins were perfectly closed. Thermocycling did not change the quality of marginal adaptation significantly. For this reason, in Table III the
660
agent
Bondlite Bondlite Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 1 Silux Enamel Bond Visar Seal
4
11 12 13 14 15
Bonding
fraction of samples showing a cervical gap (cycled and noncycled samples) are given. For most test groups, shear bond strength values at different intervals are also given in Table III. Regarding all test groups without intermediate layer (groups 1,3,5,7,9,11,13,14, and 15), no reasonable correlation could be demonstrated between the fraction of samples showing a cervical gap and the early (5-minute) or late (24-hour) bond strength (F 0.02 and F 0.06 respectively Fig. 4). For Silux resin only, combined with different bonding agents (test groups 11, 13, 14, and 15), again no correlation between fraction of samples with a marginal gap and bond strength could be demonstrated. The frac-
DECEMBER
1990
VOLUME
64
NUMBER
6
MARGINAL
INTEGRITY
OF RESTORATIVE
SYSTEMS
- .0
5 Shear
10 bond strength
15 (MPa)
20
4. Relationship between 5-minute and 24-hour shear bond strength and fraction of samples showing cervical gap for all test groups without intermediate layer. Linear regression analysis resulted in r -0.02 and 0.06, respectively.
Fig.
Table III. Fraction of restorations showing marginal gap cervically and shear bond strength for various restorative systems after initiation of curing Shear 5 min Test group
Fraction of samples with cervical gap
SD
x
SD
0.5
4.8
2.0
7.9
0.6
10.7
2.1
6.3
3.4
5.5
1.8
11.2
1.4
11.1 14.6 5.3
1.2 2.3 1.2
12.4 15.1 6.7
1.2 2.2 1.4
8.9 15.4 9.5
1.7 4.1 1.8
6.7
2.2
7.0
1.9
11.5
2.9
10.2 13.7 5.3 4.3 6.8
1.5 2.3 1.2 2.2 2.6
10.0
2.1
14.8
4.2
13.5 5.6 4.9 7.0
1.8 2.1 1.5 1.5
11.1 10.4 7.1 7.2
1.2 1.6 1.1 0.6
-
5 6 7 8
0.52b 0.39bC 0.06ef 0.03ef
9.8 13.8 3.3
9 10
0.13ed Of
-
11 12 13 14 15
0.25c Oef 0.35c 0.30Cd 0.13df
9.8 8.4 5.2 0.7 5.1
JOURNAL
OF PROSTHETIC
DENTISTRY
24 h
-
x
2.3 1.4 1.5
2.8 2.0 0.8 0.4 1.3
differences.
tion of samples showing a cervical gap did correlate inversely with Young’s module values of the restoratives (Table IV, Fig. 5). l6 For different composite resins combined with Scotchbond 2 adhesive (test groups 3,5,7,9, and ll), F was 0.86. The application of an intermediate unfilled resin layer in test groups 2,4,6,8,10, and 12 improved the quality of marginal adaptation. Significant differences at the 5% confidence level were found for test group 2 versus 1, 4 versus 3, 10 versus 9, and 12 versus 11.
THE
min
SD
0.33bC 0.06ef
mean significant
60
x
3.4
column
16 min SD
0.908 0.03e’
in second
(MPa)
x
1 2 3 4
Same superscripts
bond strength
DISCUSSION Adhesive restorative systems mostly meet the requirements of retention,17 but still fail in producing perfectly sealed margins. The quality of the restoration margin can be influenced by a tempered curing rate of the bulk material.13 The use of self-curing P-10 and Silar resins gave better results when compared with the light-curing equivalent P-30 and Silux resins. This effect may be attributed to increased flow capacity of the self-curing resin, compen-
661
KEMP-SCHOLTE
AND
DAVIDSON
Young's module (GPa) Fig. 5. Relationship between 24-hour Young’s module and fraction of samples showing cervical gap for different composite resins combined with Scotchbond 2 adhesive (test groups 1, 3, 5, 7, 9, and 11). Linear regression analysis resulted in F 0.86.
25 A -
@ P-i0
0 --- /3 Silar 20 _ - 0 Silar l
A ---
0’
0
-.
BP-10
I
I
lo
20
I
I
30 40 Time (min)
a
50
60
Fig. 6. Development of bond strength and of competitive polymerization contraction stress, which is product of linear curing contractiorP and Young’s module.18
sating for volume reduction during polymerization shrinkage. No clear relationship between marginal integrity and bond strength at any time during curing could be demonstrated in this study. This is not in agreement with findings of other investigators,6v7 perhaps because in the present study only the occurrence of a gap and not the wall-to-wall gap width was assessed.It was considered that the presence or absence of marginal gaps is more relevant than gap width. For good marginal adaptation, adhesion with at
662
least a minimal early bond strength is required, and a proper ultimate bond strength will be important for the durability of the restoration. However, other factors may be more important in obtaining a high quality of the restoration margins. In this study a clear influence of strain capacity of the restoration could be shown. This influence may be illustrated by Fig. 6, which shows the development of the dentinal bond strength during setting and an estimated maximal competitive polymerization contraction stress, calculated from the curing contraction and the
DECEMBER
1990
VOLUME
84
NUMBER
6
MARGINAL
INTEGRITY
OF RESTORATIVE
SYSTEMS
12
34
56
78
9 10
1112
7. Fraction of samples showing cervical gap for each composite resin without (first columns) and with (second columns) intermediate layer of unfilled resin. For test groups 10 and 12 scores are zero.
Fig.
Young’s module.4s I29l* Silar and P-10 resins combined with Scotchbond 2 adhesive have a comparable bond strength and curing contraction development, but differ in elasticity (Table IV). Lower Young’s module (higher strain capacity) appears to result in better marginal adaptation. Increased strain capacity of the restoration can also be obtained by the application of unfilled resin on the bonding agent as an intermediate layer before the insertion of the composite resin. The positive effect on the marginal adaptation is demonstrated in Fig. 7. Because Scotchbond 2 adhesive and Visar Seal adhesive come in a rather thick layer (50 to 150 pm) and the HEMA component does not participate in the cross-linking, these adhesives might directly contribute to the stress relaxation. It appears that slowcuring contraction and the development of stiffness, combined with rapid formation of adhesive bond, is favorable to maintain marginal integrity. No significant effect of thermocycling on the marginal integrity could be demonstrated in this study. This observation is in agreement with findings of other investigations.lgv 2o An important contributing factor to marginal integrity is water sorption of the restorative and the bonding agent. Torstenson and Brannstrom14 showed considerable gap reduction with time for restorations kept in water. In this respect, water sorption is a desirable factor. However, it also may cause degradation of the restorative and bonding agent, thus reducing the durability of the restoration. To improve adhesive systems, bond strengths have been increased and curing contraction has been reduced. Filler levels have also been increased to improve strength, hardness, and wear resistance, resulting in greater stiffness of the composite resin. However, a compromise in stiffness
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
IV. Volumetric curing contractio@ and Young’s module16 of some composite resin products (24 hours values)
Table
Curing
contraction
(%) Product Silar Silux P-10 P-30 Durafill Herculite
cond.
Young’s module OfPa)
z
SD
x
SD
2.9 3.4 3.2 3.6 3.7 3.2
0.3 0.3 0.5 0.5
9,075 9,382 25,117
167 155 429 223 88 509
0.3 0.2
23,385 6,085 15,869
may be needed in considering the curing-contraction stress that counteracts the developing bond strength.
CONCLUSIONS 1. No correlation could be demonstrated between either early or late bond strength and marginal integrity of class V composite resin restorations. 2. Marginalintegrity is inversely correlated with Young’s module of the bulk composite restorative resin. 3. Application of an unfilled low-stiffness resin as an intermediate layer between the bonding layer and bulk restorative results in improved marginal integrity. REFERENCES 1. Seichter U. Rem-Untersuchungen iiher den Zervikalen Randspalt bei Komposit-Restaurationen mit haftvermittlern. Dtsch Zahniirztl Z 1986;41:739-42. 2. Kulmann W. Dentinhaft-Komposit und Glasionomer-Zement zur Restauration zervikaler LSsionen. Dtsch Zahnlrztl Z 1985;40:622-6.
663
KEMP-SCHOLTEANDDAVIDSON
3. Vanherle G, Verschueren M, Lambrechts P, Braem M. Clinical investigation of dental adhesive systems. Part I. In vivo study. J PROWHET 15.
DENT 198655157-63.
4. Kemp-Scholte CM, Davidson CL. Marginal sealing of curing contraction gaps in class Vcomposite resin restorations. JDent Res 1988;67:8415. 5. Hansen
6. 7. 8. 9.
10. 11.
12.
16.
EK, Asmussen E. A comparative study of dentin adhesives. Stand J Dent Res 1985;93:280-7. Munksgaard EC, Irie M, Asmussen E. Dentin-polymer bond promoted by Gluma and various resins. J Dent Res 1985;64:1409-11. Komatsu M, Finger W. Dentin bonding agents: correlation of early bond strength with margin gaps. Dent Mat 1986;2:25’7-62. Davidson CL. Resisting the curing contraction with adhesive composites. J PROSTHET DENT 1986;55:446-7. Feilser AJ, De Gee AJ, Davidson CL. Setting stress in composite resin in relation to configuration of the restoration. J Dent Res 1987;66:16369. Crim GA, Chapman KW. Effect of placement techniques on microleakage of a dentin-bonded composite resin. Quintessenc Int 1986;17:21-4. Davidson CL, De Gee AJ, Feilzer AJ. The competition between the composite-dentin bond strength and the polymerization contraction stress. J Dent Res 1986;63:1396-9. Feilzer AJ, De Gee AJ, Davidson CL. Curing contraction of composite restoratives and glass-ionomer cements. J PROSTHET DENT
1’7.
18. 19.
20.
Reprint requests to: DR. CAREL L. DAVIDSON DEPARTMENT OF DENTAL L~UWESWEC 1,1066 THE NETHERLANDS
13. Davidson CL, De Gee AJ. Relaxation of polymerization contraction stresses by flow in dental composites. J Dent Res 1984;63:146-8. 14. Torstenson B, Briinnstr6m M. Contraction gap under composite resin
W. A. Gregory, The University
of chemically
D.D.S., MS.,* B. Pounder,
of Michigan,
MATERIALS
SCIENCE,
ACTA
1988;59:297-300.
Bond strengths resins
restorations: effect of hygroscopic expansion and thermal stress. Oper Dent 1988;13:24-31. Krabbendam CA, Ten Harkel HC, Duijsters PPE, Davidson CL. Shear bond strength determinations on various kinds of luting cements with tooth structure and cast alloys using a new test device. J Dent 1987;15:77-81. Braem M, Davidson CL, Vanherle G, Vandoren V, Lambrechts P. The relationship between test methodology and elastic behavior of composites. J Dent Res 1987;66:1036-9. Lambrechts P, Braem M, Vanherle G. Evaluation of clinical performance for posterior composite resins and dentin adhesives. Oper Dent 1987;12:53-87. Braem M, Lambrechts P, Vanherle G, Davidson CL. Stiffness increase during the setting of dental composites. J Dent Res 1987;66:1713-6. Munksgaard EC, Itoh K, Jorgensen KD. Dentin-polymer bond in resin fillings tested in vitro by thermoand load-cycling. J Dent Res 1985;64:144-6. Eakle WS. Effect of thermal cycling on fracture strength and microleakage in teeth restored with a bonded composite resin. Dent Mater 1986;2:114-7.
dissimilar
D.D.S.,**
and E. Bakus,
EA, AMSTERDAM
repaired
composite
D.D.S.***
School of Dentistry, Ann Arbor, Mich.
Expanded use of composite resins has necessitated repair of fractured, discolored, and former restorations. Laboratory investigations have demonstrated that new composite resin can be bonded to cured composite resin of the same chemistry. The surface chemistry of three composite resins of dissimilar matrix formulae were examined by infrared spectroscopy and the tensile bond strengths of heterogeneous repairs and the site of repair failures were determined. (J FBOSTEET DENT 1990:64:664-8.)
B
uonocorer introduced acid etching of enamel in 1955 for the adhesion of acrylic resin filling materials and Bowen developed Bis-GMA composite resins in 1962. As a result, dentistry gradually expanded their application to include complex restorations.
Composite resins have been used to restore classes 3,4 and posterior class 1,2, and 5 defects, to reveneer crowns and fixed partial dentures, to lute orthodontic brackets, to splint periodontally compromised teeth, and as a direct veneer. This popularity has necessitated repairing of composite resins because of bond failure, cohesive fracture, color changes, and loss of surface from chemical and mechanical deterioration.
This research was partially supported by the Student Summer Research Fellowship Program, School of Dentistry, The University of Michigan, Ann Arbor, Mich. *Assistant Professor, Department of Restorative Dentistry. **General Practice resident, St. Joseph’s Hospital, Pontiac, Mich. ***Clinical Instructor, Department of Restorative Dentistry. 10/l/20013
The preparation design of fractured resin surfaces for retention of new composite resin to former restorations and successful repairs has received wide attention.3-7 The sur-
664
face preparation of old composite resin has been accomplished by mechanically roughening to remove contaminated material,
cleansing
with 30 % to 50 % phosphoric
DECEMBER1999
VOLUME64
acid
NUMBER6
integrity related to bond strength and strain of composite resin restorative systems M. Kemp-Scholte,
D.D.S.,*
and
Care1
L. Davidson,
Ph.D.**
ACTA, Amsterdam, The Netherlands The shear strength of composite resin restorative systems bonded to dentin was measured and marginal integrity of class V restorations was assessed. A correlation between bond strength and marginal adaptation could not be demonstrated. The application of an intermediate layer of unfilled resin or the use of low-stiffness composite resins to improve the strain capacity of the restoration significantly influenced the quality of the marginal integrity. (J PROSTEIET DENT 1990;64:658-64.)
V
arious adhesive restorative systems have been tested in class V restorations.1*3 Although the methods of investigation were not mutually comparable, none of the available systems prevented marginal gap formation cervically.4 To enhance marginal integrity of composite resin restorations, bonding agents are used. Often the quality of such agents is expressed in terms of 24-hour bond strength. Improved bond strength is being proposed as the solution to the problem of marginal leakage of composite resin restorations.5-7 However, the marginal integrity of a composite resin restoration also depends on the configuration of the cavity,s-g the insertion technique,lO and the development of material properties during setting.‘l In this respect, curing shrinkage, l2 stiffness or strain capacity in terms of Young’s module,4 flow capacity,13 and water sorption14 of both the restorative and the bonding agent determine the marginal integrity of the restoration. Apart from possible insufficient wetting of the cavity walls by the adhesive composite resin system, polymerization shrinkage is often mentioned as an early-appearing cause of marginal gap formation. As the shrinkage develops with time during curing, the development of bond strength with time is of interest because the bond has to withstand the contraction forces. This study tested the effects of a series of bonding agents and restorative resins in cervical restorations on marginal adaptation and the relationship with bond strength during setting.
MATERIAL
AND
METHODS
Cylindrical butt-joint cavities 4 mm-wide and 2 mm deep were prepared in the cervical region of freshly extracted bovine teeth with the outline incisally located in enamel
*Research Associate,Department of Dental Materials Science; general practitioner. **Professor and Chairman, Department of Dental Materials Science.
658
Fig. 1. Schematic representation of the design of class V restorations and locations of cross sectioning and examination (bevel in enamel has not been drawn). Arrow represents direction from which photographs of Fig. 2 are taken.
and cervically in root dentin (Fig. 1). The enamel outline was beveled and acid etched. The examined bonding systems (restorative and bonding agent) and their batchnumbers are given in Table I. If the resin systems were compatible, not all bonding agents were investigated with the composite resin of the same brand. The materials were handled according to the manufacturers’ instructions. The cavities were restored by use of the material combinations listed in Table II. Ten restorations were made for each test group. Five of each group were thermocycled (600 cycles, 15’ to 60’ C). After at least 24 hours’ storage in room temperature water, the samples were cross sectioned and replicated for scanning electron microscopy (SEM) (Int Scientific Instruments Type SS40, Akashi, Wetzlar, West Germany). Each sample was classified on four locations incisally and cervically on (0) perfect marginal integrity or (1)
DECEMBER
1990
VOLUME
64
NUMBER
6
MARGINAL
INTEGRITY
OF RESTORATIVE
SYSTEMS
Fig. 2. Cross section (replica) of (A), Silux resin restoration with a marginal gap (test group 11) and (B), Silux resin restoration with an intermediate unfilled resin layer without marginal gap (test group 12). S, Silux; D, dentin. Marker represents 100 pm.
Table
I.
Products
investigated
in study
Product
Bondlite
Batch
TM
Herculite condensable Durafill Scotchbond light-curing
adhesive 1
Scotchbond light-curing
adhesive 2
Silux Enamel Bond system Silar Silux P-10 P-30 Tenure Bond
No.
Manufacturer
R 54291 A 53231 U 51346 150/30689
L
R 7BP L 7BEl P 8H5P A 8H4P 6L A 7ACl B 7CDl IA1 A 7AEl B 7AEl
L
Kerr Mfg. Co. Romulus, Mich. Kerr Mfg. Co. Kulzer & Co. GmbH Bad Hamburg, W. Germany 3M Co., St. Paul, Minn.
L
3M Co.
L S
3M Co. 3M Co.
L S
3M Co. 3M Co.
7x3
L S S L S/L
3M Co. Den-Mat Co. Santa Maria, Calif. Den-Mat Bayer Dental AG. Leverkussen, FRG
A 1142/1144 B 1143/1144 3806/139084 190287
Visar Seal Gluma Dentin Bond
S/L
L L
S, Self-cured; L, light-cured.
presence of a marginal gap (Fig. 2). Six test groups were made twice and intraexaminer scoring reliability was assessed. The results were statistically analyzed using Statistical Analysis System (General Linear Models, SAS
Inst., Cary, N.C.). Each observation was treated as independent measurement. Tests of significance on treatment method, thermocycling, and location (incisal or cervical margin) were performed by use of the Student t-test.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Shear bond strengths were measured with the device described by Krabbendam et ~1.‘~Dentin samples were prepared from the cervical region of freshly extracted bovine teeth, mounted in the sample holders, and ground with abrasive No. 240 paper grit. After the dentin was dried with a tissue, the test materials were applied according to the manufacturer’s instructions. Shear bond strength was measured in a tensilometer (Zwick 1463, Ulm, Einsingen,
659
KEMP-SCHOLTE
AND
DAVIDSON
0.25
0.35 0.13 0.30
"0
IO
20
30 40 Time (mln)
50
60
Fig. 3. Development of shear bond strength and fraction of samples showing cervical gap (at right hand side of figure) for Silux resin combined with different bonding agents (test groups 11, 13, 14, and 15).
II. Combinations of bonding systems and composite resins investigated
Table
Test group
Dentin
pretreatment
1 2 3 5 6 7 8 9 10
Gluma Bond Tenure Bond
Procedures were carried out as indicated *Self-curing
from
Intermediate
layer
Restorative
Silux Enamel Bond Silux Enamel Bond Silux Enamel Bond Silux Enamel Bond Silux Enamel Bond Silux Enamel Bond
Herculite Herculite p-10* p-10* P-30 P-30 Durafill Durafill Silar* Silar* Silux Silux Silux Silux Silux
left to right.
material.
W. Germany) with loading speed 0.1 mm/min, at 5,15, and 60 minutes and at 24 hours after initiation of the curing. For each test group six measurements were carried out. The curves in Fig. 3 were obtained with a hyperbolic function fitting. RESULTS Significant differences in marginal integrity resulted from different treatment methods and from location (p < 0.0001). Most incisal margins were perfectly closed. Thermocycling did not change the quality of marginal adaptation significantly. For this reason, in Table III the
660
agent
Bondlite Bondlite Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 2 Scotchbond 1 Silux Enamel Bond Visar Seal
4
11 12 13 14 15
Bonding
fraction of samples showing a cervical gap (cycled and noncycled samples) are given. For most test groups, shear bond strength values at different intervals are also given in Table III. Regarding all test groups without intermediate layer (groups 1,3,5,7,9,11,13,14, and 15), no reasonable correlation could be demonstrated between the fraction of samples showing a cervical gap and the early (5-minute) or late (24-hour) bond strength (F 0.02 and F 0.06 respectively Fig. 4). For Silux resin only, combined with different bonding agents (test groups 11, 13, 14, and 15), again no correlation between fraction of samples with a marginal gap and bond strength could be demonstrated. The frac-
DECEMBER
1990
VOLUME
64
NUMBER
6
MARGINAL
INTEGRITY
OF RESTORATIVE
SYSTEMS
- .0
5 Shear
10 bond strength
15 (MPa)
20
4. Relationship between 5-minute and 24-hour shear bond strength and fraction of samples showing cervical gap for all test groups without intermediate layer. Linear regression analysis resulted in r -0.02 and 0.06, respectively.
Fig.
Table III. Fraction of restorations showing marginal gap cervically and shear bond strength for various restorative systems after initiation of curing Shear 5 min Test group
Fraction of samples with cervical gap
SD
x
SD
0.5
4.8
2.0
7.9
0.6
10.7
2.1
6.3
3.4
5.5
1.8
11.2
1.4
11.1 14.6 5.3
1.2 2.3 1.2
12.4 15.1 6.7
1.2 2.2 1.4
8.9 15.4 9.5
1.7 4.1 1.8
6.7
2.2
7.0
1.9
11.5
2.9
10.2 13.7 5.3 4.3 6.8
1.5 2.3 1.2 2.2 2.6
10.0
2.1
14.8
4.2
13.5 5.6 4.9 7.0
1.8 2.1 1.5 1.5
11.1 10.4 7.1 7.2
1.2 1.6 1.1 0.6
-
5 6 7 8
0.52b 0.39bC 0.06ef 0.03ef
9.8 13.8 3.3
9 10
0.13ed Of
-
11 12 13 14 15
0.25c Oef 0.35c 0.30Cd 0.13df
9.8 8.4 5.2 0.7 5.1
JOURNAL
OF PROSTHETIC
DENTISTRY
24 h
-
x
2.3 1.4 1.5
2.8 2.0 0.8 0.4 1.3
differences.
tion of samples showing a cervical gap did correlate inversely with Young’s module values of the restoratives (Table IV, Fig. 5). l6 For different composite resins combined with Scotchbond 2 adhesive (test groups 3,5,7,9, and ll), F was 0.86. The application of an intermediate unfilled resin layer in test groups 2,4,6,8,10, and 12 improved the quality of marginal adaptation. Significant differences at the 5% confidence level were found for test group 2 versus 1, 4 versus 3, 10 versus 9, and 12 versus 11.
THE
min
SD
0.33bC 0.06ef
mean significant
60
x
3.4
column
16 min SD
0.908 0.03e’
in second
(MPa)
x
1 2 3 4
Same superscripts
bond strength
DISCUSSION Adhesive restorative systems mostly meet the requirements of retention,17 but still fail in producing perfectly sealed margins. The quality of the restoration margin can be influenced by a tempered curing rate of the bulk material.13 The use of self-curing P-10 and Silar resins gave better results when compared with the light-curing equivalent P-30 and Silux resins. This effect may be attributed to increased flow capacity of the self-curing resin, compen-
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AND
DAVIDSON
Young's module (GPa) Fig. 5. Relationship between 24-hour Young’s module and fraction of samples showing cervical gap for different composite resins combined with Scotchbond 2 adhesive (test groups 1, 3, 5, 7, 9, and 11). Linear regression analysis resulted in F 0.86.
25 A -
@ P-i0
0 --- /3 Silar 20 _ - 0 Silar l
A ---
0’
0
-.
BP-10
I
I
lo
20
I
I
30 40 Time (min)
a
50
60
Fig. 6. Development of bond strength and of competitive polymerization contraction stress, which is product of linear curing contractiorP and Young’s module.18
sating for volume reduction during polymerization shrinkage. No clear relationship between marginal integrity and bond strength at any time during curing could be demonstrated in this study. This is not in agreement with findings of other investigators,6v7 perhaps because in the present study only the occurrence of a gap and not the wall-to-wall gap width was assessed.It was considered that the presence or absence of marginal gaps is more relevant than gap width. For good marginal adaptation, adhesion with at
662
least a minimal early bond strength is required, and a proper ultimate bond strength will be important for the durability of the restoration. However, other factors may be more important in obtaining a high quality of the restoration margins. In this study a clear influence of strain capacity of the restoration could be shown. This influence may be illustrated by Fig. 6, which shows the development of the dentinal bond strength during setting and an estimated maximal competitive polymerization contraction stress, calculated from the curing contraction and the
DECEMBER
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MARGINAL
INTEGRITY
OF RESTORATIVE
SYSTEMS
12
34
56
78
9 10
1112
7. Fraction of samples showing cervical gap for each composite resin without (first columns) and with (second columns) intermediate layer of unfilled resin. For test groups 10 and 12 scores are zero.
Fig.
Young’s module.4s I29l* Silar and P-10 resins combined with Scotchbond 2 adhesive have a comparable bond strength and curing contraction development, but differ in elasticity (Table IV). Lower Young’s module (higher strain capacity) appears to result in better marginal adaptation. Increased strain capacity of the restoration can also be obtained by the application of unfilled resin on the bonding agent as an intermediate layer before the insertion of the composite resin. The positive effect on the marginal adaptation is demonstrated in Fig. 7. Because Scotchbond 2 adhesive and Visar Seal adhesive come in a rather thick layer (50 to 150 pm) and the HEMA component does not participate in the cross-linking, these adhesives might directly contribute to the stress relaxation. It appears that slowcuring contraction and the development of stiffness, combined with rapid formation of adhesive bond, is favorable to maintain marginal integrity. No significant effect of thermocycling on the marginal integrity could be demonstrated in this study. This observation is in agreement with findings of other investigations.lgv 2o An important contributing factor to marginal integrity is water sorption of the restorative and the bonding agent. Torstenson and Brannstrom14 showed considerable gap reduction with time for restorations kept in water. In this respect, water sorption is a desirable factor. However, it also may cause degradation of the restorative and bonding agent, thus reducing the durability of the restoration. To improve adhesive systems, bond strengths have been increased and curing contraction has been reduced. Filler levels have also been increased to improve strength, hardness, and wear resistance, resulting in greater stiffness of the composite resin. However, a compromise in stiffness
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
IV. Volumetric curing contractio@ and Young’s module16 of some composite resin products (24 hours values)
Table
Curing
contraction
(%) Product Silar Silux P-10 P-30 Durafill Herculite
cond.
Young’s module OfPa)
z
SD
x
SD
2.9 3.4 3.2 3.6 3.7 3.2
0.3 0.3 0.5 0.5
9,075 9,382 25,117
167 155 429 223 88 509
0.3 0.2
23,385 6,085 15,869
may be needed in considering the curing-contraction stress that counteracts the developing bond strength.
CONCLUSIONS 1. No correlation could be demonstrated between either early or late bond strength and marginal integrity of class V composite resin restorations. 2. Marginalintegrity is inversely correlated with Young’s module of the bulk composite restorative resin. 3. Application of an unfilled low-stiffness resin as an intermediate layer between the bonding layer and bulk restorative results in improved marginal integrity. REFERENCES 1. Seichter U. Rem-Untersuchungen iiher den Zervikalen Randspalt bei Komposit-Restaurationen mit haftvermittlern. Dtsch Zahniirztl Z 1986;41:739-42. 2. Kulmann W. Dentinhaft-Komposit und Glasionomer-Zement zur Restauration zervikaler LSsionen. Dtsch Zahnlrztl Z 1985;40:622-6.
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KEMP-SCHOLTEANDDAVIDSON
3. Vanherle G, Verschueren M, Lambrechts P, Braem M. Clinical investigation of dental adhesive systems. Part I. In vivo study. J PROWHET 15.
DENT 198655157-63.
4. Kemp-Scholte CM, Davidson CL. Marginal sealing of curing contraction gaps in class Vcomposite resin restorations. JDent Res 1988;67:8415. 5. Hansen
6. 7. 8. 9.
10. 11.
12.
16.
EK, Asmussen E. A comparative study of dentin adhesives. Stand J Dent Res 1985;93:280-7. Munksgaard EC, Irie M, Asmussen E. Dentin-polymer bond promoted by Gluma and various resins. J Dent Res 1985;64:1409-11. Komatsu M, Finger W. Dentin bonding agents: correlation of early bond strength with margin gaps. Dent Mat 1986;2:25’7-62. Davidson CL. Resisting the curing contraction with adhesive composites. J PROSTHET DENT 1986;55:446-7. Feilser AJ, De Gee AJ, Davidson CL. Setting stress in composite resin in relation to configuration of the restoration. J Dent Res 1987;66:16369. Crim GA, Chapman KW. Effect of placement techniques on microleakage of a dentin-bonded composite resin. Quintessenc Int 1986;17:21-4. Davidson CL, De Gee AJ, Feilzer AJ. The competition between the composite-dentin bond strength and the polymerization contraction stress. J Dent Res 1986;63:1396-9. Feilzer AJ, De Gee AJ, Davidson CL. Curing contraction of composite restoratives and glass-ionomer cements. J PROSTHET DENT
1’7.
18. 19.
20.
Reprint requests to: DR. CAREL L. DAVIDSON DEPARTMENT OF DENTAL L~UWESWEC 1,1066 THE NETHERLANDS
13. Davidson CL, De Gee AJ. Relaxation of polymerization contraction stresses by flow in dental composites. J Dent Res 1984;63:146-8. 14. Torstenson B, Briinnstr6m M. Contraction gap under composite resin
W. A. Gregory, The University
of chemically
D.D.S., MS.,* B. Pounder,
of Michigan,
MATERIALS
SCIENCE,
ACTA
1988;59:297-300.
Bond strengths resins
restorations: effect of hygroscopic expansion and thermal stress. Oper Dent 1988;13:24-31. Krabbendam CA, Ten Harkel HC, Duijsters PPE, Davidson CL. Shear bond strength determinations on various kinds of luting cements with tooth structure and cast alloys using a new test device. J Dent 1987;15:77-81. Braem M, Davidson CL, Vanherle G, Vandoren V, Lambrechts P. The relationship between test methodology and elastic behavior of composites. J Dent Res 1987;66:1036-9. Lambrechts P, Braem M, Vanherle G. Evaluation of clinical performance for posterior composite resins and dentin adhesives. Oper Dent 1987;12:53-87. Braem M, Lambrechts P, Vanherle G, Davidson CL. Stiffness increase during the setting of dental composites. J Dent Res 1987;66:1713-6. Munksgaard EC, Itoh K, Jorgensen KD. Dentin-polymer bond in resin fillings tested in vitro by thermoand load-cycling. J Dent Res 1985;64:144-6. Eakle WS. Effect of thermal cycling on fracture strength and microleakage in teeth restored with a bonded composite resin. Dent Mater 1986;2:114-7.
dissimilar
D.D.S.,**
and E. Bakus,
EA, AMSTERDAM
repaired
composite
D.D.S.***
School of Dentistry, Ann Arbor, Mich.
Expanded use of composite resins has necessitated repair of fractured, discolored, and former restorations. Laboratory investigations have demonstrated that new composite resin can be bonded to cured composite resin of the same chemistry. The surface chemistry of three composite resins of dissimilar matrix formulae were examined by infrared spectroscopy and the tensile bond strengths of heterogeneous repairs and the site of repair failures were determined. (J FBOSTEET DENT 1990:64:664-8.)
B
uonocorer introduced acid etching of enamel in 1955 for the adhesion of acrylic resin filling materials and Bowen developed Bis-GMA composite resins in 1962. As a result, dentistry gradually expanded their application to include complex restorations.
Composite resins have been used to restore classes 3,4 and posterior class 1,2, and 5 defects, to reveneer crowns and fixed partial dentures, to lute orthodontic brackets, to splint periodontally compromised teeth, and as a direct veneer. This popularity has necessitated repairing of composite resins because of bond failure, cohesive fracture, color changes, and loss of surface from chemical and mechanical deterioration.
This research was partially supported by the Student Summer Research Fellowship Program, School of Dentistry, The University of Michigan, Ann Arbor, Mich. *Assistant Professor, Department of Restorative Dentistry. **General Practice resident, St. Joseph’s Hospital, Pontiac, Mich. ***Clinical Instructor, Department of Restorative Dentistry. 10/l/20013
The preparation design of fractured resin surfaces for retention of new composite resin to former restorations and successful repairs has received wide attention.3-7 The sur-
664
face preparation of old composite resin has been accomplished by mechanically roughening to remove contaminated material,
cleansing
with 30 % to 50 % phosphoric
DECEMBER1999
VOLUME64
acid
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