J. Dent. 1991; 19: 301-303
301
Effect of filler content of light-cured composites on bond strength to bovine dentine M. Miyazaki,
K. Hinoura,
H. Onose and 6. K. Moore*
Department of Operative Dentistry, School of Dentistry, Nihon University, Materials, School of Dentistry, Indiana University, Indiana, USA
Tokyo, Japan and *Department
of Dental
ABSTRACT The bonding of light-cured composites to tooth tissues is known to be disturbed by polymerization shrinkage, and polymerization shrinkage is affected by the tiller content of composites. This in vitro research examined the relationship between the tiller content and bond strength to dentine of light-cured composites. Experimental light-cured composite systems with tiller contents of 455565 and 75 per cent by volume were used in both bond strength to dentine and shrinkage tests. The surfaces selected as substrates were a flat surface and a box-shaped cavity prepared in bovine dentine. The lowest bond strength was obtained with the 45 per cent tiller content composite in the box-shaped cavity. Bond strength increased with increasing filler content. Volumetric polymerization shrinkage decreased with increasing tiller content. The polymerization shrinkage at 120 s after light curing was 5.24 per cent for the 45 per cent filler content system, 4.77 per cent for the 55 per cent, 2.14 per cent for the 65 per cent and 1.68 per cent for the 75 per cent. The correlation between bond strength and shrinkage was greater for the cavity than it was for the flat surface. This implies that bond strength in the box-shaped cavity may have been affected more by polymerization shrinkage than with the flat surface. The findings lend support to the view that filler content is one of the important factors influencing the physical properties of composites. KEY WORDS:
Composites, Dentine bonding
J. Dent. 1991; 1991)
19: 301-303
(Received 1 1 December
1990;
reviewed 4 March 1991;
accepted 1 1 April
Correspondence should be addressed to: Dr M. Miyazaki, Department of Operative Dentistry, Nihon University School of Dentistry, l-8 Kanda-Surugadai, Chiyoda-ku, Tokyo 101, Japan.
MATERIALS AND METHODS
INTRODUCTION It has been recognized effectively
bond
for some time that materials
to calcified
tooth
tissues
facilitate
which the
of restorative dentistry. Tooth preparations to maximize retention (Duke et al., 1985; Hinoura et al., 1986), and clinically reliable dentine bonding systems have been sought for many years. However, dentine still remains a difficult substrate for reliable bonding. In addition, it is considered that the bonding of light-cured composites could be disturbed by polymerization shrinkage (Hegdahl and Gjerdet, 1977; Hansen, 1982; Bausch et al., 1982; Davidson et al., 1984; Iga, 1989) and that polymerization shrinkage is affected by the filler content of composites (Masutani et al., 1989). The purpose of this study was to investigate the effect of tiller content of light-cured composite resins on their bond strength to bovine dentine. practice
@1991 Buttenvorth-Heinemann 0300-5712/91/050301-03
Ltd.
The incisal portions of bovine incisors were ground on wet no. 240 grit Sic paper mounted on a metallurgical grinder to create a flat dentine surface c. 2 mm coronal to the pulp space. The roots were removed, and each crown was then mounted in cold-curing acrylic resin leaving the flat dentine surface exposed. The dentine surfaces were further prepared in one of two ways: finished as a flat surface or in the form of a box-shaped cavity. Final finish of the flat dentine surfaces was accomplished by grinding on wet no. 600 grit Sic paper until a 4-mm diameter area of dentine was exposed. The box-shaped cavities (depth, 1.5 mm; width, 4 mm apically and 3.3 mm incisally) were prepared with diamond burs. All the dentine surfaces were washed and dried, etched with 38 percent phosphoric acid (Clearfil Etchant; Kuraray Co., Okayama, Japan) for 40 s, then washed with tap water for 30 s, and finally dried
302
J. Dent.
1991;
19: No. 5
Table 1. Details of the composition composites tested
Code Binder resin Filler Thickner
Composition (wt %) Expt. 3 Expt. 7 Expt. 2 50 45 5
40 55 5
Table II. Details of the tensile bond strength findings
of the experimental
Resin Weight % filler
Expt. 7 45
Expt. 2 55
Expt. 3 65
Expt. 4 75
26.6 (7.0)
28.2
31.1
(6.5)
(6.6)
36.5 (9.9)
18.5 (5.5)
19.9 (8.9)
27.1 +(7.4)
32.6 (9.0)
Expt. 4
30 65 5
Flat surface
20 75 5
Box cavity
Binder resin: Bis-GMA, 55.Owt%; TEGDMA, 45.Owt%; DMAEMA, 1 .O wt %; camphorquinone, 0.5 w-t %; BHT, 0.03 wt %. Filler: Feldspar with silane coupling; average filler size, 15 frm. Activator system: camphorquinone, amine.
Results shown are mean kg/cm* with standard deviations in parentheses. n= 10. Means connected by lines are not significantly different.
with compressed air. Clearfil Photo Bond (Kuraray Co., Okayama, Japan) was mixed and applied to the dentine surfaces and irradiated with a GC Light VL-1 (GC Co., Tokyo, Japan) light curing unit for 10 s. Experimental light-cured composites with tiller contents of 45, 55, 65 and 15 per cent by volume (Table Z) were evaluated. The experimental materials were condensed into a Teflon mould (1.5 mm deep, 4 mm diameter) and applied to the flat dentine surfaces or placed in the boxshaped cavities in one increment, and cured for 60 s. After 30 min at room temperature the specimens were transferred to distilled water and stored at 37°C for 24 h. After 24 h an acrylic rod was bonded to each specimen via the composite with Alonalpha (Toa Chemical Co., Tokyo, Japan) for attachment to the testing machine. Tensile bond strengths (10 specimens per group) were measured using an Instron Testing Machine (Instron Corporation, Canton, MG USA) at a cross-head speed of 1.0 mm per min. The volumetric polymerization shrinkage of the experimental resins was determined as described by Masutani et al. (1989) and illustrated in Fig. 1. Experimental composite was placed into a Teflon mould (2.0 mm deep, 4.0 mm diameter). A GC Light was connected to a variable transformer (Type SD-135, Matsunaga, Tokyo, Japan) to apply a constant 100 volts. The specimen was light cured for 30 s. The volumetric change was recorded with a CCD Camera from the start of irradiation to 120 s.
RESULTS The tensile bond strength findings are set out in Table II. The lowest bond strength was obtained with the 45 per cent tiller content composite in box-shaped cavity. Bond strength increased with increasing filler content. These results were subjected to Anova followed by Tukey’s tests (Table ZZ). The relationship between bond strength and tiller level is shown in Fig. 2. The volumetric polymerization shrinkage of the experimental composites is shown in Fig. 3. Polymerization shrinkage of the experimental composites decreased with increasing tiller contents. The largest volumetric polymerization shrinkage was observed with the experimental composite with the lowest tiller content (45 per cent). Polymerization shrinkage at 120 s after light curing was 5.24 per cent, 4.77 per cent, 2.14 per cent and 1.68 per cent for composites l-4 respectively. The correlation between bond strength and polymerization shrinkage at 120 s is detailed in Fig. 4. Most failures were adhesive, however, the failure of the 45 per cent filled composite tended to be cohesive within the resin of the bonding system.
DISCUSSION It is of interest that the highest bond strength was obtained with the composite with the highest filler content. As bond
Visible light Still video camera Glass plate (0.5 mm in thickness)
r--
Distilled water Thermostatically controlled system Glass capillary (int. diam. 0.5 mm) Water-filled dilatometer
I)
CCD camera
Fig. 1. Volumetric polymerization shrinkage recording system.
*
Display
Miyazaki
et al.: Composite
filler content
and dentine
bond
303
5.18
101 45
I
;= = 0.95
t
50
0
I
30
I
I
I
60
I
I
I
I
I
90
I
120
Time Is)
Fig.3. Polymerization shrinkage of experimental resins. 55
60
65
70
75
Weight of filler (o/D)
Fig. 2. Correlation between the bond strength and the filler level. 0, Flat surface; A, box cavity.
y = -2.17x
+ 38.09
r2 = 0.82
The polymerization shrinkage decreased with increasing filler content. The correlation between bond strength and shrinkage was greater with the box-shaped cavity specimens than with the flat surface specimen; thus, the bond strength in box-shaped cavity specimens may be affected more by polymerization shrinkage than with flat surface specimens. It is recognized that the filler level of composites is one of the important factors influencing the physical properties of the system (Germain et al., 1985; Li et al., 1985). This study demonstrates an apparent relationship between filler level of composite systems and bond strength to bovine dentine.
References Bausch J. R., de Lange K., Davidson C. L. et al. (1982)
Clinical significance of polymerization shrinkage of composite resins. J. Prosthet. Dent. 48, 59-67.
1
2 Volumetric
3 polymerization
4
5
6
shrinkage (%)
Fig. 4. Correlation between the bond strength and the polymerization shrinkage at 120 s. 0, Flat surface; A, box cavity.
strength increased with increasing filler content (75 per cent), it was considered that the filler content may be an important factor influencing bond strength. It has been reported that the physical properties of composite increase with an increase in filler content (Germain et al., 1985; Li et al., 1985). Consequently, an increase in the physical properties of a composite might be associated with an increase in bond strength. When comparing the bond strength observed between the flat surface and box-shaped cavity specimens, the bond strength with the box-shaped cavity was relatively lower than that achieved with the flat surface. Significant differences were observed between the bond strengths with these types of specimens when using the 45 per cent and 55 per cent filled systems. On the other hand there were no significant differences when using the 65 per cent and 75 per cent filled systems.
Davidson C. L., de Gee A. J. and Feilzer A. (1984) The competition between the composite-dentin bond strength and the polymerization contraction stress. J. Dent. Res. 63, 1396-1399. Duke E. S., Phillips R. W. and Blumershine R. (1985) Effects of various agents in cleaning cut dentin. J. Oral Rehabil. 12, 295-302. Germain H. St., Swartz M. L., Phillips R. W. et al. (1985) Properties of microfilled composite resins as influenced by filler content. J. Dent Res. 63, 155-160. Hansen E. K. (1982) Visible light-cured composite resins: polymerization contraction, contraction pattern and hygroscopic expansion. Stand. J. Dent. Res. 90, 329-335. Hegdahl T. and Gjerdet N. R. (1977) Contraction stresses of composite resin filling materials. Acta Odontol. Stand. 35, 191-195. Hinoura K., Moore B. K and Phillips R. W. (1986) Influence of dentin surface treatments on the bond strengths of dentin-lining cements. Oper. Dent. 11, 147-154. Iga M. (1989) Influence of filler content on marginal sealing properties of light-cured composite resin restorations. Jpn. J. Conserv. Dent. 32, 297-315. Li Y., Swartz M. L., Phillips R. W. et al. (1985) Effect of tiller content and size on properties of composites. J. Dent. Res. 64, 1396-1401. Masutani S., Matsuzaki T., Akiyama Y. et al. (1989) Study on light cured composite resins: consideration of the continuous volumetric shrinkage of resins during light irradiation. Jpn. J. Conserv. Dent 32, 1605-1611.
301
Effect of filler content of light-cured composites on bond strength to bovine dentine M. Miyazaki,
K. Hinoura,
H. Onose and 6. K. Moore*
Department of Operative Dentistry, School of Dentistry, Nihon University, Materials, School of Dentistry, Indiana University, Indiana, USA
Tokyo, Japan and *Department
of Dental
ABSTRACT The bonding of light-cured composites to tooth tissues is known to be disturbed by polymerization shrinkage, and polymerization shrinkage is affected by the tiller content of composites. This in vitro research examined the relationship between the tiller content and bond strength to dentine of light-cured composites. Experimental light-cured composite systems with tiller contents of 455565 and 75 per cent by volume were used in both bond strength to dentine and shrinkage tests. The surfaces selected as substrates were a flat surface and a box-shaped cavity prepared in bovine dentine. The lowest bond strength was obtained with the 45 per cent tiller content composite in the box-shaped cavity. Bond strength increased with increasing filler content. Volumetric polymerization shrinkage decreased with increasing tiller content. The polymerization shrinkage at 120 s after light curing was 5.24 per cent for the 45 per cent filler content system, 4.77 per cent for the 55 per cent, 2.14 per cent for the 65 per cent and 1.68 per cent for the 75 per cent. The correlation between bond strength and shrinkage was greater for the cavity than it was for the flat surface. This implies that bond strength in the box-shaped cavity may have been affected more by polymerization shrinkage than with the flat surface. The findings lend support to the view that filler content is one of the important factors influencing the physical properties of composites. KEY WORDS:
Composites, Dentine bonding
J. Dent. 1991; 1991)
19: 301-303
(Received 1 1 December
1990;
reviewed 4 March 1991;
accepted 1 1 April
Correspondence should be addressed to: Dr M. Miyazaki, Department of Operative Dentistry, Nihon University School of Dentistry, l-8 Kanda-Surugadai, Chiyoda-ku, Tokyo 101, Japan.
MATERIALS AND METHODS
INTRODUCTION It has been recognized effectively
bond
for some time that materials
to calcified
tooth
tissues
facilitate
which the
of restorative dentistry. Tooth preparations to maximize retention (Duke et al., 1985; Hinoura et al., 1986), and clinically reliable dentine bonding systems have been sought for many years. However, dentine still remains a difficult substrate for reliable bonding. In addition, it is considered that the bonding of light-cured composites could be disturbed by polymerization shrinkage (Hegdahl and Gjerdet, 1977; Hansen, 1982; Bausch et al., 1982; Davidson et al., 1984; Iga, 1989) and that polymerization shrinkage is affected by the filler content of composites (Masutani et al., 1989). The purpose of this study was to investigate the effect of tiller content of light-cured composite resins on their bond strength to bovine dentine. practice
@1991 Buttenvorth-Heinemann 0300-5712/91/050301-03
Ltd.
The incisal portions of bovine incisors were ground on wet no. 240 grit Sic paper mounted on a metallurgical grinder to create a flat dentine surface c. 2 mm coronal to the pulp space. The roots were removed, and each crown was then mounted in cold-curing acrylic resin leaving the flat dentine surface exposed. The dentine surfaces were further prepared in one of two ways: finished as a flat surface or in the form of a box-shaped cavity. Final finish of the flat dentine surfaces was accomplished by grinding on wet no. 600 grit Sic paper until a 4-mm diameter area of dentine was exposed. The box-shaped cavities (depth, 1.5 mm; width, 4 mm apically and 3.3 mm incisally) were prepared with diamond burs. All the dentine surfaces were washed and dried, etched with 38 percent phosphoric acid (Clearfil Etchant; Kuraray Co., Okayama, Japan) for 40 s, then washed with tap water for 30 s, and finally dried
302
J. Dent.
1991;
19: No. 5
Table 1. Details of the composition composites tested
Code Binder resin Filler Thickner
Composition (wt %) Expt. 3 Expt. 7 Expt. 2 50 45 5
40 55 5
Table II. Details of the tensile bond strength findings
of the experimental
Resin Weight % filler
Expt. 7 45
Expt. 2 55
Expt. 3 65
Expt. 4 75
26.6 (7.0)
28.2
31.1
(6.5)
(6.6)
36.5 (9.9)
18.5 (5.5)
19.9 (8.9)
27.1 +(7.4)
32.6 (9.0)
Expt. 4
30 65 5
Flat surface
20 75 5
Box cavity
Binder resin: Bis-GMA, 55.Owt%; TEGDMA, 45.Owt%; DMAEMA, 1 .O wt %; camphorquinone, 0.5 w-t %; BHT, 0.03 wt %. Filler: Feldspar with silane coupling; average filler size, 15 frm. Activator system: camphorquinone, amine.
Results shown are mean kg/cm* with standard deviations in parentheses. n= 10. Means connected by lines are not significantly different.
with compressed air. Clearfil Photo Bond (Kuraray Co., Okayama, Japan) was mixed and applied to the dentine surfaces and irradiated with a GC Light VL-1 (GC Co., Tokyo, Japan) light curing unit for 10 s. Experimental light-cured composites with tiller contents of 45, 55, 65 and 15 per cent by volume (Table Z) were evaluated. The experimental materials were condensed into a Teflon mould (1.5 mm deep, 4 mm diameter) and applied to the flat dentine surfaces or placed in the boxshaped cavities in one increment, and cured for 60 s. After 30 min at room temperature the specimens were transferred to distilled water and stored at 37°C for 24 h. After 24 h an acrylic rod was bonded to each specimen via the composite with Alonalpha (Toa Chemical Co., Tokyo, Japan) for attachment to the testing machine. Tensile bond strengths (10 specimens per group) were measured using an Instron Testing Machine (Instron Corporation, Canton, MG USA) at a cross-head speed of 1.0 mm per min. The volumetric polymerization shrinkage of the experimental resins was determined as described by Masutani et al. (1989) and illustrated in Fig. 1. Experimental composite was placed into a Teflon mould (2.0 mm deep, 4.0 mm diameter). A GC Light was connected to a variable transformer (Type SD-135, Matsunaga, Tokyo, Japan) to apply a constant 100 volts. The specimen was light cured for 30 s. The volumetric change was recorded with a CCD Camera from the start of irradiation to 120 s.
RESULTS The tensile bond strength findings are set out in Table II. The lowest bond strength was obtained with the 45 per cent tiller content composite in box-shaped cavity. Bond strength increased with increasing filler content. These results were subjected to Anova followed by Tukey’s tests (Table ZZ). The relationship between bond strength and tiller level is shown in Fig. 2. The volumetric polymerization shrinkage of the experimental composites is shown in Fig. 3. Polymerization shrinkage of the experimental composites decreased with increasing tiller contents. The largest volumetric polymerization shrinkage was observed with the experimental composite with the lowest tiller content (45 per cent). Polymerization shrinkage at 120 s after light curing was 5.24 per cent, 4.77 per cent, 2.14 per cent and 1.68 per cent for composites l-4 respectively. The correlation between bond strength and polymerization shrinkage at 120 s is detailed in Fig. 4. Most failures were adhesive, however, the failure of the 45 per cent filled composite tended to be cohesive within the resin of the bonding system.
DISCUSSION It is of interest that the highest bond strength was obtained with the composite with the highest filler content. As bond
Visible light Still video camera Glass plate (0.5 mm in thickness)
r--
Distilled water Thermostatically controlled system Glass capillary (int. diam. 0.5 mm) Water-filled dilatometer
I)
CCD camera
Fig. 1. Volumetric polymerization shrinkage recording system.
*
Display
Miyazaki
et al.: Composite
filler content
and dentine
bond
303
5.18
101 45
I
;= = 0.95
t
50
0
I
30
I
I
I
60
I
I
I
I
I
90
I
120
Time Is)
Fig.3. Polymerization shrinkage of experimental resins. 55
60
65
70
75
Weight of filler (o/D)
Fig. 2. Correlation between the bond strength and the filler level. 0, Flat surface; A, box cavity.
y = -2.17x
+ 38.09
r2 = 0.82
The polymerization shrinkage decreased with increasing filler content. The correlation between bond strength and shrinkage was greater with the box-shaped cavity specimens than with the flat surface specimen; thus, the bond strength in box-shaped cavity specimens may be affected more by polymerization shrinkage than with flat surface specimens. It is recognized that the filler level of composites is one of the important factors influencing the physical properties of the system (Germain et al., 1985; Li et al., 1985). This study demonstrates an apparent relationship between filler level of composite systems and bond strength to bovine dentine.
References Bausch J. R., de Lange K., Davidson C. L. et al. (1982)
Clinical significance of polymerization shrinkage of composite resins. J. Prosthet. Dent. 48, 59-67.
1
2 Volumetric
3 polymerization
4
5
6
shrinkage (%)
Fig. 4. Correlation between the bond strength and the polymerization shrinkage at 120 s. 0, Flat surface; A, box cavity.
strength increased with increasing filler content (75 per cent), it was considered that the filler content may be an important factor influencing bond strength. It has been reported that the physical properties of composite increase with an increase in filler content (Germain et al., 1985; Li et al., 1985). Consequently, an increase in the physical properties of a composite might be associated with an increase in bond strength. When comparing the bond strength observed between the flat surface and box-shaped cavity specimens, the bond strength with the box-shaped cavity was relatively lower than that achieved with the flat surface. Significant differences were observed between the bond strengths with these types of specimens when using the 45 per cent and 55 per cent filled systems. On the other hand there were no significant differences when using the 65 per cent and 75 per cent filled systems.
Davidson C. L., de Gee A. J. and Feilzer A. (1984) The competition between the composite-dentin bond strength and the polymerization contraction stress. J. Dent. Res. 63, 1396-1399. Duke E. S., Phillips R. W. and Blumershine R. (1985) Effects of various agents in cleaning cut dentin. J. Oral Rehabil. 12, 295-302. Germain H. St., Swartz M. L., Phillips R. W. et al. (1985) Properties of microfilled composite resins as influenced by filler content. J. Dent Res. 63, 155-160. Hansen E. K. (1982) Visible light-cured composite resins: polymerization contraction, contraction pattern and hygroscopic expansion. Stand. J. Dent. Res. 90, 329-335. Hegdahl T. and Gjerdet N. R. (1977) Contraction stresses of composite resin filling materials. Acta Odontol. Stand. 35, 191-195. Hinoura K., Moore B. K and Phillips R. W. (1986) Influence of dentin surface treatments on the bond strengths of dentin-lining cements. Oper. Dent. 11, 147-154. Iga M. (1989) Influence of filler content on marginal sealing properties of light-cured composite resin restorations. Jpn. J. Conserv. Dent. 32, 297-315. Li Y., Swartz M. L., Phillips R. W. et al. (1985) Effect of tiller content and size on properties of composites. J. Dent. Res. 64, 1396-1401. Masutani S., Matsuzaki T., Akiyama Y. et al. (1989) Study on light cured composite resins: consideration of the continuous volumetric shrinkage of resins during light irradiation. Jpn. J. Conserv. Dent 32, 1605-1611.
