Journal of Oral Rehabilitation, 1992, Volume 19, pages 361-370
Characterization of inorganic fillers in visible-lightcured dental composite resins A.M. KHAN, H. SUZUKI*, Y. NOMURA*, M. TAIRA*, K. W A K A S A * , H. S H I N T A N I aili/ M. Y AM AKl* Department of Operative Dentistrv and "Department of Dental Materials. Hiroshima University School of Dentistry, Hiroshima, Japan
Summary
Inorganic fillers in seven visible-light (VL)-cured dental composite resins were examined for their size, composition, phase and content, employing the following analytical instruments. SEM observations indicated that five samples could be classified into the hybrid type while the remaining two belonged to micro-filled and sub-micron types. EDX analyses revealed that five samples contained BaO while others lacked BaO. XRD analyses showed that three were in vitreous phase, two were in the crystalline phase and two were mixtures of both. DTG thermal analyses indicated that the hybrid type composites had the higher inorganic filler content (wt%) than the composites of two other types. In conclusion, wide varieties exist in the inorganic fillers in VL-cured dental composite resins currently utilized. Introduction
Visible-light (VL)-cured dental composite resins have gained wide acceptance as hard tissue restoratives in the oral cavity due to their ease in handling and aesthetic merits (Leinfelder et al,, 1980; Wilson, Wilson & Smith, 1988). The utilization of the composites is, however, limited by their sensitivity to long-term oral-environmental exposure. Attrition, humidity and mastication forces contribute to wear and bulk fracture (Soderholm, 1985), in which the filler of the composite plays a major role. Leinfelder (1987) stated that the amount of wear is directly proportional to the size and hardness of the filler particles. Leakage of filler elements from the composite may cause the crack formation in the composite through the hydrolytic degradation of the silane coupling layer (Soderholm, 1983; Soderholm et al,, 1984) and may induce the adverse effect on the oral soft tissue (e.g. Ba^^ ion which imparts radio-opacity but is toxic) (Bowen & Reed, 1976). The manipulation of the composite is also strongly influenced by the filler. For instance, the composites containing smaller (e.g. microfilled) filler particles are easier to pack and polish, compared to the composites containing larger (e.g. conventional size) filler particles (Craig, 1985). On the other hand, the former is inferior to the latter with regard to mechanical properties such as the compressive strength (Li et al,, 1985). Although dental composites used today contain different fillers, there have been Correspondence: Dr A.M. Khan, Department of Operative Dentistry, Hiroshima University School of Dentistry, 1-2-3 Kasumi Minami-ku Hiroshima-shi 734. .lapan
361
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few studies to actually identify them (0ysaed & Ruyter, 1986; Hosoda et al., 1987). It seems, however, quite important to reveal this information for assessing the overall clinical performance ofthe composites. The purpose of this investigation was, therefore, to analyze the inorganic fillers in VL-cured dental composites currently employed by means of scanning electron microscopy (SEM) coupled with energy dispersed X-ray microprobe (EDX), X-ray diffraction (XRD) and differential thermogravimetric thermal analysis (DTG). Materials and methods
Samples — Seven commercially available VL-cured dental composite resins were studied. A list of composites examined, with details of batch numbers and manufacturers, is given in Table 1. SEM/EDX — to collect the inorganic filler from the composite, the composite paste was dissolved in acetone and centrifuged, the top clear part of the liquid was removed and the residue was freeze-dried. Scanning electron microscopy* coupled with an energy dispersed X-ray microprobet was used for the SEM/EDX examination of the inorganic filler extracted from the composite. EDX spectrum was obtained while a 500 x area was being irradiated, and the average X-ray intensity for each metallic element was measured. The EDX operating conditions were: accelerated voltage, 15 kV and counting time, 2(J0s. XRD — for the identification of the phase of the extracted inorganic filler, XRD was conducted on a diffractometer+, using copper K-alpha radiation, filtered with a diffraction-beam monochrometer. The experimental X-ray conditions were: accelerated voltage, 30kV; current, 10mA; scan rate, (2—min^') 2°min~'; and scan tange, (20), 10-50°. DTG — for the determination of the inorganic filler content in the composite paste, DTG (DTA/TG) thermal analysis was carried out with a thermal analyzer§, using the following experimental conditions: sample weight, 2 0 ± l m g ; reference material, a-alumina; DTA sensitivity, 100|.iV; TG sensitivity, 20mg; heating rate, 5°Cmin~'; temperature range, room temperature to 800°C; and atmosphere, air under a fiow of 30 ml min"' N^. Table 1. List of seven VL-curcd dental composites, with details of batch numbers and manufacturers Brand name
Batch number
Manufacturers
Silux U P-50 U Occlusin Estilux A35 Brilliant Lux CR-inlay UL Clearfil Photo Posterior
8H1 9CD2D LH06 Ch.-B.23 110889-66 CIL-3()01
3M Co.. U.S.A 3M Co., U.S.A. ICI Co., U.K. Kulzer Co., Germany Coltene Co., Switzerland Kuraray Co., Japan
HPS-1002
Kuraray, Japan
* JSM-61fK). JEOL Co., Tokyo. Japan. t 422J, Tracor Northern Co., Wisconsin, U.S.A. t Geigerflex D 2, Rigaku Co., Tokyo, Japan. § DT-30, Shimadzu Co., Kyoto, Japan.
Inorganic fillers in VL-c tired composites
363
Results
Figure 1 shows the SEM photomicrographs of the fillers in seven VL-eured composites. All filler particles had irregular shapes. Table 2 indicates the approximate particle sizes and filler types, classified according to the literature (Lutz & Phillips, 1983). The filler of Silux seemed to consist of agglomerated minute particles, embedded in a pre-polymerized organic material with the size of around 5 |im (Germain et al.., 1985), and was categorized into microfilled. The filler of Brilliant Lux was made up of small particles with the size of around 0-5 |im, and was categorized into sub-micron. The fillers of P—50, Occlusin, Estilux, CR-inlay and Clearfil Photo Posterior had the hybrid type fillers consisting of small particles with the size of around 1 |um and large particles with the size of around 15 |.tm. Figure 2 shows the EDX spectra of the fillers in seven VL-cured composites. Table 3 indicates the compositions of the fillers, checked out by the EDX standardless quantitative analyses. As can be seen, the filler of Silux was entirely composed of 100 wt% SiO2 while that of P-50 consisted of 75wt% SiO, and 25wt% ZrOj. Fillers of Occlusin, Estilux, Brilliant Lux, CR-inlay and Clearfil Photo Posterior consisted of SiO?, AI2O3 and BaO, with and without the impurities such as K2O. With regards to the BaO content in the fillers, three groups exist. Silux and P—50 had no BaO. Occlusin and Brilliant Lux contained high concentrations of BaO at around 33wt% whilst Estilux, CR-inlay and Clearfil Photo Posterior included lower amounts of BaO at around 7wt%. Figure 3 shows the XRD charts of the fillers in seven VL-cured composites. The labeling of the crystalline phases was carried out by matching with the JCPDS files (JCPDS, 1971). Table 4 summarizes the identified phases of the fillers. Silux, Occlusin and Brilliant Lux appeared to have the glass fillers, as demonstrated by their characteristic glass hallows (i.e. broad XRD peaks over 2— of around 20—25°). Fillers of both CR-inlay and Clearfil Photo Posterior seemed to be quartz (one type of crystalline SiO2). Those of P—50 and Estilux were glassy phase + crystalline ZrO2 and glassy phase + crystalline LixAl^Si^-xOd^ respectively. Figure 4 shows the DTG (DTA and TG) profiles of seven VL-cured composite pastes. The filler contents in the composites were determined by the weight at 575°C of the TG curves, with relative accordance to the international specification (LS.O., 1978) and are presented in Table 5. It became evident that the hybrid type fillers of P-50, Occlusin, Estilux, CR-inlay and Clearfil Photo Posterior had the higher filler loadings of around 87wt% in the total composite, while the filler amounts of Silux Table 2. Approximate particle sizes and filler types of the fillers in seven VL-cured composites
Material Silux P-50 Occlusin Estilux Brilliant Lux CR-inlay Clearfil Photo Posterior
Approximate filler particle size ([^im)
Filler type
0-05-10 1-20 1-20 1-20 0-1-2 1-20
mierofilled hybrid hybrid hybrid sub-micron hybrid
1-20
hybrid
364
A.M. Khan et al
(b) i ! ^ ^ ^
(c)
(d)
Fig. 1. SEM photomicrographs ot the tillers extracted trom seven VL-cured composites, (a) Silux; (b) P-50; (c) Occlusin; (d) Estilux; (e) Brilliant Lux; (f) CR-inlay; (g) Clearfil Photo Posterior.
and Brilliant Lux were mueh smaller, 61 wt% and 77wt%, respeetively. DTA curves in Fig. 4 reflect the thermal behaviours ofthe composite pastes upon heating. It appeared that at less than 200°C, the monomers of the composites cured due to the thermal energy instead of the photo-irradiation, in which the exothermic reaction was observed.
Inorganic fillers in VL-cured composites
365
(e) S1
Si
(b)
iZr
10
Fig. 2. EDX spectra of the inorganic fillers in seven VL-cured composites, (a) Silux; (b) P—50; (c) Occlusin; (d) Estilux; (e) Brilliant Lux; (f) CR-inlay; (g) Clearfil Photo Posterior.
366
A.M. Khan et al.
Table 3. Compositions of the fillers in seven VL-cured eomposites
Material
SiOz
Silux P-3() Occlusin Estilux Brilliant
UK)
Lux
CR-inlay Clearfil Photo Posterior
AI2O3
BaO
75-4 58-6 76-5
8-9 14-5
32-5
56-4 87-4
8-9 2-9
34-6
90-5
9.9
7-3
P2O5
MgO
Composition (wt%) K2O Na2O
24-6 6-4
1-5
0-8
0-3 0-1
8-5
1-2
Table 4. Identified phases of the tillers in seven VL-cured eomposites Material
Phase
Silux P-5() Ocelusin Estilux Brilliant Lux CR-inlav Clearfil Photo Posterior
Glass Glass + ZrO, Class Glass -1- Li^Al^Si:(_^O(, Glass Quartz Quartz
When heated to more than 20()°C, the polymer phase of the eomposite thermally deeomposed, eausing the complieated exothermie and endothermie reaetions. The thermal ehange of the tiller may also be eneountered in these thermal reaetions at elevated temperatures. It should be noted from the TG eurves that the composites still lost their weight when heated to more than 575°C. Discussion
It beeame clear from the instrumental analyses performed that current VL-cured composites contain fillers with wide variations in the size, composition, phase and content. The role of BaO in the filler is at first considered. Although quartz filler has an advantageous optical property of having high refractive index value comparing to that of the resin phase of the composite and thus allowing the composite to appear more translucent (Bowen & Cleek, 1972), Soderholm (1985) mentioned that today barium glass is most preferred for the filler in dental composites because of the softness, facilitating finer filler production and of the radio-opacity, facilitating detection of caries or underlying decalcified dentine. Out of seven VL-cured composites examined, however, only three (Occlusin, Estilux and Brilliant Lux) contained barium glass fillers. The fillers of two barium-containing composites (CR-inlay and Clearfil Photo Posterior) were not glass, but quartz. Two composites (Silux and P-50) did not contain BaO as well as other strong radio-opaque agents, e.g. SrO, and hence were expected to
Inorganic fillers in VL-cured composites
367
(b)
*:Crystal1 i ne ZrO^
*
J 1
1
50
40' 30 20 20 (degree)
#:Crystannne Li Al Si., 0, X
50
X
40
40
10
50
40
1 30
20 20 .(degree)
10
50
40
30 20 20 (degree)
10
(d)
3-x 5
30 20 20 (degree)
30 20 20 (degree)
10
50
40
30 20 20 (degree)
50
40
30 20 29 (degree)
10
Fig. 3. X R D charts of the inorganic tillers extracted from seven VL-curcd composites, (a) Silux; (b) P - 5 0 ; (c) Occlusin; (d) Estilux; (e) Brilliant Lux; (f) CR-inlay; (g) Clearfil Photo Posterior.
lack X-ray opacity. However, P—50 due to the presence of ZrO2 in the filler composition, may possess limited radio-opacity. According to the study by Watts (1987), the magnitude of the radio-opacity of the highly filler loaded composite could exceed that of human enamel when the filler contained more than 20wt% BaO. From this criteria, it can be suggested that only two composites (Occlusin and Brilliant Lux) have radio-opacity values in excess of that of enamel. Lutz et al. (1984) suggested that
368
A.M. Khan et al.
0 -10 -20 -30 -40 -50
TG
(a)
- DTA
0 -10 -20 -30 40 -50
/-\-
1
1
1
200
400
600
TG _^^ 0 -10 -20 - DTA 30 40 -50
TG
(e) -^
nTA -
•
-
,
.
_
_
,
800
.
-^^ .
'
"
—
'i
'
200
400
600
800
TG 0 „ ,/ '•, (f) .-^ -10 - DTA -20 1 > ,--^ -30 -40 -50
(b)
o E
o
E 0)
2
0
00 1
1
1
200
400
600
800
cu
a>
1 h-
1
1
200
400
600
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.
-
-
•
800 (q)
DTA ^ P -in — , ' _ ^ -20 ,' '^_ , - - ' -30 — -40 -50 .
800
1
'
200
400
600
800
Temperature (°C)
200
400
600
800
Temperature (°C)
Fig. 4. DTG (DTA and TG) profiles of seven VL-curcd composite pastes, (a) Silux; (b) P-50; (e) Occlusin; (d) Estilux; (c) Brilliant Lux; (f) CR-inlay; (g) Clearfil Photo Posterior.
the composites which are designed to restore posterior teeth should be more radioopaque than enamel. When mounted in the resin phase, the filler is difficult to observe. Furthermore, in this condition, polishing techniques significantly alter the surface appearance of the composite (Lambrechts & Vanherle, 1982; Northeast & van Noort, 1988). Thus, we extracted the filler from the composite, using a solvent and, by SEM, succeeded in obtaining a clear and vivid image of the filler. The particle size distribution of the filler seems to have a special relationship to the mechanical property of the composite. The increase in filler loading results in increased mechanical strength of the composite (Germain et al., 1985; Li et al... 1985). Because the fillers were most densely packed
Inorganic fillers in VL-cured composites
369
Table 5. The inorganic filler contents in seven VL-eured composites, determined at 575°C of the TG curves and expressed as mean values with standard deviations of three measurements Material Silux P-50 Occlusin Estilux BriUiant Lux CR-inlay Clearfil Photo Posterior
Inorganic filler content (wt%) 60-6 ±2-15 88-2 ±0-25 86-4 ± 0-48 85-6 ±0-25 77-1 ±0-88 87-1 ±0-15 88-0 ± 0-35
in the composites containing the hybrid type fillers, they (P-50, Occlusin, Estilux, CR-inlay and Clearfil Photo Posterior) might be utilized in the posterior segment of the mouth which is susceptible to wear (Leinfelder, 1988). The lower filler loaded composites (Silux and Brilliant Lux), however, could function satisfactorily in the anterior segment of the mouth which does not bear a similar load. EDX analysis was conducted on the relatively large spot containing more than dozens of the filler particles. Thus, we did not measure the composition of each filler particle, but identified that of the aggregate of the filler particles. It can be, however, speculated from EDX and XRD analyses that fillers of Silux, Occlusin and Brilliant Lux consist of single glass phases, those of CR-inlay and Clearfil Photo Posterior are made up of single quartz phases while those of P-50 and Estilux have more than two filler phases of different compositions. P-50 seems to contain the hybrid type SiO2 glass and minute crystalline ZrO2 fillers whereas Estilux appears to involve LixAlxSi3_xO6 glass-ceramic and SiO2-Al2O3-BaO glass fillers. The light element, Li could not be identified by EDX. Referring to the chemical stability of the filler in the oral environment, the filler containing the impurity seems to degrade more, compared with that containing no impurity. The glass filler may also disintegrate more extensively than the ceramic (i.e. crystalline) filler. The more the BaO content, the less the resistance of the filler to chemical degradation because the parent aluminosilicate network is disrupted by the relatively large barium ion (Soderholm et al.., 1984). There seems to be a correlation between particle size of the filler and filler content in the composite. The smaller the filler particle, the lower the filler content, as in the case of Brilliant Lux in contrast to those of the composites containing the hybrid type fillers. DTG (DTA/TG) thermal analyses provided valuable information on the composites which remain to be studied. At elevated temperatures of more than 575°C, some constituents of the filler and the silane coupling layer may evaporate or thermally decompose, resulting in further decrease in the weight. In the near future, development of new fillers for VL-cured dental composites is expected. Research is planned to impart functionality, such as adjustable refractive index and radio-opacity to the silica-based glass filler. An international standard to regulate the properties of the fillers in VL-cured composites is also needed. Acknowledgments
The authors express deep appreciation to JEOL Co., Tokyo, Japan for the use of
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SEM/EDX at their application laboratory in Osaka, Japan and to the manufacturers of seven VL-cured composites for providing their products. References BowFN, R.L. & Ci.iiEK, G.W. (1972) A new scries of x-ray-opaque reinforcing fillers for composite materials. .Journal of Dental Research. 51, 177. BowtN, R.L. & RHKD, L . E . (1976) Semiporous reinforcing tillers for eomposite resins: i. preparation of provisional glass formulations. Journal of Dental Research. 55, 738. CRAIG, R . G . (1985) Direct esthetic restorative materials. In: Restorative Dental Materials (ed R.G. Craig), p. 225. CV Mosby Co., St. Louis, U.S.A. GKRMAIN, H . S T . , SWARTZ, M.L., PHILLIPS, R.W., MOOKH, B . K , & ROBERTS, T . A . (1985) Properties of mierofilled eomposite resins as influenced by filler content. .Journal of Dental Research. 64, 155. HosoDA, H., YAMADA, T . , OiSLiKi, M., HosoKAWA, A. & TAKAISUKA, T . (1987) Classitieation and elemental composition of fillers on composite resin, part 2. elassifieation of light cured anterior and a/p eomposite resins (in .lapanese). .Japanese Journal of Conservative Dentistry. 30, 427. I.S.O. (1978) Resin-based dental filling materials, ISO 4049. International Organization for Standardization, Geneva, Switzerland. JCPDS (1971) Hanawalt (d-value) listings. In: Inori^anic Jnde.x to the J^owder Diffraction File (ed L.G. Berry), p. 1. Joint Committee on Powder Diffraction Standards, Pennsylvania, U.S.A. LAMBRBCHIS, P. & VANHHRLF, G . (1982) Observation and eomparison of polished composite surfaees with the aid of SEM and profilometer. Journal of Oral Rehabilitation. 9. 169. LhL-JFELDLR, K.F.I SLUDLR, T.B.; SANTOS, J . F . & WALL, J . T . (1980) Five-year clinical evaluation of anterior and posterior restorations of eomposite resin. Operative Dentistrw 5, 57. LniNtTiLDLR, K.F. (1987) Wear patterns and rates of posterior eomposite resins. International Dental Journal. 37, 152. LhiNH-LDHR, K.F. (1988) Current developments in posterior composite resins. Advances in Dental Research, 2. 115. Li, Y.. SWARTZ, M.L., PHILLIPS, R.W., MOORL, B.K. & ROBKRTS. T.A. (1985) Effeet of tiller eontent and size on properties of eomposites. Journal of Dental Research. 64. 1396. LuTZ, F. & PHMin'S, R.W. (1983) A elassifieation and evaluation of composite resin. Journal of J'rosthetic Dentistry. 50, 480. Lurz, F., PHILLIPS, R.W., ROULET, J.F. & SEICOS. J . C . (1984) In vivo and in vitro wear of potential posterior eomposites. Journal of Dental Research. 63, 914. NORTHEAST, S.E. & VAN NooRr, R. (1988) Surfaee eharaeteristies of finished posterior composite resins. Dental Materials. 4, 278. 0YSAED, H. & RuYTER, LE. (1986) Water sorption and tiller eharaeteristies of composites for use in posterior teeth. Journal of Dental Research. 65, 1315. SODERHOLM, K.-J. (1983) Leaking of tillers in dental eomposites. Journal of Dental Research. 62, 126. SODERHOLM, K . - J . , ZIC.AN, M . , RAC.AN, M . , Fisc HLSCHWEIGER, W . & BERGMAN, M . (1984) Hydrolytic degradation of dental eomposites. Journal of Dental Research. 62, 1248. SODERHOLM, K.-J. (1985) Filler systems and resin interface. In: Posterior Composite Resin Dental Restorative Materials (eds G. Vanlierle & D.C. Smith) p. 139. Peter Szule Publishing Co., The Netherlands. WAITS, D.C. (1987) Radiopaeity vs. composition of some barium and strontium glass eomposites. Journal of Dentistry. 15, 38. Wit-SON, N.H.F.. WILSON, M . A . & SMITH, G . A . (1988) A elinieal trial of a visible light eured posterior composite resin restorative material: four-year results. Quintessence International. 19, 133.
Characterization of inorganic fillers in visible-lightcured dental composite resins A.M. KHAN, H. SUZUKI*, Y. NOMURA*, M. TAIRA*, K. W A K A S A * , H. S H I N T A N I aili/ M. Y AM AKl* Department of Operative Dentistrv and "Department of Dental Materials. Hiroshima University School of Dentistry, Hiroshima, Japan
Summary
Inorganic fillers in seven visible-light (VL)-cured dental composite resins were examined for their size, composition, phase and content, employing the following analytical instruments. SEM observations indicated that five samples could be classified into the hybrid type while the remaining two belonged to micro-filled and sub-micron types. EDX analyses revealed that five samples contained BaO while others lacked BaO. XRD analyses showed that three were in vitreous phase, two were in the crystalline phase and two were mixtures of both. DTG thermal analyses indicated that the hybrid type composites had the higher inorganic filler content (wt%) than the composites of two other types. In conclusion, wide varieties exist in the inorganic fillers in VL-cured dental composite resins currently utilized. Introduction
Visible-light (VL)-cured dental composite resins have gained wide acceptance as hard tissue restoratives in the oral cavity due to their ease in handling and aesthetic merits (Leinfelder et al,, 1980; Wilson, Wilson & Smith, 1988). The utilization of the composites is, however, limited by their sensitivity to long-term oral-environmental exposure. Attrition, humidity and mastication forces contribute to wear and bulk fracture (Soderholm, 1985), in which the filler of the composite plays a major role. Leinfelder (1987) stated that the amount of wear is directly proportional to the size and hardness of the filler particles. Leakage of filler elements from the composite may cause the crack formation in the composite through the hydrolytic degradation of the silane coupling layer (Soderholm, 1983; Soderholm et al,, 1984) and may induce the adverse effect on the oral soft tissue (e.g. Ba^^ ion which imparts radio-opacity but is toxic) (Bowen & Reed, 1976). The manipulation of the composite is also strongly influenced by the filler. For instance, the composites containing smaller (e.g. microfilled) filler particles are easier to pack and polish, compared to the composites containing larger (e.g. conventional size) filler particles (Craig, 1985). On the other hand, the former is inferior to the latter with regard to mechanical properties such as the compressive strength (Li et al,, 1985). Although dental composites used today contain different fillers, there have been Correspondence: Dr A.M. Khan, Department of Operative Dentistry, Hiroshima University School of Dentistry, 1-2-3 Kasumi Minami-ku Hiroshima-shi 734. .lapan
361
362
A.M. Khan et al.
few studies to actually identify them (0ysaed & Ruyter, 1986; Hosoda et al., 1987). It seems, however, quite important to reveal this information for assessing the overall clinical performance ofthe composites. The purpose of this investigation was, therefore, to analyze the inorganic fillers in VL-cured dental composites currently employed by means of scanning electron microscopy (SEM) coupled with energy dispersed X-ray microprobe (EDX), X-ray diffraction (XRD) and differential thermogravimetric thermal analysis (DTG). Materials and methods
Samples — Seven commercially available VL-cured dental composite resins were studied. A list of composites examined, with details of batch numbers and manufacturers, is given in Table 1. SEM/EDX — to collect the inorganic filler from the composite, the composite paste was dissolved in acetone and centrifuged, the top clear part of the liquid was removed and the residue was freeze-dried. Scanning electron microscopy* coupled with an energy dispersed X-ray microprobet was used for the SEM/EDX examination of the inorganic filler extracted from the composite. EDX spectrum was obtained while a 500 x area was being irradiated, and the average X-ray intensity for each metallic element was measured. The EDX operating conditions were: accelerated voltage, 15 kV and counting time, 2(J0s. XRD — for the identification of the phase of the extracted inorganic filler, XRD was conducted on a diffractometer+, using copper K-alpha radiation, filtered with a diffraction-beam monochrometer. The experimental X-ray conditions were: accelerated voltage, 30kV; current, 10mA; scan rate, (2—min^') 2°min~'; and scan tange, (20), 10-50°. DTG — for the determination of the inorganic filler content in the composite paste, DTG (DTA/TG) thermal analysis was carried out with a thermal analyzer§, using the following experimental conditions: sample weight, 2 0 ± l m g ; reference material, a-alumina; DTA sensitivity, 100|.iV; TG sensitivity, 20mg; heating rate, 5°Cmin~'; temperature range, room temperature to 800°C; and atmosphere, air under a fiow of 30 ml min"' N^. Table 1. List of seven VL-curcd dental composites, with details of batch numbers and manufacturers Brand name
Batch number
Manufacturers
Silux U P-50 U Occlusin Estilux A35 Brilliant Lux CR-inlay UL Clearfil Photo Posterior
8H1 9CD2D LH06 Ch.-B.23 110889-66 CIL-3()01
3M Co.. U.S.A 3M Co., U.S.A. ICI Co., U.K. Kulzer Co., Germany Coltene Co., Switzerland Kuraray Co., Japan
HPS-1002
Kuraray, Japan
* JSM-61fK). JEOL Co., Tokyo. Japan. t 422J, Tracor Northern Co., Wisconsin, U.S.A. t Geigerflex D 2, Rigaku Co., Tokyo, Japan. § DT-30, Shimadzu Co., Kyoto, Japan.
Inorganic fillers in VL-c tired composites
363
Results
Figure 1 shows the SEM photomicrographs of the fillers in seven VL-eured composites. All filler particles had irregular shapes. Table 2 indicates the approximate particle sizes and filler types, classified according to the literature (Lutz & Phillips, 1983). The filler of Silux seemed to consist of agglomerated minute particles, embedded in a pre-polymerized organic material with the size of around 5 |im (Germain et al.., 1985), and was categorized into microfilled. The filler of Brilliant Lux was made up of small particles with the size of around 0-5 |im, and was categorized into sub-micron. The fillers of P—50, Occlusin, Estilux, CR-inlay and Clearfil Photo Posterior had the hybrid type fillers consisting of small particles with the size of around 1 |um and large particles with the size of around 15 |.tm. Figure 2 shows the EDX spectra of the fillers in seven VL-cured composites. Table 3 indicates the compositions of the fillers, checked out by the EDX standardless quantitative analyses. As can be seen, the filler of Silux was entirely composed of 100 wt% SiO2 while that of P-50 consisted of 75wt% SiO, and 25wt% ZrOj. Fillers of Occlusin, Estilux, Brilliant Lux, CR-inlay and Clearfil Photo Posterior consisted of SiO?, AI2O3 and BaO, with and without the impurities such as K2O. With regards to the BaO content in the fillers, three groups exist. Silux and P—50 had no BaO. Occlusin and Brilliant Lux contained high concentrations of BaO at around 33wt% whilst Estilux, CR-inlay and Clearfil Photo Posterior included lower amounts of BaO at around 7wt%. Figure 3 shows the XRD charts of the fillers in seven VL-cured composites. The labeling of the crystalline phases was carried out by matching with the JCPDS files (JCPDS, 1971). Table 4 summarizes the identified phases of the fillers. Silux, Occlusin and Brilliant Lux appeared to have the glass fillers, as demonstrated by their characteristic glass hallows (i.e. broad XRD peaks over 2— of around 20—25°). Fillers of both CR-inlay and Clearfil Photo Posterior seemed to be quartz (one type of crystalline SiO2). Those of P—50 and Estilux were glassy phase + crystalline ZrO2 and glassy phase + crystalline LixAl^Si^-xOd^ respectively. Figure 4 shows the DTG (DTA and TG) profiles of seven VL-cured composite pastes. The filler contents in the composites were determined by the weight at 575°C of the TG curves, with relative accordance to the international specification (LS.O., 1978) and are presented in Table 5. It became evident that the hybrid type fillers of P-50, Occlusin, Estilux, CR-inlay and Clearfil Photo Posterior had the higher filler loadings of around 87wt% in the total composite, while the filler amounts of Silux Table 2. Approximate particle sizes and filler types of the fillers in seven VL-cured composites
Material Silux P-50 Occlusin Estilux Brilliant Lux CR-inlay Clearfil Photo Posterior
Approximate filler particle size ([^im)
Filler type
0-05-10 1-20 1-20 1-20 0-1-2 1-20
mierofilled hybrid hybrid hybrid sub-micron hybrid
1-20
hybrid
364
A.M. Khan et al
(b) i ! ^ ^ ^
(c)
(d)
Fig. 1. SEM photomicrographs ot the tillers extracted trom seven VL-cured composites, (a) Silux; (b) P-50; (c) Occlusin; (d) Estilux; (e) Brilliant Lux; (f) CR-inlay; (g) Clearfil Photo Posterior.
and Brilliant Lux were mueh smaller, 61 wt% and 77wt%, respeetively. DTA curves in Fig. 4 reflect the thermal behaviours ofthe composite pastes upon heating. It appeared that at less than 200°C, the monomers of the composites cured due to the thermal energy instead of the photo-irradiation, in which the exothermic reaction was observed.
Inorganic fillers in VL-cured composites
365
(e) S1
Si
(b)
iZr
10
Fig. 2. EDX spectra of the inorganic fillers in seven VL-cured composites, (a) Silux; (b) P—50; (c) Occlusin; (d) Estilux; (e) Brilliant Lux; (f) CR-inlay; (g) Clearfil Photo Posterior.
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Table 3. Compositions of the fillers in seven VL-cured eomposites
Material
SiOz
Silux P-3() Occlusin Estilux Brilliant
UK)
Lux
CR-inlay Clearfil Photo Posterior
AI2O3
BaO
75-4 58-6 76-5
8-9 14-5
32-5
56-4 87-4
8-9 2-9
34-6
90-5
9.9
7-3
P2O5
MgO
Composition (wt%) K2O Na2O
24-6 6-4
1-5
0-8
0-3 0-1
8-5
1-2
Table 4. Identified phases of the tillers in seven VL-cured eomposites Material
Phase
Silux P-5() Ocelusin Estilux Brilliant Lux CR-inlav Clearfil Photo Posterior
Glass Glass + ZrO, Class Glass -1- Li^Al^Si:(_^O(, Glass Quartz Quartz
When heated to more than 20()°C, the polymer phase of the eomposite thermally deeomposed, eausing the complieated exothermie and endothermie reaetions. The thermal ehange of the tiller may also be eneountered in these thermal reaetions at elevated temperatures. It should be noted from the TG eurves that the composites still lost their weight when heated to more than 575°C. Discussion
It beeame clear from the instrumental analyses performed that current VL-cured composites contain fillers with wide variations in the size, composition, phase and content. The role of BaO in the filler is at first considered. Although quartz filler has an advantageous optical property of having high refractive index value comparing to that of the resin phase of the composite and thus allowing the composite to appear more translucent (Bowen & Cleek, 1972), Soderholm (1985) mentioned that today barium glass is most preferred for the filler in dental composites because of the softness, facilitating finer filler production and of the radio-opacity, facilitating detection of caries or underlying decalcified dentine. Out of seven VL-cured composites examined, however, only three (Occlusin, Estilux and Brilliant Lux) contained barium glass fillers. The fillers of two barium-containing composites (CR-inlay and Clearfil Photo Posterior) were not glass, but quartz. Two composites (Silux and P-50) did not contain BaO as well as other strong radio-opaque agents, e.g. SrO, and hence were expected to
Inorganic fillers in VL-cured composites
367
(b)
*:Crystal1 i ne ZrO^
*
J 1
1
50
40' 30 20 20 (degree)
#:Crystannne Li Al Si., 0, X
50
X
40
40
10
50
40
1 30
20 20 .(degree)
10
50
40
30 20 20 (degree)
10
(d)
3-x 5
30 20 20 (degree)
30 20 20 (degree)
10
50
40
30 20 20 (degree)
50
40
30 20 29 (degree)
10
Fig. 3. X R D charts of the inorganic tillers extracted from seven VL-curcd composites, (a) Silux; (b) P - 5 0 ; (c) Occlusin; (d) Estilux; (e) Brilliant Lux; (f) CR-inlay; (g) Clearfil Photo Posterior.
lack X-ray opacity. However, P—50 due to the presence of ZrO2 in the filler composition, may possess limited radio-opacity. According to the study by Watts (1987), the magnitude of the radio-opacity of the highly filler loaded composite could exceed that of human enamel when the filler contained more than 20wt% BaO. From this criteria, it can be suggested that only two composites (Occlusin and Brilliant Lux) have radio-opacity values in excess of that of enamel. Lutz et al. (1984) suggested that
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A.M. Khan et al.
0 -10 -20 -30 -40 -50
TG
(a)
- DTA
0 -10 -20 -30 40 -50
/-\-
1
1
1
200
400
600
TG _^^ 0 -10 -20 - DTA 30 40 -50
TG
(e) -^
nTA -
•
-
,
.
_
_
,
800
.
-^^ .
'
"
—
'i
'
200
400
600
800
TG 0 „ ,/ '•, (f) .-^ -10 - DTA -20 1 > ,--^ -30 -40 -50
(b)
o E
o
E 0)
2
0
00 1
1
1
200
400
600
800
cu
a>
1 h-
1
1
200
400
600
TG
.
-
-
•
800 (q)
DTA ^ P -in — , ' _ ^ -20 ,' '^_ , - - ' -30 — -40 -50 .
800
1
'
200
400
600
800
Temperature (°C)
200
400
600
800
Temperature (°C)
Fig. 4. DTG (DTA and TG) profiles of seven VL-curcd composite pastes, (a) Silux; (b) P-50; (e) Occlusin; (d) Estilux; (c) Brilliant Lux; (f) CR-inlay; (g) Clearfil Photo Posterior.
the composites which are designed to restore posterior teeth should be more radioopaque than enamel. When mounted in the resin phase, the filler is difficult to observe. Furthermore, in this condition, polishing techniques significantly alter the surface appearance of the composite (Lambrechts & Vanherle, 1982; Northeast & van Noort, 1988). Thus, we extracted the filler from the composite, using a solvent and, by SEM, succeeded in obtaining a clear and vivid image of the filler. The particle size distribution of the filler seems to have a special relationship to the mechanical property of the composite. The increase in filler loading results in increased mechanical strength of the composite (Germain et al., 1985; Li et al... 1985). Because the fillers were most densely packed
Inorganic fillers in VL-cured composites
369
Table 5. The inorganic filler contents in seven VL-eured composites, determined at 575°C of the TG curves and expressed as mean values with standard deviations of three measurements Material Silux P-50 Occlusin Estilux BriUiant Lux CR-inlay Clearfil Photo Posterior
Inorganic filler content (wt%) 60-6 ±2-15 88-2 ±0-25 86-4 ± 0-48 85-6 ±0-25 77-1 ±0-88 87-1 ±0-15 88-0 ± 0-35
in the composites containing the hybrid type fillers, they (P-50, Occlusin, Estilux, CR-inlay and Clearfil Photo Posterior) might be utilized in the posterior segment of the mouth which is susceptible to wear (Leinfelder, 1988). The lower filler loaded composites (Silux and Brilliant Lux), however, could function satisfactorily in the anterior segment of the mouth which does not bear a similar load. EDX analysis was conducted on the relatively large spot containing more than dozens of the filler particles. Thus, we did not measure the composition of each filler particle, but identified that of the aggregate of the filler particles. It can be, however, speculated from EDX and XRD analyses that fillers of Silux, Occlusin and Brilliant Lux consist of single glass phases, those of CR-inlay and Clearfil Photo Posterior are made up of single quartz phases while those of P-50 and Estilux have more than two filler phases of different compositions. P-50 seems to contain the hybrid type SiO2 glass and minute crystalline ZrO2 fillers whereas Estilux appears to involve LixAlxSi3_xO6 glass-ceramic and SiO2-Al2O3-BaO glass fillers. The light element, Li could not be identified by EDX. Referring to the chemical stability of the filler in the oral environment, the filler containing the impurity seems to degrade more, compared with that containing no impurity. The glass filler may also disintegrate more extensively than the ceramic (i.e. crystalline) filler. The more the BaO content, the less the resistance of the filler to chemical degradation because the parent aluminosilicate network is disrupted by the relatively large barium ion (Soderholm et al.., 1984). There seems to be a correlation between particle size of the filler and filler content in the composite. The smaller the filler particle, the lower the filler content, as in the case of Brilliant Lux in contrast to those of the composites containing the hybrid type fillers. DTG (DTA/TG) thermal analyses provided valuable information on the composites which remain to be studied. At elevated temperatures of more than 575°C, some constituents of the filler and the silane coupling layer may evaporate or thermally decompose, resulting in further decrease in the weight. In the near future, development of new fillers for VL-cured dental composites is expected. Research is planned to impart functionality, such as adjustable refractive index and radio-opacity to the silica-based glass filler. An international standard to regulate the properties of the fillers in VL-cured composites is also needed. Acknowledgments
The authors express deep appreciation to JEOL Co., Tokyo, Japan for the use of
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SEM/EDX at their application laboratory in Osaka, Japan and to the manufacturers of seven VL-cured composites for providing their products. References BowFN, R.L. & Ci.iiEK, G.W. (1972) A new scries of x-ray-opaque reinforcing fillers for composite materials. .Journal of Dental Research. 51, 177. BowtN, R.L. & RHKD, L . E . (1976) Semiporous reinforcing tillers for eomposite resins: i. preparation of provisional glass formulations. Journal of Dental Research. 55, 738. CRAIG, R . G . (1985) Direct esthetic restorative materials. In: Restorative Dental Materials (ed R.G. Craig), p. 225. CV Mosby Co., St. Louis, U.S.A. GKRMAIN, H . S T . , SWARTZ, M.L., PHILLIPS, R.W., MOOKH, B . K , & ROBERTS, T . A . (1985) Properties of mierofilled eomposite resins as influenced by filler content. .Journal of Dental Research. 64, 155. HosoDA, H., YAMADA, T . , OiSLiKi, M., HosoKAWA, A. & TAKAISUKA, T . (1987) Classitieation and elemental composition of fillers on composite resin, part 2. elassifieation of light cured anterior and a/p eomposite resins (in .lapanese). .Japanese Journal of Conservative Dentistry. 30, 427. I.S.O. (1978) Resin-based dental filling materials, ISO 4049. International Organization for Standardization, Geneva, Switzerland. JCPDS (1971) Hanawalt (d-value) listings. In: Inori^anic Jnde.x to the J^owder Diffraction File (ed L.G. Berry), p. 1. Joint Committee on Powder Diffraction Standards, Pennsylvania, U.S.A. LAMBRBCHIS, P. & VANHHRLF, G . (1982) Observation and eomparison of polished composite surfaees with the aid of SEM and profilometer. Journal of Oral Rehabilitation. 9. 169. LhL-JFELDLR, K.F.I SLUDLR, T.B.; SANTOS, J . F . & WALL, J . T . (1980) Five-year clinical evaluation of anterior and posterior restorations of eomposite resin. Operative Dentistrw 5, 57. LniNtTiLDLR, K.F. (1987) Wear patterns and rates of posterior eomposite resins. International Dental Journal. 37, 152. LhiNH-LDHR, K.F. (1988) Current developments in posterior composite resins. Advances in Dental Research, 2. 115. Li, Y.. SWARTZ, M.L., PHILLIPS, R.W., MOORL, B.K. & ROBKRTS. T.A. (1985) Effeet of tiller eontent and size on properties of eomposites. Journal of Dental Research. 64. 1396. LuTZ, F. & PHMin'S, R.W. (1983) A elassifieation and evaluation of composite resin. Journal of J'rosthetic Dentistry. 50, 480. Lurz, F., PHILLIPS, R.W., ROULET, J.F. & SEICOS. J . C . (1984) In vivo and in vitro wear of potential posterior eomposites. Journal of Dental Research. 63, 914. NORTHEAST, S.E. & VAN NooRr, R. (1988) Surfaee eharaeteristies of finished posterior composite resins. Dental Materials. 4, 278. 0YSAED, H. & RuYTER, LE. (1986) Water sorption and tiller eharaeteristies of composites for use in posterior teeth. Journal of Dental Research. 65, 1315. SODERHOLM, K.-J. (1983) Leaking of tillers in dental eomposites. Journal of Dental Research. 62, 126. SODERHOLM, K . - J . , ZIC.AN, M . , RAC.AN, M . , Fisc HLSCHWEIGER, W . & BERGMAN, M . (1984) Hydrolytic degradation of dental eomposites. Journal of Dental Research. 62, 1248. SODERHOLM, K.-J. (1985) Filler systems and resin interface. In: Posterior Composite Resin Dental Restorative Materials (eds G. Vanlierle & D.C. Smith) p. 139. Peter Szule Publishing Co., The Netherlands. WAITS, D.C. (1987) Radiopaeity vs. composition of some barium and strontium glass eomposites. Journal of Dentistry. 15, 38. Wit-SON, N.H.F.. WILSON, M . A . & SMITH, G . A . (1988) A elinieal trial of a visible light eured posterior composite resin restorative material: four-year results. Quintessence International. 19, 133.
