Journal of Oral Rehabilitation, 1990, Volume 17, pages 79-87
Finishing composite restorative materials F. WILSON, J. R. HEATH and D. C. WATTS Department of Restorative Dentistry, University of Manchester, Manchester, U.K.
Summary
A clinically realistic in vitro study was performed to determine the best method for smoothing trimmed surfaces of seven composite restorative materials. Soflex discs produced the smoothest surface, and little advantage appeared to be gained by prior smoothing of the surface with stones or points. A polishing paste, even when used with intermediate finishing agents, produced a rougher surface than that left by the discs. Introduction
Composite resin is the material of choice for plastic anterior restorations. There are over thirty different composite materials on the U.K. market and sixty available worldwide, varying widely in formulation, and each claiming an advantage over the others. This suggests that the ideal material has yet to be found. A major requirement for a successful restoration is the ability to take and maintain a smooth exposed surface. This contributes to patient comfort (scratches as small as 20 /iva in width can be detected (Van Noort, 1983)), enhances appearance (a glossy surface is only seen when the distance between scratches is less than the wavelength of visible light, approximately 0-5/^m), restricts the rate of plaque accumulation and reduces surface discoloration. The smoothest surface has been universally found to be that produced when the composite sets in contact with a matrix strip which is itself as smooth as possible. However, following placement of the restoration, removal of excess material situated outside the cavity margins, interfering with occlusal contacts or detracting from the ideal contour of the restoration may be necessary. Removal of the resin-rich superficial layer in order to expose the harder subsurface has also been recommended (Wilson, Davies & Von Fraunhofer, 1980). The smoothness of a composite restoration depends, inter alia, upon the components within the material, the curing system employed and the trimming instrument used. Components of composites Composites may be defined as three-dimensional combinations of at least two chemically different materials with a distinct interface (Lutz & Phillips, 1983). They contain three phases: organic (matrix); interfacial (coupling agent); and dispersed (fillers). The degree of polymerization of the organic matrix is crucial to the clinical orrespondence: Dr J. R. Heath, Department of Restorative Dentistry, Turner Dental School, Higher ambridge Street, Manchester M15 6FH, U.K.
79
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performance of any resin system, and is affected by the mode of curing and the type of resin. The highest degree of polymerization is achieved with a heat cure, and the least with a chemical cure. Light curing produces an intermediate degree of polymerization. Insufficient curing results in a soft surface which loses its translucency and becomes opaque (Bassiouny & Grant, 1978). Interfacial coupling agents are bipolar molecules, mainly organosilanes, that are liable to chemical disintegration following water absorption. Filler particles are then readily lost from the surface of the restoration, with a consequent increase in surface roughness. There are three categories of dispersed phase filler particles, based on the manufacturing technique, average particle size and chemical composition. The first category comprises macrofillers, made from quartz, glass, borosilicate or ceramic. The particles are thus purely inorganic, and are usually splinter-shaped, since they are mechanically prepared from larger pieces by grinding or crushing. Average particle size is within the range of 0-1-100 ^m. Smaller, softer and more rounded macrofillers are now being used in some products; average particle size is in the range of 1-5 pim. The second category of the dispersed phase consists of the microfillers, made from pyrogenic silica in the form of very fine glass spheres; average particle size is in the range of 0-05-0-1 jum. Insufficient of this fine filler can be mixed with the matrix monomer before the viscosity becomes unworkable. To overcome this problem, the third category of the dispersed phase was developed, namely microfiller based complexes. In these the individual microfiller particles are artificially aggregated or incorporated into spheres or splinters of polymerized resin matrix. The average particle size of the dispersed phase that is mixed with the matrix monomer is thus in the inereased range of 1-200 jum. Traditional composites contain only macrofillers within the organic resin matrix. Trimmed surfaces are not smooth; the filler size is larger than the wavelength of visible light, giving a dull, matt appearance. The more modern macrofillers are softer; trimmed surfaces are thus initially smoother but become rough following hydrolysis of the coupling agent and wear of the resin matrix, as both processes produce protrusion and plucking out of the filler particles. Prismafil is an example of this type of system. In a hybrid composite resin the organic matrix is reinforced with microfillers in order to reduce the difference in properties between the macrofillers and the unfilled matrix. Acceptable smoothness of trimmed surfaces can be achieved, but it is shortlived owing to the wear pattern inherent in a system containing macrofillers. Examples of such a system are Concise, Miradapt and Command Ultrafine. Visio Dispers differs from these materials, as it contains pre-polymerized microfine filled resin chips as the macrofiller particles. Curing system The mixing of a two-paste, chemically cured composite resin includes air, which produces porosity (both at the surface and throughout the material), partial inhibition of polymerization, and a weakening of the material. The viscosity of the two components starts to increase as soon as mixing begins; it is therefore possible thai optimal contouring of the restoration and / or placement of the matrix strip would not be achieved before the material hardens, necessitating recontouring by rotary instru-
Finishing composite restorative materials
81
ments with a high cutting rate which would result in a rough surface. For optimal initial surface smoothness, the matrix strip must be applied before the viscosity of the resin component has increased appreciably, since it is necessary for the resin to flow round the filler particles as they are depressed into the material by the strip. To avoid disruption of this surface, the strip must not be removed until polymerization is almost complete. In contrast, light-cured composites do not require mixing, and have an almost infinite working time, although the operating light can initiate setting. Polymerization also begins at the surface of the restoration, thus producing a smooth, hard surface in contact with the matrix strip. Trimming instruments Cavity-cutting burs, which may be used for gross reduction of a restoration, leave a very rough surface which must then be smoothed (Heath & Wilson, 1976). This is conventionally performed with the aid of aluminium oxide-coated polishing discs, available in a range of grit sizes. However, the discs can only be used on readily accessible convex surfaces; interdental and concave surfaces require the use of small rotary instruments, various kits of which are commercially available. Loose abrasive polishing pastes roughened the surface of early composites by removing the soft resin from around the large, hard filler particles (Heath & Wilson, 1976). Recent research (Van Noort & Davis, 1984) has shown that metallurgical grade polishing pastes used on small filler-sized composite resins produce smoother surfaces than those left by the aluminium oxide-coated discs. An additional advantage of the pastes was that they prevented thermal disruption of the surface of some composite materials that had been previously noted when using the discs. The smoothness of a trimmed composite surface thus depends on the composition of the material, the curing method used and the finishing instruments employed. This investigation was undertaken to determine the optimum finishing procedures for a range of modern composites.
Table 1. Composite materials
Code
Product
Filler
CON
Concise
Hybrid
MIR
Miradapt
Hybrid
PRI
Prismafil
Barium glass
VIS Exp.A
Visio Dispers Experimental (AC 3825B) Experimental (B0058/49) Command Ultrafine
Microfine Hybrid
oxp.T -om.U
Hybrid Hybrid
Average particle size (um) 10
Cure Chemical
Manufacturer
3M Dental Products, St Paul, MN, U.S.A. 10 Chemical Johnson & Johnson, East Windsor, NJ, U.S.A. 5 Visible light LD Caulk, Co., Milford, DE, U.S.A. 3 Visible light Espe GmbH, Seefeld, F.R.G. 8 Visible light ICI Dental, Maeclesfield, U.K. 8 Visible light ICI Dental, Maeclesfield, U.K. 3 Visible light Kerr Romulus, MI, U.S.A.
82
F. Wilson
e^al. ^^^^^^^^ ^^^^ ^^^-^'^^^^^ -
'
Materials and methods Th^ composite materials investigated are listed in Table 1. Concise, Miradapt and Command Ultrafine contain macro- and microfillers, Prismafil contains a soft macrofiller, while Visio Dispers contains microfilled complexes. The experimental materials were both light-activated anterior composites with hybrid radiopaque glass fillers. One Perspex rod, 25 mm in diameter, was prepared for each composite material. Thirty-three wells, 5 mm in diameter and 2 mm deep, were drilled in the rod in three rows of eleven. This allowed three samples of each of eleven finishes to be examined. The composite materials were placed sequentially in each well and covered with a cellulose acetate matrix strip wrapped tightly round the rod. The light-cured materials were exposed to light from a Luxor polymerization unit* for 60 s. Care was taken when mixing the chemically cured materials to trap as little air as possible. The samples were stored in water at 37°C for 1 week prior to trimming, smoothing and polishing. The materials utilized for finishing are listed in Table 2. For each composite a set of three samples of the surface left by the matrix strip was left untouched. The surface of each of the other samples was next trimmed with the tungsten carbide bur under a water spray to remove any excess material; this surface was preserved on the next three samples. The remaining 24 samples of each composite were variously treated with the otherfinishingmaterials as shown in Fig. 1 and Table 3. With the exception of the polishing paste, treatment was under dry conditions. The three grades of Soflex disc were used sequentially. The surfaces of the samples were assessed qualitatively and quantitatively by visual inspection and probing of the dried surfaces to determine their clinical acceptability and a measurement of roughness (RJ using a surface-profiling instrument, Talysurf lOf. The 'Rg' value is the arithmetical mean value of the movement of the profile above and below the centre line of the surface. Results and discussion The Ra values for the eleven surfaces investigated are listed in Table 4, and are shown graphically in Figs. 2a and b and Figs. 3a and b. The surfaces cured in contact with the matrix strip appeared to be the smoothest. Table 2. Materials utilized in finishing Product
Manufacturer
'Kemdent' cellulose acetate matrix strip Tapered fissure plain cavity cutting tungsten carbide bur 'Alpine' white finishing point Shofu finishing points Soflex discs (3 grit sizes, used sequentially) Polishing paste Hyprex 0-1 ^m
Associated Dental Products, Swindon, U.K. Jota AG, Switzerland. Amalgamated Dental, London, U.K. Shofu GmbH, Ratingen, F.R.G. 3M Company, St Paul, Minnesota, U. S. A. Engis Ltd, Maidstone, Kent, U.K.
*ICI Dental, Maeclesfield, Cheshire, U.K. tRank Taylor Hobson, Leicester, U.K.
Finishing composite restorative materials
83
Matrix Surface
Tungsten carbide bur
White finishing point
7 Shofu finishing points
8
9
iO
6
Poiishing paste
Soflex discs
Fig. 1. Flow diagram of use of finishing materials on composite samples. The numbers refer to the surface finishes discussed.
except in the case of Concise and Miradapt, which showed white and chalky patches. These may have been due to incomplete mixing of the components, resulting in removal of the matrix strip before portions of the material had set. The R^ values generally confirm these observations, but Visio Dispers, in common with Concise and Miradapt, developed smoother surfaces following treatment with Soflex discs. Following trimming, the smoothest visual results and lowest roughness values were produced by the Soflex discs, particularly in the case of surfaces 8 and 10; the Table 3. Sequence of use of finishing materials Finishing material Matrix strip
Tungsten carbide bur
White finishing stone
Shofu finishing points
4-
+
Soflex discs
Pohshing paste
Key to surface finish 1 2 3 4 5 6 7 8 9 10 11
84
F. Wilson et al.
Table 4. Mean Ra values (yxm) of the eleven finished surfaces on the seven composite materials. The standard errors of the means are shown in parentheses Surface finish
1 % 3 4 5 6 7
8 9 10 11
Composite material CON
MIR
PRI
VIS
Exp Ac
Exp (T)
Com (U)
0-220 (0-020) 1-310 (0-175) 0-978 (0-326) 0-983 (0-066) 0-281 (0-022) 1-683 (0-094) 1-233 (0-130) 0-166 (0-024) 1-244 (0-071) 0-178 (0-025) 1-128 (0-062)
1-230 (0-100) 1-250 (0-070) 0-837 (0-050) 0-646 (0-035) 0-352 (0-058) 1-156 (0-058) 0-952 (0-080) 0-300 (0-023) 1-144 (0-053) 0-262 (0-021) 0-820 (0-037)
0-058 (0-007) 0-664 (0-062) 0-471 (0-019) 0-384 (0-026) 0-082 (0-008) 0-428 (0-027) 0-336 (0-029) 0-101 (0-011) 0-380 (0-046) 0-093 (0-007) 0-268 (0-025)
0-182 (0-020) 0-542 (0-072) 0-438 (0-034) 0-326 (0-012) 0-101 (0-006) 0-461 (0-051) 0-183 (0-017) 0-108 (0-010) 0-306 (0-025) 0-118 (0-011) 0-364 (0-032)
0-109 (0-010) 0-970 (0-066) 0-662 (0-045) 0-734 (0-035) 0-170 (0-057) 0-858 (0-047) 0-658 (0-039) 0-246 (0-022) 0-879 (0-058) 0-251 (0-014) 0-649 (0-055)
0-177 (0-024) 1-233 (0-130) 0-761 (0-037) 0-634 (0-035) 0-218 (0-016) 0-704 (0-039) 0-686 (0-032) 0-231 (0-011) 0-870 (0-085) 0-229 (0-013) 0-744 (0-041)
0-072 (0-005) 0-408 (0-039) 0-648 (0-064) 0-387 (0-035) 0-099 (0-015) 0-500 (0-086) 0-394 (0-052) 0-117 (0-009) 0-452 (0-054) 0-124 (0-013) 0-231 (0-016)
(b) 1.5
I o
cc 0.5
i 0
CON
MiR
i
PRI
m VIS
Fig. 2a and b. Mean R^, values for the finished surfaces on the first four composite samples. The numbers refer to the surface finishing procedure involved.
Finishing composite restorative materials
(b) 1.5
IT
0.5
Exp.A
Exp. T
Com. U
10
Fig. 3a and b. Mean R^ values for the finished surfaces on the last three composite samples. The numbers refer to the surface finishing procedure used.
overall contour was also smooth and rounded. For most of the composite mater:'als there was little difference in R^ value between any of the three routes to the disced finish, suggesting that little advantage is gained by utilizing the intermediate stages between tungsten carbide bur and Soflex discs. Using the intermediate stages with Concise and Miradapt, however, produced smoother disced surfaces. The lustre produced by the disced surfaces was shiny with Visio Dispers, Command Ultrafine and Prismafil, while the surfaces on Concise, Miradapt and Exp.T were dull in appearance. The visual effect of using tungsten carbide burs, white stone and Shofu points was to produce a rough, matt surface on all the composite materials. Mid-range roughness values were produced by the tungsten carbide bur, followed by either white stones or Shofu points (surfaces 3 and 4, respectively). The points produced a slightly smoother surface than the stones except in the case of Exp.A, where the reverse relationship was observed. When the white stone was followed by Shofu points (surface 7), there was an increase in roughness with Concise and Miradapt; Prismafil, the experimental materials and Command Ultrafine showed little change in R^ values, while Visio Dispers became smoother, but did not reach the R^ value of the
85
86
F.
disced surface. On most composite materials, therefore, Shofu points do not produce a smooth surface finish. Using the polishing pastes on the surfaces produced by the tungsten carbide bur did not greatly reduce the R^ values, except in the case of Exp.T. Indeed, the pastes roughened the surface of Concise, the material with the largest filler particle size. The use of the intermediate finishing agents prior to the use of pastes lowered the R^ values, particularly when the stones and points were used sequentially, rather than stones alone. However, the surface roughness and contour never became as smooth and even as 'was observed following the use of the discs. Prismafil, despite its relatively large filler particle size, was rendered reasonably smooth by the polishing pastes. This was due to the soft nature of the filler, which peimitted its abrasion by the pastes. With this exception, the larger the filler particle size, the rougher the resultant surface following the use of the pohshing pastes. Composite materials with large filler particles therefore require the use of discs in order to achieve the smoothest trimmed surfaces. Thus the pastes did not produce as smooth a surface as the Soflex discs on any material, so this study does not support the findings of Van Noort & Davis (1984), who observed that the use of metallurgical grade alumina polishing paste produced a smoother surface than the use of discs on small filler-sized composite materials. This anomaly may possibly be explained by the initial flattening of the composite materials on grade 600 carborundum paper in the study of Van Noort & Davis, whereas in this investigation a more chnically realistic procedure was employed, namely the removal of excess material with a tungsten carbide bur followed by various smoothing procedures. Conclusion In this clinically realistic study, the light-cured composite materials developed the smoothest surfaces in contact with the matrix strip. The tungsten carbide burs were fast and efficient at trimming excess material, but the resultant surface required further finishing. The Soflex discs produced the smoothest trimmed surface, and there appeared to be little advantage in using intermediate finishing procedures between the bur and the discs. The white finishing stone and Shofu points produced surfaces with mid-range roughness values. The polishing paste did not produce as smooth a surface as the discs. It is therefore recommended that, whenever possible, trimmed composite surfaces should be smoothed with the Soflex discs. There is still a need for a small rotary irstrument that will produce an equivalent finish on concave surfaces. Acknowledgments The authors thank Mr A. Cash for production of the specimen rods. Professor A.A. Crant for advice and encouragement. Miss A. Winstanley for the illustrations and Mrs J. Lear for typing the manuscript. References BA.SSIOUNY, M.A. & GRANT, A.A. (1978) A visible light-cured composite restorative—clinical open assessment. British Dental Jotirnal, 145, 327. HEATH, J.R. & WILSON, H.J. (1976) Surface roughness of restorations. British Dental Journal, 140,131. LUTZ, F . & PHILLIPS, R.W. (1983) A classification and evaluation of composite resin systems. Journal of Prosthetic Dentistry, 50, 480.
Finishing composite restorative materials
87
(1983) Controversial aspects of composite resin restorative materials. British Dental Journal, 155, 380. VAN NOORT, R . & DAVIS, L . G . (1984) The surface finish of eomposite resin restorative materials. British Dental Journal, 157, 360. WILSON, G.S., DAVIES, E.H. & VON FRAUNHOFER, J.A. (1980) Micro-hardness characteristics of anterior restorative materiah. British Dental Journal, 14,%., 31. VAN NOORT, R .
Manuscript accepted 21 November 1988
Finishing composite restorative materials F. WILSON, J. R. HEATH and D. C. WATTS Department of Restorative Dentistry, University of Manchester, Manchester, U.K.
Summary
A clinically realistic in vitro study was performed to determine the best method for smoothing trimmed surfaces of seven composite restorative materials. Soflex discs produced the smoothest surface, and little advantage appeared to be gained by prior smoothing of the surface with stones or points. A polishing paste, even when used with intermediate finishing agents, produced a rougher surface than that left by the discs. Introduction
Composite resin is the material of choice for plastic anterior restorations. There are over thirty different composite materials on the U.K. market and sixty available worldwide, varying widely in formulation, and each claiming an advantage over the others. This suggests that the ideal material has yet to be found. A major requirement for a successful restoration is the ability to take and maintain a smooth exposed surface. This contributes to patient comfort (scratches as small as 20 /iva in width can be detected (Van Noort, 1983)), enhances appearance (a glossy surface is only seen when the distance between scratches is less than the wavelength of visible light, approximately 0-5/^m), restricts the rate of plaque accumulation and reduces surface discoloration. The smoothest surface has been universally found to be that produced when the composite sets in contact with a matrix strip which is itself as smooth as possible. However, following placement of the restoration, removal of excess material situated outside the cavity margins, interfering with occlusal contacts or detracting from the ideal contour of the restoration may be necessary. Removal of the resin-rich superficial layer in order to expose the harder subsurface has also been recommended (Wilson, Davies & Von Fraunhofer, 1980). The smoothness of a composite restoration depends, inter alia, upon the components within the material, the curing system employed and the trimming instrument used. Components of composites Composites may be defined as three-dimensional combinations of at least two chemically different materials with a distinct interface (Lutz & Phillips, 1983). They contain three phases: organic (matrix); interfacial (coupling agent); and dispersed (fillers). The degree of polymerization of the organic matrix is crucial to the clinical orrespondence: Dr J. R. Heath, Department of Restorative Dentistry, Turner Dental School, Higher ambridge Street, Manchester M15 6FH, U.K.
79
M": ••
F.Wilson •
e t a l
• ;
• ''•.;-^--:;:^^ •
•••'.--'—••--:^---^-;-^:^^>^---^^^ fc
•
performance of any resin system, and is affected by the mode of curing and the type of resin. The highest degree of polymerization is achieved with a heat cure, and the least with a chemical cure. Light curing produces an intermediate degree of polymerization. Insufficient curing results in a soft surface which loses its translucency and becomes opaque (Bassiouny & Grant, 1978). Interfacial coupling agents are bipolar molecules, mainly organosilanes, that are liable to chemical disintegration following water absorption. Filler particles are then readily lost from the surface of the restoration, with a consequent increase in surface roughness. There are three categories of dispersed phase filler particles, based on the manufacturing technique, average particle size and chemical composition. The first category comprises macrofillers, made from quartz, glass, borosilicate or ceramic. The particles are thus purely inorganic, and are usually splinter-shaped, since they are mechanically prepared from larger pieces by grinding or crushing. Average particle size is within the range of 0-1-100 ^m. Smaller, softer and more rounded macrofillers are now being used in some products; average particle size is in the range of 1-5 pim. The second category of the dispersed phase consists of the microfillers, made from pyrogenic silica in the form of very fine glass spheres; average particle size is in the range of 0-05-0-1 jum. Insufficient of this fine filler can be mixed with the matrix monomer before the viscosity becomes unworkable. To overcome this problem, the third category of the dispersed phase was developed, namely microfiller based complexes. In these the individual microfiller particles are artificially aggregated or incorporated into spheres or splinters of polymerized resin matrix. The average particle size of the dispersed phase that is mixed with the matrix monomer is thus in the inereased range of 1-200 jum. Traditional composites contain only macrofillers within the organic resin matrix. Trimmed surfaces are not smooth; the filler size is larger than the wavelength of visible light, giving a dull, matt appearance. The more modern macrofillers are softer; trimmed surfaces are thus initially smoother but become rough following hydrolysis of the coupling agent and wear of the resin matrix, as both processes produce protrusion and plucking out of the filler particles. Prismafil is an example of this type of system. In a hybrid composite resin the organic matrix is reinforced with microfillers in order to reduce the difference in properties between the macrofillers and the unfilled matrix. Acceptable smoothness of trimmed surfaces can be achieved, but it is shortlived owing to the wear pattern inherent in a system containing macrofillers. Examples of such a system are Concise, Miradapt and Command Ultrafine. Visio Dispers differs from these materials, as it contains pre-polymerized microfine filled resin chips as the macrofiller particles. Curing system The mixing of a two-paste, chemically cured composite resin includes air, which produces porosity (both at the surface and throughout the material), partial inhibition of polymerization, and a weakening of the material. The viscosity of the two components starts to increase as soon as mixing begins; it is therefore possible thai optimal contouring of the restoration and / or placement of the matrix strip would not be achieved before the material hardens, necessitating recontouring by rotary instru-
Finishing composite restorative materials
81
ments with a high cutting rate which would result in a rough surface. For optimal initial surface smoothness, the matrix strip must be applied before the viscosity of the resin component has increased appreciably, since it is necessary for the resin to flow round the filler particles as they are depressed into the material by the strip. To avoid disruption of this surface, the strip must not be removed until polymerization is almost complete. In contrast, light-cured composites do not require mixing, and have an almost infinite working time, although the operating light can initiate setting. Polymerization also begins at the surface of the restoration, thus producing a smooth, hard surface in contact with the matrix strip. Trimming instruments Cavity-cutting burs, which may be used for gross reduction of a restoration, leave a very rough surface which must then be smoothed (Heath & Wilson, 1976). This is conventionally performed with the aid of aluminium oxide-coated polishing discs, available in a range of grit sizes. However, the discs can only be used on readily accessible convex surfaces; interdental and concave surfaces require the use of small rotary instruments, various kits of which are commercially available. Loose abrasive polishing pastes roughened the surface of early composites by removing the soft resin from around the large, hard filler particles (Heath & Wilson, 1976). Recent research (Van Noort & Davis, 1984) has shown that metallurgical grade polishing pastes used on small filler-sized composite resins produce smoother surfaces than those left by the aluminium oxide-coated discs. An additional advantage of the pastes was that they prevented thermal disruption of the surface of some composite materials that had been previously noted when using the discs. The smoothness of a trimmed composite surface thus depends on the composition of the material, the curing method used and the finishing instruments employed. This investigation was undertaken to determine the optimum finishing procedures for a range of modern composites.
Table 1. Composite materials
Code
Product
Filler
CON
Concise
Hybrid
MIR
Miradapt
Hybrid
PRI
Prismafil
Barium glass
VIS Exp.A
Visio Dispers Experimental (AC 3825B) Experimental (B0058/49) Command Ultrafine
Microfine Hybrid
oxp.T -om.U
Hybrid Hybrid
Average particle size (um) 10
Cure Chemical
Manufacturer
3M Dental Products, St Paul, MN, U.S.A. 10 Chemical Johnson & Johnson, East Windsor, NJ, U.S.A. 5 Visible light LD Caulk, Co., Milford, DE, U.S.A. 3 Visible light Espe GmbH, Seefeld, F.R.G. 8 Visible light ICI Dental, Maeclesfield, U.K. 8 Visible light ICI Dental, Maeclesfield, U.K. 3 Visible light Kerr Romulus, MI, U.S.A.
82
F. Wilson
e^al. ^^^^^^^^ ^^^^ ^^^-^'^^^^^ -
'
Materials and methods Th^ composite materials investigated are listed in Table 1. Concise, Miradapt and Command Ultrafine contain macro- and microfillers, Prismafil contains a soft macrofiller, while Visio Dispers contains microfilled complexes. The experimental materials were both light-activated anterior composites with hybrid radiopaque glass fillers. One Perspex rod, 25 mm in diameter, was prepared for each composite material. Thirty-three wells, 5 mm in diameter and 2 mm deep, were drilled in the rod in three rows of eleven. This allowed three samples of each of eleven finishes to be examined. The composite materials were placed sequentially in each well and covered with a cellulose acetate matrix strip wrapped tightly round the rod. The light-cured materials were exposed to light from a Luxor polymerization unit* for 60 s. Care was taken when mixing the chemically cured materials to trap as little air as possible. The samples were stored in water at 37°C for 1 week prior to trimming, smoothing and polishing. The materials utilized for finishing are listed in Table 2. For each composite a set of three samples of the surface left by the matrix strip was left untouched. The surface of each of the other samples was next trimmed with the tungsten carbide bur under a water spray to remove any excess material; this surface was preserved on the next three samples. The remaining 24 samples of each composite were variously treated with the otherfinishingmaterials as shown in Fig. 1 and Table 3. With the exception of the polishing paste, treatment was under dry conditions. The three grades of Soflex disc were used sequentially. The surfaces of the samples were assessed qualitatively and quantitatively by visual inspection and probing of the dried surfaces to determine their clinical acceptability and a measurement of roughness (RJ using a surface-profiling instrument, Talysurf lOf. The 'Rg' value is the arithmetical mean value of the movement of the profile above and below the centre line of the surface. Results and discussion The Ra values for the eleven surfaces investigated are listed in Table 4, and are shown graphically in Figs. 2a and b and Figs. 3a and b. The surfaces cured in contact with the matrix strip appeared to be the smoothest. Table 2. Materials utilized in finishing Product
Manufacturer
'Kemdent' cellulose acetate matrix strip Tapered fissure plain cavity cutting tungsten carbide bur 'Alpine' white finishing point Shofu finishing points Soflex discs (3 grit sizes, used sequentially) Polishing paste Hyprex 0-1 ^m
Associated Dental Products, Swindon, U.K. Jota AG, Switzerland. Amalgamated Dental, London, U.K. Shofu GmbH, Ratingen, F.R.G. 3M Company, St Paul, Minnesota, U. S. A. Engis Ltd, Maidstone, Kent, U.K.
*ICI Dental, Maeclesfield, Cheshire, U.K. tRank Taylor Hobson, Leicester, U.K.
Finishing composite restorative materials
83
Matrix Surface
Tungsten carbide bur
White finishing point
7 Shofu finishing points
8
9
iO
6
Poiishing paste
Soflex discs
Fig. 1. Flow diagram of use of finishing materials on composite samples. The numbers refer to the surface finishes discussed.
except in the case of Concise and Miradapt, which showed white and chalky patches. These may have been due to incomplete mixing of the components, resulting in removal of the matrix strip before portions of the material had set. The R^ values generally confirm these observations, but Visio Dispers, in common with Concise and Miradapt, developed smoother surfaces following treatment with Soflex discs. Following trimming, the smoothest visual results and lowest roughness values were produced by the Soflex discs, particularly in the case of surfaces 8 and 10; the Table 3. Sequence of use of finishing materials Finishing material Matrix strip
Tungsten carbide bur
White finishing stone
Shofu finishing points
4-
+
Soflex discs
Pohshing paste
Key to surface finish 1 2 3 4 5 6 7 8 9 10 11
84
F. Wilson et al.
Table 4. Mean Ra values (yxm) of the eleven finished surfaces on the seven composite materials. The standard errors of the means are shown in parentheses Surface finish
1 % 3 4 5 6 7
8 9 10 11
Composite material CON
MIR
PRI
VIS
Exp Ac
Exp (T)
Com (U)
0-220 (0-020) 1-310 (0-175) 0-978 (0-326) 0-983 (0-066) 0-281 (0-022) 1-683 (0-094) 1-233 (0-130) 0-166 (0-024) 1-244 (0-071) 0-178 (0-025) 1-128 (0-062)
1-230 (0-100) 1-250 (0-070) 0-837 (0-050) 0-646 (0-035) 0-352 (0-058) 1-156 (0-058) 0-952 (0-080) 0-300 (0-023) 1-144 (0-053) 0-262 (0-021) 0-820 (0-037)
0-058 (0-007) 0-664 (0-062) 0-471 (0-019) 0-384 (0-026) 0-082 (0-008) 0-428 (0-027) 0-336 (0-029) 0-101 (0-011) 0-380 (0-046) 0-093 (0-007) 0-268 (0-025)
0-182 (0-020) 0-542 (0-072) 0-438 (0-034) 0-326 (0-012) 0-101 (0-006) 0-461 (0-051) 0-183 (0-017) 0-108 (0-010) 0-306 (0-025) 0-118 (0-011) 0-364 (0-032)
0-109 (0-010) 0-970 (0-066) 0-662 (0-045) 0-734 (0-035) 0-170 (0-057) 0-858 (0-047) 0-658 (0-039) 0-246 (0-022) 0-879 (0-058) 0-251 (0-014) 0-649 (0-055)
0-177 (0-024) 1-233 (0-130) 0-761 (0-037) 0-634 (0-035) 0-218 (0-016) 0-704 (0-039) 0-686 (0-032) 0-231 (0-011) 0-870 (0-085) 0-229 (0-013) 0-744 (0-041)
0-072 (0-005) 0-408 (0-039) 0-648 (0-064) 0-387 (0-035) 0-099 (0-015) 0-500 (0-086) 0-394 (0-052) 0-117 (0-009) 0-452 (0-054) 0-124 (0-013) 0-231 (0-016)
(b) 1.5
I o
cc 0.5
i 0
CON
MiR
i
PRI
m VIS
Fig. 2a and b. Mean R^, values for the finished surfaces on the first four composite samples. The numbers refer to the surface finishing procedure involved.
Finishing composite restorative materials
(b) 1.5
IT
0.5
Exp.A
Exp. T
Com. U
10
Fig. 3a and b. Mean R^ values for the finished surfaces on the last three composite samples. The numbers refer to the surface finishing procedure used.
overall contour was also smooth and rounded. For most of the composite mater:'als there was little difference in R^ value between any of the three routes to the disced finish, suggesting that little advantage is gained by utilizing the intermediate stages between tungsten carbide bur and Soflex discs. Using the intermediate stages with Concise and Miradapt, however, produced smoother disced surfaces. The lustre produced by the disced surfaces was shiny with Visio Dispers, Command Ultrafine and Prismafil, while the surfaces on Concise, Miradapt and Exp.T were dull in appearance. The visual effect of using tungsten carbide burs, white stone and Shofu points was to produce a rough, matt surface on all the composite materials. Mid-range roughness values were produced by the tungsten carbide bur, followed by either white stones or Shofu points (surfaces 3 and 4, respectively). The points produced a slightly smoother surface than the stones except in the case of Exp.A, where the reverse relationship was observed. When the white stone was followed by Shofu points (surface 7), there was an increase in roughness with Concise and Miradapt; Prismafil, the experimental materials and Command Ultrafine showed little change in R^ values, while Visio Dispers became smoother, but did not reach the R^ value of the
85
86
F.
disced surface. On most composite materials, therefore, Shofu points do not produce a smooth surface finish. Using the polishing pastes on the surfaces produced by the tungsten carbide bur did not greatly reduce the R^ values, except in the case of Exp.T. Indeed, the pastes roughened the surface of Concise, the material with the largest filler particle size. The use of the intermediate finishing agents prior to the use of pastes lowered the R^ values, particularly when the stones and points were used sequentially, rather than stones alone. However, the surface roughness and contour never became as smooth and even as 'was observed following the use of the discs. Prismafil, despite its relatively large filler particle size, was rendered reasonably smooth by the polishing pastes. This was due to the soft nature of the filler, which peimitted its abrasion by the pastes. With this exception, the larger the filler particle size, the rougher the resultant surface following the use of the pohshing pastes. Composite materials with large filler particles therefore require the use of discs in order to achieve the smoothest trimmed surfaces. Thus the pastes did not produce as smooth a surface as the Soflex discs on any material, so this study does not support the findings of Van Noort & Davis (1984), who observed that the use of metallurgical grade alumina polishing paste produced a smoother surface than the use of discs on small filler-sized composite materials. This anomaly may possibly be explained by the initial flattening of the composite materials on grade 600 carborundum paper in the study of Van Noort & Davis, whereas in this investigation a more chnically realistic procedure was employed, namely the removal of excess material with a tungsten carbide bur followed by various smoothing procedures. Conclusion In this clinically realistic study, the light-cured composite materials developed the smoothest surfaces in contact with the matrix strip. The tungsten carbide burs were fast and efficient at trimming excess material, but the resultant surface required further finishing. The Soflex discs produced the smoothest trimmed surface, and there appeared to be little advantage in using intermediate finishing procedures between the bur and the discs. The white finishing stone and Shofu points produced surfaces with mid-range roughness values. The polishing paste did not produce as smooth a surface as the discs. It is therefore recommended that, whenever possible, trimmed composite surfaces should be smoothed with the Soflex discs. There is still a need for a small rotary irstrument that will produce an equivalent finish on concave surfaces. Acknowledgments The authors thank Mr A. Cash for production of the specimen rods. Professor A.A. Crant for advice and encouragement. Miss A. Winstanley for the illustrations and Mrs J. Lear for typing the manuscript. References BA.SSIOUNY, M.A. & GRANT, A.A. (1978) A visible light-cured composite restorative—clinical open assessment. British Dental Jotirnal, 145, 327. HEATH, J.R. & WILSON, H.J. (1976) Surface roughness of restorations. British Dental Journal, 140,131. LUTZ, F . & PHILLIPS, R.W. (1983) A classification and evaluation of composite resin systems. Journal of Prosthetic Dentistry, 50, 480.
Finishing composite restorative materials
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(1983) Controversial aspects of composite resin restorative materials. British Dental Journal, 155, 380. VAN NOORT, R . & DAVIS, L . G . (1984) The surface finish of eomposite resin restorative materials. British Dental Journal, 157, 360. WILSON, G.S., DAVIES, E.H. & VON FRAUNHOFER, J.A. (1980) Micro-hardness characteristics of anterior restorative materiah. British Dental Journal, 14,%., 31. VAN NOORT, R .
Manuscript accepted 21 November 1988
