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A comparison between the microleakage of direct and indirect composite restorative systems
184
J. Dent. 1989;
17: 184-l
A comparison between the microleakage direct and indirect composite restorative systems
88
of
W. H. Douglas, R. P. Fields* and J. Fundingsland* Biomaterials Program, School of Dentistry Company, St Paul, Minnesota, USA
University of Minnesota,
Minneapolis
and *Dental
Division, 3M
KEY WORDS: Composite resins, Bonding technique, Microleakage
J Dent
1989;
17: 184-l
88 (Received 27 September 1988;
reviewed 21 November 1988;
accepted 14 April 1989)
ABSTRACT The present study compares the microleakage of direct and indirect restorations. Two dentine bonding agents were evaluated with both techniques. Class V cavities, approximately 2 mm in depth and 4 mm in diameter, were prepared in extracted human molars. Cavities were placed in either mesial or distal surfaces and were centred at the amelodentinal junction. Microleakage was rated after silver nitrate staining. With both dentine bonding agents, the indirect method resulted in significantly (P < O*OOl)reduced microleakage. Choice of adhesive for the indirect method was also significant, perhaps due to polymerization shrinkage of the composite cement used for placement. It is suggested
that the indirect method may be less technique sensitive and less dependent on the early bond strengths of different adhesives.
INTRODUCTION Composite resins enjoy wide usage in situations where they are not subjected to undue occlusal stress and where aesthetics are of prime importance. A major limitation of composites, however, is the shrinkage inherent in the polymerization process (Bowen ef al., 1982). This shrinkage leads to large contraction forces, threatening the bond formation at the hard tissue interface, especially the dentine-restorative interface (Davidson et al., 1984). The result is a marginal gap formation, as demonstrated by many investigators (Phair and Fuller, 1985; Crim, 1987). Moreover, the ingress of bacteria into the gap between the restoration and the cavity may produce pulpal pathology, as suggested by Brannstrom (Brannstrom and Nyborg, 197 1; Brannstrom and Vojinovic, 1976). While the efficacy of the bond between etched enamel and composite has been thoroughly investigated, the corresponding bond to dentine has not been adequately demonstrated. Davidson et aZ. (1984) have demonstrated disruption of the composit+dentine bond due to polymerization contraction. 0 1989 Butterworth & Co Publishers 0300-57 12/89/040184-05
$0300
Ltd.
It would appear that the management of polymerization contraction of composites at the chairside is a major factor in the control and reduction of microleakage. In the absence of a fully developed technology offering nonshrink composite resins, there are two methodologies for reducing the contraction phenomenon. The first is incremental filling, which is widely practised and is usually included in the manufacturer’s recommendations. The second is an indirect technique in which the composite restoration is cured outside the mouth and cemented into the prepared cavity using a dual cure resinbased cement. Therefore, the purpose of the present study was not to compare different materials but to report on the microleakage performance of composite restorations formed by direct and indirect techniques. MATERIALS AND METHODS Forty Class V preparations, each approximately 2 mm in depth and 4 mm in diameter, were cut in 20 extracted and cleaned (pumice and water) human third molars. The
Douglas
et al.: Microleakage
of direct and indirect
composites
185
Table I. Technique steps Group 1 1. Liner
:* 4: Adhesive
5. Cement
6. Technique
Group 2
Group 3
Group 4
Glass-ionomer cement Acid etch -
Glass-ionomer cement Acid etch -
Dual Cure Adhesive Resin 1 -
Adhesive Resin 2
Glass-ionomer cement Impression Acid etch Adhesive Resin 2
Direct microfill
Direct microfill
Glass-ionomer cement Impression Acid etch Dual Cure Adhesive Resin 1 Quartz-filled Bis-GMA/ TEGDMA Dual Cure Indirect microfill inlay
-
teeth were refrigerated in distilled water between extraction and preparation. A maximum storage time of 4 weeks was allowed. The prepared cavities extended 50 per cent onto the dentine surface and 50 per cent onto the enamel surface, with a short 45” bevel being included on the enamel margin. The cavities were divided into four groups of 10 sites each and preplanned as an analysis of variance. The technique steps are shown in Table I. In Groups 1 and 2, a glass-ionomer cement (GIC, 3M Dental Products, St Paul, MN, USA) was applied to the axial wall of the cavity. GIC was applied to a thickness of approximately O-5 mm using a ball applicator. Five minutes at room temperature was allowed for setting. This was followed by a 15-s etch with phosphoric acid gel applied to the enamel margin. Thorough washing and drying produced the typical clinical appearance of etched enamel. In Group 1, Adhesive Resin 1 (Scotchbond Dual Cure, 3M Dental Products, St Paul MN, USA) was mixed thoroughly and applied to the entire cavity surface and slightly beyond. This was followed by a steady stream of air to complete the evaporation of the ethanol component. A visible light curing unit (Visilux 2,3M Dental Products, St Paul, MN, USA) was used to irradiate the surface for 10 s. Following this, a microfill composite (Silux, 3M Dental Products, St Paul, MN, USA) was applied to the cavity in one increment with subsequent curing with a Visilux 2 curing light for a total of 60 s. The Silux was contoured before curing. No matrix was used. Finishing was performed immediately after curing. The finishing procedure involved surface reduction of the microfill using graded Sof-Lex discs (3 M Dental Products, St Paul, MN, USA). Finishing was performed dry. The finest grade Sof-Lex disc was used to produce a high lustre, especially at the exposed restorative-dentine interface. The restoration of Group 2 was essentially the same as Group 1, except that Adhesive Resin 2 (Scotchbond 2, 3M Dental Products, St Paul, MN, USA) was used immediately after the acid etch step. This involved first the application of a primer to the cavity surface and slightly beyond for 60 s, with constant agitation. Then the
Quartz-filled Bis-GMA/ TEGDMA Dual Cure Indirect microfill inlay
primer was dried using a steady stream of air, and Adhesive Resin 2 was applied to the entire primed surface and visible light-cured for 20 s. The microfill was immediately applied and finished in the manner prescribed for Group 1. Groups 3 and 4 were restored by the indirect technique. Immediately after the set of the glass-ionomer cement, the cavity area and slightly beyond was impressioned using a polyvinylsiloxane material (Express, 3M Dental Products, St Paul, MN, USA) and a model was poured using a fast-set epoxy model material (EXL 172, 3M Dental Products, St Paul, MN, USA). During the modelmaking step, the prepared teeth were stored in a saturated environment to prevent dessication of the GIC. A microfill restoration was constructed as an inlay on the model and then separated from the epoxy. The enamel margins of the teeth in Groups 3 and 4 were acid etched, washed and dried as described for Groups 1 and 2. In Group 3, Adhesive Resin 1 was applied to the cavity surface as in Group 1. In Group 4, Adhesive Resin 2 was applied to the cavity surface as in Group 2. It should be noted that this work was performed before the formal introduction of Scotchbond 2. Thus, air thinning was used to ensure a thin, uniform adhesive layer. Since the indirect restorative technique avoids the stress induced by polymerization shrinkage, a thinner Scotchbond 2 layer may suffice. The microfill inlays were then cemented into place using a dual cure, filled resin cement (EXL 188,3 M Dental Products, St Paul, MN, USA) and finished in the manner prescribed for Groups 1 and 2. The four groups of teeth were thermocycled 500 times in water between 5” and 55°C. Dwell time in each temperature was 30 s, with a 15-s transfer time between baths. Following this, the apices of the teeth were occluded using a microfill composite, if necessary, and the entire tooth, except for the restoration and a 2 mm perimeter of hard tissue, was painted with one coat of nail varnish. Immediately after the nail varnish had dried, microleakage was tested by immersing the teeth in 50 per cent silver nitrate solution for 2 h, followed by immersion in developing solution under bright light for 8 h. The teeth
186
J. Dent.
1989; 17: No. 4
Table Il. Microleakage in micrometres at the dentine-restorative groups
interface of four
Groups 1 Resin 1 Direct 330 1100 870 730 530 530 1100 1000 730 800 Mean s.d. C.V.(%)
772.0 256.8 33.3
2 Resin 2 Direct
3 Resin 1 Indirect
470 370 370 400 400 130 290 270
4 Resin 2 Indirect
370 330 130 130 220 200 67 200
20 13 0 53 47 33 53 0
6; 337.5 105-l 31-l
171.4 117-o 68.3
27.4 22.3 81-4
Table l/1 Obtained differences between means and significance levels Groups 1
2
1 :
434.5 595.6
PCO.00 1 161.1
4
744-6
310.1
Groups
were sectioned longitudinally in a me&-distal plane using a diamond-bladed circular saw (Isomet Slow Speed Saw, Buehler Ltd, Lake Bluff, IL, USA) so that the restorationdentine interface could be clearly seen. On one-half of each sectioned restoration the microleakage was scored linearly along the dentine-restoration interface using a microscope fitted with a reticule (Carl Zeiss, Oberkoken, FRG) calibrated in millimetres at X 8 magnification. Each section was also photographed at X 37.5 magnification using a Polaroid camera. The photomicrographs were then assembled for measurement and comparison. Microleakage was not observed at the enamel-restoration interface. A one-way analysis of variance was carried out on the data and statistical comparisons between the group means were determined using the Bonferroni test.
RESULTS The results of the microleakage measurement along the dentine-restorative border are shown in Table II, where mean, standard deviation and coefficient of variation are presented. One of the difficulties in this type of measurement is inadvertent overcontouring on root surfaces which may artificially reduce the observed microleakage. For this reason two data points were excluded from each of Groups 2 and 4. The analysis of variance showed that the F statistic = 39.21 and that there was a statistically significant
3 ;%Y
4 P
149.0
difference between all four groups considered together at the P
Douglas et al.: Microleakage
fig. 7. Indirect microfill inlayand Adhesive Resin 2 (Group4) showing penetration of the intact dentine by the silver stain (20 pm penetration).
obtained difference of 434.5 and P
of direct and indirect composites
187
Fig. 2. Direct microfill restoration and Adhesive Resin 1 (Group 1) showing clearly defined microleakage (530 pm penetration).
spite of the differences already observed in the resin systems employed. However, although the particular resin system may be less crucial in an indirect restorative system, it is still an influential factor. This is emphasized by the fact that the significant difference is reduced at KO.01 between Groups 3 and 4. Thus the inherent microleakage improvement in the indirect restorative system was reduced somewhat by changing from Adhesive Resin 2 to Adhesive Resin 1. This may in part be attributed to the relative thickness of the dual cure cement, which must cure immediately after the restorative placement, thus challenging the hard tissue bond due to shrinkage of the cement. In general, it may be concluded that the indirect method of placement of composite restorations offers considerable improvement in microleakage performance, particularly on the dentine-restorative interface. Further, the indirect method may be less technique sensitive and less dependent on the role of the early bond strength of different adhesive resin formulations. However, this factor cannot be completely ruled out because of the continuing part played by the dual cure adhesive in a successful restoration. References Braem M., Lambrechts P., Vanherle G. et al. (1987) Stiffness increase during the setting of dental composite resins. J. Dent. Rex 66, 1713-1716. Brannstrom M. and Nyborg H. (1971) The presence of bacteria in cavities filled with silicate cement and composite resin materials. Swed. Dent. J. 64, 149-15s. Brannstrom M. and Vojinovic 0. (1976) Response of the dental pulp to invasion of bacteria around three tilling materials. J. Dent. Child. 43, 83-89. Bowen R L., Rapson J. E. and Dickson G. (1982) Hardening shrinkage and hygroscopic expansion of composite resins. J. Dent. Res. 61,654-658.
188
J. Dent. 1989; 17: No. 4
Crim G. A. (1987) Assessment of microleakage of 12 restorative systems. QuintessenceInt. 18, 419-421. Davidson C. L., deGee A. J. and Feilzer A. (1984) Tbe competition between the composite-dentine bond strength and the polymerization contraction stress. J. Dent. Res.
63,1396-1399. Hammesfahr P. D., Huang C. T. and ShafFer S. E. (1987) Microleakage and bond strength of resin restorations with various bonding agents. Dent. Muter. 3, 194-199. Lambrechts P., Braem M. and Vanberle G. (1985) Accomplishments and expectations with posterior composite
resins. In: Vanberle G and Smith D. C. (eds), Posterior Composite Resin Dental Restorative Materials. Utrecht, Peter Sculz, pp. 521-540. Phair C. B. and Fuller J. L. (1985) Microleakage of composite resin restorations with cementum margins. J.
Prosthet. Dent. 53, 361-364. Pintado M. R and Douglas W. H. (1988 a) Microleakage compared between two dentin bonding resin systems. J. Dent. Res. 67, (Abstr. 1571), 309. Pintado M. R and Douglas W. H. (1988 b) The comparison of microleakage between two different dentin bonding resin systems. QuintessenceInt. 19, 905-907.
Correspondence should be addressed to: Dr W. H. Douglas, Biomaterials Program, 16-2 12 Moos Tower, 5 15 Delaware Street SE, Minneapolis, MN 55455, USA.
Forthcoming Original
Articles
Research
Reports
Adherence of oral streptococci to composite X Yamamoto, H. Noda and K. Kimura The nature and effects of composite finishing S. A. Whitehead and N. H. F. Wilson
resin restorative
materials
pastes
Current status of the cast metal inlay: a survey of dental schools in the UK and Hong Kong P. R H. Newsome and C. C. Youngson Dental
erosion
in patients
with chronic
alcoholism
B. G. N. Smith and N. D. Robb technique upon the compressive strength and porosity of a composite resin R G. Chadwick, J. F. McCabe, A. W G. Walls and R. Storer The effect of placement
Effects of a solution of a succinic aldehyde on elastomeric impressions R J. McCormick, D. C. Watts and N. H. F. Wilson Outlook of British dentists towards their profession L. Cohen and A. Sheiham Retrograde root-filling using antibiotic-containing radioopaque bone cement A. S. High and J. L. Ruse11 Review Clinical status of dentiue lxmding agent; W; H. Douglas and H. L. Anderson
J. Dent. 1989;
17: 184-l
A comparison between the microleakage direct and indirect composite restorative systems
88
of
W. H. Douglas, R. P. Fields* and J. Fundingsland* Biomaterials Program, School of Dentistry Company, St Paul, Minnesota, USA
University of Minnesota,
Minneapolis
and *Dental
Division, 3M
KEY WORDS: Composite resins, Bonding technique, Microleakage
J Dent
1989;
17: 184-l
88 (Received 27 September 1988;
reviewed 21 November 1988;
accepted 14 April 1989)
ABSTRACT The present study compares the microleakage of direct and indirect restorations. Two dentine bonding agents were evaluated with both techniques. Class V cavities, approximately 2 mm in depth and 4 mm in diameter, were prepared in extracted human molars. Cavities were placed in either mesial or distal surfaces and were centred at the amelodentinal junction. Microleakage was rated after silver nitrate staining. With both dentine bonding agents, the indirect method resulted in significantly (P < O*OOl)reduced microleakage. Choice of adhesive for the indirect method was also significant, perhaps due to polymerization shrinkage of the composite cement used for placement. It is suggested
that the indirect method may be less technique sensitive and less dependent on the early bond strengths of different adhesives.
INTRODUCTION Composite resins enjoy wide usage in situations where they are not subjected to undue occlusal stress and where aesthetics are of prime importance. A major limitation of composites, however, is the shrinkage inherent in the polymerization process (Bowen ef al., 1982). This shrinkage leads to large contraction forces, threatening the bond formation at the hard tissue interface, especially the dentine-restorative interface (Davidson et al., 1984). The result is a marginal gap formation, as demonstrated by many investigators (Phair and Fuller, 1985; Crim, 1987). Moreover, the ingress of bacteria into the gap between the restoration and the cavity may produce pulpal pathology, as suggested by Brannstrom (Brannstrom and Nyborg, 197 1; Brannstrom and Vojinovic, 1976). While the efficacy of the bond between etched enamel and composite has been thoroughly investigated, the corresponding bond to dentine has not been adequately demonstrated. Davidson et aZ. (1984) have demonstrated disruption of the composit+dentine bond due to polymerization contraction. 0 1989 Butterworth & Co Publishers 0300-57 12/89/040184-05
$0300
Ltd.
It would appear that the management of polymerization contraction of composites at the chairside is a major factor in the control and reduction of microleakage. In the absence of a fully developed technology offering nonshrink composite resins, there are two methodologies for reducing the contraction phenomenon. The first is incremental filling, which is widely practised and is usually included in the manufacturer’s recommendations. The second is an indirect technique in which the composite restoration is cured outside the mouth and cemented into the prepared cavity using a dual cure resinbased cement. Therefore, the purpose of the present study was not to compare different materials but to report on the microleakage performance of composite restorations formed by direct and indirect techniques. MATERIALS AND METHODS Forty Class V preparations, each approximately 2 mm in depth and 4 mm in diameter, were cut in 20 extracted and cleaned (pumice and water) human third molars. The
Douglas
et al.: Microleakage
of direct and indirect
composites
185
Table I. Technique steps Group 1 1. Liner
:* 4: Adhesive
5. Cement
6. Technique
Group 2
Group 3
Group 4
Glass-ionomer cement Acid etch -
Glass-ionomer cement Acid etch -
Dual Cure Adhesive Resin 1 -
Adhesive Resin 2
Glass-ionomer cement Impression Acid etch Adhesive Resin 2
Direct microfill
Direct microfill
Glass-ionomer cement Impression Acid etch Dual Cure Adhesive Resin 1 Quartz-filled Bis-GMA/ TEGDMA Dual Cure Indirect microfill inlay
-
teeth were refrigerated in distilled water between extraction and preparation. A maximum storage time of 4 weeks was allowed. The prepared cavities extended 50 per cent onto the dentine surface and 50 per cent onto the enamel surface, with a short 45” bevel being included on the enamel margin. The cavities were divided into four groups of 10 sites each and preplanned as an analysis of variance. The technique steps are shown in Table I. In Groups 1 and 2, a glass-ionomer cement (GIC, 3M Dental Products, St Paul, MN, USA) was applied to the axial wall of the cavity. GIC was applied to a thickness of approximately O-5 mm using a ball applicator. Five minutes at room temperature was allowed for setting. This was followed by a 15-s etch with phosphoric acid gel applied to the enamel margin. Thorough washing and drying produced the typical clinical appearance of etched enamel. In Group 1, Adhesive Resin 1 (Scotchbond Dual Cure, 3M Dental Products, St Paul MN, USA) was mixed thoroughly and applied to the entire cavity surface and slightly beyond. This was followed by a steady stream of air to complete the evaporation of the ethanol component. A visible light curing unit (Visilux 2,3M Dental Products, St Paul, MN, USA) was used to irradiate the surface for 10 s. Following this, a microfill composite (Silux, 3M Dental Products, St Paul, MN, USA) was applied to the cavity in one increment with subsequent curing with a Visilux 2 curing light for a total of 60 s. The Silux was contoured before curing. No matrix was used. Finishing was performed immediately after curing. The finishing procedure involved surface reduction of the microfill using graded Sof-Lex discs (3 M Dental Products, St Paul, MN, USA). Finishing was performed dry. The finest grade Sof-Lex disc was used to produce a high lustre, especially at the exposed restorative-dentine interface. The restoration of Group 2 was essentially the same as Group 1, except that Adhesive Resin 2 (Scotchbond 2, 3M Dental Products, St Paul, MN, USA) was used immediately after the acid etch step. This involved first the application of a primer to the cavity surface and slightly beyond for 60 s, with constant agitation. Then the
Quartz-filled Bis-GMA/ TEGDMA Dual Cure Indirect microfill inlay
primer was dried using a steady stream of air, and Adhesive Resin 2 was applied to the entire primed surface and visible light-cured for 20 s. The microfill was immediately applied and finished in the manner prescribed for Group 1. Groups 3 and 4 were restored by the indirect technique. Immediately after the set of the glass-ionomer cement, the cavity area and slightly beyond was impressioned using a polyvinylsiloxane material (Express, 3M Dental Products, St Paul, MN, USA) and a model was poured using a fast-set epoxy model material (EXL 172, 3M Dental Products, St Paul, MN, USA). During the modelmaking step, the prepared teeth were stored in a saturated environment to prevent dessication of the GIC. A microfill restoration was constructed as an inlay on the model and then separated from the epoxy. The enamel margins of the teeth in Groups 3 and 4 were acid etched, washed and dried as described for Groups 1 and 2. In Group 3, Adhesive Resin 1 was applied to the cavity surface as in Group 1. In Group 4, Adhesive Resin 2 was applied to the cavity surface as in Group 2. It should be noted that this work was performed before the formal introduction of Scotchbond 2. Thus, air thinning was used to ensure a thin, uniform adhesive layer. Since the indirect restorative technique avoids the stress induced by polymerization shrinkage, a thinner Scotchbond 2 layer may suffice. The microfill inlays were then cemented into place using a dual cure, filled resin cement (EXL 188,3 M Dental Products, St Paul, MN, USA) and finished in the manner prescribed for Groups 1 and 2. The four groups of teeth were thermocycled 500 times in water between 5” and 55°C. Dwell time in each temperature was 30 s, with a 15-s transfer time between baths. Following this, the apices of the teeth were occluded using a microfill composite, if necessary, and the entire tooth, except for the restoration and a 2 mm perimeter of hard tissue, was painted with one coat of nail varnish. Immediately after the nail varnish had dried, microleakage was tested by immersing the teeth in 50 per cent silver nitrate solution for 2 h, followed by immersion in developing solution under bright light for 8 h. The teeth
186
J. Dent.
1989; 17: No. 4
Table Il. Microleakage in micrometres at the dentine-restorative groups
interface of four
Groups 1 Resin 1 Direct 330 1100 870 730 530 530 1100 1000 730 800 Mean s.d. C.V.(%)
772.0 256.8 33.3
2 Resin 2 Direct
3 Resin 1 Indirect
470 370 370 400 400 130 290 270
4 Resin 2 Indirect
370 330 130 130 220 200 67 200
20 13 0 53 47 33 53 0
6; 337.5 105-l 31-l
171.4 117-o 68.3
27.4 22.3 81-4
Table l/1 Obtained differences between means and significance levels Groups 1
2
1 :
434.5 595.6
PCO.00 1 161.1
4
744-6
310.1
Groups
were sectioned longitudinally in a me&-distal plane using a diamond-bladed circular saw (Isomet Slow Speed Saw, Buehler Ltd, Lake Bluff, IL, USA) so that the restorationdentine interface could be clearly seen. On one-half of each sectioned restoration the microleakage was scored linearly along the dentine-restoration interface using a microscope fitted with a reticule (Carl Zeiss, Oberkoken, FRG) calibrated in millimetres at X 8 magnification. Each section was also photographed at X 37.5 magnification using a Polaroid camera. The photomicrographs were then assembled for measurement and comparison. Microleakage was not observed at the enamel-restoration interface. A one-way analysis of variance was carried out on the data and statistical comparisons between the group means were determined using the Bonferroni test.
RESULTS The results of the microleakage measurement along the dentine-restorative border are shown in Table II, where mean, standard deviation and coefficient of variation are presented. One of the difficulties in this type of measurement is inadvertent overcontouring on root surfaces which may artificially reduce the observed microleakage. For this reason two data points were excluded from each of Groups 2 and 4. The analysis of variance showed that the F statistic = 39.21 and that there was a statistically significant
3 ;%Y
4 P
149.0
difference between all four groups considered together at the P
Douglas et al.: Microleakage
fig. 7. Indirect microfill inlayand Adhesive Resin 2 (Group4) showing penetration of the intact dentine by the silver stain (20 pm penetration).
obtained difference of 434.5 and P
of direct and indirect composites
187
Fig. 2. Direct microfill restoration and Adhesive Resin 1 (Group 1) showing clearly defined microleakage (530 pm penetration).
spite of the differences already observed in the resin systems employed. However, although the particular resin system may be less crucial in an indirect restorative system, it is still an influential factor. This is emphasized by the fact that the significant difference is reduced at KO.01 between Groups 3 and 4. Thus the inherent microleakage improvement in the indirect restorative system was reduced somewhat by changing from Adhesive Resin 2 to Adhesive Resin 1. This may in part be attributed to the relative thickness of the dual cure cement, which must cure immediately after the restorative placement, thus challenging the hard tissue bond due to shrinkage of the cement. In general, it may be concluded that the indirect method of placement of composite restorations offers considerable improvement in microleakage performance, particularly on the dentine-restorative interface. Further, the indirect method may be less technique sensitive and less dependent on the role of the early bond strength of different adhesive resin formulations. However, this factor cannot be completely ruled out because of the continuing part played by the dual cure adhesive in a successful restoration. References Braem M., Lambrechts P., Vanherle G. et al. (1987) Stiffness increase during the setting of dental composite resins. J. Dent. Rex 66, 1713-1716. Brannstrom M. and Nyborg H. (1971) The presence of bacteria in cavities filled with silicate cement and composite resin materials. Swed. Dent. J. 64, 149-15s. Brannstrom M. and Vojinovic 0. (1976) Response of the dental pulp to invasion of bacteria around three tilling materials. J. Dent. Child. 43, 83-89. Bowen R L., Rapson J. E. and Dickson G. (1982) Hardening shrinkage and hygroscopic expansion of composite resins. J. Dent. Res. 61,654-658.
188
J. Dent. 1989; 17: No. 4
Crim G. A. (1987) Assessment of microleakage of 12 restorative systems. QuintessenceInt. 18, 419-421. Davidson C. L., deGee A. J. and Feilzer A. (1984) Tbe competition between the composite-dentine bond strength and the polymerization contraction stress. J. Dent. Res.
63,1396-1399. Hammesfahr P. D., Huang C. T. and ShafFer S. E. (1987) Microleakage and bond strength of resin restorations with various bonding agents. Dent. Muter. 3, 194-199. Lambrechts P., Braem M. and Vanberle G. (1985) Accomplishments and expectations with posterior composite
resins. In: Vanberle G and Smith D. C. (eds), Posterior Composite Resin Dental Restorative Materials. Utrecht, Peter Sculz, pp. 521-540. Phair C. B. and Fuller J. L. (1985) Microleakage of composite resin restorations with cementum margins. J.
Prosthet. Dent. 53, 361-364. Pintado M. R and Douglas W. H. (1988 a) Microleakage compared between two dentin bonding resin systems. J. Dent. Res. 67, (Abstr. 1571), 309. Pintado M. R and Douglas W. H. (1988 b) The comparison of microleakage between two different dentin bonding resin systems. QuintessenceInt. 19, 905-907.
Correspondence should be addressed to: Dr W. H. Douglas, Biomaterials Program, 16-2 12 Moos Tower, 5 15 Delaware Street SE, Minneapolis, MN 55455, USA.
Forthcoming Original
Articles
Research
Reports
Adherence of oral streptococci to composite X Yamamoto, H. Noda and K. Kimura The nature and effects of composite finishing S. A. Whitehead and N. H. F. Wilson
resin restorative
materials
pastes
Current status of the cast metal inlay: a survey of dental schools in the UK and Hong Kong P. R H. Newsome and C. C. Youngson Dental
erosion
in patients
with chronic
alcoholism
B. G. N. Smith and N. D. Robb technique upon the compressive strength and porosity of a composite resin R G. Chadwick, J. F. McCabe, A. W G. Walls and R. Storer The effect of placement
Effects of a solution of a succinic aldehyde on elastomeric impressions R J. McCormick, D. C. Watts and N. H. F. Wilson Outlook of British dentists towards their profession L. Cohen and A. Sheiham Retrograde root-filling using antibiotic-containing radioopaque bone cement A. S. High and J. L. Ruse11 Review Clinical status of dentiue lxmding agent; W; H. Douglas and H. L. Anderson