Effect of water spray on lining materials and their adhesion to composite and dentin cavity walls A. Ben-Amar S. Geiger R.Uberman Section of Operative Dentistry The Maurice and Gabrieia Goldschleger School of Dental Medicine Tel Aviv University Tel Aviv, israel Received September 25, 1990 Accepted July 10, 1991 Dent Mater 7:274-278, October, 1991
Abstract--The effect of an air-water spray on the adhesion of lining materials to both overlying composite restorations and cavity walls was evaluated. An in vitro study was performed on extracted molar teeth: Two resinous light-cured liners and one calcium hydroxide, chemically activated liner were compared. Teeth were restored with composite materials and subjected to cyclic thermal changes so that microleakage could be evaluated. Results indicated that adaptation between the restorative material and the liner was effective, regardless of whether the oxygen-inhibited layer was removed by being rinsed. A definite gap was detected between the Fners tested and the dentin cavity walls.
he application of liners under composite restorations is an accepted procedure. The liner should adhere to dentin cavity walls and provide protection to the dentin-pulp complex by covering the smear plugs and sealing the dentinal tubuli against chemical irritants and bacterial invasion (Pashley et al., 1990). Calcium hydroxide or glassionomer liners are activated either chemically or by visible light. An ideal cavity liner should adhere to the dentin cavity walls rather than to overlying composite restorations. The liner should not be pulled away from the dentin by contraction forces of the composite during polymerization, since this creates a fluid-filled space between liner and dentin. The combination of an imperfect gingival seal with no adhesion of liners to dentin cavity walls can lead to bacterial invasion. Bacteria and their toxins can reach the pulp by diffusion, causing pulpal inflammation. Light-cured liners usually contain a resin that leaves an oxygen-inhibited layer alter being cured. This layer remains partially polymerized (Ogura, 1989) as the atmospheric oxygen terminates growing chains of the free radicals ofthe resin (Lambrechts, 1983). This incompletely polymerized layer reacts chemically with the subsequent layer of the restorative composite. This layer should not be removed before the composite restoration is placed, based on the rationale that monomers present in the incompletelypolymerizedlayer of the liner co-polymerize with the composit~ restoration, thereby increasing the adhesion. Prior to the placement of composite, etching and rinsing procedures are performed to increase the mechanical bond of the cured resin to the etched enamel, which substantially reduces microleakage (Hembree and Andrews, 1976; Retief, 1987; Mitchem and Turner, 1974). Since the pulp may be irritated by the etchant (Retiefet al., 1974; Macko et al., 1978), it is logical for the liner to be placed before the etching and rinsing procedures, since the liner acts as a mechanical barrier against acid pen-
T
etration into the tubuli. The oxygeninhibited surface layer of the liner is actually washed away during rinsing, along with the etchant. The purpose of this study was to evaluate the effect of an air-water spray on the interface between the liner and the composite restoration, by means of SEM examination and assessment of dye penetration following a thermocycling procedure. MATERIALS AND METHODS
A total of 30 freshly extracted human molar teeth was selected. The teeth were cleaned with periodontal curettes and polished with a pumice/water slurry and a soi~ rubber cup in a slow-speed handpiece. Two separate cavities (MO and DO), with a gingival wall located 1 mm occlusal to the CEJ, were prepared by use of a #330 tungsten carbide bur in a high-speedhandpiece with an air-water spray in the following dimensions: occlusal depth, 2 ram; occlusal width, 2 ram; axial depth, 2.5 mm; and box width at the gingival wall, 4 ram. No bevel was prepared. The cavities were treated with 20% polyacrylic acid (Polyacrylic Dentin Conditioner, Ultradent Products Inc., Salt Lake City, UT) for 10 s, rinsed with water for 20 s, and dried. Teeth were then randomly divided into three groups, according to the lining material used. Group 1: Cavalite--light-cured lining material (Light Activated Cavity Liner, Kerr Manufacturing Co., l~mulus, MI). Group 2: Ultrablend--light-cured calcium fluoride liner (Ultrablend; Ultradent Products Inc., Salt Lake City, UT). Group 3: Life chemically activated calcium hydroxide lining material (Kerr Manufacturing Co., Romulus, MI)-control group. Each group was then further subdivided: Subgroup a: Enamel walls were etched and cavities rinsed with an airwater spray for 20 s after the liner was applied. Subgroup b: Enamel walls were
274 Ben-Amar et al./ Water spray effect on lining materials and their adhesion to composite and dentin cavity walls
etched and rinsed with an air-water spray for 20 s before the liner was applied. Lining materials were applied to the axial and pulpal walls of the cavities. Life and Cavalite liners were applied by means of a small applicator. Ultrablend was applied directly from the syringe by means of the needle provided by the manufacturer. Cavalite and Ultrablend were cured for 40 s in the Elipar II lightcure unit (ESPE GmbH & Co., D-8031, Seefeld, Germany), while Life was untouched for three min. Etching was carried out for 30 s by use of a gel etchant of 37% phosphoric acid applied directly with a syringe. The etchant was then rinsed with water for 20 s and dried. The bonding material was light-cured Scotchbond (3M Dental Products Division, St. Paul, MN) applied to the etched enamel and dentin walls, and gently spread with a stream of air before being cured for 20 s. A hybrid posterior composite (Light-Cured LC1000 Posterior Composite, Southern Dental Industries Ltd., Bayswater, Victoria, Australia) was incrementally inserted (in three layers) and each layer cured for 40 s, first from an occlusal and then from a proximal direction. Finishing was carried out with use of white alpine stones and a water spray at high speed, followed by polishing with Soflex discs (3M Co., St. Paul, MN) in a slow-speed handpiece. The restored teeth were kept in tap water for seven d at 37°C, and then thermocycled 100 times in temperaturecontrolled water baths, between 5°C + 2°C and 55°C + 2°C for 10 s at each temperature, with a 10-second dwell time between immersions. Apices in all teeth were sealed with acrylic. The other surfaces, except for the restorations and their margins, were coated with two layers of nailvarnish, then immersed in 0.5% Basic Fuchsin dye for 24 h, rinsed, and dried. Each tooth was sectioned mesiodistally along the center of the restoration by means of an Isomet saw (Isomet saw, Buehler Ltd., Evanston, IL). The sections were examined in a binocular microscope and a stereomicroscope (Wild M8, Wild Leitz Ltd., Heerbrugg, Switzerland) and evaluated for dye penetration and for the adaptation ofthe liners to the restorative material. Dye penetration was evaluated between the cavity walls and the restorative materials, the liner and the dentin wall, the liner and the composite, and at
Fig. 1. Perfect adaptation between the resin liner and composite (without the liner being rinsed). C = composite, I = junction between liner and restoration, and L = resin liner.
Fig. 2. Perfect adaptation belwee~the resin liner and composite (the liner was rinsed before the overlying composite was inserted). C = composite; L : resin liner.
the gingival wall, according to the scale shown in Table 1. Three sections in each group were prepared and examined by SEM (JSM-840A, JEOL, Japan), at numerous points at x200 and x400. The sections were examined for gap width between the liners and dentin cavity walls, and, for adaptation, between the liners and overlying composite. Photomicrographs were taken.
The results were evaluated by Student's t test at the composite/gingival wall interface, and paired t test for the other groups. RESULTS
Binocular and stereomi."croscope examination revealed an almost perfect adaptation between the restorative material and cavity liners and between cavity
Dental Materials / October1991 275
tween the liner and restoration, regardless of the rinsing procedure. A gap of 320 p. was found between the liners and dentin cavity walls in all sections (Fig. 3). Rinsing the cavity and lining materials before insertion of the composite had no effect on their adhesion to each other compared with the restored teeth, where the lining materials were not rinsed before restoration. There was a higher leakage assessment at the gingival wall when no rinsing was carried out, but this was not statistically significant. DISCUSSION
Fig. 3. A gap between the liner (L) and dentin cavity wall (D).
The oxygen-inhibited layer created on the superficial surface of the resinous light-cured materials is, at present, considered to be important for the adaptation of liners to the composite restorative material. This study evaluated the effect of the oxygen-inhibited layer on the adaptation of liners to the restorative material and to the axial and pulpal walls of the preparation. When an air-water spray was used for 20 s on the light-cured lining material, the shiny oxygen-inhibited layer was removed, and a non-glossy adherence was observed. It was expected that the removal of this shiny surface would prevent or reduce the adhesion of the restorative material to the liner and that the shrinkage of the composite restoration toward the light source during polymerization would create a gap between the cured restoration and the liner. In sections where a hard-setting Ca(OH) 2 liner (Life) was applied and rinsed with an air-water spray before the composite was inserted, the outer surface ofthe liner did not appear smooth in relation to the restoration but as an irregular non-homogenous area (Fig. 4). This irregularity was probably the result of surface erosion by the air-water spray.
Fig. 4. Irregular non-homogenous outer surface of the Ca(OH)= liner. Life = DY, D = dentin, and C = composite. A gap between the liner and dentin cavity wall.
liners and axial and pulpal walls in all groups tested. There was no significant difference between groups tested in the degree of dye penetration at the gingival margins (p > 0.05), whereas minimal gingival dye penetration was found at the tooth/composite interface, and no leakage was found at the pulpal floor. Dye penetration at the gingival wall did not reach more than halfway between
the DEJ and the axial wall (Table 2). SEM examination revealed that, in all groups where resinous light-cured liners were used (Cavalite and Ultrablend), there was near-perfect adaptation between the liners and cornposite, regardless of whether liners were rinsed with an air-water spray (Figs. 1 and 2). Sections with hard set Ca(OH)2 liner (Life) showed less adaptation be~
TABLE 1
CATEGORIES OF DYE PENETRATIONAT THE GINGIVALWALLS OF THE RESTORATIONS Category Dye Penetration
0 1
No dye penetration
2
Dyepenetrationupto halfofthedentinalwall
3
Dye penetrationup to the axialwall
Dye penetrationup to DEJ
276 Ben-Amar et al./Water spray effect on lining materials and their adhesion to composite and dentin cavity walls
Despite the irregularity, near-perfect adaptation between the liner and the compositewas still achieved. Ameasurable gap was not visible in most sections (85%); in the other samples (15%), a gap ofup to 1 11wasmeasured. It is assumed that this phenomenon has no clinical significance for bacterial penetration, since many bacteria range in size from 1-3 ~m (Pashley, 1990). Where the superficial surface of the calcium hydroxide liner was not rinsed, sections showed perfect adaptation between the liner and the restoration, without any regularity of its superficial surface. A gap of 3-20 ~twas detected between the liner and dentin cavity walls in all groups (Figs. 3 and 4). The rinsing procedure had no effect on the creation of these gaps. In general, no difference in gap width was found with Ca(OH)~liners and dentin and the resinous light-cured liners and dentin (3-15 ~ and 5-20 ~t, respectively) (p > 0.05). The gap creation between the resin liners (Cavalite and Ultrablend) and the dentin cut surface could be explained by their contraction toward the ligh~ source. In addition, polymerization of the composite draws the liner toward it, further away from the dentin. Ca(OH) 2 liner, not being a resin, has no chemical bond with the composite material. Therefore, the poly-merizationcontraction forces ofthe composite have no effect on these liners. When hardened, chemically activated Ca(OH) 2 liners have negligible contraction and dimensional change. Since no significant gaps were found between Life and the composite restoration, this suggests that, by use of an
incremental technique, the amount of shrinkage of the compositeis reduced by progressive curing of each increment. This technique provides relatively good adaptation between the liner and the restorative material and limits microleakage at the gingival walls ofthe restorations (Podshadely et al., 1988; Leclaire et al., 1986). All available composite materials contract during polymerization. As a result, a small degree of dye penetration at the gingival cavity wall was evident in all groups tested. Dye penetration did not exceed half the distance from the cavosurface margin to the axial wall in any of the samples. Slightly deeper dye penetration was found at the gingival wall (Subgroup b), where the enamel walls were etched and rinsed before the liner was applied, compared with samples where the liners were rinsed by an air-water spray before the composite was inserted (Subgroup a). No significant statistical differences were found between these two subgroups (p > 0.05). Since dye penetration did not reach the axial or pulpal walls, it could not be used to evaluate the degree of microleakage at other interfaces: liner/composite, or liner/dentin walls. Thus, a SEM study was conductedto evaluate the gap width at these sites. In the enamel of the gingival wall, the resin bonding served as an adhesive agent for composite to dentin. The liners had no influence on dye penetration at that specific area, since they did not reach the enamel section of the wall. The gingival cavity walls were located 1 mm occlusal to the CEJ, where the amount of enamel is reduced, and thus
the bond strength to dentin is not sufficient to withstand the contraction forces associated with polymerization (Torstenson and Br~nnstrSm, 1988). This usually results in a small gap at the cervical cavity wall (Gross et al., 1985). The results of this study showed no significant differences between the groups tested. However, it is recommended that an acid-etch technique be used (on enamel cavity margins) with appropriate rinsing of the etchant after the liner is applied. This liner prevents possible damage by the etchant to the dentino-pulpal complex by creating a physical barrier that seals the tubuli. CONCLUSIONS
The results ofthis in vitro study indicate that: (1) the removal of the incompletely polymerizedoxygen-inhibitedlayer from the superficial surfaces ofthe light-cured resinous liners, before insertion of the composite material, does not have a detrimental effect on the adhesion of the liners to the compositematerial or to the dentin cavity wall; (2) the air-water rinsing procedure can affect the outer surface of the chemically activated, hard-setting Ca(OH), liner; and (3) all liners tested (in scanning electron micrographs) exhibited a gap between the liners and dentin cavity walls. REFERENCES
GROSS,J.D.; RETIEF,D.H.; and BRADLEY, E.L. (1985): Microleakage of Posterior Composite Restorations, Dent Mater 1:7-10. HEMBRE~, J.H., JR. and ANdReWS,J.T.
TABLE 2
DEGREEOF DYE PENETRATION Dye Penetration Liqer/axialwall Liner/pulpalw a l l of the cavity of the cavity
Grouptested
Presenceof oxygeninhibited layer (n = 10)
Composite restoration/ gingival wall of the cavity
Group No. 1
-"
0
0
0
0
Cavalite
++
1
0
0
0
Group No. 2
-'
1
0
0
0
Ultrablend
++
1.5
0
0
0
Group No. 3
Rinsingthe liner
1
0
0
0
Life No rinsingthe liner 1.5 0 "-: Rinsingof the liner. The oxygen-inhibitedlayer was removed from the liner. *+: No rinsingof the liner. The oxygen-inhibitedlayer exists on the outer surface of the liner.
0
0
Liner/composite interface
Dental Materials~October 1991 277
(1976): In vitro Microleakage of Several Acid Etch Composite Systems, IADR Prog & Abstr 55 (Spec Iss B): Abst. No. 309. LA~mRECHTS,P. (1983): Basic Properties of Dental Composites and Their Impact on Clinical Performance, Leuven, Belgium: Katholieke Universiteit, p. 35. LZCLAIRE, C.C.; B~, L.W.; HARGRAVZ, J.W.; and PELLZU, G.B.,JR. (1986): A 2-Stage Composite Resin Filling Technique and Microleakage Below the CEJ, JDent Res 65:248,Abstr.No. 799.
MACKO, D.J.; RUTHBERG, M.; and LANGZLASD, I~ (1978): Pulpal Response totheApplicationofPhosphoric Acid to Dentin, Oral Surg Oral
Med Oral Pathol 45:930-945. MITCtIEM,J.C. and TURNER,L.R. (1974): The Retentive Strength of Acid Etch Retained Resin, J Am Dent Assoc 89:1107-1110. OGURA,M. (1989): A Study on Lightcured Composite Resins--Consideration of the Thickness of the Lowpolymerized Zone on the Surface of Composites by Knoop Hardness Measurements, J Nihon Univ Sch Dent 31:156-157. PASHLEY,D.H. (1990): Interaction of Dental Materials with Dentin. In: Proceedings, Conference on EnamelDentin-Pulp Bone Periodontal Tissue, Chicago,Interaction with Dental Materials 3:6. PASHLEY, E.L.; GALLOWAY, S.E.; and
PASHLZY,D.H. (1990): Protective Effects ofCavity Liners on Dentin, Oper Dent 15:10-17. PODSHADELY,A.G.; GULLETT,C.E.; and BINKLEY, T.X. (1988): Interface Strength of Incremental Placement of Visible Light-cured Composites, J Am Dent Assoc 110:932-934. RETIEF,D.H. (1987): Are AdhesiveTechniques Sufficient to Prevent Marginal Leakage?, Oper Dent 12:140-145. RETmF,D.H.;AusTIN,J.C.; andFAvrI,L.P. (1974): Pulpal Response to Phosphoric Acid,J Oral Pathol 3:114-122. TORSTENSON, B. and BRANNSTROM, M. (1988): Composite Resin Contraction Gaps Measured with a Fluorescent Resin Technique, Dent Mater 4:238-242.
278 Ben.Amar et al. / Water spray effect on lining materials and their adhesion to composite and dentin cavity walls
Abstract--The effect of an air-water spray on the adhesion of lining materials to both overlying composite restorations and cavity walls was evaluated. An in vitro study was performed on extracted molar teeth: Two resinous light-cured liners and one calcium hydroxide, chemically activated liner were compared. Teeth were restored with composite materials and subjected to cyclic thermal changes so that microleakage could be evaluated. Results indicated that adaptation between the restorative material and the liner was effective, regardless of whether the oxygen-inhibited layer was removed by being rinsed. A definite gap was detected between the Fners tested and the dentin cavity walls.
he application of liners under composite restorations is an accepted procedure. The liner should adhere to dentin cavity walls and provide protection to the dentin-pulp complex by covering the smear plugs and sealing the dentinal tubuli against chemical irritants and bacterial invasion (Pashley et al., 1990). Calcium hydroxide or glassionomer liners are activated either chemically or by visible light. An ideal cavity liner should adhere to the dentin cavity walls rather than to overlying composite restorations. The liner should not be pulled away from the dentin by contraction forces of the composite during polymerization, since this creates a fluid-filled space between liner and dentin. The combination of an imperfect gingival seal with no adhesion of liners to dentin cavity walls can lead to bacterial invasion. Bacteria and their toxins can reach the pulp by diffusion, causing pulpal inflammation. Light-cured liners usually contain a resin that leaves an oxygen-inhibited layer alter being cured. This layer remains partially polymerized (Ogura, 1989) as the atmospheric oxygen terminates growing chains of the free radicals ofthe resin (Lambrechts, 1983). This incompletely polymerized layer reacts chemically with the subsequent layer of the restorative composite. This layer should not be removed before the composite restoration is placed, based on the rationale that monomers present in the incompletelypolymerizedlayer of the liner co-polymerize with the composit~ restoration, thereby increasing the adhesion. Prior to the placement of composite, etching and rinsing procedures are performed to increase the mechanical bond of the cured resin to the etched enamel, which substantially reduces microleakage (Hembree and Andrews, 1976; Retief, 1987; Mitchem and Turner, 1974). Since the pulp may be irritated by the etchant (Retiefet al., 1974; Macko et al., 1978), it is logical for the liner to be placed before the etching and rinsing procedures, since the liner acts as a mechanical barrier against acid pen-
T
etration into the tubuli. The oxygeninhibited surface layer of the liner is actually washed away during rinsing, along with the etchant. The purpose of this study was to evaluate the effect of an air-water spray on the interface between the liner and the composite restoration, by means of SEM examination and assessment of dye penetration following a thermocycling procedure. MATERIALS AND METHODS
A total of 30 freshly extracted human molar teeth was selected. The teeth were cleaned with periodontal curettes and polished with a pumice/water slurry and a soi~ rubber cup in a slow-speed handpiece. Two separate cavities (MO and DO), with a gingival wall located 1 mm occlusal to the CEJ, were prepared by use of a #330 tungsten carbide bur in a high-speedhandpiece with an air-water spray in the following dimensions: occlusal depth, 2 ram; occlusal width, 2 ram; axial depth, 2.5 mm; and box width at the gingival wall, 4 ram. No bevel was prepared. The cavities were treated with 20% polyacrylic acid (Polyacrylic Dentin Conditioner, Ultradent Products Inc., Salt Lake City, UT) for 10 s, rinsed with water for 20 s, and dried. Teeth were then randomly divided into three groups, according to the lining material used. Group 1: Cavalite--light-cured lining material (Light Activated Cavity Liner, Kerr Manufacturing Co., l~mulus, MI). Group 2: Ultrablend--light-cured calcium fluoride liner (Ultrablend; Ultradent Products Inc., Salt Lake City, UT). Group 3: Life chemically activated calcium hydroxide lining material (Kerr Manufacturing Co., Romulus, MI)-control group. Each group was then further subdivided: Subgroup a: Enamel walls were etched and cavities rinsed with an airwater spray for 20 s after the liner was applied. Subgroup b: Enamel walls were
274 Ben-Amar et al./ Water spray effect on lining materials and their adhesion to composite and dentin cavity walls
etched and rinsed with an air-water spray for 20 s before the liner was applied. Lining materials were applied to the axial and pulpal walls of the cavities. Life and Cavalite liners were applied by means of a small applicator. Ultrablend was applied directly from the syringe by means of the needle provided by the manufacturer. Cavalite and Ultrablend were cured for 40 s in the Elipar II lightcure unit (ESPE GmbH & Co., D-8031, Seefeld, Germany), while Life was untouched for three min. Etching was carried out for 30 s by use of a gel etchant of 37% phosphoric acid applied directly with a syringe. The etchant was then rinsed with water for 20 s and dried. The bonding material was light-cured Scotchbond (3M Dental Products Division, St. Paul, MN) applied to the etched enamel and dentin walls, and gently spread with a stream of air before being cured for 20 s. A hybrid posterior composite (Light-Cured LC1000 Posterior Composite, Southern Dental Industries Ltd., Bayswater, Victoria, Australia) was incrementally inserted (in three layers) and each layer cured for 40 s, first from an occlusal and then from a proximal direction. Finishing was carried out with use of white alpine stones and a water spray at high speed, followed by polishing with Soflex discs (3M Co., St. Paul, MN) in a slow-speed handpiece. The restored teeth were kept in tap water for seven d at 37°C, and then thermocycled 100 times in temperaturecontrolled water baths, between 5°C + 2°C and 55°C + 2°C for 10 s at each temperature, with a 10-second dwell time between immersions. Apices in all teeth were sealed with acrylic. The other surfaces, except for the restorations and their margins, were coated with two layers of nailvarnish, then immersed in 0.5% Basic Fuchsin dye for 24 h, rinsed, and dried. Each tooth was sectioned mesiodistally along the center of the restoration by means of an Isomet saw (Isomet saw, Buehler Ltd., Evanston, IL). The sections were examined in a binocular microscope and a stereomicroscope (Wild M8, Wild Leitz Ltd., Heerbrugg, Switzerland) and evaluated for dye penetration and for the adaptation ofthe liners to the restorative material. Dye penetration was evaluated between the cavity walls and the restorative materials, the liner and the dentin wall, the liner and the composite, and at
Fig. 1. Perfect adaptation between the resin liner and composite (without the liner being rinsed). C = composite, I = junction between liner and restoration, and L = resin liner.
Fig. 2. Perfect adaptation belwee~the resin liner and composite (the liner was rinsed before the overlying composite was inserted). C = composite; L : resin liner.
the gingival wall, according to the scale shown in Table 1. Three sections in each group were prepared and examined by SEM (JSM-840A, JEOL, Japan), at numerous points at x200 and x400. The sections were examined for gap width between the liners and dentin cavity walls, and, for adaptation, between the liners and overlying composite. Photomicrographs were taken.
The results were evaluated by Student's t test at the composite/gingival wall interface, and paired t test for the other groups. RESULTS
Binocular and stereomi."croscope examination revealed an almost perfect adaptation between the restorative material and cavity liners and between cavity
Dental Materials / October1991 275
tween the liner and restoration, regardless of the rinsing procedure. A gap of 320 p. was found between the liners and dentin cavity walls in all sections (Fig. 3). Rinsing the cavity and lining materials before insertion of the composite had no effect on their adhesion to each other compared with the restored teeth, where the lining materials were not rinsed before restoration. There was a higher leakage assessment at the gingival wall when no rinsing was carried out, but this was not statistically significant. DISCUSSION
Fig. 3. A gap between the liner (L) and dentin cavity wall (D).
The oxygen-inhibited layer created on the superficial surface of the resinous light-cured materials is, at present, considered to be important for the adaptation of liners to the composite restorative material. This study evaluated the effect of the oxygen-inhibited layer on the adaptation of liners to the restorative material and to the axial and pulpal walls of the preparation. When an air-water spray was used for 20 s on the light-cured lining material, the shiny oxygen-inhibited layer was removed, and a non-glossy adherence was observed. It was expected that the removal of this shiny surface would prevent or reduce the adhesion of the restorative material to the liner and that the shrinkage of the composite restoration toward the light source during polymerization would create a gap between the cured restoration and the liner. In sections where a hard-setting Ca(OH) 2 liner (Life) was applied and rinsed with an air-water spray before the composite was inserted, the outer surface ofthe liner did not appear smooth in relation to the restoration but as an irregular non-homogenous area (Fig. 4). This irregularity was probably the result of surface erosion by the air-water spray.
Fig. 4. Irregular non-homogenous outer surface of the Ca(OH)= liner. Life = DY, D = dentin, and C = composite. A gap between the liner and dentin cavity wall.
liners and axial and pulpal walls in all groups tested. There was no significant difference between groups tested in the degree of dye penetration at the gingival margins (p > 0.05), whereas minimal gingival dye penetration was found at the tooth/composite interface, and no leakage was found at the pulpal floor. Dye penetration at the gingival wall did not reach more than halfway between
the DEJ and the axial wall (Table 2). SEM examination revealed that, in all groups where resinous light-cured liners were used (Cavalite and Ultrablend), there was near-perfect adaptation between the liners and cornposite, regardless of whether liners were rinsed with an air-water spray (Figs. 1 and 2). Sections with hard set Ca(OH)2 liner (Life) showed less adaptation be~
TABLE 1
CATEGORIES OF DYE PENETRATIONAT THE GINGIVALWALLS OF THE RESTORATIONS Category Dye Penetration
0 1
No dye penetration
2
Dyepenetrationupto halfofthedentinalwall
3
Dye penetrationup to the axialwall
Dye penetrationup to DEJ
276 Ben-Amar et al./Water spray effect on lining materials and their adhesion to composite and dentin cavity walls
Despite the irregularity, near-perfect adaptation between the liner and the compositewas still achieved. Ameasurable gap was not visible in most sections (85%); in the other samples (15%), a gap ofup to 1 11wasmeasured. It is assumed that this phenomenon has no clinical significance for bacterial penetration, since many bacteria range in size from 1-3 ~m (Pashley, 1990). Where the superficial surface of the calcium hydroxide liner was not rinsed, sections showed perfect adaptation between the liner and the restoration, without any regularity of its superficial surface. A gap of 3-20 ~twas detected between the liner and dentin cavity walls in all groups (Figs. 3 and 4). The rinsing procedure had no effect on the creation of these gaps. In general, no difference in gap width was found with Ca(OH)~liners and dentin and the resinous light-cured liners and dentin (3-15 ~ and 5-20 ~t, respectively) (p > 0.05). The gap creation between the resin liners (Cavalite and Ultrablend) and the dentin cut surface could be explained by their contraction toward the ligh~ source. In addition, polymerization of the composite draws the liner toward it, further away from the dentin. Ca(OH) 2 liner, not being a resin, has no chemical bond with the composite material. Therefore, the poly-merizationcontraction forces ofthe composite have no effect on these liners. When hardened, chemically activated Ca(OH) 2 liners have negligible contraction and dimensional change. Since no significant gaps were found between Life and the composite restoration, this suggests that, by use of an
incremental technique, the amount of shrinkage of the compositeis reduced by progressive curing of each increment. This technique provides relatively good adaptation between the liner and the restorative material and limits microleakage at the gingival walls ofthe restorations (Podshadely et al., 1988; Leclaire et al., 1986). All available composite materials contract during polymerization. As a result, a small degree of dye penetration at the gingival cavity wall was evident in all groups tested. Dye penetration did not exceed half the distance from the cavosurface margin to the axial wall in any of the samples. Slightly deeper dye penetration was found at the gingival wall (Subgroup b), where the enamel walls were etched and rinsed before the liner was applied, compared with samples where the liners were rinsed by an air-water spray before the composite was inserted (Subgroup a). No significant statistical differences were found between these two subgroups (p > 0.05). Since dye penetration did not reach the axial or pulpal walls, it could not be used to evaluate the degree of microleakage at other interfaces: liner/composite, or liner/dentin walls. Thus, a SEM study was conductedto evaluate the gap width at these sites. In the enamel of the gingival wall, the resin bonding served as an adhesive agent for composite to dentin. The liners had no influence on dye penetration at that specific area, since they did not reach the enamel section of the wall. The gingival cavity walls were located 1 mm occlusal to the CEJ, where the amount of enamel is reduced, and thus
the bond strength to dentin is not sufficient to withstand the contraction forces associated with polymerization (Torstenson and Br~nnstrSm, 1988). This usually results in a small gap at the cervical cavity wall (Gross et al., 1985). The results of this study showed no significant differences between the groups tested. However, it is recommended that an acid-etch technique be used (on enamel cavity margins) with appropriate rinsing of the etchant after the liner is applied. This liner prevents possible damage by the etchant to the dentino-pulpal complex by creating a physical barrier that seals the tubuli. CONCLUSIONS
The results ofthis in vitro study indicate that: (1) the removal of the incompletely polymerizedoxygen-inhibitedlayer from the superficial surfaces ofthe light-cured resinous liners, before insertion of the composite material, does not have a detrimental effect on the adhesion of the liners to the compositematerial or to the dentin cavity wall; (2) the air-water rinsing procedure can affect the outer surface of the chemically activated, hard-setting Ca(OH), liner; and (3) all liners tested (in scanning electron micrographs) exhibited a gap between the liners and dentin cavity walls. REFERENCES
GROSS,J.D.; RETIEF,D.H.; and BRADLEY, E.L. (1985): Microleakage of Posterior Composite Restorations, Dent Mater 1:7-10. HEMBRE~, J.H., JR. and ANdReWS,J.T.
TABLE 2
DEGREEOF DYE PENETRATION Dye Penetration Liqer/axialwall Liner/pulpalw a l l of the cavity of the cavity
Grouptested
Presenceof oxygeninhibited layer (n = 10)
Composite restoration/ gingival wall of the cavity
Group No. 1
-"
0
0
0
0
Cavalite
++
1
0
0
0
Group No. 2
-'
1
0
0
0
Ultrablend
++
1.5
0
0
0
Group No. 3
Rinsingthe liner
1
0
0
0
Life No rinsingthe liner 1.5 0 "-: Rinsingof the liner. The oxygen-inhibitedlayer was removed from the liner. *+: No rinsingof the liner. The oxygen-inhibitedlayer exists on the outer surface of the liner.
0
0
Liner/composite interface
Dental Materials~October 1991 277
(1976): In vitro Microleakage of Several Acid Etch Composite Systems, IADR Prog & Abstr 55 (Spec Iss B): Abst. No. 309. LA~mRECHTS,P. (1983): Basic Properties of Dental Composites and Their Impact on Clinical Performance, Leuven, Belgium: Katholieke Universiteit, p. 35. LZCLAIRE, C.C.; B~, L.W.; HARGRAVZ, J.W.; and PELLZU, G.B.,JR. (1986): A 2-Stage Composite Resin Filling Technique and Microleakage Below the CEJ, JDent Res 65:248,Abstr.No. 799.
MACKO, D.J.; RUTHBERG, M.; and LANGZLASD, I~ (1978): Pulpal Response totheApplicationofPhosphoric Acid to Dentin, Oral Surg Oral
Med Oral Pathol 45:930-945. MITCtIEM,J.C. and TURNER,L.R. (1974): The Retentive Strength of Acid Etch Retained Resin, J Am Dent Assoc 89:1107-1110. OGURA,M. (1989): A Study on Lightcured Composite Resins--Consideration of the Thickness of the Lowpolymerized Zone on the Surface of Composites by Knoop Hardness Measurements, J Nihon Univ Sch Dent 31:156-157. PASHLEY,D.H. (1990): Interaction of Dental Materials with Dentin. In: Proceedings, Conference on EnamelDentin-Pulp Bone Periodontal Tissue, Chicago,Interaction with Dental Materials 3:6. PASHLEY, E.L.; GALLOWAY, S.E.; and
PASHLZY,D.H. (1990): Protective Effects ofCavity Liners on Dentin, Oper Dent 15:10-17. PODSHADELY,A.G.; GULLETT,C.E.; and BINKLEY, T.X. (1988): Interface Strength of Incremental Placement of Visible Light-cured Composites, J Am Dent Assoc 110:932-934. RETIEF,D.H. (1987): Are AdhesiveTechniques Sufficient to Prevent Marginal Leakage?, Oper Dent 12:140-145. RETmF,D.H.;AusTIN,J.C.; andFAvrI,L.P. (1974): Pulpal Response to Phosphoric Acid,J Oral Pathol 3:114-122. TORSTENSON, B. and BRANNSTROM, M. (1988): Composite Resin Contraction Gaps Measured with a Fluorescent Resin Technique, Dent Mater 4:238-242.
278 Ben.Amar et al. / Water spray effect on lining materials and their adhesion to composite and dentin cavity walls
