By J. GEIRSSON, A.V. RITTER, H.O. HEYMANN, and E.J. SWIFT Jr. Department of Operative Dentistry, University of North Carolina at Chapel Hill

This investigation evaluated the in vitro bond strengths of a new light-cured self-etching one-bottle dental adhesive (iBond, Heraeus Kultzer) when applied to 600-grit polished bovine enamel and dentin surfaces. The control materials were Gluma Comfort Bond + Desensitizer, a "traditional" etch-and-bond one-bottle light-cured dental adhesive, and Prompt L-Pop, a commercially available "self-etching" light-cured adhesive. Sixty bovine incisors were mounted in phenolic rings with cold-cure acrylic resin. The labial surface of each tooth was ground to expose enamel (n=30) and dentin (n=30). A resin-based composite (Charisma) post was bonded to the treated enamel or dentin surface, and bond strengths were determined in shear mode 24 hr after bonding using an Instron universal testing machine. Means shear bond strengths varied from 17.02 MPa (Gluma Comfort Bond + Desensitizer, dentin) to 5.11 MPa (Prompt L-Pop, dentin). iBond resulted in bond strengths to enamel that were not statistically different than the enamel bond strengths obtained with Gluma Comfort Bond + Desensitizer and with Prompt L-Pop. In dentin, iBond produced bond strengths significantly higher than Prompt L-Pop, and significantly lower than Gluma Comfort Bond + Desensitizer. iBond bond strengths to enamel and dentin were comparable. In conclusion, the new light-cured self-etching adhesive iBond provides similar bond strengths to enamel, but lower bond strengths to dentin, than a proven "etch-and-bond" adhesive.

INTRODUCTION

The purpose of this in vitro study was to determine the enamel and dentin bond strengths of a new experimental self-etching light-cured dental adhesive system (iBond, Heraeus Kulzer), and to compare it to a "etch-and-bond" one-bottle adhesive (Gluma Comfort Bond + Desensitizer, Heraeus Kulzer) and to a "self-etching" dental adhesive (Prompt L-Pop, 3M ESPE, St Paul, Minnesota).

Chemical Compositions

Product/Manuf. Composition Batch #
iBond (Heraeus Kulzer) UDMA, 4-META Acetone, H2O #VP050901Ge2 Exp. date: 09/2003
Gluma Comfort Bond + Desensitizer (Heraeus Kulzer) UDMA, 4-META, HEMA, Maleic Acid, Polycarboxylic acid ester, Glutardialdehyde, Ethanol, H2O #010035 Exp. date: 05/2003
Gluma Etch 20 (Heraeus Kulzer) 20 % Phosphoric Acid, H2O #135032 Exp. date: 03/2003
Prompt L-Pop (3M ESPE) Methacrylated phosphoric esters, H2O #113472 Exp. date: 11/2002
Charisma A2 (Heraeus Kulzer) Micro-hybrid composite #L-39 Exp. date: 11/2003

MATERIALS AND METHODS

Sixty bovine teeth refrigerated in a solution of 0.5% Chloramine T (Fisher Scientific) for up to three days after extraction were used in this study. The teeth were cleaned of debris and mounted in phenolic rings (Buehler Ltd., Lake Bluff, Illinois) with cold-cure acrylic resin (Trayresin, Dentsply York Division, York, Pennsylvania). The labial surface of each tooth was ground with an Isomet mechanical grinder (Buehler Ltd.) to expose dentin (30 specimens) or enamel (30 specimens) and was subsequently polished for 1 minute with wet 240-, 400-, and 600-grit silicon carbide abrasive paper (Buehler Ltd.). Specimens were randomly assigned to six experimental groups (n=10), and treated as follows:

Group 1 - iBond, enamel

The prepared enamel was conventionally air-dried. Immediately after dispensing, copious amounts of iBond were applied to the entire enamel surface with a microbrush in three coats. The coated surface was left undisturbed for 30 s. iBond was spread carefully with a gentle stream of oil-free air to volatilize solvent (distance of air syringe: 2 cm), until no movement of the adhesive film was detectable. Air-drying was continued for a few seconds to volatilize the solvent without removing the active ingredients from the surface. Surface was visibly glossy, both after application of iBond and after evaporation of the solvent. Coverage of the entire enamel surface was ensured. If the enamel surface did not appear shiny, additional coats of iBond were applied as described above. iBond was light-cured for 20 seconds with a Translux Energy (Heraeus Kulzer) halogen light-curing unit


Group 2 - Gluma Comfort Bond + Desensitizer, enamel.

The prepared enamel was etched with 20% phosphoric acid (Gluma Etch 20 gel etchant, Heraeus Kulzer) for 30 sec and then rinsed with water for 15 sec. Excess water was blotted with tissue paper (Kimwipes EX-L,Kimberly-Clark Corp., Roswell, Georgia), leaving the surface visibly moist. Gluma Comfort Bond + Desensitizer (GCBD) adhesive was applied immediately to the etched enamel surface in three consecutive coats, leaving the surface wet and undisturbed for 15 sec. The solvent and excess water were evaporated with a gentle stream of oil-free compressed air from an air syringe (for approx. 3-15 s.), keeping the air syringe 2 cm from the surface. If the surface didn't look uniformly shiny additional coats of adhesive were applied. The adhesive was light-cured for 20 sec with a Translux Energy halogen light-curing unit


Group 3 - Prompt L-Pop, enamel.

The prepared enamel was blotted with a tissue paper, leaving the surface visibly moist. Prompt L-Pop adhesive was applied with agitation to the surface for 15 s. The adhesive was gently air-dried with oil-free compressed air from an air syringe for 2 sec, keeping the air syringe 2 cm from the surface, and light-cured for 10 sec with a Translux Energy halogen light-curing unit.

Group 4 - iBond, dentin.

Immediately after dispensing, copious amounts of iBond were applied to the entire dentin surface with a microbrush in three coats. The coated surface was left undisturbed for 30 s. iBond was spread carefully with a gentle stream of oil-free air to volatilize solvent (distance of air syringe: 2 cm), until no movement of the adhesive film was detectable. Air-drying was continued for a few seconds to volatilize the solvent without removing the active ingredients from the surface. Surface was visibly glossy, both after application of iBond and after evaporation of the solvent. Coverage of the entire dentin surface was ensured. iBond was light-cured for 20 seconds with a Translux Energy halogen light-curing unit.

Group 5 - Gluma Comfort Bond + Desensitizer, dentin.

The prepared dentin was etched with 20% phosphoric acid (Gluma Etch 20 gel etchant, Heraeus Kulzer) for 20 sec and then rinsed with water for 15 sec. Excess water was blotted with tissue paper (Kimwipes EX-L, Kimberly-Clark Corp.), leaving the surface visibly moist. GCBD adhesive was applied immediately to the etched dentin surface in three consecutive coats, leaving the surface wet and undisturbed for 15 sec. The solvent and excess water were evaporated with a gentle stream of oil-free compressed air from an air syringe (for approx. 3-15 s.), keeping the air syringe 2 cm from the surface. The dentin surface looked uniformly shiny, otherwise additional coats of adhesive were applied. The adhesive was then light-cured for 20 sec with a Translux Energy halogen light-curing unit.

Group 6 - Prompt L-Pop, dentin.

The prepared dentin was blotted with a tissue paper, leaving the surface visibly moist. Prompt L-Pop adhesive was applied with agitation to the surface for 15 s. The adhesive was gently air-dried with oil-free compressed air from an air syringe for 2 sec, keeping the air syringe 2 cm from the surface, and light-cured for 10 sec with a Translux Energy halogen light-curing unit.

A resin-based composite (Charisma, A2, Heraeus Kulzer) was applied to the treated surface with a #5 gelatin capsule (Torpac Inc., Fairfield, New Jersey). The capsule was seated securely against the surface, excess material was removed, and the composite was light-cured for a total of 160 sec (40 sec from each perpendicular direction) using a Translux Energy (Heraeus Kulzer) curing light. The intensity of the light was monitored with a Curing Radiometer (Demetron/Kerr, Danbury, Connecticut), to be in excess of 500 mWcm2. After 24 h in distilled water at 37ºC, the shear bond strengths were measured with an Instron Universal Testing Machine model 4411 (Instron Co., Canton, Massachusetts) using the MTS Testworks (MTS, Eden Prairie, Minnesota) software to record the data. A blunted knife-edge-shearing rod with a crosshead speed of 0.5 cm/min was used to load the specimens until fracture. The distance from the probe to the dentin surface was monitored using a spacer of two celluloid matrices. Shear bond strengths (SBS) were determined in MPa by dividing the bonded area (4.5mm - capsule internal diameter) by the force needed to de-bond the specimens. The data were subjected to one-way ANOVA. Tukey HSD post-hoc test was applied because ANOVA revealed statistical differences among the groups. The significance level was set at p=0.05.

RESULTS

Mean shear bond strengths (± standard deviation) and statistical grouping are shown in the Table:

Material Substrate Mean SBS# SD Statistics*
GCBD Enamel 15.32 2.2 AB
iBond Enamel 12.24 2.66 BC
Prompt LP Enamel 11.67 0.8 BC
GCBD Dentin 17.02 3.72 A
iBond Dentin 11.15 3.36 C
Prompt LP Dentin 5.11 3.43 D
#n=10; *p=0.05 [ANOVA + Tukey HSD post-hoc)Means with the same letter are not statistically different

The following graph illustrates the results for comparison reasons:

DISCUSSION

For both enamel and dentin substrates, the highest mean bond strength values were obtained with Gluma Comfort Bond + Desensitizer (GCBD), followed by iBond. Prompt L-Pop resulted in the lowest mean bond strengths for both enamel and dentin. For GCBD, there was no statistical significant difference between enamel and dentin bond strengths (15.32 MPa vs. 17.02 MPa respectively, p=0.77). iBond presented a similar result, with no statistical significant difference bond strengths to dentin as compared to enamel (12.24 MPa vs. 11.15 MPa respectively, p=0.96). For Prompt L-Pop, bond strengths to enamel were significantly higher than to dentin (11.67 MPa vs. 5.11 MPa respectively, p<0.001).

Upon visual examination of the de-bonded interfaces, most of the fractures were adhesive failures in the bonded interface. Some of the GCBD specimens failed cohesively in dentin. Some of the Prompt L-Pop dentin specimens failed while still in the incubator, which demonstrate poor interaction of the adhesive with the dentin substrate.

iBond proved to be as effective for enamel bonding as the other adhesives tested. iBond enamel bond strengths were statistically equivalent to GCBD and Prompt L-Pop enamel bond strengths. For dentin, iBond proved to be more effective than the other self-etching adhesive tested, and less effective than GCBD. iBond dentin bond strengths were significantly lower than GCBD bond strengths, and significantly higher than Prompt L-Pop bond strengths.

With iBond, SBS to enamel and dentin were higher than for Prompt L-Pop, the difference being statistically significant in dentin.

The enamel bond strengths generated with iBond were not statistically different than the dentin bond strengths generated with iBond.

CONCLUSIONS

The new adhesive iBond provided similar mean bond strength to enamel, but lower mean bond strength to dentin, than the etch-and-bond adhesive. iBond provided significantly higher mean bond strengths to dentin, and similar mean bond strength to enamel, when compared to the control self-etching adhesive.

ACKNOWLEDGEMENTS

This investigation was supported by Heraeus Kultzer.