Comparative evaluation of microshear bond strength of the caries-affected dentinal surface treated with conventional method and chemomechanical method (papain).

BACKGROUND: There is a growing interest in chemomechanical excavation (papain) in permanent molar teeth. There are several studies dealing with primary molar teeth. AIM: The aim of this study was to evaluate the influence of conventional method and Carie-care (chemomechanical method) on the microshear bond strength (μSBS) and the type of failure of an adhesive system to caries-affected dentin of permanent molar teeth.
MATERIALS AND METHODS: Twenty permanent molar teeth with carious lesions extending into the dentin were selected. Through the center of the carious lesion, teeth were sectioned mesiodistally and divided into two groups based on the method of caries excavation (conventional and chemomechanical method). The time required for the completion of excavation procedure was noted. Samples were again divided into two subgroups in each according to the method of restoration (Ketac N100 and Filtek Z350 composite). The bonded interface was subjected to μSBS testing in a universal testing machine. Fractured surfaces were examined under a stereomicroscope, and representative specimens were examined under scanning electron microscope for the type of failure. STATISTICAL ANALYSIS: It was achieved with unpaired t-test and Kruskal-Wallis H-test at 5% level of significance.
RESULTS: The μSBS values of Carie-care groups were similar to that of the conventional method. The μSBSs of resin composite were significantly (P < 0.001) more than that of resin glass ionomer bonded irrespective of the method of caries excavation.
CONCLUSION: A papain-based chemomechanical agent can be used safely as a method for caries removal when employing conventional adhesive systems.

INTRODUCTION

Traditional means of cavity preparation is based on a philosophy of extension for prevention and includes high-speed handpieces and slow rotating instruments. However, this method usually induces pain, annoying sounds, vibration, and removes the healthy tooth structure rendering it less durable in the long run.[1] Therefore, chemomechanical removal of caries has been developed as an alternative to the conventional method.

The chemomechanical method of caries removal was first introduced in 1975 by Habib et al. by using 5% sodium hypochlorite, which was followed by the introduction of GK-101, caridex system, and Carisolv.[234567] However, in view of their certain disadvantages such as short shelf life, high corrosiveness, requirement of specialized instruments, and high cost; a newer product was introduced in Brazil, which is commercially known as Papacarie.[238]

Recently Carie-care system has been introduced in India by Uni-Biotech Pharmaceuticals Pvt. Ltd., which is a papain-based gel formulation that allows the atraumatic chemomechanical removal of caries and allows the maximum preservation of healthy dental structures.[9] The advantage of Carie-care is its ease of application which does not need special instruments.

In the operative treatment of carious lesions in dentin, the morphology and nature of the prepared dentin surface influences the bonding of adhesive restorative materials.[310] Previous studies[111213] speculated that the roughened surface created by chemomechanical caries removal offers better prerequisites for micromechanical retention and resin penetration which results in higher bond strength.

However, little is known about the performance of adhesive restorations on caries-affected dentin that has been prepared with the papain-based system in permanent dentition.

The purpose of this study was to evaluate the influence of conventional method and Carie-care on the microshear bond strength (μSBS) and the type of failure of an adhesive system to caries-affected dentin of permanent molar teeth. The time required for the complete excavation of caries was evaluated.

MATERIALS AND METHODS

A total of 20 freshly extracted human permanent molar teeth with Class I caries were collected and stored in 0.1% thymol solution. Teeth were washed under water, and extrinsic deposits were removed using hand scalars.

Carious lesions extending into the dentin were assessed with Dental Operating Microscope (Carl Zeiss OPMI PICO Surgical Microscope, Germany) and Radio-Visuo-Graphy (Kodak RVG 5100, Care Stream Health, Inc., NY, USA). Roots were removed. Through the center of the carious lesion, teeth were sectioned in the mesio-distal plane using a disk rotating at low speed. Then the samples were (20 teeth, after sectioning leading to 40 samples) divided into four groups randomly.

Group I: Caries excavation done with conventional method and restored with Ketac N100 (A2 shade, 3M ESPE, St. Paul, MN, USA).

Group II: Caries excavation done with conventional method and restored with Filtek Z350 composite (universal restorative, A2 shade, 3M ESPE, St. Paul, MN, USA).

Group III: Caries excavation done with Carie-care gel and restored with Ketac N100.

Group IV: Caries excavation done with Carie-care gel and restored with Filtek Z350 composite.

Groups I and II were treated with the conventional method, caries was removed using round steel burs (sizes 3 and 5) in a slow-speed handpiece. Caries removal was verified visually and tactually; the cavities were examined using magnifying loupes (×2.5) and probed to verify hard dentin.

Groups III and IV were treated with Carie-care (Vittal Mallya Scientific Research Foundation, Bengaluru, Karnataka, India), caries was removed using clear Carie-care gel, according to the manufacturer's directions. The carious lesion was covered with Carie-care gel and left undisturbed for 1 min. When the gel was cloudy, it was removed gently by scraping with spoon excavator after which additional fresh gel was applied to the excavation site. The procedure was repeated until the gel was clear, caries removal was complete, and the dentin was hard on probing. Meanwhile, time for completion of excavation procedure was noted for all the groups.

The prepared specimens were examined to find a flat surface suitable for testing; this was placed in contact with a glass slide and attached with sticky wax around the specimen periphery. A plastic ring (internal diameter 15 mm) was placed around the specimen and filled with an acrylic resin block. When the acrylic was set, the glass slide and sticky wax were removed, providing a flat dentinal surface ready for bonding.

Groups I and III were restored with resin-modified glass ionomer cement (RMGIC). Dentin conditioner was applied and a PVC tube (internal diameter = 0.97 mm, 2 mm high; Microtube Extensions, Sydney, Australia) was placed on the dentin surface and light-cured together with the adhesive for 10 s. The tube was filled with RMGIC and light-cured for 20 s. The tube was removed with a number 11 scalpel blade, leaving a 2-mm high resin cement rod bonded perpendicularly to the dentin.

Groups II and IV were restored with resin composite. Dentin surfaces were etched with 37% phosphoric acid (3M ESPE, St. Paul, MN, USA) for 15 s, rinsed with distilled water, and the excess was removed with absorbent paper, to leave the dentin visibly moist. An adhesive, 3M ESPE Single Bond (SB; 3M ESPE, St. Paul, MN, USA), was applied to all prepared areas of specimens according to the manufacturer's directions with a microbrush tip and a PVC tube (internal diameter = 0.97 mm, 2 mm high) was placed on the dentin surface and light-cured together with the adhesive for 20 s. The tube was filled with resin composite and light-cured (Monitex GT 1200, Taiwan) for 40 s, and then the tube was removed. All specimens were stored in distilled water at 37°C for 24 h prior to testing.

The bonded interface was subjected to μSBS testing in an universal testing machine (DL 2000; Emic Sao Jose de Pinhas, PR, Brazil) with a loop of ligature wire (Unitex, diameter 0.009 inches, TP Orthodontics, Leeds, UK) delivering a force parallel to the bonded surface at a crosshead speed of 1.0 mm/min. The μSBS values were calculated for each specimen using the formula:

Microshear bond strength (MPa) = shear force (N)/cross-sectional area (mm2)

Fractured surfaces were examined under a stereomicroscope, and digital images were obtained. Failures were classified as: Adhesive failure; cohesive dentinal failure; cohesive resin failure; or a mixed failure.

The stereomicroscopic images were studied, and representative specimens were retrieved from the plastic ring, air-dried for 2 days on filter paper, mounted on an aluminum stub with conductive silver liquid, gold sputter-coated, and examined using a field-emission scanning electron microscope (SEM) (Philips XL 30 FEC, Eindhoven, The Netherlands). The data were analyzed by unpaired t-test and Kruskal-Wallis H-test at 5% level of significance.

RESULTS

A unpaired t-test revealed that the time taken by Groups III and IV was significantly (P < 0.001) more than Groups I and II as shown in Table 1.

Table 1

Comparison of mean time (seconds) required for removal of caries for different caries removal techniques

Table 2 shows the multiple group comparisons between groups using unpaired t-test and revealed that the μSBSs between Groups I and II, Groups I and IV, Groups II and III, and Groups III and IV was statistically significant (P < 0.001). Whereas μSBSs between Groups I and III, Groups II, and IV was statistically insignificant.

Table 2

Comparison of mean microshear bond strength values (in MPa) of caries affected dentin after different caries removal techniques

Kruskal-Wallis H-test revealed that most of the failures were adhesive failures (70%). However, there was no statistically significant difference (P = 0.999) among different groups as shown in Table 3.

Table 3

Comparison of distribution of modes of failure of resin composite bonded to permanent tooth dentin following different caries removal techniques

DISCUSSION

The mean time taken for caries removal by Groups III and IV (Carie-care method) was significantly more than Groups I and II (conventional method). The results of this study are in accordance with studies[21415] who recorded 5.4 min2, 6 min,[14] and 5.5 min,[15] respectively, for caries removal using Papacarie®. The reason for the increased time in the present study may be because multiple applications of Carie-care gel were done to achieve complete caries removal. As per the manufacturer, each application of papain gel should be of 60 s. However, at the end of single application complete caries excavation was not evident and which required two to three applications.

However, according to an in vivo study,[16] it was mentioned that time taken with initial few cases was much higher than the conventional method. However, with time and development of expertise the reverse took place with papain gel taking lesser time.[17]

In the clinical scenario, the conventional method of caries removal includes: The administration of local anesthesia followed by the removal of caries which will be equal to that of the chemomechanical method of caries removal. In in vitro studies, this time factor was not taken into account, and chemomechanical method showed more time to complete the procedure compared to conventional method.

The results of μSBS values of this study are in accordance with a study,[18] which recorded 10.83 ± 4.69 MPa and 10.87 ± 5.97 MPa, respectively, for the shear bond strength of resin composite to caries-affected dentin after caries removal using conventional method and Papacarie®. Similarly, another study[19] recorded 13.9 ± 2.4 MPa and 10.9 ± 2.3 MPa, respectively, for the tensile bond strength of resin composite to caries-affected dentin after caries removal using conventional method and Papacarie®.

Carie-care, a gel based on papain, chloramines, and toluidine blue, however, is inexpensive compared with Carisolv and has a similar use, indication and chemomechanical caries removal efficiency. Papain makes it easy to clean necrotic tissues and secretions and reduces tissue repair time, in addition to not affecting sound tissues close to the lesion.[8] This substance lacks a plasmatic antiprotease — antitrypsin — which prevents its proteolytic action on tissues that are considered normal. It is also considered a chemical debridement agent, which helps in the healing process and acts as an anti-inflammatory agent.[818] Chloramine helps to soften the carious dentin, thus facilitating its removal from the degraded portion of the carious dentin collagen is colored by the solution used in chemical and mechanical caries removal. This product has antimicrobial effectiveness mainly regarding Streptococcus mutans and Lactobacillus and is biocompatible with oral tissues.[18]

It was suggested that changes in bond strength values after the use of chemical agents to remove carious lesion may occur due to micromorphologic alterations. Using SEM, the presence of a residual smear layer was detected on the dentinal surfaces of permanent teeth treated with conventional techniques. In comparison, the surfaces treated with Papacárie® exhibited two different patterns of remaining dentin. A regular and “cracked” surface can be observed, with little smear layer and exposed dentinal tubules in some regions. It can also result in a very irregular and rough surface covered by an amorphous layer indicating the presence of smear layer obliterating the dentinal tubules.[20] Nevertheless, the present study used an adhesive system that involves the application of phosphoric acid on all of the dental substrate. This may remove the entire smear layer, giving the dental substrate an irregular appearance after the use of the chemomechanical agent. Self-etching adhesive systems are requiring the use of a weak acid, however, do not completely remove the smear layer to form the hybrid layer. When using these systems, different results can be expected than those found in this research.

Morphological studies have shown that chemomechanically treated surfaces showed the consistent removal of smear layer and exposed dentinal tubules of the carious dentin. In a study[21] where an estimate of smear plug formation was attempted by counting occluded tubules showed that on permanent dentin, Carisolv left a smear layer occluded tubules similar to that seen following rotary instrument.

However, in the present study, there were no statistical difference in the μSBSs of resin composite to caries-affected dentin prepared with the mechanical and chemomechanical method. This is in accordance with the studies which showed the chemomechanical method did not influence the bond strength.[2223242526]

For the specimens restored with RMGIC, the μSBS did not vary significantly in both the experimental groups. This is in accordance with the study,[24] where the shear bond strength of two glass ionomers bonded to dentin after caries removal either with caridex or conventional method was evaluated.

A unpaired t-test revealed that the resin composite groups showed significantly (P < 0.05) higher shear bond strength values compared to resin modified glass ionomer groups, irrespective the method of caries excavation. This is in accordance with a study,[27] where shear bond strength value of composite resin has the higher value (9.84 ± 1.06 MPa) than both resin reinforced glass ionomer (6.99 ± 1.28 MPa) and conventional glass ionomer cement (4.05 ± 0.73 MPa) after 24 h.

The selected samples of the tested specimen were analyzed under SEM to evaluate the mode of failure. The dominant failure modes in the present study were adhesive failures (70%) in Groups I, II, and III whereas 80% in Group IV. The predominance of adhesive failures for the carious dentin groups is probably related to the difficulty of the bonding resin to infiltrate into the exposed, altered collagen mesh. The lack of correlation in shear bond strength between the failure mode and treatment type seen in the present study supports observations of others,[41028] suggesting that failure mode may relate more to the restorative material than treatment type.

In future studies should focus on the long-term evaluation of the bond quality and the assessment of other modern adhesives such as self-etching primers and all-in-one adhesive systems. As the Papacarie gel can preserve the healthy collagen in affected dentin, the hybridization of this dentin with bonding agents containing nano-bioactive agents might improve the bond strength and clinical durability of the bond. Further research can be aimed at this.

CONCLUSION

Within the limitations of this study, we can conclude that, papain-based chemomechanical agent can be employed more conveniently in patients with anxiety and psychological distress as it is equally efficient as mechanical preparation when conventional adhesive systems are used.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.