Effect of caries excavation by Carisolv and SmartPrep burs on dentin hardness — An in vitro study

INTRODUCTION

Globally, dental caries is the most common non-communicable disease posing a major public health hazard.^[1] The advent of adhesive restorative materials coupled with alternative therapeutic approaches has ushered in the era of minimal intervention dentistry. The guiding principle, here, is to “do no harm” as put forward by Hippocrates oath in the field of medicine and dentistry.^[3] Keeping in tune with this concept, we are now welcoming “minimal Hazardous Dentistry” that is retaining as much as natural tooth structure as possible.

During the operative treatment of carious dentin, only the superficial layer (infected dentin/soft dentin) which is heavily infected and softened requires removal before restoration placement. The affected layer (firm dentin) is partially demineralized but not contaminated with bacteria. This layer of carious dentin can be remineralized and should be preserved.

Conventionally, a round tungsten carbide bur has been employed to facilitate caries excavation and is one of the most effective methods. However, the problems are as follows: Fear of drill, noise, vibrations, pain, and discomfort while removing carious dentin.^[2] Added to that is the possibility of uncontrolled dentin removal due to a lack of tactile feedback.

More patient-friendly minimally invasive approaches like a chemomechanical caries removal (CMCR) method – Carisolv and SmartPrep burs were therefore used in this study.

CMCR is a non-invasive technique of eliminating only the infected dentin through a chemical agent.^[4] They chemically dissolve the degraded soft collagen in the infected dentin which can gently be excavated with negligible discomfort to the patient. At the same time, the affected demineralized dentin which is remineralizable, can be safely preserved. It is designed to reduce the need for anesthesia, maintain tooth structure, reduce the use of rotating devices, and effectively relieve anxiety.^[5] Specialized hand instruments with permanent or interchangeable tips are used to remove the carious tissue layer by layer. Compared to manual excavation, Carisolv is a promising technique for occlusal caries removal.

The agent that is used in the present study is Carisolv gel which can be applied to the carious lesion and using specially designed hand instruments the soft dentin can be peeled away without causing any pain.

SmartPrep burs are ceramic burs made of polyamide polymer. They are self-limiting in their action, capable of only removing the soft infected dentin. In contact with affected or normal dentin, they lose their cutting efficiency. This bur system is designed to distinguish healthy dentin from carious dentin based on the hardness of sound dentin and was developed to remove decayed dentin without harming healthy tooth structure. It is combined with a specially designed polymer to remove carious dentin without harming healthy tooth structure. The bur’s minute polymer flutes wear away as they come in contact with healthy hard dentin. This self-limiting characteristic helps to ensure that unhealthy dentin is removed carefully.^[6]

Hardness tests can serve as objective clinical markers to differentiate between infected, affected, and non-carious dentin. Vickers hardness test is a simple, reliable, and quick method of assessing the hardness of brittle materials like tooth structure. The hardness of dentin might be a useful marker in this respect since the hardness of carious dentin is significantly lower than that of non-carious healthy dentin.

This study aimed to evaluate the efficiency of two different methods of caries removal, namely, chemomechanical methods (Carisolv) and SmartPrep burs by measuring the hardness of remaining dentin after caries removal using Vicker’s indenter. The morphological structure of the cavity floor was also analyzed using a scanning electron microscope.

MATERIALS AND METHODS

RESULTS

Vickers hardness test

The mean Vickers hardness number (VHN) of the surrounding healthy surface using SmartPrep and Carisolv was almost the same [Graph 1], whereas the mean VHN of the prepared surface using Carisolv showed a higher value than the SmartPrep burs [Graph 2]. The difference in mean VHN of the prepared and healthy surface was found to be higher in SmartPrep compared to Carisolv [Graph 3].

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Graph 1:

Mean VNH of the surrounding healthy surface.

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Graph 2:

Mean VNH of the prepared surface.

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Graph 3:

Mean VNH in the groups for difference in prepared and healthy surfaces.

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DISCUSSION

Since the introduction of rotary instruments, operative treatment of carious lesions has resulted in considerable removal of tooth structure which contradicts the new principle of minimal intervention dentistry.^[7] To overcome these drawbacks, many alternative methods such as chemomechanical techniques, air abrasion, sono-abrasion, ultrasonic instrumentation, lasers, caries detecting dyes, and polyamide burs have been introduced for caries removal.^[8]

Deep dentinal caries consist of two layers each having distinct ultramicroscopic and chemical structures.^[9] An alternative method of caries removal selectively removes the infected outer layer of carious dentin which is irreversibly denatured and not remineralizable.^[9]

In an attempt to develop a selective caries removal rotary instrument, a “plastic” bur, SmartPrep bur, is made of a medical-grade polymer with slightly lower mechanical properties than sound dentin which has been recently developed.^[10] The polymer material has a Knoop hardness number (KHN) of 50 and is designed to have a hardness greater than carious, infected dentin (0–30 KHN) but lower than healthy dentin (70–90 KHN).^[2,10]

According to the manufacturer, if the bur touches sound or caries affected dentin, it quickly becomes dull and produces undesirable vibration, making further cutting impossible.^[10] Thus, polymer burs are more efficient in treating soft carious lesions while retaining the harder affected dentin. For this reason, the SmartPrep bur has been suggested as it can be used without the need for local anesthesia, increasing patient comfort.^[11,12]

CMCR involves the chemical softening of caries dentin followed by its removal by gentle excavation. Carisolv is available as a twin syringe, one containing sodium hypochlorite solution and the other a viscous gel that contains three amino acids: Lysine, leucine, and glutamic acid together with carboxymethylcellulose to make it viscous. Erythrosine dye is added to make it readily visible during use. The contents of the two syringes are mixed immediately before use as their effectiveness begins to fade after 20 min.^[13]

The operative steps include application of the solution, scraping off the carious dentin with special excavators, rinsing, and repetition of the procedure until all caries are removed.

Many studies^[14,16] have shown that this method is more accepted by pediatric patients who responded positively, but its disadvantage is that it takes a longer time than conventional mechanical methods.

Thus, in the present study, the efficacy of these two techniques SmartPrep (SS White, Lakewood, NJ, USA) and Carisolv (Carisolv Mediteam, Savedalen, Sweden) was evaluated. The hardness of remaining dentin after caries removal was measured and compared with that of surrounding dentine using the Vickers hardness test.

Knowledge of the mechanical properties of caries affected dentin is important to help the clinician understand how much a substrate reacts under masticatory loading conditions and help to predict the behavior of the tooth-restoration interface. Hardness is the ability of a material to resist a permanent indentation. The hardness of carious dentin is slightly lower than that of non-carious dentin.^[15] Microhardness analysis has been used as a method to assess the loss of minerals in dental tissues because the reduction in hardness value presents a linear relation to mineral loss.^[17] Therefore, the hardness of dentin can serve as an objective clinical marker between caries infected, caries affected, and non-carious dentin.

The hardness of human teeth has been determined by a variety of methods out of which Vickers hardness testing was adapted in this study because it is easy and quick and only requires a tiny area of specimen surface for testing. It has been proved that indentation load is crucial for VHN values and that with the lower loads, it is difficult to read the indentation marks. Studies have reported that the use of a load of 100 g gave a clear indentation to be observed under the microscope.^[18] Hence, in the present study, a load of 100 g for 15 s was employed for the microhardness test.

According to the results of the present study, it was observed that the mean difference in VHN of healthy dentin and that of a prepared dentin were highest in the SmartPrep group. Since the mean difference is greater for SmartPrep burs, it can be inferred that the hardness of dentin prepared by SmartPrep bur was much less than the surrounding healthy dentin [Graph 3].

According to the results of this study, SmartPrep burs were less effective in removing infected carious dentin studies have reported presence of smear layer on bur -treated teeth.^[21] Despite having a negative rake angle, when pressure is applied, the polymer bur starts to abrade and loses its efficiency quickly. Even the soft light brown lesions were not easily removed. It is supported by other researchers.^[23]

Carisolv showing a lesser mean difference between prepared and healthy dentin indicates that Carisolv was more reliable for removing infected carious dentin while retaining affected carious dentin [Graph 3]. Gentle hand excavation may provide adequate tactile feedback with controlled carious excavation. This was also noted in the study by Lennon et al.^[19]

In the second part of the study, the surface characteristics of these two methods were observed using a scanning electron microscope. The morphological analysis of caries excavation by the SmartPrep burs showed a surface covered with debris and a smear layer. There were no open dentinal tubules [Figure 1].

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Figure 1:

SEM analysis using SmartPrep burs.

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SEM observation of the dentin surface after using Carisolv revealed a rough scaly surface with large areas of open dentinal tubules. There was almost no smear layer, similar to our findings [Figure 2]. Hossain et al.^[22] and Sakoolnamarka et al.^[20] reported a minimal smear layer and open dentinal tubules after chemomechanical caries removal with Carisolv™. In contrast, a study by Ajilal et al.^[24] revealed a rough and granular dentin surface with partially patent dentinal tubules and a residual smear layer. Given these diverse results, it appears that the CMCR technique is sensitive and shows variability according to the operator.

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Figure 2:

SEM analysis using Carisolv.

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The results of SEM observation of the present study demonstrated that Carisolv possessed some distinguishing features compared to SmartPrep burs. Carisolv creates surface roughness and structural changes that may be advantageous for adhesive restorations and techniques such as immediate dentin sealing, deep margin elevation, and cavity optimization.

CONCLUSION

Carisolv proved to be superior to SmartPrep burs in conservatively removing the infected carious dentine. Regarding smear layer removal, SmartPrep burs demonstrated more debris and smear layer removal with patent dentinal tubules which can increase the dentin surface receptiveness for an adhesive restoration.