Comparative evaluation of efficacy of two minimally invasive caries removal techniques on fracture resistance of the teeth restored with composite: An SEM study.

AIM: The aim of the study was to evaluate and compare the efficacy and fracture resistance of the teeth restored with composite using two minimally invasive caries removal techniques under a scanning electron microscope. MATERIALS AND
METHODOLOGY: Forty-five freshly extracted human permanent molars with Class I and II dentinal caries were selected. Diamond bur group (15): The carious lesion was excavated using round diamond bur until hard dentine was detected. Polymer bur group (15): Carious lesion was removed using polymer burs in circular motions. V-cariesolve gel group (15): Carious lesion was covered with V-cariesolve gel for 30 s and was scraped using a spoon excavator. The time required for the caries removal by each group was recorded. The effectiveness of caries excavation was verified using caries indicator dye. The smear layer removal was assessed using a scanning electron microscope. The cavities were restored with composite resin and fracture resistance of teeth was evaluated. All the data were tabulated and analyzed using Kruskal-Wallis test for overall comparison followed by Mann-Whitney U-test for pairwise comparison.
RESULTS: The mean time taken for caries excavation by diamond bur group was less (86.13 s), retention of smear layer was less with diamond bur group, and the median score for staining of infected dentin was more (3) in V-cariesolve gel group. Fracture resistance was highest (1.53) with diamond bur group (P < 0.001).
CONCLUSION: Caries removal efficacy and fracture resistance for diamond bur group were better compared to polymer bur group and v-cariesolve gel. Copyright:

INTRODUCTION

The science of operative dentistry is advancing toward the approach of minimally invasive dentistry. It involves the principle of ’Prevention of extension’ on the contrary to the principle of “Extension for prevention” given by G. V Black.[1] The theory of minimally invasive dentistry focuses on practicing the science of identifying, diagnosing, and intervention at the soonest and treating at a microscopic level.[1]

Carious lesions comprised two distinct layers: superficial infected dentin and deeper affected dentin. Infected dentin is infiltrated with microorganisms, its organic matrix is degraded substantially and cannot be demineralized; hence, it should be removed.[2] The affected dentin can be remineralized as collagen is denatured reversibly; thus, it must be retained during cavity preparation.[3]

The most commonly used rotary instruments for caries removal are carbide and diamond burs. Due to extensive removal of sound tooth structure along with carious lesion, it weakens the remaining tooth structure. Thus, minimally invasive techniques of caries excavation were developed such as polymer burs and v-cariesolve gel.[1] Polymer burs are instruments produced by a medical grade polymer with the Knoop Hardness Number (KHN) 50 which are considered as “dentin safe,” as it selectively removes only carious dentine of 20–30 KHN,[4] the bur starts getting abraded as soon as it reaches healthy dentin of 54–65 KHN. Since the bur removes only infected dentin, it prevents the irritation to the odontoblasts which results in reduced patients discomfort level.[5] V-cariesolve gel is a chemomechanical caries removal agent containing a purified enzyme derived from the plant “Caprica papaya.” This gel is specially invented for excavation of carious dentin using only the hand instruments and reducing the use of rotary instruments. It consists of papaya extract (papain), chloramine, clove oil, etc., Papain is a proteolytic enzyme which has anti-inflammatory and antibacterial properties. Papain affects only carious tissues, and it lacks alpha 1anti trypsin, a plasmatic antiprotease system, thus inhibiting proteolysis. The absence of protease allows papain to split the partially degraded collagen molecules of infected dentin. It also promotes chemical debridement and cicatricial process. Chloramine dissolves the carious dentin by the process of chlorination of partially degraded collagen, thus softening the carious dentin promoting its removal. Clove oil is an antiseptic and natural analgesic used in dentistry mainly for its soothing effect and inhibits bacterial growth.

Extensive search of a literature yielded no studies which have compared the fracture resistance using these two minimally invasive caries excavation methods with diamond bur. Hence, the aim of the study was to evaluate the efficacy of two minimally invasive techniques of caries removal against diamond burs using the scanning electron microscope followed by fracture resistance of teeth restored with composite.

MATERIALS AND METHODOLOGY

Forty-five freshly extracted human permanent molars were collected from the department of oral and maxillofacial surgery, cleaned, and stored in 10% formalin.[6] The teeth with Class I and II coronal caries extending midway through the dentin, which was confirmed using radiovisiography, were selected for the study. To avoid the error of nonhomogenicity between Class I and Class II carious samples, affecting fracture resistance of teeth, the artificial proximal walls were built to all the samples of Class II samples using high-strength packable composite (3M ESPE Filtek Z350). The Class V caries, deep carious lesion, pulp exposure, or potential for pulp exposure were excluded from the study. The samples which fulfilled the inclusion criteria were mounted in acrylic blocks.

The specimens were numbered and randomly divided into three experimental groups:

Group 1: 15 samples – Diamond burs (control group)

Group 2: 15 samples – Polymer burs

Group 3: 15 samples – V-Cariesolve gel

The method followed in our study for excavation of carious lesion was similar to that of the method given by Divya et al.[7]

Diamond bur method

The excavation of carious lesion was carried out using ball round diamond bur of ISO size 4 (Dia-Burs, Mani Medical India, Pvt. Ltd., Delhi) at a slow speed airotor handpiece (NSK Pana air FX SB2 00000000. Made in Japan) till the complete soft dentin was removed and hard dentin was detected which was further confirmed by applying firm pressure on the dentin using shepherd hook explorer in which the dentin should not get penetrated[7] [Figure 1a].

Figure 1

(a) Caries removal by diamond bur group, (b) caries removal by polymer bur group, (c) application of V-cariesolve gel group

Polymer bur method

The excavation of a carious lesion was done using polymer burs (SmartPrep, SS White Burs, Inc., Lakewood, NJ, USA) in circular movements from the center of the lesion to periphery till the instrument becomes blunted and should no longer be able to use. The hard dentin was checked using an explorer[7] [Figure 1b].

V-cariesolve method

The carious lesion was covered with V-cariesolve gel (Vishal Dentocare Ltd., Gujarat, India) for 30 s [Figure 1c] and was scraped gently using a spoon excavator after the gel appeared cloudy. The procedure of caries removal was continued until the gel was no longer cloudy.[7]

The time required for complete excavation of caries of all the samples was noted in seconds using a stopwatch. The confirmation of presence of infected dentin was done using caries detecting dye (Reveal, PREVEST DenPro, India) for 10 s, followed by rinsing with water for 10 s. Efficacy was graded numerically as 0, 1, 2, 3, 4, and 5 according to the grading system proposed by Prabhakar A et al.[4] To mimic the oral environment, the specimens were stored in artificial saliva for 2 weeks. After decoding of the samples, two blinded evaluators viewed the samples under Zeiss EUOMA10 scanning electron microscope at 20 kV and 10 Pa vacuum viewing status at a magnification of ×2000 and ×3000 to assess the smear layer removal using different caries excavation methods and graded them as reported by Somani R et al[8] Using 37% phosphoric acid, the cavities were etched followed by thorough rinsing for 15 s and bonding agent (ESPE Universal adhesive) was applied and cured for 15 s followed by a composite buildup (3M Filtek) and curing for 30 s for each layer. The restored cavities were subjected under a universal testing machine (Model 4466, Instron Inc., Canton, MA, USA) at the crosshead speed of 1 mm/s to check for the fracture resistance of the teeth.[9] The numerical data (scores) for time required for complete caries removal, confirmation of presence of infected dentin using dye, efficacy of smear layer removal, and fracture resistance were charted and analyzed statistically by Kruskal–Wallis test for comparison within the groups followed by Mann–Whitney U-test for pairwise comparison using IBM corporation USA 14.0 version. P < 0.001 was considered to be significant.

RESULTS

The data were analyzed between all the groups to determine the significant difference between them. The mean value of time duration for caries removal by diamond bur group (86.13 s) was less than polymer bur group (142.80 s) and V-cariesolve gel group (193.67 s) Table 1. The median value for staining of infected dentin in diamond bur group was 0, and for polymer bur group and v-cariesolve gel group, the median value was, indicating that the Diamond bur group showed the better removal of infected dentin. SEM evaluation as per Munshi et al.'s classification revealed that diamond bur group with median value of 1 showed less smear layer, which was significantly different compared to polymer bur group (median 2) and v-cariesolve gel group (median 3). The fracture resistance was less with polymer bur group with the mean value of 0.95 and highest with diamond bur group with the mean value of 1.53.

Table 1

Comparison of time taken for complete caries removal, confirmation of presence of infected dentin, efficacy of smear layer removal, and fracture resistance within the groups by Kruskal–Wallis test

	n	Mean	SD	25th percentile	Median	75th percentile	Kruskal–Wallis test
Time taken (in secs)
Diamond	15	86.13	10.20	80.0	81.0	94.0	<0.001, significant
Polymer	15	142.80	27.21	118.0	132.0	172.0
V-cariesolve	15	193.67	23.10	180.0	197.0	210.0
Dye
Diamond	15	0.00	0.00	0.0	0.0	0.0	<0.001, significant
Polymer	15	1.07	0.80	0.0	1.0	2.0
V-cariesolve	15	0.67	0.49	0.0	1.0	1.0
SEM
Diamond	15	1.27	0.46	1.0	1.0	2.0	<0.001, significant
Polymer	15	2.00	0.76	1.0	2.0	3.0
V-cariesolve	15	2.80	0.41	3.0	3.0	3.0
Fracture resistance
Diamond	15	1.53	0.52	1.1	1.7	1.9	<0.016, significant
Polymer	15	0.95	0.63	0.7	1.0	1.1
V-cariesolve	15	1.32	0.45	1.0	1.3	1.6

SD: Standard deviation, SEM: Scanning Electron Microscope

According to Mann–Whitney U-test, all the parameters were statistically significant between diamond bur and polymer bur group. Pairwise comparison between diamond bur and v-cariesolve gel group showed that all the parameters except fracture resistance (P = 0.213) have displayed statistically significant difference. Similarly, between polymer bur and v-cariesolve gel group except for smear layer removal with P = 0.136, all the other parameters have exhibited statistically significant difference.

DISCUSSION

The purpose of minimally invasive dentistry is to preserve a sound tooth structure and increase the longevity of the restoration. The conventional techniques used to excavate the caries can lead to excessive removal of a sound tooth structure resulting in injury to the pulp and increased patient's discomfort level. Hence, the aim of the present study was to evaluate the smear layer removal and fracture resistance of the teeth restored with composite using minimally invasive caries removal techniques such as polymer burs and v-cariesolve gel.

For better correlation of all the factors for caries excavation methods, detailed experiment was carried out which includes all the parameters such as time duration for caries excavation, confirmation of presence of affected dentin by staining with dye, and evaluation of residual smear layer and fracture resistance that affects the final longevity of the restoration.

As per the results obtained, the mean time duration for complete caries removal by diamond bur group was less. The reason attributed could be due to the high rotational speed (>20,000 rpm) of the diamond bur with the frictional force presenting negative rake angle that results in abrading the tooth surface rather than cutting of tooth structure during cavity preparation.[7] In polymer bur group, the time duration for excavation of carious lesion was more because of the very low rotational speed of the bur (500–800 rpm),[10] the path taken by the instrument while removing the infected dentin and the polymer bur is less hard (50 KHN) compared to healthy dentin (66–80 KHN). These results are in line with those obtained in a study by Prabhakar A, Kiran NK.[4] Similarly, the time duration for complete caries excavation by V-cariesolve gel is longer compared to the other two groups because of multisteps that were involved in the procedure of caries removal which is similar to the studies performed by Banerjee et al., Dammaschke et al., and Yazici et al.[11]

The presence of infected dentin was detected by using caries detecting dye(Reveal) that consists of Green F D C and Propylene glycol, which helps in visual demarcation between infected carious dentin and reminerizable sound dentin by its capability to selectively stain the carious dentin the staining was more in polymer bur group and v-cariesolve gel group, as only infected dentin was removed preserving affected dentin Table 2. There was no staining in the diamond bur group as both infected and affected dentin were removed.[4]

Table 2

Scoring criteria for the assessment of the efficacy of caries removal

Score	Efficacy
0	Caries completely removed
1	Caries present in the base of the cavity preparation
2	Caries present in the base and/or in one wall of the cavity preparation
3	Caries present in the base and/or two walls of the cavity preparation
4	Caries present in the base and/or more than two walls of the cavity preparation
5	Caries present in the base, walls, and margins of the cavity preparation

It was found that the diamond bur group showed very few occluded dentinal tubules, indicating presence of less amount of smear layer [Figure 2a. The reason could be due to very high rotational speed of the bur with a continuous water jet that flushes away the smear layer Table 3. Similarly, there was a retention of dense smear layer with no visible dentinal tubules in v-cariesolve gel[8] [Figure 2c]. The probable reason attributed could be noninvolvement of rotary instrumentation, as it is a chemomechanical caries removal technique and as the cavities were rinsed off following gel application during caries excavation procedure, we expected higher removal of smear layer compared to polymer bur group which was used with low rotational speed without water jet[1] showing moderate occlusion of dentinal tubules indicating presence of moderate amount of smear layer [Figure 2b]. This difference in the smear layer removal between v-cariesolve gel and polymer bur group was not statistically significant. Hence, we were unable to verify if one of the groups had a better smear layer removal efficacy over the other. A study with a higher sample size may help us identify if this is really the condition to be focused. Such a study might also help us to explain the reason for higher fracture resistance that we observed in V-cariesolve gel group.

Figure 2

(a) Diamond bur group showing moderate smear layer with visible dentinal tubules, (b) Polymer bur group showing dense smear layer with few visible dentinal tubules, (c) V-cariesolve gel group showing dense smear layer with no visible dentinal tubules

Table 3

Grading system for retention of smear layer

Grade	Retention of smear layer
Grade 0	Absence of smear layer
Grade 1	Moderate smear layer
Grade 2	Dense smear layer with visible dentinal tubules
Grade 3	Dense smear layer with no visible dentinal tubules

Total etch technique was used to etch the dentin in all the groups, but the fracture resistance is directly associated with the amount of smear layer present on the surface of dentin which ultimately contributes to development of resin–dentin interdiffusion zone.[12] In the current study, the diamond bur group has shown highest fracture resistance as the retention of smear layer was minimal leading to stronger resin–dentin interdiffusion zone. The teeth under v-cariesolve gel group have shown less retention of smear layer, this could be due to complete removal of gel by rinsing off the teeth using water and acid etching procedure during composite restoration. The polmer bur group, though exhibiting lesser amount of smear layer compared to v-cariesolve gel, forms a weak resin–dentin interdiffusion zone, resulting in the lowest fracture resistance.[1] This could be due to influence of various other factors such as type of bonding agent used, teeth storage medium, duration, and microhardness of dentin of freshly extracted teeth and stored teeth.[13]

Hence, by comparing the results of the present study, diamond bur group has shown a better caries removal efficacy as well as fracture resistance compared to two minimally invasive caries excavation methods such as v-cariesolve gel and polymer bur group. However, future studies should focus on using newer chemomechanical caries removal agents which removes the smear layer more efficiently and hastens the efficacy of caries removal which is observed to be less in v-cariesolve gel and also using recent generation bonding agents that improves the fracture resistance.

CONCLUSION

Within the limitations of the study, it can be concluded that diamond bur group was better in caries removal efficacy and fracture resistance, compared to polymer bur group and v-cariesolve gel group.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.