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ORIGINAL ARTICLE
Year : 2016  |  Volume : 14  |  Issue : 1  |  Page : 88-94

Comparison of dentin hardness between conventional drill and chemomechanical methods in primary and permanent dentition using nanoindenter


1 Department of Pedodontics and Preventive Dentistry, Vinayaka Mission Sankarachariyar Dental College, Salem, Tamil Nadu, India
2 Department of Public Health Dentistry, J.K.K. Nattraja Dental College and Hospital, Komarapalayam, Namakkal, Tamil Nadu, India
3 Center for Nano Science and Technology, K.S.R. College of Technology, Tiruchengode, Tamil Nadu, India
4 Department of Periodontics, J.K.K. Nattraja Dental College and Hospital, Komarapalayam, Namakkal, Tamil Nadu, India

Date of Web Publication15-Mar-2016

Correspondence Address:
M Kruthika
Department of Pedodontics and Preventive Dentistry, Vinayaka Mission Sankarachariyar Dental College, Ariyanoor, Salem - 636 308, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2319-5932.178725

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  Abstract 

Introduction: Latest theories regarding the rationale of carious dentin removal are beginning to question the amount of tissue that needs to be excavated to successfully treat a carious tooth. It is not always easy to make a decision at which point to stop excavation because there is an apparent lack of objective clinical markers. However, hardness of dentin might be a useful marker in this respect. Nanoindentation test is a variety of indentation hardness test applied to small volumes such as teeth which contain nanosized structures. Aims: To compare and evaluate the nanohardness of dentin after chemomechanical (Carie-care) method of caries removal with the conventional (rotary instrument) method of caries removal in primary and permanent teeth using nanoindenter. Materials and Methods: An in vitro randomized controlled trial was conducted using fifteen primary and fifteen permanent extracted molars with active carious lesion extending into the dentin. The primary and permanent molars were further randomly divided into two subgroups by sectioning the samples into two halves. Caries removal was done using conventional drill (CD) and chemomechanical caries removal (CMCR) (Carie-care) methods. Following the caries removal, the test specimens were subjected for evaluation of nanohardness of dentin using nanoindenter. Student's t-test, analysis of variance, and Bonferroni test were used. Results: Statistically significant difference between the 4 groups with a P < 0.05 was obtained. Conclusions: After caries removal, the hardness of remaining dentin was found to be harder after CMCR method than with the CD method in both primary and permanent teeth, and the remaining dentin of the permanent teeth was found to be harder than the primary teeth after caries removal.

Keywords: Carie-care, chemomechanical caries removal, conventional drill, nanohardness


How to cite this article:
Kruthika M, Ramesh K, Shankar S, Kumar V S, Karthik A, Sasikumar P K. Comparison of dentin hardness between conventional drill and chemomechanical methods in primary and permanent dentition using nanoindenter. J Indian Assoc Public Health Dent 2016;14:88-94

How to cite this URL:
Kruthika M, Ramesh K, Shankar S, Kumar V S, Karthik A, Sasikumar P K. Comparison of dentin hardness between conventional drill and chemomechanical methods in primary and permanent dentition using nanoindenter. J Indian Assoc Public Health Dent [serial online] 2016 [cited 2019 Aug 25];14:88-94. Available from: http://www.jiaphd.org/text.asp?2016/14/1/88/178725


  Introduction Top


G. V. Black (1891) concept of “Extension for prevention” for the treatment of caries is replaced today by “Prevention of Extension” leading to the new philosophy of “Minimal Intervention Dentistry” as it is of fundamental importance to use conservative procedures that minimize the removal of healthy tooth structure and simultaneously prevent the lesion progression.[1] The disadvantages of using conventional drill (CD) method include the possibility of overextending the cavity, removal of healthy tissue, pressure and heat on the pulp, vibration, noise, pain stimulation, and the need for local anesthesia has encouraged developing an alternative method for caries removal such as lasers, air abrasion, ultrasound, and chemomechanical caries removal (CMCR).[2]

Chemomechanical elimination of carious dentin has so far proved to be a promising method, particularly in pediatric dentistry, and for anxious or medically compromised patients which has the capacity to distinguish the internal carious tissue (affected dentin) from the more superficial and highly infected tissue (infected dentin)[3],[4] by which it affords pulp protection and remineralization of affected dentin.

Latest theories regarding the rationale of carious dentin removal are also beginning to question the amount of tissue that needs to be excavated to successfully treat a caries tooth while removing demineralized dentin. It is not always easy to make a decision at which point to stop excavation because there is an apparent lack of objective clinical markers. However, hardness of dentin might be a useful marker in this respect.[5]

Hardness analysis has been used as a method to assess loss and reincorporation of minerals to the dental tissue because the reduction in the numerical hardness value presents a linear relation to mineral loss.[6] Furthermore, a strong relationship exists between hardness of dentin and the respective bond strength.[7] Hence, hardness provides a first step toward predicting the behavior of dentin/restoration interfaces.[8] Nanoindentation test is a variety of indentation hardness test applied to small volumes such as teeth which contain nanosized structures.[9] This technique has the ability to produce small indentations under small loads.[10]

Thus, the aim of the study was to compare and evaluate the nanohardness of the dentin after CMCR (Carie-care) method with conventional method (CD-rotary instrument) in both primary and permanent teeth using nanoindenter.


  Materials and Methods Top


Study design and setting

This was an in vitro randomized controlled trial.

Sample selection

Fifteen primary molars (Group-1) with active carious lesion extracted due to normal physiological root resorption and fifteen permanent molars (Group-2) with active carious lesion extracted due to periodontal pathology were collected.

Teeth that had active caries lesion with open cavities, easily accessible caries, and radiographically caries extending half the distance through the dentin, with no radiographic evidence of internal resorption were included in the study, and teeth with any developmental tooth defects, caries extending to the pulp, and caries involving only enamel were excluded from the study.

The samples selected were cleaned in running water to remove the visible debris. All the soft and extrinsic deposits attached to the root portion of the teeth were removed using a hand scaler and the samples were stored in 10% formalin [11] for 2 weeks according to guidelines for infection control of extracted teeth used for research and teaching given by the Centers for Disease Control and Prevention.[12]

Each sample was placed in the jig and the carious portion of the tooth was divided into two halves by passing the diamond disc through the middle of the carious lesion in mesiodistal direction [5] (split tooth methodology). The sectioning was done with micromotor and a diamond disc using water as coolant [Figure 1].
Figure 1: Splitting of tooth into two halves

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Thus, samples were further divided into two subgroups and the groups were:

  • Group 1a: Cavity prepared using CD method (rotary instrument-bur) in primary molars; Group 1b: Cavity prepared using CMCR (Carie-care) in primary molars
  • Group 2a: Cavity prepared using CD method (rotary instrument-bur) in permanent molars; Group 2b: Cavity prepared using CMCR (Carie-care) in permanent molars.


Cavity preparation

A matrix band was placed between the two halves of each tooth along the cut line for separation [Figure 2]. For CD group, carious tissue removal was performed with a spherical diamond point (Mani– BR-31, 41, 45) with the largest diameter compatible with the cavity size using water as a coolant until an unstained hard pulpal floor was reached to ensure no carious lesion is left behind [Figure 3]. For CMCR group, the gel was used as per the manufacturer instruction which was applied and left in the cavity for 1 min [Figure 4]. When the gel was cloudy, it was removed gently by scraping using spoon excavator without applying pressure [Figure 5]. The gel was reapplied until it presented a light coloring, indicative of nonexistence of softened carious tissue. The gel was then removed and the cavity was wiped with a moistened cotton pellet and rinsed with water as per the manufacturer instruction. Complete caries removal was confirmed using a dental explorer by passing it easily over hard sound dentin which did not “catch” or give a “tug-back” sensation [Figure 6].[13]
Figure 2: Placement of matrix band along the cutline

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Figure 3: Caries removal using conventional drill method

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Figure 4: Caries removal using chemomechanical caries removal method

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Figure 5: Caries removal using spoon excavator in chemomechanical caries removal method

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Figure 6: Confirming complete carious tissue removal using visual clinical criteria

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Nanoindendation test

The specimens were placed in the jig and sectioned horizontally at the level of floor of the cavity and then at the cementoenamel junction using diamond disc and water coolant [Figure 7]. The samples were subjected to nanohardness test in the nanoindenter (Hysitron TI 750H Ubi) [Figure 8].[14] The tests were performed in load-controlled feedback mode to a peak force of 500 µN for permanent teeth and 250 µN for primary teeth.[15] A load function consisting of 5-s loading to peak force segment, followed by 5-s hold segment, and 1-s unloading segment was used (standard testing mode used: Quasi-static nanoindentation). Nanohardness readings at six different points on every specimen for both CD and CMCR were generated. The indents were spaced approximately 50–100 µm apart and performed using automation.
Figure 7: Sectioning of teeth specimens above the floor of the cavity and at the cementoenamel junction

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Figure 8: Image of the position of indentation captured by charge-coupled device camera on the monitor

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Statistical analysis

The data obtained were subjected to statistical analysis using SPSS Inc. Released 2008. SPSS Statistics for Windows, Version 17.0. Chicago: SPSS Inc. for descriptive and analytical statistics. To compare the mean nanohardness between the two methods (CD and CMCR groups) in the primary and permanent groups, unpaired Student's t-test was used. To compare the mean nanohardness between the 4 subgroups, analysis of variance (ANOVA) was used and to find out the exact significance among 4 groups, a post hoc test, i.e. Bonferroni test was performed. A P< 0.05 was considered statistically significant.


  Results Top


The mean nanohardness of dentin at 6 different sites were evaluated for 15 primary teeth and 15 permanent teeth for both CD and CMCR methods, and the results were tabulated [Table 1].
Table 1: Nanohardness of dentin for every primary and permanent teeth sample following conventional drill and chemomechanical caries removal methods (all four subgroups)

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The mean nanohardness of dentin in both primary and permanent teeth obtained from the CMCR group (376.90 and 574.60, respectively) was found to be very highly significant compared to that of the CD group (183.63 and 363.12) with P<0.05 [Table 2] and [Table 3].
Table 2: Mean nanohardness of dentin in primary teeth following conventional drill and chemomechanical caries removal methods

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Table 3: Mean nanohardness of dentin in permanent teeth following conventional drill and chemomechanical caries removal methods

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The mean nanohardness of dentin for all the 4 subgroups was compared using ANOVA. The comparison showed an existence of statistical significance between the subgroups with P< 0.05 [Table 4].
Table 4: Mean nanohardness of dentin in both primary and permanent teeth following conventional drill and chemomechanical caries removal methods

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Multiple comparisons among the 4 subgroups using post hoc Bonferroni test showed that the mean difference in the nanohardness of dentin between the primary CMCR and permanent CD method was found to be highly statistically significant (P - 0.002). Moreover, the comparison between all the other subgroups was found to be very highly statistically significant (P - 0.000) [Table 5].
Table 5: Multiple comparisons between all four subgroups

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  Discussion Top


Even today, the operative dentistry focuses on cavity design and selecting restorative materials. Less effort has been placed on incorporating what is known about the pattern of caries progression and how it relates to caries removal or excavation.[16] Hence, based on these concepts, minimal intervention dentistry is introduced which require the removal of only the infected dentin and preservation of the affected dentine which is also necessary for supporting the future restoration.

Carie-care, a recently introduced CMCR agent, was preferred in this study as it is a gel prepared from papain and chloramines, which is less expensive than Carisolv [17] and can be used similarly to papacarie.

Knowledge of the mechanical properties of caries-affected dentin is important to understand how such a substrate reacts under masticatory loading conditions [18] and to help predict the behavior of the tooth/restoration interface.[19] Microhardness testing such as Vickers and Knoop indenters are commonly used for this purpose.[20] However, large errors are observed with these testings as it requires direct imaging, usually visual measuring, of the width or area of the indentations, to obtain hardness.[21]

To overcome the disadvantages of microindentation methods, nanoindentation technology has been recently introduced as a reliable way to study the nanomechanical alterations of mineralized tissues [22],[23],[24],[25],[26] as it is a nondestructive method in which very small indentations (<1 mm) are produced using loads of a few milli-Newtons [27],[28] and it allows more indentations to be executed per specimen, and the specimens were better scanned to select the appropriate location for indentations.

Various literature regarding the microhardness values of permanent teeth [5],[29],[30],[31],[32] after caries removal are available, but only very few studies are reported for primary teeth.[2],[30],[33],[34] In spite of the differences existing between primary and permanent teeth in terms of their degree of mineralization, structure, mineral loss, and reactivity to fluoride,[35],[36] only a few studies are reported that specifically deal with primary tooth microhardness after caries removal. Currently, there are no reports which directly compare the hardness of remaining dentin in primary and permanent teeth after caries removal using CD and CMCR.

All the previous studies reported in the literature have evaluated the hardness of remaining dentine after caries removal using only the microindentation tests such as Knoop hardness number or Vicker hardness number, which is rather a gross test.[37],[38] Thus, to compare this study with the previous reported studies, the hardness numbers obtained in the previous studies were converted to MPa values using online softwares.[39],[40]

The mean nanohardness of dentin in primary teeth following CD was 183.63 MPa which was lower than the values reported by Al-Rawi (559.2 MPa).[33] This could be attributed to the fact of variations in the caries extension and remaining dentin thickness as the hardness of primary dentin deteriorates as a function of distance toward the pulp. Such deterioration in mechanical behavior is likely to correspond to change in both the inorganic content and histological structure of dentin.[41]

The mean nanohardness of dentin in primary teeth following CMCR method was 376.90 MPa which was almost similar to the study reported by Prabhakar et al. (363.8 MPa)[34] but lower than the studies reported by Flückiger et al. (500.53 MPa)[30] and Al-Rawi (559 MPa).[33]

The mean nanohardness of dentin in permanent teeth following CD was 363.12 MPa which was comparatively lower than the study reported by Qasim and Suliman (594.28 MPa).[5] This could be due to the variations in the depth and site of indentation in the teeth selected which was governed by several factors such as the calcification level of dentin, the difference in dentinal tubule density at different locations (increased tubule density near the pulp was shown to correspond with reduced hardness), the reduced hardness of the inter-tubular dentin when approaching the pulp, and the distance from the dentinoenamel junction.[19]

The mean nanohardness of dentin in permanent teeth following CMCR method was 574.60 MPa which was marginally higher than the study reported by Ramamoorthi et al. using Carie-care (556.70 MPa).[42]

On comparing the hardness values of other studies reported using Carisolv with the present study, the results obtained were similar to studies reported by Sankar et al. (587.4 MPa)[32] and Ramamoorthi et al. (573.99 MPa)[42] but slightly lower than the study reported by Qasim and Suliman (606.6 MPa).[5] Thus, based on the results obtained from the present study and comparison with the previous studies, Carie-care was found to have similar efficacy as Carisolv.

There was a statistically significant difference found between the nanohardness of remaining dentin after caries removal using CD and CMCR methods in both dentition teeth samples. This could be due to the reason that the bur removed the carious affected dentin along with the infected dentin leading to over preparation of the cavity with lesser remaining dentin thickness.[32],[43]

Similarly, a statistically significant difference was found between the nanohardness of dentin in primary and permanent teeth samples after two methods of carious removal in the present study. This variability in the hardness of dentin is a function of several parameters such as position, tubule dentistry, microstructure, and age of the dentin substrate.[44]

Limitations of the study include small sample size, caries detection with basic methods, utilization of gross sectioning method to split the tooth, and in vitro measurement of hardness of dentin.


  Conclusions Top


The remaining dentine after caries removal using CMCR method was harder than CD method in both primary and permanent teeth. The remaining dentine of the permanent teeth was harder than the primary teeth after caries removal using both the CMCR and CD methods. Carie-care being a new product in the market needs further clinical trials and long-term in-vivo follow-up studies.

Acknowledgment

I acknowledge Dr. Manivasagam (Department of Nano Technology) for giving us technical support and my mother and father Mrs. Meenamurali and Dr. S. Murali, respectively for constant support and encouragement.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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