|Year : 2014 | Volume
| Issue : 2 | Page : 53-57
Effect of calcium hydroxide pastes and vehicles on root canal dentin microhardness
María G Pacios1, Gastón Lagarrigue1, Nicolás Nieva2, María E López3
1 Laboratory of Materials Assays, School of Dentistry, San Miguel de Tucumán, Tucumán, Argentina
2 Laboratory of Solid State Physics, School of Exact Sciences and Technology, San Miguel de Tucumán, Tucumán, Argentina
3 Department of Biological Chemistry, School of Dentistry, National University of Tucumán, San Miguel de Tucumán, Tucumán, Argentina
|Date of Web Publication||19-May-2014|
María E López
Cátedra de Química Biológica, Facultad de Odontología-UNT, Av. Benjamín Aráoz 800, (4000) - San Miguel de Tucumán
Source of Support: None, Conflict of Interest: None
Background: Calcium hydroxide pastes used in the endodontic therapy may produce changes in the physical properties of the dentin. Objective: The purpose of this study was to evaluate the effect of calcium hydroxide pastes and their vehicles on microhardness of root canal dentin. Materials and Methods: Sixty maxillary anterior teeth were used. The crowns of the teeth were removed at the cemento-enamel junction. Canals were instrumented, horizontally sectioned into 2 segments, embedded in acrylic resin, and polished. A total of 120 specimens were randomly divided into 12 groups. Specimens stayed in contact with the vehicles or the pastes prepared with the calcium hydroxide powder and the same vehicles. The vehicles are: Distilled water, chlorhexidine, carticaine in the anesthetic solution, propylene glycol, monochlorophenol and monochlorophenol - propylene glycol. The references Vickers microhardness were obtained prior the application of the medicaments. Samples were then exposed to the medicaments for 3, 7, and 14 days, and microhardness measured again. The results were statistically analyzed by one-way ANOVA, Tukey test, and regression. Results: All vehicles and pastes, except distilled water, significantly decreased the microhardness of the root dentin; however, calcium hydroxide + camphorated monochlorophenol - propylene glycol and camphorated monochlorophenol - propylene glycol showed the highest decrease. Conclusion: Vehicles contribute to calcium hydroxide reduction of root canal dentin microhardness as constituent of endodontic pastes.
Keywords: Calcium hydroxide pastes, calcium hydroxide vehicles, dentin microhardness, root canal dentin
|How to cite this article:|
Pacios MG, Lagarrigue G, Nieva N, López ME. Effect of calcium hydroxide pastes and vehicles on root canal dentin microhardness. Saudi Endod J 2014;4:53-7
|How to cite this URL:|
Pacios MG, Lagarrigue G, Nieva N, López ME. Effect of calcium hydroxide pastes and vehicles on root canal dentin microhardness. Saudi Endod J [serial online] 2014 [cited 2020 Feb 19];4:53-7. Available from: http://www.saudiendodj.com/text.asp?2014/4/2/53/132715
| Introduction|| |
The success of a root canal treatment depends on the method and quality of instrumentation, irrigation, disinfection, and the three-dimensional obturation of the root canal. Calcium hydroxide is widely used in endodontics as an intracanal disinfectant, since it has been shown to be effective in a wide range of situations.  The antibacterial effect is partially due to the fact that it reaches a pH over 11, preventing the growth and the survival of oral bacteria.  Calcium hydroxide alters the biological properties of bacterial lipopolysaccharides, upsetting the transportation mechanism in bacterial membranes, as well as inactivating enzymes, resulting in cell toxicity. ,, Several authors ,, have proposed associations of calcium hydroxide with different vehicles, such as polyethylene glycol, propylene glycol, glycerin, anesthetics, iodoform, and camphorated p-monochlorophenol to maximize its qualities. Fava and Saunders  concluded that the vehicle with which calcium hydroxide is mixed to form the paste used in endodontics affects the physical and chemical properties of the compound and hence, its clinical applications.
The measurement of microhardness is one of the simplest non-destructive mechanical characterization methods. Hardness is measured as the resistance to the penetration of an indenter, which is necessarily harder than the sample to be analyzed. A hardness test provides a numerical value that allows a distinction between materials submitted to the penetration of a specific indenter. The values obtained depend on several factors, such as Young`s modulus of the material, yield stress in compression, and anisotropy, amongst others.  The visualization of the indentation mark allows the measurement of its diagonals and thus, the determination of the Vickers hardness number (VHN). As dentin microhardness is sensitive to composition and surface changes, its reduction by some chemical substances such as gutta-percha solvents, irrigation solutions, and intracanal medicaments were previously demonstrated. Eldeniz et al.  demonstrated that the irrigation of the root canal either with ethylenediaminetetraacetate acid (EDTA)/citric acid or citric acid/sodium hypochlorite (NaOCl) solutions reduced the microhardness. Ari et al.  showed that NaOCl, H2O2, and EDTA significantly decreased dentin microhardness; however, chlorhexidine did not affect it. Oliviera et al.  concluded that chlorhexidine and NaOCl solutions reduced microhardness of the root canal dentin at 500 and 1000 ΅m from the dentin pulp interface. In relation to calcium hydroxide pastes, Yoldas et al.  demonstrated that they reduce dentin microhardness; however, there are no studies that comparatively evaluate the influence of calcium hydroxide (CH) vehicles on dentin microhardness. The clinical relevance of evaluating the effect of calcium hydroxide pastes and vehicles on root canal dentin microhardness is based on the relative softening effect exerted on the dentinal walls that could benefit a rapid preparation of small tight root canals. These alterations may also affect the adhesion and sealing ability of sealers to the treated dentin surfaces.  The comparison between calcium hydroxide pastes and their vehicles may evidence if the effect is due to the mixture or particularly to the vehicle itself.
The aim of this in vitro study was to evaluate the effect of calcium hydroxide pastes and their vehicles on microhardness of the root canal dentin.
| Materials and methods|| |
Sixty human maxillary incisors freshly extracted for periodontal reasons were used. The selection of teeth was made on the basis of their similarity in size and morphology and absence of any cracks or defects. Debris, calculus, and soft tissue remnants on the root surfaces were cleaned using a Gracey curette (Hu-Friedy, California, USA). Teeth were kept in 0.5% NaOCl overnight for surface disinfection and stored at -15ºC in a plastic case, until they were used.
The crowns were removed at the cement-enamel junction using a low-speed automatic precision cut-off machine (Miniton Struers, Rodovre, Denmark), with a 0.3 mm thickness and 75 mm diameter diamond cut-off wheel under continuous water cooling. The canals were instrumented with the step-back technique up to a #50 master apical K-file (Dentsply Maillefer, Ballaigues, Switzerland). The working length was determined by visualizing the tip of a size 15 K-file (Dentsply Maillefer, Ballaigues, Switzerland) extending beyond the apical foramen and subtracting 1 mm from that length of the file. After each instrument was used, the root canals were irrigated with 1 ml of distilled water. Then, they were dried with paper points. The middle third of each root was selected in order to avoid microhardness variations among the different thirds of the root canal dentin. the They were sectioned horizontally ,, into 2 root slices 2 mm thick using a low-speed saw automatic precision cut-off machine (Miniton Struers, Rψdovre, Denmark), with a 0.3 mm thickness and 75 mm diameter diamond cut-off wheel under continuous water cooling. The root canal segments were mounted with acrylic resin, and the dentin surfaces were ground and polished using 600, 1000, 1500, and 2500 silicon carbide papers in sequence, using a plate polishing machine (PUL-01 Prazis, Buenos Aires, Argentina). A final polish with a diamond paste of 0.25 ΅m was done.
The root segments (n = 120) were randomly divided into 12 groups (n = 10) and stayed in contact with the CH pastes or their vehicles as follows: Distilled water (DW), 2% chlorhexidine (CHX) (ICN Biomedicals Inc, Ohio, USA), 4% carticaine in the anesthetic solution (AS) (Totalcaina Forte, Microsules-Bernabσ Lab., Buenos Aires, Argentina), 99.5% propylene glycol (PG) (Anedra Lab, Buenos Aires, Argentina), camphorated monochlorophenol (CMCP) (Farmadental Lab, Buenos Aires, Argentina), and CMCP-PG. Calcium hydroxide pastes were prepared by adding the vehicles to the calcium hydroxide powder (Anedra Lab, Buenos Aires, Argentina), using 50 mg of powder per 50 ΅l of vehicle (ratio 1:1). Distilled water was selected as a control vehicle. A drop of the different vehicles or pastes was contacted with the polished surface of the root canal dentin segments and maintained in relativity humidity at 37ºC for 0 (before to contact the vehicles or the pastes) (time control), 3, 7, and 14 days. During each placement time, all the vehicles or the pastes were freshly prepared. Specimens were cleaned with abundant distilled water in between microhardness determinations.
Measurements were determined on dentin sections using a microhardness tester (Ernest Leitz, Wetzler, Germany). For each specimen, 3 indentations were made at approximately 1 mm from the pulp-dentin interface using a force of 300 mg for 15 seconds. The diamond-shaped indentations were observed under a metallographic microscope (Olympus BX-60M, New York, USA). The micrographic images were recorded with a digital camera (Sony Exwave, New Jersey, USA), and the measurements of the indentation diagonals were made using image-analysis software (PMD Software Version 1.2). The average value of the 2 diagonals was used to calculate the VHN for each specimen.
Data were statistically analyzed using analysis of variance (ANOVA), Tukey's multiple comparison tests, and regression analysis. Statistical analysis was performed at a level of significance of 95% (P < 0.05).
| Results|| |
[Table 1] shows mean dentin VHN values and standard deviations for different vehicles. All vehicles, except DW, significantly decreased root dentin microhardness. Anesthetic solution, PG, CMCP, and CMCP-PG differed significantly from the control at 3, 7, and 14 days, while CHX differed significantly from the control only at 7 and 14 days. Distilled water showed statistically higher values and CMCP-PG showed statistically lower values than the rest of the vehicles at the end of the experiment.
|Table 1: Mean and standard error of microhardness measurements of dentin segments in contact with|
calcium hydroxide vehicles
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[Table 2] shows mean dentin VHN values and standard deviations for different pastes. All pastes significantly decreased root dentin microhardness. Calcium hydroxide + CMCP and CH + CMCP-PG differed significantly from control at 3, 7, and 14 days, while CH + DW, CH + AS, CH + CHX, and CH + PG differed significantly from control only at 7 and 14 days. Calcium hydroxide + DW showed statistically higher values and CH + CMCP-PG showed statistically lower values than the rest vehicles at the end of the experiment.
|Table 2: Mean and standard error of microhardness measurements of dentin segments in contact with|
calcium hydroxide pastes
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[Figure 1] evidences the differences in microhardness exerted by calcium hydroxide pastes and their vehicles on root dentin. At all times, calcium hydroxide pastes showed lower microhardness values than the vehicles alone. All vehicles effected root dentin compared to DW; however, microhardness with CHX was higher than with DW.
|Figure 1: Comparison of root canal dentin microhardness of calcium|
hydroxide pastes and their vehicles
Click here to view
| Discussion|| |
In this study, calcium hydroxide pastes made contact with the root canal dentin, and their action was determined through a physical property such as microhardness. Horizontal sections of the middle third of human root canal dentin were prepared to be exposed to the indenter of microhardness tester. This methodology ,,,, could simulate the clinical scenario since measurements were performed in all cases at approximately 1 mm from the pulp cavity. However, other methodology consider to split the tooth longitudinally. 
Calcium hydroxide vehicles used to prepare the pastes, although having no clinical significance, were also included for the purpose of evidencing if the observed effects in each case would be due to vehicles or to the result of calcium hydroxide mixtures. In relation to the inclusion of days 3 and 7, they were selected in order to evaluate if a continuous effect could be observed through time until day 14 th .
The VHN has traditionally been employed to evaluate materials presenting a certain morphological homogeneity, e.g., metals. However, it has also been used on biological material like dentin, which is far less homogenous and may lead to deviations in the results because of differences in regions adjacent to the dentin tissue.  Pashley et al.  reported an inverse correlation between dentin microhardness and tubular density. The degree of mineralization and the amount of hydroxyapatite in the intertubular dentin are considerable factors in determining the intrinsic hardness profile of the dentin structure.
In this study, aqueous, viscous, and oily vehicles  were used to prepare calcium hydroxide pastes, and dentin microhardness of vehicles alone was also evaluated at 1 mm from the pulp cavity. Camphorated monochlorophenol is clinically used mixed with PG since PG majored the working paste consistence into the root canal. ,, Results indicate that all calcium hydroxide pastes and all vehicles reduce the microhardness of the root dentin, except distilled water. The significant alterations on dentin microhardness after the treatments indicate a direct effect of these medicaments on the components of the dentin structure. Viscous and oily vehicles,  alone and associated to calcium hydroxide, reduced dentin microhardness more than aqueous vehicles. Chlorhexidine solution had the only effect through time; however, the paste showed a similar behavior than the others. Calcium hydroxide pastes were more effective than vehicles alone in reducing the dentin microhardness, which might be explained by the organic dissolving properties of the high pH value of calcium hydroxide.  Since dentin is exposed to fractures after the endodontic treatment, reduction in microhardness may facilitate the preparation of the root canal and the adhesion of sealers to the treated dentin.  However, the effect of these pastes and vehicles on other mechanical properties such as flexural and compressive strength should also be analyzed.
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[Table 1], [Table 2]