Solubility and pH of calcium hydroxide lining cements

Solubilidade e pH dos cimentos forradores de hidróxido de cálcio

ABSTRACT

Objective:

To analyze the solubility and the potential of hydrogen ions in calcium hydroxide-based lining cements used in dentistry to protect the dentin-pulp complex during rehabilitation treatments.

Methods:

The evaluated cements bear the commercial names Dycal (Dentsply Sirona), Hydcal (Maquira), Hydro C (Dentsply Sirona), and light-cured Biocal (Biodinâmica). Solubility measurements followed the methodologies proposed by the American National Standards Institute and the American Dental Association, while the potential of hydrogen was determined using a digital pH meter.

Results:

Solubility exhibited no significant differences either individually or between the groups. Regarding the potential of hydrogen, the results were as follows: Dycal 12.06, Hydcal 12.06, Hydro C 10.5, and light-cured Biocal 8.48, highlighting disparities between the groups.

Conclusion:

There were no statistically significant differences in the descriptive analysis of the solubility of the tested calcium hydroxide cements. However, the descriptive analysis of the pH of the cements revealed statistically significant variances between the groups.

Indexing terms
Calcium hydroxide; Dentistry; Operative dentistry

RESUMO

Objetivo:

Analisar a solubilidade e o potencial de íons hidrogênio em cimentos forradores à base de hidróxido de cálcio utilizados em odontologia para proteção do complexo dentino-pulpar durante tratamentos reabilitadores.

Métodos:

Os cimentos avaliados possuem os nomes comerciais Dycal (Dentsply Sirona), Hydcal (Maquira), Hydro C (Dentsply Sirona) e Biocal fotopolimerizável (Biodinâmica). As medidas de solubilidade seguiram as metodologias propostas pelo American National Standards Institute e pela American Dental Association, enquanto o potencial de hidrogênio foi determinado por meio de pHmetro digital.

Resultados:

A solubilidade não apresentou diferenças significativas individualmente ou entre os grupos. Em relação ao potencial de hidrogênio, os resultados foram os seguintes: Dycal 12.06, Hydcal 12.06, Hydro C 10.5 e Biocal fotopolimerizável 8.48, evidenciando disparidades entre os grupos.

Conclusão:

Não houve diferenças estatisticamente significativas na análise descritiva da solubilidade dos cimentos de hidróxido de cálcio testados. Entretanto, a análise descritiva do pH dos cimentos revelou variações estatisticamente significativas entre os grupos.

Termos de indexação
Hidróxido de cálcio; Odontologia; Dentística operatória

INTRODUCTION

Untreated dental caries lead to the destruction of the dental organ, resulting in extensive cavities that require protection for the dentin-pulp complex. Calcium hydroxide-based cements are widely used in various clinical situations in dentistry for direct and indirect protection of the dentin-pulp complex, as temporary dressings, and for the fixation of temporary prosthetics [¹]. Its initial recognition as a therapeutic agent in dental practice dates back to 1838 by Nygren. However, it was only established in the market in 1920 by Hermann, with the results obtained with Calxyl - the first calcium hydroxide-based material used in pulp exposures - [²].

This material is biocompatible, raises the pH of the environment, stimulates tissue mineralization by releasing calcium and hydroxyl ions, promotes the formation of reparative dentin and exhibits antimicrobial action [³]. The action of these properties occurs sequentially. While hydroxyl ions induce a high pH, inhibiting enzymatic microbial growth and releasing alkaline phosphatase involved in mineralization, calcium ions are crucial in stimulating mineralized tissue formation [⁴,⁵].

Nevertheless, the physical and mechanical properties of this cement, such as solubility and resistance, have raised questions, given that cavity liners should demonstrate resistance to solubility in water, to organic acid conditioning solvents, as well as support restorations and withstand occlusal forces during mastication [⁶].

In this regard, calcium hydroxide cements have disadvantages. They are susceptible to the effects of saliva and microorganisms in the oral environment, exhibit high solubility, are prone to degradation over time, show deficiencies in dentin barrier formation, and lack chemical and mechanical adhesion to dentin and restorative materials. Nonetheless, these materials promote the healing of the dentin-pulp complex and act against infection [⁷,⁸].

Considering that these cements hold great importance in dental practice, they must be used to enhance the performance of their properties, aiming to prevent or, at least, minimize potential shortcomings in their intended functions. Therefore, the objective of this study is to analyze the pH and solubility of calcium hydroxide-based cavity lining cements.

METHODS

This article is an experimental, observational research with a quantitative approach. The calcium hydroxide-based cavity lining cements evaluated were Dycal (Dentsply Sirona, Bogotá, Colombia), Hydcal (Maquira, Maringá, Brazil), Hydro C (Dentsply Sirona, Bogotá, Colombia), and light-cured Biocal (Biodinâmica, Paraná, Brazil).

For solubility testing, the American National Standards Institute/American Dental Association (ANSI/ADA, 2000) specification number 57 was used. Five circular Teflon^® (Polytetrafluoroethylene, DuPont, HABIA, Knivsta, Switzerland) molds with a thickness of 1.5 mm and an internal diameter of 7.75 mm were used for each cement. The molds were placed on a thin cellophane sheet supported by a glass plate (40 X 80 X 5 mm). The cement to be tested was manipulated and placed inside the mold. A waterproof nylon thread with a diameter of approximately 0.5 mm was then inserted into the softened cement mass.

Subsequently, another glass plate of the exact dimensions as the one placed under the cement, wrapped in cellophane, was placed on top of the mold filled with the material. A weight of 100 g was placed on top of this assembly. The entire setup was transported to a climate-controlled chamber with a temperature of 310 ± 2K and a relative humidity of 95 ± 5%.

After an interval three times longer than the previously determined setting time for each cement, the sample was removed from the mold, any loose particles or residues were removed, and it was weighed, rounded to the nearest 0.001 g, using a precision scale with an accuracy of 0.0001 g (Ohaus Corporation, New Jersey, NJ, USA).

Then, the test specimens were suspended, two by two, by securing the nylon threads inside plastic containers with lids containing 7.5 ml of distilled and deionized water and placed in an oven at 310 ± 2K for 24 hours. After the required time, the samples were rinsed with distilled and deionized water. Any excess was removed with the help of absorbent paper, kept in a dehumidifier for 24 hours, and re-weighed after 24 hours. The pH measurement was carried out using a digital pH meter, which was previously calibrated with buffer solutions (pH 4.0 and 7.0).

RESULTS

The data were previously organized and distributed in the Microsoft Excel program for an initial descriptive analysis of the cement groups in relation to the initial weighting and their weight after 24 hours, as well as pH. Statistical analyses were conducted using the R software (statistical and graphical programming language) and SPSS Statistics, considering a significance level of 5% (p-value <0.05).

Table 1
Descriptive analysis of the weight measurements of the cements before and after 24 hours.

	Hydcal			Hydro C			Dycal			Biocal
	Initially	After 24h		Initially	After 24h		Initially	After 24h		Inítially	After 24h
Mean	0.1492g	0.1112g		0.1682g	0.1641g		0.1681g	0.1531g		0.1471g	0.1355g
Standard Error	0.0127g	0.0179g		0.0092g	0.0119g		0.0109g	0.0097g		0.0073g	0.0167g
Median	0.1462g	0.1079g		0.1654g	0.1649g		0.1701g	0.1609g		0.1486g	0.1464g
Standard Deviation	0.0283g	0.0401g		0.0206g	0.0267g		0.0244g	0.0217g		0.0162g	0.0373g

Table 2
Descriptive analysis of the pH of the cement samples.

Descriptive analysis	Hydcal	Hydro C	Dycal	Biocal
Mean	12.06	10.5	12.06	8.48
Standard Error	0.186011	0.402492	0.05099	0.193391
Median	12.30	10.8	12.10	8.40
Standard Deviation	0.42	00.9	0.11	0.43

Tests were conducted to compare the cement groups before and after 24 hours and to assess the homogeneity and normality of the data. Subsequently, independent samples Student’s t-tests were applied to the corresponding groups.

Table 3
Comparisons between the corresponding independent groups of cements.

Cements (Initially x After 24h)	t-start	gl	p-value
Hydcal	1.73	8	0.12*
Hydro C	0.27	8	0.80*
Dycal	1.02	8	0.34*
Biocal	0.64	8	0.54*

• Note:
• ^*
  The data showed no statistically significant differences in the means of the cement samples between the first and second weighings (p-value >0.05).

Regarding the pH of the samples, the Kruskal-Wallis test revealed statistically significant differences between the distributions of the samples in the cement groups (χ² = 15.9; df = 3; p-value = 0.001). Thus, Mann-Whitney tests were conducted, due to the non-normality of the data, to compare the groups, resulting in the following outcomes:

Table 4
Comparison between the groups.

	Hydcal	Hydro C	Dycal	Biocal
Hydcal	--	0.01*	0.55	0.01*
Hydro C	--	--	0.01*	0.02*
Dycal	--	--	--	0.01*
Biocal	--	--	--	--

• Note:
• ^*
  Statistically significant results (p-value < 0.05),
• indicating differences between the groups.

DISCUSSION

In the present study, four different brands of calcium hydroxide-based cements were evaluated. In dental clinical practice, these cements are intended for use as protection of the dentin-pulp complex, temporary dressings, and fixation of provisional prostheses. Therefore, their widespread use is attributed to several advantages in clinical application, such as antimicrobial action and the ability to promote mineralized tissue formation, thereby creating a biomechanical barrier in procedures like pulp capping and pulpotomies. However, these cements also come with some disadvantages, including low mechanical resistance, solubility in the oral environment, and a lack of adhesion to cavity walls, making them susceptible to failure. Consequently, there is a need for further research to validate their effectiveness [⁹].

Of the evaluated calcium hydroxide cements, three of them — Dycal, Hydcal, and Hydro C — are chemically activated and consist of a base paste and a catalyst paste. The fourth evaluated cement was Biocal, which is photoactivated. These cements contain an alkaline content that reduces infection, stimulates the healing of the dentin-pulp complex, and promotes the formation of a mineralized barrier through the activation of tissue enzymes [¹⁰].

With the aim to investigate the response of calcium hydroxide cement in terms of its solubility and pH in the oral environment after the post-acid-conditioning wash, minimal statistical differences were observed after the samples had been immersed in distilled water for 24h, in both the initial and subsequent weight measurements individually, as well as in the comparison between the groups. This finding is substantiated by the statistical methodology conducted to assess the data homogeneity, which included weight data, mean, standard error, median, and standard deviation, thereby not indicating significant changes in the calcium hydroxide cements after the solubility test.

In light of this, it can be asserted that calcium hydroxide cement, despite its relative solubility in the oral environment and following acid conditioning, demonstrates substantial resilience to meet the clinical requirements for which it is recommended. As an example, its properties in the formation of a mineralized barrier are vital in procedures such as pulpotomies and pulp capping [¹¹].

Regarding the pH of calcium hydroxide cements, known for their antimicrobial properties, significant differences were observed between the groups, affecting the efficacy of these cements in terms of antimicrobial activity. This observation is supported by a detailed analysis of each cement’s data and the statistical analysis conducted between the following groups: Hydcal/Hydro C, Hydcal/Biocal, Hydro C/Dycal, Hydro C/Biocal, and Dycal/Biocal. Therefore, Hydcal exhibits less variation in data and superior performance in achieving the expected pH concentration compared to the other cements. Meanwhile, Biocal shows lower effectiveness in pH value and approaches neutrality. This is highly relevant, as numerous microorganisms inhabit the oral cavity, and considering the increased vulnerability of dental tissues following procedures like pulpectomies and pulpotomies, the capacity to combat bacteria plays a crucial role in preventing the need for more invasive interventions [¹²].

Considering the data collected in this study and the scientific literature, the importance of the clinical use of calcium hydroxide cement as a temporary dressing acting as a mineralized barrier and its antimicrobial action becomes evident [¹³]. Thus, the results emphasize the significance of this material, even when available from different brands and in chemically activated or photoactivated forms. In the analysis of the results, solubility did not show significant differences, either individually or between the groups. However, it is worth noting that the light-cured Biocal cement displayed a pH closer to neutral, which can be considered a disadvantage, as the alkaline pH of these cements is one of their main benefits in cases of caries processes. Consequently, close monitoring of clinical cases within dental practice is imperative to confirm the material’s efficacy and longevity. Hence, it is advisable to continue the clinical use of this material, substantiated by proven results for dental applications [¹⁴].

CONCLUSION

In the descriptive analysis of the solubility of the tested calcium hydroxide cements, no statistically significant differences were found. However, when analyzing the pH of the cements, statistically relevant differences were observed between the groups.

How to cite this article

• Resende MEA, Almeida WC, Furtado SAS, Falcão CAM, Ferraz MAAL. Solubility and pH of calcium hydroxide lining cements. RGO, Rev Gaúch Odontol. 2024;72:e20240033. http://dx.doi.org/10.1590/1981-86372024003320240007

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Edited by

Assistant editor: Luciana Butini Oliveira

Publication Dates

• Publication in this collection
  21 Oct 2024
• Date of issue
  2024

History

• Received
  24 Jan 2024
• Accepted
  28 June 2024