Effect of incorporation of a new antimicrobial nanomaterial on the physical-chemical properties of endodontic sealers.

OBJECTIVES: The objective of the study is to incorporate the nanostructured silver vanadate (AgVO3) decorated with silver nanoparticles at endodontic sealers AH Plus, Sealapex, Sealer 26, and Endofill, at concentrations of 2.5%, 5%, and 10%, and to evaluate physical-chemical properties.
MATERIALS AND METHODS: The study was to evaluate the radiopacity using digital radiography (n = 5), the tooth color change in 48 incisors (n = 3) for 7, 30, 90, and 180 days in a spectrophotometer, and the topographic distribution in a confocal laser (n = 5). The radiopacity was analyzed by Kruskal-Wallis test and the permutation (α = 0.05) and the color and topographical distribution by descriptive statistical analysis.
RESULTS: The AgVO3 had no effect on the radiopacity of Endofill and Sealapex (P > 0.05) and at 2.5% concentrations increased the radiopacity of Sealer 26 and AH Plus (P < 0.05). The Endofill 10% showed less color change, and the major changes were the modified groups in 180 days. The AgVO3 showed a circular topographic distribution in areas of the sealers.
CONCLUSION: It was found that the addition of AgVO3 did not affect the radiopacity of Endofill and Sealapex however, increased the radipacity of Sealer 26 and AH Plus. For modified groups, the greatest color change was promoted after 180 days, except for Endofill with 10%. Topographic distribution of nanomaterial affected the color change of theevaluated sealers.

INTRODUCTION

The modification of endodontic sealers with antimicrobials and nanoparticles helps reduce microorganisms in the root canals.[1] However, the addition of these agents may modify the physical properties depending on the concentration added.[2]

The nanostructured silver vanadate (AgVO3) decorated with silver nanoparticles (AgNPs) is a nanomaterial that has shown antimicrobial activity when incorporated into the acrylic resins[3] and endodontic sealers.[4] In addition, because of its antimicrobial activity, AgNPs were incorporated into various dental materials.[5] However, they present thermodynamic instability and agglomerations.[56] The AgVO3 solves these problems since it stabilizes the AgNPs associating them with vanadate nanowires.[6]

The agglomerations and the dispersion pattern of the nanoparticles affect the physical-chemical, optical, mechanical, and microbiological properties of the materials.[78] These properties are required for endodontic sealers, such as radiopacity, which are used to assess the quality of the obturation.[9] In addition, it can prevent tooth color changes, which occur when its components diffuse through the dentinal tubules during or after setting.[1011]

The AgNPs are alternative radiopacifier agents that can improve physicochemical properties and guarantee antimicrobial activity.[12] However, to remedy the disadvantages of AgNPs, the aim of this paper is to incorporate the AgVO3 to four endodontic sealers at different concentrations and to evaluate the radiopacity, tooth color change, and topographic distribution.

MATERIALS AND METHODS

Nanostructured AgVO3 decorated with AgNPs was synthesized according to the methodology described by de Castro et al.[3]

Different compositions of endodontic sealers [Table 1] were modified with 0% (control), 2.5%, 5%, and 10% of AgVO3. Samples were prepared by mixing the AgVO3 percentages (by weight), proportionally incorporated into the powder or base paste of the endodontic sealer, and weighed on a precision scale.

Table 1

Description of the composition of the endodontic sealers used

For the radiopacity test, the specimens (n = 5) were obtained from acrylic plates with four wells (1.0 mm depth × 5.0 mm diameter). The samples containing 0%, 2.5%, 5%, and 10% of AgVO3 were placed in well, and the plates were placed in a stove at 37°C until the setting of the sealers. The acrylic plate was placed on the VistaScan phosphor plate X-ray scanner (©Drr Dental AG, Bietigheim-Bissingen, BW, Germany) alongside another acrylic plate that contained an aluminum scale, thickness varying from 1 to 10 mm, in uniform 1 mm steps. The radiographic images were acquired by a SPECTRO 70X digital X-ray (Dabi Atlante Indústrias Médico Odontológicas Ltda., Ribeirão Preto, SP, Brazil) at 70 kVp and 8 mA, exposure time of 0.25 s, and a standardized 30-cm sensor-to-focus distance.[13] The mean value of the grayscale tones of the aluminum scale and of the specimens was evaluated using Image J software (National Institutes of Health, Bethesda, MD, USA) selecting a region of interest of 30 pixel × 30 pixel (variation of ±1). The mean grayscale value was converted to millimeter aluminum equivalent values (mmAl).

The tooth color change was evaluated in central and lateral, upper, and lower healthy incisors (n = 3) (Ethics Committee Approval – Process No. 42108815.0.0000.5419), which were selected and sectioned in the horizontal plane of the middle third of the root. The canals were instrumented with K-type files #40 (DENTSPLY, Petrópolis, RJ, Brazil) and irrigated with 2.5% sodium hypochlorite (Ciclo Farma, Serrana, SP, Brazil) and ethylenediaminetetraacetic acid (Trissódico Líquido, Biodinâmica, Ibiporã, PR, Brazil) for 3 min. Next, the canals were irrigated with distilled water and dried with paper cones (DENTSPLY, Petrópolis, RJ, Brazil). The cavities were filled with newly manipulated endodontic sealers and sealed with a 3M Single Bond adhesive system (3M ESPE, St. Paul, MN, USA) and the Filtek Z250TM composite resin (3M ESPE, St. Paul, MN, USA). The teeth were stored in individual containers with distilled water covering the dental crown and placed on the stove at 37°C.

The color measurement was performed before and after 7, 30, 90, and 180 days of the insertion of sealers in the root canal using a portable color spectrophotometer (XRITE Incorporated, SP 62S, Grand Rapids, MI, USA) and the CIE L*a*b* system, which consists of the L* coordinates that indicates luminosity (L* = 0 [black]–L* = 100 [white]), a* whose color characteristic varies from green (−a) to red (+a), and b* blue (−b) to yellow (+b). The tooth color change was calculated by ΔE (ΔE = √ [ΔL*]2 + [Δa*]2 + [Δb*]2), where Δ L*, Δa*, and Δb* are expressed by the difference between the initial sample and the color evaluation times of the corresponding coordinate (ΔL* = L*final – L*initial, Δa* = a*final – a*initial, Δb* = b*final – b*initial). The active point of the spectrophotometer was placed in the middle third of the vestibular face of the dental crown, performing three readings to obtain the arithmetic mean. For the color evaluation, always in the same tooth area, they were individually included in heavy addition silicones (Adsil Putty Soft, Coltene, Vigodent S/A Indústria and Comércio, Rio de Janeiro, RJ, Brazil) and molded in the equipment.

In topographic analysis, the specimens were obtained in a manner similar to radiopacity (n = 5). The topographical distribution of AgVO3 in the sealers was evaluated using a laser confocal microscope LEXT OLS4000® (Olympus, Tokyo, Japan), the most representative area was selected, and the topographic image acquisition of the specimens was performed using a ×50 magnification lens and ×1074 optical zoom.

For the statistical analysis, the radiopacity was analyzed by Kruskal–Wallis test and permutation using the R software (R Foundation, Vienna, Austria) (α = 0.05). The descriptive statistical analysis was used to evaluate the tooth color and topographic distribution of AgVO3; the numeric data were evaluated using the SAS Output System, v9.4 (SAS Institute, Cary, NC, USA).

RESULTS

For the radiopacity, there was no significant difference between the control groups and the groups modified with AgVO3 for Endofill and Sealapex (P = 0.399 and P = 0.316, respectively). The 2.5% group of Sealer 26 showed higher radiopacity than the control (P = 0.022) and the other modified groups (P < 0.05). The AH Plus control presented lower radiopacity than the 2.5% group (P = 0.006) and did not differ from the other groups. The 10% AH Plus presented radiopacity lower than 2.5% and 5% (P = 0.002 and P = 0.034, respectively), which did not differ among themselves (P = 0.221) [Table 2].

Table 2

Radiopacity of the endodontic sealers modified with different concentrations of nanostructured silver vanadate decorated with silver nanoparticles

Considering ΔE >3.7, the most significant tooth color changes were observed at 180 days for all modified groups, except for Endofill 10%. In comparison to the control groups, the greatest tooth color change in Endofill was with the incorporation of 2.5%; for AH Plus, it was with 2.5% and 10%; for Sealapex, it was with 5% and 10%; and for Sealer 26, it was with 10%, at different evaluation times [Figure 1].

Figure 1

Mean and standard deviation of the ΔE values of tooth color change. (a) AH Plus. (b) Sealapex. (c) Sealer 26. (d) Endofill

In topographic analysis, it was observed that for all groups modified with different concentrations of AgVO3, there was a topographical distribution pattern with dispersed smaller nanoparticles and agglomerations in random areas [Figure 2]. It is suggested that these agglomerations influenced the tooth color change in the groups modified with AgVO3.

Figure 2

Images of endodontic sealers in laser confocal microscope (×1074), arrows indicate agglomeration of AgVO3. (a) AH Plus 0%. (b) AH Plus 2.5%. (c) AH Plus 5%. (d) AH Plus 10%. (e) Endofill 0%. (f) Endofill 2.5%. (g) Endofill 5%. (h) Endofill 10%. (i) Sealapex 0%. (j) Sealapex 2.5%. (k) Sealapex 5%. (l) Sealapex 10%. (m) Sealer 26 0%. (n) Sealer 26 2.5%. (o) Sealer 26 5%. (p) Sealer 26 10%

DISCUSSION

Nanotechnology is applied in the advancement of dental materials, which have the advantages of penetration in the dentinal tubules and antimicrobial activity.[11] The modification of endodontic sealers with antimicrobials and nanoparticles increases their antimicrobial effectiveness.[12] However, the use of antimicrobial additives may alter the physical properties of these materials, depending on the concentration that is added.[2] After the verification of the antimicrobial activity by Teixeira et al.,[4] in this study, the AgVO3 was added to four endodontic sealers and the radiopacity, tooth color change, and topographical distribution were evaluated.

The addition of AgVO3 observed by the topographic analysis showed that similar to that found by de Castro et al.,[3] the AgVO3 had a circular scatter, as shown in Figure 2, with the presence of smaller and dispersed nanoparticles, and random agglomerations, independent of the AgVO3 concentration or sealer type. This may be attributed to the manipulation characteristic, since it was carried out according to clinical practice, as in this study the objective did not include changing the dispersion of the nanomaterial.

The evaluation of the radiopacity with an optical densitometer was dispensed, and digital images were used,[13] obtaining a gray value per pixel in specialized software.[1314] The minimum radiopacity of sealing materials should be 3 mmAl.[15] In this study, all groups presented higher radiopacity than what is recommended. The addition of AgVO3 was increased for AH Plus and Sealer 26 2.5%, and in the clinical context, this increase has no relevant impact since all groups presented radiopacity above the recommended minimum. Studies that have evaluated the radiopacity of endodontic sealers modified with antimicrobial agents observed a reduction of this property, such as in Ruiz-Linares et al.[2] and in Viapiana et al.[16]

The sealers used in endodontics have the potential to cause changes in tooth color.[1011] These changes can be evaluated by spectrophotometers, equipment that eliminates subjective interpretations by the naked eye,[1117] and by CIE L*a*b* system, used to evaluate the color of dental materials.[18] Tooth color changes can be expressed by ΔE, where a value above 3.7 characterizes tooth color change perceptible to the naked eye.[171920]

The tooth color changes caused by endodontic sealers are time dependent, with the greatest change occurring between 180 days[1719] and 365 days.[21] In this study, the sealers modified with AgVO3 showed tooth color changes perceptible at 180 days, considering ΔE >3.7,[1920] except Endofill 10% (ΔE = 2.57), and Sealer 26 10% showed the greatest change.

The endodontic sealers were inserted to fill the canal and the pulp chamber. Clinically, the obturation traces should be removed from the chamber to prevent dental staining.[1721] In addition, anatomical differences may cause greater tooth color changes from one tooth to another. In this study, extracted teeth were used, and although they were maintained in 100% humidity, in vitro tests do not reproduce the clinical and biological conditions of a tooth in vivo.[20]

Silver and other heavy metals, present in the composition of restorative and obturator materials, can stain dentine, and their corrosion changes from gray to black.[101117] The AgVO3 consists of nanoscale silver, which may have contributed to the greatest tooth color change in the modified groups. In addition, zinc oxide, which composes Endofill, undergoes oxidation due to its binding to eugenol.[17] This can explain the perceptible changes in the control group. After 180 days, the color change of teeth sealed with Endofill 10% was imperceptible it can be explained by the reduction of the sealer componentes associated with the production of oxides.

These differences between the groups modified with AgVO3 correlate with the topographical distribution pattern since the optical properties of the nanoparticles are caused by plasmon resonance, in which the wavelength absorption of the visible light spectrum is dependent on the nanoparticle size.[22] Thus, smaller nanoparticles absorb light at smaller wavelengths and nanoparticle aggregates at longer wavelengths, causing changes in the color transmitted.[23] It is therefore likely that the modified endodontic sealers have more agglomerated nanoparticles.

Thus, the results suggest that using AgVO3 incorporated into sealers, the same maintained and improved the radiopacity. Different methods can be performed to evaluate tooth color change of the dental structure. And, to make feasible the use of these materials, further studies of the physical-chemical properties should be carried out.

CONCLUSION

It was found that the addition of AgVO3 did not affect the radiopacity of Endofill and Sealapex however, increased the radipacity of Sealer 26 and AH Plus. Greater color change was observed for groups modified with the nanomaterial after 180 days, except to Endofill 10%. Topographic distribution of nanomaterial affected the color change of the evaluated sealers. The topographical distribution of AgVO3 affected the tooth color change.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.