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ORIGINAL ARTICLE
Year : 2020  |  Volume : 12  |  Issue : 1  |  Page : 47-51

Effect of Different Levels of Salivary pH on the Shear Bond Strength of Two Orthodontic Adhesive Systems for Bracket Placement: An In-vitro Study


1 Division of Orthodontics, School of Dentistry, Universidad Peruana Cayetano Heredia, Lima, Perú
2 Division of Orthodontics, School of Dentistry, Universidad Científica del Sur, Lima, Perú

Date of Submission14-Sep-2019
Date of Decision04-Dec-2019
Date of Acceptance16-Dec-2019
Date of Web Publication12-Jun-2020

Correspondence Address:
Angelita Leonarda Carpio Contreras
Division of Orthodontics, Faculty of Dentistry, Universidad Peruana Cayetano Heredia, Lima, Perú. Av. Honorio Delgado 430, San Martin de Porres.

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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jofs.jofs_109_19

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  Abstract 


Introduction: The aim of this study was to compare the effect of four different salivary pH levels on the shear bond strength (SBS) of two orthodontic adhesive systems for bracket placement. Materials and Methods: This in-vitro experimental study was performed on 72 premolars extracted for orthodontic reasons. They were randomly assigned into two groups according to the adhesive system employed: Orthocem (light-cure adhesive, FGM®) or Transbond-XT (3M Unitek). Each group involved nine specimens incubated in artificial saliva at four pH levels regarding previous studies: acidic pH (4.8 and 5.8), control pH (6.8) and alkaline pH (7.8), during two months. Once removed, shear bond strength with a universal testing machine was applied. The SBS comparisons between adhesive systems was obtained using t-test and for salivary pH levels in each group one-way ANOVA and Tukey tests were used (P < 0.05). Results: Transbond-XT adhesive system showed the greater SBS, mainly in the neutral salivary pH (11.18 ± 2.82 Mpa) followed by the alkaline (10.33 ± 2.49 Mpa) (P > 0.05). Significant differences were found regarding to both acidic pH levels (pH 4.8 and 5.8) with values between 6 and 8 MPa (P < 0.05). Moreover, Orthocem adhesive system had lower SBS values, with greater value in the neutral salivary pH (6.24 Mpa), don’t achieved significant differences with the other pH levels; 4.74 Mpa for pH 4.8 and 5.05 Mpa for pH 5.8. Conclusion: Transbond XT orthodontic adhesive system showed only greater values of SBS only for the control and alkaline pH levels; for acidic pH levels there was no difference between the two systems. This situation must be taken into account by clinicians.

Keywords: Orthodontic adhesive systems, salivary pH, shear bond strength


How to cite this article:
Carpio Contreras AL, López AM, Arriola-Guillén LE. Effect of Different Levels of Salivary pH on the Shear Bond Strength of Two Orthodontic Adhesive Systems for Bracket Placement: An In-vitro Study. J Orofac Sci 2020;12:47-51

How to cite this URL:
Carpio Contreras AL, López AM, Arriola-Guillén LE. Effect of Different Levels of Salivary pH on the Shear Bond Strength of Two Orthodontic Adhesive Systems for Bracket Placement: An In-vitro Study. J Orofac Sci [serial online] 2020 [cited 2020 Dec 5];12:47-51. Available from: https://www.jofs.in/text.asp?2020/12/1/47/286478




  Introduction Top


Saliva is a high complexity biological fluid, one of its most outstanding properties is the buffering capacity consisting in salivary pH levels regulation, being 6.8 the pH of saliva. Bicarbonate is considered the main buffer of saliva, its concentration changes depending on the salivary flow; but also, phosphate and proteins are considered salivary buffers.[1],[2],[3],[4] Some medical conditions are associated with salivary pH changes, as Sjögren’s syndrome in which patients have xerostomia and a decrease salivary pH in a range of 5.4–5.5.[5],[6],[7],[8] Contrary, individuals with chronic generalized gingivitis or chronic generalized periodontitis have increased salivary pH in a range approximate of 7.43–11.65. Diabetes mellitus patients have a significant increase incidence of periodontitis.[8],[9],[10],[11]

In orthodontic practice, bonding is a procedure highly important and over the years the techniques for the bracket placement have been modified, using different orthodontic adhesive systems. The American Society for Testing and Materials (ASTM) defines adhesion as the force capable of holding materials joined by means of surface bonds. Buonocore et al.[12] introduced the technique of acid etching and since then, the concept of bonding began to be used in dentistry. Besides, Reynolds et al.[13] suggest that the minimum required force for bracket bonding is in a range between 6 and 10 MPa.[13],[14],[15],[16],[17],[18],[19],[20],[21]

With the new advances, these requirements seem to have been adequately achieved. Bonding failure can be caused by many factors, such as acidic beverages intake. In this regard, Oncag et al.[16] and Ullusoy et al.[17] concluded that the acidic pH of some beverages decalcify the enamel surrounding the brackets, which have negative effect on bonding at the bracket-enamel interface, reducing the shear bond strength (SBS).

In the clinical practice, efficient bonding guarantees that the brackets do not detach in approximately two years of treatment. Some factors like a masticatory force cannot be controlled directly by the clinician, but internal factors such as acidic salivary pH, typical in some individuals, could be controlled with specific advices to restrict acidic foods and beverages avoiding its consequences on tooth enamel and failures in the adhesion of the brackets. Therefore, the purpose of this study was to compare the effect of four different salivary pH levels on the shear bond strength of two orthodontics adhesive systems for bonding brackets.


  Materials and Methods Top


Ethical approval for this study, was provided by the Ethical Committee of Peruvian University Cayetano Heredia SIDISI number 100509, on 09 March 2017. The sample included 72 premolars extracted for orthodontic reasons unrelated to the study. Two groups of 36 teeth were formed. The first group used the orthodontic adhesive system Orthocem (light-cure adhesive, FGM® Joinville, SC, Brasil) and in the second group the orthodontic adhesive system Transbond XT (light-cure adhesive, 3M Unitek, Monrovia, CA, USA) was employed. In both groups the specimens were divided into four subgroups of nine pieces each according to the different pH levels. Acid pH (4.8, 5.8), control pH (6.8), alkaline pH (7.8); subsequently they were incubated two months in artificial saliva according to the parameters set in the research work of Toodehzaeim et al.[18] Healthy premolars, uni or bi radicular, were included and premolars with enamel hypoplasia, fissures, cracks, erosions, or treated with any chemical agent previous to the study were excluded.

The selected teeth were washed with running water and then stored in physiological saline solution (NaCl 0.9%) at room temperature. Prophylaxis of the premolars was performed, using a Robinson brush and prophylactic paste (Dentsply); afterwards, the horizontal and vertical references were drawn with a mechanical pencil (mine 0.5mm); to position the bracket in the center of the dental crown, first the vertical axis was drawn on the vestibular surface of the anatomical crown, then using a stainless steel articulated bracket positioner (Morelli®, Sorocaba, BR) was drawn a horizontal line to the anatomical crown center. Finally, the vestibular surface was conditioned with 37% phosphoric acid Condac37 (FGM Orthodontics Products, Joinville, SC, BR) for 30 seconds, rinsed with running water for 30 seconds and dried with air from the triple syringe.

In this study, stainless steel premolar brackets were used, prescription Roth 0.022"x 0.028" (Master Series TM, American Orthodontics, Sheboygan). In the first group, a layer of the light-curing orthodontic adhesive system Orthocem (FGM® Joinville, SC, Brasil) was placed on the surface of the bracket mesh. The brackets were placed at the intersection of the vertical and horizontal lines drawn on the buccal surface of the premolars, after removing the excess material with a dental scaler, adhesive was cured using light-emitting diode (LED) light curing unit (LED Lamp B, Woodpecker) with a power of 850mW/cm2, for 20 seconds in each gingival surface, mesial and distal. In the second group, the same procedure was carried out using the light-curing orthodontic adhesive system Transbond XT (3M Unitek, Monrovia, CA, USA). For both orthodontic adhesive systems, the manufacturer’s protocol was followed ([Figure 1]A, 1B, 1C, 1D).
Figure 1 Sequence of procedures for the adhesion of the brackets. A. Cleaning the tooth for adequate adhesion of the brackets. B. Etching acid to condition the tooth enamel. C. Locating the bracket in its correct position in the tooth. D. Polymerization of the bracket adhered to the dental enamel.

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Each subgroup was incubated in artificial saliva with a specific pH under similar conditions for two months. The pH levels of the solutions for the groups were acidic pH (4.8 and 5.8), control pH (6.8) and alkaline pH (7.8). The solutions were changed weekly. The artificial saliva used was prepared in the Laboratory of Production and Services, Department of Exact Sciences − Chemical Section, Faculty of Sciences and Philosophy of the Peruvian University Cayetano Heredia, with the following formulation, 0.4g NaCl, 1.21g KCl, 0.78g NaH2PO4. 2H2O, 0.005g Na2S. 9H2O, 1g CO (NH2) 2, and the buffers were used to adjust the pH.

The sample was placed in Vitacron fast curing self-curing acrylic supports, measuring 5mm x 5mm, these were labeled with the initial letter of the adhesive system and the salivary pH level. The shear bond strength was measured using a universal testing machine (CMT-5L, LG), with an approximation of 0.001N; at a speed of 0.5 mm/min. Each bracket adhered to the tooth surface was placed parallel to the direction of load application. To measure the diameter of the brackets, a 200 mm digital Vernier (Mitutoyo) was used, with an approximation of 0.01mm, in the Laboratory specialized in mechanical tests of HTL materials ([Figure 2]A, 2B).
Figure 2 Procedures for the shear bond strength test. A. Positioning the tooth with the bracket attached to begin the mechanical test. B. Shear bond strength test.

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Statistical analyses

The data was entered in the statistical program SSPS 22.0 (IBM, Armonk, NY, USA). The Levene test and the Kolmogorov-Smirnoff test were performed to verify the data normality and the homogeneity, as well as the degree of dispersion of the data in the resistance to shear. Descriptive statistics was calculated for all groups. The comparison between the adhesive systems was made with the Student t-test. For the comparison in each adhesive cement between the different salivary pH values, the one-way ANOVA test and Tukey’s multiple comparisons test were used. The level of significance was set to P < 0.05.


  Results Top


[Table 1] showed both orthodontic adhesive systems the Transbond XT and Orthocem achieved the maximum resistance with salivary pH neutral. However, Transbond XT adhesive system showed the greater values (11.18 ± 2.82 Mpa) followed by the alkaline pH (10.33 ± 2.49 Mpa) (P > 0.05) and showed significant differences with both acidic pH levels (pH 4.8 and 5.8) that had the lower values 6.78MPa and 8.51 MPa respectively (P < 0.05). Orthocem adhesive system had lower values of resistance, although its greater value was in the neutral salivary pH (6.24 Mpa) don’t achieved significant differences with the other pH levels; 4.74 Mpa for pH 4.8, 5.05 Mpa for pH 5.8 and 4.98 Mpa for pH 7.8.
Table 1 Comparison of the values of shear bond strength by pH according to type of orthodontics adhesive systems

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  Discussion Top


In orthodontic practice, good bonding is important for effective treatment. However, bonding failures often occur. Saliva has a direct relationship with adhesion, therefore this study compares the effect of four different levels of salivary pH, two acidic pH 4.8 and 5.8, a control pH 6.8 (according to the parameters set in the research work of Toodehzaeim et al.),[19] and one alkaline pH 7.8 on shear bond strength of two commercial orthodontic adhesive systems, in order to select a good option for each patient.

There is no research to the understanding of the authors that compares shear bond strength between different salivary pH levels, that include alkaline pH; and those that exist, include very acidic values that usually are not present in the individuals.[19] Although the saliva has a buffer capacity, the acidic pH values show more risk of damage to tooth enamel. Thus, the findings in this investigation showed for both orthodontic adhesive systems the lowest mean value of shear bond strength belonged to the acidic pH group (4.8), and the highest values correspond to the group of control pH (6.8), in orthodontics that the minimum required force for bracket bonding is in a range between 6 to 10 MPa.[13],[15]

The maintenance of pH in the oral cavity is very important; when the pH in the oral cavity is stable, there is a decrease in the amount of demineralization; some conditions such as, periodontal disease, diabetes mellitus, Sjögren’s syndrome, cause a significant change in the composition of saliva, pH and buffer capacity. In individuals with Sjögren’s syndrome are much lower compared to those individuals with normal control.[7] The decrease in salivary pH produces enamel demineralization, and a reduction of shear bond strength, causing failure in the bracket-tooth junction,[16],[19] other studies indicate that the acidic pH of some beverages, does not have significant effects on shear bond strength, but acidic pH affects tooth enamel producing erosion and microfiltration.[18]

The present study includes the evaluation of the effect of alkaline pH (7.8). No studies have been found in the literature evaluating the effect of alkaline pH on shear bond strength. Many authors conclude that as the condition progresses, from health to gingivitis or periodontitis, there is a statistically significant gradual increase in pH levels.[8],[9] It’s important to consider that some medical health conditions are associated with periodontal disease such as diabetes mellitus.[10] Sharma et al.[20], compared the shear bond strength of four orthodontic adhesive systems without specifying salivary pH values, they found that the Transbond XT adhesive system achieved the highest shear bond strength (15 MPa); Finally, they conclude that all the orthodontics adhesive systems achieved recommended values (5.9–7.8 MPa). In our study despite the exposure to the different pH levels, we can see that the shear bond strength was maintained on recommended values at neutral and alkaline pH levels with the Transbond XT.

Busato et al.[22] evaluated the SBS and compared the same adhesive systems used in our study, Transbond XT and Orthocem FGM; unlike our study, there were no statistically significant differences, but the study did not consider salivary pH levels. In our study, Transbond XT adhesive system achieved higher shear bond strength values in relation to Orthocem. At acidic pH, the values of Orthocem adhesive system decrease below the values of force required for orthodontic treatment, but they remain in ranges suitable at neutral pH. The Transbond XT adhesive system remains within the ranges of forces necessary despite the acidity of artificial saliva; this adhesive system would be indicated for patients who have any condition in which there is salivary pH modification. Besides, our in-vitro study tried to reproduce oral saliva characteristics, using, artificial saliva with different pH levels; because its variation modifies the shear bond forces values in adhesive systems. Maintenance of salivary pH at adequate levels, can be obtained by decreasing the intake of acid beverages, good oral health and the detection of different medical health conditions; all these requirements are favorable for increasing SBS and bonding capacity in orthodontics treatments.


  Conclusion Top


Based on the results transbond XT orthodontic adhesive system showed only greater values of SBS for the control and alkaline pH levels, but for acidic pH levels there was no difference between the two systems.

Financial support and sponsorship

This research didn’t have sponsors.

Conflicts of interest

The authors don’t have conflicts of interest.



 
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