Comparison of Corrosion Properties of Temporary Anchorage Devices in Artificial Saliva, With and Without Fluoride - an in Vitro Study
Carllin Kuriakose
1, Rohit M
2, Shetty Suhani Sudhakar
3*,Glodwin Antony
4, Shendre Shrikant
5,Kenneth F.H.Tan
61Private Practitioner, Wayanad, Kerala, India
2Private Practitioner, Kozhikode, Kerala, India
3Srinivas Institute of Dental Sciences, Mangalore, Karnataka, India
4Private Practitioner, Ernakulam, Kerala, India
5,6Oxford dental college, Bangalore, Karnataka, India
*[email protected] ABSTRACT
Objectives: To compare the surface changes of three commercially available miniscrews after immersing in artificial saliva with and without fluoride.
Methods: The miniscrews were divided in to three groups-group I(Absoanchor), group II(SK Ti implant),group III(JSV Miniscrews) and were subjected to 2 hours of electrochemical testing using a three electrode setup after being immersed in two artificial saliva solutions- one with fluoride and one without fluoride. The surface topography of these samples were analysed using SEM scanning. The results of the study was subjected to statistical evaluation and conclusion was drawn.
Results: Absoanchorminiscrews showed higher corrosion resistance behavior than S K Ti implant and JSV miniscrews in artificial saliva solution with and without fluoride.
Interpretation and Conclusion: There was a significant drop in corrosion resistance properties in all the three groups when artificial saliva solution containing fluoride was used as the testing medium, thus concluding that topical fluorides may be vital and useful in improving the patient’s oral hygiene maintenance, it must be used judiciously as it might be a factor contributing to miniscrew corrosion and failure
.
Keywords
Miniscrews, TAD, Corrosion, Three cell electrochemical testing, SEM
Introduction
Temporary anchorage devices (TADs) or orthodontic miniscrews are commonly used as an additional anchorage component in fixed orthodontic treatment. Miniscrew failure is one of the major concern for any orthodontist. Failure is a multifactorial problem and most of the current literature shows a success rate of miniscrews is greater than 80%.1 Temporary anchorage devices remain in the oral cavity for prolonged time, thus biodegradation can occur in this period.This can accelerate due to mechanical, chemical or electrochemical process and this deterioration is called corrosion.
Miniscrew mobility and/or loss of anchorage or stability is a typical mode of failure in miniscrews.2 These TADs within the mouth interact continuously with aggressive agents such as bacterial biofilm and saliva leading to corrosion of the metal due to the electrochemical reaction that occurs. Orthodontic materials have to withstand physical, mechanical, and biological assaults in the patient’s mouth and must be biocompatible in that aggressive environment. Although fluoride therapy is indicated during orthodontic treatment in order to reduce the incidence of dental caries, there are reports that fluoride decreases the stability of the passive layer typically formed on titanium- based surfaces, thereby decreasing its corrosion resistance due to potential metal ion release.
TADs are made of titanium alloyed with aluminum and vanadium to form titanium alloy Ti-6Al-4V for increased strength, fracture and corrosion resistance. Their corrosion resistance compared with stainless steel alloys, are much
recycled miniscrews, broken miniscrews and miniscrews removed from patient’s mouth.
Miniscrews of three different companies having similar dimensions each of 1.3 mm diameter and 8mm length were selected for the study. A total number of 90 Miniscrews were selected and grouped as follows- Group 1 : Consist of 30 Miniscrews of Absoanchor (DentosInd), Group 2 : Consist of 30 Miniscrews of SK Ti implant (SK surgicals) and Group 3 : Consist of 30 Miniscrews of JSV Miniscrews (JSV ortho)
15 Miniscrews of each group was tested for corrosion resistance behaviour after immersing in artificial saliva solution (First medium) and the other 15 Miniscrews of each group was tested for corrosion resistance behaviour after immersing in artificial saliva solution to which 1500 ppm fluoridefrom sodium fluoride was added(Second medium). The tip of each miniscrews (standard 3mm level) was coated with nail polish (Lakme true wear color SS 1) and mounted in epoxy resin (Araldite standard epoxy adhesive) to allow for electrode connection and isolation.
Preliminary surface analysis of the miniscrews was done with the Scanning Electron Microscope (SEM) for surface topography as shown in figure 1.
FIGURE 1 - SEM SCANNING UNIT
An electrochemical cell as shown in figure 2 was used as the corrosive environment for studying the corrosion resistance of miniscrews. The cell consisted of a platinum electrode which acts as counter electrode, calomel electrode as reference electrode and miniscrews sample as the working electrode which was connected to a potentiostat. Artificial saliva solution with and without fluoride was used as the electrolyte mediums. Fluoride was added in the form of sodium fluoride. According to their group and the medium miniscrews were tested by placing the samples in the electrochemical cell for 2 hours. The change in the potential was recorded by a potentiostat.The open circuit potential was recorded with electrochemical testing and results were tabulated as shown in figure 2.
FIGURE 2 – THREE CELL ELECTROCHEMICAL TESTING UNIT
After the electrochemical tests, the samples are then analyzed using Scanning electron microscope (SEM) for studying the surface changes
.
Data Analysis
The statistical calculations were performed using the software SPSS for Windows (Statistical Presentation System Software, SPSS Inc. 1999, New York) version 19.0.The following statistical methods were employed in the present study. Descriptive statistics including mean, standard deviation.
Null Hypothesis: There is no significant difference in the score between the groups i.e. η1=η2=η3
Alternate Hypothesis: There is a significant difference in the score recorded between the groups i.e. η1≠η2≠η3
Level of Significance: 0.05
Results (Times New Roman, bold, 12)
The descriptive detail of corrosion potential values measured at the end of the 2 hour immersion period are shown in Tables 1.
TABLE 1- DESCRIPTIVE DETAILS OF THE STUDY GROUPS
Group ARTIFICIAL
SALIVA N Mean Std.
Deviation Minimum Maximum
GROUP I:
ABSOANCHOR
WITHOUT
FLUORIDE 15 159.07 14.245 137 183
WITH
FLUORIDE 15 -267.93 16.140 -293 -234
WITHOUT
15 107.20 8.419 95 123
FLUORIDE
Group ARTIFICIAL
SALIVA N Mean Std.
Deviation T-value P-value
GROUP I:
ABSOANCHOR
WITHOUT
FLUORIDE 15 159.07 14.245
76.82 0.001*
WITH
FLUORIDE 15 -267.93 16.140
GROUP II: SK TI IMPLANT
WITHOUT
FLUORIDE 15 107.20 8.419
101.69 0.001*
WITH
FLUORIDE 15 -457.00 19.770
GROUP III: JSV MINISCREWS
WITHOUT
FLUORIDE 15 102.13 7.864
115.23 0.001*
WITH
FLUORIDE 15 -476.53 17.788
*significant at the 0.05 level
ANALYSIS OF MINI SCREW SURFACES BY MEANS OF SCANNING ELECTRON MICROSCOPY
Figure 3 shows scanning electron microscopy images (SEM) before the electrochemical testing of group 1, 2 and 3.
Micro analysis of Absoanchor miniscrews, S K implants and JSV miniscrews demonstrated more adhered particles and a higher number of darkened spots as well as rough patches on their surfaces when samples were immersed in artificial saliva solution containing fluoride, as compared to the samples immersed in artificial saliva solution as shown in figure 4 an figure 5. Absoanchor miniscrews showed minimal surface changes when compared to S K implants and JSV miniscrews.
Figure 3- Scanning electron microscopy images (SEM) before the electrochemical testing. Figure 3(a),3(b)- group 1((ABSOANCHOR), 3(c).3(d)- Group 2 (S K TI IMPLANT) and 3(e),3(f)- group 3(JSV ORTHODONTICS)
Figure 4- Scanning electron microscopy images (SEM) after the electrochemical testing in artificial saliva solution without fluoride . Figure 4(a),4(b)- group 1((ABSOANCHOR), 4(c).4(d)- Group 2 (S K TI IMPLANT) and
4(e),4(f)- group 3(JSV ORTHODONTICS)
cause of poor performance and rejection of implants. Although fracture is frequently associated with a smaller diameter miniscrews, it may be conjectured that corrosion may be a confounding factor in the fracture process as observed in fractographic analyses of conventional dental implants.7
Fixed orthodontic treatment with compromised oral hygiene can result in enamel demineralization and dental decay.
Orthodontists commonly prescribe a daily topical fluoride to address this potential treatment complication. Fluoride promotes the formation of calcium fluoride in the teeth which stimulate remineralization while protecting against acid attack.8
Fluoride being more electronegative have a greater affinity to oxygen which degrades the passive layer on the miniscrews. Topical fluoride solutions have shown to produce stress corrosion cracking of commercially pure titanium.9 This study examined how fluoridated environment affects the miniscrew corrosion. Miniscrews were tested in two artificial saliva solutions one without fluoride and one with fluoride. Electrochemical cell was used as the testing medium. Additionally the surface topography of the miniscrew were assessed qualitatively using a Scanning Electron Microscope.
In the present study, Absoanchorminiscrew showed high Open Circuit Potential (OCP) values in artificial saliva medium when compared with the other two groups, indicating a higher corrosion resistance of Absoanchorminiscrews than the other two groups. S K implant and JSV miniscrews showed almost similar OCP values with similar corrosion resistance properties. The metal composition and internal microstructure of mini- implants are important factors to be evaluated, in order to improve the mechanical properties and decrease the risk of mini-implant fracture. SEM scanning has been used to study the surface changes that occurs during corrosion.9 Additionally the miniscrews were assessed to check for surface corrosion of the implant topography. Huang et al utilized atomic force microscopy to measure the three-dimensional surface topography of NiTiarchwires in various fluoride containing environments in order to check for the variation of the surface topography.10
In the present study, when artificial saliva solution containing fluoride was used as the testing medium there was a significant drop in corrosion resistance properties in all the three groups suggesting that fluoride have a detrimental effect on the corrosion properties of miniscrews.
In a similar study on corrosion of temporary anchorage devices in artificial saliva solution showed that there was no significant differences in corrosion properties of temporary anchorage devices in artificial saliva but addition of 1500 ppm of fluoride significantly reduced the corrosion properties of the temporary anchorage devices. Testing was done using an electrochemical cell were they recorded the potential changes. All the three groups showed a similar corrosion resistance behavior. There was no surface examination done on this study.11
Studies have compared the corrosion resistance of Titanium,cobalt–chromium, iron-chromium–nickel based orthodontic brackets on fluoride mouthwashes which showed a decrease in corrosion resistance in Ti group of brackets. A glass electrochemical cell was used with the thermostat and the surface was later analyzed using SEM.
This study indicated that in artificial saliva the three brackets displayed satisfactory electrochemical properties, with Ti being the most passive.8 In this study orthodontic brackets were tested which differs from an orthodontic minisrew and the testing medium selected was fluoridated mouthwashes. In the present study artificial saliva solution was used as the testing media which resembles the oral environment and fluoride (1500ppm) was added from sodium fluoride.
The findings of the present study are also in agreement with a study conducted by Mane et alwhere rectangular NiTi and CuNiTi wires were immersed in in fluoride solution and artificial saliva for 90 minutes at 37°C and analyzed using optical microscope to see the fluoride effect on the wire topography. They concluded that using topical fluoride agents leads to corrosion of surface topography indirectly affecting the mechanical properties of the wire that will lead to prolonged orthodontic treatment12
In the present study both electrochemical and SEM /EDS data suggest that there is an increased tendency for corrosion to occur in miniscrews under the influence of fluoride The composition of miniscrews, type and
quantity of fluoride prophylactic agent, manufacturer defects, duration of exposure, miniscrews length and diameter, surgical placement procedure all these factors affect the corrosion of the miniscrews in the oral environment.13,14
Conclusion
This study was conducted to compare the corrosion resistance behaviour of three commercially available orthodontic miniscrews and thereby analyse which one of these miniscrews undergoes more corrosion in artificial saliva with and without fluoride. The findings of this study rejected the null hypothesis and established that there is a significant difference in the corrosion behaviour of these miniscrews.
The present study found that:
1) There was a significant drop in corrosion resistance properties in all the three groups when artificial saliva solution containing fluoride was used as the testing medium. Absoanchorminiscrews showed higher corrosion resistance behaviour than S K Ti implant and JSV miniscrews in artificial saliva solution with fluoride. S K Ti implant showed slightly higher corrosion resistance when compared to JSV miniscrews.
2) The surface analysis of these three miniscrews using SEM scanning revealed that Absoanchorminiscrews poses better surface homogeneity than S K Ti implant and JSV miniscrews in both fluoridated and non-fluoridated artificial saliva solution.
The results of the present study suggest that though the usage of topical fluorides may be vital and useful in improving the patient’s oral hygiene maintenance, it must be used judiciously as it might be a factor contributing to miniscrew corrosion and failure
.
Limitations and Future Studies
- The characteristics of the oral environment are complex and difficult to replicate in any artificial saliva and in in vitrostudies in general. Similarly, the concentration of fluoride used in this study was within the range Limitation observed in toothpastes reported in clinical studies39 However, in the clinical situation, the miniscrews may be exposed to a variety of amounts and forms of fluoride-containing agents, including sodium fluoride, sodium monofluorophosphate, stannous fluoride, or amino fluoride, that may impact their electrochemical response.
Scope for future studies is orrosion of miniscrews can lead to leaching out of corrosion products, which have shown to have biological effects.40, 41 .The present study did not investigate the effect of metal ions that are released in the fluoride solutions. Further studies can be done to evaluate the effect of other factors affecting corrosion in the oral environment like plaque, microbial factors, strain etc. Although the results obtained from this in vitro study cannot be directly applied to the in vivo conditions of the oral environment, they are useful for relative comparison of the type of miniscrews and the use of fluoridated dental aids that are used during fixed orthodontic therapy.
Acknowledgement (Times New Roman, bold, 12) Nil
References
[1]
Dorr LD, Bloebaum R, Emmanual J, Meldrum R. Histologic, biochemical, and ion analysis of tissue and fluids retrieved during total hip-arthroplasty. ClinOrthopRelat Res 1990; 261:82-95.[2]
Lugowski SJ, Smith DC, McHugh AD, Van Loon JC. Release of metal ions from dental implant materials[11]
Knutson KJ and Berzins DW. Corrosion of orthodontic temporary anchorage devices. Eur J Orthod2013;35:500–506.[12]
Mane PN ,Pawar R, Ganiger C, Phaphe S.Effect of fluoride prophylactic agents on the surface topography of NiTi and CuNiTi wires. J Contemp Dent Pract 2012; 13(3):285-288.[13]
Topouzelis N, Tsaousoglou P. Clinical factors correlated with the success rate of miniscrews in orthodontic treatment.Int J Oral Sci 2012; 4(1): 38–44.[14]
Topcuoglu T, Bicakci AA, Avunduk MC, Inan ZDS.Evaluation of the effects of different surface configurations on stability of miniscrews. Sci. World J2013;(1)396091.[15]
Twetman S, Axelsson S, Dahlgren H, Holm AK, Källestål C, Lagerlöf F et al. Caries-preventive effect of fluoride toothpaste: a systematic review. ActaOdontolScand 2003; 61(6):347-55.[16]
de Morais LS, Serra GG, Albuquerque Palermo EF, Andrade LR, Müller CA, Meyers M A,et al.Systemic levels of metallic ions released from orthodontic mini-implants. Am J OrthodDentofacialOrthop 2009; 135: 522–529.
[17]
Alves CBC, Segurado MN, Dorta MCL, Dias FR, Lenza MG, Lenza MA. Evaluation of cytotoxicity and corrosion resistance of orthodontic mini-implants.Dental Press J Orthod 2016; 21(5): 39–46.
