Introduction

As we know, nickel-titanium and stainless steel wires are widely used in orthodontic practice. Since most people do not follow a satisfactory oral hygiene regime during treatment, orthodontic treatment may have detrimental effects on tooth structures or periodontium. For this reason, using different mouthwashes to control dental caries or periodontal disease is recommended to patients. However, chemical agents may be potentially damaging to metal components of orthodontic appliances (1, 2).

Chlorhexidine is an agent with antibacterial properties, which is widely used in clinical dentistry, and has a special affinity for oral structures. The effect of Chlorhexidine in inhibiting plaque formation and reducing bacteria in the oral cavity, including streptococci, is well established in the literature (3).

Persica is another mouthwash that is widely used in the Middle East and proven to have antibacterial effects on cariogenic bacteria (4); the effects of this mouthwash have been investigated in the UK, USA and the Middle East (5-7).

Hydrogen peroxide (H202) is an effective bactericidal agent that catalyzes salivary peroxidase to form products with antibacterial properties (8, 9). It has been proven that even low levels of H202, either directly or by adding H202-generating systems, would be the most effective approach for inhibiting acid production and growth of streptococci(1).

Although orthodontic alloys show resistance against corrosion in various solutions as a result of the thin passive oxide film on their surface, this protective layer is susceptible to some chemical disruption (10-12).

The corrosion of orthodontic appliances in the oral environment has concerned clinicians about two principle issues: absorption of corrosion products in the body with local or systemic effects and the effect of corrosion on metal parts with regard to friction. Corrosion can adversely affect tooth movement because of the induced pitting and porosity on the surface of metal parts, which consequently increase the friction between the wire and the bracket slot. The friction behavior between an orthodontic wire and brackets can affect surface topography and vice versa (13). According to our knowledge, there has not been any studies on the effect of different mouthwashes (Except fluoride mouthwashes and Chlorhexidine) on surface topography of orthodontic archwires, therefore the purpose of the present study was to evaluate the effects of the three mouthwashes on surface characteristics of nickel–titanium NiTi and stainless steel (SS) wires.

Materials and Methods

1. Pre-processing: consisted of removal of noise and improving the images. In this phase, we used an air filter (smoothing) on the image to reduce sensitivity of the instrument to fine details in later phases. Since these particles had more brightness compared to the other parts of the image, a filter planar (Binarization( was used to identify them. Then, the areas identified were expanded by a morphology operator (dilation). Finally, these areas were replaced with average points of surrounding areas (figure1).
2. Hole nomination: In the second phase, hole candidates by morphological operators hat-top and hat-bottom, were identified (figure2).
3. Calculation of confidence factor of each hole: confidence factor was calculated for each hole based on the brightness values ​​of the boundary of each hole and its surrounding area. The possibility that the candidate area is detected as a hole increases with higher confidence factor.

1. Hole detection: based on reliability values, ​​ real holes were identified among candidate holes. The rate of cavity area and their number was measured in five regions of each sample (figure3).
2. Measuring cavities: In this process nine parameter values ​​ W1, W2, W3, T1, T2, T3, R1, R2, R3 were determined for each image.

Figure 1. Pre-processing applied on a sample image :(A) The original image.

Figure 1(B). Detected noise particles

Figure 1(C). Removing noise particles from the image

Figure 2. Nominate holes part of the sample image: (A) an improved image.

Figure2(B). Internal surface of hole from conversion of thehat – bottom

Figure2(C). External hole borders from conversion of the hat-top

Figure 2(D). Holes have been nominated

Figure 3. Identified holes for a sample image: (A) an improved image.

Figure 3(B). Identified holes Tables

Results

The effects of Chlorhexidine, hydrogen peroxide and Persica on topography properties of NiTi and SS wires were compared with 2 control groups. The mean values of corrosion percentage and hole count of NiTi and SS wires in different mouthwashes and artificial saliva are shown in Table 1.

Comparison pairs of corrosion percentage of NiTi wires (Table 2) showed that There was significant difference between Persica and as-received (P=0.049) and Chlorhexidine and as-received (p=0.20) arch wires.

Aspect of hole numbers in NiTi wires, there were no significant difference between none of the groups (P-value>0.05) but it is interesting that in this wire is highest corrosive appearance was in as-received group.

Comparison of the number of cavities and corrosion percentage of SS wires in pairs are shown in Table 3. In this type wire, Chlorhexidine was dominant media for corrosive effect but non-significant (P-value>0.05)

Table1. The mean of corrosion percentage in NiTi and SS wires

SD: Standard Deviation

Table 2. A comparison between different mouthwashes and control groups in NiTi wires

Table3. A comparison between different mouthwashes and control groups in SS wires