Mechanical Properties and Clinical Efficacy of Two Nickel-Titanium (NiTi) Archwires

PICO QUESTION:

• Does the amount of the resolution of the anterior lower arch crowding increase in the patients with superelastic NiTi archwire compared with the patients with heat-activated NiTi archwire during the first three months of orthodontic treatment and/or its mechanical properties change after three months of clinical use?

Population: Orthodontic patients with moderate anterior mandibular crowding Intervention: .014" Superelastic NiTI archwire (3M Unitek, Monrovia, CA) Comparison: .014" Heat activated NiTi archwire (3M Unitek, Monrovia, CA)

Outcomes:

Primary Outcomes:

• Quantity of resolution of anterior mandibular crowding every month for three months
• Mechanical properties measured by tensile test and three point bending test before and after the three first months of orthodontic treatment.

Secondary Outcomes: Archwires deformation under oral conditions during the first three months of the orthodontic treatment.

AIMS

GENERAL AIM To compare the changes of the mechanical properties measured by tensile test and three point bending test of two NiTi archwires (heat-activated and super-elastic); when exposed to the oral conditions during the first three months of orthodontic treatment and to evaluated the clinical efficacy in lower anterior arch crowding resolution.

SPECIFIC AIMS

• To recruit 54 orthodontic patients, 13-25 years old, without extraction into a randomized clinical trial design, single-blinded trial, into the effects of NiTi arch-wires alloy in the resolution of the anterior mandibular crowding during the three first months of the orthodontic treatment.
• To test the hypothesis that, compared the resolution of the anterior mandibular crowding in the first three months of orthodontic treatment, with those to receive NiTi heat-activated arch-wire, those assigned to receive superelastic NiTi archwire
• More amount of resolution of the anterior mandibular crowding
• Differences in the changes of mechanical properties after clinical use
• Less archwire deformation

METHODS

OVERVIEW OF DESIGN Study Design: Randomized clinical trial

• Randomized clinical trial in 54 orthodontic patients with moderate crowding. They are going to be randomly assigned in to two intervention groups, each group with 27 patients. One group are going to be treated with heat-activated NiTi archwires and the other group with super-elastic NiTi archwires.
• Blinding: It is not possible to blind patients and clinical staff, but we are going to blind the operators who will perform the measurements and the data analysis (single-blinded).

We are going to have an exact clinical protocol for both groups with the only difference being in the NiTI arch-wire alloy.

MBT prescription .022 slot. Alginate impressions and cast models at the beginning of the study, immediately after the first, second and third month of the orthodontic treatment.

Measures of anterior lower arch crowding resolution are going to be taken by previously-calibrated operators.

Arch-wires deformation are going to be evaluated by visual observation every month in monthly clinical visits.

The measures of the mechanical properties measured by tensile test and three point bending test of two NiTi archwires (heat-activated and super-elastic); are going to take before and after the first three months of orthodontic treatment.

DESIGN FOR SAMPLING

Study Population:

• Orthodontic patients from the orthodontic department clinic of the UniCIEO

Sampling:

• No probabilistic: convenience sample
• Consecutive sample of consenting patients

PLANS FOR RECRUITMENT

Patients of the Clinic University (UniCIEO) that meet the selection criteria and accept to participate.

MEASUREMENTS

MAIN PREDICTOR VARIABLE

• Type of NiTi Alloy used (NiTi superelastic arch-wire; NiTi heat-activated arch-wire)

POTENCIAL CONFOUNDING VARIABLES - Age

• Sex

OUTCOME VARIABLES

Plaster models Outcomes:

• Quantity of anterior mandibular crowding resolution measured monthly

Mechanical Properties Outcomes:

• Measured in vitro with an Instrom before and after three months of the orthodontic treatment by tensile test and three point bending test

Archwire Outcomes:

• Archwire deformation measure at monthly visit, by visual evaluation

STATISTICAL ISSUES

APPROACH TO STATISTICAL ANALYSIS

The data will be processed in the statistics program Stata 14 (Stata Corp 2011. Stata Statistical Software: Release 14. College Station, TX: Stata Corp LP). Qualitative variables are going to be described by frequencies and percentages; quantitative variables will resume as average and standard deviation. The association between qualitative variables will be calculated by Chi-square test. For two group comparisons, we are going to use the t test or Wilcoxon-Mann-Whitney test. Significance level is going to be set at P\<0.05.

HYPOTHESIS, SAMPLE SIZE AND POWER

Hypothesis:

Null Hypothesis H0: compared the resolution of the anterior mandibular crowding in the first three months of orthodontic treatment, with those to receive NiTi heat-activated archwire, those assigned to receive superelastic NiTi archwire

• Same amount of resolution of the anterior mandibular crowding
• Same changes in mechanical properties after clinical use
• Same archwire deformation

Alternate Hypothesis Ha: compared the resolution of the anterior mandibular crowding in the first three months of orthodontic treatment, with those to receive NiTi heat-activated archwire, those assigned to receive superelastic NiTi archwire

• More amount of resolution of the anterior mandibular crowding
• Differences in the changes of mechanical properties after clinical use
• Less archwire deformation

Sample size calculation and power:

It was calculated with the software Epidat (software Epidat version 4.1). With 90% power and a 5% level of significance and with standard deviation data from a previous study, the sample should comprise at least 27 patients per group.

QUALITY CONTROL AND DATA MANAGEMENT

Bias Control:

Selection bias:

• Randomization

Information bias:

• The principal investigators are going to train the observers in the theoretical and practical issues of all the measures of the variables of this study developing an operations manual.
• The observers are going to be calibrated and evaluated in intra and extra observer concordance by Bland Altman plot with previously fixed acceptable limits.
• All variables, are going to be re-measured after two weeks in subjects randomly selected.
• Random and systematic errors are going to be calculated with Dahlberg´s formula and dependent t test, respectively.
• Same clinical protocol for groups, the only difference in the intervention. All clinical and laboratory procedures will meet quality standards. The research team will take care of the data in order to be reliable and accurate The research team will take care that complete and accurate records will be maintained Statistical methods are going to be pre-specified and carefully followed The results are going to be clearly and fairly reported