The aims of this trial were to assess the effect of changing 0.019X0.025-inch SS working archwire monthly on the rate of space closure, to compare the frictional resistance of unchanged and new working archwires in-vitro, and to assess its effect on the rate of space closure, to record the amount of ion concentration in the saliva before orthodontic treatment, before space closure and one month after space closure.

The aims were to assess the effect of changing 0.019X0.025-inch SS working archwire monthly on the rate of space closure, to compare the frictional resistance of unchanged and new working archwires in-vitro and to assess its effect on rate of space closure, to record the amount of ion concentration in the saliva before orthodontic treatment, before space closure and one month after space closure and to compare the rate of teeth movement into fresh and old extraction sites.

Trial design: Randomized controlled clinical trial with a split-mouth design. Setting: Jordan University of Science and Technology(JUST) Postgraduate Dental Teaching Clinics and labs.

Participants and interventions: Twenty-eight subjects with bimaxillary proclination requiring extraction of all first premolar teeth participated in this study. In the upper arch two groups were identified; group 1 having the extraction space closed using the same working archwire throughout 3 visits after insertion, and group 2 with the working archwire changed monthly.

The working archwire in the upper arch was split into 2 halves in the midline and each one half was connected to the other by a wide joining hook. Patients were followed-up monthly for three months. At every follow up visit upper alginate impressions were taken and the working archwire in the upper arch was changed on one side only. Upper follow-up models were scanned using digital scanner and spaces were measured using digital software.

Three unstimulated saliva samples were collected from each patient; prior to commencement of treatment, when 0.019X0.25-inch SS archwire was reached and before space closure and one month after space closure.

The rate of extraction space closure in the upper arch, ion concentration in saliva samples measured using inductively coupled plasma mass spectrometer (ICP-MS) and frictional resistance of the working archwires was measured using universal mechanical testing machine.

Inclusion Criteria:

• Age ≥ 16 years
• Proclined upper and lower incisors (Ui/max >115 o, Li/mand >99o)
• Mild upper and lower arch crowding (<4mm) or no crowding
• Need for upper and lower first premolars extraction
• Skeletal I malocclusion (1\

The intervention was randomly allocated to either the right or left side using the permuted random block size of 2 with 1:1 allocation ratio. The random sequences for each intervention to either right or left sides was concealed in opaque envelopes and shuffled before the intervention to increase the unpredictability of the random allocation sequence. Each patient was asked to pick a sealed envelope to assign the intervention to either the right or left side. Allocation concealment was aimed to prevent selection bias and to protect the assignment sequence until allocation.