Thirty-three (n=33) participants from the Department of Orthodontics and Pediatric Dentistry, University of Szeged will be randomly assigned into two groups.

A randomly assigned, split-mouth design will be used to avoid inter-individual biologic variation between patients. First, it will be randomly determined whether the upper or lower jaw would be involved in the study; after choosing the jaw blindly, the actual dental arch in the mouth will further be divided vertically, into right and left halves (quadrants) in each patient. One half will be the experimental side (i.e. the test quadrant) and will receive laser therapy, while the other half will be the placebo side (i.e. placebo quadrant) which will receive no laser, only placebo therapy.

In the experimental group, a low-level medical gallium-aluminum-arsenide (GaAlAs) diode laser device (wavelength 980 nm, power: 100mW, producing 6 J energy), with continuous wave will used on the 1st permanent molars in the test quadrants. Using the split mouth design, patients will receive only a single dose immediately after the placement of orthodontic separators. Specified points in each quadrant will be treated from mesial, central and distal directions on the mucosa both buccally and lingually/palatinally with 10-10 sec for each, altogether for 60 sec, producing 36 J energy per molar. During the placebo treatment session, a similar procedure to that of the laser treatment session will be carried out, but with no laser irradiation. Therefore, to control the patient's pain-related behavior, and to maintain the blinded protocol, the handpiece will also be held on the placebo treatment side without laser irradiation following a similar application protocol.

Patients will be instructed to denote their pain sensation levels (which is expected to be the primary come measure of the study), according to the localization (upper/lower jaw; right/left side) and the given appointments following the treatments: at 0 hours (i.e. within 5 minutes of placing the elastic separators), at 6 hours , at 12 hrs , at 24 hrs , at 48 hrs and at 72 hrs ,after treatment (laser/placebo) in resting position of the mandible (spontaneous pain) and during mastication, on a Visual Analog Scale (VAS), ranging from 0 (no pain) to 100 (severe pain).

After finishing the development of the jaws, effective treatment of orthodontic anomalies needs fixed appliances. During initiation of routine orthodontic treatment with fixed appliances, placing elastic separators is a part of the process to achieve adequate space for orthodontic bands, which may lead to a considerable pain experience. This pain experience is a key barrier to the completion of orthodontic treatment processes, therefore, different approaches have been considered to reduce pain due to orthodontic treatment. Earlier studies have evaluated the effects of low level laser therapy (LLLT) on reducing pain caused by orthodontic elastic separators, however, the reported results are still contradictory: while some investigations supported the notion of analgetic effects, while other studies could not verify it. Therefore, due to the controversial position of LLLT as a treatment modality in orthodontic pain, recent reviews on this topic indicated that further, well-designed randomized controlled trials are needed to clarify the role and usefulness of LLLT in reduction of orthodontic pain.

Therefore, the aim of the present study will be to assess the effect of LLLT in reducing pain following orthodontic elastic separator placement in individuals treated with fixed orthodontic appliances, using a randomized, double-blind placebo-controlled split-mouth study design.

Thirty-three (n=33) participants from the Department of Orthodontics and Pediatric Dentistry, University of Szeged will be randomly assigned into two groups. A randomly assigned, split-mouth design will be used to avoid inter-individual biologic variation between patients. First, it will be randomly determined whether the upper or lower jaw would be involved in the study; after choosing the jaw blindly, the actual dental arch in the mouth will further be divided vertically, into right and left halves (quadrants) in each patient. One half will be the experimental side (i.e. the test quadrant) and will receive laser therapy, while the other half will be the placebo side (i.e. placebo quadrant) which will receive no laser, only placebo therapy.

In the experimental group, a low-level medical gallium-aluminum-arsenide (GaAlAs) diode laser device (wavelength 980 nm, power: 100mW, producing 6 J energy), with continuous wave will used on the 1st permanent molars in the test quadrants. Using the split mouth design, patients will receive only a single dose immediately after the placement of orthodontic separators. Specified points in each quadrant will be treated from mesial, central and distal directions on the mucosa both buccally and lingually/palatinally with 10-10 sec for each, altogether for 60 sec, producing 36 J energy per molar. During the placebo treatment session, a similar procedure to that of the laser treatment session will be carried out, but with no laser irradiation. Therefore, to control the patient's pain-related behavior, and to maintain the blinded protocol, the handpiece will also be held on the placebo treatment side without laser irradiation following a similar application protocol.

Patients will be instructed to denote their pain sensation levels (which is expected to be the primary come measure of the study), according to the localization (upper/lower jaw; right/left side) and the given appointments following the treatments: at 0 hours (i.e. within 5 minutes of placing the elastic separators), at 6 hours , at 12 hrs , at 24 hrs , at 48 hrs and at 72 hrs ,after treatment (laser/placebo) in resting position of the mandible (spontaneous pain) and during mastication, on a Visual Analog Scale (VAS), ranging from 0 (no pain) to 100 (severe pain).

Eligible participants of the study are going to be included from the pool of patients at the Department of Orthodontics and Pediatric Dentistry (Faculty of Dentistry, University of Szeged) requiring orthodontic treatment.

Inclusion Criteria:

• individuals aged between 18 and 50 years
• completely erupted second molars without open interproximal contacts of the first molars
• good general health, without the existence of systemic diseases
• adequate oral hygiene and healthy periodontium
• no previous orthodontic treatment

Exclusion Criteria:

• those who did not fulfill the general inclusion criteria
• patients who had undergone prior oral LLLT
• who were using painkillers or other NSAIDs
• those who were consumed tobacco products
• pregnant or lactating women