1 week before the placement of the Hyrax appliance

The day of the first clinical observation of sutural opening (5-7 days after activation)

The day of completion of active expansion (3-4 weeks)

The day of completion of the 3-month reinforcement period

Plaque index (PI), gingival index (GI) and probed pocket depth (PPD) scores will be recorded at T0, T1, T2 and T3 assessment periods to evaluate the periodontal status and oral care effectiveness of the participants. PPD is the distance between the gingival margin and the sulcus base. Measurements will be made at 6 different sites (mesio-vestibular, vestibular, disto-vestibular, mesio-oral, oral, disto-oral) of each tooth using a Williams periodontal probe (Hu Friedy, Chicago, Illinois, USA). During the measurements, care will be taken to position the probe as parallel as possible to the long axis of the tooth and not to apply excessive force.

8-OHdG is the most frequently encountered and best known mutagenicity of more than 20 oxidative base damage products of ROS in DNA. Since it is easily detected in living cells and body fluids, it is the most commonly used oxidative DNA damage marker.

Serum and saliva levels will be measured using a suitable ELISA kit (Cayman Chemical DNA/RNA Oxidative Damage ELISA Kit Item No.589320) according to the manufacturer's instructions. The measurement principle is as follows: It is based on the competition between 8-OHdG from the sample and 8-OHdG-acetylcholinestarase conjugate (8- OHdG Tracer) from the kit for a limited amount of 8-OHdG monoclonal antibody covering the plate well. The colour intensity measured spectrophotometrically at 410 nm is directly proportional to the tracer and inversely proportional to the amount of free 8-OHdG in the sample.

Total Oxidative Status (TOS) is a current method used to detect lipid peroxidation and oxidative stress. TOS is considered to be a superior method compared to other methods due to the impracticality of measuring different oxidant molecules individually and the inability to fully reflect the interaction of oxidant molecules with each other. Total Antioxidan Status (TAS) is a biochemical parameter obtained as a result of the sum of the antioxidant capacities of all antioxidants in the biological samples examined. Oxidative Stress Index (OSI) is a proportional value obtained by dividing TOS by TAS. It is directly affected by total oxidative and antioxidant status and reveals the final oxidative status in a practical and understandable way.

OSI value was calculated according to the following formula. OSI = TOS (mmol H2O2 Equiv./L) / TAS (mmol Trolox Equiv./L) x 100

Plaque index (PI) scores will be recorded at T0, T1, T2 and T3 assessment periods to evaluate the periodontal status and oral care effectiveness of the participants. The amount and thickness of plaque causing gingival inflammation will be determined. The teeth will be dried by spraying light air and isolated. Each tooth will be scored by measuring with a probe from the gingival margin in six areas (mesiobuccal, distobuccal, mesial, distal, oral, vestibule).