Study Design: A randomized controlled trial with two parallel arms and an allocation ratio of 1:1.

Setting: The study will be conducted in the orthodontic department of Riyadh Elm University hospitals in Riyadh City, Saudi Arabia.

Participants: Patients undergoing fixed or clear aligner orthodontic treatment referred to REU dental hospital will be randomly allocated to either the clear aligner group or the fixed orthodontic appliance group.

Intervention: Prior to orthodontic treatment, all patients will receive phase I periodontal therapy and oral hygiene instructions. Fixed orthodontic appliances will be bonded using metallic brackets with a 0.022-inch slot and 0.014-inch NiTi archwires. Clear aligner patients will receive Invisalign® treatment.

Outcomes and Saliva Collection: Salivary samples will be collected using the spitting method at baseline (T0) and follow-up time points according to the study protocol. Salivary flow rate, pH, and buffering capacity will be assessed as described in the proposal.

Randomization and Blinding: Randomization will be performed using a random number generator with allocation concealment via opaque envelopes. The investigators involved in outcome assessment and data analysis will be blinded.

Ethical Considerations: The study will be submitted to the Institutional Review Board at Riyadh Elm University and conducted in accordance with IRB policies.

This study is a randomized controlled clinical trial designed to evaluate changes in salivary parameters in patients undergoing fixed orthodontic treatment or clear aligner therapy. Patients referred to the orthodontic department of Riyadh Elm University dental hospital will be screened for eligibility and randomly allocated into two parallel groups with an allocation ratio of 1:1.

Prior to the initiation of orthodontic treatment, all participants will undergo phase I periodontal therapy and receive standardized oral hygiene instructions. Patients in the fixed orthodontic appliance group will be treated using metallic brackets with a 0.022-inch slot and initial 0.014-inch nickel-titanium archwires. Patients in the clear aligner group will receive clear aligner treatment according to the prescribed protocol.

Salivary samples will be collected using the spitting method at baseline before the start of orthodontic treatment (T0) and at subsequent follow-up time points as specified in the study protocol. Salivary flow rate, salivary pH, and buffering capacity will be assessed at each time point using standardized methods described in the proposal.

Randomization will be carried out using a random number generator, with allocation concealment ensured through the use of opaque sealed envelopes. The investigators involved in outcome assessment and data analysis will be blinded to group allocation.

This study will be conducted following approval from the Institutional Review Board (IRB) of Riyadh Elm University and in accordance with institutional ethical guidelines.

Inclusion Criteria:

• Class I, II and III skeletal malocclusion.
• Age ≥18 undergoing fixed or Clear aligner orthodontic treatment.

Exclusion Criteria:

• Current medications including antibiotic use within the past 3 months that affect salivary flow and composition.
• Active smoking including vaping and E-cigarette use.
• Diagnosis of systemic diseases/conditions such as Sjogren's syndrome, diabetes, chronic kidney diseases, neurological conditions.
• Active dental caries or signs of gingivitis and/or periodontitis
• Less than three months of orthodontic treatment since it is characterized by acute, temporary changes and patient adaptation to the new appliances.
• Requiring single arch treatment to standardize the research and eliminate a potential confounding variable
• Crown restoration is excluded due to their material properties which may affect salivary composition.
• Pregnancy due to the physiological variation in salivary flow and composition due to hormonal changes.
• Presence of mouth breathing may lead to inconsistent salivary flow rate, Changes in Salivary Composition and pH
• Poor oral hygiene with high levels of dental plaque, calculus, and gingival inflammation can independently alter salivary flow rate, pH, and buffer capacity there by acting as confounding variable.

The outcome assessor, and data analyst will be blinded.