The current study aims to evaluate the accuracy of different techniques used to record the centric relation.

The sample size was determined based on a previous study by Revilla-León et al. (2023), which indicated that 18 participants per group would provide sufficient power for statistical analysis. Eligible participants will be adults above 18 years of age with good oral health who are fully or partially dentate. Exclusion criteria include complete edentulism, absence of posterior stops, temporomandibular joint disorders, and limited mouth opening.

Centric relation (CR) will be recorded for all participants using three methods. In Group 1 (Conventional), a 2 mm Lucia jig fabricated from pattern resin (Dura-lay) will be positioned intraorally with the participant reclined at 45°. Polyvinyl siloxane (PVS) bite registration material will be injected bilaterally from the canines to first molars and allowed to set. Alginate impressions, facebow records, and subsequent mounting on a semi-adjustable articulator will be performed, and the casts will be digitized with a laboratory scanner. In Group 2 (Intraoral Scanner), the iTero Element scanner (Align Technology, San Jose, CA) will be used to capture maxillary and mandibular arches. The same Lucia jig will be placed intraorally, and the bite will be digitally captured using the PVS record. In Group 3 (Optical Jaw Tracking), the Modjaw system will be used with previously acquired iTero scans. The Lucia jig will again standardize mandibular position during CR registration. All recordings will be performed by a single experienced prosthodontist to ensure consistency.

For accuracy assessment, STL files from all recordings will be imported into Geomagic Control X (3D Systems). Six digital markers will be placed on maxillary and mandibular reference scans at standardized anatomical landmarks (buccal surfaces of first molars, canines, and central incisors). Thirty-six baseline inter-landmark distances will be calculated. Each experimental scan will then be aligned to the reference scan using a best-fit alignment protocol, with marker coordinates transferred from the reference scan to maintain consistency and avoid manual errors. Inter-landmark distances will be recalculated for each experimental scan. Accuracy will be assessed in terms of trueness (mean absolute deviation between reference and experimental measurements) and precision (consistency of distances within each group).

Data will be statistically analyzed using analysis of variance (ANOVA), with significance set at p < 0.05.

Inclusion Criteria:

1. Adults above the age of eighteen years
2. Presenting with good oral health
3. Fully or partially dentate

Exclusion Criteria:

1. Fully edentulous
2. Partially dentate with lack of posterior stops
3. Temporomandibular Joint Disorders (TMD)
4. Limited mouth opening