this study will test the ability of the Jaw Tracking Device to detect occlusal contacts as an additional data that could be used during diagnosis and occlusion analysis and the results will be compared to contacts gotten from articulating paper and that will be tested at different head position to also detect the changes related to change in condylar position.

Each subject will be subjected to three different head positions (upright, semi supine 45° and supine position). Positioning of the participants will be standardized as much as possible. A Goniometer (ISICO, Transparent, 360°, India) that has been used in a previous study will be used to standardize all head postures. All participants will be instructed to initially sit in a standard dental chair with the backrest and their arms resting freely at their sides, eyes looking straight. The starting position for cervical flexion will be assumed after the clinician manually adjusts the participant's neck so that the center of the external acoustic meatus to the base of the nose representing the reference plane (camper plane) is parallel to the floor. The axis will be centered over the external acoustic meatus, and the fixed arm of the goniometer will be held vertically, while the movable arm will be aligned with the reference plane . For the supine position, the participant will lay down on his back in the horizontal position with the dental chair adjusted so as to be parallel to the floor . For the semi supine position, the participant's head will be adjusted so that the movable arm of the goniometer is aligned at 45 degrees with the vertical arm that will be centered over the external acoustic meatus. The head rest will be then adjusted to support the head at this position throughout the registration procedure.

Occlusal contact registration :

At each head position, occlusal contacts will be registered using the jaw tracking device and an articulating paper. The occlusal contacts will be assessed by asking the participant to close the mouth in MIP and maintain dental contact. The number of occlusal contacts per tooth will be counted and recorded at each head position for each method then the obtained data will be compared. To determine the inter-rater reliability of the jaw tracking device and articulating paper, the contact points were classified in a dichotomy variable , meaning the presence or absence of contact per tooth, regardless of the surface amount or contact intensity. The presence of any contact, no matter the intensity or its surface, was considered as the presence of contact .

The position of the condyles will be determined using the electronic position analysis (EPA) of the jaw tracking device. The position of the condyles in the upright head position will be considered as the reference. Any change (deviation in mm) from this reference when the head position is changed to supine or semi-supine will be recorded.

Inclusion Criteria:

• Healthy dentate subjects.
• Between 20 and 25 years irrespective of gender.
• No reported pain or history of pain in TMJ and neck region.
• No sign and symptoms of myofascial pain dysfunction.
• Class I jaw relationship with intact dentition.

Exclusion Criteria:

• Any abnormal range of mandibular movements.
• Any postural abnormality of cervical spine system such as scoliosis and kyphosis.
• No history of chronic pain or pathology or previous surgery related to masticatory system or cervical spine or TMD symptoms at least 1 year before study.

because these are personal data