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Guiding plane and Occlusal rest seat Design & Preparation Dr.Emad Hanbali Guiding planes : two or more vertically parallel surfaces of abutment teeth, so shaped to direct a prosthesis during placement and removal. Functions : . To provide for one path of placement and removal of the restoration. . To ensure the intended actions of other components of the RPD. . To eliminate gross food traps . Width : 1/2 the width of the distance between the tips of adjacent buccal and lingual cusps. 1/3 the buccal lingual width of the tooth. Height : 2/3 of the length of the enamel crown portion from the marginal ridge cervically. Surveying at the selected path of insertion and removal of the RPD. Zero tilt survey line Insertion tilt survey line F Follow the buccolingual contour during the preparation. Do not slicew Length of guiding plane 2-3 mm. Occlusal rest seat Design & Preparation Rest A rigid component resting in a recessed preparation on the occlusal, lingual or incisal surface Provides vertical support Occlusal Rest Seat Form Conventional Form: rounded triangle Occlusal Rest Seat Form Rounded triangular shape – Apex near center of tooth Occlusal rest seat 3D: - Mesio - distally. - Bucco - lingually. - Occluso - gingivally Dimensions: Mesio – distally : premolars 1 / 3 molars 1 /4 Occlusal Rest Seat Form Base of triangle should be one third the bucco-lingual width of the tooth Occluso-gingivally ( depth ) Occlusal Rest Seat Form Marginal ridge must be lowered and rounded 1-1.5mm – Bulk of metal to prevent fracture Occlusal Rest Seat Form Floor inclined towards the center Angle formed by rest and minor connector should be less than 900 Occlusal Rest Seat Form Deepest portion is central Occlusal Rest Seat Form Floor should be concave or spoon shaped ball-&-socket joint Prevents horizontal stresses & torque Occlusal Rest Seat Form Directs the occlusal forces along the long axis of the tooth Prevent orthodontic movement Result of force applied when angle is greater than 90 degrees . Preparation of Rest Seats Occlusal Rest Seats – Diamonds 8801- 014 38006 -135 – Medium round carbide burs #2, #4 8801- 014 Preparation of Rest Seats Keep in enamel No anesthesia Rounded triangle Deepest part of rest seat Marginal ridge reduction 1.5 mm SAUSER SHAPE GP Molar occlusal rest seat Modified Occlusal rest seat Occlusal Rest Seat Form Adjacent Tooth – Rest not flared to facial line angle – Lingual flared more - space for minor connector Double Embrasure Rest Seat Form Adjacent teeth, the form is also modified Flared more dramatically on facial and lingual line angles Double Embrasure Rest Seat Form Provides space for the retentive & bracing arms Ensure all line angles are smoothed Preserve the contact between the adjacent teeth Interproximal Occlusal Rest Seats Care must be exercised to avoid violation of contact point. E N J O Y