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Final year Bds prosthodontics- this has notes of face bow
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Are those that orient the mandible to the cranium in such a way, that, when mandible is kept in its most posterior position, the mandible can rotate in sagittal plane around an imaginary transverse axis passing through or near the condyles. Orientation jaw relation gives the angulation of the maxilla in relation to the base of the skull. It is necessary to do orientation jaw relation before doing any other jaw relation. Use of face bow minimizes the occlusal error in the restoration as the cast will be oriented as close to as they are in the patient. DEFINITION: An instrument used to record the spatial relationship of the maxillary arch to some anatomical reference points and then transfer this relationship to an articulator; it orients the dental cast in same relationship to the opening axis of the articulator; customarily the anatomical reference are the mandibular transverse horizontal axis and one other selected anterior reference point- GPT 9. HISTORY: 1880-HAYES-caliper with median incisal point localized in relation to the two condyle 1890-WALKER-clinometer used to obtain the relative position of lower casr in relation to condylar mechanism GYSI- instrument for registering the condylar path and facebow 1899 -SNOW-simple instrument which has become prototype for all the facebow constructed in present days
It is the imaginary line between mandibular condyle around which the mandible can rotate within the sagittal plane. It allows for correct recording of centic relation and if transferred to articulator teeth contact each other in the articulator exactly as they do in the patient mouth When an incorrect axis is transferred to an articulator, teeth will b placed with any increase or decrease in vertical dimension of occlusion. The different schools of thought regarding the transverse hinge axis has led to the evolving of four main groups: Group I - absolute location of axis; Group II - arbitrary location of axis; Group III - non believers in transverse axis location; Group IV - split axis rotation. CLASSIFICATION: A.BASED ON EXACT TERMINAL HINGE AXIS LOCATION
Requires assistant to hold the face bow in place D.BASED ON THE INTERCONDYLAR DISTANCE EQUILIBRATION Spring bow o It is an earpiece face bow made of spring steel and simply springs open and close to various head widths. Most commonly used face bow (Hanau facebow) o Advantage The one piece design of bow eliminates the moving parts and maintenance problems encountered with other models. It is easy and efficient to use. Parts of sterilizable parts and can be direct/indirectly mounting capability. o Disadvantage Inabilities to measure intercondylar distance. Calibrated condylar rods o Condylar rods are graduated. They adjusted bilaterally until equally reading are achieved on both sides Slidematic face bow o Anterior horizontal arm of the bow composed of two sliding arms that allow for mediolateral movement of the bow till the 2 condylar rods contact the posterior reference points PARTS OF THE FACE BOW
The maxillary cast in the articulator is the baseline from which all occlusal relationships start. Therefore, it should be positioned in space by identifying three points of which two points are located posterior to the maxillae and one point located anterior to it. The posterior points are referred to as the posterior points of reference and the anterior one is known as the anterior point of reference. The spatial plane formed by joining the anterior and posterior reference points is called plane of orientation Fig- Ear piece Third reference point locater Bite fork stem Support bite fork index Bite fork Transfer rod Transfer jig U shaped frame or bow.
A definitive cusp fossa or cusp to marginal ridge relation is desired. When inter occlusal check record are used for verification of jaw position When the occlusal vertical dimension is subjected to change and alternation of tooth occlusal surface are necessary to accommodate the change To diagnose exiting occlusion in patient mouth CONTRA INDICATION: [Heartwell]