rest seat تكملة محاضرة
ثالث اسنان كركوك/ 2017/1/4صناعة عملي
b. Extended Occlusal Rest
Used in situation in which the most posterior abutment is a mesially tipped molar, to minimize further tipping of the abutment and to ensure that the forces are directed down the long axis of the abutment. This rest should extend more than one-half the mesiodistal width of the tooth
c. Interproximal occlusal rest
These rest seats are prepared as individual occlusal rest seats, with the exception that the preparations must be extended farther lingually than is ordinarily accomplished .When such rest seats are prepared, care must be exercised to avoid reducing or eliminating contact points of abutment teeth. However, sufficient tooth structure must be removed to allow adequate bulk of the component for strength and to permit the component to be so shaped that occlusion will not be altered.
d. Internal Occlusal Rests
Used for partial denture that is totally tooth supported, used for both occlusal support and horizontal stabilization
2. Lingual rest and rest seat:
Lingual rests are associated with anterior teeth.
Lingual rest preparation
First method: A slightly rounded V is prepared on the lingual surface at the junction of the gingival and the middle one third of the tooth. The apex of the V is directed incisally. The mesio-distal length of the preparation should be a minimum of 2.5 to 3mm, labio-lingual width about 2mm, and incisal-apical depth a minimum of 1.5mm. This preparation of the tooth starts with an inverted cone shaped bur and progresses to a smaller tapered bur with a round end to complete the preparation.
Second method: A ball type of rest may be used in a prepared seat. Such a rest seat may be prepared in tooth surfaces with overly sufficient enamel thickness or may be prepared in restorations placed in teeth in which enamel thickness is inadequate. Ball type rests are better suited for conservative restorations (e.g., silver amalgam, pin inlays, composite resin) in anterior teeth than are the inverted V types of rest seats.
3. Incisal rest and rest seat:
The incisal rest are placed at the incisal angles of the anterior teeth and on the prepared rest seat, they are generally placed on enamel.Incisal rest and rest seat
An incisal rest seat is usually placed on the mesio- or disto-incisal angle of the incisor teeth with the deepest portion towards the center of the tooth. It is predominantly used as an auxiliary rest or an indirect retainer.Mechanically, a lingual rest is preferable to an incisal rest, because the lingual rest is placed nearer to the center of rotation of the tooth and therefore, will have less tendency to tip the tooth.
Esthetically, the metal of the rest shows at the incisal edge
Form and location:
-Incisal rest seat should be approximately (2.5mm) wide and (1.5mm) deep so that the rest will be strong without having to exceed the natural contour of the incisal edge.
D. implant as a rest
Implants can also be considered to serve as a rest when one takes advantage of the vertical stiffness characteristic they possess. In this application, they can serve to resist tissue ward movement alone and may be considered useful for retentive needs as well.
When implant used as a rest, implants can serve to efficiently resist vertical movement and provide positive support. This use allows a low profile connection (i.e., close to the ridge),