05. rest seats and types of rests

principles of design of rest seats and different types of rests

1. REST AND REST SEATS DR SHOAIB RAHIM BDS, FCPS ASSISTANT PROFESSOR

2. DEFINITION REST Rigid extension of a removable partial denture that contacts the occlusal, incisal, cingulum, or lingual surface of a tooth or restoration, the surface of which is commonly prepared to receive it REST SEAT The prepared recess in a tooth or restoration developed to receive the occlusal, incisal, cingulum, or lingual rest

3. FUNCTIONS Provide vertical support Maintains components in their planned positions Maintains established occlusal relationships by preventing settling of the denture Prevents impingement of soft tissue Directs and distributes occlusal loads to abutment teeth

4. FUNCTIONS Prevents extrusion of abutment tooth Prevents ingress of food Provides resistance to lateral displacement Contributes to indirect retention

5. FORMS OF REST AND REST SEATS Occlusal Rest Cingulum Rest Incisal Rest Implants as Rest

6. OCCLUSAL REST

7. REQUIREMENTS Rounded triangular As long as it is wide (2.5mm) Marginal ridge must be lowered to permit sufficient bulk of metal for strength and rigidity (approximately 1.5 mm) Floor of occlusal rest seat should be apical to marginal ridge and occlusal surface, and should be spoon shaped (2mm) The angle formed by occlusal rest and vertical minor connector should be less than 90 degrees

8. TYPES OF OCCLUSAL RESTS Double Occlusal Rest Extended Occlusal Rest Interproximal Occlusal Rest Internal Occlusal Rest

9. DOUBLE OCCLUSAL REST More than 90 degree angle Mesial and distal side Lone tilted abutment To support ring clasp

10. EXTENDED OCCLUSAL REST Kennedy Class II, modification 1 and Class III situations with mesially tipped molar

11. MODIFIED EXTENDED OCCLUSAL REST Severely tilted abutment In the form of an onlay to restore occlusal plane 1-2 mm bevel on buccal and lingual occlusal surface to provide stabilization 1-2 mm guiding plane on mesial surface of abutment

12. INTERPROXIMAL OCCLUSAL REST Prepared as individual occlusal rest seats but with extended lingual preparation Prevent food impaction

13. INTERNAL OCCLUSAL REST Tooth supported cast partial denture Occlusal support and horizontal stabilization Support derived from floor Horizontal stabilization derived from near vertical walls Outline form is slightly dovetailed Elimination of buccal clasp and favorable rest seat location

14. IMPLANT AS REST

15. Advantage of vertical stiffness Prevent tissue-ward movement Also provide retention Low profile connection Alter or eliminate fulcrum location for prosthesis movement

16. SUPPORT FOR RESTS Made on sound enamel or any restoration material If fissures are found on occlusal surface then they should be removed and restored first Best abutment for cast partial denture is protected abutment Preparation with burs and polishing points

17. SUPPORT FOR RESTS Rest seats in crowns and inlays are somewhat larger and deeper Rest seats for tooth-supported dentures may be made slightly deeper than those that support a distal extension base Internal rest seats are created first in wax, either with suitable burs in a handpiece holder or by waxing around a lubricated mandrel

18. LINGUAL REST

19. JUSTIFICATIONS Anterior tooth may be the only abutment available for occlusal support Anterior tooth occasionally may be used to support an indirect retainer or an auxiliary rest Root form, root length, inclination of the tooth, and crown to root ratio must be considered Lingual rest is preferable to incisal rest because it is placed closer to horizontal axis of rotation of abutment

20. REQUIREMENTS Rounded V shape at junction of gingival and middle third Mesiodistal length 2.5-3 mm, labiolingual width 2 mm and inciso -apical depth 1.5 mm Prepared with inverted cone followed by tapered stones Prepared according to path of insertion

21. MODIFICATIONS/ ALTERNATIVES Most satisfactory lingual rest from standpoint of support is one that is placed on prepared rest seat in cast restoration Maybe placed on lingual surface of cast veneer crown, a three-quarter crown, inlay, laminate veneer, composite restoration, or etched metal restoration Conservative restorations in anterior teeth may be better suited for ball types of rest seats than inverted V types of rest seats Sapphire ceramic orthodontic brackets bonded to lingual surfaces of mandibular canines and shaped as rest seats maybe used

22. INCISAL REST

23. RECOMMENDATIONS Placed at the incisal angles of anterior teeth Provides definite support with relatively little loss of tooth structure and little display of metal Used predominantly as auxiliary rests or as indirect retainers More likely than lingual rest to lead to some orthodontic movement of tooth because of unfavorable leverage factors Prepared in the form of a rounded notch at the incisal angle with deepest portion of the preparation apical to incisal edge

24. RECOMMENDATIONS Notch should be beveled both labially and lingually Lingual enamel should be partly shaped to accommodate the rigid minor connector Width should be 2.5 mm and depth should be 1.5 mm Incisal rest should be over-contoured slightly to allow for labial and incisal finishing to the adjoining enamel

25. JUSTIFICATIONS They may take advantage of natural incisal faceting Tooth morphology does not permit other designs Such rests can restore defective or abraded tooth anatomy Incisal rests provide stabilization Full incisal rests may restore or provide anterior guidance

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