This document discusses different types of tooth rests used in partial dentures. There are four main types: 1) Occlusal rests, which contact the biting surface of posterior teeth. 2) Lingual rests, which contact the inside surface of teeth. 3) Incisal rests, which contact the front surface of anterior teeth. 4) Embrasure hooks, which span the gap between two teeth. Occlusal rests are the most common type and involve preparing the tooth with a rounded triangular rest seat for the denture to fit into. The preparation aims to direct forces along the tooth's long axis and not raise the vertical biting dimension.

1. 5- a. Types of tooth Rests

3. Dr. Amal Fathy Kaddah
Prof. of Prosthodontic,
Faculty of Oral &Dental Medicine,
Cairo University
Types of Tooth Rests

5. RESTS AND
REST SEATS

6. 1
2
5
3
4

7. Definition Rests are Rigid
Extensions of a
Partial Denture,
Placed in Rest Seats,
Which are Prepared
on Either the
Occlusal, Lingual
Surfaces or Incisal
Edges of the Teeth,
Providing Support to
the Partial Denture

8. The Quality of the Prosthesis to
Resist Displacement Towards
Denture Supporting Structures
Support

9. The Prepared Recess in a Tooth or
Restoration Created to Receive
Occlusal, Incisal, or Lingual Rest
Rest seat

11. I- Occlusal Rest
II- Lingual Rests
III. Incisal Rest
IV-Embrasure Hooks
1) Primary rest
2) Secondary or auxiliary
rest
Rests
Rests

12. Rests are either a part of a clasp
assembly or an auxiliary rest
Types of Rests

13. A Rigid Extension
of a RPD That
Contacts the
Occlusal Surface of
a Posterior Tooth
I- Occlusal Rest
or Restoration, on a Rest Seat Specially
Prepared to Receive it

14. Forms and Requirements of
Rest Seat Preparation
1- Should be rounded
triangular in shape.
2. The base of the triangle at
the marginal ridge about 2.5
mm in width, and
3. Its rounded apex is
directed towards the center
of the tooth

15. Rest Seat
Apex is directed
towards the
center
Rounded
Triangular
m 2.5 mm

16. 3. Inclined apically as it approaches the center of the tooth
4- The marginal ridge is lowered approximately 1 to 1.5 mm of
teeth in relation to a vertical line (permit sufficient bulk)
1mm
Rest Seat

17. 5- The floor of the rest seat should
be spoon shaped
??

18. 6- Rests, should be prepared in
Sound Enamel.
8-If an amalgam restoration is present, it
could be replaced by a cast restoration
(occlusal rests can be prepared in an
old amalgam restoration. ????? why
7- Rests, could be prepared in cast
restorations, crowns or inlays.

19. • Flow of Amalgam registers
deformation during setting.
• Creep denotes the deformation of
the set amalgam
• High residual mercury >>
High creep & lower strength, low
fracture resistant

20. proximal surface preparation
(Guiding planes and elimination of
undesirable undercuts)
9- Preparations for
the occlusal rest
must precede or
follow
GUIDING PLANES
??

21. 10. A high survey line may also result in deformation of the
clasp because, on insertion, the clasp is prevented from
moving down the tooth by contact with the occlusal
surface. If the patient persists in trying to seat the denture,
the clasp is bent upwards rather than flexed outwards.

22. Properly prepared R.S. helps to control
stress by directing forces transmitted
to abutment teeth down the long axis
of those teeth. The periodontal
ligament is capable of withstanding
vertical forces of far greater
magnitude than off-vertical, (near
horizontal) or torsional force
Rest Seat

23. Requirements of the Occlusal Rest
I-O.R. must fit the tooth ( minimize food
collection and preserve their location
in relation to the tooth
2- It must be strong enough to withstand
the loads without deform
3-It must not raise the vertical
dimension of occlusion

24. Prevent slippage of the prosthesis
creating an orthodontic like force
To direct the forces along the long
axis of the tooth
4- The angle between the minor
connector and the rest should be less
than 90˚

25. Occlusal Rest
Fit- Strong-not Raise the Vertical Dimension

26. Occlusal Rest
Than
90o

27. Not Raise the Vertical Dimension

28. Floor is Spoon shape
and not raise the
vertical dimension

29. Not Raise
The V.D.
Fit Direction
of Apex
Rounded
TriangularRigid
Spoon
floor
2.5 mm
in Width
Strong
1 to 1.5 Mm
Thickness

30. 2-Transmitting vertical stress along the
long axis of the tooth
Functions of the occlusal rest
6- It may act as indirect retention
3-Secure the clasp in its proper position
4- Distributing the occlusal load
5- Resistance to lateral displacement of the
prosthesis ???
1- Support

31. 1-Support

32. Transmitting vertical stress along the
long axis of the tooth

33. Secure the clasp in its proper
position

34. Distributing the Occlusal Load

35. It may act as indirect retention

36. Resistance to Lateral Displacement of the
Prosthesis but applying damaging horizontal
forces on abutment teeth

37. ‫من‬ ‫ل‬‫العاق‬
‫التجارب‬‫وعظته‬

38. Special Considerations
1- Boxed shaped occlusal rest
• Induces forces on
the abutment
??????
• The use of a box-shaped rest
seat within a cast restoration
may result in the rest applying
damaging horizontal loads on
the abutment tooth.
• These rest seats should be
restricted to tooth-supported
dentures where the periodontal
health of the abutment teeth is good.

39. •Induces
forces on
the
abutment
??????
•Provide Guide-surfaces
•Employed Only on a
Perfectly Periodontally
Healthy Tooth
•Helps in Preventing Lateral
Movement of the Denture
•It Provides Increased
Denture Retention

40. 2-Tipped Molar (Mesially
Inclined Mandibular Molar)

41. a- An Additional Occlusal Rest in
the Distal Fossa

42. b- Molar With Rest Preparation Extended
From Mesial Marginal Ridge to Distal
Triangular Fossa

43. Extending the occlusal rest over the center of the mesio-
distal fissure, allows for the transmission of the vertical
load over the whole occlusal surface and directs the
forces along the long axis of the tooth.

44. c- A casting is required, such as full
veneer crown or onlay

46. 3- Interproximal occlusal rest
seats

47. 4- Embrasure Rest
A Gap Between Two Molars

48. 4- Embrasure Rest
a- One simple circle clasp, and the rest recesses
should be fashioned on the two abutment teeth

49. B- two simple circle clasps jointed
together, and the occlusal rest can be
used to bridge a gap between teeth

50. 5- Internal Rest (the Milled Rest,
the Semiprecision Attachment)

51. You can only go
as far
as you push
‫تأتي‬ ‫العزم‬ ‫أهل‬ ‫قدر‬ ‫على‬
‫العزائم‬