Post on 22-May-2018
Rest Seat And
Rest Seat PreparationPresented by:
Dr. Tushar Bhagat
BDS, MDS (Prosthodontics)
Diploma in Advance Implantology (Romania)
Content & References
2
• Definition of rest seat (B.p.no.67)
• Purpose of rest seat (B.p.no.67)
• Types of rest seat. Primary & Auxiliary Rest seat (A.p.no.44)
• Various forms of rest seat
– Occlusal rest & rest seat (Proximal RS, Long occlusal RS, Embrasure RS)
(A.p.no.44-47; B.p.no.68-71)
– Lingual or cingulum RS (Inverted “V” RS, Ledge RS, Ball RS) (A.p.no.47-48;
B.p.no. 76-78)
– Incisal RS (A.p.no.48-49)
• Re-contouring / Enameloplasty & Dimpling (Stewart’s-p.no.286)
• Definition
• Reasons for re-contouring
• Dimpling
Introduction
• Rest is a component of a direct RPD (direct &
indirect retainer).
• Rest designated by the surface of the tooth
prepared. (occlusal rest, incisal rest etc.)
3
lingual
buccal
Retentive arm
Bracing arm
Definition
• Rest: The component of RPD that transfer
forces down the long axis of the abutment teeth
are called as Rest.
4
Ref: Stewart’s Removable partial prosthodontics. P.n.43
Definition
• Rest seat: the prepared surface of teeth into
which rest fits are called as Rest Seat.
5
Ref: Stewart’s Removable partial prosthodontics. P.n.43
Lect.No.4. Abutment
teeth preparation.
Types of Rest Seat
1) The rest that is part of retentive clasp assembly is
referred as primary rest seat.
2) The rest that is additional support or indirect retainer
retention is called auxiliary rest or secondary rest.
6
Ref: Stewart’s Removable partial prosthodontics. P.n.44
auxiliary rest primary rest seat.
Primary rest seat
• Prevents vertical movements of prosthesis towards
tissues.
• Transmit applied forces to supporting teeth.
• Seat should be shallow & saucer shape so that it should
function like ball and socket joint
7
Ref: Stewart’s Removable partial prosthodontics. P.n.44
Auxiliary rest seat
• Used as indirect retainers in extension base RPD
(Class I, II & long span Class IV)
• Placed anteriorly or posteriorly to the axis of rotation to
prevent extension bases from lifting away from
underlying ridge.
8
Ref: Stewart’s Removable partial prosthodontics. P.n.44
Purpose of rest
1) Maintained component in planned position.
2) Maintain established occlusal relationship
by preventing settling of the denture.
9
Ref: McCraken Removable partial prosthodontics. P.n.67.
Purpose of rest
3) Prevent impinging of soft tissue.
4) Direct and distribute occlusal load to
abutment teeth.
10
Ref: McCraken Removable partial prosthodontics. P.n.67.
Function of rest seat
1) To maintain a planned clasp-tooth
relationship.
2) To prevent extrusion of abutment teeth.
11Lect.No.4. Abutment
teeth preparation.
Function of rest seat
3) To provide positive reference seats in
rebasing and/or impression procedures.
4) To serve as an indirect retainer by
preventing rotation of the partial denture
(Class I or II RPD’s only).
12Lect.No.4. Abutment
teeth preparation.
Criteria for preparation of rest
seat
High speed hand piece with coolant.
Light pressure while preparing seat.
Good visibility.
Preparation entirely in enamel, (better avoid
anaesthesia).
Medium round bur (diamond or carbide.)
13
Types of rest seat
A. Occlusal rest seat
B. Lingual / cingulum rest seat
C. Incisal rest seat
D. Intracoronal / precision rest
14
Ref: Stewart’s Removable partial prosthodontics. P.n.44
Posterior rest seat
I. Occlusal rest seat Proximal RS
II. Long occlusal rest seat
III. Embrasure rest seat
Posterior tooth rest seat form
• Rest should not be placed on
inadequately prepared tooth.
• Outline form is triangular with base
of triangle located at marginal
ridge & the rounded apex directed
toward the centre of tooth.
16
Ref: Stewart’s Removable partial prosthodontics. P.n.44
Posterior tooth rest seat form
• Shape should follow outline of
mesial or distal fossa.
• Should occupy 1/3rd to 1/2 the
mesiodistal diameter of tooth.
• And approx. ½ the buccolingual
width of the tooth measured from
cusp tip to tip. 17
Ref: Stewart’s Removable partial prosthodontics. P.n.45
Posterior tooth rest seat form
• The floor of the rest seat must
inclined slightly towards the centre
of tooth.
• Floor should be concave or saucer
shape.
18
Ref: Stewart’s Removable partial prosthodontics. P.n.45
Posterior tooth rest seat form
• The most common mistake
insufficient reduction of marginal
ridge.
• 1.0 – 1.5mm thick where it crosses
marginal ridge.
19
Ref: Stewart’s Removable partial prosthodontics. P.n.45
Proximal rest seat
• The preparation is at least 1.0 mm deep with a
slightly deeper portion (0.5 mm) called the
POSITIVE SEAT located toward the center of
the preparation.
20Lect.No.4. Abutment
teeth preparation.
Embrasure occlusal rest seat
• The EMBRASURE OCCLUSAL REST is
located in a fossa adjacent to another
tooth .
• Its size, shape and dimensions are
similar to the proximal occlusal rest
preparation EXCEPT that the flare of the
facial margin is limited by the proximal
contact with the adjacent tooth21
Anterior rest seat
Lingual / cingulum rest
•Preferable placed on maxillary canine.
Incisal rest
•Placed on anterior teeth.
23
Ref: Stewart’s Removable Prosthodontics. P.no.47
Lingual / cingulum rest
seat
24
Placed on the lingual surface of maxillary
canines and incisors and in maxillary and
mandibular surveyed crowns.
Lingual / cingulum rest
seat
25
Rarely use on natural mandibular
incisors and canines because
there is usually insufficient
enamel thickness for an adequate
lingual rest preparation.
Lingual / cingulum rest
seat
27
There are three types of lingual rest
preparations based on their shape:
Inverted V shaped
Ledge shaped
Ball rest seat
Inverted ‘V’ rest seat 28
This type of rest are made in canines and
incisors having a prominent cingulum.
They follows the contours of the cingulum.
Shape is usually ‘V’ when viewed from the
lingual.
Inverted ‘V’ rest seat 29
The floor of the inverted ‘V’
rest seat preparation is placed
in the bulk of the cingulum.
The floor is deepest toward the
center of the tooth thus
forming a positive faciolingual
seat.
Inverted ‘V’ rest seat 30
Preparation extends more cervically on
the mesial and distal thus forming a
positive mesiodistal seat.
The preparation extends through the
marginal ridges.
The cingulum shaped rest preparation
is approximately 1.0 mm deep pulpally
and cervically.
Ledge / Cingulum ledge
rest seat
Usually prepared on lingual
surface of maxillary anterior teeth.
Step like preparation from mesial
to distal.
The opposite ridge should not be
reduced.
31
Ledge / Cingulum ledge
rest seat
1.5 mm deep,
Should be perpendicular to the
long axis of the tooth,
Location at the junction of the
middle & gingival 3rd of the tooth.
32
Ball rest seat
Ball rest seat is preferable used as
auxiliary rest or indirect retainer.
It can be given in both maxillary &
mandibular anterior.
At the cingulum.
34
Anterior rest seat
Lingual / cingulum rest
• Inverted V
• Cingulum Ledge
• Ball rest seat
Incisal rest
• Placed on anterior teeth.
36
Incisal rest seat
Incisal rests are placed on the incisal edges of
mandibular incisors.
They are not placed on maxillary incisors
because the minor connector of the rest would
interfere with occlusion and the facial portion
of the rest would be very visible and
unaesthetic.
37
Incisal rest seat
Incisal rests are usually located in
the mesial or distal half of the tooth.
The rest should also be located so
that it will direct forces parallel to
the long axis of the tooth when
occlusal forces are applied to the
prosthetic teeth.
38
Incisal rest seat
The mesiodistal dimension of the rest
preparation should be 1.5 – 2.5 mm and the
depth at least 1 mm to provide adequate space
for a bulk of metal for the rest
39
Guide plane preparation
Define as, two or more parallel, vertical surfaces of
abutment teeth, so shaped to direct the prosthesis
during placement & removal.
40
Ref: McCraken Removable Prosthodontics. P.no.155
Rule for Guide plane
preparation
Proximal guide plane surface should be 1/3 to 1/2
distance between buccal & lingual cusp.
Vertically minor connector contact enamel of tooth
on proximal surface about 2/3 its length.
41
1/3 to 1/2
Buccal
Lingual 2/3 its length
Function of Guide plane
I. To provide for one path of placement & removal
II. To ensure the intended action of reciprocal,
stabilizing & retentive components
III. To provide stabilization against horizontal rotation
of dentures.
IV. To eliminate gross food entraps between
abutment & component of RPD.
42
Ref: McCraken Removable Prosthodontics. P.no.155
Enameloplasty
Conservation must be rule when
doing recontouring enamel surface.
Used to create retentive undercuts
Term used as “Dimpling”
Depression approximately 4 mm MD
& length occlusogingival height
43
Ref: Stewart’s Removable Prosthodontics. P.no.286