4 mouth prearation for rpd
DESCRIPTION
for clinic 4 students, spring 2014, lectured for health and population institute doctors 2014TRANSCRIPT
presented by;
Dr; Hamada Mahross
DR HAMADA MAHROSS
Mouth preparation
It is the procedures used to prepare
the mouth to receive RPD with
minimal damaging effect on
dentoalveolar structure.
As a general rule:-
The preservation of already existing is
more important than restoring the
already lost.
Muller DeVan (1952)
DR HAMADA MAHROSS
Steps of mouth preparation
• Relief of Pain and Infection
• oral surgical preparation,
• conditioning of abused and irritated tissue,
• periodontal preparation,
• occlusal discrepancy.
• preparation of abutment teeth.
DR HAMADA MAHROSS
1- Relief of Painand
control Infection:
DR HAMADA MAHROSS
Dental conditions;
causing discomfort as endodontic
treatment or restorative filling for
carious teeth.
Gingival tissues;
should be treated to prevent
exacerbation of inflammatory
response as scaling, root planning,
and prophylaxis should be
performed.DR HAMADA MAHROSS
2- ORAL SURGICAL PREPARATION:
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- Exostosis and Tori, Sharp bony
spicules should be removed and
knifelike crests,
- Hyperplasic Tissue, maxillary labial
and mandibular lingual frena,
Hyperkeratosis, Erythroplasia, and
Ulcerations,
- Dentofacial Deformity,
Osseointegrated Devices or
Augmentation of Alveolar Bone.
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• Extractions, Removal of Residual Roots, impacted
teeth, Cysts and Odontogenic Tumors,
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3- CONDITIONING OF ABUSED AND
IRRITATED TISSUE
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Tissue recovery program includes;
- rinsing the mouth three times a day
with a prescribed saline solution.
- massaging the residual ridge areas,
palate, and tongue with a soft
toothbrush.
- removing the prosthesis at night.
- using a prescribed therapeutic
multiple vitamin.
- Removing the ill-fitting dentures.
- Use of Tissue Conditioning Materials.DR HAMADA MAHROSS
4- periodontal preparation
DR HAMADA MAHROSS
The periodontal health of the
remaining teeth, especially those
to be used as abutments, must be
evaluated:-
(1) Type, location, and severity of
bone loss;
(2) Location, severity, and distribution
of furcation involvements;
(3) Alterations of the periodontal
ligament space;DR HAMADA MAHROSS
Tooth mobility• Each tooth should be evaluated carefully
for mobility.
• Normal mobility is in the order of 0.05 to
0.10 mm.
- Grade I mobility; less than 1 mm of
movement in a buccolingual direction.
- grade II; mobility in the buccolingual
direction is between 1 to 2 mm.
- grade III; greater than 2 mm of mobility in
the buccolingual direction and/or the
tooth is vertically depressible.DR HAMADA MAHROSS
5- Correction of
Occlusal Plane
Discrepancies;
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The occlusal plane in most
partially edentulous
mouths will be uneven.
The severity of this unevenness will
determine the treatment needed
to correct;
1- If supraeruption is minor,
the occlusal plane may be corrected
by carefully recontouring the
surfaces of the teeth.
DR HAMADA MAHROSS
2- If moderate supraeruption,
correction of the occlusal plane
may require the placement of
cast restorations such as onlays
or crowns.
3- If supraeruption is extreme,
extraction of the offending teeth
may be the only logical solution.
DR HAMADA MAHROSS
- downward growth of the Tuberosities causing the interarch space
may be extremely limited and may preclude the placement of an
acceptable prosthesis.
- Surgical reduction of the Tuberosities may be required to provide
adequate restorative space.
DR HAMADA MAHROSS
Treatment of mesial tipped
molars.
1- The ideal solution is to upright
such teeth orthodontically.
2- If minor, enameloplasty.
3- If moderate, onlays or crowns.
4- if severe, surgical intervention.
DR HAMADA MAHROSS
DR HAMADA MAHROSS
malalignments may be corrected using
enameloplasty procedures
Moderate malalignments
may be corrected using
properly designed fixed
restorations.
(b) Tooth preparation is
intended to correct
malalignment. (Notice the
angulations of the bur.)
(c) The finished
preparation permits
placement of a suitable
crown,
(d) The resultant crown
displays the desired
angulation and contours.
DR HAMADA MAHROSS
tooth preparation may threaten the pulpal tissues,
(a) Tipped molar with a prominent mesial pulp horn,
(b) The likelihood of mechanical exposure contraindicates tooth preparation,
(c) The tooth is endodontically treated before preparation,
(d) A core is placed and the preparation is completed. In turn, a properly
contoured crown will be placed
DR HAMADA MAHROSS
- pier abutment; A lone-standing tooth
adjacent to an extension base area.
- placing a clasp on such a tooth leads to
periodontal destruction and abutment
loss.
Treatment;
- Splinted by the placement
of a fixed partial denture.
- supported by place rests
and anterior and posterior
guide plate or half and half
clasp.
- generally; pier abutments may receive rests, but are not clasped.
6- Preparation of
abutment teeth:
DR HAMADA MAHROSS
1. Reshaping of abutment teeth.
a-Enameloplasty:
b- Developing Guiding Planes:
c- Changing Height of Contour:
2. Crowns.
3. Rest seat preparation.
DR HAMADA MAHROSS
1. Reshaping of abutment teeth.
a-Enameloplasty:
b- Developing Guiding Planes:
c- Changing Height of Contour:
DR HAMADA MAHROSS
a- Enameloplasty:
• first accomplished on a diagnostic
cast to reveal whether reshaping of
enamel surfaces is possible.
• Preparation performed by a
carborundum impregnated rubber
wheel or point placed in a low-speed
hand piece. Light, intermittent
pressure and moderate speed should
be used during polishing procedures.DR HAMADA MAHROSS
b- Developing Guiding Planes:
Guiding planes;
are surfaces on proximal or lingual surfaces of
teeth that are parallel to each other and,
more importantly, to the path of insertion and
removal of a RPD.
functions:
1- On the proximal walls adjacent to edentulous
spaces they provide parallism needed for
ensuring stabilization.
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2- Minimize wedging action between RPD and abutment.
3- Decrease undesirable space between RPD and the abutment tooth
to increase retention by frictional resistance.
4- On lingual surfaces of teeth provides maximum resistance to lateral
stresses exerted by retentive arm during insertion and removal of
RPD (reciprocation).
DR HAMADA MAHROSS
Dimensions of the Guiding Plane:
It is prepared by cylindrical diamond in the following
dimensions:
occlusogingivally it is 2-4 mm in length prepared flat on
the occlusal third of the abutment.
Buccolingually it is 3-4 mm in width and curved in
harmony with the existing tooth contour.
DR HAMADA MAHROSS
Generally, guide surface preparations
for extension RPDs are 1.5-2mm
shorter than tooth supported RPD,
leaving a small space below the
gingival extent of the preparation.
The space in conjunction with
physiologic relief, prevents the guide
plate from binding against the
abutment during functional
movements of the extension base.
DR HAMADA MAHROSS
c- Changing Height of Contour
- The retentive clasp arm should be ideally located at the junction of the gingival and middle thirds not higher, for
- esthetic purpose and
- for definite mechanical advantage.
DR HAMADA MAHROSS
- But when, the height of contour lies near the
occlusal surface in the tipped tooth this can be
lowered by grinding (enameloplasty).
- High survey line may cause deformation of the
clasp.
DR HAMADA MAHROSS
Modification of Retentive Undercut:
- When there is insufficient undercut
these teeth can be modified by
increasing amount of the undercut;
By creation of gentle depression
(concavity) about 4mm in
mesiodistal length and 0.01inch
deep (not a pit or hole).
- This concavity is prepared by using a
small, round end tapered diamond
stone.DR HAMADA MAHROSS
DR HAMADA MAHROSS
- using a round diamond bur in a high-speed
headpiece can also used.
- The bur is moved in an anteroposterior direction
(arrow), and avoid creating undermined by its head.
2. Crowns.
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Indication of cast crown;
1- When the remaining teeth do not posses natural contours
and the enamel surfaces cannot be modified to create
undercut.
2- in case of extensive caries, defective restoration, tooth
fracture, and endodontically treated teeth.
DR HAMADA MAHROSS
Preparations must follow
established guidelines for taper and
reduction. Notice that a rest seat
has been included in the
preparation (arrow).
The height of contour
is marked using an
analyzing rod in the
vertical arm of a dental
surveyor.
undercut is verified
by analyzing rod and
measured by
undercut gauge.
Guiding planes are created
and refined using a wax
knife
discoid instrument is used to finalize
rest seat contours.
DR HAMADA MAHROSS
DR HAMADA MAHROSS
3. Rest seatpreparation.
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functions of rests:
Direct the forces parallel to long
axis of the abutment.
Prevents the gingival
displacement of a RPD ( occlusal
stopper).
Maintains the relationship
between a clasp assembly and
the tooth.
DR HAMADA MAHROSS
Rest Seat Preparation for
Posterior Teeth:
1) Occlusal Rest Seat in Enamel:
- The basically outline form of an occlusal
rest seat is triangular, with its base
directed at the marginal ridge and the
apex inclined toward the tooth center,
- occupying about 1/2 of the buccolingual
width of the occlusal surface, and the
apex should be rounded as all margins
of the preparation. DR HAMADA MAHROSS
- occlusal rest must be at least 1
mm thick at its thinnest point if
chrome alloy is used for
framework and about 1.5 mm
if gold is to be used.
- Extension of the rest seat
mesiodistally about one third
to one half of the mesiodistal
diameter.DR HAMADA MAHROSS
- The floor of the occlusal rest seat
must be inclined toward the center
of the tooth to place the deepest
part of the rest nearly at the center
of the preparation.
- The floor of the rest seat should be
spoon in shape not flat.
- Any sharp angle should be
smoothed.
DR HAMADA MAHROSS
- occlusal rest seat prepared using round
diamond burs, diamond bur with rounded
ends and tapering sides.
- When using round diamond bur care to
avoid creation of mechanical undercut at
the peripheries of the preparation.
- The spoon shape preparation to act as ball
and socket.
DR HAMADA MAHROSS
Occlusal Rest Seat on the Surface of an
Existing Cast-metal Restoration:
- sufficient space should be present; so
the patient must be informed if
perforation occurred and must be
replaced.
- The instrumentation and procedures for
preparing rest seats on existing fixed
restorations are identical to those for
preparing rest seats on enamel
surfaces.
DR HAMADA MAHROSS
Occlusal Rest Seats on an Amalgam Restoration:
- multiple-surface amalgam restoration is less desirable than
a rest seat preparation on sound enamel or a cast
restoration.
- The amalgam alloy tends to deform (creep) when exposed
to constant load.
- Care must be taken to avoid weaken the proximal portion of
the amalgam restoration at the ismuth during preparation.
DR HAMADA MAHROSS
Embrasure Rest Seat
This preparation crosses the occlusal embrasure of two approximating
posterior teeth, from the mesial fossa of one tooth to the distal
fossa of the adjacent tooth; to receive an embrasure clasp.
DR HAMADA MAHROSS
- diamond bur with a rounded end and Tapering
sides is preparing embrasure rest seats.
- Contact between the teeth should not be
broken since this may result in tooth
migration or food impaction.
- the embrasure rest seat at the facial and lingual
embrasures, should be 3.0 to 3.5 mm wide
and 1.5 to 2.0 mm deep.
- In some circumstances it may also be necessary
to reduce and recontouring the cusp of the
tooth in the opposing arch.
DR HAMADA MAHROSS
Rest Seat Preparation for Anterior Teeth:
Indications:
1- When there is no posterior tooth to place an occlusal rest.
2- Maxillary canine is mainly used for lingual or cingulum rest, because the
morphology of the tooth permits preparation of the seat.
3- It is rarely used on incisors when the canine is missing. In this case multiple rests
should be used to distribute the force over a number of incisors.
4- To prepare rest seat in the enamel there should be (prominent cingulum, good
oral hygiene, and low caries index).
DR HAMADA MAHROSS
1-the outline form of a cingulum rest
seat should be crescent shaped when
viewed from the lingual aspect. Its
broadest portion is in the middle of
the lingual surface and get less broad
as it approaches the proximal surface.
DR HAMADA MAHROSS
2- V-shaped when viewed from the
proximal; with rounded line angles. (This
permits direction of the force along the
long axis of the tooth).
3- Mesiodistal length of preparation should
be a minimum of 2.5 mm.
labiolingual width about 2 mm,
and incisal apical depth a minimum of 1.5
mm.
DR HAMADA MAHROSS
4- It is often difficult to obtain a positive apically
inclined rest seat due to tooth angulations or
anatomy.
The use of cast restoration may be required to
establish a definite rest seat.
DR HAMADA MAHROSS
Cingulum Rest Seat preparation:
- using a carbide inverted cone bur (side end
cutting surfaces) in a high speed hand
piece.
- The preparation is finished, polished,
smoothen, and gently rounded using a
rubber wheel in a low speed hand piece.
- A cylindrical diamond stone with a
rounded tip should be used to prepare the
rest seat.
- A spherical instrument tends to create
unwanted undercuts.DR HAMADA MAHROSS
DR HAMADA MAHROSS
seats.restcingulumBonded
DR HAMADA MAHROSS
45o
Marginal Ridge Rest
2- Incisal Rest Seats in Enamel:
- are least desirable rest seats for
anterior teeth. Because of its bad
esthetic, interference with
occlusion, and its damaging
effect on abutment.
DR HAMADA MAHROSS
Indications:
1- Incisal rests are used mostly on mandibular
canines when the abutment is sound and
when a cast restoration is not indicated.
2- It may be used as an auxiliary rest for
indirect retention.
Disadvantages:
a) The bad esthetic of metal.
b) Greater mechanical leverage than lingual
rests, due to longer minor connector.
DR HAMADA MAHROSS
1- usually placed near a proximal
surface, mostly on the proximal distal
line angle of the tooth for esthetic.
2- When viewed from the facial surface,
its floor is concave in shape and
inclined toward the center of the
tooth to direct the force along to the
long axis of the tooth.
DR HAMADA MAHROSS
3- When viewed from the proximal, the outline form is
convex (saddle shape) with buccal and lingual bevels.
4- All borders are rounded and smooth.
5- Its dimensions are approximately (2.5 mm wide and 1.5
mm deep).
DR HAMADA MAHROSS
Preparation:
1- An initial depth cut is made,
using a tapered cylindrical
stone, at the junction of the
middle and the mesial or
distal third of the abutment
tooth.
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2- The walls of the rest seat are created by flaring the
edges of the depth cut preparation and beveling
the Buccal and lingual walls with finishing bur.
DR HAMADA MAHROSS
Rest seat evaluation
• Rest preparations can be evaluated with soft, non-sticky wax.
• The wax is pressed into the recess, removed, and
inspected for proper form.
• using caliper to measure the thickness of rest.
DR HAMADA MAHROSS