4 mouth prearation for rpd

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:

DR HAMADA MAHROSS

- 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.

DR HAMADA MAHROSS

• Extractions, Removal of Residual Roots, impacted

teeth, Cysts and Odontogenic Tumors,

DR HAMADA MAHROSS

3- CONDITIONING OF ABUSED AND

IRRITATED TISSUE

DR HAMADA MAHROSS

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;

DR HAMADA MAHROSS

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.

DR HAMADA MAHROSS

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.

DR HAMADA MAHROSS

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.

DR HAMADA MAHROSS

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.

DR HAMADA MAHROSS

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