INTRODUCTION,

CLASSIFICATION & BIOMECHANICS

of PARTIALLY

EDENTULOUS arches

DR. ANUSHA SINGH

CONTENTS:

Indication against use of FPD Indication for RPD Parts of RPD Steps in the treatment of an RPD patient Advantages and disadvantages of RPD Requirements of an acceptable classification Classifications mechanical principles applicable in removable

prosthodontics forces acting on partial dentured Causes of failure of RPD Conclusion References

The art and science of replacing absent body parts is termed prosthetics , and any artificial part is called a prosthesis.

The term prosthesis and appliance are often confused & interchangeable.

Appliance is correctly used only to refer to a device worn by a patient in the course of treatment, such as a orthodontic appliance, surgical appliance.

PROSTHODONTICS

FIXED

REMOVABLE MAXILLOFACIAL

complete Partial

extracoronal Intacoronal

REMOVABLE PARTIAL DENTURE

‘‘ Any prosthesis that replaces some teeth in a partially dentate arch . It can be removed from mouth and placed at will.’

- GPT 8

INDICATIONS AGAINST USE OF FIXED PARTIAL DENTURES

Youth Patient large dental pulps and lack of clinical crown height.

Advanced Age Reduced life expectancy and Frequently failing general health

contraindicate the expensive and tedious dental procedures

Long edentulous span

Excessive loss of bone As they are unable to support a fixed prosthesis

and it is necessary to provide support for the lips or cheek or to obtain proper tooth position for the artificial tooth

INDICATIONS FOR RPD

Long edentulous span :contraindicates use of fixed partial denture

No abutment tooth posterior to edentulous space

Reduced periodontal support of remaining teeth: loss of bony support so unable to support a fixed prosthesis.

Need for cross-arch stabilization: The fixed partial denture can provide excellent an anterioposterior stabilization but limited lateral, or buccolingual, stabilization.

Physical or emotional problem of the patient :The lengthy preparation and construction for fpd can be tiring

Esthetics of primary concern in replacement of multiple missing anterior teeth :Three-dimensional denture tooth on a denture base may have a more lifelike appearance than some pontics

After recent extraction : teeth immediately following extraction are replaced with temporary removable partial dentures that can be relined as resorption occurs.

Patient desire :To avoid operative procedures on sound, healthy teeth and for eco nomic reasons.

ADVANTAGES OF RPD Does not sacrifice sound healthy tooth Economic

Easier to repair

A properly designed partial denture will assist in support of existing teeth

help to balance bite. This means better chewing and a healthier jaw joint.

Add support to the cheeks & lips.

existing natural teeth extracted for any reason, new teeth can be added

DISADVANTAGES OF RPD Low patient acceptance.

The clasps sometimes show when the patient smiles.

The bar across the palate interferes

with taste. It may feel bulky and may cause the patient to gag at first.

food collects under it during eating. It should be removed from the mouth and cleaned after every meal and at night.

As the partial is repeatedly taken in and out, it can wear anchor teeth and loosen them.

Caries may develop under clasp component especially if patient fails to keep the prosthesis and abutment clean.

PARTS OF A REMOVABLE PARTIAL DENTURE

The components of a removable partial denture are:

1. Major connector2. Minor connector3. Rest4. Direct retainer5. Indirect retainer6. Denture base7. Artificial tooth replacement

MAJOR CONNECTOR Def: The major connectors connect the parts of

the prosthesis located on one side of the arch with those on the opposite side. All other parts of the partial denture are attached to it either directly or indirectly.

Properties: Be rigid Provide vertical support and protect the soft

tissues Provide a means of obtaining indirect retention

where indicated

MINOR CONNECTOR

  Def: The connecting link between the major

connector or base of a rpd and the other units of the prosthesis, such as clasp assembly, indirect retainers, occlusal rests, or cingulum rests.

Functions : To transfer functional stress to the abutment

teeth. To transfer the effect of the retainers, rests,

and the stabilizing components to the rest of the denture.

REST A rest is a rigid extension of a partial denture that

contacts a remaining tooth (or teeth) to dissipate functional forces.

 

DIRECT RETAINER

  A clasp or attachment placed on an

abutment tooth for the purpose of holding a removable denture in position.

INDIRECT RETAINER

  A part of RPD which assists the direct

retainers in preventing displacement of distal extension denture bases by functioning through lever action on the opposite side of the fulcum line.

DENTURE BASE AND TOOTH REPLACEMENTS

Denture base is the part of the denture that forms the tissue surface of the denture over the edentulous area.

o helps to distribute the forces acting on the denture over the entire residual ridge.

o It holds the tooth replacements in position.

Tooth replacements reproduce the contour and function of the missing teeth.

PARTIAL DENTURE SERVICE DIVIDED INTO SIX PHASES

first phase patient education.

second phase diagnosis, treatment planning, design of the partial denture framework, treatment sequencing, and execution of mouth preparations.

third phase provision of adequate support for the distal extension denture base.

fourth phase establishment and verification of harmonious occlusion

fifth phase involves initial placement procedures and a review of instructions given the patient to optimally maintain oral structures and the provided restorations.

sixth phase follow-up services by the dentist through recall appointments for periodic evaluation of the responses of oral tissue to restorations and of the acceptance of the restorations by the patient.

FIRST PHASE: Patient education

"The process of informing a patient about a health matter to secure informed consent, patient cooperation, and a high level of patient compliance.“

give written suggestions to reinforce the oral presentations.

SECOND PHASE: diagnosis , treatment planning n mouth prep.

thorough medical and dental histories.

The complete oral examination including both clinical and radiographic interpretation

Evaluation of the occlusal plane, the arch form, and the occlusal relations of the remaining teeth accomplished by clinical visual evaluation and diagnostic mounting.

The surveyor is instrumental in diagnosing and guiding the appropriate tooth preparation and verifying mouth preparation

THIRD PHASE: provision of support for distal extension

primary supporting area should be recorded or related under some loading so that the base may be made to fit the form of the ridge when under function.

distal extension base must be made as equal to and compatible with the tooth support as possible.

FOURTH PHASE:

For the distal extension base, however, jaw relation records should be made only after verifying the fit of the framework to the abutment teeth and opposing occlusion

FIFTH PHASE :

occurs when the patient is given possession of the removable prosthesis.

occlusal harmony be ensured

the processed bases must be reasonably perfected to fit the basal seats.

ascertained that the patient understands the suggestions and recommendations given by the dentist

SIXTH PHASE: Periodic recall

Periodic re-evaluation of the patient is critical .

These examinations must monitor the condition of the oral tissue, the response to the tooth restorations, the prosthesis, the patient's acceptance, and the patient's commitment to maintain oral hygiene.

6-month recall period is adequate for most patients,

CLASSIFICATION

Need for classification:

Formulate a good treatment plan

Anticipate difficulties for the design

Communication

Designing according to occlusal load

REQUIREMENTS

1. Allow visualization of the type of

partially edentulous arch being

considered

2. Permit differentiation between tooth-

supported and tissue-supported partial

dentures

3. Serve as a guide to the type of design to

be used

4. Be universally acceptable

CUMMER’S CLASSIFICATION

Proposed by Cummer in 1920

First professionally recognized

classification

Based upon choice of number and position

of direct retainer

CLASS I

Partially dentulous arch in which two

diagonally opposite teeth are chosen as

abutment for direct retainers with an

indirect retainer as auxillary attachment

CLASS II Partially dentulous arch in which two

diametrically opposite teeth are chosen as

abutments for attachment of direct

retainer with an indirect retainer as

auxillary attachment

CLASS III Partially dentulous arch in which one or

more teeth on the same side are chosen

as abutments for attachment of direct

retainer with or without indirect retainer

CLASS IV Partially dentulous arch in which three or

more teeth are chosen as abutments for

attachment of direct retainer without use

of indirect retainer

KENNEDY CLASSIFICATION

Dr.Edward Kennedy (1925)

Most widely used

Original classification contains 4 classes

based on relationship of edentulous spaces

to abutment teeth

Class I

Bilateral edentulous areas located

posterior to the remaining natural teeth

(most common)

CLASS I I

Unilateral edentulous area located

posterior to the remaining natural teeth

CLASS III

Unilateral edentulous area with natural

teeth both anterior and posterior to it

CLASS IV

Single,bilateral edentulous area located

anterior to the remaining natural teeth

(least common)

Dr. O.C. Applegate (1960) modified Kennedy classification by including 2 more classes:

CLASSV Edentulous area bounded anteriorly and

posteriorly by natural teeth but in which anterior abutment (lateral incisor)is not suitable for support

CLASS VI Teeth adjacent to the space are capable of

total support of required prosthesis

APPLEGATES RULES RULE 1 Classification should follow rather than

precede any extractions of teeth that might alter the original classification.

RULE 2 If a third molar is missing and not to be

replaced, it is not considered in the classification.

RULE 3 If a third molar is present and is to be used

as an abutment, it is considered in the classification.

RULE 4 If a second molar is missing and is not to be

replaced, it is not considered in the classification .

RULE 5 The most posterior edentulous area/areas

always determine the classification.

RULE 6 Edentulous areas other than those determining

the classification are referred to as modifications and are designated by their number.

RULE 7 The extent of the modification is not

considered, only the number of additional edentulous areas.

RULE 8 There can be no modification areas in Class IV

arches.

BAILYN’S CLASSIFICATIONProposed by Bailyn Based on whether the prosthesis is tooth-

borne, tissue-borne ,or a combination of the two.

RPD

Saddle areas anterior Saddle areas posterior

to First premolar to canine

ANTERIOR(A) POSTERIOR(P)

SUB-DIVISIONS:

CLASS I :Bounded Saddle(not more than three teeth missing. Tooth-supported

CLASS II: Free end saddle(there is no distal abutment tooth). Tooth Tissue-supported

CLASS III: Bounded saddle (more than three teeth missing ). Tooth Tissue-supported

MAUK’S CLASSIFICATION By Mauk in 1942

Based on : - number and position of the

remaining teeth - number ,length and position of

the spaces

CLASS IBilateral space with no teeth posterior to it

CLASS II Bilateral

space with teeth

present posterior to one

space

CLASS IIIBilateral space with teeth present posterior to both spaces

CLASS

IV Unilateral

posterior space with or

without teeth

posterior to it

CLASS VAnterior space withUnbroken posteriorarch

CLASS VI

Irregular spaces around

the arch

BECKETT’S SYSTEM

Proposed by Beckett in 1953

3 classes

Based on whether the denture base is tooth-borne, tissue-borne or a combination of the two

Widely used in Australia

CLASSI Saddles(denture bases ) which are tooth-borne

CLASS 2 saddles(denture bases)

which are mucosa-borne

CLASS 3inadequate abutments and mucosa to support the saddle

FRIEDMAN’S SYSTEM

Introduced by Friedman in 1953

Based on three segments types : ‘A’ Anterior space ‘B’ Bounded posterior

space ‘C’ Cantilever

‘A’ anterior space

‘B’ bounded posterior

space

‘C’ CantileverPosterior free –end space

‘C-A-B’space

CRADDOCK CLASSIFICATION

By Craddock in 1954

CLASSI : saddles supported on both sides by substantial abutment teeth

CLASSII: vertical biting forces applied to denture resisted entirely by soft tissues

CLASSIII: tooth –supported at only one end of the saddle

SKINNER’S SYSTEM

Given by C.N Skinner in 1957

Based upon the relationship of the abutment teeth to the supporting residual alveolar ridge

Classified into 5 classes

CLASSI Teeth present both anterior and posterior to denture base

CLASS II RPDs –teeth are

posterior to

denture base

CLASS IIIabutment teeth are related anterior to denture base

CLASS IV denture base both

anterior and posterior

to remaining teeth

CLASS V abutment teeth are unilateral to denture base

WATT etal CLASSIFICATION IN 1958

Based on type of support derived1. Entirely tooth-borne: denture rests on

abutment teeth2. Entirely tissue-borne: denture rests on soft

tissue3. Partially tooth-borne and Partially tissue-

borne: rest both on tissue and teeth

APPLEGATE-KENNEDY SYSTEM

By O.C Applegate in 1960

Is a modification of Kennedy classification

Based on : - ability of boundary teeth to supply

abutment facilities for the partial denture -the location of the edentulous spaces in

relation to the teeth which remain

CLASS I All remaining teeth are anterior to bilateral

edentulous space Most frequently occurring Mandible(highest incidence)

CLASS II Remaining teeth of either right or left side are

anterior to unilateral edentulous ridge

CLASS IIIEdentulous space bounded by teeth both

anteriorly and posteriorly

CLASS IV Edentulous space lies anterior to the remaining

teeth which bound it both to right and left of median line

CLASS V -Edentulous space bounded anteriorly and

posteriorly by teeth but the anterior boundary tooth not

suitable for abutment service-Mostly in maxillary arch

CLASSVIEdentulous space bounded anteriorly and

posteriorly by teeth and where boundary teeth are capable of

total support

SWENSON CLASSIFICATION

Proposed by Swenson and Terkla

4 classes based on relationship of edentulous spaces to abutment

CLASS IArch with one free end denture base

CLASS II arch

with two free end

denture base

CLASS IIIEdentulous space posteriorly on one or both sides but with teeth present anteriorly and posteriorly to each space

CLASS IV anterior

edentulous space with 5 or

more anterior teeth

missing

COSTA’S CLASSIFICATION By Eugene Costa in 1974 (Romania)

Based on describing the partially edentulous spaces

Terminologies used Anterior- edentulous space in anterior dental

arch Lateral- edentulous space bounded both

mesially and distally by remaining teeth Terminal- edentulous space not bounded distally by remaining teeth Spaces identified starting from right to left

‘A’ Anterior

‘L’ Lateral

‘T’ Terminal

OSBORNE-LAMMIE system

Proposed in 1974

-CLASS I: mucosa-borne-CLASSII: tooth-borne-CLASSIII: combination of I & II

WILD’S CLASIFICATION 3 classes: CLASS I –Interruption of dental arch(bounded)

CLASSII-Shortening of dental arch(free end)

CLASS III-Combination of I & II

Not well known in English literature

MC GARRY CLASSIFICATION

Developed by The American College of

Prosthodontists(ACP) in 2002 ,McGarry et al

Based on diagnostic finding and treatment planning

Class I This class is characterized by ideal or

minimal compromise in the location and

extent of edentulous area (which is

confined to a single arch), abutment

conditions, occlusal characteristics, and

residual ridge conditions.

Class II This class is characterized by moderately

compromised location and extent of edentulous

areas in both arches, abutment conditions

requiring localized adjunctive therapy, occlusal

characteristics requiring localized adjunctive

therapy, and residual ridge conditions.

Class III This class is characterized by substantially

compromised location and extent of edentulous

areas in both arches, abutment condition requiring

substantial localized adjunctive therapy, occlusal

characteristics requiring reestablishment of the

entire occlusion without a change in the occlusal

vertical dimension, and residual ridge condition.

Class IV This class is characterized by severely

compromised location and extent of edentulous

areas with guarded prognosis, abutments requiring

extensive therapy, occlusion characteristics

requiring reestablishment of the occlusion with a

change in the occlusal vertical dimension, and

residual ridge conditions.

20.ICKClassification System partially edentulous arches incorporating

implants placed or to be placed in the edentulous spaces for an RPD

The classification begins with the phrase "Implant-Corrected Kennedy (class)," followed by the description of the classification. It can be abbreviated as :

(i)  ICK I, for Kennedy class I situations,(ii)  ICK II, for Kennedy class II situations,(iii)  ICK III, for Kennedy class III situations, and(iv)  ICK IV, for Kennedy class IV situations.

Sulieman S. Al-Johany, & Carl Andres , 2008

BIOMECHANICAL CONSIDERATIONS

Biomechanics basically deals with application of mechanical principles to biological tissues.

designing an RPD should be based on thorough understanding of the various forces that will act on RPD : direction and magnitude of these forces,

one can select the components of the RPD and position them to counteract, control or minimize these stresses, without compromising the health.

An understanding of simple machines should enhance our rationalization of the design of R.P.D’s to accomplish the objective to preserve oral structures.

Machines can be divided into 2 general categories: simple and complex.

The six simple machines are: lever, wedge, screw, wheel and axle, pulley and inclined plane.

 

‘lever’ and ‘inclined plane’ deserve most of our attention in designing a R.P.D.

Mechanical principles applicable in Removable

Prosthodontics

Lever principle

Inclined plane

Snowshoe principle

L beam effect

Lever: A simple machine consisting of a rigid bar pivoted on a fixed point and used to transmit force, as in raising or moving a weight at one end by pushing down on the other.

The support point of the lever is called the fulcrum,

Fulcrum line of a removable partial denture: (GPT-8): a theoretical line around which a removable partial denture tends to rotate

Three classes of levers (based on location of fulcrum, resistance and direction of effort (force).

Class IClass IIClass III

Class I lever

Fulcrum lies in the centre, Resistance is at one end and force at the other.

This type of lever can occur in patients with distal extension partial dentures.

The Direct retainer will be - Fulcrum,

Effort end lies on the point- Area where the artificial teeth are located

Load is the region of the Anterior end of the major connector.

Using AN ADDITIONAL REST (INDIRECT RETAINER) TO SHIFT THE FULCRUM LINE PREVENTS LEVER ACTION IN THESE DENTURES.

A cantilever is a beam supported at only one end and can act as a first class lever. A cantilever design should be avoided.

When force is directed against unsupported beam, cantilever can act as a first class lever.

Mechanical advantage is in favour of effort arm

Cast circumferential direct retainer engages mesiobuccal undercut and is supported by disto occlusal rest. If rigidly attached to abutment it may impart detrimental first class lever force to abutment

Mesial rest concept for distal extension removable partial denture

Distal occlusal rest: Gingival extremity of denture base adjacent to posterior abutment tends to move in an arc towards the tooth

Mesial rest Mesial rest is to alter the fulcrum

position and the resultant clasp movement,

disallowing harmful engagement of the abutment tooth

Bar type of retainer, minor connector contacting guiding plane on distal surface of premolar, n mesio occlusal rest used to reduce cantilever force when denture rotates towards residual ridge

Tapered wrought wire retentive arm,minor connector contacting guiding plane on the distal surface of premolar, and mesio occlusal rest.

This design is applicable when distobuccal undercut cannot be found or created or when tissue undercut contraindicates placing bar type retentive arm.

Class II lever

Fulcrum is at one end effort at the opposite end and resistance in the centre.

This type of lever action occurs in indirect retention of a rpd.

when a displacing force tends to lift a denture from one end(effort), the anterior most point of the major connector will act as the axis of rotation (fulcrum), the intermediate zone of the denture, which is lifted by the force, will form the resistance of the lever.

Class III lever

Fulcrum is at one end, resistance at opposite end and effort is in the centre. this type of lever action does not occur in partial dentures.

Inclined plane

Forces against an inclined plane may result in

•deflection of that which is applying the forces or• •may result in movement to the inclined plane,

• neither of these is desirable.

If angle greater than 90 degrees

Forces not along long axis

Slippage of prosthesis away from the abutment

Orthodontic like forces

Abutment severely tilted

Snowshoe principle

This principle is based on distribution of forces to as large an area as possible.

A partial denture should cover maximum area possible within the physiologic limits so as to distribute the forces over a larger area.

L beam effect : This principle is applicable to the antero-

posterior palatal bar or strap major connector.

In this component there are two bars /strap lying perpendicular to each

other. The ant. and post. bars are joined by flat longitudinal elements on each side of the lateral slopes of the palate.

The two bars lying in two different planes produce a structurally strong L beam effect that gives excellent rigidity to the prosthesis.

FORCES ACTING ON PARTIAL DENTURE

Distal extension rpd will rotate when force is directed on the denture base.

Differences in displaceability of the periodontal ligament of the supporting abutment teeth and soft tissue covering the residual ridge permit this rotation.

This rotation is in combination of directions rather than unidirectional

1. Fulcrum on horizontal plane:

Extends through the principle abutments.

Rotational movement of the denture in the sagittal plane.

Greatest in magnitude n most damaging

Force on abutment mesio-apical or disto-apical

(greatest vector in apical direction)

a) Denture base moves away from supporting tissues:

Counteracted by: direct retainer and indirect retainer

b) Denture base moves towards the supporting tissues:

Counteracted by:

• Occlusal rest• Tissues of supporting ridge

2. Fulcrum on the sagittal plane:

• Less in magnitude but can be damaging

extends through the occlusal rest on the terminal abutment and along the crest of the residual ridge on one side of the arch

Counteracted by:

Rigidity of major and minor connector and their ability to resist torque.

Close adaptation of the denture base along the lateral slopes and the buccal slopes of the palate and ridge.

Direct retainer design

3. Fulcrum located in midline just lingual to the anterior teeth (fulcrum is

vertical)

Rotational movement of denture in horizontal plane or flat circular movements of the denture

Counteracted by :

Stabilizing components (reciprocal arm and minor connector)

Rigid major connector

close adaptation of denture base

CAUSES OF FAILURE OF CLASP RETAINED PARTIAL DENTURES:

 Diagnosis and treatment planning1. Inadequate diagnosis2. Failure to use a surveyor properly during treatment planningMouth preparation procedures1. Failure to properly sequence mouth preparation procedures2. Inadequate mouth preparations3. Failure to return supporting tissue to optimum health before

impression procedures4. Inadequate impressions of hard and soft tissueDesign of the framework1. Failure to use properly located and sized rests2. Flexible or incorrectly located major and minor connectors3. Incorrect use of clasp designs4. Use of cast clasps that have too little flexibility, are too broad

in tooth coverage, and have too little consideration for esthetics

Laboratory procedures

1. Problems in master cast preparation a. Inaccurate impression b. Poor cast-forming procedures c. Incompatible impression materials and gypsum products

2. Failure to provide the technician with information to enable the technician to execute the design

3. Failure of the technician to follow the design and written instructions

Support for denture bases

1. Inadequate coverage of basal seat tissue

2. Failure to record basal seat tissue in a supporting form

Occlusion

1. Failure to develop a harmonious occlusion

2. Failure to use compatible materials for opposing occlusal surfaces

Patient-dentist relationship

1.Failure of the dentist to provide adequate dental health care information

2. Failure of the dentist to provide recall opportunities on a periodic basis

3. Failure of the patient to exercise a dental health care regimen and respond to recall

CONCLUSION

A removable partial denture designed and fabricated so that it avoids the errors and deficiencies listed is one that proves the partial denture can be made functional, esthetically pleasing, and long lasting without damage to the supporting structures. The success or failure of a partial denture will depend more than anything else upon the design used. The design should conform to the requirement.

BIBLIOGRAPHY1.Mc Cracken;Removable Partial Prosthodontics 11th

edn.

2.Stewart; clinical removable partial prosthodontics 2nd edn.

3. Miller EL: Systems for classifying partially dentulous arches. J Prosthet Dent 1970;24:25-40   

.4.Applegate O.C: The Rationale of Partial Denture Choice J Prosthet Dent 1960;10:891-907

5. Skinner C: A classification of removable partial denture based upon the principles of anatomy and physiology. J Prosthet Dent 1959;9:240-246  

6. Costa E: A simplified system for identifying partially edentulous dental arches. J Prosthet Dent 1974;32:639-645

 

7. McGarry TJ, Nimmo A, Skiba JF, et al : Classification system for partial edentulism. J Prosthodont 2002;11:181-193

9 . Avant: universal classification for removable partial denture situations .J prosth dent 1960;16:533

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