Principles of Removable Partial Denture Design According to Kennedy Classification

Presented By-Dr. Ha-Meem FattahaDepartment of ProsthodonticsSapporo Dental College & Hospital

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Learning Objectives:

• To formulate denture design according to individual patient’s oral condition and Kennedy classification.

• To obtain a thorough knowledge of mechanical and biological factors involving RPD design.

• To prevent any harm to remaining oral structures.

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Introduction:

Designing a removable partial denture can be considered similar to the classic, multifaceted design problem in conventional engineering. It is important for clinicians who provide removable partial denture to understand the possible movements of denture during function. Thorough knowledge about design principle helps to provide useful, functional removable partial denture by understand how to maximize every opportunity for providing and maintaining a stable prosthesis.

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Kennedy Classification:

Kennedy class- I : Bilateral free end saddle

Kennedy class- II : Unilateral free end saddle

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Kennedy Classification:

Kennedy class- III : Unilateral bounded saddle

Kennedy class- IV : Single , anterior bounded saddle

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RPD Classification :

According to support, RPD can be classified as-

• Tissue supported : Kennedy class i & ii dentures

• Tooth- tissue supported : Kennedy i & ii dentures

• Tooth supported : Kennedy class iii & iv dentures

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To be successful, how a RPD design should be?

Successful RPD

Harmless

Simple

Comfortable

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Essentials of partial denture design :

Design of a partial denture framework should be developed based on following concepts-

• Where the prosthesis is supported?

• How the support is connected?

• How the prosthesis is connected?

• How the retention and support are connected?

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Tooth supported RPD:

To develop the design , determination of support of the denture is necessary. Following factors of the abutment tooth must considered-

1. Periodontal health2. Morphology of crown and root3. Crown-root ratio4. Bone index area5. Location of the tooth in the arch6. Length of edentulous span7. The opposing dentition

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Tooth-tissue supported RPD:

In tooth- tissue supported partial denture, attention should be given both in -

• Abutment tooth

• Edentulous ridge areas

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Edentulous ridge area:

In evaluating the potential support available from these areas, consideration must be given to-

1. The quality of the residual ridge2. The extent to which the residual ridge is covered by

denture base3. The type and accuracy of the impression registration4. The design characteristics of the partial denture

framework5. The anticipated occlusal load

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A, The longer the edentulous area covered by the denture base, the greater the potential lever action on the abutment teeth.B. The flat ridge will provide good support, poor stability. C. The sharp spiny ridge will provide poor support, poor to fair stability.D. Displaceable tissue on the ridge will provide poor support and poor stability.

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What is biomechanics?

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

According to GPT, Biomechanics is an application of theprinciples of engineering design as implemented in living

organism.

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Why dentist should know this?

In the oral cavity one would find a number of sources of stress generation. However when a dentist try to create an artificial replacement of that natural component which is lost, he should know the possible movements of the prosthesis during function. Should be able to logically design the component parts of RPD to control these movements, prevent harm to the remaining oral structures and make it fully functional and adaptable.

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Forces are prime biomechanical concern.… WHY?

RPD are objects that move when placed in function. It has to be in a state in which opposing forces or influences are balanced. Keeping in mind “Perpetual preservation of what is remaining is more important than meticulous replacement of what is lost”, forces should be given major consideration while designing a partial denture.

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Considerations related to force:

Goal: Minimize the destructive force

1. Magnitude of force

2. Direction of force

3. Duration

4. Frequency

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How to balance effects of force:

Forces can be minimized by

Selection of design

Selection of abutment tooth

Location of

components of RPD

Development of harmonious occlusion

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Forces acting on RPD:

The forces acting on appliance can be vast in magnitude and direction. They can be broadly categorized as –

1. Vertical force - Displacing force - Dislodging force 2. Horizontal force 3. Torsional force

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Vertical force:

• Displacing stress: Those force which transmits along the long axis of the

teeth in a crown to apex direction and also on the ridge mucosa, are known as displacing force. These are least harmful if within physiologic limit.

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• Dislodging force: These are forces which tend to lift the partial denture

form its rest position.

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Horizontal force

They originate as a component of rhythmic chewing. These forces are effective in lateral and anterior-posterior direction. These lateral forces are most damaging.

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Torsional force:

It is a combination of vertical and horizontal force. Torsion is noted most frequently where a long segment acts upon the first abutment it engages. Where the ridge mucosa has higher resiliency, torque is higher. Torque applies rotation about a fixed point.

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Rotational movements of RPD:

Movements of RPD does not occur singularly. All occur at the same time. Gross movement of the denture may be small but potential damage to the abutment tooth may be large.

The greatest movement possible found in the tooth-tissue supported prosthesis which is rotation.

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When a force is placed on the distal extension base, the framework will rotate in relation to the three cranial planes.

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How this movements can be prevented?

Rotation around vertical axis:

Resisted by-• Reciprocal clasp arms• Minor connectors

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How this movements can be prevented?

Rotation around longitudinal axis:

Resisted by-• Rigidity of major and minor connector and their ability to resist torque.

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How this movements can be prevented?

Rotation around horizontal axis:

Resisted by-• Action of retentive clasparms on terminal abutments.

• Action of stabilizingminor connectors

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Problems of free end saddle:

As in free end saddles edentulous ridge must bears some part of masticatory load, ridge resorption can occur.

On the other hand, the abutment tooth is subjected to torques which may lead to premature break down of its supporting bone.

That’s why formulating treatment plan of free end saddle dentures are more difficult.

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Treatment of free end edentulous area:

Following methods can be used to overcome problems with free end saddle dentures-

1.Reducing the load by - i)Using canines and premolar instead of premolars

and molars. ii)Using narrow teeth. iii)Leaving a tooth off the saddle.

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2. Distributing the load between teeth and ridges. i) By varying the connection between clasp and saddle- -Stress breaking -Combining rigid connector and gingivally approaching

clasp -Combining rigid connector and occlusally approaching

clasp

ii) By anterior placement of occlusal rest. iii) By mucocompression.

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3. Distributing the load widely. i) Over more than one abutment tooth on each side. ii) Over the maximal area of edentulous ridge.

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Treatment of tooth bounded edentulous area:

Horizontal forces acting on Kennedy class-iii prosthesis may lead to instability of the denture. Following measures can be taken to avoid this problem-

1. Provision of lingual and buccal cusp contacts. 2. Use of wide occlusal rests.

3. Provision of adequate bracing.

4. Provision of adequate retention.

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Conclusion:

All of the previous slides discuss factors that influence retention, stability and resistance form of partial denture. These should be considered during designing RPD to provide best service and function of the prosthesis.

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References:

• Partial Dentures ( Fourth Edition) By John Osborne,George Alexander Lammie

• McCracken’s Removable Partial Proshodontics ( Eleventh Edition) By Alan B. Carr, Glen P. MacGivney, Devid T. Brown • Textbook of Prosthodontics By Deepak Nallaswamy

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THANK YOU!!!