Biomechanics of Removable of Partial Dentures

26
BIOMECHANICS OF REMOVABLE PARTIAL DENTURES By: Dr. Muhammad Ali Faridi BDS, Mclindent (Restorative Dentistry) Department of Prosthodontics

description

A look at bio-mechanical principles involved in removable partial denture design and their role in primary and secondary retention.

Transcript of Biomechanics of Removable of Partial Dentures

BIOMECHANICS OF REMOVABLE PARTIAL

DENTURESBy: Dr. Muhammad Ali Faridi

BDS, Mclindent (Restorative Dentistry)

Department of Prosthodontics

INTRODUCTION

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

• In the oral cavity one would find a number of sources of stress generation, the human body is built in such a manner that it learns to adapt to any stressful situation.

• However when we try to create an artificial replacement of that natural component which is lost, we are at a loss in making it fully functional and adaptable

Our Goal…..

• Provision of a useful, functional removable partial denture by understanding how to maximize and maintaining stability in the prosthesis.

• Design a prosthesis where the stress does not exceed the physiological load.

Biomechanics and Design solutions

•Designing a removable partial denture can be considered as a multifaceted design problem in conventional engineering , which is characterized as being open ended and ill structured.

The Design Process…..NeedTooth replacement

Definition of problemProvision of stable removable prosthesis

objectivesLimited functional movement within tooth-tissue tolerance

Background informationForces of occlusion, tissue “load-displacement” character and potential for movement, biomechanical principles applied to specific features of this unique mouth, removable partial denture component parts assigned to control movement

Choice of a solution (among alternatives) for applicationBased on prior experience, principles and concepts learned from school and textbooks, and applicable clinical research

BIOMECHANICAL CONSIDERATIONS• The supporting structures for removable partial

dentures (abudment teeth & residual ridges) are subjected to forces and their capability to resistance depends upon:

1.What typical forces require resistance

2.Duration and intensity of the forces

3.Influence of material used and application

4.Changes due to resistance over time

• Consideration of the forces inherent in the oral cavity is critical !!

• This includes the direction, duration, frequency and magnitude of the force.

• In the final analysis, it is bone that provides the support for a removable prosthesis (i.e. the alveolar bone by way of the periodontal ligament and the residual ridge through soft tissue covering)

• An appropriate design includes the selection and location of components in conjunction with a harmonious occlusion.

Mechanics & Partial Dentures: The connection ??????

• An understanding of simple machines applied to the design of removable partial dentures helps to accomplish the objective of preservation of oral structures.

• A removable partial denture designed without an understanding of the simple mechanical principles will do more harm then good.

Machines

1.Simple Machines

2.Complex Machines

Simple Machines

TYPES OF LEVERS

•Cantilever: A beam supported at one end and can act as a first class lever.

•Should be avoided.

•The most efficient means of addressing the potential effects of a lever is to provide a rigid element at the unsupported end to disallow movement.

• A tooth is apparently better able to resist vertically directed forces than non-vertical , torqueing or horizontal forces.

POSSIBLE MOVEMENTS OF PARTIAL DENTURE

• The possible movements in a partial denture do not occur independently but rather occur dynamically at the same time across the underlying tissue.

• The greatest movement is found in the tooth tissue supported partial dentures, because of the reliance on the distal extension supporting tissue to share the functional loads.

•One movement is rotation about an axis through the most posterior abudments.

• This axis maybe through occlusal rests or any other rigid portion of a direct retainer assembly located occlusally or incisally to the height of the contour of the abudments.

• This axis is known as the fulcrum line , is the centre of rotation as the distal extension base moves toward the supporting tissue when an occlusal load is applied.

• The second type of movement seen is rotation about a longitudinal axis as the distal extension base moves in a rotary direction about the residual ridge.

• This movement is resisted primarly by the rigidity of major and minor connectors and their ability to resist torque.

• Third type of movement is rotation about an imaginary vertical axis located near the center of the dental arch.

• This movement occurs under function because diagonal and horizontal occlusal forces are applied on the partial denture.

Tooth Supported Partial Denture• Movement of the base towards the edentulous

ridge is prevented primarily by occlusal rests on the abutment teeth and the rigid portion of the framework located occlusal to the height of contour.

• In the tooth supported denture the only movement of any significance are horizontal.

• The use of intracoronal rests is permissible. It provides not only occlusal support but also notable horizontal stabilization.

Movements in Tooth Supported Partial Denture

• The first of the three movements can be controlled in a tooth supported partial denture.

• The second movement i.e. along the longitudinal axis can be controlled using rigid components of direct retainers , which have the ability to resist torque.

• The third type of movement occurs in all partial dentures,therefore stabilizing components must be added into the design.

Impact of Implants on Movements in Partial Dentures

• The greatest benefit of implants is to improve stability by improving support.

•Minimizing rotation about an axis in a kennedy class I or II or any long modification span.

REFRENCES:

• McCracken's Removable Partial Prosthodontics , 12th Edition By Alan B. Carr, DMD, MS and David T. Brown, DDS, MS.

• Understanding Partial Denture Design,1st Edition by Kenneth Tyson , Robert Yemm , Brendan Scott.