Raju designing of class i and class ii/ dental crown & bridge courses

DESIGNING OF CLASS I AND CLASS II
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

CONTENTS
 INTRODUCTION
 HISTORY
 PRINCIPLES OF DESIGNING
 PHILOSOPHIES OF DESIGNING
 BIOMECHANICAL CONSIDERATIONS
 ESSENTIALS OF PARTIAL DENTURE
DESIGN
 DESIGNING OF CLASS I
 DESIGNING OF CLASS II
 CONCLUSION
 BIBLIOGRAPHY

INTRODUCTION
The design process is a series of steps that leads toward
a solution of the problem and includes; identifying a need,
definition of the problem, setting design objectives,,
developing a design rationale, devising and evaluating
alternative solutions, and providing the solution.

 Authorities in the field of removable partial denture design
may differ on their approach in developing the design of
each individual prosthesis.
 There is however, complete agreement that the correct
design incorporates proper use and application of
mechanical and biologic principles.
 Simple mechanical principles have to understood and
applied in designing of the removable partial denture.

HISTORY – EVOLUTION OF RPD DESIGN
1711 - First description of RPD was by Heister - he carved a
block of bone to fit the mouth
1728 - Pierre fauchard father of modern dentistry decribed
costruction of lower RPD using two carved blocks of ivory
joined together by metal labial and lingual connectors.
1880 - First maxillary RPD using palatal connector was by
balkwell

1746 - Retentive clasps were first discussed by Mouton.
1899 - Bonwill introduced claping abutments with gold
circumferential clasps
1913- Roach introduced wrought wire clasp
1914- Infra bulge clasp was first mentioned by Henrichsen
1930 - Infra bulge clasp did not gain popularity untill Roach
promoted this concept

 Prothero coined the term “fulcrum line”
 1950 - 1970 Invetigative years
 1970 to present – Research

Principles of design by A.H. Schmidt (1953)
1. The dentist must have a thorough knowledge of both the
mechanical and biologic factors involved in removable
partial denture design.
2. The treatment plan must be based on a complete
examination and diagnosis of the individual patient.

3. The dentist must correlate the pertinent factors and
determine a proper plan of treatment.
4. A removable partial denture should restore form and
function without injury to the remaining oral structure.
5. A removable partial denture is a form of treatment and
not a cure.

PHILOSOPHIES OF DESIGNING
1. Stress Equalization
2. Physiologic Basing
3. Broad Stress Distribution

STRESS EQUALIZATION
Stress Equalizer-: According to GPT 8
A device which relieves the abutment teeth of all or
part of occlusal forces.
The rigid connection between the denture bases and
the direct retainer on the abutment teeth is damaging and
that some type of stress director or stress equalizer is
essential to protect the vulnerable abutment teeth.

Devan determined that the mucoperiosteum of the residual
ridge offers only 0.4 % of the support provided by a periodontal
ligament.
Soft tissues are 250 times more displaceable than are the
adjacent teeth

TYPES OF STRESS EQUALIZERS
Type I:
1. Hinges,
2. Sleeves and cylinders,
3. Ball –and-socket devices.

Type II:
Designs having flexible connection which include the
use of wrought wire connection, divided major
connectors or other flexible devices for movement of
distal extension.

ADVANTAGES
1. Forces are distributed on abutment and the soft tissue.
2. Minimize the tipping forces on abutment tooth.
3. Minimal direct retention is required- as denture base acts
more independently.
4. Has the massaging or stimulating effect on the underlying
bone and soft tissue.

Disadvantages
1. Fragile,complex and costly.
2. Requires constant maintenance.
3. Difficult to repair.
4. Bulky and annoying to patient.

PHYSIOLOGIC BASING
1. The equalization of stress can be best and most simply be
accomplished by some form of physiologic basing, or
lining, of the denture base.
2. Mucosa is recorded in its functioning form.

ADVANTAGES
1. Physiologically stimulating effect on underlying tissue
2. Simplicity in design and construction
3. Lightweight prostheses requiring minimal maintenance and
repair.
4. Reduced stresses on abutment tooth, hence retained for longer
period.

DISADVANTAGES
1. Premature contacts.
2. Decreased effect of indirect retention.
3. Not well stabilized against lateral forces.

BROAD STRESS DISTRIBUTION
Advocates believe that excessive trauma to remaining teeth and
the residual ridge can be prevented by distributing occlusal forces
over as much the available area of teeth and soft tissue as possible.

ADVANTAGES
1. Broad stress distribution.
2. Excellent horizontal stabilization.
3. Removable splinting
4. Easier and less expensive to
construct.
5. Less danger of distortion and
breakage of denture
6. Decreased chance of relining

DISADVANTAGES
1. Less comfortable.
2. Requires good maintenance of oral hygiene.

BIOMECHANICAL CONSIDERATIONS.
A better understanding of the methods of controlling
forces on RPD may be achieved by a brief review of the
development of forces. This considers the application of
mathematical formulas.
As Tylman states, “ Great caution and reserve are
essential whenever an attempt is made to interpret
biological phenomenon entirely by mathematical
computation.”

SIMPLE MACHINE
1. Lever
2. Wedge
3. Inclined plane
4. Screw
5. pulley
6. Wheel and axle

LEVER
 A lever is a rigid bar supported somewhere along its length.
It may rest on the support or may be supported from above.
 There are three types of levers;

CLASS I
A class-1 lever has its fulcrum located somewhere
between the effort and the resistance
Ex:Distal extension removable partial denture

CLASS II
With a class-2 lever, the fulcrum is at one end, the effort is at
the other end and the resistance is in the middle
Seen as indirect retention in removable partial denture

CLASS III
 In a class-3 lever, the fulcrum is at one end and the effort
is applied between the fulcrum and the resistance.

INCLINED PLANE
 Forces against the inclined
plane may result in
deflection of that which is
applying the force or may
result in the movement of
the inclined plane .
 Neither of these results
are desirable

WEDGE
A wedge by definition is a solid object with a broad base and
its two sides arising to intersect each other forming an acute
angle opposite the base.

FORCES ACTING ON THE PARTIAL DENTURE
Forces acting on a distal extension partial denture are a
result of a composite of forces arising from the three
principal fulcrums.
A. Fulcrum on the sagittal plane.
B. Fulcrum on the vertical plane.
C. Fulcrum on the horizontal plane.

FULCRUM ON THE SAGITTAL PLANE

The fibers of periodontal ligament are arranged so that
axially aligned forces are resisted 17 times greater than are
non axial forces

FULCRUM ON THE FRONTAL PLANE

FULCRUM ON THE HORIZONTAL PLANE

FACTORS INFLUENCING MAGNITUDE OF STRESSES
TRANSMITTED TO ABUTMENT TEETH
1. Length of span.
2. Quality of support of ridge.
3. Clasp.
1. Quality
2. Design.
3. Length
4. Material.
4. Abutment tooth surface
5. Occlusal harmony.

LENGTH OF SPAN

QUALITY OF SUPPORT OF RIDGE

QUALITIES OF CLASP
Type of clasp:
 More flexible the clasp less stress is transmitted to the
abutment tooth.
 But at the same time it contributes less resistance to the
lateral and vertical stresses transmitted to the residual
ridges.
 Periodontal condition of abutment teeth.

DESIGN OF CLASP
 A clasp is designed so that it is passive
 the reciprocal arm contacts the tooth before the retentive tip
passes over the greatest bulge of the abutment tooth.

LENGTH OF CLASP
 Clasp length may be increased by using a curved
rather than a straight course on an abutment tooth
 Doubling the length of clasp will increase its
flexibility 5 fold

MATERIAL USED FOR CLASP FABRICATION
Cromium-cobalt alloy ( higher modulous of elasticity)being
more rigid will exert greater stress on the abutment tooth
than will a gold clasp.

AMOUNT OF CLASP SURFACE IN CONTACT WITH
TOOTH
The greater tooth to metal contact between the clasp
and the tooth, the more will be the stress exerted on to the
tooth

ABUTMENT TOOTH SURFACE
 Gold surface crown or restoration offers more frictional
resistance to clasp arm movement than does the enamel
surface of the tooth.
 Greater stress is exerted on a tooth restored with gold than
on a tooth with intact enamel.

OCCLUSAL HARMONY.
When deflective occlusal contacts are present
between opposing teeth destructive horizontal forces
which are magnified by leverage are transmitted to the
abutment and ridge.
 Force exerted by natural teeth –300 pounds per square
inch.
 Complete denture – 30 pounds per square inch.

AREA OF BASE TO WHICH LOAD IS APPLIED
Ideally,the occlusal load should be applied in the center of
the denture –bearing area, both antero-posteriorly and
bucco-lingually

DESIGN CONSIDERATIONS IN THE CONTROL OF
STRESS
1. Direct retention
• Adhesion ,cohesion
• Frictional
• neuromuscular
1. Clasp position
• Quadrilateral
• Tripod
• bilateral
1. Clasp design
• Circumferential clasp
• Bar clasp.
• Combination clasp
1. Splinting of abutments
2. Indirect retention
3. Occlusion
4. Denture base
5. Major connector

Design considerations for stress control
 At present there is no way that all forces can be totally
negated or countered.
 Long term clinical observations have proved that a design
philosophy that strives to control these forces within the
physiologic tolerance of the teeth and supporting structures
can be successful.

Direct retention
 The retentive clasp arm is responsible for transmitting
most of the destructive forces to the abutment teeth.
 Clasp retention should be kept at the minimum yet provide
adequate retention to prevent dislodgement of the denture.
 Other components should be used to contribute for the
retention so that amount of retention provided by clasp can
be reduced

ADHESION AND COHESION
 For adhesion and cohesion to work
I. Maximum area of available support should be used.
II. Denture base should be accurately adapted to the
underlying mucosa.
 Though peripheral seal cannot be developed due to
presence of teeth .Atmospheric pressure helps in retention
of the maxillary partial denture when accurately adapted to
the underlying mucosa.

FRICTIONAL CONTROL

NEUROMUSCULAR CONTROL
 The innate ability of the patient to control the action of the
lips, cheeks, tongue can be a major factor in the retention of
a denture.
 A properly contoured denture base, however, can aid the
patient’s neuromuscular control of the prosthesis.

CLASP POSITION
 The position of retentive clasp is more important than the
number of retentive clasp used in any design.
 The number of clasps used is determined by classification.

QUADRILATERAL CONFIGURATION

TRIPOD CONFIGURATION
 Used primarily for class 2 arches.

BILATERAL CONFIGURATION
Used in class 1 cases.
In this configuration the clasps exert little neutralizing
effect on the leverage induced stresses generated on to
the denture base. These stresses must be controlled by
other means.

SPLINTING OF ABUTMENTS
It increases the periodontal ligament attachment area
and distributes the stress over a larger area of support.

OCCLUSION AS A METHOD OF STRESS CONTROL
1. Harmonious intercuspation
2. Size of food table
3. Occlusal pattern of posterior teeth
I. sharp cutting surfaces
II. steep cuspal inclines

DENTURE BASE AS A METHOD OF STRESS CONTROL
1. size and configuration of the base
2. accuracy of adaptation of the base of tissue
3. form of polished surface

ESSENTIALS OF PARTIAL DENTURE DESIGN.
It should be systemically developed and outlined on an
accurate diagnostic casts.

FIRST STEP
 Decide how the partial denture has to be supported.
 If Tooth supported.
Evaluate :
1. Periodontal health
2. Crown and root morphologies
3. Crown to root ratio.
4. Location of tooth in arch.
5. Length of edentulous span.
6. Opposing dentition.

IF TOOTH AND TISSUE SUPPORTED.
1. Quality and contour of supporting bone and mucosa
2. Extent to planned coverage of ridge.
3. Type and accuracy of impression registration.
4. Accuracy of denture base.
5. Design characteristics of the component parts of
framework.
6. Anticipated occlusal load.

SECOND STEP
 Connect the tooth and tissue support units.
 These connection is facilitated by designing and locating
major and minor connectors in compliance with the basic
principles and concepts.

THIRD STEP.
Determine how the partial denture is to be retained.
Select clasp design that will
1. Avoid direct transmission of tipping or torquing
forces to the abutment
2. Accommodate the basic principles of clasp design by
definitive location of components parts correctly
positioned on abutment tooth surfaces.
3. Provide retention against reasonable dislodging
forces.
4. Be compatible with undercut locations,tissue
contour,and esthetic desires of the patient.

FOURTH STEP
Connect the retention units to the support units

FIFTH STEP.
Outline and join the edentulous area to the already
established design components.

1. Direct retention :
The main objective should be restoration of the
function and appearance and the maintenance of
comfort, with great emphasis on preservation of the
health and integrity of the remaining oral structures.
CLASS I AND CLASS II DESIGN

2. CLASPS
1. simplest type of clasp should be used
2. clasp should have a good stabilizing quality, remain passive
until activated by functional stress.

CLASPS IN CLASS I PROSTHESIS
 Requires only two retentive
clasps, one on each side.

CIRCUMFERENTIAL CLASP

If a distobuccal undercut is present, the vertical
projection retentive clasp is preferred.

REVERSE CIRCLET CLAP

 If mesiobuccal undercut
is present, wrought wire
clasp is indicated.
 The reciprocal or bracing
arm must be rigid.
COMBINATION CLASP

 One school of thought advocated
omitting of the distal rest in favour
of a mesial rest is that the forces are
directed to the ridge in more
vertical direction which are better
tolerated by the ridge.

CLASPS IN CLASS II PROSTHESIS

 If a modification space
is present, clasp the
teeth adjacent to the
edentulous space.
 Tripod configuration.

3. RESTS
 rests seats should be
prepared so that stress will
be directed along the long
axis of the teeth
 In most instances rests
should be placed next to
the edentulous space.

4. INDIRECT RETENTION
 should be located as far
anterior to the fulcrum
line as possible
 two indirect retainers
should be used for class I
prosthesis.
 indirect retainers should
not be placed more
anterior than canines

one indirect retainer can be
used on the side opposite
the edentulous space in a
class II design

 should be placed in
properly prepared rest
seats so that forces will be
directed along the long
axis of the teeth
 Lingual plating can also
be used as an effect
indirect retainer.

MAJOR CONNECTOR
 Should be rigid
 Not impinge on the gingival
tissues
 Support from the hard
palate .

 Can be extended onto the
lingual surfaces of the
tooth to increase rigidity,
distribute lateral forces,
improve indirect retention,
and eliminate food
impaction

MINOR CONNECTORS
 Rigid
 It’s position should enhance comfort, cleanliness and to
place teeth.

OCCLUSION
1. centric relation should coincide with centric occlusion
2. harmonious occlusion
prosthetic teeth should minimize the stresses;
1. fewer teeth, narrow buccolingually.
2. placed over the crest of the ridge.
3. should display sharp cutting edges and ample escapeways.

DENTURE BASES
1. broader coverage to distribute forces without interfering
with functional movement of tissues.
2. selective pressure impressions for distal extension.

CONCLUSION:
Adequate time must be spent in properly diagnosing the
particular case and devising a workable treatment plan. Once
this is done the mechanical task of laying out the “nuts and
bolts” of removable partial denture design can be carried out
to ensure that our patients receive full benefits of our
knowledge and skills.

REFERENCES
1. Removable partial prosthodontics- Mc Crackens 11th
ed
2. Clinical removable partial prosthodontics- Stewart 2nd
3. Removable denture prosthodontics- A.A.Grant
4. Partial dentures- John Osborne 4th
ed
5. Textbook of removable partial dentures- Kratochvil
6. Removable partial prosthodontics- Grosso- Miller 3rd
edition.

7. Indirect retention in partial denture design.
J Prosthet Dent 2003, 90, 1-5.
8. Evolution of removable partial denture design
Journal Of Prosthodontics 1994, 3,158.
9. Removable partial denture designing: forces as primary
concern
J Indian prosthodont soc 2006,6,179.

Thank you
Thank youwww.indiandentalacademy.com

Raju designing of class i and class ii/ dental crown & bridge courses

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Raju designing of class i and class ii/ dental crown & bridge courses