Biomechanical considerations / dental implant courses by Indian dental academy

INDIAN DENTAL ACADEMY
Leader in Continuing Dental Education
www.indiandentalacademy.com

CONTENTS:
• 1. Introduction
• 2. Abutment evaluation
• 3. Biologic considerations
• 4. Factors affecting form and termination of the f.p.d
• 5. Mechanical considerations
• 6. factors affecting retention
• 7. resistance form
• 9. Conclusion
• 10. References

Terms
• Axial inclination: the alignment of the long axis of
the tooth to a horizontal plane
• Bevel: the process of slanting or sloping the finish
line
• chamfer: a finish line design for tooth preparation in
which gingival aspect meets the external surface at an
obtuse angle
• Clearance: a condition in which bodies may pass
each other without hindrance.

• Finish line: the line of demarcation
• Margin: the outer edge of a crown, inlay, onlay or
other restoration.
• Resistance form: the feature of a tooth preparation
that enhance the stability of a restoration and resist
dislodgement along an long axis other than the path
of placement

• Retention form: the feature of a tooth preparation
that resists dislodgement of a crown in a vertical
direction or along the path of placement

Introduction
• Fixed Prosthodontics is concerned with the
replacement of missing tooth structure. Pierre
Fauchard (1747) was the first person to describe the
process by which roots of maxillary anterior teeth
were selected for the restoration of single and
multiple teeth

• Biomechanical considerations in fixed prosthodontics can be
divided into following categories:
• 1.Evaluating the abutment tooth and its supporting tissues for
their ability to withstand occlusal forces and their long-term
prognosis.
• 2.Biomechanical considerations, which are governed by the
tooth preparation design, form, & occlusal relationship of the
prosthesis fabricated.
• 3.Mechanical considerations, which affect the integrity and
durability of the fixed partial denture.

ABUTMENT EVALUATION
• Crown – root ratio
• Root configuration.
• Periodontal ligament area or root surface area
• Mobility.
• Endodontic status
• Root proximity.
• Tilt
• Caries

• Crown-root ratio:
• The optimum crown- root ratio for a tooth to be
utilized as a FPD abutment is 2:3. A ratio of 1:1 is the
minimum ratio that is acceptable.

• Root Configuration
•
• Multi rooted posterior teeth with widely separated
roots will offer better support than those that
converge, fuse or generally present a conical
configuration

• Root surface area / periodontal ligament area:

Mobility:

• Endodontic status:

TILT:

• Caries:

BIOLOGIC CONSIDERATIONS
• These affect the health of oral tissues. Procedures
involving living tissues must be carefully executed to
avoid unnecessary damage. Poor preparation leads to
inadequate marginal fit or deficient crown contour,
and plaque control around these restorations will
became more difficult impeding long term
maintenance of oral health.

• Prevention of Damage during tooth preparation :
• 1.Iatrogenic damage to the adjacent tooth
• 2.Damage to the soft tissues
• 3.Pulpal degeneration

• Conservation of tooth structure :
 Use of partial rather than complete coverage
retainers.
 Preparing teeth with minimum taper.
 Preparing of occlusal surface so reduction follows the
anatomic planes.
 Preparations of axial surfaces so tooth are prepared
evenly.
 Selection of a conservative margin where indicated.
 Avoidance of unnecessary apical extension.

• FACTORS AFFECTING FORM AND
TERMINATION OF THE FPD
• Axial reduction
• Margin integrity
• Margin Placement

Axial reduction

• Indications for Sub gingival margin placement:
 Additional retention,
 esthetics,
 root sensitivity,
 modifications of axial contour,
 proximal contact extending to gingival crest,
 caries,
 erosion or restorations extending Sub gingival

• Margin adaptation:
• Margin geometry/ configuration: any configuration
of margin should have these characteristics
 Ease of preparation
 Acceptable adaptation
 Adequate contour
 Sufficient strength
 Conservation of tooth structures

Margin geometry/ configuration:
Shoulder is the finish line for all-
ceramic restorations

The chamfer is the finish line for cast metal
restorations

Occlusal considerations

• The number and area of occlusal contacts have a
profound influence on the distribution of occlusal
forces.
• The larger the total area of contact over which a
given occlusal force is applied, the less stress is
concentrated at any point.
• As total number of occlusal contacts increases in an
occlusal scheme, the force is applied over a greater
number of locations, also reducing the localized
stress. Large number of contacts results in more
cutting or grinding surfaces to facilitate mastication

MECHANICAL CONSIDERATIONS:
• Providing retention form
• Providing resistance form
• Preventing deformation of the restoration

• Retention Form: This is the ability of the restoration to
withstand forces acting in the same direction as path of
withdrawal. Sticky foods & chewing gum have been
known to remove restorations in the line of draw.
•
• Factors:
– Magnitude of dislodging forces
– Geometry of tooth preparation
– Roughness of fitting surface of casting
– Materials being cemented
– Film thickness of luting agent

• FACTORS AFFECTING RETENTION
• Taper-
• Too large a taper will decrease the retention

Surface area:

Freedom of displacement

• Type of preparation

• Roughness of the surfaces being cemented
• air- abrading with 50μm of alumina. O’Conner(1990)
showed that air abrasion increased retention by 64%.

• Types of luting agent:
• Adhesive resin cements seem to be most retentive.
However, the decision regarding which agent to use
is also based on other factors

RESISTANCE FORM
• Magnitude and direction of dislodging forces
• Physical properties of Luting agent: modulus of
elasticity and compressive strength of the Luting
cement have an effect on resistance to deformation.
• Glass Ionomer and resin cements have higher
compressive strength

Geometry of preparation

• walls of shorter preparations should have as little
taper as possible to increase resistance. It can also
be increased placing grooves in the axial walls.

• Teeth with short diameter and short walls have
better resistance than teeth with larger diameter but
short walls. The preparation on the smaller tooth will
have a short rotational radius for the arc of
displacement, and the incisal portion of axial wall will
resist displacement.
• The larger rotational radius on the larger
preparation allows for a move gradual arc of
displacement, and the axial wall does not resist
removal.

• Alloy selection:

Conclusion:
• Biomechanics is of prime consideration in achieving
an aesthetic functional and durable fixed prosthesis so
every dentist should have a thorough knowledge
about this biomechanics of tooth preparation as every
step in this plays a major role in the fixed prosthesis
success.

References:
• Rosenstiel SF, Land MF,Fugimoto:Contemporary
fixed Prosthodontics,3rd edition,St louis ,2001 Mosby.
• Shillinburg HT, Hobo S, WhitSett LD, Jacobi R,
Brackett SE: Fundamentals of fixed Prosthodontics,
3rd edition, Illinios Quintessence.
• WFP Malone, DL Koth, E Cavazos Jr, Da Kaiser, SM
Morgano: Tylman’s Thoery and practice of fixed
Prosthodontics, 8th edition. Ishiyaku EuroAmerica,
inc. publishers. Tokyo. St Louis.
•

Biomechanical considerations / dental implant courses by Indian dental academy

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (19)

Similar to Biomechanical considerations / dental implant courses by Indian dental academy

Similar to Biomechanical considerations / dental implant courses by Indian dental academy (20)

More from Indian dental academy

More from Indian dental academy (20)

Recently uploaded

Recently uploaded (20)

Biomechanical considerations / dental implant courses by Indian dental academy