◦ Bone density
◦ Load bearing capacity
◦ Linear configurations and implant overload
Treatment planing with dental implants
◦ Edentulous maxilla
◦ Edentulous mandible
◦ Partially edentulous patients
Clinical strategies to avoid implant overload
and other prosthetic considerations
◦ Connecting implants with natural dentition
◦ Immediate or early loading in posterior dentition
Available bone is particularly important in
implant dentistry and describes the external
architecture or volume of the edentulous area
considered for implants.
The internal structure of bone is described in
terms of quality or density - biomechanical
◦ Modulus of elasticity
Most dense bone is
◦ Anterior mandible
◦ Anterior maxilla
◦ Posterior mandible
◦ Posterior maxilla ( least dense bone)
Adell et al
◦ 10% greater success rate in anterior mandible as
compared to anterior maxilla
Schnitman et al
◦ Reported lower success rate in posterior mandible
as compared with anterior mandible
Highest clinical failure – posterior maxilla
◦ Where the force magnitude is greater and bone
density is poorer
◦ Class I bone structure: The ideal bone type consists
of evenly spaced trabeculae with small cancellated
◦ Class II bone structure: The bone has slightly larger
cancellated spaces with less uniformity of the
◦ Class II bone structure: Large marrow-filled spaces
exists between bone trabeculae.
The bone density may be different near the
crest, compared with the apical region where
the implant is planned.
The most critical region of bone density is the
crestal 7 to 10mm of bone.
Therefore, when the bone density varies from
the most crestal to apical region around the
bone, the crestal 7 to 10mm determines the
treatment plan protocol.
Bone density is directly proportional to the
strength of the bone before micro fracture.
A ten fold difference in bone strength from
D1 to D4.
D2 bone exhibited a 47% to 68% greater
ultimate compressive strength compared with
Elastic modulus describes the amount of
strain ( changes in length divided by the
original length) as a result of a particular
amount of stress.
Relates to stiffness of the material.
The elastic modulus of bone is more flexible
When higher stresses are applied to an
implant prosthesis, the titanium has lower
strain (change in shape) compared with the
◦ The difference between the two materials may
create micro strain conditions of pathologic
overload and cause implant failure.
But when stresses applied are low, the micro
strain difference between titanium and bone
is minimized and remains in the adapted
window zone, maintaining load bearing
lamellar bone at the interface.
The initial bone density not only provides
mechanical immobilization of the implant
during healing, but after healing also permits
distribution and transmission of stresses
from the prosthesis to the implant –bone
Open marrow spaces or zones of
unorganized fibrous tissue do not permit
controlled force dissipation or micro strain
conditions to the local bone cells.
More the area is in contact with the implant
interface so more force dissipation. (BIC)
BIC % is more in cortical bone as compared to
D1 – 85% BIC
D2 – 65 to 75% BIC
D3 – 40 to 50% BIC
D4 – fewer areas of BIC
Crestal bone loss and early implant failure
after loading results may occur from excess
stress at the implant-bone interface.
As a result of the correlation of bone
density, elastic modulus bone strength, and
bone implant contact percent, when a load is
placed on the implant, the stress contours in
the bone are different for each bone density.
D1 – strains are near the crest, stress in this
region are of less magnitude
D2 – sustains a highly greater crestal
strain, intensity of stress extends apically
D4 – greatest crestal strains and stress are
extended farthest apically along the implant
Four facts form the basis for treatment plan
modification in functioning of the bone
◦ Each bone has a different strength
◦ Bone density affects the elastic modulus
◦ Bone density result in different amount of bone-
implant contact percentage
◦ Bone density differences result with a different
stress-strain distribution at the bone implant
A thorough understanding of implant
biomechanics is essential if implant –retained
restorations are to be employed predictably.
◦ The load bearing capacity of implants supporting
the restoration must be greater than the anticipated
loads during function.
◦ If the loads applied exceed load bearing capacity of
the implants, the prosthesis, or the supporting
bone, implant overload may result in mechanical or
◦ A resorption –remodeling response of the bone around
the implant is provoked , leading to progressive bone
◦ In some cases, bone loss around the implant progresses
until the implant is no longer supported and
osseointegration is lost.
Brunski J et al 2000
◦ Screws that secure the restoration may bend, loosen, or
◦ The most devastating type – fracture of the implant
Osseo integrated implants and prosthesis are
rigidly connected with the jawbone, and no
movement is possible.
Any movement of a dental implant is indicative of
failure or loss of osseointegration ( fibrous
As a result of this rigid relationship, the dental
implant, the attached implant –retained
restoration, and the surrounding bone are not
adaptive to adverse or excessive forces.
If occlusal loads exceeds the tolerance of the
implant, the connecting components, the
attached prosthesis, or the supporting bone
to withstand the stress, then
fatigue, fracture, or failure will occur.
Cantilevers on the prosthesis should be
reduced or preferably eliminated; therefore
the terminal abutments in the prosthesis are
the key positions.
◦ Force magnifiers
Three adjacent pontics should not be
designed in the prosthesis
The canine and the first molar sites are the
key positions, especially when adjacent teeth
An arch is divided into 5 segments. When
more than one segment of the arch is being
replaced, a key one implant position is at
least one implant in each segment.
The quantity and quality of bone support around the
◦ Influence load bearing capacity
◦ Resistance to occlusal loading
Bone appositional index
◦ Percentage of bone-to-implant contact
The lower the bone-to-implant contact and the lower the
bone density surrounding the implants and the resistance
to occlusal loading
the lower will be the support of the implants and the
resistance to occlusal loading.
The bone appositional bone index in the
post. Maxilla ranges from 30-60% whereas in
ant. Mandible its 65-90%
Anatomic structures and lack of bone height in
the posterior mandible and maxilla limit the
amount of available bone for placement of long
implants and thus reduce the potential for bone-
◦ Techniques like lateral nerve repositioning is possible
but has a moderately high morbidity.
◦ Sinus floor elevation and bone augmentation procedures
- enabled to increase the height of bone available in the
post. Maxilla thus allowing for the placement of longer
implants with improved results.
The implants with an altered
microtopography (acid etched) can achieve a
greater bone-to-implant contact in poor
quality bone (eg. Trabecular bone of posterior
maxilla) than implants with a machined
◦ Lazzara Rj et al IJPRD 1999
◦ Trisi P et al JP 2003
Earlier in 1980 and 1990, posterior maxilla were
restored with one or two implants or in some pts. 2
implants were used to support with three of four
◦ Currently it is imperative, that treatment of
posterior segments with one implant for every
missing tooth that will be restored.
◦ Also if space permits, it is desirable to use a
minimum of three implants to replace the missing
posterior teeth in the maxilla.
When implants are arranged in a linear
fashion, the biomechanics with respect to
anticipated bone response are quite
unfavorable compared with a configuration
where the implants are arranged in a non-
linear (curvilinear or staggered) fashion.
Arranging implants in a nonlinear manner
creates a more stable base that is more
resistant to the torquing forces created by off
centre contacts and lateral loads.
◦ This is particularly true when loads are not applied
along the long axis of the implant.
Implant supported FPD restoring partial posterior
quadrants – nonaxial loads can cause sufficient
load magnification at the bone-to-implant
interface, resulting in bone resorption and higher
rates of implant failure.
This has been supported by numerous FEA
studies, which clearly demonstrate that non-axial
forces significantly increase the stress
concentration to the cortical bone around the
neck of the implant.
Finite element analysis (FEA) is a computerized
investigative method that uses a mathematic
model to assess stress in various objects and
their surroundings when subjected to forces. It is
useful in generating a hypothesis and testing
basic biomechanical mechanisms but cannot be
relied on for definitive answers.
Only hard clinical evidence is undisputed and any
assumption or predictions that are made by FEA
needs to be validated clinically.
Using the finite element analysis (FEA), Pierrisnard and
colleagues showed that greater implant length did not
positively affect the way stresses were transferred to the
implant but found that increasing implant diameter
reduced the intensity of stress along the length of the
Iplikcioglu and Akca using the same method observed that
wider implants rather than longer implants registered
lower stress value to the whole system, suggesting that
the use of short, wide implants could increase the load-
bearing capacity of implants and implant prosthesis.
Baggi and colleagues also used FEA to show that increases
in implant width reduced stress more than increases in
Non axial loads can lead to implant
overload (load magnification)
Precipitates a resorptive remodeling
response of the bone around the neck
of the implant
When load persists, the bone loss
progresses and can lead to implant
Brunski et al proposed that excessive occlusal
loads lead to micro damage
(fractures, cracks) of the bone adjacent to the
implant, which provokes a resorptive
Linear implant configuration in the posterior
mandible and posterior maxilla are particularly prone
to bone loss when loads are not applied axially.
Bone loss in posterior Implants is more damaging
because implants in these areas are primarily
supported by the cotical bone around the coronal
Therefore, posterior implant should be positioned
such that occlusal forces can be directed down the
long axis of the implant (axial loads).
Also, the final restoration will be more simple
and more cost effective to fabricate when
angled or custom abutments are not
Extreme damage is seen in cases of posterior
Implant supported restoration with a cantileverd
pontics when nonaxial occlusal forces are
Because occlusal forces were directed to the
pontic created torquing forces around the neck
of the implant closest to the cantilever.
Therefore, cantilevered pontics are
contraindicated for unilateral posterior, implant
Angulation of the implants in relation to the
plane of occlusion and the direction of the
occlusal load - important factor in optimizing
the transfer of occlusal forces to implants.
Earlier in 1980s, many implants placed in
posterior Maxilla exhibited buccal angulation
or resulted in restorations with buccal
cantilever or may be excessive distal
Minor discrepancy in angulations are not
significant, but if loads are at an angle of 20
degrees or more to the axis of the
implant, load magnification resulting in
resorptive remodeling response of the
Partially edentulous patients
◦ Multiunit restoration in post quadrants
◦ Single – tooth implants in post. Quadrants
◦ Poor ridge form, conventional maxillary denture is
◦ 2 or 4 implants will provide greater stability and security
of maxillary denture in function when the maxillary ridge
is severely resorbed and lacks resistance to lateral
◦ Intact mandibular anterior dentition but lacks posterior
Support. Implants in the maxilla can offset the
potentially destructive effects on the premaxillary region
when a mandible with natural anterior teeth and missing
posterior teeth opposes and edentulous maxilla.
If pt. Cannot tolerate palatal coverage.
◦ The palateless denture, which may enhance their
sensation of taste and texture or may simply provide a
◦ To inhibit gag reflex
◦ Large palatal tori
Then minimum of 4 implants with adequate A-P
spread allows the fabrication of an implant
assisted over denture without palatal coverage.
The maxillary sinus limits the height of bone
available for implant placement in the
posterior region. As a result, the A-P spread
is limited. If the A-P spread is inadequate to
provide support, a full-palatal-coverage
overlay denture is recommended.
Due to alveolar ridge resorption after tooth loss
in premaxillary region, the adequate support for
the upper lip is lacking.
Thus, in most pts. Its advisable to construct an
implant – assisted maxillary overdenture (not an
implant supported fixed prosthesis.)
Lower cost, improved hygiene access, and
predictable speech articulation benefits that favor
the use of an overlay denture in the edentulous
maxilla over an implant – supported fixed
Implant-assisted overlay denture.
A, Clinical photograph of four-implant bar in the maxilla designed to retain a
palateless overlay denture.
B, Photograph of clip and attachment design of palateless overlay denture.
C, Cross-section of Hader bar clip attached to anterior bar (inset).
D, Axis of rotation and function of resilient attachment.
Mandibular complete denture is more
problematic as compared to maxilla
◦ Specially for pts. With severely resorbed atrophic
Lack of stability and retention
The 2 implant assisted over denture is the
best treatment for such patients
Place two implants in the anterior mandible
with a connecting bar.
One or two clips retain the denture over the
Fixed implant supported prosthesis require
4,5 or 6 implants arranged in an appropriate
arc of curvature with at least 1cm of A-P
Implant-assisted overlay denture.
A, Clinical view of overdenture in occlusion.
B, Photograph of mandibular overlay denture (tissue-bearing surface) designed
for an implant bar attached to two implants in the anterior mandible.
C, Clinical view of bar attached to two implants in the anterior mandible.
D, Illustration demonstrating how axis of rotation allows denture to rotate
around the bar.
Multiunit restorations in posterior quadrants
◦ Lowest success for short span restorations in posterior
Maxillary sinus. Inferior nerve position and also quality of bone
◦ Therefore, rough implants will improve the bone anchorage
but in some pts. It may not provide anchorage to support
unilateral, implant supported, FPD if implants are too short.
◦ Also, the acid etched surfaces – much better anchorage (
bone deposited is harder and denser and more resistant to
Single tooth implants in posterior quadrants
◦ Maxilla Vs mandible
◦ In mandibular first molar - conventional diameter
3.75 or 4.0 mm - unfavorable results
◦ When external hex-headed implants were used –
loosening of the screw
because the diameter of the implant head is much
smaller than the size of the occlusal surface.
Tipping of restoration – leads to stretching and
loosening of the screw
Single-tooth restoration in the posterior mandible supported by a wide-
A, Clinical photograph of healing abutment on wide-diameter implant.
B, Photograph of laboratory model with single molar.
C, Clinical photograph of molar crown supported by wide-diameter implant.
The use of wide-diameter (external hex) implants eliminates the problem of
screw loosening for single-tooth, posterior, implant-supported crowns.
1. Place implants perpendicular to the occlusal plane
2. Place implants in tooth positions
3. Use an implant for each unit being replaced
4. Avoid the use of cantilevers in linear configurations
5. Avoid connecting implants to teeth
6. If connecting implants to teeth, use a rigid
7. Control occlusal factors such as cusp angles and
width of occlusal table
8. Restore anterior guidance if possible
Multiunit implant restorations should be
splinted to maximize implant support
(sharing the loads), and emergence profiles
should be developed with open embrasure
spaces to facilitate oral hygiene.
Occlusal design for implant-supported
prostheses is an essential and integral
determinant of overall treatment planning.
The risk of implant overload can be minimized by
◦ limiting the width of the occlusal table of the implant-
supported fixed partial denture,
◦ flattening the cusp angles,
◦ avoiding the use ofcantilevered restorations,
◦ and restoring the anterior guidance provided by the
it is advisable to keep implant-supported
restorations separate from natural teeth
◦ Implants and teeth function differently and
connecting them can lead to complications such as
screw loosening and intrusion of natural dentition.
◦ Teeth have the capacity to move under functional
occlusal loads while implants do not.
Specifically, if implants are to be connected to
the natural dentition, it should be done in a
◦ either with screw-retained attachments or
◦ with copings secured by permanent cement.
◦ Tooth preparation should allow good
retention, teeth should be periodontally healthy and
stable, and the occlusal scheme should be good.
◦ implants are placed in good quality bone
◦ Are used to retain implant assisted overlay denture
But in cases of posterior quadrants, the
immediate or early loading is inadvisable
The importance of biomechanics and the limitations
of implant systems were initially underestimated.
Over the years, clinical experience and research
underscored the importance of biomechanics in the
success and predictability of implant-retained
The rigid nature of implant-retained restorations and
the lack of forgiveness in these systems demands a
revised approach to treatment planning that is now
The biomechanics must be factored into the planning
at the beginning of any implant treatment to achieve
long-term, predictable success.