dr.neha srivastava ipo seminar.pptx

1
OCCLUSAL CONSIDERATIONS FOR
IMPLANT SUPPORTED PROSTHESIS
Dr. Neha Srivastava Sahai
Assistant Professor
Dept. of Prosthodontics

 Introduction
 Implant protective occlusion(IPO)
 Occlusal considerations for implant prosthesis
Premature occlusal contacts
Influence of surface area
Mutually protected articulation
Implant body orientation and influence of load direction
Crown cusp angle
Cantilevers and Implant protective occlusion
Crown height and IPO
Occlusal contact points
Implant crown contour
Design to the weakest arch
Occlusal materials
Conclusion
References 2

 The clinical success and longevity of endosteal dental implants
as load-bearing abutments are controlled largely by the
mechanical setting in which they function.
 The treatment plan is responsible for the design, number and
position of the implants.
 After successful surgical and prosthetic rehabilitation with a
passive prosthesis, achievement of rigid fixation, proper
crestal bone contour, gingival health due to the mechanical
stress and/or strain beyond the physical limits of hard tissues
have been suggested as the primary cause of initial bone loss
around implants.
4

5
Bone loss
the probing depths are greater than 5 mm
Gingiva more
prone to shrink
Larger looking crown & loss of
interdental papillae
expose the implant crest module
Anaerobic bacteria are more
likely to be present
More biomechanical
complication
Mechanical failure
Esthetic failure

 Such noxious stresses and loads applied to the implant and
surrounding tissues result primarily from occlusal contacts.
Complications (prosthetic and/or bony support) reported in
follow-up studies underline occlusion as a determining factor
for success or failure.
 The choice of an occlusal scheme for implant-supported
prosthesis is broad and often controversial. Almost all
concepts are based on those developed with natural teeth and
are transposed to implant support systems with almost no
modification.
6

 Jemt et al. found that after fixed implant
reconstructions are placed into edentulous
patients, the displacement of the jaw during
mandibular opening and function is similar in
velocity and movement to that in patients with
natural teeth.
 Gartner et al. also demonstrated similar habitual
chewing for implant patients and patients with
natural teeth.
 During maximal occluding forces, electromyograms
demonstrated that the implant patient group
activated similar working and nonworking muscles
as patients with natural dentition.
 Therefore, it appears logical to derive implant
occlusion from occlusal principles for the natural
dentition.
7

 However, several conditions indicate that
implant prostheses are at greater
biomechanical risk than natural teeth.
 As a result, some of the occlusal concepts for
implants should be modified from concepts
for the natural dentition.
8

 Biomechanical parameters are excellent indicators of the
increased risk because they are objective and can be measured.
One can determine which condition presents greater risk, and
by how much the risk is increased. Hence the occlusal
concepts developed in this seminar stem from biomechanical
risk factors.
 The final element is the development of an occlusal scheme
that minimizes risk factors and allows the restoration to
function in harmony with the rest of the stomatognathic
system. If a clinical condition is likely to increase the
biomechanical stress to the implant prosthetic system, the
dentist implements occlusal mechanisms to decrease the stress.
9

Consequences of biomechanical overload:-
 Early implant failure
 Early crestal bone loss
 Immediate to late implant failure
 Immediate to late implant bone loss
 Screw loosening
 Uncemented restoration
 Component fracture
 Porcelain fracture
 Prosthesis fracture
 Periimplant disease
 Poor esthetic result (from tissue shrinkage after bone loss)
10

NATURAL TEETH IMPLANT
Bone ---pdl----tooth interface
Pdl (viscoelastic, resilient)---
reduces stress at crestal bone
region(dissipates energy) -----
force transmission (ideal strain
condition) ----cortical like (not
anatomical str) bone formation
around tooth
Direct bone---implant
interface
Occlusal load------transmitted
to contiguous bone
11
No force dissipated
No cortical lining
An implant receives a greater impact force than a natural
tooth because it is not surrounded by a periodontal complex.

mobility to dissipate forces---
reversible(returns back to
original position on removal of
forces)
thereby protecting adjacent
bone interface and prosthetic
components.
Irreversible mobility------health
is compromised and failure is
imminent.
12

Dissipated rapidly from crest of
bone to apex of tooth
Immediate primary movement
apically 56- 108µm
Pivots two third down towards
apex----------minimizing crestal
load
Implant does not exhibit a
primary immediate movement
Secondary movement 10-
50µm(viscoelastic bone)
Does not pivots apically
Less dissipation of forces to
surrounding bone
Concentrates greater forces on
crestal bone region
Lateral forces
14
Therefore, if an initial lateral or angled load of equal magnitude and
direction is placed on an implant crown and a natural tooth,
Implant sustains high
proportion of load
Biomechanical
risk

Width and cross sectional area
Nt > implant
 The greater the width of a transosteal structure (tooth or
implant), the lesser magnitude of stress transmitted to the
surrounding bone.
16
Molars have greater dimensions than premolars (greatest bite forces in
molar region), and the maxillary molars have greater root surface area
than the mandibular counterparts to compensate for the difference in
surrounding bone density and form.
The size of the implant often is decided by the existing bone volume
rather than the amount and direction of force.

Cross-section shape at the crest
is biomechanically optimized to
resist lateral (buccolingual)
loads because of the tooth’s
bending fracture resistance
(moment of inertia) and the
direction of occlusal forces.
e.g., mandibular anterior teeth
are greater in size in the
faciolingual directions (to resist
protrusive forces),
Are almost all round in cross-
section, which is less effective
in resisting lateral bending
loads and consequent stress
concentration in the crestal
region in the jaws.
Size of implant is determined
by amount of bone available
rather than amount and
direction of forces.
17

closer to that of bone( than any
other available dental implant
biomaterial)
Greater the flexibility
difference between two
materials (metal and bone or
tooth and bone), ---------the
greater the potential relative
motion generated between the
two surfaces upon loading at
the transosteal region--------
(under similar mechanical
loading) greater stresses and
strains at the crest of bone .
18
Hence, under similar mechanical loading conditions, implants generate
greater stresses and strains (especially at the crest) to the bone
compared with a natural tooth.

Precursor signs -----reversible and
include hyperemia and occlusal or
cold sensitivity. Professional treatment
is done to reduce the sensitivity,
usually by occlusal adjustment and a
reduction in force magnitude. ------
patient fails to seek professional
treatment---- increase in mobility (to
dissipate the occlusal forces)--------
still fails----- tooth may
orthodontically migrate away from the
cause of the occlusal stress.
Absence of initial reversible signs and
symptoms of trauma.
The magnitude of stress may cause
bone microfractures, place the
surrounding bone in the pathologic
loading zone causing bone loss, and
lead to the mechanical failure of
prosthetic or implant components(
without any warning signs more
advanced complications).
Cannot move orthodontically away
from the offending force.
19

overall increase in the periodontal
membrane thickness
an increased radiopacity and
thickness of the cribriform plate
around the tooth, observed on
radiographs and not just localized at
the crest.
The tooth can show clinical signs of
increased stress such as enamel wear
facets, stress lines, lines of Luder (in
amalgam fillings), cervical abfraction,
and pits on the cusps of teeth.
The loss of crestal bone around the
implant is not reversible without
surgical intervention and results in a
decreased implant support and
increased sulcus depth around the
abutment.
As a result, unless the density of bone
increases or the amount or duration of
force decreases, the condition is likely
to progress and even accelerate until
implant loss.
20

Proprioception and occlusal awareness
 Proprioception helps early detection of occlusal loads and
interferences.
 Lack of proprioception leads to higher bite force on implant
prosthesis( four folds).
 Implants and teeth also have different proprioceptive
information relayed by both entities.
 Teeth deliver a rapid, sharp pain sensation under high pressure
that triggers a protective mechanism. On the other hand,
implants deliver a slow, dull pain that triggers a delayed
reaction, if any.
22

 Teeth benefit from increased occlusal awareness compared to implants.
 Jacobs and van Steenberghe, evaluated occlusal awareness by perception
of an interference.
 When teeth oppose each other----- an interference perception ---
approximately 20m.
 An implant opposing a natural tooth-------interference perception -------
48m, (more than twice as poor).
 An implant opposing implant-------interference perception------- 64m
 When a tooth opposes an implant overdenture ---------- 108m (5 times
poorer than teeth opposing each other).
23

 Mericke- Stern et al measured oral tactile senstivity with steel
foils. The detection threshold of minimal pressure was
significantly high for implants than natural teeth.
 Hammerle et al reported that the mean threshold value for
implants (100.6g) was 8.75 times higher than that for natural
teeth(11.5g).
24

 As a result, premature occlusal contacts on teeth are usually
associated with a modification of arc of closure and with a
decreased force, before centric occlusion or full interdigitation.
In addition, the mandible may close in a different position to
avoid the premature contact and result in centric occlusion
different from centric relation occlusion.
 Unfortunately, because of the decreased occlusal awareness of
implants, the premature contact does not trigger such as an
adaptation.
 In addition, premature contacts are often on smaller areas of load
and therefore result in greater stress (S=F/A). They are most
often on inclines of posterior teeth, which also generates an
angled load of greater stress to the implant bone interface.
25

Loading
 The tooth slowly erupts into occlusion and is present in the
mouth from childhood. The surrounding bone has developed
in response to the biomechanical loads. The permanent teeth
are gradually introduced, while others are present. Hence
periodontal tissues have had time to organize in order to
sustain increasing loads, including those brought to bear by an
attached prosthesis.
 The only progressive bone loading around an implant is
performed by the prosthodontist, and in a much more rapid
and intense fashion.
26

 When implants or teeth are subjected to repeated
occlusal loads, microscopic stress fractures, work
hardening, and fatigue may result. Fatigue fractures are
related to the amount of stress and the number of cycles
of load.
 The cementum and bone around a tooth root are able to
repair the micro damage.
 The implant components, coping screws, or cement
cannot adjust or repair to these conditions and
ultimately fracture.
27

To conclude,
 The natural tooth, with its modulus of elasticity similar to
bone, periodontal ligament, and unique cross-sections and
dimensions constitutes a near perfect optimization system to
handle stress. In fact, the stress is handled so well, bacteria-
related disease is the weak link.
 An implant handles stress so poorly (capturing the stress at the
crest of the ridge), has an elastic modulus 5 to 10 times that of
bone, and is unable to increase mobility without failure that
stress is the weakest link in the system. As a result, ways to
decrease stress are a constant concern to minimize the risk of
implants complications.
29

 A proper occlusal scheme is a primary requisite for long-term
survival, especially when parafunctions are present.
 A poor occlusal scheme both increases the magnitude of loads
and intensifies mechanical stresses (and strain) at the crest of
the bone.
 Implant Protective Occlusion (IPO) was previously known as
medial positioned-lingualized occlusion. IPO concept
addresses several conditions to decrease stress to the implant
interface.
33

 The implant-protective occlusion (IPO)
concept refers to an occlusal plan specifically
designed for the restoration of endosteal
implants, providing an environment for
reduced biomechanical complications and
improved clinical longevity of both the
implant and prosthesis.
34

 A primary goal of an occlusal scheme is to
maintain the occlusal load that has been
transferred to the implant system within the
physiologic and biomechanical limits of each
patient.
 The forces generated by a patient are
influenced by ranges of parafunction,
masticatory dynamics, implant arch position
and location, arch form, and crown height.
 The implant dentist can address these force
factors best by selecting the proper position,
number and implant size, increasing bone
density when necessary by progressive bone
loading, and selecting the appropriate occlusal
scheme using stress-relieving design elements.
35

• No premature occlusal contacts or
interferences
• Mutually protected articulation
• Implant body angle to occlusal load
• Cusp angle of crowns (cuspal inclination)
• Cantilever or offset loads
• Crown height (vertical offset)
• Implant crown contour
• Occlusal contact positions
• Timing of occlusal contacts
• Protect the weakest component
36

 Maximal intercuspation (MI) is defined as the complete
intercuspation of the opposing teeth independent of
condylar position.
 Centric occlusion (CO) is defined as the occlusion of
opposing teeth when the mandible is in centric relation
(CR). This may or may not coincide with the tooth
position of MI.
 The potential need for occlusal adjustments to eliminate
deflective tooth contacts as the mandible closes in CR
and the evaluation of their potential noxious effects on
the existing dentition and the planned restoration is
important to evaluate.
38

Correction of the deflective contacts before
treatment by:
 Selective odontoplasty (a subtractive
technique)
 restoration with a crown (with or without
endodontic therapy)
 extraction of the offending tooth.
39

 Dentists should determine whether they are going to
ignore or control the occlusion of the patient.
 Determine the need for occlusal correction before
restoration of the implant patient is the observation of
negative symptoms related to the existing condition. This
may include
 Temporomandibular joint (TMJ) conditions,
 tooth sensitivity,
 mobility,
 wear,
 tooth fractures,
 cervical abfraction,
 porcelain fracture.
40

 As a general rule, the more teeth replaced or restored, the
more likely the patient is restored to CO.
 For example, if a completely edentulous mandible is to be
restored with an implant-supported fixed prosthesis, CO
provides consistency and reproducibility between the
articulator and the intraoral condition.
 On the other hand, when one anterior tooth is being
replaced, the existing MI position is often satisfactory to
restore the patient.
41

 A fundamental biomechanical formula is stress equals force
divided by the area over which the force is applied (S = F/A).
 Therefore, during either maximum intercuspation or CO, No
occlusal contact should be premature, especially on an implant
supported prosthesis.
 Premature occlusal contacts often result in localized lateral
loading of the opposing contacting crowns
 surface area of a premature contact is small
 premature contact is most often on an inclined plane
 The implant is rigid, and the premature implant load cannot be
released by increased mobility or occlusal material wear as
with a natural tooth.
43

 The premature contact on an implant system contributes
to a higher risk of early abutment screw loosening,
porcelain fracture, early loading failure, and crestal bone
loss.
 The elimination of premature occlusal contacts is
especially important when habitual parafunction is
present because the duration and magnitude of occlusal
forces are increased.
 The elimination of premature contacts is more critical
than in natural teeth because of the lack of proprioception
and the implant inability to move and dissipate the forces.
Because of increased proprioception, an initial premature
occlusal contact on a tooth often affects the closure of the
mandible to result in an MI position different from CO. A
premature contact on an implant crown does not benefit
from such protective features; as a result, the implant
system is at increased risk.
44

 Forces acting on dental implants are referred to as vectors
(defined in both magnitude and direction). Occlusal forces are
typically three-dimensional, with components directed along
one or more of the clinical coordinate axes.
46

 The teeth are designed primarily for long-
axis loads. The natural tooth roots in the
majority of the mouth are perpendicular to
the curves of Wilson and Spee.
 Implants are also designed for long-axis
loads, less stress was observed under a long-
axis load compared with angled loads.
47

 Implants are designed for a long axis load to the implant body.
Stress contours were primarily concentrated at the transosteal
(crestal) region. An axial load over the long axis of an implant
body generates a greater proportion of compressive stress than
tension or shear forces.
48
Any load that is applied at an
angle may be separated into
normal (compressive and
tensile) and shear forces. The
greater the angle of loads to the
implant long axis, the greater
the compressive, tensile and
shear stresses.

 When FEA evaluates the
direction of the force
changed to a more angled or
horizontal load, the
magnitude of the stress is
increased by 3 times or
more.
 In addition, rather than a
compressive type of force
primarily, greater tensile
and shear forces are also
demonstrated and increase
more than 10 times
compared with the amount
found with an axial force.
These stress contours
resemble the pattern of
early crestal bone loss on
implants.
49

 Binderman in 1970 evaluated 50 endosteal implant designs
and found that all sustained lesser stress under a long axis
load.
 Whether the occlusal load is applied to an angled implant or
an angled load is applied to implant body perpendicular to
occlusal plane, the results are similar.
50

 An axial load over the long axis of an implant
body generates less overall stress and a greater
proportion of compressive stress compared
with an angled force to the implant body.
 When an implant body is loaded along its long
axis, a 100-N force results with an axial force
component of 100 N, and no lateral force
component is observed.
 Therefore, the implant body should be
positioned perpendicular to the curves of
Wilson and Spee, just as with natural teeth.
51

 An implant body may be positioned with a 15-degree
angle to avoid the facial concavity and therefore is
positioned at 15 degrees to the occlusal load. This angled
implant may be restored during prosthetic reconstruction
with a 15-degree angle abutment.
 However, in the 15-degree angled implant body, the load
to the facial bone increases by 25.9% compared with an
axial load.
 Hence, the risk of crestal bone loss is increased with an
angled implant.
 The occlusal porcelain may be loaded in the long axis
with the angled abutment, but the abutment screw
loosening and implant component fracture risks increase
in direct comparison to the load applied to the bone.
52

 The effect of offset or angled loads
to bone is further exacerbated
because of the anisotropy of cortical
bone. Anisotropy refers to the
character of bone, whereby its
mechanical properties, including
ultimate strength, depend on the
direction in which the bone is
loaded. Cortical bone of human long
bones has been reported as strongest
in compression, 30% weaker in
tension, and 65% weaker in shear.
Therefore IPO attempts to eliminate
or reduce all shear loads to the
implant to bone interface.
54

 Therefore not only does
the crestal bone load increase
around the implant with angled
forces, but the amount of stress
the bone may withstand is also
decreased. The greater the
angle of load, the lower the
ultimate strength.
55

 Porcelain, titanium components, and cements are also
weakest to shear components of a load.
 Therefore, IPO attempts to eliminate or reduce all shear
loads to the implant system because the bone,
porcelain, titanium components, and cement are
weakest to shear loads.
56

 Any occlusal load applied at an angle to the
implant body may be separated into normal
(compressive and tensile) and shear forces.
57

 The primary component of the occlusal force should
therefore be directed along the long axis of the implant body,
not on an angle or following an angled abutment post. Angled
abutments are used only to improve the path of insertion of the
prosthesis or the final esthetic result.
 The angled abutment, which is loaded along the abutment
axis, will transmit a significant moment load to both the
implant crestal region and abutment screw, proportional to its
angle of inclination. In addition, the angled implant often
requires an angled abutment. Angled abutments are fabricated
in two pieces and are weaker in design than a one-piece post.
58

 Barbier and Schepers histologically evaluated implants
loaded in the long axis versus off-axis loading in dogs.
The long-axis–loaded implants had lamellar bone at the
interface. Lamellar bone is mineralized and organized and
is called loadbearing bone in orthopedics. The off-axis–
loaded implants had woven bone at the interface. Woven
bone is bone of repair. It is less mineralized, unorganized,
and weaker than lamellar bone.
 Hence, the greater strains in the bone with offaxis
loading may cause the bone to repair and places it at a
higher risk of overload and resorption.
59

 In the anterior maxilla, labial concavities may require that
the implant be angled away from the labial bone and the
abutment toward the facial crown contour. These implant
bodies are more frequently loaded at an angle, and an angled
prosthetic abutment is required. As a result, larger diameter
implants or a greater number of implants are indicated to
minimize the crestal bone stress on each abutment.
 IPO aims at reducing the force of occlusal contacts, increasing
implant number, and/or increasing implant diameter for
implants subjected to angled loads or with an increased crown
height or on the cantilever portion of a prosthesis.
60

 In conclusion, the microstrain of the crestal bone is
increased with an angled load and may shift from an axial
load within physiologic limits to an angled load in the
pathologic overload zone and, as a consequence, result in
bone loss.
 The occlusal porcelain is weaker to shear and may
fracture, the cement that retains the prosthesis is weakest
to shear and may become unretained, the abutment screw
more likely becomes loose with shear loads, the crestal
bone region may resorb, and implant components fracture
more often with higher shear loads.
61

 The primary component of the occlusal force
therefore should be directed along the long
axis of the implant body, not at an angle or
following an angled abutment post.
62

 Whether the occlusal load is applied to an angled implant
body or an angled load (e.g., premature contact on an
angled cusp) is applied to an implant body perpendicular to
the occlusal plane, the results are similar.
 A biomechanical risk increases to the implant system.
 The implant surgeon may place the implant body ideally,
perpendicular to the occlusal plane, yet the restoring dentist
then may load the implant crown at an angle. Similar
noxious forces are increased in shear, and a decrease in
bone strength occurs to the crestal bone, an increase of
shear loads on implant components, and the abutment
screws.
63

 Most implant bodies inserted at an angle of greater than 12
degrees to the occlusal plane require an angled abutment.
 The surgeon and restoring dentist should understand that
angled abutments are fabricated in two pieces and are weaker
in design than a two-piece straight abutment without an angle.
 Because less metal flanks the abutment screw on one side of
an angled abutment, it therefore is at more risk of fracture or is
less able to be reduced in width for ideal crown contours.
 Furthermore, a larger transverse load component develops at
the abutment screw and crest of the ridge as a result of angled
loads and increases the risk of abutment screw loosening.
64

(1) adding an additional implant in the edentulous space
next to the most angled implant,
(2) increasing the diameter of the angled implants, or
(3) selecting an implant design with greater surface area.
Of the three options, increasing the implant number is
most effective to reduce overall stress to the system
65

 The restoring dentist may reduce the
overload risk by
(1) splinting the implants together,
(2) reducing the occlusal load on the second
implant and further reducing the load on
the third implant, and
(3) eliminating all lateral or horizontal loads
from the most angled implant and
completely eliminating them in all posterior
regions.
66

 The natural dentition reduces the increased
stress to the maxilla by increasing the size of the
roots compared with mandibular incisors and
increasing the mobility of the tooth.
 Therefore, in the maxilla, a larger-diameter
implant or a greater number of implants are
indicated to minimize the crestal bone stress on
each abutment, especially in patients exhibiting
severe bruxism. Ridge augmentation may be
necessary before implant placement to improve
implant position or facilitate the use of a wider-
diameter implant.
67

69
•The angle of force to the
implant body is influenced
by cusp inclination. Angled
cusp results in angled forces
to crestal bone.
•The ideal occlusal contact
over an implant crown
therefore should be ideally
on flat perpendicular surface
to implant body.

 The posterior natural dentition often has steep
cuspal inclines, and 30-degree cusp angles have
been designed in denture teeth and natural tooth
prosthetic crowns.
 The greater cusp angles are often considered
more esthetic and may even incise food more
easily and efficiently.
 To negate the negative effect of an angle cusp
contact, the opposing teeth need to occlude at
the same time in two or more exact positions on
the ipsilateral cusp angles of the crowns.
 This is not possible in a clinical setting.
70

 The occlusal contact over an implant crown
therefore should be ideally on a flat surface
perpendicular to the implant body.
 This occlusal contact position usually is
accomplished by increasing the width of the
central fossa to 2 to 3 mm in posterior
implant crowns, which is positioned over the
middle of the implant abutment.
 The opposing cusp is recontoured to occlude
the central fossa of the implant crown directly
over the implant body
71

 This position is accomplished by increasing the width of the
central groove to 2-3 mm in posterior implant crown, which
are positioned over the middle of the implant abutment.
 Occlusal schemes and crown occlusal anatomy must
incorporate axial loads to implant body, to avoid noxious
effects of lateral forces.
72

 If healthy anterior teeth
and/or natural canines are
present, the occlusion
allows those teeth to
distribute horizontal loads
in excursions, while the
posterior teeth disocclude
during excursions.
74
This has been called mutually protected occlusion because the
posterior teeth protect the anterior teeth in CO, and the anterior teeth
protect the posterior teeth in mandibular excursions.
This occlusal design is based on the concept of using the
maxillary canine as the key of this occlusion scheme to avoid lateral
forces on the posterior teeth.
The mutually protected articulation concept is used in IPO.

 Anterior, compared with posterior bite force measurements and
electromyographic studies provide evidence that the stomatognathic
system elicits significantly less force when the posterior segments are
not in contact. As a result, all lateral excursions of IPO opposing fixed
prostheses or natural teeth should disocclude the posterior
components. The resultant lateral forces are thus distributed only to
the anterior segments of the jaws, resulting in a decrease in overall
occlusal force magnitude because of diminished muscle firing and
recruitment.
 For example, the maximum bite force in the posterior regions of the
mouth (with no anterior occlusal contact) is 200 to 250 psi. The
maximum bite force in the anterior region (with no posterior occlusal
contact) is 25 to 50 psi.
 Two thirds of the temporalis and masseter muscle do not contract
when posterior teeth disocclude.
75

 In addition, the TMJ and teeth complex form
a class 3 lever condition (i.e., the nutcracker).
As a result, the closer the object is placed
toward the hinge (TMJ), the greater the force
on the object.
 In addition, the greater lateral mobility of the
anterior teeth compared with the posterior
teeth (108 microns vs. 56 microns) also
decreases the consequences of the lateral
forces during excursions.
76

 The anterior guidance of implant prosthesis with anterior implant
should be as shallow as practical. Steeper the incisal guidance greater
the force on implants.
 According to Weinberg and Kruger, for every 10 degree change in
angle of disclusion there is 30% difference in load.
77

78
 The incisal guidance should be less than 20 degrees.
 However because the condylar disc assembly is usually
20 to 22 degrees, the incisal guidance should be greater
than this amount to separate the posterior teeth. When
the incisal guidance is less than the angle of the
eminentia of the TMJ, the posterior teeth will still
contact in excursions.
 Hence, in most patients, an incisal guidance of at least
23 to 25 degrees is suggested in IPO.

 The increase in load that occurs from the
incisal guidance angle is further multiplied by
the crown height above the initial occlusal
contact (the vertical overbite) because it acts
as a lever while the mandible slides down the
incline plane
 the vertical overbite reduced to less than 4
mm,
79

 A missing maxillary canine is indicated for a
single tooth implant crown.
 The proprioceptive mechanism of the natural
canine in excursions blocks approximately
two thirds of the activity of the masseter and
temporalis muscles and decreases the bite
force when posterior teeth disocclude.
 Hence, the natural canine periodontal
ligament nerve complex helps decrease the
force in excursions
80

 There is a proprioawareness transmitted through the bone
from an implant but a reduced amount compared with a
natural tooth.
 A mutually protected occlusion is still a benefit when a
single-tooth canine implant is restored.
 In other words, a greater decrease in lateral forces occurs
when a natural anterior tooth root is involved in the
excursion compared with an implant crown, but an implant
crown also can decrease the force and is better than a pontic
in the canine position.
 In addition, the class 3 lever mechanism of the canine
position still is able to reduce the force in excursions when
the posterior teeth do not contact.
81

 If single tooth implant replaces a canine, no contact
must occur under light forces and occlusion is
adjusted under heavy bite force in protrusion.
 No occlusal contact occurs on the single-tooth canine
implant crown during mandibular excursions to the
opposite side.
 During protrusion, no contact on the canine implant
crown is ideal. If a contact is necessary, it is adjusted
so a light bite force has no occlusal contact on the
implant crown. Under a heavy bite force in protrusive
movements, the canine implant crown may contact.
82

 Decrease in lateral force is improved when natural
tooth is involved in excursion due to decrease in bite
force by proprioceptive mechanism. Therefore it is
preferable to involve lateral incisor or premolar.
 This occlusal scheme should be followed whether or
not anterior implants are in the arch. However, if
anterior implants must disocclude the posterior teeth
in excursion, two or more implants splinted together
should help dissipate the lateral forces.
83

 A cantilever may be considered a class 1 lever. For example, if
two implants are 10 mm apart and are splinted with a
cantilever of 20 mm, the following mechanics result: the
mechanical advantage of the cantilever is 20 mm/10 mm, or 2.
 Force on cantilever-compressive
abutment-tensile.
 cement and screws are weaker
to tensile loads
85
Because the implant is
more rigid than a tooth, it
acts as a fulcrum with
higher force transfer. It is
a higher risk to cantilever
from an implant than a
tooth

 greater the force on the cantilever, the even
greater the forces on the implants
 The greater the length of the cantilever, the
greater the loads on the implants.
 shorter the distance between the implants,
greater the force on the implant system
 The cantilever force also varies as a result of
implant number
86

 A clinical report by Lundquist et al correlated long cantilevers
with crestal bone loss, and are common cause of prosthetic
component failure(screw)
 It is a class one lever, with a mechanical advantage of 2.
Therefore, whatever force applied to the cantilever force twice
as great as that will be applied to the farthest abutment.
87

 IPO goals at reducing the force at lever, pontic region compared
with that over implant abutments.
 No lateral load is applied to the cantilever.
 occlusal contact force may be reduced on the cantilevered
portion of the prosthesis.
 parafunctional forces (which are the most damaging) are
significantly reduced
88

 Crown height with lateral
load may act as a vertical
cantilever and a magnifier of
stress at the implant to bone
interface.
 Greater the height, greater is
the resulting crestal moment.
 Angled load on implant
crown is at a greater risk than
load on angled implant body,
as crown acts as a lever and
therefore all the forces are
magnified.
90

 Therefore, the doctor should be aware the
noxious effects of a poorly selected cusp
angle, or an angled load to the implant crown
will be magnified by the crown height
measurement.
 If a load perpendicular to the curves of Wilson
and Spee is applied to an angled implant
body the crown height is not a force
magnifier (lever) when there is no cantilever
or lateral load.
91

 When teeth are present, the maxillary dentate posterior ridge is
positioned slightly more facial than its mandibular counterpart.
Once the maxillary teeth are lost, the edentulous ridge resorbs in a
medial direction as it evolves from Division A to B, Division B to C,
and Division C to D. As a result, the maxillary permucosal implant
site gradually shifts toward the midline as the ridge resorbs.
 As a result of ridge resorption in width the maxillary posterior
implant permucosal site may even be lingual to the opposing natural
mandibular tooth. The posterior mandible also resorbs lingually as
the bone resorbs from Division A to B. As a consequence, endosteal
implants are also more lingual than their natural tooth predecessors.
93

 A buccal or lingual cantilever in the posterior
regions is called an offset load, and the same
principles of force magnification from class 1
levers apply.
 Offset loads may also result from buccal or
lingual occlusal contacts and create moment
forces, which increase compressive, tensile,
and shear forces to the entire implant system
94

 Wider root form implants can accept, Narrower
implant bodies are more vulnerable
 A facial profile similar to a natural tooth on the
smaller-diameter implant results in cantilevered
restorative materials.
 crown contour is often designed as a ridge lap
pontic
 facial porcelain most often is not supported by a
metal substructure because the gingival region of
the crown is also porcelain.
 increase the risk of porcelain fracture.
 This risk is compounded further by the higher
impact force
95

 The extended crown contours not only increase offset loads
but also often result in ridge laps or porcelain extension at
the facial gingival margin of the implant abutment.
 As a result, home care in the sulcular region of the implant
is impaired by the overcontoured crown design.
 The narrower posterior occlusal table facilitates daily
sulcular home care. Thus, a narrow occlusal table combined
with a reduced buccal contour (in the posterior mandible)
facilitates daily care, improves axial loading, and decreases
the risk of porcelain fracture.
 However, in the esthetic zone, the ridge lap design may be
necessary to restore the implant rather than removing it,
bone grafting, and replacing the implant.
96

 The posterior mandible resorbs lingually as the bone
resorbs from division A to B. As a result, endosteal
implants are also more lingual than their natural tooth
predecessors.
 The division C–h and D mandibular ridge shifts to the
buccal compared with the maxillary arch.
98

 The mandibular implant crown should be reduced from the buccal
and the maxillary crown reduced from the lingual.
 Thus, the “stamp cusp” offset load is reduced.
 The reduced buccal contour in the posterior mandible is of no
consequence to cheek biting because the buccal horizontal overjet is
maintained (and increased).
 The lingual contour of the mandibular implant crown is similar to a
natural tooth. This permits a horizontal overjet to exist and push the
tongue out of the way during occlusal contacts (just as natural
teeth).
 As with the natural tooth, the lingual cusp has no occlusal contact.
99

 During mastication, the amount of force used
to penetrate the food bolus may be related to
occlusal table width.
10
0

 In the esthetic zone (high lip position during smiling), the
buccal contour of the maxillary implant crown is similar to
a natural tooth. This improves esthetics and maintains the
buccal overjet to prevent cheek biting.
 there is no occlusal contact on the buccal cusp.
 Ideally, when maxillary posterior implants are in the
esthetic zone, they are positioned more facial than the
center of the ridge.
 The lingual contour of a maxillary implant crown should be
reduced because it is out of the esthetic zone and is a stamp
cusp for occlusion (which is an offset load)
10
1

 When the maxillary posterior teeth are
out of the esthetic zone, the crown may
be designed for a crossbite
10
2

 In summary, restorations mimicking the
crown contour and occlusal anatomy of
natural teeth often result in offset loads
(increased stress and risk of associated
complications), complicated home care, and
an increased risk of porcelain fracture. As a
result, in nonesthetic regions of the mouth,
the occlusal table should be reduced in width
compared with natural teeth
10
3

 “How does the bite feel? Is the crown too high?”
 There has been an ongoing controversy regarding whether a
rigidly fixated implant may remain successful when splinted to
natural teeth.
 The sudden, initial tooth movement ranges from 8 to 28m in
a vertical direction under a 3 to 5 lb load, depending on the
size, number, and geometry of the roots and the time elapsed
since the last load application.
 Once the initial tooth movement occurs, the secondary tooth
movement reflects the property of the surrounding bone and is
very similar to the bone implant movement.
10
4

 The axial movement of an implant has no initial, sudden
movement and ranges from 3 to 5 m with little correlation to
the implant body length.
10
5

 When teeth oppose each other, the combined intrusive
movements of the contacting elements may be 56m (28m +
28m).
 When a tooth opposes an implant, the combined intrusive
movement is
(initially only 28µm)
33m (28m + 5m).
10
6

 When implant prostheses oppose each other, the
biomechanical mismatch between teeth in the rest of the mouth
and implants increase. The total combined movement may be
10m, compared with 56m in the rest of the mouth, and
contrary to the teeth that move immediately, even with light
loads, the implants only move this amount under a heavy
occlusal load. A lighter load may generate a total implant
movement of less than 3m.
10
7

 Therefore, although the occlusal design in occlusion may be
ideal, premature contacts on implant will occur due to sudden
initial intrusion of teeth.
1- Occlusal prematurities are ideally eliminated on teeth before
implant reconstruction.
2- Thin articulating paper (less than 25m thickness) is then
used for the initial implant occlusal adjustment in centric
relation occlusion under a light tapping force. The implant
prosthesis should barely contact, and the adjacent teeth should
exhibit greater initial contacts. Only axial occlusal contacts
should be present on the implant crown.
10
8

 Once the equilibration with a light bite force is completed, a
heavier centric relation occlusal force is applied. The contacts
should remain axial over the implant body and may be of
similar intensity on the implant crown and the adjacent teeth
under greater bite force to allow all elements to react similar to
the occlusal load.
 Hence, to harmonize the occlusal forces between implants and
teeth, the dentist evaluates a heavy bite force occlusal
adjustment because it depresses the natural teeth, positioning
them closer to the less depressed implant position, and
therefore permits equal sharing of the occlusal load.
10
9

 When all posterior teeth on one or both the quadrants are implants-----
same occlusal timing is suggested.
Light bite force-----anterior natural teeth are heavier in centric occlusion
Heavy bite force ------similar contact force created around the arch in
centric occlusion.
 When implant prosthesis oppose each other in the same quadrant
Implant –implant section-------heavy bite force occlusal adjustment in
centric occlusion (56µm )
Tooth-tooth section-------light bite force adjustment(heavy contacts)
 Light and heavy bite force occlusal adjustments are not required in
cases where
Complete arch maxillary and mandibular implant supported prosthesis
Complete arch implant supported prosthesis opposing complete natural
teeth.
11
1

 When anterior implants and
teeth are not connected –
The initial lateral movement of
healthy anterior teeth ranges
from 56 to 108m before
secondary tooth movement.
Anterior implant movements
are not immediate and range
from 10 to 50m. Because
of the greater discrepancies
in lateral movement, the
occlusal adjustment in this
direction is more critical to
implant success and
survival.
11
2

 Light force and thin
articulating
paper(20m) are first
used to ensure that no
implant crown contact
occurs during the initial
occlusal or lateral
movement of the teeth.
A heavier force during
centric occlusion and
excursions is then used
to develop similar
occlusal contacts on
both anterior implants
and natural teeth.
11
3

 To compensate for the difference in 100 microns of horizontal
movement between maxillary anterior implants and anterior
teeth, two modifications are required.
 The first is to enameloplastythe facial incisal contact of the
mandibular incisal edge.
 The second modification is often the lingual contour of a
maxillary anterior crown is more concave than a natural tooth
to accommodate the heavy bite force occlusal adjustment
11
4

 Unlike teeth, implants do not extrude, rotate, or migrate under
occlusal forces. Natural teeth exhibit mesial drift and slight
changes in occlusal position do occur over time.
 No occlusal scheme will prevent mesial drift and minor tooth
movement from occurring. An integral part of the IPO
philosophy is the regular evaluation and control of occlusal
contacts at each regularly scheduled hygiene appointment.
This permits the correction of minor variations occurring
during long-term function and also helps prevent porcelain
fracture and other stress-related complications on the
remainder of the natural teeth.
11
5

 For implants joined to natural teeth a similar scenario is used
for the occlusal equilibration.
 A light force and thin articulating paper are used, and the
implant crown exhibits minimum contact compared with the
natural abutment crown. A gradient of force is designed on the
pontics. A heavy bite force is then used to establish equal
occlusal contacts for all abutments and the entire prosthesis,
whether implant or natural.
11
6

 An important parameter in IPO is the adequate surface area to
sustain the load transmitted to the prosthesis.
Mechanical stress = Force magnitude/cross sectional area over
which that force is applied.
 When implants of decreased surface area are subject to
angled or increased loads, the stress and strain is magnified in
the interfacial tissues. This can be minimized by placing an
additional implant in the region of concern.
11
8

 When forces are increased in magnitude, direction or duration
(e.g., parafunction), ridge augmentation maybe required to
improve implant placement, reduce crown height, and increase
implant width and number to compensate for the increased
loads.
 The prosthesis type may also be modified from a fixed
restoration (FP-1 to FP-3) to a removable prosthesis (RP-4).
This is most effective when nocturnal parafunction is present
because the restorations may then be removed while sleeping.
In addition support may be gained from the soft tissue (RP-5
restorations).
11
9

 Wider diameter root form implants have a greater area of
bone contact at the crest than narrow implants (resulting from
their increased circumferential bone contact areas). As a result,
for a given occlusal load, the mechanical stress at the crest is
reduced with wider implants compared with narrow ones.
 Natural teeth follow similar principles of diameter and
surface area as just described. The anterior region of the mouth
is characterized by reduced bite force compared with the
posterior region. Consequently, the anterior tooth cross section
is smaller, and the surface area is reduced compared with the
greater diameter and surface area of posterior teeth.
12
0

 Occlusal contact position determines
the direction of forces.
 An occlusal contact on a buccal cusp
may be an offset load when the
implant is under the central fossa and
the buccal cusp is cantilevered from
the implant body. Angled cusp will
introduce angled load.
 Similar is the case with marginal ridge,
where the forces are more damaging,
having greater chances of porcelain
fracture. Moment force may lead to
abutment screw loosening.
12
2

 Marginal ridge occlusal contact is not an offset force when
located between two implants splinted together. In addition
metal framework supports porcelain, minimizing risk of
fracture.
 The ideal primary occlusal contact therefore will reside within
the diameter of the implant, within the central fossa.
 Secondary occlusal contact should remain within 1 mm of the
periphery of implant to reduce moment forces.
12
3

 Any complex engineering structure will typically fail at its
“Weakest link”, and dental implant structures are no
exception.
 The amount of force distributed to a system can be
reduced by stress relieving components that may dramatically
reduce impact loads to the implant support. The soft tissue of
a traditional completely removable prosthesis opposing
implant prosthesis is displaced more than 2 mm and is an
efficient stress reducer. Lateral loads do not result with as
great a crestal load to the implants because the opposing
prosthesis is not rigid.
12
5

 The most common implant treatment, which includes a
traditional soft tissue supported complete denture, is a
maxillary denture opposing a mandibular implant supported
restoration. The occlusal scheme for this condition raises the
posterior occlusal plane, uses a medial positioned lingualized
occlusion, and has a bilateral balanced scheme. Whether the
mandibular restoration is FP-1, FP-2, FP-3, RP-4, or RP-5, the
maxillary denture follows these guidelines.
12
6

 The mandibular implant supported restoration may exert
greater force on the premaxilla than a mandibular denture and
cause accelerated bone loss. Therefore modification of the
occlusal scheme aims at protecting the premaxilla under a
maxillary denture by the total elimination of anterior contacts
with the mandibular anterior teeth in centric occlusal relation.
 Reduced occlusal forces with an absence of lateral
contacts in excursions are recommended on posterior
cantilevers or anterior offset pontics whenever possible. This
minimizes the moment forces on the abutments.
 It is better for mandibular cantilever pontics to oppose
maxillary implants than the reverse situation.
12
7

 The local occlusal considerations in implant dentistry
include the transosteal forces, bone biomechanics, basic
biomechanics, differences in natural teeth and implants,
muscles of mastication and occlusal force, and bone
resorption. The incorporation of all these factors lead to an
occlusal scheme (IPO) discussed in this seminar.
 Occlusal schemes consider the weakest component, full or
partial edentulous arches, and posterior or anterior teeth and /
or implants. An IPO is a consistent approach for implant
occlusal schemes.
 The material from which the occlusal region are
fabricated may affect implant loading and also affect implant
reaction forces to the opposing arch. These occlusal material
also affect wear and fracture, which affects the occlusal
contacts, vertical occlusal dimension, and esthetics.
12
9

 Misch CE : Dentistry of bone and effect on treatment plans,
surgical approach, healing and progressive loading. Int. J.
Oral implantol 6:23-31, 1990.
 Misch CE : Progressive bone loading, Pract Periodontics
Aesthet Dent. 2:27-30, 1990.
 Misch CE : Progressive bone loading. In Misch CE, editor;
Contemporary implant dentistry, pp 623-650, St. Louis, 1993,
Mosby.
 Bidez MW, Misch CE : Force transfer in implant dentistry;
basic concepts and principles, Oral implant 18: 264-274,
1992.
 Isidor F : Loss of osteointegration caused by occlusal load of
oral implants, Clin Oral Implant Res.7:143-152, 1996.
13
1

 Misch CE: Three dimensional finite element analysis of two
plate form neck designs, Master’s thesis, University of
Pittsburgh, 1989.
 Muhlemann HR : Tooth mobility : review of clinical aspects
and research findings, J. Periodontal 38:686 1967.
 Van Steenbergh D : A retrospective multicenter evaluation of
the survival rate of fixed prosthesis on four or six implants
and modum Branemark in full edentulism. J. Prosthet Dent.
61:217-223, 1989.
 Chee WWL, Cho GC : A rationale for not connecting to
natural teeth, J. Prosthod.6(1) :7-10, 1997.
13
2

 Williamson EH, Lundquist DO: Anterior guidance its effect
on electromyographic activity of the temporal and masseter
muscles, J. Prosthet Dent. 49:816-823, 1983.
 Schupe RJ et al : effects of occlusal guidance on jaw muscles
activity, J Prosthet Dent 51:811-818, 1984.
 Ogawa Tet al:Impact of implant number, distribution and
prosthesis material on loading on implants supporting fixed
prostheses. J Oral . 2010 Jul;37(7):525-31.
 LinkeviciusT,VladimirovasE: Veneer fracture in implant-
supported metal-ceramic restorations.Part I: Overall success
rate and impact of occlusal guidance. Stomatologija, Baltic
Dental and Maxillofacial Journal, 10:133-139, 2008.
13
3

Division A Bone
 The primary component of the occlusal force is
evaluated during the treatment-planning phase. In an
edentulous ridge with abundant height and width and little
resorption, the implant may be placed in a more ideal position
for occlusion and esthetics.
 Offset loads are used to describe cantilevered buccal or
lingual occlusal contacts, not directed along the long axis of
the implant body. When offset loads are generated at an angle,
the distance between the offset contact and the long axis acts
as a moment arm that magnifies the effect of the lateral force.
13
4

 The most common implant placement corresponds to a central
position in the residual ridge.
 The implant osteotomy begins in the center of the crest and is
gradually increased to the optimal width indicated in relation
to the recipient bone.
 Facial concavities are avoided, and the thinner facial cortical
bone is protected, to limit surgical complications such as labial
dehiscence. As a consequence, whether in the maxilla or the
mandible, the implant is frequently placed under the central
fossa region of the former natural tooth.
13
5

 To load the implant body in an axial direction, the primary
occlusal contact should therefore be the central fossa region in
Division A bone. Thus for maxillary implant opposing
mandibular natural teeth, the mandibular buccal cusp acts as the
primary tooth contact.
 Because bone loss occurs at the expense of the facial plate,
a modified buccal contour anatomy may need to be generated in
Division A or B mandibles. The occlusal table width is reduced
to favor an axial load on the implant in nonesthetic regions.
13
6

 The Division A mandibular
implant is placed under the
central fossa region of the natural
tooth. When opposing a natural
maxillary molar, the primary
contacting cusp becomes the
maxillary lingual cusp opposing
the mandibular implant crown,
with the mandibular buccal cusp
of decreased height and width
over the implant body. Hence all
contacts are situated medially
compared with those on natural
teeth.
13
7

 The lingual contour of the mandibular implant crown is
similar to the original natural dentition in position, complete
with horizontal overlap to the maxillary lingual cusp to
prevent tongue biting during function. There is no occlusal
contact on the lingual cusp, so offset loads during parafunction
are eliminated.
13
8

 In esthetic zone, when maxillary
implant opposing mandibular
natural teeth
the posterior maxillary
crown is reduced only from the
lingual aspect, compared with a
natural maxillary molar, to
reduce the occlusal table width.
such a reduction increases the
lingual overjet when the teeth
are in occlusion.
13
9

Narrower opposing mandibular occlusal tables are desirable
to direct occlusal forces over the maxillary implant body. As
a result, when opposing maxillary implants, the buccal
cusps of natural mandibular teeth (or crowns on implants)
should be recontoured to minimize offset loads in centric
relation occlusion.
The maxillary buccal cusp may then be retained for
esthetics, but the functional occlusal table is reduced.
14
0

 When esthetics are not a concern the distal one half of the first
molar and / or the entire second molar is often restored in
cross bite to improve the direction of forces.
 In the posterior esthetic regions of the maxilla with facial bone
resorption and / or lingually placed implants, a wider occlusal
table is required to project the facial contours for ideal
esthetics.
Bone grafting to increase bone width may be required in
these esthetics zones, so a larger diameter implant may be
placed that permits restorations of the buccal contours with
maintenance of cervical contours with emergence profiles,
which permit proper hygiene of the sulcular regions.
14
1

 Posterior implants opposing each other
attempt to axially load both entities. The
facial cusp of the maxillary crown is
required for esthetics. The other contours of
the opposing crowns are reduced in width to
minimize the occlusal table width and
axially load the implants.
 Whenever possible the portions of an
implant crown that are not supported by an
axially positioned implant should be
recontoured so they do not receive occlusal
loads. Alternatively, several additional
implants should be used to dissipate the
force.
14
2

DIVISION B BONE
 Division B bone has maxillary and mandibular implants
positioned under the lingual cusp when compared with the
original natural tooth position.
 As a result, mandibular crowns require even more reduced
buccal contours to avoid offset occlusal contacts. The primary
contact of occlusion on an opposing natural posterior
maxillary tooth is the lingual cusp, which is reshaped to
axially load the implant.
14
3

 The buccal cusp of the mandibular implant crown is
located near the original central fossa of the natural tooth.
 The medially positioned Division B mandibular implant
crown may have a central fossa, but it is more lingual than the
original position.
 The lingual contour of the crown is similar to that of the
original natural tooth and has an overjet with the opposing
natural tooth to prevent biting the tongue during function. The
mandibular posterior implant may, on occasion, be angled
medially because of the sub mandibular fossa.
14
4

 A Division B maxillary implant is often
placed under the palatal cusp region of the
original natural tooth. The maxillary
occlusal table cannot always be reduced
from the facial aspect for esthetic reasons;
therefore the buccal cusp is offset facially
but left completely out of occlusion (as
with natural teeth) in centric relation
occlusion and during all mandibular
excursions. The buccal cusp of the
opposing natural tooth is recontoured in
width and height to reduce offset loads to
the opposing crown on the maxillary
implant.
14
5

 The primary occlusal contact is centric relation
occlusion is the maxillary palatal cusp over the implant body
and the central fossa region of the mandibular natural tooth.
Bone augmentation for larger implant width is more indicated
in the maxilla because of the less dense bone and the
prosthetic needs to replace an esthetic buccal crown contour.
 When Division B implants are placed in both arches, the
maxillary and mandibular prostheses are similar to that
described in the previous scenario. However, it is usually not
possible to load both arches with an axial load, so the weakest
implant in bone density, width, or prosthesis type (fixed vs.
removable) determines the axial load, because it is the most
vulnerable arch.
14
6

 When further resorption occurs and the ridge evolves into
Division C or D, the maxillary palatal cusp becomes the
primary contact area, situated directly over the implant body.
Hence the occlusal contacts differ from those of a natural tooth
and may even be positioned more medial than the natural
palatal cusp when the implant is placed in Division C or D
bone.
14
7

 Fixed prostheses on natural teeth opposing FP-1 to RP-4
implant restorations should follow mutually protected occlusal
schemes whenever possible. In protrusion, there should be
total absence of posterior contacts, especially for cantilevered
posterior units.
 The masticatory force generated during lateral excursions is
decreased in absence of posterior contacts. This assists in
reducing the noxious effect of lateral forces on the anterior
implants. Two or more implants should share any lateral force,
and lateral excursions should occur as far forward as is
practical and include the canine.
14
8

 Minimal occlusal contact in the cantilevered regions and the
total absence of posterior lateral contacts during excursions are
indicated when opposing the natural dentition or a fixed
restorations.
 Mandible exhibits tortional movements in opening and
clenching((primarily posterior to mental foramen). Therefore
sufficient no. of anterior implants may replace all mandibular
teeth with rigid bilateral cantilevers.
 Seven to eight implants to support a complete implant
prosthesis in two separate units are suggested in the mandible
for a fixed restoration opposing a fixed prosthesis or natural
teeth with inadequate to severe stress factors.
14
9

 In the edentulous maxilla, flexure of the bone is not a
concern. A full arch prosthesis may be fabricated in one
section.
 Eight to ten maxillary implants most often are required for
a twelve unit fixed prosthesis opposing a fixed dentition on
teeth and / or implants with moderate to severe stress factors.
Posterior implants are more critical in the maxilla, in order to
eliminate cantilevers and increase the anteroposterior implant
distance, which further decreases stress to the maxillary
anterior implants.
15
0

• Recommended to have a mutually
protected occlusion.
• In centric it is necessary to have 30m
clearance at the anterior region
• disocclusion should be employed.
• To avoid localization of stresses
anterior group function should be
employed.
• The anterior guidance should be made
slightly flatter than natural teeth to
avoid over stresses on the fixtures.
15
1
Mandibular edentulous case for
fully bone anchored bridge

o Clearance of the anterior teeth should be smaller than the
natural teeth.
o Amount of disocclusion required is same as natural teeth since
the anterior guidance is provided by the remaining anterior
natural teeth.
 Protrusive : 1.1mm
 Non working side : 1.0 mm
 Working Side : 0.5 mm
15
2
Kennedy Class I

• In centric the posterior osseointegrated bridge should have
30m open contacts, while anterior teeth also should have 30
m open contacts and begin to contact under strong bite
pressure.
• Amount of disocclusion required is same as natural teeth since
the anterior guidance is provided by the remaining anterior
natural teeth.

15
3
Kennedy Class II

 Vertical dimension is
maintained by remaining
natural teeth
 The osseointegrated
bridge should contact only
under strong pressure.
 Amount of disocclusion
required is same as natural
teeth since the anterior
guidance is provided by
the remaining anterior
natural teeth.
15
4
Kennedy Class III

 To minimize horizontal loads group
function occlusion is recommended.
 During lateral movement posterior
teeth on working side can bear the
horizontal load while non working side can
be discluded.
 Anterior guidance should be flatter than
natural dentition to minimize load induced
on the fixture during protrusive movement.
 Amount of disclussion suggested is as
follows
◦ Protrusive : 0.8 mm
◦ Non- working side : 0.4 mm
◦ Working side : 0.0 mm
15
5
Kennedy Class IV

Anterior Tooth Position
 Centric stops or pressure from the tongue and muscle positions
usually prevent continued extrusion of anterior natural teeth.
 Maxillary anterior prosthetic teeth are positioned forward of the
anterior supporting bone to satisfy phonetic and esthetic
requirements.
 Moment forces result from contact with the anterior teeth, which
may cause instability of the maxillary prosthesis. Therefore the
maxillary denture usually does not have anterior incisal centric
stops. This helps protect the premaxilla from excess forces in
centric occlusion relation and initial excursions of the mandible, as
the premaxilla is vulnerable to resorption from external stresses.
15
6

 Posterior Tooth Position
In complete dentures, the position of the mandibular posterior
teeth is often determined first. Bone support concepts of
occlusion often position the mandibular teeth perpendicular to
the edentulous ridge. This positions the central fossa of the
posterior mandibular teeth more medial than that of their
natural predecessors in Division B, but more facial in Division
C, and very facial in Division D compared with the natural
tooth placement.
15
7

 The maxillary teeth are then situated farther facially than the
original teeth, if a normal cusp fossa relation is maintained.
Consequently, maxillary denture teeth are always placed
lateral to the resorbing bony support, and the condition is
compounded in cases of advanced atrophy (Division C or D
bone).
15
8

 The basic, concept of lingualized occlusion was first
introduced by Gysi. Later Payne suggested the maxillary
buccal cusps of posterior teeth should be reduced, so only the
lingual cusps would be in contact. Pound discussed a similar
concept, but reduced the buccal cusp of the mandible and
introduced the term “lingualized” occlusion. Pound also
placed the lingual cusp of the mandibular posterior teeth
between lines drawn from the canine to each side of the
retromolar pad. Consistent in the Philosophy of Payne and
Pound, was the belief that the palatal cusp should be the only
area of maxillarytooth contact. These occlusal schemes were
designed to narrow the occlusal table and improve
mastication, reduce forces to the underlying bone, and help
stabilize a lower denture. The techniques of Payne and Pound
may be modified further to a medial positioned lingualized
occlusion, proposed by Misch.
15
9

 Medial Positioned Lingualized occlusion : Laboratory
steps
1. Mount the upper cast using a face bow record. Mount the
lower cast using the centric relation record. Set the horizontal
condylar guidance according to the protrusive record.
2. Set the maxillary and mandibular anterior teeth for esthetics,
phonetics, and lip support.
3. Cut back the posterior flange of the lower record base to
expose the retromolar pad. Outline the retromolar pad in
pencil. Draw a line from the lingual border of the pad to the
mesial aspect cuspid. The central fossa of mandibular
posterior teeth will be set along this line.
16
0

4. Using a flat plane or 10 degree mold, set the mandibular
posterior teeth in a compensating curve. The curve should
have both a mediolateral and anteroposterior dimension that
progressively develops as the teeth are set posteriorly. The
curve starts with the first premolar and becomes more
accentuated in the molar region (closer to the condyle) (i.e.,
first premolar 0 to 5 degrees, second premolar 5 to 10
degrees, first molar 15 to 20 degrees, second molar 20 to 25
degrees). The anteroposterior angle of the curve is the second
molar region and should ideally approximate the horizontal
condylar guidance (i.e., 20 to 25 degrees).
5. Drop the incisal pin of the articulator 1 to 2 mm.
16
1

6. Using a 30 to 33 degree mold, set the maxillary posterior
teeth with the buccal cusp tilted out facially. The lingual cusp
should contact the central groove of the mandibular teeth
(this will be the only tooth contact point). There should be no
contact between the mandibular buccal cusp and the
opposing maxillary tooth.
16
2

7. Return the incisal pin to the original position (up 1 to 2 mm).
8. Using articulating paper to check the contacts, grind a small
fossa in the mandibular tooth for the maxillary lingual cusp
tip. Continue to adjust the occlusion until the incisal pin
touches the incisal table. Check for balanced occlusion in
excursions.
9. Festoon the set up for the try in appointment.
16
3

• Recommended occlusion for overdenture is fully balanced
occlusion with lingualized occlusion.
• Incase maxillary overdenture is opposed by a mandibular
fully bone anchored bridge, in centric a small clearance is
recommended in the anterior teeth, while posterior contact
simultaneously.
• Disocclusion is not employed here.
16
4
Maxillary edentulous case for overdenture

 The materials selected for the occlusal surface of the
prosthesis affect the transmission of forces and the
maintenance of occlusal contacts. In addition, occlusal
material fracture is one of the most common complications for
restorations on natural teeth or implants. Therefore it is wise to
consider the occlusal material for each individual restoration.
Occlusal materials maybe evaluated by esthetics, impact force,
a static load, chewing efficiency, fracture, wear, interarch
space requirements, and accuracy of castings. The three most
common groups of occlusal material are fixed prostheses on
implants are reviewed with relevance to the previous eight
criteria.
16
6

 Esthetics is a major concern for patients. The most
esthetic material available today is porcelain. Acrylic is
acceptable for esthetics, and metal is a poor choice of
materials when esthetics is the chief criterion. However, there
are many situations in which esthetics is not an important
aspect of the restorations. For example, when a maxillary
second molar is restored, most patients do not expose this area
when smiling or laughing.
16
7

 The materials on the occlusal aspect of the prostheses
affect the transmission of force to the bones. Impact loads give
rise to brief episodes of increases force, primarily related to
the speed of closure and the dampening effect of the occlusal
material. The hardness of material is related to its ability to
absorb stress from impact loads. All porcelain occlusal surface
exhibits a hardness 2.5 times greater than that of natural teeth.
Acrylic resin has a Knoop hardness of 17 kg/mm2, and enamel
has a 350 kg/mm2 hardness. A composite resin may exhibit a
hardness of 85% that of enamel. Therefore impact loads are
lowest with acrylic, increase with composite and metal
occlusals, increase even more with enamel, and further
increase with porcelain. As a consequence, it has been
suggested to use resin because of its dampening
characteristics.
16
8

 Clenching patients do not have a considerable amount of stress
reduction when acrylic versus porcelain materials are used on
the occlusal surfaces.
 Progressive bone loading is performed with acrylic
transitional prostheses. This material may reduce the impact
force on the early implant bone interface. As the bone matures
and its density increases, the need for force reduction
decreases.
16
9

 Fixed prostheses exhibit an improve efficiency compared
with removable soft tissue borne prostheses, regardless of the
occlusal material.
 Acrylic was 30% less efficient than porcelain or metal,
whereas there was no difference between gold and porcelain.
17
0

The definition of wear is the deterioration, change or loss of a
surface caused by use. The factors affecting the amount of
wear include magnitude, angle, duration, speed, hardness, and
surface finish of the opposing force and surface, together with
the lubricant, temperature, and chemical natural of the
surrounding environment. Most occlusal wear occurs as a
result of bruxism. An intuitive feeling is the harder the
occlusal material, the less the wear. However, surface hardness
has been shown to be a poor indicator of wear rate. Acrylic
resin wears 7 to 30 times faster when opposing gold, resin,
enamel, or polished porcelain, compared with gold opposing
gold, enamel or porcelain. Gold occlusal surface exhibit less
volume loss (sum of loss of opposing occlusal surfaces) than
any other combination of materials. Porcelain opposing
porcelain wears more than porcelain opposing gold or metal.
17
1

 The wear rate of occlusal materials, especially in the partially
edentulous patient with unrestored teeth, should be similar to
enamel. In this way, occlusal changes will not dramatically
change the occlusal scheme. Lambrechts et al in an in vivo
investigation reported vertical wear of premolar and molar
tooth enamel to be 20 to 40 um per year when opposing the
enamel of natural teeth.
17
2

 In principle, for the partially edentulous patient it would be
better to have more occlusal wear on implants, rather than less,
because the additional forces on the teeth are better tolerated
than on implant prostheses. As a result, total volume wear may
favor porcelain opposing enamel for the implant prosthesis
opposing teeth in the partially edentulous patient and metal
opposing enamel in the other regions of the mouth that require
restorations of natural teeth.
 The use of gold, regardless of the opposing combination,
always provides the least total volume loss.
17
3

 Adhesive wear occurs when one hard surface slides over a
surface of lesser hardness. As a result, wear fragments of one
material adhere to the other material. Gold occlusal surfaces
are observed to have gold particles adhered to enamel. This
may account for less total volume loss when opposing other
materials.
17
4

 For full arch implant supported prostheses, the restoring
doctor may consider metal occlusal to minimize wear and
prolong the accuracy of occlusal scheme long term. Porcelain
in esthetic regions opposing gold in the more nonesthetic area
or metal occlusal in both arches when parafunction or
marginal interarch space is present are the material most often
selected as implant occlusal materials.
17
5

 Materials fracture is one of the more common factors that
lead to refabrication of a prosthesis. Porcelain, acrylic and
composite fractures occur under excessive loads or even with
a lesser load of longer duration, angulation, or frequency.
Acrylic or composite materials fracture more easily. The
compressive strength of acrylic resin is 11,000 psi, compared
with 40,000 psi for enamel. Composite resin is 3 times
stronger than acrylic.
 Porcelain opposing porcelain is not suggested with
extreme parafunction, because it may fracture more often than
porcelain opposing metal. Metal occlusals do not easily
fracture, provide good wear resistance, and have minimum
impact load compared with porcelain.
17
6

 Metal shrinkage is 10 times less than porcelain or acrylic
and therefore permits the fabrication of a more passive casting.
When accuracy of the casting is paramount, as with screw
retained restorations, the occlusal material may make a
significant difference. This is most important in regions of
long spans and / or with a large volume of materials.
17
7

 Acrylic restorations receive their strength from bulk and
therefore require greater interarch space. Metal occlusals
require the least amount of space. In addition, when increased
retention of a cement retained prosthesis is required, a high
abutment and greater retention may be accomplished with a
metal occlusal. Porcelain is intermediate in the interarch space
requirement.
17
8

 Therefore when all seven criteria are evaluated, metal is
an excellent occlusal material, with improved properties in
accuracy, wear, fracture resistance, abutment retention, and
good qualities for impact or static force. Esthetics is best
satisfied with porcelain, which has improved properties
compared with acrylic concerning fractures and retention.
17
9

 J.B. Brunskin and J.A. Hipp in 1984 studied the in vivo
forces on dental implants. Methods are presented for
measuring vertical force components or bridged titanium
dental implants in dog mandibles. These methods have
included custom made strain gauge transducers, plus hard
wiring and telemetric schemes for data collection. The
essential components of the measurements system are
described, and typical bite force data are illustrated
18
0

 Parker et al in 1991 reviewed the occlusal considerations in
restorative dentistry. The major topics include the assessment
and treatment of occlusal wear, the controversies surrounding
treatment position of the mandibular condyles, occlusal
considerations in osseointegrated prosthesis, the two way
relationship between occlusal factors and temporomandibular
disorders, design criteria and longevity studies in resin
bonded, fixed partial denture.
18
1

 Hobo et al in 1991 presented a case report on occlusion for
osseointegrated prosthesis and concluded that the concept of
occlusion suitable for osseointegrated prosthesis is basically
the same as the gnathological occlusion. However the natural
tooth sinks about 30µm during function, while an
osseointegrated bridge which is supporte only by the bone
does not sink. Therefore it is necessary to adjust the centric
contacts of the osseointegrated fixed bridge slightly more open
than the natural teeth. During the eccentric movement, in order
to minimize horizontal loading, the concept of disocclusion is
generally used.
18
2

 James et al in 1993 discussed the edentulous implants an
emphasized that the occlusal contacts of the final fixed
restoration are affected significantly by implant position.
Lateral occlusal forces, may lead to abutment screw fracture.
They may be due to either excessive lateral occlusal pressure
or a malposed implant that requires non axial loading during
normal function.
18
3

 C.E. Misch et al in 1994 discussed an implant protected
occlusal on a biomechanical rationale. The clinical success and
longevity of endosteal dental implants are controlled, in a
large part, by the mechanical milieu within which they
function. The occlusion is a critical component of such a
mechanical environment. “Implant protected occlusion” refer
to an occlusal scheme that is often uniquely specific to the
restoration of endosteal implant prosthesis. Implant
orientation and the influence of load direction, the surface area
of implants, occlusal table width, and protecting the weakest
area are blended together from a biomechanical rationale to
provide support for a specific occlusal philosophy.
18
4

 Tashkandi et al in 1996 did an analysis of strain at selected
bone sites of a cantilevered implant supported prosthesis. the
results revealed that the maximum strain occurred at the strain
gauge positioned on cortical bone over the apex of the most
distal implant under 10 and 20 lb loading conditions.
 Osamu et al in 2002 did a study on influence of supra
structure materials on strain around an implant under two
loading conditions. The results showed under static and non
impact dynamic loading the three super structure materials
tested (highly filled composite resin, acrylic resin and gold
alloy), had the same influence on the strain transmitted to the
bone simulant that surrounded a single implant.
18
5

 Steven et al in 2004 did a study of stress transfer of four
mandibular implant overdenture cantilevered designs. His
results concluded that under load all prosthetic designs
demonstrated a low stress transfer to the ipsilateral abutment
and to the contralateral side of the arch. The plunger retained
prosthesis retained by two implants demonstrated a more
uniform stress transfer to the ipsilateral terminal abutment than
the clip retained prosthesis retained by three implants and
provided more retention.
18
6

 Lucie et al in 2004 Did a finite element analysis on the
influence of implant length and diameter on stress distribution.
Results showed an increase in the implant diameter decreased
the maximum equivalent stress around the implant neck more
than an increase in the implant length, as a result of a more
favorable distribution of the simulated masticatory forces
applied in this study.
18
7

 Ogawa T et al in 2008 conducted a study to evaluate axial
forces and bending moments (BMs) on implants supporting a
complete arch fixed implant supported prosthesis with respect
to number and distribution of the implants and type of
prosthesis material. Maximum BMs were highest when
prostheses were supported by three implants compared to four
and five implants (P < 0.001). The BMs were significantly
influenced by the implant distribution, in that the smallest
distribution induced the highest BMs (P < 0.001). Maximum
BMs were lowest with the titanium prosthesis (P < 0.01). The
resultant forces on implants were significantly associated with
the implant number and distribution and the prosthesis
material.
18
8

 Linkevicius T et al in 2008 conducted a study to define the
fracture rate of implant supported metal-ceramic restorations
delivered in private practice, and to identify if a restoration's
contact during eccentric mandible movements has any
influence on ceramic fracture rates. Within the limitations of
the trial, they concluded that ceramic veneer fracture rate was
6.7% in 380 restorations, and a conclusion that a restoration's
contact during eccentric excursions may significantly enlarge
fracture rates can be made.
18
9

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