text of oral implantology by Misch

1. Available Bone and
Dental Implant
Treatment Plans
SHREYA RASTOGI

2. CONTENTS
 INTRODUCTION
 LITERATURE REVIEW
 AVAILABLE BONE
implant width
implant height
available bone height
available bone width
available bone length
available bone angulation
crown height space
 DIVISIONS OF AVAILABLE BONE
 SUMMARY
 REFERENCES

3. INTRODUCTION
 Amount and density of available bone in the edentulous site of the
patient are the primary determining factors in predicting individual patient
success.
 Previously, available bone was the primary intraoral factor influencing
the treatment plan.
Today the prosthodontic needs and desires of the patient
should be first determined, relative to the number, size and position of
missing teeth.
Patient force factors and bone density also plays a major role in
the treament plan.
-Greenfield(1913)

4. LITERATURE REVIEW
 Tallegren (1972)- reported the amount of bone loss occurring the first year
after tooth loss is almost 10 times greater than the following years.
 Atwood DA (1962)-The posterior edentulous mandible resorbs at a rate
approximately four times faster than the anterior edentulous mandible.
 Tallegren A (1972)-The anterior maxilla resorbs in height slower than the
anterior mandible. However, the original height of available bone in the
anterior mandible is twice as much as the anterior maxilla. Therefore the
resultant maxillary atrophy, although slower, affects the potential available
bone for an implant patient with equal frequency
 Pietrokowski and coworkers (1978)-The residual ridge shifts palatally in
the maxilla and lingually in the mandible as related to tooth position, at the
expense of the buccal cortical plate in all areas of the jaws, regardless of
the number of teeth missing.
 Tallegren A et.al (1991)-After the initial bone loss, the maxilla continues to
resorb toward the midline, whereas the mandibular basal bone is wider than
the original alveolar bone position and results in the late mandible
resorption progressing facially.

5.  Bone volume classification was proposed by Lekholm and
Zarb in 1985-described five stages of jaw resorption, ranging
from minimal to extreme. The mandibular resorption was only
described in loss of height.

6. Fallschüssel in 1986-The six resorption categories of maxillary arch ranged
from fully preserved to moderately wide and high, narrow and high, sharp and
high, wide and reduced in height, and severely atrophic.
The classifications of Zarb and Lekholm, and Fallschüssel do not describe the
actual resorption process in chronological order and are more descriptive of the
residual bone.
Another bone resorption classification, which included the expansion of the
maxillary sinuses, was also proposed by Cawood and Howell in 1988.

7.  In 1985, Misch and Judy established four basic divisions of
available bone for implant dentistry in the edentulous maxilla and
mandible, which follow the natural resorption phenomena of each
region, and determined a different implant approach to each
category
These original four divisions of bone were further
expanded with two subcategories to provide an organized approach
to implant treatment options for surgery, bone grafting, and
prosthodontics
In 1985 Misch and Judy
presented a
classification of
available bone (div
A,B,C,D) which is
similar in both the
arches

8. AVAILABLE BONE
 Available bone describes the amount of bone in the edentulous
area considered for implantation.
 It is measured in terms of
 Width
 height
 Length
 Angulation
 Crown height space

9. Implant Width
 The width of the root form implant is often related to the diameter and
the mesio-distal length of the available bone
 All sizes and designs of implants do not have the same surface area.
 With a greater surface area of implant-bone contact, less stress is
transmitted to the bone, and the implant prognosis improved.
(S = F/A)
 E.g.- cylinder root form implant 1 mm greater in diameter will have a
total surface area increase of approximately 20% to 30%.

10. Implant Height
 The height of the implant is directly proportional to its total surface
area.
 Increased height affects the initial stability of the implant, the overall
amount of bone-implant interface, and a greater resistance to
rotational torque during abutment screw tightening.
 After healing the crestal region is the zone that receives the majority
of the stress therefore, implant length is not as effective as the width
to decrease crestal loads around an implant
 The minimum height for endosteal implants, long term survival is
related to the density of bone. The more dense bone may
accommodate a shorter implant (i.e., 8 mm), and the least dense,
weaker bone requires a longer implant (i.e., 12 mm).

11. Available Bone Height
 A panoramic radiograph is the most common method for the
preliminary determination of the available bone height.
 The height of available bone is measured from the crest of the
edentulous ridge to the opposing landmark

12. Available Bone Width
 After adequate height is available, the next most significant criterion
affecting long-term survival of endosteal implants is the width of the
available bone.
 The width of available bone is measured between the facial and lingual
plates at the crest of the potential implant site.
 The crest of the edentulous ridge is most often supported by a wider
base. In most areas, because of this triangular-shaped cross section,
for a narrow ridge, an osteoplasty provides greater width of bone,
although of reduced height.

13. Available Bone Length
 The mesiodistal length of available bone in an edentulous area is
often limited by adjacent teeth or implants.
 the implant should be at least 1.5 mm away from an adjacent tooth
and 3 mm from an adjacent implant.
 in case of a single-tooth replacement, the minimum length of available
bone necessary for an endosteal implant depends on the width of the
implant.
 The tooth has its greatest width at the interproximal contacts, is
narrower at the cement-enamel junction (CEJ), and is even narrower
at the initial crestal bone contact, which is 2 mm below the CEJ. The
ideal implant diameter corresponds to the width of the natural tooth 2
mm below the CEJ, if it also is 1.5 mm from the adjacent tooth. In this
way, the implant crown emergence through the soft tissue may be
similar to a natural tooth.

14. Available Bone Angulation
 Bone angulation is the fourth determinant for available bone.
 The initial alveolar bone angulation represents the natural tooth root
trajectory in relation to the occlusal plane. Ideally, it is perpendicular to
the plane of occlusion, which is aligned with the forces of occlusion and
is parallel to the long axis of the prosthodontic restoration.
 The maxillary anterior teeth are the only segment in either arch that
does not receive a long axis load to the tooth roots, but instead are
usually loaded at a 12- degree angle because the roots of the maxillary
teeth are angled toward a common point approximately 4 inches away.
 The limiting factor of angulation of force between the body and the
abutment of an implant is correlated to the width of bone.
 Greater width of bone offers some latitude in angulation at implant
placement Therefore ,an acceptable bone angulation in the wider
ridge may be as much as 25 degrees.

15. Crown Height Space
 The crown height space (CHS) is defined as the vertical distance from
the crest of the ridge to the occlusal plane.
 It affects the appearance of the final prosthesis and the amount of
moment force on the implant and surrounding crestal bone during
occlusal loading.
 The CHS may be considered a vertical cantilever.
 The greater the CHS, the greater the moment force with any lateral
force or cantilever.
 For an ideal treatment plan, the CHS should be equal to or less than
15 mm for ideal conditions.

16. DIVISIONS OF AVAILABLE
BONE

17. Division A (Abundant Bone)
 Division A abundant bone often forms soon after the tooth is
extracted. The abundant bone volume remains for a few years,
although the interseptal bone height is reduced and the original
crestal width is usually reduced by more than 30% within 2 years.

19.  An FP-1 restoration requires a Division A ridge. However, an
FP-2 prosthesis most often also requires a Division A bone.
 An FP-3 prosthesis is most often the option selected in the
anterior Division A bone when the maxillary smiling lip position
is high or a mandibular low lip line during speech exposes
regions beyond the natural anatomical crown position.
 limited CHS is more common in Division A bone, and a final RP-
4 or RP-5 result may require osteoplasty before implant
placement.

22. Division B(Barely Sufficient
Bone)
 As the bone resorbs, the width of available bone first decreases at the
facial cortical plate, because the cortical bone is thicker on the lingual
aspect of the alveolar bone, especially in the anterior regions of the jaws.
 There is a 25% decrease in bone width the first year and a 40% decrease
in bone width within the first 1 to 3 years after tooth extraction. The
posterior mandibular height resorbs four times faster than the anterior
region.
 The posterior maxillary regions exhibit less available bone height (as a
consequence of sinus expansion) and have the fastest decrease of bone
height than any intraoral region.

23.  Three treatment options are available for the Division B
edentulous ridge:
1. Modify the existing Division B ridge to another division by osteoplasty
to permit the placement of root form implants of 4 mm or greater in width.
When more than 12 mm of bone height results, the bone
converts to Division A. When less than 12 mm of bone height results, the
bone converts to Division C–h.
2. Insert a narrow Division B root form implant.
3. Modify the existing Division B bone into Division A by augmentation. To
select the proper approach to this bone category, the final prosthesis
must first be considered.
When a Division B ridge is changed to a Division A by osteoplasty
procedures, the final prosthesis design has to compensate for the
increased CHS.

25.  An RP-4 or RP-5 restoration most often requires option 1—
osteoplasty—where adequate CHS is created to permit the fabrication
of the overdenture and superstructure bar with attachments without
prosthetic compromise.
 The second main treatment option includes Smaller diameter root form
implants (3.0 to 3.5 mm) which are designed primarily for Division B
available bone.
 The third alternative treatment for Division B bone is to change it into a
Division A by grafting the edentulous ridge with autogenous or a
combination of allograft and alloplast with or without guided bone
regeneration techniques

26.  An alternative for the augmentation approach for Division B bone
is bone spreading. A narrow ostotomy may be made between the
bony plates and bone spreaders are tapped into the edentulous
site. The Division B ridge may be expanded to a Division A with
this technique and allow a Division A implant or an alloplast to be
inserted.
 Grafted ridges will more often be used when a fixed prosthesis is
desired, whereas ridges treated with osteoplasty before implant
placement are likely to be supporting removable prostheses.
For example, in the partially edentulous anterior maxilla,
augmentation is most often selected because of esthetics. In
the edentulous anterior mandible, osteoplasty is common.

28. Division C (Compromised Bone)
 The Division C ridge is deficient in one or more dimensions (width,
length, height, or angulation) regardless of the position of the
implant body into the edentulous site.
 The resorption pattern occurs first in width and then in height. As a
result, the Division B ridge continues to resorb in width (although
height of bone is still present) until it becomes inadequate for any
design of endosteal implant. This bone category is called Division
C minus width (C–w)
 The resorption process continues, and the available bone is then
reduced in height (C–h).
 Moderate to advanced atrophy is seen

29. The C–w bone will resorb to a C–h ridge as fast as the A resorbs to
B and faster than B resorbs to C–w. In addition, without implant or
bone graft intervention, the C–h available bone will eventually
evolve into Division D (severe atrophy).

30.  There is one uncommon subcategory of Division C, namely C–a.
In this category, available bone is adequate in height and width,
but angulation is greater than 30 degrees regardless of implant
placement
 When present, this condition is most often found in the anterior
mandible; other less-observed regions include the maxilla with
severe facial undercut regions or the mandibular second molar
with a severe lingual undercut.

31. Treatment o Division C

32.  A C–w ridge may be treated by osteoplasty. An osteoplasty
converts the ridge to C–h and, in the anterior mandibular region,
most often to a width suitable for root form implants.
 C-w cannot be converted to Division A, because the CHS is
larger than 15 mm.
 The C–h posterior maxilla is a common and unique edentulous
condition. The residual ridge resorbs in width and height after
tooth loss, similar to other regions.However, because of the initial
ridge width dimension, a decrease of 60% in dimension still is
adequate for 4-mm-diameter implants.
 Sinus grafts, which elevate the maxillary sinus floor membrane in
cases of sinus expansion after tooth loss were developed by
Tatum in the mid-1970s.

33.  Shorter endosteal implants are the most common options.
A C–h root form implant is usually 4 mm or greater in width at
the crest module and 10 mm or less in height.
 Circumferential or unilateral subperiosteal implants - permit the
placement of mandibular posterior prosthodontic units without risks
of paresthesia from nerve repositioning or lengthened treatment time
associated with autogenous bone grafts and endosteal implants
 An alternative method of treatment for the maxilla is to fabricate a
traditional denture in Division C arches after changing the division
with non resorbable hydroxyapatite.
This treatment option is often indicated for a conventional
maxillary denture on a C–w anterior maxilla. augmented ridge is only a
delay tactic for bone resorption, because it does not stimulate or
maintain bone mass.

35. Division D (Deficient Bone)
 Long-term bone resorption may result in the complete loss of the
residual ridge, accompanied by basal bone atrophy
 Severe atrophy describes the clinical condition of the Division D
ridge.

36.  Completely implant-supported overdentures are indicated in Div
D whenever possible, to decrease the soft tissue and nerve
complications, but require anterior and posterior implant
support, which almost always require bone augmentation before
implant placement.
 Autogenous iliac crest bone grafts to improve the Division D are
strongly recommended before any implant treatment is
attempted.
 After autogenous grafts are in place and allowed to heal for 5 or
more months, the bone division is usually becomes Division
C–h or A and endosteal implants may be inserted.

39.  The autogenous bone grafts are not intended for improved denture
support.
If soft tissue–borne prostheses are fabricated on
autogenous grafts, 90% of the grafted bone resorbs within 5 years as
a result of accelerated Resorption
 The completely flat Division D maxilla should not be augmented with
only hydroxyapatite to improve denture support. Inadequate ridge
form exists to guide the placement of the material.
 The partially or completely edentulous patient with a posterior
Division D maxilla and healthy anterior teeth or implants may
undergo sinus graft procedures with a combination of local
autogenous bone, demineralized freeze-dried bone and calcium
phosphate bone Substitutes. After 6 to 8 months is restored to
Division A or C–h,
 An RP-5 removable restoration is usually indicated for Division D
with only anterior implants.

40. SUMMARY
 The primary criterion for proper implant support is the amount of
available bone.
 Four divisions of available bone, based on the width, height,
length, angulation, and crown height space in the edentulous site,
have been presented.
 Division A root form implants are optimally used and most often as
independent support for the prosthesis.
 Division B bone
-provide adequate width for narrower, small-diameter root from
endosteal implants
- changed to Division A by augmentation or osteoplasty

41.  The Division C edentulous ridge exhibits
- moderate resorption and presents more limiting factors for
predictable endosteal implants.
- augmentation is done before implant placement to upgrade the
division is influenced by the prosthesis, patient force factors,
and patient’s desires.
 The Division D
-edentulous ridge corresponds to basal bone loss and severe
atrophy, resulting in dehiscent mandibular canals or a
completely flat maxilla.
- augmentation with autogenous bone before implant and
prosthodontic reconstruction

42. References
 Contemporary Implant Dentistry (3rd Edition)
-Carl E. Misch