This document discusses bone considerations for dental implant therapy. It describes the different types of bone, including cortical, cancellous, woven bone and their properties. It also discusses factors like available bone height, width, density and their effect on implant treatment planning and surgical protocols. Insufficient bone requires augmentation procedures like bone grafts or sinus lifts to provide adequate support for dental implants. The success of implants placed in deficient bone depends on careful treatment planning and surgical skill.

1. Bone consideration in
dental implant therapy
Prepared by:
Roshna Talib Mustafa

2. Introduction
Bone is a dynamic biological tissue composed of
metabolically active cells that are integrated into a rigid
framework.
Primary stability of the implant has been proposed to
be the most important factor responsible for the
success of implant therapy, which is primarily
determined by the density of the bone.

3. Biological aspect of bone
The bone is covered by periosteum, a layer known as the
mother of bone. The periosteum is a tough, vascular layer of
connective tissue that covers the bone but not its articulating
surfaces.
Primarily, there are three types of bone: woven bone, cortical
bone, and cancellous bone.

4. Woven bone is formed during embryonic development,
during fracture healing and in some pathological states
such as hyperparathyroidism and Paget's disease.
Cortical bone/compact/lamellar bone is remodeled
from woven bone by means of vascular channels that
invade the embryonic bone from its periosteal and
endosteal surfaces.

5. Cancellous bone /trabecular bone lies between cortical bone
surfaces containing bony trabeculae.
Bone resorption is particularly more on the labial wall as well
as there is bone deposition within the extraction socket.
During the first 3 months, the rate of bone resorption is
highest which gradually reduces after 6 months.
Remodeling is generally complete and stabilized after 1-2
years . The rate of bone resorption in the mandible is 3-4
times higher than in the maxilla.

6. The bone resorption pattern is different in maxilla and mandible. In the
maxilla resorption of the alveolar ridge occurs mainly on the buccal
aspect.
This is because of the reason that the buccal cortical bone of the
maxilla is thinner as compared to the palatal bone.
So, the remodeling of the maxilla is in a centripetal fashion which
makes the maxilla smaller.
In case of the mandible, the buccal cortical plate is thinner than the
lingual cortical plate in all areas except in the molar region. So, bone
resorption in the mandible occurs primarily lingually in the premolar
areas and buccally in the molar segments.

7. Available bone
The availability of sufficient bone is a must for implant placement. If
the bone is insufficient, bone augmentation procedures are carried out.
Various classifications have been proposed to classify the available
bone both quantitatively and qualitatively.
Atwood's classification (1979) proposed a classification for the
edentulous mandible. ridge resorption in a horizontal direction was
considered.
In 1985, Misch and Judy are classified bone into following types based
on macroscopic cortical and trabecular characteristics(D1,D2,D3,D4
and D5).

9. D1 type bone
This type of bone is primarily composed of almost all cortical bone. it is
primarily present in the anterior mandible.
In this type of bone, the bone to implant contact (BIC) is greatest and
exceptional initial implant stability can be achieved.
But, due to its high density, there are fewer blood vessels providing a
significant portion of nutrient and blood supply to the periosteum.

10. A conservative flap reflection is advised in this case to
minimize the impact of disruption of blood vessels during and
after the surgery. Another problem is the generation of heat
during osteotomy.
To minimize the heat production during drilling a pre-cooled
sterile saline solution should be used with drill speed more
than 1500 rpm.
The drill should be used in slow pumping motion which
further reduces heat generation.

11. D2 type bone
This type has thick cortical bone, which surrounds the coarse
trabecular bone.
It is most suitable for implant placement and post-operative healing.
This type of bone is primarily found in the anterior and posterior
mandible.
A modification in the drill pattern is advised to overcome this problem.
Reduced number of drills, as well as reduced drill speed to less than
(1500 rpm), are advocated in this type of bone.

12. D3 type bone
In this type of bone central fine trabecular bone is covered by a porous
crestal layer of cortical bone. It is found in the anterior and posterior maxilla
but also in the posterior mandible.
The bone to implant contact is significantly reduced in the D3 type of bone. A
modification in the drill pattern is advised to overcome this problem.
Reduced number of drills, as well as reduced drill speed less than (900 rpm)
is advised.
Care should be taken while using drills. Because of less density, there are
chances of perforation of the buccal plate, especially in the maxillary anterior
region.
One advantage of this type of bone is high vascularity due to the fine
trabecular bone. It aids in healing around the implant.

13. D4 type bone
This type of bone is a nightmare for implantologists. The bone
is formed of fine trabecular pattern with the often absence of
cortical bone. This type of bone is commonly found in the
posterior maxilla.
In this case also a modified drill protocol is advised because
the bone to implant contact is least in this case. An undersized
osteotomy with use of osteotomes to condense rather than
remove bone is indicated.
D5 type bone
This is an immature and non-mineralized bone, not suitable
for implant placement.

14. Available Bone Height
The available bone height is measured from the crest of the
edentulous ridge to the opposing limiting anatomical
landmarks such as inferior alveolar canal in the mandible and
the floor of the nasal cavity and maxillary sinus in the maxilla
which can be identified during radiographic assessment.
The canine eminence region in the maxilla and the first
premolar region in the mandible offer the greatest bone
height column of bone.

15. An implant 3 mm longer provides more than 10% increase in surface
area. The increase in length of the implant provides better initial
stability, which is one of the most important factors responsible for
implant success. The requirement of length is reduced in cases of
dense bone.
In the maxillary and mandibular posterior regions due to the presence
of limiting structures, i.e. maxillary sinus and mandibular canal
respectively, the available bone height is less.
The use of wider and shorter implants is indicated in these regions. It is
recommended that 2 mm of bone height between a critical structure
and the implant should be maintained to avoid any surgical error.

16. Available Bone Width
The available bone width is measured between the facial and lingual
plates at the crest of the potential implant site. Usually, the crest of the
alveolar ridge is triangular in shape with a broad base.
Available Bone Length
It is the mesiodistal length of available bone in the edentulous area
limited by adjacent teeth or implants. As a guideline, it is
recommended that the ideal mesiodistal distance between an implant
and a tooth is 1.5-2 mm and 3- 4 mm between each implant.

17. The required bone length for implant placement is
actually related to the bone width. For implant
diameter of 3.75 mm, the minimum bone width
required is 5 mm.
So, the minimum bone length required is 7 mm. In
cases where the bone width available is less, the
implants with smaller diameters have to be used which
changes the bone length requirements also.

18. Available Bone Angulation
The angulation of the bone is a significant feature because the occlusal
forces on the implant are directed from the implant body to the
surrounding bone.
In mandible, the angulation of implant placement progressively
increases from premolar to the second molar region because of the
presence of submandibular fossa creating a deep lingual undercut.
Because of bone angulation, some areas in the bone do not allow us to
place the implant in the desired position.
The use of angled abutments in these areas helps us to achieve
parallelism as well as desired positioning of the abutment.

19. Crown / Implant body ratio
This ratio plays an important role in the long-term success of an
implant. Ideally, the crown/implant body ratio should be less than 1,
i.e. the fixture should be longer than the crown portion.
In cases where it is difficult to achieve, the treatment plan should be
modified to incorporate more number of implants or wider implants to
counter the increased stress.

20. Deficient Bone
This clinical condition is complete resorption of the alveolar bone and
continued resorption of the basal bone resulting in a completely flat
maxilla. The resorption of the nasal spine may also be evident.
In the case of the mandible, the continued resorption up to superior
genial tubercles may be evident.
Bone augmentation procedures have to be carried out to have
sufficient support for implant placement.

21. The surgical skill required is greater and the prosthetic outcome has a
guarded prognosis.
Fixed restorations are almost always contraindicated due to significant
crown height.
Because of the complexities involved, the complications during surgery
as well as implant failures are more likely to happen in this bone
division.

22. insufficient bone
is most difficult to treat. In this bone type, the bone loss is severe
which increases the probability of implant failure in the absence of
bone augmentation to provide adequate bone support.
The bone augmentation to upgrade the division of bone is highly
recommended in these cases. The autogenous block graft can be done
with a healing period of around 6 months before the implants are
placed.
In the maxillary posterior region, sinus uplift is necessary to provide
adequate bone support to implants. Care must be taken during the
surgery not to perforate the Schneiderian membrane.

23. Subperiosteal implants are indicated in advanced ridge
resorption cases, so they present a good treatment option.
It must be remembered that operative as well as post-
operative complications are most commonly involved with this
type of treatment.
A carefully designed treatment plan and operator's skill are
the aim the success of implant therapy in these patients.

24. Thank you