1. science
2. medicine
3. surgery
4. transplants

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ORIGINAL HYPOTHESIS
A new view on bone graft in dental
implantation: Autogenous bone mixed with
titanium granules
Yeke Wu, Yunqiang Yang1, Yuqiao Zhou2, Yifei Gu3, Xuewei Fu3
Department of Orthodontics, West China School of Stomatology, Sichuan University, Chengdu, 1Center of Stomatology, Huazhong University
of Science and Technology, Wuhan, 2Department of Oral Medicine, 3State Key Laboratory of Oral Diseases, West China School of Stomatology,
Sichuan University, Chengdu, China
A B S T R A C T
Introduction: Dental implants have been widely applied in clinic for many years. However, the success rate is still challenging mainly
because of bone deficiency. An ideal bone graft is traditionally thought to guide and induce new bone regeneration as well as been
absorbed completely by human body. The Hypothesis: Autogenous bone mixed with titanium granules might be an ideal bone
graft for dental implantation. Evaluation of the Hypothesis: First, we analyzed advantages of grafts of autogenous bone mixed with
titanium granules, such as serving as a stable scaffold for wound healing and tissue regeneration, creating suitable microenvironment
for implant–bone integration, shortening the new bone’s creeping distance, etc. Then we creatively hypothesized a novel alternative
bone graft with premixed autogenous bone and non-absorbent titanium granules. Apart from repairing bone deficiency, our
hypothesis could promote the integration between new bone and titanium implant from the perspective of microenvironment. We
believe that the method is promising and worth extension in clinical application.
Key words
words: Autogenous bone graft, bone deficiency, dental implant, titanium granule
Introduction
Dental implants have been a feasible technique in
the oral rehabilitation of edentulous and partially
dentate patients with good long-term predictability
for many years. [1] However, with the increasing
frequency of implant placement, it is inevitable that
the number of complications will also rise.[2] Among
them bone deficiency ranks as one of the most often
encountered problem. Numerous modalities of bone
graft are proposed for the management of patients’
bone insufficiency. Currently, the main methods of
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DOI:
10.4103/2155-8213.110187
bone graft used clinically are as follows: (i) autogenous
bone graft, which are derived from ilium, mandibular
angle, chin, etc; (ii) artificial bone graft, such as bio-oss,
hydroxyapatite, tricalcium phosphate, etc, mainly based
on the guided bone regeneration (GBR) theory; and (iii)
autogenous bone mixed with artificial bone.[3-5] These
methods have their own merits as well as limitations.
Autogenous bone is still the gold standard for defects
filling caused by pathologies and traumas, and mainly
for alveolar ridge reconstruction, allowing the titanium
implants installation. It is characterized by osteogenic,
osteoinductive and osteoconductive properties, as well
as the lack of possible immunological reactions.[6,7]
Nevertheless, it also has disadvantages as its limitation
of drawing materials and easy to be absorbed.[8,9] For
artificial bone graft bio-oss, the absorption process is
fairly slow. Worse still, patients have to pay extra fee
and suffer from the large bone defects.
Titanium, a special metal with excellent biocompatibility
and low resorbability, has long been used in implant
Corresponding Author: Dr. Yang Yunqiang, No. 1095, Libera on Road, Wuhan, Hubei 430030, China. E-mail: [email protected]
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Wu, et al.: Autogenous bone graft with titanium granules for dental implantation
dentistry. Dental implant composed of titanium can
perform mastication/chewing function for a long
time after implantation. The first application of the
irregularly shaped and porous titanium granules (PTG),
TigranTM PTG in 1995 showed favorable osteoconductive
and thrombogenic effects. [10] They imitated bone
properties, stimulated osteoblasts colonization and
osseointegration, and kept their volume during the
entire healing period which ensures mechanical
stability. Thereafter, titanium granules have been widely
used for sinus floor augmentation, peri-implantitisrelated bone regeneration, furcation defects repair,
onlay augmentation of deformed alveolar process, cystic
cavities reconstruction, filling of extraction sockets,
etc.[11-13]
Traditional viewpoint for bone graft is primarily that
graft should guide and induce new bone regeneration
as well as been absorbed completely by human body.[14]
Nowadays, we mainly focus on the filling of bone
deficiency, instead of new bone regeneration and
osseointegration. Hence, we need to seek for novel
approach to settle the problem of bone deficiency, and
improve the success rate of dental implantation.
The Hypothesis
In the paper, we hypothesized a novel approach of
bone graft with pre-mixed autogenous bone and
titanium granules (with a potential size of 0.7-1 mm)
for bone deficiency repair, thus to reduce absorption
after implant placement and improve the success rate
of dental implantation. Such titanium granules are
currently commercially available as Tigran™ (http://
www.tigran.se/en/).
Evaluation of the Hypothesis
Advantages
As described in GBR, autogenous bone is easy to
be absorbed and could not stabilize blood clot
and granulation tissue to guide and induce new
bone regeneration.[15-17] This is the major drawback
of autogenous bone graft. However, it contains
lots of cytokines and bone precursor cells that are
necessary for osteogenesis, consequently promotes
bone regeneration.[4,6,7] On the other hand, titanium
is a special metal with excellent biocompatibility and
non-resorbable. Therefore, when autogenous bone is
mixed with titanium granules, they can act as stable
scaffold without being absorbed due to their close
integration with bone. However, titanium granules
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Dental Hypotheses
should be processed beforehand to form a hydrophilic
surface for blood adhering, thus stabilize blood clot and
promote formation of granulation tissue. If possible,
bone morphogenetic protein could also be added on
titanium surface to promote the integration with bone.
Furthermore, the granule maybe designed with foramen
to enhance the integration with dental implant, using
techniques of acid etching, sandblasting, coating, etc.
Bone metabolism is a dynamic equilibrium of
osteogenesis and bone desorption. A layer of
titanium oxide was found to form spontaneously
on metallic titanium surface for calcified bone
matrix deposition, constituting the basis for good
biocompatibility of dental implant. The bonetitanium integration would provide a biocompatible
surface for cell/tissue adherence and regeneration,
similar to normal healing process. In addition, the
recommendation that placement of dental implant
immediately after tooth extraction to minimize bone
loss has also verified the aforementioned theory.[1,18]
Moreover, titanium can rarely be absorbed, so the
integration between dental implant and bone is
relatively stable. Taken together, the titanium granules
with autogenous bone containing lots of bone precursor
cells and cytokines may act as various active centers for
osteogenesis and induce local new bone regeneration.
Thus, they function as a whole and prevent alveolar
bone absorption and collapse, thereby increasing the
success rate of dental implant.
Burchardt introduced the term “creeping substitution”
to describe the process of autogenous bone graft
incorporation in 1983. [19] Nowadays, creeping
substitution theory still predominates in the field of bone
grafting, that is, new bone replaces implant materials.[4]
When autogenous bone mixed with titanium granules
is implanted, titanium granules per se occupy certain
space and cannot be absorbed, thus they decrease
creeping substitution space and shorten the creeping
distance, all of which benefits bone grafting.
During bone grafting, bone tissue competes with soft
tissue for survival space.[20] The integration between
titanium and bone tissue is greater than that between
titanium and soft tissue. Therefore, after autogenous
bone mixed with titanium granules is implanted,
titanium granules have priority to integrate with bone
tissue. Thus, the implant height is maintained stable,
like controlled tissue regeneration (CTR) technique,[21-23]
and entry of soft tissue is prevented. Thereby, the
success of dental implant is guaranteed.
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Wu, et al.: Autogenous bone graft with titanium granules for dental implantation
The bone-implant integration is a complex process, in
which microenvironment around bone tissue definitely
altered. However, the mechanisms involved are poorly
understood. After implant placement, there is no
obvious distinction between oxide layer surface and
bone, even though the width of the interaction region
of implant and peri-implant bone is greater than 1 mm.
Hanawa had discovered a series of interesting alterations
when observed implants with loading in clinic.[24] The
formation of an inert titanium oxide layer, as thick as
about 2000 m was found on the implant surface 6
years after implantation. Analysis of this newly formed
layer revealed that it contains organics and inorganics
(Ca, P, S), indicating that the oxide layer on implant
surface is very sensitive to the intake and rise of these
mineral ions and can respond to them, even though it
is coated by a layer of protein. Moreover, exposure of
the pure titanium or titanium alloy surface to the blood
led to spontaneous formation of titanium phosphate
and calcified compound containing hydroxyl groups on
oxide layer surface, which suggested a reaction between
titanium and water, mineral ions, and plasma had
happened. Interestingly, it would accelerate calcium
phosphate deposition on pure titanium surface in case
of low PH at the implant area.
Therefore, the oxide layer is a dynamic system. It plays
the role of bone remodeling and forms a compatible
interface between implant and bone. The interface
may even spread to neighboring areas. Integration
process of titanium granules and new bone induced
a microenvironment in advance fitting for integration
of titanium and bone. In the later implantation,
the local environment will be more appropriate to
osseointegration. So our hypothesis is highlighted in
promoting osseointegration at microenvironment level,
leading to increasing success rate of implantation. The
characteristics of inorganic materials that undergo
surface modifications on its own surface, or so-called
physiologic camouflage to adapt to the need of body, are
very rare in other inorganic materials. The application
of titanium as graft material for bone graft not only
involves bone mass but also induces osseointegration
from the essence of bone and titanium integration,
thus allowing the new generated bone more adapted
to osseointegration.
Disadvantages
Although our hypothesis has so many aforementioned
merits, it still has some shortcomings. First, the surface
treatment of titanium granule is relatively a difficult
technology, and determination of particle size is also
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somewhat hard as we intend to find the most suitable
particle sizes.
Second, titanium granule plays an important role in our
hypothesis, but the proportion of granules in mixture is
difficult to quantify. As certain amount of bone mass is
needed in implantation, we need to find out the most
appropriate proportion.
Third, the biggest innovation of this hypothesis is
inducing proper microenvironment ahead of time,
to make newly formed bone tissue adapt better to
osseointegration. So our hypothesized method is not
suitable for immediate implant, so one must implant
bone graft first and then insert the implants.
In clinical settings, we observed that the success
rate of implantation is higher when using titanium
mesh or membrane for bone graft. So, we deduce that
our hypothesis is of great clinical significance and
expect to be of great interest for both basic and clinical
researchers.
The characteristics of inorganic materials that undergo
surface modifications on its own surface, or so-called
physiologic camouflage to adapt to the need of body, are
very rare in other inorganic materials. We carefully take
the prominent features of titanium into consideration.
Autogenous bone mixed with titanium granules can
be expected to apply as a new method for bone graft
in dental implantation. The idea could promote the
integration of bone and implant from the perspective of
microenvironment in addition to restore bone deficiency.
If applicable, it will bring new ideas and views to the
dental implants and bone graft. Furthermore, we could
try to use titanium as a carrier to restore a variety of
bone deficiency clinically. The titanium just acts as the
reinforcing steel in the steel and concrete and it has
broad prospects for application in the bone repair of
cleft palate, jaw cyst, etc.
However, there is no existence on any research on
autogenous bone mixed with titanium granules applied
to bone graft and it is just a hypothesis as stated above.
Moreover, the volume of titanium granule and the
proportion between titanium granule and autogenous
bone are needed to be discussed. To some extent
evidences from recent studies have supported our
hypotheses. Further well-designed, double-blinded,
randomized and controlled animal experiments and/or
clinical trials with larger sample size in this field are
essential to perfect our hypothesis.
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Wu, et al.: Autogenous bone graft with titanium granules for dental implantation
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Cite this article as: Wu Y, Yang Y, Zhou Y, Gu Y, Fu X. A new view on bone
graft in dental implantation: Autogenous bone mixed with titanium granules.
Dent Hypotheses 2013;4:13-6.
Source of Support: Nil, Conflict of Interest: None declared.
Jan-Mar 2013 / Vol 4 | Issue 1