the fixation of dental implants
TRANSCRIPT
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The Fixation of Dental
Implants
4B16 Biomechanics of Tissues and Implants
Tom Eastaway (07485476)
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Introduction
Teeth are primarily lost as a result of gum disease (OCDDI). Other causes include injury,
congenital defects and cavities. Missing teeth should be replaced with prosthetics for both
health and cosmetic reasons. A missing tooth can leave the gum and jaw bone vulnerable todamage, and can cause difficulties in biting and chewing which may eventually lead to
malnutrition. A visible gap in teeth may also cause people to become self -conscious about
smiling or talking (DiMatteo, 2011). A missing tooth can also cause the adjacent teeth to
shift and make them more susceptible to damage and loss (OCDDI).
An implanted replacement tooth consists of an implant which is set into the jaw bone
(endosseous) and an external crown attached to it (Linkow, 1970). An endosseous dental
implant is a screw, typically metal, which acts as an artificial root. Implants are widely seen
as being preferable to dentures since they do not slip, click, or have to be removed for
cleaning.
In this report the current endosseous dental implant practice is described, and the merits of
this technique and potential improvements are discussed.
Dental Implantology Background
Modern dental implants are typically made of titanium (DiMatteo, 2011). Most metals
corrode in the presence of bodily fluids and tissue, releasing ions which may have negative
impacts on health or lead to implant rejection. Titanium is recognised as being completelyimmune to corrosion in the body, as are many titanium alloys (AZOM, 2003). Combined with
its high strength-to-weight ratio, among other factors, this has led to titanium being the
material of choice for dental implants for several years.
Early designs of endosseous dental implants resembled the shape of a natural tooth root,
since it was assumed that this design would be the most effective (Linkow, 1970). However
it is now known that a screw is a more effective shape since it provides a grip onto which
bone grows (osseointegration). The concept of osseointegration was first proposed by
Swedish orthopaedic surgeon Per-Ingvar Brånemark in the 1960s (Depprich et al., 2008).
Metallic implants must be rigidly fixed into living bone, with direct contact between t hesurface of the implant and the bone itself (i.e. with no intermediate soft -tissue interface).
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Current Typical Implantation Procedure
The process of dental implantation begins with an assessment of the viability of the patient
factors such as age (bones not yet being fully developed) and whether or not the patient
smokes are taken into account, and an X-ray and CT scan are performed. In instances of insufficient bone or gum tissue a separate graft procedure may be required before
implantation can take place (DiMatteo, 2011).
The implantation of the endosseous implant is done in a single sitting, excluding t he
addition of a crown which is done after successful osseointegration is observed (after three
to six months). After the administration of either a local anaesthetic or a sedative
(DiMatteo, 2011), the first step of a dental implantation procedure is the drilling of a small -
diameter pilot hole in the jaw bone using a bur (a hard metal alloy dental drill bit) or
trephine (a small crown saw) (Linkow, 1970). Particular care is required during pilot hole
drilling since inaccuracy can potentially damage vital structures such as nerves in the bone.Surgical guides based on CT scans are often made to aid oral surgeons (DiMatteo, 2011).
The pilot hole is gradually widened using progressively wider helical burs (Linkow, 1970).
The implant screw is placed in the widened hole and to aid recovery and osseointegration
either a healing cap (a protective cover screw fitting) or an abutment and a temporary
crown fitting. The gum is sutured over the healing cap, usually using self-dissolving stitches
(Dental Health Directory). If the abutment is not placed during the initial procedure, it is
placed after healing provided that the implant is successful (DiMatteo, 2011). At this time
the permanent crown is made from an impression, shaded to match the existing teeth and
attached to the abutment (Dental Health Directory).
Emerging Practices and Technologies
Image-Guided Implant P lacement
In order to overcome the difficulty of drilling accurate pilot holes, an emerging practice is to
use image-guided implant placement technology, of which two emerging types exist. The
first uses computer-designed surgical splints made using sterolithography (the fabrication of
solid objects by solidifying layers of UV -curable resin on top of one another). These custom-designed splints greatly reduce the duration of an operation, but have the disadvantage that
they cannot be adjusted during the operation. The second technology is real -time image-
guided navigation. This gives the oral surgeon a much better view of the procedure and
allows adjustments to be made during the procedure if the implant position deviates from
the computer-planned position. However the cost of the equipment required for real -time
navigation is often prohibitive (Cheung, 2007).
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Implant Material
Research into materials for implants is in progress, with two main aims: Firstly to improve
implant success rates by maximising the effectiveness of osseointegration, and secondly to
give the appearance of a natural bone colour and translucency in case any part of the
implant below the crown is visibly exposed.
Titanium and its alloys are effective osseointegrators since a passive oxide layer forms on
the surface of the implant. This layer protects the implant from further oxidation (Castilho,
2006) and creates a surface topography which has proven to give an osseointegration
success rate of over 95% in recent years (Cheung, 2007). However the disadvantage of
titanium is that its appearance does not match that of teeth. Zirconia (also known as
zirconium oxide or zirconium dioxide, ZrO 2) is an alternative material viable for use in dental
implants, since it has high fracture toughness, good chemical resistance and is also
biocompatible (New Dental Implants, 2009) zirconia has been shown good results for
artificial ball heads in total hip replacements (Depprich et al., 2008). It may be preferable for
patients because its opaque white colour is virtually indistinguishable from the colour of
teeth, and because some patients may feel more comfortable with a ceramic implant than
with a metal implant (New Dental Implants, 2009).
A study by Depprich et al. (2008) comparing the osseointegration effectiveness of titanium
and zirconia implants found that bone-to-implant contact was slightly better for titanium
implants after 1, 4 and 12 weeks, but concluded that the difference was not statistically
significant (Depprich et al., 2008).
Single-Stage Treatment
It is now possible for placement of the implant and of the artificial crown to be performed in
a single sitting. In the past it was necessary to fit the implant and wait for osseointegration
to occur, before attaching the abutment and crown at a later date (after up to six months).
However the advent of the use of 3D CT scans in implantology has allowed the development
of surgical protocols and products (such as Nobel Biocares Immediate Function) which suit
all indications and bone types. This flexibility allows oral surgeons to fit the implant and the
crown in the same visit, giving patients functioning teeth immediately (ClearChoice).
Tissue Engineering An Alternative to Implants
Dental implants can fail over time due to their inability to remodel with their surr oundings,
as can be the case with all synthetic implants (Rahaman & Mao, 2005). However, alternative
to artificial dental implants may be possible in the very near future. A new approach under
investigation is to use mesenchymal stem cells, harvested from deciduous teeth, which may
be implanted in vivo with a temporary biocompatible hydrogel scaffold. Studies have shown
successful growth of teeth in immunodeficient mice and also in an adult human tooth
socket (Mao, 2008).
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The use of stem cells as a replacement has the potential not only to eliminate some of the
factors which lead to failure of implants, but also to improve patients viability for tooth
restoration, since a similar approach may be adopted as an alternative to bone and tissue
grafting in patients with insufficient periodontal tissue for tooth restoration.
Conclusion
Dental implants have reached a success rate of up to 95%. Possible reasons for failure
include insufficient bone or tissue mass at the implant site and inaccurate drilling during the
implantation procedure. In some cases grafting can be performed to repair the tissue at the
implant site, although this requires an extra procedure. Recent developments in 3D CT
scanning are helping to overcome the problems of insufficient tissue and drilling difficulties.
Ideally all dental implant procedures should use real -time imaging technology for surgical
guidance, but this is not possible due to the cost of the equipment required.
Implant material research is generally geared towards the use of zirconia. Since this is a
relatively new material in dental implants it may be necessary to further investigate its long-
term effectiveness. The only apparent advantage of the material is its colour, since its
performance over 12 weeks has been shown to be roughly equal to that of titanium and
titanium alloys. Pending further research, it appears that titanium is an adequate implant
material, since the colour of the implant itself should not be visible.
The established method of placing an implant and waiting for up to six months for
osseointegration is gradually being replaced by single-stage treatment which seems to
benefit the patient in terms of comfort, practicality and cost. Given current implant success
rates it appears to make sense in most cases to perform this type of procedure, provided
that the patient is made aware of the risks of failure.
In the coming years we can expect a paradigm shift in the treatment of tooth loss as
research progresses in regeneration by stem cell growth as an alternative to artificial
replacement. In the mean time advances in imaging and developments in more flexible
implant products promise the best chances of improving implant success rates.
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Bibliography
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of Materials: http://www.azom.com/Details.asp?ArticleID=1794
Castilho. (2006). Surface Characterization of Titanium Based Dental Implants. Brazilian Journal of
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Cheung. (2007). Advances in Dental Implantology. T he Hong Kong Medical Diary: Dental Bulletin Vol.
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Dental Health Directory. (n.d.). Dental Implants - T he Basic Procedure. Retrieved March 2011, from
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Appendices
Titanium implant screw. (Brånemark et al., 1983)
Artists impression of complete implant assembly (ClearChoice)
Implant planning on maxilla using Nobel Guide software (Cheung, 2007)