the fixation of dental implants

8/7/2019 The Fixation of Dental Implants

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The Fixation of Dental

Implants

4B16 Biomechanics of Tissues and Implants

Tom Eastaway (07485476)



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).



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).



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).



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.



Bibliography

AZOM. (2003, 1 11). T itanium Alloys in Medical Applications. Retrieved March 2011, from The A to Z

of Materials: http://www.azom.com/Details.asp?ArticleID=1794

Castilho. (2006). Surface Characterization of Titanium Based Dental Implants. Brazilian Journal of

Physics Vol. 36, Issue 3B .

Cheung. (2007). Advances in Dental Implantology. T he Hong Kong Medical Diary: Dental Bulletin Vol.

12, Issue 10 .

ClearChoice. (n.d.). Advances in Implant Dentistry . Retrieved March 2011, from ClearChoice Dental

Implant Centers: http://www.clearchoice.com/understanding-dental-implants/advances-in-dental-

implant-technology.html

Dental Health Directory. (n.d.). Dental Implants - T he Basic Procedure. Retrieved March 2011, from

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DiMatteo. (2011, 3 23). Dental Implants: T ooth Implant Procedure and Recovery Information.

Retrieved March 2011, from Consumer Guide to Dentistry:

http://www.yourdentistryguide.com/implants/

Linkow. (1970). T heories and T echniques of Oral Implantology Vol. 1. St Louis: The C. V. Mosby

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Mao. (2008). Stem Cells and the Future of Dental Care. New York State Dental Journal .

New Dental Implants. (2009). Zirconia Dental Implants: Is Ceramic Better than Metal? Retrieved from

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http://www.orlandodenturesandimplants.com/causes-orlando-tooth-loss

Rahaman & Mao. (2005). Stem cell-based composite tissue constructs for regenerative medicine.

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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)

the fixation of dental implants

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