Dental Implants

Dental implants are used to replace missing teeth with artificial teeth that look and function much like the real thing. Dental implants are particularly useful when the adjacent teeth may be in good condition so that preparing these teeth for a bridge is not desirable, when security of the prosthesis is paramount (eg: public speakers) or for helping to retain removable dentures in difficult circumstances.

People sometimes confuse post crowns with implants, but they are quite different. A post crown is used where the root of the tooth has been retained by doing a root canal treatment, but where little or no tooth may be available above gum level. So a post is permanently cemented into a retained root which is held in place by the original periodontal membrane and the part of the post above gum level acts as a ‘core’ on to which the crown or bridge restoration can then be cemented.

With an implant the root or roots of the teeth or tooth have been extracted (or the tooth was developmentally absent) and the root of the tooth is effectively replaced with a metal screw inserted directly into the jawbone. This relies upon successful biointegration of the implant into the surrounding bone (known as osseointegration).

There is also a major cost differential with implant surgery usually involving several appointments usually spread out over a period of 3-9 months and the implants and other fixtures typically being quite expensive and the procedure quite involved.

Implants can either be used to support permanent prostheses such as crowns or bridges or to act as ‘clips’ to help retain removable partial or complete dentures securely. In particular lower full dentures are notoriously problematic as there may be very little bony ridge available to support the denture and all the adjacent structures (tongue, lips, and cheeks) apply pressures that tend to dislodge the denture.

The processes involved in provision of implant prostheses

Initial assessments will usually include a panoramic X-ray and having impressions taken to make models made of the mouth. There should be a full discussion of the procedure and, if necessary, further X-ray investigations may be required to assess bone quality and quantity.

Extraction of the tooth (if necessary) may be followed by immediate placement of the implant or it may be considered best (especially if the tooth was infected) to allow the socket some initial healing before placing the implant. This may be done under general anaesthesia if treatment is extensive, but is often done under local anaesthesia possibly in combination with intravenous sedation if required. Typically future appointments will only require a local anaesthetic unless the patient is extremely anxious.

There may be some bruising and swelling after the implant is placed. At this stage there will be stitches that may need removing after a week or so and a soft diet is advisable during initial healing.

A protective ‘cap’ may be visible and a temporary replacement tooth may or may not have been provided while the implant integrates into the bone. There are usually several months between this initial placement and any further work.

Once the dentist is confident that the implant has successfully osseointegrated they will uncover the cap surgically (if necessary) and place what is known as an abutment into the implant. This will support the permanent restoration and impressions are usually taken and sent to the laboratory for the permanent restoration to be fabricated. This may happen over two or three appointments.

Finally, the crown or bridge is then checked and cemented or screwed into place at the next visit – although some implant systems have a friction fit.

Sometimes the abutment is integral to the implant which negates the need for an extra appointment, but also means that there is a visible metal stump while the implant integrates.

Some dentists provide same-day implants and restorations, but these tend to be less successful and there is also some difficulty controlling the aesthetics of the gum level. This approach tends to provide a tooth for show rather than function as the bite is deliberately relieved to allow the implant to osseointegrate.

dental implant

IMPLANT COMPONENTS AND IMPLANT IN SITU

Considerations when considering implant placement

The factors that the dentist should be assessing as likely to affect the outcome of placing an implant prosthesis include:

  • General health. Firstly, the dentist may need to provide antibiotic cover for some conditions during surgery. And secondly they need to be fully informed about pre-existing health conditions that may affect the outcome such as poorly controlled diabetes or high blood pressure. Any other recent or current health issues or treatments eg: radiotherapy or other surgery may also influence the timing and advisability of treatment.
  • Any prescription or over-the-counter pharmaceuticals that may influence treatment – particularly steroid therapy.
  • The ability and willingness of the patient to pay for treatment.
  • The motivation and ability to endure some fairly arduous treatment and to attend several dental appointments over a period of months.
  • The ability and willingness to maintain and care for the implant prosthesis once it is in place.
  • A successful outcome is also highly dependent upon the status of the rest of the mouth so that a sixteen year old who has lost a tooth in an accident, but has an otherwise healthy mouth should be assured of a good result in the right hands. However (and more often the case), a middle-aged or elderly patient with health problems who smokes, is casual about oral hygiene and has moderately advanced gum disease might be far less guaranteed a successful outcome. Pre-existing periodontal problems may need to be addressed first in order to stabilise the condition in the rest of the mouth before considering placement of an implant-retained prosthesis.
  • Current or chronic stress can profoundly affect the ability to heal.
  • Any particular dental anxieties or phobias that might affect treatment.
  • Whether heavy drinking, smoking or taking recreational drugs may affect the outcome.
  • Nutritional status also influences the ability of the bone to heal.
  • Last, but not least, the quality and quantity of bone available for implant placement. If a tooth was lost after chronic periodontal disease or required a surgical extraction then the amount of bone present may be compromised. This also depends upon how long ago the tooth being replaced was removed since the bone rapidly atrophies when it no longer has to work to support the teeth. In some cases it can become blade-like underneath the gum. Another issue is that the bone quality in the upper jaw tends to be less dense that that in the lower jaw and the depth of bone available may also be seriously compromised by the presence of the maxillary sinuses and the floor of the nose.

Bone grafting and implants

Bone grafts may be indicated if there isn’t enough bone or your bone is too soft to support an implant. Bone grafts can either be from an extraction site, or other body part such as the hip or skull (autologous), from a cadaveric human bone bank (allograft), from another species eg: cow (xenograft), or synthetic (often made of hydroxyapatite or other naturally occurring and biocompatible substances) with similar mechanical properties to bone. Most bone grafts act as a scaffold and are resorbed and replaced as the natural bone heals over a period of months.

Another option is the use of Goretex membranes which work to temporarily hold the soft tissue back and allow bony healing to take place and these membranes are later removed. Such membranes can be placed across the mouth of an extraction site for example and may or may not be used in combination with bone grafting. This procedure is designed to encourage bone growth and is called guided tissue regeneration (GTR).

With implant surgery great care is usually taken to wash and cool the surgical site and to use very slowly rotating drills to preserve the viability of the adjacent bone (unlike most orthopaedic surgery). This is key to obtaining osseointegration of the implant.

The risks of implant surgery

The recognised risks associated with implant placement include:

  • The potential for local or systemic infections including bacterial endocarditis (an infection that affects the heart valves)
  • Damage to an adjacent nerve which can cause pain, numbness or tingling in the teeth, gums, lips or chin
  • Damage to adjacent teeth if the implant is not angled correctly at insertion
  • Damage to adjacent blood vessels causing haemorrhage and bruising
  • Unintentional perforation of the floor of the nose or the maxillary sinuses (in the cheeks)
  • Inevitable temporary swelling or bruising of your gums and face after implant placement
  • Possible persistent pain at the implant site
  • Possible chronic inflammation of the gum around the implant known as hyperplasia which can be unsightly
  • Local bone loss around the implant potentially leading to failure or the need to surgically remove the implant

Materials used for implant prostheses

Most dental implants are either made out of pure titanium or a titanium alloy although some have hydroxyapatite coatings. There are 38 different grades of titanium alloy, with Grades 1- 4 being considered ‘pure’ and Grade 5 which contains approximately 6% aluminium, 4% vanadium, 0.25% iron and 0.2% oxygen most commonly being used for medical and dental applications.

Titanium is used for dental implants and orthopaedic applications (pins, screws, plates, hip replacements, etc) because it has several physical properties that make it the most suitable option. These include being strong, corrosion resistant, non-magnetic (this means patients do not set off scanners and can safely submit to magnetic resonance imaging), and a poor conductor of heat and electricity. And although titanium is twice as stiff as bone it is still a better match than most other materials.

The surface of the titanium has usually been prepared using a high-temperature plasma arc which removes the surface atoms, thus exposing fresh titanium that is instantly oxidised.

At our current level of understanding, titanium appears to be non-toxic. In fact, we are estimated to consume 0.8 milligrams of titanium every day from plants which mostly contain about 2 parts per million of titanium and this mostly passes through the body without being absorbed.

“Implants are made of biologically compatible materials which have undergone extensive testing over a period of several years. Since these materials are largely metals such as titanium, and have never been living tissue, there is no likelihood of causing an antigen-antibody response which could cause rejection similar to that which sometime occurs with heart and kidney transplants.”

American Academy of Implant Prosthodontists

However, this statement from the American Academy of Implant Prosthodontists either deliberately sidesteps or overlooks the health issues that metals can pose to the body.

There are also no reports of contact allergies with titanium, unlike most metals. And whilst some materials are regarded as biocompatible (ie: compatible with living tissue and unlikely to be rejected), titanium is actually classified as bioinductive which means that the cells of the body appear to embrace it. See the diagram below of the intimate connection between the titanium surface and a bone cell (osteocyte). The reason for this is not understood.

AN OSTEOCYTE ON TITANIUM

The abutments may be made of a variety of material including titanium, gold alloys or zirconia and the substructures for the crown and bridge prosthesis may also be titanium, a metal alloy or all ceramic (eg: alumina, zirconia).

Continued in Potential Issues With Dental Implants



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