Dental Implants: Pros and Cons
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.
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, MELISA (Memory Lymphocyte Immuno-Stimulation Assay) testing reveals titanium to be the third most common metal allergy detected amongst the samples submitted. 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. The reason for this is not understood.
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).
Potential issues with dental implants
Other, less well recognised issues when considering implant-retained prostheses include:
Synthetic bone grafts These are foreign materials made of ceramics such as calcium phosphates, and calcium sulphate that may or may not have been treated with a growth factor such as strontium which appears to help induce bone growth. By definition these materials do not belong in the human body although they are resorbed and merely act as a temporary scaffold for the bone to grow around.
Xenografts and human bone grafts These are either bone grafts from another species (xenograft) or a human cadaver and whilst the bone has often been sterilised and desiccated, the potential may still exist for transmission of an infection or DNA.
Autologous bone grafts There is no issue with infection or rejection since the bone is grafted from the same individual, but often the donor site can be very sore - especially in the case of taking a graft from the hip crest.
Mechanical failures Bone and teeth bend and implants and metal prosthesis don't as a rule. So when a prosthesis is bridging a large span, and especially if it is across the midline (where there is a flexible suture in the bone) this may prove to be an issue which may ultimately cause failure of the prosthesis or supporting implants.
Smoking This is both a greater risk factor for tooth loss from periodontal disease and for implant failure. Smokers are much more likely to get post-surgical infections and heal more slowly. According to one study the failure rate for implants in smokers was over ten times that in non-smokers (Feb 2007 Journal of Periodontology). Smokers are strongly advised to cut out or reduce smoking prior to, during and after the implant surgery to improve the chances of success.
Implant failure The implant may fracture or fail to integrate with the surrounding bone - or bone may subsequently be lost after initial osseointegration. With some implant failures, you can have the implant removed, wait for some bony healing and try again. Sometimes though the failure can be pretty catastrophic if the implant itself fractures and significant bone may be lost in the surgical removal of the remaining fragment.
Infections These can either be local to the implant possibly resulting in ultimate failure or systemic causing problems in other organs or systems. Infection is the number one cause for dental implant failure.
Cavitations The problem of cavitations ie: infected and necrotic holes that form in the jawbone after extraction is not generally recognised by most dentists and may account for some of the implant failures as implants may be being placed into an undetected pre-existing cavitation.
Galvanic currents All alloys are mixtures of metals of different reactivities, which by definition tend to create galvanic or electrical currents. The various different metals used for the implant, abutment and restoration especially when combined with the other metals already present in the mouth may create complex electrical activity within the mouth which may disrupt neuron activity in the adjacent brain and endocrine organs.
Toxic metals Some of the metals used in some of the alloys eg: aluminium are known to at least have the potential to be toxic.
Meridian blockage By and large allopathic medicine and dentistry does not recognise the presence of the energy meridians through which life force energy or Chi circulates. All the meridians pass through teeth and their sockets and placing any metal or combination of metals in the path of a meridian might cause a blockage which may cause health issues at remote sites that may never be connected to the initiating factor. For this reason, some holistic practitioners think that there is no place at all for implanting metals into the body either in medicine or dentistry.
Open access With teeth there is a periodontal membrane which acts as an interface between the tooth and the jaw bone and which is policed by the cells of the immune system. With implants there is no such structure and there is essentially just a cuff of gum overlying the jawbone so that this region may effectively act as a route of ingress into the body.
Scar tissue Scar tissue is created not only at the implant site, but also at any donor bone graft site. Scars may have a long-term detrimental effect on health as outlined in Book Review: Doctors Are More Harmful Than Germs.
There is no doubt that - in the hands of a practitioner who is skilled and knowledgeable - implants can be successful and transform some people's quality of life. However, when they go wrong or are done by someone with inadequate experience or knowledge the consequences can also be pretty serious and expensive to correct.
It is important to be fully informed when making decisions that can potentially affect not only your dental health, but your general health too. And elective surgery is definitely not the place to cut corners. Remember that, in the words of the old adage:
"You may not always get what you pay for, but you always pay for what you get."