Zirconium Dental Implants
Dental implants have enabled people who are missing or have lost teeth to have either a secure removable appliance(s) or permanently fixed replacement teeth rather than wearing dentures as many of their parents and grandparents did.
Titanium dental implants were first introduced nearly 40 years ago and have become fairly widely used particularly in the last couple of decades. However, with use, demand has risen from both patients and dentists for non-metallic dental implants to replace missing teeth roots for a variety or reasons including aesthetics and health concerns.
To this end, research has been feverish, however, the mouth provides a complex and challenging environment for any implanted material. Criteria include:
The ability to withstand the cyclical compressive and shearing stresses induced during chewing
A constantly wet environment
Frequent changes in temperature and pH
Resistance to surface abrasion
Stability so that the material does not degrade with age appreciably
Resistance to the actions of the microbial biofilms that form on implanted materials
Exposure to a variety of chemicals (ie: foods, drinks, mouthwashes, toothpastes, etc)
That the material not be so stiff that it stresses bone or fractures, but not so flexible that it provides inadequate support ie: that it matches the physical properties of bone and tooth as closely as possible
That the material be radio-opaque (so that it shows on x-rays)
That is has good aesthetics
That bacteria and food does not unduly accumulate upon the material and
Most importantly, the requirement that the material is biocompatible!
To this end, the spotlight over the last decade or so has fallen upon zirconium which is a grey-white transition metal or metalloid in its pure form. It belongs to the same chemical group in the periodic table as titanium which has an atomic weight of 22 with zirconium sitting directly below it with an atomic weight of 40. Zirconium also resembles titanium in its pure metallic form and the name is derived from the Arabic words zar and gun which translate as meaning 'gold'.
It is mined as zirconium silicate ore which is also known as zircon and which is found in countries such as India, Thailand, Australia and Sri Lanka. The metal zirconium is very resistant to corrosion and for this reason is often used as an alloying material.
As zirconium dioxide (ZrO2) or zirconia it is classified as a ceramic and can exist in different lattice forms when heated to high temperatures in a process known as transformation toughening. The element yttrium is added to stabilise these crystalline forms.
In one of the lattice structures, zirconium dioxide forms what is called (incorrectly) cubic zirconia - a clear synthetic gemstone used to make diamond-like jewellery. The other tetragonal crystalline form produces an opaque white zirconia which is very hard, tough and chemically resistant. This form is used in laboratory equipment, dental restorations, dental implants, ceramic knives and surgical blades, the brake pads of sports cars and as a refractory material in jet engines and the space shuttle. This form is much closer in composition to natural teeth than titanium.
A history of ceramic dental implants
Yttria stabilised zirconia has been successfully used in medical applications such as orthopaedic hip prostheses since the 1980s. And the first zirconium dental implants (Bioceram) were first introduced in the early 1980s and although these osseointegrated, the fact that they were a one-piece design meant that they had limited applications. Various improvements in chemical and surface treatments over the years have improved osseous healing.
Approximately 20 years ago, Professor Schulte from Tübingen, Germany developed implants made of aluminium oxides but these suffered quite high rates of loss and were discontinued. Then approximately 10 years ago, Professor Sandhaus from Geneva, Switzerland developed ceramic implants made of zirconium oxide.
The Paracelsus Klinik in Switzerland which is a centre for holistic medical and dental treatment started using zirconia implants ten years ago. They monitor their patients and found their results with this first generation of zirconia implants to be disappointing. However, in 2005 they started using a new generation of zirconium implants (Z-Look3-Implantat) with much more success. And since 2009 they have been using the Ziraldent and two-piece implant system, Zeramex.
Some manufacturers such as the Swedish Nobel Biocare, Swiss Z-Systems and Spanish CeraRoot come from a dental implant background, whereas others such as the US companies Zimmer and Biomet, and the Korean Acucera have a history of manufacturing orthopaedic appliances. Several zirconia dental implant systems have recently been approved for use by the FDA in the USA.
The first set of surgical instruments made from zirconium was not developed and deployed until the second half of 2005. This development means that the patient need have no contact with metals during the procedure and reduces the potential for inflammatory or immune reactions in those sensitised to metals.
The problems with titanium implants
Any implant in the body is a foreign substance and has the potential to provoke immune and autoimmune reactions. And by definition, any dental implant breaches the surface of the mouth which is heavily populated with microbes and may also allow the ingress of pathogenic species directly into the alveolar bone and body. For more on this topic, please refer to the article Dental Implants: The Pros and Cons.
In addition, all implants also form a biofilm whereby microbes grow on the implant surface under a protective covering and these biofilm infections are thought to account for 80% of human infections. See the article How Bacteria Communicate for more information.
Particular considerations in relation to the use of titanium implants include:
Allergic reactions Between 0.5% and 1% of all patients display allergic reactions to titanium implants. This figure may rise with continued exposure as titanium leaches from the implant provoking an immune response. Recent studies feature a growing number of reports of adverse reactions to all kinds of titanium implants and are a real cause for concern.
Galvanic and electrical activity Typically, titanium dental implants have several metal components which screw together with the crown or bridge being screwed or cemented into place on top. This allows for angulation changes between the angle at which the (possibly receded) bone permits placement of the implant and the angle required for function and aesthetics of the crown or bridge. The presence of any metal in the mouth and particularly the combination of metals that often occurs in routine dentistry in the presence of electrolytic saliva generates a voltage. This electrical activity causes the autonomic nervous system (ANS) to become stressed and often manifests as some kind of impairment that may only be detected years later. In addition, the currents produced are frequently much greater than those employed by the nervous system and may disrupt neuron signalling.
Metallosis This term refers to the release of metal ions from the implant into the surrounding tissues (regional stress) and the associated energy meridian (meridian stress). This usually affects the soft tissues most, however titanium ions have been found in the blood, jaw, lymphatic nodes, lung and spleen. In animal experiments, titanium ions have been found in an area of approximately 3 cm surrounding the implant. Sometimes the presence of titanium in the tissues may result in pain in the region or the implant area. One animal study showed pathological changes in the spleen within just 72 hours of exposure to titanium.
Formation of titanium oxides Titanium oxides form on the surface of the titanium implants and this is thought to have several effects. First, these titanium oxides interfere with phagocytosis (immune cells which engulf foreign particles) and osteoblast function (the cells which synthesise bone). These effects are thought to result in the prevention of proper in-growth and approximation of bone to the implant. These metal oxides also cause free radical damage in the region.
Calcium/titanium interactions In addition to inhibition of osteoblast function it appears that the body may 'mistake' titanium ions (Ti2+) for calcium ions (Ca2+) which carry the same charge and are similar having approximately the same atomic weight and size. This results in the tissues surrounding the implant becoming calcium deficient.
Titanium and fluorine Any exposure to the highly reactive halogen, fluorine, either through the water supply or toothpaste causes a reaction between the fluorine and titanium which amplifies the toxic effects of fluorine. For more on this topic refer to the article The Health Risks of Fluoride.
Blockage of meridian flows Acupuncturists use metal needles inserted temporarily at strategic points on acupuncture meridians to redistribute the body's energies. The permanent insertion of a metal implant on a meridian (all the teeth or sockets have energy meridians flowing through them) will cause unintended blockage or redirection of energy flows. The consequences for each individual will differ depending upon their general constitution and which meridian(s) is/are affected. For more information about meridians please refer to the articles Acupuncture Meridians: The Proof and Meridians Reference.
Electromagnetic antennae Reports from the use of cephalic titanium implants and some dentists suggest that titanium implants act as antennae for electromagnetic radiation. Each metal has an oscillation which varies between 2 and 5 gigahertz which can resonate with radio waves and magnetic fields of the same frequency. The antennae used in cell phones are frequently made of titanium because of their ability to resonate with the near-microwave radiation used in mobile phone transmissions. This too may put the autonomic nervous system (ANS) and endocrine systems into a long-term stress state causing metabolic disorders, disrupting blood flow and nerve conduction, and may particularly cause insomnia. Refer to the podcast Are the Metals in your Mouth Acting as Antennae? for more on this topic.
Lymphocyte transformation This is where either continuous or a second exposure to an antigen causes lymphocytes to transform, increasing in size, proliferating and becoming blastic cells.
Temperature conduction Unlike teeth, titanium transmits heat from foods and drinks to the bone and surrounding tissues and this may cause problems with osseointegration.
Gum aesthetics A prime consideration in the aesthetic result achieved with implant restorations is the aesthetics of the gums or so called 'red aesthetics'. With titanium implants the metal can shine through the bone and gum in front teeth producing a dark shadow and with any gum recession the metal implant can become exposed which can be very unsightly and hard to remedy. Also, as many titanium implants are buried while bony healing takes place and are later uncovered and restored there can be loss of tissue in general and the papillae in particular (the gingival crests between the teeth) which can produce ugly black triangles between the teeth when restored.
Cytotoxicity Titanium is cytotoxic with smaller particles proving more toxic than larger ones. This can lead to induced cell death (apoptosis) and also to an increase in the level of tumour suppressor proteins. In addition, increases in certain interleukins have been observed in orthopaedic patients with titanium hip prostheses. Interleukins are a group of signalling molecules deployed by the immune system which control white blood cell activity. Dr Thomas Rau, the Director of the Paracelsus Clinic has concluded that in their experience 15% of all those with titanium dental implants will go on to develop auto-immune diseases within 2-3 years of implant placement.
DNA damage Several studies suggest that titanium implants cause DNA damage or upregulation of a number of genes compared to bony healing. One study found that the genetic mutations induced by exposure to particulate titanium were comparable to those found with exposure to the heavy metals, cadmium and nickel, and to low-dose radiation.
Bony healing A recognised issue with titanium implants is that there can be early bone resorption shortly after implant placement.
Finally, there is also a danger to dentists, chair-side and laboratory staff who inhale titanium particles whilst working with this material.
The advantages of zirconia implants
The advantages offered by zirconia dental implants over titanium dental implants include:
Metal-free An increasing number of biological dentists are recognising the benefits of practising entirely metal-free dentistry upon the health of their patients. No long-term data on the success of zirconia dental implants exists since they have only been in use primarily in mainland Europe for 10 years. However, zirconium has been used extensively for orthopaedic implants for several decades and this data indicates that they are more biocompatible than titanium. Some authorities have expressed concern that there may be an issue with the zirconia implants degrading from a tetragonal crystalline form to a monoclonal form with age.
No allergic reactions There are no known allergic reactions to zirconium ceramic.
Is bio-inert In contrast to titanium which has free electrons, zirconium dioxide has proven to be totally bio-inert. This means that zirconia does not form oxides, interact with fluoride or deplete calcium in the way that titanium does. Testing before and after zirconia dental implant placement using several urine, blood and lymphocyte transformation tests indicates that they are well tolerated by the body.
Electrically and galvanically neutral The lack of free electrons also means that zirconia is galvanically and electrically neutral and so will not act as antennae for EM radiation or create electroacupuncture effects on the energy meridians.
No temperature conduction Zirconium is also a very poor conductor of temperature which will not transmit heat or cold from the mouth to the surrounding bone.
Promotes bone growth Several studies have now shown that bone is deposited at the surface of the zirconium implant and even that new bone growth is promoted. This can result in 'peaking' where bone is seen to form on x-ray rather than being lost as sometimes happens with titanium implants. The surface charge of zirconium oxide is thought to account for this effect along with various surface finishes which have also been shown to aid osseointegration.
The images below are courtesy of Depprich et al, Head & Face Medicine, 2008, 4:30. As can be seen from these microscopic sections of bone adjacent to both titanium and zirconia implants there appears to be good bony healing with the tissue approximating the implant surface in both cases. In this study, the zirconia showed slightly less bony contact than the titanium, although this was not statistically significant. Healing around zirconia implants takes slightly longer than with titanium.
Promotes gingival health Animal experiments and observations in humans support the idea that the gum tissue regenerates around zirconium implants in a way that does not happen with either natural teeth or titanium implants. However, these positive soft tissue responses tend only to occur when other dental metals have been removed.
Hygienic Ceramic implants and crowns retain less plaque and calculus than titanium implants and even less than natural teeth. In addition, the one-piece design of many zirconia implants means that there are no margins where component parts meet under the gum and this also leads to better gingival health.
No blockage of meridian flows Energy meridian flows can be measured using electrical skin resistance (EAV) at specific acupoints and the readings may serve to indicate both the energy flows in any given meridian and the overall health of the individual's energy system. Tests using EAV before and after implant placement have shown zirconium to be well tolerated by the energy system. And anecdotal reports are that many people have experienced improvements in chronic health conditions after the extraction of root-filled and infected teeth and placement of zirconium implants.
Aesthetics An advantage of zirconium implants is that they are white which means that there is no ugly shadowing of the gums in front teeth and that the metal components are not exposed with any gum recession.
Cost It is approximately ten times more costly to produce zirconia than titanium implants since the ceramic has to be worked using diamond instruments. However, due to the simplified one-piece design and procedure the total costs are comparable to, or less than, those for titanium implant retained restorations.
Cytotoxicity The news about zirconia isn't all good as all implanted materials have the potential to cause an immune response and there is some evidence that zirconium dioxide particles can induce apoptosis (cell death), and cause increases in levels of tumour suppressor proteins. Some experts such as Dr Hal Huggins maintain that all implanted xenomaterials have the potential to cause immune system breakdown and the only thing in question is the timeframe taken for this to occur. It is also, according to Dr Huggins exceedingly hard for people so affected to recover their health.
In addition to those properties listed above, the special considerations of the potential radioactivity and physical properties of zirconia implants are addressed in more detail below.
Zirconia implants and radioactivity
One of the risks posed by the medical and dental use of zirconia implants is that of radioactivity since zirconium silicate ore is often contaminated with radioactive isotopes including radium (226Ra) and thorium (228Th). For this reason only the purer ores from Sri Lanka can be used for zirconia dental implants and all manufacturers are required to produce a declaration of radioactivity for all their zirconium based dental products.
The concern is that radioactivity from the implants may lead to oral or other cancers over time. However, to put the risk in context, the radioactivity of zirconium is equivalent to that of the alumina that has been used in medical orthopaedic appliances and dental ceramics and also that of the cobalt chrome prostheses used in orthopaedics. There is also the issue that much of the radiation is absorbed by the implant itself with only the surface emissions posing a risk to the individual.
The radioactivity of zirconium is also less than that measured for samples of water, milk, vegetables and meat. It is also well within European radiation limits specified for general external exposure of the human body and also for local internal exposure of organs and tissue, and was found to be no more than the ambient radiation of the surroundings in one study. The zirconia powders available too such as those from Nilcra Ceramics have been measured by the Australian Radiation Laboratory and found to be well below acceptable limits.
The physical properties of zirconia implants
The physical stresses placed upon implants are considerable - and are different for the back teeth which bear the heavy compressive loads of chewing and for the front teeth which bear oblique shearing loads and which guide the jaws as they open and close (known as anterior guidance).
Natural teeth come suspended in a periodontal membrane which allows for some tooth mobility and bone too is somewhat flexible. The lower jaw bends slightly on opening and closing the mouth and the sutures in the bones of the skull and jaws also flex a little. In contrast, implants are fixed rigidly to the bone.
The simple fact is that no material will ever marry the flexibility and stiffness of tooth and bone as well as the real thing which has been created embryologically as a single functional unit. However, the 1 year success rate of zirconia implants is 98% and the 5 year success rate is 95%.
The one-piece design of zirconia implants results in significantly higher stability and the bending strength of some brands of zirconia implants has been shown to be 4 times that of titanium (Z-Look3-implants 1500 MPA compared to 400 MPA for titanium). However, the newer zirconia implants have a flexural strength and fracture toughness almost twice as high as that of alumina.
The earlier forms of zirconia implants were prone to fracture. There are still reports about zirconia implants fracturing especially in dense bone sites when being torqued into position. However, good quality control by the manufacturer, careful surgical technique and avoiding their use in areas of dense bone are thought to have resolved this issue.
Other zirconia dental implant systems have been developed which employ CAD/CAM technology to machine a physiological tooth shape and insert it directly into the extraction socket.
Immediate placement of dental implants
The concept of immediate implantation (ie: extracting the tooth and placing the implant at the same visit) is designed to preserve all the supporting soft and hard tissues.
With traditional techniques involving extracting the tooth and waiting for bony healing for several months before burying the implant in the bone whilst it osseointegrates for a few more months there can be rapid loss of both height and width of the supporting bone and loss of the papillae (the gum crests between the teeth). This can present challenges achieving an aesthetic result when it comes to the gum contours especially in highly visible areas leading to the appearance of ugly 'black triangles' between the teeth.
Immediate implantation is not indicated in all cases and is particularly not advisable in the presence of infection. Sometimes too, immediate implant placement may require augmentation of bone using bone substitutes and/or absorbable membranes. Typically zirconia implants are placed at one appointment and then left to integrate into the bone for between 3 and 6 months protected by a guard rail or provisional denture while they osseointegrate.
Fairly frequently, the teeth being extracted have reached the end of their restorable life and may be brittle due to being heavily filled, root-filled and possibly having crowns with posts. Sometimes these teeth are hard to remove without damage to the adjacent area (ie: a 'surgical' extraction) and this can rule out immediate placement too.
With some of these immediate placement implant systems the periodontal membrane and the bone surrounding the extracted tooth are removed as the bone is prepared to receive the implant. This overcomes the issues posed by retaining the periodontal membrane which can lead to the formation of a jaw cavitations.
This issue is not widely accepted by dentists, but may account for some of the failures associated with dental implants as they are placed in bony sites that have not fully healed. For more on this topic refer to the article Dental Cavitations.
Health considerations in relation to dental implants
Of course, all the usual provisos that relate to implant treatment apply with zirconia implants. Considerations include whether it is technically possible (ie: whether there is sufficient quality and quantity of bone, etc), whether the patient can afford treatment, and whether they are motivated to go through the procedures involved and can maintain adequate standards of oral hygiene. In addition, the long-term viability of dental implants is strongly influenced by habits such as smoking, drinking alcohol and taking drugs.
In addition, there are considerations relating to health and it is not considered advisable to place ceramic implants in patients who are in a poor state of health due to autoimmune diseases, osteoporosis, advanced rheumatism, cancer, and inflammatory conditions, in addition to some mental and psychiatric disorders.
Clinics such as the Paracelsus Klinik conduct a general medical examination and run comprehensive urine and blood tests prior to treatment for parameters such as hormonal status, osteoporosis, immunoglobulin E (indicates allergy) and inflammation in addition to assessing the patient's energetic status using electroacupuncture. In addition, all materials are tested for biocompatibility prior to implant placement. And any existing medical conditions are treated prior to implant placement and vitamins, minerals and amino acids taken prior to, during and after implant placement may aid healing.
When it comes to the future of replacing missing teeth, the prospect of bioengineering tissue cultures using the patient's stem cells on collagen matrices is looking increasingly hopeful. However, the best strategy has to be to prevent dental disease where possible by maintaining a clean mouth and avoiding processed foods and sugar that are known to cause decay. In relation to teeth the old adage that "An ounce of prevention is worth a pound of cure" really does hold true.