Dental implantology. Glossary
A dental implant is a “root” device, usually made of titanium, used in dentistry to support restorations that resemble a tooth or group of teeth to replace missing teeth.
In 1952 the Swedish orthopedic surgeon, P I Brånemark, was interested in studying bone healing and regeneration, and adopted the Cambridge designed ‘rabbit ear chamber’ for use in the rabbit femur. Following several months of study he attempted to retrieve these expensive chambers from the rabbits and found that he was unable to remove them. Per Brånemark observed that bone had grown into such close proximity with the titanium that it effectively adhered to the metal. Brånemark carried out many further studies into this phenomenon, using both animal and human subjects, which all confirmed this unique property of titanium.
Although Brånemark had originally considered that the first work should centre on knee and hip surgery, he finally decided that the mouth was more accessible for continued clinical observations and the high rate of edentulism in the general population offered more subjects for widespread study. He termed the clinically observed adherence of bone with titanium as ‘osseointegration’. In 1965 Brånemark, who was by then the Professor of Anatomy at Gothenburg University in Sweden, placed his first titanium dental implant into a human volunteer.
Albrektsson et al. (1981) presented information on a series of background factors that needed control in order for a reliable osseointegration of an implant to ensue. These factors involved:
- the bio compatibility
- surface condition of an implant
- the status of the host bed
- the surgical technique at insertio
- the loading conditions applied afterward s.
Exactly these factors are,where the main difference between basal implants and conventional dental implants comes from.
The conventional dental implants are predominantly two parts, root form titanium screws, what are imbedded in the spongeous(soft) bone. Currently there are thousands of companies to produce conventional implants, in one hand, but with very similar features in the other hand. That makes the market for conventional dental implants very competitive, what in turn, makes the companies to try to distinguish between each other, by inventing new “unique” features of their implants like “nano- surfaces”, “hydrophylic surfaces”, new systems for connecting the two parts of the implants and so on. The reality is that all these market driven novelties have no any clinical value.
The main disadvantage of these implants is that they are not being placed where it is appropriate and in the way that is appropriate, i.e. in the soft bone without cortical support. That is the reason, why these implants rely so much on the so called osseointegration.
Another potential disadvantage is their thick collar area and their rough surface, what is a prerequisite for development of periimplantitis(the tissue inflammation around dental implant, what progresses further down into adjacent to the implant bone).
The third disadvantage is the bigger volume of the implant and the requirement the whole rough surface to be submerged in to the bone. That requires voluminous bone areas where conventional dental implants to be placed, and often when such areas are missing, expensive and extensive bone build up procedures are necessary (so called bone grafting).
According to the conventional thinking, the osseointegration represents a direct connection between bone and dental implant without interposed soft tissue layers. Clinically it manifested itself by the stability of the implant in to the bone.
“Osseointegration is a process, whereby clinically asymptomatic rigid fixation of alloplastic materials is achieved, and maintained, in bone during functional loading.”(Zarb & Albrektsson 1991).
The biological entity of osseointegration though, is a “foreign body reaction” of the host tissue towards the implant. It was proposed the term “extraterritorialization”of the implants because osseointegration was regarded as a delimiting reaction – a process of “cystification”, as it is. An implant thus becomes extraterritorialized as cortical bone forms in the interface area, ultimately reducing the blood supply and exterminating any osteocytes near the implant. The reality is, that nobody can predict the course of this “foreign body reaction” of the host tissue to the newly installed dental implant.
There are two scenarios possible:
1. The first one is the “desired“ one- the reaction of the bone tissue towards the implant by the process of “extraterritorialization”, i.e. the formation of a highly mineralized protective osseous barrier, what in traditional implant dentistry is called “osseointegration”.
2. The second scenario is unwanted – the reaction of the bone towards the implant by the process of fibrous tissue formation. This is regarded “as a rejection of the implant by the body”.
Fortunately in 95-98% of the cases the bone reacts towards the implants by the process of extraterritorialization. This is of special importance for the conventional dental implants, what are imbedded in the soft bone areas and rely on the “osseointegration” in order to function.
The osseointegration is a time consuming process, that is the reason, why the conventional dental implants are being left for months undisturbed, before employing in to function.
On the grounds of the deep understanding of the bone physiology and by implementation of the principals of the orthopaedic surgery in to the field of dentistry, the concept of basal implantology has been invented
Bone grafting procedures
Bone grafting is a surgical procedure that replaces missing bone in order to repair bone fractures that are extremely complex, pose a significant health risk to the patient, or fail to heal properly.
Bone generally has the ability to regenerate completely but requires a very small fracture space or some sort of scaffold to do so. Bone grafts may be autologous (bone harvested from the patient’s own body, often from the iliac crest), allograft (cadaveric bone usually obtained from a bone bank), or synthetic (often made of hydroxyapatite or other naturally occurring and biocompatible substances) with similar mechanical properties to bone. Most bone grafts are expected to be reabsorbed and replaced as the natural bone heals over a few months’ time.
The principles involved in successful bone grafts include osteoconduction (guiding the reparative growth of the natural bone), osteoinduction (encouraging undifferentiated cells to become active osteoblasts), and osteogenesis (living bone cells in the graft material contribute to bone remodeling). Osteogenesis only occurs with autografts.
Bone grafting in dental implantology.
Bone grafting in dental implantology includes variety of sometimes complex surgical procedures as: GBR(Guided Bone Regeneration), Sinus lift procedure, Vertical and horizontal augmentations with block grafts, Split ridge augmentation, Distraction osseogenesis. All these techniques aim at building up new bone in the area of atrophy in jaw bones, in order to provide basis for “prosthetically correct” placement of root form dental implant. Recently this area of dental implantology grew up as a multimillion industry.
It is important to realize though, that bone grafting procedures in dental implantology, contradict to some fundamental principles in the nature, such as : principle of maximal strength with minimum mass and principle of maximum effectiveness with minimum energy. What means – the bone is available only where it is necessary.
When the teeth are gone, parts of the jaw bones responsible for supporting the teeth, are no longer necessary, and to preserve energy, they undergoe resorption. In edentulous patients, the function in the stomatognathic system decreases as a whole, and in compliance with the above mentioned principles, the bone decreases its volume and mass accordingly.
The bone grafting techniques, in dental implantology, are aiming at artificially recreating the bone in the areas of jaws, where it is not necessary from the bio-mechanical and biological point of view. The bone itself doesn’t need to be grafted, from the bone perspective, the artificial grafting procedures, performed just to provide bone volume for placement of bulky root form implants, are unnecessary and unnatural. That is the reason, why in the long run, vast majority of bone grafting procedures are doomed to complications and implants placed in grafted areas are succumbed to failure.
In basal implantology, performing bone grafting , just to anchor implants, is not necessary, hence all of the complications, associated with the bone build up procedures, are avoided.