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 »  Home  »  Dental Implant 2  »  Replacement Therapy and the Immediate Post-Extraction Dental Implant
Replacement Therapy and the Immediate Post-Extraction Dental Implant
Introduction.

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Luc W. J. Huys, LTH, BDS, DDS, DSc, IOM
Private practice, Brugge, Belgium.
Oral Implantology and Dento-Alveolar Surgery, Hospital Queen Fabiola, Blankenberge, Belgium.


Extraction, as well as prosthetic rehabilitation, was already performed in the time of the pharaohs. Today, it seems that everything having to do with dental treatments has changed and improved, except the extraction. The result of any extraction is still always the same; alveolar bone loss. We agree that a sufficient amount of alveolar bone provides the patient with the tool they need throughout their life for function, esthetics, and prosthetic rehabilitation. Technology today offers us enough materials, such as bone grafts and implants, to eliminate most complications, whether immediate or delayed, associated with any extraction. Today, most dental schools throughout the world offer excellent education in different areas, be it the classical conservative dentistry, endodontics, periodontics, implantology, or other specialized surgery. Each university tries to be aware of all the new techniques, and millions of dollars are spent worldwide to acquire the latest and most innovative materials and instruments. Therefore, it is astonishing and almost unbelievable that one of the first and elementary procedures of our profession, the extraction, is still performed as it was done 50 years ago, or 500 years ago, or even 5,000 years ago! That is, destructively and not preventively. The result of any extraction is well known; 40% to 60% alveolar bone loss in the first two to three years and then a resorption rate of 0.5% to 1% every year for the rest of the patient’s life.
The potential consequence for the patient is dramatic; pocket formation, shifting of the remaining teeth, bulging out of the maxillary sinus, and gap formation between bridgework and the gingiva. When a full mouth extraction is performed, the results are even more dramatic: loss of vertical dimension on unesthetic facial lines, loss of retention of a denture, and impossible or extremely difficult to place implants.
Replacement therapy, the immediate replacement of the lost root(s) to prevent the loss of alveolar bone in height and width, may be the answer. The word “prevention” should be essential to any clinician. Replacement therapy means, “When you take something out of the alveolar bone, you should immediately place something back into the socket.” But what should you place back? The aim of any treatment is to have predictable results and success in the simplest way.

Overview Of Bone Grafting Materials.
Grafts are used to provide host bone with a scaffold for bone regeneration, restoring bone loss caused by trauma, surgery, dental disease, and extraction. Grafting is also being performed to improve the outcome of implant dentistry and in maxillary sinus lift procedures.

Mechanisms Of Bone Regeneration.
Bone regeneration through grafting is accomplished by three different processes: osteogenesis, osteoinduction, and osteoconduction.  Osteogenesis is the formation and development of bone, even in the absence of local undifferentiated stem cells. Osteogenic grafts differentiate and facilitate the different phases of bone formation, even in soft tissues, or activate quicker bone growth. Osteoinduction is the transformation of undifferentiated mesenchymal or stem cells into osteoblasts or chondroblasts that are found only in living bone. Bone formation is enhanced and may even extend or grow in places where it is not normally found.
Osteoconduction is the process that provides a physical matrix or bioinert scaffold suitable for deposition of new bone. Those graft materials require the presence of existing bone or host stem cells to encourage bone to grow across their surface.

The Types Of Materials.
The mechanisms by which the grafts act are normally determined by their origin and composition. Of all the bone graft materials, autogenous bone is still regarded as being the gold standard because it is the only osteogenic grafting material. Grafted autogenous bone heals through osteogenesis, osteoinduction, and osteoconduction. The stages overlap during the healing process. It can be harvested from the iliac crest or from intraoral sites. It has, however, some serious disadvantages:
  1. it needs a harvesting procedure;
  2. it consequently creates another bony defect with an additional extra healing site, an extra infection risk, and extra possibility for postoperative complications;
  3. there is a risk of having an insufficient amount of material;
  4. it burdens the patient with a second surgical procedure; and
  5. most importantly of all, there is the risk of resorption!
Those shortcomings have led to the use of readily available grafts. Here we can choose between allografts, xenografts, and alloplasts. Allografts are obtained from other individuals of the same species but from disparate genotypes. Donors can be living related persons, living unrelated persons, and cadavers. The grafts are processed under complete sterility and stored in bone banks. However, those grafts, as freeze-dried bone allograft and demineralized freeze-dried bone allograft, are osteoconductive.
Demineralization removes the mineral phase and exposes the underlying bone collagen and growth factors, mainly bone morphogenetic protein. However, sterilization by gamma radiation kills most of the bone morphogenetic protein present. Irradiated cancellous (bone radiation, #25,000 Gy) has been used more recently, and Tatum et al reported that this material provided a response closest to autogenous bone.6 The clinical relevance and the osteoconductive and regenerative potential of such bone preparations are questionable. In brief, histologic studies in a variety of models, including long bones, calvaria, and alveolar ridge, provide little if any evidence of a long-term benefit of these materials.  Allografts always induce a host-immune response, and some important disadvantages (rejection, infection, and non-unions) are associated with the use of tissues from individuals. Other disadvantages include the necessity for rigid fixation and, again, the risk of resorption.
Xenografts are obtained from a species other than the host. Two well-known xenografts are natural hydroxyapatite and deorganified bovine bone. Hydroxyapatite is used in most forms; porous or non-porous, resorbable or non-resorbable, blocks or particles, plain or mixed with plaster. But, even with all those different available forms, the results are never predictable. Lastly, it is impossible to place implants in a hydroxyapatite-treated ridge. Deorganified bovine bone, besides being from bovine origin, requires combination with autogenous bone, and the use of a membrane is always recommended.
Xenografts appear to incorporate into bone. However, their slow resorption rates affect the quality of the newly formed bone and ultimately their clinical relevance. Moreover, public perception of these materials reduces their acceptance. The recent worldwide developments concerning bovine spongiform encephalopathy disease have strengthened the fear of disease transmission. Moreover, potential for immunologic reactions and uncertain outcomes limit the use of those graft materials.
High expectations have been placed on the use of alloplasts. Recent advances have greatly improved the use of alloplasts in selected dental cases. They are available in a variety of textures, sizes, and shapes. They can be macroporous (.350 mm) or microporous (,350 mm), crystalline or amorphous, and granular or molded. They include ceramics (synthetic hydroxyapatite and tricalcium phosphate), calcium carbonates, composite polymers, and bioactive glass ceramics. Although they all have some very positive properties, most of them are difficult to use and handle, are brittle, and migrate after placement. Most of them require the use of barrier membranes and their accompanying difficulties, making the treatment more expensive without predictable and excellent results. Most importantly, far from being osteogenetic, they merely are osteoconductive; therefore, providing only a physical matrix or bioinert scaffold suitable for new bone deposition.
The proper selection of a graft or combination of grafts can be made by knowing the physical and chemical properties of the materials. It is critical that any graft material does not compromise bone formation by obstructing the wound space, negating or delaying the native osteogenic potential of the site, or compromising the mechanical properties of bone. This includes load-bearing and dental implant placement possibilities and implant osseointegration.
Another type of material that can be placed into an extraction socket is the dental implant. The alveolar ridge is preserved to preclude bone loss by placing implants into the socket. Titanium implants can be placed predictably and successfully into healed alveolar bone, and they osseointegrate completely when the correct protocol is followed.
After years of practicing the two-stage implantology in which the implant integrates under the sutured gum and must be uncovered in a second stage, the ITI technique (Straumann, Waldenburg, Switzerland) showed that single-stage screw implants work as well as the twostaged technique. In addition to the advantage of offering the patient only one implant surgery, it eliminates the transmucosal abutment step. Furthermore, because the majority of forces on an implant are situated around the neck of the implant, eliminating a screwed junction at that level provides much more security when the rehabilitation is placed.