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.

Placing an implant immediately into a fresh extraction socket neutralizes the waiting time of six to eight months. There is less burden on the patient because drilling is reduced to a minimum. The combination of a screw implant and a bone graft is still needed to fill the gap between the implant and the socket because most types of implants were designed to be placed into healed alveolar ridges. The bone graft provides the following:

1. an increased initial stability to the implant, which is placed 2 to 5 mm apically into the socket;
2. a wider bucco-lingual (or -palatal) diameter around the neck of the implant where the forces are greater; and
3. prevention of any soft tissue ingrowth and, thus, potential loss of the implant.

The materials of choice for replacement therapy are single-stage implants (ITI [Straumann]) and composite polymers (Bioplant HTR [Bioplant Inc., South Norwalk, CT]) because one of the aims is to have predictable results and success in the simplest way.
The ITI system (Straumann) has been used successfully and clinically documented since 1974. ITI implants (Straumann) are all made of commercially pure titanium grade 4 (ISO 5832/11). The endosseous portion has a microporous titanium plasma coating with a roughness and thickness of approximately 20 mm and increases the area for bone apposition. The supracrestal cervical portion (neck) is cup-shaped (diameter, 4.8 mm) with a height of 2.8 mm and has a smooth machined surface to facilitate tissue management. An 8-degree morse taper connection is used with the whole range of titanium abutments, creating a friction fit connection and a micro-gap of less than 10 mm. The types of implants are hollow cylinder, hollow screw, and solid screw. All have a diameter of 4.1 mm and lengths varying between 8 mm, 10 mm, 12 mm, and 14 mm.
Bioplant HTR Synthetic Bone allograft (Bioplant Inc.) is a chemical mixture of porous polymethylmethacrylate spheres coated with polyhydroxylethylmethacrylate and an outer layer of calcium hydroxide carbonate graft. It is non-resorbable, hydrophilic, and microporous (opening, 250–350 mm). The granules average in size from 550/550 mm (HTR-40) to 700/750 mm (HTR-24) (Figs. 6 and 7). With a negative surface charge of 210 mV, it was shown first in animal experiments12– 13 and later in clinical studies14– 21 that it is a suitable material for bone replacement in general trauma treatment and oral surgery. The material does not require a barrier membrane19,20,22 and has substantial compressive strength up to 1800 psi. It possess several unique properties that are thought to be the result of the negative surface charge of 210 mV:

1. no epithelial ingrowth (no need to use any type of membrane);
2. no migration;
3. ease of handling and contouring; and
4. no colonization by bacteria.

Therefore, it not only adheres to surrounding bone but also to metal, such as titanium.
Dr. R. Becker (University of Syracuse) and Dr. R. Salkind (Rutgers University) showed that a negative charge between 28 mV and 212 mV facilitates and enhances bone healing and formation. Studies on salamanders proved that those animals use such extremely weak currents to regenerate lost body parts. Used in bone diseases (eg, osteomyelitis), the same negative charge provides complete healing.

The Procedures.
Hopeless teeth were extracted in 147 patients between 19 and 71 years of age, and a total of 556 ITI (Straumann) single stage screw implants (162 hollow screws and 394 solid screws, Ø 4.1 mm) were placed immediately 2 mm to 5 mm apically into the extraction sockets. Bioplant HTR-24 and HTR-40 (Bioplant Inc.) previously wetted with the marrow bleeding obtained from the drilling were packed firmly into the void between bone and implants. Primary closure was done with Vicryl (Ethicon Inc., Somerville, New Jersey) Rapid 2/0 or 3/0 for suturing the flap(s) and Vicryl Normal 4/0 around the neck of the implants. Prosthetic rehabilitation was done three to six months postoperatively and was obtained by placement of ball retained overdentures, implant cemented bridges, implant-tooth cemented bridges, or single crown.
Notice that patient selection was not done according to the standard selection criteria because the aim was to treat any patient, including those with alcohol, drug, or nicotine abuse, blood coagulation disorders, endocrine illnesses, poor oral hygiene, etc. The only contraindications were patients requiring chemotherapy and patients with psychotic illnesses. Also, it must be stated that most ball retained overdentures in the maxilla were placed on only two implants and not on the customary four implants. Four implants are most widely recommended in the literature, but because a ball-retained overdenture is soft tissue supported, the idea was that there would be no difference between upper and lower success rates if the osseointegration of the implants were accomplished. Four implants in the maxilla were only used in cases where the mandibular natural teeth could act as good and healthy antagonists.

RESULTS.
The graft material, Bioplant HTR (Bioplant Inc.), always produced an immediate additional stabilization of the implants and helped stop bleeding. Because of its naturally slight negative charge of 210 mV, the material sticks to the titanium and the host bone, stays where it is placed, and seems to discourage the colonization of microorganisms. During the healing period, no allergic reaction, inflammation, swelling, or pain was ever reported. Significantly, no soft tissue ingrowth was ever seen clinically or radiographically. Nineteen implants were lost during the osseointegration period in six patients. All those patients were diabetic and/or heavy smokers. Interesting, however, was the fact that not all of the implants placed in those patients were lost. At least one implant always integrated normally.
After removal of those failing implants and after a healing period of 12 weeks, implants were again placed. Those implants showed little if any problems afterward, but the cases were considered to be failures. During the follow-up period of at least seven years and a maximum now of 10 years, not a single implant loss of the remaining 537 ITI (Straumann) implants was reported. No measurable loss of bone height and width was seen clinically or radiographically.
Of those 19 lost implants, 15 (79%) were hollow screws, resulting in the later use of more solid screw implants. Four of the six patients were male, and two were female.

CONCLUSIONS.
The 7 to 10 year follow-up shows that ITI (Straumann) onestage screw implants are indeed as predictable and successful as conservative two-stage implants. More importantly, they can be placed in extraction sockets in combination with a graft material. The material used here, Bioplant HTR (Bioplant Inc.), proved to be an excellent graft material for this purpose; extremely easy to use and highly suitable to stick to the implants and not migrate (Fig. 16). This alloplast alone and not mixed with autogenous bone but wetted with sanguinous marrow seems to act as a barrier membrane. It forms initially dense or very dense fibrous tissue under the gum flap, preventing epithelial and connective tissue ingrowth around the implant(s) and providing excellent osseointegration.
The hollow screw ITI (Straumann) type showed a much higher failure rate when compared with the ITI solid screw implant, perhaps in dicating that the hollow space inside the implant is the reason for the problem. Another important finding is that two maxillary implants combined with a ball retained overdenture are indeed sufficient if the immediate implants are placed in the maxillary canine or premolar sockets and if the mandible is also edentulous.
Applying replacement therapy, using single stage (ITI-type) implants in combination with this microporous composite polymer, is predictable and successful. However, specially designed (ITI-type) implants for use in extraction sockets and/or wider implants would even improve simplicity and success. Adding the extraordinary properties of the growth factors and cytokines24 to stimulate bone more rapidly (and of tissues) to this bone substitute would without doubt enhance the rapidity of osseointegration. This would fulfill the goal of replacement therapy by providing every clinician and, thus, every patient with materials to replace hopeless teeth and prevent the socalled inevitable alveolar bone loss postextraction in the most efficient, simple, and secure manner.

Addendum.
The author wishes to state that since the start of this study 10 years ago the range of ITI implants (Straumann) has changed. The company now offers the choice between a TPS (Titanium Plasma Spray) implant surface and an SLA (Sand-blasted, Large grit, Acid-etched) implant surface. Wide solid screw implants (diameter, 4.8 mm) are offered with a neck of diameter, 4.8 mm or diameter, 6.5 mm as well as. An Esthetic Plus type is also available in which the height of the smooth neck is only 1.8 mm. Also, the hollow types are reduced to only a 3.5-mm diameter hollow cylinder (15-degree angled or not) in their Esthetic Line, showing that their findings correspond with the above conclusion.  

REFERENCES.

1. Christensen GJ. Ridge preservation: Why not? J Am Dent Assoc. 1996; 127:669–670.
2. Gross JS. Bone grafting materials for dental applications: A practical guide. Compend Contin Educ Dent. 1997:1013– 1038.
3. Misch CE, Dietsh F. Bone-grafting materials in implant dentistry. Implant Dent. 1993;2:158–167.
4. Lane JM. Bone graft substitutes. West J Med. 1995:565–567.
5. Frame JW. HA as a biomaterial for alveolar ridge augmentation. Int J Oral Maxillofac Surg. 1987;16:642–655.
6. Tatum OJ. Jr. Osseous grafts in intra-oral sites. J Oral Implantol. 1996;22: 51–52.
7. Pinholt EM, Haanaes HR, Donath K, et al. Titanium implant insertion into dog alveolar ridges augmented by allogenic materials. Clin Oral Implants Res. 1994:213–219.
8. Caplanis N, Sigurdsson TJ, Rohrer MD, et al. Effect of allogeneic, freezedried, demineralized bone matrix on guided bone regeneration in supraalveolar peri-implants defects in dogs. Int J Oral Maxillofac Implants. 1997;12:634– 642
9. Isaksson S, Alberius P, Klinge B. Influence of three alloplastic materials on calvarial bone healing. Int J Oral Maxillofac Surg. 1993:375–381.
10. Rummelhart JM, Mellonig JT, Gray JL, et al. Bone allografts in periodontal therapy. J Periodontol. 1989;60: 655–663.
11. Rosenlicht J. Immediate postextraction placement of an alloplast and titanium screw implant. Pract Periodontics Aesthet Dent. 1993;5:53–55.
12. Ashman A, Moss ML. Implantation of porous polymethylmethacrylate resin for tooth and bone replacement. J Prosthet Dent. 1977;37:657–665.
13. Binderman I, Goldstein M, Horowitz I, et al. Grafts of HTR polymer versus Kiel bone in experimental long bone defects in rats. Am Soc for Testing and Mat; Special Tech Pub. 1988;3:370–376.
14. Ashman A, Bruins P. A new immediate hard tissue replacement (HTR) for bone in the oral cavity. J Oral Implantol. 1982;10:419–452.
15. Yukna RA, Greer RO. Human Gingival tissue response to HTR polymer. J Biomed Mater Res. 1992;26:517–527.
16. Yukna RA. Clinical evaluation of HTR polymer bone replacement grafts in human mandibular grade II molar furcations. J Periodontol. 1994;65:342–349.
17. Murray VK. Clinical applications of HTR polymer in periodontal surgery. Compend Contin Educ Dent. 1988: S342–S347.
18. Schmier MG, Powers DL, Sander T. Incorporation of HTR polymer and autogenetic cortical bone grafts. The 15th Ann Meeting of the Soc of Biomater, Florida, 1989.
19. Gross JS. A guide to ridge preservation using HTR synthetic bone following tooth extraction. Gen Dent. 1995;43:364–367.
20. Froum S, Orlowski W. Ridge preservation utilizing an alloplast prior to implant placement—Clinical and histological case reports. Pract Periodontics Aesthet Dent. 2000;12:393–402.
21. Ashman A. Ridge preservation: Important buzzwords in dentistry Gen Dent. 2000;48:304–312.
22. Boyne P. Use of HTR in tooth extraction sockets. Gen Dent. 1995:470– 473.
23. Boyne P. Bone induction and the use of HTR polymer. Compend Contin Educ Dent. 1998:337–341.
24. Barboza E, Caula A, Machado F. Potential of recombinant human bone morphogenetic protein-2 in bone regeneration. Implant Dent. 1999;8:360–366.