Table of Contents
Bone Grafting 3
Socket preservation and Bone Grafting
There are three ways to preserve bone
1. Rootform Implants
When a tooth is extracted, it is possible to replace it with an artificial tooth root called an implant. Implants are generally (though not always) made from titanium and if properly placed, bone will grow around it and actually attach to it, a process called osseointegration. An implant is the most expensive form of socket preservation, but it is always considered the best thing to do after extracting a functioning tooth since it is the closest thing to a natural tooth replacement offered by dental science today. The implant may be placed at the time a tooth is extracted (or if the socket bone has been preserved, it can be placed later). The dentist drills a perfectly shaped and sized hole in the empty socket, and screws a titanium “root” into it. This implant is then covered by suturing the gums over it, and allowed to heal for about six months. Implants are the only permanent way to prevent bone loss after an extraction.
Sometimes the dentist will fill in any remaining space around the implant with bone grafting material, and then cover the implant and the bone graft with a collagen membrane. Between the implant itself, and the bone graft material, epithelial cells are prevented from migrating into the socket. During the healing process, the bone surrounding the titanium implant osseointegrates with the titanium, and the bone graft material is removed by osteoclasts and replaced with the patient’s own bone by osteoblasts. At the end of the healing period, the dentist uncovers the implant and attaches an abutment to it. The abutment sticks up out of the gums and serves as an anchor for a crown. This combination of implant, abutment and crown serves as a very firm and permanent tooth. With good hygiene, a crown/abutment placed on an implant can last as long as a healthy natural tooth.
The popularity of rootform implants is growing at an exponential rate. It is beginning to become popular to extract seriously damaged teeth that were formerly restorable and replace them immediately with implants which have better long term prognoses. Implants have the additional benefit of not being susceptible to decay like a natural tooth.
Bone grafts are the best non-implant form of socket preservation. Bone grafts are very effective at preserving bone height, and they also create more bone for an implant later on. There are three types of bone graft material.
Xenogenic grafts are made from animal bone, most frequently bovine (cattle) or porcine bone. Xenografts are processed in such a way that all organic material is removed leaving only the hydroxyapatite component. (hydroxyapatite is the mineral that makes natural bone and teeth hard.) The bone structure remaining is very porous and has about the same structure as natural bone (see image to the right). When you look at an x-ray of normal human bone, you can see a web like pattern in the marrow spaces. The web like pattern is called trabeculation, and it has the same general pattern as the demineralized bovine bone that you can see on the right. Xenogenic grafting has been shown to be one of the most effective methods of creating bone in areas where there is none. Xenogenic grafts are known to be osteoconductive, which means that it supports the formation of new bone by acting as a matrix or scaffolding for extension or apposition of new bone from existing bone (i.e. the patient’s own bone). Xenografts also may have varying degrees of osteoinductivepotential, which means that in addition to acting as a simple scaffolding, the graft material may actually stimulate the patient’s own mesenchymal cells to transform into osteoblasts (bone-forming cells) hastening the replacement of the graft material with the patient’s own bone. Xenograft grafting materials are generally resorbed and replaced entirely with the patient’s own bone.
Alloplastic grafts are made from synthetic material such as ceramic material (bioactive glass), tricalcium phosphate, calcium sulfate (plaster) and hydroxyapatite, (the hard mineral that makes up teeth and bones). The most popular brand of alloplast today is called Bioplant (a highly magnified microsphere is seen in the image to the right). It is made of very thin microspheres of methyl methacrylate (plastic) which are perforated, and coated inside and outside with Ca(OH)2. During healing, the osteoblasts and osteoclasts migrate inside and between the spheres and form new bone within and around them. Alloplastic graft material constitutes the second of the most popular forms of bone grafting material in dentistry. Alloplastic grafts are known to be osteoconductive and have varying degrees of osteoinductive potential. Alloplastic materials may, or may not be resorbed and replaced by the patient’s own bone. Plaster always resorbs, but bioactive glass does not. When not resorbed, the material remains behind as an implant acting as a sort of scaffolding that is surrounded by the patient’s own bone. Non-resorbable alloplastic bone grafting materials, can be used in most oral applications, but they are especially good for permanent ridge augmentation procedures because the resulting bone is unlikely to further resorb over time.
Allografts are derived from human sources and are obtained from tissue banks. They are made from freeze dried human cadaver bone, or bone from living donors such as people undergoing total hip replacement. The allograft is prepared by treating a section of cadaver bone to remove all soft tissue, then texturing the bone surface to produce a pattern of holes of selected size, density, and depth. It is processed in such a way that it is well cleaned, sterile, and free of viruses. Allogenic grafting material is osteoconductive and has a higher osteoinductive potential than xenografts or alloplastic grafts.
Autografts are made from the patient’s own bone. Bone is taken from a donor site, such as the crest of the pelvic bone and transferred to the surgical site where bone is needed. An autograft is considered the gold standard in bone grafting because in addition to being osteoconductive and osteoinductive, it is known to be osteogenic, which means that itsupports the formation of new bone by direct interaction with and stimulation of osteoblasts (bone-forming cells). This phenomenon is based on the contribution of the patient’s own living cells that are contained in the graft. Autogenous bone can promote osteogenesis, with the new bone being generated from endosteal osteoblasts and marrow stem cells that are contained within the graft material. An autograft is the most predictable grafting technique available, however it leaves a second surgical site in need of healing which causes extra discomfort after the surgical procedure. In dentistry, bone can sometimes be scavenged from areas adjacent to the primary surgical site. However, since the advent of the artificial bone substitutes, this is rarely done today. On the other hand, whenever an implant is placed, there is generally some bone “sawdust” in the flutes of the drills used to create the space for the implant, and this material is often scraped out of the drills and added to the xenograft or alloplastic grafting material that the dentist plans to use in the grafting procedure.
The dentist mixes the bone graft granules with the patient’s blood and forces it into the socket immediately after the tooth is extracted. The mixture is held in place either by tightly suturing the gums over the socket, or by suturing a collagen membrane over it. Over the course of four to six months, the patient’s body resorbs the artificial bone and replaces it with his or her own. A bone graft is nearly 100% effective at preserving bone height.
Collagen is a component of connective tissue. The collagen used in dental procedures is derived from bovine Achilles tendon. Collagen is a connective tissue protein which forms fibers. It is the elastic material underlying your skin that makes it tough and rubbery. In its pure form, collagen is not species specific. Cattle have about the same collagen as humans. Since all other bovine organic material is removed from it during processing, the human body does not reject it as it would for foreign tissues. The material is supplied in the form of a soft, fibrous “plug” in a single use sterile vial . After an extraction, the dentist places a collagen plug into the socket and sutures it in place. The sutures are removed in a week.
A collagen plug is a good deal less expensive than a bone graft, and the procedure for placing it is easier. This procedure may preserve between 50% and 70% of the original bone height. Unfortunately, it is a much less predictable method of socket preservation than bone grafting.
Finally, note that the only way to permanently preserve bone after a dental extraction is by placing a titanium implant, or by using non-resorbable alloplastic graft materials in the site. Even well preserved socket bone will eventually resorb over a period of many years if it is not kept in function. An implant signals to the body that the bone is in use, and therefore necessary. This is the body’s way of saying “use it or lose it”. Alloplastic graft materials remain in the socket as a permanent implant material and act as a scaffolding to maintain the intervening natural bone that infiltrates between the alloplastic particles.