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2- Allografts:

•         They are grafts taken from another individual of the same species

•         Because the individuals are usually genetically dissimilar, the graft is treated to reduce its antigenicity, usu. It is freeze-dried

3-Xenografts:

•         They are taken from one species and grafted to another

•         Because dissimilarity of these grafts is greater they are treated more vigorous to reduce its antigenicity.

#Alografts & Xenografts:

•         It is totally passive, but offers a hard matrix for host site elements to replace

•         It doesn,t require another site of operation in the host.

# A combination:

A combination of allogenic graft with autogenous shell was favoured as a way for better osteoinduction.

4- Alloplastic materials:

•         Requirements:

–       Adequate Mechanical properties to withstand cyclic stresses.

–       Non-toxic

–       Non-carcinogenic

–       Immunologically inert

•         Examples:

–       Hydroxyapatite

–       Tricalcium phosphate

–       Bioactive glass

•         Hydroxyapatite and other calcium materials are known to

–       1-interact with and can even incorporate into living bone tissue.,

–       2-they do not resorb.

–       3-Their biocompatibility is excellent, and

–       4- they appear to bond to bone by natural cementing mechanisms &  allows for tissue ingrowth without the formation of a fibrous capsule.

–       5- these materials are brittle and lack much strength

•         Nonceramic forms also exist and come as a powder that is mixed in the operating room to fill bony defects, due to their lack of strength and potential for fracture, they should not be used in load-bearing areas. This may limit their use in mandibular augmentation.

#-Modifications:

•         1-Barrier Membranes:

–       Guided bone regeneration by covering the graft site by a membrane to exclude undesirable cell types from the area where bone healing is taking place.

•         2-Osteostimulation:

–       Fifteen residue peptide(p-15)

–       Recombinant bone morphogenic proteins(rhBMP-2)

–       Platelet-rich plasma

These biological materials are used in conjunction with alloplastic materials to stimulate, enhance or accelerate bone formation at the host site.

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Distraction Osteogenesis

          History of the Procedure: Distraction was introduced first by Codvilla nearly a hundred years ago and subsequently was popularized during the 1940s by Ilizarov, who developed a single-stage procedure to lengthen long bones without the use of grafting material. However, in the early 1990s, experimental investigation intensified following reports from New York University on lengthening of dog mandibles and from Constantino and Friedman et al, who used DO to successfully close canine segmental lower jaw defects.

Thereafter, several studies (within a variety of animal models) demonstrated the application of osteodistraction at a number of different sites including the mandible, lower maxilla, mid face, and cranial vault. In 1992, the first clinical results of craniofacial DO were reported by McCarthy et al in a small series of patients with congenital mandible deformities. Since then, several larger series with longer follow-up periods have appeared. More recently, the technique has been successfully used for midfacial and upper craniofacial skeletal defects.

Method: The underlying principle of DO, as described by Ilizarov, is “the mechanical induction of new bone between bony surfaces that are gradually distracted.” The process of DO begins with careful preoperative assessment and planning, which are critical to success. At the initial surgery, osteotomies are performed and the distraction device is inserted. A waiting period (latency phase) is allowed to elapse during which bone healing is initiated at the bony gap. In this early period, periosteal integrity is restored and callus formation begins. The bone segments at either end of the gap then are progressively distracted over a period of several days (distraction phase) during which osteogenesis is induced, thus producing a so-called regenerate of immature bone laid down between the cut bone ends. Over time, the bone remodels into a more mature state (consolidation phase), and the surrounding soft tissues adapt to their new positions and lengths.

Based on matrix arrangement, bone tissue can be classified as follows:

Based on developmental origin, bones can be classified as follows:

 Microscopic structure of bone

Bone cells

During bone remodeling, osteoblasts deposit a layer of osteoid seam of approximately 10 mm thick on the surface of preexisting bone, which then begins to mineralize in approximately 20 days. This interval is known as the mineralization lag time.

Microscopic architecture of bone

4-Systemic Diseases-Hereditary and acquired

There are some systemic disease that may affect bone function like Osteoporosis and Diabetes, which are more in old age. These diseases may affect the decision of treatment surgically.

          Other disorders endanger the life of the patient during surgery, severe heart and respiratory diseases, and end-stage diseases are also a contraindication for surgery. Also patients receiving radiotherapy or chemotherapy.

          A hereditary disorder, namely osteogenesis imperfacta, also may affect our decision. Other Hereditary Syndromes may be the need for these treatment modalities as the best choice(see problems)

*Genetic basis of some syndromatic cases:

          Some genetic disorders affecting the meiotic division may be of concern to our subject, as failure of of homologous chromosome pair to separate during meiosis will result in a zygote with 45 chromosomes only, which is called monosomy, or a zygote with 47 chromosomes, which is called trisomy. The best known example of trisomy is Down's syndrome or trisomy 21. Among features of Down's syndrome are facial clefts, a shortened palate, a protruding and fissured tongue, and delayed eruption of teeth. Other types of trisomy or monosomy either leads to early death of the infant or rarely manifest themselves in dental defects.

          Autosomal Dominent inheritance affected gene is generally inherited from one parent. The trait appears in every generation and can be transmitted by the affected parent to statistically half of the children. Examples of autosomal dominant conditions include achondroplasia, cleidocranial dysostosis, Treacher Collins syndrome, osteogenesis impeerfecta, and some forms of amelogenesis imperfecta.

          When the malformationis due to autosomal recessive inheretence, the abnormal gene can express itself only when it is received from both parents. Examples include chondroectodermal dysplasia, some cases of microcephaly and cystic fibrosis.

          All of these conditions are classified as genetic defects. The expression  of the genotype is affected by the environment in which the embryo develops, and the final outcome of the development is termed the phenotype. Adverse factors in the environment can result in excessive deviation from a functional; and accepted norm; the outcome is described as a congenital defect.  

5-Bone Healing

After the tooth has been extracted, the defect is immediately filled by a blood clot(the hemostatic response). The epithelial cells bordering the socket begin to proliferate and migrate across the clot, so that after 10 days the socket is epithelialized. Within the clot, the inflammatory response takes place, involving first neutrophils and then macrophages. The Proliferative and synthesizing phase is a little different from the skin because the cells invading the clot are not fibroblasts but cells from the adjacent bone marrow that have osteogenicpotential. Bone formation begins after about 10 days after extraction; by 10 to 21weeks , the extraction site can no longer be distinguished.(Ten Cate)

6-Facial Growth