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BONE Bone is a highly specialized connective tissue with a mineralized extracellular matrix. CELLULARITY Osteoblasts Osteocytes Bone lining cells O steoclasts

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Osteoblasts Osteoblasts are cuboidal cells that secrete Type 1 collagen & the noncollagenous proteins. Also regulate mineralization of bone matrix. Osteocytes Osteocyte is a mature osteoblast which both synthesizes & resorbs bone.

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Bone lining cells They are flat, fusiform cells covering inactive bone surfaces. Osteoclasts They arise from fusion of mononuclear precursor cells & function to resorb bone.


ARCHITECTURE The outer shell of the bone is made up of Cortical bone which provides the mechanical support. It is composed of concentric sheets of collagen fibrils in the form of lamellar bone. The centrally located Cancellous bone controls the metabolic functions of bone. The matrix of cancellous bone is loosely organised .




BONE TYPES ACCORDING TO VARIABLE DENSITIES D1 BONE Dense cortical bone. D2 BONE Dense cortical bone outside with inner coarse trabecular bone.

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D3 BONE Porous crestal layer of cortical bone & fine trabecular bone underneath cortical bone. D4 BONE Composed primarily of fine trabecular bone & often the absence of cortical bone.

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D5 BONE A very soft bone with incomplete mineralization & large intertrabecular spaces. This type of bone is most often immature bone in a developing sinus graft.



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Maxillae is a fusion of two bones along the palatal fissure which forms the upper jaw. Maxillae form the floor of the orbit for each eye, the sides and lower walls of the nasal cavities and the hard palate. The lower border of the maxilla supports the upper teeth. Each maxilla contains an air space called The maxillary sinus.

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Maxillary sinus maintains a close relationship with the alveolar ridge in the posterior region. Roots of the first & second molars are often found in the maxillary antrum . Therefore, when teeth are lost, the maxillary sinus tends to expand into the remaining residual alveolar bone causing its absorption.

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In edentulous severely resorbed maxillae, the floor of the sinus is often the crest of residual alveolar ridge & bone level may approximate the level of floor of nasal cavity. Antroplasties are indicated in such cases. Also, bone grafting should be constructed vertically to 2mm superior to the longest implant possible.

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When placing an implant in the anterior maxillary region of resorbed maxilla , caution must be taken with respect to incisive foramen that might be close to the remaining alveolar crest. The incisive canal is found adjacent to the nasal septum 8 to 18 mm behind the anterior aspect of floor of nasal fossa.

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The nasal septum marks the upper end of incisive canal , which contains the terminal branches of nasopalantine nerve, the greater palantine artery & Stenson’s canal. Pterygoid plates can be chosen for implant placement instead. The maxillary tuberosity contacts the anterior pterygoid process & forms pterygopalantine fossa.

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Pterygopalantine fossa houses the maxillary artery which divides into posterosuperior alveolar artery Descending palantine artery Sphenopalantine artery & infraorbital artery. The pterygoid process has two plates ; one lateral & medial. Both point downward & perpendicular to the body & greater wing of sphenoid forming a V-shaped concavity- Pterygoid fossa.

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When an implant is placed in this region , its path comes from the maxillary tuberosity & aims into the pterygoid process, passing the lateral pterygoid plate medially & process posteriorly & superiorly avoiding pterygoid fossa. Placement of implant in this dangerous zone can cause severe haemorhage of pterygoid muscles & pterygoid plexus.

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Anterior maxillae has an outer porous Cortical bone & inner fine trabecular bone. Posterior maxillae chiefly contains D4 bone, f ine trabecular bone.


MANDIBLE Mandible is a horse-shoe shaped bone which forms the lower jaw.

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The body is thick, has a rounded lower border & carries the alveolar process on its upper border. The alveolar process of the lower jaw is far more stronger than that of the upper jaw. Only in the incisor & canine areas , the outer & inner plates of alveolar processes are thin, but rapidly thicken distally. In the anterior part, alveolar process is narrow labiolingually & the alveolar bone proper fuses for most of the root length with the outer & inner alveolar plates.

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The lower part of anterior mandible extend up to the mandibular symphysis , passing through a depression called the incisive fossa where the Levator menti is attached, positioned below the housing for the incisor teeth. Lingually , the mandible is concave with up to four genial tubercles placed in pairs. The two superior genial tubercles attach the genioglossus muscles & two inferior tubercles attach geniohyoideus ms.

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An oval depression The sublingual fossa , is found bilaterally by the genial tubercles. Just beneath sublingual fossa , the internal oblique line lodges the myohyoid ms that runs posteriorly up to the last two molars bilaterally. When teeth are lost , bone resorbs & limits the implant placement due to the proximity of Inferior alveolar nerve & mental foramen in posterior mandible.

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In anterior mandibular region, if bone is severely resorbed , attention is given to the genial tubercles & mental foramen for onlay bone graftings in two-stage or one –stage implant procedure. The mental nerve before exiting through the mental foramen may present an anterior loop that runs inferior-medial-lateral or inferior to mental foramen. The loop may extend for 1mm to 7mm anteriorly.

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Once the mental nerve leaves the mental foramen, it produces three branches : anterior , middle & posterior. The foramen is usually located slightly inferior toward the border of the mandible, although it can be found one third inferiorly to the mandible rather than superiorly. The foramen is commonly located around the apex of second premolar although can be found at apex of the first premolar.

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The posterior mandible is limited for implant placement because of bone loss & proximity of the inferior alveolar nerve & vessels. The mandibular canal may have a distance of 1mm from the third molar & approx 3mm from first molar. In cases of implant placement for first mandibular molar, an implant as long as the tooth root or shorter may be preferred.

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In cases of severe bone resorption & little residual bony ridges, a lateralization procedure of inferior alveolar nerve can be an option. The inferior alveolar nerve enters mandibular foramen , which is located in approximately the center if mandibular ramus on the inner surface. It runs inferiorly & anteriorly , passing medially & laterally below the apex & buccally to the roots of molars & premolars until it reaches mental foramen.

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In case of an anterior loop variation , the nerve may extend up to 8mm forard ,& then the loop runs superiorly, posteriorly & medially to the medial aspect of mental foramen. The nerve then splits into incisive & mental nerve .

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Also the lowest point along the course of the mandibular canal is 5.9mm plus 2.2mm when measured from the inferior mandibular border.

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Anterior mandible has dense cortical bone. Posteriorly, mandible has both cortical & trabecular bone of varying density in the form of D2 & D3 bones.

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The trabecular bone is most dense next to the teeth where it forms the cribriform plate. Between the teeth , the bone is usually most dense near the crest & least dense near the apex.



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