Academic literature on the topic 'Lamellar bone tissue'

Most invasive dental procedures involving removal of teeth or bone are followed by uneventful healing. However, dentists should be aware that generalized abnormalities of bone, such as osteoporosis and Paget’s dis­ease of bone, may complicate these procedures and, rarely, can lead to ongoing clinical problems. The effects of radiotherapy to the jaws and bisphosphonate treatment are well-described causes of osteonecrosis and delayed healing. Diagnosis of bone disorders often depends on integrating the results of clinical, imaging, pathological, genetic, and biochemical investigations. Although the bony skeleton is often thought of as forming just a rigid framework, it should be remembered that bone is a living, responsive tissue that plays an important role in metabolism. During development, some bones develop from a cartilaginous template and others, such as most of the craniofacial bones, form in fibrous membranes. Bone matrix is laid down by osteoblasts that are derived from the extensive meshwork of bone-lining cells that cover the bone surfaces. The bone matrix contains osteocytes that are responsive to mechanical stresses. Bone matrix is removed by osteoclasts that move over the bone sur­face, resulting in scalloped pits termed Howship’s lacunae. Bone mat­rix can be woven or lamellar in pattern. Pathologists often examine sections of bony lesions in polarized light to determine whether the pattern of the collagenous matrix is woven or lamellar, because it can be pivotal for diagnosis. It is also important for clinicians to be aware that, in order to produce a histological section of bone, the tissue must first be fixed and then demineralized to soften the matrix. When a bone biopsy is performed, the patient should be made aware that additional time will be needed to process the biopsy. Following extraction of a tooth, the socket rapidly fills with blood, which then clots. Granulation tissue, which consists of proliferating endothelial cells and fibroblasts derived from remnants of the periodontal ligament and surrounding alveolar bone, grows into the clot and organization commences. Osteoclasts begin to remodel the crestal bone and remove any small spicules of bone detached during the extraction.

Osteogenesis is a complex process of bone formation involving several phases and utilizes various cell, metabolites, hormones, and organic and inorganics components. Numerous genetic factors mediate bone formation. Initially, progenitor cells produce osteoblastic lines, which pass through three major cell differentiation stages: proliferation, maturation of matrix, and mineralization. Based on embryonic origin, ossification is of two types: intramembranous and endochondral. In intramembranous ossification, mesenchymal cells in ossification center directly differentiate into osteoblasts, without prior cartilage formation. It involves mesenchymal cell proliferation in highly vascularized areas of embryonic connective tissue, leading to primary ossification center formation. These cells then synthesize bone matrix at periphery, with continuous differentiation into osteoblasts. The resulting bone undergoes reshaping and is eventually replaced by mature lamellar bone. Sufficient blood supply and communication among cells by lacunar-canalicular system are crucial for bone synthesis and maintenance. In contrast, endochondral ossification begins with the formation of primary ossification center within cartilage. Chondrocytes undergo proliferation, expanding the cartilage through cartilage matrix deposition. Central region of cartilage sees the maturation of chondrocytes into hypertrophic chondrocytes. As primary ossification center forms, marrow cavity expands toward epiphysis. The process is completed by subsequent stages of endochondral ossification in various zones of ossification.

A thorough understanding of upper eyelid anatomy is essential for the ptosis surgeon. The upper eyelid consists of skin, orbicularis, septum, tarsus, levator, Muller’s muscle, and conjunctiva. The skin and orbicularis form the anterior lamella. Conceptually, the orbicularis may be subdivided according to its topography into pretarsal, preseptal, and orbital components (over the orbital rim and extending to the frontalis muscle superiorly). The orbital septum is a fibrous lamellar structure arising from the periosteum over the superior and inferior orbital rims. In the upper eyelid, the orbital septum fuses with the levator aponeurosis approximately 2 to 5 mm above the superior tarsal border in Caucasians. In Asian patients, the septum extends further inferiorly into the eyelid. Preaponeurotic orbital fat is normally located behind the orbital septum in the preaponeurotic space. The preaponeurotic fat is an important landmark for surgeons as it lies immediately anterior to the levator aponeurosis. The tarsus of the upper eyelid is a firm, dense connective-tissue plate that provides rigidity to the eyelid. The upper tarsal plate measures approximately 10 mm vertically in the center of the eyelid. The tarsal plate is usually 1 mm thick. The levator complex originates from the periorbita of the lesser wing of the sphenoid at the annulus of Zinn. The muscular portion of the levator in adults is approximately 36 mm long, while the aponeurosis is 14 to 20 mm long. The bony attachments of the aponeurosis are via its horizontal expansions, the medial and lateral horns. The lateral horn, which is much stronger than the medial horn, passes through the lacrimal gland and divides it into the palpebral and orbital lobes. The lateral horn attaches to the periorbita of the orbital tubercle and to the lateral canthal tendon. The medial horn is a thin, delicate structure. It attaches loosely with the posterior portion of the medial canthal tendon and curves medially and posteriorly to insert at the posterior lacrimal crest and the adjacent periorbita of the medial orbital wall. Whitnall’s superior transverse ligament (Whitnall’s ligament) is a condensation of the fascial sheaths of the levator muscle located superior to the area of transition of the levator muscle to the levator aponeurosis (musculoaponeurotic junction).