Bone Anatomy and Osteoclasts Overview

Osteoclasts and Bone Structure

• Osteoclasts possess a large volume and contain 50-100 nuclei.
• Bone trabeculae exhibit a mosaic appearance with demarcation by reversal lines (lignes basophiles inversées).
• Active phases see bone marrow highly vascularized, increasing bleeding risk during extraction.
• Advanced stages involve acellular spherical masses fusing into large sclerotic areas, contributing to osteomyelitis risk during extraction.
• Treatment options include normalizing biological markers, use of bisphosphonates if active, and managing dental work.

Cherubism

• Hereditary, bilateral, symmetric disease with autosomal dominant inheritance, variable expressivity, and high penetrance.
• Linked to SH3BP2 gene on chromosome 4 (4p16), impacting osteoblastic and osteoclastic activity.
• Primarily affects maxilla, notably mandible with expansion and aesthetic changes.
• Clinical symptoms present between ages 2-5 and stabilize by puberty, usually normalizing by age 30.
• Predilection for the angle of the mandible and ascending ramus causes non-painful bilateral swelling, affecting facial appearance and function.
• Dental anomalies include agenesis and abnormal eruption patterns of molars, primarily impacting primary teeth.

Osteosclerosis and Osteitis

• Idiopathic osteosclerosis presents dense bone regions, not linked to infection or neoplasms, occurs mostly in the posterior mandible and is asymptomatic.
• Osteitis condensante results from inflammation (e.g., pulp disease), often seen in young individuals with dental issues, characterized by radio-opacity at the apex.
• Localized osteoporotic defects occur due to hematopoietic tissue collection, predominantly in edentulous areas of adult women, presenting as radiotranslucent regions.

Central Giant Cell Granuloma (CGCG)

• Benign intraosseous lesions more prevalent in women, particularly under 30 years, with predilection for the anterior mandible.
• Clinical forms include non-aggressive (slow growth, low recurrence) and aggressive (fast growth, high recurrence) variants, manifesting with pain, paresthesia, or expansion.
• Radiographically, CGCG appears as well-defined, non-corticated lesions; histopathology reveals vascularized stroma with mononuclear and multinucleated giant cells.
• Treatment varies: conservative for non-aggressive cases and larger excision for aggressive types.

Fibro-osseous Lesions

• Normal bone is replaced by collagen fibers; categorized as developmental, reactive, or neoplastic.
• Fibrous dysplasia has a GNAS gene mutation on chromosome 20, can be monostotic or polyostotic, impacting individuals variably based on the age of onset.
• Symptoms include facial asymmetry, vision/hearing issues, and skeletal deformities related to polyostotic fibrous dysplasia, associated with Jaffe-Lichtenstein and McCune-Albright syndromes.

Cemento-osseous Dysplasias

• Most prevalent benign fibro-osseous lesions in maxillaries, with disorganized bone production but no malignant transformation risk.
• Types include periapical (more frequent in black women, asymptomatic, typically non-expansive), focal (mostly in women aged 20-50), and florid (bilateral and multifocal).
• Cementoblastoma characterized by well-defined, unilocular lesions with potential tooth movement but non-malignant behavior.

Benign Neoplasms

• Cemento-ossifying fibroma has a strong predilection for women and mandibular premolar-molar areas; it appears well-defined radiographically and has excellent prognosis.
• Chondroma, a cartilage tumor in maxillae, requires differentiation from low-grade chondrosarcoma.
• Osteoma is a slow-growing neoplasm that can cause asymmetry, primarily in the head and neck; associated with Gardner syndrome, linked to APC gene mutations.
• Osteoblastoma and osteoid osteoma, while rarer, primarily affect young patients, with specific characteristics regarding pain and radiographic appearance.

Clinical Considerations

• Importance of diagnosis through radiographic evaluation and histopathology for distinguishing lesions.
• Management of conditions ranges from conservative monitoring to surgical interventions depending on growth patterns and symptoms presented.

Buccal Cavity Conditions

• Symmetrical enlargement of the alveolar ridge and lowering of the palatine vault can lead to denture incompatibility and diastema formation.
• Radiographic findings include loss of differentiation between spongy and cortical bone, bone hypertrophy, osteolysis, and generalized hypercementosis.
• Lytic phase shows osteoporosis with decreased bone density, while osteoblastic phase indicates general thickening of the external skull and loss of lamina dura.
• Laboratory findings usually show normal phosphocalcic balance and elevated markers indicating bone remodeling (pyridinolines, deoxypyridinolines, N-telopeptides).
• Histopathological features include areas of osteolysis next to bone apposition and abnormal lamellar bone due to increased osteoblast activity.
• Treatment aims to restore aesthetics and function, often requiring extraction of primary teeth.

Paget's Disease of Bone

• Also known as osteitis deformans, characterized by increased bone remodeling, leading to disorganized bone structure and deformities causing pain.
• Second most common metabolic bone disease after osteoporosis, notably affecting older populations in England and Western Europe, more prevalent in men.
• Etiology linked to both environmental and genetic factors that disrupt osteoclast and possibly osteoblast functions, with mutations in the SQSTM1 gene as a common factor.
• Phases of the disease:
  • Lytic phase: active osteoclasts lead to rapid bone resorption.
  • Mixed phase: resorption coupled with excessive abnormal deposition by osteoblasts.
  • Sclerotic phase: dominant bone deposition results in weak, poorly organized bone quality.
• Clinical symptoms can range from asymptomatic to severe pain in affected areas such as the iliac bones and skull, with the skull showing a progressive increase in circumference.
• Dental implications include high risk of osteomyelitis during procedures, especially extractions due to changes in the bone structure.
• Treatment includes use of bisphosphonates for active cases and adjustments to dental appliances.

Cherubism

• Hereditary condition that is bilateral and symmetric, following an autosomal dominant inheritance pattern with variations in expression but high penetrance.
• Genetic mutation in the SH3BP2 gene on chromosome 4 affects osteoblastic and osteoclastic activity predominantly in the maxilla.
• Symptoms commonly appear during childhood and stabilize around puberty, often resulting in facial aesthetic changes due to maxillary expansion.
• Can cause dental anomalies including agenesis of molars and premature loss of primary teeth.
• Radiological features include bilateral, multilocular lesions causing thinning and perforation of cortical bones, especially around the mandible.
• Histopathologically noted for a cellular proliferation within a highly vascularized stroma with populations of mononuclear and multinucleated giant osteoclastic cells.
• Treatment varies; non-aggressive cases may require conservative management while aggressive cases necessitate surgical excision.

Benign Fibro-Osseous Lesions

• Characterized by the replacement of normal bone by collagen fibers; can resemble immature bone or dental cement-like materials.
• Fibrous dysplasia is a developmental defect linked to mutations in the GNAS gene, appearing in monostotic or polyostotic forms, the latter being more common in women.
• Monostotic dysplasia predominantly affects the maxilla, while polyostotic may impact multiple bones leading to deformities and associated syndromes like Jaffe-Lichtenstein and McCune-Albright.
• Treatment for fibrous dysplasia is conservative, focusing on management through growth stabilization, with surgical interventions reserved for severe deformities.

Other Tumors and Lesions

• Fibro cement-ossifying tumors are benign neoplasms prevalent in women, particularly associated with premolars and molars.
• Chondromas are cartilage tumors found in the maxilla and are differentiated from chondrosarcomas.
• Osteomas consist of mature bone primarily in the head and neck region, known for asymptomatic slow growth.
• Gardener syndrome is associated with multiple osteomas and carries a risk of colorectal malignancy, thus necessitating vigilant monitoring.

General Treatment Notes

• Many benign conditions require conservative management, especially fibrous dysplasia.
• Surgical intervention is indicated for aggressive forms of conditions like cherubism and significant deformities from dysplasia.
• Regular monitoring of symptoms and radiological changes is crucial for all conditions mentioned.