Residual Ridge Resorption Overview

Residual Ridge Resorption (RRR)

• Residual bone is the portion of maxillary or mandibular bone remaining after tooth loss.
• Residual ridge is the portion of residual bone and its soft tissue covering remaining after tooth removal.
• Residual ridge crest is the most prominent continuous surface of the residual ridge.
• Residual ridge resorption is the diminishing quantity and quality of residual ridge after tooth extraction.
• RRR is a chronic, progressive, and irreversible process.
• The rate of RRR is fastest in the first 6 months after extraction.
• Bone resorption continues throughout life at a slower rate.
• Post-extraction, inflammatory reactions occur, and the socket is temporarily sealed by blood clotting.
• Tissue integrity is restored within a week, and new bone formation is evident in the socket within two weeks.
• The socket is progressively filled with new bone within 6 months.
• Residual ridge alveolar bone undergoes lifelong catabolic remodeling post-extraction.

Bone Structure and Function

• Osteocytes: Cells responsible for bone metabolic activity.
• Intercellular substance (bone matrix): Consists of fibrils (calcified cementing substance) primarily polymerized glycoprotein, bound to mineral salts (calcium carbonate and phosphates).

Pathology of RRR

• Gross pathology: Reduction in the size of the bony ridge under the mucoperiosteum.
• RRR is categorized into different configurations in a system of six orders, based on the Atwood order. These are related to the pre- and post- extraction states and include high/low and well-rounded configurations.
• Microscopic pathology: Osteoclastic activity on the external surface of the residual ridge crest.

Pathogenesis of RRR

• Following extraction, sharp edges of remaining bone are rounded off by external osteoclastic resorption.
• Bone crest becomes increasingly narrow.
• A knife-edged crest becomes shorter and flatter, then low, or depressed over time.
• The process of RRR is chronic, progressive, irreversible, and cumulative.

RRR Classification (American College of Prosthodontists, based on bone height - mandible only)

• Type I: Residual bone height of 21mm or greater.
• Type II: Residual bone height of 16-20mm.
• Type III: Residual bone height of 11-15mm.
• Type IV: Residual bone height of 10mm or less.

Direction of Bone Resorption

• Maxilla: Resorption is upward and inward.
• Mandible: Resorption is outward and wider.
• The different patterns of resorption (centripetal in maxilla, centrifugal in mandible) affect the overall appearance of the jaw.

Patterns of Bone Resorption

• In mandible, significant proportions of bone loss occur in the labial side of the anterior residual ridge, with equal loss on the buccal and lingual aspects in the premolar region, and lingual loss in the posterior molar region.
• In maxilla, bone loss primarily occurs on the labial/buccal side.

Maxilla vs Mandible

• Anterior mandible resorbs up to four times faster than maxilla.
• Maxillary and mandibular denture areas differ.

Consequences of RRR

• Loss of sulcus width and depth
• Displacement of muscle attachments
• Altered inter-alveolar ridge relationship
• Formation of sharp, spiny, or uneven ridges
• Exposure of the mandibular nerve
• Foraminal location problems
• Impacted upon ability to retain dentures.

Etiology of RRR

• Disequilibrium between osteoblasts and osteoclasts.
• Increased osteoclastic activity.
• Factors affect bone formation and resorption: Systemic factors and local factors. These factors include hormonal, nutritional, and other systemic factors.

Systemic Factors

• Estrogen
• Thyroxin
• Growth hormone
• Androgens
• Calcium
• Phosphorus
• Vitamin D
• Protein
• Fluoride

Local Biochemical factors

• Endotoxins
• Osteoclast-activating factor (OAF)
• Prostaglandins
• Human gingival bone-resorption stimulating factors
• Heparin

Anatomic Factors

• Amount of bone: Quantity of bone (high/low, broad/narrow, rounded/spiny).
• Quality of bone: Density of bone (denser bone is less prone to resorption).

Metabolic Factors

• Nutritional and some hormonal factors
• Dietary Factors- Protein, Vitamins and Minerals

Pituitary Glands & Hypophysis

• Hypophysis is the master gland of the endocrine system.
• Dysfunction impacts general health and oral cavity.

Thyroid Glands

• Important for metabolism
• Hyperthyroidism lead to negative nitrogen balance and osteoporosis.
• Thyroxin impacts kidneys, causing calcium and phosphorus excretion, decreasing bone density.

Parathyroid Glands

• Maintain blood calcium levels through bone mobilization.

Islets of Langerhans

• Insulin deficiency, poor tissue healing and rapid bone loss.
• Diabetes mellitus associated with reduced healing.

Suprarenal Glands

• Corticoids (e.g., cortisone) have adverse effects on bone.
• Prolonged use of corticoids is a concern in certain conditions.

Gonads

• Sex hormones are important for bone health.
• Declining hormone levels in aging are associated with increased bone resorption.

Metabolic Factors (Dietary)

• Dietary proteins, carbohydrates, fats, vitamins and minerals crucial to bone health.
• Protein is essential during bone development and repair.
• Vitamins and minerals are also essential for bone building.

Treatment and Prevention of RRR

• Prevention of tooth loss: Maintaining natural teeth is key.
• Optimal tissue management: Healthy tissue prior to denture insertion.
• Impression procedures: Minimal pressure techniques.
• Denture design: Adequate coverage, relief from non-stress bearing zones, appropriate size to reduce force per unit area
• Maintaining Interocclusal distance: To avoid increased resorption.

Other Considerations

• Overdentures: Impacted upon ability to reduce the amount of resorption.
• Preprosthetic surgery: Bone or tissue alterations.
• Nutritional factors and diet counseling.
• Immediate dentures: Effectiveness in reducing resorption.
• Patient Habits (e.g., bruxism) influence patterns of resorption.