Residual Ridge Resorption

Residual Ridge Resorption (RRR)

Definition and Importance

  • Alveolar Bone: The bony portion of the maxilla and mandible that holds tooth roots via the periodontal ligament, crucial for the stability of teeth and prosthetic devices.

  • Residual Ridge: The shape and size of the alveolar ridge after tooth extraction and subsequent healing, which can significantly impact the fit and function of dentures.

  • Healing initiates with the inflammatory response, which includes the formation of a blood clot that seals the extraction socket, setting the stage for tissue repair and bone formation.

Healing Process

  • Epithelial tissue proliferation begins within the first week post-extraction, quickly restoring tissue integrity and aiding in the overall healing process.

  • Histological examination reveals active bone formation as early as two weeks after extraction; however, complete filling of the extraction socket with new bone can take approximately six months.

  • The residual ridge undergoes lifelong remodeling, with the most significant changes occurring during the first six months following tooth loss.

Rate of RRR

  • The rate of residual ridge resorption varies considerably among individuals and even at various locations within the same individual, influenced by numerous factors.

  • Understanding RRR is vital because it affects the function of removable prostheses; therefore, treatment for edentulous patients should encompass ongoing maintenance and monitoring of the residual ridge.

  • RRR is characterized as chronic, progressive, irreversible, and cumulative, underscoring its long-term implications on oral health.

Structural Characteristics of Alveolar Bone

Bone Structure

  • Comprises a robust hard compact outer layer and a spongy, resilient inner structure, which collectively provide support and defense against mechanical stresses.

  • Bone Elements:

    • Osteocytes: Bone cells that regulate metabolic activity and maintain bone homeostasis.

    • Intercellular Substance (Bone Matrix): Contains calcified fibrils and mineral salts such as calcium carbonate and phosphates, which are bound to proteins, providing structural integrity to the bone.

    • Osteoblasts: Cells actively involved in bone formation; they can transform into osteocytes when trapped within the bone matrix.

    • Osteoclasts: Large cells responsible for bone resorption, breaking down bone tissue by eliminating organic and inorganic components.

Pathology of RRR

  • Following tooth extraction, a reduction in the bony ridge size occurs under the mucoperiosteum, potentially leading to an excess of mucoperiosteum that can complicate denture fitting.

  • The shapes and sizes of residual ridges vary greatly after resorption, influencing the design and placement of prostheses.

Configuration of Residual Ridges (Atwood System)

  • The Atwood system categorizes residual ridges into six orders, reflecting morphological changes from pre-extraction to post-extraction healing:

    • Order 1: Pre-extraction state with an intact lower central incisor socket and thin cortical plates, indicating a healthy ridge.

    • Order 2: Post-extraction condition showing initial clot formation and socket filling, representing early healing.

    • Order 3: A high, well-rounded residual ridge featuring a narrow crest and a remolded trabecular structure, evident of early success in healing.

    • Order 4: Characterized by a knife-edged ridge with evident narrowing, indicating moderate resorption.

    • Order 5: A low, well-rounded ridge resulting from the loss of the knife-edge configuration that indicates advanced resorption.

    • Order 6: Depressed ridge where resorption has progressed to a point below the genial tubercle, indicating severe change and compromise of the ridge structure.

Bone Resorption Dynamics

Post-Extraction Resorption

  • Following extraction, sharp bone edges smooth out through the process of external osteoclastic resorption, which is essential for preparing the ridge for potential prosthetic fitting.

  • RRR is chronic and cumulative; thus, it influences denture fitting and stability over time, necessitating careful monitoring and adjustment.

Comparative Resorption in Maxilla vs. Mandible

  • Maxilla: Resorption occurs upward and inward (centripetal), leading to various alterations in the appearance and contour of the upper jaw.

  • Mandible: Resorption tends to be outward and widens (centrifugal), which can lead to flattening of the lower jaw and alterations in facial aesthetic.

Patterns of Bone Loss

  • Mandibular Anterior Regions: The loss occurs predominantly on the labial side, impacting aesthetics and function in the anterior segment.

  • Premolar Regions: Show equal loss on both buccal and lingual sides, which is representative of a balanced resorption pattern.

  • Posterior Molar Regions: Experience greater loss on the lingual aspect, which can complicate methods for supporting prostheses.

  • Maxillary Bone Loss: Primarily occurs on the labial or buccal surfaces, which may change the overall arch form and space available for denture base.

  • Clinical observation shows that the anterior mandible resorbs significantly faster than the maxilla, underscoring the need for careful denture design and ongoing assessment.

Consequences of RRR

  • Loss of sulcus width and depth can affect the retention and stability of removable prosthetics, leading to discomfort for the patient.

  • Displacement of muscle attachments near the ridge crest can lead to functional challenges during mastication and speech.

  • A reduction in the vertical dimension of occlusion (VDO) alters the appearance of the face and can lead to aesthetic concerns for the patient.

  • Morphological changes can result in uneven residual ridges, complicating the fitting and retention of dentures.

  • Exposure of the mandibular canal wall poses risks to the mandibular nerve, potentially leading to sensory disturbances or pain.

Assessment of RRR

  • Various assessment methods are utilized, including diagnostic casts, cephalograms, and orthopantomograms; however, Cone Beam Computed Tomography (CBCT) is preferred for accurate three-dimensional measurements without distortion, providing vital insights into the residual ridge condition.

Etiology and Factors Affecting RRR

Anatomic Factors

  • The amount and quality of bone available in the residual ridge heavily influence resorption rates, with denser bone reducing the overall resorption rate compared to less dense bone.

Metabolic Factors

  • Body metabolism balances bone formation and resorption, meaning that systemic health significantly affects the RRR process.

Hormonal Influences

  • Hormones such as those from the pituitary gland, thyroid, parathyroid, insulin, and adrenal glands can significantly influence bone density and resorption rates.

Dietary Factors

  • Nutrient intake is critical for bone health; deficiencies in proteins, vitamins, and minerals can impair bone maintenance and lead to increased RRR. Notably, vitamin D and calcium deficiencies lead to osteoporosis and heighten RRR.

Functional and Prosthetic Factors

  • Functional stress from factors like the frequency, intensity, duration, and direction of forces can impact bone health, while poorly designed or ill-fitting prosthetics can exacerbate resorption by causing improper force distribution and lack of rest for the supporting structures.

Treatment and Prevention of RRR

  • Preventing the loss of natural teeth is ideal, where possible, to maintain bone structure and health.

  • Maintaining optimal tissue health prior to taking impressions is essential for ensuring successful outcomes in prosthetic rehabilitation.

  • Selective pressure impression techniques can help manage the stress on supporting structures, thus reducing the potential for RRR.

  • Proper nutrition is vital, with an emphasis on adequate calcium and vitamin D intake to support bone health.

  • Surgical interventions, such as osseous reconstruction or vestibuloplasty, may be necessary for severe cases of resorption.

  • The use of immediate dentures after extraction has shown to reduce ridge resorption due to the stimulation of the residual ridge during the healing process.

  • Implementing overdentures and dental implants can provide additional stability and help to avert the RRR process by anchoring to the underlying bone structure.