35.6 Radiology of Periodontal Bone Loss and Jaw Lesions

3. Radiographic Assessment of Periodontal Bone Loss

Periodontal Alveolar Crest Morphology

   A. Healthy Alveolar Crest          B. Horizontal Bone Loss           C. Vertical / Infrabony Defect

      CEJ       CEJ                      CEJ       CEJ                     CEJ       CEJ
       │         │                        │         │                       │         │
       ▼         ▼                        ▼         ▼                       ▼         ▼
     ──┬─────────┬──                    ──┬─────────┬──                   ──┬─────────┬──
       │ 1–2 mm  │                        │         │                       │         │
     ══╪═════════╪══ Alveolar Crest       │ Resorbed│                       │         │
       │ Cortical│                        │ >2 mm   │                       │ ╲ Angle │ Infrabony
       │ Lamina  │                      ══╪═════════╪══ Resorbed Crest      │  ╲ Defect
       │ Dura    │                      (Parallel to CEJ line)              │   ══════ Crest

Normal Periodontal Architecture

In a periodontally healthy adult, the alveolar bone crest is situated 1.0 to 2.0 mm apical to the cemento-enamel junction (CEJ). The crest forms a sharp, distinct angle with the root surface and is covered by a continuous, well-defined radiopaque cortical plate (crestal lamina dura) that blends uninterrupted into the radicular lamina dura lining the socket.

Horizontal vs Vertical Bone Loss

• Horizontal Bone Loss:
  • The crestal bone margin undergoes uniform, generalized resorption such that the remaining alveolar crest remains parallel to an imaginary line connecting the CEJs of adjacent teeth.
  • Measured as a percentage of total root length ($< 15%$ mild, $15%-33%$ moderate, $> 33%$ severe bone loss).
• Vertical (Angular) Bone Loss:
  • The crestal bone resorbs unevenly along the root surface of a single tooth, creating an oblique, trench-like infrabony pocket.
  • The remaining bone crest is not parallel to the imaginary line connecting adjacent CEJs.
  • Often associated with localized occlusal trauma, food impaction, or aggressive localized disease.
• Furcation Involvement:
  • In multirooted mandibular and maxillary molars, inflammatory destruction of inter-radicular bone presents as a triangular radiolucency within the furcation area.
  • Classification (Hamp / Lindhe): Grade I (incipient bone loss $< 3\text{ mm}$ horizontally into furcation), Grade II (cul-de-sac defect $> 3\text{ mm}$ horizontally but not through-and-through), Grade III (through-and-through probeable defect).

4. Differential Diagnosis: Radiolucent Jaw Lesions

Radiolucent Jaw Lesions Differential Framework
  │
  ├── Periapical Radiolucencies (Centered at Root Apex)
  │     ├── Periapical Granuloma ────> Non-vital; loss of lamina dura; chronic inflammatory tissue
  │     ├── Radicular (Periapical) ──> Non-vital; well-defined sclerotic corticated border; >60% of cysts
  │     └── Periapical Scar ─────────> Asymptomatic, stable fibrous defect following surgical endodontics
  │
  ├── Follicular & Non-Inflammatory Odontogenic Cysts
  │     ├── Dentigerous Cyst ────────> Attached strictly at CEJ of unerupted crown (e.g. 38, 13)
  │     └── Odontogenic Keratocyst ──> Anteroposterior growth; scalloped borders; Gorlin-Goltz syndrome
  │
  ├── Benign Odontogenic Tumours
  │     └── Ameloblastoma ───────────> Multilocular 'soap-bubble'; marked expansion; root resorption
  │
  └── Non-Odontogenic Anatomical Variants
        └── Stafne Defect ───────────> Below IAN canal; anterior to angle; salivary tissue; NO biopsy

Periapical Radiolucencies

• Periapical Granuloma: Chronic mass of vascular granulation tissue and inflammatory cells (macrophages, lymphocytes) at the apex of a non-vital tooth following pulpal necrosis. Radiographically presents as a round or oval radiolucency with loss of the apical lamina dura; border may be well-defined or poorly defined, but lacks a dense corticated rim.
• Radicular Cyst (Periapical Cyst): The most common odontogenic cyst ($60%$ to $65%$ of all jaw cysts). Arises from necrotic pulp infection stimulating the dormant epithelial rests of Malassez within the periodontal ligament. Presents as a round, unilocular radiolucency centered at the apex of a non-vital tooth, typically characterized by a sharp, thin, well-defined radiopaque corticated (sclerotic) margin (unless acutely infected).
• Periapical Scar: Occurs when a surgical apicectomy or periapical curettage heals with dense, mature collagenous connective tissue rather than bone. Radiographically presents as a well-demarcated, circumscribed radiolucency at the apex of a root-treated tooth. The patient is asymptomatic, and serial radiographs confirm that the lesion remains completely stable in size over months and years. Requires no intervention.

Cysts & Benign Odontogenic Tumours

5. Radiopaque & Mixed-Density Jaw Lesions

Radiopaque & Mixed-Density Lesions
  │
  ├── True Radiopaque Lesions
  │     ├── Condensing Osteitis ─────> Apex of non-vital/inflamed tooth; low-grade reactive sclerotic bone
  │     ├── Idiopathic Osteosclerosis> Vital tooth; non-inflammatory dense bone island; stable
  │     └── Exostoses / Tori ────────> Torus palatinus (midline palate), Torus mandibularis (lingual premolar)
  │
  └── Mixed-Density Lesions
        ├── Cemento-Osseous Dysplasia> Triphasic; anterior mandible; vital teeth; BIOPSY CONTRAINDICATED
        ├── Compound Odontoma ───────> Multiple tooth-like denticles in radiolucent halo (Anterior maxilla)
        ├── Complex Odontoma ────────> Amorphous conglomerate mass in radiolucent halo (Posterior mandible)
        └── Cementoblastoma ─────────> Radiopaque mass fused to root apex with radiolucent rim; vital molar

Purely Radiopaque Entities

1. Condensing Osteitis (Focal Sclerosing Osteomyelitis):
   • A localized, reactive sclerotic bone proliferation occurring at the root apex of a tooth with a non-vital, chronically necrotic, or irreversibly inflamed pulp.
   • Represents a hyperplastic tissue response where low-grade chronic microbial irritants stimulate osteoblasts rather than osteoclasts.
   • Radiographically presents as a diffuse, non-expansile radiopacity surrounding the apex, with loss or widening of the apical PDL space.
   • Management: Resolves or regresses following successful root canal therapy or extraction of the infected tooth.
2. Idiopathic Osteosclerosis (Dense Bone Island / Enostosis):
   • A localized, developmental focus of compact lamellar bone within the cancellous trabecular space.
   • The adjacent tooth is completely VITAL, the periodontal ligament space is normal, and there is no surrounding radiolucent halo or history of pulp pathology.
   • Remains static over time; requires no clinical intervention.
3. Exostoses and Tori:
   • Benign nodular outgrowths of dense cortical bone.
   • Torus Palatinus: Located in the midline of the hard palate.
   • Torus Mandibularis: Located on the lingual aspect of the mandible superior to the mylohyoid line, typically bilateral in the canine-premolar region.

Mixed-Density Lesions

1. Cemento-Osseous Dysplasia (COD):
   • Benign fibro-osseous condition where normal trabecular bone is replaced by cellular fibrous tissue and disordered cementum-like calcifications. Types include Periapical COD (predilection for anterior mandibular teeth in middle-aged African/Afro-Caribbean or Asian females), Focal COD, and Florid COD (symmetrical involvement across multiple quadrants).
   • Triphasic Radiographic Maturation:
     • Early (Osteolytic) Stage: Well-defined radiolucency at the apex, closely mimicking periapical periodontitis.
     • Intermediate (Cementoblastic) Stage: Mixed radiolucent-radiopaque lesion with central calcifications.
     • Mature Stage: Dense, lobulated radiopaque mass surrounded by a thin, uniform radiolucent border.
   • The Cardinal Clinical Rule: All associated teeth are completely VITAL.
   • Biopsy Contraindication: Surgical biopsy or unnecessary tooth extraction is strictly contraindicated. The dysplastic cementoid mass is avascular and hypovascular; surgical exposure introduces oral microflora into non-vascular bone, precipitating catastrophic, refractory chronic osteomyelitis that is extremely difficult to manage.
2. Odontomas (Odontogenic Hamartomas):
   • Compound Odontoma: Consists of multiple small, identifiable malformed tooth-like structures (denticles) surrounded by a thin radiolucent fibrous capsule. Predilection for the anterior maxilla; frequently obstructs eruption of permanent incisors or canines.
   • Complex Odontoma: Consists of an amorphous, disorganized conglomerate mass of enamel, dentine, and cementum bearing no morphological resemblance to a tooth, enclosed within a uniform radiolucent halo. Predilection for the posterior mandible.
3. Cementoblastoma (True Cementoma):
   • A true benign neoplasm of cementoblasts.
   • Characteristic appearance: A bulbous, dense radiopaque mass intimately fused to the root apex of a vital permanent mandibular molar or premolar, bordered by a distinct, well-circumscribed radiolucent rim.
   • Causes root resorption and expansion; requires surgical enucleation with tooth removal.