Section 1: Molecular and Cellular Mechanisms of Root Resorption

The OPG/RANK/RANKL System

Root resorption involves a sophisticated molecular signaling system similar to bone
remodeling. The key players are:
 RANKL (Receptor Activator of Nuclear Factor Kappa-B Ligand): A protein
expressed by periodontal ligament cells, cementum, and dental pulp
 RANK: The receptor on odontoclast precursors
 OPG (Osteoprotegerin): A decoy receptor that inhibits the process
When tissue damage occurs, RANKL expression increases, binding to RANK receptors and
triggering odontoclast differentiation. This system is essential for understanding how
resorption begins at the molecular level.
Odontoclast Characteristics
Odontoclasts are specialized cells that resorb dental tissues. Key features include:
 Smaller than osteoclasts with fewer nuclei
 Create Howship lacunae: shallow depressions on mineralized tissue surfaces
 Bind via integrins to RGD (arginine-glycine-aspartic acid) sequences in extracellular
proteins
 Require fewer sealing zones compared to osteoclasts
Three Phases of Root Resorption
Research has identified that root resorption occurs in three distinct phases:
1. Initiation phase: Damage to protective layers
2. Resorption phase: Active tissue destruction
3. Repair/arrest phase: Either healing or continued destruction

Section 2: Transient Apical Breakdown (TAB) - A Unique

Entity
Definition and Characteristics
Transient Apical Breakdown is a self-limiting resorption of the apical portion of the root
following dental trauma. Unlike other forms of resorption, TAB:
 Occurs only in teeth with fully formed roots (closed or half-closed apices)
 Resolves spontaneously within 12 months without treatment
 Shows characteristic radiographic changes that disappear over time
Prevalence and Associations
A comprehensive study of 637 traumatized teeth revealed:
 Overall prevalence: 4.2%
 Subluxation injuries: 2.2%
 Extrusion injuries: 11.3%
 Lateral luxation injuries: 12.3%
 Not seen in: Severe injuries (intrusion) or developing teeth
Clinical Presentation
 Mild tooth discoloration that resolves within a year
 Delayed response to sensitivity testing that returns to normal
 Widening of PDL space on radiographs
 Loss of apical lamina dura that reappears with healing
Important Diagnostic Consideration
TAB may be a radiographic artifact due to:
 Subtle tooth displacement at injury time
 Limitations of 2D radiography
 Variations in radiographic angulation
 The tooth settling back into its socket over time
Clinical Pearl: A 10-degree vertical shift in radiographic angle can eliminate the appearance
of the lesion, confirming TAB diagnosis.

Section 3: The Pericanalar Resorption Resistant Sheet

(PRRS)
Structure and Function
Advanced imaging has revealed a protective layer around the root canal:
 Composition: Predentin, dentin, and occasionally bone-like tissue
 Thickness: 200-300 micrometers (with some areas up to 400 micrometers)
 Function: Protects against internal resorption progression
Clinical Significance
Understanding PRRS helps explain:
 Why some teeth resist internal resorption
 The pattern of resorption progression
 Potential therapeutic targets for prevention
Advanced Imaging
Modern NanoCT imaging with specialized software (CTan, CTvol, CTvox) allows:
 3D visualization of PRRS
 Color-coded thickness mapping
 Identification of vulnerable areas

Section 4: Updated Prevalence and Diagnostic Data

External Surface Resorption (ESR)
Recent CBCT studies show higher prevalence than previously thought:
 Impacted third molars causing ESR:
o Conventional radiography: 0.3-24.2%
o CBCT detection: up to 54.9%
 Impacted canines causing incisor resorption:
o Conventional imaging: 12.5%
o CBCT studies: 46-67.5%
External Cervical Resorption (ECR)
Diagnostic accuracy has improved significantly:
 Periapical radiographs: 49% accuracy
 CBCT: 89% accuracy
 Correct Heithersay classification:
o Radiographs: 32%
o CBCT: 70%
Predisposing Factors for ECR
A study of 347 teeth revealed:
 59% were multifactorial
o 38% had 2 factors
o 17% had 3 factors
o 3% had 4 factors
 Most common factor: Orthodontics (45.7%)
Survival Rates
Long-term studies show:
 ECR Class 3 lesions: 70.3% five-year survival
 ECR Class 4 lesions: 28.6% five-year survival

Section 5: The 3D Classification System for ECR (Patel

Classification)
Components
This modern classification considers three dimensions:
1. Height (1-4):
o 1: At CEJ level or coronal to bone crest
o 2: Extends into coronal third of root
o 3: Extends into middle third
o 4: Extends into apical third
2. Circumferential Spread (A-D):
o A: ≤90°
o B: >90° to ≤180°
o C: >180° to ≤270°
o D: >270°
3. Proximity to Root Canal (d/p):
o d: Confined to dentin
o p: Probable pulpal involvement
Example: A lesion classified as "2Bp" extends into the coronal third, involves 90-180° of
circumference, and likely involves the pulp.

Section 6: Contemporary Treatment Advances

Regenerative Endodontic Procedures (REP)
REP has emerged as a treatment option for root resorption:
For Internal Root Resorption:
 Instrument entire canal length
 Place medicaments (calcium hydroxide or triple antibiotic paste)
 Create blood clot or use platelet-rich fibrin as scaffold
 Seal with MTA or Biodentine
 Success reported up to 3 years with arrest of resorption
For External Replacement Resorption:
 Similar protocol but focused on arresting ankylosis
 Some cases show reversal of resorption
  Particularly valuable in young patients
Alternative to Trichloroacetic Acid (TCA)
Due to carcinogenic concerns with TCA:
 Sodium hypochlorite with microbrush is now preferred
 Applied directly to resorptive tissue
 Equally effective without toxicity concerns
Bioactive Materials
Modern materials show superior outcomes:
 Biodentine: Induces odontoblast differentiation
 MTA: Excellent biocompatibility and sealing
 Calcium silicate cements: Promote hard tissue formation
Special Considerations
Emdogain Application: Limited success (7/15 teeth) for ERR treatment Wind Instrument
Players: Potential risk factor for ECR Clear Aligners: May have different resorption patterns
than fixed appliances

Section 7: Clinical Management Updates

Diagnostic Approach
1. Always consider CBCT for suspected resorption
2. Use parallax technique to differentiate internal from external
3. Monitor asymptomatic ECR with annual reviews
4. Document with standardized classifications
Treatment Decision Making
For ECR:
 Asymptomatic, non-progressive → Monitor
 Symptomatic or progressive → Active treatment
 Consider patient age, tooth strategic value
For ERR in Growing Patients:
 Decoronation if unrestorable
 REP if salvageable
 Autotransplantation as alternative
 Avoid implants until growth complete
Emerging Concepts
Hypoxia-Inducible Factor: Found in ECR lesions, suggesting tissue hypoxia role
Molecular Targeting: Future therapies may target RANKL/OPG system Stem Cell
Therapy: Potential for true regeneration

Section 8: Evidence-Based Guidelines

Position Statements and Guidelines
Recent consensus documents provide guidance:
European Society of Endodontology (2018-2021):
 Specific ECR management protocols
 CBCT usage guidelines
 Traumatic injury management
  Intentional replantation criteria
AAE/AAOMR (2015):
 CBCT recommended for resorption diagnosis
 Specific imaging protocols
IADT Guidelines (2020):
 Updated trauma management
 Emphasis on early intervention

Section 9: Future Directions and Research Needs

Current Research Gaps
 Long-term outcomes of REP for resorption
 Molecular mechanisms of TAB
 Optimal recall intervals for monitoring
 Predictive factors for progression
Emerging Technologies
 Advanced imaging: Beyond CBCT to micro-CT
 Biomarkers: Early detection through molecular markers
 Targeted therapies: RANKL inhibitors, stem cell applications
 AI diagnosis: Pattern recognition for early detection

Key Takeaways for Clinical Practice

1. Root resorption is more common than previously thought - especially with
modern imaging
2. TAB is a distinct entity that requires recognition to avoid overtreatment
3. CBCT has revolutionized diagnosis - use it when indicated
4. REP offers new hope for previously untreatable cases
5. Multifactorial etiology is the rule - consider all risk factors
6. Early detection remains crucial - implement systematic screening
7. Classification systems aid communication - use standardized terminology

Study Questions
1. What molecular system regulates odontoclast differentiation?
2. How does TAB differ from other forms of periapical pathology?
3. What is the significance of PRRS in internal resorption?
4. How has CBCT changed our understanding of resorption prevalence?
5. When should REP be considered for resorption treatment?
6. What are the components of the 3D ECR classification?
7. Why is sodium hypochlorite preferred over TCA?