2.4 Endodontics
Key Takeaways
- The AAE 2009 consensus terminology (still the international standard) classifies pulpal diagnoses as normal, reversible, symptomatic/asymptomatic irreversible pulpitis, pulpal necrosis, previously treated, and previously initiated therapy
- Periapical diagnoses include normal apical tissues, symptomatic/asymptomatic apical periodontitis, acute/chronic apical abscess, and condensing osteitis
- Working length is determined by combining an electronic apex locator (EAL) with a confirmatory working length radiograph
- Sodium hypochlorite (2.5-5.25%) is the primary endodontic irrigant; EDTA (17%) removes the smear layer; calcium hydroxide is the standard inter-appointment medicament
- Endo-perio lesions require distinguishing primary endodontic from primary periodontal pathology, as this determines whether root canal treatment, periodontal therapy, or both are indicated
Pulpal and Periapical Diagnoses: AAE Consensus Terminology
The American Association of Endodontists (AAE) Consensus Conference on Diagnostic Terminology (2009) established the classification most widely used in UK and international practice. This terminology remains the standard reference; the AAE and European Society of Endodontology (ESE) have been working on an update since 2023, but the 2009 framework is the established system for examination purposes.
Pulpal Diagnoses
| Diagnosis | Key Features |
|---|---|
| Normal pulp | Symptom-free; normally responsive to sensibility testing |
| Reversible pulpitis | Inflammation should resolve on removal of the irritant; brief, stimulus-evoked pain |
| Symptomatic irreversible pulpitis | Vital, inflamed pulp incapable of healing; lingering thermal pain, spontaneous or referred pain |
| Asymptomatic irreversible pulpitis | Vital, inflamed pulp incapable of healing; no symptoms but inflammation from caries, trauma, or previous treatment |
| Pulp necrosis | Death of the pulp; non-responsive to sensibility testing; may be partial or total |
| Previously treated | Tooth has been endodontically treated and obturated |
| Previously initiated therapy | Partial endodontic therapy (pulpotomy or pulpectomy) has been started but not completed |
Periapical (Apical) Diagnoses
| Diagnosis | Key Features |
|---|---|
| Normal apical tissues | Not sensitive to percussion or palpation; intact lamina dura on radiograph |
| Symptomatic apical periodontitis | Painful response to biting, percussion, or palpation; may or may not have radiographic radiolucency |
| Asymptomatic apical periodontitis | Apical radiolucency of pulpal origin; no clinical symptoms |
| Acute apical abscess | Rapid onset; spontaneous pain; pus formation; swelling; systemic symptoms possible |
| Chronic apical abscess | Gradual onset; little discomfort; intermittent sinus tract discharge |
| Condensing osteitis | Diffuse radiopaque lesion at the apex; response to chronic low-grade inflammation |
Distinguishing Acute Apical Abscess from Phoenix Abscess
A phoenix abscess is an acute exacerbation of a pre-existing chronic apical periodontitis. It presents with acute symptoms (pain, swelling, pus) but is superimposed on a chronic lesion with an existing radiolucency. A primary acute apical abscess arises from necrotic pulp without a pre-existing chronic lesion and may show no radiographic changes in early presentation.
Root Canal Anatomy and Access Preparation
Access Cavity Principles
- Outline form — the access cavity should provide straight-line access to the canal orifices
- Removal of caries and restorative material — all carious dentine and leaking restorations must be removed before endodontic treatment
- Location of canal orifices — use the pulp chamber floor as a guide; orifices are typically located at the angles of the floor
- Removal of pulp horns and roof of the chamber — ensure complete de-roofing to remove all pulp tissue
Common Canal Configurations
| Tooth | Typical Canals | Notes |
|---|---|---|
| Upper central incisor | 1 | Single canal in >99% of cases |
| Upper first premolar | 2 (buccal and palatal) | Occasionally 3 canals |
| Upper first molar | 3 (MB1, MB2, DB, palatal) | MB2 is commonly missed; present in >70% of cases |
| Lower incisor | 1 (often 2) | Second canal present in ~30-40% |
| Lower first premolar | 1 (often 2) | Second canal present in ~25% |
| Lower first molar | 3 (mesial buccal, mesial lingual, distal) | Distal canal may split into two; middle mesial canal in ~15% |
Working Length Determination
Accurate working length is critical: it determines the apical limit of instrumentation and obturation. The ideal apical terminus is at the apical constriction (the narrowest point of the root canal), typically 0.5-1 mm short of the radiographic apex.
Methods
- Electronic apex locator (EAL) — the primary method; measures the change in electrical impedance at the apical constriction. Accuracy is high (>90%) even in the presence of fluid. EALs should be used in conjunction with radiographic confirmation.
- Working length radiograph — a periapical radiograph with a file in place at the estimated working length. Used to confirm the EAL reading and detect canal curvature or aberrations.
- Paper point method — in cases where the apex is open (resorption, immature apex), a paper point moistened with blood or fluid at the tip indicates the apical extent.
Common Errors
- Short working length — under-instrumentation leaves infected tissue in the apical third; leads to persistent apical periodontitis
- Long working length — over-instrumentation damages the periapical tissues and compromises the apical seal
Irrigation
Irrigation is essential for cleaning the root canal system, dissolving organic and inorganic tissue, and disinfecting the canal space that instruments cannot reach.
Principal Irrigants
| Irrigant | Concentration | Action |
|---|---|---|
| Sodium hypochlorite (NaOCl) | 2.5-5.25% | Dissolves organic tissue (pulp, collagen); antibacterial; the primary irrigant |
| EDTA | 17% | Chelates calcium; removes the smear layer; opens dentinal tubules |
| Chlorhexidine gluconate | 2% | Antibacterial; substantivity; does not dissolve tissue |
| Citric acid | 10% | Alternative smear layer remover |
Irrigation Protocol
- NaOCl throughout instrumentation (dissolves tissue, disinfects)
- EDTA as a final rinse (removes smear layer created by instrumentation)
- NaOCl again (flushes debris and continues disinfection)
Important: NaOCl and chlorhexidine should NOT be mixed, as they form a toxic brown precipitate (para-chloroaniline). Flush the canal with saline or EDTA between them.
Safety Considerations
NaOCl is cytotoxic if extruded beyond the apex. NaOCl accident (extrusion into periapical tissues) causes severe pain, swelling, and tissue damage. Prevent by using a side-venting needle, keeping the needle loose in the canal, and never binding the needle.
Obturation
The goals of obturation are to create a fluid-tight seal along the entire length of the root canal system, preventing bacterial re-entry and sealing any remaining bacteria within the canal.
Techniques
| Technique | Description | Advantages |
|---|---|---|
| Cold lateral condensation | Master cone coated with sealer, lateral spreader compacts gutta-percha, accessory cones added | Simple; predictable; low equipment cost |
| Warm vertical condensation (Schilder) | Heated plugger softens and compacts gutta-percha vertically | Better adaptation to canal irregularities; denser fill |
| Warm horizontal condensation (Buchanan System B) | Heat source softens gutta-percha for vertical and horizontal compaction | Good apical control; efficient |
| Single cone (with bioceramic sealer) | Single gutta-percha cone matched to final rotary file, with a bioceramic sealer | Fast; uses hydraulic seal; increasingly evidence-supported |
| Carrier-based (Thermafil) | Gutta-percha on a carrier, heated and inserted | Fast; good for curved canals; difficult to retrieve for retreatment |
Sealers
All obturation techniques require a sealer to fill gaps between the gutta-percha and canal wall. Common types:
- Zinc oxide eugenol (ZOE) sealers — traditional; antibacterial; can stain
- Epoxy resin sealers (e.g., AH Plus) — good seal; widely used; some shrinkage on setting
- Bioceramic sealers (e.g., EndoSequence BC Sealer) — hydrophilic; expand on setting; biocompatible; increasingly preferred
Inter-Appointment Medicaments
Between appointments, the canal is dressed with a medicament to maintain disinfection and prevent bacterial regrowth.
Calcium Hydroxide
Calcium hydroxide (Ca(OH)2) is the standard inter-appointment medicament:
- pH 12.5 — highly alkaline; destroys bacterial cell walls
- Effective against Enterococcus faecalis and Candida albicans (common endodontic pathogens)
- Dissolves residual necrotic tissue
- Requires at least 7 days in the canal for maximum effect
- Placed as a thick slurry using a lentulo spiral or syringe
Alternatives
- Antibiotic pastes (e.g., triple antibiotic paste: metronidazole, ciprofloxacin, minocycline) — used in regenerative endodontics; risk of discolouration and bacterial resistance
- Chlorhexidine gel — alternative where calcium hydroxide is ineffective
Endo-Perio Lesions
Endo-perio lesions are conditions where endodontic and periodontal pathology coexist or mimic each other. Accurate diagnosis is essential because the primary source of the lesion determines the treatment.
Classification
| Type | Description | Primary Treatment |
|---|---|---|
| Primary endodontic | Pulp necrosis causes drainage through the periodontal ligament; mimics a periodontal pocket | Root canal treatment alone |
| Primary periodontal | Periodontal disease causes secondary pulp involvement through lateral canals | Periodontal treatment; RCT only if pulp is necrotic |
| True combined | Independent endodontic and periodontal lesions converge | Both RCT and periodontal treatment required |
Diagnostic Clues
- Primary endodontic lesion: isolated deep pocket on one tooth, pulp is necrotic, radiolucency extends from apex along the lateral periodontal ligament; responds to RCT alone
- Primary periodontal lesion: generalised periodontal disease, vital pulp, multiple sites involved; periodontal therapy is the primary treatment
- Vital pulp testing is the key discriminator: a vital pulp with a deep localised pocket suggests a primary periodontal lesion; a necrotic pulp with a draining sinus suggests a primary endodontic lesion
Cracked Tooth Syndrome
Cracked tooth syndrome is an incomplete fracture of a vital posterior tooth, often involving the marginal ridge and extending subgingivally.
Features
- Sharp pain on release of biting pressure (pathognomonic)
- Pain on cold stimuli (reversible pulpitis may progress to irreversible pulpitis)
- Difficulty localising the pain (referred pain common)
- Often affects mandibular molars with large restorations
- Crack may be visible with magnification (loupes, microscope) or revealed by transillumination (light blocked at the crack) or methylene blue dye
Diagnosis
- Tooth sleuth (a plastic instrument for biting on individual cusps) — pain on release is diagnostic
- Bitewing or periapical radiograph — may show no abnormality or a faint radiolucent line
- Periodontal probing — a narrow deep pocket adjacent to a crack suggests the crack extends to the root surface
Management
- Identify the crack and its extent
- Provisional restoration (e.g., orthodontic band or full-coverage provisional crown) to hold the tooth together and assess symptoms
- If symptoms resolve and the pulp remains vital: definitive full-coverage restoration (crown)
- If the pulp becomes necrotic or the crack extends below the alveolar crest: extraction is often the only option
Single vs Multiple Visit Endodontics
The debate over single-visit versus multiple-visit root canal treatment centres on the role of inter-appointment medication and the risk of flare-ups.
Evidence Summary
| Factor | Single Visit | Multiple Visit |
|---|---|---|
| Post-operative pain | Slightly higher in some studies | Similar overall |
| Healing of apical periodontitis | Comparable | Comparable |
| Success rate | Comparable for teeth without apical periodontitis | Comparable |
| Indication | Teeth with vital pulp, no apical periodontitis, single-rooted | Teeth with apical periodontitis, complex anatomy, persistent symptoms |
Current consensus: Single-visit endodontics is acceptable for selected cases (vital pulp, no apical periodontitis, straight canals, adequate time and isolation). Multiple-visit treatment with calcium hydroxide dressing is preferred for teeth with apical periodontitis, complex anatomy, or persistent exudate.
Endodontic Failure and Retreatment
Causes of Failure
- Persistent or secondary infection — the most common cause; residual bacteria in the canal system or leakage
- Missed canals (e.g., MB2 in upper molars, second canal in lower incisors)
- Inadequate obturation — short fill, voids, or poor condensation
- Coronal leakage — inadequate final restoration allows bacterial re-entry
- Root fracture — vertical root fracture is untreatable and requires extraction
- Iatrogenic errors — perforation, ledge formation, separated instruments
Retreatment
Non-surgical retreatment involves removing the existing root filling, re-instrumenting the canal, and re-obturating. Indications include persistent apical periodontitis, inadequate previous obturation, and missed canals.
Surgical endodontics (apicoectomy with root-end filling) is indicated when non-surgical retreatment is not feasible or has failed, when a post prevents access to the canal, or when a persistent cyst is suspected.
Prognosis
- Primary root canal treatment: 85-95% success for teeth with vital pulp and no apical periodontitis
- Non-surgical retreatment: 70-85% success
- Surgical retreatment: 80-90% success with modern microsurgical techniques and bioceramic root-end filling materials
A patient presents with a lower first molar that is tender to percussion and shows a radiolucency at the apex. The tooth gives no response to electric pulp testing or cold thermal testing. There is no swelling or sinus tract. What is the most likely combined pulpal and periapical diagnosis?
During root canal treatment of an upper first molar, the clinician has completed instrumentation and is ready for the final irrigation sequence. Which of the following irrigation protocols is most appropriate, and what is the key safety concern when using sodium hypochlorite?
A 55-year-old patient has a localised 8 mm probing depth on the mesial aspect of a lower first molar. The remaining periodontium is healthy (all other sites 3 mm or less). The tooth gives no response to electric pulp testing. What is the most likely diagnosis, and what is the primary treatment?