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root canal prep (If no blood supply root system infected, Aims: removal…
root canal prep
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Aims: removal pulp tissue, debris, microorganisms from canal; shape for filling & sealing. Goals of tx: chemomechanical debridement (remove bacteria from canal system), shaping (of canal system for filling), filling (obturation – of canal system w placement of restoration)
Stages root canal therapy: endo assessment incl pre-op radiograph, access cavity, root canal prep, intracanal med, temporarisation, filling root canals, coronal restoration
Access cavity: opening in crown, for localisation, prep, shaping, disinfection & 3D fillings of RC system, success depends on this
Access cav req: removal all pulp chamber, direct vision chamber floor & canal orifices, instruments into root canal openings, access direct as possible to apical third of canal, support for temps, 4 walls
Access cav: unimpeded path to pulp space & apical foramen, conservation coronal structure shouldn't preclude proper design, eliminate obstruction
Anatomy of pulp-chamber floor: relationship of pulp chamber to crown – Krasner & Rankow 2004
- Law of centrality: pulp chamber centre @ level of CEJ
- Law of concentricity: walls of pulp chamber concentric to external surface @ level of CEJ
- Law of CEJ: distance from external surface o wall of pulp chamber same throughout circumference @ level of CEJ
Relationships on pulp-chamber floor:
- Law of symmetry: exc mx molars, orifices of canals equidistant from line in mesial distal direction thru pulp-chamber floor
- Law of symmetry: exc mx molars, orifices of canals perpendicular to line in mesial distal direction across centre of floor of pulp chamber
- Law of colour change: colour of pulp-chamber floor darker than walls
Working length determination: estimated working length (EWL) – measured on pre-op radiograph, electronic apex locator (EAL) working length – measured w EAL attached to #10 K-file inside canal to EWL (rubber stopper for WL), radiographic working length – confirm EWL & EAL WL by taking PA of #10 file in canal (0.5-1mm short of radiographic apex)
Law of orifice location:
- Orifices of canals @ junction of walls & floor
- Orifices of canals @ angles in floor-wall junction
- Orifices of canals @ terminus of root developmental fusion lines
Concepts for canal prep: divide into smaller steps, teeth lengths 20-25mm, crowns 10mm, roots 10-15mm, coronal, middle & apical thirds 5mm, pre-enlarged coronal canals better access to apical third
Pathfinding & coronal flaring: small K-files (#08 or #10) to explore canal, flare coronal & middle part canal w Gates Glidden or NiTi rotary instruments, Stepdown (handfiles) Crown-down (rotary NiTi) technique – larger to smaller instruments
Termination of prep: largest file @ determined working length ‘master apical file’, #25 or #30 depending on type (larger for 1 root, smaller for multi-rooted or calcified canals), narrow canals #20 but may need enlargement for filling (unless NiTi rotary file systems)
Canal prep techniques: standardised (Ingle 1961), step-back (Weine 1972), anticurvature filing (Abou-Rass 1980), step-down (Goerig 1982), double flared (Fava 1983), crown-down pressure-less (Morgan & Montgomery 1984), balanced force (Roane 1985)
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NiTi instruments: shape memory & superelasticity, canal curvature better than SS-files, torsional frac, fatigue frac, decr cutting efficiency (Vickers Knoop hardness 300-350 vs 530 for SS), hand & rotary files
Speed & torque controlled motor w auto-reverse, special reduction handpiece
Irrigation bleach (sodium hypochlorite antibacterial, dissolves organic tissue), lots, deep, stir, recapitulation – small file to working length
Reaming (drilling) – reamers/K files:
- Penetration: into canal
- Rotation: clockwise twisting in ¼ (curved) to ½ turn (straight) canal
- Retraction: withdrawn to cut dentine
Filing (rasping) – K-files/H-files:
• K-files: tighter spiral w cutting angle cut on withdrawal
• H-files: +ve rake angle on retraction
Hedstrom Files (H files): Cutting spirals in round tapered wire, no reaming/drilling
RC prep = lubricant, dry w paper points, dress w Ca(OH)2 (not setting) for > week, spin material into canal w Pastinject
Temp in access cav >4mm (2 stages), grey Cavit (soft), glass ionomer or IRM (intermediate restorative material)
Notes: prep of canals done w coronal part 1st (crown-down prep; 3 stages)-
- Coronal prep: glass-glidden drills or rotary NiTi orifice enlargers, removes infected, prevents debris apically, penetration antibacterial irrigants, working length using films & electronic apex locator, radiograph w instrument in canal w length from ref
- Termination of prep: ‘apical stop’, find size of file binding @ apex, prep canal 3 or 4 instruments larger, final file ‘master apical file’ (MAF), keeping apical termination small so dependent on size of natural canal and if infected, overall taper of canal, filling technique chosen
- Apical flare: joins apical prep w coronal, ‘step backs’ from apex using larger instruments @ shorter lengths, trend in canal prep to use rotary NiTi instruments, more flexible than SS & greater taper than standard (0.02mm/mm), slow speed w speed & torque controlled motor w auto-reverse, special reduction handpiece used w motor
NaOCl as irrigant (EDTA containing cream) on instruments as lubricant, paper points dry canals, nonsetting calcium hydroxide dressing in canal between visits using rotary instruments (Pasinject), temp of grey Cavit covered by glass ionomer or IRM in access cavity
Vocab: recapitulation (small file to working length for irrigant movement and ensure canal length not lost), circumferential filling (working files around walls of canal to instrument max area of dentine), anticurvature filling (filling outer curve of canal away from furcation to avoid strip perf), elbows & zips by files straightening in canals as moved – prebend, transporations (movement of central part of canal lat while filing)