Attempt to remove any live pulp using a barbed broach rotated 180° and slowly withdrawing. Care! Barbed broaches may break if lodged in the canal. Do not use in narrow canals.
Step 2 - Cleaning and shaping
Determine working length. A small diameter file (eg #10-15) is inserted until the apical constricture is felt by digital tactile sense.
Slide the endodontic stop down the file until it contacts the occlusal tooth margin.
Radiography to confirm instrument reaches apical stricture.
Measure working length from the endondtic stop using an endodontic ruler. Mark this length on all files to be used with an endodontic stop. Calculate the working length of your file on the first radiograph and put rubber endodontic stops on each file to guide you.
Start with a small file (eg #10-15), using files appropriately:
H-files: push-pull only.
K-files: push-pull or push-rotate clockwise 90° and pull.
Use files sequentially, so that each file is inserted to working length until it moves freely.
Clean, white dentin chips should be seen coming out with the file.
Irrigate between files. A luer-lock syringe attached to a side-exit endodontic needle is used. Full strength bleach (5.25% NaOCl) is the irrigant of choice, which may be warmed in a bay-bottle warmer to 37° to increase efficacy. Care! This must not be forced peri-apically as it is extremely irritant to tissues. Soft tissues must be protected.
Move the needle continuously up and down in the canal, never flush if the needle is bound in the canal, and use suction at the access point if possible.
Flushing with NaOCl serves to help sterilize the canal and dissolve organic (pulpal) debris.
Recapitulate. Return to a small file every so often to remove dentinal debris that may be lodged at the apex.
Removal of the smear layer may be enhanced by using a chelating agent such as EDTA (RC Prep). This helps to lubricate the file and softens the dentinal walls to improve debridement.
Filing continues until clean, white dentinal shavings are seen on two subsequent files,andthe next file binds before reaching the working length. This is themaster file.
Radiograph with master file in canal.
Shaping uses files to create a funnel-shaped preparation, which not only enhances the irrigating, but also is the optimal shape for subsequent filling (obturation).
Step 3 - Dry the canal
Dry the canal with sterile paper points . These are handled using college forceps.
Paper points come in different lengths (eg human [21 mm] vs veterinary [50 mm] and sizes (ISO sizes or fine/medium/coarse). Keep changing the points until they come out dry. You should not see blood on the paper points. If you do, it is either due to over instrumentation (perforation) or under-instrumentation (some pulp remains).
Step 4 - Obturation
This describes the process of 3-dimensionally sealing the cleaned and shaped root canal. It should seal the apex from peri-apical fluids and seal any remaining bacteria withing the canal.
Obturation combines a core material and a root canal sealer.
The standard core material is gutta percha which is available in ISO sized points (also called cones).
Different types of root canal sealer are used, and the operator should be familiar with the properties and indications for use for each material, eg:
Zinc oxide Eugenol sealers, epoxy resins, calcium hydroxide based sealers.
There are many different obturation techniques including cold lateral condensation, warm vertical compaction, continuous wave condensation and thermoplastic injection and carrier-based gutta percha. The following describes cold lateral condensation.
A gutta percha master cone is selected which is of similar size and taper to the final master file used during shaping. A master cone should fit neatly into the apex of the root canal and a 'tug-back' should be appreciated when removed from the canal. Radiograph to confirm fit.
Mix the chosen sealer according to manufacturer's instructions and apply to the root canal. This may be performed either with a spiral paste-filler on a low-speed handpiece, by injection or coating the master file.
Insert the master cone to the apex of the tooth. A sharp ended spreader is placed laterally to this and twisted to remove after 30 seconds. Immediately insert an accessory cone. Continue this until the canal cannot accept further cones.
A plugger is then used to vertically compact the gutta percha cones.
Step 5 - Radiograph
Radiograph the tooth again to ensure that the canal is completely filled and no void exists, particularly at the apex. In canine teeth remember the canal is oval shaped, therefore obtain a lateral and occlusal view to properly assess the fill quality.
If an apical seal has not been perfected, two options are possible. Either Continue lateral and/or vertical compaction techniques to improve the denseness of the filler. Or Remove the obturation and start again.
Step 1 - Restoration
All gutta percha and sealer must be removed from the coronal access area using a spoon excavator or round diamond bur on a low-speed handpiece.
A base of glass ionomer is placed over the ends of the gutta percha and light-cured. Eugenol will prevent proper curing of resin-based materials if contact is allowed. Dycal is used as a physical barrier to prevent this.
Fill access point with a restorative - either a composite or glass ionomer. Follow the instructions supplied with the material carefully, especially with regard to acid etching or bonding. Place incremental layers no deeper than 2 mm,and light-cure for the recommended time. Consider the occlusal forces that may be palced on the restoration when deciding which material to use.
Shape and smooth the restoration to re-create the original contours and prevent any underhang that may be plaque retentive. Use medium or fine diamond burs to remove bulk composite and then fine diamond burs, fine polishing points or disks for final polishing.
Remember that the quality of the final resoration has a direct impact on the overall success of the procedure. A good quality obturation will fail if a poor quality restoration is placed.
Step 2 - Final radiograph
Final radiograph should assess the resoration quality.
Post-operative antimicrobial therapy is controversial. Perioperative therapy should be considered in cases of abscessed non-vital teeth, especially if the patient is immune-compromised.
Failure can occur and is often related to ongoing infection due to improper technique at any of the three main stages, or if the coronal seal is lost post-operatively.
Long term Aftercare
Follow-up radiographs at 6 months, 1 year, 2 years and 5 years. Dogs do not often show signs of oral pain, and clinical abscesses are rare. The success of therapy can only be judged radiographically and should be considered as part of the follow-up care.
Radiographic evidence of success would be the lack of any new periapical lucency, or resolution of a previous lucent area.
Reasons for treatment failure
Failure may be noted by the appearance of a new peri-apical lucency or one that has enlarged since treatment.
A failed root canal must either be re-treated by a standard technique, or a surgical apicoectomy procedure performed.
Root canal therapy in dogs may carry up to a 95% success rate, but there are no comparable studies in the cat.