Definition of Endodontics
Endodontics is a branch of dentistry dealing with diseases of pulpal and periradicular tissues. It encompasses the study of the biology of the normal pulp, the aetiology, diagnosis, prevention, and treatment of diseases and injuries of the pulp, and associated periradicular conditions.
Functions of the Dental Pulp
1. Formation of dentine (coronal and radicular)
2. Maintenance of tooth (fluid environment)
3. Defence mechanism (secondary dentine, reparative dentine, fluid flow)
4. Age changes (peritubular dentine, more solid tooth)
5. Sensation (pain)
Aetiology of Pulp and Periapical Disease
a. Coronal ingress through tooth fractures, cracks, leaking restorations
b. Radicular ingress - Periodontal disease, cracks, fractures, breakdown of RCT
a. Accidental: Tooth fracture, luxation, avulsion (cage biting, road trauma, animal fights, rock chewing)
b. Physiological: Attrition, abrasion, occlusal trauma
a. Cavity preparation (heat, depth, dehydration, exposure of tubules)
b. Surgical trauma to adjacent teeth
c. Orthodontic movement
d. Periodontal treatment
e. Radiation therapy for cancer
b. Internal resorption
c. Tooth resorptions
Pulpal Pathology Due to Bacteria
The pulp space is capable of containing millions of bacteria. The bacteria produce toxins (especially endotoxins), which diffuse through dental tissues into the periradicular tissues.
Bacterial byproducts act on host tissues in two ways:
1. Enzymes and metabolic products can exert a direct tissue toxic effect.
2. Components from the bacterial cell (i.e., endotoxin) can trigger inflammatory defence reactions.
Pulpal Response to Injury
The response of the pulp to injury depends on the status of the pulp at that time (i.e., inflamed or not).
With mild injury, odontoblasts die and there is acute inflammation in the subodontoblastic layer, but resolution will occur, and cells in the subodontoblastic layer will differentiate into odontoblasts and instigate reparative dentine.
With major injury, some pulpal tissue dies, and there is acute inflammation in adjacent tissues - a walling off of affected tissues and subsequent fibrosis. However, if there is continuing inflammation, there will be further necrosis, eventually involving the whole pulp.
Some of the theories about the causes of pulpal necrosis include:
1. Limited drainage from the pulp
2. Limited access for repair (from one direction only - the apical end)
3. Pulp is surrounded by nonflexible tissue (e.g., like the brain encased in bone)
The Aims of Endodontic Treatment
1. To remove from the root canal system all organic matter that is capable of either decomposing into tissue-destructive byproducts or that can support bacterial growth
2. To remove or destroy all bacteria present in the root canal system
1. To prepare the root canal space to a form, which allows complete three-dimensional filling
2. To fill the prepared space with a biocompatible filling material in order to completely seal the coronal and apical ends of the canal. The apical end of the root canal filling should be placed as close to the cementodentinal junction. Finally, a complete coronal seal should be placed.
Methods Used to Accomplish These Aims
1. Aseptic technique
2. Debridement of the root canal system
3. Irrigation with disinfecting agents
4. Medication if required with antimicrobial dressings
Biomechanical Preparation of Root Canals
Access to the root canal system is gained with high-speed burs, pulp burs, and Gates-Glidden burs. Straight-line access to the apex should be aimed for. A Gates-Glidden bur can be used on the out-stroke to flare the coronal portion of the canal. Gates-Glidden sizes up to a size 6 can be used to open up and flare the coronal access.
A combination of mechanical instrumentation as well as chemical irrigation.
In curved canals, it is best to pre-curve stainless steel files. Working length should be established first. (A preoperative radiograph will help in the determination of working length.)
Once working length has been established with the aid of a working length radiograph, the apex can be enlarged (about 3 file sizes larger than the first file that binds slightly at the apex), and the last file used at the apex is called the master apical file (MAF).
All filing should be performed in a wet canal (i.e., irrigated with 1–4% sodium hypochlorite) and in a circumferential filing technique engaging all the inner walls of the canal.
Canine teeth in dogs can have a midroot constriction that will need to be enlarged to allow for better cleaning and better obturation of the canal.
The apical extent of the tooth is instrumented first, and once the apex has been enlarged to a certain file size (MAF), the working length is reduced by 1-mm increments, and the next file size up is used to prepare the canal until a funnel-shaped canal is produced. Recapitulation, with the master apical file, should be performed between each file change to reestablish working length.
Crown Down Technique
This technique utilises Gates-Glidden burs at the coronal end of the preparation and then utilises instruments in a large to small file size sequence until the apex is reached.
Irrigation of the canals can be performed by using 1–4% sodium hypochlorite and 17% ethylene diamine tetraacetic acid (EDTA).
Sodium hypochlorite - Has a flushing action, dissolves organic matter, is antibacterial, and has a minor bleaching action.
EDTA - Has a flushing action, chelates dentine (softens), prevents buildup of a smear layer (inorganic matter), is antibacterial, and aids canal negotiation.
Drying the Canal
Paper points (at working length) are used to dry the canal prior to obturation.
There are a number of mechanical rotary instrumentation systems available in the human dental market, but the light speed system is the most common system used by veterinary dentists. It utilises coronal third, mid-root third, and apical third shaping with mechanically driven titanium files to prepare the canal for obturation.
Obturation - Filling of the Canal(s)
To fill the prepared space with a biocompatible filling material in order to completely seal the coronal and apical ends of the canal. The apical end of the root canal filling should be placed as close as possible to the cementodentinal junction. The root filling must fill the entire canal space.
1. Core material - Gutta Percha (GP) points - satisfy all requirements when used with sealer cement. GP contains approximately gutta percha 22%, wax and resins 5%, zinc oxide 70%, metal sulphates 3%.
2. Sealer - AH 26* (DeTrey/Dentsply): An epoxy resin with powder and liquid. Properties: biocompatible, good adhesion, effective sealing, low solubility, mixes easily, flows well, radiopaque, ample working time, small particle size, and good compressive strength. Zinc oxide-eugenol is also a commonly used sealer cement in veterinary endodontics.
Obturation Technique for Gutta Percha
Lateral condensation is the recommended method for most situations. The best seal occurs if a spreader tip reaches within 1 mm of the working length during GP seating.
Basically, lateral condensation technique involves the fitting of a master GP point at working length (dipped in AH26) and then accessory points placed with a spreader so that the whole canal is filled with GP points and AH26 cement.
The tags of GP points are burnt off and the GP condensed into the canal with a plugger. Next, clean out the access cavity with a cotton pellet dipped in 70% alcohol to dissolve excess AH26, and then dry the canal and place your final restoration (usually a layer technique of glass ionomer cement with a composite resin placed above this).
Other Obturation Techniques
There are a number of thermoplastic GP delivery systems on the market (Obtura - Obtura Spartan; Thermafil - Dentsply, ResilonTM). These systems use alpha phase gutta percha, which flows when heated. Alpha phase has the same chemical formula as regular beta phase GP, but has been annealed by a proprietary process to achieve a lower molecular weight, resulting in different physical properties.
Thermafil has a plastic carrier delivery system with the carrier coated with the GP. When heated, alpha phase becomes exceedingly sticky and tacky, and has excellent flow characteristics. This heated gutta-percha exhibits a wetting phenomenon that causes it to adhere to the plastic carrier for transportation down the root canal without stripping away from the carrier. The flow properties allow the gutta percha to obturate available lateral and accessory canals. The GP sets in approximately 2–3 minutes.
Today, there is a cold self-curing GP obturation system available. This product combines gutta percha with sealer cement (GuttaFlow - Coltene/Whaledent).
Properties of GuttaFlow
GuttaFlow comprises a unique mixture of gutta percha (GP), polydimethylsiloxane sealer, and nano-silver particles (preservative) contained in a plastic capsule. The particle size of GP is less than 30 µm. It is introduced cold into the canal(s) and allowed to chemically cure. The root canals(s) are chemico-mechanically prepared in a similar way to other canal preparation techniques. There are no special considerations required for the use of GuttaFlow material except that the final irrigant used in the canal should be 0.9% sterile saline.
A great disadvantage of heated GP obturation systems is the shrinkage that is associated with the cooling of the heated GP. This may lead to micro-leakage due to the pulling away of GP from the dentinal walls.
GuttaFlow has been shown to expand slightly as it sets (0.2% expansion), resulting in an excellent seal as it sets. GuttaFlow also flows very well, thus reaching all areas of the root canal system. It can penetrate into dentinal tubules also. GuttaFlow also becomes less viscous under pressure (thixotropic), offering 3-dimensional sealing of the root canal space and filling of lateral canals.
Most root canal sealers are water soluble and dissolve over the years (not as important in veterinary dentistry as in man). GuttaFlow shows a solubility of 0.0%. It is also biocompatible and nontoxic to tissues even when extruded from the canal apex.
All endodontic cases should be reviewed to assess whether the treatment has been successful.
Success can be based on clinical examination (no draining sinus or loss of coronal restoration) as well as radiographs taken on a regular basis.
On subsequent radiographs, there should be no further loss of periradicular bone and there should be healing of any radiolucent areas that were present prior to treatment.
In the past 15 years, there have been a number of advancements in the delivery of endodontic services. The use of nickel titanium rotary instrumentation, the use of apex locators, and cold and heated obturation techniques have all contributed to better outcomes for patients.
Whenever performing endodontic therapy, procedural errors can occur. Common errors include fracture of endodontic instruments within the canal, perforation of the root or pulpal floor. Zipping (transportation of the apex) or ledging of the canal with overzealous instrumentation can also occur. Other errors, such as loss of working length and perforation through the apex, are possible.
The clinician should be aware of the possibility of these errors occurring. Steps can be taken to prevent such errors, including not reusing damaged or weakened hand files or rotary files, which can easily fracture. Following correct instrumentation procedures, including recapitulation with the master apical file and the use of copious amounts of flushing solution to dislodge debris within the canal(s), is recommended.
Even by taking such precautions, procedural errors may still occur. The early identification of the error and its correction can still lead to an acceptable clinical outcome.
Root canal therapy offers a good alternative to extraction, especially for the "cornerstone" teeth such as the canine tooth and the carnassial tooth (maxillary 4th premolar and mandibular 1st molar). The loss of a mandibular canine tooth, especially, may cause the tongue to hang out. In cats, the loss of the maxillary canine tooth may cause trauma to the upper lip from the mandibular canine tooth. Also, for police dogs, the canines are essential for grasping and securing criminals.
The success rate of RCT depends on a number of factors but can be considered to be reasonably high (around 80%).