Endodontic Treatment

Take Home Message—Pulpotomy, pulpectomy and apicoectomy are endodontic techniques to preserve teeth with endodontic disease. Careful case selection, meticulous technique and owner compliance are necessary preconditions for a successful outcome.

I. Introduction

Endodontics, from the Greek endo (inside) and odons (tooth), is a specialist sub-field of dentistry concerned with the treatment of the tooth pulp and the tissues surrounding the apex of a tooth.¹ Endodontic treatment is aimed at the preservation of teeth affected with pulp or apical infection.² Because equine dentition is fundamentally different from brachyodont species,^3-6 endodontic techniques can not be simply adopted from the human or even small animal field, but rather have to be critically evaluated before being applied to equine dentistry.

In man oral approaches are used for endodontic procedures and to surgically access the apical areas of teeth (apicoectomy). In equines the length of the equine reserve crown usually requires a surgical approach through the maxillary or mandibular bone. Other factors such as the complex endodontic anatomy, the length of the dental rows in conjunction with a limited ability to open the mouth and the size of equine cheek teeth make endodontic surgery significantly more demanding in horses compared to small animals or humans.

II. Etiology of endodontic infection

The most common causes of apical infection are anachoretic infection, gross idiopathic dental fractures, external traumatic fractures, extension of periodontal disease and extension of infundibular caries.^2,7,8 Thermal damage caused by power equipment can also result in thermal pulpitis or even pulp necrosis.⁹

III. Endodontic techniques and approaches in the horse

In selected cases, affected teeth may be preserved with endodontic techniques. Depending on the nature and duration of endodontic disease the pulp may be vital or necrotic.

The presence of vital or necrotic pulp tissue dictates any further therapeutic action. Endodontic procedures can basically be divided into vital (pulpotomy) and mortal (pulpectomy) techniques. During pulpotomy only the infected portion of the pulp is removed. The remaining (healthy) pulp is capped with calcium hydroxide or mineral trioxide aggregate (MTA) to induce the production of tertiary dentine. Pulpectomy on the other hand results in the total removal of any pulp tissue.

IV. Management of acute pulp exposure (pulpotomy)

Acute pulp exposure can occur accidentally during routine dental procedures. Consequently the equine dentist should be acquainted with the basic principles of pulpotomy and pulp capping. It is frequently stated that pulp exposure under such conditions does not require treatment. However, scientific studies to support this hypothesis have yet to be perfomed.

Prior to any endodontic work radiographs should be obtained. If the extent of the lesion does not preclude dental preservation, endodontic surgery can be attempted. Local anesthesia of the maxillary or mandibular nerves facilitates the procedure in the standing horse.¹⁰

After debridement has been performed, 2-3 mm of the clinical crown should be removed to avoid occlusal pressure.² The pulp cavity is then enlarged with high speed dental burs. Contaminated dentine lining the walls of the pulp chambers is removed simultaneously. In curved incisor root canals the pulp cavity can be accessed in a straight drill plane from the intact labial crown.¹¹ Bleeding indicates that the vital pulp has been reached. Drilling should be continued for some additional millimeters to remove the infected part of the pulp (pulpotomy). The occlusal end of the drill hole is shaped like an inverted cone (undercut) to prevent the loss of filling material. Haemostasis is subsequently performed using cotton pellets or paper points soaked in adrenaline. Compressed air can also be used to gently dry the drill hole. The dried cavity is then filled with calcium hydroxide paste (Ca(OH)₂) or MTA which have a strong anti-microbial effect (primarily due to their high pH)¹² and might also act as a tertiary dentine stimulant. Subsequently, 2-3 mm of the occlusal endodontic calcium hydroxide cement or MTA can be removed and replaced with a glass ionomer¹³ or a composite restoration according to manufacturers’ guidelines.

Whilst the technique described above can easily be performed on equine incisors, treatment of acute pulp exposure in cheek teeth using an intraoral approach is significantly more demanding. Long-handled instruments and long shafted, angled dental drills are required as well as dental mirrors or, preferably, a 90° oral endoscope¹⁴ to visualize the surgical site.

Although often discussed anecdotally, no scientific studies or objective long-term reports of case series on the outcome of pulpotomy of cheek teeth using an intraoral approach appear to have been published to date.

V. Pulpectomy in incisor or canine teeth

When devitalized tissue is observed within the pulp canal, preserving the affected tooth might still be an option. If the structure of the dentine is still intact and (periapical) osteolysis cannot be detected on radiographs, a pulpotomy and subsequent endodontic treatment might be performed.

Access to the Pulp Canal

For unobstructed and straight insertion of endodontic instruments into the pulp canal, an approach is created with a round burr mounted on a handpiece of the dental unit. In order to be able to access the entire surface of the bent pulp canal of most incisor teeth and all canines, drilling of an access close to the gingival margin might be necessary. The access cavity might be enlarged and shaped with a Gates-Glidden drill to facilitate straight insertion of root canal instruments.

A 50-60 mm barbed broach is inserted into the pulp canal until resistance is felt. The instrument is then rotated to interlock the fine barbs with the pulp. Subsequently the barbed broach is slowly removed from the canal, ideally together with the infected pulp. Frequently pulp remnants remain inside the canal and have to be extricated during root canal preparation. A fine Hedstroem file (ISO 15) with a rubber endodontic stop is inserted to the depth of the canal (working length) and a radiograph taken to ascertain that the instrument tip is located at the most apical aspect of the canal. It is advisable to take radiographs from different angels as the apical foramen might not be located at the tip of the root. When the correct insertion depth has been determined, the file is withdrawn from the canal. The distance from the rubber stop to the tip of the instrument is measured and transferred to all other root canal instruments using rubber endodontic stoppers.

Pulp Canal Preparation

For removal of necrotic pulp tissue, infected dentine and debris, Hedstroem files with a working length of 60 mm and variable diameters between 0.2-1 mm (ISO 20 – ISO 100) are used. The files are inserted to the rubber stop and the walls of the canal are filed and debrided. Care must be taken not to insert the file deeper as indicated by the rubber stopper. Rotating the files in a clockwise direction during preparation increases the risk of jamming and subsequent breakage of the instrument.

Gentle pressure is applied to the dentine wall of the pulp canal during retraction of the files to extricate debris from the canal. As soft infected dentine is removed from the canal, the diameter of the canal increases and larger files can be used. Flushing with EDTA-solution and sodium hypochlorite solution (NaClO, 3-5%) during canal preparation should be repeatedly performed. The finest file is used to extricate debris from the area of the apical foramen to prevent packing. An effort is made to instrument a conical canal shape of continuously decreasing diameter towards the apex. This facilitates efficient irrigation with disinfecting solutions and later obturation.

To remove the adhering smear layer from the canal walls, flushing with 20-40% citric acid or 17% EDTA solution is performed. The final disinfection of the canal may be performed with 2% chlorhexidine solution or with 3% sodium hypochlrite solution. Saline solution is used to remove the disinfectant from the canal. Long (55 mm) sterile paper points are used to dry the pulp canal. Fresh dry paper points are repeateldly inserted until the tips remain dry after removal.

Temporary Filling

In cases of purulent or necrotizing pulpitis or apical abscessation a temporary filling with calcium hydroxide paste (Ca(OH)2) is used. Calcium hydroxide has a high pH (11- 12.6) and bactericidal properties. Used as a temporary filling material it helps to reduce the bacterial concentration inside the pulp canal and the adjacent dentin tubules. A lentulo spiral paste filler on a slow speed handpiece is used to feed the paste into the canal. Finally a temporary capping with composites or cements is applied.  [...]