Performing vital pulpotomies: why and how (Proceedings)

Pulp physiology

Anatomy

Dentinal pulp occupies the interior cavity of the tooth. It consists of loose connective tissue intercellular substance, vessels, nerves, and fibers. Anatomically, the pulp is divided into a coronal pulp and root pulp, corresponding to the anatomical crown and the root. The anatomical crown is covered by enamel. In older animals, there may be differences in the distribution and density of cells and fibers of the root canal, however there is no principal difference in the tissue constituents. The outline of the pulp chamber, particularly in young animals teeth, usually follows the exterior morphology of the dentin. As the animal ages the pulp chamber is reduced by continual dentinal deposition throughout, and markedly reduced in areas of attrition.

Histology

The pulp morphologically is divided into four areas: 1) the odontoblastic layer covering the periphery of the pulp chamber, enclosed in dentine, with processes extending into the dentinal tubules. 2) the layer of Weil (cell poor layer), that appears next to the odontoblastic layer in mature teeth 3) a cell rich layer, between the cell poor layer and the central pulp and 4) the pulpal center. The pulal center differs from the rest of the pulp only by having a smaller number of cells per unit than the cell rich layer.

The pulp connects with the periapical tissue through apex in each root, with the possibility of many shapes and apical foramina in each tooth. The vetodontist must be aware of this phenomenon. It is of the utmost importance in endodontic therapy. In young animals in which the apical foramen is not yet fully developed, the pulp connects with the surrounding periapical tissue in a wide area. During development of the root, the foramen narrows by lengthening of the root and by deposition of dentin and cementum, but during this period the walls of the foramen still consist entirely of dentin. With increasing age and with exposure to physiologic functioning, a layer of cementum may cover the dentin at varying lengths into the root canal. Cementum does not maintain an equal distance from the foramen throughout the circumference of the root canal. Root development usually results in one main and one or more lateral canals, in ground sections, appearing as an apical delta of varying configurations.

Lateral or accessory canals, though not as common in dog and cats, may occur and connect the pulpal tissue with the periodontal ligament at any level of the root, but are most frequently found in the apical third of the root. Connective tissue of the pulp continues directly to the periodontal ligament through these lateral and accessory canals. Endodontic success may be influenced by the obturation of these canals especially those of significant diameter. In cases of progressing periodontal disease, if the bacterial plaque reaches and involves the soft tissue of lateral canals, pulp involvement will result.

Pulpal function

Pulpal functions are formative, nutritive, sensory, and defensive - formative in that it produces dentin. The development of the pulp is a gradual process that varies with the individual tooth. Development of the pulp takes place after the development of the dental organ, from mesenchymal cells, known as the dental papilla, directly under the dental organ. A distinct basement membrane divides the cellular elements of the dental organ and the dental papilla from each other, and the concentration of cells in the dental papilla stands out clearly from the surrounding oral tissues.

Dentin and pulp share an integral relationship with the odontoblastic processes. When a lesion invades the dentin, the odontoblastic processes and the pulp are involved.

As maturation occurs additional layers of dentin are added. Each dental tubule containing a vital odontoblast. The dentinal tubule tapers to a cone like shape to the dentinoenamel/dentinocementum junction. The dentinal tubules and odontoblastic process are less voluminous at the periphery of the tooth tapering to a almost closed structure at the cemental wall. The cellular, cytoplasmic content of the dentinal tubules is significant in all endodontic treatment. Open dentinal tubules can lead to pulpal pathology.

Normal healthy pulpal tissues continue dentinal deposition at a slow rate throughout life. This is referred to as "calcifying down" of the pulp chamber. Pulpal pathology decreases dentinal deposition. Dentin deposition ceases with tooth mortality

Nutrition

The pulp provides nutrient to the surrounding tissues during development. After development dentin metabolism continues via the odontoblastic processes. The narrow pulp canals of older animals continues to remain vital with pulpal circulation intact and functional.

Sensory

The sensory function of the pulp is response to pain. This is accomplished through the nervous intervention via the apical foremen. Nerve bundles enter the pulp splitting into finer bundles then into unmylinated fibers that enter the odontoblastic layer. Pulpal nerves seem to remain unchanged in older animals. After pulpal necrosis of the coronal pulp with apical inflammation, nerves may still persist in the apical area.

Defense

Pulpal response to injury is inflammation. Inflammation produces a chemotactic response that slows the destructive action to the pulp. Continual irritation will result in pulpal death in spite of a strong response to the irritation from a well vascularized pulp.

Vessels

The dental pulp is a blood rich organ. The numerous vessels that pass through the apical foremen and are distributed throughout the pulp. Most vessels are thinned walled with large lumen. When circulation is cut off, as seen with traumatic severance of vascular supply to the pulp, or periodontal involvement to the apical area, pulpal necrosis result form lac of nutrients to the pulp. It has been demonstrated that the pulp contains lymph vessels through experiments with calcium hydroxide and its rapid uptake into the pulp during pulp capping and pulpotomy procedures.

Vital pulpotomy

Vital pulpotomy is the treatment of choice when treating healthy, freshly exposed pulp in immature animals where the root apex is still open and the dentine wall is thin. The remaining treated vital pulp will continue to produce dentine. closing the apex and thickening the dentine wall. Following the removal of the coronal pulp, the remaining healthy pulp is encouraged to produce a secondary dentine bridge by treating it with calcium hydroxide. This is rarely the technique of choice for mature animals with closed apices and thick dentine walls, unless performed under sterile conditions as a disarming procedure.

If the pulp is treated within one hour of accidental exposure, and inflammation and infection are minimal. the prognosis is good. The longer the pulp has been exposed, the poorer the prognosis. The health of the pulp can be assessed by the color and flow of the pulpal blood on excising the coronal 8 mm of pulp; bright, red, free-flowing hemorrhage suggests healthy pulpal tissue. This is a very subjective assessment and should be used with caution. It is a helpful guide in situations where the time of the exposure is unknown.

Surgical crown height reduction is a sterile procedure, which should prevent infection of the pulp. The procedure is usually limited to the canine teeth, where it may be used to treat traumatic malocclusions (e.g. medially displaced lower canines impinging on the hard palate) or as a disarming technique.

Procedure

1. A radiograph is taken if possible to check for additional fractures and other complicating factors. The surgical site is isolated and disinfected with a suitable agent such as Maxicide or Betadine or chlorhexidine.

2. If possible isolate the tooth from contamination by wrapping the sterile glove. A hole is made in the glove for the diseased tooth to protrude through.

3. Select a round diamond bur that will approximate the exposed pulpal diameter and place it preferably in a high speed dental hand piece. With sterile water irrigation the diamond bur is inserted into the pulp chamber. cutting through the coronal pulp to a depth of 8-10 mm. At high speed. a sharp diamond bur cuts the tissue without tearing as would be the case with steel or carbide burs. Care should be taken to avoid pushing dentine shavings onto the pulp as this will increase pulpal hemorrhage.

4. Access to the pulp chamber may be enlarged as necessary with a larger diamond bur. The pulp is amputated as atraumatically as possible to remove any infected pulp and create space for the medicaments to treat and protect the pulp. The aim is to reach healthy pulpal tissue while minimizing damage.

5. Hemorrhage, if present is controlled by inserting the blunt end of large sterile paper points or a small damp sterile cotton pellet into the canal and gently pressing them on to the pulp. The paper points should not be continually removed and reinserted, but left in contact with the vital pulpal tissue for 3-5 minutes to encourage clotting. When sterile cotton wool dampened with sterile saline is used to control hemorrhage; care must be taken not to leave any threads of cotton wool in the canal.

6. Hemorrhage in healthy is usually controlled in approximately 5 minutes. Hemorrhage continuing beyond this time usually indicates the presence of inflamed pulp; this must be removed. Another 1 mm of pulp is amputated and the paper points or cotton reapplied. If hemorrhage is still uncontrolled the procedure is repeated. Continual hemorrhage usually indicates advanced pulpal pathology. Conventional endodontic therapy is indicated in these cases.

7. Calcium hydroxide powder is placed directly on to the pulp This will control residual minor hemorrhage. The powder is carried to the vital pulpal tissue on a sterile plastic filling instrument (beaver-tail) and inserted in small increments into the pulp chamber with the blunt end of a sterile paper point. the calcium hydroxide powder is gently packed on to the pulp a depth of 3-4 mm.

8. A hard-setting calcium hydroxide cement, such as Hypo-cal, can be placed on top of the calcium hydroxide powder with a ball-point applicator to provide additional protection and insulation of the pulp. The hard setting calcium hydroxide lends some strength to the base calcium hydroxide.

9. A suitable bur such as a pear-shaped bur, size 330, is used to clean the remaining coronal 4 mm of pulp chamber walls, removing excess cement and debris. An very slight undercut is made into the pulpal walls to create a retentive shelf for the final filling. As little dentine as possible should be removed when making the undercut so to minimize weakening of the tooth. The site is flushed with pressurized water and dried with oil free air.

10. A glass-ionomer or composite is used to fill the prepared site. The manufactures. instructions should be followed exactly in preparing the tooth's surface and mixing the materials. Using the round end to the plastic filling instrument. the material is packed into the prepared site. It is essential that the restorative material is tightly condensed against the cavity walls.

11. Rough tooth edges and restorative material are smoothed with a finishing bur, diamond, or sandpaper disk. followed by rubber abrasives-polishing- wheels.

12. A radiograph is taken for evaluation of the procedure, and for comparison with one to be taken 6-9 months post-operatively. The 6-9 months post operative radiograph should show thicker intercanal walls, a closed apex, and possibly the formation of a dentinal bridge between the calcium hydroxide and the pulp.