Methods for Removal of root filling material in preparation for posts

Methods for Removal of root filling material in preparation for posts

Obturation techniques

Gutta-percha is today the universally accepted core material used for root canal obturation. However, the techniques for placement differ, but all require the use of sealing cement. Obturation techniques include cold lateral compaction of gutta-percha points, compaction of gutta-percha that has been heat softened in the canal and compacted (eg System B), thermoplastisised gutta-percha which is injected into the canal (eg Obtura and UltraFil) and finally compaction of gutta-percha which has been placed in the canal and softened by mechanical means (eg McSpadden compactors). These obturation techniques are unlikely to have an impact on the final apical seal once post space preparation has been carried out. An alternative obturation technique also exists which involves heated gutta-percha surrounding a plastic or metal carrier (eg Thermafil). The carrier ensures that the gutta-percha passes to the correct working length and is left in situ with the gutta-percha. During mechanical gutta-percha removal of this system, there is greater potential to disrupt the apical gutta-percha and a number of dye leakage studies have supported this hypothesis. It would therefore be prudent not to use such obturation techniques if placement of a post is anticipated.

Chemical removal

Solvents such as oil of eucalyptus, oil of turpentine and chloroform have been used to soften gutta-percha for removal, with the latter two being the most effcicient. However, some of these materials and especially chloroform are hazardous to use as they are toxic and potentially carcinogenic. Oil of turpentine is less toxic, but there is concern that solvents in general lead to a dimensional change in the gutta-percha, leading to increased microleakage. This together with the fact that it is difficult to control the depth of softening of the gutta-percha and potential leakage of the solvents into the periradicular tissues should be sufficient to discourage their use for gutta-percha removal for post placement. They are however a necessary adjunct in root canal re-treatment cases.

Thermal removal

A heated instrument such as a lateral compactor can be inserted into the gutta-percha to the desired length to soften and remove the gutta-percha. However, in narrow canals, fine instruments lose their heat quickly and gutta-percha removal can be difficult. A System B spreader is ideal for removal of gutta-percha.

System B with heated plugger (200°C) in foreground, with rubber stop placed at the desired length for gutta-percha removal  

From a pre-operative radiograph a plugger should be chosen of the correct dimensions that is likely to bind at the desired post length and this position should be marked on the plugger with a rubber stop. The tip should be placed in the gutta-percha and with the heat applied driven slowly to the desired post length in about 2–3 seconds. The heat should be removed and the plugger allowed cooling for about 7–10 seconds, twisted and then removed with the coronal gutta-percha. Alternatively, a short burst of heat to the plugger will allow for easy removal. It is important that the plugger is sufficiently hot to completely soften the gutta-percha. If too cool, it will result in the gutta-percha remaining sticky with the risk of dislodging the apical gutta-percha. An instrument such as a Buchanan plugger can then be used to vertically compact the softened gutta-percha. Such a technique is useful in removing old gutta-percha which can become quite hard.

Buchanan plugger  

Some authors would suggest that gutta-percha should be removed with heated techniques as a routine and mechanical removal only used if heat is insufficient.If mechanical removal is used, a heated instrument can be used to soften the most coronal gutta-percha, so that it can be vertically compacted and adapted to the canal walls to create a seal.

Mechanical removal

Mechanical removal of gutta-percha is efficient and probably the most commonly used technique, but it is a technique that can result in the most damage to tooth tissue. If done incorrectly, it can weaken the root unnecessarily, damage the periodontium and in some cases lead to root perforation.

Periapical radiograph showing teeth 13 and 12 used as double abutments for a fixed-fixed conventional bridge 

 Periapical radiograph of tooth 23 with a post that poorly fits the prepared post hole 

A non-end cutting bur such as a Gates-Glidden or Peeso reamer should be used for gutta-percha removal, as these will cut and remove the relatively softer gutta-percha preferentially to the dentine of the canal walls.

The sequence in which the burs are used is important so that a rise in temperature at the root surface, which could damage periodontal cells, is avoided and the risk of preferentially cutting away root dentine to one side of the root canal is reduced.

 Periapical radiograph of root filled central incisor teeth (top left) from which the diameter of the post to be used can be estimated  

Temperature rise on the root surface has been investigated in a number of studies. A Gates-Glidden bur rotating at 8,000 rev min^-1 results in a small rise in temperature at the root surface. However, both tapered and parallel-sided post drills produce a significant increase in temperature in excess of 17°C. Peeso reamers also generate significant rises in temperature, higher than that reached with Gates-Glidden burs and Parapost twist drills. To reduce this temperature increase, which could potentially damage cells in the periodontal ligament, it is important that the smaller sized Gates-Glidden burs are used first, working up through the sizes in turn, until no gutta-percha is removed apically. At this stage the smallest post drill can be used, again working up through the size sequence until the final post size is reached.

A NOTE ON PTERYGOPALATINE FOSSA

PTERYGOPALATINE FOSSA

The pterygopalatine fossa—

           A small, pyramid-shaped space.

           Situated between the maxilla, sphenoid, and palatine bones.

           It communicates via canals, fissures, and foramina with various regions of the skull.

          The contents of the pterygopalatine fossa include

                     The terminal portion of the maxillary artery;

                     The pterygopalatine ganglion;

                     The maxillary division of the trigeminal nerve; and branches of these structures.

Maxillary Artery

The third, or pterygopalatine portion, of the maxillary artery enters the pterygopalatine fossa from the infratemporal fossa via the pterygomaxillary fissure

Maxillary artery and its distribution in the deep face

Branches of the pterygopalatine portion of the maxillary artery are the posterosuperior alveolar, infraorbital, greater palatine, pharyngeal, and sphenopalatine arteries as well as the artery of the pterygoid canal.

The posterior superior alveolar artery branches from the maxillary artery as that vessel enters the pterygomaxillary fissure. It travels on the maxillary tuberosity and enters the posterior superior alveolar foramen accompanied by the like-named nerve. The vessel ramifies within the maxilla to vascularize the maxillary sinus, molars, and premolars as well as the neighboring gingiva.

The infraorbital artery, a continuation of the maxillary artery, enters the orbit through the inferior orbital fissure, lies in the infraorbital groove, leaves the orbit via the infraorbital canal, and enters the face by way of the infraorbital foramen. Branches of the infraorbital artery are the orbital branches, serving the lacrimal gland and the inferior oblique and inferior rectus muscles; the anterior superior alveolar branches, which vascularize the anterior teeth and the maxillary sinus; and the facial branches.

The greater palatine artery and its branch, the lesser palatine artery, pass through the pterygopalatine canal and gain entrance to the palate via the greater palatine and lesser palatine foramina, respectively, to vascularize the hard and soft palates as well as associated structures. The pharyngeal branch passes dorsally, through the pharyngeal canal, to vascularize the auditory tube, sphenoidal sinus, and portions of the pharynx. The sphenopalatine artery leaves the pterygopalatine fossa via the sphenopalatine foramen on its medial wall to enter the nasal fossa. The distribution of this vessel and its branches is discussed later in this chapter. The small artery of the pterygoid canal passes through the posterior wall of the pterygopalatine fossa via the pterygoid canal. It supplies part of the auditory tube, pharynx, middle ear, and sphenoidal sinus.

Maxillary Nerve

The maxillary division of the trigeminal nerve enters the pterygopalatine fossa at its posterior boundary via the foramen rotundum. While in the fossa, it gives off the zygomatic nerve, which, passing into the orbit through the inferior orbital fissure, will bifurcate to form the zygomaticotemporal and zygomaticofacial nerves.

The maxillary division of the trigeminal nerve

The posterior superior alveolar nerves also branch from the maxillary nerve, exit the fossa via the pterygomaxillary fissure, and enter the maxillary tuberosity to serve the maxillary sinus, molars, and adjacent gingiva and cheek. The maxillary nerve then enters the orbit by way of the inferior orbital fissure and is referred to as the infraorbital nerve.

While in the pterygopalatine fossa, the maxillary nerve communicates with the pterygopalatine ganglion via two small trunks, the pterygopalatine nerves; however, these nerves do not bear a functional relationship with the ganglion. Postganglionic parasympathetic fibers derived from the ganglion ride along and distribute with branches of the maxillary division of the trigeminal nerve.

Pterygopalatine ganglion and associated nerves and arteries

Orbital branches are slender nerves that supply the periosteum of the orbit and the mucoperiosteum of the ethmoidal and sphenoidal sinuses. The greater palatine nerve and its branches, the lesser palatine and posterior inferior nasal branches, descend through the pterygopalatine canal to supply regions of the palate, gingiva, tonsil, and lateral wall of the nasal fossa.

Posterior superior nasal branches leave the pterygopalatine fossa via the sphenopalatine foramen to serve the posterior aspect of the nasal fossa and part of the ethmoidal sinus. Its nasopalatine branch grooves the vomer bone in its path to the incisive foramen of the anterior hard palate, which it supplies. The pharyngeal nerve traverses the pharyngeal canal to innervate part of the nasopharynx.

Pterygopalatine Ganglion

The pterygopalatine ganglion seems to be functionally associated with the maxillary division of the trigeminal nerve because it is suspended by the pterygopalatine nerves within the fossa. It is, however, a parasympathetic ganglion of the facial nerve (cranial nerve VII).

This ganglion receives its parasympathetic preganglionic root by way of the pterygoid canal, which opens onto the posterior wall of the fossa. The preganglionic parasympathetic fibers synapse with postganglionic parasympathetic cell bodies within the ganglion. Postsynaptic parasympathetic fibers leave the ganglion and distribute with branches of the maxillary division of cranial nerve V. These fibers are secretomotor in function. They provide parasympathetic flow to the lacrimal gland and mucosal glands of the nasal fossa, palate, and pharynx.