Color.Atlas.of.Endodontics-ublog.tk

FIGURE 2-3 Coarse grit flame-shaped diamonds and a few sizes of tapered round-ended diamonds can work wonders for refining access outlines and blending canal orifices. These diamonds can safely cut natural and decayed tooth structure, precious and nonprecious crowns, PFM crowns, and all-porcelain crowns.

control, predictability, and ease; this is one reason they are used for the most delicate crown preparations. Perhaps their use should not be restricted to providing restorative treatment. Crown-preparation style diamonds seem to come in more sizes and shapes than any

other bur.

After the initial penetration into the pulp chamber has been accomplished, many clinicians advise using a round carbide to finish unroofing the chamber. Although this technique may work in some cases, it is very difficult to perform, especially on a tooth with a small access. The result of this technique is often an overprepared, uneven, gouged wall that catches the tips of files and hampers the placement of files. A much better and safer option is to use an appropriately sized tapered diamond to open and flare the access. The long cutting surface of the diamond can simultaneously open the cavosurface of the access and smooth irregularities in the access walls. The tip removes the last tags and remnants of the chamber roof and blends the dentin from the cavosurface to the canal orifice.

Penetrators and Metal Cutters

Metal cutting burs are highly practical adjuncts for use with full nonprecious castings and nonprecious sub-

structures of PFM crowns (Figure 2-4). The additional expense of using one or two new penetrating burs as opposed to numerous regular carbide fissure burs is offset by the time savings and reduced frustration.

Because of the difficulty in cutting through many restorative materials, especially nonprecious materials, the clinician is often tempted to shortchange the access preparation. Having an arsenal of sharp, new burs specially designed to penetrate these materials helps keep frustration to a minimum.

Surgical Length Burs

Surgical length burs permit displacement of the handpiece away from the incisal or occlusal surface of the tooth, greatly increasing visibility of the cutting tip of the instrument (see Figures 2-1 and 2-4, C). With technical skill, practice, and patience, the clinician can use surgical length burs to gain access in the majority of teeth, including maxillary second molars. Surgical length burs are often useful in teeth that present the greatest problems with access and visibility.

Mueller Burs

Clinicians contemplating tackling difficult or risky cases3 or those for whom referral is not an option should include Mueller burs in their armamentaria. Mueller burs are long-shaft, carbide-tipped burs used in a low-speed latch handpiece (Figures 2-5 and 2-6). They appear similar to Gates Glidden burs, but have a round carbide tip instead of the noncutting tip of the Gates Glidden bur. The long shaft is useful for working deep in the radicular portion of the tooth. In addition, it displaces the

handpiece away from the occlusal surface, allowing the clinician to see the cutting tip in action. An added bene-

fit of Mueller burs that is not well known even in the endodontic community is that unlike ultrasonics that leave

a ragged, rough, dusty, debris-filled cut, Mueller burs leave a clean, shiny surface when used on intact dentin. This surface contrasts well with the "white dot" or "white line" connective tissue remnant that was left as the pulp receded. The use of Mueller burs and a microscope makes treating even the most severely calcified

teeth less stressful and more predictable.

Mueller burs (Brasseler USA, Savannah, GA) are used after the gross coronal access has been achieved and a reasonable but unsuccessful search for the pulp chamber or canals has been completed. The access preparation is thoroughly dried and an appropriately sized Mueller bur is selected. The clinician uses the burs in a brushing motion to search for white dots or white lines representing the calcified canal. While the clinician cuts, the endodontic assistant uses short, light blasts of air to blow out the dentin dust, which is then evacuated by high-volume suction. Water is not used during the process because color differences in the dentin that indicate canal location are more evident in dry dentin. This technique is made even more efficient with the use of a Stropko irrigator on an air-only syringe.

Because these burs are carbide, they do not endure sterilization cycles well and become dull quickly. A few uses are all that can be reasonably expected before they become dull.

Ultrasonics

The CPR tips are available in nitride (gold-yellow) and NiTi (green, blue, and purple) (Figure 2-7). The extremely fine tips coupled with the small handpiece allow unprecedented visibility (Figure 2-8). Ultrasonic tips can be used to remove pulp stones and to cut dentin while locating additional canals.

Canal Orifice Flaring Instruments

An especially important step in preparation for rotary instrumentation is flaring of the canal orifice. As discussed earlier, rotary NiTi instruments cannot be precurved, have very flexible tips, and produce muted tactile sense because of the handpiece. Keeping these limitations in mind, the clinician should spend a few minutes flaring the canal orifices; this technique pays great dividends in increased speed and decreased frustration. Several instruments are available to aid in orifice flaring. These include Gates Glidden drills, GT rotary files (Dentsply Tulsa Dental, Tulsa, OK), and orifice shapers (Figures 2-9 through 2-11).

FIGURE 2-9 Much of the fear associated with Gates Glidden burs can be mitigated by using the short versions in sizes #4 to #6. New Gates Glidden drills may tend to be drawn into the canal. They can be run backward until they are slightly dull.

FIGURE 2-10 This GT rotary file has a #35 tip, 1.25 mm maximum flute diameter, and a .12 taper. It can be used at up to 700 RPM for orifice flaring. In patent canal cases, it can be used as a

single instrument replacement for the entire set of Gates Glidden

burs or orifice shapers.

VISION, MAGNIFICATION,

AND ILLUMINATION

Although ultrasonic and Mueller bur techniques can be used without magnification, they are faster, more predictable, and safer with magnification. The operating microscope is the greatest teacher of endodontic anatomy 4 (Figure 2-12). Previously difficult cases become stress

free with microscope use, and previously impossible cases become routine. With the enhanced vision and illumination of the microscope, the clinician operates in an entirely different mode-visually.

To become proficient with the microscope, the clinician should not pull it into service on only the most difficult cases. In fact, without the use of the microscope the clinician may not even be aware of factors increasing

the difficulty of the case and therefore miss cues only visible with the magnification and illumination the micro-

scope provides (Figure 2-13).

constraints on access design. They are unforgiving of poor access design, irregularities in the access walls, and poor blending of the walls and pulpal floor into the canal orifice.

UNCOMPLICATED ACCESS PREPARATIONS

Given the goals and constraints of endodontic access, a distinctive shape is required for each tooth type based on the most common anatomic features of the crown as well as the radicular morphology. Maxillary central and lateral incisors share common coronal and radicular anatomy,5,6 as do the maxillary premolar and molar tooth groups. The same can be said for the mandibular teeth. Although maxillary and mandibular canine teeth share common coronal and radicular form, the lack of two canals in the maxillary canine as well as less frequent lingual inclination result in a somewhat more constrained access form in the maxillary canine.

Some degree of attrition occurs in the natural adult dentition and dictates some changes in endodontic access design. Because one of the traditional anatomic landmarks (the incisal edge) has been lost, the clinician may be tempted to make the access midway between the "new" incisal edge and the cervical edge. This results in an access that is too cervically positioned.

In light of recent changes in the understanding of canal anatomy, the increased use of rotary NiTi instruments, and the advent of predictable bonding to natural tooth structure with many of new restorative materials, the time may be ripe to reconsider current notions of endodontic access design. Any one of these factors alone might merit rethinking of the access for endodontic treatment, but taken together, they dictate change.

The use of rotary NiTi instruments places even stricter

Maxillary Incisors

In uncomplicated cases, both maxillary central and lateral incisors share a common triangular-shaped access from the lingual surface of the tooth. The classic access design places the access centrally on the lingual surface between the incisal edge and the cervical edge7 ( Figure 2-14). This design is reflective of the poor restorative choices available in the past as well as the limited options for "hiding" the access more cervically. Such a design results in a much larger amount of dentin removal at the lingual cervical edge to gain straight-line access. With improved esthetic bonded composites, the classic access form can be modified by placing it considerably more incisally (Figure 2-15). The initial penetration should be approximately in the middle of the lingual surface of the tooth, not just above the cingulum as has been previously described.' After locating the canal, the clinician uses a long, tapered diamond to extend the access even further incisally and laterally. An additional modification for use with rotary instrumentation is to slightly notch the middle of the incisal extent of the access (see Figure 2-15). This allows even better straightline access and greatly decreases the potentially catastrophic cervical flexure of the rotary instruments that can contribute to premature, unexplained fracture.

In anterior teeth the clinician must take care to remove all the coronal tissue and debris from the chamber. Material left in the chamber can cause tooth discoloration. The pulp horns are common locations for residual tissue (Figure 2-16).

Maxillary Canines

In uncomplicated cases the maxillary canine access is rather broad from buccal to lingual, which reflects the broad buccolingual shape of the root and the canal space (Figures 2-17 and 2-18). In the adult dentition the incisal edge of the maxillary canine has usually undergone significant attrition (Figure 2-19). This alters the normal anatomic landmarks for endodontic access midway between the cervical bulge and the incisal tip (see Figure 2- 19). Therefore the endodontic access will be located in a more incisal position than would be the case on a "vir-

gin" tooth. This modification to access may occur on any tooth but is most common with the maxillary and mandibular anterior teeth.

Maxillary Premolars

Although not all maxillary premolars have two canals,' they should all be approached from the assumption that they have separate buccal and lingual canals (Figure 2-20). This dictates a broad buccolingual access form that is somewhat constrained in the mesiodistal dimension (Figure 2-21). The maxillary premolar access is never round.