Dentists who may refer many (or most) of their molar endodontics because of perceived difficulty will often consider treating the premolar because it is though of as "easier". Yet attempting to treat this "easy" tooth can result in a higher than expected rate of complications. This month's Endo Fax will discuss access into premolars and how to prevent procedural errors that prevent successful treatment. For this discussion we will assume that a diagnosis has been made and that endodontic treatment is definitely indicated. Generalists are surprised to learn that most endodontists will agree; premolars (especially necrotic mandibular premolar teeth) can be some of the most difficult teeth in the mouth to treat. It is also the tooth that results in unusually high levels of access perforations that I frequently must attempt to repair. These perforations can be difficult to seal non-surgically because they are interproximal. They can also result in the need for expensive periodontal crown lengthening procedures (many times at the dentist's expense), less than optimal periodontal results and compromised post treatment aesthetics. In rare cases, forced eruption can be used to expose the perforated area to allow coverage with a casting, but this is time consuming, expensive and requires orthodontic treatment. In this month's EndoFiles Fax we will focus on attaining efficient, accurate access to the chamber and orifices, thereby minimizing the risk of perforation and preventing the need for these other complicated rehabilitative procedures.
STEP 1 - Pre-Operative Radiographs - How Many and Why?
Although it is a cliché, "take a good film" is probably one of the most important pretreatment steps in determining where to look. Why are films so important?
1. To Determine Root Anatomy
Before contemplating treatment of bicuspid teeth, it is MANDATORY that you have at least two (and in some cases three) views of the tooth in question. This includes a paralleled "straight on" image as well as "mesial shift" and in rare cases "distal shift" shots. Distorted or poorly angled images are useless. The purpose of the images is to identify the number and position of the roots as well as their relative length. Chasing a "second canal" too far buccally or lingually is one of the major reasons for access perforation. Highly splayed roots often mean that the canal orifices can sometimes be very far apart bucco-lingually. Overlapping or fused roots can mean that the orifices are quite close together. This helps you determine the lateral limits of your access.
For example/ Orthodontic extraction of a single maxillary bicuspid can often result in confusion as to which bicuspid remains. Is the remaining bicuspid a "4" or a "5"? This will make a big difference in whether you need to look more carefully for a second root and/or canal. In the case of the 3-canalled bicuspid, the orifices are often clustered very close together. It is very easy to "miss" a canal if you do not realize there is a third root.
2. To Locate the Chamber
We also need to ascertain the position of the pulp chamber as it relates to the deepest part of the restoration and/or caries. These landmarks can guide us toward the orifices and keep us away from perforating the side of root. Don't forget to take a Bitewing. It gives the best view for this purpose.
3. To Look for the "Fast Break"
The "Fast Break" is a term used in endodontics that relates to the splitting off of a single canal into two separate canals. In the premolar, the "break" is most often bucco-lingual. Therefore in "straight on" radiographs you will see a large, thick coronal canal that suddenly narrows and becomes difficult to discern. That is the level of the "break" and that is the depth at which you should suspect the canal bifurcates into more that one canal. Mandibular premolars can have MANY canals coming of this break; so don't be surprised if sometimes your file does not take two distinct paths. Multiple canal mandibular premolars (with a single root) are not as uncommon as you would suspect. That is what makes them so difficult to treat, especially in necrotic cases.
4. To Determine the Axis of the Crown as Relates to Root Axis
Orthodontic movement, restoration, tooth loss, drifting and natural a natural anatomy can frequently result in the roots of the premolar NOT being in the direct vertical relationship to the crown. When this occurs, it is imperative that this be taken into consideration during access. Otherwise it is very easy to perforate on the proximal surfaces. When this occurs, perforation is frequently subgingival or subcrestal and results in a big periodontal problem that may threaten restorability. Remember that the occlusal surfaces of mandibular premolars are often tilted lingually. Going "straight in" perpendicular to this occlusal surface can result in buccal perforation.
5. To Decide the Relative Difficulty of the Case
Teeth with no radiographically visible canals (especially in non vital cases) can present some of the highest levels of difficulty of any tooth in the mouth. Before attempting to access these cases, it is important to assess whether there appears to be a canal present. At what level it can be seen radiographically (receded pulp? mid root? Apical third?). This must be factored in with (6) the relative thickness of the root.6. Relative Thickness of the RootThis is often an under-rated consideration in cases where deep proximal restorations have resulted in recession of the pulp space into the root. In these cases, the margin for error during access is minimal. Wandering proximally in these teeth is a recipe for perforation. Take frequent films to determine where you are relative to the root face.
Step 2 - Hints for Better Access into Premolars
1. Magnification - If you don't have Loupes, you should not be doing cases like these. They are an absolute necessity.
2. Transillumination - Do not be in a hurry to place a dam. One you have started the access, use a light source (Transillumination Wand, Fibreoptic handpiece, Curing light) placed up against the buccal gingiva. It can help you locate the orifice, since the pulp will transmit light differently that the dentin.
3. Mark the Crown - Draw a pencil line on the crown face that indicates the axis of the roots. This will help you orient the bur during access.
4. Remove all proximal surface restorations during access. Preserving these restorations is unnecessary since these teeth will be crowned after treatment. Removal of these restorations can show pulp caps or deeper areas of the tooth where you are more likely to locate the chamber. Use these landmarks and consult your bitewing films.
5. Do not hesitate to remove cusps. Occasionally, secondary dentin or restorations can make it impossible to have direct line access to the orifices without removing the cusp tip. Premolars must be restored with full cuspal coverage, so retention of the cusps is unnecessary and limiting to proper access.
6. POSITION THE PATIENT
The most frequent error that leads to access perforation in premolars is improper patient positioning in the chair. In Mandibular premolars, there is a tendency for clinicians to lay the patient back a bit in the chair to allow for better visibility. This is a mistake. As the bur is placed in the tooth, there is a natural tendency to cut "downward' ie/ toward the floor. This results in distal perforation. For mandibular premolars, sit the patient up as much a feasible during access. Try to maintain the arch parallel to the floor. Now you can cut almost straight down (perpendicular to the floor) and not risk perforation. In the Maxilla, the opposite is true. We often tilt the patient's head very far back to see better using direct vision. If we do not correct for these adjustments, cutting vertically WITHOUT A MIRROR can result in mesial perforation of the chamber. When using a mirror in the maxilla, we may do the opposite: position the patient horizontally and then have them tilt down a bit to allow us to use a mirror. In that case, and adjustment must be made because cutting vertically (rather than horizontally) WITH A MIRROR can result in distal perforation of the chamber. In those cases, it may be better to place the patient horizontal with the arch perpendicular to the floor. You then cut horizontally (sideways) to make access using a mirror. The key is understanding that patient position can affect the "perceived" angle of the bur and making sure that you do NEVER cut at 45 degrees, either mesial or distal to the axis of the tooth.