As a general dentist who performs specialty dental procedures, I work hard to improve my skills to provide the best care to my patients. When I see something a specialist does differently than me, I try to incorporate that into my own practice. Recently, I have seen more conservative accesses, a.k.a. “ninja access,” from local endodontists. In theory, because these conservative accesses preserve more tooth structure, they improve the longevity of the tooth. In cases where we drill through an existing crown, it should also mean the crown is stronger than if we put a larger hole through it.
Difficulties
One of the difficulties of upper molars is the fourth canal. Most first maxillary first molars, I believe north of 95%, have a second mesiobuccal canal (MB2). Just because the canal is there, does not we can successfully instrument and negotiate it. But, the canal should be found in the vast majority of these teeth, and a dentist should make every effort to instrument it. The mistake I have seen, and one that I have some experience with, is attempting to instrument the canal and perforating the tooth. Know when to cut your losses! However, you should be able to obturate an MB2 the vast majority of the time.
A conservative access increases the difficulty of finding and treating MB2. You are decreasing the amount of light that can enter the field, and making it harder to see. Also, despite making a ninja access, it is important to keep straight-line access to each canal. Not having straight-line access increases the chances you will separate a file. Lastly, it is difficult to place multiple gutta-percha points at the same time when the access is barely large enough to fit them all.
Advantages of the Ninja Access
There are a number of advantages to performing a ninja access. First, it preserves a lot more tooth structure which increases the strength of the tooth after treatment. When I explain how root canals weaken teeth to patients, I use a Halloween jack-o’-lantern analogy. Pumpkins are pretty tough before you hollow them out. You could probably stand on one and not crush it. But hollow it out, and it’s going to lose a lot of strength.
Imagine removing only a small part of the jack-o’-lantern’s insides. It will be weaker than it was to start, but a lot stronger than if you hollow it out entirely. The same is true of teeth. This analogy works pretty well with patients.
Another key advantage of the ninja access comes when you are treating a previously crowned tooth. Just like a tooth, the more structure you take away from a crown, the weaker it will be.
Lastly, the smaller your access, the less buildup material you need to fill it. Also, a smaller area means a reduction in overall shrinkage during polymerization. Going back to your dental school days, you may remember a concept called configuration factor, or “C” factor. In the case of an access fill, the C factor is typically 5.
Most dentists place dual-cure composite into the access and then light cure. The idea here is that deep composite will self-cure over time, but the top 2-3mm will cure with the light. Light cured composites tend to place more stress on surrounding structures than self-cured composites do. This can result in stresses on the tooth that lead to early failure, or de-bonding of the composite from surrounding tooth structure. Polymerization shrinkage is typically measured in percentages. The larger the volume of composite, the larger distance will be covered by that percentage shrinkage. 1% of 2mm is double 1% of 1mm. So, the risk of de-bonding or material failure is higher as the volume of composite becomes larger.
Sometimes Smaller is Better
There are a variety of opinions on the subject of endo access design. Some clinicians argue that a larger access improves convenience form and straight-line access, allowing better visualization and less stress on instruments. These same clinicians might argue too that a larger access leads to faster completion of root canals.
I won’t argue with any of these points. I think the ninja access is ideal in certain situations. However, it isn’t right for every root canal. Being a doctor means understanding the problem and considering the optimal solutions. Much of this comes down to judgment. A ninja access preserves more tooth and crown structure and strength. It may not be right for every root canal, but I believe it is something to strive for whenever possible.