In part 1 of this two part ‘endo made easy’ series, the concept of creating larger master apical diameters in canal preparation was discussed. Creating master apical diameters to sizes larger than those traditionally used clinically has been shown in endodontic literature to provide cleaner canals.
Larger apical preparations are consistent with greater volumes of irrigation and removal of dentin in the apical third, a location where it is needed most to ensure the creation of the cleanest canal possible.
Traditionally, the average master apical file used in a clinical setting has been of 25 or 30 mm in size. This is irrespective of the taper of the final prepared canal. Larger master apical files in the context mentioned here will refer to preparations taken to an average 50 or 60 mm diameter at the minor constriction of the apical foramen.
As well as improving the cleanliness of the canals, the creation of larger master apical foramans also offer a number of other benefits. For instance, it can make cone fit and obturations easier. Smaller apical preparations can often be less well defined and regular meaning the obturation will possess less material to fill the space.
Obtaining ‘tugback’ is made much easier if it can be accomplished with a larger cone rather than a smaller one. Larger cones are less likely to bend, deform or kink and so will slide into place more easily.
The risks associated with the creation of larger apical foramens are minimal, provided that the canal is not transported and is not blocked with debris during instrumentation. As long as the process is carried out appropriately, then there should be no inherent risks.
The potential for iatrogenic effects to take place can be reduced as long as the glide path is achieved prior to the use of rotary nickel titanium files. It is also important to ensure that the files are used in an appropriate sequence, with the correct touch and motion too, in order to prevent any unwanted side effects.
In general terms the correct sequence would be from larger tip sizes to smaller ones and from larger tapers to smaller tapers too. The correct touch refers to a very gentle one that seeks to engage a minimal amount (ideally 1 -2 mm) of dentin in any given insertion.
An excellent method to use when creating master apical foramans is one that uses a combination of the LightSpeed file rotary nickel titanium file system from LightSpeed USA (San Antonio TX, USA) and the K3 system from SybronEndo (Orange, CA, USA).
The LightSpeed system is smooth shafted and the files cut on their ends only. They are also available in a wide range of tip sizes. The K3 system has up to a size 60 in its 0.4 and 0.6mm taper series and its 0.2mm tapers are available up to a 45-tip size.
The creation of larger master apical foramans has clinical applicability for general dentists and specialists alike, in my empirical opinion. This is as the literature advocating their generation is too conclusive to encourage the use of traditional instrumentation sizes. I am also of the opinion that, in time, the use of larger apical sizes will become more commonplace.
Finally, to establish what the ideal master apical file size should be for any canal, you need to gauge the apex first and then decide on the final apical diameter. For example, if a 25K file resists movement through the apical foramen at the minor constriction (the minor constriction is the ideal filling place for terminating obturations) then this is the diameter of the foramen. Using this information, the final preparation above this level of the canal can then be determined and prepared.
In this example, if a size 25 K file resists displacement through the apex, then the canal can usually quite easily be taken to at least a size 50 with the methods mentioned previously.