Theory Three...File Flush, Fill Flush

• The Concept behind Theory Three is that the canal should be completely prepped and then completely filled to the apex. Most even advocate that there be a small puff of sealer extruded through the apex.
• Advantages
  • Clinically, Can be surer of seal because it can be seen on a radiograph.
  • If problems occur they occur while treating. Since the canal is patent, the only problems likely to occur are trauma to the tissues beyond the apex. These are usually transitory in nature.
  • Better Drainage in Non Vital Cases. Since there is patency, if there is exudate in the space beyond the apex, it can escape while preparing or the canal can be left unsealed to promote drainage in the days before sealing.
  • Canal is cleaner since there is no part of the canal left unprepared.
  • More predictable results in deltas and bifurcations.
• Disadvantages
  • More risk of overinstrumentation since the goal is to go to the apex, there is a possibility that instruments can traumatize the tissues beyond.
  • More post operative pain due to trauma.
  • More risk of overfills simply because of the patency.
  • Harder to determine apical length.

    If one is attempting to get to the apex there is a possibility of error wherease if one's intention is to prepare short, it matters very little just HOW short.

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Why Theory Three

Two Major Factors That Favor Theory Three
• Xray Distortion in Curved Canals.

  If a canal is curved bucco-lingually and many are, and if the radiograph is taken bucco-lingually which most are, then if the tip of the probing file is short of the apex, the distortion caused by the curve can make it difficult to know where the tip of the file is relative to the apex.

  And this is particularly true of a filling.

  If there is a puff of cement beyond the apex, there is little doubt that the rest of the canal is filled, especially in a cement filling since puffs cannot occur INSIDE the canal.

• Two Canals One Apex.

  The idea is that with rare exceptions, if there one canal is filled to the apex, the other canal will be sealed off from apical tissues as well.

  If, on the other hand, one fills short it may be short of the junction of the two canals and thus exposes the entire unprepared unfilled canal to the apical tissues.

• When Do You Want the Clinical Problems?

  In cases where the canal is completely sealed, any problems are usually caused by trauma, which are while the patient is still under treatment and can be handled with analgesics and occasionally with antibiotics.

  Problems that occur with underfills are usually infectious processes and can only be solved by retreatment, frequently after months or years have gone by and after a restoration or post has been cemented.