Ultrasonic Retrocavity Preparation
The aim Is to create a clean and well conformed type 1 cavity into the already sectioned root. It must have walls that are parallel to the major axis and well centered into the root, in order not to weaken the root walls; and deep enough to retain the biocompatible material of obturation. The retrocavity should have 3 mm depth when a previous retreatment has been done: the "Rule of Threes”.
Retrocavity preparation has been dramatically improved since ultrasonic microtips and micromirrors were introduced.
TIP Micro ultrasonic tips and micromirrors allow real-time control of what microtips are doing.
TIP The surgical field must be dry when introducing the micromirror into the osteotomy window.
- Ultrasonic microtips: Kim surgical tips, Carr tips CT, UT, SJ (SybronEndo), Kayhat tips (Satelec), Berutti tip (EMS)
- Ultrasonic unit
- Low magnification (4x) is used for microtip alignment with the long axis of the root.
- Medium magnification (10-16x) is used for retrocavity preparation.
- High magnification (20-25x) is used for retrocavity final inspection.
Ultrasonic Microtip Types
They are normally about 0.25 mm in width and 3 mm in length. Basically they are made of stainless steel, uncovered or covered by diamond or zirconium oxide. They were developed to be used with an ultrasonic unit at the power recommended by the manufacturer.
Microtips work by vibration, and vibration needs space; if pressure is applied, no space is available and vibrations will disappear. Therefore, microtips should be used with a light, sweeping motion with short upward and downward and forward and backward strokes under copious irrigation.
Choosing a small microtip for a small canal or delicate anatomy, and a big microtip for a big canal, will increase efficiency, reduce the time for retrocavity preparation and prevent microfractures from occurring.
Never push the microtip down hard! The lighter the touch, the more efficient the cutting will be. An abrasive coating increases cutting efficiency and decreases the ultrasonic unit power required.