Ultrasonic vibration has been used for many years to remove calculus from the tooth surface, but more recently has been employed in endodontics. With more practitioners using magnification aids such as loupes and often headlamps, the opportunity exists to use ultrasonically oscillating tips to remove dentine far more precisely and accurately then with high or low speed rotary burs.
Dedicated piezoelectric units are required, such as the Satalec P5, and a number of different dedicated tips have been devised and gradually refined for a variety of uses. The first generation consisted of smooth stainless steel tips, but more recent designs have employed surface layers of Zirconium Nitride or diamond grit.
1 Refinement of access cavity axial walls. Larger round-ended tips such as the Obtura Spartan BUC-1 or CPR-2 tips are used to smooth and define the axial walls so that all canal orifices are clearly visible and files may be worked in the canals without interference from coronal dentine.
2 In situations where a pulp has been chronically irritated over a long period of time, the tissue may have calcified sometimes totally! The tips mentioned above, or those with a round or pear shaped tip like the BUC-2, will dislodge these pulp stones or cut their way through completely sclerosed coronal pulp to expose the undamaged pulpal floor.
3 If the canal orifices are also sclerosed, smaller and sharper ended tips such as the BUC-3, or the CPR-3 through to the longer but finer CPR-5, may be used to chip away the calcified tissue until a canal lumen is located, sometimes a considerable distance down into the root structure. Great care should be exercised not to go off-line and perforate! This calcified pulp tissue is darker and grey than normal dentine and clearly visible when magnifying aids are employed. Where an extra canal such as the MB2 in maxillary molars is suspected, a trough may be cut along the line or groove that runs from the MB1 towards the Palatal canal using an instrument like the BUC-2 - the vast majority of MB2 canal orifices are situated within a 2mm area palatal to the MB1.
4 Fine non-handled endosonore files (usually about #15) may be held in a dedicated holder and attached to the ultrasonic handpiece. The file is placed into a partly or completely prepared canal filled with irrigant and allowed to vibrate at ultrasonic frequency - the file tip should not be in contact with the canal walls as it becomes damped and ineffective, although it still has the potential to cut inappropriate areas of dentine! The marked eddy currents produced (acoustic microstreaming) will enhance the cleaning abilities of all irrigants - the cleanest canals are those irrigated with sodium hypochlorite and EDTA or citric acid, stirred up with short bursts of this 'endosonic' activity.
5 Ultrasonic vibration may be used to break-up cement lutes and allow castings and particularly posts to be removed. Conventional 'perio' tips may be employed, or substantial dedicated tips like the CPR-1.Whereas the ultrasonic tips are used dry inside pulp chambers and canals to aid visibility, water-cooling MUST be utilised on metal castings, otherwise overheating and subsequent necrosis of the surrounding bone may occur. Even if posts refuse to budge after ultrasonic vibration, subsequent removal with post removal kits is often facilitated.
6 The removal of existing root filling materials may be aided by ultrasonics. Old G.P. can be softened with any narrow tip, and pulp chambers generally easily cleaned up with tips like the BUC-1 or CPR-2. Insoluble pastes are the most difficult material to remove, but narrow tips such as the CPR-3, 4 or 5 will do the job, provided they are used, under magnification, only in the straight portions of canals - they will not go round curves!
7 Silver points are likely to break up if touched directly with ultrasonic tips - instead the exposed head of a point should be grasped with fine haemostats, or similar, and the ultrasonic tip applied to the forceps to provide sufficient vibration to aid dislodgement of the point.
8 It is possible to use these instruments to aid in the removal of fractured instruments, but only in the hands of specialists or expert practitioners using microscopes!
9 Finally, ultrasonic tips like the KiS 1 and 2 diamond-coated tips are widely used to prepare root-end cavities following root resection during apical surgery. They cut a 3mm long prep down the long axis of the root and are perhaps the most important change in the armamentarium of surgical endodontics in over a decade.
|Dr Anthony Hoskinson BDS MSc|
Specialist Endodontist, Chequers Endodontics Practice, 7 Chequers Drive, Prestwood, Great Missenden, Buckinghamshire HP16 9DU