Endodontic instruments

Dissection of Post-Embryonic Structures 1. No. 0 paintbrush. 2. Forceps (Dumont 5). 3. Odontologic needles (Senseus FlexoFile endodontic instrument or similar). 4. Razor blades. 5. Kimwipes . 

Nickel-titanium alloys, based upon the equi-atomic intermetallic compoimd NiTi, have very low values of elastic modulus (approximately 35 GPa), compared to stainless-steel alloys (approximately 160-180 GPa) [4]. As a consequence, nickel-titanium alloys have considerable clinical importance for endodontic instruments, permitting negotiation of curved root canals with much greater facility than traditional stainless-steel instruments [5], and for orthodontic wires that have a much more favourable light-force delivery for tooth movement than traditional stainless-steel orthodontic wires [6,7],... 

R-phase, which serves as an intermediate phase to facilitate the transformation between martensite and austenite. Formation of the R-phase is reported to arise from the presence of dislocations and precipitates [11]. A substantial dislocation density is expected in the vwought nickel-titanium endodontic instruments and orthodontic wires, which are subjected to extensive mechanical deformation during manufacturing processes [12], Microstructural precipitates are a consequence of the inevitable deviation of the nickel-titanium alloy composition from the equi-atomic NiTi composition [13,14],... 

The structural transformation between austenite and martensite occurs when the mechanical stress attains a certain level, or with an appropriate temperature change, A reversible twinning process takes place at the atomic level, which can result in superelastic behaviour and shape memory [8], The properties of the nickel-titanium endodontic instruments and orthodontic wires depend critically upon the nature and proportions of the NiTi phases in their microstructures, as discussed in the following sections. While X-ray diffraction has been used to study the phases in nickel-titanium endodontic instruments [15,16] and orthodontic wires [7,17,18], this analytical technique is limited to a near-surface region less than 50 pm in depth for metallic materials [19], and study of the phase transformations with temperature is not generally convenient. In contrast, DSC can provide information about the phases present in bulk nickel-titanium endodontic instruments and orthodontic wires with facility, and the effect of temperature changes on the NiTi phase transformations is easily studied. 

The manufacturing of nickel-titanium rotary endodontic instruments, which involves machining of a wire blank into a variety of cross-sectional shapes that depend upon the particular product, is described in a recent review article [20], In that article it is stated that the nickel-titanium alloy for these instruments is in the superelastic condition, for which the alloy has the austenitic structure. This statement is highly plausible, because extensive reversible elastic strain (up to approximately 10% for uniaxial tension) could then occur in the instrument when the stress in the root canal reaches the level that causes transformation from austenite to martensite [21], The first published verification [22] of this superelastic condition was obtained by our research group from DSC experiments on nickel-titanium rotary instruments in the as-received condition. A subsequent study evaluated the rotary instruments after clinical use [23]. 

Approximate values from DSC plots for two brands of as-received nickel-titanium endodontic instruments [22], Reproduced with permission from Elsevier Science. 

Since our pioneering study on as-received [22] nickel-titanium endodontic instruments, other DSC studies have confirmed that as-received instruments are in the superelastic condition, which persists after numerous sterilization cycles [28,29]. As would be expected, mechanical properties of these instruments are related to the phase transformation behaviour of the nickel-titanium alloy [30]. Accordingly, suitable elevated-temperature heat treatment may favourably alter the mechanical properties of these instruments [31,32], as was previously found for nickel-titanium orthodontic wires [21,33]. 

The health care industry has many possible applications for cryogenics. In 2005, Texas A M University Health Science Center-Baylor College of Dentistry investigated the effect of cryogenic treatment of nickel-titanium on instruments used by dentists. Past research had been conducted on stainless-steel endodontic instruments with no significant increase in wear resistance. This research demonstrated an increase in microhardness but not in cutting efficiency. 

Periodontal procedures including surgery, scaling and root planing, probing, and recall maintenance Dental implant placement and reimplantation of avulsed teeth Endodontic (root canal) instrumentation or surgery only beyond the apex... 

P. Carotte, Endodontics Part 5. Basic instruments and materials for root canal treatment, Br. Dent. J. 197 (2004) 455 64. 

---