ortho - the international C.E. magazine of orthodontics

ortho1_201242 I I technique_ archwire wiredemonstratedasuperelasticplateauof80g(Fig. 31). It is possible to alter the superelastic character- istics of the wire in any desired section and apply an optimal force to each tooth with a single archwire. This creates the possibility to obtain with a sin- gle archwire, the specific biological force to move specific teeth, with no patient trauma and fewer archwire changes (Fig. 32). BioforceIonGuard To minimize friction, DENTSPLY GAC created a nickel-titanium wire that underwent an ion implan- tation process but did not affect the unique supere- lastic properties of Bioforce and NEOSENTALLOY. Ion implantation was originally developed for use in semiconductor applications. At low temperature, a highenergybeamofionsareusedtomodifythesur- facestructureandchemistry.Theionimplantationis notalayeronthesurface,therefore,itdoesnotaffect the dimensions or properties of the material and can be applied to virtually any material. Ion implanta- tion improves wear resistance, surface hardness, resistance to chemical attack and, most importantly, reduces friction (Fig. 33). Ryan9 showed that the ion-implantation process does reduce the frictional forces produced during tooth movement. This process tends to increase stress-fatigue, hardness and wear, regardless of the composition of the material. The stainless-steel wire produced the least fric- tionalforceduringinvitrotoothmovement,followed by treated nickel-titanium, treated beta-titanium, untreated nickel-titanium and, finally, untreated beta-titanium. There were statistically significant differences in the amount of movement seen with the ion-implants wires compared with their un- treated counterparts (Fig. 34). Bedolla and Teramoto,10 in contrast with Ryan´s study, in an in vitro study reported that Bioforce IonGuard, which shows the smoothest surface (Fig. 35), generated the least frictional force, followed by stainless-steelanduntreatedNiTi,andthecombina- tion of Bioforce IonGuard with In-Ovation® brackets showed the less frictional forces (Figs. 36, 37). Differentialscanningcalorimetry Overthepastdecade,differentialscanningcalor- imetry has been used to study nickel-titanium arch- wirealloys.InconventionalDSC,twosmallpans,one containingthematerialtobeanalyzedandtheother aninertreferencematerial,suchasindiumareheated at the same rate, typically 5°C or 10°C per minute. The changes in the thermal power difference for thetwopansarerelatedtochangesintheheatcapac- ity. It is useful for studying phase transformations in the nickel-titanium archwire alloys. There are important phase transformations for nickel-titanium alloys: Temperatures at which the transformation from cooling begins, martensite- start(Ms);temperatureatwhichmartnesitepeaksor isfinished(MporMf);temperatureatwhichausten- ite begins, austenite start (As); and temperature at which austenite peaks or is finished (Ap or Af). In some cases, an intermediate R-phase (Rhom- bohedral crystal structure) may form during this transformation process. Bradley et al.11 to clarify the differences in the phase transformation for major types of nickel- titanium wires, performed a DSC study, the results of which follow. Fig. 35 Fig. 36 Fig. 37 Fig. 38