| Objective:Pulp disease and periapical disease are common diseases in oral cavity, and endodontic therapy is an effective treatment. As the main instrument for root canal preparation, the cutting efficiency, flexibility and fatigue resistance of NickelTitanium(Ni-Ti) rotary files are superior to those of stainless steel files. But when preparing severely curved root canal or multi-curved canals, Ni-Ti files may still cause canal transportation or instrument fracture. During root canal irrigation and instrument disinfection, sodium hypochlorite(Na Cl O) and high-pressure steam may cause Ni-Ti files to corrode. Aiming at the above-mentioned problems, we developed a retainer platform for root canal image capture and an apparatus for cyclic fatigue testing of Ni-Ti rotary files; observed the canal transportation of severely curved root canals or multi-curved canals after preparation; compared the shaping ability of different Ni-Ti files and analyzed the influence factors; evaluated the shaping ability,cyclic fatigue resistance and corrosion resistance of M3 files.Contents:1. Referring to the relevant literature, a self-developed retainer platform for root canal image capture and an apparatus for cyclic fatigue testing of Ni-Ti rotary files were made.2. Using the retainer platform made above to capture the root canal images pre- and postinstrumentation, the central axis deviation was measured by computer software so as to observe the canal transportation of severely curved root canals(L-shaped) or multi-curved canals(S-shaped) after preparation.3. Using the above method, the shaping ability of Pro Taper Universal(PTU),Wave One(WO)and Pro Taper Next(PTN)in severely curved root canals or multi-curved canals were observed.4. After making some unused Ni-Ti rotary files rotate in cyclic fatigue testing apparatus, the effects of cyclic fatigue on the shaping ability of Ni-Ti files were observed.5. The comprehensive performance of M3 Ni-Ti rotary files was evaluated, such as the shaping ability, cyclic fatigue resistance and corrosion resistance.Methods:1. Referring to the relevant literature, a retainer platform for root canal image capture was developed, which make the positions of the camera and resin blocks unchanged; an apparatus for 45°, 60° or 90° cyclic fatigue testing of Ni-Ti rotary files was made, which ensured the arc length of curved root canals changeless in various angles by adjusting the bending radius.2. The imported standardized L-shaped or S-shaped root canals in resin blocks were prepared with PTU, the root canal images pre- and postinstrumentation were captured, and then the central axis deviation we measured by computer software through which the canal transportation after preparation could be observed.3. Using the above method, the shaping ability of PTU, WO and PTN was compared according to the deviation curve after preparation of L-shaped or S-shaped root canals.4. After making unused WO Primary reciprocating in the 60° cyclic fatigue testing apparatus for one minute, the shaping ability of WO Primary treated or not was compared.5. The shaping ability of M3 in simulated L-shaped root canals, the number of cycles to failure(NCF) of M3 in cyclic fatigue testing apparatus with 45° curved canals, as well as the anti-fatigue fracture ability and corrosion resistance of M3 after rotating in 5.25% Na Cl O or / and autoclave sterilization were observed.Results:1. After preparation, the most obvious transportation was located in the curved part of L-shaped root canals, especially in the midpoint of the curved part(P < 0.05).The coronal curve and the apical curve of S-shaped root canals were both obviously deviated(P < 0.05). All the deviation directed toward the concave wall of the curved canals.2. In simulated L-shaped root canals, WO caused the largest transportation at the curved section(P < 0.05); PTN caused the least transportation at the apical constriction(P < 0.05), but produced the largest transportation at the straight section(P < 0.05); PTN maintained the canal curvature best(P < 0.05). In S-shaped canals, PTN preserved the coronal curvature best(P < 0.05), but all these 3 file systems straightened the apical curvature.3. There was no significant difference about the transportation caused by totally new WO primary and the ones after rotating in the cyclic fatigue testing apparatus for one minute.4. The transportation caused by M3 was less than PTU in the curved section of L-shaped root canals(P < 0.05) and the NCF of M3 in 45° cyclic fatigue testing apparatus was higher than PTU(P < 0.05). After the combination action of 5.25%Na Cl O and autoclave sterilization for 10 times, the polarization resistance of M3 was increased by two orders, the electrochemical reaction impedance increased,and the polarization curve had obviously passive areas. But 5.25% Na Cl O or/and autoclave sterilization had no obvious effect on the anti-fatigue fracture ability of M3.Conclusions:1. The self-developed retainer platform for root canal image capture makes the images pre- and postinstrumentation could be superposed, and the apparatus for cyclic fatigue testing of Ni-Ti rotary files simulated clinical situations, which makes the experiment repeatable.2. The shaping ability of Ni-Ti rotary files can be evaluated according to the central axis transportation of root canals after preparation, which is measured by computer software. The method is more accurate and easy to operate.3. When preparing severely curved root canals, PTN could better preserve the original curvature and apical constriction; when preparing multi-curved canals, all these 3 file systems straightened the apical curvature obviously. Thus, the superelastic files are recommended when preparing multi-curved canals.4. The cyclic fatigue has no significant effects on the shaping ability of WO primary,which indicates that the repeated use of WO primary will not cause root canal morphology to change dramatically.5. The shaping ability and the anti-fatigue fracture ability of M3 can meet clinical requirements, and the combination action of 5.25% Na Cl O and autoclave sterilization can improve the corrosion resistance of M3. |
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