Pulpal Temperature Variances During Step-by-step Adhesive Restorative Procedure Using Three Different High-irradiance Light-curing Units.

The rise in temperature in pulp tissues is related not only to heat transfer by high-irradiance light-curing units (LCUs), but also to restorative procedures. This research aimed to compare the rise in pulp temperature (PT) induced by three LCUs at each restorative step while considering the influence of resin composite shade and thickness. To accomplish this, the investigators used a proposed experimental model replicating pulp fluid circulation with a controlled, simulated intraoral temperature in bovine incisors. The recorded external and internal PT ranged from 36.7°C to 37.1°C and 32.7°C to 33.0°C, respectively. A significant decrease of internal temperature was recorded during class V preparation, followed by a progressive and representative rise of temperature in the subsequent restorative steps. The temperature was significantly higher during light curing of the adhesive system using Valo compared to light curing using Elipar and Radii Cal. However, none of the analyzed devices produced a temperature that exceeded the pulp tolerance limit (a temperature increase over 5.5°C). The paired test showed no significant difference in pulp temperature associated with the thickness of the increment of resin composite. However, shade was found to have more influence on the amount of energy absorbed by pulp tissue-A1 samples showed significantly higher temperature variation compared to samples using the A4 shade of resin composite. To conclude, the microcirculation and the performance of procedures under constant air-water flux dissipate the heat absorbed by the pulp. Additionally, the data suggest that all three LCUs analyzed can be safely used in clinical procedures, and that the resin composite shade may influence the amount of irradiance delivered to the tooth surface and represents a significant factor in pulp temperature variance.

Flexibility and torsional behaviour of rotary nickel-titanium PathFile, RaCe ISO 10, Scout RaCe and stainless steel K-File hand instruments.

AIM: To assess and compare the flexibility and torsional resistance of PathFile, RaCe ISO 10 and Scout RaCe instruments in relation to stainless steel K-File hand instruments. METHODOLOGY: Rotary PathFile (sizes 13, 16 and 19; .02 taper), Race ISO 10 (size 10; 0.02, 0.04 and 0.06 tapers), Scout RaCe (sizes 10, 15 and 20; 0.02 taper) and hand K-File (sizes 10, 15 and 20; 0.02 taper) instruments were evaluated. Alloy chemical composition, phases present and transformation temperatures were determined for the NiTi instruments. For all instruments, diameters at each millimetre from the tip as well as cross-sectional areas at 3 mm from the tip were measured based on ANSI/ADA Specification No. 101 using image analysis software. Resistance to bending and torsional resistance were determined according to specification ISO 3630-1. Vickers microhardness measurements were also taken in all instruments to assess their strength. Data were analysed using analysis of variance (α = 0.05). RESULTS: The alloys used in the manufacture of the three types of NiTi instruments had approximately the same chemical composition, but the PathFile instruments had a higher Af transformation temperature and contained a small amount of B19' martensite. All instruments had diameter values within the standard tolerance. The bending and torsional resistance values were significantly increased relative to the instrument diameter and cross-sectional area. CONCLUSIONS: PathFile instruments were the most flexible and the least torque resistant, whilst the stainless steel instruments were the least flexible although they were more torque resistant than the NiTi instruments.

Physical and mechanical properties of twisted or ground nickel-titanium instruments.

AIM: To compare the flexibility, torsional resistance and structural and dimensional characteristics of instruments produced by twisting with those of a geometrically similar nickel-titanium (NiTi) system produced by a grinding process. METHODOLOGY: The mean diameters along the flute and the pitch length of size 25, .04 taper, size 25, .06 taper, and size 25, .08 taper Twisted File (TF) (SybronEndo, Orange, CA, USA), and size 25, .04 taper, and size 25, .06 taper RaCe instruments (FKG, La Chaux-de-Fonds, Switzerland) (n = 10 each) were measured according to ANSI/ADA specification No. 101. Two pairs of instruments were found to have similar diameters at 3 mm from the tip: TF size 25, .06 taper and RaCe size 25, .04 taper, and TF size 25, .08 taper and RaCe size 25, .06 taper. The cross-sectional areas at 3 mm from the tip were determined. These instruments were then submitted to energy-dispersive X-ray spectroscopy, X-ray diffraction, differential scanning calorimetry (DSC), and Vickers microhardness measurements. Bending moment at 45° and maximum torque at fracture were measured (n = 10) according to specification ISO 3630-1. Data were analysed using analysis of variance (α = 0.05). RESULTS: The two types of instruments had approximately the same chemical composition, phase constitution, and austenite finishing temperatures. TF instruments had significantly (P ≤ 0.001) lower Vickers microhardness values and were more flexible than RaCe instruments (P = 0.016), but had similar (TF size 25, .08 taper and RaCe size 25, .06 taper, P = 0.916) or significantly higher (TF size 25, .06 taper and RaCe size 25, .04 taper, P ≤ 0.001) torsional resistance. CONCLUSIONS: Comparison of TF and RaCe instruments of similar measured dimensions revealed that the different manufacturing methods employed for producing these instruments gave rise to different mechanical behaviours.

Torsional behaviour of rotary NiTi ProTaper Universal instruments after multiple clinical use.

AIM: To assess the influence of multiple clinical uses on the torsional behaviour of ProTaper Universal rotary NiTi instruments. METHODOLOGY: Root canal treatments were performed on patients using the ProTaper Universal rotary system to prepare canals. Ten sets of instruments were used by an experienced endodontist, each set being used in five molar teeth. After clinical use, S1, S2, F1 and F2 instruments were analysed for damage by optical and scanning electron microscopy. The used sets, along with a control group of 10 sets of new instruments, were then torsion tested based on the ISO 3630-1 specification. Data obtained were subjected to a one-way analysis of variance (anova) with alpha = 0.05. RESULTS: The use of the ProTaper Universal rotary instruments by an experienced endodontist allowed for the cleaning and shaping of the root canal system of five molar teeth without fracture. The maximum torque for instruments S2, F1 and F2, and the angular deflection at fracture for instruments S2 and F1 were significantly lower following clinical use. The largest decrease in maximum torque was 18.6% (P = 0.014) for S2 instruments. The same maximum percent decrease was found for angular deflection at fracture for F1 instruments (P = 0.009). CONCLUSIONS: Torsional resistance and angular deflection of used instruments, as compared to that of new instruments, were reduced following clinical use.