Objective: article 1- The aim of this study was to evaluate the impact of body temperature on the cyclic fatigue resistance of different NiTi alloys used for the manufacturing of Reciproc Blue R25 (RB 25.08; VDW, Munich, Germany), X1 Blue File 25 (X1 25.06; MK Life Medical and Dental Products, Porto Alegre, Brazil) and WaveOne Gold Primary (WOG 25.07; Dentsply Maillefer, Ballaigues, Switzerland). Article 2- evaluate the cyclic and torsional fatigue resistance of Nickel-Titanium rotary instruments with similar cross sectional design and manufactured by different thermal treatments. Methodology Article 1- Sixty instruments of the RB 25.08, X1 25.06 and WOG 25.07 systems were used (n = 20). Cyclic fatigue tests were performed at room temperature (20° ± 1 °C) and at body temperature (37° ± 1 °C). The instruments were reciprocated until fracture occurred in a stainless steel artificial canal with a 60° angle and a 5-mm radius of curvature. The time to fracture (TTF) was recorded. Also, the number of cycles to fracture (NCF) was calculated. Data were analysed using one-way ANOVA and Tukeys tests for inter-group comparison at both temperatures and for the reduction of cyclic fatigue at body temperature. For intra-group comparison at the different temperatures, the unpaired t test was used. Article 2- eighty instruments of Hyflex CM (HCM; #25/.06) Vortex Blue (VB; #25/.06), Sequence Rotary File (SRF; #25/.06) and EdgeSequel (EDF #25/.06) were used (n=20). Cyclic fatigue test evaluated the time and number of cycles to failure (NCF) in a stainless steel artificial canal with 60° and 5-mm radius of curvature (n=10). The torsional test (ISO 3630-1) evaluated the maximum torque and distortion angle to failure in the 3 mm from the tip (n=10). The topographic features of fractured surface of instruments were assessed using scanning electron microscopy (SEM). Data were analyzed using one-way ANOVA and Tukey tests, and the level of significance was set at 5%.Results: Article 1- The cyclic fatigue test at 20 °C showed that RB 25.08 and X1 25.06 presented significantly higher TTF and NCF than WOG 25.07 (P < 0.05). At 37 °C, all groups presented significant reduction of TTF and NCF (P < 0.05). RB 25.08 presented significant higher TTF than WOG 25.07 (P < 0.05). Regarding the NCF, there was no significant difference among the groups (P > 0.05). The WOG 25.07 presented the lowest percentage reduction of cyclic fatigue (P < 0.05). Article2- The HCM presentedthe longest time and highest NCF to cyclic fatigue compared with all the groups (P<0.05). The SRF presented similar time as, (P<0.05) and lower NCF (P<0.05) to fatigue than VB. Relative to the torsional test, HCM presented the lowest torque load and the highest distortion angleof all the groups(P<0.05). The SRF and EDF presented similar torque load (P>0.05). There was no difference among VB, SRF and EDF regarding the distortion angle (P>0.05). The SEM analysis showed typical features of cyclic and torsional fatigue for all instruments tested. Conclusion: Article 1- The body temperature treatment caused a marked reduction of the cyclic fatigue resistance for all reciprocating instruments tested. The RB 25.08 and X1 25.06 systems presented similar results at both temperatures tested. However, WOG 25.07 presented the lowest percentage reduction in fatigue resistance at body temperature. Clinical relevance Cyclic fatigue resistance of NiTi reciprocating instruments has been evaluated at room temperature. However, the fatigue resistance significantly decreases upon exposure to body temperature, which could affect the mechanical behaviour of the NiTi instruments during root canal preparation. Article 2- The HCM presented the highest cyclic fatigue resistance and angular rotation to failure. However, the VB showed higher torsional strength to failure.

Obejtivo: Artigo 1- avaliar o impacto da temperatura corporal a resistencia a fadiga cíclica de diferentes Ligas de NiTi usadas na fabricação dos instrumentos: Reciproc Blue (Vdw Munich), X1 Blue (MK Life, Porto Alegre), Waveone Gold (Dentsply Ballaigues). Artigo 2- avaliar a resistência à fadiga cíclica e torcional de instrumentos rotatórios de níquel-titânio com secções transversais semelhantes e confeccionados com diferentes tipos de tratamentos térmicos: Hyflex CM (HCM 25/.06), Vortex Blue (VB 25/.06), Sequence Rotary File (SRF 25/.06) e EdgeSequel (EDF 25/.06) (n=20). Metodologia: Artigo 1- 60 instrumentos de Reciproc Blue, X1 Blue e Waveone Gold foram usados (n=20). Teste de fadiga cíclica foram realizados em temperatura ambiente (20º C + - 1) e a temperatura corporal (37º +-1). Os instrumentos foram acionados no movimento reciprocante ate ocorrer a fratura em um canal artificial de aço inox com curvatura num ângulo de 60º e 5mm Raio. O Tempo de frartura foi registrado TTF foi registrado. Tambem o Numero de Ciclos para fratura NCF foi calculado. Artigo 2- O teste de fadiga cíclica avaliou o tempo TTF e o número de ciclos para a fratura (NCF) dos instrumentos em canal artificial com 60° de curvatura e 5mm de raio (n=10). O teste de torção avaliou o torque máximo e a deflexão angular para a fratura dos 3mm da ponta dos instrumentos (n=10). Após o teste de torção e de fadiga cíclica, os instrumentos foram avaliados em microscopia eletrônica de varredura (MEV) (n=10). Os dados foram analisados empregando-se os testes ANOVA e de Tukey, sendo selecionado um nível de significância de 5%. Resultados: Artigo 1- O teste da fadiga cíclica a 20º C mostrou que Reciproc Blue 25/08 e X1 Blue 25/06 apresenta significantemente maior TTF a NCF que Waveone Gold 25/07. Em 37º C, todos os grupos apresentaram significante redução do TTF e NCF. Reciproc Blue 25/08 apresentou significantemente amaior TTF que Waveone Gold 25.07. Referente ao NCF não houve diferença significante entre os grupos. Waveone Gold 25.07 apresentou menor porcentagem de redução no teste de fadiga cíclica. Artigo 2- HCM apresentou o maior tempo e NCF entre todos os instrumentos avaliados (p0,05) e menor NCF (p0,05). Conclusao: Artigo 1- A temperatua corporal provoca uma significativa redução na resistência a fadiga cíclica de todos os intrumentos reciprocantes testados. Reciproc Blue e X1 Blue apresentaram similar resultados em ambas temperaturas testadas. Waveone Gold apresentou menor porcentagem de redução a resistência a fadiga na temperatura corporal. Artigo 2- O HCM apresentou maior resistência à fadiga cíclica e deflexão angular. Entretanto, o VB apresentou maior resistência torcional para a fratura.