Resumo Este estudo avaliou o impacto do pré-alargamento do canal usando uma lima K de tamanho #25 na incidência de fraturas de três instrumentos reciprocantes após múltiplos usos. Após um glide path realizado com uma lima K de tamanho #15, os instrumentos (Reciproc R25, Reciproc Blue R25, e WaveOne Gold Primary) foram inicialmente usados em 936 canais radiculares. Depois, para o segundo e terceiros usos (933 e 927 canais, respectivamente), um pré-alargamento usando uma lima K de tamanho #25 no comprimento de trabalho foi realizado. Radiografias periapicais avaliaram a localização e o comprimento dos fragmentos, e os testes qui-quadrado compararam as frequências observadas e esperadas (α = 5%). A incidência de fraturas durante o reuso variou de 0% a 0,64%. Reciproc não fraturou durante o reuso (P = 0,99), mas sofreu duas fraturas no terceiro uso (P = 0,000). Reciproc Blue e WaveOne Gold tiveram, cada um, uma fratura durante o segundo (P = 0,000) e terceiro (P = 0,000) usos. Após o pré-alargamento do canal usando uma lima K de tamanho #25 em 1.860 canais, apenas 6 instrumentos fraturaram (0,32%), sugerindo que esta abordagem pode prolongar a vida útil desses instrumentos e servir como uma alternativa para sua reutilização com risco reduzido de fratura. préalargamento pré alargamento 25 #2 15 #15 R25 R Primary 93 radiculares Depois 933 (93 92 respectivamente, respectivamente , respectivamente) fragmentos quiquadrado qui quadrado α 5%. 5 5% . 5%) 0 064 64 0,64% P 0,99, 099 0,99 99 0,99) 0,000. 0000 0,000 000 tiveram 1860 1 860 1.86 0,32%, 032 0,32% 32 (0,32%) 2 # #1 R2 9 (9 06 0,64 09 0,9 0,00 00 186 86 1.8 03 0,32 3 (0,32% ( 0,6 0, 0,0 18 8 1. 0,3 (0,32 (0,3 (0, (0

Abstract This study assessed the impact of pre-enlarging the root canal using a size 25 K-file on the fracture incidence of three reciprocating instruments after multiple uses. After a glide path performed with a size 15 K-file, the instruments (Reciproc R25, Reciproc Blue R25, and WaveOne Gold Primary) were initially used in 936 root canals. Then, for the second and third uses (933 and 927, respectively), a pre-enlargement using a size 25 K-file at the working length was done. Periapical radiographs assessed fragment location and length, and chi-square tests compared observed and expected frequencies (α = 5%). The fracture incidence during reuse ranged from 0% to 0.64%. Reciproc did not fracture during reuse (P = 0.99), but experienced two fractures in the third use (P = 0.000). Reciproc Blue and WaveOne Gold each had one fracture during the second (P = 0.000) and third (P = 0.000) uses. Following a pre-enlargement using a size 25 K-file for the second and third uses in 1,860 canals, only 6 instruments fractured (0.32%), suggesting that this approach may prolong the lifespan of these instruments and serve as an alternative for their reuse with a reduced risk of fracture. preenlarging pre enlarging 2 Kfile K file 1 Kfile, file, R25 R Primary 93 canals Then 933 (93 927 respectively, respectively , respectively) preenlargement enlargement done chisquare chi square α 5%. 5 5% . 5%) 0 064 64 0.64% P 0.99, 099 0.99 99 0.99) 0.000. 0000 0.000 000 1860 860 1,86 0.32%, 032 0.32% 32 (0.32%) R2 9 (9 92 06 0.64 09 0.9 0.00 00 186 86 1,8 03 0.32 3 (0.32% ( 0.6 0. 0.0 18 8 1, 0.3 (0.32 (0.3 (0. (0

Abstrac The aim of the present study was to evaluate the cyclic fatigue, torsional resistance and surface roughness of Reciproc R25 instruments in four different situations, namely as new instruments and as instruments tested after clinical preparation of one, two or three maxillary molars with four root canals. The total time required to perform each root canal preparation was recorded. Cyclic fatigue resistance was determined by the time to fracture using a customized testing device (n = 10 per group). The torsional test evaluated the torque and angle of rotation to failure according to ISO 3630-1 (n = 10 per group). The roughness of the working parts of new and used instruments was evaluated with a profilometer (n = 5 per group). Statistical analysis was performed using one-way ANOVA and Tukey’s test. The level of significance was set at 5%. No fractures or deformations were observed after clinical use. Higher preparation time was needed during the third use of the instruments for all root canals (p < 0.05). There were no significant differences among the groups in regard to either cyclic fatigue or torsional resistance (p > 0.05). Regarding the roughness measurements, groove depth was higher on new and one- versus two- or three-maxillary-molar-prepared instruments (p < 0.05). It can be concluded that the clinical use of Reciproc instruments increased preparation time and decreased surface roughness. However, clinical use did not affect the cyclic fatigue or torsional resistance of the Reciproc instruments.