Changes in hardness and surface topography of tissue conditioners submitted to chemical disinfection.

AIM: The aim of this study was to evaluate the longitudinal effect of chemical disinfection on Shore A hardness, surface roughness (Ra) and morphology of two tissue conditioners (Dura Conditioner [DC] and Softone [SO]). METHODS: Twenty-four specimens (2 mm-thick) were made of each material and randomly divided into three groups (N.=8): control (no disinfection), 10 000 ppm chloride solution (sodium hypochlorite) and Corega Tabs solution (peroxide solution). Soaking was performed daily for 15 min, and Shore A hardness and Ra were measured at baseline and 3, 7, 10, and 14 days. Data were analyzed by repeated measures ANOVA and Bonferroni's test (alfa= 0.05). RESULTS: Chemical disinfection for 14 days with sodium hypochlorite and Corega Tabs affected differently the tested materials. Hardness varied from 8 to 20 for DC and from 8 to 23 for SO with significant interaction (P<0.05) between material and disinfection treatment up to day 7. Ra values (in microm) varied from 1.51 to 4.35 for DC and from 2.08 to 4.15 for SO; there was a significant difference between disinfection treatments (P=0.043) but not between materials (P=0.119). Sodium hypochlorite groups displayed smaller Ra values than the control groups, but did not differ from Corega Tabs groups. Scanning electron microscopy showed different pattern of degradation for each material. CONCLUSIONS: The results suggest that the effect of chemical disinfection on degradation of tissue conditioners is material-specific, but hardness is less affected than surface topography. The overall results support the use of the tested materials for up to three days, independently from the disinfection treatment.

Influencia de la polimerización adicional en las propiedades de una resina Ormocer® / Influencie of post-curing in Ormocer® mechanical properties

Los objetivos de este estudio fueron evaluar y comparar la influencia de la polimerización adicional con calor y presión de vapor o calor y nitrógeno presurizado en la resistencia a la compresión, módulo de elasticidad y microdureza Vickers de una resina compuesta Ormocer®. Para esto, se confeccionaron 45 muestras cilíndricas con 3 mm de diámetro y 6 mm de altura en una matriz de PTFE. La resina compuesta Admira (Voco,Cuxhaven, Germany) fue introducida gradualmente y fotopolimerizada por 40 s con el aparato XL-1500 (3MESPE, St. Paul, MN, EUA). Seguidamente, las muestras fueron almacenadas en un horno a 37ºC por 24 horas y divididas aleatoriamente en tres grupos. Las muestras del grupo I (control) fueron testadas inmediatamente después del período de almacenamiento. En el grupo II, las muestras fueron sometidas a 120ºC bajo presión de vapor de agua por 20 min y, en el grupo III, las muestras fueron polimerizadas adicionalmente a 140°C con presión de 60 lbs. de nitrógeno durante 10 minutos. Inmediatamente, las muestras fueron testadas en una máquina de ensayo universal (Emic DL 2000, São José dos Pinhais, Paraná, Brazil) a 0,5 mm/min hasta quese fracturaron. Los valores de resistencia a la compresión (MPa), módulo de elasticidad (GPa) y microdureza Vickers (VHN) fueron tratados estadísticamente con ANOVA/Tukey (p < 0,05). Los valores de resistencia (MPa,DP) fueron: grupo I (control) 114,25b (±34,74); grupo II 127,64b (±33,27); grupo III 167,97a (±40,15). Módulo de elasticidad (GPa, DP): grupo I (control) 6,11b (±0,35); grupo II 8,45ab (±0,33); grupo III 11,31a (±0,47). Microdureza Vickers (VHN, DP): grupo I (control) 47,26b (6,32); grupo II 58,63a (13,92); grupo III 63,69a (8,86). Se puede concluir entonces, que el método de polimerización adicional a 140°C bajo presión de 60 lbs de nitrógeno aumentó significativamente la resistencia a la compresión, y ambos métodos adicionales de cura aumentaron significativamente el módulo de elasticidad y microdureza Vickers de la resina compuesta Admira (p < 0,05) (AU)

The purposes of this study were evaluate and compare the influence of post-curing with heat and steam pressure or heat and nitrogen pressure in the compressive strength, elastic modulus and Vickers microhardness of an Ormocer® composite resin. Forty-five cylindrical samples with 3 mm diameter and 6 mm high were manufacture using a PTFE mould. The composite resin Admira (Voco, Cuxhaven, Germany) was inserted incrementally and cured for 40 s with XL-1500 (3M ESPE, St. Paul, MN, EUA). After that, the samples were stored in a stove at 37ºC for 24 hours and randomly divided in three groups. The samples of group I (control) were tested just after the stored period. In group II, the samples were submitted to 120ºC with water steam for 20 min, and for group III, the samples was post-cured at 140°C under 60 lbs of nitrogen for 10 min. The samples were tested with universal testing machine (Emic DL 2000, São José dos Pinhais, Paraná, Brazil) at 0.5 mm/min until fracture. Data of compressive strength (MPa), elastic modulus (GPa), and Vickers microhardness (VHN) were statistically evaluated with ANOVA/Tukey (p < 0.05). The mean values of compressive ;;strength (SD) were: group I (control) 114.25b (±34.74); group II 127.64b (±33.27); group III 167.97a (±40.15); elastic modulus (SD): group I (control) 6.11b(±3.5); group II 8.45ab (±3.34); group III 11.31a(±4.7); Vickers microhardness (SD): group I (control) 47.26b (2.7); group II 58.63a (2.3) and group III 63.69a (3.5). It is possible to conclude that the post-curing method at 140°C under 60 lbs of nitrogen improved significantly the compressive strength, and both methods improved the elastic modulus and microhardness (p < 0.05) (AU)