Surface roughness and wear of resin cements after toothbrush abrasion

Increased surface roughness and wear of resin cements may cause failure of indirect restorations. The aim of this study was to evaluate quantitatively the surface roughness change and the vertical wear of four resin cements subjected to mechanical toothbrushing abrasion. Ten rectangular specimens (15 × 5 × 4 mm) were fabricated according to manufacturer instructions for each group (n = 10): Nexus 3, Kerr (NX3); RelyX ARC, 3M ESPE (ARC); RelyX U100, 3M ESPE (U100); and Variolink II, Ivoclar/Vivadent (VL2). Initial roughness (Ra, µm) was obtained through 5 readings with a roughness meter. Specimens were then subjected to toothbrushing abrasion (100,000 cycles), and further evaluation was conducted for final roughness. Vertical wear (µm) was quantified by 3 readings of the real profile between control and brushed surfaces. Data were subjected to analysis of variance, followed by Tukey’s test (p < 0.05). The Pearson correlation test was performed between the surface roughness change and wear (p < 0.05). The mean values of initial/final roughness (Ra, µm)/wear (µm) were as follows: NX3 (0.078/0.127/23.175); ARC (0.086/0.246/20.263); U100 (0.296/0.589/16.952); and VL2 (0.313/0.512/22.876). Toothbrushing abrasion increased surface roughness and wear of all resin cements tested, although no correlation was found between those variables. Vertical wear was similar among groups; however, it was considered high and may lead to gap formation in indirect restorations.

Influence of Volume and Activation Mode on Polymerization Shrinkage Forces of Resin Cements

The concern with the polymerization shrinkage of restorative resin composites also applies to resin cements. The aim of this study was to evaluate the influence of volume and polymerization mode on forces generated during polymerization shrinkage (FGPS) of resin cements. Two light-cured resin cements - Variolink II (VL; Ivoclar Vivadent) and Nexus 3 (NX; Kerr) - and two self-cured resin cements - Multilink (ML; Ivoclar Vivadent) and Cement Post (CP; Angelus) - were inserted between two rectangular steel bases (6x2 mm) with distance set at 0.1, 0.3 and 0.5 mm, establishing a variation of volume. These steel bases were attached to a universal test machine with 50 kg load cell and forces (N) were registered for 10 min. Values of maximum forces generated by each material were subjected to two-way ANOVA and Tukey's test for individual comparisons (α=0.05). VL, NX and CP developed increasing FGPS as the volume of material increased, while ML presented the opposite behavior. It may be concluded that higher volume increases FGPS even with a concomitant decrease of C-factor, unless the resin cements present lower force generation rates as a function of time in combination with a low C-factor, resulting in stress relief and consequently lower values of FGPS.

Preocupação com a contração de polimerização de resinas compostas restauradoras também tem sido associada aos cimentos resinosos. O objetivo deste artigo foi avaliar a influência do volume e do modo de polimerização sobre as forças geradas durante a contração de polimerização (FGPS) de cimentos resinosos. Dois cimentos de ativação dual: Variolink II (VL - Ivoclar Vivadent) e Nexus 3 (NX - Kerr) e dois de ativação química: Multilink (ML - Ivoclar Vivadent) e Cement Post (CP - Angelus) foram inseridos entre as duas bases de aço retangulares (6x2 mm) com a distância ajustada em 0,1, 0,3 e 0,5 mm, estabelecendo uma variação no volume. Estas bases de aço foram fixadas a uma máquina de teste universal (Emic DL 500, com célula de carga de 50 kg) e as forças (N) foram registradas por 10 min. Os valores máximos de tensões geradas por cada material foram submetidas à ANOVA a dois critérios, seguido do teste de Tukey (p<0,05) para comparações individuais. VL, NX e CP desenvolveram maiores FGPS quando o volume de material aumentou, enquanto ML apresentou o comportamento inverso. Maiores volumes aumentam as FGPS mesmo com redução concomitante do Fator-C, a menos que o cimento resinoso apresente uma baixa taxa de geração de força em função do tempo associado a um baixo Fator-C, o que resulta em alívio das tensões e consequentemente menores valores de FGPS.