Effect of additives on the compressive strength and setting time of a Portland cement

Improvements in strength and setting time of Portland cements (PC) are needed to enhance their performance as endodontic and load bearing materials. This study sought to enhance the compressive strength and setting time of a PC by adding one of the following additives: 20 percent and 30 percent poly-methylmethacrylate (PMMA), 20 percent and 30 percent irregular and spherical amalgam alloys, and 10 percent CaCl2. The control consisted of unreinforced PC specimens. Setting time was determined using a Gillmore apparatus according to standardized methods while compressive strength was measured using a universal testing machine after 21 hours or 60 days of water storage. Data were analyzed by ANOVA, Tukey and Games-Howell tests (á = 5 percent). All additives significantly decreased both initial and final setting times as compared with the PC-control (p < .05). 30 percent PMMA and 30 percent irregular alloy had the lowest values of initial setting time. 30 percent irregular alloy also produced the lowest values of final setting time while 30 percent spherical alloy yielded the highest (p < .05). No differences were detected between the compressive strength values of 21 hours and 60 days. While 10 percent CaCl2, 20 percent and 30 percent PMMA produced values significantly lower than the PC-control, 30 percent spherical alloy significantly improved the compressive strength of the reinforced PC (p < .05). In summary, all additives significantly reduced the setting time and 30 percent spherical amalgam alloy yielded a significant increase in compressive strength for the tested PC, which might represent an improved composition for PCs to expand their use as endodontic and potentially load bearing materials.

Microtensile bond strength of adhesive systems of single and multiple steps / Resistência à microtração dos sistemas adesivos de única e múltipla etapas

OBJECTIVE: To evaluate the microtensile bond strength of ten dentin adhesive systems. MATERIAL AND METHOD: Sixty human molars were cut to the dentine level and restored with a hybrid composite and one of the adeshive systems. Each teeth were sectioned to obtain sticks measuring 1.0 ± 0.2 mm2, which were then stressed at a crosshead speed of 1mm/min in auniversal testing machine until failure. The failure modes were verified using optical microscopy. RESULTS: One Up Bond FTM, All Bond 2TM, One Step PlusTM, Adper Prompt L-PopTM, OneStepTM, Single BondTM and Clearfil SE BondTM presented no statistically significant differences (p>0.05); the lowest bond strength values were obtained with Scotchbond MPTM, Prime&Bond NTTM and ExciteTM (p<0.05). CONCLUSION: The self etch primer systems and conventional systems exhibited the highest bond strength to dentin, except for Scotchbond MPTM, Prime&BondNTTM and ExciteTM. Adhesive fractures accounted for 69% of the total fractures.

OBJETIVO: Avaliar a resistência adesiva de dez sistemas adesivos. MATERIAIS E MÉTODOS: Os dentes foram seccionados em forma de palitos com tamanho de 1.0 ± 0,2 mm2 e tracionados com velocidade de 1mm/min. Os tipos de fraturas foram verificados utilizando o microscópio óptico. RESULTADOS: Os sistemas adesivos (One Up Bond FTM, All Bond 2TM, One Step PlusTM, Adper Prompt L-PopTM, One StepTM, Single BondTM e Clearfil SE BondTM apresentaram os maiores valores de resistência adesiva em dentina. Os sistemas ScotchbondMPTM, Prime&Bond NTTM e ExciteTM apresentaram menor resistência. CONCLUSÃO: Os sistemas autocondicionantes e os convencionais apresentaram maior resistência adesiva em dentina. Os sistemas Scotchbond MPTM, Prime&Bond NTTM e ExciteTM apresentaram menor resistência adesiva. As fraturas adesivas representaram 69% do total das fraturas.

Impact of refrigeration on the surface hardness of hybrid and microfilled composite resins

This in vitro study evaluated the Knoop hardness of the composite resins Charisma® (C) and Durafill VS® (D) polymerized in 3 different conditions: at room temperature (A) (23 ± 1°C); refrigerated at 4 ± 1°C and immediately photo-activated after removal from the refrigerator (0); and, refrigerated at 4 ± 1°C and photo-activated after a bench time of 15 min at room temperature (15). One hundred and twenty specimens (4 mm diameter and 2 mm depth) were made using a stainless steel mold and following manufacturer's instructions. All specimens were tested immediately after polymerization (I) and after 7 days of water storage in the dark at room temperature (7d). The data were subjected to ANOVA and post-hoc Tukey's test (a=0.05). On the top surface, CAI was statistically similar to C15I and DAI to D15I (p>0.05). On the bottom surface, CAI presented higher hardness values when compared to COI and C15I (p<0.05). The D groups showed no significant differences (p>0.05) on the bottom surfaces for any tested polymerization condition. After 7 days of storage, the Knoop hardness decreased significantly (p<0.05) for groups C7d and D7d except for C07d, which was not different from COI at either surface (p>0.05). D07d showed higher Knoop hardness (p<0.05) values on the top surface when compared to the other groups.

O objetivo do presente estudo in vitro foi avaliar a dureza Knoop das resinas compostas, uma resina híbrida (Charisma - C) e uma de micropartículas (Durafill VS - D) quando polimerizadas à temperatura ambiente (A) (23 ± 1°C); refrigeradas (4 ± 1°C) e fotoativadas imediatamente após a remoção do refrigerador (0); e refrigeradas (4 ± 1°C), com tempo de espera de 15 min após a remoção do refrigerador para fotoativação (15). Cento e vinte corpos-de-prova com 4 mm de diâmetro por 2 mm de altura foram confeccionados em uma matriz de aço inoxidável. Cada corpo-de-prova foi testado imediatamente após a fotoativação (I) e, após 7 dias de armazenamento (7d) em ambiente escuro com umidade relativa a 100 por cento, à temperatura do ambiente (23 ± 1°C). Quando testada imediatamente após a polimerização, na superfície de topo CAI foi estatisticamente semelhante à C15I e DAI à D15I. Na base, a resina composta CAI, teve maiores valores de dureza quando comparados à COI e C15I. Os grupos do material D não mostraram diferenças significantes com relação ao efeito da refrigeração na base. Sete dias após, os valores de dureza Knoop caíram tanto para C7d quanto para D7d com exceção de C07d que não diferiu de C07d nas diferentes superfícies, e D07d que mostrou maiores valores de dureza no topo.