Amato Patrícia Alves Ferreira, Martins Renato Parsekian, dos Santos Cruz Carlos Alberto, Capella Marisa Veiga, Martins Lídia Parsekian
Private practice, Ribeirão Preto, São Paulo, Brazil.
Invited professor, Orthodontic Program, Araraquara School of Dentistry, São Paulo State University, Araraquara, São Paulo, Brazil; private practice, Araraquara, São Paulo, Brazil.
Am J Orthod Dentofacial Orthop. 2014 Jul;146(1):40-6. doi: 10.1016/j.ajodo.2014.03.022.
The aim of this study was to assess the influence of curing time and power on the degree of conversion and surface microhardness of 3 orthodontic composites.
One hundred eighty discs, 6 mm in diameter, were divided into 3 groups of 60 samples according to the composite used-Transbond XT (3M Unitek, Monrovia, Calif), Opal Bond MV (Ultradent, South Jordan, Utah), and Transbond Plus Color Change (3M Unitek)- and each group was further divided into 3 subgroups (n = 20). Five samples were used to measure conversion, and 15 were used to measure microhardness. A light-emitting diode curing unit with multiwavelength emission of broad light was used for curing at 3 power levels (530, 760, and 1520 mW) and 3 times (8.5, 6, and 3 seconds), always totaling 4.56 joules. Five specimens from each subgroup were ground and mixed with potassium bromide to produce 8-mm tablets to be compared with 5 others made similarly with the respective noncured composite. These were placed into a spectrometer, and software was used for analysis. A microhardness tester was used to take Knoop hardness (KHN) measurements in 15 discs of each subgroup. The data were analyzed with 2 analysis of variance tests at 2 levels.
Differences were found in the conversion degree of the composites cured at different times and powers (P <0.01). The composites showed similar degrees of conversion when light cured at 8.5 seconds (80.7%) and 6 seconds (79.0%), but not at 3 seconds (75.0%). The conversion degrees of the composites were different, with group 3 (87.2%) higher than group 2 (83.5%), which was higher than group 1 (64.0%). Differences in microhardness were also found (P <0.01), with lower microhardness at 8.5 seconds (35.2 KHN), but no difference was observed between 6 seconds (41.6 KHN) and 3 seconds (42.8 KHN). Group 3 had the highest surface microhardness (35.9 KHN) compared with group 2 (33.7 KHN) and group 1 (30.0 KHN).
Curing time can be reduced up to 6 seconds by increasing the power, with a slight decrease in the degree of conversion at 3 seconds; the decrease has a positive effect on the surface microhardness.
本研究旨在评估固化时间和功率对3种正畸复合材料的转化率和表面显微硬度的影响。
180个直径6毫米的圆盘，根据所用复合材料分为3组，每组60个样本——Transbond XT（3M Unitek，蒙罗维亚，加利福尼亚州）、Opal Bond MV（Ultradent，南乔丹，犹他州）和Transbond Plus Color Change（3M Unitek）——每组再进一步分为3个亚组（n = 20）。5个样本用于测量转化率，15个样本用于测量显微硬度。使用具有多波长宽光发射的发光二极管固化单元，在3种功率水平（530、760和1520毫瓦）和3个时间点（8.5、6和3秒）进行固化，总能量始终为4.56焦耳。每个亚组的5个样本进行研磨，并与溴化钾混合制成8毫米的片剂，与另外5个用相应未固化复合材料同样制成的片剂进行比较。将这些片剂放入光谱仪中，使用软件进行分析。使用显微硬度测试仪对每个亚组的15个圆盘进行努氏硬度（KHN）测量。数据通过2水平的2次方差分析进行分析。
发现在不同时间和功率下固化的复合材料的转化率存在差异（P <0.01）。当光固化8.5秒（80.7%）和6秒（79.0%）时，复合材料显示出相似的转化率，但在3秒时（75.0%）并非如此。复合材料的转化率不同，第3组（87.2%）高于第2组（83.5%），第2组高于第1组（64.0%）。显微硬度也存在差异（P <0.01），8.5秒时显微硬度较低（35.2 KHN），但6秒（41.6 KHN）和3秒（42.8 KHN）之间未观察到差异。与第2组（33.7 KHN）和第1组（30.0 KHN）相比，第3组具有最高的表面显微硬度（35.9 KHN）。
通过提高功率，固化时间可缩短至6秒，3秒时转化率略有下降；这种下降对表面显微硬度有积极影响。
