牙科Vita mark Ⅱ可切削陶瓷赫兹触压循环疲劳研究

目的 研究Vita mark Ⅱ可切削陶瓷在赫兹触压循环加载下的疲劳模式。方法 应用半径为3.18 mm的碳化钨球对Vita mark Ⅱ可切削陶瓷标准试件进行循环加载,然后测试加载后试件残余三点的弯曲强度,观测试件表面及次表面的损伤情况。结果 在相对均质的Vita mark Ⅱ可切削陶瓷赫兹触压循环疲劳中存在两种损伤模式,即经典的张应力驱动的锥状裂纹（脆性模式）及剪切应力驱动的显微损伤的累积（类塑性模式）,前者以加载点周围同心圆样锥状裂纹为特征,后者产生继发性锥状裂纹和放射状裂纹。锥状裂纹的产生导致试件强度的首次下降,后继的更为严重的强度下降由放射状裂纹引起。结论 牙科Vita mark Ⅱ可切削陶瓷赫兹触压循环疲劳包括低循环周期下的脆性模式以及高循环周期下的类塑性模式。     

牙科氧化锆瓷摩擦磨损性能的研究

目的研究牙科氧化锆瓷的摩擦磨损性能以及与天然牙釉质摩擦磨损性能匹配情况。方法微摩擦磨损试验机上,以滑石瓷为对磨物,人工唾液润滑下对Upcera ST和Zenostar Zr Translucent氧化锆瓷、牙釉质和饰面瓷进行摩擦磨损实验。实验前,用激光共聚焦显微镜测试件表面粗糙度Ra;实验结束后,光学显微镜下观察滑石瓷磨斑形貌、测量滑石瓷磨斑面积;激光共聚焦显微镜测量试件磨斑宽度;扫描电镜下观察试件磨斑的微观形貌。采用单因素方差分析进行统计学分析。结果饰面瓷的磨斑宽度大于其它3种材料（P〈0.01）,饰面瓷对磨物滑石瓷磨斑面积大于氧化锆瓷和牙釉质（P〈0.05）。结论与饰面瓷对比,氧化锆瓷具有更佳耐磨性及较低对磨物磨损,并且与天然牙釉质的磨擦学性能相似。     

牙科着色氧化锆陶瓷饰瓷前后的力学性能及断裂模式分析

目的:本研究对牙科氧化锆陶瓷着色及构筑饰面瓷前后的力学性能及断裂模式进行分析.方法:球磨混合一定组分的着色剂(氧化铁及氧化铈)和3Y-TZP(钇稳定氧化锆)粉体制备着色氧化锆陶瓷.根据ISO6872牙科陶瓷标准,制备着色和未着色氧化锆陶瓷的三点弯曲强度样品和构筑饰面瓷后的双层瓷样品,核心瓷与饰面瓷的厚度比为1:1.对所获得样品进行三点弯曲强度、断裂韧性和维氏硬度测试.采用X射线衍射(XRD)分析物相结构,扫描电镜(SEM)观察样品的断裂模式.结果:白色氧化锆陶瓷与着色氧化锆陶瓷的三点弯曲强度分别为1301 MPa和1203:MPa,统计学结果显示二者间没有明显差异,构筑饰面瓷后的三点弯曲强度分别为817 MPa和803 MPa,统计学结果显示二者间没有明显差异,但构筑饰面瓷后比单一材料样品强度降低,二者间有显著差异.在所有的双层瓷样品中,断裂模式的应力位移曲线显示为单峰断裂模式,断裂起始于核心瓷的张应力面中心区域同时发生饰面瓷的破碎和瓷层剥脱.结论:对氧化锆粉体的适当着色并没有明显影响材料的机械性能,着色和未着色氧化锆材料与饰面瓷具有良好的物理匹配性.     

改良液式冲蚀对3Y-TZP氧化锆基底与饰面瓷结合强度的影响

目的:探讨采用改良液式冲蚀方式对3Y-TZP氧化锆基底表面进行冲蚀后,对其与饰面瓷间结合强度的影响.方法:制作[8 mm×8 mm×3 mm(±0.02)]氧化锆试件块174个,根据不同尺寸的刚玉磨粒、不同的喷砂压强、不同的喷砂时间,采用传统喷砂方式进行分组处理(实验组),在氧化锆处理面上饰面瓷.表面未做处理的氧化锆试件直接上饰面瓷作为对照组,应用电子万能测力计检测各组试件与饰面瓷间的最大剪切力,计算剪切强度.分别用传统干式喷砂、改良液式冲蚀方式在相同条件下(150 μm,0.6 MPa,30 s)处理氧化锆试件块,用扫描电镜下观察处理面,再上饰面瓷,计算剪切强度,与对照组进行组间比较.采用SPSS17.0软件包对数据进行统计学分析.结果:采用传统干式喷砂方式,在0.4 MPa压强作用下,以110 μm A12O3喷砂粉喷砂20 s时,氧化锆与饰面瓷之间的剪切强度最大,显著大于对照组(P＜0.05);改良液式冲蚀组饰面瓷的结合强度显著大于传统干式喷砂处理组及对照组(P＜0.01).扫描电镜下可见,采用改良液式冲蚀的试件表面呈现均匀的粗糙面:采用传统干式喷砂处理的试件表面呈现不均匀的粗糙面,部分位置可见微裂纹.结论:对3Y-TZP氧化锆表面喷砂,能够增强其与饰面瓷间的结合强度;改良液式冲蚀比传统干式喷砂更适用于3Y-TZP氧化锆的表面处理.     

表面多孔涂层对氧化锆与饰面瓷界面结合强度的影响

目的：以表面抛光、喷砂为对照,研究表面多孔涂层对氧化锆与饰面瓷界面剪切结合强度的影响。方法：按照Schmitz-Schulmeyer法测量氧化锆与饰面瓷的剪切结合强度。制作氧化锆基底样本60个（IO×5×5mm）,分为三组（抛光组：耐水碳化硅砂纸逐级抛光至1200#;喷砂组：1lOμmA1203颗粒在3bars的压力下喷砂10sec,距离10mm;涂层组：质量分数为55wt％的氧化锆粉浆涂塑氧化锆表面,致密烧结）,每组20个。表面烧结饰面瓷（5×3×3mm）。每组取10个样本,5℃／55℃水域中交替循环5000次。万能材料试验机测试剪切结合强度,加载速度0．5mm／min。对测试结果进行双因素方差分析（α=0．05）。SEM观察样本断裂模式。结果：涂层组剪切结合强度与抛光组和喷砂组差异均有统计学意义（P〈0．05）;喷砂组与抛光组间差异无统计学意义（P〉0．05）;各组温度循环后剪切结合强度差异均无统计学意义（P〉0．05）。SEM观察显示,涂层组样本以饰面瓷的内聚断裂为主;抛光组和喷砂组以界面断裂为主。结论：表面多孔涂层可显著提高氧化锆与饰面瓷的剪切结合强度,并能耐受短期的人工老化,而结合强度无明显下降。     

不同表面处理方式对Kavo氧化锆基底与饰瓷结合强度的影响

目的:研究不同表面处理方法对Kavo氧化锆底层材料与Noritake Cerabien饰面瓷结合强度的影响。方法:选择Kavo氧化锆陶瓷作为底层材料,随机分为4组,每组8个试件。A组为染色液浸泡着色+表面不喷砂;B组为染色液浸泡着色+表面喷砂;C组为不浸泡染色液+表面不喷砂;D组为不浸泡染色液+表面喷砂。4组底层材料采用粉浆涂塑法烧结饰面瓷后,使用材料试验机测试其剪切强度,采用SPSS10.0软件包对数据进行统计学分析。结果:采用喷砂处理的2组(B组和D组)材料,其剪切强度均高于未喷砂的2组(A组和C组),差异具有显著性(P<0.01);浸泡染色处理对剪切强度的无显著影响,A组与C组、B组与D组之间的差异无显著性(P>0.05)。结论:对Kavo氧化锆基底表面进行喷砂处理,可以提高基底冠与饰面瓷的结合强度;而浸泡染色则对两者结合力的强度无显著影响。     

硅藻土基底瓷与饰面瓷厚度比对抗弯强度的影响

目的:探讨不同基底瓷与饰面瓷厚度比对硅藻土基全瓷材料结合强度的影响。方法:硅藻土基底瓷尺寸为16 mm×5. 4 mm×1 mm,随机分为4组,表面堆塑不同厚度的IPS e.max饰面瓷,分别为不烧结（A组）、0.6 mm（B组）、0.8 mm（C组）和1.0 mm（D组）,测定不同分组的抗弯强度并观察陶瓷试件的断裂模式,扫描电镜观察断面显微形貌。采用SPSS 17.0软件包对数据进行单因素方差分析。结果:随着饰面瓷厚度的增加,抗弯强度也随之增强,其中C组抗弯强度最大,达到（277.24±15.47） MPa。结论:基底瓷与饰面瓷厚度比可显著影响硅藻土基底瓷与饰面瓷的抗弯强度。     

两种最大载荷值下牙科脆性陶瓷赫兹触压循环疲劳研究

目的比较两种最大载荷值下牙科脆性陶瓷赫兹触压循环疲劳损伤模式。方法应用赫兹触压实验方法对VitamarkⅡ可切削陶瓷标准试件进行循环加载,然后测试加载后的残余3点弯曲强度,观测试件表面及次表面损伤。结果500 N最大载荷下,Vita markⅡ可切削陶瓷低周循环触压疲劳损伤为经典脆性模式,而高周循环下为类塑性模式。200 N最大载荷下则主要表现为以环状裂纹为代表的脆性模式。结论不同最大载荷值下,牙科脆性陶瓷展示不同的触压疲劳模式。即使在相对较小的载荷下,只要达到一定的循环加载周期,牙科脆性陶瓷强度也会显著降低。     

氟磷灰石玻璃陶瓷、长石质饰瓷与天然牙摩擦磨损性能的研究

目的：研究牙科氟磷灰石玻璃陶瓷、长石质饰瓷与天然牙在干摩擦和唾液润滑条件下的摩擦磨损学性能。方法：制备涂覆IPS-emaxcream和Vita vm9 2种饰面瓷的氧化锆-饰面瓷双层材料试样,尺寸为20 mm×20 mm×4.5 mm,各20个。利用MMV-1摩擦磨损试验机,通过设置不同大小的垂直载荷和转速,分别在干摩擦和唾液润滑条件下,对2种氧化锆-饰面瓷试样进行摩擦磨损试验。采用SPSS 17.0软件包进行单因素方差分析和t检验,确定各组间摩擦系数和磨损量是否存在差异。结果：氟磷灰石玻璃陶瓷在唾液润滑条件下的动态摩擦系数和磨损量显著大于干摩擦条件下的数值;与氟磷灰石玻璃陶瓷相反,长石质饰瓷在干摩擦时的动态摩擦系数和磨损量显著大于在唾液润滑条件下的数值。在干摩擦和唾液润滑条件下,氟磷灰石玻璃陶瓷的磨损量均小于长石质饰瓷。扫描电镜显示,在唾液润滑条件下,氟磷灰石玻璃陶瓷及对应天然牙表现出比干摩擦更为严重的磨损表面。在干摩擦条件下,长石质饰瓷及对应天然牙较氟磷灰石玻璃陶瓷磨损更为严重,在唾液润滑条件下差异较小。结论：与长石质饰瓷相比,氟磷灰石玻璃陶瓷与天然牙在干摩擦条件下表现出更优越的耐磨损性能。加入唾液后,能减少2种饰瓷摩擦磨损性能之间的差异。     

纳米SiO2溶胶对氧化锆基底与饰面瓷结合强度的影响

目的:探讨采用溶胶-凝胶技术在氧化锆表面制备薄纳米SiO2涂层对氧化锆基底与饰面瓷结合强度的影响,指导氧化锆全瓷冠的制作.方法:将软质氧化锆试件切割成15 mm×10 mm×2.5 mm大小的长方形瓷块40片,分为4组,每组10件,分别采用4种处理方式.A组-仅经1450℃结晶处理;B组-先经30％纳米SiO2溶胶渗透后,再经1450℃结晶处理;C组-先经1450℃结晶,然后用30％纳米SiO2溶胶渗透,再经1450℃热处理;D组-表面涂布纳米SiO2溶胶后,1450℃结晶处理;E组-镍铬合金烤瓷组,使用失蜡铸造法制作12 mm×8 mm×2 mm长方形镍铬合金条块10件.5组试件在其表面堆塑直径为5 mm、高4 mm的饰面瓷圆柱,然后进行剪切强度测试.采用SPSS 19.0软件包对数据进行统计学分析.结果:5组试件的剪切强度分别为A组(28.12±2.95) MPa、B组(31.09±3.94) MPa、C组(25.60±2.45) MPa、D组(31.75±4.90) MPa、E组(28.67±3.95) MPa.单因素方差分析显示5组间具有显著差异(P＜0.05),其中,C组与B组和D组均具有显著差异.结论:①溶胶-凝胶技术在结晶致密前氧化锆基底表面制备纳米SiO2涂层,能提高氧化锆基底与饰面瓷的结合强度;②在结晶致密的氧化锆基底表面制备纳米SiO2涂层,能降低氧化锆基底与饰面瓷的结合强度;③氧化锆与氧化锆专用饰面瓷的结合强度与常用金属与饰面瓷的结合强度一致;④通过溶胶-凝胶技术在结晶致密前的氧化锆基底表面导入SiO2溶胶,提高氧化锆与饰面瓷结合强度的技术路线切实可行.     

Effect of Test Environment and Microstructure on the Flexural Strength of Dental Porcelains

Purpose: The objective of this study was to verify the influence of test environment on the flexural strength of dental porcelains with distinct microstructures. Material and Methods: Disk‐shaped specimens from three dental porcelains with distinct leucite content (VM: zero; CE: 12; NS: 22 vol%) were manufactured and tested for biaxial flexural strength in air and immersed in artificial saliva. The results were analyzed by means of two‐way ANOVA and Tukey‘s test (α= 0.05). Results: The flexural strength (MPa) obtained for ambient air and artificial saliva environments, respectively, were: 110.0 ± 16.0 and 81.5 ± 10.8 for VM; 51.9 ± 4.0 and 42.0 ± 4.7 for CE; 72.0 ± 11.5 and 63.6 ± 5.8 for NS. A numerical decrease in the mean flexural strength was observed for all groups when specimens were tested under artificial saliva; however, the difference was only statistically significant for VM. Conclusions: The results indicate that the effect of water immersion on the flexural strength of dental porcelains varies according to their leucite content, as only the material without leucite in its microstructure (VM) showed significant strength degradation when tested under water.     

Physical properties of current dental nanohybrid and nanofill light-cured resin composites

Objectives

The purpose of this work was the detailed study of sorption characteristics of water or artificial saliva, the determination of flexural strength and the flexural modulus, and the study of the thermal stability of some current commercial dental light-cured nanocomposites containing nano-sized filler particles.

Methods

Three nanohydrid dental composites (Tetric EvoCeram (TEC), Grandio (GR) and Protofill-nano (PR)) and two nanofill composites (Filtek Supreme Body (FSB) and the Filtek Supreme Translucent (FST)) were used in this work. The volumetric shrinkage due to polymerization was first determined. Also the sorption, solubility and volumetric increase were measured after storage of composites in water or artificial saliva for 30 days. The flexural strength and flexural modulus were measured using a three-point bending set-up according to the ISO-4049 specification, after immersion of samples in water or artificial saliva for 1 day or 30 days. Thermal analysis technique TGA method was used to investigate the thermal stability of composites.

Results

GR and TEC composites showed statistically no difference in volumetric shrinkage (%) which is lower than the other composites, which follow the order PR < FSB < FST. The amount of sorbed water and solubility is not statistically different than those in artificial saliva. In all the composites studied the amount of water, which is sorbed (% on composite) is not statistically different than the amount of water, which is desorbed and follows the order: GR < TEC < PR < FSB < FST. After immersion in water for 1 day the highest flexural strength showed the FSB and the lowest TEC. GR, PR and FST showed no statistically different flexural strength. The flexural modulus of composites after immersion for one day follows the order TEC < PR≤FST < FSB < GR.

Significance

Among the composites studied, Grandio had the lowest polymer matrix content, consisting mainly of Bis-GMA. It showed the lowest polymerization shrinkage and water sorption and the highest flexural strength and flexural modulus after immersion in water or artificial saliva for 30 days. The water and artificial saliva generally showed the same effect on physical properties of the studied composites. Thermogravimetric analysis gave good information about the structure and the amount of organic polymer matrix of composites.     

T-ZnOw树脂基托在不同pH值浸泡液中物理性能的变化

目的研究T-ZnOw树脂基托在不同pH值浸泡液中的物理性能。方法按质量比将5%的T-ZnOw添加到树脂基托中,37℃条件下,分别放入pH值=7的去离子水、pH值=6的人工唾液及pH值=5的醋酸溶液中浸泡,每24h更换浸泡液。分别在浸泡前、浸泡2周、4周、8周后取出试件,进行冲击强度、弯曲强度、硬度的检测。结果添加和未添加T-ZnOw的基托,浸泡2周后在不同浸泡液中,人工唾液组、醋酸溶液组和去离子水组的冲击强度与硬度无显著差异（P〉0.05）;人工唾液组的弯曲强度和弹性模量大于醋酸组,小于去离子水组,而醋酸组的弯曲强度与弹性模量小于去离子水组。浸泡4周、8周后,人工唾液组和醋酸溶液组的冲击强度、弯曲强度和弯曲弹性模量、硬度有不同程度降低,去离子水组物理性能无明显变化（P〉0.05）。在同一种浸泡液中,浸泡相同时间,添加T-ZnOw的基托的物理性能优于未添加者。结论 3种浸泡液中,去离子水浸泡对T-ZnOw树脂基托材料物理性能无明显影响。添加T-ZnOw的基托的物理性能优于未添加者。     

Effects of water immersion on mechanical properties of new esthetic orthodontic wire.

New fiber-reinforced plastic orthodontic wire (FRP wire) was fabricated with polymethyl methacrylate (PMMA) for the matrix and biocompatible CaO-P(2)O(5)-SiO(2)-Al(2)O(3) (CPSA) glass fibers for fibers that have not only high esthetics but also mechanical properties similar to those of metal wires. The purpose of this study was to evaluate the effects of water immersion on the mechanical properties of this new wire. The fiber-reinforced plastic orthodontic wire specimens were 0.5 mm in diameter with 29.1% to 60. 4% volume fraction of fibers that were 20 microm in diameter. A three-point flexural test was performed to obtain the elastic modulus and flexural load at the deflection of 1 mm under dry and wet conditions. Stress relaxation of the wires was tested under dry and wet conditions, and the wire diameters were measured before and at 20 days after immersion. The results showed that there were changes in the elastic modulus up until 10 days and in flexural load up until 20 days after immersion. The values of these two at 30 days after immersion were 93% and 87%, respectively, of those before immersion. Stress relaxation occurred rapidly from the start of immersion until about 60 minutes under dry conditions and about 120 minutes under wet conditions and then approached saturation. The swelling of hydrated fiber-reinforced plastic orthodontic wires affected the wire diameter, although this effect was not significant. The results of this study therefore suggest that the mechanical properties of fiber-reinforced plastic orthodontic wires are reduced by water immersion in the initial stage.     

Flexural properties of the bulk fiber-reinforced composite DC-tell used in fixed partial dentures

PURPOSE: The aim of this study was to measure the flexural properties of fiber-reinforced composite (FRC) used in frameworks of fixed partial dentures. In addition, the influence of water storage on the properties was determined. MATERIALS AND METHODS: Rhombic test specimens for four groups were milled from bulk FRC material DC-Tell. The test specimens of the first group were stored and tested dry. In the second group, the test specimens were water stored for 3 months at 37 +/- 1 degrees C and tested in water. The specimens of the third group were also water stored, but they were tested dry at room temperature. Water-stored test specimens of the fourth group were dehydrated and tested dry at room temperature. A three-point bending test was used to measure the flexural properties. The quantity of glass fibers in the test specimens was determined by combustion analysis. Water uptake was calculated after 3 months of water immersion. The direction and length of fibers were examined, and elemental composition was determined. RESULTS: Water storage decreased the flexural strength by 66% and flexural modulus by 60%. After dehydration, the flexural strength did not recover to the same level as the flexural strength of the dry-group specimens. The fiber content was 38% by volume. Water uptake was 3 wt%. The reinforcement of DC-Tell was short fibers in random orientation, and the elemental composition of fibers was similar to that of E-glass. CONCLUSION: Water storage decreases the flexural properties of the bulk fiber-reinforced composite DC-Tell. This may restrict the use of DC-Tell as a framework of crowns and bridges in the oral cavity in the long term.     

Degradation of repaired denture base materials in simulated oral fluid

This in vitro study evaluates the degradation of repaired denture bases upon immersion in a simulated oral fluid. Denture base materials (Luciton 199), after being repaired by Repair Material and Triad, using three different joint surface designs (butt, round and 45 degrees bevel), were immersed onto 99.5 vol.% ethanol/water solution (with similar solubility parameter) for various amounts of time (0-72 h). The flexural loads of the six combination of groups were measured by the three-point bending tests using a universal testing machine. Acoustic emission (AE) during sample fracturing were processed using the MISTRA 2001 system. The fracture pattern and surface details of the interface were examined with a scanning electronic microscope (SEM). Data were analysed using three-way ANOVA and Tukey LSD tests. SEM micrographs of the fracture interface were used to differentiate the fracture mode. The flexural loads (2.72 +/- 0.51 Kgf) of the round joint specimens were significantly higher (P< 0.05) than those (butt: 1.66 +/- 0.38 Kgf, 45 degrees bevel: 1.93 +/- 0.41 Kgf) of the other two designs. This corresponds to the microscopic examination in which more cohesive failure mode was found for the round joint group after storage. The flexural loads (2.54 +/- 0.39 Kgf) of the specimens repaired with Triad were significantly higher (P < 0.05) than those (1.59 +/- 0.40 Kgf) of specimens repaired with Repair Material. Significant progressive reduction of the flexural load and/or AE signals of the specimens was noted in proportion to the length of time of the immersion in the simulated oral fluid. Mechanical strength of a denture base repaired with a round joint design and light-cured material is significantly higher after immersion in simulated oral fluid.     

Effect of water on the physical properties of resin-modified glass ionomer cements.

OBJECTIVES: Resin-modified glass ionomer cements (GIC) are available for clinical use as restorative materials or as liners and bases. This work was conducted to study the effect of water sorption on the physical properties of several resin-modified GIC, by changing the samples' storage conditions. METHODS: The water sorption, the flexural strength, the flexural elastic modulus, the Vickers hardness and the dimensional changes of five resin-modified GICs were measured using specimens aged for 24 h to 3 mon. The specimens were stored at 37 degrees C, either in a dry environment (A), immersed in water (B), stored in a humid environment (C), stored in a humid environment for 1 h and then immersed in water (D), or immersed in water and subsequently dried (B + A). An analysis of variance was used to compare the results. RESULTS: The resin-modified GIC absorb during the first 24 h large amounts of water (114-172 mg/cm3) compared to the conventional GIC (30-63 mg/cm3). Water alters the physical properties of resin-modified GICs: With regard to dry specimens, a decrease in the flexural strength of 20 to 80% was observed for samples immersed in water. Decreases in their flexural elastic modulus (50 to 80%) and in their hardness (approximately 50%) were also observed. Water sorption also provoked an expansion in volume of the immersed specimens, ranging from 3.4 to 11.3% after 24 h. SIGNIFICANCE: The flexural strength and Vickers hardness of the resin-modified GICs are sensitive to the water contained in the tested specimens. A correlation was established between the decrease in their physical properties and the water uptake. However, it should not be concluded that these materials are not adequate for use in applications in direct contact with oral fluids. Probably, resin-modified GIC placed in oral cavities would not be affected to the same extent as in in vitro tests. In an oral environment, the constituents of saliva will certainly decrease the rate of water sorption and will hence delay its effects.     

Effect of water storage on the flexural properties of three glass fiber-reinforced composites

PURPOSE: The effect of water sorption on the flexural strength and flexural modulus of three fiber-reinforced composites was studied. MATERIALS AND METHODS: Bar-shaped specimens of each material were prepared according to the manufacturers' instructions. The flexural strength and modulus of each specimen were tested after the specimens were immersed in distilled water for 1, 7, 60, and 180 days. SEMs were taken to examine the mode of failure. The volume percentage of fiber content of each fiber-reinforced composite was experimentally estimated. RESULTS: The ascending order of flexural strength and modulus among the materials was generally: FibreKor < Stick < Vectris. The flexural strengths of Stick and FibreKor specimens at 1 and 180 days were not significantly different. Although the 180-day Vectris specimens possessed significantly lower flexural strength than the 1-day specimens, the flexural strengths of Vectris specimens at 1, 7, 60, and 180 days remained significantly higher than those of Stick and FibreKor. The difference in flexural modulus for each fiber-reinforced composite related to the duration of water immersion was not significant. CONCLUSION: Water immersion affected the flexural strengths of the three composites to a different degree but did not affect their flexural moduli significantly. For each duration of water immersion, the flexural property of the fiber-reinforced composite, in ascending order of significant difference, was: FibreKor < Stick < Vectris.     

An investigation into bisphenol-A leaching from orthodontic materials

Objective:To quantitatively determine the bisphenol-A (BPA) leached from orthodontic materials during simulated intraoral exposure.Materials and Methods:Samples of orthodontic materials were subjected to simulated abrasion, immersion in artificial saliva, thermal shock via temperature cycling, and simulated intraoral exposure. Sample aliquots were collected for up to 2 weeks after artificial saliva immersion, derivatized, then analyzed for BPA by gas chromatography/mass spectroscopy.Results:Quantifiable amounts of leached BPA were observed from a thermoformed orthodontic retainer material (7.63 µg/g of material) and an orthodontic adhesive (2.75 µg/g of material). BPA leaching was only observed within the first 3 days of artificial saliva immersion.Conclusions:Under the test conditions, BPA was observed to leach from two orthodontic materials. While the quantities of leached BPA were below the reference dose for daily intake, existing data of low-dose effects and medical disorders associated with elevated urinary BPA levels suggest that BPA exposure, and thus the use of the leaching materials identified in this study, should be reduced or eliminated.     

Influence of environmental conditions on dental composite flexural properties.

OBJECTIVE: To determine if increased relative humidity and temperature simulating intraoral environmental conditions adversely affect flexural properties of dental composites. METHODS: Specimen fabrication followed ANSI/ADA specification 27 for resin-based filling materials, except that ambient laboratory conditions (47% relative humidity at 22 degrees C) or simulated intraoral conditions (90% relative humidity at 35 degrees C) were used when fabricating and polymerizing specimens. Ten specimens were made of each of three commercially available composites at each condition. As per the specification, after aging specimens in 10 ml of deionized water at 37 degrees C for 24 h, flexural properties were measured using a 3-point bend test. RESULTS: A two-factor ANOVA and Fisher's least significant difference (LSD) post hoc (alpha=0.05) indicated there were significant differences in flexural modulus and strength as a function of material, with Z250=TPH>Prodigy. However, neither flexural modulus nor flexural strength of any material was adversely influenced by fabrication conditions. SIGNIFICANCE: Although the flexural properties did not decrease with respect to fabrication conditions, the flexural modulus of some of the materials (TPH Spectrum and Z250) increased when specimens were fabricated at simulated intraoral temperature and relative humidity. Thus, simulation of these factors may be important in laboratory testing, since the resultant properties may better reflect flexural properties associated with dental composite restorations placed clinically.