Hardness and diametral tensile strength of a hybrid composite resin polymerized with different modes and immersed in ethanol or distilled water media

OBJECTIVES: The aim of this in vitro study was to evaluate the microhardness and diametral tensile strength of a hybrid composite resin (Z250, 3M ESPE) polymerized with four different modes of light exposure and immersed in two different media. METHODS: Composite resin specimens were randomly polymerized according to the experimental groups (conventional, 550 mW/cm(2)/30 s; soft start, 300 mW/cm(2)/10 s + 550 mW/cm(2)/20 s; high intensity, 1060 mW/cm(2)/10 s; pulse delay, 550 mW/cm(2)/1 s + 60 s of waiting time + 550 mW/cm(2)/20 s) and immersed in one of two media (distilled water or absolute ethanol) for 24 h. After that, microhardness (M) and diametral tensile strength (DTS) tests were performed. RESULTS: For DTS, there were no statistical differences among the polymerization modes, however, ethanol medium groups presented statistically lower DTS (p < 0.05) than water medium. For the M test, samples immersed in ethanol medium presented lower M for almost all groups. Conventional mode presented higher M values for the groups immersed in water medium. In ethanol medium, conventional and pulse delay groups presented higher M values, statistically different (p < 0.05) from the high intensity group. For all experimental conditions, the top surface showed higher M than the bottom surface. SIGNIFICANCE: Different polymerization modes can be related to the different polymer structures formed, and consequently with different physical properties of resin composite. The immersion media can alter the physical properties of resin composites of different polymer structures.     

Protective effect of the in situ formed short-term salivary pellicle

Salivary pellicle, as previously investigated, protects the enamel surface after certain processes of maturation against the influence of acidic agents. The aim of the present study was to investigate the protective effect of the short-term salivary pellicle formed in situ over periods of 3, 60 and 120 min. Six human volunteers used intraoral acrylic splints with bovine enamel samples fixed at the buccal and palatal sites of the maxillary first molars and second premolars. Enamel specimens (n = 252) with and without pellicle were immersed for 60 s in 1.0% citric acid solution under agitation. Knoop surface hardness (KHN) of uneroded polished enamel was measured as a baseline and estimated immediately after erosive treatment reflecting the microhardness loss (DeltaKHN). The amounts of calcium dissolved from the eroded enamel surface were analysed by atomic absorption spectroscopy and scored in mg/l per 10 mm2 of enamel surface area. In addition, the scanning electron microscope was used for the micromorphological examination of the erosive alterations of the enamel surface. The average microhardness loss values after erosion of the enamel samples with buccally/palatally formed pellicle layers were measured as 139.1/144.9 DeltaKHN for 3 min pellicle, 145.9/146.9 DeltaKHN for 60 min pellicle and 141.7/138.6 DeltaKHN for 120 min pellicle. Calcium release values from the specimens with buccal/palatal pellicles were amounted to 15.0/14.9, 16.5/15.9 and 15.3/17.4 mg/l per 10 mm2 for 3, 60 and 120 min-old pellicles, respectively. No significant differences were related to the pellicle formation time and intraoral site (buccal or palatal) in all tested series (ANOVA, P < 0.05). However, significant protection of the enamel surface provided by the pellicle layer was observed on all pellicle-covered surfaces if compared to the non-covered enamel samples (calcium release: 25.6 mg/l per 10 mm2; microhardness loss 187.0 DeltaKHN). These data were in accordance with the morphologic alterations caused by citric acid on the pellicle-covered and pellicle non-covered specimens. It could be concluded that salivary pellicle formed in situ within a period of 3 min offers protection of enamel against citric acid. However, pellicle does not completely inhibit the erosive action of citric acid under the conditions of the present study.     

氯化镧对脱矿釉质再矿化的影响

为了了解镧对脱矿釉质矿化的影响，以基础矿化液及含１０ｐｐｍｌａ＾３＋或氟的矿化液分别处理脱矿后人牙釉质，再作实验开窗区剖面表及里的显微硬度测定，结果显示各试验组表层硬度明显低于内层硬度，但１００μｍ以内各点之硬度值比较差异均无显著性，以各实验组相比较，表层硬度值之间差异有显著性，其他层次相应点之间硬度值无无显著性。     

Effect of fluoride containing bleaching agents on enamel surface properties

OBJECTIVES: To evaluate the effects of fluoridated bleaching agents and post-bleaching fluoridation treatment on the whitening efficiency and microhardness of bovine enamel. METHODS: Twenty five freshly extracted bovine incisors were cut into halves, embedded and then divided into the following five groups: Group 1, untreated controls; Group 2, treatment with 10% carbamide peroxide (CP) bleaching agent; Group 3, treatment with 10% CP followed by a 0.9% sodium fluoride gel application, Group 4, treatment with 10% CP containing 0.11% fluoride; Group 5, treatment with an experimental bleaching agent consisting of 10% CP and 0.37% fluoride. Groups 2-5 were treated 8h per day for 14 days then immersed in saliva for 2 weeks. Enamel morphology changes were evaluated under SEM on Day 14. Changes in enamel color and microhardness were evaluated on Days 7 and 14, and compared with the baseline data. Additionally, microhardness was determined on post-bleaching Days 21 and 28. RESULTS: After 2 weeks, an erosion pattern was noted on the specimens in Groups 2 and 3. Groups 4 and 5 showed a milder demineralized pattern. All the bleached enamel specimens revealed increased whiteness and overall color value. Groups 2 and 3 showed significantly decreased enamel microhardness compared to their baseline data. The specimens treated with fluoridated bleaching agents showed relatively less reduction in enamel microhardness than those treated with nonfluoridated agents during the bleaching treatment. CONCLUSIONS: The fluoridated bleaching agents produced less demineralization of surface morphology and microhardness. The addition of fluoride did not impede the whitening effect.     

Effects of energy and sports drinks on tooth structures and restorative materials

Sports and energy drinks are consumed by more people than ever. Sports and energy drinks may enhance physical resistance, stimulate metabolism, prevent rehydration and replace electrolytes during high activity efforts. However, these drinks often have a low pH and are acidic, which can erode enamel and dentin, and increase dentine hypersensitivity. In addition to the adverse effects of sports and energy drinks on tooth structures, they often have the potential to damage restorative materials. These drinks often contain artificial colors which have potential to discolor resin composite materials and glass ionomers. The acidic nature of these drinks could also lead to a degradation, increase in wear, and roughening of the surface of the restorative materials. Many of the negative consequences of sport and energy drinks can be related to their over-consumption among children and teenagers. Patients should be advised to have a healthy diet, and consume soft and energy drinks in moderation, to avoid any negative dental or health consequences. The over-consumption of sports and energy drinks which are high in sugar and have the lowest pH are most likely to cause avoidable dental problems.     

人体距骨显微硬度的分布特征研究

目的 探讨人体距骨显微硬度的分布特征。方法 自河北医科大学解剖教研室标本库中,纳入年龄＞40岁、既往身体健康、无慢性病史的新鲜冰冻尸体标本3具,取其右侧距骨。以距骨颈基底部为界将距骨分为距骨头颈和距骨体两部分,并将距骨头颈部纵向平分为内、外两部分,将距骨体分别沿横向和纵向平分为前、后两部分和内、外两部分。用慢速锯沿距骨长轴进行切割,将骨骼制成若干厚3 mm的骨组织切片,并用砂纸打磨。应用维氏方法测量骨切片骨皮质和骨松质不同区域的硬度值。采用50 g力加载50 s、维持12 s标准操作方法测定,同一区域选取5个有效值,全体有效值的平均值作为该部位的硬度值。结果 本研究共制备18个骨组织切片,测量180个位点。三具标本距骨总体骨硬度为(36.70±5.77)HV。距骨头颈部硬度为(37.68±5.22) HV,距骨体硬度为(36.20±5.99)HV,两者比较差异无统计学意义(t=1.624, P＞0.05);距骨头颈部内侧硬度为(38.60±5.17) HV,略高于其外侧的(36.76±5.19) HV,但差异无统计学意义(t=1.376, P＞0.05)。距骨体内侧硬度为(37.78±5.23) HV,高于外侧的(34.63±6.32) HV ,差异有统计学意义(t=2.971, P＜0.01);距骨体前、后两部位硬度值分别为(36.38±5.50) HV和(36.03±6.49) HV,差异无统计学意义(t=0.375, P＞0.05)。结论 本研究首次报道应用维氏硬度方法分析人体距骨维氏硬度的分布规律:距骨头颈部与体部硬度无明显差异,距骨体内侧骨硬度大于外侧,是匹配内侧的高应力的结果,符合人体正常生理功能。     

Microhardness of sub-restoration dentine in primary molars after carious tissue removal to soft and firm dentine

ObjectivesTo compare the microhardness of sub-restoration dentine after selective carious tissue removal and placing glass ionomer restorative cement.MethodsForty-three primary molars with carious lesions extended to the inner third of dentine in subjects aged 8–12 years were included. The teeth were randomly assigned to the following carious tissue removal conditions: Group 1 - removal to the soft dentine, Group 2 - removal to the firm dentine, and Group 3 - removal to the hard dentine. Following restoration with glass ionomer restorative cement for three to six months, 30 tooth samples underwent microhardness testing performed on sub-restoration dentine and sound dentine. The Wilcoxon signed-rank test was used to compare the microhardness values of sound dentine and sub-restoration dentine within the group. The Kruskal–Wallis test was used to analyse the microhardness of the sub-restoration dentine across the three groups.ResultsAll 30 teeth available for analysis were asymptomatic, with no signs of pulpitis. The average microhardness values of sub-restoration dentine and sound dentine ranged from 16 to 23 KHN and 20 to 27 KHN, respectively. In each group, the microhardness value of the sub-restoration dentine was significantly lower than that of the sound dentine (p < 0.01). There were no significant differences in the microhardness values of sub-restoration dentine relative to that sound dentine among three groups (p = 0.86).ConclusionThe microhardness values of sub-restoration dentine with selective carious tissue removal were comparable to those with complete carious tissue removal after glass ionomer restorative cement placement.     

Characteristics of biofilm-induced degradation at resin–dentin interfaces using multiple combinations of adhesives and resins

ObjectiveWe aimed to evaluate morphological, mechanical and chemical characteristics at resin–dentin interfaces using multiple combinations of adhesives and resins after a short-term biofilm-induced degradation.MethodsCervical cavities were prepared in bovine incisors, treated by Clearfil SE Bond 2 (SE) or FL-Bond II (FL), restored by Clearfil Majesty ES Flow (ES) or Beautifil Flow Plus (BFP) and grouped into SE-ES, SE-BFP, FL-ES and FL-BFP. After biofilm challenge, interfacial gaps and dentin wall lesions were examined by optical coherence tomography (OCT). Gap depth (GD), gap pattern scale (GPS) and dentin wall lesion depth (WLD) were evaluated from confocal laser scanning microscope. Microhardness of dentin lesions was measured with a Vickers microhardness tester. Chemical elements in resins and dentin wall lesions were analyzed by scanning electron microscopy and energy dispersive X-ray spectrometry (SEM/EDS). Morphological structures of interfacial gaps were observed by SEM.ResultsOCT could detect adhesive-dentin-bonded and adhesive-dentin-debonded gaps. SE-containing groups showed significantly lower GPS than FL-containing groups. FL-BFP showed significantly lower WLD than FL-ES. Microhardness of dentin wall lesions was higher than that of outer lesions and they showed significant differences in FL-BFP. SE-BFP showed a lower GPS curve and higher intensities of Ca and P in the upper half of dentin wall lesions than other groups. From SEM, microgaps between filler and matrix, break and loss of matrix, separation of adhesive matrix with hybrid layer occurred at interfacial gaps.SignificanceThe morphological, mechanical and chemical characteristics of resin–dentin interfacial degradation depend on the component and chemistry of restorative materials.     

紫地榆牙膏对牙釉质脱矿和再矿化作用的研究

目的 评价紫地榆不同溶剂提取物牙膏抑制釉质脱矿和促进再矿化作用的影响.方法 检测紫地榆不同溶剂提取物牙膏处理离体牙前后乳酸盐缓冲液中磷离子浓度的变化,测定出磷溶出率,评价紫地榆不同溶剂提取物牙膏抑制釉质脱矿作用;此外,制作人工龋釉质块模型,取洛氏硬度值无统计学差异的25例脱矿釉质块,随机分为A、B、C、D、E5组(P＞0.05),分别进行体外再矿化,检测经紫地榆不同溶剂提取物牙膏处理前后釉质表面显微硬度值,从而评价紫地榆不同溶剂提取物牙膏对釉质再矿化的作用.结果 乙酸乙酯组、正丁醇组、水层组的釉质溶解度降低率与空白牙膏组比较有统计学意义(P＜0.01),但3组的作用无统计学意义(P＞0.05);而对于再矿化前后牙釉质表层显微硬度值,除乙酸乙酯牙膏组和空白牙膏组变化差异无统计学意义(P＞0.05),正丁醇牙膏组和水层牙膏组再矿化前后牙釉质表层显微硬度值变化有统计学意义(P＜0.01),但均低于NaF牙膏组(P＜0.01).结论 紫地榆3种不同溶剂提取物都具有抑制釉质脱矿的作用,且3种提取物的作用无统计学意义.正丁醇取物牙膏组和水层牙膏组均能促进人工脱矿牛切牙再矿化,但效果弱于NaF牙膏组(20g/L).     

The effect of 24h non-stop hydrogen peroxide concentration on bovine enamel and dentine mineral content and microhardness

Objectives

Tooth bleaching agents may adversely affect tooth structure. The aim of this study was to investigate the effect of hydrogen peroxide concentration on mineral loss and microhardness of bovine teeth.

Methods

Twenty-six freshly extracted intact bovine incisor teeth were stored in distilled water. Five teeth were sectioned and four samples (2 mm × 2 mm × 1.5 mm) each of enamel and dentine were obtained from each tooth. The samples of enamel and dentine were divided into four groups and immersed in either 0%, 3%, 10% or 30% (w/v) hydrogen peroxide solutions for 24 h at 37 °C. Samples from the solutions were taken for ion release analysis using inductively coupled plasma mass spectrometry. The remaining 21 teeth were mounted in epoxy resin and the upper surface of the specimens were ground and polished to expose the enamel and dentine for microhardness measurements. These specimens were randomly divided into three equal groups and Vickers microhardness values were recorded on the enamel and dentine surfaces of each group before and after bleaching.

Results

The differences in ion release concentration after treatment with 0% (control) and each of 3%, 10% and 30% hydrogen peroxide (w/v) were statistically significant (p < 0.025). The release of calcium and phosphorous ions increased with increasing hydrogen peroxide concentrations. A significant reduction (p < 0.05) in Vickers microhardness values for enamel was recorded after bleaching.

Conclusions

Ion release from both enamel and dentine increased with increasing hydrogen peroxide concentration. Microhardness of enamel decreased significantly with bleaching.