In vitro cytotoxicity evaluation of elemental ions released from different prosthodontic materials

ObjectivesThis study investigated the cytotoxicity of elemental ions contained in four fixed prosthodontic materials (gold, nickel–chromium, stainless-steel alloys and CAD–CAM ceramics).Materials and methodsAccording to the determination of elements released from prosthodontic materials by using inductively coupled plasma mass spectroscopy, similar amounts of elements Pd, Ag, Zn, Cu, Ni, Cr, Mo, Be, Fe, Al, and K were prepared as salt solutions. Wells with a tenfold higher concentration of the tested elements were used as positive controls, while a well without any tested element was used as a negative control. These salt solutions were tested for cytotoxicity by culturing mouse L-929 fibroblasts in the salt solutions for a 7-day period of incubation. Then, the percentage of viable cells for each element was measured using trypan blue exclusion assay. The data (n = 5) were statistically analyzed by ANOVA/Tukey test (p < 0.05).ResultsThe results showed a statistically significant difference for the cytotoxic effect of the tested elements salt solutions. For the released element concentrations the lowest percentage of viable cells (mean ± SD) was evident with Zn, Cu or Ni indicating that they are the highly toxic elements. Be and Ag were found to be intermediate in cytotoxic effect. Fe, Cr, Mo, Al, Pd or K were found to be the least cytotoxic elements.SignificanceZn and Cu released from gold alloys, and Ni released from nickel–chromium alloys, which are commonly used as fixed prosthodontic restorations, show evidence of a high cytotoxic effect on fibroblast cell cultures.     

Artificial salivas for in vitro studies of dental materials

Objectives: An artificial saliva (AS) of defined composition is necessary for testing the performance of materials that serve in the mouth as natural saliva is too variable. The chemistry involved is critically important. Many AS recipes can be found in the literature, but the stability of tooth material, i.e. hydroxyapatite (HAP), in most of these has not been addressed. In fact, few contain all major ionic components with concentrations in the physiological range. The aim of the present study was (a) to review reported AS formulae from their inception in 1931 to date, (b) to compare the stability of HAP in various reported AS, and (c) to investigate the individual effects of ionic components present in the reported formulae on the stability of HAP.

Methods: A computer algorithm, RAMESES, for solving multiple equilibrium equations, was employed for all calculations.

Results: There was a marked difference between two groups, i.e. those with and without the presence of Ca; those with Ca were supersaturated with respect to HAP in the physiological pH range, the saturation pH ranging from about 4.5 to 6.0. There was also an approximately 180-fold range in solubility at pH 7, due to the individual effects of components such as phosphate, carbonate and citrate. Acetate, lactate and sulphate showed smaller effects, others have no appreciable effect.

Conclusions: All components and equilibria of relevance to saliva must be included in the system for detailed models. Continued systematic development of a standardized AS is essential.     

In vitro color change of composite-based resins

The adsorption of staining materials to resin restoratives was considered to be influenced by the physico-chemical properties of the resin-based monomers. To study the effects of the surface characteristics of resins on staining, we prepared five visible-light-cured experimental resins without fillers. Staining of these resins was colorimetrically measured. The staining solutions used were the Oil Orange and the Food Red 3 solutions. With the Oil Orange solution, the materials with higher hydrophobicity showed higher staining. With the Food Red 3 solution, the materials with higher water sorption showed higher staining.     

In vitro study of edge-strength of provisional polymer-based crown and fixed partial denture materials

OBJECTIVES: To evaluate in vitro the edge-strength of polymer-based provisional crown and fixed partial denture materials at increasing distances from an edge. METHODS: Three dimethacrylate-based provisional crown and fixed partial denture materials (Protemp 3 Garant, Luxatemp, and fast set Temphase) and one monomethacrylate-based one (Trim) were selected. Seven disk-shaped specimens of 12mm in diameter and 2.5mm in thickness for each material were fabricated and stored at 37 degrees C and 80% relative humidity for 1 month. The edge-strength was measured by using a CK 10 testing machine at a distance of 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0mm from the edge of the specimen. All experiments were carried out in triplicate at each distance at 23+/-1 degrees C. The data were statistically analyzed using one-way ANOVA and the multiple comparison Scheffé test at the significance level of 0.05. RESULTS: Trim showed severe deformation without chipping during loading at all distances. Protemp 3 Garant showed indentation at over 0.8mm from the edge, and for Luxatemp and fast set Temphase over 0.6mm from the edge without chipping. At 0.5mm from the edge, the highest values (2073.7N) were displayed by Protemp 3 Garant, approximately three times those of fast set Temphase (767.3N) and Luxatemp (697.0N) (p<0.05). The strengths of fast set Temphase and Luxatemp were not significantly different (p>0.05). Linear regression between the distance from the edge to 0.7mm and strength values of Protemp 3 Garant produced a correlation coefficient, R=0.99. SIGNIFICANCE: The dimethacrylate-based provisional materials tested were stronger in edge-strength than the monomethacrylate-based one which showed severe deformation without fracture.     

In vitro cytotoxicity of three dentine bonding agents

While several studies have been reported on the physical testing of dentine bonding agents, very few studies have been involved with their biological evaluation. This report describes a new in vitro method for assessing the cytotoxicity of these materials through dentine simulating their clinical use. An experimental bonding agent, now marketed as Tripton by ICI Dental, Scotchbond 2 and GLUMA were exposed to BHK-fibroblasts through 100 and 500 μm slices. All materials were significantly cytotoxic compared with controls through both thicknesses of slice. The ICI Dental experimental material was the least toxic through 100 μm slices (68·8 per cent of controls) followed by Scotchbond 2 (54·2 per cent) with GLUMA the most cytotoxic (26·9 per cent). However, with 500 μm slices values for the ICI Dental experimental material and GLUMA were similar (70·8 and 66·6 per cent respectively), with Scotchbond 2 exhibiting greatest toxicity (52·6 per cent). The results indicate that these materials are considerably more cytotoxic than most restorative materials which have been tested using a similar system. It is anticipated that all materials, in particular Scotchbond 2, could cause severe reactions in deep cavities in vivo in the absence of an adequate lining.     

In vitro fluoride release from restorative materials in water versus artificial saliva medium (SAGF)

Objectives. An extensive number of investigations have focused in recent years on the process of fluoride release by glass–ionomer cements. In order to compare the fluoride release of two recent resin-modified glass–ionomer cements (RMGICs) and one compomer, we investigated the initial and subsequent fluoride release in distilled water and in a mineral medium with composition similar to saliva (SAGF), as well as the renewal effect of the media on the release.Method. A preliminary thermodynamic study defined conditions under which the measurements by fluoride-selective electrode potentiometry were not affected by the presence of Ca²⁺ ions in SAGF. Disk-shaped samples (5 mm×3 mm) for each material were placed in 5 ml of distilled water (n=12) or 5 ml of SAGF (n=12) and fluoride released was measured after 1, 2 and 7 days. For the investigation of medium renewal effect, RMGIC samples were dipped into distilled water for 5 days. Subsequently 12 samples of each material were placed for 7 days into water or SAGF, with or without daily renewal of the medium before fluoride-release measurements. The elements present on the surface of the RMGICs were analyzed by scanning electron microscopy.Results. RMGICs released significantly more fluoride in water than in artificial saliva. The presence of CaF₂ at the interface accounts for this phenomenon. The thickness of the CaF₂ layer depends on the speed of its initial formation and renewal of the testing medium. A pattern of CaF₂ formation was proposed.     

In vitro fluoride release from restorative materials in water versus artificial saliva medium (SAGF)

OBJECTIVES: An extensive number of investigations have focused in recent years on the process of fluoride release by glass-ionomer cements. In order to compare the fluoride release of two recent resin-modified glass-ionomer cements (RMGICs) and one compomer, we investigated the initial and subsequent fluoride release in distilled water and in a mineral medium with composition similar to saliva (SAGF), as well as the renewal effect of the media on the release. METHOD: A preliminary thermodynamic study defined conditions under which the measurements by fluoride-selective electrode potentiometry were not affected by the presence of Ca2+ ions in SAGF. Disk-shaped samples (5 mm x 3 mm) for each material were placed in 5 ml of distilled water (n = 12) or 5 ml of SAGF (n = 12) and fluoride released was measured after 1, 2 and 7 days. For the investigation of medium renewal effect, RMGIC sample were dipped into distilled water for 5 days. Subsequently 12 samples of each material were placed for 7 days into water or SAGF, with or without daily renewal of the medium before fluoride-release measurements. The elements present on the surface of the RMGICs were analyzed by scanning electron microscopy. RESULTS: RMGICs released significantly more fluoride in water than in artificial saliva. The presence of CaF2 at the interface accounts for this phenomenon. The thickness of the CaF2 layer depends on the speed of its initial formation and renewal of the testing medium. A pattern of CaF2 formation was proposed.     

In vitro measurement of vertical denture displacement by denture adhesives

Vertical displacement of dentures by denture adhesives has been considered to be a major problem. An in vitro method was developed to assess this phenomenon and results show that a minimum displacement occurred with “true” adhesives. The vehicle did have a slight effect on adhesive distribution. Denture cushions were unsatisfactory.     

Luminescence of selected dental composites in vitro

OBJECTIVES: The work was motivated by the necessity to evaluate the emission changes of dental composites, as the emission under UV light is one of the important optical parameters of the hard tooth tissue. METHODS: Fulfill extra, Artemis and Durafill VS materials in A3.5 shade were tested. Coffee, tea, red wine and distilled water (blank) were used as staining drinks. The samples were soaked for 7 days. Total luminescence matrices were collected with an interval of 1nm in emission and 10nm in excitation, in the front-face geometry. RESULTS: The exposure of dental composites to staining drinks caused a reduction in luminescence intensity by up to 40%, the magnitude of the reduction depending on the drink and on the composite material. In the special case of the intrinsically weak fluorescent Durafill VS, the exposure to coffee apparently caused an increase in luminescence intensity due to coffee components adsorbed on the sample surface. SIGNIFICANCE: It is important to improve the emission stability of dental composites. The presently proposed methods are effective in evaluating the emission of dental composites. Emission needs to be tested in addition to color, as the two parameters are uncorrelated.     

Non-linear in vitro wear of posterior composites with time

Several clinical studies have found the wear rate of posterior composites to be nonlinear, with greater wear occurring initially. This relationship and its causes were sought in an in vitro test that used the Taber Abraser. Three commercial composites--Marathon, Occlusin, and P-30--were tested. Sixteen cured samples of each were initially finished with 600-grit paper and then abraded by medium-grit wheels for 30,000 cycles. Periodically, the weight losses were recorded and then converted to volume losses. Analysis included comparison of volume losses per 5000-cycle interval and comparison of first derivatives (wear rate) and second derivatives of the best-fit second-order regression line. Significant differences (p less than 0.05), as analyzed by ANOVA, were consistently realized between the volume losses for the first interval and those for subsequent intervals. Rank, with regard to wear resistance, depended on whether volume loss or initial wear rate was compared. The Taber Abraser did show non-linear trends similar to those observed clinically. Initial surface preparation, which apparently contributes to the greater early wear rates recorded in this in vitro study, may also be a factor clinically.     

Fatigue and wear of dental materials

Fatigue and wear are two of the many basic physical processes which contribute to the degradation of restorative materials. The mechanisms of these are discussed in the context of general engineering and the dental environment. More work is required to define the processes involved in intraoral degradation of materials.     

镁基金属对粪肠球菌的体外抑制作用

目的 评价纯镁和镁铜合金对粪肠球菌的体外抗菌效果.方法 选取因正畸新鲜拔除的人的单根管下颌前磨牙40颗,随机分为4组,每组10颗牙.所有牙齿清理根管后灭菌,建立粪肠球菌感染根管模型.每组分别用以无菌生理盐水为赋形剂调制的氢氧化钙糊剂(A组)、镁粉糊剂(B组)、镁铜合金粉糊剂(C组)、生理盐水(D组)进行根管封药7天.封药前后分别取样,接种在普通营养琼脂平板上培养,计数菌落.结果 封药前4组根管内细菌量的差异无统计学意义(P＞0.05).D组封药前后根管内细菌量无统计学差异(P＞0.05).A、B、C3组封药后根管内细菌量均明显减少,与封药前细菌量比较,差异具有统计学意义(P＜0.05).A、B、C3组间两两比较,封药后根管内细菌减少量差异无统计学意义(P＞0.05).结论 纯镁和镁铜合金对粪肠球菌均有一定的抗菌效果.但各组根管内仍有粪肠球菌残留,关于镁和镁铜合金在口腔临床医学中的应用价值还需要进一步研究.     

氢化镁颗粒对牙周致病菌具核梭杆菌的体外抗菌作用

目的 评价微米氢化镁（MgH₂）颗粒对牙周炎致病菌具核梭杆菌的体外抗菌作用,研究可能的抗菌机制。方法 通过扫描电镜（SEM）和X射线衍射仪（XRD）对实验材料MgH₂颗粒的尺寸大小、表面形貌和晶相结构进行表征。使用电子顺磁共振技术（EPR）研究其释放行为,同时使用菌落计数实验（CFU）、溴化四甲基偶氮唑盐法（MTT）研究了MgH₂颗粒对具核梭杆菌的抗菌效应。结果 MgH₂颗粒呈现为尺寸不均一的微米级球状颗粒,平均尺寸为10.52 μm。XRD谱图具有属于MgH₂的（110）、（101）、（200）及（211）特征面的衍射信号。在菌落计数实验（CFU）实验中,当材料浓度达到 1.5 mg/mL和 2 mg/mL时有显著的抑菌效果,抗菌率分别为45.69 %和79.24 %。在MTT实验中,具核梭杆菌的活性随着MgH₂颗粒浓度的增加而逐渐降低,当MgH₂颗粒浓度达到2 mg/mL时,其活性接近于零。结论 MgH₂颗粒对具核梭杆菌有着良好的抑菌效果,在临床应用方面具有良好的前景。     

酸蚀对人磨牙抗压强度影响的体外研究

目的 研究饮食引起的酸性口腔环境对人磨牙抗压强度的影响,评估咬合坚硬食物应力下的脆性折断风险,结合体外压缩强度试验和数值计算进行定量评估。方法 采用乙酸水溶液对尺寸差异较小的人磨牙进行体外等效酸蚀处理,分无酸蚀、轻度、中度和重度酸蚀组。对全部牙体进行压缩强度试验,建立有限元模型分析断裂破坏过程和规律。结果 4组牙体破坏形式相似,均为无屈服阶段的脆性断裂。在无酸蚀组出现最大破坏载荷为2.79 kN,在重度酸蚀组出现最小破坏载荷为1.30 kN。有限元分析结果表明：牙体破坏时最大与最小应力分别为289 MPa和141 MPa。本研究等效重度酸蚀体外实验表明磨牙强度下降53.4%。数值模拟结果预测,当垂直牙体咬合受力时,符合几何突变处出现最大应力集中的规律。结论 酸蚀对牙体抗压强度有显著影响,长期酸蚀在咬合坚硬食物条件下,存在局部应力集中导致的脆断风险。     

In vivo and in vitro study of the effects of chlorpromazine on tooth mineralization in rats and mice

The effects of chlorpromazine (CPZ) on tooth mineralization were examined using incisor dentine in adult rats and cultured tooth germs of mandibular first molars dissected from mouse embryos. CPZ (10, 50 and 250 mg/kg, s.c.) substantially inhibited dentine mineralization as evaluated by contact microradiographs. Plasma calcium and phosphorus concentrations were not decreased by CPZ (10 and 50 mg/kg). Physicochemical effects were not involved in the action of CPZ on the mineralization. In vitro experiments showed that CPZ (1 and 10 μM) inhibited mineralization and alkaline phosphatase (ALP) activity in the tooth germs. As CPZ has the properties of a calmodulin antagonist, the calmodulin antagonists W-7 and W-5 were also examined. Both inhibited mineralization and ALP activity in tooth germs; W-5 had less effect than W-7. These in vivo and in vitro findings suggest that CPZ inhibited cell-mediated mineralization in dentine without affecting the calciumdashregulating system and physicochemical mineral deposition. In addition, calmodulin could be involved in cell-mediated mineralization.     

高功率半导体激光对复杂根管消毒效果的体外研究

目的 评价高功率半导体激光联合次氯酸钠对体外复杂根管的消毒效果。方法 通过CBCT筛选含峡区的离体牙42颗,体外建立复杂根管感染模型,将离体牙随机分为4组,A组：半导体激光组+0.9% NaCl溶液; B组：半导体激光+5.25% NaClO; C组:5.25% NaClO; D组：空白对照组;每组10颗牙齿,经消毒处理后收集冲洗液,进行细菌培养、菌落形成单位计数、SEM观察及细菌活死染色后激光聚焦显微镜（ CLSM）观察分析,定量比较各组对粪肠球菌的杀灭效果。结果 ① A、B、C组处理后的杀菌率分别为33.9%、98.4%和82.8%,均高于D组的3.68%（ P<0.05）,其中B组杀菌率最高; ②扫描电镜结果显示：激光结合次氯酸钠组获得最好的根管壁清理效果; ③ CLSM图像荧光强度IOD值分析结果显示： B组红色荧光强度高于其余3组（ P<0.05）。结论 半导体激光辅助根管消毒有助于复杂根管（含峡区）的消毒;高功率（ 2.5 W）半导体激光结合传统根管化学消毒值得推广。     

In vivo confocal microscopy in clinical dental research: An initial appraisal

Until recently, the in vivo microscopic investigation of intraoral tissues at high resolution has been virtually impossible. Confocal microscopy enables high-resolution imaging to be achieved below semitransparent surfaces in intact living specimens, but this may still be impractical for intraoral applications because of the need to stabilize the sample. The development of a steadying objective (x 240 overall mag.) which is held against the sample surface and is focused by moving internal elements, avoids the need for fine adjustment of the living sample under the microscope to achieve a change of focus. It is therefore more comfortable and also reduces the problems of movement due to the pulse. The objective was used with a tandem scanning microscope, with images recorded via a SIT video camera. Using this system internal tooth structure (e.g. enamel prisms/adhesive restoration interfaces) and the lining cells of the gingival crevice through to the junctional epithelium may be examined. It is also possible to image the oral mucous membrane, focusing to the capillary loops in the basal layers, where streaming red blood cells can be seen. Access is limited to the anterior regions as far back as the premolar teeth. Applications could include caries research, soft and hard tissue responses to biomaterials (e.g. implants), wound healing and monitoring the effect of periodontal treatment regimens. This new technique offers numerous exciting opportunities for the microscopic investigation of many clinical operative procedures in vivo, allowing the response of the tissues to be non-destructively monitored, over time, at high resolution.     

Comparative wear ranking of dental restorative materials utilizing different wear simulation modes

summary The aim of this study was to compare the wear of seven different restorative materials using two different wear simulation modes. This included a non-impact sliding wear test (rotary pin and disc) and an impact-cum-sliding wear test (masticatory simulator). The difference in wear ranking between the two wear tests was compared as well as the correlation of wear to the hardness of the materials. Hardness ranking in the order of decreasing hardness was as follows: Dispersalloy^® (DA), P50^® (P50), Hi-Dense^(r) (HD), TPH^® (TPH), Fuji II LC^® (FJ), Dyract^® (DR) and Vitremer^® (VM). For volumetric wear using the non-impact sliding test, the following ranking in the order of decreasing wear resistance was obtained: DA, TPH, DR, HD, VM, FJ, P50. The results for volumetric wear with impact-cum-sliding wear testing in the order of decreasing wear resistance were: TPH, DR, P50, AR, FJ, VM, HD. Results showed that there is no correlation between hardness and wear resistance. There is also no correlation between impact-cum-sliding wear and non-impact sliding wear. Impact wear should be considered in future two-body wear assessment of materials.