Bio-inspired dental multilayers: Effects of layer architecture on the contact-induced deformation

The ceramic crown structures under occlusal contact are idealized as flat multilayered structures that are deformed under Hertzian contact loading. Those multilayers consist of a crown-like ceramic top layer, an adhesive layer and the dentin-like substrate. Bio-inspired design of the adhesive layer proposed functionally graded multilayers (FGM) that mimic the dentin–enamel junction in natural teeth. This paper examines the effects of FGM layer architecture on the contact-induced deformation of bio-inspired dental multilayers. Finite element modeling was used to explore the effects of thickness and architecture on the contact-induced stresses that are induced in bio-inspired dental multilayers. A layered nanocomposite structure was then fabricated by the sequential rolling of micro-scale nanocomposite materials with local moduli that increase from the side near the soft dentin-like polymer composite foundation to the side near the top ceramic layer. The loading rate dependence of the critical failure loads is shown to be well predicted by a slow crack growth model, which integrates the actual mechanical properties that are obtained from nanoindentation experiments.     

Properties of tooth enamel in great apes

A comparative study has been made of human and great ape molar tooth enamel. Nanoindentation techniques are used to map profiles of elastic modulus and hardness across sections from the enamel–dentin junction to the outer tooth surface. The measured data profiles overlap between species, suggesting a degree of commonality in material properties. Using established deformation and fracture relations, critical loads to produce function-threatening damage in the enamel of each species are calculated for characteristic tooth sizes and enamel thicknesses. The results suggest that differences in load-bearing capacity of molar teeth in primates are less a function of underlying material properties than of morphology.     

Micro-rotary fatigue of tooth-biomaterial interfaces

The bonding effectiveness of restorative materials to tooth tissue is typically measured statically. Clinically tooth/composite bonds are however subjected to cyclic sub-critical loads. Therefore, in vitro fatigue testing of dental adhesives should predict better the in vivo performance of adhesives. The objective of this study was to determine the fatigue resistance of two representative adhesives, a self-etch and an etch&rinse adhesive, bonded to enamel and dentin. Therefore, tooth/composite interfaces were cyclically loaded using a miniaturized version of a rotating beam fatigue testing device. Subsequently, the load at which 50% of the specimens fail after 10(5) cycles, was determined as the median micro-rotary fatigue resistance (microRFR). For both adhesives, the microRFR was about 30-40% lower than the corresponding micro-tensile bond strength (microTBS) to both enamel and dentin. Analysis of the fracture surfaces by Feg-SEM revealed typical fatigue fracture patterns. It is concluded that resin/tooth interfaces are vulnerable to progressive damage by sub-critical loads, with the 3-step etch&rinse adhesive being more resistant to fatigue than the 2-step self-etch adhesive.     

Quantitative analysis of the calcium and phosphorus content of developing and permanent human teeth.

It was the aim of this study to investigate the distribution of Ca, P and C in predentin, dentin and enamel in human tooth buds and permanent teeth by EDX element analysis. The mandible of a 16-week-old human fetus containing eight mineralizing tooth buds and three human permanent molars were fixed in formaldehyde and embedded in Technovit 9100. Serial sections of 80 microm thickness of the mandible were cut in the frontal-dorsal direction, and polarized light micrographs were taken of these sections. The permanent teeth were cut in mesio-distal direction. The sections were investigated with scanning electron microscopy and EDX element analysis with a Philips XL 30 FEG scanning microscope and an EDAX energy-dispersive X-ray system using spot measurements, EDX line-scans and element mapping. Quantitative measurements were made in predentin, mineralizing dentin adjacent to predentin, mature dentin, mineralizing enamel and young enamel of developing teeth and mature enamel of permanent teeth. In developing teeth the Ca and P content increased rapidly from outer predentin towards mineralizing dentin. In enamel prisms of developing teeth the Ca and P content increased linearly from the surface towards the enamel-dentin junction. In permanent teeth only a small layer of predentin was found. The Ca and P content in enamel and circumpulpal dentin of permanent teeth was higher than in developing teeth. The Ca/P ratio differed between predentin and dentin areas reflecting different calcium phosphate compositions, but it was the same in mineralizing and young enamel. The differences in the distribution of Ca and P reflect different mineralizing patterns of the enamel and dentin matrices.     

Alteration of dentin–enamel mechanical properties due to dental whitening treatments

The mechanical properties of dentin and enamel affect the reliability and wear properties of a tooth. This study investigated the influence of clinical dental treatments and procedures, such as whitening treatments or etching prior to restorative procedures. Both autoclaved and non-autoclaved teeth were studied in order to allow for both comparison with published values and improved clinical relevance. Nanoindentation analysis with the Oliver–Pharr model provided elastic modulus and hardness across the dentin–enamel junction (DEJ). Large increases were observed in the elastic modulus of enamel in teeth that had been autoclaved (52.0 GPa versus 113.4 GPa), while smaller increases were observed in the dentin (17.9 GPa versus 27.9 GPa). Likewise, there was an increase in the hardness of enamel (2.0 GPa versus 4.3 GPa) and dentin (0.5 GPa versus 0.7 GPa) with autoclaving. These changes suggested that the range of elastic modulus and hardness values previously reported in the literature may be partially due to the sterilization procedures. Treatment of the exterior of non-autoclaved teeth with Crest Whitestrips?, Opalescence? or UltraEtch? caused changes in the mechanical properties of both the enamel and dentin. Those treated with Crest Whitestrips? showed a reduction in the elastic modulus of enamel (55.3 GPa to 32.7 GPa) and increase in the elastic modulus of dentin (17.2 GPa to 24.3 GPa). Opalescence? treatments did not significantly affect the enamel properties, but did result in a decrease in the modulus of dentin (18.5 GPa to 15.1 GPa). Additionally, as expected, UltraEtch? treatment decreased the modulus and hardness of enamel (48.7 GPa to 38.0 GPa and 1.9 GPa to 1.5 GPa, respectively) and dentin (21.4 GPa to 15.0 GPa and 1.9 GPa to 1.5 GPa, respectively). Changes in the mechanical properties were linked to altered protein concentration within the tooth, as evidenced by fluorescence microscopy and Fourier transform infrared spectroscopy.     

Photons and evolution: Quantum mechanical processes modulate sexual differentiation

This paper will show that the fractional difference in the human gender ratio (GR) between the GR_{at death} for those born in solar cycle peak years (maxima) and the GR_{at death} in those born in solar cycle non-peak years (minima), e.g., 0.023, divided by Π, yields a reasonable approximation of the quantum mechanical constant, alpha, or the fine structure constant (FSC) 0.007297… or 1/137. This finding is based on a sample of approximately 50 million cases using common, readily available demographic data, e.g., state of birth, birth date, death date, and gender. Physicists Nair, Geim et al. had found precisely the same fractional difference, 0.023, in the absorption of white light (sunlight) by a single-atom thick layer of graphene, a carbon skeleton resembling chicken wire fencing. This absorption fraction, when divided by Π, yielded the FSC and was the first time this constant could “so directly be assessed practically by the naked eye”. As the GR is a reflection of sexual differentiation, this paper reveals that a quantum mechanical process, as manifested by the FSC, is playing a role in the primordial process of replication, a necessary requirement of life. Successful replication is the primary engine driving evolution, which at a biochemical level, is a quantum mechanical process dependent upon photonic energy from the Sun. We propose that a quantum-mechanical, photon-driven chemical evolution preceded natural selection in biology and the mechanisms of mitosis and meiosis are manifestations of this chemical evolution in ancient seas over 3 billion years ago. Evolutionary processes became extant first in self-replicating molecules forced to adapt to high energy photons, mostly likely in the ultraviolet spectrum. These events led to evolution by natural selection as complex mixing of genetic material within species creating the variety needed to match changing environments reflecting the same process initiated at the dawn of life. Both evolutionary mechanisms coexist and are interactive. The periodic energy of solar maxima is likely modulating the human genome from maternal integument to an embryo in utero with non-local mechanisms intrinsic to quantum mechanics.     

Microtensile bond strength of etch and rinse versus self-etch adhesive systems

The aim of this study was to compare the microtensile bond strength of the etch and rinse adhesive versus one-component or two-component self-etch adhesives. Twelve intact human molar teeth were cleaned and the occlusal enamel of the teeth was removed. The exposed dentin surfaces were polished and rinsed, and the adhesives were applied. A microhybride composite resin was applied to form specimens of 4?mm height and 6?mm diameter. The specimens were sectioned perpendicular to the adhesive interface to produce dentin-resin composite sticks, with an adhesive area of approximately 1.4?mm(2). The sticks were subjected to tensile loading until failure occurred. The debonded areas were examined with a scanning electron microscope to determine the site of failure. The results showed that the microtensile bond strength of the etch and rinse adhesive was higher than that of one-component or two-component self-etch adhesives. The scanning electron microscope examination of the dentin surfaces revealed adhesive and mixed modes of failure. The adhesive mode of failure occurred at the adhesive/dentin interface, while the mixed mode of failure occurred partially in the composite and partially at the adhesive/dentin interface. It was concluded that the etch and rinse adhesive had higher microtensile bond strength when compared to that of the self-etch adhesives.     

不同玷污层对4种树脂粘接系统粘接强度及粘接耐久性的影响

文题释义： 玷污层：牙体预备时由于车针的高速切割和挤压，牙本质表面形成厚1-5 μm的玷污层，它由无机物碎屑和凝固的胶原纤维碎屑组成。切割碎屑深入牙本质小管口形成管塞。磷酸酸蚀处理能够去除牙本质表面的玷污层及污物，而自酸蚀粘接剂则因为酸性较弱仅能对牙本质表面的玷污层及杂质进行部分溶解，并最终将剩余的玷污层包含在内形成混合粘接层。 甲基丙烯酰癸氧基二氢磷酸酯(10-MDP)：是一种性能优良的酸性功能单体，与羟基磷灰石反应生成的难溶性钙盐形成“纳米层状结构”，强烈吸附于牙本质表面，这一特点被认为能够增强粘接性能，并且对胶原纤维有保护作用，长期观察发现其可以提高粘接剂的耐久性。 背景：当用旋转式或手动器械处理牙表面时，在牙釉质和牙本质上由切割和磨损产生的碎片形成了玷污层。玷污层是影响牙和修复材料之间粘接的重要因素，明确玷污层对不同种类粘接剂的影响对口腔医生的临床选择与正确使用具有重要的临床意义。 目的：评价使用不同金刚砂车针预备的试件在人工唾液中存储24 h与100 d后，对4种粘接剂与牙本质粘接强度的影响。 方法：获取离体人磨牙80颗，分别进行600号碳化硅砂纸(对照)、中细粒度金刚砂车针、标准粒度金刚砂车针、粗粒度金刚砂车针4种牙本质表面处理，每种处理20颗；每种处理方法内分4个亚组，分别以两步法自酸蚀粘接剂Optibond Versa(VSA组)、一步法自酸蚀粘接剂Optibond All in One(AIO组)、通用型粘接剂Single Bond Universal(SBU组)及全酸蚀粘接剂Bond 5(GLU组)进行树脂粘接。粘接完成后，将试件置于人工唾液中37 ℃储存24 h及100 d，随后进行微拉伸强度测试，使用扫描电镜观察牙本质端断裂面，并对断裂模式进行分析。 结果与结论：①储存24 h：使用两步法粘接剂或全酸蚀粘接剂的情况下，不同表面处理组间的粘接强度比较差异无显著性意义(P > 0.05)；使用一步法粘接剂或通用型粘接剂的情况下，仅粗粒度车针组粘接强度低于砂纸组(P < 0.05)。使用砂纸或中细粒度车针的情况下，仅AIO组与VSA组粘接强度比较无差异；使用标准粒度车针的情况下，仅AIO组与VSA组、GLU组与SBU组粘接强度比较无差异(P > 0.05)；使用粗粒度车针的情况下，VSA组与AIO组、GLU组、SBU组粘接强度比较差异均有显著性意义(P < 0.05)，其余组间比较无差异(P > 0.05)；②储存100 d：使用两步法粘接剂或全酸蚀粘接剂的情况下，不同表面处理组间的粘接强度比较差异无显著性意义(P > 0.05)；使用一步法粘接剂的情况下，仅粗粒度车针组粘接强度低于砂纸组(P < 0.05)；使用通用型粘接剂的情况下，仅标准粒度车针组、粗粒度车针组粘接强度低于砂纸组(P < 0.05)。使用砂纸或中细粒度车针的情况下，仅VSA组与SBU组粘接强度无差异(P > 0.05)；使用标准粒度车针的情况下，仅SBU组与VSA组、GLU组与SBU组、GLU组与VSA组粘接强度无差异(P > 0.05)；使用粗粒度车针的情况下，仅VSA组与AIO组粘接强度无差异(P > 0.05)；③仅在使用两步法粘接剂的情况下，不同表面处理组100 d后的粘接强度与24 h比较差异有显著性意义(P < 0.05)；④与浸泡24 h相比，VSA组、SBU组、GLU组浸泡100 d后的粘接界面断裂和混合断裂比例略有增加，其中VSA组变化最大；与其他组比较，GLU组浸泡24 h与100 d的粘接界面断裂和混合断裂模式比例均超过50%；⑤结果表明，使用不同粒度车针预备产生了不同的玷污层，对一步法自酸蚀粘接剂粘接强度产生了显著影响，对两步法自酸蚀粘接剂和全酸蚀粘接剂未产生显著影响；存储时间对不同粘接剂产生了显著影响。 ORCID: 0000-0002-1639-6498(郑适泽) 中国组织工程研究杂志出版内容重点：生物材料；骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性；组织工程     

A natural functionally graded biocomposite coating – Human enamel

Human enamel has been found to be a coating with excellent mechanical performance, and has undergone extensive investigation and discussion. However, most of the reported studies consider the enamel as a homogeneous anisotropic biocomposite. The current study illustrated the graded properties of the biocomposite from its functional load-bearing direction. Within the thickness of the enamel, from the outer surface towards the enamel–dentin junction (EDJ), the elastic modulus (E(x)) and hardness (H(x)) of enamel exist in an exponential relationship with normalized thickness (x) as E(x) = 111.64x^0.18 (R² = 0.94) and H(x) = 4.41x^0.16 (R² = 0.87) GPa, respectively. Moreover, the creep ability of enamel increases towards the EDJ. The graded properties of the biocomposite can be explained by both microstructural and compositional changes along the thickness of the material towards the EDJ. Finite element analysis indicates that the graded properties of enamel have important roles in reducing the enamel–dentin interface stresses and maintaining the integrity of the multilayer tooth structure. The results provide a new angle to understand the excellent mechanical behaviour of the multilayer tooth structure and may inspire the development of new functionally graded materials and coating structures.     

Interfacial chemistry of class II composite restoration: structure analysis

The gingival margins of class II composite restorations are particularly vulnerable to marginal leakage and secondary caries. In identifying the factors contributing to caries development, the molecular structure and differences in the structure at the proximal and gingival margins have been largely overlooked. The purpose of this study was to compare the molecular structure at the adhesive/dentin interface of the proximal and gingival walls of class II composite restorations. Class II preparations were cut in 12 unerupted third molars with a water-cooled high-speed dental handpiece. The prepared teeth were randomly selected for treatment with Single Bond (SB) + Z100 (3M). Teeth were restored, per manufacturer's directions, under humidity and temperature characteristic of the oral cavity. Restored teeth were kept in sterile Delbecco's phosphate saline for 48 h. The samples were sectioned occluso-gingivally and micro-Raman spectra were acquired at approximately 1.5-microm spatial resolution across the composite/adhesive/dentin interfaces. Samples were wet throughout spectral acquisition. Raman spectral characteristics at the proximal and gingival margins were distinctly different; the depth of demineralized dentin was 6-7 microm at proximal margin, 12-13 microm at gingival margin. SB adhesive penetrated the depth of demineralized dentin in a gradient at the proximal margin. The "single bottle" adhesive used in this study, gradually penetrated the depth of the demineralized dentin at the proximal margin but failed to infiltrate the depth at the gingival margin, leaving a thick exposed collagen layer.     

Interaction patterns between dentin and adhesive on prepared class V cavities in vitro and in vivo

The interface between dentin and an acetone-based single-component adhesive system (Prime&Bond 2.1, DeTrey Dentsply, Germany) was morphologically investigated by scanning electron microscopy (SEM). Interaction patterns of human teeth were correlated in vivo and in vitro. The SEM examination proved that the formation of a hybrid and an adhesive layer, the peri- and intratubular adhesive penetration, as well as hiatus and nanoleakage formation were no different on vital and nonvital dentin within the limitation of the experimental arrangement of this study.     

Nanolayering of phosphoric acid ester monomer on enamel and dentin

Following the "adhesion-decalcification" concept, specific functional monomers possess the capacity to primary chemically interact with hydroxyapatite (HAp). Such ionic bonding with synthetic HAp has been demonstrated for 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP), manifest as self-assembled "nanolayering". In continuation of that basic research this study aimed to explore whether nanolayering also occurs on enamel and dentin when a 10-MDP primer is applied following a common clinical application protocol. Therefore, the interaction of an experimental 10-MDP primer and a control, commercially available, 10-MDP-based primer (Clearfil SE Bond primer (C-SE), Kuraray) with enamel and dentin was characterized by X-ray diffraction (XRD), complemented with transmission electron microscopy interfacial ultrastructural data upon their reaction with enamel and dentin. In addition, XRD was used to study the effect of the concentration of 10-MDP on nanolayering on dentin. Finally, the stability of the nanolayers was determined by measuring the bond strength to enamel and dentin when a photoinitiator was added to the experimental primer or when interfacial polymerization depended solely on the photoinitiator supplied with the subsequently applied adhesive resin. XRD confirmed nanolayering on enamel and dentin, which was significantly greater on dentin than on enamel, and also when the surface was actively rubbed with the primer. Nanolayering was also proportional to the concentration of 10-MDP in the primer. Finally, the experimental primer needed the photoinitiator to obtain a tensile bond strength to dentin comparable with that of the control C-SE primer (which also contains a photoinitiator), but not when bonded to enamel. It is concluded that self-assembled nanolayering occurs on enamel and dentin, even when following a clinically used application protocol. The lower bonding effectiveness of mild self-etch adhesives to enamel should be ascribed in part to a lower chemical reactivity (nanolayering) with enamel HAp.     

Analysis of fracture and deformation modes in teeth subjected to occlusal loading

An analysis of fracture and deformation modes in tooth enamel subjected to occlusal loading is presented. Several competing modes are identified: deformation by yield beneath the indenter; median cracking from the ensuing plastic zone and analogous radial cracking from the dentin–enamel junction along the load axis; and margin cracking from the cervical enamel–cement junction. The analysis, based on a simple model of tooth geometry, presents relations for the critical loads to initiate these damage modes within the enamel, and to drive ensuing cracks longitudinally around the tooth walls to failure. The relations are explicit in their dependence on characteristic tooth dimensions – enamel thickness and cuspal radius – and on material properties – modulus, hardness, toughness and strength. Provision is made to incorporate properties of the occlusal contact, whether from opposing dentition or intervening food particles. All these features are demonstrated on critical-load master diagrams. A characteristic feature of the damage evolution is the gradual evolution of each mode with increasing load, so that failure is generally a prolonged rather than abrupt event. This accounts for the remarkable damage tolerance of natural teeth. The equations may enable basic predictions of tooth responses for humans and animals under a variety of specified dietary and functional conditions.     

Remineralization of artificial dentinal caries lesions by biomimetically modified mineral trioxide aggregate

Fluoride-releasing restorative materials are available for remineralization of enamel and root caries. However, remineralization of dentin is more difficult than remineralization of enamel due to the paucity of apatite seed crystallites along the lesion surface for heterogeneous crystal growth. Extracellular matrix proteins play critical roles in controlling apatite nucleation/growth in collagenous tissues. This study examined the remineralization efficacy of mineral trioxide aggregate (MTA) in phosphate-containing simulated body fluid (SBF) by incorporating polyacrylic acid and sodium tripolyphosphate as biomimetic analogs of matrix proteins for remineralizing caries-like dentin. Artificial caries-like dentin lesions incubated in SBF were remineralized over a 6 week period using MTA alone or MTA containing biomimetic analogs in the absence or presence of dentin adhesive application. Lesion depths and integrated mineral loss were monitored with microcomputed tomography. The ultrastructure of baseline and remineralized lesions was examined by transmission electron microscopy. Dentin remineralization was best achieved using MTA containing biomimetic analogs regardless of whether an adhesive was applied; dentinal tubules within the remineralized dentin were occluded by apatite. It is concluded that the version of MTA employed in this study may be doped with biomimetic analogs for remineralization of unbonded and bonded artificial caries-like lesions in the presence of SBF.     

Fatigue crack propagation path across the dentinoenamel junction complex in human teeth

The human tooth structures should be understood clearly to improve clinically used restorative materials. The dentinoenamel junction (DEJ) plays a key role in resisting crack propagation in teeth. The aim of this study was to determine the fracture toughness of the enamel-DEJ-dentin complex and to investigate the influence of the DEJ on the fatigue crack propagation path across it by characterizing fatigue-fractured enamel-DEJ-dentin complexes using optical and scanning electron microscopy. The results of this study showed that the fracture toughness of the enamel-DEJ-dentin complex was 1.50 +/- 0.28 Mpa x m(1/2). Based on the results of this investigation, it was concluded that the DEJ complex played a critical role in resisting crack propagation from enamel into dentin. The DEJ complex is, approximately, a 100 to 150 microm broad region at the interface between enamel and dentin. The toughening mechanism of the DEJ complex may be explained by the fact that crack paths were deflected as cracks propagated across it. Understanding the mechanism of crack deflection could help in improving dentin-composite as well as ceramic-cement interfacial qualities with the aim to decrease the risk of clinical failure of restorations. Both can be viewed as being composed from a layer of material of high strength and hardness bonded to a softer but tougher substratum (dentin). The bonding agent or the luting cement layer may play the critical role of the DEJ in improving the strength of these restorations in clinical situations.     

老年口腔疾病修复粘接材料的研究与应用

背景：随着粘接材料性能的不断提高和粘接技术的不断更新,粘接修复的临床应用日益广泛。复合树脂粘接材料对牙釉质、牙本质、陶瓷、金属和高分子的粘接以及水门汀对牙釉质、牙本质和金属的粘接已基本成为口腔疾病修复的常规治疗手段。 目的：探讨口腔修复粘接材料的研究与应用进展。 方法：检索口腔修复粘接材料相关的研究文献,检索词为“口腔修复(dental repair),粘接材料(adhesive material),口腔粘接剂(dental adhesive or dental bonding agent）,合成树脂(synthetic resin),水门汀(cement),牙釉质胶粘剂(enamel bonding agent),牙本质胶粘剂(dentin bonding agent),聚羧酸锌水门汀(zinc polycarboxylate cement),玻璃离子水门汀(glass ionomer cement),树脂改性的玻璃离子水门汀(resin-modified glass ionomer cement)”,语言分别设定为中文和英文。 结果与结论：目前在临床上被广泛使用的口腔粘接材料可分为2大类：一类为合成树脂类,另一类为水门汀类。合成树脂类粘接材料主要有牙本质粘接剂和牙釉质胶黏剂;水门汀类粘接材料主要有无机水门汀、聚羧酸锌水门汀、玻璃离子水门汀、树脂改性的玻璃离子水门汀、复合玻璃体。随着口腔医学的发展及社会人口老龄化,对于口腔材料会有更多的需求,对粘接牙体组织的新材料会有更高的要求。因此,粘接材料将处于口腔材料研究的重要地位。     

Biodegradable hydrogels based on novel photopolymerizable guar gum–methacrylate macromonomers for in situ fabrication of tissue engineering scaffolds

Guar gum (GG) is a non-ionic polysaccharide that is found abundantly in nature and has many properties desirable for biomedical applications. In the present work GG with molecular weights ranging from 74 to 210 kDa was modified with glycidyl methacrylate (GMA) to produce a series of water-soluble photopolymerizable guar gum–methacrylate (GG–MA) macromonomers of different molecular weights. We investigated the effects of molecular weight of GG–MA macromonomers from 102 to 216 kDa and with percent degree of methacrylation (%DM) ranging from 14% to 56% on the properties of GG–MA hydrogels. GG–MA hydrogels exhibited a three-dimensional open cell microstructure with an average pore size ranging from 10 to 55 μm and an average pore density of from 2.4 × 10⁶ to 8.6 × 10⁷ pores cm⁻³. The hydrogels exhibited equilibrium swelling ratios ranging from 22% to 63%. The degree of in vitro enzymatic biodegradation of the hydrogels decreased linearly with increasing gel content and the degree of methacrylation of the respective macromonomers. The human endothelial cell line EA.hy926 was photo-encapsulated in the GG–MA hydrogels. Cells remained viable at low macromonomer concentrations, but cell viability decreased sequentially as the macromonomer concentration increased. GG–MA hydrogels with a 0.05 wt.% GG–MA macromonomer concentration revealed excellent endothelial cell proliferation, similar to that of the Matrigel™ control.     

Hardness, elasticity, and ultrastructure of bonded sound and caries-affected primary tooth dentin

Biomechanical properties of bonded dentin are important factors for resin restoration. We evaluated the hardness and elastic modulus of bonded sound and caries-affected primary tooth dentin using a one-step adhesive system, and observed the microstructure of the bonded interface. Six sound and six carious primary teeth were used. For sound teeth, flat occlusal dentin surfaces were prepared with a water-cooled high-speed diamond bur. For carious teeth, infected dentin was stained with a caries detector and removed with a water-cooled low-speed round steel bur and hand instruments. The prepared dentin was bonded with One-Up Bond F Plus (Tokuyama Dental Co., Tokyo, Japan). The resin-dentin interface and dentin beneath the interface were measured with a nano-indentation tester and observed with SEM and TEM. For both the carious and sound teeth, there was no significant difference between the hardness of the interfacial dentin and dentin 10-80 microm beneath the interface. However, the Young's modulus of the interfacial dentin was significantly lower than the dentin 40-80 microm (carious teeth) or 50-80 microm (sound teeth) beneath the interface. Both the hardness and Young's modulus of the interfacial dentin were not significantly different between the carious and sound teeth. Compared to the sound dentin, the hybrid layer on the caries-affected dentin was thicker and exhibited more complicated morphologic features. The thickness of the hybrid layers was generally less than 1 microm.