Analysis of the surface characteristics and mineralization status of feline teeth using scanning electron microscopy

External resorption of teeth by odontoclasts is a common condition of unknown origin affecting domestic cats. Odontoclastic resorptive lesions involve the enamel cementum junction (ECJ, cervix) and root surface, leading to extensive loss of enamel, dentine and cementum. This study was undertaken in order to determine whether features of the surface anatomy and mineralization of feline teeth could explain why odontoclastic resorptive lesions are so prevalent in this species. Backscattered electron scanning electron microscopy was used to study enamel, cementum and dentine in non-resorbed, undemineralized teeth from adult cats. Analysis of the ECJ revealed thin enamel and cementum and exposed dentine at this site. Furthermore, enamel mineralization decreased from the crown tip to the ECJ, and dentine mineralization was lowest at the ECJ and cervical root. Analysis of cementum revealed variations in the organization and composition of fibres between the cervical, mid- and apical root although no significant differences in mineralization of cementum were detected between different regions of the root. Reparative patches associated with resorption of cementum by odontoclasts and repair by cementoblasts were present on the root surface. In conclusion, results suggest that the ECJ and cervical dentine could be at a greater risk of destruction by odontoclasts compared with other regions of the tooth. The relationship of these features to the development and progression of resorption now requires further examination.     

改性玻璃离子水门汀应力松弛蠕变实验

文题释义：黏弹性力学：连续介质力学的重要分支,又称黏弹性理论,研究黏弹性物质的力学行为、本构关系及其破坏规律,以及黏弹性体在外力和其他因素作用下的变形和应力分布。聚合物、混凝土、金属、岩石、土壤、石油、肌肉、血液和骨骼等,在一定条件下既具有弹性性质又具有黏性性质,这种兼具弹性和黏性性质的材料称为黏弹性材料,含黏弹性固体与黏弹性流体,又可分为线性黏弹性体和非线性黏弹性体。线性黏弹性体的两种极端情况即为胡克体(遵循胡克定律)和牛顿流体(遵循牛顿粘性定律)。 生物力学：是应用力学原理和方法对生物体中的力学问题定量研究的生物物理学分支,其研究范围从生物整体到系统、器官(包括血液、体液、脏器、骨骼等),从鸟飞、鱼游、鞭毛和纤毛运动到植物体液的输运等。 物力学的基础是能量守恒、动量定律、质量守恒三定律并加上描写物性的本构方程。生物力学研究的重点是与生理学、医学有关的力学问题,依研究对象的不同可分为生物流体力学、生物固体力学和运动生物力学等。 背景：以往对改性玻璃离子水门汀的力学性能研究多以压缩、弯曲实验居多,关于玻璃离子水门汀加入锶羟基磷灰石后的应力松弛、蠕变实验研究鲜有报道。 目的：对比分析传统玻璃离子水门汀、复合树脂釉质粘接剂、改性玻璃离子水门汀的应力松弛、蠕变特性。 方法：按质量比15%向玻璃离子水门汀中加入掺锶羟基磷灰石,制备改性玻璃离子水门汀。制作改性玻璃离子水门汀、复合树脂釉质粘接剂与传统玻璃离子水门汀试样,3组各取10个试样进行应力松弛实验,另取10个试样进行蠕变实验。 结果与结论：①应力松弛实验7 200 s时,传统玻璃离子水门汀组应力下降了1.18 MPa,复合树脂釉质粘接剂组应力下降了1.39 MPa,掺锶羟基磷灰石复合玻璃离子水门汀组应力下降了1.38 MPa;传统玻璃离子水门汀组应力下降量小于掺锶羟基磷灰石复合玻璃离子水门汀组、复合树脂釉质粘接剂组(P < 0.05),掺锶羟基磷灰石复合玻璃离子水门汀组和复合树脂釉质粘接剂组应力下降量无差异(P > 0.05)。②蠕变实验7 200 s时,传统玻璃离子水门汀组应变上升了0.24%,复合树脂釉质粘接剂组应变上升了0.33%,掺锶羟基磷灰石复合玻璃离子水门汀组应变上升了0.32%;传统玻璃离子水门汀组应变上升量小于掺锶羟基磷灰石复合玻璃离子水门汀组、复合树脂釉质粘接剂组(P < 0.05),掺锶羟基磷灰石复合玻璃离子水门汀组试和复合树脂釉质粘接剂组应变上升量无差异(P > 0.05)。③结果表明,15%掺锶羟基磷灰石提高和改善了玻璃离子水门汀的黏弹特性,有利于其与黏结物体的黏结,有利于提高黏结强度。 ORCID: 0000-0003-1024-5733(丁洁) 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     

High-resolution ZTE imaging of human teeth

MRI with zero echo time (ZTE) is achieved by 3D radial centre‐out encoding and hard‐pulse RF excitation while the projection gradient is already on. Targeting short‐T₂ samples, the efficient, robust and silent ZTE approach was implemented for high‐bandwidth high‐resolution imaging requiring particularly rapid transmit‐receive switching and algebraic image reconstruction. The ZTE technique was applied to image extracted human teeth at 11.7T field strength, yielding detailed depictions with very good delineation of the mineralised dentine and enamel layers. ZTE results are compared with UTE (ultra‐short echo time) MRI and micro‐computed tomography (μCT), revealing significant differences in SNR and CNR yields. Compared to μCT, ZTE MRI appears to be less susceptible to artefacts caused by dental fillings and to offer superior sensitivity for the detection of early demineralisation and caries lesions. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of Enamel Prism Decussation and Chemical Composition on the Biomechanical Behavior of Dental Tissue: A Theoretical Approach to Determine the Loading Conditions to Which Modern Human Teeth are Adapted

This theoretical study explored whether the directions of loads to which modern human molars are commonly subjected to are reflected in the biomechanical behavior of the tissue itself. A detailed finite element model of a piece of decussating enamel (M³ paracone) was created, taking into account differences in crystal orientation between the prism head and the interprismatic matrix, and was tested under differently angled mediolateral loads (i.e., mimicking various stages of the chewing cycle). Second, although teeth are highly mineralized, they also contain organic material and water, while in modern humans, there are systematic differences in chemical composition from the outer enamel surface to the dentinoenamel junction. To test the biomechanical effects of this gradient in mineralization a second set of models with gradually changing properties was created and subjected to the same loads. Chemically heterogeneous enamel yielded overall lower stress levels than homogenous enamel, especially at extreme loading angles. However, the general trends regarding the increase in tensile stresses at more oblique angles, and the number of nodes exhibiting tension, were comparable between the different set‐ups. The findings support suggestions that (a) the biomechanical behavior of dental tissue is the combined result of micromorphology and chemical composition and (b) that the range of loading directions, to which teeth are normally subjected to, can be inferred from dental microanatomy. For (palaeo)biological applications, the findings suggest that the absolute strength of teeth (e.g., bite force) cannot be predicted with certainty, whereas kinematic parameters of the masticatory apparatus can. Anat Rec, 2007. © 2008 Wiley‐Liss, Inc.     

Structural Relationship Between the Primary Crystal Formations and the Matrix Macromolecules in Different Hard Tissues. Discussion of a General Principle

For many years we have investigated the earliest crystal formations of different developing hard tissues (matrix vesicle, bone, dentine, enamel, etc.) by different electron microscopic measurements. It was observed that primarily Ca-phosphate (apatite) “chains,” composed of nanometer sized particles (dots, islands), exist, which coalesce rapidly to needles. For the mineralization of collagen (e.g., bone, dentine) the center to center distances between the dots in the mineral chains represent the distances between nucleating sites, so-called “active sites” of collagen which bind primarily Ca for a subsequent nucleation. For the mineralization of noncollagen macromolecules (e.g., enamel) the same principle of mineral nucleation at such “active sites” exists being represented indirectly by corresponding center to center distances between the dots in the mineral chains.     

运用色度学分析技术对离体乳牙脱矿与再矿化时间的实验研究

目的运用数码照相和色度分析技术观测不同酸蚀时间对离体乳牙釉质脱矿以及再矿化时间的影响,以寻找乳牙合适的脱矿及再矿化时间。方法将60颗离体上颌乳中切牙牙冠唇面开窗包埋。标本随机分为4个处理组,32%的磷酸凝胶分别酸蚀开窗面15s(组1)、30s(组2)、45s(组3)和60s(组4),使开窗面脱矿,再将其置于人工唾液中分别再矿化8h、24h、48h、72h及1周。脱矿后采用2%亚甲基蓝对开窗面进行染色,数码照相,运用图像分析软件对图像进行色度分析,记录色度参数,运用SPSS19.0对实验数据进行统计学分析。结果酸蚀15s后染色,其色度值变化即可被计算机所识别;酸蚀15s再矿化72h、酸蚀30s再矿化48h、酸蚀45s和60s再矿化24h时的色度值与矿化前的色度值相比,差异具有统计学意义,其P值分别为0.01、0.037、0.047和0.011。结论运用色度学技术分析乳牙脱矿与再矿化的时间,提示乳牙釉质最合适的酸蚀时间为15s,再矿化时间为72h。     

Influence of exposure time to saliva and antioxidant treatment on bond strength to enamel after tooth bleaching: an in situ study

Objectives

This study evaluated the influence of different exposure times to saliva in situ in comparison with an antioxidant treatment on composite resin bond strength to human enamel restored after tooth bleaching.

Material and Methods

Forty human teeth specimens measuring 5x5 mm were prepared and randomly allocated into 5 groups with 8 specimens each: Gct (control group, restored on unbleached enamel); Gbl (restored immediately after bleaching); Gsa (bleached, treated with 10% sodium ascorbate gel for 60 min and restored); G7d (bleached, exposed to saliva in situ for 7 days and restored); and G14d (bleached, exposed to saliva in situ for 14 days and restored). Restored samples were cut into 0.8 mm² sticks that were tested in microtensile. Specimens were microscopically analyzed and failure modes were classified as adhesive, cohesive, or mixed. Pretest and cohesive failures were not considered in the statistical analysis, which was performed with one-way ANOVA and Tukey''s post-hoc test (α=0.05), with the dental specimen considered as the experimental unit.

Results

Mean bond strength results found for Gbl in comparison with Gct indicated that bleaching significantly reduced enamel adhesiveness (P<0.01). However, no statistically significant differences were found between Gct, Gsa and G7d (P>0.05). Bond strength found for G14d was significantly higher than for Gsa (P<0.01). Fractures modes were predominantly of a mixed type.

Conclusions

Bonding strength to bleached enamel was immediately restored with the application of sodium ascorbate and exposure to human saliva in situ for at least 7 days. Best results were obtained with exposure to human saliva in situ for 14 days. Treatment with sodium ascorbate gel for 60 min may be recommended in cases patients cannot wait for at least 7 days for adhesive techniques to be performed.     

正常唾液及氟化物对脱矿年轻恒牙牙釉质的再矿化作用

目的:用显微硬度测量法研究正常人体唾液及氟化物对碳酸饮料酸蚀的年轻恒牙牙釉质的再矿化作用。方法:收集口腔正畸门诊减数拔牙所拔除的新鲜、健康年轻恒牙23颗,制成牙釉质样本90块,随机分为对照A组、实验B组及实验C组;每组又分为三个亚组(A1、A2、A3、B1、B2、B3、C1、C2、C3),其中A1、B1、C1浸泡在雪碧中1周、A2、B2、C2浸泡在芬达中1周、A3、B3、C3浸在百事可乐中1周,每组10个牙块。A组牙浸泡完后直接用显微硬度仪做表面硬度测试;B组牙用蒸馏水冲洗干净后分别浸泡于装有正常人体唾液的容器中,将容器置于37℃恒温箱中,定期摇动容器,1月后取出用显微硬度仪做表面硬度测试;C组牙则用蒸馏水冲洗干净后,每日早中晚3次用含氟牙膏涂布牙齿开窗处表面10 min,再分别放入装有正常人体唾液的容器中,将容器置于37℃恒温箱中,定期摇动容器,1月后取出用显微硬度仪做表面硬度测试。结果:正常人体唾液及氟化物均能使脱矿后年轻恒牙牙釉质表面硬度明显升高(P<0.05),且两者之间有统计学差异(P<0.05)。结论:正常人体唾液及氟化物对脱矿年轻恒牙的再矿化作用明显。     

早产对脑性瘫痪儿童乳牙釉质发育的影响

目的研究早产因素对脑瘫儿童乳牙釉质发育缺陷的影响。方法选择135名脑瘫患儿,与62名正常儿童对比,进行乳牙釉质发育缺陷状况的统计调查。同时比较脑瘫儿童中早产与乳牙釉质发育缺陷发生的关系。结果脑瘫儿童组中早产儿童乳牙釉质发育缺陷的患病率明显高于足月组,有统计学差异（P〈0.05）。结论早产的脑瘫儿童更容易发生乳牙釉质发育缺陷。