Enamel microstructure and microstrain in the fracture of human and pig molar cusps

The role of microstructure in enamel strain and breakage was investigated in human molar cusps and those of the pig, Sus scrofa. Rosette strain gauges were affixed to cusp surfaces (buccal human M3, n=15, and lingual pig M1, n=13), and a compressive load was applied to individual cusps using an MTS materials testing machine. Load and strain data were recorded simultaneously until cusp fracture, and these data were used to estimate enamel stresses, principal strains, and stiffness. Fractured and polished enamel fragments were examined in multiple planes using scanning electron microscopy (SEM). Human cusp enamel showed greater stiffness than pig enamel (P=0.02), and tensile stress at yield was higher (17.9 N/mm2 in humans versus 8.9 N/mm2 in pigs, P=0.06). SEM revealed enamel rod decussation in both human and pig enamel; however, only pig enamel showed a decussation plane between rod and inter-rod crystallites. Human inter-rod enamel was densely packed between rods, whereas in pig enamel, inter-rod enamel formed partitions between rows of enamel rods. Overall, human enamel structure enabled molar cusps to withstand horizontal tensile stress during both elastic and plastic phases of compressive loading. In contrast, pig cusp enamel was less resistant to horizontal tensile stresses, but appeared to fortify the enamel against crack propagation in multiple directions. These structural and biomechanical differences in cusp enamel are likely to reflect species-level differences in occlusal function.     

Impact of school sealant programs on oral health among youth and identification of potential barriers to implementation

BackgroundSchool sealant programs (SSPs) increase sealant prevalence among children lacking access to oral health care. SSPs, however, are substantially underused. From 2013 through 2018, the Centers for Disease Control and Prevention funded 18 states for SSP activities in high-need schools (≥ 50% free and reduced-price meal program participation). From 2019 through 2020, the authors assessed SSPs' impact in reducing caries and how states expanded SSPs. The authors also discuss potential barriers to expansion.MethodsFor Aim 1, the authors used a published methodology and SSP baseline screening and 1-year retention data to estimate averted caries over 9 years attributable to SSPs. For Aim 2, the authors used state responses to an online survey, phone interviews, and annual administrative reports.ResultsUsing data for 62,750 children attending 18.6% of high-need schools in 16 states, the authors estimated that 7.5% of sound, unsealed molars would develop caries annually without sealants and placing 4 sealants would prevent caries in 1 molar. Fourteen states reported SSP expansion in high-need schools. The 2 most frequently reported barriers to SSP expansion were levels of funding and policies requiring dentists to be present at assessment or sealant placement.ConclusionsThe authors found that SSPs typically served children at elevated caries risk and reduced caries. In addition, the authors identified funding levels and policies governing supervision of dental hygienists as possible barriers to SSP expansion.Practical ImplicationsIncreasing SSP prevalence could reduce caries. Further research on potential barriers to SSP implementation identified in this study could provide critical information for long-term SSP sustainability.     

模型转化法建立磨牙及其牙周组织的三维有限元模型

目的建立下颌第二恒磨牙及其牙周膜、牙槽骨的分析用模型。方法应用CAE软件3D MAX6.0及CATIA4.0生成磨牙及其牙周组织的三维有限元模型,利用HYPERMESH划分网格,生成可分析的三维有限元实体模型。结果建立了下颌第二恒磨牙及其牙周膜、牙槽骨的三维有限元模型,可以分别进行受力状态下应力、应变的分析。结论该模型可供口腔正畸矫治中磨牙的受力分析应用。     

The spectrum of NLRP7 mutations in French patients with recurrent hydatidiform mole

Objectives

The NLRP7 gene (19q13.42) is associated with recurrent and/or familial hydatidiform moles. Several mutations, histopathological types and reproductive outcomes have been described. We studied our recurrent hydatidiform mole cases recorded since 1999 in order to identify links between clinic, histology and genetics.

Study

We present here the gestational history and the spectrum of NLRP7 mutations in our French series.

Design

We performed a retrospective study from clinical forms received for genetic diagnosis. Cases declaration was based on a voluntary initiative coming from French practitioners, subjected to patients’ agreement.

Results

Among 12 recurrent hydatidiform moles investigated, we identified 3 cases of confirmed homozygous NLRP7 mutation and 3 cases of heterozygous NLRP7 mutation. One patient bore a novel mutation p.Leu880Ser in a homozygous state.

Conclusions

We here identified a new homozygous NLRP7 mutation. Unfortunately, no modern therapeutic option has proven effective to obtain evolutive pregnancies. Then, fundamental and clinical researches seem to be necessary. Moreover, collecting RHM cases is essential.     

两种方法修复磨牙缺损的临床疗效观察

目的 观察用钴铬合金嵌体和银汞合金修复磨牙缺损的临床疗效.方法 选择磨牙牙体缺损患者100例,随机分为两组,分别使用金属嵌体修复和银汞合金直接充填,在修复后6个月、4年复诊,对患者口内两种充填体进行疗效评价.结果 修复后6个月银汞合金直接充填组成功率为95.8％,钴铬合金嵌体组成功率为98.0％,经卡方检验两者临床疗效差异无统计学意义(P＞0.05).修复后4年银汞合金充填组成功率为60.0％,钴铬合金嵌体组成功率为84.8％,卡方检验显示嵌体组临床疗效明显优于银汞合金组,差异有统计学意义(P＜0.05).结论 嵌体修复磨牙邻(牙合)面洞缺损的方法是有效且可行的,其长期临床疗效优于银汞合金直接充填.     

下颌第一恒磨牙三维有限元模型的建立

目的 建立合理而精确的下颌第一恒磨牙三维有限元模型。方法通过螺旋CT扫描的方法,利用PhotoShop等图像处理软件,通过特定的SolidWorks2010有限元软件建立下颌第一恒磨牙的三维有限元模型。结果准确地建立了牙釉质、牙本质、髓腔、牙槽骨、牙周膜等组织形态的三维有限元模型。结论本实验建模方法可行性强,方便快捷,具有良好的生物力学与几何相似性,为临床口腔医师提供了一种简捷而精确的有限元建模方法。     

新疆乌鲁木齐市756例青少年第三磨牙发育的X线分析

目的调查分析新疆乌鲁木齐市不同年龄组第三磨牙（M3）的发育程度。方法对乌鲁木齐市口腔医院就诊的756例5～18岁青少年,通过对全颌曲面断层片的观察分析,将M3牙胚发育程度按Nolla分期方法进行统计分析。结果在5、6岁时男孩女孩均无M3牙胚组织出现,7岁时,女孩开始出现M3牙胚组织,而男孩从8岁时开始出现。男女均在11,岁后,M3的发生率趋于稳定。M3缺失4个、3个、2个、1个的比例分别为4．2％、3．6％、13．3％、10．9％;M3的发育阶段个体年龄差异较大。结论本次调查结果显示女孩的M3发育较男孩早,不论男孩还是女孩,M3牙胚的发育稳定年龄提前。M3的发育无明显固定的发育时间和年龄。     

下颌第二恒磨牙解剖特点及临床意义初步探讨

目的　分析下颌第二恒磨牙解剖特点并探讨其临床意义。方法　观察 10 6 2颗离体下颌第二恒磨牙 ,对其牙根形态、颈部釉突及龋坏情况进行分类统计 ,结合文献探讨相关临床意义。结果　下颌第二磨牙多为双根型 ,变异根型占 4 7.6 5 % ,以槽状根居多 ,占 31.6 4 %。牙颈部釉突发生率高达 74 .4 8% ,以颊面及舌面I级者居多。受检牙有 4 3.6 0 %龋坏 ,累及 6 17个牙面 ,其中以远中面受累最多。结论　下颌第二恒磨牙牙根变异率高 ,远中面龋坏多见 ,防治时应当注意 ,该牙颈部釉突发生率高与单独牙周病变相关     

双轨式磨牙远移器矫治牙列拥挤

目的　研制一种支抗力强 ,可使上、下颌第二或第一磨牙同时等量或不等量后移 ,不需要特殊配合即能产生理想磨牙后移效果的口内力矫治装置 ,用于牙列轻、中度拥挤的矫治。方法　选择牙弓拥挤量在 4～ 8mm的患者 ,利用自行研制的双轨式磨牙远移器 ,推上、下颌第二磨牙向远中移位。当第二磨牙后移到位时 ,利用第二磨牙稳定装置 ,稳定第二磨牙并牵引第一磨牙向远中移位。当第一磨牙后移到位时 ,再依次后移第二、第一前磨牙及尖牙等 ,直至拥挤解除 ,牙齿排列整齐。结果　经 33例牙列轻、中度拥挤患者临床应用观察 ,单颗第二磨牙最大后移量达 7mm ,单个牙弓长度最大增量 11 4mm。并实现了上、下颌 4颗第二或第一磨牙同时后移。经头颅侧位片测量证实 ,支抗牙无明显唇倾 (P >0 0 5 )。结论　双轨式磨牙远移器是一种不依赖患者特殊配合即能产生快速、高效、整体磨牙后移效果的口内力装置。