The effects of induced prenatal hypothyroidism on lamb mandibular third primary molars.

Intrauterine thyroidectomies were performed on nine lambs on or about the ninety-sixth postconception day. Seven other control and shamoperated lambs, and the cretin lambs were sacrificed immediately after birth. The mandibles were removed and sectioned at the midline. The right side molars were removed by dissection and caliper measured. The distal cusps of the third primary molars were sectioned, dehydrated, and embedded in Bioplastic. A slow speed diamond saw was used to section the plastic blocks and the embedded teeth. Subsequent grinding and polishing produced high quality 75 micrometer sections of the lamb molar cusps. No significant differences in tooth size or enamel thickness existed. Microscopic examinations show that parts of the cretin enamel were poorly calcified, an observation that was correlated to the intrauterine thyroidectomies. The data suggest that hypothyroidism alters ameloblastic activity during the secretory phase of enamel formation.     

Rat wct mutation induces a hypo-mineralization form of amelogenesis imperfecta and cyst formation in molar teeth

Our previous findings have demonstrated that the rat autosomal-recessive mutation, whitish chalk-like teeth (wct), induces enamel defects resembling those of human amelogenesis imperfecta (AI) in continuously growing incisor teeth. The present study clarifies the effect of the wct mutation on the morphogenesis and calcification of rat molar teeth. Formalin-fixed maxillae obtained from animals aged 4-30 days were examined by electron probe micro-analysis (EPMA) and by immunocytochemistry for amelogenin, ameloblastin, and enamelin. There were no distinct differences in the calcium and phosphorous contents and the amount of enamel between homozygous mutant and wild-type teeth during postnatal days 4–11. Although the mineral density in the enamel matrix considerably increased in the wild-type teeth until day 15, no changes occurred in mutant teeth during days 11–30. The immunoreactivity for enamel proteins in the secretory-stage ameloblasts in mutant teeth was similar to that in the wild-type teeth, and subsequently mutant maturation-stage ameloblasts became detached from the enamel surface, resulting in odontogenic cyst formation between the enamel organ and matrix until day 7 and the expansion of the cyst around the whole tooth crown on day 15. On day 30, the erupted mutant teeth presented morphological changes such as enamel destruction and tertiary dentin formation in addition to low mineral density in the enamel. Thus, the wct mutation prevents mineral transport without disturbing the synthesis of enamel proteins in molar teeth because of the absence of maturation-stage ameloblasts, in addition to the occurrence of odontogenic cysts. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. This work was supported in part by KAKENHI (B) (no. 16390523 to H.O.) and KAKENHI (C) (no. 18592002 to T.U.) from MEXT, Japan.     

Occlusal surface pattern of the lower molars and the second deciduous molar among the living Polynesians

The occlusal surface pattern of the lower molars and the second deciduous molar among the Polynesians living in Western Samoa was studied on plaster casts. The following are the characteristic traits of this race. The occlusal surface pattern of the first and second lower molars falls within the range of variation of the Mongoloid racial group. In general, the variation of the furrow pattern is remarkable, but the tendency of reduction of number of cusps is not conspicuous. The frequency of C₆ in the lower molars and C₇ in m₂ is far higher than in any other population, but the frequency of C₇ in M₁ or M₂ is not noticeably different.     

Functional patterns of molar occlusion in platyrrhine primates

Mechanico-functional features of molar form were studied in Callithrix, Alouatta, Pithecia and Cebus. Molars of Callithrix and Alouatta are adapted to loading foods under relatively high occlusal pressure; those of Pithecia and Cebus, under relatively low occlusal pressure. General functional considerations suggest that these taxa are adapted to insectivorous, folivorous, frugivorous and omnivorous diets, respectively. The physical properties of foods, principally mechanical strength and deformability, determine the selective pressures involved in the evolutionary adaptation of molar form. A dietary classification based upon percentages of foods eaten does not always reflect morphological adaptations. Homologous parts of teeth and homologous parts of the masticatory cycle do not always subserve equivalent functions. The relevance of functional occlusal analysis for deciphering phylogeny and explaining evolutionary grades is stressed.     

窝沟封闭和涂氟同时应用对乳磨牙龋病干预的研究

目的:探讨同时应用窝沟封闭和涂氟预防干预乳磨牙预防龋齿的效果,为学龄前儿童乳磨牙龋齿的预防提供新的干预措施。方法:通过Cariostat法对150名学龄前儿童乳磨牙进行龋蚀活跃性试验,将其分为龋活跃高危人群和低危人群,检查其乳磨牙患龋情况,计算龋均。随机抽取30名龋活跃高危人群儿童做为实验组1,30名龋活跃低危人群儿童做实验组2,应用窝沟封闭和多乐氟护齿剂同时对乳磨牙进行龋病预防干预;同时抽取30名龋活跃低危人群做对照组应用多乐氟护齿剂对乳磨牙进行龋病预防干预,于干预后6、12、18个月计算龋病发病率。结果:龋活跃高危人群和低危人群的患龋率分别为68.75%、28.6%,两组比较有显著性差异(P<0.05)。干预后6个月时,实验组1、实验组2、对照组龋病发病率分别为12.3%、11.6%、13.1%,三组比较无显著性差异(P>0.05);12个月时,龋病发病率分别为12.4%、11.8%、23.2%,实验组1、实验组2比较无显著性差异(P>0.05),实验组1、实验组2均显著低于对照组,有显著性差异(P<0.05);18个月时,龋病发病率分别为13.2%、12.9%、29.3%,实验组1、实验组2均显著低于对照组,有显著性差异(P<0.05),但实验组1、实验组2比较无显著性差异(P>0.05)。结论:同时应用窝沟封闭和涂氟对乳磨牙可以有效防龋,降低学龄前儿童的龋发病率。     

Phenotype and animal domestication: A study of dental variation between domestic,wild, captive,hybrid and insular Sus scrofa

Background

Identifying the phenotypic responses to domestication remains a long-standing and important question for researchers studying its early history. The great diversity in domestic animals and plants that exists today bears testament to the profound changes that domestication has induced in their ancestral wild forms over the last millennia. Domestication is a complex evolutionary process in which wild organisms are moved to new anthropogenic environments. Although modern genetics are significantly improving our understanding of domestication and breed formation, little is still known about the associated morphological changes linked to the process itself. In order to explore phenotypic variation induced by different levels of human control, we analysed the diversity of dental size, shape and allometry in modern free-living and captive wild, wild x domestic hybrid, domestic and insular Sus scrofa populations.

Results

We show that domestication has created completely new dental phenotypes not found in wild boar (although the amount of variation amongst domestic pigs does not exceed that found in the wild). Wild boar tooth shape also appears to be biogeographically structured, likely the result of post-glacial recolonisation history. Furthermore, distinct dental phenotypes were also observed among domestic breeds, probably the result of differing types and intensity of past and present husbandry practices. Captivity also appears to impact tooth shape. Wild x domestic hybrids possess second molars that are strictly intermediate in shape between wild boar and domestic pigs (third molars, however, showing greater shape similarity with wild boar) while their size is more similar to domestic pigs. The dental phenotypes of insular Sus scrofa populations found on Corsica and Sardinia today (originally introduced by Neolithic settlers to the islands) can be explained either by feralization of the original introduced domestic swine or that the founding population maintained a wild boar phenotype through time.

Conclusions

Domestication has driven significant phenotypic diversification in Sus scrofa. Captivity (environmental control), hybridization (genome admixture), and introduction to islands all correspond to differing levels of human control and may be considered different stages of the domestication process. The relatively well-known genetic evolutionary history of pigs shows a similar complexity at the phenotypic level.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-014-0269-x) contains supplementary material, which is available to authorized users.     

超声冲洗技术在磨牙iRoot BP Plus牙髓切断术中的应用效果

摘要 目的：探究超声冲洗技术在磨牙iRoot BP Plus牙髓切断术中的应用效果。方法：2015年8月到2020年5月选择在本院进行诊治的可复性牙髓炎患者123例作为研究对象,根据随机信封1:1抽签原则把患者分为超声组62例与对照组61例,所有患者均给予iRoot BP Plus牙髓切断术,对照组给予常规冲洗,超声组给予超声冲洗,对比患牙边缘状况、术后不良反应、钙化桥形成与手术成功率。结果：（1）超声组术后3个月、6个月与12个月的手术成功率分别为100.0 %、100.0 %、98.4 %,对照组分别为100.0 %、95.1 %、86.9 %,超声组术后12个月的手术成功率高于对照组（P<0.05）。（2）超声组术后3个月、6个月与12个月的钙化桥形成率分别为51.6 %、98.4 %和100.0 %,对照组为18.0 %、50.8 %、100.0 %,超声组术后3个月、6个月钙化桥形成率均高于对照组（P<0.05）。（3）超声组术后12个月的不良反应发生率为3.2 %,低于对照组的16.4 %（P<0.05）。（4）超声组术后12个月的患牙边缘染色完整性、边缘完整性分别为98.4 %、98.4 %,高于对照组的85.2 %和88.5 %（P<0.05）。结论：超声冲洗技术在磨牙iRoot BP Plus牙髓切断术中的应用能改善患牙边缘状况,减少术后不良反应的发生,还可促进钙化桥形成,提高手术成功率。     

Dental topography and diets of Australopithecus afarensis and early Homo

Diet is key to understanding the paleoecology of early hominins. We know little about the diets of these fossil taxa, however, in part because of a limited fossil record, and in part because of limitations in methods available to infer their feeding adaptations. This paper applies a new method, dental topographic analysis, to the inference of diet from fossil hominin teeth. This approach uses laser scanning to generate digital 3D models of teeth and geographic information systems software to measure surface attributes, such as slope and occlusal relief. Because it does not rely on specific landmarks that change with wear, dental topographic analysis allows measurement and comparison of variably worn teeth, greatly increasing sample sizes compared with techniques that require unworn teeth. This study involved comparison of occlusal slope and relief of the lower second molars of Australopithecus afarensis (n=15) and early Homo (n=8) with those of Gorilla gorilla gorilla (n=47) and Pan troglodytes troglodytes (n=54). Results indicate that while all groups show reduced slope and relief in progressively more worn specimens, there are consistent differences at given wear stages among the taxa. Early Homo shows steeper slopes and more relief than chimpanzees, whereas A. afarensis shows less slope and relief than any of the other groups. The differences between the two hominin taxa are on the same order as those between the extant apes, suggesting similar degrees of difference in diet. Because these chimpanzees and gorillas differ mostly in fallback foods where they are sympatric, results suggest that the early hominins may likewise have differed mostly in fallback foods, with A. afarensis emphasizing harder, more brittle foods, and early Homo relying on tougher, more elastic foods.     

Incisor-molar relationships in chimpanzees and other hominoids: implications for diet and phylogeny

In chimpanzees, the cutting edge of the incisor battery is longer in relation to the length of the molar row than in any other hominoid, extant or fossil, the only other lineage approaching it being the orangutan. Apart from their increased mesio-distal dimensions, the upper and lower incisors of chimpanzees differ in additional ways from those of almost all other hominoids. The I2/ is enlarged, so that the difference in size between it and the central upper incisor is less than it is in the heteromorphic upper incisors of other hominoids. The lower incisors are expanded mesio-distally, so much so that isolated I/2 crowns can resemble upper central incisors. In chimpanzees the lingual surface of the lower incisors is generally more procumbent than it is in other hominoids, which have more vertically oriented incisor crowns and there is a greater difference in enamel thickness between labial and lingual sides. The re-orientation of the lower incisor crown is reflected in the root, which in lateral view is anteriorly concave in chimpanzees whereas it is more orthogonal or convex in other hominoids. The molars of chimpanzees, especially the lowers, have extensive and relatively deep occlusal basins, and the main cusps are peripheralised and labio-lingually compressed, making them more trenchant than those of other hominoids. This paper examines the incisor-lower molar proportions in extinct and living hominoids and develops a new hypothesis about the evolution of the dentition of chimpanzees and links it to their diet. It also examines the incisor-molar proportions of hominids and African apes in order to throw light on the phylogenetic relationships between them. It is shown that chimpanzees are highly derived in this respect and that several recent ideas concerning the chimp-like appearance of the last common ancestor of hominids and African apes are likely to be incorrect.This revised version was published online in April 2005 with corrections to the cover date of the issue.