Complete Tooth Research Articles

The effect of mechanical oral hygiene procedures on bleeding on probing

The purpose of the present study was to investigate the effect of mechanical oral hygiene procedures on bleeding on probing in relation to age and periodontal status. The study was carried out on 49 individuals divided into 7 experimental groups according to age and having been either treated for destructive periodontal disease or having an intact healthy periodontium. In order to eliminate any pre-existant gingival inflammation, all subjects received a carefully controlled oral hygiene program. At the start of the experiment, all subjects were instructed to abstain from oral hygiene procedures for 24 h. Thereafter, clinical baseline measurements were carried out, including bleeding on probing (BOP) using a standardized probing pressure. Next, all subjects cleaned their teeth according to their normal oral home care protocol using a multitufted toothbrush, toothpicks and interdental brushes. BOP scores were again assessed 30 min after completed tooth cleaning procedures. The results revealed a significant increase in BOP after the mechanical oral hygiene procedures in every individual in all experimental groups (p less than 0.05). Further analysis showed that the increase in BOP was independent of the periodontal status of the subjects. However the BOP scores after mechanical oral hygiene procedures were higher in the young age groups. It was concluded that the diagnostic predictability of BOP in the treatment of periodontal diseases might be affected by temporarily elevated BOP scores shortly after mechanical oral hygiene procedures.

A morphometric study of bone and tooth volumes in the pipid frog Xenopus laevis (Daudin), with comments on the importance of tooth resorption during normal tooth replacement

Volumetric estimations of teeth and bone on serial sections using a semiautomatic image analyzer indicate that, in the polyphyodont dentition of the pipid anuran Xenopus laevis (Daudin), the mean volume of the dentine composing the teeth is about 23.5% of the volume of the supporting maxillae and premaxillae. During tooth replacement, osteoclasts resorb up to 98% of the dentine. Teeth may be resorbed rather than shed in order to conserve tooth constituents because, if shedding of complete teeth did occur, a quantity of calcified tissue equal to perhaps 45 times the volume of the bone of the upper jaw might be lost over an animal's projected life span of about 13-15 years.

根未完成歯不完全脱臼後の歯髄および歯周組織の変化に関する実験的研究

Experimental subluxation was conducted on the bilateral upper lateral incisors with incomplete root in 39 young dogs (3 in control group) and pathohistologic and neuropathohistologic investigations were made. The results were as follows : 1. In the subluxated teeth with incomplete root, the periodontal fibers were restored to the former state on 20th day. 2. None of the cases showed ankylosis between the alveolar bone and subluxated teeth. 3. Revascularization was found in the dental pulp of the subluxated teeth with incomplete root. It was confirmed that a large number of new blood vessel extended from the periodontium to the root pulp from 7th day and reached the coronal pulp on and after 20th day. 4. The dental pulp showed edema immediately after the experimental subluxation and necrosed in places. However organization of the pulp progressed and fibrosis extended to the whole pulp on 30th day. 5. Odontoblasts disappeared in places after the experimental subluxation of the teeth but were recovered on 30th day. Predentin was formed and the pulp was strictured by the deposited dentin. 6. The existence of the epithelial sheath of Hertwig was greatly related to growth of the root. Dentin-like hard tissues began to extend along the epithelial sheath of Hertwig in the root apex on 7th day and apparent growth of the root was noted thereafter with time. 7. In the subluxated teeth with incomplete root, neurotomesis and Wallerian degeneration occurred concurrently in the intraperiodontal nerve tissues. Immediately after experimental subluxation of the teeth, the intraperiodontal nerve fibers and nerve fascicle were severed at the ruptures of the periodontium and degeneration of nerve fibers proceeded with time centering on the ruptures of the periodotium, and ranged over the whole periodontium. These findings were noted until 10th day. 8. In the subluxated teeth with incomplete root, only Wallerian degeneration occurred in the intrapulpal nerve tissues. The nerve tissues invading into the pulp were severed at the ruptures of the periodontium in the apex regions immediately after experimental subluxation of the tooth. The nerve fibers remaining in the pulp decreased with time and the nerve fibers exhibiting degenerative findings disappeared on 15th day. 9. As to regeneration of nerve in the periodontium of the subluxated teeth with incomplete root, marked proliferation of Schwann cells occurred on 7th day from the tip of nerve fascicles on the gingival side and in vasoneural space of the alveolar bone, and fine nerve fibers appeared along that arrangement. On 10th day, the nerve fascicle consisting of fine nerve fibers extended on the side of the alveolar bone up to the midlevel of the root and reached the periodontium in the alveolar crest regions on 20th day. On 30th day, the nerve distribution was approximately completed in the periodontium. 10. As to regeneration of nerve in the pulp of the subluxated teeth with incomplete root, a large number of fine nerve fibers and nerve fascicle invaded through the opened apical foramen on 10th day. The nerve distribution appeared to be restored with the peak on 20th day. However the nerve tissues in the pulp decreased slightly after 30th day. On the basis of the foregoing, the subluxated teeth with incomplete root keep the normal positions in the alveolar bone and mature as complete teeth supported by the periodontium which recovered morphologically and functionally. But the pulp is strictured and fibrosed and the sense response of the pulp is thought to be lowered slightly.

Tooth replacement in adult Xenopus laevis (Amphibia: Anura)

To determine the time scale of tooth replacement in adult Xenopus laevis (Daudin), three large females of similar size were kept in aquaria at 25 °C for ten weeks. They were anaesthetized twice weekly with MS 222 and impressions of their upper jaws were taken using thin sheets of dental gold‐casting wax. Because the erupted tips of the teeth were small (100 μm), the impressions were enlarged by projection so that the presence or absence of a tooth at each locus in the jaw could be recorded. Each half of each animal's jaw was analysed separately and a statistical analysis of the records yielded results for the duration of the Replacement Cycle and Functional Life of the teeth. The range of the median Replacement Cycle time between specimens was 910–1,010h, that of the Functional Life 580–700 h and that of the Gap Period (the time over which loci were unoccupied by functional teeth) 230–420 h. A tentative time scale for the complete tooth development cycle (from tooth germ initiation to complete resorption) was calculated by extrapolation from the results and ranged from 59.07 to 71.29 days.

A mechanism for tooth pattern reversal in sharks: The polarity switch model.

In many shark families the tooth cusps are deflected in a posterior direction. In tooth pattern reversal, one (or a few) tooth families have cusps which are deflected in an anterior direction. This tooth pattern reversal is attributed to a splitting of hypothetical tooth protogerms. After splitting, both parts of the protogerm regenerate and form complete tooth germs.A 'Polarity Switch Model' is proposed according to which tooth germs with curved cusps have an asymmetric (polarized) double gradient. The model states that, depending on where the splitting takes place within the protogerm, either both teeth have a normal posterior deflection, or the deflection of the posterior tooth is switched into the opposite direction. On the basis of the specimens available, a switch in polarity occurs only when the protogerms are injured: It does not occur when protogerms become split during the normal process of adding new tooth families.

Physical properties of human tooth enamel and enamel sheath material under load

Some of the material contained in this paper has appeared elsewhere in the form of brief notes. Interest in these published notes has induced the author to prepare this paper in which interesting aspects of the techniques used and the results obtained are grouped together. Changes which may be observed in the form birefringence of enamel are described and related to the fluid of the enamel. The ability of enamel to change its volume under load is considered and its ‘effective” Poisson's ratio is discussed. When compared with the behavior of complete teeth under axial load this change of volume is similar to the volume of free water in the enamel. The measurement of interstitial contact areas leads to effective values for the elastic modulus of enamel and enamel sheath material. The requirement that part of the water content of enamel is forcibly displaced by the presence of compressive stress systems is discussed and particular reference is made to the spread of caries lesions in enamel.

NUMERICAL VARIATIONS IN THE DENTITION OF SOME PINNIPEDS.

AbstractThe numerical variations observed in the dentition of the northern sea lions, fur seals and seals are summarized as follows: (1) There is a reappearance of the right maxillary second molar in the northern sea lion dentition and of the first deciduous premolar in the fur seal dentition, which may be interpreted as examples of evolutionary recession towards the full mammalian dentition. (2) There is a complete tooth reduction of the molars in the sea lion dentition. (3) There is the presence of a “Dentes geminati” of the second premolar and the supernumerary tooth in the right upper jaw and of the supernumerary tooth between the second and third premolars in the left upper jaw of an adult fur seal, which may be associated with the division of the second premolar tooth germ. (4) There is an appearance of a pair of supernumerary teeth lying lingually to the root of lower permanent central (second) incisors, being of interest in suggesting that they are either the appearance of the successors of the recent central incisors or the reappearance of the permanent first incisors, in the fur seal dentition. (5) There is a tooth reduction in the permanent dental formula from \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm I}\,\frac{{\rm 3}}{{\rm 2}}{\rm C}\,\frac{{\rm 1}}{{\rm 1}}{\rm P}\,\frac{{\rm 4}}{{\rm 4}}{\rm M}\frac{{\rm 1}}{{\rm 1}}\,{\rm to}\,{\rm I}\,\frac{{\rm 3}}{{\rm 1}}{\rm C}\,\frac{{\rm 1}}{{\rm 1}}{\rm P}\,\frac{{\rm 3}}{{\rm 4}}{\rm M}\frac{{\rm 1}}{{\rm 1}} $\end{document} in the seal, which was associated with a “Dentes confusi” in the same category of the dentition.

THE ONTOGENY OF MOLAR PATTERN

SUMMARYThe crown pattern of the tooth is essentially that of the surface of the dentine (dentine‐enamel junction), modified by the deposition of enamel which may be uneven in thickness. The dentine‐enamel junction preserves in the completed tooth the form of the membrana praeformativa, the basement membrane of the inner enamel epithelium of the enamel organ. Folding of this membrane creates the crown pattern.The inner enamel epithelium is subjected to pressure from both sides. On the basal side there is the rapidly growing mesenchyme of the dental papilla, and on the occlusal side there is the stellate reticulum, which swells by the accumulation of fluid. The stellate reticulum prevents distortion of the epithelium by growth of the papilla, and thus ensures that folding of the epithelium is due to its intrinsic growth pattern. This makes for more accurate control of the crown pattern, the details of which are of importance in the function of chewing.The enamel knot is a region of the inner enamel epithelium from which cells are contributed to the stellate reticulum. It represents the tip of the primary cusp. The enamel cord (‘enamel septum’) which consists of cells which are in process of transforming into stellate reticulum, has been confused with two other structures that develop later: a cleavage septum, preparatory to the formation of crown cementum, and an epithelial septum, found in marsupials and crocodilians. The epithelial nodules of monotremes are probably degenerate relics of an epithelial septum.The inner enamel epithelium is a diaphragm passing across the interior of the dental follicle, and folding to adapt its increased area to a confined space. The cement organ, which in some mammals develops from the follicle, probably plays no part in the deformation of the epithelium, but the follicle as a whole may be subject to compression by adjacent follicles.A cusp is a centre of precocious maturation of the cells of the inner enamel epithelium. Here growth ceases (perhaps after a transitory burst of mitosis) and eventually the hard tissues are deposited. The process starts at the tip of the cusp and extends basally, so that growth continues longest in the valleys, intensifying the crown relief. Dens in dente is due to retarded maturation of an area of the enamel epithelium.Throughout the development of the crown there is a marginal zona cingularis, where growth continues. The crown pattern depends upon the position and the stage of growth in which cusps are differentiated from the zona cingularis, by accelerated maturation of groups of cells. Cusps which appear late in development stand low on the crown and frequently form part of a cingulum. Changes in the timing of cusp formation play an important part in serial modifications of pattern, as well as in phylogeny.Ridges are probably produced by tensions set up in the epithelium by the relative movement of cusps, owing to unequal growth or to changes in the shape of the follicle. They form in areas where growth has slowed down but the apposition of hard tissues has not begun.The lobes of the basal outline of the tooth are produced by growth centres in the papilla, which cause evagination of the follicle. Each growth centre is supplied by a bundle of blood vessels. The roots form in relation to these blood vessels, and so reflect the organization of the papilla. Hertwig's epithelial sheath grows between the follicle and the base of the papilla, the direction of its growth being controlled by the surrounding tissues owing to the absence of stellate reticulum on the basal portion of the tooth.There is no constant relation between cusps and roots, although marginal cusps frequently arise in association with lobes of the basal outline. The crown pattern results from an interaction between the growth pattern of the inner enamel epithelium and that of the papilla, the latter controlling the shape of the margin which limits the folding epithelium.

無根歯の発生学的研究

The development of lower incisors of white rats (Rattus norvegicus albinus) for each stage of embryonic, newborn, and adult lives was studied. The summary is as follows. 1) At the 13th day of the embryonic life, the oral epithelium lining the anterior portion of the mandibular process has thickened symmetrically on both sides. This is the primitive dental lamina. The lamina extends gradually outer and downwards in proportion to the development of the embryo. The periphery of the lamina is covered by a single layer of short columnar cells, and the inside is filled with cells containing spherical or spheroidal nuclei. 2) At the 14th day of the embryo, the lower free margin of the dental lamina swells roundly to shape the so-called bud stage. 3) From the 15th to the 16th day, posterior portion inside the bud becomes concave to form the so-called cap stage. On the 16th day, however, with progressing development, the posterior end of the enamel cap is separated into two parts, dorsal and ventral. Active cell division characterizes this stage so that the round cells concentrates densely at the central portion of the inner concavity to build the enamel knot which finally assumes the shape of the enamel organ. It is to be noted that a longitudinal streak is seen to traverse along the ventral surface of the enamel cap, which is presumed to have some relation to degenerative process in the dental lamina of permanent tooth. 4. On the 18 th and 19 th day, after further proliferation and increase of depth of the concave surface, the enamel organ forms the bell form. The enamel knot disappears gradually and this stage is characterized by the further differentiation of the cells of the enamel organ, each layer becomes distinct, i. e. the enamel organ consists of the outer and the inner epithelium, the stellate reticulum, and the stratum intermedium. At the same time the dental papilla becomes clear. The outer enamel epithelium arranges on the convex surface of the enamel organ. The mesenchym which is enclosed by the enamel organ consists of the young connective tissue, and the mesenchymal cells which face the inner enamel epithelium become odontoblasts and the dental papilla at this stage shows the figure of the primary pulp. 5. In the period of completion of hard tissue which occurs in the course from the 20 th day of the embryonic life to the 10 th day after birth, the cylinder of enamel organ becomes longer and longer and shows rudimentary shape of tooth. Enamel organ degenerates in turn of inner, outer, dorsal side, except backend and ventral side. The inner and outer enamel epitheliums unite and arrange as a layer of flat cells, and the inner enamel epithelium secretes a thin Haematoxyline stainable layer. But soon after this layer becomes Haematoxyline-unstainable and remains transparent. On the other hand, the ventral side grows further and the pre-enamel is heaped on the pre-dentin. The apex tissue of the dental papilla becomes fibrous and builds bone-like dentin. Pre-dentin and calcified dentin is heaped on the pre-enamel, and this heap is in turn of ventral, inner, outer, dorsal side. A mass of the epithelial cells in the enamel organ neck part remains also in this stage, but it disappears on about 7 th day after birth. The author perceives that this mass of epithelial cells plays the part of inducement of oral epitheliums into deep mesenchymal tissues. 6. In completion stage, the enamel, dentin and bone-like dentin increase in size, and in calcification degree. After formation of the hard tissue is completed, tooth germ begins to erupt. Formation of the enamel and dentin is nearly as well as human, but as 1 mentioned above, tranparent zone is the secretion of the inner enamel epithelium and the cement cannot be seen. 7. The area of the backend of completed tooth shows young enamel organ, but inner, outer, dorsal side of the forward part is about the same with degeneration type

XV.—OnRhamphodopsis, a Ptyctodont from the Middle Old Red Sandstone of Scotland

In 1858 C. H. Pander described asPtydodusa number of teeth from Upper Devonian limestones in Russia. His admirable figures of complete teeth and of sections through them established the very chimæroid structure of these bodies. Since that time similar teeth have been repeatedly described, and have served for the establishment of three genera and many species from rocks of Middle and Upper Devonian age.

The growth of embryo bones transplanted whole in the rat’s brain

An earlier study (Willis, 1935) showed that in rats the brain is a very favourable nidus for the growth of implanted embryo tissues. Following the introduction of small quantities of embryo mince, large masses of bone and cartilage, epidermal, and mucosal cysts, salivary and other glands, skeletal muscle, and teeth were obtained; and in the most successful implants the rate of growth and differentiation approximated to that of an intact animal. The perfect growth of complete teeth in these experiments suggested that it might also prove possible to grow complete bones in the same way. This hope has been realized; it has proved possible, following the intracerebral implantation of early cartilaginous primordia of the limb buds of young embryos, to obtain well-formed long bones such as femur or tibia nearly 2 cm long in the brains of the host rats. In some of the experiments two long bones with an intervening joint have developed.

A case of generalized osteitis fibrosa demonstrating the effect of hyperparathyroidism on tooth development

The effect of hyperparathyroidism on the developing teeth of a young patient (aged fifteen) suffering from generalized osteitis fibrosa has been studied. Although the mandible, as well as the maxilla, was extensively affected by the disease and the teeth were surrounded by bone showing marked resorption, there was no evidence of resorption inside of the teeth. Contrarily, the unusually good teeth with no cavities and only one filling, as well as the formation of pulp stones, point to the fact that due to the hypercalcemia the calcification of the dental structures is increased rather than depleted. The most striking effects of hyperparathyroidism are as follows: (1) interruption of the tooth development, producing marked defects in dentin formation, seen as deeply stained contour lines, which are probably records of very severe or active phases of the disease; (2) formation of osteodentin, produced when odontoblasts are destroyed ; and (3) formation of osteocementum deposited at the root surfaces in excessive amounts. A completed tooth in a person who has contracted the disease in later life would probably show none of these changes in the dentin. It may be concluded that teeth present a very stable deposit of calcium, which is not readily resorbed, because it was not affected in this severe case of hyperparathyroidism. This is in line with the findings of Bauer, Aub and Albright1 who state that the bone trabeculae serve as the most available source of calcium. It also concurs with the statement of Jaffe, Bodansky, and Blair8 that labile calcium is found in the regions of most active bone growth. There is no continuous resorption and apposition in the adult tooth as there normally is in bone; therefore calcium salts are not readily available from this source. Since calcium is not resorbed from dentin in hyperparathyroidism, the further conclusion may be drawn that resorption does not occur in other systemic diseases such as pregnancy, osteomalacia, or diseases due to avitaminosis.

New Yields from the Oldoway Bone Beds, Tanganyika Territory

IN NATURE for Oct. 24, 1931, a letter from us was published giving the first results of our work at Oldoway in Tanganyika Territory; we should be grateful if the following additional results could be recorded: (1) Bed No. 1, the lowest bed in the Oldoway series, has now yielded an extensive fauna which includes Deinotherium sp., Hipparion sp., and also Elephas (antiqus recki?). The Deinotherium cannot be regarded as a derived fossil, since five complete teeth were found amongst a partially articulated skeleton. In Bed 1, at two different sites, we have found artefacts of a Pre-Chellean type actually with Deinotherium.