A specific nanomanufacturing challenge.

For a science to become a technology, a certain level of control has to have been established over the way items are fabricated for manufacture and use. Here we first consider the challenge of making and using a LEGO(®) brick scaled down by a factor of 10(n) for n = 0-6 in each spatial dimension, i.e. from millimetres to nanometres. We consider both the manufacture and the subsequent properties of the nanobricks that pertain to their use in constructing and dismantling structures. As n increases, the ability to use fails first, to manufacture fails second and to fabricate fails last. Applied to the vast literature in nanoscience, this process emphasises the unmanufacturability of most nanoscale artefacts.

Coherent dynamics of a telecom-wavelength entangled photon source.

Quantum networks can interconnect remote quantum information processors, allowing interaction between different architectures and increasing net computational power. Fibre-optic telecommunications technology offers a practical platform for routing weakly interacting photonic qubits, allowing quantum correlations and entanglement to be established between distant nodes. Although entangled photons have been produced at telecommunications wavelengths using spontaneous parametric downconversion in nonlinear media, as system complexity increases their inherent excess photon generation will become limiting. Here we demonstrate entangled photon pair generation from a semiconductor quantum dot at a telecommunications wavelength. Emitted photons are intrinsically anti-bunched and violate Bell's inequality by 17 standard deviations High-visibility oscillations of the biphoton polarization reveal the time evolution of the emitted state with exceptional clarity, exposing long coherence times. Furthermore, we introduce a method to evaluate the fidelity to a time-evolving Bell state, revealing entanglement between photons emitted up to 5 ns apart, exceeding the exciton lifetime.

A method of calculating human deciduous crown formation times and of estimating the chronological ages of stressful events occurring during deciduous enamel formation.

Knowledge of deciduous crown formation times is useful in forensic anthropology and when aging juvenile remains from an archaeological context. Until now, histological techniques for calculating enamel formation times in deciduous teeth have been completely dependent on being able to visualise clear daily incremental markings. In the first part of this study we took twenty deciduous teeth where daily incremental markings were easily visible on both aspects of the crown and used these as the basis for generating regression equations to predict enamel formation times. We were then able to use these regression equations to calculate deciduous crown formation times in a further fifty deciduous teeth where it was not possible to see daily increments. We present here new data for deciduous crown formation times based on these regression equations. In the second part of this study these regression formulae were applied blind to teeth from two individuals with known medical histories. The formulae were able to successfully determine the times of prenatal and postnatal enamel formation relative to the neonatal line and also to correctly estimate the ages at which accentuated 'stress lines' occurred during the period of deciduous crown formation.

Longstanding dental pathology in Neandertals from El Sidrón (Asturias, Spain) with a probable familial basis.

Two Neandertal specimens from El Sidrón, northern Spain, show evidence of retained left mandibular deciduous canines. These individuals share the same mitochondrial (mtDNA) haplotype, indicating they are maternally related and suggesting a potential heritable basis for these dental anomalies. Radiographs and medical CT scans provide evidence of further, more extensive dental pathology in one of these specimens. An anomalous deciduous canine crown morphology that developed before birth subsequently suffered a fracture of the crown exposing the pulp sometime after eruption into functional occlusion. This led to death of the tooth, periapical granuloma formation and arrested deciduous canine root growth at an estimated age of 2.5 years. At some point the underlying permanent canine tooth became horizontally displaced and came to lie low in the trabecular bone of the mandibular corpus. A dentigerous cyst then developed around the crown. Anterior growth displacement of the mandible continued around the stationary permanent canine, leaving it posteriorly positioned in the mandibular corpus by the end of the growth period beneath the third permanent molar roots, which, in turn, suggests a largely horizontal growth vector. Subsequent longstanding repeated infections of the expanding cyst cavity are evidenced by bouts of bone deposition and resorption of the boundary walls of the cyst cavity. This resulted in the establishment of two permanent bony drainage sinuses, one through the buccal plate of the alveolar bone anteriorly, immediately beneath the infected deciduous canine root, and the other through the buccal plate anterior to the mesial root of the first permanent molar. It is probable that this complicated temporal sequence of dental pathologies had an initial heritable trigger that progressed in an unusually complex way in one of these individuals. During life, this individual may have been largely unaware of this ongoing pathology.

Structure and compositional characteristics of caniniform dental enamel in the tuatara Sphenodon punctatus (Lepidosauria: Rhynchocephalia).

OBJECTIVE: The evolution of dental tissues in relation to tooth function is poorly understood in non-mammalian vertebrates. We studied the dentition of Sphenodon punctatus, the sole remaining member of the order Rhynchocephalia in this light. METHODS: We examined 6 anterior maxillary caniniform teeth from adult Sphenodon by scanning electron microscopy, nano-indentation and Raman spectroscopy. RESULTS: The elastic modulus (E) for tuatara enamel was 73.17 (sd, 3.25) GPa and 19.52 +/- 0.76 Gpa for dentine. Hardness (H) values for enamel and dentine were 4.00 (sd, 0.22) and 0.63 +/- 0.02 Gpa respectively. The enamel was thin (100 gm or less), prismless and consisted of grouped parallel crystallites. Incremental lines occurred at intervals of about 0.5 to 1 rm. There were tubular structures along the enamel dentine junction running from the dentine into the inner enamel, at different angles. These were widened at their base with a smooth, possibly inorganic lining. Enamel elastic modulus and hardness were lower than those for mammals. CONCLUSIONS: The presence of enamel tubules in the basal part of the enamel along the EDJ remains speculative, with possible functions being added enamel/dentinal adhesion or a role in mechanosensation.

Preserved microstructure and mineral distribution in tooth and periodontal tissues in early fossil hominin material from Koobi Fora, Kenya.

The aim of this study was to explore further the preservation of tissues and the mineral distribution in 1.6 million-year-old fossil hominin material from Koobi Fora, Kenya attributed to Paranthropus boisei (KNM-ER 1817). Bone, dentine and cementum microstructure were well preserved. Electron microprobe analysis of dentine and bone revealed an F-bearing apatite. Calcite now filled the original soft tissue spaces. The average Ca/P atomic ratio was 1.93, as compared to 1.67 in biological hydroxyapatite, indicating that the Ca-content had increased during fossilization. Analytical sums for mineral content were approximately 90 wt%. Some of the remaining 10 wt% may be preserved organic material. Demineralized dentine fragments showed irregularly distributed tubules encircled with a fibrous-like electron-dense material. A similar material was observed in demineralized dentine. Within this, structures resembling bacteria were seen. In demineralized bone an electron-dense material with a fibrous appearance and a banding pattern that repeated every 64 nm, similar to that of collagen, was noted. SEM of an enamel fragment (KNM-ER 6081) showed signs of demineralization/remineralization. Retzius lines, Hunter-Schreger bands and prism cross-striations spaced 3.7-7.1.microm apart were noted. Prisms were arranged in a pattern 3 configuration and deeper areas containing aprismatic enamel were occasionally observed. We conclude that a great deal of informative microstructure and ultrastructure remains preserved in this fossil material. We also hypothesize that the high mineral content of the tissues may 'protect' parts of the organic matrix from degradation, since our findings indicate that some organic matrix may still be present.

Microstructure of dental hard tissues and bone in the Tuatara dentary, Sphenodon punctatus (Diapsida: Lepidosauria: Rhynchocephalia).

The Tuatara, Sphenodon, is a small reptile currently restricted to islands off the coast of New Zealand where it feeds mainly on arthropods. A widely held misconception is that 'Sphenodon does not have real teeth' and instead possesses 'serrations on the jaw bone'. One hatchling and one adult dentary were examined under SEM. Two longitudinal ground sections 100-microm thick were prepared through a lower canine tooth and its supporting tissues. There was clear evidence of aprismatic enamel (primless enamel) containing dentine tubules crossing the EDJ, dentine, cementum and a basal-bone attachment. Enamel increments averaged approximately 3 microm/day and extension rates were approximately 30 microm/day. The base of the tooth consisted of basal attachment bone that graded from few cell inclusions to lamella or even Haversian-like bone with evidence of remodeling. A string of sclerosed pulp-stone like structures filled the pulp chamber and were continuous with the bone of attachment. Bone beneath the large central nutrient mandibular (Meckel's) canal was quite unlike lamella bone and appeared to be fast growing and to contain wide alternating cell-rich and cell-free zones. Bone cells were rounded (never fusiform) and had few, if any, canaliculi. The dentine close to the EDJ formed at about the same rate as enamel but also contained longer period increments approximately 100 microm apart. These were spaced appropriately for monthly lunar growth bands, which would explain the basis of the banding pattern observed in the fast growing basal bone beneath the Meckel's canal.

Molar development in common chimpanzees (Pan troglodytes).

Numerous studies have reported on enamel and dentine development in hominoid molars, although little is known about intraspecific incremental feature variation. Furthermore, a recent histological study suggested that there is little or no time between age at chimpanzee crown completion and age at molar eruption, which is unlikely given that root growth is necessary for tooth eruption. The study presented here redefines growth standards for chimpanzee molar teeth and examines variation in incremental features. The periodicity of Retzius lines in a relatively large sample was found to be 6 or 7 days. The number of Retzius lines and cuspal enamel thickness both vary within a cusp type, among cusps, and among molars, resulting in marked variation in formation time. Daily secretion rate is consistent within analogous cuspal zones (inner, middle, and outer enamel) within and among cusp types and among molar types. Significantly increasing trends are found from inner to outer cuspal enamel (3 to 5 microns/day). Cuspal initiation and completion sequences also vary, although sequences for mandibular molar cusps are more consistent. Cusp-specific formation time ranges from approximately 2 to 3 years, increasing from M1 to M2, and often decreasing from M2 to M3. These times are intermediate between radiographic studies and a previous histological study, although both formation time within cusps and overlap between molars vary considerably. Cusp-specific (coronal) extension rates range from approximately 4 to 9 microns/day, and root extension rates in the first 5 mm of roots range from 3 to 9 microns/day. These rates are greater in M1 than in M2 or M3, and they are greater in mandibular molars than in respective maxillary molars. This significant enlargement of comparative data on nonhuman primate incremental development demonstrates that developmental variation among cusp and molar types should be considered during interpretations and comparisons of small samples of fossil hominins and hominoids.

Variation in modern human enamel formation times.

Most of what we know about the timing of human enamel formation comes from radiographic studies on children of known age. Here, we present new longitudinal data derived from a histological analysis of tooth enamel. Two samples, one from southern Africa and one from northern Europe, contained all anterior and molar tooth types. Two further samples contained only one tooth type: canines from a medieval Danish sample and third molars from a modern North American sample. Data were collected on 326 molars and 352 anterior teeth. Each tooth was sectioned and prepared for polarized light microscopy. We used daily enamel cross striations to determine cuspal enamel formation time, recorded the periodicity of long-period striae in the lateral enamel, and used this value to calculate enamel formation times for each decile of crown length. We present data that reveal some of the processes whereby differences in enamel formation times arise between our samples. Mean cuspal enamel formation times were similar in southern African and northern European anterior teeth, but differed in certain molar cusps. All the southern African anterior teeth completed enamel formation earlier. The greatest difference in mean chronological age at enamel completion was 5.2 vs. 6.2 years of age in lower canines. However, enamel completion times in the molar teeth showed few differences between the samples, with mean times for the longest forming cusps all falling between 3.0 years and 3.45 years. Our data suggest fewer differences between samples and smaller ranges of variation than in many radiographic studies and present a more realistic picture of worldwide variation in enamel formation times.

Dental development and life history in Anapithecus hernyaki.

The sample of Anapithecus from Rudabánya, Hungary, is remarkable in preserving a large number of immature individuals. We used perikymata counts, measurements of root length and cuspal enamel thickness, and observations of the sequence of tooth germs that cross match specific developmental stages in Anapithecus to construct the first composite picture and time scale for dental development in a pliopithecoid (Catarrhini, Primates). We conclude that the age of eruption of M1 in Anapithecus was similar to various macaque species (approximately 1.45 months), but that M2 and M3 emergence were close to 2.2 and 3.2 years, respectively (both earlier than expected for similarly sized cercopithecoids). There may have been little difference in individual tooth formation times between cercopithecoids and Anapithecus, but the degree of molar overlap during M1, M2, and M3 crown development, which is extreme in Anapithecus, is fundamentally different. Overall dental development in Anapithecus was very rapid. Old World monkeys appear derived in lacking significant molar overlap, and hominoids may be derived in having longer tooth formation times, both resulting in longer overall dental development times. This is consistent with the general conclusion that the Pliopithecoidea is an outgroup to the Cercopithecoidea and the Hominoidea. On the other hand, rapid dental formation in Anapithecus may be an apomorphy indicative of an unusually rapid life history or unique pressures related to diet and maturation. Folivory and/or predation pressure may be responsible for generating selection to more rapidly erupt permanent teeth and possibly attain adult body masses in Anapithecus. Whatever the case, Anapithecus, with an M3 emergence of approximately 3.2 years, is dramatically faster than any extant catarrhine of similar body mass. This represents yet another unusual attribute of this poorly known fossil catarrhine.

Perikymata spacing and distribution on hominid anterior teeth.

We documented the spacing and distribution of perikymata on the buccal enamel surface of fossil hominin anterior teeth with reference to a sample of modern human and modern great ape teeth. A sample of 27 anterior teeth attributed to Australopithecus (5 to A. afarensis, 22 to A. africanus) and of 33 attributed to Paranthropus (6 to P. boisei, and 27 to P. robustus) were replicated and sputter-coated with gold to enable reflected light microscopy of their surface topography. Anterior teeth were then divided into 10 equal divisions of buccal crown height. The total perikymata count in each division of crown height was recorded using a binocular microscope fitted with a vernier micrometer eyepiece. Then the mean number of perikymata per millimeter was calculated for each division. Similar comparative data for a modern sample of 115 unworn human anterior teeth and 30 African great ape anterior teeth were collected from ground sections. Perikymata counts in each taxon (together with either known or presumed periodicities of perikymata) were then used to estimate enamel formation times in each division of crown height, for all anterior tooth types combined. The distributions of these estimates of time taken to form each division of crown height follow the same trends as the actual perikymata counts and differ between taxa in the same basic way. The distinction between modern African great apes and fossil hominins is particularly clear. Finally, we calculated crown formation times for each anterior tooth type by summing cuspal and lateral enamel formation times. Estimates of average crown formation times in australopiths are shorter than those calculated for both modern human and African great ape anterior teeth. The data presented here provide a better basis for exploring differences in perikymata spacing and distribution among fossil hominins, and provide the first opportunity to describe four specimens attributed to Homo in this context. Preliminary data indicate that differences may exist among the species attributed to early Homo, especially between Homo ergaster and Homo rudolfensis on the one hand, and Homo habilis sensu strico on the other.

Brief communication: the timing of linear hypoplasias on human anterior teeth.

One hundred and fifteen unworn anterior teeth were sectioned longitudinally with a diamond saw and prepared for histological examination by polarized light microscopy. Incremental markings in the enamel of each tooth were used to estimate the average total crown formation times of each tooth type. The total time taken to form the crowns of each tooth type was apportioned by 1) cuspal enamel formation and 2) each tenth percentile of total tooth height. Based on these data, and on histological estimates for the time of initiation of mineralization in each anterior tooth, the following conclusions can be drawn. Little if any visible surface enamel is likely to form before the end of the first year after birth in any anterior tooth type. No relation exists between tooth crown height and the total time taken to form enamel. Anterior crown formation is nonlinear and slows towards the cervix in all teeth. The estimated mean chronological age at crown completion ranged in this study from between around 4 years for lower central incisors to around 6 years for lower canines. We suggest that these combined findings will be useful for devising more reliable ways to estimate the timing of linear enamel hypoplasias than some methods currently in use.

Effect of temperature on the separation of DNA fragments by high-performance liquid chromatography and capillary electrophoresis: a comparative study.

This study investigates the effect of experimental temperature on the separation of DNA fragments, 21-587 bp, by both high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). The results show that the temperature plays an important role in the HPLC separation of DNA fragments. The optimum temperature was found to be between 40 and 50 degrees C for HPLC, while 25 degrees C was the optimum temperature for the CE separation. Also, although CE migration times became shorter, efficiency and resolution decreased with an increase in temperature from 25 to 50 degrees C, but the separation was not significantly affected. Also, the optimum HPLC temperature might be different depending on the fragment sizes to be resolved.

Morphological variation in great ape and modern human mandibles.

Adult mandibles of 317 modern humans and 91 great apes were selected that showed no pathology. Adult mandibles of Pan troglodytes troglodytes, Pongo pygmaeus pygmaeus and Gorilla gorilla gorilla and from 2 modern human populations (Zulu and Europeans from Spitalfields) were reliably sexed. Thirteen measurements were defined and included mandibular height, length and breadth in representative positions. Univariate statistical techniques and multivariate (principal component analysis and discriminant analysis) statistical techniques were used to investigate interspecific variability and sexual dimorphism in human and great ape mandibles, and intraspecific variability among the modern human mandibles. Analysis of interspecific differences revealed some pairs of variables with a tight linear relationship and others where Homo and the great apes pulled apart from one another due to shape differences. Homo and Pan are least sexually dimorphic in the mandible, Pan less so than Homo sapiens, but both the magnitude of sexual dimorphism and the distribution of sexually dimorphic measurements varied both among and between modern humans and great apes. Intraspecific variation among the 10 populations of modern humans was less than that generally reported in studies of crania (74.3% of mandibles were correctly classified into 1 of 10 populations using discriminant functions based on 13 variables as compared with 93% of crania from 17 populations based on 70 variables in one extensive study of crania). A subrecent European population (Poundbury) emerged as more different from a recent European population (Spitalfields) than other more diverse modern populations were from each other, suggesting considerable morphological plasticity in the mandible through time. This study forms a sound basis on which to explore mandibular variation in Neanderthals, early Homo sapiens and other more ancient fossil hominids.

A comparative study of cross striation spacings in cuspal enamel and of four methods of estimating the time taken to grow molar cuspal enamel in Pan, Pongo and Homo.

Cusps of three second permanent molar teeth belonging to Pan, Pongo and Homo respectively, were chosen where enamel cross striations were easily observed and measured using polarizing light microscopy. Prisms were tracked outwards on photomontages from the dentine horn to the surface of the tooth just lateral to the central gnarled enamel over the cusp tip. Approximately monthly zones of enamel formation were identified and mean cross striation spacings calculated for each zone within each of the three cusps and for the whole of each cusp in total. Enamel secretion rates ranged from 2.5 to 6.5 microns per day with an overall mean value in Pan and Homo of 4 microns per day and of 4.4 microns per day in Pongo for the cuspal enamel. Two of these cusps (of Pan and Pongo) and another of a third permanent molar of Homo were selected for further analysis. Four methods were employed to estimate cuspal enamel formation time. (i) Total counts of enamel cross striations were made through the lateral cuspal enamel on photomontages. The points in the dentine and at the enamel dentine junction (EDJ) corresponding to the end of cuspal enamel formation were defined using incremental and accentuated markings. (ii) Measurements of the average daily rates of dentine formation in each cusp were divided by the length of the axial cuspal dentine formed to give the time of cuspal dentine formation. (iii) A cumulative prism length was calculated close to the EDJ to the end of cuspal enamel formation and divided by the mean cross striation repeat interval along the EDJ to give an estimate of cuspal enamel formation time. (iv) A cumulative time for cuspal enamel formation along the EDJ was calculated by summing successive extension rates for known lengths of the EDJ. This was computed using the formula derived by Shellis (Archs. oral Biol. 29: 697-705, 1984) based on the average daily rate of enamel secretion, the angle of the prisms to the EDJ and the angle of the incremental lines to the EDJ. Each of these methods gave results to within 5% or 10% of a average value for cuspal enamel formation time derived for each cusp. There was no clear indication of additional enamel decussation in any of the cusps studied beyond that recorded in the total counts of cross striations as the prisms were tracked in two dimensions through the lateral cuspal enamel. The results of this study suggest that any one of the methods outlined here may give equivalent estimates of cuspal enamel formation if suitable incremental markings exist in the region being studied.

Observations on stria morphology in the lateral enamel of Pongo, Hylobates and Proconsul teeth.

The enamel of certain primates (orang-utans, siamangs and the early Miocene fossil hominoid, Proconsul) occasionally contains striae of Retzius that appear distinct from those more typical of the lateral and cervical enamel of other anthropoids. These striae can be described as "S-shaped" since their contour is markedly sinuous as it passes from the enamel dentine junction (EDJ) to the tooth surface. "S-shaped" striae have never been described in the comparative literature on primate enamel and yet they may be of some phylogenetic significance. This study explores the interrelationship between four variables in the enamel of an orang-utan, a siamang and a specimen of Proconsul heseloni (from Rusinga Island, Kenya) all of which contain "S-shaped" striae. The morphological components of this form of stria have been quantified here. The four variables measured were (1) prism width; (2) the angle the prisms make to the EDJ; (3) the angle the striae of Retzius make with respect to the EDJ, and (4) the daily rate of enamel formation. Each of these four variables was measured in inner enamel close to the EDJ, in enamel mid-way between the EDJ and the enamel surface, and in outer enamel. Our aim was both to quantify the components of "S-shaped" striae and to attempt to offer a developmental explanation for the appearance of these striae in fully formed enamel. We conclude that "S-shaped" striae may be associated with regions of lateral enamel where prism width either remains constant or even reduces as the enamel surface is approached. This, together with an increase in the linear daily rate of enamel secretion towards the outer enamel, a cervical inclination in the angulation of the prisms with respect to the EDJ, and an increased angulation of the striae of Retzius to the EDJ are all features that characterize "S-shaped" striae. This description will facilitate identification and quantification of any similar striae in the enamel of other primates. It will also allow careful comparison of each of the four variables one with another which may in turn help in establishing "S-shaped" striae as developmentally homologous between species.

Comparative dental development and microstructure of Proconsul teeth from Rusinga Island, Kenya.

Eighteen histological sections were prepared from eleven teeth attributed to Proconsul heseloni and two molar teeth attributed to Proconsul nyanzae. Measurements of spacings and counts of daily incremental markings in both enamel and dentine were possible in the majority of these tooth sections. Measurements of the spacings and angles to the enamel dentine junction (EDJ) of regular striae of Retzius and of equivalent markings in dentine were also made. In addition to these measurements, counts of perikymata were made on replicas of all other Proconsul teeth housed in the National Museum of Kenya, Nairobi, that preserved good perikymata on any aspect of their tooth surface. The sequence of crown formation in Proconsul and the crown formation times of the enamel and dentine were estimated from these data. In addition, the rates of root extension were estimated using the formula derived for this purpose by Shellis (Archs. oral Biol. 29, 697-705, 1984) and estimates of the total period of root formation subsequently made for premolar and molar teeth based on measurements of root length. A composite chart of dental development for P. heseloni is presented which suggests M3 root completion was between six and seven years of age. In general Proconsul molar teeth have high stria angles to the EDJ, a high ratio of enamel formed with respect of dentine formed at the same time, median values of rates of enamel formation close to the EDJ in excess of 4 microns per day and the occasional presence of "S-shaped" striae in the lateral enamel. There is no evidence to suggest that Proconsul from Rusinga Island, Kenya, had relatively thin enamel on molar or premolar teeth. When all of these data are considered in a comparative context, Proconsul emerges overall as hominoid-like in its enamel and dentine microstructure and as most similar to Pongo but with some features shared with Pan and Homo. Similar data for other Miocene primates will have considerable bearing on how these data are interpreted. These new data on dental microanatomy and on dental development in Proconsul make a further contribution to our understanding of the total morphological picture of this early Miocene primate.

Caroline Crachami, the Sicilian dwarf (1815-1824): was she really nine years old at death?

Caroline Crachami (C.C.) considered to have had the Seckel syndrome was one of the most extreme cases of dwarfism ever recorded. Reputedly born in Sicily in 1815, she attracted much attention when exhibited in England before her death on 3 June 1824. Although she is said to have been 9 years old at death, published descriptions give her a dental age varying from 2 to 7 years. Examination of her skull in the Royal College of Surgeons of England demonstrated a more or less erupted complete deciduous dentition, with no erupted permanent teeth. Radiographs showed agenesis of several permanent teeth. It was concluded that the dental age of C.C. was 3 years (+/- 6 months). Perikymata were evident in the surface enamel encircling the crown of the partially exposed maxillary left first permanent molar. Their distribution and spacing were normal, with no evidence of developmental retardation. The distance between the periradicular bands in the root near the cement-enamel junction was also normal. We conclude that the dental age of C.C. was similar to her chronological age and that at death she was about 3 and not 9 years old. The reason that she was said to be nearly 9 when exhibited in England we believe was related to financial considerations, as people would be generally less impressed with a dwarf only 3 years old. The new age we give C.C. has implications on the diagnosis of her medical condition.

Comparative observations on the spacing of short-period (von Ebner's) lines in dentine.

The spacing of short-period incremental markings in dentine was measured in longitudinal ground sections and in longitudinal demineralized silver-stained sections of permanent human canines and premolars. Measurements were made (i) within 50 microm from the granular layer of Tomes (GLT), (ii) between 100 and 200 microm from the GLT, and (iii) in the axial plane of the tallest cusps. Median values for the spacing of calcospheritic lines closest to the GLT in the ground sections increased from 1.8 to 2.8 microm as the lines gradually coalesced into a laminar pattern beyond the GLT pulpally. Median values for the spacing of short-period lines in the cuspal dentine, where dentine formation is known to be fastest, were 4.1 microm. Markings in the demineralized sections were between 25 and 39% closer together, presumably due to contraction and shrinkage during specimen preparation. The spacings of short-period incremental lines measured on ground sections of non-human primate dentine (gibbon, siamang, orang) and on pig dentine, all between 100 and 200 microm from the GLT, clustered between 2.5 and 3.5 microm. Apart from gibbon dentine (in which spacings were closer together in this position than in the others), the distribution of measurements was not significantly different in pig, orang or human dentine. However, none of the data for the comparative samples presented here revealed spacings of short-period lines anywhere close to the 16 microm previously reported for circumpulpal dentine in animals. These data suggest that there may be many other animals where the mode and, to some extent, rate of dentine mineralization close to the root surface follows a common pattern. While data for the spacing of incremental markings in dentine provide no evidence for their periodicity, it is clear that the measurements made in the ground sections match the reported daily rates of mineralization at these locations, whereas those in demineralized silver-stained sections do not. Tissue shrinkage is probably a better explanation for this than the generally accepted view that they represent 12 h increments of dentine mineralization. This study provides a better basis for identifying and describing these lines, and for distinguishing them from other kinds of incremental markings in dentine.

A comparison of two prophylaxis angles: disposable and autoclavable.

In a clinical trial, the authors evaluated the effectiveness of stain, plaque and debris removal, as well as patient and hygienist acceptance, of the disposable prophylaxis angle vs. the autoclavable prophylaxis angle. Thirty patients received a dental prophylaxis by hygienists for up to 45 minutes. A clinician performed blinded pre- and post-prophylaxis evaluations for stain, plaque and debris. A matched pairs t-test determined significant differences (P < .05) between groups. Significantly less stain, plaque and debris remained following use of the disposable vs. the autoclavable angle.