Dentin Regions Research Articles

Effect of hydrostatic pressure on regional bond strengths of compomers to dentine

Objectives: The aim of this study was to evaluate the effect of hydrostatic pressure on the regional bond strengths of compomers to dentine. Methods: Thirty freshly extracted molars were ground flat to expose the dentine and randomly divided into two groups for bonding: no hydrostatic pressure and hydrostatic pressure of 15 cm H 2O. Xeno CF, Dyract AP and F 2000 were applied to dentine surfaces pretreated by the respective bonding systems following the manufactures’ instructions, and then restored with Clearfil AP-X. After 24 h storage in water, the teeth were sectioned into 0.7-mm thick slabs and visually divided into three regional subgroups: the region communicating with the pulp through dentinal tubules (pulp horn); the region between the pulp horns (center); and the region between the pulp horn and DEJ (periphery). The specimens were trimmed to a cross-sectional area of 1 mm 2 and subjected to the micro-tensile bond test. The data were analyzed by one- and three-way ANOVA, and Fisher's PLSD ( p<0.05). Results: There were no significant regional differences of bond strengths for all the compomers tested ( p>0.05). However, hydrostatic pressure significantly decreased the bond strength of F 2000 to all regions ( p<0.05), while the bond strength of Dyract AP significantly decreased only at the pulp horn region ( p<0.05). On the other hand, the bond strengths of Xeno CF seemed not to be affected by hydrostatic pressure ( p>0.05). For Dyract AP and F 2000, the fracture modes were affected by hydrostatic pressure, while, for Xeno CF, there were no significant differences between the fracture modes with non- or positive hydrostatic pressure. Significance: Simulated pulpal pressure of 15 cm H 2O had a greater influence on the bond strengths of compomers to dentine than did dentine regions. Therefore, when measuring the bond strengths of compomers to dentine under the simulated in vivo conditions, the wetness of the dentine surface, as well as the intrinsic properties of each material should be seriously considered.

An electron probe x-ray microanalytical study of dentine minerals in sucrose-fed or glucocorticoid-medicated rats.

A high sucrose diet and glucocorticoid medication reduced dentine formation in molars of growing rats. This study was undertaken to determine whether the treatment schedules could have produced commensurate reductions in dentine minerals, and the particular concentrations of calcium (Ca) and phosphorus (P). Forty Spraque-Dawley rats were weaned at the age of 3 weeks. Tetracycline was injected i.p. to produce a fluorescent line which demarcated the preweaning from the postweaning dentine. The animals were then divided into two groups. Control rats were fed a commercial rat chow, test animals were fed a 43% sucrose diet. Half the animals in each group were also subjected to surgical implantation (s.c.) of cortisone pellets which released 0.42 mg into the circulation over a 24-hour period. At the end of the 6 week trials rats were killed and the mandibles were defleshed and prepared for electron probe microanalyzer. Each animal served as its own control, as the content of Ca, P, and total minerals were analyzed in the pre- and postweaning regions of dentine. During the preweaning there were no differences between the groups in any minerals. There was a slight reduction of minerals during the postweaning compared with the preweaning. During the postweaning, the sucrose diet significantly reduced the amount of Ca, P, and total minerals compared with the preweaning. During the postweaning, the sucrose diet reduced Ca compared with glucocorticoid medication and total minerals compared with other groups. On the contrary glucocorticoid medication seemed to compensate the reduction of minerals induced by the sucrose diet.

Microprobe analysis of teeth by synchrotron radiation: environmental contamination

An X-ray fluorescence set-up with microprobe capabilities, installed at the Laboratoire pour l’Utilisation du Rayonnement Électromagnétique (LURE) synchrotron (France) was used for elemental determination in teeth. To evaluate the influence of living habits in dental elemental composition nine teeth collected post-mortem were analysed, five from a miner and four from a fisherman. All teeth from the fisherman were healthy. From the miner some teeth were carious and one of them was filled with metallic amalgam. Teeth were sliced under the vertical plane and each slice was scanned from the root to the enamel for elemental profile determination. The synchrotron microprobe resolution was of 100 μm and incident photons of 18 keV energy were used. The elemental concentration values found suggest heterogeneity of the teeth material. Moreover, the distinct profiles for Mn, Sr, Br and Pb were found when teeth from the miner and from the fisherman are compared which can be associated with dietary habits and environmental influence. Higher concentrations of Mn and Sr were found for the fisherman teeth. In addition, Br was only observed in this group of teeth. Pb levels are higher for the miner teeth in particular for dentine regions. The influence of amalgam, such as, increase of Zn and Hg contents in the teeth material, is only noticed for the immediate surroundings of the treated cavity.

Characterization of enamel and dentin response to Nd:YAG picosecond laser ablation.

We investigated the main characteristics of human dental tissue under Nd:YAG picosecond laser ablation. The use of ultrashort laser pulses for teeth ablation prevents overheating and is an alternative for mechanical material removal; it also minimizes the volume of damaged material. Laser pulses of picosecond at 15 Hz repetition rates from a Q-switched and mode-locked Nd:YAG laser were focused on sound human molars for 30 seconds. Variation of light intensity in the pulse train allowed us to obtain drilled holes with different characteristics. Enamel and dentin surfaces were examined by optical and scanning electron microscope (SEM). The samples consisted of three sound human molars. The ablation rate was determined after taking an average of all samples. Images from the SEM showed an interesting contrast between the morphology of the ablated enamel and dentin regions. In enamel, the ablated region appears to be more superficial than in dentin. The dentin fragility normally causes cracks that originate in the ablated region. The ablation rates in both enamel and dentin demonstrate a saturation behavior as the laser intensity increases. Furthermore, the ablation rate in dentin is about eight times greater than in enamel for the same laser fluence. Our results show an important correlation between the surface morphology and the pulsed laser fluence, which is compatible to the ablation mechanisms presented when ultrashort laser pulses are used.

Nanoscale Correlation of Structure and Mechanical Properties of a Human Tooth

Abstract The human tooth is a functionally-gradient structural composite material composed of collagen and hydroxyapatite (HAP). The outer most region is a hard enamel layer consisting primarily of HAP. Underneath is dentin region, which is composed of HAP with a significant fraction of collagen fibers. It has been demonstrated that it is possible to perform nano-indentation on sub-micron regions of tooth using either a standard nanoindentor or modified cantilever type atomic force microscope tip (AFM). In this study, we report nano-mechanical properties of dentin and enamel regions of a human tooth, measured with a nanoindentor attached to an AFM using a vertical force, in correlation with the microstructures observed with TEM. TEM and nano-indentation samples were prepared from a juvenile human incisor tooth. The tooth was first sectioned into 1 mm thick slices along its length, each containing both dentin and enamel regions. A slice was taken to prepare a TEM sample and an adjacent slice was used for nano-indentation measurements.

A light microscopic and ultrastructural examination of calcified dental tissues on horses: 4. Cement and the amelocemental junction.

Ultrastructural examinations showed the diameter of cement lacunae to be greater in infundibular cement than in peripheral cement of upper cheek teeth, which in turn was greater than in the peripheral cement of the lower cheek teeth. However, numbers of lacunae/unit area remained similar in these 3 dentinal region. Two types of cemental hypoplasia were found in equine cheek teeth. The first type was termed central infundibular cemental hypoplasia and was confined to the central region of infundibular cement. The cement adjacent to these frequently large defects was very porous and contained large vascular channels. In recently erupted cheek teeth, these central infundibular cemental defects were filled with connective tissue. The size of these cemental defects, the relationships of such defects with the occlusal surface and the degree of porosity of cement surrounding these defects may be important in the development of cemental caries. The second type of cemental defect was found at the amelodentinal junction of both peripheral and infundibular cement and was termed junctional cemental hypoplasia and appeared as spaces varying from focal, to long narrow defects along the amelocemental junction with the adjacent cement of normal appearance. Peripheral cement was deposited both directly, i.e. on unresorbed or resorbed enamel surfaces or indirectly, where the cement was separated from enamel by a thin calcified layer. The surface of unresorbed enamel had a pitted appearance, with the bases of the pits formed by enamel prisms and the pit walls by interprismatic enamel. The cemental surface of resorbed enamel contained depressions of variable shapes and sizes. These depressions which are believed to be caused by the resorption of enamel by odontoclasts were both focal and diffuse and were more marked on the cemental surface of infundibular as compared to peripheral enamel.

Quantitative electron-spectroscopic diffraction (ESD) and electron-spectroscopic imaging (ESI) analyses of dentine mineralisation in rat incisors.

Primary crystal formations in all hard tissues are, according to our investigations, Ca-phosphate chains composed of nanometer sized particles (dots) which develop along the matrix macromolecules. In circumpulpal dentine the centre-to-centre distances between the dots inside the chains reflect the distances between the crystal nucleating sites ("active sites") along the collagen matrix macromolecule. The centre-to-centre distances at the surface of the mineralised collagen fibrils probably reflect the distances between nucleating sites of noncollagenous proteins attached to collagen. These needle-like chains of dots coalesce in lateral directions to form ribbon-like crystallites. The morphological results are supported by correlated small area diffraction studies in the same regions of dentine. We have found that the first appearing Bragg-reflection has a lattice spacing value of 0.388 nm, which corresponds to the (111) apatite value. For the earliest crystal formations the intensity of the (002) reflection is higher than that of the (300)-reflection. A maximum of the net-signal-intensity ratio of the (002) to (300) Bragg-reflection appears at the mineralisation front. This peak repeats with decreasing height 3 to 5 times with a distance range of about 8-16 microm through the whole dentine zone, which corresponds to the distances of the incremental lines, called "von Ebner lines".

Influence of human tooth cryopreservation on dentin bond strength

Objectives. The goal of this study was to evaluate the effects of cryopreservation of teeth on dentin bond strength as a function of remaining dentin thickness. Methods. Flat occlusal surfaces of human dentin were prepared in 54 freshly extracted teeth and 54 thawed, cryopreserved teeth. In each group, 18 bonds were performed in superficial dentin, 18 in mid-coronal, and 18 in deep dentin. A resin composite cylinder, 3 mm in diameter and in height, was bonded orthogonally to the surface. After storage in distilled water at room temperature for 1 wk, the bonded cylinders underwent shear testing at a crosshead speed of 0.5 mm min −1. The mean remaining dentin thickness was calculated after longitudinally sectioning the debonded samples through the center of the bonded area. Non-parametric statistical analyses were used to correlate the shear bond strength with the remaining dentin thickness among the storage modes and within the different dentin regions. Results. The lowest shear bond strength values were found in the deep dentin of both fresh and cryopreserved dentin, while the values in deep and mid-coronal dentin were not significantly different in fresh and cryopreserved dentin. In the superficial and mid-coronal dentin of cryopreserved samples, the shear bond strength values were identical. There was a significant difference between the shear bond strength values in the superficial dentin of fresh teeth compared to the values for cryopreserved teeth. Significance. According to the experimental conditions, tooth cryopreservation shows some promise as a substitute for freshly extracted teeth, provided that the experiments are performed in mid-coronal and deep dentin.

Enamel free areas in rodent molars--ultrastructure of basement membrane in rat tooth germ.

At the cusp tip of rodent molar, there is a region of dentin without an enamel cap. This region is called enamel free area (EFA). The surface collagen arrangement has been reported to differ between the EFA and the dentin covered with the enamel (DCE). To clarify the cause of this difference, we observed the ultrastructure of the basement membrane and the distal ends of the inner enamel epithelium (IEE) in rats. At 20 days prenatal, distal ends of IEE were relatively flat on both the DCE and EFA. Ultrastructurally, there was no difference between the basement membranes. At newborn, no marked changes were observed in the morphology of the distal end of IEE on the DCE or the EFA, but aperiodic microfibrils perpendicular to basal lamina were denser and longer on the DCE than the EFA. At 2 days postnatal, cytoplasmic extensions from distal end of IEE penetrated through basal lamina, and these extensions were more developed on the DCE than the EFA. On the DCE, collagen fibrils ran into and between cytoplasmic extensions and were arranged perpendicular to the surface. On the EFA, collagen fibrils ran parallel to the surface, and few collagen fibrils ran into and between cytoplasmic extensions. These findings suggested that the differences in the collagen arrangement between the EFA and DCE are associated with the developmental state of aperiodic microfibrils in the basal lamina beneath IEE and the morphology of the distal end of IEE.

Dissimilar Expression Patterns for the Extracellular Matrix Proteins Osteopontin (OPN) and Collagen Type I in Dental Tissues and Alveolar Bone of the Neonatal Rat

Osteopontin (OPN) is a phosphorylated, sialic acid containing glycoprotein that can be extracted from the mineralized extracellular matrix of bone. In the present study we determined the expression patterns of OPN in dental tissues and alveolar bone of 1–3 day old (neonatal) rats by means of 1) immunohistochemistry, 2) Northern blotting and 3) in situ hybridization. We compared these patterns with those of type I collagen.We localized collagen typeI expression in osteoblasts adjacent to alveolar bone and in odontoblasts lining predentin/dentin, but not in the epithelial ameloblasts. For OPN, we observed a weak antigenicity in predentin. Although generally no cellular immunostaining was found, very occasionally a minor immunoreactivity was detected in a small number of premineralizing incisor odontoblasts. On the mRNA level, however, no OPN transcripts could be detected in odontoblasts, either by in situ or by Northern hybridization analyses. Also the odontoblasts of the bone-like dentin (osteodentin) region in the tip of incisors were negative for OPN. In contrast, however, osteoblasts of alveolar bone showed strong positive signals with all three techniques, confirming the sensitivity and specificity of the detection methods.From the data obtained in this study, it can be concluded that during early stages of dentinogenesis OPN presumably is not expressed in developing rat tooth germs. The weak immunostaining observed sporadically in some young odontoblasts is probably due to resorption of OPN of non-dental origin entrapped in the predentin.

A scanning electron microscopic study on the distribution of peritubular dentine in cheek teeth of Cervidae and Suidae (Mammalia, Artiodactyla)

Distribution of peritubular dentine was studied in cheek teeth of fallow deer (Dama dama), roe deer (Capreolus capreolus) and wild boar (Sus scrofa). In the two cervid species, especially intense peritubular dentine formation was found in the outer regions of mid and cuspal coronal dentine. In these areas a marked asymmetry occurred, peritubular dentine being predominantly secreted onto the side of the dentinal tubule walls nearest to the dentinoenamel junction. Intensity and asymmetry of peritubular dentine formation decreased cervically. In root dentine, the walls of the dentinal tubules were covered with only a thin peritubular dentine layer of even thickness. Here, in contrast to peripheral coronal dentine, the volume of intertubular dentine far exceeded that of peritubular dentine. In porcine coronal dentine, PTD asymmetry, being of lesser extent than in cervids, was observed only in peripheral areas of cuspal and flank regions of the cheek teeth. Because peritubular is more highly mineralized than intertubular dentine, the relative volume of dentine made up from the two components has an important influence on dentinal wear resistance. The significance of variations in volume and distribution of peritubular dentine between different dentinal regions for achieving and maintaining a functional occlusal surface is shown for cervid cheek teeth. Our results suggest that dentinal structure (in addition to enamel structure) should be taken more into consideration when discussing occlusal surface morphology in herbi- and omnivores from a functional point of view.

Electron Probe X-Ray Microanalysis of Calcium and Phosphorus Distribution in Developing Hamster Tooth Germs in vitro and in vivo

The aim of the present study was to investigate the spatial distribution of Ca and P in dentin and enamel of developing first (M1) and second (M2) maxillary hamster molars (age: 3-5 days) in comparison with cultured molars. For culturing the germs were dissected from 3-day-old hamsters and incubated for 1 and 2 days, respectively, in a modified BGJb medium. Electron probe X-ray measurements were carried out on 3 regions extending in a vertical axis from cusp tip over cusp middle to cusp base next to the cervical loop region. Neither the in vivo nor the in vitro group was statistically different in the Ca and P concentration in the regions of dentin. In both groups the measurements in enamel showed a gradient with an increase in Ca and P from enamel surface towards dentin-enamel junction and a gradient with an increase from cusp base towards cusp tip. Direct comparison of the in vivo group with the in vitro group did not demonstrate a statistical difference between the mineral content of the 4-day-old germs and the 1-day culture germs, respectively the 5-day-old germs and the 2-day culture germs. The results indicate a high correspondence between the mineralization process of in vitro and in vivo tooth germ development.

X-ray microanalytical histochemistry of human circumpulpar and mantle dentine

An X-ray microanalytical histochemistry study was carried out, on thick sections observed under scanning electron microscopy, of five freshly extracted human premolars and five molars. In particular the circumpulpar and mantle dentine were examined to determine levels of calcium, phosphorus and sulphur, the basic elements involved in the process of biomineralization. Semiquantitative analysis was subsequently performed after the appropriate ZAF (Z, atomic number; A, absorption; F, secondary fluorescence) correction. Ca/P mass ratio was found to be similar for both regions in molars and slightly higher in circumpulpar dentine in premolars implying that this parameter is independent of the processes of biomineralization in the two dentinal regions. In contrast, statistically significant differences were recorded in sulphur content upon comparing mantle and circumpulpar dentine between premolars and molars ( P < 0.02). If sulphur, which has been associated with sulphated glycosaminoglycans (GAGs) decreases as mineralization progresses it would therefore seem reasonable to posit sulphur-rich areas in both topographical regions of the matrix—more significant in premolars than molars—able to undergo subsequent mineralization if required. The possible application of these findings in remineralization therapies is suggested.

Membrane structures in the pulp-dentin border zone. A freeze-fracture study of demineralized human teeth.

The membrane morphology of cells in the pulp-dentin border zone in human teeth was scrutinized by means of the freeze-fracture technique. The tissue was fractured and replicated after mild demineralization in Na-EDTA. This procedure did not seem to influence the preservation of the tissue significantly. The odontoblastic cell bodies and their long processes lying within the predentinal and dentinal tubules were exposed. The technique made it possible to analyze the structural features of the apical part of the odontoblastic layer, including the 'terminal bar' region. This area exhibited large, irregularly shaped gap junctions. In some regions clusters of many small membranous pits or caveolae apparently representing pinocytotic vesicles were seen. The odontoblastic process displayed membrane protuberances projecting outward and abutting the inner tubular wall. In the predentinal and the adjacent dentinal regions, fine-caliber fibers (approximately 0.1-0.4 micron in diameter), presumably nerves, appeared in intimate relationship with the odontoblastic cell processes. At these sites the cell membrane displayed aggregations of membrane-associated particles, presumably gap junctions.

Membrane structures in the pulp-dentin border zone

The membrane morphology of cells in the pulp-dentin border zone in human teeth was scrutinized by means of the freeze-fracture technique. The tissue was fractured and replicated after mild demineralization in Na-EDTA. This procedure did not seem to influence the preservation of the tissue significantly. The odontoblastic cell bodies and their long processes lying within the predentinal and dentinal tubules were exposed. The technique made it possible to analyze the structural features of the apical part of the odontoblastic layer, including the ‘terminal bar’ region. This area exhibited large, irregularly shaped gap junctions. In some regions clusters of many small membranous pits or caveolae apparently representing pinocytotic vesicles were seen. The odontoblastic process displayed membrane protuberances projecting outward and abutting the inner tubular wall. In the predentinal and the adjacent dentinal regions, fine-caliber fibers (approximately 0.1-0.4 μm in diameter), presumably nerves, appeared in intimate relationship with the odontoblastic cell processes. At these sites the cell membrane displayed aggregations of membrane-associated particles, presumably gap junctions.

The ultrastructure of dentinal tubules from erupted human premolar teeth.

Different regions of crown dentin from erupted human premolars were examined ultrastructurally to determine the contents of the dentinal tubules. Odontoblast processes were limited to inner dentin, and nerve fibers were not observed in any tubules examined.

Making earthwatch work

In the present study, we investigated the fusion process between amorphous microparticles of the calcium salt of the physiological polymer comprising orthophosphate units, of inorganic polyphosphate (polyP), and enamel.This polymer was incorporated as an ingredient into toothpaste and the fusion process was studied by electron microscopy and by synchrotron-based X-ray tomography microscopy (SRXTM) techniques.The data showed that toothpaste, supplemented with the amorphous Ca-polyP microparticles (aCa-polyP-MP), not only reseals tooth defects on enamel, like carious lesions, and dentin, including exposed dentinal tubules, but also has the potential to induce re-mineralization in the enamel and dentin regions. The formation of a regeneration mineralic zone on the tooth surface induced by aCa-polyP-MP was enhanced upon exposure to artificial saliva, as demonstrated by SRXTM. Energy dispersive X-ray analysis revealed an increase in the calcium/phosphorus atomic ratio of the enamel deposits to values characteristic for the particles during the treatment with polyP applied in the toothpaste, indicating a fusion of the particles with the tooth mineral.Our results suggest that toothpaste enriched with aCa-polyP-MP is a promising biomimetic material for accelerating enamel and dentin restoration.

An Autoradiographic Study of the Sensory Innervation of Teeth. I. Dentin

Autoradiography of axoplasmically transported proteins revealed that the coronal dentin of rat molar teeth receives sensory innervation from the trigeminal ganglion. The labeled processes appear to run in dentinal tubules and sometimes reach the peripheral dentinal region near the enamel.