Outer Enamel Surface Research Articles

Effect of light energy on peroxide tooth bleaching

Light-activated bleaching is a method of tooth whitening. The authors conducted a study to compare the whitening effects and tooth temperature changes induced by various combinations of peroxide bleaches and light sources. The authors randomly assigned 250 extracted human teeth halves into experimental groups (n = 10). A placebo gel (control), a 35 percent hydrogen peroxide or a 10 percent carbamide peroxide bleach was placed on the tooth surface and was irradiated with no light (control); a halogen curing light; an infrared, or IR, light; an argon laser; or a carbon dioxide, or CO2, laser. Color changes were evaluated immediately, one day and one week after treatment using a value-oriented shade guide and an electronic dental color analyzer. The outer enamel and inner dentin surface temperatures were monitored before and immediately after each 30-second application of light using a thermocouple thermometer. Color and temperature changes were significantly affected by an interaction of the bleach and light variables. The application of lights significantly improved the whitening efficacy of some bleach materials, but it caused significant temperature increases in the outer and inner tooth surfaces. The IR and CO2 laser lights caused the highest tooth temperature increases. Dentists performing an in-office bleaching technique with the use of an additional light source to accelerate tooth whitening should consider the specific bleaching agent being used, as well as the potential risks of heating teeth. A specific combination of bleach and light that demonstrates good color change and little temperature rise should be selected for in-office tooth bleaching.

Morphometrical Study of the Dentino-enamel Junction of the Labial Surface of the Maxillary Central Incisor

The labial surface of the upper central incisor has mesial and distal marginal ridges, and these vary in form and development. We measured the height of the labial marginal ridges of the upper central incisors, which had double-shovel (DS) and no double-shovel (NDS) on the outer enamel surface (OES) and dentino-enamel junction (DEJ) using a 3D scanner. Enamel thickness of the labial surface was also measured in these specimens. Mesiodistal and buccolingual diameters on both OES and DEJ were measured for the comparison of OES and DEJ structures. We obtained the following results ; 1. On the DEJ, DS incisors had more sharp and clear ridges than on the OES. 2. The mesial marginal ridge (MMR) was significantly higher than the distal marginal ridge (DMR) on both OES and DEJ of DS incisors. 3. There were no significant differences of the enamel thicknesses at the three points of the labial surface, such as mesial and distal marginal ridges and the central ridge. 4. The enamel thickness of the DS was significantly thicker than that of the normal incisor at the center of the labial surface, the average of which was 0.91 mm in DS and 0.73 in NDS incisors. 5. No significant differences of both mesiodistal and buccolingual diameters of OES and DEJ were found between averages of NDS group and DS group. 6. Both mesiodistal diameter and buccolingual diameter on OES had a strong correlation to the corresponding diameters on DEJ. The enamel substance at the central labial surface of the DS was significantly thicker than that of the NDS, and marginal ridges in DS observed in OES were clearer and more developed in the DEJ, which was an anatomical base for crown development.

Microhardness and chemical composition of human tooth

Hardness of human tooth, both in enamel and dentin, has been measured at different sites using a Vicker's diamond. In this work we show that these values are almost constant all along the enamel and dentin thicknesses. Indentations were done from outer enamel surface to inner dentin layer, going through the enamel-dentin junction, both in transverse and longitudinal samples. Geometrical well-shape indentation uniformity was checked both with light and with scanning electron microscopes, and the chemical composition of the tooth was analyzed with characteristic X-ray energy dispersive spectroscopy. Hardness measurements were in the range from 270 to 360 VHN for enamel and 50 to 60 VHN for dentin. Cervical zone in longitudinal section showed the lowest value while in transverse sections the highest. All the hardness values were statically significative. Tour results indicate that the difference between enamel and dentin hardness has nothing to do with the content of Na, Cl and Mg, but the percentage of organic and inorganic materials in enamel and dentin.

A three-dimensional analysis of enamel distribution patterns in human permanent first molars

The morphology of the enamel cap and the thickness of the enamel of human molars are regarded as closely related to function. Previously, enamel thickness has been studied in specific sections only, not the distribution patterns of the entire crown. Here, the three-dimensional distribution pattern of the enamel of human permanent first molars was examined with a newly developed system. A distinctive pattern of enamel thickness common to all the individuals examined was found, regardless of the variation in absolute enamel thickness among individuals. It was confirmed that the lingual faces of upper molars and the buccal faces of lower molars have thicker enamel than the other crown faces. Moreover, in lower molars, enamel was significantly thicker at the hypoconid than at the protoconid crown face. The distal face tended to exhibit thicker enamel than either mesial or lingual faces, owing to the thicker hypoconulid enamel. It is suggested that the gradients of thickness within a molar are not necessarily manifested according to direction, but are the result of cusp-specific patterning. The distribution of enamel in the occlusal fovea was found to correspond to the morphology of the outer enamel surface, with the exception of the distinctly thin enamel at and near the tip of the mesiobuccal cusps in both upper and lower molars. The thickness of the enamel in that region might therefore be related to developmental timing or the topography of the enamel–dentine junction, rather than to functional demand. When viewed from a whole-crown, three-dimensional perspective, enamel thickness patterns are in part, but not entirely, explained as an adaptation to functional demand.

Mechanical properties of in situ demineralised human enamel measured by AFM nanoindentation

Diet-induced demineralisation is one of the key factors in surface changes of tooth enamel, with soft drinks being a significant etiological agent. The first step in this dissolution process is characterised by a change in the mechanical properties of the enamel and a roughening of the surface. The objective of this pilot study was to measure early stages of in situ induced hardness changes of polished human enamel surfaces with high accuracy using a nanoindenter attached to an atomic force microscope (AFM). Human unerupted third molars were cleaned, sterilised with sodium hypochlorite, sectioned and embedded in epoxy resin. The outer enamel surface was polished and the samples partly covered with a tape, allowing a 2-mm-wide zone to be exposed to the oral environment. Samples were fitted in an intra-oral appliance, which was worn from 9 a.m. to 5 p.m. for one day. During this time the volunteer sipped 250 ml of a drink over 10 min periods at 9.00, 11.00, 13.00 and 15.00 h. Three different drinks, mineral water, orange juice and the prototype of a blackcurrant drink with low demineralisation potential were used in this study. At the end of the experiment the samples were detached from the appliance, the tape removed and the surfaces chemically cleaned. The surface hardness and reduced Young's modulus of the exposed and unexposed areas of each sample were determined. In addition, high resolution topographical AFM images were obtained. This study shows that by determining the hardness and reduced Young's modulus, the difference in demineralisation caused by the drinks can be detected and quantified before statistically significant changes in surface topography could be observed with the AFM. The maximum decrease in surface hardness and Young's modulus occurred in the samples exposed to orange juice, followed by those exposed to the blackcurrant drink, while exposure to water led to the same values as unexposed areas. A one-way ANOVA showed a statistically significant difference between the changes in hardness for the drinks at a 95% confidence level ( p=0.0000), while a Kruskal–Wallis test proved a statistically significant difference between the changes in the reduced Young's modulus at a 95% confidence level ( p=0.0000). Thus, it was possible to detect differences in demineralisation potential in an in situ study at a very early stage. Further investigations with greater subject numbers and a larger quantity of samples are necessary to fully evaluate the potential of this method.

Determination of some trace elements in human tooth enamel.

Determination of seven elements (Cu, Fe, Mg, Mn, Pb, Sr and Zn) in whole enamel and surface layers of extracted non-carious human teeth by FAAS, ETA AAS, ICP-AES and ICP-MS (Pb) is demonstrated. Techniques are described for obtaining whole enamel and its acid dissolution. Fifty microm width enamel layers from outer enamel surface to a 200 microm depth were successively etched in 1 mL of 3 M HClO4 for 3 min dissolution periods. Enamel samples were analyzed for populations under and over 20 years of age and enamel from Bronze Age teeth. Concentrations of microelements in the whole enamel and in the first surface layer (50 microm depth) were compared. With exception of Sr and Mg, all elements show significantly higher concentrations in the first layer than in whole enamel and higher concentration in teeth of individuals over 20 years, which demonstrate the cumulative effect of these elements. The Cu, Fe, Mn, Pb and Zn concentrations in four layers of erupted and non-erupted teeth decreased while Mg and Sr concentrations increased toward enamel-dentine junction. The concentrations of most elements were almost constant as they approached the 150 microm layer. This concentration gradient may result from interaction between saliva and teeth and supports the hypothesis that the surface de- and re-mineralization process is effective at most to 150 microm from the enamel surface.

X-ray microtomographic study of mineral distribution in enamel of mandibular rat incisors.

X-ray microtomography was used to study the mineral concentrations in sequential slices of enamel of 5 mandibular incisors which showed an increase from approximately 1.0 to approximately 2.7 g cm(-3) from the apex towards the incisal end. For points at the same distance from the apex, there were differences up to 0.6 g cm(-3) between the teeth. The change of mean concentrations in the slices with distance could be modelled as (different) saturating exponentials. Under the assumption of a uniform growth rate of a mandibular incisor of 0.6 mm per day and a common time origin for the start of maturation (taken as a mineral concentration of 1 g cm(-3)), the distances were transformed to a common time frame to give a pooled data set. A single saturating exponential could be fitted to this pooled transformed data; this was: Cm = 2.84-1.94exp (-0.18d) where Cm is the mean mineral concentration (g cm(-3)) and d the time (days) from the start of maturation. This gives an asymptotic concentration of 2.84 g cm(-3) towards the incisal end, with a time constant of 7.7 days. The mineral concentration distribution functions were found to be more positively skewed closer to the apex, but more negatively skewed towards the incisal end. The difference between the higher mineral concentration in the outer enamel and the enamel near the amelodentinal junction (ADJ) was approximately 3%. The direction of maximum increase in concentration from the outer enamel surface to the ADJ meets the boundary of the ADJ at approximately 80 degrees. Three dimensional surface rendering of isodensity contours showed that the previously described C-shaped pattern of mineralisation is not solely a surface phenomenon, but extends through the depth of the enamel.

Tooth enamel structure in the hyaenid Chasmaporthetes lunensis lunensis from the Late Pliocene of Italy, with implications for feeding behavior

ABSTRACT Hunter-Schreger Bands (HSB) and the outer enamel surface of the teeth of the hunting hyena Chasmaporthetes lunensis lunenesis Del Campana, from Olivola (late Pliocene, Italy) has been analysed. As in the bone crushing hyenas (Crocuta, Hyaena, and Pachycrocuta) C. I. lunensis possesses complex HSB, with both horizontal and vertical components. However the less intense folding of the HSB and the smooth outer enamel surface suggest a more primitive structure than that in the bone crushing hyenas. This is consistent with the hypothesis that Chasmaporthetes was not an extremely specialized bone eater.

下顎第2乳臼歯エナメル象牙境の形態学的研究

Morphologies of the DEJ which might have phylogenetically primitive characters are important for understanding the phylogeny of the human teeth. Morphological traits on the outer enamel surface (OES) can be observed clearly on the dentino-enamel junction (DEJ) as a distinct ridge or a process even if they are not distinct on the OES. We observed ten characters on the OES and DEJ of lower second deciduous molars (m2), and examined significant differences of these frequencies between the DEJ and OES. We also compared the frequencies of occurrence with the lower permanent first molar (M1) and searched for morphological relationship among four surfaces by distance analysis.The following results were obtained;1. On the buccal surface of m2, frequencies of occurrence of characters on the DEJ were almost higher than on the OES. And on the DEJ, frequencies of occurrence of the buccal marginal ridge (mesial) and protostylid of the m2 were higher than in M1.2. On the occlusal surface of the DEJ of m2, frequency of occurrence of metaconid distal accessory tubercle forming the seventh cusp was higher than on the OES. Frequencies of occurrence of the middle trigonid crest, distal trigonid crest, sixth cusp, seventh cusp and mesial accessory tubercle of the m2 were higher than in M1.3. The distance analysis indicated that there was a strong resemblance between the DEJ of m2 and of M1, and between the OES of m2 and of M1. This study suggested that the frequencies of primitive crown characters were retained most in the DEJ of the m2 among four surfaces in the m2-M1 series.

Spatial Distribution of Naturally Occurring 210Po and 226Ra in Children's Teeth.

Deciduous and permanent teeth extracted from juveniles for orthodontic purposes have been analysed using α-sensitive plastic track detectors for the spatial distribution of total α-activity and naturally occurring 210Pb-supported 210Po and 226Ra. The distribution of these radionuclides is nonuniform, with 210Po being primarily associated with outer enamel and 226Ra with the pulp. The observations suggest that 210Pb/210Po concentrates at the interface of enamel with saliva or blood, by means of unidirectional ionic exchange with calcium. In contrast, 226Ra concentrates in the predentine band at the interface with pulp and with systemic blood circulation, where its uptake is permitted by the incomplete calcification in this band. Activity concentration was measured in 900 teeth. Total concentration on the outer enamel surface of deciduous teeth, permanent teeth from children ⩽10 years and permanent teeth from children > 10 years give respective mean values of 8·63±0·26, 5·76±0.48 and 7·00±0·15 Bq kg-1. 226Ra concentration on the corresponding longitudinal sections comprising pulp, dentine and annular enamel give respective mean values of 0·715±0·055, 0·418±0·083 and 0·514±0·029 Bq kg-1. Mean activity concentration in 32 foetal teeth was 2·05±0·31 Bq kg-1. The results form the basis of more detailed studies of (1) age-dependent uptake of α-radionuclides in teeth and their microdistribution, and (2) the geographical variation in activity concentration with respect to environmental factors such as domestic radon exposure.

Orientational micro-Raman spectroscopy on hydroxyapatite single crystals and human enamel crystallites.

Single crystals of synthetic hydroxyapatite have been examined by orientational micro-Raman spectroscopy. The observed Raman bands include the PO4(3-)/OH-internal and external modes over the spectral range from 180 to 3600 cm-1. The Raman-active symmetry tensors (A, E1, and E2) of crystal-class C6 have been assigned to these bands. Intensities of the Raman bands are invariant to the orientation of the a- or b-axis of a single crystal, but depend solely on the c-axis orientation. Changes in the spectral profile thus reflect changes in the c-axis orientation, which, with respect to the known excitation/observation coordinates, can be determined through the angular dependencies of Raman bands due to A and E2 symmetries. The useful bands are those of the PO4(3-)v4 vibrational mode, which contains relatively well-defined bands due to E2 (581 cm-1) and A (593 cm-1) symmetries. A preliminary Raman study on crystallites near the intact outer surface of human enamel has also been carried out. Strong orientational dependencies similar to those of hydroxyapatite single crystals have been observed among the bands in enamel spectra. This suggests that the crystallites in the region investigated are highly oriented. The results were consistent with an averaged orientation of the crystallite c-axis being perpendicular to the outer surface.

Comparison of three lasers on dental pulp chamber temperature change.

Previous studies have reported dental pulp chamber temperature changes using only one beam size per laser. This study was designed to evaluate the effects of beam size, wattage, and energy density on pulp chamber temperature changes of extracted human teeth for three lasers (CO 2, Argon, Nd:YAG). During laser irradiation of the outer enamel surface, a thermocouple was placed in the pulp chamber which measured and recorded the temperature changes. This was done for each combination of lasing dosimetry parameters. In all cases the recorded temperatures increased with the increase in beam size for a given energy density (J/cm 2) and wattage. Also, the recorded temperatures increased with increased energy density for a given wattage and beam size.

Comment on the new maxillary finds from Klasies River, South Africa

The morphology and variability of the Middle Stone Age (MSA) hominin fossils from Klasies River Main Site have been the focus of investigation for more than four decades. The mandibular remains have figured prominently in discussions relating to robusticity, size dimorphism, and symphyseal morphology. Variation in corpus size between the robust SAM-AP 6223 and the diminutive SAM-AP 6225 mandibles is particularly impressive, and the difference between the buccolingual diameters of their M2s significantly exceeds recent human sample variation. SAM-AP 6223 and SAM-AP 6225 are the only Klasies specimens with homologous teeth (M2 and M3) that permit comparisons of crown morphology. While the differences in dental trait expression at the outer enamel surfaces of these molars are slight, diffeomorphic surface analyses of their underlying enamel-dentine junction (EDJ) topographies reveal differences that are well beyond the means of pairwise differences among comparative samples of Later Stone Age (LSA) Khoesan and recent African homologues. The EDJs of both SAM-AP 6225 molars and the SAM-AP 6223 M3 fall outside the envelopes that define the morphospace of these two samples. Although the radiocarbon dated LSA individuals examined here differ by a maximum of some 7000 years, and the two Klasies jaws may differ by perhaps as much as 18,000 years, it is difficult to ascribe their differences to time alone. With reference to the morphoscopic traits by which the SAM-AP 6223 and SAM-AP 6225 EDJs differ, the most striking is the expression of the protoconid cingulum. This is very weakly developed on the SAM-AP 6223 molars and distinct in SAM-AP 6225. As such, this diminutive fossil exhibits a more pronounced manifestation of what is likely a plesiomorphic feature, thus adding to the morphological mosaicism that is evident in the Klasies hominin assemblage. Several possible explanations for the variation and mosaicism in this MSA sample are discussed.

Secondary caries in situ around fluoride-releasing light-curing composites: a quantitative model investigation on four materials with a fluoride content between 0 and 26 vol%.

In the literature, secondary caries around composite restorations is reported often. Fluoridated composites are therefore interesting materials because they might reduce or inhibit secondary caries. In this article an in situ model investigation is presented in which the effect of F-releasing composites on enamel demineralisation around an artificial gap of 200 microns width was quantified after 1 month. The fluoride content of the composites varied between 0 and 26 vol%. The beneficial effect of the fluoride released was larger in the gap than at the outer enamel surface. In the gap, all fluoridated composites reduced the enamel demineralisation statistically significantly with respect to the non-fluoridated control. Microradiography showed a reduction of lesion depth values of 27-45%, and a reduction of mineral loss values of 25-56%. At the outer enamel surface next to the artificial gap, a beneficial fluoridation effect was measurable only near the most fluoridated composite. The results indicate that fluoridated composites may play a role in the future prevention of secondary caries.

A conservative postorthodontic treatment of enamel stains

The purpose of this presentation is to describe a method used to remove or improve superficial stains in the enamel including mild decalcification present before and after orthodontic therapy. This procedure 1,2 is only successful in the treatment of stains involving the outer enamel surface and is not effective for treating generalized pigmentation of the enamel and/or dentin. A step-by-step approach for the removal of the superficial enamel stains is presented.

Crystal growth on the outer enamel surface—An alternative to acid etching

Over the past 2 years an increasing concern has developed about the possible iatrogenic effects of phosphoric acid-etch bonding techniques on the enamel surface. There is an evident heed to develop a mechanical or chemical retention system that would not alter (or would minimally alter) the outer enamel surface. An alternative to the conventional phosphoric acid etch technique has been developed. A preliminary clinical trial showed promising performance under normal clinical conditions. These results were achieved with a minimal loss of surface enamel as evidenced by scanning electron microscopy. Debonding and cleanup were greatly facilitated. Creating a micromechanical retentive surface by the formation of a crystalline interface is a potential alternative to phosphoric acid etching.

Pre-eruptive protein-energy malnutrition and acid solubility of rat molar enamel surfaces

Rat dams were fed diets containing either 8 or 25 per cent protein during lactation. Owing to a 1-day difference in molar eruption, pups were killed on either day 17 or 18. The first and second maxillary molars were dissected out and were acid-treated in a sealed plastic chamber through which 10 mM acetic acid (pH 4.5) flowed at a constant rate. Fractional collections were made over 1 h and analysis of Ca, P and F made to evaluate acid solubility. Mineral dissolution in the 8 per cent group, compared to the 25 per cent protein group, was increased in the following proportions: Ca 25.5 per cent, P: 17.'6 per cent, F: 5.8 per cent. The enamel dissolved from molars of rats in the 8 per cent protein group showed a high Ca:P ratio. The increase in acid solubility due to differences in chemical composition of the outer enamel surface may contribute to the increase in caries susceptibility associated with protein-energy malnutrition.

A mechanism for dental caries based on chemical processes and diffusion phenomena during in-vitro caries simulation on human tooth enamel

Artificial carious lesions were produced in a range of lactate buffers containing disodium-methane-hydroxy-diphosphonate and the depths of the lesions were measured. The depth of the body of the lesion depended on the calculated concentration of un-ionized lactic acid (HL), and the innermost boundary depended on HL concn. and pH. Apparent diffusion coefficients of the order 10 −10cm 2/s were calculated from the boundary movement. A mechanism is proposed for the caries process. Diffusion, predominantly of the un-ionized chemical species HL, H 3PO 4, CaHPO 4, Ca(H 2PO 4) 2 and CaL 2 occurs through the intercrystalline and interprismatic pores of enamel filled with water and protein. Dissolution takes place throughout the lesion by H + and L − as HL dissociates. The outer enamel surface is partly protected by reversible adsorption of suitable chemical species.

An Evaluation of Primary Enamel Pretreatments and Their Effects on Resin Retention

The effects of various enamel pretreatments on bond strengths between primary enamel and resin were investigated. Pretreatments included: removal of the outer enamel surface, varied exposure to phosphoric acid, and the use of an organic coupling agent. Results indicated highest bond strengths utilizing acid pretreatments and an organic coupling agent.

Electron probe analysis of human teeth: [formula omitted] ratios in incipient carious lesions

The electron probe has been used to study the distribution of calcium and phosphorus in incipient carious lesions in human teeth. The findings indicate that the outer surface layer of natural white spot lesions of enamel may contain either greater or lesser amounts of mineral than the outer surface of adjacent non-carious enamel. The average Ca P ratio over the entire lesion was found to be essentially normal. There appears to be a redistribution of calcium and phosphorus in the subsurface zone of decalcification with extreme losses adjacent to hypermineralized areas. The Ca P ratio was always lower than normal in the hypermineralized areas because of excess phosphorus, whereas in the hypomineralized areas the Ca P ratio was high because of low phosphorus.