Enamel Sections Research Articles

A study on the degree of conversion of light curing composite resin according to the thickness of tooth structure penetrated by light and applied light curing time

Physical properties of composite resins such as strength, resistance to wear, discoloration, etc depend on the degree of conversion of the resin components. The purpose of this study was to evaluate the degree of conversion of the composite resins according to the thickness of tooth structure penetrated by light and applied light curing time. The coronal portions of extracted human teeth (one anterior tooth, three posterior tooth) was embedded by pink denture material. the mounted teeth were cut into three illumination sections (1mm thickness enamel section, 1mm thickness dentin section, 2mm thicknes dentin section) and one backing section with cutting wheel. Thin resin films were made by using 6kg pressure between slide glass during 5 minutes Thin resin film was light cured on coupled illumination section during 40sec, 80sec and 120sec. each illumination section was coupled as follows; no tooth structure(X), ename section(E), enamel section + 1mm dentin section(ED1), enamel section + 2mm dentin section(ED2), enamel section + 1mm dentin section + 2mm dentin section(EDD). To simulate the clinical situation more closely, thin resin films was cured against a backing section of tooth structure. The degree of conversion of carbon double bonds to single bonds in the resin films were examined by means of Fourier Transform Infrared Spectrometer. The results were obtained as follows ; 1 As curing time was increased, conversion rate was increased and as tooth thickness which was penetrated by curing light was increased, conversion rate was decreased. 2. At all tooth thickness groups, conversion rate between 80sec and 120sec was not significantly increased(P＞0.05). 3. At 40sec group and 80sec, conversion rate between no tooth structure(X) group and 1mm enamel section(E) group was not significantly decreased(P＞0.05). 4. At 80sec group and 120sec, conversion rate between 1mm enamel section(E) group and 1mm enamel section + 1mm dentin section(ED1) group was not significantly decreased(P＞0.05).

Enamel Lead Biomarker for Prenatal Exposure Assessment

The development of the enamel biomarker for heavy metal exposure assessment is designed to improve studies of dose–effect relationships to embryonic anomalies, particularly neurotoxic dysfunction. This report documents initial demonstrations of ambient lead (Pb) relative to calcium (Ca) in histological cross sections of deciduous tooth enamel of three human subjects, by use of ion mass spectrometry. The goal of this research was to measure Pb and Ca in tooth enamel for use as a temporal biomarker in assessing prenatal and postnatal exposure. This involves measurement of these heavy metals in enamel at high spatial resolution along histological transects following the temporal pattern of enamel growth. The technique may be applied when completely developed to cross-sectional and longitudinal research.

Measurements of Manganese with Respect to Calcium in Histological Enamel Cross Sections: Toward a New Manganese Biomarker

Airborne Mn may become an important route of exposure if the use of Mn-containing gasoline additives becomes more widespread. We report on the measurement of manganese and calcium in histological cross sections of shed deciduous tooth enamel of three human subjects. The goal of this research was to measure Mn in tooth enamel for use as a biomarker in assessing manganese exposure in cross-sectional and longitudinal studies. The histological locations can be time-specific (analogous to examining growth rings in trees). This technique, which may identify critical windows of exposure, can be important for evaluating potential vulnerability of the fetus and neonate to inhaled or ingested Mn.

A continuous culture biofilm model of cariogenic responses.

To validate an in vitro model for the analysis of physiological and ecological responses to sugar challenge in bacterial populations, and subsequent changes in enamel mineralization. A seven-organism bacterial consortium was grown in a biofilm mode on enamel and hydroxyapatite (HA) surfaces in a continuous culture system and exposed to repeated sucrose challenges. This produced 'pH-cycling' conditions within the system. Populations on HA surfaces were enumerated. Changes in relative proportions of the different populations, and in the total viable count, were observed, between different treatments. Microradiography of the enamel sections showed increasing demineralization with increasing sucrose concentration. The lesions formed were similar to 'white-spot' lesions found in vivo. Differences in the quality of biofilms formed were also observed using Confocal Laser Scanning Microscopy. An in vitro model has been validated for the analysis of both physiological and ecological responses to sucrose challenges in bacterial populations, and subsequent changes in enamel mineralization. This model should facilitate the study of changes in bacterial populations in response to application of putative anticaries agents and concomitant changes in enamel mineralization.

Effect of Tooth–Bound Fluoride on Enamel Demineralization/ Remineralization in vitro

The effect of tooth–bound fluoride (F) on enamel caries formation was investigated under the condition that loosely bound F was essentially absent. Eighteen thin enamel sections, prepared from the lingual or buccal surfaces of extracted human molars, were embedded in acrylic resin with the enamel surfaces exposed. The sections were placed in a pH 7 remineralizing solution (RS; 1.2 mmol/l Ca, 0.72 mmol/l P, 30 mmol/l KCl, 50 mmol/l HEPES) for 5 days, and were randomly divided into 3 groups: (1) control group that received no treatment, (2) acidulated phosphate fluoride (APF) group that received 5 cycles of a 4 min treatment with APF gel followed by immersion in the RS for 2 days (RS changed daily) and (3) dicalcium phosphate dihydrate (DCPD) – APF group that received 5 cycles of a 4–min pH 2.1 DCPD–forming solution followed by 4 min APF gel and then placed in the RS for 2 days. After the treatment cycles, the sections were washed in a constant composition F titration system to remove loosely bound F. An in vitro model, which consisted of cycles of de– (6 h) and remineralization (18 h) each day for 5 days, was used to produce caries–like lesions in the specimens. The ΔZ (mineral loss) values, measured by quantitative microradiography, of the lesions formed in the three groups were (mean ± standard deviation; n = 6) 91.2±12.3 Ìm for the control group, 41.3±10.1 Ìm for the APF group and 21.2±4.8 Ìm for the DCPD–APF group. The same system produced lesions in untreated shark enamel with a mean ΔZ of 4.4±0.3 Ìm (n = 12). One–way fixed–effects ANOVA indicated that mineral loss was significantly different among the different groups (p<0.05). The results showed that enamel resistance to lesion formation increased with increasing tooth–bound F content. Shark enamel was much more resistant to demineralization than human enamel.

Enamel demineralization under driving forces found in dental plaque fluid.

The present study was carried out to examine the kinetics of enamel demineralization in vitro under driving forces for demineralization (i.e., the degree of saturation with respect to enamel, DS(En)) similar to those found in dental plaque fluid. Thin sections of human enamel were exposed at 25 degrees C to lactic acid solutions with DS(En) values (DS(En) = [(Ca2+)5(OH-)(PO4(3-))3/K(En)]1/9; K(En) = 5.5 x 10(-55)) ranging from 0.28 to 0.79. Lesion development was monitored by quantitative microradiography. Enamel mineral loss in solutions with DS(En) values of 0.28, 0.32 and 0.36 was first detected after 3, 3, and 7 wk of continuous exposure, respectively. Consistent with previous findings, subsurface demineralization was observed and rates of mineral loss increased significantly with decreasing DS(En) values. However, no mineral loss was observed in sections of enamel exposed to solutions with DS(En) values of 0.41 and 0.79, even after 11 months. These results suggest that (outer) enamel mineral behaves as a mineral phase that is less soluble than that dictated by the solubility product constant (K(En)) used in this study. Furthermore, these results indicate that the kinetics and general features of the demineralization process are maintained over a wide range of DS(En) values, including conditions that better reflect those found in the oral cavity. These findings are particularly relevant to the assessment of the cariogenic potential of dental plaque fluids.

Detailed Mass Spectrometric U-series Analyses of Two Teeth from the Archaeological Site of Pech de l'Aze II: Implications for Uranium Migration and Dating

We report Th/U ages obtained by thermal ionization mass spectrometry of cross-sections of two teeth from the archaeological site of Pech de l'Aze II. The aim of this study is to reconstruct the pathways and time dependency of uranium uptake into different constituents of the two teeth. A previous ESR dating study of the two teeth yielded age estimates in the range of about 130,000 to 200,000 years, which was in agreement with the geological assignment of Riss for layers from which the specimens were recovered. The closed system U-series ages of all analyses range from 48 to 137ka, thus yielding age-estimates which are between 30 and 90ka too young. The apparent closed system U-series ages of the dentine and cement fractions at the top of the teeth are the oldest, becoming gradually younger towards the interior of the two teeth. The difference between apparent U-series ages of dentine at the outer and inner parts of the two teeth is about 35ka. The enamel sections show the same patterns in U concentration and progression of apparent Th/U ages as the adjacent dentine samples, but with generally younger ages. Our results indicate that uranium migrates both from the top and the base into the dentine of the teeth and from there into the adjacent enamel. Depending on the position of the sample, significant uranium uptake appears to have taken place over many tens of thousands of years. Modelling the U-uptake histories using a parametric model shows that, for the cement and dentine components, uptake is intermediate between linear uptake (LU) and early uptake (EU=closed system). The enamel, although often assumed to approximate more closely a closed system, shows evidence of more recent U uptake. These results also imply that it is not possible to use a simple, single parameter U-uptake model for all components of a given tooth, either for U-series or ESR dating.

Kinetics of enamel demineralization in vitro.

Previously, we reported that the rate (R) of hydroxyapatite dissolution in acetic, lactic, and phosphoric acid solutions is a function of the degree of saturation with respect to the dissolving mineral, DS (defined as the ratio of the mean ionic activity product for hydroxyapatite [Ca5OH(PO4)3] in solution to its solubility product constant), and the sum of the acid activities (sumBiH) in solution: R = K(1-DS)m(sumBiH)n. The present study was undertaken to explore the general validity of this model in describing the kinetics of enamel demineralization. Thin sections of human enamel were exposed to partially saturated 0.1 mol/L lactic acid solutions, at two different DS levels, and at pH values of 4.3 to 6.0. Thin sections of human enamel were also exposed to solutions with four different concentrations of acetic and lactic acids (pH 4.3) with three different DS values and, at one DS value, to solutions of propionic acid. Mineral loss was monitored by quantitative microradiography. In solutions with pH values of 4.3 and 5.0, "lesions" were formed with well-defined surface layers, whereas, in solutions with pH 6.0, "lesions" were produced with no apparent surface layers. The formation of relatively intact surface layers was consistent with predicted phase transformations. Rates of mineral loss were found to be inversely proportional to both the degree of saturation with respect to enamel mineral, DS(En), and the pH of the solution and increased with increased activities of each organic acid, consistent with the proposed model. However, at the same DS(En) and acid activity, rates of demineralization were the same in the acetic and propionic acid solutions, whereas rates of demineralization in lactic acid were greater. It is suggested that specific interactions of acid species with enamel mineral may modify the rate of enamel demineralization. These in vitro findings suggest that relatively small differences in DS(En) values found in plaque fluid may result in very significant differences in the rate of enamel demineralization in vivo.

Transmission FT-IR microspectroscopy of mineral phases in calcified tissues

Fourier-transform infrared microspectroscopy (FT-IRM) was used to study bone mineralization processes in an in vivo model and in enamel in osteogenesis imperfecta. Finally, the ability of FT-IRM to map new bone formed in implanted macroporous calcium phosphate biomaterial from sections was reported for the first time. FTIRM allowed the correlation of the microstructure of bone formation in the in vivo model with modifications in carbonate and phosphate environments of the mineral phases during maturation. FT-IRM analysis on enamel sections revealed changes in the mineral environment of carbonate and phosphate ions and probably in the size of enamel crystals. These modifications contributed to the fragility of enamel in osteogenesis imperfecta. The infrared functional group imaging of a part of implanted biomaterial and the bone ingrowth provided the visualization of chemical modifications occurring in biomaterial implants at 20 μm spatial resolution. The use of FT-IRM, in conjunction with appropriate sampling methods and data analysis should provide further insight into the molecular structure of mineral phases of calcified tissues and help to elucidate mineralization processes, skeletal disorders and properties of the biomaterials used as bone substitute.

Measurement of Enamel Remineralization Using Microradiography and Confocal Microscopy

Tooth minerals are lost and regained constantly in a normal, human oral environment. Different methods have been developed to measure this gain and loss in enamel minerals; however, these methods deal with different problems, such as being time consuming or involving the use of X–rays. The aim of this study was to determine if remineralization measured in a thin enamel section (TS) by transversal microradiography (MR) can be reliably monitored by measuring lesion parameters (area, total and average dye fluorescence) on the same TS or on half a tooth (HT) with confocal laser scanning microscopy (CLSM). Thirty–six human enamel specimens were demineralized for 96h, and then half of each specimen was covered with an acid–resistant nail varnish. Specimens were divided into three groups (12/group) and subjected for 20 days to a cyclic remineralization regimen with consisted daily of a 4–hour acid challenge, four 1–min treatment periods with 0, 250 or 1,100 ppm F dentifrice slurries (1:2; dentifrice:water) and 20 h in pooled, human saliva, at room temperature. Specimens were cut and analyzed by MR, then stained with a fluorescent dye (0.1mM rhodamine B) for 1 h and analyzed using CLSM. Both MR and CLSM detected significantly greater remineralization (p<0.05) in the specimens treated with the fluoride–containing dentifrices than in the specimens treated with 0 ppm F. Significant differences were detected between specimens treated witht the fluoride–containing dentifrices by MR and CLSM (HT area and total fluorescence). Statistically significant (p<0.05) Pearson correlation coefficients were calculated between the MR and CLSM data: difference in MR mineral content (ΔM) versus HT lesion area = 0.71; ΔM versus HT total fluorescence = 0.70; ΔM versus HT average fluorescence = 0.61; ΔM versus TS lesion area = 0.88; ΔM versus TS total fluorescence = 0.63, and ΔM versus TS average fluorescence = 0.40. It is concluded that confocal microscopy in either TS or HT may provide valid surrogates (area and total fluorescence) for MR measurements in enamel remineralization studies.

Stable carbon and oxygen isotopes in human tooth enamel: Identifying breastfeeding and weaning in prehistory

This paper investigates the utility of stable carbon and oxygen isotopes in human dental enamel to reveal patterns of breastfeeding and weaning in prehistory. Enamel preserves a record of childhood diet that can be studied in adult skeletons. Comparing different teeth, we used δ13C to document the introduction of solid foods to infant diets and δ18O to monitor the decline of breastfeeding. We report enamel carbonate δ13C and δ18O of 33 first molars, 35 premolars, and 25 third molars from 35 burials from Kaminaljuyú, an early state in the valley of Guatemala. The skeletons span from Middle Preclassic through Late Postclassic occupations, ca. 700 B.C. to 1500 A.D. Sections of enamel were removed from each tooth spanning from the cusp to the cemento-enamel junction. Stable isotope ratios were measured on CO2 liberated by reaction of enamel with H3PO4 in an automated carbonate system attached to a VG Optima mass spectrometer. Within a skeleton, teeth developing at older ages are more enriched in 13C and more depleted in 18O than teeth developing at younger ages. Premolars average 0.5% higher in δ13C than first molars from the same skeleton (P = 0.0001), but third molars are not significantly enriched over premolars. The shift from first molars to premolars may be due to the shift to solid foods from lipid-rich milk. After 2 years, when premolars begin to mineralize, the δ13C in childhood diets did not change systematically. First molars and premolars are similar in δ18O, but third molars average 0.7% lower than first molars (P = 0.0001) and 0.5% lower than premolars (P = 0.0003). First molar and premolar δ18O is heavier, because breast milk is more enriched in 18O than is drinking water. Hence, many children continued to nurse during the period of premolar formation. Together, these results indicate that Kaminaljuyú children had begun to eat solid maize foods before the age of 2 years but continued to drink breast milk until much later. Am J Phys Anthropol 106:1–18, 1998. © 1998 Wiley-Liss, Inc.

Stable carbon and oxygen isotopes in human tooth enamel: identifying breastfeeding and weaning in prehistory.

This paper investigates the utility of stable carbon and oxygen isotopes in human dental enamel to reveal patterns of breastfeeding and weaning in prehistory. Enamel preserves a record of childhood diet that can be studied in adult skeletons. Comparing different teeth, we used delta13C to document the introduction of solid foods to infant diets and delta18O to monitor the decline of breastfeeding. We report enamel carbonate delta13C and delta18O of 33 first molars, 35 premolars, and 25 third molars from 35 burials from Kaminaljuyú, an early state in the valley of Guatemala. The skeletons span from Middle Preclassic through Late Postclassic occupations, ca. 700 B.C. to 1500 A.D. Sections of enamel were removed from each tooth spanning from the cusp to the cemento-enamel junction. Stable isotope ratios were measured on CO2 liberated by reaction of enamel with H3PO4 in an automated carbonate system attached to a VG Optima mass spectrometer. Within a skeleton, teeth developing at older ages are more enriched in 13C and more depleted in 18O than teeth developing at younger ages. Premolars average 0.5/1000 [corrected] higher in delta13C than first molars from the same skeleton (P = 0.0001), but third molars are not significantly enriched over premolars. The shift from first molars to premolars may be due to the shift to solid foods from lipid-rich milk. After 2 years, when premolars begin to mineralize, the delta13C in childhood diets did not change systematically. First molars and premolars are similar in delta18O, but third molars average 0.7/1000 [corrected] lower than first molars (P = 0.0001) and 0.5/1000 [corrected] lower than premolars (P = 0.0003). First molar and premolar delta18O is heavier, because breast milk is more enriched in 18O than is drinking water. Hence, many children continued to nurse during the period of premolar formation. Together, these results indicate that Kaminaljuyú children had begun to eat solid maize foods before the age of 2 years but continued to drink breast milk until much later.

Reproducibility of TMR for the determination of longitudinal mineral changes in dental hard tissues.

Transverse microradiography (TMR) of thin sections is the principal method for determining mineral changes in experimental lesions. Because it has become also the standard by which newly-developed methods are validated, demands on all steps of the procedure are high. Thin sections of enamel and dentin require high-precision cutting or lapping to preserve surface structures, but their different brittleness and elasticity preclude a uniform procedure. Image analysis permits the measurement of fine details at a micron scale, but because most studies are aimed at overall mineral changes, they are usually lost on broadening of the scan areas and averaging of experimental groups. Small errors in repositioning of the scan areas for repetitive measurements may yield distorted lesion profiles, while quantitative data such as the integrated mineral loss are hardly influenced. A major reason for "irreproducibility" of TMR are the different definitions of the lesion parameters as used by various research groups. We recommend that these definitions be agreed on if the full potential of TMR as an international standard is to be utilized.

Lattice fringe continuity in the absence of crystal continuity in enamel.

Since high-resolution transmission electron microscopy (HRTEM) provides information on a nearly atomic level, the confidence level with this method is very high. Thus, when lattice fringe continuity is found between two enamel crystals in proximity, such continuity has been taken as evidence of crystal fusion (Daculsi and Kerebel, 1977). Similarly, selected-area dark-field (SADF) electron microscopic imaging has been used to study the axial and spatial orientation of crystals. These studies have shown that there is apparent continuity between enamel and dentin crystals (Arsenault and Robinson, 1989). This observation supported the hypothesis that enamel crystallites are initiated by crystallites in dentin. We have used both HRTEM and SADF methods to identify instances of spatial relationship between crystallites in sections of rat incisor enamel and shark enameloid. In each instance of apparent continuity, goniometric tilting was used to examine the continuous interface. All instances where two crystallites seemed to come into contact, and where HRTEM imaging showed the lattice fringes to be directly continuous, were separated into individual crystallites when the specimen was tilted a few degrees. Thus, adjacent crystallites can show lattice fringe continuity in the absence of real crystallite contact. When instances of overlapping crystallites were examined by SADF imaging, the overlapping crystallites gave a single bright image. Goniometric tilting revealed separate crystallites. Thus, neither lattice fringe continuity nor image continuity under SADF can be used as evidence of crystal continuity unless goniometric rotation and tilting are applied when spatial relationships are suspected.

Failure to demonstrate a protein coat on enamel crystallites by morphological means

Phosphotungstic acid (PTA) treatment of section of Epon-embedded enamel dissolves the crystallites and stains material postulated to be crystal-bound proteins. Alternative, capillarity forces within the channels left after crystallite removal may draw in PTA. This prediction was tested on three systems. (1) Protein free synthetic hydroxyapatite was embedded in Epon; treatment of thin sections with PTA removed most crystals, leaving empty holes outlined by stain that could not represent protein. (2) Sections of rat incisor enamel were treated with PTA and then re-embedded in Epon and sectioned at 90° to the original plane. In these sections-of-section the cut ends of dissolved crystallite profiles were coated with stain. To determine if stained protein coats can be detected in the absence of the crystallite profiles, Epon sections were partially demineralized with formic acid, re-embedded in Epon and sections-of section were PTA treated. Previously extracted crystallites left no stained coats, and only the crystallites that were not removed by formic acid left PTA-stained outlines. (3) PTA-treated sections of dogfish shark enameloid were flooded with 5-nm colloidal gold particles and sections-of-section were prepared. The presence of gold particles on the section surface and in holes previously occupied by crystallites suggested that PTA solution could also be sucked into similar holes. It is concluded that PTA outlines are not crystal-bound proteins but artefacts caused by stain lining holes left in the section when the crystallites have been extracted.

Application of scanning microradiography and X-ray microtomography to studies of bones and teeth

In scanning microradiography (SMR), a thin section is stepped across a 15- μ m diameter X-ray beam and the transmitted intensity measured at each point. This technique has permitted more accurate measurements of the spatial variation of the mineral concentration in sections of dentin and enamel than conventional photographic microradiography. Moreover, because the section is not in close contact with an emulsion, SMR allows continuous study while the specimen is bathed in a reaction solution. The present studies have been particularly directed to gaining an understanding of the formation and repair of carious lesions in teeth: one particular puzzle is subsurface demineralization, in which the initial loss of mineral appears to take place some 20 to 50 μ m below the tooth surface. SMR studies are reported here on the demineralization in dilute acids and the subsequent partial remineralization in supersaturated calcium phosphate solutions in model systems for dental caries. In order to develop a theoretical model for de- and remineralization of carious lesions, it is necessary to quantify transport processes within the tooth. To this end, we are developing a method of measuring effective diffusion coefficients of strongly X-ray-absorbing ions in water within permeable solids in which the diffusion coefficient varies with position. The method uses sequential concentration/distance profiles determined by SMR. As a test, diffusion coefficients of potassium iodide in water within a permeable glass frit have been measured. X-ray microtomography (XMT) can be carried out by adding an axis of rotation to the SMR apparatus. Using this method, linear absorption coefficients, and hence mineral concentrations, can be measured in 15 × 15 × 15- μ m 3 voxels. This has advantages over SMR in that superposition within the depth of the section and errors in determining its thickness are avoided. XMT studies of de- and remineralization similar to those described above for SMR, and also XMT studies of the variation in mineral concentration in the cortical bone of a rat femur along its length, are reported.

Application of Scanning Microradiography and X-Ray Microtomography to Studies of Bones and Teeth

In scanning microradiography (SMR), a thin section is stepped across a 15-μm diameter X-ray beam and the transmitted intensity measured at each point. This technique has permitted more accurate measurements of the spatial variation of the mineral concentration in sections of dentin and enamel than conventional photographic microradiography. Moreover, because the section is not in close contact with an emulsion, SMR allows continuous study while the specimen is bathed in a reaction solution. The present studies have been particularly directed to gaining an understanding of the formation and repair of carious lesions in teeth: one particular puzzle is subsurface demineralization, in which the initial loss of mineral appears to take place some 20 to 50 μm below the tooth surface. SMR studies are reported here on the demineralization in dilute acids and the subsequent partial remineralization in supersaturated calcium phosphate solutions in model systems for dental caries. In order to develop a theoretical model for de- and remineralization of carious lesions, it is necessary to quantify transport processes within the tooth. To this end, we are developing a method of measuring effective diffusion coefficients of strongly X-ray-absorbing ions in water within permeable solids in which the diffusion coefficient varies with position. The method uses sequential concentration/distance profiles determined by SMR. As a test, diffusion coefficients of potassium iodide in water within a permeable glass frit have been measured. X-ray microtomography (XMT) can be carried out by adding an axis of rotation to the SMR apparatus. Using this method, linear absorption coefficients, and hence mineral concentrations, can be measured in 15 X 15 X 15-μm3 voxels. This has advantages over SMR in that superposition within the depth of the section and errors in determining its thickness are avoided. XMT studies of de- and remineralization similar to those described above for SMR, and also XMT studies of the variation in mineral concentration in the cortical bone of a rat femur along its length, are reported.

Nonlinear Regression Analysis of Impedance Data from Dental Hard Tissues

Impedance measurements have been used to characterize a wide variety of biological systems, including bacterial suspensions, aqueous solutions of biological polyelectrolytes, and biological tissues. This paper describes how the impedance response of biological systems can be modeled and analyzed numerically using networks of passive electrical components. The advantage of this approach is that the entire frequency response can be represented accurately by a small number of discrete components with associated magnitudes. The methods of model selection and nonlinear regression of the data using an appropriate model are described and illustrated using typical impedance responses of dentine and enamel sections obtained from extracted adult human teeth.

A single-section model for enamel de- and remineralization studies. 1. The effects of different Ca/P ratios in remineralization solutions.

A prerequisite for the accurate measurement of differences between pre- and post-experimental mineral profiles in single sections by quantitative microradiography is a high degree of reproducibility of the analytical procedures. We have determined the reproducibility of both the production and analyses of microradiographs. Lesions were made in seven single bovine enamel sections and radiographed three times. Each microradiograph was then analyzed on three different occasions by use of an image analysis system. This resulted in only small standard deviations in the lesion parameters. The method was used to determine the sites of mineral deposition in lesions in single sections during remineralization in three different solutions, one of which contained 1.5 mmol/L Ca and 0.9 mmol/L PO4 (standard solution); the other two solutions were low in either Ca or PO4, but all three had the same degree of supersaturation. The mineral profiles and lesion parameters were determined after lesion formation and after remineralization for 4 days, 1, 2, and 3 weeks. The decrease in IML (integrated mineral loss) in the lesions remineralized in the standard solution was greatest during the first week. Lesion profiles revealed that, under non-standard conditions, mineral deposition was retarded in the deeper part of the lesion, in contrast to the even distribution of mineral deposition from the standard solution. Differences in IML changes and lesion profiles between these bovine enamel experimental groups diminished when remineralization continued for 2 and 3 weeks. Possibly, the reactivity of mineral surfaces in newly made lesions affected the diffusion of remineralizing ions from low concentration solutions to the lesion front.

Scanning microradiographic and microtomographic studies of remineralisation of subsurface enamel lesions

Scanning microradiography (SMR) and X-ray microtomography (XMT) were used to study remineralisation of subsurface enamel lesions quantitatively at a resolution of about 10 µm. With SMR, the mineral changes during de- and re-mineralisation could be measured as a function of time and position in the same tooth section. The results showed that remineralisation occurred in ten out of the 17 enamel sections; it essentially stopped after eight weeks and complete repair was never seen, even after 14 weeks. The amount of mineral gained in the subsurface maximum and subsurface minimum for each were very similar, but differed between sections. XMT also showed partial remineralisation, but again no complete repair. There was no evidence of a ‘barrier’ to remineralisation caused by nearly complete remineralisation of the surface enamel.