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PubMed2001

Molecular regulation of odontoblast activity under dentin injury.

Pulp tissue responds to dentin damage by laying down a tertiary dentin matrix (reactionary or reparative) beneath the site of injury. Reactionary dentin is secreted by surviving odontoblasts in response to environmental stimuli, leading to an increase in metabolic activities of the cells. The inductive molecules that determine the success of the pulp healing may be released from the damaged dentin as well as from the pulp tissue subjacent to the injury. This paper will schematically consider two major growth factors probably implicated in the control of odontoblast activity: TGF beta-1 released from demineralized dentin and NGF from pulp. To analyze their role with an in vitro system that mimics the in vivo situation, we have used thick-sliced teeth cultured as described previously. The supply of factors was accomplished by means of a small tube glued onto the dentin. The tube was filled with TGF beta-1 (20 ng/mL) or NGF (50 ng/mL), and slices were cultured for 4 or 7 days. Results showed that TGF beta-1 binding sites are strongly detected on odontoblasts in the factor-rich zone. A strong expression of alpha 1(I) collagen transcripts was also detected. In the NGF-rich environment, p75NTR was re-expressed on odontoblasts and the transcription factor NF-kappa B activated. Modifications in the odontoblast morphology were observed with an atypical extension of the cell processes filled with actin filaments. These results suggest that odontoblasts respond to influences from both dentin and pulp tissue during pulp repair.

Actin Cytoskeleton↗

PubMed1992

A comparison of leakage of filling materials in demineralized and non-demineralized resected root ends under vacuum and non-vacuum conditions.

A study was conducted to compare the marginal apical leakage of root-end filling materials under vacuum and non-vacuum conditions, and to assess the effect of demineralization by application of citric acid to the root ends on the apical marginal leakage of root end filling materials. The root canals of 148 extracted human canines and premolars were handfiled and sealed with gutta-percha and Roth's 801 sealer using cold lateral condensation. The teeth were divided into 8 groups that received retrofilling materials. The materials tested were amalgam, IRM and gutta-percha/sealer with and without successive application of citric acid. Half of the specimens were placed under vacuum conditions in methylene blue dye, and the other half were placed in the dye for the same time period without exhausting air from the flask. The teeth were split longitudinally and the extent of dye penetration was determined with a stereomicroscope and eyepiece micrometer. The most evident difference in dye penetration was found between the positive control groups. Under vacuum conditions, the positive controls showed complete penetration of the unobturated canal system with dye. With passive immersion only partial penetration of the unobturated canal system occurred. Application of citric acid to the root end did not adversely affect the seal of amalgam, IRM or gutta-percha/sealer.

Acid Etching, Dental↗

PubMedDate not supplied

In vitro fluoride dose-response study of sterilized enamel lesions.

Currently our intra-oral model uses enamel specimens that have been disinfected by soaking in buffered formalin (pH 6.8). However, because of increasing emphasis on infection control, it is important to identify a way to sterilize these specimens. The aim of this study was to determine if autoclaved, or gas sterilized, lesioned enamel responds to fluoride (F) in the same way alcohol-disinfected enamel lesions do. Seventy-two formalin-disinfected, human enamel specimens (3 mm) were lesioned in demineralizing solution for 96 h and were then divided into three groups. One group was autoclaved; one group was gas sterilized (ethylene oxide), and the remaining 24 specimens were further disinfected in 70% ethanol for 10 min. Specimens in each group were then treated 4 times/day for 4 weeks with 0, 250 or 1,100 ppm F dentifrice slurries in an in vitro cycling, remin/demin model. Following treatment, fluoride uptake was analyzed by microdrill biopsy, and lesion depth and mineral content changes (DeltaM) were determined by transverse microradiography. Data were analyzed by one-way ANOVA analysis. In all three groups of specimens there were significant (p<0.05) differences in fluoride uptake in response to different fluoride treatments. Autoclaved lesions failed to provide dose- response data with regard to changes in lesion mineral content. Because formalin and 70% alcohol are only disinfectants, and autoclaving altered the responsiveness of enamel lesions, results from this study suggest that, of the methods tested, gas sterilization is the preferred method for sterilizing enamel specimens that will be used in intra-oral studies.

Analysis of Variance↗

PubMed1996

Correlative transmission electron microscopy examination of nondemineralized and demineralized resin-dentin interfaces formed by two dentin adhesive systems.

The resin-dentin interface formed by two dentin adhesives, Optibond (OPTI, Kerr) and Scotchbond Multi-Purpose (SBMP, 3M), was ultramorphologically examined by transmission electron microscopy (TEM). Ultrastructural information from nondemineralized and demineralized sections was correlated. It was hypothesized that the different chemical formulations of the two adhesives would result in a different morphological appearance of the hybrid layer. Ultrastructural TEM examination proved that each of the two dentin adhesive systems was able to establish a micromechanical bond between dentin and resin with the formation of a hybrid layer. However, the interfacial hybridization process that took place to produce this resin-dentin bond appeared to be specifically related to the chemical composition and application modes of both systems. OPTI consistently presented with a hybrid layer with a relatively uniform ultrastructure, electron density, and acid resistance. These three parameters were found to be more variable for the hybrid layer formed by SBMP. Characteristic of SBMP was the identification of an amorphous phase deposited at the outer surface of the hybrid layer. Although both adhesive systems investigated follow a total-etch concept, their specific chemical formulations result in different interfacial ultrastructures that are probably related to different underlying bonding mechanisms. The clinical significance of these morphological findings, however, is still unknown.

Acid Etching, Dental↗

PubMed2006

Effect of polymers used in saliva substitutes on demineralized bovine enamel and dentin.

PURPOSE: To evaluate the effects of porcine mucin- and carboxymethylcellulose-based (CMC) solutions on the inhibition of demineralization of pre-demineralized bovine enamel and dentin in vitro. Additionally the sugar substitutes sorbit or xylit were added to the various solutions. METHODS: 54 enamel and dentin samples were prepared from 14 freshly extracted permanent bovine central incisors. The samples were demineralized (pH 5.0 for enamel and pH 5.5 for dentin; 14 days) and subsequently exposed to either mucin- or CMC-based solutions combined with xylit and sorbit at pH 5.5. After in vitro exposure, the specimens were cut perpendicular to the enamel/dentin surface and the sections were ground (4000 grit) to a uniform thickness (100 microm). Mineral loss and lesion depths were evaluated from microradiographs with a dedicated software package (TMR 2.0.27.2). RESULTS: For both dental hard tissues, storage in the mucin-containing solutions resulted in significantly higher lesion depths (deltaLD), but lower mineral loss values (deltadeltaZ) compared to the CMC-containing solutions (P< 0.05; 2-way ANOVA). For the dentin specimens, significant differences in deltadeltaZ were observed between sorbit and xylit (P< 0.05; 2-way ANOVA). The mineral loss and lesion depths of the enamel specimens did not differ significantly after storage in the various solutions (P> 0.05; Bonferroni post hoc test). For the dentin specimens stored in the solution containing mucin/xylit the mineral loss was significantly decreased compared to the other mucin groups as well as to the CMC/xylit solution (P< 0.05; Bonferroni post hoc test).

Analysis of Variance↗

PubMed1987

Intracrystalline structure of enamel crystals affected by caries.

Enamel crystals in the demineralized zones in early caries lesions of human teeth were observed by high-resolution electron microscopy. The enamel crystals frequently exhibited perforations in their centers and defects of various sizes on their lateral surfaces. There were a number of small electron-lucent spots, suggesting that the dissolution of crystals had taken place there. These spots were in especially large numbers near the central dark line. The central perforations, the lateral defects, and the small spots had a common habit which formed regularly along the crystalline a- and b-axes. In many cases, when the central dark line was seen, the perforations were located a few unit cells away from the line. The perforations seem to result from a fusion of small spots, which enlarge by involving other small spots. The lateral defect seemed to enlarge by removal of unit cells and progression along the a- and b-axes. In the regions where the small spots were present, however, the enlargement of the defects also progressed involving the spots. The central dark line seems to be rather resistant to dissolution. One of the main factors for the central perforation of the crystals is thought to be the presence there of especially large numbers of defective sites.

Adult↗

PubMed1999

Artificial caries removal and inhibition of artificial secondary caries by pulsed CO2 laser irradiation.

PURPOSE: To investigate the inhibition of artifical secondary caries around restorations placed after removal of artificial caries by pulsed CO2 laser irradiation and by mechanical means. MATERIALS & METHODS: Beveled cavities were prepared mechanically on the facial surfaces of extracted human molars. Each cavity was subsequently exposed to an artificial caries (demineralizing) solution (pH 5.0) for 7 d to generate a demineralized zone approximately 100-200 microns thick on the cavity surface. The artificial carious/demineralized zones of the cavities were removed by a pulsed CO2 laser operating at a wavelength of 9.3 microns with pulse duration of 100 microseconds and an irradiation intensity of 5 J/cm2. Artificial control caries were removed mechanically with a carbide bur in a slow speed handpiece. The cavities were slightly undercut and restored with a resin-based composite without etching and bonding and the restored teeth were subjected to pH cycling solutions for 10 d as follows: Demineralization solution, pH 4.5 for 6 hrs, followed by remineralization solution, pH 7.0 for 18 hrs. Cycled teeth were sectioned through the restorations and the resulting lesions were analyzed in thin section using polarized light and Knoop microhardness. RESULTS: Mean microhardness delta Z values, indicating mineral loss were: 549 (SD 191) for control, and 140 (SD 127) N = 11. This difference is significant with t = 5.543 and P = 0.000 (Paired t-test). Caries penetration: Control side--231 microns (SD 71), Laser treated side: 123 microns (SD 79) N = 6. This difference is significant with t = 5.198 and P = 0.003 (Paired t-test). The results show that the laser treatment not only removed artificial caries, but also inhibited decalcification of the cavity wall in a subsequent artificial caries challenge by as much as 81% compared to control samples. No etching and bonding was used in this pilot study, which might have influenced the results. Future studies should address the inhibition effect of the laser treatment as compared to adhesive techniques, fluoride treatments and fluoride release restorative materials. CONCLUSION: Caries removal by a pulsed lambda = 9.3 microns CO2 laser produces a cavity surface morphology with marked resistance to artificial secondary caries as compared to mechanical removal.

Carbon Dioxide↗

PubMed2002

Bonding of self-etch and total-etch adhesives to carious dentin.

Carious dentin is partially demineralized and contains mineral crystals in the tubules. This may permit the deeper etching of intertubular dentin but prevent resin tag formation during bonding. We hypothesize that resin adhesives will produce lower bond strengths to caries-infected and caries-affected dentin compared with normal dentin. We tested this by measuring the microtensile bond strength of a total-etch adhesive and an experimental self-etching adhesive (ABF) to caries-infected, caries-affected, and sound dentin and by correlating those results with ultrastructural observations. The bond strengths of both adhesives to sound dentin were significantly (p < 0.05) higher than those to caries-affected dentin, which, in turn were significantly (p < 0.05) higher than those to caries-infected dentin. For both adhesives, hybrid layers in caries-affected dentin were thicker but more porous than those in sound dentin. The lower bond strengths may be due to the lower tensile strength of caries-affected dentin. Clinically, this may not be a problem, since such lesions are normally surrounded by normal dentin or enamel.

Acid Etching, Dental↗

PubMed1997

Effect of pH and calcium concentration on calcium diffusion in streptococcal model-plaque biofilms.

Demineralization during a cariogenic episode is affected by storage and transport in dental plaque of ions released from enamel, and by the effect on both of plaque fluid pH and ion concentrations. To investigate this, 45Ca effusion from a condensed film of streptococci was measured at pH 7, 6 and 5, and 0-20 mmol/l calcium. Cells were loaded into effusion chambers and the appearance of 45Ca and [3H]-inulin in carrier-containing but initially tracer-free buffer was measured. Ratios of 45Ca and [3H]-inulin activity in the initial suspending solution and at equilibrium in the clearance solution, permitted calculation of extracellular volume and bound calcium. The rate of Ca appearance was proportional to the retarded diffusion coefficient (rDe), which was related to the effective diffusion coefficient (De) by: rDe = De/(1 + R) in which R is the ratio of bound to free Ca2+. The rate of Ca2+ effusion increased with calcium concentration, converging on a value of 2.8 x 10(-10) m2/sec. At low pH it reached convergence at a lower [Ca]. This demonstrates that calcium effusion is dependent on binding, so a high proportion of binding sites in plaque will reduce mineral loss in vivo. Loss of binding sites at low pH will increase mineral loss.

Algorithms↗

PubMed1997

The relationship between surface free-energy and kinetics in the mineralization and demineralization of dental hard tissue.

The interfacial free-energy is an important factor in the regulation of mineralization and dissolution at the surfaces of dental hard tissues. However, few thermodynamic studies have been aimed at the elucidation of the interfacial terms. Contact angle measurements (sessile drop and thin layer wicking) and kinetic dissolution and growth techniques have been used to study the interfacial properties of root dentin (D), human enamel (E), and hydroxyapatite (HAP). The interfacial tensions between water (w) and each of these phases were calculated from contact angle data according to surface tension components theory. The values gamma wD = 4.5 x 10(-3) J m-2, gamma wE = 8.8 x 10(-3) J m-2, and gamma w,HAP = 10.4 x 10(-3) J m-2 were of the same order of magnitude as those obtained from dissolution kinetic data (pH = 4.5): gamma wD = 1.4 x 10(-3) J m-2, gamma wE = 3.2 x 10(-3) J m-2, and gamma wHAP = 9.3 x 10(-3) J m-2. Kinetics studies of the crystallization of HAP on HAP, dentin, and enamel yielded the interfacial free-energy values, gamma wHAP = 17.1 x 10(-3) J m-2, 17.7 x 10(-3) J m-2, and 9.4 x 10(-3) J m-2, respectively, probably reflecting the interfacial energies of the deposited phases rather than those of the dental hard-tissue substrata. The lower interfacial tension values are consistent with the higher solubilities of these solid phases: logKSO = -52.0, -55 approximately 57, and -58 approximately 59, for root dentin, enamel, and HAP, respectively, expressed as an equivalent HAP ionic product. The higher interfacial free-energy is also consistent with the slower mineralization of HAP on dentin and enamel surfaces.

Crystallization↗

PubMedDate not supplied

Demineralization of dentin by Streptococcus mutans biofilms grown in the constant depth film fermentor.

To develop a bacterial demineralization model, we grew Streptococcus mutans biofilms in a constant depth film fermentor (CDFF) and studied the effects of sucrose pulsing frequency (SPF) in time on dentin demineralization. S. mutans biofilms were grown in dentin specimens with grooves and on dentin surface specimens for 20 days. During the experiments, 2% sucrose was pulsed either 4 or 8 times per day for periods of 30 min. Diluted brain-heart infusion medium containing 25 mM PIPES buffer and 1.5 mM CaCl2 was pulsed as the alternative growth medium. Specimens with intact biofilms were taken out on days 5, 12 and 20. The model was assessed by viable counts of the biofilm, mineral loss and lesion depth in the dentin specimens (by transversal microradiography) and pH measurements in the groove (by pH microelectrode). The results showed that biofilms formed on the dentin surface specimens were constant in viable counts for the low SPF, while this parameter tended to increase with time under the high SPF. Lesions with intact surfaces were formed and the lesion size increased significantly over time and increased significantly with increasing SPF. Typical Stephan curves were found after sucrose pulsing. The pH inside the groove returned to neutral under low SPF, but remained below 6.5 under high SPF. With the CDFF S. mutans biofilm model, lesions can be created in dentin within reasonable experimental time periods, as a result of the presence of a biofilm and in response to carbohydrate challenges.

Analysis of Variance↗

PubMed1998

Factors affecting the development of carious lesions in bovine teeth in vitro.

This study aimed to determine the effect of temperature, duration of exposure, position on enamel surface, and type of demineralization solution on the production of caries-like lesions in bovine enamel in vitro, and to establish the conditions for the formation of artificial caries in bovine enamel. Caries-like lesions were produced in incisal, middle and cervical sites on enamel samples, with either an acidified hydroxyethylcellulose gel system or a partially saturated acidic buffer solution at either 20 degrees C or 37 degrees C for 3, 4, or 5 days. Lesion variables (mineral loss/lesion depth) were quantified. Regular subsurface lesions were produced in all specimens in acidic buffer solution within 3 days at either temperature. In gel, caries-like lesions were produced in 62% of the specimens at 37 degrees C and in 49% at 20 degrees C, while the remaining specimens were either eroded or softened. Mineral loss and lesion depth were significantly greater with buffer than with gel, and with increased length of exposure in either solution. There were no significant differences in either variable with position or temperature in either solutions, though numerically both variables were greater at the cervical site, and at 37 degrees C in either solution. It was concluded that caries-like lesions can be consistently produced in bovine enamel with a partially saturated acidic buffer solution at 20 degrees C or 37 degrees C within 3 days.

Analysis of Variance↗

PubMed2001

Varnish or polymeric coating for the prevention of demineralization? An ex vivo study.

OBJECTIVE: The ability of an experimental coating, Odyssey, to prevent demineralisation ex vivo was compared with that of a fluoride varnish, Duraphat and a chlorhexidine-containing varnish, Cervitec. DESIGN: an ex vivo single-blind study. SETTING: Hard tissue research laboratory. MATERIALS AND METHODS: thirty bovine enamel blocks 0.5 cm x 1.5 cm were divided into 6 groups of 5 specimens. The enamel blocks were then allocated to one of 6 surface treatments. INTERVENTIONS: (1) surface left unprepared (control), (2) Duraphat application, (3) Cervitec application, (4) experimental polymer coating, (5) enamel conditioned with 10% citric acid and coated with the experimental polymer coating Odyssey (O + C), (6) enamel etched for 30 sec with 37% phosphoric acid and coated with the experimental coating (O + E). All specimens were cycled for 7 days through a daily procedure of demineralisation for 4 hours and remineralisation for 20 hours, and exposed to an equivalent of 2 months toothbrushing. A single operator blinded to the treatment allocation of each specimen carried artificial lesion depth assessment out using computer-assisted transverse microradiography. RESULTS: The control group had the greatest mean lesion depth (97.16 + 29.8 microm) with the Duraphat group exhibiting the lowest mean lesion depth (24.53 + 15.44 microm). The Duraphat, Odyssey, O + C and O + E groups all had significantly less lesion depth when compared with no surface preparation (p < 0.05 for all comparisons). There were no significant differences between any of the Odyssey groups. CONCLUSIONS: The efficacy of Duraphat application in preventing demineralisation ex vivo has been demonstrated in the present study, but clinical trials are required to assess its usefulness in orthodontic practice.

Analysis of Variance↗

PubMed2004

The effect of dehydration on quantitative light-induced fluorescence analysis of early enamel demineralization.

The purpose of this study was to determine the effect of hydration [distilled water (DH2O) and saliva] on lesions of varying severity and determine an optimal drying method to obtain reliable quantitative light-induced fluorescence (QLF) readings. Ten previously extracted molars were placed into a demineralizing solution for 7, 14 and 21 days. Between each demineralizing cycle the teeth were removed. To test for in vitro reliability the teeth were rinsed in DH2O for 1 min and then QLF images were taken every 10 s (control cycle with no drying employed - bench drying only). This was repeated following (i). compressed air drying for 30 s or 15 s and (ii). 30 s cotton wool roll application (CWR). To test for in vivo reliability the experiment was repeated using whole human saliva in place of DH2O. Control groups demonstrated the effect of hydration on QLF reliability; at 7 days reliable results were obtained after 370.4 s (DH2O) and 432.3 s (saliva). Air drying of both DH2O and saliva-rinsed teeth reduced reliability time to 2.1 (+/-6.0) and 3.2 s (+/-7.6), respectively. Cotton wool roll application produced reliable results in 89 s with DH2O and 110 s with saliva. As lesion severity increased [14 days mean deltaQ 115 (+/-90.2), 21 days mean deltaQ 168.0 (+/-120.7)] time to reach reliability significantly increased under control drying and CWR (P > 0.05). Time taken for compressed air-dried teeth to produce reliable results was not significantly different across the groups. Compressed air-drying for 15 s produces reliable results with both DH2O and saliva-hydrated lesions. Future in vivo experiments will be required to determine if the air-drying can be reduced further in a clinical situation.

Dental Caries↗

PubMedDate not supplied

Microtensile bond strength of glass ionomer cements to artificially created carious dentin.

In this laboratory study, the microtensile bond strengths of a conventional glass ionomer cement (GIC) and a resin modified glass ionomer cement (CRMGIC) to artificially created carious dentin and sound dentin were compared, and the ultrastructural morphology of the fractured interface was examined with a low-vacuum scanning electron microscope (SEM). The specimens were divided into 4 groups: 1) a conventional GIC (Ketac-Fil Plus Aplicap) placed on sound dentin; 2) a conventional GIC placed on artificially created carious dentin; 3) an RMGIC (Photac-Fil Aplicap) placed on sound dentin and 4) an RMGIC placed on artificially created carious dentin. Artificial carious lesions were created using a chemical demineralizing solution of 0.1 M/L lactic acid and 0.2% carbopol. GIC buildups were made on the dentin surfaces according to the manufacturer's directions. After storage in distilled water at 37 degrees C for 24 hours, the teeth were sectioned vertically into 1 x 1 x 8-mm beams for the microtensile bond strength test. The microtensile bond strength of each specimen was measured, and failure mode was determined using an optical microscope (40x). The fractured surfaces were further examined with SEM. Two-way analysis of variance showed that the mean microtensile bond strengths of a GIC and an RMGIC to carious dentin were significantly lower than those to sound dentin, and the mean microtensile bond strengths of Photac-Fil to both sound and carious dentin were significantly higher than those of Ketac-Fil Plus. Chi-square tests indicated that there was a significant difference in failure mode between the sound dentin and carious dentin groups. In sound dentin groups, cohesive failure in GIC was pre- dominant; whereas, mixed failure was predominant in carious dentin groups. SEM examination showed that the specimens determined to be cohesive failures under light microscopy in the Photac-Fil/Sound Dentin group were actually mixed failures under high magnification of SEM.

Adhesiveness↗

PubMed1999

1H-NMR analysis of microbial-derived organic acids in primary root carious lesions and saliva.

In addition to lowered pH values, the molecular profile and concentrations of microbial-derived organic acids in carious dentin are important demineralization parameters involved in the induction, development and progression of dental caries. High-resolution proton ((1)H) NMR spectroscopy was employed to examine the organic acid status of primary root carious lesions. (1)H-NMR analysis of post-neutralized perchloric acid extracts of active carious lesions revealed that at an operating frequency of 600 MHz, the (1)H-NMR-detectable organic acid composition of carious dentin samples (mean molecular percentage content +/- standard error; the mean molecular percentage content is defined here as the mean of the concentration of each (1)H-NMR-visible organic acid/anion expressed as a percentage of total (1)H-NMR-detectable organic acid/anion level in each sample) was acetate 51 +/- 2%, formate 37 +/- 2%, lactate 5 +/- 1%, propionate 3 +/- 0.8%, pyruvate 2.4 +/- 0.3%, n-butyrate 1.2 +/- 0.2%; succinate 0.1 +/- 0.1%; iso-butyrate, n- and iso-valerate, and n- and iso-caproate (total) <0.2%. Further components detectable included alanine, glycine, choline, phosphorylcholine, trimethylamine oxide, methanol, glycolate and assorted saccharides. In view of their high dissociation constants (K(a)), our results demonstrate that formic and pyruvic acids (K(a) = 1.77 x 10(-4) and 3.20 x 10(-3) mol/dm(3), respectively) contribute substantially to the decreased pH values associated with active caries lesions (cf. lactate K(a) = 1.40 x 10(-4) mol/dm(3)), and hence the pathogenesis of primary root caries.

Aged↗

PubMed2001

Effect of pulsed Nd:YAG laser irradiation on acid demineralization of enamel and dentin.

OBJECTIVE: The purpose of this study was to investigate the effect of Nd:YAG laser irradiation on the acid demineralization of enamel and dentin by spectrophotometry. A mechanism of acquired acid resistance is also proposed. SUMMARY BACKGROUND DATA: The ability of Nd:YAG laser irradiation to the enhanced resistance to artificial caries formation is still controversial. METHODS: A pulsed Nd:YAG laser at 1.064-micron wavelength was used to irradiate the human enamel and dentin samples from 20 extracted human molars at the parameters of 1, 2, and 3 W and 20 pps for a total of 9 sec after painting with black ink. Samples were then subjected to 2 microliters of 0.1 M lactic acid solution (pH 4.8) for 24 h at 36 degrees C. The parts per million (ppm) of calcium ion (Ca2+) dissolved in each solution was determined by atomic absorption spectrophotometry and the morphological changes were also investigated by scanning electron microscopy (SEM). RESULTS: The lowest mean Ca2+ ppm was recorded in the samples irradiated at 3 W, in those by irradiated at 2 W and 1 W. The unlased samples showed the highest Ca2+ ppm. SEM observation showed that in the lased areas, the smear layer was partially melted and the underlying primary enamel or dentin seemed to be thermally degenerated. CONCLUSIONS: The results of this study suggested that melted smear layer and underlying enamel or dentin degenerated thermally by the heat treatment of Nd:YAG laser might play a major role to enhance resistance to artificial caries-like formation.

Calcium↗

PubMed1994

Some "sealants" seal--a scanning electron microscopy (SEM) investigation.

White spot lesions of enamel around orthodontic brackets as a result of demineralization have been well documented in the orthodontic literature. Various methods of treatment have been attempted to reduce or eliminate this danger. The purpose of this study was to evaluate, by means of scanning electron microscopy, the polymerization of the sealant layer around orthodontic brackets with direct and indirect methods of bonding. Twenty-four sound human lateral maxillary incisor teeth were collected, cleaned, divided equally into four groups A through D, and stored in 70% ethyl alcohol. Their buccal surfaces were pumiced, etched with 37% phosphoric acid for 1 minute, and washed under running water for 30 seconds. Metal brackets were bonded with the chemically cured BIS-GMA resin, Ortho Concise, as follows: group A, indirectly bonded with coping; group B, indirectly bonded without coping; and group C, directly bonded; light activated Transbond was used in group D, directly bonded brackets. After washing in alcohol for 20 seconds, all teeth were dried, and sectioned longitudinally, through the middle of the bracket. All were subjected to 5% hydrochloric acid for 30 seconds and then washed under running water for 30 seconds. After drying and sputter coating, the teeth were viewed under scanning electron microscopy. Groups A and D showed a sealant layer surrounding the brackets and covering the buccal enamel. Groups B and C showed total absence of a cured sealant layer around the brackets or surrounding enamel.(ABSTRACT TRUNCATED AT 250 WORDS)

Bisphenol A-Glycidyl Methacrylate↗