Cross-sectional Microhardness Testing Research Articles

Effectiveness of carbonate removal and demineralization inhibition in primary teeth using a 9.3-μm carbon dioxide laser

BackgroundStudies on permanent dental enamel have shown that irradiation with a 9.3-μm carbon dioxide (CO2) laser can safely inhibit caries progression in vivo and carieslike lesion formation in vitro. The authors conducted a study to investigate whether 9.3-μm CO2 laser irradiation could safely inhibit carieslike lesion formation in primary teeth in vitro. MethodsTeeth were irradiated with a 9.3-μm CO2 laser at a pulse fluence of 0.8 J/cm2 and scanned automatically over a target area of 5.8 mm2. Two test groups of 15 extracted human molars each were used: (1) laser-irradiated and (2) laser-irradiated plus additional fluoride. Both groups used nonirradiated areas as nonlaser-treated controls. After irradiation, artificial carieslike lesions were generated through a validated pH-cycling protocol. Relative mineral loss (ΔZ) was determined by cross-sectional microhardness testing in depth. Fourier transform infrared spectroscopy was performed on additional 10 irradiated samples to investigate the removal of acid-soluble carbonate groups from the mineral. ResultsInhibition of carieslike lesion formation relative to untreated enamel was (1) laser-irradiated alone: 56.2%, (2) fluoride alone: 55.0%, (3) laser plus fluoride: 76.5% (significantly different from 1 and 2; P < 0.01). Carbonate removal by laser irradiation (SD) was 50.4% (7.7%) at the surface and detectable to a depth of at least 14 μm. ConclusionIrradiation with 9.3-μm CO2 laser on primary teeth reduced the formation of carieslike lesions and was associated with significant removal of acid-soluble carbonate groups from the enamel mineral. This inhibition was accomplished without an unsafe rise in pulpal temperature and without significant microscopic or visible damage to the enamel surface.

Demineralization prevention with a new antibacterial restorative composite containing QASi nanoparticles: an in situ study.

ObjectivesTo investigate whether a newly developed dental composite with quaternary ammonium silica dioxide (QASi) nanoparticles incorporated with other fillers into the restorative material demonstrates antibacterial activity by reducing enamel demineralization in an in situ gap model.Materials and methodsTwenty subjects wearing a lower removable partial denture (RPD) with acrylic flanges on both sides of the mouth were recruited into the 4-week in situ study. The gap model consisted of an enamel slab placed next to a composite, separated by a 38-μm space. In the split-mouth design on one side of the RPD, the composite was the Nobio Infinix composite (Nobio Ltd., Kadima, Israel), and the contralateral side used a control composite. Each participant received enamel slabs from one tooth. The gap model was recessed into the RPD buccal flange, allowing microbial plaque to accumulate within the gap. After 4 weeks of continuous wearing, decalcification (∆Z mineral loss) of the enamel slabs adjacent to the gap was determined by cross-sectional microhardness testing in the laboratory.ResultsThe ∆Z for the antibacterial composite test side was 235±354 (mean±standard deviation [SD]; data reported from 17 participants) and statistically significantly lower compared to ∆Z of the control side (774±556; mean±SD) (paired t-test, P<0.0001; mean of test minus control −539 (SD=392), 95% confidence interval of difference: −741, −338).ConclusionsThis in situ clinical study showed that composites with QASi antibacterial particles significantly reduced demineralization in enamel adjacent to a 38-μm gap over a 4-week period in comparison to a conventional composite.Clinical relevanceComposites with QASi nanoparticle technology have the potential to reduce the occurrence of secondary caries.Trial registrationClinicalTrials.gov #NCT04059250

In vitro CO2 9.3-μm short-pulsed laser caries prevention-effects of a newly developed laser irradiation pattern.

Caries prevention with different lasers has been investigated in laboratory studies and clinical pilot trials. Objective of this in vitro study was to assess whether 9.3-μm microsecond short-pulsed CO2 laser irradiation enhances enamel caries resistance without melting, with and without additional fluoride application. Seven groups of enamel, totaling 105 human enamel samples, were irradiated with 2 different carbon dioxide lasers with 2 different energy application systems (original versus spread beam; 9.3μm wavelength, pulse repetition rate 43Hz vs 100Hz, fluence ranges from 1.4 to 3.9J/cm2, pulse duration 3μs to 18μs). The laboratory pH-cycling was performed with or without additional fluoride, followed by cross-sectional microhardness testing. To assess caries inhibition, the mean relative mineral loss delta Z (∆Z) was determined. To evaluate for melting, scanning electron microscopy (SEM) examinations were performed. For the non-laser control groups with additional fluoride use, the relative mineral loss (ΔZ, vol% × μm) ranged between 512 ± 292 and 809 ± 297 (mean ± SD). ΔZ for the laser-irradiated samples with fluoride use ranged between 186 ± 214 and 374 ± 191, averaging a 58% ± 6% mineral loss reduction (ANOVA, P < 0.01 to P < 0.0001). For the non-laser-treated controls without additional fluoride, the mineral loss increased (ΔZ 914 ± 422 to 1224 ± 736). In contrast, the ΔZ for the laser-treated groups without additional fluoride ranged between 463 ± 190 and 594 ± 272 (P < 0.01 to P < 0.001) indicative of 50% ± 2% average reduction in mineral loss. Enhanced caries resistance was achieved by all applied fluences. Using the spread beam resulted in enhanced resistance without enamel melting as seen by SEM. CO2 9.3-μm short-pulsed laser irradiation with both laser beam configurations resulted in highly significant reduction in enamel mineral loss. Modifying the beam to a more homogenous profile will allow enamel caries resistance even without apparent enamel melting.

Evaluation of the Preventive Effect of Composites Containing Silver and TiO2 Nanoparticles on Demineralization around Orthodontic Brackets

The aim of this study was to investigate the antidemineralization effect of composites containing silver and titanium dioxide (TiO2) nanoparticles used for bonding brackets to tooth specimens. A total of 75 freshly extracted teeth were etched and primed and then randomly assigned to three adhesive groups: (1) conventional orthodontic adhesive, (2) conventional adhesive mixed with TiO2 nanoparticles, and (3) conventional adhesive mixed with silver nanoparticles. In each group, brackets were bonded with the pertinent adhesive. Teeth were painted with varnish on all surfaces except a 2-mm rim around brackets. Specimens were subjected to a cariogenic process in a circulating microbial model inoculated with Streptococcus mutans and Lactobacillus casei for 12 days and subsequently sectioned for cross-sectional microhardness testing. In each specimen, enamel microhardness was determined in three locations: 25-30 μm and 1.5 mm away from the bracket and under the varnish-protected enamel. Hardness of enamel in the first two locations was reported as a percentage of the protected enamel hardness. Enamel hardness was higher at 25-30 μm away from brackets in both the experimental groups (p value < 0.05), and the nanoparticles acted similarly in this location (p value = 0.992). At 1.5 mm away from the brackets, there was no difference between experimental and control groups (p value > 0.05); the effect of TiO2 attenuated in this location while silver remained as potent. Both nanoparticles resulted in decreased demineralization at 25-30 μm from the bracket but farther away the effect of TiO2 was diminished. According to the results of this study, composites containing silver and TiO2 nanoparticles can be suggested as anti-demineralization adhesives in case their biocompatibility is proved.

Effect of Heavy Metals Contamination from Cigarette Smoke on Sound and Caries-Like Enamel.

In this study, we sought to evaluate the influence of cigarette smoke and pH cycling on the chemical composition and surface/cross-sectional enamel microhardness. A total of 40 dental blocks obtained from bovine incisors were divided into four groups (n=10): no treatment (control); exposure to cigarette smoke (CS); exposure to pH cycling (PC); and exposure to cigarette smoke and pH cycling (CS-PC). The samples were analyzed by synchrotron radiation micro X-ray fluorescence, bench mode X-ray fluorescence, as well as surface microhardness (SMH) and cross-sectional microhardness (CSMH) testing. The SMH results were submitted to analysis of variance (ANOVA) and Tukey's test. The CSMH results were evaluated using split-plot ANOVA and Tukey's test. A high amount of Cd and Pb and traces of Ni and As were observed in enamel and dentin after exposure to cigarette smoke (CS and CS-PC). The SMH and CSMH of CS were statistically higher when compared with the control. The PC and CS-PC showed lower SMH and CSMH. We conclude that exposure to cigarette smoke promoted heavy metal deposition in enamel/dentin. In addition, it increased the enamel microhardness but did not promote a protective effect on the in vitro development of caries. The clinical significance of this work is that there is significant bioaccumulation of heavy metals from cigarette smoke on the surface and in the enamel and dentin.

Efficacy of erbium-doped yttrium aluminum garnet laser with casein phosphopeptide amorphous calcium phosphate with and without fluoride for remineralization of white spot lesions around orthodontic brackets.

Objective:This study aimed to assess the efficacy of erbium-doped yttrium aluminum garnet (Er:YAG) laser, pastes containing casein phosphopeptide amorphous calcium phosphate (CPP-ACP) with and without fluoride and their combination for prevention of white spot lesions in the enamel.Materials and Methods:This in vitro experimental study was conducted on 90 extracted sound premolars. The teeth were then randomly divided into six groups of 15: (1) Control, (2) laser, (3) CPP-ACP with fluoride (GC MI Paste, Recaldent™ 900 ppm as NaF), (4) CPP-ACP without fluoride (GC Tooth Mousse Recaldent™), (5) laser + CPP-ACP with fluoride, and (6) laser + CPP-ACP without fluoride. In each group, enamel surface was exposed to the remineralizing agent. The teeth were then subjected to pH cycling for 14 days. The teeth were then sectioned, polished, and underwent cross-sectional microhardness testing at 20–160 μ depth quantitatively. Using the Simpson's rule, the amount of mineral loss was calculated in each group. Statistical Analysis Used: ANOVA was used for the comparisons, and Tukey's test was applied for pairwise comparisons.Results:The highest mean volume percentage of microhardness at 20–60 μ depth belonged to the group laser + CPP-ACP with fluoride and the lowest belonged to the control group (P = 0.001). The differences were not significant at 80-120 μ depth (P > 0.05). These finding are confirmed according to △Z (mineral loss).Conclusion:Based on these results, Er: YAG laser was able to decrease demineralization and was a potential alternative to preventive dentistry and was more effective when combined with CPP-ACP products.

Effect of Fluoride-containing Restorative Materials on Dentin Adhesion and Demineralization of Hard Tissues Adjacent to Restorations.

This study evaluated (1) the dentin bond strength of fluoridated restorative systems following aging and (2) the enamel/dentin microhardness around restorations after a pH-cycling regimen. Sixty-four human third molars and four restorative systems were used. A resin-modified glass ionomer (GC Fuji II LC) was used as a fluoride-containing material in the positive control group, while Adper Easy Bond adhesive and Filtek Z350 XT composite resin, which are not fluoridated, were used together in the negative control group. Beautifil II composite resin and FL-Bond II adhesive, both fluoride-containing materials, were compared to Bond Force and Estelite Sigma Quick restorative system, which only contain fluoride in the adhesive. For dentin bond strengths, specimens of each material were fabricated for two test groups (n=8): group 1: tested after 24 h; group 2: tested after 1 year of storage in artificial saliva. Both groups were tested using a microtensile method. For the cross-sectional microhardness test, standardized Class V cavities were prepared and filled with the different restorative systems. After experiencing repeated thermocycling and being subjected to pH-cycling, the teeth were sectioned. The microhardness was measured in enamel and dentin at 50 μm from the cavity wall and at six depths in relation to the surface subjected to pH cycling. None of the restorative systems showed decreased bond strength after storage for one year in artificial saliva. No significant differences in microhardness were observed among the restorative materials on enamel and dentin. All the restorative systems evaluated presented stable bond strength after one year of storage. The pH cycling caused a reduction in the superficial enamel microhardness close to the cavity wall. In dentin, the demineralization affected the superficial and sub-surface areas.

Effect of acidulated phosphate fluoride – gel and foam – on enamel caries-like lesion of primary teeth: an in vitro study

The purpose of this study was to evaluate in vitro the effect of APF, gel and foam, for 1 to 4 minutes, on artificial enamel caries-like lesion of primary teeth submitted to the pH cycling. The specimens with medium values of initial superficial enamel micro-hardness between 272 and 331KHN were selected for the formation of the artificial caries lesion. Later, they were randomly divided into 6 groups (n=15): no pH cycling control, cycled control, gel 1min, gel 4min, foam 1min and foam 4min.The no pH cycling control group was maintained in an humid environment, while the application of APF and the pH cycling were accomplished. After, the specimens were sectioned at the center for the enamel cross-sectional micro-hardness test. The values of micro-hardness of the depths from 20 to 180mm were converted into percentile of mineral volume (%Vol) and the area of mineral recovery (∆ZR) was calculated. In spite of there is no statistically significant differences, it was observed through the analysis of the ∆ZR a difference in the values for the groups gel 1min and foam 4min (p&gt;0.05). The evaluation of %Vol indicated a significant difference only at 60mm depth (p=0.005). This study concluded that a single application of APF gel or foam, for 1 or 4 minutes, do not remineralize artificial enamel caries-like lesion of primary teeth

Histological and microhardness evaluation of early artificial carious lesions in human and bovine enamel: in vitro study

Objective: Early carious lesions in bovine and humanenamel developed in vitro using a pH cycling regimenwere compared. Material and Methods: Fifteencentral bovine incisors and fifteen recently extractedhuman third molars were randomly divided into twogroups: ten for the cross-sectional microhardness test(MT) and five for polarized light microscopy (PLM)analysis. Enamel blocks measuring 5 x 5 mm weremade from the buccal face of the teeth. The blocksused for the MT were sliced into two halves: “A” and“B”. “A” slices were embedded in acrylic resin, withthe face of the dentin-enamel junction left exposedfor the MT prior to pH cycling. “B” slices and wholeblocks were coated with acid-resistant varnish,except a 3 x 3 mm central window, and submitted tothe pH cycling regimen (demineralizing solution for3 h and remineralizing solution for 21 h) over fiveconsecutive days. The “B” slices were then submittedto the MT and the whole blocks were processed forthe PLM study. Results: The PLM analysis revealedshallow, extensive lesions in the bovine enamel,hardly showing the superficial, dark and translucentzones, as well as deep cavity lesions in the humanenamel, with the body of the lesion and the darkzone evident. The MT revealed a significant decreasein microhardness in the superficial levels of thebovine enamel caries and at all depth levels of thehuman enamel caries. Conclusion: The pH cyclingregimen adopted led to the development of deeperand more demineralized carious lesions in humanenamel than bovine enamelKeywordsDental caries; Dental enamel; Microhardness tests; Polarization microscopy.

Assesment of artificial caries lesions through scanning electron microscopy and cross-sectional microhardness test

To assess through scanning electron microscopy (SEM) and cross-sectional microhardness (CSMH) test whether the methodology exposed in this experiment can be used to produce artificial active white spot lesions (AAWSLs) on smooth unabraded human dental enamel. Ten human permanent molars were used in this experiment. One section of each tooth was double coated with nail varnish except for a limited central area sized 2.5 mm × 1 mm (2.5 mm 2 ). Each specimen was individually exposed to 10.4 ml of a demineralizing solution at pH 5.0, during 42 days (37°C) without agitation. Samples were sectioned in the center of the AAWSL and one half was analyzed in SEM and the other half was subjected to CSMH. Descriptive statistics was performed to determine mean depth of the lesion. The mean depth of AAWSL was 100 μm (s.d. =12.1) and a white dull rough surface could be detected by the unaided eye. SEM images demonstrated that although some surface areas of the lesion appeared to be relatively intact, erosion was present. A prismatic pattern of dissolution was observed in all samples with an enlargement of the prism sheaths and some samples had also sites of destruction of prism cores. This methodology can be used to induce AAWSLs in human dental enamel but surface erosion has to be taken into account when performing CSMH test.

Systemically alendronate was incorporated into dental tissues but did not cause morphological or mechanical changes in rats teeth

This study evaluated the effect of the systemic use of sodium alendronate in rats in vivo. Forty-five Wistar rats aged 36 to 42 days and weighing 200 to 230 g were randomly assigned to a control group (n = 20), which received distilled water, and an experimental group (n = 25), which received 2 weekly doses of 1 mg/kg of chemically pure sodium alendronate. The animals were killed after 60 days of treatment. The tibias were removed for analysis of bone mineral density by dual-energy X-ray absorptiometry (DXA). Then, the maxillary incisors were extracted for analysis of the mineralized dental tissues using fluorescence spectroscopy (FS), scanning electron microscopy (SEM), bright field microscopy (BFM), and cross-sectional microhardness (CSMH) testing. DXA and CSMH data were subjected to statistical analysis by Kruskal-Wallis test (5% significance level). The experimental group presented higher bone mineral density than the control group by DXA. FS analysis revealed presence of alendronate in the mineralized dental tissues of the specimens of the experimental group. Significant morphological differences were not found by SEM and BFM. Enamel and dentin (100 and 300 μm from the dentinoenamel junction) CSMH data did not show significant difference between the control and experimental groups. Based on the obtained results, we conclude that while alendronate increased the bone mineral density and was incorporated into the mineralized dental tissues it did not cause significant alterations in the morphology and microhardness of rat incisor enamel and dentin.

Effect of a glass ionomer cement and a fluoride varnish on cross-sectional microhardness values of artificial occlusal caries: In vitro study

Active white spot lesions (WSLs) are a great concern to clinicians. This in vitro experiment analyzed cross-sectional microhardness (CSMH) values of occlusal artificially induced active WSLs (control groups D/A, D/B and D/C) along with experimental groups where these lesions were: Exposed to an artificial high risk cariogenic challenge (HRCC) using pH cycling; treated with a glass ionomer cement (GIC) and then exposed to artificial HRCC; or a fluoride varnish (FV) and afterwards submitted to the same artificial HRCC. Sixty unerupted human third molars were sectioned buccolingually on the occlusal surface and demineralized for 42 days. One half of each tooth was allocated to control groups (D/A, D/B, and D/C) and the other were used as test groups: A (pH cycling); B (GIC + pH cycling); and C (FV + pH cycling). CSMH test was performed for sound, demineralized, and treated specimens. Different depths for CSMH values did not have a normal distribution (Kolmogrov-Smirnov test) and for that matter Wilcoxon and T Test were applied (significance level of 5%). Mean depth of the lesion was 120 μm. A number of samples both in the test groups (n = 37) as in control groups (n = 47) had a lower Knoo p value (softening) or surface erosion. Comparisons between control and test groups only showed statistical difference at a depth 140 μm (P = 0.010) in control group D/A and for test group B at 20 μm (P = 0.004) and at 40 μm (P = 0.007). This in vitro study demonstrated that the use of GIC over an artificial active WSLs and exposed to an artificially HRCC setting tend to express some effect in increased surface KHN values.

Effect of fluoride gels on occlusal fissures in primary molars: an in vitro study

To assess the effect of the application of fluoride gels on the acid resistance of occlusal enamel in primary molars. Forty-five primary second molars were randomly assigned to three groups: a) control (pH-cycling); b) 2% NaF gel/pH-cycling; and c) 1.23% APF gel/pH-cycling. Specimens were longitudinally sectioned in the buccal-lingual direction and used for cross-sectional microhardness testing. Knoop hardness values were converted into vol.% mineral and mineral loss (ΔZ) was then calculated. The response variables were vol.% mineral and ΔZ. Data were tested using parametric tests at a significance level of 5%. No statistically significant differences were found between groups regarding vol.% mineral or ΔZ. A single application of a high concentration fluoride compound does not promote greater resistance to demineralisation in enamel pits and fissures, regardless of the product used.

Caries inhibition in vital teeth using 9.6-μm CO2-laser irradiation

The aim of this study was to test the hypothesis that in a short-term clinical pilot trial short-pulsed 9.6 μm CO(2)-laser irradiation significantly inhibits demineralization in vivo. Twenty-four subjects scheduled for extraction of bicuspids for orthodontic reasons (age 14.9 ± 2.2 years) were recruited. Orthodontic brackets were placed on bicuspids (Transbond XT, 3M). An area next to the bracket was irradiated with a CO(2)-laser (Pulse System Inc, Los Alamos, New Mexico), wavelength 9.6 μm, pulse duration 20 μs, pulse repetition rate 20 Hz, beam diameter 1100 μm, average fluence 4.1 ± 0.3J∕cm(2), 20 laser pulses per spot. An adjacent nonirradiated area served as control. Bicuspids were extracted after four and twelve weeks, respectively, for a quantitative assessment of demineralization by cross-sectional microhardness testing. For the 4-week arm the mean relative mineral loss ΔZ (vol% × μm) for the laser treated enamel was 402 ± 85 (mean ± SE), while the control showed significantly higher mineral loss (ΔZ 738 ± 131; P = 0.04, t-test). The difference was even larger after twelve weeks (laser arm ΔZ 135 ± 98; control 1067 ± 254; P = 0.002). The laser treatment produced 46% demineralization inhibition for the 4-week and a marked 87% inhibition for the 12-week arm. This study shows, for the first time in vivo, that the short-pulsed 9.6 μm CO(2)-laser irradiation successfully inhibits demineralization of tooth enamel in humans.

Inhibitory properties of Coffea canephora extract against oral bacteria and its effect on demineralisation of deciduous teeth

ObjectivesThe antibacterial activity of Coffea canephora extract was evaluated in vitro against Streptococcus mutans and Streptococcus sobrinus. The viability of planktonic cells was analysed by susceptibility tests (MIC and MBC) and time-kill assays. The effect of the extract on dental demineralisation was also investigated. MethodsPrimary 1st molar fragments (n=24) were inoculated with a saliva pool and sustained in a multiple plaque growth system for 10 days to form biofilm. The biofilm was treated with light roasted C. canephora extract at 20%, Milli-Q water (negative control) and chlorhexidine (positive control) once a day, during a week. Blank controls comprised fragments without treatment. Biofilm pH was monitored in the last day of treatment. Changes in tooth mineralisation were assessed by cross-sectional microhardness (CSMH) test. ResultsMIC and MBC for S. mutans were 7±2mg/mL and 160±0mg/mL, respectively, showing no activity for S. sobrinus. The extract produced a 4-log reduction in the number of colonies of S. mutans after 3-h treatment (p<0.05) with undiluted extract (20%) and MBC concentration (16%). There was no difference among negative/blank controls and coffee plaque pH. Differences between CSMH values of dental fragments subjected to the coffee extract and to chlorhexidine were not significant. At depths up to 30μm from the enamel surface, coffee extract and chlorhexidine promoted higher CSMH values when compared to blank/negative controls (p<0.05). ConclusionOur data suggest that light roasted C. canephora extract is beneficial as an anticariogenic substance.

Combined effects of nano-hydroxyapatite and Galla chinensis on remineralisation of initial enamel lesion in vitro

Objectives The aim of the present study was to investigate the combined effects of nano-hydroxyapatite and Galla chinensis on remineralisation of initial enamel lesion. Methods Bovine enamel blocks with in vitro produced initial lesion were used. The lesions were subjected to a pH-cycling regime for 12 days. Each daily cycle includes 4 × 3 min application with one of five treatments: NaF (positive control), deionised water (negative control), crude aqueous extract of G. chinensis (GCE), nano-hydroxyapatite (nano-HA) and GCE with nano-HA. The samples were subsequently evaluated using a microhardness tester, polarised light microscopy (PLM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results Surface hardness measurements and integrated mineral recovery value obtained from cross-sectional microhardness test (CSMH) revealed that all the treatment groups had significantly greater effect on enhancing remineralisation than that of the negative control group. Detailed investigation of both CSMH and PLM indicated that nano-HA would only help mineral deposition predominate in the outer layer of lesion and had limited capacity to reduce the lesion depth significantly. In GCE–nano-HA combined treatment group, more mineral deposition occurred in the lesion body and lesion depth was reduced significantly. Meanwhile, significantly greater mineral deposition in the outer portion of the lesion was also observed in comparison with GCE group. The results of XRD and SEM also showed that GCE could influence the deposition and adsorption of nano-HA. Conclusion There was a significant synergistic effect of combined GCE and nano-HA treatment on promoting the remineralisation of initial enamel lesion.

Effect of time in hardness test on artificially demineralized human dental enamel

A cross-sectional microhardness (CSMH) test was carried out in human dental enamel exposed to a demineralizing solution in order to evaluate two different times of indentation in sound tissue and artificially induced caries. Twenty caries-free extracted human molars had one of their smooth surfaces sectioned and the enamel surface was isolated with nail polish except for an area of 6 mm 2 . These specimens were submitted to artificially induced enamel caries on a lactate buffer containing 0.1 ppm fluoride (F) during 28 days. All specimens were bisected to create groups A and B in which CSMH test was performed employing a Knoop indenter with a 25 g load for 5 or 10 s, respectively. Student’s paired t-test (p<0.05) was used to determine statistically significant differences between groups A and B in 7 depths. There were no significant differences between any of the analyzed depths. Since the present experiment showed no significant difference when comparing indentations made with a 25 g load during either 5 or 10 s in different depths, this method can be used with either one of the time intervals tested without compromising a CSMH test on artificially demineralized human enamel.

In vivo inhibition of demineralization around orthodontic brackets

Demineralization around orthodontic appliances is a problem. Suboptimal oral hygiene, long intervals between appointments, and potentially poor patient cooperation with using fluoride dentifrices and mouth rinses necessitate a compliance-free means of preventing tooth decay. The hypothesis of this study was that fluoride released by glass ionomer cement inhibits the formation of carious lesions around orthodontic brackets in vivo. Brackets were bonded on 2 first premolars in 21 randomized, consecutively selected patients 11 to 18 years old. Eleven test-group subjects were bonded with fluoride-releasing glass ionomer cement, and 10 control subjects were bonded with composite resin (no fluoride). The teeth were extracted after 4 weeks, sectioned, and evaluated quantitatively by cross-sectional microhardness testing. Fluoride levels in patient saliva were measured by the Taves diffusion method in samples taken at days 0 (baseline), 1, 2, 3, 7, 14, 21, and 28 to determine whether fluoride from the glass ionomer cement influenced the overall intraoral fluoride levels. The results demonstrated significantly more demineralization around the brackets of the control patients (P <.01, Wilcoxon signed rank test). For whole-mouth salivary fluoride levels, no significant overall difference between the groups (P >.05) and no noticeable trend within groups (P >.05) were found. These results indicate that using fluoride-releasing glass ionomer cement for bonding orthodontic brackets successfully inhibited caries in vivo. This cariostatic effect was localized to the area around the brackets and was statistically significant after 4 weeks. (Am J Orthod Dentofacial Orthop 2003;123:10-4)

CO2 laser inhibitor of artificial caries-like lesion progression in dental enamel.

Several studies during the last 30 years have demonstrated the potential of laser pre-treatment of enamel or tooth roots to inhibit subsequent acid-induced dissolution or artificial caries-like challenge in the laboratory. The overall objective of ongoing studies in our laboratories is to determine, systematically, the optimum sets of parameters for carbon dioxide laser irradiation that will potentially effectively inhibit dental caries in enamel and tooth roots. The aim of the present study was to examine the roles of wavelength and fluence in the prevention of caries progression in vitro in enamel by means of a pH-cycling model. The hypothesis to be tested was that the highly absorbed 9.3- and 9.6-microm wavelengths would be efficiently converted to heat, creating a temperature sufficiently high to reduce the acid-reactivity of the mineral and inhibit caries-like lesion progression in dental enamel. One hundred and sixty caries-free tooth crowns were cleaned and varnished with acid-resistant varnish, leaving one exposed window of enamel. Twelve groups of 10 enamel samples were irradiated in their individual windows by one of the four wavelengths (9.3, 9.6, 10.3, or 10.6 microm) of a tunable CO2 laser. Energy per pulse was 25, 50, 100, 200, or 250 mJ (25 pulses). Repetition rate was 10 Hz, and beam diameter was 1.6 mm. Fluence conditions of 1 to 12.5 J/cm2 per pulse were produced. All teeth, including 40 non-irradiated controls, were subjected to pH-cycling to produce artificial caries-like lesions. Results were assessed by cross-sectional microhardness testing. Inhibition of caries progression of from 40% to 85% was achieved over the range of laser conditions tested. At 9.3 and 9.6 microm, 25 pulses at absorbed fluences of 1 to 3 J/cm2 produced inhibition on the order of 70% with minimal subsurface temperature elevation (< 1 degree C at 2 mm depth), comparable with inhibition produced in this model with daily fluoride dentifrice treatments. Safety and efficacy studies will be required in animals and humans before these promising laboratory results can be applied in clinical practice.

Demineralization and remineralization evaluation techniques.

This paper compares the experimental techniques utilized to assess the de- or remineralization of enamel or dentin in intra-oral studies. In in situ studies, it is important for one to know how much mineral has been lost or gained, and where the loss or gain occurred. The main emphasis in this paper is on techniques suitable for direct or indirect mineral quantification. The measuring techniques considered are microradiography, iodine absorptiometry, various microhardness tests, polarized light, light-scattering, iodide permeability, and wet chemical analysis. The various techniques are compared concerning suitability for the determination of mineral content in vol% (or wt%), mineral changes in vol% micron (or kg.m-2), and mineral distributions. Furthermore, sample preparation, the importance of protein penetration, nominal mineral loss range, the estimated mineral loss threshold, and the applicability to dentin are compared and considered. It is concluded that, although more than ten techniques are available for the measurement of changes after de- or remineralization in situ, transverse microradiography is the most practical technique for the direct and quantitative measurement of mineral content, mineral changes, and mineral distributions. Cross-sectional microhardness testing and light-scattering are also practical indirect techniques for quantitative mineral loss (or gain) determination in intra-oral studies.