Quantitative analysis of the degree of demineralization for bleached enamel by optical coherence tomography

BACKGROUND

Tooth bleaching imparts whitening effects along with adverse effects such as increased tooth sensitivity and enamel surface changes. Herein, we employed optical coherence tomography (OCT), a nondestructive optical detection technique, for evaluation of tooth enamel after treatment with peroxide-based bleaching agents.

METHODS

Fifteen enamel samples were bleached using 38% acidic hydrogen peroxide-based bleach, subjected to OCT scanning, and then cross-sectioned and imaged under polarized light microscopy (PLM) and transverse microradiography (TMR). OCT cross-sectional images were compared with PLM and TMR. The depth and severity of demineralization produced in the bleached enamel were measured by OCT, PLM, and TMR. Comparison between the three techniques was performed using Kruskal-Wallis H non-parametric test and Pearson correlation.

RESULTS

In comparison with PLM and TMR, OCT clearly detected the changes in the enamel surface after hydrogen peroxide bleaching. Significant correlations (p<0.05) were observed in lesion depth between OCT and PLM (r=0.820), OCT and TMR (r=0.822), and TMR and PLM (r=0.861). There was no statistically significant difference in demineralization depth values measured by OCT, PLM, and TMR (p>0.05).

CONCLUSION

OCT can allow real-time, non-invasive imaging of artificially bleached tooth models and automatically measure the early changes in the enamel lesion structure upon exposure to hydrogen peroxide-based bleaching agents.

Enamel and Dentin Etching with Glycolic, Ferulic, and Phosphoric Acids: Demineralization Pattern, Surface Microhardness, and Bond Strength Stability

This study evaluated the etching pattern, surface microhardness, and bond strength for enamel and dentin submitted to treatment with phosphoric, glycolic, and ferulic acids. Enamel and dentin blocks were treated with phosphoric, glycolic, and ferulic acid to evaluate the surface and adhesive interface by scanning electron microscopy (2000×). Surface microhardness (Knoop) was evaluated before and after etching, and microtensile bond strength was evaluated after application of a two-step adhesive system (Adper Single Bond 2, 3M ESPE) at 24 hours and 12 months storage time points. Analysis of variance (ANOVA) and Tukey's test showed a decrease in the microhardness values for both substrates after application of each acid (p<0.0001). The reduction percentage was significantly higher for enamel treated with phosphoric acid (59.9%) and glycolic acid (65.1%) than for ferulic acid (16.5%) (p<0.0001), and higher for dentin that received phosphoric acid (38.3%) versus glycolic acid (27.8%) and ferulic acid (21.9%) (p<0.0001). Phosphoric and glycolic acids led to homogeneous enamel demineralization, and promoted the opening of dentinal tubules, whereas ferulic acid led to enamel surface demineralization and partially removed the smear layer. The adhesive-enamel interface showed micromechanical embedding of the adhesive in the interprismatic spaces when phosphoric and glycolic acids were applied. Ferulic acid showed no tag formation. Microtensile bond strength at both time points, and for both substrates, was lower with ferulic acid (p=0.0003/E; p=0.0011/D; Kruskal Wallis and Dunn). The bond strength for enamel and dentin decreased when using phosphoric and glycolic acids at the 12-month time evaluation (p<0.05). Glycolic acid showed an etching pattern and microhardness similar to that of phosphoric acid. Ferulic acid was not effective in etching the enamel or dentin, and it did not provide satisfactory bond strength to dental substrates.

Artificial Caries Lesion Characteristics after Secondary Demineralization with Theobromine-Containing Protocol

Developing artificial caries lesions with varying characteristics is needed to adequately study caries process in vitro. The objective of this study was to investigate artificial caries lesion characteristics after secondary demineralization protocol containing theobromine and fluoride. Sixty bovine enamel slabs (4 × 3 mm) were demineralized using a Carbopol-containing protocol for 6 days. A baseline area (2 × 3 mm) was protected with acid-resistant nail varnish, after which specimens were exposed for 24 h to a secondary demineralization protocol containing acetic acid plus one of four fluoride/theobromine combinations (n = 15): theobromine (50 or 200 ppm) and fluoride (0 or 1 ppm). Specimens were sectioned and analyzed using transverse microradiography for changes in mineral content, lesion depth, and surface layer mineralization. Data was analyzed using paired t-test and analysis of variance followed by Bonferroni test at 0.05 significance level. After secondary demineralization, fluoride-containing groups had significantly deeper lesions (p = 0.002 and 0.014) compared to the group with 0 ppm fluoride and 50 ppm theobromine. Mineral content and lesion depth were significantly different compared to baseline for all groups. Theobromine did not show an added effect on mineral uptake. Theobromine-containing groups exhibited particularly deep lesions with a more uniform mineral profile in the presence of fluoride.

Development and calibration of biochemical models for testing dental restorations

Currently, resin composites are the most popular materials for dental restoration in clinical practice. Although the properties of such materials have been improved significantly, together with better clinical techniques used for their placement, early restoration failure still occurs too frequently. As clinical studies take years to complete, and new resin composites are being produced at ever increasing pace, laboratory assessment using accelerated but representative tests is necessary. The main types of failure in resin-composite restoration are tooth/restoration fracture and secondary caries, which are caused by a combination of mechanical and biochemical challenges. In this study, a biofilm model (S. mutans) and a chemical model (lactic-acid buffer) for producing artificial caries in bovine dentin are developed and calibrated against in situ data. Using a power law relationship between the demineralization depth and challenge duration, scale factors that convert the in vitro durations to the equivalent clinical durations are determined for different pH values for each model. The scale factors will allow the synchronization of biochemical and mechanical challenges in terms of their rates of action to potentially test resin-composite restoration in an accelerated but clinically representative manner. STATEMENT OF SIGNIFICANCE: Although the properties of resin composites for dental restoration have been improved significantly, early restoration failure still occurs too frequently. As clinical studies take years to complete, accelerated laboratory testing is necessary. Resin-composite restoration fail mainly through fracture and secondary caries, caused by a combination of mechanical and biochemical challenges. In this study, a biofilm and a chemical model for producing artificial caries in bovine dentin are calibrated against in situ data. Using a power law relationship between demineralization depth and challenge duration, scale factors are determined for different pH for each model. The scale factors will allow the synchronization of biochemical and mechanical challenges in testing resin-composite restoration in an accelerated but clinically representative manner.

Effects of bleaching using 10% carbamide peroxide with calcium or amorphous calcium phosphate on enamel mineral content and hardness

This study evaluated enamel mineral content and surface microhardness before and after bleaching treatment using 10% carbamide peroxide (CP) containing calcium (Ca) or amorphous calcium phosphate (ACP). Thirtysix bovine slabs were randomly allocated into 3 groups (n = 12) according to bleaching treatment: G1 Opalescence PF 10% (CP), G2 NiteWhite ACP (CP+ACP), and G3 Opalescence PF (10%) with calcium (CP+CA). The bleaching agent was applied on enamel surface for 6 h/day over a period of 21 days. Enamel surface was evaluated by Knoop microhardness (KNH) and micro energydispersive Xray fluorescence spectrometry (μEDXRF) at baseline and at after bleaching treatment. Data were statistically analyzed by repeated measures ANOVA and Tukey's test (α = 0.05). There was a significant decrease in microhardness after bleaching treatments for all study groups, but no difference between bleaching gels. There was no difference in the Ca/P ratio measured by μEDXRF for all groups at the study times, but the mean value was lower in group CP+CA than in group CP+ACP. Group CP was similar to both CP+ACP and CP+CA. It can be concluded that enamel microhardness decreased after the bleaching process, regardless of the presence of calcium or ACP, but there was no significant change in the Ca/P ratio of enamel after bleaching for each tested gel. This indicates that the bleaching gels have erosive potential, causing softening of enamel without promoting surface loss, regardless of the presence of calcium of ACP ions.

Effect of Toothpaste Use Against Mineral Loss Promoted by Dental Bleaching

AIM

To investigate the effect of different toothpaste formulations used prior to dental bleaching with 35% hydrogen peroxide (HP) on the mineral content and surface morphology of enamel.

METHODS

Seventy bovine enamel blocks (4×4×2 mm) were submitted to in vitro treatment protocols using a toothbrushing machine prior to dental bleaching or a placebo procedure (n=10) as proposed in the following groups: unbleached control (PLA), bleached control (HP), and brushing with differing toothpastes prior to HP bleaching, including: potassium nitrate toothpaste containing sodium fluoride (PN), sodium monofluorophosphate/MFP toothpaste (FT), arginine-carbonate (8% arginine) (PA) or arginine-carbonate (1.5% arginine) toothpaste (SAN), and toothpaste containing bioactive glass (NM). Phosphorus concentration in gel ([P]) was evaluated (μg of P/mg of gel), and the elemental levels (wt%) of Ca, P, and Na as well as the proportion between Ca and P and spectra graphics were determined using an energy-dispersive X-ray spectrometer (EDS). The surface morphology was assessed using scanning electron microscopy (SEM). The data were subjected to analysis of variance and the Tukey test (α=0.05).

RESULTS

HP demonstrated the greatest [P] values in gel, being statistically different from PLA. The [P] of NM was statistically similar to PLA. HP showed a significant decrease in the Ca% and Ca/P values when compared to PLA in EDS analysis. PA showed Ca/P values statistically different from HP. In accordance with SEM analysis, the PA, SAN, and NM groups presented a smooth and uniform enamel surface, while HP and FT demonstrated some alterations in morphology.

CONCLUSION

The toothpastes containing bioactive glass or arginine carbonate used prior to dental bleaching were effective in protecting enamel against mineral loss promoted by the whitening procedure.

Prognosis test by visualization of demineralized dentin under restorations to prevent initial wall-lesions initiated by lactic acid

PURPOSE

To visualize the complete protection of restored dentin in the acidic environment by the complete impregnation of resin into demineralized dentin.

METHODS

Class V cavities prepared in extracted human molars composed of enamel, cementum and dentin surfaces were sealed using either 4-META/MMA-TBB resin with conditioning periods of 10, 30, 60 seconds with 10% citric acid and 3% ferric chloride mixed aqueous solution (10-3) or Single-Bond 2 adhesives prior to restoration with light-cured resin-composite. Specimens were either immersed in artificial saliva or 0.1 mol/L buffered lactic acid solutions at 37°C for 14 days. After immersion in 0.5% basic fuchsin dye for 24 hours, the extent of dye penetration at the margin was measured. SEM micrography was used to investigate the quality of hybridized dentin when immersed in HCl followed by NaOCl solutions.

RESULTS

After lactic acid exposure, dye penetration into the adjacent demineralized cementum/dentin was found to be significantly lower than the leakage distance under 30 and 60 seconds and Single-Bond 2 specimens. Leakage-free margins were found in 10-second conditioning period specimens for both control and after soaking in buffered lactic solution with the stable hybridized dentin after chemical challenge.

CLINICAL SIGNIFICANCE

A leakage-free interfacial layer, provided by complete hybrid layer formation, can block lactic acid penetration. Using this novel prognosis test for visualization of demineralized dentin, clinical restorations are likely to be more reliably predictable in the prevention of initial wall-lesions, post-operative hypersensitivity and/or pulpal infection.

Efficacy of fluoride varnishes for preventing enamel demineralization after interproximal enamel reduction. Qualitative and quantitative evaluation

Objectives

To evaluate quantitatively and qualitatively the changes produced to enamel after interproximal reduction and subjected to demineralization cycles, after applying a fluoride varnish (Profluorid) and a fluoride varnish containing tricalcium phosphate modified by fumaric acid (Clinpro White).

Materials and methods

138 interproximal dental surfaces were divided into six groups: 1) Intact enamel; 2) Intact enamel + demineralization cycles (DC); 3) Interproximal Reduction (IR); 4) IR + DC; 5) IR + Profluorid + DC; 6) IR + Clinpro White + DC. IR was performed with a 0.5 mm cylindrical diamond bur. The weight percentage of calcium (Ca), phosphorous (P) and fluoride (F) were quantified by energy-dispersive X-ray spectrometry (EDX). Samples were examined under scanning electron microscopy (SEM).

Results

The weight percentage of Ca was significantly higher (p<0.05) in Groups 1, 2 and 5 than Groups 4 and 6. No significant differences were detected in the weight percentage of Ca between Group 3 and the other groups (p>0.05). The weight percentage of P was similar among all six groups (p>0.05). F was detected on 65% of Group 6 surfaces. SEM images of Groups 4 and 6 showed signs of demineralization, while Group 5 did not.

Conclusions

Profluorid application acts as a barrier against the demineralization of interproximally reduced enamel.

Continuing Etching of an All-in-One Adhesive in Wet Dentin Tubules

Self-etch adhesives that etch and prime simultaneously are becoming more acidic. We hypothesized that the degree of acidic monomer conversion at the interface and within the tubules was high enough that the acidic reaction would be very self-limiting. Dentin surfaces prepared from extracted, unerupted human third molars were treated with Prompt L-Pop (3M ESPE). The prepared teeth were stored in normal saline, and specimens retrieved at intervals ≤ 4 wks were randomly selected for light, scanning electron microscopic and micro-Raman spectroscopic analysis. Morphologic and spectroscopic analyses indicated dentin demineralization and adhesive penetration throughout the demineralized layer and tubules. Increased dentin demineralization and loss of adhesive integrity were noted after aqueous storage. The degree of monomer conversion at the interface was consistently greater than conversion within the tubules. Fluid within the tubules may inhibit monomer conversion. The acidic characteristics of this adhesive may be retained and, thus, continue to affect/demineralize the surrounding dentin.

Ca, Pi, and F in the Fluid of Biofilm Formed under Sucrose

Calcium (Ca), inorganic phosphorus (Pi), and fluoride (F) concentrations are low in the whole plaque biofilm formed under exposure to sucrose. It was hypothesized that this would be reflected in the biofilm fluid, where these low values should greatly influence the de/remineralization process. Dental biofilms were formed in situ over enamel blocks mounted in palatal appliances and exposed 8 times/day to distilled water, glucose+fructose, or sucrose solutions for 14 days. While Ca, Pi, and F concentrations in the whole biofilms were significantly lower in the glucose+fructose and sucrose groups, no effect on biofilm fluid was observed, even after a cariogenic challenge. An increase in whole biofilm mineral ions was observed 24 hrs after the carbohydrate treatments were suspended, but this effect was also not observed in the fluid. These results suggest that there is a homeostatic mechanism that maintains biofilm fluid mineral ion concentration, regardless of its total concentration in the whole biofilm.

[Durability of protective effect of resin-based coating material on root surface]

OBJECTIVE

To compare the durability of resin-based root-surface coating material and all-in-one self-etching adhesive on root surface in vitro.

METHODS

Human extracted premolars or molars with intact roots were selected. The cementum was removed using a periodontal scaler to expose root dentin. The root surface was coated with an acid-resistant nail varnish, leaving a window of 3 mm×3 mm on the exposed dentin.The window was covered with either PRG Barrier Coat (PRG) or Clearfil S3 Bond (CS3). After water aging for 14 d, specimens were immersed in acid buffer at pH 4.5 for 4 d and the demineralization buffer was changed every 24 h. Then the specimen was split longitudinally through the center of the 'window' and the cross-sectional surface was observed with scanning electron microscope (SEM). After fixed and dehydrated, the prepared samples were coated with platinum. The coating material, root dentin and the interface was observed by scanning electron microscope (SEM). The thickness of the coating material was measured on the SEM images. Regarding toothbrush wear test, coronal dentindisks were prepared and covered with PRG and CS3, respectively. After storage in water for 24 h, the specimen was subjected to the toothbrush wear tester for 100, 200, 300, 500, 700, 1 500 brushing cycles. A slurry of fluoride toothpaste (1:2 ratio of toothpaste and deionized water by weight) was used and the brushing load was 300 N. The surface microstructure of remaining coating material was analyzed using SEM. The wear depths were determined by a profilometer. Statistical analysis was performed with SPSS 20.0 by one-way ANOVA. The level of significance was at 0.05.

RESULTS

Application of PRG Barrier Coat produced a coating layer of (47.1±27.3) μm, while CS3 presented a thin film of (5.7±2.1) μm in thickness. The exposed dentin was hermetically sealed and no obvious gap was observed at the interface in both PRG and CS3 groups. There was no dentin demineralization observed in both groups after water aging. The wear depths of PRG and CS3 increased along with the numbers of brushing cycles. PRG wore at a significant lower pace than CS3 did (P<0.05).

CONCLUSION

PRG coating resin had similar performances as CS3 on protecting root dentin from demineralization after water aging. What's more, PRG demonstrated a higher toothbrush wear resistance than CS3. We concluded that PRG Barrier Coat contained S-PRG filler may be an effective coating material for protecting exposed root from both chemical and mechanical challenges. Further studies should be carried out to evaluate the long-term reliability of the rootsurface coating materials under the clinical setting.

Dental demineralization and caries in patients with head and neck cancer

Concurrent chemoradiation (CCR) therapy is a standard treatment for patients with locally advanced head and neck cancer (HNC). It is well documented that CCR causes profound acute and late toxicities. Xerostomia (the symptom of dry mouth) and hyposalivation (decreased salivary flow) are among the most common treatment side effects in this cohort of patients during and following treatment. They are the result of radiation-induced damage to the salivary glands. Patients with chronic hyposalivation are at risk for demineralization and dental cavitation (dental caries), often presenting as a severe form of rapidly developing decay that results in loss of dentition. Usual post-radiation oral care which includes the use of fluoride, may decrease, but does not eliminate dental caries associated with radiation-induced hyposalivation. The authors conducted a narrative literature review regarding dental caries in HNC population based on MEDLINE, PubMed, CLNAHL, Cochrane database, EMBASE, and PsycINFO from 1985 to 2014. Primary search terms included head and/or neck cancer, dental caries, dental decay, risk factor, physical symptom, physical sequellea, body image, quality of life, measurement, assessment, cost, prevention, and treatment. The authors also reviewed information from National Institute of Dental and Craniofacial Research (NIDCR), American Dental Association (ADA), and other related healthcare professional association web sites. This literature review focuses on critical issues related to dental caries in patients with HNC: potential mechanisms and contributing factors, clinical assessment, physical sequellea, negative impact on body image and quality of life, potential preventative strategies, and recommendations for practice and research in this area.

Weaker dental enamel explains dental decay

Dental caries continues to be the most prevalent bacteria-mediated non-contagious disease of humankind. Dental professionals assert the disease can be explained by poor oral hygiene and a diet rich in sugars but this does not account for caries free individuals exposed to the same risk factors. In order to test the hypothesis that amount of amelogenin during enamel development can influence caries susceptibility, we generated multiple strains of mice with varying levels of available amelogenin during dental development. Mechanical tests showed that dental enamel developed with less amelogenin is "weaker" while the dental enamel of animals over-expressing amelogenin appears to be more resistant to acid dissolution.

Zoledronate and ion-releasing resins impair dentin collagen degradation

This study analyzed the amounts of solubilized telopeptides cross-linked carboxyterminal telopeptide of type I collagen (ICTP) and C-terminal crosslinked telopeptide of type I collagen (CTX) derived from matrix-metalloproteinases (MMPs) and cysteine cathepsins (CTPs) subsequent to application of a filler-free (Res.A) or an ion-releasing resin (Res.B) to ethylenediaminetetraacetic acid (EDTA)-demineralized dentin with or without zoledronate-containing primer (Zol-primer) pre-treatment. The chemical modification induced following treatments and artificial saliva (AS) storage was also analyzed through attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Totally EDTA-demineralized specimens were infiltrated with Res.A or Res.B with or without Zol-primer pre-treatment, light-cured, and immersed in AS for up to 4 wk. ICTP release was reduced following infiltration with Res.B and further reduced when Res.B was used with Zol-primer; remarkable phosphate mineral uptake was attained after AS storage. CTX release was increased in Res.A- and Res.B-treated dentin. However, when Zol-primer was used with Res.A, the CTX release fell significantly compared to the other tested resin-infiltration methods. In conclusion, zoledronate offers an additional inhibitory effect to the ion-releasing resins in MMP-mediated collagen degradation. However, Zol-primer induces a modest reduction in CTX release only when used with resin-based systems containing no ion-releasing fillers.

Calcium and magnesium levels in primary tooth enamel and genetic variation in enamel formation genes

PURPOSE

Evidence exists that a genetic component in caries susceptibility is related to variation in enamel formation genes. The purpose of this study was to explore the trends of demineralization and remineralization of teeth from individuals whose genotypes for selected genes (ENAM, MMP20, TUFT, TFIP, and AMBN) are known.

METHODS

In this study, primary baseline teeth (20) were exposed to an artificial caries solution, followed by a remineralizing solution. Biopsies of each tooth category (baseline, carious, and fluoridated) were completed via an acid wash solution. Concentrations of magnesium and calcium were measured using an optical emission spectrometer instrument. Allele and genotype frequencies for calcium and magnesium levels were compared between each tooth category. To help interpret the results, we also calculated odds ratios.

RESULTS

Calcium levels exceeded magnesium levels in each sample. In addition, mineral concentration varied among samples. Associations could be seen between genetic variation in ENAM (P=.0003 baseline values for calcium, P<.001 baseline values for magnesium, P<.04 artificial caries values for magnesium) and AMBN (P<.02 artificial caries values for calcium) with mineral concentration.

CONCLUSIONS

Our results suggest that genetic variation of enamel formation genes may influence calcium and magnesium concentrations of teeth and impact the development of caries.

Ferric sulphate alterations on primary dentin and the adhesive interface

PURPOSE

The purpose of this study was to test the hypothesis that the pulp medication ferric sulphate (FS) may remain on primary dentin, affecting its microchemical structure and the bond strength of adhesives to primary dentin.

MATERIALS AND METHODS

The effects of FS and pre-bonding conditioning (37% phosphoric acid [PA] for 15 s or a self-etching primer, with or without the use of 2% chlorhexidine [CHX]) on FS-treated primary dentin were characterized using optical microscopy with Masson's and Perls' stains, variable-pressure SEM/energy-dispersive x-ray spectroscopy (VP-SEM/EDS), Fourier transform infrared spectroscopy (FT-IR), and x-ray diffraction. Ferric sulphate was applied for 30 s or 1 h for microchemical analysis. The adhesive interface and the bond strength were studied by VP-SEM/EDS and the μTBS test (1 mm2 bars, crosshead speed 0.5 mm/min), respectively. The study groups were: etch-and-rinse (E&R, Excite) adhesive (group 1); FS+E&R (group 2); FS+CHX+E&R (group 3); self-etching (SE, Adper Scotchbond) adhesive (group 4); FS+SE (group 5); FS+CHX+SE (group 6).

RESULTS

Ferric sulphate application produced demineralization, gypsum formation, and adsorption of Fe on the dentin surface, and it modified the collagen structure of primary dentin. There were no effects of FS on bond strength of the tested etch-and-rinse adhesive system. FS slightly reduced the bond strength between the primary dentin and the SE adhesive, and the values were not restored by CHX (group 4 = 17.58 ± 5.52 MPa > group 5 = 14.26 ± 7.08 MPa = group 6 = 13.96 ± 4.87 MPa).

CONCLUSIONS

Ferric sulphate alters the microchemical structure of primary dentin and can impair the adhesive strength of some self-etching adhesives.

DENTINE CARIES: ACID-TOLERANT MICROORGANISMS AND ASPECTS ON COLLAGEN DEGRADATION

Dental caries is a common disease all over the world, despite the fact that it can be both effectively prevented and treated. It is driven by acids produced by oral microorganisms as a consequence of their metabolism of dietary carbohydrates. Given enough acid challenge, eventually the tooth enamel barrier will be broken down, and the carious lesion will extend into underlying hard tissue, forming a macroscopic cavity in the dentine. In comparison to biofilm on enamel, a dentine carious lesion provides a vastly different environment for the residing microorganisms. The environment influences the types and numbers of microorganisms that can colonize the dentine caries lesion. The overall aims for this thesis are to enumerate and further study microorganisms found in established dentine caries lesions and also to illuminate how host-derived proteolytic enzymes might contribute to this degradation, not only to better understand the caries process in dentine but also to find incitements for new methods to influence the natural progression of caries lesions. In Paper I, the numbers of remaining viable microorganisms after completed excavation using two excavation methods were investigated. Samples of carious dentine tissue were collected before and after excavation and cultivated on different agar media in different atmospheres. Analysis was performed by counting the number of colony-forming units (CFUs). Key findings: The number of remaining microorganisms after excavation was low for both methods, but some microorganisms always remained in the cavity floors even when the cavities were judged as caries free using normal clinical criteria. In Paper II, the acid tolerant microbiota in established dentine caries lesions was investigated. Samples were taken as in Paper I, but on three levels (superficial, center of lesion, floor of lesion after completed excavation). The samples were cultivated in anaerobic conditions on solid pH-selective agar media of different acidity. Key findings: Each investigated lesion harbored a unique microbiota in terms of both species composition and numbers of microorganisms. This indicates that various combinations of aciduric microorganisms can colonize, survive in and probably also propagate dentine carious lesions. We also found that solid pH-selective agars can be used successfully to select acid-tolerant microorganisms in caries lesions. This would preserve their phenotypic traits for further study. In Paper III, the relation between salivary levels of matrix metalloproteinase-8 (MMP-8), salivary levels of tissue inhibitor of MMP (TIMP-1), and the presence of manifest caries lesions in a large number of subjects was investigated. Saliva samples were collected and analyzed for concentrations of MMP-8, TIMP-1 and total protein using immunofluorometric assays, enzyme linked immunosorbent assays and Bradford assays, respectively. Key findings: Subjects with manifest caries lesions had significantly elevated levels of salivary MMP-8 compared to subjects without caries lesions. TIMP-1 was not significant in any case. In Paper IV, a new method for generating bioactive demineralized dentine matrix substrate (DDM) was developed using a dialysis system and two different demineralization approaches (acetic acid or EDTA). The generated DDM was subsequently analyzed for the presence of type 1 collagen, active MMP-8 and hydroxyproline (HYP) levels using SDS-PAGE, ELISA or immunofluorescence assay. Key findings: Both demineralization methods produced a substrate rich in collagen and with preserved MMP-8 activity. This report presents new knowledge on the composition of the acid tolerant dentine caries microbiota from three levels in dentine carious lesions and on the efficacy of operative caries removal on the numbers of viable microorganisms in the caries free cavity using two operative methods. Moreover, the basic mechanisms behind collagen degradation in the dentine caries process are studied from both a clinical and laboratory perspective. The report also provides a reference for further studies on dentine caries microbiology and dentine caries collagen degradation mechanisms, both of which are known only in part.

Enamel etching for bonding fixed orthodontic braces

BACKGROUND

Acid etching of tooth surfaces to promote the bonding of orthodontic attachments to the enamel has been a routine procedure in orthodontic treatment since the 1960s. Various types of orthodontic etchants and etching techniques have been introduced in the past five decades. Although a large amount of information on this topic has been published, there is a significant lack of consensus regarding the clinical effects of different dental etchants and etching techniques.

OBJECTIVES

To compare the effects of different dental etchants and different etching techniques for the bonding of fixed orthodontic appliances.

SEARCH METHODS

We searched the following electronic databases: the Cochrane Oral Health Group's Trials Register (to 8 March 2013), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2013, Issue 2), MEDLINE via OVID (to 8 March 2013), EMBASE via OVID (to 8 March 2013), Chinese Biomedical Literature Database (to 12 March 2011), the WHO International Clinical Trials Registry Platform (to 8 March 2013) and the National Institutes of Health Clinical Trials Registry (to 8 March 2013). A handsearching group updated the handsearching of journals, carried out as part of the Cochrane Worldwide Handsearching Programme, to the most current issue. There were no restrictions regarding language or date of publication.

SELECTION CRITERIA

Randomized controlled trials (RCTs) comparing different etching materials, or different etching techniques using the same etchants, for the bonding of fixed orthodontic brackets to incisors, canines and premolars in children and adults.

DATA COLLECTION AND ANALYSIS

Two review authors extracted data and assessed the risk of bias of included studies independently and in duplicate. We resolved disagreements by discussion among the review team. We contacted the corresponding authors of the included studies to obtain additional information, if necessary.

MAIN RESULTS

We included 13 studies randomizing 417 participants with 7184 teeth/brackets. We assessed two studies (15%) as being at low risk of bias, 10 studies (77%) as being at high risk of bias and one study (8%) as being at unclear risk of bias. Self etching primers (SEPs) versus conventional etchantsEleven studies compared the effects of SEPs with conventional etchants. Only five of these studies (three of split-mouth design and two of parallel design) reported data at the participant level, with the remaining studies reporting at the tooth level, thus ignoring clustering/the paired nature of the data. A meta-analysis of these five studies, with follow-up ranging from 5 to 37 months, provided low-quality evidence that was insufficient to determine whether or not there is a difference in bond failure rate between SEPs and convention etchants (risk ratio 1.14; 95% confidence interval (CI) 0.75 to 1.73; 221 participants). The uncertainty in the CI includes both no effect and appreciable benefit and harm. Subgroup analysis did not show a difference between split-mouth and parallel studies.There were no data available to allow assessment of the outcomes: decalcification, participant satisfaction and cost-effectiveness. One study reported decalcification, but only at the tooth level. SEPs versus SEPsTwo studies compared two different SEPs. Both studies reported bond failure rate, with one of the studies also reporting decalcification. However, as both studies reported outcomes only at the tooth level, there were no data available to evaluate the superiority of any of the SEPs over the others investigated with regards to any of the outcomes of this review.We did not find any eligible studies evaluating different etching materials (e.g. phosphoric acid, polyacrylic acid, maleic acid), concentrations or etching times.

AUTHORS' CONCLUSIONS

We found low-quality evidence that was insufficient to conclude whether or not there is a difference in bond failure rate between SEPs and conventional etching systems when bonding fixed orthodontic appliances over a 5- to 37-month follow-up. Insufficient data were also available to allow any conclusions to be formed regarding the superiority of SEPs or conventional etching for the outcomes: decalcification, participant satisfaction and cost-effectiveness, or regarding the superiority of different etching materials, concentrations or etching times, or of any one SEP over another. Further well-designed RCTs on this topic are needed to provide more evidence in order to answer these clinical questions.

Accelerated fatigue of dentin with exposure to lactic acid

Composite restorations accumulate more biofilm than other dental materials. This increases the likelihood for the hard tissues supporting a restoration (i.e. dentin and enamel) to be exposed to acidic conditions beyond that resulting from dietary variations. In this investigation the fatigue strength and fatigue crack growth resistance of human coronal dentin were characterized within a lactic acid solution (with pH = 5) and compared to that of controls evaluated in neutral conditions (pH = 7). A comparison of the fatigue life distributions showed that the lactic acid exposure resulted in a significant reduction in the fatigue strength (p ≤ 0.001), and nearly 30% reduction in the apparent endurance limit (from 44 MPa to 32 MPa). The reduction in pH also caused a significant decrease (p ≤ 0.05) in the threshold stress intensity range required for the initiation of cyclic crack growth, and significant increase in the incremental rate of crack extension. Exposure of tooth structure to lactic acid may cause demineralization, but it also increases the likelihood of restored tooth failures via fatigue, and after short time periods.

Cariogenic potential of commercial sweeteners in an experimental biofilm caries model on enamel

OBJECTIVE

Scarce evidence is available on the cariogenic potential of the widely used commercial sweeteners. The aim of this study was to evaluate the effect of several sweeteners on enamel demineralisation and on the cariogenic properties of Streptococcus mutans biofilms in an artificial caries model.

METHODS

S. mutans-UA159 biofilms were cultured on bovine enamel slabs and exposed to one of the following commercial sweeteners in tablet or powder form: stevia, sucralose, saccharin, aspartame or fructose. Ten percent sucrose and 0.9% NaCl were used as caries-positive and caries-negative controls, respectively. Slabs/biofilms were exposed to the sweeteners three times per day for 5min each time. After 5 days, biofilms were recovered to determine: biomass, bacterial counts and intra- and extracellular polysaccharides. Surface microhardness was measured before and after the experiment to assess enamel demineralisation, expressed as percentage of surface hardness loss (%SHL). Data were analysed using analysis of variance (ANOVA) and Bonferroni (p<0.05).

RESULTS

All tested commercial sweeteners, except fructose, showed less enamel demineralisation than sucrose (p<0.05). Only saccharine showed less biomass and intracellular polysaccharides than the rest of the groups (p<0.05). Stevia, sucralose and saccharine reduced the number of viable cells when compared with sucrose (p<0.05). All sugar alternatives reduced extracellular polysaccharide formation when compared with sucrose (p<0.05).

CONCLUSIONS

Most commercial sweeteners appear to be less cariogenic than sucrose, but still retaining some enamel demineralisation potential. Products containing stevia, sucralose and saccharine showed antibacterial properties and seem to interfere with bacterial metabolism. Further studies are necessary to deepen these findings.

Anti-demineralization effect of a novel fluoride-releasing varnish on dentin

PURPOSE

To investigate the laboratory anti-demineralization effect of a novel fluoride-releasing varnish containing surface reaction-type prereacted glass-ionomer (S-PRG) filler.

METHODS

Paired specimens were cut from bovine root dentin. One of each pair was used for the S-PRG group, and the other served as a control (n = 6). A 1 x 3 mm test surface was made on each specimen with the fluoride-releasing varnish. The novel fluoride-releasing varnish is categorized as a two-bottle-type self-etch adhesive. These liquids were mixed, applied on the test surface, and light-cured for 10 seconds. As a control, an S-PRG filler-free varnish was applied in the same manner. Each specimen was immersed in 8% methylcellulose gel demineralization system (1.5 mM Ca, 0.9 mM PO4, 0.1 M acetic acid, pH 5.0) for 7 days at 3 degrees C. The mineral profiles and integrated mineral loss (IML) of the lesions were obtained by transversal microradiography and analytical software.

RESULTS

The S-PRG group exhibited significantly thicker surface layer than the control group. Furthermore, the S-PRG group showed significantly lower IML (3,459 vol% xmicropm) than the control group (4,687 vol% xmicropm) ( P < 0.05, Welch's two-sample t-test). The novel fluoride-releasing varnish increased acid resistance of root dentin in the vicinity of the coated surface.

Microhardness change of enamel due to bleaching with in-office bleaching gels of different acidity

OBJECTIVE

The aim of this study was to assess the enamel microhardness treated with three in-office bleaching agents, containing 35% hydrogen peroxide with different acidity.

MATERIALS AND METHODS

Bovine incisors were divided into three groups that received the following bleaching agents: Whiteness HP, Total Bleach and Opalescence Xtra. Three gel applications/10-min each, totaling 30-min of bleaching treatment, were made on the teeth and activated with a blue LED (1000 mW/470 nm) combined to a LASER (120 mW/795 nm) device (Easy Bleach-Clean Line). Vickers hardness (VH) was evaluated at baseline and after the bleaching procedure. The values of Hardness loss [HNL] (% reduction) were calculated. The two-sample t-test was used for comparison of the HNL of the three bleaching products (5% level of significance).

RESULTS

The Opalescence Xtra, which had the lowest pH value (pH = 4.30), showed a significant increase of HNL when compared with Total Bleach bleaching agent, which had the highest pH value (pH = 6.62).

CONCLUSIONS

The 35% hydrogen peroxide bleaching agents resulted in a reduction in surface enamel microhardness and bleaching with the most acid agent resulted in a significant enamel hardness loss compared to the less acid agent (4.30 vs 6.62). Strategies proposed to reduce the enamel loss after bleaching treatment may include the use of daily fluoride therapy, mouth rinsing (fluoride, milk and sodium bicarbonate solution), fluoride/bicarbonate dentifrices without abrasives, do not toothbrush immediately after bleaching, fluorides and calcium add to bleaching agents.

Quantitative remineralization evolution kinetics of artificially demineralized human enamel using photothermal radiometry and modulated luminescence

Human molars were subjected to demineralization in acid gel followed by incubation in remineralization solutions without or with fluoride (1 or 1000 ppm). Photothermal radiometry (PTR) and modulated luminescence (LUM) frequency scans were performed prior to and during de/remineralization treatments. Transverse Micro-Radiography (TMR) analysis followed at treatment conclusion to determine mineral loss and lesion depth. The remineralization process illustrated a complex interplay between surface and subsurface mineral deposition, confining the thermal-wave centroid toward the dominating layer. Experimental amplitudes and phases were fitted to a coupled diffuse-photon-density-wave and thermal-wave theoretical model used to quantitatively evaluate evolving changes in thermal and optical properties of de/remineralized enamel lesions. Additional information obtained from the LUM data corroborated the remineralization kinetics affecting the PTR signals. The results pointed to enhanced effectiveness of subsurface lesion remineralization in the presence of fluoride.

The influence of daily application of fluoride products on subsurface bovine enamel lesions stored in saliva substitutes

PURPOSE

To evaluate in the laboratory the effects of daily fluoride applications on remineralization of subsurface bovine enamel lesions stored in different saliva substitutes.

METHODS

Enamel specimens were prepared (n = 144) and demineralized (subsurface lesions; 37 degrees C; pH 4.95; 10 days). Before and after demineralization, specimen surfaces were partly covered with nail varnish (control of sound/demineralized enamel). The specimens were either stored (5 weeks; 37 degrees C) in mineral water (W, control, S(OCP) 0.7, pH 7.0), Glandosane (G, S(OCP) 0.3, pH 5.2), or modified Saliva Natura (SN, S(OCP) 2.0, pH 5.98), and were submitted to the following treatments twice daily: (0) no treatment; (ES) immersion in pure Elmex Sensitive mouthrinse (10 minutes); (D) brushing with Duraphat toothpaste/storage solution slurry (5 seconds + contact time 115 seconds; ratio 1:3); (ES+D) combination of ES and D treatments. Mineral parameters before and after storage/treatment were evaluated from microradiographs.

RESULTS

Specimens stored in G showed significantly higher demineralization compared to the other solutions (P < 0.05, ANOVA, Tukey's post hoc test); the combined treatment with fluoride products significantly reduced the demineralizing effect of G. After 2 and 5 weeks, specimens stored in SN revealed a higher remineralization compared to the control solution (P < 0.05). Daily application of fluoride products did not promote an additional effect on remineralization of specimens stored in SN (P > 0.05).

Mineral distribution of artificial dentinal caries lesions after treatment with fluoride agents in combination with saliva substitutes

OBJECTIVE

Some saliva substitutes have been shown to demineralize dentine in vitro. This effect is counteracted by the application of various fluorides. In contrast, remineralizing saliva substitutes might be supported by these treatments, depending on the dynamics during remineralization. The aim of this in vitro study was to evaluate the effects of fluoride mouthrinses or gels in combination with de-/remineralizing saliva substitutes on dentinal subsurface lesions.

DESIGN

Demineralized bovine dentine specimens were stored either in mineral water [saturation with respect to octacalcium phosphate (S(OCP)): 0.7], Glandosane (G, S(OCP): 0.3) or in a modified saliva substitute Saliva natura (SN, S(OCP): 1.9) for five weeks (37°C). Fluoride agents were applied twice daily for 10 min (n = 15/group): no treatment, Meridol mouthrinse, Elmex sensitive solution, ProSchmelz fluoride gel, Elmex gelée. After storage thin sections were prepared and mineral losses before and after storage were evaluated from microradiographs.

RESULTS

Specimens stored in G alone showed significantly higher mineral loss compared to those stored in water, SN or G in combination with any additional treatment (p < 0.05). Storage in SN and treatment with ProSchmelz fluoride gel led to significantly higher remineralization compared to all other groups (p < 0.05) and resulted in distinct mineral gain within the lesion body.

CONCLUSIONS

Under the in vitro conditions chosen, use of fluoride agents in combination with a demineralizing saliva substitute resulted in reduced mineral loss. Storage in modified Saliva natura in combination with the application of ProSchmelz fluoride gel induced the most pronounced remineralization also of deeper lesion areas.

Changes in surface morphology and mineralization level of human enamel following in-office bleaching with 35% hydrogen peroxide and light irradiation

The objective of this study was to evaluate the alterations on surface morphology and mineral loss of human enamel following in-office bleaching with 35% hydrogen peroxide and light irradiation. Dental enamel samples were obtained from human third molars and randomly divided into 10 groups (n = 10). The control group remained untreated. Bleached groups were treated with one of three whitening products. Bleaching was performed in a single session, during which bleaching gel was applied to the enamel surface three times for 10 minutes each time. During treatment, the bleaching agents were either irradiated by a halogen light or an LED/diode laser or were not irradiated at all. Microhardness testing was performed with a Knoop indentor and the surface morphologic observations were carried out by scanning electron microscopy (SEM). Cross-sectional microhardness (CSMH) and polarized light microscopy (PLM) were used to measure the depth of demineralization. The results revealed a significant decrease in surface microhardness values and changes to the enamel morphology after bleaching. CSMH and PLM showed that bleached enamel presented lower volume percentage of mineral up to 40 micrometers from the enamel surface and demineralization areas located in the subsuperficial region of enamel, respectively. It was concluded that 35% hydrogen peroxide can alter the surface morphology and the mineralization level of the dental enamel surface and sub-surface regardless of what type of bleaching light is used.

Review of the effects of infiltrants and sealers on non-cavitated enamel lesions

PURPOSE

The aim of the present study was to perform a review of the effects of infiltrants and sealers on the inhibition of enamel demineralisation.

MATERIALS AND METHODS

The authors searched the Cochrane Library, Embase, PubMed and Web of Science (ISI) for papers published between January 1970 and September 2008. The main search terms were 'artificial caries' or 'caries treatment' or 'caries-like lesion' or 'white spot lesion' or 'enamel demineralisation' or 'natural caries' and 'enamel' and 'sealant' or 'resin infiltration'. The inclusion criteria were studies that produced artificial non-cavitated enamel lesions before the application of sealant in in vivo or in vitro studies. Studies excluded were those that had not produced artificial non-cavitated enamel lesions before the application of sealant; had evaluated the inhibition of enamel demineralisation around restorations, sealant and orthodontic bracket/bands; had not evaluated the inhibition of enamel demineralisation after the sealant application; and had not applied sealant materials. Selected papers were given scores, from A to C, according to predetermined criteria.

RESULTS

Eighteen studies were identified and included in the project critical appraisal. Two papers were classified as Grade A, nine as Grade B and seven as Grade C.

CONCLUSIONS

It can be concluded that while fissure sealing acts as a diffusion barrier on the top of the lesion surface, the infiltration technique creates a barrier inside the lesion by replacing the mineral lost with a low-viscosity light-curing resin.

Molar-incisor-hypomineralisation and dioxins: new findings

AIM

According to our earlier study, molar-incisor-hypomineralisation (MIH) was associated with the exposure of a child via mother's milk to polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) in a group of Finnish children born in 1987. Since the levels of PCDD/Fs and PCBs in mother's milk/placenta have remarkably decreased, it was important to find out if an association still exists.

METHODS

The study group was composed of 167 mothers and their children. Placental samples from the mothers were collected in maternity hospitals in Helsinki and Oulu in 1995--1999 and concentrations of the 17 most toxic PCDD/PCDF and 36 PCB congeners were measured. After 7-10 years the children were examined for MIH and the mothers were interviewed on the duration of breast-feeding.

RESULTS

MIH was found in 24 children (14.4%). The duration of breast-feeding ranged from 0 to 30 months (mean=7.2+/-4.7). WHOPCDD/FTEQ ranged from 2.5 to 39.1 pg/g fat (mean=13.7+/-6.8) and WHOPCBTEQ from 0.7 to 9.8 pg/g fat (mean=2.7+/-1.4). The mean sum of PCDD/Fs was 196+/-105 pg/g fat and that of PCBs was 57.2+/-28.1ng/g fat. The total exposure to PCDD/Fs, which was calculated from the placental concentration (used as a proxy for the milk concentration) and duration of breastfeeding, was not associated with the occurrence or severity of MIH. Neither was the total exposure to PCBs associated with the occurrence or severity of MIH.

CONCLUSION

At prevailing levels, exposure of a child via placenta/mother's milk to PCDD/Fs and PCBs is not associated with MIH.

Effects of 10% carbamide peroxide treatment and sodium fluoride therapies on human enamel surface microhardness

This study sought to evaluate the microhardness of enamel submitted to 10% carbamide peroxide treatment and different methods of remineralization involving sodium fluoride (NaF). Non-erupted third molars were used and 75 enamel blocks with standardized dimensions (4.0 x 4.0 x 2.0 mm) were obtained. Enamel blocks were randomly divided into five groups (n = 15): one control (no bleaching and no fluoride treatment), one receiving a 10% carbamide peroxide treatment, one receiving 10% carbamide peroxide plus acidulated phosphate fluoride, one receiving 10% carbamide peroxide with 0.2% NaF, and one receiving 10% carbamide peroxide and 0.05% NaF. There were no differences among four of the groups (p > 0.05); the group receiving 10% carbamide peroxide only was different from all other groups (p < 0.05). Based on these results, NaF therapies are recommended during carbamide peroxide bleaching treatments.

Demineralizing action of EGTA in endodontics

The demineralization of dentin obtained by treatment with a chelating agent ethylene diamminotetracetic acid (EDTA) or ethylene glycol-bis(beta-aminoethyl ether)-N-tetraacetic acid (EGTA), is a dynamic process involving chelation and solubilization. The actions of the EDTA and EGTA on dentin are influenced by the pH. Increasing mM concentrations of EDTA or EGTA the equivalent pH decreases in a similar slope to 80 mM chelator concentration. Increasing the chelator concentration different data were obtained: with EGTA the pH decreases slightly while with EDTA goes back up to the initial values. After 80 mM, EDTA reduces the activity on the dentin, and EGTA continues to work at higher concentrations. We demonstrated that EGTA solubilized more of 60 percent of dentin while EDTA gives about 20% at the maximal of the solubility.

Temporal relationship between sucrose-associated changes in dental biofilm composition and enamel demineralization

The aim of this study was to investigate the temporal relationship between changes in biofilm composition and enamel demineralization following exposure to sucrose. A crossover blind study was conducted in situ in three phases, during which 12 volunteers, divided into three groups, subjected enamel slabs 8 times/day to water (negative control), 10% glucose + 10% fructose (active control) or 20% sucrose solution. Biofilms accumulated for 3, 7 and 14 days were collected and analyzed biochemically and microbiologically, and mineral loss from enamel (deltaZ) was evaluated. Significantly higher deltaZ was found in the sucrose group after 7 days. However, on the 3rd day, lactobacilli, insoluble extracellular polysaccharide (EPS) and intracellular polysaccharide were significantly higher, and the calcium, inorganic phosphorus and fluoride concentrations in the biofilm were significantly lower in the sucrose group than in the negative controls. The only significant difference compared to glucose + fructose treatment was a higher insoluble EPS concentration. The data suggest that, although sucrose induces significant enamel demineralization only after 7 days of biofilm accumulation, changes in the biofilm composition are observed earlier.

Dental enamel dissolution after alendronate treatment

PURPOSE

To evaluate the effect of treatment with a bisphosphonate (alendronate) on human dental enamel dissolution in vitro.

METHODS

The dissolution of each enamel sample was evaluated by monitoring the calcium release in 0.1M lactic acid solution at pH 4.5 (acidic solution) during dissolution tests, after topical alendronate treatment with 0.1M alendronate solutions at pH 5.0, pH 7.4 and pH 9.0.

RESULTS

Data showed that alendronate treatment, both at pH 5.0 and pH 7.4, obtained a statistically significant reduction of enamel demineralization during dissolution test reaction time (45 minutes). The protective effect was not present after treatment at pH 9.

Development of fibre-optic confocal microscopy for detection and diagnosis of dental caries

We report on the development of a fibre-optics-based confocal imaging system for the detection and potential diagnosis of early dental caries. A novel optical instrument, capable of recording axial profiles through caries lesions using single-mode optical fibres, has been developed. The practical study illustrates that miniature confocal devices based around single-mode optical fibres may provide additional diagnostic information for the general dental practitioner.

Effect of ethylene oxide sterilization on enamel and dentin demineralization in vitro

For in situ studies into caries prevention, sterilization of tooth samples is essential. However, sterilization may influence the caries process itself. The aim of this study was to assess the effect of sterilising sound human enamel and dentin with ethylene oxide on lesion depth and mineral loss before and after in vitro demineralization. Lesion depth and mineral loss were measured using transversal microradiography (TMR). The experiment was carried out with 32 enamel and 32 dentin samples. We found a significant reduction of lesion depth due to sterilization in demineralized enamel (-9.8microm; 95% CI: -15.1 to -4.4microm). The small effect of sterilization on demineralized enamel is considered to be irrelevant for in situ studies of de- and remineralization.

Co-site digital optical microscopy and image analysis: an approach to evaluate the process of dentine demineralization

AIM

To introduce and explore the potential of digital optical co-site microscopy and image analysis for the observation of changes in dentine surfaces during demineralization. The effect of ethylenediamine tetraacetic acid (EDTA) was evaluated quantitatively and longitudinally.

METHODOLOGY

Three maxillary human molars were sectioned transversely at the cemento-enamel junction, and the crowns discarded. Subsequently, discs approximately 3 mm thick were cut in the cervical third of the root and a standardized smear layer produced. Co-site image sequences of the dentine surface subjected to 17% EDTA were obtained over the experimental period (15, 30, 60, 180 and 300 s). Sixteen images were obtained in each dentine sample for each experimental time, thus, a total of 48 image fields were obtained. For each field, an image analysis routine automatically discriminated open dentine tubules and measured their number, area fraction and minimum diameter, thus allowing the quantification of the demineralization process. The Student t-test was used to analyse the data.

RESULTS

The number of open tubules remained essentially constant during the demineralization process. The area fraction increased from 9% to 32%. Tubule minimum diameter increased from 1.5 to 3.0 microm. The changes over time for the area fraction and minimum diameter were significant for comparison between all experimental times (P<0.05).

CONCLUSIONS

The methodology developed for longitudinal observation of dentinal surfaces was fast, robust and reproducible. It could be easily extended to other chelating substances, thus contributing to the understanding of the demineralization process and in establishing an optimal time-effect relationship in the clinical application.

Susceptibility of acid-softened enamel to mechanical wear--ultrasonication versus toothbrushing abrasion

The study aimed to compare the amounts of softened enamel removable by ultrasonication and by toothbrushing abrasion of briefly eroded samples. Thirty bovine enamel samples were demineralized in hydrochloric acid (pH 2.1) for 60 s and were then either brushed with 350 brushing strokes in toothpaste slurry (group A) or distilled water (group B) or were ultrasonicated for 120 s (group C). Enamel loss was measured after 10, 20, 50 and then after every 50 brushing strokes or after 5, 30, 60 and 120 s ultrasonication. Samples were indented with a Knoop diamond after erosion, and enamel loss due to abrasion or wear was calculated from the change in indentation depth after mechanical treatment. Within- and between-group comparisons were performed by ANOVA or t test. Initially, enamel loss increased with increasing brushing treatment or ultrasonication time. Enamel loss did not increase after 300 brushing strokes in group A (534 +/- 169 nm) or 250 brushing strokes in group B (423 +/- 80 nm), or after 60 s ultrasonication (231 +/- 72 nm). Enamel loss was significantly higher in groups A and B than in group C. The results confirm that ultrasonication removes only the outer, more highly demineralized part of the softened enamel layer. Results also indicate that toothbrushing abrasion removes more softened enamel from briefly eroded enamel than ultrasonication, and therefore probably removes partly demineralized enamel from the deeper part of the softened layer. In vivo, excessive toothbrushing might remove the softened enamel layer almost completely.

A comparison of terahertz pulsed imaging with transmission microradiography for depth measurement of enamel demineralisation in vitro

Terahertz pulsed imaging (TPI) is a relatively new, non-ionising and non-destructive imaging technique for studying hard tissues which does not require tooth section preparation, unlike transmission microradiography (TMR). If TPI can measure the depths of caries/demineralisation lesions accurately the same tooth samples could be reused and remeasured during in vitro and in situ studies on de- and/or re-mineralisation. The aim of this study was to compare TPI and TMR for measuring the depths of a range of artificially induced bovine enamel demineralised lesions in vitro. Bovine slabs with artificial caries, induced to different levels of demineralisation by two different but standard demineralisation techniques ('acid gel' and 'carbopol') were measured by TPI and TMR and the readings compared. The set of TPI/TMR measurements obtained on the gel-demineralised slabs showed an extremely high coefficient of determination (r(2) = 0.995). Detailed analysis of the results and theoretical considerations (involving the relationship between refractive index profiling and mineral loss profile) are used to explain the findings and show that for acid gel lesions TPI is measuring demineralisation in the range of 47% of that of TMR depth plus an intercept of 16 microm, with further calculations allowing the TMR depths to be determined to within 5% using TPI.

Micromorphology and surface roughness of sound and demineralized enamel and dentin bleached with a 10% carbamide peroxide bleaching agent

PURPOSE

To evaluate the micromorphology and surface roughness of sound and demineralized enamel and dentin treated with a 10% carbamide peroxide bleaching agent in situ for 3 weeks.

METHODS

A 10% carbamide peroxide bleaching agent, Opalescence (OPA) was evaluated and a placebo agent (PLA) not containing carbamide peroxide, was used as a control group. Forty dental slabs [10 sound enamel slabs (SE), 10 demineralized enamel slabs (DE), 10 sound dentin slabs (SD) and 10 demineralized dentin slabs (DD)] were randomly fixed on the facial surface of the first maxillary molars and second maxillary premolars of 10 volunteers. Demineralized enamel and dentin fragments were obtained by a dynamic model using demineralizing and remineralizing solutions. The volunteers were divided into two groups that received the bleaching or the placebo agent in different sequences and periods in a double blind 2 x 2 cross-over study with a wash-out period of 2 weeks. Roughness was performed on the slab surfaces followed by scanning electron microscope (SEM) evaluations. The images were evaluated by three calibrated examiners in duplicate in two different periods at x1500 (SE and DE) and x2000 original magnification (SD and DD).

RESULTS

The Wilcoxon test showed significant differences in roughness for SE and DE treated with OPA or PLA, with rougher surfaces treated with OPA. No differences in roughness were observed for SD or DD treated with OPA or PLA. As the Kappa value for the inter-examiner agreement of SEM evaluations showed "moderate" reproducibility (0.41 < k< 0.60) in Period 1 and "substantial" (0.61 < k < 0.8) in Period 2, the latter was considered for the statistical analysis. The McNemar test showed no significant differences between SE, DE, SD or DD treated with OPA or PLA.

Effect of bleaching agents on calcium loss from the enamel surface

OBJECTIVES

To compare the Ca2+ loss of enamel treated with 38% hydrogen peroxide (HP), 35% HP with light, and 10% carbamide peroxide (CP).

METHOD AND MATERIALS

Ten extracted premolars were sectioned buccolingually and longitudinally so that 4 specimens were obtained from each tooth. The specimens were randomly assigned to 1 of 4 groups to receive the following bleaching agents: 38% HP, 35% HP with light, 10% CP, and no agent (control). The specimens were treated with an artificial caries solution (pH 4) for 16 days; the solution was replaced on days 4, 8, 12, and 16. Calcium concentration was determined by an atomic absorption spectrophotometer. Repeated measures ANOVA was performed on concentrations on days 4, 8, 12, and 16.

RESULTS

At the end of day 16, calcium ions released per square millimeter were calculated cumulatively as follows: 38% HP group: 27.52 +/- 5.22 microg/mL; 35% HP with light group: 25.15 +/- 4.99 microg/mL; 10% CP group: 19.53 +/- 4.03 microg/mL; control group: 18.35 +/- 4.00 microg/mL. The differences between the control group and the 35% HP with light group and between the control group and 38% HP group were statistically significant. Although demineralization differences were observed between the control group and the 10% CP group, this difference was not significant.

CONCLUSIONS

It can be concluded that 35% HP with light and 38% HP may cause significantly more loss of Ca2+ from the enamel surfaces than 10% CP. Also, 10% CP does not vary significantly from the control.

Shear bond strength of an amorphous calcium-phosphate–containing orthodontic resin cement

INTRODUCTION

Amorphous calcium phosphate (ACP) materials have recently been introduced with the promise of reducing demineralization around orthodontic brackets. The purpose of this in vitro study was to compare the shear bond strength of orthodontic brackets bonded with enamel using a commercially available orthodontic adhesive containing ACP to that of brackets bonded with a conventional resin-based orthodontic adhesive.

METHODS

Thirty extracted molars were collected. The first group of 30 brackets was bonded to either the mesiobuccal or distobuccal tooth surface with a conventional resin-based composite adhesive. The second group of 30 brackets was bonded with the ACP adhesive to the buccal cusp that was not used by the first group. Each tooth received 2 brackets; 1 bonded with a conventional resin-based composite adhesive and the other with the ACP-containing orthodontic adhesive. Specimens were stored in water at 37 degrees C for 24 hours and then tested for shear bond strength in an Instron universal testing machine. A paired t-test was used to compare the mean shear bond strength between the 2 adhesives. The ARI scores were analyzed using the chi-squared test. All statistical tests were performed at alpha =.05.

RESULTS

The t-test detected a highly significant difference in the mean shear bond strength between the 2 groups (P <.001). There was no evidence to suggest a statistical difference between the groups' ARI scores (P = .37).

CONCLUSIONS

Under the conditions of this in vitro study, orthodontic brackets bonded to teeth with an ACP-containing composite material failed at significantly lower forces than brackets bonded to teeth with the conventional resin-based composite orthodontic cement.

Effect of an iron mouthrinse on enamel and dentine erosion subjected or not to abrasion: An in situ/ex vivo study

OBJECTIVES

This in situ/ex vivo study evaluated whether a rinse with an iron solution could reduce wear and the percentage of microhardness change of human enamel and dentine submitted to erosion followed by brushing after 1 or 30min.

DESIGN

During 2 experimental 5-day crossover phases (wash-out period of 10 days), 10 volunteers wore intraoral palatal devices, with 12 specimens (6 of enamel and 6 of dentine) arranged in 3 horizontal rows (4 specimens each). In one phase, the volunteers immersed the device for 5min in 150mL of cola drink, 4 times a day. Immediately after immersion, no treatment was performed in one row. The other row was brushed after 1min using a fluoride dentifrice and the device was replaced into mouth. After 30min, the remaining row was brushed. In the other phase, the procedures were repeated, but after immersion the volunteers rinsed for 1min with 10mL of a 10mM ferrous sulphate solution. Changes in surface microhardness (%SMH) and wear (profilometry) of enamel and dentine were measured. Data were tested using ANOVA and Tukey's tests (p<0.05).

RESULTS

The enamel presented more wear than dentine, under all experimental conditions. The iron solution caused a significant reduction on the %SMH in enamel, and a significant reduction on the wear in dentine, regardless the other conditions.

CONCLUSIONS

Rinsing with an iron solution after an erosive attack, followed or not by an abrasive episode, may be a viable alternative to reduce the loss of dental structure.

An investigation using atomic force microscopy nanoindentation of dental enamel demineralization as a function of undissociated acid concentration and differential buffer capacity

Acidic drinks and foodstuffs can demineralize dental hard tissues, leading to a pathological condition known as dental erosion, which is of increasing clinical concern. The first step in enamel dissolution is a demineralization of the outer few micrometres of tissue, which results in a softening of the structure. The primary determinant of dissolution rate is pH, but the concentration of undissociated acid, which is related to buffer capacity, also appears to be important. In this study, atomic force microscopy nanoindentation was used to measure the first initial demineralization (softening) induced within 1 min by exposure to solutions with a range of undissociated acid concentration and natural pH of 3.3 or with an undissociated acid concentration of 10 mmol l-1 and pH adjusted to 3.3. The results indicate that differential buffering capacity is a better determinant of softening than undissociated acid concentration. Under the conditions of these experiments, a buffer capacity of >3 mmol l-1 pH-1 does not have any further effect on dissolution rate. These results imply that differential buffering capacity should be used for preference over undissociated acid concentration or titratable acidity, which are more commonly employed in the literature.

Resin Infiltration of Artificial Enamel Caries Lesions with Experimental Light Curing Resins

To prevent enamel lesions from further demineralization, a complete and homogeneous penetration of low-viscosity resins ('infiltrants') should be accomplished. With commercially available adhesives, this goal might not be achieved because of their penetration capabilities. On this note, the Penetration Coefficient (PC) describes the penetrativity of liquids and might be employed to develop optimal infiltrants. Thus, the aim of this study was to compare the penetration abilities of 12 experimental infiltrants (BisGMA/TEGDMA comonomers showing varying PCs) with a commercially available adhesive (Excite, Vivadent). In each of the 156 bovine enamel specimens, four subsurface lesions were created. Three of the four lesions were infiltrated with either the adhesive or one of 12 experimental resins for either 10, 22, or 40 seconds, and subsequently light-cured. Specimens were studied using confocal microscopy and penetration depths were determined. A good correlation between PC and penetration depth was thereby observed (Pearson's correlation coefficient, r=0.820).

Impact of the acid flow rate on dentin erosion

OBJECTIVE

The study aimed to evaluate the erosive effects of acids flowing with different velocities and duration on dentin previously pre-treated with distilled water or human saliva.

METHODS

Bovine dentin surfaces were submitted to a 10 min demineralisation with hydrochloric or citric acid (pH 2.3, 37 degrees C) in an artificial mouth at flow rates of 3, 2.25, 1.5, 0.75 or 0.15 ml/min or in 30 ml of the respective acid without movement (each subgroup n=16 specimens). Prior to the demineralisation, half of the specimens of each group were either pre-treated with distilled water or human saliva for 120 min. After 2, 5 and 10 min demineralisation, profilometric traces of dentin loss were performed perpendicular to the direction of acid flow at three sites (A-C) with intervals of 500 microm. The first profile (A) was taken in a distance of 1.5 mm from the acid starting to flow over the sample. Thus, median dentin loss at each site was calculated and statistically analysed by five-way ANOVA.

RESULTS

Dentin loss increased with increasing acid flow rate and demineralisation time and was higher for demineralisation with citric acid compared to hydrochloric acid. For given flow rates of 0.15 to 3 ml/min, measurement of dentin loss yielded highest values for site A and decreasing values for sites B and C. For all groups, no significant differences of dentin loss were observed between specimens pre-treated with distilled water or human saliva.

CONCLUSION

Under the conditions of this study, both duration of demineralisation and acid flow rate but not pre-treatment with distilled water or saliva influence the extent of dentin erosion.

Effect of Lesion Characteristics and Mineralising Solution Type on Enamel Remineralisation in vitro

The aim was to study the effect of lesion preparation technique and solution composition on remineralization of artificial lesions in vitro. Lesions were prepared with similar total mineral loss, but different mineral distribution, i.e., low (14.0) or high R (34.8) values. Lesions from both groups were remineralized (10 days, 37 degrees C) in two different solutions, with similar supersaturation with respect to hydroxyapatite (St), but calcium:phosphate ratios representing either hydroxyapatite stoichiometry or plaque fluid (PF). Remineralization was quantified microradiographically, mineral distribution was compared with natural white-spot lesions. Mineral loss and depth decreased significantly, and surface-zone mineral content (Zmax) increased significantly, in all lesions. Overall there was a significant relationship of decreasing remineralization with increasing Zmax, but not within either lesion type. PF was significantly more efficient than St in high-R lesions, with lesions remineralizing almost completely in PF. Remineralization was not significantly different in PF or St for low-R lesions but in high-R lesions, PF was more efficient than St, possibly through differences in relative saturations with respect to different calcium phosphates. Differences in area:solution ratios and baseline Zmax values may also have explained the different response to PF. Low-R lesions were similar to natural white-spot lesions in terms of mineral distribution, whereas high-R were not. Concluding, both lesion and remineralizing solution type had a marked influence on remineralization. It is proposed that use of low-R lesions would be more appropriate where more physiologically relevant mineral distribution is required, whereas high-R lesions would be appropriate for studying inherent remineralizing efficiency.

Effect of Frequency of Sucrose Exposure on Dental Biofilm Composition and Enamel Demineralization in the Presence of Fluoride

It has been suggested that enamel would resist higher frequencies of sucrose exposure if fluoride from water or dentifrice is being used. However, the effect of increasing frequencies of sugar on dental biofilm composition is not well known. Ten volunteers living in a fluoridated area wore palatal appliances bearing human enamel slabs during 14 days. The slabs were exposed to 20% sucrose solution 0 (control), 2, 4, 6, 8 or 10 times/day and the volunteers used fluoride dentifrice 3 times/day. Enamel demineralization was significantly greater than control for sucrose frequencies higher than 6 times/day. However, biofilm mass, total microbiota, total streptococci, lactobacilli counts and insoluble extracellular polysaccharide concentration increased, while Ca, P(i) and F concentration in whole biofilm decreased significantly, with frequencies of sucrose exposure lower than 6 times/day. The findings confirm that fluoride can reduce enamel demineralization if sucrose consumption is not higher than 6 times/day, but changes in the biochemical and microbiological composition of the biofilm are observed with lower frequencies of sucrose use.

Chemical interaction of phosphoric acid ester with hydroxyapatite

Among functional monomers used in contemporary dental adhesives, 10-methacryloyloxydecyl dihydrogen phosphate (MDP) has been found to interact chemically with hydroxyapatite (HAp) most intensively and stably. This effect was thought to be the basis of the superior bonding effectiveness of MDP-based self-etch adhesives to enamel/dentin. To elucidate fully the chemical interaction and reactivity of MDP with HAp, we used (31)P CP-MAS NMR spectroscopy and powder x-ray diffraction. In an aqueous ethanol solution, Ca ions were leached from HAp to form, at short term, a MDP-calcium salt (CaMHP(2)) layered structure on the HAp surface. When MDP was allowed to interact for longer time (< 24 hrs), CaHPO(4).2H(2)O precipitated on top of this MDP-calcium salt layered structure. In conclusion, the intense chemical interaction of MDP with HAp must be ascribed to superficial dissolution of HAp induced by the MDP adsorption and subsequent deposition of MDP-calcium salt with a solubility lower than that of CaHPO(4).2H(2)O.

The composition and structure of bovine peritubular dentin: Mapping by time of flight secondary ion mass spectroscopy

The dentin layer of the tooth is a complex mineralized tissue traversed by a closely packed system of tubules. Each tubule is surrounded by highly mineralized tissue referred to as peritubular dentin (PTD). The remaining mineralized collagen network between the tubules is the intertubular dentin (ITD). A TOF-SIMS analysis of the PTD constituents has been used to compare the PTD to the ITD. The PTD differs from the ITD not only in the degree of mineralization but also in the amount and nature of the mineral elements and amino acids. The organic matrix of the PTD consists of a unique collagen free assembly of proteins rich in glutamic acid, where the ITD organic matrix is collagen-rich and Asp-rich. The apparent concentration of organic fragment ions observed in the PTD in the TOF-SIMS negative ion mode was much higher than expected. The PTD was found to be rich in Ca2+, Na+, Mg2+, and K+. The amount of Mg2+ and K+ in the PTD was significantly reduced after deproteination, while Ca2+ and Na+ were still accumulated in the PTD. This implies that Mg2+ and K+ are mainly associated with the organic matrix rather than with the mineral of the PTD.

Thirty-five percent carbamide peroxide application causes in vitro demineralization of enamel

OBJECTIVES

The objective of this in vitro study was to investigate whether a high concentration 'in-office' bleaching agent affected the mineral content of enamel and dentin.

METHODS

A commercially available 35% carbamide peroxide bleaching agent was applied for 2h to sectioned teeth (n=11). Specimens were then immersed in artificial saliva at 37 degrees C for a further 24h to simulate the oral environment. Tomographic images of these sections were obtained (micro-CT 80, Scanco, Switzerland) prior to and post-bleach application. Eight three-dimensional regions of interest (ROI), starting from the enamel surface extending to the dentinoenamel junction, were selected for each section. The hydroxyapatite equivalent mineral concentrations (g/cm(3)) of the ROIs were calculated. Any changes in mineral content as a consequence of the bleaching procedure were calculated in relation to each ROI.

RESULTS

There was a significant reduction in the mineral content of enamel specimens post-bleach application extending to a depth of 250microm (paired t-test, p<0.05); this reduction in mineral content was greatest in the ROI's closest to the tooth surface. There was, however, no significant difference in the mineral content of dentin as a consequence of bleaching.

SIGNIFICANCE

This in vitro study has shown that significant demineralization of enamel occurred following bleaching with 35% carbamide peroxide. The concept that 'in-office' bleaching is a non-destructive cosmetic procedure should be reconsidered.

Effect of CHX on the Decalcifying Effect of 10% Citric Acid, 20% Citric Acid, or 17% EDTA

The objective of this study was to measure the demineralization capacity of 10% and 20% citric acid and 17% EDTA after three time periods and to determine whether it was modified by the addition of 1% of commercial chlorhexidine (CHX). Three slices of 2-mm thickness were cut from the cervical third of the root of ten bovine incisors and sectioned into two equal parts, obtaining six specimens per tooth. Specimens were assigned to one of six groups (n = 10) for immersion in 25 ml of the above mentioned solutions or 25 ml of these same solutions plus 1% CHX (Hibimax). At 3, 10, and 15 min of immersion, the concentration of Ca2+ was measured by atomic absorption spectrophometry. The demineralization effect of all solutions was time-dependent (F = 158,448; p < 0.001), without significant differences among them (p = 0.783). Addition of 1% CHX did not modify the demineralizing capacity of these solutions. In the first three minutes, significantly more [Ca2+] was obtained when 17% EDTA was used in comparison with the other solutions.