Fluoride, pH Value, and Titratable Acidity of Commercially Available Mouthwashes

AIM

The primary objective of this work was to assess total soluble fluoride (TSF), pH values, and titratable acidity (TA) of various mouthwashes "in vitro," and the second was to compare fluoride content on labels with measured TSF.

METHODS

Commercial mouthwashes were collected and analysed. Company, type, manufacturer data, and active ingredients (essential oils [EO], cetylpyridinium chloride [CPC], chlorhexidine [CHX], and fluoride) were described. TSF, pH, and TA capacity were measured. Descriptive quantitative analysis were performed per mouthwash.

RESULTS

In total, 54 mouthwashes from 20 brands were included. These included mouthwashes with the active ingredients EO (n = 11), CPC (n = 17), CHX (n = 18), and fluoride (n = 32); 27 mouthwashes with more than 1 of these active ingredients; and 4 with none of the above-mentioned ingredients. Fluoride was present in different formulations; most contained sodium fluoride (NaF), and a few had sodium monofluorophosphate and amine fluoride + NaF. The pH values of all evaluated mouthwashes ranged from 4.1 to 7.9. Twenty mouthwashes presented pHs below 5.5, of which 10 contained fluoride. TA ranged from 0 to 48. According to the manufacturer data, mouthwashes with fluoride had concentrations from 217 to 450 ppm, with 90% in the range from 217 to 254 ppm. Laboratory data revealed that TSF ranged from 229 to 500 ppm, with 90% in the range from 229 to 337 ppm. A statistically significant difference was observed between measured TSF and the labelled fluoride content on the packaging of the fluoride mouthwashes (mean difference, 43.92 ± 34.34; P < .001). Most of these mouthwashes contained at least the amount of fluoride as mentioned on the packaging (93%).

CONCLUSION

The pH values and TA of commercially available mouthwashes showed a large variation. TSF levels of the fluoride mouthwashes were found to be at least the amount of fluoride as labelled. Dental care professionals should be aware of the pH, TA, fluoride content, and other active ingredients of different mouthwashes to better understand their potential impact on oral health.

Fatigue behaviour of a self-healing dental composite

OBJECTIVE

Novel self-healing resin-based composites containing microcapsules have been developed to improve the mechanical performance of dental restorations. However, the long-term fatigue behaviour of these self-healing composites has still been hardly investigated. Therefore, this manuscript studied the fatigue behaviour of self-healing composites containing microcapsules by subjecting the specimens to traditional staircase tests and ageing in a custom-designed chewing simulator (Rub&Roll) to simulate oral ageing physiologically relevant conditions.

METHODS

To prepare self-healing composite, poly(urea-formaldehyde) microcapsules containing acrylic self-healing liquids were synthesized. Subsequently, these microcapsules (10 wt%) and initiator (benzoyl peroxide, BPO, 2 wt%) were incorporated into a commercial flowable resin-based composite. Microcapsule-free resin-based composites with and without BPO were also prepared as control specimens. A three-point flexural test was used to measure the initial flexural strength (Sinitial). Subsequently, half of the specimens were used for fatigue testing using a common staircase approach to measure the fatigue strengths (FS). In addition, the other specimens were aged in the Rub&Roll machine for four weeks where after the final flexural strength (Sfinal) was measured.

RESULTS

Compared to Sinitial, FS of all tested specimens significantly decreased as measured through staircase testing. After 4 weeks of ageing in the Rub&Roll machine, Sfinal was significantly reduced compared to Sinitial for microcapsule-free resin-based composites, but not for the self-healing composites (p = 0.3658). However, the self-healing composites are still in the experimental phase characterized by a low mechanical strength, which still impedes further clinical translation.

SIGNIFICANCE

Self-healing composites containing microcapsules exhibit improved fatigue resistance compared to microcapsule-free non-self-healing composites.

TROG 15.03/ANZUP International Multicenter Phase II Trial of Focal Ablative STereotactic RAdiotherapy for Cancers of the Kidney (FASTRACK II)

PURPOSE/OBJECTIVE(S)

Stereotactic body radiotherapy (SBRT) is an emerging non-invasive alternative for primary renal cell cancer (RCC) in patients unsuitable for surgery. The objective of the FASTRACK II clinical trial was to investigate the efficacy of SBRT for primary RCC.

MATERIALS/METHODS

This non-randomized, intergroup multi-institutional phase II study was activated in 7 Australian centers and 1 Dutch center, through the Trans Tasman Radiation Oncology Group (TROG) and the Australian and New Zealand Urogenital and Prostate Cancer Trials Group (ANZUP). Eligible patients had biopsy confirmed diagnosis of primary RCC with a single lesion within a kidney, ECOG performance ≤2 and were medically inoperable, high risk or declined surgery. For tumors ≤4 cm a single fraction of 26 Gy was prescribed, for tumors > 4 cm, 42 Gy in three fractions was prescribed. The primary outcome of the study was to estimate the efficacy of SBRT for primary RCC, defined as local control based on RECIST criteria. The study was powered assuming that 1-year local control would be 90%, with the null hypothesis of ≤80% considered undesirable and not worthy of proceeding to a future randomized controlled trial.

RESULTS

Between July 2016 and February 2020, 70 patients were enrolled with a median follow-up of 42 months. Median age was 77 years. Forty-nine patients were male (70%), median BMI was 32 and median Charlson comorbidity score was 7. The median [IQR] RENAL complexity score was 8 [7-10]. Biopsy confirmation was 100%. Twenty-three patients (33%) had T1a disease. The median (interquartile range [IQR]) tumor size was 4.6cm [3.7-5.5]; it was 3.3cm [3.0-3.6] in those receiving single fraction (n = 23), and 5.3cm [4.6-6.0] in those receiving 3-fraction SBRT (n = 47). During real-time pre-treatment quality assurance review, 10 cases (14.3%) required resubmission for protocol deviation, 2119 variables were assessed at final review, and final protocol compliance was 99.3%. Seven (10%) patients experienced grade 3 treatment-related adverse events, with no grade 4 or 5 events observed. Eleven (16%) patients reported no adverse events. Local control was 100% throughout the lifetime of the trial (p<0.001). Cancer-specific survival was also 100% throughout the lifetime of the trial. Freedom from distant failure (95% CIs) at 1 and 3 years was 99% (90-100%). Overall survival (95% CIs) at 1 and 3 years was 99% (90-100%) and 82% (70-89%), respectively. Baseline mean eGFR (95% CI) was 61.1 mLs/min (56.6; 65.6) and reduced by -10.8 mLs/min (-13.0; -8.6) by 1-year, by -14.6 mLs/min (-17.0; -12.2) by 2-years and plateaued thereafter.

CONCLUSION

In the first multicenter prospective trial of a non-surgical primary RCC cohort, enrolling mostly T1b+ disease, SBRT was an effective treatment strategy with no observed local failures. We observed an acceptable side effect profile and renal function after SBRT. These outcomes support the design of a future randomized clinical trial of SBRT versus surgery for primary RCC. The trial was registered with ID: NCT02613819.

Remineralization of Demineralized Enamel and Dentine Using 3 Dentifrices-An InVitro Study

Objectives: To monitor the electrical resistance of artificially demineralized enamel and root dentine after exposure to different fluoridated dentifrices and, using transversal microradiography, to quantify remineralization. Materials and methods: This in-vitro blind investigation used 20 extracted teeth (four groups of five each). Each group was exposed to one test dentifrice [Colgate PreviDent (5000 ppm F), Colgate Winterfresh gel (1100 ppm F), Fluocaril Bi-Fluoré (2500 ppm F) and placebo (without fluoride)] three times daily for three minutes for 4 weeks. In between exposure to the test dentifrices, teeth were stored in a saliva storage solution. An Electrical Caries Monitor measured the electrical resistance at baseline and during the four-week test period at weekly intervals. The measurements were log transformed and Duncan's multiple range test applied. Remineralization was quantified using transversal microradiography. Results: Log mean (SD) electronic carries monitor (ECM) measurements in enamel at baseline and after 4 weeks of exposure to the test dentifrices were 4.07(1.53) and 3.87(0.90) (Placebo-Fluocaril), 4.11(1.86) and 4.64(1.43) (Colgate Winterfresh gel), 4.81(0.9) and 4.21(1.20) (Fluocaril Bi-Fluoré), and 4.60(0.88) and 3.76(0.9) (Colgate PreviDent). Corresponding measurements in dentine were 2.13(0.89) and 3.06(0.87) (Placebo-Fluocaril), 1.87(0.63) and 2.88(1.32) (Colgate Winterfresh gel), 2.47(1.20) and 1.65(0.60) (Fluocaril), and 2.16(0.00), and 2.34(1.07) for Colgate PreviDent. Lesion depth (µm) after microradiography in enamel was 100.1 (Placebo), 50.6 (Colgate Winterfresh gel), and 110.2 (Fluocaril, and 97.1 (Colgate PreviDent), and corresponding values in dentine were 169.7, 154.8, 183.7, and 153.5. The correlation of ECM and microradiographic parameters was negative (p < 0.05). Conclusion: Exposure of artificially demineralized enamel and root dentine to fluoridated dentifrices and saliva storage solution resulted in remineralization as follows: Colgate Winterfresh > Colgate PreviDent > Placebo-Fluocaril > Fluocaril Bi-Fluoré. Remineralization in teeth of the Placebo dentifrice group may be attributed to the presence of calcium and phosphate ions in the saliva storage solution.

Preserved Responsiveness of Secondary Somatosensory Cortex in Patients with Thalamic Stroke

Cortical representations may change when somatosensory input is altered. Here, we investigated the functional consequences of partial "central" deafferentation of the somatosensory cortex due to a lesion of the ventroposterior lateral nucleus (VPL) in patients at a chronic stage after solitary infarction of the thalamus. Event-related functional magnetic resonance imaging during electrical index finger stimulation of the affected and nonaffected side was performed in 6 patients exhibiting contralesional sensory deficits (mainly hypesthesia). Involvement of the VPL and additional nuclei was determined by high-resolution magnetic resonance imaging (MRI) and subsequent MRI-to-atlas coregistration. For the group, statistical parametric maps showed a reduced activation of contralateral primary somatosensory cortex (SI) in response to stimulation of the affected side. However, no significant difference in the activation of contralateral secondary somatosensory cortex (SII) compared with stimulation of the nonaffected side was detected. Correspondingly, the ratio of SII-to-SI activation for the ipsilesional hemisphere was markedly elevated as compared with the contralesional hemisphere. For preserved responsiveness of SII in thalamic stroke comparable with that of the contralesional hemisphere, possible explanations are a direct thalamocortical input to SII mediating parallel information processing, nonlinear response behavior of SII in serial processing, or reorganizational processes that evolved over time.

Sub-area-specific Suppressive Interaction in the BOLD responses to simultaneous finger stimulation in human primary somatosensory cortex: evidence for increasing rostral-to-caudal convergence

In the primary somatosensory cortex (SI) of non-human primates, receptive field properties have been shown to differ between its sub-areas with increasing convergence in areas 1 and 2 as compared with area 3b. In this study, we searched for a similar functional organization of human SI. We performed fMRI in healthy subjects during separate or simultaneous electrical stimulation of the second and third finger of the right hand. Activation patterns in response to stimulation of single fingers reflected the somatotopical arrangement within the hand area of SI. Somatotopy was more clear-cut in area 3b as compared with areas 1 and 2. The response to simultaneous stimulation was considerably smaller than the summed responses to separate stimulation of each finger alone, pointing to a suppressive interaction effect. A region-of-interest analysis in the representational areas of the second and third finger revealed sub-area-specific differential suppressive interaction with an increase along the rostral-caudal axis (areas 3b, 1 and 2: 26, 32.7 and 42.2%, respectively). These findings on differences in the topographic as well as functional organization between sub-areas of SI support the notion of increasing convergence and integration from area 3b to areas 1 and 2 in human subjects.

Evidence for a rostral-to-caudal somatotopic organization in human primary somatosensory cortex with mirror-reversal in areas 3b and 1

Medial-to-lateral somatotopy is a well-established feature of the human primary somatosensory cortex (SI); however, it is unknown whether, similarly to non-human primates, a rostral-to-caudal somatotopic arrangement exists as well. Therefore, in this functional magnetic resonance imaging (fMRI) study on eight healthy human subjects, five circumscribed skin areas sequentially located on the third finger and the palm of the hand were stimulated with innocuous electrical pulses. Within area 3b of contralateral SI, successive cortical representation sites ordered in a rostral-to-caudal fashion were seen in the group analysis and in six individual subjects. The fingertip was located most rostrally, whereas the proximal parts of the finger as well as the distal palm were represented at more caudal locations. Within area 1, the group analysis revealed a similar pattern of discrete representations. However, in contrast to area 3b, the fingertip was located most caudally, whereas the more proximal parts of the finger were found to be represented rostrally within area 1. Thus, the representation pattern of area 1 appeared as a 'mirror image' of that of area 3b. In comparison to the representations of the finger and the distal palm, the proximal palm was found to be represented at a more medial position of the postcentral gyrus.

Erosion-inhibiting effect of sodium fluoride and titanium tetrafluoride treatment in vitro

The prevention of dental erosion with fluoride is still largely unknown territory. It was the aim of this study to determine the erosion-inhibiting effect of topical neutral 1% sodium fluoride (NaF) application and an application of a 4% titanium tetrafluoride (TiF4) solution compared with no treatment. Ten bovine incisors were selected and three enamel samples prepared from each tooth. One sample from each tooth was assigned to one of three experimental groups. The experimental treatments were: no fluoride application (control); 4 min application of neutral 1% NaF gel; and 4 min application of 4% TiF4 solution. All of the specimens were repeatedly exposed to 50 mm citric acid solution containing 0.4 mm CaCl2, and 2.2 mm KH2PO4 at pH 3.0 over four consecutive days. The acid exposure was performed in intervals and the intensity was increased over the days of the experiment. Enamel dissolution was determined by calcium content measurement of the acid solution after exposure, using atomic absorption spectroscopy. A statistically significant erosion-inhibiting effect was found for both NaF and TiF4 treatments compared with the control group from an erosion exposure time of 3 min. The reduction of calcium loss, however, was higher for the TiF4-treated specimens than the NaF-treated. From 16 min of erosion exposure, the erosion-inhibiting effect was significantly stronger in the TiF4 than the NaF group. The relative reduction of calcium loss compared with the control group remained stable for the TiF4 group, whereas for the NaF group the relative reduction decreased with cumulative erosion time. It is concluded that topical TiF4 application provides a potential treatment option in erosion prevention.

Event-related fMRI of the somatosensory system using electrical finger stimulation

Cortical signal intensity changes due to brief (1 s) innocuous electrical stimuli applied to the second and fifth finger of the right hand were measured by means of fMRI at 1.5 T. The activation pattern in this event-related fMRI approach closely resembled that obtained in recent block-design studies. Activations were found in contralateral primary (SI) and bilaterally in secondary (SII) somato-sensory cortex as well as in posterior parietal cortex, insula, and supplementary motor area (SMA). In SI, the somatotopic organization of the hand area is demonstrated, more clearly to be seen in area 3b than in area 1 and 2. In conclusion, the feasibility to employ event-related somatosensory stimulation paradigms in fMRI studies is demonstrated.

Fluoride and urea chewing gums in an intra-oral experimental caries model

The aim of the present investigation was to evaluate the effect of sugar-free chewing gums containing fluoride (F) and urea in an intra-oral experimental caries model. Placebo chewing gums (without any active ingredient) and no gum served as controls. Fifteen subjects participated in a cross-over, single-blind study. Demineralised enamel and dentine blocks were embedded in circular plastic discs and bonded to the buccal surfaces of the lower canines and first premolars. The discs were removed and analysed using transversal microradiography after each of the six 4-week periods during which the subjects used either test or placebo products or no product. The results revealed that frequent use of sugar-free chewing gum is sufficient to inhibit further demineralisation of previously demineralised enamel and dentine specimens in the oral cavity. Comparing F, urea and placebo gums, the data showed that there was little or no difference between the products, except for an inhibitory effect on the chewing side of the dentition after using F chewing gums.

Somatotopic organization of human secondary somatosensory cortex

This fMRI study investigated the human somatosensory system, especially the secondary somatosensory cortex (SII), with respect to its potential somatotopic organization. Eight subjects received electrical stimulation on their right second finger, fifth finger and hallux. Within SII, the typical finding for both fingers was a representation site within the contralateral parietal operculum roughly halfway between the lip of the lateral sulcus and its fundus, whereas the representation site of the hallux was found more medially to this position at the fundus of the lateral sulcus, near the posterior pole of the insula. Somatotopy in SII seems to be less fine-grained than in primary somatosensory cortex (SI), as, in contrast to SI, no separate representations of the two fingers in SII were observed. A similar somatotopic representation pattern between fingers and the hallux was also observed within ipsilateral SII, indicating somatotopy of contra- as well as ipsilateral SII using unilateral stimulation. Further areas exhibiting activation were found in the superior and inferior parietal lobule, in the supplementary and cingulate motor area, and in the insula.

Representational overlap of adjacent fingers in multiple areas of human primary somatosensory cortex depends on electrical stimulus intensity: an fMRI study

Functional magnetic resonance imaging (fMRI) was used to examine the influence of non-painful electrical stimulus intensity on the BOLD response in human primary somatosensory cortex (SI). In ten healthy subjects, index and middle finger of the right hand were stimulated separately at two different stimulus intensities. The activated volume of single finger representations as well as the volume of representational overlap of the two activations increased following an increase in stimulus intensity. This effect was seen in two different subdivisions of SI, one in the depth of the central sulcus, presumably corresponding to Brodmann area (BA) 3b, and one on the crown of the postcentral gyrus, presumably corresponding to BA 1/2. Relative overlap (ratio of overlap volume to volume of individual finger representation) was larger in BA 1/2 than in BA 3b. Additionally, in both areas relative overlap increased significantly from low to high stimulus intensity. Relative overlap did not change when different correlation thresholds were employed arguing against an unspecific 'spillover effect'. Analysis of signal intensity time courses indicated that the response difference to high versus low stimulus strength was not present during the initial seconds of stimulation, during which both led to a similar signal intensity increase. Only during the following maintenance level of the response did the response to high stimulus intensity reach a significantly higher plateau level than the one due to low intensity stimulation, an effect which was present in both areas, BA 3b and BA 1/2, respectively.

Relationship between mineral distributions in dentine lesions and subsequent remineralization in vitro

Though the mineral distribution of the dentine carious lesion varies largely from tooth to tooth and from patient to patient, there are two main distribution profiles that characterize natural carious lesions in dentine. These profiles include softened and subsurface lesion types. The mineral distribution relationship between the starting profile and the profile after remineralization is not known. In order to study the relational aspects, we have produced demineralized dentine samples in vitro with mineral profiles similar to those of typical natural carious lesions, and subsequently remineralized the samples in a remineralizing solution with various fluoride concentrations (0, 2 and 10 ppm F). The mineral distributions were obtained by using an improved microradiographic technique. In addition, the nature of deposited mineral was analyzed by diamond-coupled total internal reflectance spectroscopy. Definite relationship was observed between the original lesion mineral distribution and the mineral distributions following remineralization. The amount of mineral present in approximately the first 50 microm of the lesion influenced the overall mineral profile after remineralization, possibly through influencing ion transport. If the amount was high (> approximately 10 vol%), the deposited mineral was confined to the surface (0-50 microm). The original mineral at those depths acted like a nucleus of mineral regrowth when the amount of residual mineral was intermediate, and like a transport barrier when the surface layer was well mineralized. If a surface barrier was not present, mineral was deposited at deeper depths in the lesion. Fluoride effect on dentine remineralization was dependent on the original mineral content and its distribution in the lesion. Although a high concentration of fluoride was very effective in low-mineral lesions, it produced hyperremineralization on well-mineralized subsurface lesions so that it prevented effective remineralization especially in deeper lesions.

Influence of nail varnish on the remineralization of enamel single sections assessed by microradiography and confocal laser scanning microscopy

Single-section techniques are attractive in enamel de- and remineralization investigations because they allow longitudinal studies in which mineral changes can be assessed by microradiography (TMR). Nail varnish (NV) is in general applied to coat the cut thin-section sides. The aims of this study were to investigate: (1) NV penetration depth in cut surfaces of demineralized enamel, (2) the influence of NV on cut surfaces of demineralized enamel on TMR, (3) the influence of NV penetration on a following remineralization. Cut surfaces of thin sections of demineralized enamel were NV coated; the NV was peeled off and the penetration depth assessed by confocal laser scanning microscopy. The NV penetration was 18+/-5 micrometer (mean+/-SD) in demineralized enamel. To evaluate the possible influence of NV on TMR, cut surfaces of thin sections of demineralized enamel were coated (twice) and microradiographed before and after nail varnishing. The NV effect (total effect of penetrated and surface NV) on the main parameters of TMR, Ld and DeltaZ, was less than 5% of the mean values. In the remineralization experiment (remineralization with 1.5 mM Ca2+, 0.9 mM phosphate, pH 7, 1 ppm F for 1 and 2 weeks), lesions in bulk samples, lesions in thin sections with NV-coated cut surfaces and lesions in thin sections in a PMMA (polymethylmethacrylate) holder were compared. (1) The remineralization of bulk samples and of NV-coated thin sections is different in one aspect. The amounts of mineral deposited in the lesions expressed as DeltaZ are comparable after 1 week. But because the NV penetrates part of the lesion outside, there was an Ld difference. The lesion depth difference between bulk lesions and NV-coated lesions in thin sections was statistically significant and was about 19% less in NV-coated lesions after 1 week; after 2 weeks of remineralization there was no difference in Ld between bulk- and NV-coated lesions any more. (2) There was no difference in remineralization efficacy between lesions in bulk samples and lesions in thin sections in the PMMA holder.

Effect of toothpicks with and without fluoride on De- and remineralization of enamel and dentine in situ

The aim of this investigation was to study the effect of the interproximal use of fluoride (F)-impregnated and non-impregnated birch toothpicks on the degree of de- and remineralization of enamel and dentine in situ. Ten volunteers with complete dentures in the upper jaw participated. Each subject had four specimens: (1) sound enamel, (2) demineralized enamel, (3) sound dentine and (4) demineralized dentine; placed pairwise at two approximal sites (15/16 and 25/26) of the maxillary prosthesis. The study involved three test periods (A, B and C), each lasting 4 weeks. In A, the subjects used F toothpicks (impregnated in 4% NaF) and, in B, nonimpregnated toothpicks 3 times daily. During period C, no toothpicks were used. Dentifrice or other F-containing products were not allowed during the 4-week periods. Transversal microradiography was used to determine lesion depth (ld) and mineral loss (DeltaZ). The results revealed that all the sound samples lost mineral during the three experimental periods; DeltaZ for both enamel and dentine was less for A and B compared with C (p<0.01) and less for A compared with B and C for dentine (p<0.05, p<0.01). The demineralized samples also lost mineral, apart from dentine, during periods A and B, i.e. when F-impregnated and non-impregnated toothpicks were used; ld for enamel and DeltaZ for dentine were less for A compared with C (p<0.05). Four weeks' use of toothpicks, especially F-impregnated toothpicks, thus reduces the demineralization of enamel and dentine at approximal sites in situ.

The remineralization of EDTA-treated human dentine

The remineralization of whole human dentine treated with a neutral EDTA solution was investigated: the treatment periods were 15, 30 and 120 min. From the literature it is known that EDTA removes noncollagenous proteins (NCPs) from dentine powders. In order to extract more phosphoproteins from dentine lesions, in part of this work samples were also treated with 1 M NaCl or 4 M guanidine chloride solutions. All the dentine samples after the treatments mentioned were immersed subsequently in a remineralizing solution without fluoride for 2 weeks and microradiographed. To investigate the effects of fluoride, samples treated with EDTA for 120 min were also remineralized with 2 ppm fluoride in solution. The results presented show that: (1) Measurable remineralization did not occur when fluoride was free in the remineralizing solution. Because remineralization occurred neither at the lesion front nor in the nonmineral part of the surface-softened tissue, presumably the NCPs (inhibitors) of underlying dentine diffused into the tissue during the remineralization period. (2) 2 ppm fluoride caused remineralization at the lesion front. In this case we assume fluoride either acted as nucleating agent or overcame the NCP effects at the lesion front.

In vitro remineralization of in vivo and in vitro formed enamel lesions

Thin sections of natural white spot enamel lesions (WS) and of artificial in vitro lesions (VL) were remineralized simultaneously in vitro. The sections, clamped in a PMMA holder, were microradiographed at baseline and after remineralization in a calcium- and phosphate-containing solution (pH = 7.0; 1 ppm F) after 2 and 4 weeks. All data were analyzed with respect to baseline. The results show that the lesion depth values did not change significantly during 2 and 4 weeks of remineralization. The mineral accumulation (change in DeltaZ), however, was substantial and significant in WS and VL. In WS the change in mineral accumulation was roughly proportional to the amount of mineral at baseline. The WS accumulated more than two times the amount of mineral than VL in the same periods of remineralization. After 4 weeks of remineralization the maximum mineral value Vmax in the surface layer of the WS was nearly up to the sound enamel level thick approximate87 vol%. This study shows that the technique and calculation procedure described make this single section method attractive for longitudinal demineralization-remineralization studies in vitro or in situ. Both WS and VL samples obviously remineralized in vitro similarly with respect to the baseline. Furthermore, this in vitro work indicates that remineralization inhibitors present in saliva, and previously penetrated into the enamel tissue, do not influence remineralization later on.

The effect of window width on the demineralization of human dentine and enamel

When lesion formation in dental enamel or dentine is studied in vitro, a well-defined area of the material, a 'window', is exposed to the demineralization medium. In the present experiments, we report the effect of window width on lesion formation in enamel and dentine. Rectangular windows, longest dimension always 5 mm and shortest dimension varying from 0.5 to 5 mm, were exposed to demineralization media. Lesions in dentine were formed by placing the specimens in an acidified unstirred 6% carboxymethyl cellulose (CMC) gel, an unstirred 0.5% CMC gel, a mildly stirred 0.5% CMC gel, or in a mildly stirred demineralization solution. Lesions in enamel were formed only in an unstirred acidified 6% CMC gel. pH in the demineralization media was 5.0 in all experiments. The microradiographic technique was used to assess lesion depth and mineral loss (vol% x microm) of lesions formed. Lesions formed in the unstirred gels were deeper, and there was a larger mineral loss, the narrower the window. There was no effect of window size on lesions formed in stirred systems. These effects can be explained by the strong dependence of concentration gradient in stirred gels just outside the exposed window on the window size. The phenomenon found here in vitro may at least partly explain why secondary caries may lead to localized, but relatively deep, lesions.

Cariostatic effect of a light-cured, resin-reinforced glass-ionomer for bonding orthodontic brackets in vivo. A combined study using microradiography and confocal laser scanning microscopy

The aim of this study was to evaluate in vivo the cariostatic potential of the resin-reinforced glass-ionomer (Vitremer core build-up restorative; 3M Dental Product Division) when used as a bonding agent for orthodontic brackets. The mineral distribution and topography of the enamel surface adjacent to the bracket base was determined by quantitative microradiography (TMR) and confocal laser scanning microscopy (CLSM). The study was designed in split-mouth technique using 9 pairs of premolars to be extracted for orthodontic reasons. One tooth of each pair was bonded with the resin-reinforced glass-ionomer, and the control contralateral premolar with the non-fluoridated composite (Concise, 3M Dental Products Division). After 4 weeks all teeth were extracted and stored until analysis. The lesion depths and mineral loss values in enamel adjacent to brackets bonded with Vitremer were significantly lower than in teeth bonded with the composite, indicating that the resin-reinforced glass-ionomers significantly reduced caries lesion development in vivo. CLSM images show a severe cariogenic challenge around orthodontic brackets and support TMR measurements.

Electron probe microanalysis and transverse microradiography studies of artificial lesions in enamel and dentin: a comparative study

In cardiology and research involving the interactions between restorative materials and dental hard tissues, it is important for small changes in tooth mineral content to be measurable. Currently, transverse microradiography (TMR) is the most accepted tool for the above purpose. Electron Probe Microanalysis (EPMA) can yield both qualitative identification of elements and quantitative compositional information. The purpose of this study was to compare the mineral distribution in well-defined artificial lesions, in dentin and enamel, by the use of both TMR and EPMA on the same sample. The good correlation between the two sets of data validates EPMA as a technique and helps in the interpretation of its results. The data from TMR analysis are expressed as vol% of mineral, while EPMA gives the levels of Ca and phosphate in wt%. The conversion between the two sets of data is complicated by the fact that local density is, as yet, unknown.

The caries-preventive effect of titanium tetrafluoride on root surfaces in situ as evaluated by microradiography and confocal laser scanning microscopy

The aim of the present study was to investigate the cariostatic effect of titanium tetrafluoride (TiF4) on in situ-induced lesions on human root surfaces. Analysis of the samples was carried out by quantitative microradiography (TMR) and confocal laser scanning microscopy (CLSM). Pre-molar roots, sectioned into four pieces, were used for sample preparation. Before they were mounted into the recesses prepared in the acrylic intra-oral appliances, two root pieces from each tooth were treated with 4% TiF4 for 1 min, while the remaining two pieces served as controls. The appliances were worn by 12 volunteers for 4 wks. After 4 wks with no fluoride supplementation, the root pieces were removed and analyzed by TMR and CLSM. The TMR results showed that the TiF4 treatment reduced lesion depth and total mineral loss by 56% and 62%, respectively. CLSM images agreed well with the TMR measurements. A dense light-reflecting surface layer with almost intact subsurface structures was evident in the TiF4-treated samples.

Caries development in fluoridated and non-fluoridated deciduous and permanent enamel in situ examined by microradiography and confocal laser scanning microscopy

The aim of the study was to compare initial caries development in fluoridated and non-fluoridated deciduous and permanent enamel in situ. Enamel slabs were mounted in removable appliances and worn for 4 wks. Significantly larger lesions developed in deciduous than in permanent enamel when no topical fluorides were used. Fluoride mouthrinsing partly prevented lesion development in deciduous and completely in permanent enamel. Initial enamel caries not detected by microradiography can be visualized by CLSM (confocal laser scanning microscopy).

Cerebral haemoglobin oxygenation during sustained visual stimulation--a near-infrared spectroscopy study

Using near-infrared spectroscopy, we investigated the time-course of the concentrations of oxygenated haemoglobin, [oxy-Hb], and deoxygenated haemoglobin [deoxy-Hb], in the occipital cortex of healthy human adults during standard sustained visual stimulation. Within a few seconds after stimulation (by coloured dodecahedron), we observed a decrease in [deoxy-Hb], peaking after 13 s ('initial undershoot'). In the subsequent 1-2 min, in seven out of ten subjects, [deoxy-Hb] gradually returned to a plateau closer to the baseline level. After cessation of stimulation, there was a 'post-stimulus overshoot' in [deoxy-Hb]. There was a statistically significant correlation between the size of the 'initial undershoot' and the post-stimulus overshoot'. The concentration of oxyhaemoglobin increased upon functional activation. However, in the mean across all subjects there was no 'initial overshoot'. After approximately 19 s it reached a plateau and remained constantly elevated throughout the activation period. After cessation of activation there was a 'post-stimulus undershoot' of oxyhaemoglobin. It is important to consider the time-course of haemoglobin oxygenation when interpreting functional activation data, especially those data obtained with oxygenation-sensitive methods, such as BOLD-contrast fMRI.

Microradiography and confocal laser scanning microscopy applied to enamel lesions formed in vivo with and without fluoride varnish treatment

The aim of the present investigation was to combine 2 techniques suitable for lesion characterization: quantitative microradiography (TMR) and confocal laser scanning microscopy (CLSM) on in vivo induced lesions with and without a fluoride varnish (Duraphat) treatment. Orthodontic bands were attached to premolars to be extracted for orthodontic reasons to induce enamel caries on the buccal surfaces. In the caries development part of the study, 1 tooth of each pair received at the start 1 topical application with the fluoride varnish Duraphat, the contralateral tooth serving as untreated control. All teeth were extracted after 4 weeks. In the caries progression part, the premolars were banded for 4 weeks without any treatment to induce caries, 1 premolar in each pair was then extracted and analyzed. The contralateral tooth received one Duraphat application and was extracted after another 2 weeks. In the caries development part of the study, TMR analysis showed that the Duraphat treatment on sound enamel reduced lesion depth by 48% compared to the untreated control. In the caries progression part, no significant difference was found between the untreated teeth extracted after 4 weeks and the fluoride treated lesions extracted after another 2 weeks. CLSM images agreed well with the TMR measurements. In the fluoride treated lesions, the CLSM images showed more light scattering indicating precipitation of material.

Raman spectra of human dentin mineral

Human dentin mineral has been investigated by using micro-Raman spectroscopy. Fluorescence and thermal problems were largely avoided by preparing dentin samples by grinding and ultrasonic agitation in acetone. The Raman spectral features were consistent with those of impure hydroxyapatite containing CO3 and HPO4. While spectral differences between enamel and dentin were clearly observable as changes in the bandwidth of the PO4(3-)V1 band and the intensities of the OH-, CO3(2-) and HPO4(2-) bands, the technique could not detect spectral differences between coronal and root dentin. NaOCl, NaF and APF-gel treatments caused measurable changes in intensities of the bands due to CO3(2-) and HPO4(2-); the results were found to be useful for band assignments. After NaOCl treatment, the Raman bands, presumably due to amide and HPO4(2-), were lost, but the band intensity of the CO3(2-)V1 bands increased by 35-60%. This increase coincided with the appearance of a new broad band (250-300 cm-1). The same treatment on enamel caused no increase in the CO3(2-)V1 band intensity. This NaOCl-induced carbonate could be removed within 20 h in a 1000 ppm NaF solution. These findings indicate that the carbonate ions induced by the NaOCl treatment are presumably in or on the mineral surface. After 3 min of APF-gel treatment on NaOCl-pretreated dentin, the intensities of the hydroxyapatite phosphate bands dropped by approximately 20%, and newly formed CaF2 and HPO4 bands became observable.

Effect of sodium hypochlorite treatment on remineralization of human root dentine in vitro

Dentine consists simplified of mineral and of several organic components. Sodium hypochlorite (NaOCl) is a well-known nonspecific proteolytic agent capable to remove organic material. The aim of this study was to investigate the influence of organic material removal from artificial dentine lesions by means of NaOCl pretreatment on subsequent remineralization with and without fluoride. Human root dentine samples were demineralized in an acidic gel (pH = 5) at 37 degrees C for 2 weeks. After 2 min of pretreatment with a 0.4, 2 or 10% NaOCl solution, the samples were remineralized in a 20 mM HEPES buffer (pH = 7) containing 1.5 mM Ca(2) and 0.9 mM phosphate with or without addition of 10 ppm F(-) as NaF at 37 degrees C for 8 days. Mineral profiles were assessed by means of transversal microradiography after diol treatment to avoid shrinkage caused by drying. In a separate experiments the dentine contraction caused by 10% NaOCl was assessed. The contraction (negligible for sound dentine) was found to be about 12% for the lesions. The remineralization results showed that pretreatment with a 10% NaOCl solution for 2 min, increased lesion remineralization. After NaOCl treatment, the amount of accumulated mineral increased by about 27% without F in the remineralization solution, and by about 4% with 10 ppm in solution. The in vitro results suggest that removal of organic materials from dentine lesions is an interesting approach to enhance remineralization.

Effect of post-brushing water rinsing on caries-like lesions at approximal and buccal sites

The aim was to study the effect of two different water rinsing procedures after toothbrushing with an NaF-containing dentifrice on the degree of de- or remineralization of enamel and dentine at approximal and buccal sites. Seven adults, wearing complete dentures, participated in two experimental periods (A and B) in a randomised order. During period A, they brushed with the dentifrice for 2 min, followed by 1-min active mouthrinse with the toothpaste-foam combined with 10 ml of water. No more water was used after the slurry had been spat out. During period B, the brushing was followed by 3 thorough rinsings of approximately 15 ml water each. These two procedures were carried out twice daily, i.e. in the morning (after breakfast) and in the evening (just before bedtime), during 3 months. Demineralized enamel and dentine samples were mounted at two locations--approximally and buccally--in the first molar region of the upper prostheses. Quantitative microradiography (TMR) was used to assess the lesion depth (ld) and the mineral loss (delta Z). The results showed that the approximally located samples continued to lose mineral during both periods A and B. However, the ld and delta Z values for enamel (p < 0.01) and dentine (p < 0.05) increased less during A than B. The buccally located enamel and dentine samples remineralized during the experiment, but no statistically significant differences were found for the ld and delta Z values of either enamel or dentine between periods A and B.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of air-drying on hyper-remineralization of demineralized dentine: a study on bulk as well as on thin wet section of bovine dentine

The influence of air-drying on the remineralization of demineralized bovine dentine was examined in wet bulk samples, in dried bulk samples as well as in wet thin sections. Bulk samples of bovine dentine were first demineralized in an acidic gel (pH = 5) at 37 degrees C for 3 weeks. After 24-hour pre-treatment of either air-drying or immersion in water, the bulk samples were remineralized in a solution containing 1.5 mM Ca, 0.9 mM phosphate and 10 ppm F (pH = 7) at 37 degrees C for 2, 4 or 8 days. Separately thin sections prepared from demineralized bulk dentine were immersed in water for 24 h and were also exposed to the remineralization solution for 2, 4 or 8 days. The results show that air-drying of the bulk samples increased remineralization of dentine considerably; the microradiographic parameters (ld, delta Z and la) show that the degree of remineralization ranks: thin wet sections > bulk dried > bulk wet. Especially, the remineralization inside lesions was greatly enhanced in thin sections and dried samples. It is presumed that the increased remineralization in dried samples is caused by a 'sponge effect', in which the remineralization fluid is sucked up in a dried shrunken lesion, resulting in fast and deep penetration of remineralization solution and/or presumably increased nucleation.

Effect of air-drying on demineralized and on sound coronal human dentine: a study on density and on lesion shrinkage

Recently, several papers investigated the linear dimensional changes in dentine after air-drying. This paper pertains to weight changes, volume changes, and density changes caused by air-drying of sound and demineralized intact dentine. The densities of sound and artificially demineralized human coronal dentine were measured in the wet state and after various drying periods of up to 24 h. The volume was assessed either by means of a pyknometer (wet samples) or by means of dimension measurements. The air-drying experiments were done using a Mettler thermobalance at room temperature. The density of wet sound coronal dentine was found to be 2.24 +/- 0.12 g.cm-3; the value of wet demineralized dentine was about 1.6 g.cm-3. The data show that previously published density values of powdered sound dentine may have been influenced by powdering effects, air-drying, and air inclusion. In whole demineralized air-dried dentine, air inclusion can be very severe: up to 30% by volume. The results show furthermore that in demineralized dentine we have two drying stages: during the first one (up to about 10 min of air-drying), the lesions shrink about 23%, while a main part of the water in the lesion evaporates, and air is incorporated into the tissue; during the second stage (drying longer than 10 min), the lesions hardly shrink anymore, but water is evaporated mainly from underlying sound dentine, followed by air incorporation.

The diameter of dentinal tubules in human coronal dentine after demineralization and air drying. A combined light microscopy and SEM study

The diameter of dentinal tubules after demineralization and/or air drying has been quantified using light microscopy and scanning electron microscopy (SEM). The tubule diameter was assessed at a distance of about 1.5 mm (range 1.0-2.0 mm) from the pulp. Tubule diameter was measured in the wet state, after 10-min and 12-hour air drying as well as after critical point drying (CO2) by SEM. The results show that drying effects on tubule diameter are small in sound tissue, but are sizeable in demineralized dentine. Comparing light microscopic (wet) and SEM observations show that the differences in tubule diameter are small for sound but substantial for demineralized dentine. An important result is that in the wet state the diameters of the tubules (being 1.3 +/- 0.2 microns in sound dentine) are 2.5 +/- 0.3, 2.2 +/- 0.3 and 1.7 +/- 0.2 microns after 1, 2 and 3 weeks of demineralization, respectively. The decreased tubule diameter with increasing demineralization may be important for permeability and transport phenomena in dentine caries and presumably in hypersensitivity.