J.L. Ruben

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 μm 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 μm). 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.

Effect of Titanium Tetrafluoride, Amine Fluoride and Fluoride Varnish on Enamel Erosion in vitro

This study aimed at evaluating the effect of 1 and 4% titanium tetrafluoride (TiF4) gels, amine fluoride (AmF) 1 and 0.25% and a fluoride varnish (FP) on the prevention of dental erosion. Two experimental groups served as controls, one with no pretreatment and another one pretreated with a fluoride-free varnish (FP-blanco). Dental erosion was modelled using bovine enamel samples submitted to alternate cycles of acid exposure in citric acid and remineralization in artificial saliva. Calcium loss of all samples involved in the study was quantified by atomic absorption spectroscopy and erosion depths were estimated. Two samples of each experimental group were also analyzed by white light confocal microscopy. The cumulative erosion depth (in µm) after 72 min was: TiF4 gel 1% 8.29 ± 0.39; TiF4 gel 4% 8.27 ± 0.55; AmF 1% 8.69 ± 0.66; AmF 0.25% 8.86 ± 0.33; FP 3.43 ± 1.07; FP-blanco 14.86 ± 1.59 and control 9.77 ± 0.49. A statistically significant protective effect (p ≤ 0.001) was found only for the group pretreated with the fluoride varnish. Within the limitations of an in vitro study it may be concluded that topical applications of the fluoride varnish tested have a protective effect on the prevention of dental erosion.

Effect of Xylitol and Sorbitol in Chewing-Gums on Mutans Streptococci, Plaque pH and Mineral Loss of Enamel

Seventeen subjects with more than 3 x 10(5) mutans streptococci per millilitre of saliva completed this randomised, cross-over study. Four different chewing-gums, containing: (1) 70% xylitol, (2) 35% xylitol + 35% sorbitol, (3) 17.5% xylitol + 52.5% sorbitol, and (4) 70% sorbitol, were tested. The participants used 12 pieces of each gum per day for 25 days. During the four experimental periods, they wore a removable palatinal plate containing two demineralised enamel samples, and brushed their teeth with a non-fluoridated toothpaste. The results showed that an increased concentration of xylitol in the gum resulted in a lower number of mutans streptococci in both saliva and dental plaque, although the decreases were only significant in the saliva samples (p < 0.01). The pH drop in plaque, measured in vivo after a 1-min mouthrinse with a 10% sorbitol solution, was least pronounced after the 70% xylitol gum and most pronounced after the 70% sorbitol gum period (p < 0.01). No significant differences were found after a mouthrinse with a 10% sucrose solution. All demineralised enamel samples lost mineral during the experimental periods. However, the lesion depth as well as the mineral loss values, assessed microradiographically, did not differ significantly between the four chewing-gums.

Cariostatic effect and fluoride release from a visible light curing adhesive for bonding of orthodontic brackets

This study was designed to investigate the cariostatic potential in vivo of a visible light-curing adhesive for the bonding of orthodontic brackets. The fluoride release of the adhesive in water and saliva was also measured. Ten orthodontic patients with premolars to be extracted participated. One bracket with Heliosit-Orthodontic (no fluoride) was positioned on the buccal surface of one premolar (control), and another bracker with Orthodontic cement VP 862 (containing fluoride) was positioned on the experimental contralateral premolar. The adhesives were cured with a Heliolux II lamp and the teeth were extracted after 4 weeks. The patients used a fluoride toothpaste during the experiment. The mineral content of the enamel adjacent to the brackets was determined by quantitative microradiography. The fluoride release from disk-shaped plates of, the fluoride adhesive was measured in water for a 6-month period and in human saliva for 24 hours. The fluoride adhesive reduced lesion depths by about 48% than the nonfluoride adhesive (P<0.05, t, test). The largest release of fluoride from the plates in water was observable within the first week. However, a significant amount of fluoride was still released after 6 months. The fluoride release in saliva was significantly lower in human saliva at pH 7 than in water (P<0.01, t test). When salivary pH was lowered to 4, to mimic a cariogenic challenge, the amount of fluoride released increased up to the value measured in water. It was concluded that the regular use of fluoride toothpastes is insufficient to inhibit lesion development around orthodontic brackets. A fluoride-releasing adhesive reduced lesion development significantly adjacent to brackets compared with a nonfluoride adhesive. The fluoride release was found to be pH dependent and more rational in vivo than may be observed in water.

Reduction of Erosive Wear in situ by Stannous Fluoride-Containing Toothpaste

Background/Aims: Stannous fluoride (SnF) has been suggested as a dental erosion-preventive agent. The aim of this single-centre, randomized, double-blind, in situ study was to evaluate the effect of toothpastes with SnF in the prevention of erosive enamel wear. Methods: A combined split-mouth (extra-oral water or toothpaste brushing) and crossover (type of toothpaste) set-up was used. Twelve volunteers wore palatal appliances containing human enamel samples. Three toothpastes were used, in three consecutive runs, in randomized order: two toothpastes containing SnF (coded M and PE) and one toothpaste containing only sodium fluoride (coded C). On day 1 of each run the appliances were worn for pellicle formation. On days 2–5 the samples were also brushed twice with a toothpaste-water slurry or only water (control). Erosion took place on days 2–5 extra-orally 3 times a day (5 min) in a citric acid solution (pH 2.3). Enamel wear depth was quantified by optical profilometry. The effect of toothpastes was tested using General Linear Modeling. Results: Average erosive wear depth of control samples was 23 µm. Both SnF toothpastes significantly reduced erosive wear: M by 34% (SD 39%) and PE by 26% (SD 25%). The control toothpaste reduced erosive wear non-significantly by 7% (SD 20%). Both SnF-containing toothpastes significantly reduced erosive wear compared to the sodium fluoride toothpaste. Conclusion: We conclude that SnF-containing toothpastes are able to reduce erosive tooth wear in situ.

Inhibition of Erosive Wear by Fluoride Varnish

It has been suggested that fluoride products with a protective mechanical component are advantageous in the prevention of erosive wear. The aim of this study was to evaluate in situ the effect of fluoride varnish (FV) in the prevention of wear due to erosion and combined erosion and toothbrush abrasion. Eleven volunteers wore for 3 weeks, during working hours, appliances containing 2 control and 2 FV-treated human enamel samples. Erosion took place extraorally 3 times a day (5 min) in the soft drink Sprite. At the end of each experimental day one control and one FV sample (C-er+abr and FV-er+abr) were brushed (5 s) with fluoridated dentrifice. The remaining control and FV sample (C-er and FV-er) were left unbrushed. Enamel volume loss was quantified by optical profilometry at day 5, 10 and 15. A statistically significant progression in enamel loss was found for the C-er, C-er+abr and FV-er+abr groups (p < 0.001, p < 0.001 and p = 0.001, respectively) but not for the FV-er group (p = 0.053). The values of cumulative normalized volume loss (×108 µm) at day 15 were: C-er 5.53 ± 2.14, C-er+abr 5.70 ± 2.07, FV-er 0.79 ± 0.67 and FV-er+abr 2.76 ± 1.35. The FV-er and FV-er+abr groups showed significant lower volume loss than the C-er group (p < 0.001 and p = 0.005, respectively) and the C-er+abr group (p < 0.001 and p = 0.002, respectively). The results indicate that fluoride varnish is effective in the reduction of erosive wear.

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.

Brushing abrasion of eroded bovine enamel pretreated with topical fluorides

Topical fluorides have been proposed for the prevention of erosive dental wear. This study evaluated the in vitro effect of a single professional application of 4% titanium tetrafluoride (TiF4), 1% amine fluoride (AmF) and 0.1% difluorosilane varnish (FV) in preventing wear due to combined erosion and brushing abrasion. One hundred and eight bovine enamel samples were used. Control groups were not pretreated with any product (C), pretreated with a fluoride-free varnish (FV-bl) or pretreated with fluoride varnish and subsequently submitted to varnish removal (FV-r). Wear was modeled by submitting the fluoride-treated and control groups to 3 cycles of the following regimens: erosion/remineralization (er/remin), abrasion/remineralization (abr/remin) or erosion/abrasion/remineralization (er/abr/remin). Erosion was simulated by immersion of the samples for 10 min in citric acid 50 mM (pH 3). Abrasion was carried out for 1 min (200 strokes, load 150 g) in a wear device. Remineralization (2 h artificial saliva) took place between the cycles. Two-way ANOVA showed that there was a significant interaction (p ≤ 0.001) between the fluoride treatments and the wear regimens. Under er/remin a significant wear protective effect was found for the FV, FV-r and FV-bl groups. Abr/remin resulted in some enamel loss for the TiF4 and AmF groups, but the amounts lost were not statistically significant (p = 0.185 and p = 1.000, respectively). Under er/abr/remin all products showed a significant protective effect, except for TiF4. It was concluded that FV and AmF protected bovine enamel against erosion followed by brushing abrasion in vitro.

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 2ppm 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) 2ppm 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.

Relative Cariostatic Effects of KOH-soluble and KOH-insoluble Fluoride in situ

The relative cariostatic effects of fluoride as fluorapatite, CaF2, loosely-bound fluoride, or KOH-soluble fluoride are debated. The present study was carried out to investigate this further in an intra-oral caries model. Pairs of premolars extracted for orthodontic reasons were used. Enamel from one tooth of each pair was used as control (untreated). Two slabs were cut from the enamel of the other contralateral premolar. These slabs were treated with 2% NaF for 24 h. One slab was then treated with 1 mol/L KOH twice for 24 h for removal of all loosely-bound fluoride. The slabs treated with 2% NaF and then with 1 mol/L KOH would contain the KOH-insoluble fluoride. Those treated with only 2% NaF would, in addition, contain KOH-soluble fluoride. Each slab, control, KOH-insoluble F, and KOH-soluble and insoluble F was mounted on different upper removable appliances. The slabs were covered with orthodontic banding material, thus allowing space for plaque accumulation. Five individuals wore the appliance in three separate four-week periods. The slabs were analyzed by quantitative microradiography. The average mineral loss (ΔZ) was 1680 ± 1000 vol% x μm in the control teeth, 620 ± 76 vol% x μm in the KOH-soluble and -insoluble F teeth, and 2167 ± 1278 vol% x μm in the KOH-insoluble F teeth. The average lesion depths were 90 ± 41 μm in the control teeth, 35.3 ± 5.5 μm in the KOH-soluble F teeth, and 88 ± 35 μm in the KOH-insoluble F teeth. It was concluded that only KOH-soluble fluoride reduced mineral loss and lesion depths significantly, compared with the untreated teeth.