Effect of carboxymethylcellulose-based saliva substitutes on predemineralised dentin evaluated by microradiography

OBJECTIVE: This study investigated the effect of six lab-produced saliva substitutes based on carboxymethylcellulose (CMC) differing in octacalciumphosphate saturations (OCP-s) on mineralisation of bovine dentin in vitro. DESIGN: Dentin specimens were prepared (n=234); prior to and after demineralisation (37 degrees C; pH 5.0; 7 d), one-third of each specimen surface was covered with nail varnish (control of sound dentin). Subsequently, specimens (n=13) were exposed to either one of the six CMC-based solutions (OCP-s: 0, 0.5, 1, 2, 4, and 8) at pH 6.5 or to Glandosane for 5 and 10 weeks (37 degrees C). Two aqueous solutions (OCP-s: 0 and 1) served as controls. After storage, thin sections were prepared and mineral loss was calculated by transversal microradiography. RESULTS: After both storage periods specimens immersed in Glandosane revealed a significantly increased mineral loss compared to all other solutions (p<0.05; Bonferroni post hoc test). Control solution with OCP-s=1 induced a significant remineralisation (p<0.05; adjusted paired t-test). Only after 5 weeks exposure to the CMC-based solution with an OCP-s=2 a significant remineralisation compared to baseline (p<0.05) as well as a significantly increased mineral gain of the surface area compared to higher saturated solutions (p<0.05; Bonferroni post hoc test) could be observed. CONCLUSIONS: CMC seems to hamper dentin remineralisation, although after 5 weeks a mineral gain could be induced with slightly supersaturated CMC-solutions with respect to OCP.     

Influence of calcium phosphates added to mucin-based saliva substitutes on bovine dentin.

OBJECTIVES: Remineralization of dentin by mucin-containing saliva substitutes might be inhibited by sialic acids bound to mucin, which are known to complex calcium. Thus, the aim of this investigation was to evaluate the effects of various mucin-containing solutions, differing in calcium phosphate concentrations, to be used as saliva substitutes on demineralized bovine dentin in vitro. METHOD AND MATERIALS: Bovine specimens (153) were embedded in epoxy resin, polished (4,000 grit), and partly covered with nail varnish (control of sound dentin). After demineralization for 14 days (pH 5.5), the specimens (n = 9) were exposed to 14 mucin-based solutions (30 g/L) at 2 different pH values (5.5 or 6.5) and differing in saturation with respect to apatites. Two fluoride-free solutions and the commercially available saliva substitute Saliva Orthana(Orthana, Kastrup) served as controls. Differences in mineral loss (deltadeltaZ) and lesion depth (deltaLD) between the values prior to and after storage in the various solutions were evaluated from microradiographs of thin sections (100 microm). RESULTS: The general linear model revealed an almost significant dependency on calcium for deltadeltaZ (P = .050) and a significant dependency on calcium for deltaLD (P = .037). pH influenced deltadeltaZ significantly (P < .001), whereas deltaLD was not influenced significantly (P = .169). Neither deltadeltaZ (P = .475) nor deltaLD (P = .703) were influenced significantly by phosphate. CONCLUSION: Even with low concentrations of calcium and phosphates, mucin-based saliva substitutes are capable of inhibiting demineralization of bovine dentin, whereas with solutions supersaturated with respect to apatites, a remineralizing effect could be observed.     

Effect of mucin alone and in combination with various dentifrices on in vitro Remineralization

The aim of this in vitro study was to evaluate the effect of combining various fluoridated dentifrices with mucin on remineralization of bovine enamel. Enamel specimens were embedded in epoxy resin, partly covered with nail varnish, and demineralized in a lactic acid solution (pH 5.0, 14 days). Parts of the demineralized areas of the specimens were then covered with nail varnish. Half of the samples were exposed to a mucin-containing (2.7 g/l) remineralizing solution, the other half to a mucin-free remineralizing solution for 30 days. In each group, the specimens were divided into four subgroups, which were brushed twice a day with a toothpaste containing sodium, stannous/amine, or amine fluoride. The specimens of the fourth subgroup were not brushed, but stored in one of the two solutions. Mineral loss and lesion depth were evaluated from microradiographs. After the remineralization period, specimens that were brushed with one of the dentifrices and stored in the mucin-containing remineralizing solution reacquired more mineral than those brushed and stored in the mucin-free solution (p < 0.05; Bonferroni post hoc test). The results indicate that mucin in combination with various fluorides seems to affect enamel remineralization significantly. Thus, mucin could be considered as an additive to saliva substitutes or mouthwashes in patients with hyposalivation.     

Effect of various calcium/phosphates ratios of carboxymethylcellulose-based saliva substitutes on mineral loss of bovine enamel in vitro

OBJECTIVES: The present study evaluated the effects of various calcium and phosphate concentrations and ratios of carboxymethylcellulose (CMC)-based solutions on the mineral loss of predemineralised bovine enamel in vitro. METHODS: Bovine enamel specimens were prepared, polished and partly covered with nail varnish, thus serving as control of sound enamel. After demineralisation (37 degrees C; pH 5.0; 14 days) the specimens were exposed to CMC-based solutions (20g/l) with various saturations with respect to apatites containing 0.1mM NaF, CaCl2 (0-32 mM) and KH2PO4 (0-52 mM) at two different pH values (5.5 or 6.5). A fluoride-free solution served as control, and four commercially available products were tested as well. The differences in mineral loss (DeltaDeltaZ) between the values prior to (DeltaZ Demin) and after storage (DeltaZ Effect) in the various solutions were evaluated from microradiographs of thin sections (100microm). RESULTS: The general linear model revealed a significant dependency for DeltaDeltaZ on 'calcium' (p<0.001), 'phosphate' (p=0.023), 'fluoride' (p=0.002) and 'pH' (p<0.001). With increasing calcium and phosphate concentrations an increase in DeltaDeltaZ could be observed up to the solution containing the third highest saturation with respect to octacalciumphosphate (3.2), showing a significant remineralisation (p<0.05; t-test). The commercially available products as well as the control groups revealed significantly reduced DeltaDeltaZ values compared to this group (p<0.01; Bonferroni). CONCLUSIONS: A saturation with respect to octacalciumphosphate of 3.2 and a pH of 6.5 enables CMC-based solutions to remineralise bovine enamel in vitro.     

pH-cycling of enamel and dentin lesions in the presence of low concentrations of fluoride

F-dentifrice usage causes slightly elevated fluoride levels in saliva. Therefore, the effects of permanent low fluoride concentrations versus daily dentifrice treatments were studied on enamel and dentin lesions in a pH-cycling model of alternating demineralization and remineralization. Groups received 1) no fluoride treatment. 2) 3 μM (0.06 ppm) F continuously present during re- and demineralization or 3) daily 5–min F-dentifrice treatments. Solutions were analyzed for changes in calcium and fluoride. Cumulative results (10 d) showed that for the non-fluoride group the dentin lesions increased, while for enamel lesions mineral uptake and loss were balanced. Addition of 3 μM F caused small, non-significant, enhancement of remineralization (1–7%). while demineralization was significantly inhibited for both tissues (9–23%). The daily dentifrice treatments resulted in a balance between mineral uptake and loss of dentin, due to inhibited demineralization (-33%) and enhanced remineralization (+ 79%). For enamel, the F-dentifrice treatments resulted in 43% reduction of demineralization, with no significant effect on remineralization. Fluoride loss from the 3 μM F cycling solutions was significant (up to 50%) and constant during the experimental period. Microradiographic analysis showed remineralization at the lesion front in enamel. In dentin, the lesion depth was increased in all groups, with concomitant mineral deposition in the surface region of the dentifrice group. Results indicate that slightly elevated fluoride levels may be considerably less effective in inhibiting lesion progression in dentin than in enamel, and suggest mineral uptake and loss to occur at similar depths for enamel lesions, while demineralization and remineralization occur at different depths in dentin.     

Evaluation of the remineralising capacities of modified saliva substitutes in vitro

Objective

In this in vitro study the effects of various calcium and phosphate additions to a commercially available saliva substitute on remineralisation of demineralised dentin were investigated.

Design

Bovine dentin specimens (n = 70) were prepared. Before and after demineralisation (37 °C, pH 5.0, 5 days), one-quarter of each specimens surface was covered with nail varnish (control sound/demineralised tissue). Specimens were exposed either to original Saliva natura (SN 0) or to three modified versions (SN 1, SN 2 and SN 3) formulated with different degrees of saturation with respect to octacalciumphosphate (OCP) and dicalcium phosphate dihydrate (DCPD) for 2 and 5 weeks (37 °C). An aqueous solution (Buskes remineralising solution) served as positive control (PC). Differences in mineral loss (deltadeltaZ) and lesion depth (deltaLD) before and after storage were evaluated from microradiographs.

Results

After both storage periods dentin specimens immersed in SN 0 revealed significantly higher mineral losses (indicated by deltadeltaZ) and higher lesion depths (indicated by deltaLD) compared to all other solutions (p < 0.05; ANOVA). Specimens stored in SN 1 and 3 showed significantly higher mineral losses compared with PC (p < 0.05). No differences could be observed between SN 2 and PC (p > 0.05). Only SN 2 significantly remineralised from 2 to 5 weeks storage (p < 0.05; t-test).

Conclusions

An experimental Saliva natura solution (SN 2) with S_OCP = 2 and S_DCPD = 1.4 showed highest remineralising capacity. Similar or better remineralisation could not be achieved with slightly higher or lower saturated solutions.     

Linseed based saliva substitutes and their effect on mineral dissolution of predemineralized bovine dentin in vitro

OBJECTIVES: Polymers used in saliva substitutes might inhibit remineralization. The present study evaluated the effects of various calcium, phosphate, and fluoride concentrations of linseed based solutions on the mineral loss of predemineralized bovine dentin in vitro. METHODS: Dentin specimens were prepared, embedded and polished. The specimens were demineralized (pH 5.6; 6 d; 37 degrees C) and half of each sample was covered with nail varnish. Subsequently, the specimens (n=10) were exposed to 14 linseed based solutions (calcium 0-1.1 mM; phosphate 0-7.7 mM, fluoride 0-0.03 mM) at pH 5.5 and 6.5 as well as to Salinum for 14 days (37 degrees C). The differences in mineral loss (DeltaDeltaZ) between the values prior to and after storage in the solutions were evaluated from microradiographs of thin sections. RESULTS: After the exposure to the various solutions decreased mineral contents compared to those after demineralization could be observed (p<0.05; paired t-test) whereas for the specimens stored in solution with the highest calcium and phosphate concentration no significant change in mineral loss could be evaluated (p>0.05). Salinum induced a significantly greater mineral loss compared to the equivalent saturated solution (p<0.05; ANOVA, Bonferroni). The general linear model revealed a significant dependency for DeltaDeltaZ on 'phosphate' (p=0.000) and 'fluoride' (p=0.001), but not on 'calcium' (p=0.397) and 'pH' (p=0.368). CONCLUSIONS: The addition of calcium, phosphates, and fluorides seems to have a positive effect on the remineralizing qualities of linseed based saliva substitutes.     

Effects of irradiation on in situ remineralization of human and bovine enamel demineralized in vitro

The objective of this study was to evaluate the effects of irradiation and surface condition on in situ remineralization of demineralized human and bovine enamel. Specimens (n=96) obtained from 24 human molars and 24 bovine incisors were prepared. The surfaces of half of the specimens were abraded while the others remained natural. Each of the 12 human and bovine abraded and sound specimens was irradiated fractionally up to 46.5 Gy (3.1 Gy/day, 5 days/week), while the remaining samples were not irradiated. Prior to and following the demineralization (pH 5.0; 14 days) all specimens were partly covered with nail varnish (control). After in vitro demineralization 2 irradiated and 2 nonirradiated specimens were inserted into both buccal aspects of 12 intraoral appliances, which were worn by 12 persons for a period of 6 weeks. All samples were brushed twice a day with a fluoride-containing toothpaste. Mineral analyses revealed a significant influence on mineral loss (DeltaZdemin), mineral gain (DeltaDeltaZ), lesion depth (LDdemin), and lesion depth reduction (DeltaLD) of the variables 'material' and 'irradiation' (p<0.05; ANOVA). Reciprocal interactions could be observed between these two variables for DeltaZdemin, DeltaDeltaZ, and LDdemin, due to significantly reduced values found for the irradiated, abraded bovine specimens compared to the nonirradiated ones (p<0.05; Bonferroni post hoc test). It can be concluded that neither irradiation nor abrasion influenced in vitro demineralization or in situ remineralization of the human specimens, whereas abrasion hampered demineralization in irradiated, bovine specimens.     

Effect of various Ca2+/PO4(3-) concentrations of linseed-based saliva substitutes on enamel in vitro

Remineralization might be hampered by various polymers used in saliva substitutes. Thus, the present study evaluated the effects of various calcium and phosphate concentrations of linseed-based solutions on the mineral loss of pre-demineralized bovine enamel in vitro. A commercially available saliva substitute (Salinum) based on linseed was tested as well. Enamel specimens were prepared from bovine incisors and embedded in epoxy resin. One-third of each sample was covered with nail varnish (control of sound enamel). After demineralization (37 degrees Celsius; pH 5.0; 14 days) another third of the samples was nail-varnished again. Subsequently, the specimens (n = 10) were exposed to 12 linseed-based solutions (Ca(2+) addition 0-2 mM; PO4(3-) addition 0-3.2 mM) at pH 5.5 and 6.5 as well as to Salinum) for 14 days (37 degrees Celsius). The differences in mineral loss between the values prior to and after the storage in the various solutions were evaluated from microradiographs of thin sections (100 mum). The general linear model revealed a significant dependency for the mineral loss on 'calcium' (P = 0.003), but not on 'pH' (P = 0.397) and 'phosphate' (P = 0.094). Salinum) induced a significant greater mineral loss compared with equivalently saturated solutions (P < 0.05; anova, Bonferroni). The solution with the highest calcium and phosphate concentration showed the greatest mineral gain (P = 0.033; paired t-test). The addition of calcium and phosphate seems to have a positive effect on the remineralizing qualities of linseed-based saliva substitutes.     

The effect of commercially available saliva substitutes on predemineralized bovine dentin in vitro

OBJECTIVE: The objective of this study was to evaluate the effects of various saliva substitutes (Artisial; Glandosane; Oralube; Saliva medac; Oralbalance) on the lesion depth and the mineral content of predemineralized bovine dentin in vitro. MATERIALS AND METHODS: Ninety-six dentin samples were prepared from 24 freshly extracted bovine incisors. The samples were predemineralized (pH 5.5; 10 days), and subsequently exposed to the various artificial salivas. A carbonate-reduced mineral water (Hirschquelle) as well as the mouthwash solutions Meridol and biotène served as controls. Lesion depth and mineral loss were evaluated from microradiographs of thin sections (110 microm) by a dedicated software package (TMR 1.24). RESULTS: After storage in Glandosane and biotène, the results indicated a significant mineral loss and an increase in lesion depth (P < 0.01; Wilcoxon). In contrast, specimens stored in Oralube showed a decrease in lesion depth and an increase in mineral content (P < 0.05; Wilcoxon). CONCLUSIONS: Thus, the use of neither Glandosane nor biotène can be recommended in dentate patients with severe xerostomia.     

Inhibition of lesion progression by the penetration of resins in vitro: influence of the application procedure

This study compared the progression of sealed initial enamel lesions penetrated with a fissure sealant (Helioseal, Vivadent) or various adhesives (Heliobond, Excite, Vivadent; Resulcin, Merz; Solobond M, Voco; Prompt L-Pop, 3M-ESPE) after exposure to a demineralizing solution, in vitro. From 27 bovine teeth, 54 enamel specimens were prepared and covered with nail varnish (control), thus obtaining three windows for treatment. After demineralization (pH 5.0; 14 days), two of the windows (A, B) were etched with phosphoric acid (20%; 5 seconds); whereas, the third area served as the control (C). The specimens were divided randomly into six groups (n=9), and the material was applied (90 seconds) either once (A) or twice (B). Light-curing followed each application. Half of the area of each specimen window was then covered with nail varnish, and the samples were again stored in the demineralizing solution (pH 5.0; 14 days). The specimens were cut perpendicular to the surface, and both enamel slabs were studied after infiltration using a fluorescent, low viscous resin (VIRIN) and confocal microscopy (CLSM). Lesion depths were calculated (ImageJ) from the surface to that point in the lesion where the grey values clearly changed to a darker grey. After demineralization, mean lesion depths (SD) (14 days) were measured at 105 (21) microm. The second demineralization led to a mean progression of the lesion depths of 52 (31)%. Adper Prompt L-Pop and Solobond M could not significantly prevent lesion progression after a single application (p > 0.05; t-test); however, the second application of Solobond M significantly decreased lesion progression (p < 0.05; t-test). Helioseal, Heliobond, Resulcin Monobond and Excite showed significantly better inhibition of the demineralization compared to the other materials (p < 0.05; Bonferroni). It can be concluded that the penetration of adhesives into initial lesions inhibited a further demineralization in vitro.     

Microradiographic study on the effects of salivary proteins on in vitro demineralization of bovine enamel

The aim of this investigation was to evaluate the effects of various proteins on in vitro demineralization of bovine enamel. From each of 100 bovine incisors two samples were prepared. The specimens were embedded in epoxy resin and polished up to 4000 grit. Subsequently, the specimens' surfaces were partly covered with nail varnish, thus serving as control of sound enamel. The specimens were divided randomly into five groups (n = 40) and demineralized in a solution of constant composition (pH 5.0; 10 days). For each subgroup of specimens (n = 10) 4 L were taken and either low (50% of medium conc.), medium, or high (150%) concentrations of the proteins [human albumin (100% conc. = 7 mg L(-1)), mucin (577.5 mg L(-1)), immunoglobulin G (IgG) (46 mg L(-1)), casein isolated from bovine milk (1.2 g L(-1))] or amino acid [l-Proline (7 mg L(-1))] were added to 1 L of the demineralizing solution, whereas 1 L served as control. Mineral loss and lesion depth (LD) were evaluated from microradiographs of thin sections (110 mum) by a dedicated software package (TMR 1.24). No differences were found between the five control groups (P > 0.05; ANOVA). Albumin, l-Proline, and IgG did not affect enamel demineralization, whereas the addition of both casein and mucin resulted in significant reductions of both mineral loss and LDs (P < 0.01; Tukey's test). Within the limitations of an in vitro study, the present investigation indicates that casein and mucin seem to affect enamel demineralization significantly. Thus, these proteins might be helpful as an additive to saliva substitutes or mouthwashes if the quality of saliva is altered.     

Combined effects of carbon dioxide laser and fluoride on demineralized primary enamel: an in vitro study

This in vitro study aimed at evaluating the efficacy of a CO(2) laser (10.6 microm) alone or combined with acidulated phosphate fluoride (APF) on the inhibition of lesion progression in primary enamel. The specimens were treated with/without CO(2) laser and/or APF and submitted to pH cycling. Microhardness analysis was performed and the enamel mineral loss values were obtained. The groups treated with laser and/or APF presented lower mineral loss when compared to the control group (p < 0.05). Laser irradiation alone or combined with APF decreased lesion progression in primary enamel. However, the combined treatment did not show any significant additional effect.     

A quantitative analysis of mineral loss and shrinkage of in vitro demineralized human root surfaces

Demineralization of dentin specimens proceeds at a faster rate than that of enamel. Although this is generally accepted, a quantification of the rate of formation of root lesions is hampered by the shrinkage of the lesions when these are dried prior to microradiographic analysis. This leads to a significant underestimation of the lesion depth and total mineral loss. The aim of this paper was to quantitate the rate of mineral loss during root lesion formation in vitro and to determine the shrinkage of root specimens as a result of drying. Unerupted roots of human teeth were subjected to a demineralizing system of 0.1 mol/L lactate buffer (pH = 4.8) with 0.2 mmol/L methanehydroxydiphosphonate during four, 11, 22, and 44 days. The root lesions were assessed by quantitative microradiography. The demineralizing solutions were analyzed to determine the amounts of root tissue dissolved. A comparison of these two sets of data showed that, with the demineralizing system used, root lesions may shrink up to 62%. Fixation of the specimens in fixative did not affect this shrinkage. Chemical analysis showed that mineral loss proceeded linearly with time. From the data-sets of this study, a model was developed to compensate for the shrinkage in the dentin specimens. In this way, it was possible to calculate the lesion depth at four demineralization times as being 130, 220, 320, and 530 microns, respectively. These values were in agreement with a microscopic determination of the lesion depth.     

Differences in bonding to acid-etched or Er:YAG-laser-treated enamel and dentin surfaces

STATEMENT OF PROBLEM: Er:YAG (erbium-doped yttrium aluminium garnet) lasers have been effective in the removal of dental tissues. It has been suggested that they are also useful for preparing dental surfaces for adhesion, but results to date have been controversial. PURPOSE: This study compared the tensile strength of bracket-tooth bonds obtained after preparation of the surface for adhesion (dentin or enamel) by conventional acid-etching or by Er:YAG laser etching and investigated microstructure of resin-tooth interfaces using the 2 procedures. MATERIAL AND METHODS: Eighty healthy human premolars were used. Brackets were cemented to acid-etched enamel, laser-etched enamel, acid-etched dentin, or laser-etched dentin (20 teeth per group). Dentin was previously exposed using a high-speed handpiece. Acid-etching was with 37% orthophosphoric acid (15 seconds for enamel, 5 seconds for dentin). Laser etching was with Er:YAG laser (four 200 mJ pulses per second for enamel; four 160 mJ pulses per second for dentin). Brackets were bonded with autocuring resin paste, having first applied a primer (dentin only) and then light-cured bonding resin. Tensile strength was determined with a universal testing machine. Data were analyzed with 2-way ANOVA and subsequent t test with Bonferroni correction. Fracture patterns were compared by the Wilcoxon test with Bonferroni correction. For SEM studies of the resin-tooth interface, a total of 12 premolars were used (3 for each tissue per treatment combination). RESULTS: Mean tensile bond strength for acid-etched enamel (14.05 +/- 5.03 MPa) was significantly higher (P<.05) than for laser-etched enamel (8.45 +/- 3.07 MPa), and significantly higher (P<.05) for acid-etched dentin (4.70 +/- 2.50 MPa) than laser-etched dentin (2.48 +/- 1.94 MPa). Bond failure after laser etching was due to microcohesive fracture of tooth tissue. SEM studies of both resin-enamel and resin-dentin interfaces indicated extensive subsurface fissuring after laser etching. CONCLUSION: Adhesion to dental hard tissues after Er:YAG laser etching is inferior to that obtained after conventional acid etching. Enamel and dentin surfaces prepared by Er:YAG laser etching show extensive subsurface fissuring that is unfavorable to adhesion.     

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.     

Susceptibility of bleached enamel and root dentin to artificially formed caries-like lesions

PURPOSE: To evaluate in vitro the susceptibility of caries-like lesion formation on enamel and root dentin that had been bleached with carbamide peroxide agents. METHODS: 150 slabs of bovine enamel and root dentin were ground flat and polished. According to a randomized complete block design, the specimens were then allocated to be bleached with agents (Rembrandt) containing 12% [CP12], 16% [CP16], 22% [CP22] or 30% [CP30] of carbamide peroxide over 21 days. The control group remained unbleached. Afterwards, all specimens were randomly distributed between two subgroups (n= 15): one was subjected to alternating demineralizing and remineralizing solutions to induce caries-like lesions and the other was not. Enamel specimens were cycled four times in demineralizing (pH 5.0) and remineralizing solutions (pH 7.0), while root dentin specimens were cycled twice. Microhardness measurements were carried out at the post-bleaching and at the post-caries lesion formation phases. RESULTS: In the post-bleaching condition, microhardness values for both enamel and root dentin were dependent on the bleaching agent used. At the post-caries formation stage, there was a significant interaction between the bleaching treatment and substrate condition (carious or noncarious) for enamel and root dentin. Regardless of the bleaching agent, carious enamel and root dentin presented significantly lower microhardness values as compared to the noncarious counterparts. For carious enamel, those specimens exposed to CP16 exhibited higher microhardness values than the subset group formed by CP22, CP30 and unbleached samples. Both subsets did not differ from CP12. For carious root dentin, no difference was observed among the microhardness values attained as a result of the different bleaching treatments.     

The effect of human saliva substitutes in an erosion–abrasion cycling model

Saliva may affect dental erosion–abrasion by reducing demineralization, enhancing remineralization, and acting as lubricant. This study tested the effect of human saliva substitutes in an erosion–abrasion cycling model designed for enamel and root dentin. Specimens were randomly assigned into the following groups (n = 8): artificial saliva (AS), artificial saliva + mucin (AS+M), deionized water (DIW, negative control), and pooled human saliva (HS, clinical reference). Each group was submitted to a cycle of 5 min in 1% citric acid (pH 3.75), 30 min in the testing solutions, and toothbrushing (enamel, 500 strokes; dentin, 150 strokes, ～200 g load) in fluoridated dentifrice (1,100 p.p.m. NaF) slurry. Specimens were rinsed and dried after each procedure. This cycle was repeated three times each day, for 3 d. Substrate loss was measured daily using optical profilometry. Analysis of variance (anova) and Tukey tests (α=0.05) showed a significant increase in enamel and dentin wear throughout the experiment for all groups. At the end of the experiment, enamel wear for each group was ranked as: (AS)<(AS+M) and (HS)<(DIW), with AS+M not differing from HS. For dentin, groups AS and AS+M did not differ from each other or from DIW, but showed significantly higher wear than HS. The artificial saliva with mucin showed promise as a potential substitute for human saliva in the enamel erosion–abrasion cycling model. For dentin, none of the artificial salivas performed similarly to human saliva.     

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.     

Erosion and attrition of human enamel in vitro part I: interaction effects

Objective. The aim of the study in vitro was to measure the interplay of attrition and erosion of human enamel under several different pH conditions.

Materials and methods. Cusp and smooth surface enamel specimens were prepared from unerupted human third molar teeth. Cusp and smooth surface specimens opposed each other in a wear machine under a load of 600 g. The machine simulated tooth grinding for 30 min (2280 wear cycles). Six groups of 10 specimens were worn in the following environmental conditions: saline, citric acid at pH values of 3.2, 5.5 or 7.0 and two cycling groups (pH 3.2/saline or saline/pH 3.2). Additionally, 10 smooth surface specimens were exposed to the same fluids without attrition. Tissue loss on smooth surface specimens was determined by profilometry. The worn specimen surfaces were studied by SEM.

Results. Attrition depth in saline and pH 7.0 citric acid was 25.5 μm. At pH 3.2 and 5.5 attrition depths were 6.0 and 4.3 μm, respectively. Cycling in saline/citric acid and vice versa produced attrition depths of 9.2 and 7.9 μm, respectively. In the erosion only specimens lesion depths were 3.0, 1.2 and 0 μm at pH 3.2, 5.5 and 7.0 and saline, respectively. Attrition specimens at pH 7.0 and in saline showed very rough surfaces. At low pH enamel surfaces appeared flat and smooth.

Conclusions. Enamel wear in neutral conditions is significantly higher than in acidic conditions (p<0.05), apparently due to a smoothing effect of erosion on contacting surfaces.