In vitro studies investigating the dentin tubule-occlusion properties of an experimental anhydrous stannous fluoride dentifrice.

PURPOSE: To evaluate in vitro the ability for an experimental anhydrous 0.454% w/w stannous fluoride dentifrice to occlude dentin tubules. METHODS: Scanning electron microscopy (SEM) was used to assess tubule occlusion and the resistance of the occlusion to dietary acid in a 4-day model, where bovine dentin was treated with product twice daily with acid challenges administered on Days 3 and 4. The reduction in hydraulic conductance of the dentin following treatment was also measured. RESULTS: The experimental stannous fluoride dentifrice was effective at reducing the hydraulic conductance of dentin by occluding tubules. The occlusion was resistant to challenge with grapefruit juice.

A comparative in vitro study investigating the occlusion and mineralization properties of commercial toothpastes in a four-day dentin disc model.

OBJECTIVE: The objective of this study was to evaluate the relative level of dentin tubule occlusion and dentin mineralization conferred by a 5% w/w calcium sodium phosphosilicate (45S5)/1450 ppm fluoride toothpaste in comparison to a range of commercial toothpastes reported to occlude dentin tubules. METHODS: Two separate experiments were employed to (i) determine the level of dentin tubule occlusion, and (ii) explore the change in dentin mineralization conferred by a number of marketed toothpastes and controls, following twice-daily brushing in a longitudinal, acid challenge-based, dentin disc model. In Study I, 192 bovine dentin discs, polished and etched in citric acid to provide a smooth dentin surface with patent tubules, were divided into eight treatment groups and subjected to brushing with one of seven test toothpastes or deionized water over four days. Prior to and between treatments, the dentin samples were stored in saliva. The test products were fluoridated toothpastes containing: calcium sodium phosphosilicate (45S5); strontium acetate; arginine/calcium carbonate; amine fluoride; calcium sulphate/diphosphate; stannous fluoride; casein stabilized amorphous calcium phosphate toothpaste; and a non-occluding negative control, deionized water. At the end of each treatment day (1 though 4), one group of samples was removed for scanning electron microscopy (SEM) analysis and graded on a categorical visual scale to assess the level of dentin tubule occlusion. A subset of samples from Study I was also cross-sectioned and examined using SEM. For the exploratory mineralization study (Study II), 120 dentin specimens were prepared as previously described and divided into four treatment groups consisting of A, C, F, and a tooth sealant varnish (I), and subjected to the treatment regimen described in Study I. The dentin samples were assessed for changes in surface microhardness using an indenter fitted with a Knoop probe and the level of dentin occlusion. RESULTS: In Study I, the 5% w/w calcium sodium phosphosilicate/1450 ppm fluoride-containing toothpaste (A), the stannous fluoride-containing toothpaste (F), and the strontium acetate-containing toothpaste (B) delivered the highest level of occlusion following four days of twice-daily brushing and a twice-daily acid challenge on days 3 and 4. Surface analysis of a subset of Study I samples, following four days of treatment, indicated that the 5% w/w calcium sodium phosphosilicate/1450 ppm fluoride-containing toothpaste formed a distinct layer at the surface of dentin. For Study II, surface microhardness analysis revealed that the 5% w/w calcium sodium phosphosilicate/1450 ppm fluoride-containing toothpaste (A) delivered significantly more surface hardening then the control or competitor toothpastes on days 2 and 4. CONCLUSION: Desensitizing toothpastes reported to operate by an occlusion mechanism have been observed to confer varying degrees of dentin tubule occlusion and dentin mineralization over four days in an acid challenge-based in vitro model. A 5% w/w calcium sodium phosphosilicate/1450 ppm fluoride-containing toothpaste was observed to impart a significant level of dentin tubule occlusion and surface hardening, and form durable occlusive deposits following four days of twice-daily brushing in vitro.

An in vitro investigation of two currently marketed dentin tubule occlusion dentifrices.

OBJECTIVE: The objective of this study was to evaluate the relative level of dentin tubule occlusion afforded by two dentifrices specifically developed to occlude dentin tubules, following finger-applied dab-on application and by repeated brushing, in a longitudinal acid-challenge-based dentin disk model. The impact of a dietary acid alone (grapefruit juice) on the level of dentin tubule occlusion conferred by each product following dab-on application was also explored in a separate short-term stand-alone exploratory dentin disk-based in vitro study. METHODS: For the longitudinal study, 120 bovine dentin discs, polished and etched in citric acid for two minutes to provide a smooth dentin surface with patent tubules, were divided into three treatment groups and subjected to a finger application of the dentifrice only, or a combination of finger application and brushing. Prior to and between treatments, the dentin samples were stored in saliva (for > 60 minutes). The test products were an 8% w/w strontium acetate dentifrice (currently marketed as Sensodyne Rapid Relief), an arginine-based dentifrice (marketed as Colgate Sensitive Pro-Relief), and deionized water. For the exploratory acid resistance study, 24 dentin samples were divided into two treatment groups. Treatment consisted of a single dab-on application with the test dentifrices to the hydrated surface of dentin, followed by exposure to either a 30-second or 10-minute grapefruit juice acid challenge. For both models, at the end of each treatment period, the samples were removed for scanning electron microscopy analysis and graded on a categorical visual scale. All data were analyzed statistically by unpaired t-test comparison. RESULTS: In the longitudinal (four-day) model, the strontium acetate-based dentifrice occluded dentin tubules significantly better than the currently marketed arginine-based dentifrice post-dab-on treatment and grapefruit juice challenge (p < 0.0001). At all other time points, the strontium acetate dentifrice demonstrated significantly better occlusion than the arginine-based dentifrice (p < or = 0.0001). In the exploratory acid resistance model, the level of occlusion observed for the strontium acetate dentifrice was statistically significantly greater when compared to the arginine dentifrice following 10-second and 10-minute (p < 0.0001) exposures to grapefruit juice. CONCLUSION: A strontium acetate dentifrice is observed to deliver statistically significantly greater levels of dentin tubule occlusion when compared to the arginine dentifrice following dab-on and brushing application under dietary acid-challenge conditions in this in vitro model. This study suggests that the arginine-containing dentifrice may be more susceptible to acid-mediated dissolution than the strontium-based dentifrice under the conditions employed in this in vitro model.

Development of an acid challenge-based in vitro dentin disc occlusion model.

OBJECTIVE: The objective of this study was to evaluate the utility of a novel acid challenge-based dentin disc occlusion model, and to compare the occluding effect and acid resistance exhibited by currently marketed occlusion dentifrices in vitro. METHODS: Ninety-six bovine dentin discs were polished and etched in citric acid (6% w/w) for two minutes to provide a smooth dentin surface with patent tubules. The discs were divided into three treatment groups. Each treatment group was brushed (Oral-B Vitality Precision Clean/EB 17 FlexiSoft head) twice a day, for up to four days, with either a strontium acetate dentifrice (Sensodyne Rapid Relief), an arginine-based dentifrice (Colgate Sensitive Pro-Relief), or water. Prior to and between treatments, the dentin samples were stored in human saliva. On days 3 and 4, following dentifrice treatment and incubation in saliva (60 minutes), the samples were subjected to a grapefruit juice challenge. Eight samples from each treatment group were removed from the study on each day and analyzed by scanning electron microscopy (SEM). The SEM images were graded according to a categorical occlusion scale, and the data were analyzed by ANOVA. RESULTS: The strontium acetate dentifrice occluded dentin tubules significantly better than the negative control (water) on days 1 through 4 (day 4 p < or = 0.0001). The marketed occlusion-based dentifrices demonstrated various degrees of dentin tubule occlusion over the four days. The strontium acetate dentifrice demonstrated significantly better occlusion than a currently marketed arginine-based occlusion dentifrice on day 1 (p = 0.0337), day 2 (p = 0.0021 ), and day 4 (p < or = 0.0001). CONCLUSION: An in vitro model has been developed that can differentiate the dentin tubular occlusive effects of currently marketed occlusion dentifrices. Surface analysis reveals that the occluding deposits vary according to product, and that some are more susceptible to acid mediated dissolution.

The determination of equilibrium constants, DeltaG, DeltaH and DeltaS for vapour interaction with a pharmaceutical drug, using gravimetric vapour sorption.

The application of gravimetric vapour sorption (GVS) to the characterisation of pharmaceutical drugs is often restricted to the study of gross behaviour such as a measure of hygroscopicity. Although useful in early development of a drug substance, for example, in salt selection screening exercises, such types of analysis may not contribute to a fundamental understanding of the properties of the material. This paper reports a new methodology for GVS experimentation that will allow specific sorption parameters to be calculated; equilibrium constant (K), van't Hoff enthalpy change (DeltaH(v)), Gibbs free energy for sorption (DeltaG) and the entropy change for sorption (DeltaS). Unlike other reports of such type of analysis that require the application of a specific model, this method is model free. The analysis does require that over the narrow temperature range of the study DeltaH(v) is constant and there is no change in interaction mechanism.