The effect of hydrogen peroxide concentration on metal ion release from dental casting alloys.

There are concerns that tooth bleaching agents may adversely affect dental materials. The aim of this study was to test the hypothesis that increasing concentrations of hydrogen peroxide (HP) are more effective than water at increasing metal ion release from two typical dental casting alloys during bleaching. Discs (n = 28 for each alloy) were prepared by casting and heat treated to simulate a typical porcelain-firing cycle. Discs (n = 7) of each alloy were immersed in either 0%, 3%, 10% or 30% (w/v) HP solutions for 24 h at 37 degrees C. Samples were taken for metal ion release determination using inductively coupled plasma-mass spectrometry and the data analysed using a two-way anova followed by a one-way anova. The surface roughness of each disc was measured using a Talysurf contact profilometer before and after bleaching and the data analysed using a paired t-test. With the exception of gold, the differences in metal ion concentration after treatment with 0% (control) and each of 3%, 10% and 30% HP (w/v) were statistically significant (P < 0.05). Metal ion release from the two alloys increased with increasing HP concentrations (over 3000% increase in Ni and 1400% increase in Pd ions were recorded when HP concentration increased from 0% to 30%). Surface roughness values of the samples before and after bleaching were not significantly different (P > 0.05) Exposure of the two dental casting alloys to HP solutions increased metal ion release of all the elements except gold.

The effect of 24h non-stop hydrogen peroxide concentration on bovine enamel and dentine mineral content and microhardness.

OBJECTIVES: Tooth bleaching agents may adversely affect tooth structure. The aim of this study was to investigate the effect of hydrogen peroxide concentration on mineral loss and microhardness of bovine teeth. METHODS: Twenty-six freshly extracted intact bovine incisor teeth were stored in distilled water. Five teeth were sectioned and four samples (2 mm x 2 mm x 1.5 mm) each of enamel and dentine were obtained from each tooth. The samples of enamel and dentine were divided into four groups and immersed in either 0%, 3%, 10% or 30% (w/v) hydrogen peroxide solutions for 24h at 37 degrees C. Samples from the solutions were taken for ion release analysis using inductively coupled plasma mass spectrometry. The remaining 21 teeth were mounted in epoxy resin and the upper surface of the specimens were ground and polished to expose the enamel and dentine for microhardness measurements. These specimens were randomly divided into three equal groups and Vickers microhardness values were recorded on the enamel and dentine surfaces of each group before and after bleaching. RESULTS: The differences in ion release concentration after treatment with 0% (control) and each of 3%, 10% and 30% hydrogen peroxide (w/v) were statistically significant (p<0.025). The release of calcium and phosphorous ions increased with increasing hydrogen peroxide concentrations. A significant reduction (p<0.05) in Vickers microhardness values for enamel was recorded after bleaching. CONCLUSIONS: Ion release from both enamel and dentine increased with increasing hydrogen peroxide concentration. Microhardness of enamel decreased significantly with bleaching.

The effect of hydrogen peroxide concentration on metal ion release from dental amalgam.

OBJECTIVES: The aim of this study was to investigate the effect of hydrogen peroxide (HP) concentration on metal ion release from dental amalgam. METHODS: Dental amalgam discs (n=25) were prepared by packing amalgam into cylindrical plastic moulds (10 mm diameter and 2 mm height). The discs were divided into five equal groups and each group was immersed in 20 ml of either 0%, 1%, 3%, 10% or 30% HP solution for 24 h at 37 degrees C. Samples were taken for metal ion release determination (Hg, Ag, Sn and Cu) using inductively coupled plasma mass spectrometry (ICP-MS). The surface roughness of each disc was measured before and after bleaching. RESULTS: The differences in concentration of metal ions released after treatment with 0% (control) and each of 1%, 3%, 10% and 30% HP were statistically significant (p<0.05). Metal ion release for the elements (Hg, Ag, Sn and Cu) increased with exposure to increasing concentrations of HP. Surface roughness measurements of the samples before and after treatments with HP solutions were not significantly different (p>0.05). CONCLUSIONS: Exposure to HP bleaching agent was associated with increased metal ion released from dental amalgams compared to treatment with a control solution. Ion release was in proportion to the peroxide concentration tested, with the highest concentration associated with the greatest metal ion release for all elements investigated.

The effect of carbamide peroxide treatment on metal ion release from dental amalgam.

OBJECTIVES: There is concern that hydrogen peroxide generated by tooth bleaching agents may cause enhanced metal ion release (including mercury) from dental amalgam following contact. The aim of this in vitro study was therefore to investigate the effect of a carbamide peroxide (CP) based tooth bleaching gel on metal ion release from dental amalgam. METHODS: Dental amalgam discs were prepared according to the manufacturers' instructions. These were treated with either a 10% carbamide peroxide (CP) gel or a 0% CP gel for 24h. Discs were carefully wiped with cotton wool before immersion in distilled water (20 ml) for 24h at 37 degrees C. Following immersion, water samples were taken for metal ion release determination (Ag, Cu, Hg and Sn) using inductively coupled plasma mass spectrometry methods. The specimens were further evaluated for surface changes using scanning electron microscopy (SEM) and Talysurf surface roughness measurements. RESULTS: The differences in concentration of metal ions released after treatment with the 10% CP gel and a placebo gel treatment were not statistically significant (p>0.05). For example, mercury release following treatment with the 10% CP gel and the 0% CP gel was found to be 1.17(0.5) and 0.57(0.1)microgcm(-2), respectively. Roughness measurements for samples treated with the 10% CP gel and 0% CP gel were 2.23(0.47) and 1.74(0.16)microm, respectively, again showing no significant difference between groups (p>0.05). SEM images of the amalgam surfaces showed no apparent differences between treatments. SIGNIFICANCE: Treatment with a 10% CP gel did not significantly enhance subsequent metal ion release from dental amalgams compared to a control gel, contradicting previously published studies.

Impact of cone beam computed tomography (CBCT) on diagnostic thinking in endodontics of posterior teeth: A before- after study.

OBJECTIVES: The aim of this study was to evaluate the impact of limited volume CBCT upon diagnosis as part of endodontic management of posterior teeth. The null hypothesis that CBCT does not make any difference in endodontic diagnosis was tested. METHODS: A single-centre "before-after" study was conducted in a secondary healthcare establishment. Eligible patients were all adults aged 18 years or over who were referred to a specialist endodontic unit. Further inclusion criteria were that the cases were either re-treatment or de novo root canal treatment where the anatomy was judged to be complex. Exclusion criteria included vulnerable groups and de novo endodontic treatment with uncomplicated root canal anatomy. As well as a full history and clinical examination, a high quality colour photographic intraoral image, two paralleling technique periapical radiographs and limited volume CBCT examination were carried out for each patient. All components, except the CBCT dataset, were combined into a Powerpoint presentation and assessed by 4 observers. A questionnaire was designed for the observers as part of the study. RESULTS: CBCT information only changed the radiological findings and the final diagnosis in a minority of cases. There was no clear evidence that CBCT increases the confidence of observers or that CBCT was helpful in making a diagnosis. CONCLUSIONS: Routine use of CBCT cannot not be justified on the basis of a change in diagnosis and carefully selected use is appropriate. CLINICAL SIGNIFICANCE: CBCT is being increasingly used in the field of endodontics. The benefits gained from the use of CBCT must be carefully balanced against the increased radiation dosage. Determination of selection criteria for the use of CBCT in endodontics is, therefore, essential.

Methods used in dentin bonding tests: an analysis of 50 investigations on bond strength.

Researchers have carried out a variety of investigations to determine the properties of available dentin bonding systems. The test methods and variables used in 50 published investigations of bond strength were analyzed. Among the studies analyzed, shear tests predominated, being used in 80% of the studies; dentin from human molar teeth was used most often (in 88% of investigations); and the most prevalent time of testing was 24 hours postcuring. However, a number of potential variables were not recorded in a high proportion of articles, among these the film thickness, the type of dentin tested, and the surface condition (moist or dry). The mode of failure was recorded in only 42% of the investigations assessed. It was found that there is little standardization of test methods in studies of dentin bond strength and that a number of variables are often either not recorded or reported.

Effects of bleaching on mercury ion release from dental amalgam.

The chemical reactions that take place at the amalgam surface when exposed to bleaching agents are not well-understood. It is known, however, that mercury ions are released from dental amalgam when bleached. We hypothesized that increasing concentrations of hydrogen peroxide are more effective than water at increasing mercury ion release from dental amalgam. We prepared dental amalgam discs (n = 65) by packing amalgam into cylindrical plastic molds and divided them into 13 equal groups of 5 discs each. The discs in each group were individually immersed in either 0%, 3.6%, 6%, or 30% (w/v) hydrogen peroxide at exposure periods of 1, 8, 48, and 168 hrs. Samples were taken for mercury ion release determination by inductively coupled plasma mass spectrometry. There were significant increases in mercury release between control and all other hydrogen peroxide concentrations at all exposure times (p < 0.05).