Effect of potassium oxalate based dessensitizing agents on human dentin permeability. In vitro study.

Author(s)

Angela Destefani Segala

• Document type: Doctoral Thesis
• Press: Bauru.
• Institution: Universidade de São Paulo (USP). Faculdade de Odontologia de Bauru (FOB/SDB)
• Defense date: 2000-03-17

Examining board members

Jose Carlos Pereira; Jose Humberto Damante; Carlos Eduardo Francischone; Wilson Garone Filho; Narciso Garone Netto

• Advisor: Jose Carlos Pereira

Abstract

Potassium oxalate has been used to reduce dentin hypersensitivity. Studies have shown that the reaction of this salt with dentin substrate may result in calcium oxalate crystals deposits over and inside dentin tubules, reducing fluid filtration and dentin hypersensitivity. The aim of this study was to evaluate the variation of fluid filtration of dentin treated with different formulations of potassium oxalate gels, under five different pre-conditioned dentin surfaces It was used the method suggested by Pashley, Steward e Galloway (1984) for the measurement of hydraulic conductance of dentin. The dentin reaction with the gels were also evaluated by means of Scanning Electron Microscopy, X-Ray Microanalysis (EDS) and X-Ray Diffraction (XRD). Two hundred dentin discs 1 mm in thickness, obtained from human extracted third molars, were divided into 20 groups of ten specimens each. The groups corresponded to the following experimental materials: 3 % potassium oxalate gel - pH 4; 6 % potassium oxalate gel - pH 4; 3 % potassium oxalate gel - pH 2,5 and 1,23 % fluoride gel - pH 3,6-3,9, applied to dentin under the following surface conditions: air-dried, blot dried, wet, acidic air-dried and acidic blot-dried. Other 40 dentin discs were prepared for SEM analysis using the same experimental materials under one of the surface treatments studied in the hydraulic conductance. Dry dentin discs were then chosen for SEM and X-Ray studies. The specimens were divided in five groups of ten corresponding to the five materials used. The pattern of crystals deposition on the dentin surface and inside the tubules were assessed by SEM images and analyzed thought a digital analysis software. At the same time eight new dentin discs reproducing the same conditions as for SEM were prepared for EDS (Electron Dispersive Spectroscopy) in order to asses the elemental analysis of the crystals. Eighteen complementary discs were prepared for X Ray Diffraction Analysis for the study of the molecular composition of the crystals produced by the different experimental materials. This analysis was complemented with nine pellets of powdered dentin to compare the reactivity and the basic composition of dentin substrate. General MANOVA and post-hoc Duncan tests were performed on the dada of hydraulic conductance. Regardless of surface pre-treatment the 3 % potassium oxalate gel - pH 2,5 showed the lowest dentin filtration (p<0,05) even after citric acid challenge. In general, air-drying the dentin was the best surface pre-treatment (p<0,05). The interaction between the material and surface pretreatment showed values of hydraulic conductance similar for most of combinations, but the 3 % potassium oxalate gel - pH 2,5 under wet condition assumed the best tendency for filtration decreasing. The Fluoride Gel showed the weakest performance when compared with the other materials, regardless surface pre-treatment. The potassium oxalate gels used in this investigations significantly reduced dentin filtration. MANOVA and Duncan tests were also performed to the SEM results and showed that the potassium oxalate gels precipitated crystals deposits over the dentin surface and inside the dentin tubules as well in statistically similar patterns. No crystals were seen on dentin surface in the specimens treated with Fluoride Gel, but only a few crystals inside the tubules. The range of crystal average penetration into the tubules was 7,52 to 9,41 µm. The X-Ray Microanalysis of crystals evidenced the presence of calcium, phosphorus and oxygen equally for the four materials used. The X-Ray Diffraction of the dentin discs evidenced the presence of calcium oxalate and calcium potassium phosphate. Calcium fluoride was observed in the specimens treated with Fluoride Gel. The dentin discs were more reactive with the materials studied then the dentin powdered specimens. One may conclude that the potassium oxalate gels studied in this investigation applied on dry dentin have a great potential for tubule occlusion and consequently a clinical applicability on dentin hypersensitivity. (AU)