The association of mercury from dental amalgam with urinary selenium

>Magister Scientiae - MScBackground: Dental amalgam has been the traditional material for filling cavities in teeth. Mercury (Hg) is a component of dental amalgam, from where it is continuously released and deposited in different tissues, mostly in the brain and the kidneys. Selenium is an important essential element in the human body. Mercury exposure from dental amalgam fillings associated with reduced the levels of selenium. Aims and objectives: The aims of the current study were to investigate the leaching of mercury from dental amalgam fillings and also to investigate the relationship between the leached mercury from dental amalgam fillings and selenium concentrations in the bloodstream. The objective was to determine the mercury from dental amalgam fillings and urinary selenium levels. Methods: Samples were collected from patients attending Tygerberg Oral Health Centre, Cape Town (South Africa). 107 patients who had 1-12 dental amalgam fillings provided the samples of urine, buccal swabs and did the chewing gum test. The samples were analysed by using inductively coupled plasma-mass spectrometry. The data were analysed by IBM (p<0.05) test with an SPSS computer software package version 24. The study involved analyses of samples of urine (n=107), chewing gum and buccal swabs (n= 102). Results: The median urinary concentrations of mercury and selenium in female and male samples were 0.40 μg/L, 0.60 μg/L Hg and 26.29 μg/L, 29.32 μg/L Se respectively. While the median Hg concentrations in chewing gum test and buccal swabs samples in female and male were 2.04 mg/g, 1.89 mg/g Hg and 0.16 μg/L, 0.09 μg/L respectively. Conclusion: The excretion of urinary selenium concentration was influenced by concentration of mercury in urine and age of participants but not affected by concentrations of mercury in buccal swabs, chewing gum and gender of participants

Development of anti-bacterial, re-mineralising and selfadhesive dental composites

The project aim was characterisation of antibacterial releasing, remineralising and self-adhesive novel dental composites. Commercially available bulk filling and flowable composites were tested in order to provide benchmark properties for successful dental composite materials. 20 wt. % of light curable urethane dimethacrylate based liquid was mixed with 80 wt. % glass filler containing 10 wt. % CHX and 0 - 40 wt. % CaP. Conversion versus depth with 20 or 40 s light exposure was assessed by FTIR. Solidification depth and polymerisation shrinkage were determined using ISO 4049 and 17304 respectively. Subsequent volume expansion and biaxial flexural strength and modulus change upon water or simulated body fluid (SBF) immersion were determined over 4 and 6 weeks respectively. Precipitation of hydroxyapatite on the surfaces of light cured discs after storage in water versus SBF was assessed weekly up to 4 weeks using SEM with EDX, Raman and XRD. Mass of precipitate that could be scraped from the surfaces was determined gravimetrically after 12 weeks. CHX release into solution or associated with the hydroxyapatite layer over 12 weeks was determined using UV spectrometry. Biaxial flexural strength and modulus were determined after 1 month immersion in SBF. The shear bond strength between experimental formulations and Ivory dentine etched with phosphoric acid was assessed. Separate adhesive agent ‘iBond’ was applied to dentine and the shear strength was compared with that when experimental composite was attached directly to the dentine without iBond use. Conversion decreased linearly with both depth and CaP content. Shrinkage was ~3% for experimental materials. Early water sorption increased linearly, whilst strength and modulus decreased exponentially to final values when plotted versus square root of time. Maximum volumetric expansion increased linearly with CaP rise and balanced shrinkage at 10-20 wt. % CaP. Experimental composites initial strength and modulus decreased linearly with increasing CaP. Hydroxyapatite layer thickness / coverage from SEM images, Ca/Si ratio from EDX and normalised hydroxyapatite Raman peak intensities were all proportional to both time in SBF and CaP wt. % in the filler. Hydroxyapatite was, however, difficult to detect by XRD until 4 weeks. Early CHX release was proportional to the square root of time and to CaP level and twice as fast in water compared with SBF. After 1 week, CHX continued to be released into water. In SBF, however, any released CHX became entrapped within the precipitating hydroxyapatite layer. At 12 weeks HA entrapped CHX was proportional to the CaP filler wt. % and up to 14% of the total in the sample. CHX formed 5 to 15% of the HA layer with 10 to 40 wt. % CaP respectively. Shear bond strength has increased upon addition of CaP up to 20 wt. %. Formulations with 0 wt. % CaP and no adhesive monomer exhibited the lowest shear strength of ~ 3 MPa. Upon addition of 4Meta and still absence of CaP, the shear strength increased up to 13 MPa. Formulations with 20 wt. % CaP experienced the highest shear strength of ~ 25 MPa irrespective of the addition of adhesive monomers. The high strength, hydroxyapatite precipitation and surface antibacterial accumulation should reduce tooth restoration failure due to fracture, aid demineralised dentine repair and prevent subsurface carious disease respectively

Characterization of dentine to assess bond strength of dental composites

This study was performed to develop alternating dentine adhesion models that could help in the evaluation of a self-bonding dental composite. For this purpose dentine from human and ivory was characterized chemically and microscopically before and after acid etching using Raman and SEM. Mechanical properties of dentine were determined using 3 point bend test. Composite bonding to dentine, with and without use of acid pre-treatment and/or the adhesive, were assessed using a shear bond test. Furthermore, micro gap formation after restoration of 3 mm diameter cavities in dentine was assessed by SEM. Initial hydroxyapatite level in ivory was half that in human dentine. Surface hydroxyapatites decreased by approximately half with every 23 s of acid etch. The human dentine strength (56 MPa) was approximately double that of ivory, while the modulus was almost comparable to that of ivory. With adhesive use, average shear bond strengths were 30 and 26 MPa with and without acid etching. With no adhesive, average bond strength was 6 MPa for conventional composites. This, however, increased to 14 MPa with a commercial flowable "self-bonding" composite or upon addition of low levels of an acidic monomer to the experimental composite. The acidic monomer additionally reduced micro-gap formation with the experimental composite. Improved bonding and mechanical properties should reduce composite failures due to recurrent caries or fracture respectively

Development of dental composites with reactive fillers that promote precipitation of antibacterial-hydroxyapatite layers.

The study aim was to develop light-curable, high strength dental composites that would release calcium phosphate and chlorhexidine (CHX) but additionally promote surface hydroxyapatite/CHX co-precipitation in simulated body fluid (SBF). 80wt.% urethane dimethacrylate based liquid was mixed with glass fillers containing 10wt.% CHX and 0, 10, 20 or 40wt.% reactive mono- and tricalcium phosphate (CaP). Surface hydroxyapatite layer thickness/coverage from SEM images, Ca/Si ratio from EDX and hydroxyapatite Raman peak intensities were all proportional to both time in SBF and CaP wt.% in the filler. Hydroxyapatite was, however, difficult to detect by XRD until 4weeks. XRD peak width and SEM images suggested this was due to the very small size (~10nm) of the hydroxyapatite crystallites. Precipitate mass at 12weeks was 22wt.% of the sample CaP total mass irrespective of CaP wt.% and up to 7wt.% of the specimen. Early diffusion controlled CHX release, assessed by UV spectrometry, was proportional to CaP and twice as fast in water compared with SBF. After 1week, CHX continued to diffuse into water but in SBF, became entrapped within the precipitating hydroxyapatite layer. At 12weeks CHX formed 5 to 15% of the HA layer with 10 to 40wt.% CaP respectively. Despite linear decline of strength and modulus in 4weeks from 160 to 101MPa and 4 to 2.4GPa, respectively, upon raising CaP content, all values were still within the range expected for commercial composites. The high strength, hydroxyapatite precipitation and surface antibacterial accumulation should reduce tooth restoration failure due to fracture, aid demineralised dentine repair and prevent subsurface carious disease respectively

Demineralization-remineralization dynamics in teeth and bone

Biomineralization is a dynamic, complex, lifelong process by which living organisms control precipitations of inorganic nanocrystals within organic matrices to form unique hybrid biological tissues, for example, enamel, dentin, cementum, and bone. Understanding the process of mineral deposition is important for the development of treatments for mineralization-related diseases and also for the innovation and development of scaffolds. This review provides a thorough overview of the up-to-date information on the theories describing the possible mechanisms and the factors implicated as agonists and antagonists of mineralization. Then, the role of calcium and phosphate ions in the maintenance of teeth and bone health is described. Throughout the life, teeth and bone are at risk of demineralization, with particular emphasis on teeth, due to their anatomical arrangement and location. Teeth are exposed to food, drink, and the microbiota of the mouth; therefore, they have developed a high resistance to localized demineralization that is unmatched by bone. The mechanisms by which demineralization-remineralization process occurs in both teeth and bone and the new therapies/technologies that reverse demineralization or boost remineralization are also scrupulously discussed. Technologies discussed include composites with nano- and micron-sized inorganic minerals that can mimic mechanical properties of the tooth and bone in addition to promoting more natural repair of surrounding tissues. Turning these new technologies to products and practices would improve health care worldwide

Conversion, shrinkage, water sorption, flexural strength and modulus of re-mineralizing dental composites

Cure, volumetric changes and mechanical properties were assessed for new dental composites containing chlorhexidine (CHX) and reactive calcium phosphate-containing (CaP) to reduce recurrent caries

Polymethacrylates.Material Selection For Medical Applications:Requirements For Several Kinds of Medical Applications

This chapter reviews several cases of methacrylate-based polymers used for medical applications. The main chemicals and fillers used for elaborating biomaterials are presented, together with the main synthesis reactions. Their properties are recalled and discussed using the well-established structure-properties relationships of polymer physicochemistry. Last, the main degradation mechanisms are recalled, together with their consequences on the engineering properties of polymethacrylates, in order to predict the long-term in vivo behavior of such complex materials

Demineralization&ndash;remineralization dynamics in teeth and bone

Ensanya Ali Abou Neel,1&ndash;3 Anas Aljabo,3 Adam Strange,3 Salwa Ibrahim,3 Melanie Coathup,4 Anne M Young,3 Laurent Bozec,3 Vivek Mudera4 1Division of Biomaterials, Operative Dentistry Department, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia; 2Biomaterials Department, Faculty of Dentistry, Tanta University, Tanta, Egypt; 3Department of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, London, UK; 4UCL Institute of Orthopaedics and Musculoskeletal Sciences, Royal National Orthopaedic Hospital, Stanmore, London, UK Abstract: Biomineralization is a dynamic, complex, lifelong process by which living organisms control precipitations of inorganic nanocrystals within organic matrices to form unique hybrid biological tissues, for example, enamel, dentin, cementum, and bone. Understanding the process of mineral deposition is important for the development of treatments for mineralization-related diseases and also for the innovation and development of scaffolds. This review provides a thorough overview of the up-to-date information on the theories describing the possible mechanisms and the factors implicated as agonists and antagonists of mineralization. Then, the role of calcium and phosphate ions in the maintenance of teeth and bone health is described. Throughout the life, teeth and bone are at risk of demineralization, with particular emphasis on teeth, due to their anatomical arrangement and location. Teeth are exposed to food, drink, and the microbiota of the mouth; therefore, they have developed a high resistance to localized demineralization that is unmatched by bone. The mechanisms by which demineralization&ndash;remineralization process occurs in both teeth and bone and the new therapies/technologies that reverse demineralization or boost remineralization are also scrupulously discussed. Technologies discussed include composites with nano- and micron-sized inorganic minerals that can mimic mechanical properties of the tooth and bone in addition to promoting more natural repair of surrounding tissues. Turning these new technologies to products and practices would improve health care worldwide. Keywords: demineralization, remineralization, teeth, bone and calcium phosphate