published_or_final_version / Paediatric Dentistry / Master / Master of Dental Surgery

published_or_final_version / Paediatric Dentistry / Master / Master of Dental Surgery

Objective: To compare the adhesive strength in dentin of three universal adhesive systems in vitro by means of the shear test. Materials and methods: Seventy-five bovine teeth were selected and cut. Dentin was exposed from the buccal surface of the crowns with 220 grit sandpaper, and samples were then inserted in transparent acrylic bases (15x10mm). The samples were randomly divided in 3 groups (n=25): G1-Universal adhesive system Scotchbond™ Universal (3M ESPE-USA); G2-Universal adhesive system Peak Universal Bond (Ultradent); G3-Universal adhesive system Tetric N-Bond (Ivoclar Vivadent). The adhesive procedures were carried out according to the instructions of each manufacturer and the restorative procedures were carried out with micro-cylinders (made of Tygon type tubing 0.79x1.5mm) of the composite resin Filtek™ Z350XT-A2 (3M ESPE-USA). The samples were incubated at 37ºC (+/-5ºC) for 24 hours. Adhesive strength was evaluated in a universal test machine by means of the shear test (0.5mm/ min, 500N) and the resulting fracture type was evaluated with a Dinolite digital microscope (x200). The results were analyzed by descriptive statistics (Mean±SD), and inferential statistics by a one-way ANOVA. Results: No statistically significant differences were found between the universal adhesive systems evaluated G1 (14.91±4.76), G2 (16.90±4.11) and G3 (17.34±4.04)/(p=0.114). Conclusions: The shear test resulted in similar values of immediate adhesive strength of the three universal adhesive systems used. / Revisión por pares

A tendência atual de simplificação de sistemas adesivos transformou-os em polímeros altamente hidrofílicos e prontamente susceptíveis à permeação de água através de sua estrutura. Estudos recentes têm demonstrado que os sistemas adesivos simplificados se comportam como membranas semipermeáveis, permitindo o movimento de fluidos através da sua estrutura. Soluções a base de oxalato de potássio são efetivos agentes de redução da condutividade hidráulica dentinária. Quando são aplicados na dentina após o condicionamento ácido, podem ser utilizados em associação com os sistemas adesivos sem o comprometimento da adesão. Este trabalho objetivou avaliar os efeitos dos sistemas adesivos AdheSE, One Up Bond F e Single Bond, associados ou não a uma solução a base de oxalato de potássio, na condutividade hidráulica da dentina. Foram realizados preparos de coroas totais em terceiros molares humanos que tiveram suas raízes secionadas e a polpa coronária removida. Os segmentos coronários obtidos foram conectados ao ?Medidor de Fluxo? (Flodec?System, De marco Engineering, Switzerland). A condutividade hidráulica dos espécimes foi mensurada antes e após a aplicação dos sistemas adesivos Single Bond -3M ESPE, One UP Bond F -Tokuyama Inc, AdheSe- Ivoclar- Vivadent. Os adesivos foram aplicados seguindo as recomendações do fabricante (grupos SBF, ADF e OBF), de forma experimental (grupos ADE e OBE), e em combinação com uma solução a base de oxalato de potássio (grupos SBO, ADO e OBO). Cada espécime teve seu valor de permeabilidade original ( smear layer) e máxima (após condicionamento ácido) medidos anteriormente, os quais serviram como parâmetros para o cálculo das respectivas alterações frente aos tratamentos, expressas em porcentagem. Após a determinação da condutividade hidráulica, os preparos foram moldados para obtenção de réplicas em resina, as quais foram examinadas em MEV (JEOL 2800, Japão) para qualificar a permeação de fluido através do adesivo. A Análise de variância a 2 critérios mostrou que apesar dos procedimentos adesivos causarem uma redução significante (p< 0.05) na condutividade hidráulica da dentina condicionada, nenhum foi capaz de eliminar completamente a passagem de fluidos através do adesivo polimerizado. Para os três adesivos testados, o tratamento com o oxalato de potássio foi o tratamento mais eficaz na redução da permeabilidade dentinária e esta diferença foi estatisticamente significante quando comparada aos outros tratamentos (p<0,05). Não houve diferença entre os três sistemas adesivos estudados com relação à redução da permeabilidade dentinária (p> 0,05). A análise das réplicas em MEV mostrou que mesmo após a polimerização do adesivo, a transudação de fluidos pôde ser identificada na superfície de todas réplicas examinadas. Nenhum dos sistemas adesivos testados foi capaz de eliminar a permeação de fluidos através da dentina, contudo a associação destes adesivos com uma solução a base de oxalato de potássio reduziu de forma significante a permeabilidade dentinária. / There is an ongoing trend to move away from classical multi-component bonding systems toward simplified adhesives. An immediate consequence of adhesive simplification is the intrinsic permeability to water that result from their increase in hydrophilicity. Current studies have demonstrated that single-step adhesives may act as semi-permeable membranes that allow water diffusion through its structure. Oxalate desensitizers are effective in reducing the hydraulic conductance of dentin. When oxalates are used after acid- etching they do not interfere with subsequent resin bonding. The objective of this study was to test the effects of adhesives systems with or without the application of an oxalate desensitizer on dentin permeability. Crown preparations were made from human extracted teeth. After the roots were sectioned and the coronal pulp removed, the crown segments were connected to an automatic flow-recording device (Flodec-System, De Marco Engineering, Switzerland). Fluid conductance was measured before and after the bonding procedures with the adhesives Single Bond -3M ESPE, One UP Bond F -Tokuyama Inc and AdheSe- Ivoclar Vivadent. Specimens were prepared and tested after the surface had been bonded according to manufacturer?s instructions (SBF,ADF and OBF groups) , in a experimental way (ADE and OBE groups) or integrating with a oxalate desensitizer gel (SBO, ADO and OBO groups). For each specimen, fluid flow across the smear-layer and bonded dentin was expressed as a percentage of acidetched dentin, which was assigned a value of 100% flow rate. After the hydraulic conductance measures, impressions were taken from the crown segments and epoxy resin replicas were produced for SEM examination. Two-Way ANOVA reveled that the adhesive systems reduced dentin permeability significantly (p< 0.05) compared to acid etched dentin, but no bonding system was able to eliminate the fluid flow though dentin. For the three bonding systems tested, treating the acid-etched dentin with potassium oxalate prior to the application of the adhesive was the most effective in reducing the hydraulic conductance of the specimens, and this difference was significant (p< 0.05) when comparing to the other treatments. There were no significant differences among the adhesives in their ability to reduce dentin permeability (p> 0.05). SEM micrographs of resin replicas showed that transudation of dentinal fluid droplets could be identified on the surfaces of all replicas examined.

There have been some reported negative effects on dental hard tissues associated with tooth bleaching. This in situ study evaluated the effect of 10% carbamide peroxide dental bleach on the dentin fracture toughness and microhardness. Compact tension fracture toughness dentin specimens, were prepared from extracted molars, irradiated and fitted into custom-made bleaching trays. The bleaching trays were loaded with either bleach (10% Carbamide Peroxide gel, Opalescence, Ultradent, n=34) or placebo gel (control group, n=31) and worn overnight for approximately 14 nights. Dentin specimens were tested 24-48 hrs after the end of treatment. The mean values for dentin fracture toughness were: 2.22 ± 0.71 & 2.26 ± 0.86 (MPa m ½) and for microhardness were: 66.80 ± 40.14 & 53.35± 42.52 (KHN) for bleaching and control respectively. Independent t-test showed no significant difference in dentin fracture toughness and microhardness after 14 days of in situ bleaching using 10% carbamide peroxide.

There have been some reported negative effects on dental hard tissues associated with tooth bleaching. This in situ study evaluated the effect of 10% carbamide peroxide dental bleach on the dentin fracture toughness and microhardness. Compact tension fracture toughness dentin specimens, were prepared from extracted molars, irradiated and fitted into custom-made bleaching trays. The bleaching trays were loaded with either bleach (10% Carbamide Peroxide gel, Opalescence, Ultradent, n=34) or placebo gel (control group, n=31) and worn overnight for approximately 14 nights. Dentin specimens were tested 24-48 hrs after the end of treatment. The mean values for dentin fracture toughness were: 2.22 ± 0.71 & 2.26 ± 0.86 (MPa m ½) and for microhardness were: 66.80 ± 40.14 & 53.35± 42.52 (KHN) for bleaching and control respectively. Independent t-test showed no significant difference in dentin fracture toughness and microhardness after 14 days of in situ bleaching using 10% carbamide peroxide.

published_or_final_version / Paediatric Dentistry / Master / Master of Dental Surgery

published_or_final_version / Dental Materials Science / Master / Master of Science in Dental Materials Science

Silver compounds have become popular for the treatment of arresting dental caries and dentine hypersensitivity. This study investigated the interaction of silver compounds in demineralised dentine under different conditions. Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), ion chromatography (IC) and inductively coupled plasma-mass spectroscopy (ICP-MS) were used to analyse these interactions. A systematically-approached literature review was conducted on silver compounds in dentistry. They have been demonstrated to be effective for preventing and arresting caries, as well dentine desensitivity. The mode of action of silver compounds on carious teeth includes inhibition of demineralisation process and anti-bacterial effect. Reaction products of Silver Diammine Fluoride (SDF) on dentine in different saliva substitutes were determined. Dentine samples were stored in deionised water (DIW), non-protein artificial saliva (NPAS), basal medium mucin (BMM), and un-stimulated whole saliva (UWS). These samples were chemically demineralised. Afterwards 38 wt-% SDF was applied. Dentine surfaces were analysed by SEM and showed different surface deposits and coatings. EDX, XPS and XRD detected metallic silver and silver compounds (predominantly AgCl) were formed and the amount was highest in NPAS group. BMM and UWS groups showed similar reactions. Sulphur was detected only in BMM and UWS groups. Chemical composition of BMM and UWS were determined by IC. Dentine samples were pre-saturated with BMM, UWS and DIW and then chemically demineralised. Either of 42 wt-% AgNO3, 22 wt-% AgF and 38 wt-% SDF was applied. Treated samples were replaced in their respective “saliva”. The exposed surface and a cross-section of dentine was analysed by quantitative EDX. A precise linear relation of the silver standard wires (wt-%) according to EDX counts was obtained (R2 > 0.99). The amount of silver was concentrated between 0 to 60 μm in depth. BMM groups yielded the highest amount of silver for AgF and AgNO3 compounds (p < 0.06), which may be related to the greater concentration of salivary protein and chloride in BMM solution. ICP-MS was used to quantitatively determine silver present on SDF-treated dentine. Dentine samples were pre-saturated with BMM or UWS and chemically demineralised. Afterwards 10 wt-%, 24 wt-% or 38 wt-% of SDF was applied and the treated samples were re-placed with respective “saliva” daily for 5 days. Dentine samples were then digested in 70% HNO3 and silver concentration was determined by ICP. For UWS, silver was in proportion to the application of various concentrations of SDF. However, for BMM, the higher amount of silver at 10 wt-% and 38 wt-% SDF suggests an interaction effect with excessive salivary protein and chloride. Reaction products of silver compounds on dentine can be determined by the combined SEM-EDX, XPS and XRD techniques. Both modified SEM-EDX and ICP techniques are qualified for quantitative comparison of silver concentration between treatment groups. The interaction effects of silver with different in vitro salivary components should be considered in future investigations as this may affect the chemical reaction outcomes. / published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

Chemomechanical caries excavation is an excellent example of conservative caries removal methods due to its ability to reliably preserve a greater thickness of caries-affected dentine (CAD). Chemomechanical caries removal (CMCR) agents dissolve the denatured collagen fibrils leaving the sound and partially degraded fibrils intact. Also, one of the main advantages of the CMCR method is its characteristic visual excavation end point sign, after this point, the solution fails to become turbid. Chemomechanical caries removal agents are classified based on their chemistry into sodium hypochlorite (NaOCl)- or enzyme-based CMCR agents. The aim of this project was to evaluate the efficacy of currently available chemomechanical caries removal methods and their effects on tooth substrate, residual bacteria, and bonding to dentine with either resin- or resin-modified glass ionomer (RM-GIC)-based adhesives. The current project was designed to answer five research questions. The first research question aimed to compare the caries excavation time between CMCR and rotary caries removal methods. According to the outcome of this study, the NaOCl-based CMCR method is more time consuming compared with the enzyme-based CMCR method. Furthermore, no significant difference in caries excavation time was found between the enzymebased CMCR and the caries-detector guided rotary caries excavation method. The second research question investigated the effects of CMCR methods on surface topography, hardness and chemical structure of dentine. The morphological analysis showed that there was no smear layer formed following enzyme-based CMCR; while it was partially absent after the NaOCl-based CMCR method. Also, the Vickers hardness of residual dentine following both CMCR methods was lower than the hardness of dentine following the rotary caries removal method. Moreover, the outcome of this study also revealed that the CMCR methods investigated had no adverse effect on the chemical structure of dentine. The third research question was regarding the evaluation of the antibacterial effects of CMCR agents. Accordingly, a study was conducted on coronal cariesfree dentine discs using a modified non-invasive protocol. This confocal laser scanning microscopy study reported that the enzyme-based CMCR agent (Papacarie) showed an antimicrobial effect similar to 2% chlorhexidine gluconate solution (gold standard antibacterial solution). The NaOCl-based CMCR agent (Carisolv) showed a weak antibacterial activity, which could be improved by subsequent application of a silver diamine fluoride and potassium iodide agent. The ‘adhesion studies section’ of this project consists of three studies and was conducted to answer the fourth and fifth research questions of this project. The outcomes of the first and second studies showed that surface treatment of dentine with 37% phosphoric acid for 5 seconds had no adverse effect on bonding of RMGIC adhesives to both sound and caries-affected dentine, which addressed the fourth research question. The purpose of the last research question was to evaluate the effect of CMCR method on bonding of MDP-containing self-etch and RM-GIC adhesives to residual caries-affected dentine. It was concluded that CMCR methods had no adverse effects on bonding to dentine and both adhesive systems showed good bond strengths to caries-affected dentine. / published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy