Marginal and internal fit of zirconia copings obtained using different digital scanning methods

Abstract The objective of this study was to evaluate the marginal and internal fit of zirconia copings obtained with different digital scanning methods. A human mandibular first molar was set in a typodont with its adjacent and antagonist teeth and prepared for an all-ceramic crown. Digital impressions were made using an intraoral scanner (3Shape). Polyvinyl siloxane impressions and Type IV gypsum models were also obtained and scanned with a benchtop laboratory scanner (3Shape D700). Ten zirconia copings were fabricated for each group using CAD-CAM technology. The marginal and internal fit of the zirconia copings was assessed by the silicone replica technique. Four sections of each replica were obtained, and each section was evaluated at four points: marginal gap (MG), axial wall (AW), axio-occlusal edge (AO) and centro-occlusal wall (CO), using an image analyzing software. The data were submitted to one-way ANOVA and Tukey's test (α = 0.05). They showed statistically significant differences for MG, AO and CO. Regarding MG, intraoral scanning showed lower gap values, whereas gypsum model scanning showed higher gap values. Regarding AO and CO, intraoral digital scanning showed lower gap values. Polyvinyl siloxane impression scanning and gypsum model scanning showed higher gap values and were statistically similar. It can be concluded that intraoral digital scanning provided a lower mean gap value, in comparison with conventional impressions and gypsum casts scanned with a standard benchtop laboratory scanner.

Reparación ósea utilizando sulfato de calcio en defectos óseos de tibia de conejos / Bone repair using calcium sulfate in bone defects of rabbit tibiae

La regeneración ósea en reconstrucción del proceso alveolar junto al uso de implantes oseointegrables son ampliamente utilizados, existiendo una amplia variabilidad de productos. El objetivo de esta investigación es estudiar la reparación ósea asociada a un sustituto óseo a base de sulfato de calcio cubierto con membrana biológica en defectos creados en tibia de conejos. Se seleccionaron 12 conejos de entre 3 y 6 meses para ser intervenidos; de acuerdo a protocolos de anestesia ya conocidos se realizó la técnica con acceso a ambas tibias donde se realizaron 2 defectos de 2,6 mm de diámetro; se formaron cuatro grupos siendo el grupo I de relleno con coágulo sanguíneo, grupo II relleno con coagulo cubierto con membrana de colágeno, grupo III relleno con sulfato de calcio y grupo IV relleno con sulfato de calcio cubierto con membrana biológica. Se realizó la eutanasia a los 21 y 42 días y posteriormente se procedió a procesar y analizar láminas histológicas con tinción de hematoxilina y eosina. Se realizó la histomorfometría comparativa analizando los datos con prueba ANOVA y prueba de Turkey considerando un valor de p<0,05 para significancia estadística. Los resultados demostraron que todos los defectos mostraron patrones regulares de reparación ósea; los grupos rellenados con coágulo mostraron formación ósea estadísticamente menor que el presentado por los defectos rellenos con el sulfato de calcio, aunque estos últimos presentaron mayores indicadores de presencia de proceso inflamatorio; el grupo IV fue el que presentó los mejores niveles de reparación ósea a los 21 y 42 días. Se concluye que la reparación ósea en defectos menores es viable de ser realizada con este biomaterial y que la cobertura con membrana de colágeno puede ser útil en la regeneración ósea guiada.

Bone regeneration in the alveolar process and dental implant are widely used and there are a lot of different products. The aim of this research was to know the bone reparation associated to bone substitute with calcium sulfate and a biological membrane in created defects in rabbit tibiae. Were selected 12 rabbit between 3 and 6 month to be operated; using previous anesthesia protocols was do it a surgical defect in the right and left tibiae with 2.6 mm diameter; four groups were created: group I with blood clot fill, group II with blood clot fill plus biological membrane, group III with calcium sulfate and group IV with calcium sulfate plus biological membrane. The euthanasia was made in 21 and 42 days before surgery and was obtained histological plate using hematoxillin and eosin. The histomorphometry was made and statistical analysis using ANOVA and Turkey test with p<0.05 to obtain statistical differences. Were observed in the all created defects a regular bone reparation; the group I and II, with blood clot, showed a minor bone reparation than group III and IV with calcium sulfate, but these last one show an important inflammatory process; the group IV presented the better results at 21 and 42 euthanasia days in term of bone formation. It´s conclude that calcium sulfate can be used in bone reparation of minor defects and the biological membrane can be used in guide bone regeneration with success.

Biocompatibility and setting time of CPM-MTA and white Portland cement clinker with or without calcium sulfate

Objective: To evaluate the biocompatibility and the setting time of Portland cement clinker with or without 2% or 5% calcium sulfate and MTA-CPM. Material and Methods: Twenty-four mice (Rattus norvegicus) received subcutaneously polyethylene tubes filled with Portland cement clinker with or without 2% or 5% calcium sulfate and MTA. After 15, 30 and 60 days of implantation, the animals were killed and specimens were prepared for microscopic analysis. For evaluation of the setting time, each material was analyzed using Gilmore needles weighing 113.5 g and 456.5 g, according to the ASTM specification Number C266-08 guideline. Data were analyzed by ANOVA and Tukey's test for setting time and Kruskal-Wallis and Dunn test for biocompatibility at 5% significance level. Results: Histologic observation showed no statistically significant difference of biocompatibility (p>0.05) among the materials in the subcutaneous tissues. For the setting time, clinker without calcium sulfate showed the shortest initial and final setting times (6.18 s/21.48 s), followed by clinker with 2% calcium sulfate (9.22 s/25.33 s), clinker with 5% calcium sulfate (10.06 s/42.46 s) and MTA (15.01 s/42.46 s). Conclusions: All the tested materials showed biocompatibility and the calcium sulfate absence shortened the initial and final setting times of the white Portland cement clinker.

Portland cement with additives in the repair of furcation perforations in dogs / Cimento Portland com aditivos na reparação de perfurações radiculares em cães

PURPOSE: To evaluate the use of Portland cements with additives as furcation perforation repair materials and assess their biocompatibility. METHODS: The four maxillary and mandibular premolars of ten male mongrel dogs (1-1.5 years old, weighing 10-15 kg) received endodontic treatment (n=80 teeth). The furcations were perforated with a round diamond bur (1016 HL). The perforations involved the dentin, cementum, periodontal ligament, and alveolar bone. A calcium sulfate barrier was placed into the perforated bone to prevent extrusion of obturation material into the periradicular space. The obturation materials MTA (control), white, Type II, and Type V Portland cements were randomly allocated to the teeth. Treated teeth were restored with composite resin. After 120 days, the animals were sacrificed and samples containing the teeth were collected and prepared for histological analysis. RESULTS: There were no significant differences in the amount of newly formed bone between teeth treated with the different obturation materials (p=0.879). CONCLUSION: Biomineralization occurred for all obturation materials tested, suggesting that these materials have similar biocompatibility.

OBJETIVO: Avaliar o uso de cimentos Portland aditivados na reparação de perfurações radiculares e a biocompatibilidade destes materiais. MÉTODOS: Oitenta pré-molares, quatro da arcada dentária superior e quatro da arcada inferior de 10 cães machos, sem raça definida, com idade em torno de um a um ano e meio, pesando entre 10 e 15 kg foram submetidos a tratamento endodôntico, sendo realizadas perfurações nas furcas com broca de diamante 1016 HL. A cavidade envolveu dentina e cemento, como também periodonto e o osso alveolar. Na porção óssea da obturação, barreira de sulfato de cálcio foi utilizada evitando extravasamento do cimento para o espaço periodontal. Foi realizada a distribuição randomizada dos cimentos MTA (controle), Portland tipo II, Portland tipo V e Portland branco estrutural nas obturações. Os dentes foram restaurados com resina composta. Após 120 dias realizou-se eutanásia, retirada dos dentes, preparação e análise histológica. RESULTADOS: Entre os cimentos não houve diferença estatística significante quanto à neoformação óssea (p=0,879). CONCLUSÃO: Ocorreu biomineralização com os diferentes cimentos usados no estudo, sugerindo que estes são similares em termos de biocompatibilidade.

Influence of delayed pouring on irreversible hydrocolloid properties

The aim of this study was to evaluate the physical properties of irreversible hydrocolloid materials poured immediately and after different storage periods. Four alginates were tested: Color Change (Cavex); Hydrogum (Zhermack); Hydrogum 5 (Zhermack); and Hydro Print Premium (Coltene). Their physical properties, including the recovery from deformation (n = 3), compressive strength (n = 3), and detail reproduction and gypsum compatibility (n = 3), were analyzed according to ANSI/ADA specification no. 18. Specimens were stored at 23ºC and humidity and were then poured with gypsum immediately and after 1, 2, 3, 4, and 5 days. The data were analyzed by two-way analysis of variance (ANOVA) and Tukey's test at p < 0.05. All of the alginate impression materials tested exhibited detail reproduction and gypsum compatibility at all times. Hydro Print Premium and Hydrogum 5 showed recovery from deformation, as established by ANSI/ADA specification no. 18, after 5 days of storage. As the storage time increased, the compressive strength values also increased. Considering the properties of compounds' recovery from deformation, compressive strength, and detail reproduction and gypsum compatibility, irreversible hydrocolloids should be poured immediately.

Does the contact time of alginate with plaster cast influence its properties?

The aim of this study was to verify the influence of the time of contact between alginate and gypsum after the modeling procedure on the properties of the plaster cast, such as surface detail, dimensional stability and microhardness. Thirty cylindrical specimens of orthodontic gypsum Type III were made by means of impressions of a stainless steel master model which had five reference lines in the upper surface. The samples were divided into two groups: Group 1 (G1) - with time of contact of 1 hour; and Group 2 (G2) - 12 hours of contact. All the specimens were stored up to 48 hours until they underwent laboratory testing. Surface detail and dimensional stability were tested by one calibrated examiner using a visual analysis and a profilometer (Profile Projector Nikon model 6C, Nikon Corporation, Tokyo, Japan), respectively, to evaluate the quality of reproduction of the lines and the distances between them. The microhardness was determined for each sample by making six indentations with a Vickers diamond pyramid indenter (Buehler, Lake Bluff, USA) under a load of 100 gF for 15 s. The results showed significant difference (P £ 0.05) between groups in two of the three properties examined: surface detail and microhardness, which decreased as the time of contact rose. The 12-hour time of contact between alginate and the plaster cast is not recommended because it influences the quality of the plaster cast.

Single step approach to make diagnostic impressions of both the arches and face bow transfer: A novel technique.

Context: Mounting the maxillary and mandibular dentulous casts for Diagnostic purpose requires many steps (including making maxillary and mandibular impressions, face-bow transfer, and bite registration) or many appointments. A simple new technique of doing all of this together without compromising on the accuracy can save time over the conventional mounting procedure. Aim: To compare the accuracy of a new technique of a single-step diagnostic mounting procedure with that of the conventional diagnostic mounting procedure. Materials and Methods: Ten dentulous patients with the full complement of teeth and without any history of temporomandibular disorder and orthodontic treatment were selected for this study. A detachable metal triple tray to replace the fork part of the face bow fork that further could be attached to face bow was fabricated. Dual-arch impressions and face-bow transfer were made in these subjects using this modified triple tray. These mountings were compared with the ones done with the conventional mounting procedure. Five linear measurements (using stable reference points on the articulator and the cast) were made and the values obtained by both the methods were compared. Statistical Analysis: The Student's 't' test for statistical analysis was used in this study. Results: The measurement values obtained by the single-step method were almost similar to the ones obtained by the conventional method. The various mean measurements for the single step and conventional methods were 37.7 ± 6.8 and 38.5 ± 6.5 mm; 70.0 ± 4.4 and 70.1 ± 4.2 mm; 57.0 ± 4.9 and 57.3 ± 4.2 mm; 71.3 ± 4.5 and 71.0 ± 4.6 mm; and 58.7 ± 2.5 and 58.3 ± 2.3 mm; respectively. The differences between the values obtained by the conventional and single-step methods were not statistically significant. Conclusion: The single-step procedure of diagnostic mounting can be used as an alternative to the conventional method, without compromising the quality of mounting.

Surface detail reproduction and dimensional accuracy of stone models: influence of disinfectant solutions and alginate impression materials

This study compared the surface detail reproduction and dimensional accuracy of stone models obtained from molds disinfected with 2% sodium hypochlorite, 2% chlorhexidine digluconate or 0.2% peracetic acid to models produced using molds which were not disinfected, with 3 alginate materials (Cavex ColorChange, Hydrogum 5 and Jeltrate Plus). The molds were prepared over matrix containing 20-, 50-, and 75-µm lines, performed under pressure with perforated metal tray. The molds were removed following gelation and either disinfected (using one of the solutions by spraying followed by storage in closed jars for 15 min) or not disinfected. The samples were divided into 12 groups (n=5). Molds were filled with dental gypsum Durone IV and 1 h after the start of the stone mixing the models were separated from the tray. Surface detail reproduction and dimensional accuracy were evaluated using optical microscopy on the 50-µm line with 25 mm in length, in accordance with the ISO 1563 standard. The dimensional accuracy results (%) were subjected to ANOVA. The 50 µm-line was completely reproduced by all alginate impression materials regardless of the disinfection procedure. There was no statistically significant difference in the mean values of dimensional accuracy in combinations between disinfectant procedure and alginate impression material (p=0.2130) or for independent factors. The disinfectant solutions and alginate materials used in this study are no factors of choice regarding the surface detail reproduction and dimensional accuracy of stone models.

Este estudo comparou a reprodução de detalhes da superfície e alteração dimensional de modelos de gesso obtidos a partir de moldes desinfetados com hipoclorito de sódio 2%, digluconato de clorexidina 2%, ou ácido peracético 0,2% a modelos confeccionados utilizando moldes que não foram desinfetados com três alginatos (Cavex ColorChange, Hydrogum 5, Jeltrate Plus). Os moldes foram preparados sobre matriz contendo linhas de 20, 50 e 75 µm realizado sob pressão com moldeira de metal perfurada. Os moldes foram removidos após a geleificação e desinfetados (utilizando uma das soluções por pulverização, armazenados em frascos fechados durante 15 min) ou não desinfetados. Assim, as amostras foram divididas em 12 grupos (n=5). Os moldes foram preenchidos com gesso dental Durone IV e uma hora após a manipulação do gesso os modelos foram separados da moldeira. A reprodução de detalhes da superfície e a precisão dimensional foram avaliadas usando microscopia óptica na linha 50 µm com 25 mm de comprimento, de acordo com a norma ISO 1563. Os resultados de precisão dimensional (%) foram submetidos à ANOVA. A linha de 50 µm foi completamente reproduzida por todos os alginatos, independentemente do processo de desinfecção. Não houve diferença estatisticamente significativa nos valores médios de precisão dimensional nas combinações entre procedimento de desinfecção e alginato (p=0,2130), ou para fatores independentes. Soluções desinfetantes e alginatos utilizados neste estudo não são fatores de escolha em relação à reprodução de detalhes da superfície e alteração dimensional de modelos de gesso.

Sulfato de calcio: propiedades y aplicaciones clínicas / Calcium sulfate: properties and clinical applications

Durante más de cien años el sulfato de calcio se ha distinguido de otros biomateriales, por ser uno de los materiales aloplásticos más simples y que presenta la más larga historia clínica como material sintético. Entre sus principales propiedades destacan que es de fácil obtención, capacidad de osteoconducción, es totalmente absorbible, no provoca reacciones de inflamación o antigénicas, fácil modelado y fuerza de compresión semejante al tejido óseo. Todas éstas características son necesarias para ser usado como sustituto óseo. Sin embargo, diferencias en la morfología y estructura de sus cristales, la porosidad, propiedades mecánicas y en la constitución química del sulfato de calcio puede alterar significativamente sus propiedades biológicas. El objetivo de la presente revisión es conocer las propiedades del sulfato de calcio y sus diferentes aplicaciones clínicas como sustituto óseo en procedimientos regenerativos.

For over 100 years, the calcium sulfate has stood out from other biomaterials, for being one of the simplest alloplastic materials and having the longest history as synthetic material. It is readily available, has osteoconductive properties, is completely absorbed, does not cause inflammation or antigenic reactions, can be modeled to defect, has compressive strength similar to bone tissue and can be used as a vehicle for in situ release of chemotherapeutic agents. All these features are required to be used as a bone substitute. However, differences in morphology, crystal structure, porosity, mechanical properties and chemical constitution of calcium sulfate can significantly alter its biological properties. The aim of this study was to determine through a review of the literature, the properties of calcium sulfate and its various clinical applications as bone substitute in regenerative procedures.

Efficacy of five rotary systems versus manual instrumentation during endodontic retreatment

The purpose of this study was to evaluate the efficiency of ProFile, GT, ProTaper, Race and K3 rotary instruments compared with hand K-files for removal of gutta-percha during retreatment. Sixty mandibular premolars were instrumented with GT rotary files and filled by thermomechanical compaction of gutta-percha and AH Plus sealer. The teeth are randomly divided into 6 groups of 10 specimens each. The roots were split longitudinally, digital images were created using a flatbed scanner, and the areas with remaining filling material were demarcated using Image Tool 1.21 software. The results indicate that GT left significantly less (p<0.05) remaining filling material (1.18 ± 1.47) than hand (3.70 ± 3.16) and Hero instruments (2.99 ± 2.58). There was no statistically significant difference (p<0.05) among the others techniques: ProFile (1.99 ± 2.66), ProTaper (2.00 ± 1.99) and K3 (2.71 ± 2.87) when compared with GT. In conclusion, GT, ProFile, ProTaper and K3 were more effective in removing gutta-percha than manual and Hero instruments.

O propósito deste estudo foi avaliar a eficiência dos instrumentos rotatórios ProFile, GT, ProTaper, Race e K3 comparados com limas K para a remoção do material obturador durante o retratamento. Sessenta pré-molares inferiores foram instrumentados com o sistema rotatório GT e obturados usando a técnica de compactação termomecânica de guta-percha com cimento AH Plus. Os dentes foram divididos aleatoriamente em seis grupos de dez espécimes cada. As raízes foram seccionadas longitudinalmente, imagens digitais foram criadas através de um scanner, e as áreas de remanescentes de material foram medidas usando o programa Image Tool 1.21. Os resultados indicaram que o GT deixou significantemente menos material remanescente (1,18 ± 1,47) do que os instrumentos manuais (3,70 ± 3,16) e os instrumentos Hero (2,99 ± 2,58) (p<0,05). Não houve diferença estatisticamente significante entre as outras técnicas ProFile (1,99 ± 2,66), ProTaper (2,00 ± 1,99) e K3 (2,71 ± 2,87) quando comparadas com o GT. Como conclusão, GT, ProFile, ProTaper e K3 foram revelados como mais efetivos em remover a guta-percha do que os instrumentos manuais e os instrumentos Hero.

Comparative study of physico-chemical properties of MTA-based and portland cements

The purpose of this investigation was to evaluate the physicochemical properties of gray and white structural and nonstructural Portland cement, gray and white ProRoot MTA and MTA BIO. The water/powder ratio, setting time, solubility and pH (hydrogen-ion potential) changes of the materials were evaluated. Tests followed specification #57 from the American National Standard Institute/ American Dental Association (2000) for endodontic sealing materials and pH was determined by a digital pHmeter. The test results were statistically analyzed by variance analyses for global comparison and by the complementary Tukey's test for pairwise comparisons (5%). Considering the water/powder ratio, no significant difference (p>0.05) was observed among the cements. MTA BIO (33.10±2.30) had the lowest setting time (p<0.05), gray Pro- Root MTA (10.10±2.70) had the highest (p<0.05). White nonstructural Portland cement (2.55±0.08) had the highest solubility (p<0.05), while gray ProRoot MTA (1.03±0.12) had the lowest (p<0.05), although all materials showed solubility values in compliance to ANSI/ADA. No difference (p>0.05) was observed among materials when considering pH evaluation. The pH levels were highly alkaline immediately after immersion in solution, remaining stable throughout the test period. The authors conclude that the cements had similar water/powder proportions. MTA BIO had the shortest setting time and gray ProRoot MTA had the lowest solubility. All cements had similar behavior in the pH analysis.

A proposta desse trabalho foi de avaliar as propriedades fisicoquimicas dos cimentos Portland cinza e branco estrutural e nao estrutural, do ProRoot MTA cinza e branco e do MTA BIO. Foram avaliadas a proporcao po-liquido, tempo de endurecimento, solubilidade e variacao do pH dos cimentos. Os testes seguiram as normas que determinam a especificacao numero 57 da ANSI/ ADA para cimentos obturadores e a variacao de pH foi analisada por meio de pHmetro digital. Os resultados dos testes foram analisados estatisticamente por meio de teste de analise de variancia e pelo teste de Tukey para comparacao entre pares, com nivel de significancia de 5%. Nao foram evidenciaram diferencas estatisticamente significantes (p>0,05) entre os cimentos no que se refere a proporcao po-liquido. O MTA BIO (33,10±2,30) mostrou os menores valores de tempo de endurecimento (p<0,05), enquanto o ProRoot MTA cinza (102,10±2,70) mostrou os maiores resultados (p<0,05). Todos os materiais mostraram valores de solubilidade dentro dos padroes da ANSI/ADA, sendo que o cimento ProRoot MTA cinza (1,03±0,12) apresentou a menor solubilidade (p<0,05) e o Portland branco nao estrutural (2,55±0,08), a maior (p<0,05). No que se refere a variacao do pH, nao foram determinadas diferencas significantes entre os materiais (p>0,05). Os niveis de pH mostraram-se altamente alcalinos, imediatamente apos a imersao em agua, mantendo-se estavel ao longo do periodo de teste. Concluiu-se, que os cimentos estudados tiveram proporcoes po-liquido similares. O MTA BIO apresentou tempo de endurecimento mais curto e a menor solubilidade foi apresentada pelo ProRoot MTA cinza. Todos os cimentos tiveram comportamento semelhante na analise do pH.

Linear dimensional changes in plaster die models using different elastomeric materials

Dental impression is an important step in the preparation of prostheses since it provides the reproduction of anatomic and surface details of teeth and adjacent structures. The objective of this study was to evaluate the linear dimensional alterations in gypsum dies obtained with different elastomeric materials, using a resin coping impression technique with individual shells. A master cast made of stainless steel with fixed prosthesis characteristics with two prepared abutment teeth was used to obtain the impressions. References points (A, B, C, D, E and F) were recorded on the occlusal and buccal surfaces of abutments to register the distances. The impressions were obtained using the following materials: polyether, mercaptan-polysulfide, addition silicone, and condensation silicone. The transfer impressions were made with custom trays and an irreversible hydrocolloid material and were poured with type IV gypsum. The distances between identified points in gypsum dies were measured using an optical microscope and the results were statistically analyzed by ANOVA (p < 0.05) and Tukey's test. The mean of the distances were registered as follows: addition silicone (AB = 13.6 µm, CD=15.0 µm, EF = 14.6 µm, GH=15.2 µm), mercaptan-polysulfide (AB = 36.0 µm, CD = 36.0 µm, EF = 39.6 µm, GH = 40.6 µm), polyether (AB = 35.2 µm, CD = 35.6 µm, EF = 39.4 µm, GH = 41.4 µm) and condensation silicone (AB = 69.2 µm, CD = 71.0 µm, EF = 80.6 µm, GH = 81.2 µm). All of the measurements found in gypsum dies were compared to those of a master cast. The results demonstrated that the addition silicone provides the best stability of the compounds tested, followed by polyether, polysulfide and condensation silicone. No statistical differences were obtained between polyether and mercaptan-polysulfide materials.

An evaluation of the mechanical properties of Type III and Type IV gypsum mixed with two disinfectant solutions.

Background and Objectives: This in-vitro study was conducted to evaluate the strength and properties of Type III and Type IV gypsum mixed with disinfectant solutions. Materials and Methods: Type III and Type IV gypsum were used for the study. Three different mixing solutions namely waterqueous solutions of 0.525% sodium hypochlorite and 2% glutaraldehyde were used. Gypsum materials were subjected to further modification by adding a mixture of 1.0% gum arabic and 0.132% calcium hydroxide before mixing with the disinfectant solutions, at two different liquid/powder (L/P) ratios for each. Both, the unmodified and the modified gypsum were tested for compressive and tensile strength after one hour and one week from the start of the mix. The crystalline configuration of the fracture fragments of the unmodified and modified set gypsum were studied under the scanning electron microscope. Results: The disinfectant solutions reduced the strength of both Type III and Type IV gypsum. Water showed higher-strength, which was followed by 0.525% sodium hypochlorite and 2% glutaraldehyde. The modified Type III and Type IV gypsum with reduced L/P ratio also showed strength values less than that of the control groups. Interpretation and Conclusion: Chemical disinfectants reduced the strength of gypsum when used as water substitutes. Gum Arabic and calcium hydroxide additives permitted lower L/P ratio, however, there was still excess water retained in the set gypsum that lowered the strength values of Type III and Type IV gypsum. Hence, further reduction of L/P ratio may increase the properties of the modified Type III and Type IV gypsum.

Avaliação e comparação de propriedades físicas e mecânicas de materiais de moldagem experimentais / Assessment and comparison of mechanical and physical properties of commercial and experimental gypsums

OBJETIVO: O objetivo deste estudo foi avaliar e comparar in vitro propriedades fisicas e mecanicas (resistencias a compressao e a tracao diametral, tempo de presa, fidelidade de copia e dureza) de gessos comerciais, cujas composicoes foram alteradas. MATERIAL E METODO: Foram confeccionados 40 corpos-de-prova para cada tipo de gesso e submetidos aos testes citados (n=10). Os corpos-de-prova obtidos para verificacao da resistencia a tracao foram antes submetidos a analise de dureza. Os tempos de presa foram analisados imediatamente apos a manipulacao dos materiais e os demais ensaios propostos foram realizados apos 7 dias da obtencao das amostras. RESULTADOS: Os valores obtidos nos testes foram analisados estatisticamente (1-way ANOVA, Tukey, p<0.05); observou-se que Exp1 apresentou melhor reproducao de detalhes e Exp2 o menor tempo de presa em relacao aos materiais comerciais (p<0.05). Nas demais propriedades, os gessos experimentais apresentaram comportamentos semelhantes aos comerciais. CONCLUSOES: Concluiu-se que as alteracoes na composicao dos gessos contribuiram para a melhoria na reproducao de detalhes no grupo Exp1, e diminuicao no tempo de presa no grupo Exp2.

OBJECTIVE: The purpose of this study was to evaluate and to compare in vitro mechanical and physical properties (compression and diametral tensile strength, setting time, loyalty to copy and hardness) of commercial and experimental gypsums (Exp1 and Exp2), whose compositions were altered. MATERIAL AND METHOD: Forty specimens were obtained for each type of gypsum (n=10). The specimens obtained to verify tensile strength were submitted to hardness analysis before. The setting time were analysed immediately after the manipulation of materials and the other tests were conducted 7 days after the specimens were obtained. RESULTS: The values were analyzed statistically (1-way ANOVA, Tukey, p <0.05) and it was observed that Exp1 showed better reproduction of details and Exp2 presented lesser setting time than commercial materials (p <0.05). As regards to other properties, experimental gypsums showed similar behavior to commercial gypsums. CONCLUSION: It was concluded that alterations in gypsum composition contributed to the improvement in reproduction of details in Exp1 group, and promoted a decrease in setting time in Exp2.

hydration of C3A systems in sodium chloride solutions

This study attempts to generate information about the chemistry of the hydration reaction of tricalcium aluminate [C3A] in 0.1 M sodium chloride solutions for hydration times up to one week at room temperature. The effect of gypsum, lime and alite on the progress of the reaction was investigated and the behavior of the dissolved ions was related to that of the solid phases. It is found that the hydration of C3A in 0.1 M sodium chloride solutions, also in the presence of gypsum, lime and alite has shown quite modification compared to that in water. The calcium chloro aluminate hydrate is a major phase formed in the different systems. It appears as a sole hydration product during the hydration of C3A alone in sodium chloride solutions, shows up together with ettringite phase in the presence of gypsum and predominates the ettringite phase in the presence of lime and alire. The hydration rate and the consumption of C3A in sodium chloride solution occur faster in the presence of gypsum than that in the presence of lime and alite

Effect of cervical relining of acrylic resin copings on the accuracy of stone dies obtained using a polyether impression material

The purpose of this study was to evaluate the accuracy of the respective dies after polyether elastomeric procedure in the presence or absence of cervical contact of the acrylic resin shell with the cervical region, establishing a comparison to dies obtained with stock trays. This study consisted of three groups with 10 specimens each: 1) acrylic copings without cervical contact, (cn); 2) acrylic copings with cervical contact (cc); 3) perforated stock tray, (st). The accuracy of the resulting dies was verified with the aid of a master crown, precisely fit to the master steel die. ANOVA test found statistically significant differences among groups (p<0.001). Tukey's test found that the smallest discrepancy occurred in group cn, followed by cc, while the st group presented the highest difference (cc x cn: p=0.007; st x cn: p<0.001; st x cc: p<0.001).

Resistencia compresiva y traccional exhibida por un polímero alternativo utilizado en modelos odontológicos / Compressive and tensile resistance by an alternative polymer used in dental models

Este estudio pretendió evaluar el comportamiento de resistencia a la tensión de modelos odontológicos obtenidos a partir de una resina epóxica de uso industrial modificada con circonita. A la resina Epoxiglass 1504 y el endurecedor Epoxiglass 1603 les fue adicionada circonita en una proporción de 1 para 1 en peso; modificada de esta manera fue manipulada siguiendo las instrucciones del fabricante, el cual establece una proporción de 35 por ciento en peso entre la resina y el endurecedor. Fueron realizadas 15 impresiones de un modelo matriz, utilizando silicona de adición, siendo vaciados con Epoxiglass 1504, Epoxiglass 1504 modificada y Yeso Piedra tipo IV, obteniéndose 60 cuerpos de prueba en total. Las características de los mismos fueron: 12 mm. de altura y 6.0 mm. de diámetro. Los cuerpos de prueba fueron divididos en dos grupos de 30 cada uno, de estos uno de ellos fue sometido al ensayo mecánico de compresión y el otro al de tracción por compresión diametral, utilizando una máquina universal de ensayos DL2000 EMIC, con una célula de carga de 2000kgf y velocidad de 0,5mm/min. Los resultados fueron analizados con el análisis estadístico ANOVA y comprobación con el test de Tuckey con grado de exactitud de 5 por ciento verificando que: los modelos de resina epóxica Epoxiglass 1504 mostraron resistencia a compresión y resistencia a tracción por compresión diametral superior a los modelos de yeso tipo IV; la circonita aumenta la resistencia a tracción por compresión diametral de la resina Epoxiglass 1504. Frente a estos resultados, se puede concluir que la resina epoxica Epoxiglass 1504 se presenta como un material viable para la obtención de modelos odontológicos, así como también, que la circonita mejoró comportamiento mecánico del material en relación a las propiedades mecánicas estudiadas.

This study evaluated the tensil behavior of dental models obtained using an industrial epoxic resin modified with zirconita. The Epoxiglass resin 1504 and the hardener Epoxiglass 1603 were added with zirconita in a ratio of 1/1 in weight. The modified resin was manipulated in accordance with the manufacturer's specifications, which establishes a relation of 35% in weight between the resin and the hardener. Fifteen moldings of a matrix were conducted using addition silicone. Then, they were filled with epoxic resin Epoxiglass 1504, resin Epoxiglass 1504 modified or type IV Durone plaster, which provided 60 test specimens with 12mm of height and 6mm of diameter. Thirty specimens were submitted to the compression assay and thirty to the traction assay by diametrical compression, using the universal machine DL2000 (EMIC), with a load cell of 2000 Kgf and 0,5mm/mim speed. The results were analyzed by Variance analysis followed by Tukey test with significance level set at 5%. It was verified that models made of Epoxiglass 1504 presented superior tensile strenght for diametrical compression and also superior compressive strength than models made of plaster type IV. The zirconita increased the tensile strenght for diametrical compression of the epoxic resin Epoxiglass 1504. In accordance to the present results, it was verified that the epoxic resin Epoxiglass 1504 is a viable material for dental modeling and that the zirconita provides mechanical benefit for the epoxic resin.

Esse estudo avaliou o comportamento tensil de modelos odontológicos obtidos a partir de uma resina epóxica de uso industrial modificada com zirconita. A resina Epoxiglass 1504 e o endurecedor Epoxiglass 1603 foram carregados com zirconita numa proporção de 1/1 em peso. A resina modificada foi manipulada de acordo com as especificações do fabricante, que estabelece uma relação de 35% em peso entre a resina e o endurecedor. Foram realizadas quinze moldagens de uma matriz, os moldes foram obtidos com silicone de adição e preenchidos com resina epóxica Epoxiglass 1504, resina Epoxiglass 1504 modificada e gesso tipo IV Durone, o que proporcionou 60 corpos de prova com 12mm de altura e 6mm de diâmetro. Trinta corpos de prova foram submetidos ao ensaio de compressão e trinta ao ensaio de tração por compressão diametral, empregando-se a máquina universal de ensaios DL2000 da EMIC, com célula de carga de 2000Kgf e velocidade de 0,5mm/mim. Os resultados foram analisados com Teste de Variância e Tukey com significância de 5%, e verificou-se que: Modelos obtidos em resina epóxica Epoxiglass 1504 apresentam superior resistência à tração por compressão diametral que modelos obtidos em gesso tipo IV; Modelos obtidos em resina epóxica Epoxiglass 1504 apresentam superior resistência à compressão que modelos obtidos em gesso tipo IV; A zirconita aumenta a resistência à tração por compressão diametral da resina epóxica Epoxiglass 1504. Diante dos resultados encontrados, verificou-se que a resina epóxica Epoxiglass 1504 apresenta-se como material viável para a modelagem odontológica e que a zirconita proporciona ganho mecânico para a resina epóxica.

Comparative evaluation of the effect of palatal vault configuration on dimensional changes in complete denture during processing as well as after water immersion.

Polymerization shrinkage is one of the major drawbacks of the acrylic resin. The present study was conducted to evaluate the dimensional changes occurring in the dentures, constructed on the casts having different configurations of the palatal vault, during processing and the effect of water sorption on the processed dentures. Eight maxillary edentulous casts having U, F and V configurations of palatal vault were selected and complete dentures were fabricated. Dimensional changes occurring in the processed dentures were studied in different regions during processing as well as after water sorption. It was observed that dimensional changes in frontal and vertical planes were maximum in V shaped palatal vault dentures. Water sorption partly compensated for the dimensional changes that occurred during processing.