A comparison of two soldering techniques on the misfit of bar-retained implant-supported overdentures.

PURPOSE: This study was conducted to measure and compare the effect of the soldering method (torch soldering or ceramic furnace soldering) used for soldering bars to bar-retained, implant-supported overdentures on the fit between the bar gold cylinder and implant transgingival abutment. MATERIALS AND METHODS: Thirty-two overdenture implant bars were manufactured and screw retained into two Bränemark implants, which were attached to a cow rib. The bars were randomly distributed in two groups: a torch-soldering group and a porcelain-furnace soldering group. Then all bars were cut and soldered using a torch and a ceramic furnace. The fit between the bar gold cylinders and implant transgingival abutments was measured with a light microscope on the opposite side to the screw tightening side before and after the bar soldering procedure. The data obtained were statistically processed for paired and independent data. RESULTS: The average misfit for all bars before soldering was 33.83 to 54.04 µm. After cutting and soldering the bars, the misfit increased up to a range of 71.74 to 78.79 µm. Both before and after the soldering procedure, the bars soldered using a torch showed a higher misfit when compared to the bars soldered using a porcelain furnace. After the soldering procedure, the misfit was slightly lower on the left side of the bars, which had been soldered using a ceramic furnace. CONCLUSIONS: According to our data, the soldering of bars using the torch or furnace oven soldering techniques does not improve the misfit of one-piece cast bars on two implants. The lower misfit was obtained using the porcelain furnace soldering technique.

Estudio de la microdureza superficial de 28 aleaciones comerciales para amalgama de plata / No disponible

Objetivos: El artículo pretende comparar la microdureza superficial de diferentes amalgamas comerciales con polvo metálico de morfología diferente al objeto de determinar la influencia que el contenido de los diferentes elementos metálicos del polvo y el contenido en mercurio residual presente en la aleación fraguada ejercen sobre el citado parámetro. Material y métodos: Un total de 28 aleaciones comerciales para amalgama de plata dispensadas en forma de cápsulas fueron sometidas a ensayos de microdureza superficial. Probetas de cada material fueron preparadas de acuerdo a la Especificación ISO 1559:1995y sobre la superficie de las mismas se realizaron 9 indentaciones Vickers abarcando una matriz de 600 x 600 μm a 1 hora, 3 horas,24 horas, 7, 15 y 30 días. Muestras del polvo fueron sometidas a Fluorescencia de Rayos X (RFX) para determinar el porcentaje en peso de Ag, Sn, Cu y Zn. A su vez probetas de material preparadas según especificación ISO fueron pesadas previamente y posteriormente sometidas a 600º C en un horno durante 3 horas, de acuerdo con las indicaciones obtenidas en un ensayo termo gravimétrico previo, para determinar el porcentaje en peso de Hg residual. Resultados: Se usó contraste estadístico mediante Anova y test de Tukey. Hasta las 24 h. las aleaciones esféricas e híbridas mostraron una microdureza significativamente mayor (p>0.000) que el resto de las morfologías. No obstante, las limallas esféricas e híbridas mostraron una microdureza similar a los 30 días. A su vez, las limallas mostraron un contenido significativamente menor en plata y mayor en cobre y en mercurio residual que el resto de las aleaciones (p<0.001), (..)(AU)

Objectives: Compare surface microhardness of different commercial silver amalgams with different powder morphology and to determine the influence of the powder metal elements and the percentage of residual mercury on the said parameter. Methods: 28 encapsulated commercial lathe cut, spherical, admixed and hybrid alloys for silver amalgam were subjected to microhardnesstests. Samples for each material were prepared according to the ISO1559:1995 specification, 9 Vickers indentations were made on the surface of a 600 x 600 μm matrix at 1h, 3h, 24h, 7 days, 15 days and 30 days. Ray fluorescence X (RFX) were used to determine the weight percentage of Ag, Sn, Cu, Zn. Results: Anova and Tukey test were used. Up to 24 h., spherical and hybrid alloys showed a significantly greater micro hardness (p>0.000)than the other morphologies. Nevertheless, lathe cut, spherical and hybrid showed a similar behaviour at 30 days. Lathe cut showed a significantly lower silver content but higher Cu and Hg than the other alloys (p>0.001), whilst the admixed showed a significantly lower Sncontent (p>0.001). The results showed that Cu and Sn exercised apositive influence on micro hardness, Ag a negative influence whilst the residual Hg almost nothing. Significance: In recent years, there has been a tendency towards short-term hardening as mechanical protection because this prevents premature fracturing of the restoration facilitating fast removal of the matrix band, but reduces the manipulation time therefore difficultiesin condensation, porosity and lamination might arise. At this moment in time, the influence of microhardness on restoration survival is unknown, however, it might prove valuable if a significant correlation can be found between this property and clinical performance (..) (AU)

Advances in the history of composite resins.

The use of composite resins as direct restoration material in posterior teeth has demonstrated a great increase, due to esthetic requirements and the controversy regarding the mercury content in silver amalgams. In this article, we have reviewed the composition modifications which have occurred in materials based on resins since their introduction over a half a century ago which have enabled great improvements in their physical and mechanical properties. Likewise, we have highlighted current lines of research, centered on finding the ideal material for replacing silver amalgam as a direct filling material.

A history of dental amalgam.

OBJECTIVES: Silver amalgam alloy has been used as a dental restorative material since the beginnings of restorative dentistry. It rose as an easily manipulated and low cost material in comparison to other restorative techniques of the time, but it had poor dimensional stability and clinical behavior. Successive research led to the standardization of both its composition and some aspects of its mechanical properties, which have contributed to its widespread acceptance. Nevertheless, the risk of environmental toxicity generated by mercury and its poor esthetics have given rise to the search for alternative and more promising materials. This article endeavors to give a brief historical description of the main events which have led to development of modern silver amalgam alloys. SIGNIFICANCE: It is concluded that extensive knowledge of the use of silver amalgam alloy has made it the most widely used restorative material for the posterior oral cavity. However, in recent years its preponderance has been brought into question even though some innovative ideas have been suggested which could help improve this material in the future.

Candida albicans adherence to resin-composite restorative dental material: influence of whole human saliva.

OBJECTIVE: Attachment of Candida albicans to oral surfaces is believed to be a critical event in the colonization of the oral cavity and in the development of oral diseases such as Candida-associated denture stomatitis. Although there is considerable information about the adhesion of C albicans to buccal epithelial cells and prosthetic materials, there is very little information about the adhesion of C albicans to composite restorative materials. The purpose of this study was to investigate the degree of adhesion of C albicans to a resin-composite restorative material (Herculite). METHODS: The adhesion of 2 strains of C albicans, a germinative and a germ tube-deficient mutant, was studied by a visual method after incubating the fungus and the resin with and without human whole saliva. RESULTS: In absence of saliva, the adhesion of the C albicans germinative isolate to the resin showed an increase in parallel with the germination, reaching a maximum at the end of the experiment (120 minutes). However, no significant differences were observed in the adhesion of the agerminative mutant during the period of time studied. In the presence of saliva, the adhesion of both isolates to the resin was significantly lowered. CONCLUSION: Germination and the presence of human whole saliva are important factors in the adhesion of C albicans to the resin-composite restorative material Herculite.

Effectiveness of Sonicare power toothbrush to remove chlorhexidine stains.

PURPOSE: To describe the effect of Sonicare power toothbrush on removing chlorhexidine stains from human teeth. MATERIALS AND METHODS: Two cases with chlorhexidine staining were treated with Sonicare power toothbrush for a 4-week period. Clinical evaluations occurred at baseline, 2 weeks from baseline and 4 weeks from baseline. Stain level was assessed with the Lobene Tooth Stain Index. The labial surface of each stained incisor or canine was divided into two regions: margin and body. RESULTS: Sonicare reduced the average area of stain score by 58.5-63.3% after 2 weeks and 68.3-76.7% after 4 weeks. The average intensity of stain scores was reduced by 50.0-56.5% and 58.9-69.6% after 2 and 4 weeks, respectively.