Resistência ao impacto de revestimentos para fundições odontológicas, em diversas condições de temperatura no forno

The impact strenght of four dental casting investments is investigated as a function of heat loss after removal of tu a furnace temperature of 700ºC, at different time intervals. Attention is called to the fact hat a graphical relationship between temperature loss and lmpact strenght, even hough obtained from averages of 10 experiments, but without a statistical analysls, may induce to erroneous conclusions.

Perda de temperatura em revestimentos odontológicos, após sua remoção do forno

The time elepsed between the removal from the furnace of a castin cylinder and the casting proper, depends on the knowledge and ability of the operator. The heat loss, after removal of a furnace temperature of 700ºC at different time intervals, was mensured in four dental casting investiments, using different volumes of investment, with or without the protection of a casting ring and with or without asbestos liner. The results, presented in the form of tables and graphs, tell us about the importance of this additional technical detail, in the dental casting operation. Temperature losses in the order of from 100º to 200ºC were verified, already two minutes after removal from the furnace.

Os revestimentos brasileiros na atualidade, face aos requisitos de suas normas ou especificações: a influência de condições higroscópicas de prêsa em suas curvas de expansão térmica

One of the single, main responsible factors of sucess or insucess of the dental gold cast restoration, with relation to it’s future clinical performance, relies upon the casting investiment. To be reliable, the investiment should possess certain characteristcs, certain minimum requirements established and accepted as specifications. In the present research work, 6 different investments, were investigated: 5 manufactured in Brazil (of which 3 in an exprimental phase) and one manufactured in the United States. It was found that two of the brazilian investments (R4 and R5), most widely used by the dentists in this country, do not comply to the specifications. The investigation of the 3 investments which are in an experimental phase of production, leaves us to believe that in the near future, the dentists in Brasil will have at their disposal, an investment, manufactured in this country, that compiles to the specifications. A modified method is suggested, to verify the dimensional changes that occur in dental casting investments, that is more, in accordance with the continuity of the thecnical procedures followed in the construction of a dental gold cast restorarion.

Retention Forces of Prosthetic Clasps over a Simulated Wearing Period of Six Years In-Vitro: Direct Metal Laser Melting Versus Dental Casting

This study determinates the persistence of retention force in Akers-clasps for removable partial dentures made from Co-Cr alloy. Therefore, standardized computer-aided designed (CAD) clasp #1 specimens were made by direct metal laser melting (DMLM, n = 10) and by lost-wax dental casting (DC) of computer-aided manufactured (CAM) replicas (n = 10, DC) from two comparable Co-Cr alloys. The retention force was tested after manufacturing for 9000 cycles of setting and removal from a molar tooth crown analog made from zirconia; simulating in-vitro a duration of six years in service. The first and last 360 cycles (T0 and T1, 3 months each) of all specimens were selected for comparison of retention forces between the materials. A constant decrease of 6% from the initial retention force (T0 = 4.86 N, SD = 0.077; T1 = 4.57 N, SD = 0.037) was detected at the DC specimens, and an increase of 4% in DMLM specimens (T0 = 5.69 N, SD = 0.078; T1 = 5.92 N, SD = 0.077); all differences were statistically significant (p < 0.0001). Even if these deviations are not of clinical relevance, further studies and applications should investigate the fatigue behavior of laser melted Co-Cr-alloys for dental application.