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PubMed1997

Cast-forming Actinomyces israelii canaliculitis.

BACKGROUND: Primary chronic canaliculitis is an uncommon disease usually caused by Actinomyces israelii (streptothrix). Actinomyces israelii is a cast-forming Gram-positive anaerobe that is difficult to isolate and identify. We present a case that demonstrates the typical clinicopathological presentation of this unusual condition and discuss management options. METHODS AND RESULTS: A 10-year-old girl presented with a 6 month history of intermittent 'conjunctivitis' and discharge from her 'pouted' left lower punctum. Microbiology confirmed probable A. israelii infection, but topical treatment failed. Exploration under anaesthesia revealed a canalicular diverticulum and three canaliculiths. Histological examination of the canaliculiths demonstrated that they consisted of solid casts of Actinomyces. Punctoplasty, removal of the casts, and adjunct antibiotic therapy resulted in resolution of the canaliculitis. CONCLUSIONS: Primary chronic canaliculitis should be considered in any patient who presents with chronic or recurrent conjunctivitis and the eyelid should be inspected for a discharging and 'pouting' punctum. Failure of the condition to resolve on topical treatment requires surgical exploration of the canalicular system and removal of any casts. Extensive surgery is not always required.

Actinomyces↗

PubMed1997

Fracture analysis of cast pure Ti and Ti-6Al-4V alloy for dental use.

The fracture behavior of cast two types of pure Ti and Ti-6Al-4V alloy was understood by acoustic emission (AE) analysis during a fracture toughness test. Specimens for test were cast by the lost wax method using a specially designed Ti casting machine of pressure-different method for dental use. A fatigue crack was inserted from the machined notch tip into the body of a specimen in the range of 0.45-0.55 a/W. Acoustic emission signals released during the fracture toughness test were detected by two sensors attached to both ends of the specimen. Then the signals were recorded and analysed by the PAC 3000/3104 system. From the early stage of the fracture toughness test, AE signals started to be released in all types of specimens tested. A reaction layer with the investment materials of about 50-100 microns was thought to be the result of the AE release from an early stage of the fracture toughness test. A microfracture behavior of the cast pure Ti and Ti alloys was proposed based on the results obtained from the AE releasing pattern and fracture surface findings.

Acoustics↗

PubMed2005

Evaluation of different bonded investments for dental titanium casting.

The properties of several different investments were investigated including phosphate bonded, magnesia bonded, and alumina cement investments. Measurements included the setting expansion, thermal expansion, and compressive strength of investments, as well as the tensile strength, elongation, Vickers hardness (VHN) and surface roughness of titanium castings. For phosphate bonded investment, the setting expansion after being mixed with its own mixing solution was 2.10%, which was larger than the other investments; the thermal expansion was -0.25% at 200 degrees C, the compressive strength 14 and 5 MPa after heating. For titanium cast in phosphate bonded investment, the hardness on its top surface was 655 Hv, the tensile strength was 379 MPa, the elongation was 19.4%, and the surface roughness was 2.29 microm. Although the thermal expansion of phosphate bonded investment is small, the setting expansion is large enough to compensate for the shrinkage of titanium castings. As its thermal expansion at T > or = 600 degrees C was constant and its heating-cooling cycle was almost reversible, these two properties can reduce the thermal shock and thus avoid cracking of the investment.

Aluminum Oxide↗

PubMed1977

A comparison of the casting ability of precious and nonprecious alloys for porcelain veneering.

The alloys tested varied with respect to their castability. This variability is related to density. Problems caused by low density may be solved by increasing the casting force. For all parameters measured in the laboratory, Thermocraft, a precious alloy, proved to be the most satisfactory- Wiron S, a nonprecious alloy, was comparable to Degudent Universal, a gold alloy. The application of Wiron S as a successful gold substitute should, therefore, be further investigated clinically. Equipment, investment, and casting techniques, all designed for the casting of gold alloys, were also used for the nonprecious alloys. These are standard facilities readily available in clinical practice. Modifications or technical improvement to these factors may result in more successful application to the other nonprecious alloys.

Dental Alloys↗

PubMed1980

Evaluation of three variables affecting the casting of base metal alloys.

All the vented samples with sprue widths of 2 mm or more were defect free, whereas the corresponding unvented samples had extensive voids and porosity in all but one casting. All castings with a sprue width of 1 mm were defective regardless of whether or not vents were used. The thickness of the investment above the pattern had no effect on casting results.

Dental Alloys↗

PubMed1995

Contamination of titanium castings by aluminium oxide blasting.

OBJECTIVES: It is desirable that the surfaces of surgical implants be uncontaminated by foreign materials to avoid untoward tissue reactions, and grit blasting is widely assumed to leave clean metal surfaces. SEM examination and X-ray microanalysis of a recovered 'pure' titanium implant casting that was associated with tissue breakdown revealed embedded particles of alumina. The casting had been cleaned of investment by blasting with alumina grit. METHODS: A variety of treatments of cast titanium plates was used: (a) to establish that the observed aluminium was due to the blasting grit, and (b) to determine whether removal of investment could be achieved effectively by other means. SEM examination and X-ray microanalysis were used. RESULTS: The detected aluminium was associated with embedded fragments identified as coming from the blasting grit. Acid-pickling and mechanical (rotary instrument) trimming produced minimally contaminated surfaces. CONCLUSIONS: Whilst unproven, the presence of the alumina is viewed with great concern as a possible causative agent in the observed tissue breakdown and procedures avoiding alumina blasting are recommended as a precautionary measure.

Aluminum Oxide↗

PubMed2004

Evaluation of shear bond strength at the interface of two porcelains and pure titanium injected into the casting mold at three different temperatures.

STATEMENT OF PROBLEM: Titanium has physical and mechanical properties, which have led to its increased use in dental prostheses despite casting difficulties due to high melting point and formation of oxide layers which affect the metal-ceramic bond strength. PURPOSE: This in vitro study evaluated the shear bond strength of the interface of 2 dental porcelains and pure titanium injected into a mold at 3 different temperatures. MATERIAL AND METHODS: Using commercially pure (cp) titanium bars (Titanium, Grade I) melted at 1668 degrees C and cast at mold temperatures of 430 degrees C, 700 degrees C or 900 degrees C, 60 specimens were machined to 4 x 4 mm, with a base of 5 x 1 mm. The 4-mm surfaces were airborne-particle abraded with 100 microm aluminum oxide before applying and firing the bonding agent and evaluating the 2 porcelains (Triceram/Triline ti and Vita Titankeramik). Ten specimens were prepared for each temperature and porcelain combination Shear bond testing was performed in a universal testing machine, with a 500-kg load cell and crosshead speed of 0.5 mm/min. The specimens were loaded until failure. The interfaces of representative fractured specimens of each temperature were examined with a scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Data for shear bond strength (MPa) were statistically analyzed by 2-way ANOVA and the Tukey test (alpha=.05). RESULTS: The results showed significant differences for the metal/porcelain interaction effect (P=.0464). There were no significant differences for the 2 porcelains (P=.4250). The Tukey test showed a significant difference between the pair cp Ti 430 degrees C Triceram and cp Ti 900 degrees C Triceram, with respective mean values and SDs of 59.74 +/- 11.62 and 34.03 +/- 10.35 MPa. CONCLUSION: Triceram porcelain showed a bond strength decrease with an increase in the mold temperature for casting titanium. The highest bond strength for Vita porcelain and the best metal-ceramic interface observed with the SEM were found with the mold temperature of 700 degrees C.

Air Abrasion, Dental↗

PubMed1995

Effects of firing cycle and surface finishing on distortion of metal ceramic castings.

The "as-cast" fit of metal ceramic restorations has been reported to deteriorate during the high-temperature firing cycles used for application of porcelain veneer. In this study, thermocycling and surface finishing or cold working were examined for their effects on marginal adaptation of metal ceramic castings. Methods for minimizing the loss of marginal adaptation were evaluated, and casting variables were eliminated by construction of acrylic resin measuring dies directly in the restorations. Thermocycling of metal ceramic restorations resulted in increased marginal openings, and all of the loss of marginal fit occurred during the first thermocycling of the alloy. The restorations that were cold worked and then oxidized by conventional manipulation had substantially more marginal opening than any other group. A fourfold, statistically significant improvement (p < 0.001) in the marginal adaptation of a metal ceramic restoration was observed when the initial thermal cycle was completed before the specimens were finished.

Acrylic Resins↗

PubMed1996

The influence of alloy composition and casting procedure upon the corrosion behaviour of dental alloys: an in vitro study.

The influence of the composition and the casting process upon the electrochemical corrosion of a selection of palladium-based alloys and non-precious metal alloys has been investigated in vitro using an electrochemical method. No influence of the casting process upon the corrosion resistance was observed with palladium-based alloys. Changes in the crystallographic structure effected by the different composition of the alloys were found, the casting process did not cause significant effects. With nickel-chromium alloys rather low corrosion stabilities were observed.

Chemical Phenomena↗

PubMed2001

New method for divesting cobalt-chromium alloy castings: sandblasting with a mixed abrasive powder.

STATEMENT OF PROBLEM: Because the conventional divesting method for cobalt-chromium (Co-Cr) alloys is laborious, a more convenient method is desirable. PURPOSE: This study compared sandblasting with a mixed powder composed of aluminum oxide and glass beads to sandblasting with single powders (carborundum, aluminum oxide, and glass beads) when a Co-Cr casting was removed from the investment mold. MATERIAL AND METHODS: Rectangular plates with the 2 surfaces simulating the inner and outer surfaces of a removable partial denture framework were fabricated with Co-Cr alloys. Four kinds of sandblasting powders were used to remove the remnants of investment molds. Total time (seconds) required for each procedure was measured, as was the surface roughness (Ra) of each specimen after sandblasting. SEM was used to analyze the powders themselves and the sandblasted specimen surfaces. RESULTS: Glass beads alone and the mixed powder of aluminum oxide and glass beads generated a smoother surface compared with aluminum oxide and carborundum powders. The use of the mixed powder significantly reduced the time of the sandblasting procedure. SEM revealed that glass beads generated fewer scars, followed by the mixed powder and then aluminum oxide. The surface sandblasted by carborundum powder was always the roughest. CONCLUSION: Sandblasting Co-Cr castings with the mixed powder effectively decreased treatment time and resulted in smooth, clinically acceptable casting surfaces.

Aluminum Oxide↗

PubMed2004

Measurement of the setting expansion of phosphate-bonded investment materials: part II--An evaluation of the Casting-Ring Test at 10 laboratories.

The Casting-Ring Test has the potential to fulfil the requirement for a reliable 'Standard' test to measure the setting expansion of phosphate-bonded investment materials. The purpose of this study was to investigate the reproducibility of the measurements and the value that is produced at 10 test sites. The Casting-Ring Test apparatus, three phosphate-bonded investment products and one ring liner product were sent to the 10 participants, together with a detailed test protocol. Participants were asked to use their normal vacuum mixers. Reproducibility at individual sites was good. However, there were significant differences between test sites for the mean setting expansions, attributed to the range of vacuum mixers employed. From these results, the Casting-Ring Test appears to satisfy the requirements for adoption as an ISO standard test. The effect produced by different vacuum-mixer models would be manifest in any test. Not only does this have implications when determining the value of setting expansion for product information, but such a range of setting expansions will also be reproduced during production of moulds in commercial dental laboratory practice. However, for any specific product and vacuum-mixer combination, the setting expansion will be consistent and will not vary from mould to mould.

Chemical Phenomena↗

PubMed1991

Effect of vacuum and supertemperature on mold filling during casting.

A comparison of the effect on mold filling of using vacuum vs. a protective gas of Ar during casting has been carried out. A conventional gold casting alloy and a NiCr-alloy without Be have been cast at three temperatures into two different mold patterns: a mesh screen and a cylindrical crown with a 30 degrees sharp margin. In all cases the application of vacuum rather than a protective gas of Ar was found to be beneficial for the mold filling. A reduction of the back pressure due to the trapped gases in the last part of the mold to be filled with metal was assumed to be the major reason for this effect. A reduced surface tension of the melt may also contribute. An improved mold filling was also observed for both nets and crown margins with increasing supertemperature of the melt. Physical reasons for this effect have been suggested.

Argon↗

PubMed1993

Skin holes of titanium casting.

The present study describes refractories which contribute to formation of skin holes of Ti casting. Plates consisting of quartz (Qu) and cristobalite (Cr) powders and Qu- and Cr-MgO mixtures were fired at high temperatures and used as phosphate-free molds. The cross-section of the castings was investigated using an optical microscope and an electron probe microanalyzer. Whereas the castings into the Qu molds were almost complete, those into the Cr molds were incomplete. The surface reaction zone of the Qu molds formed a typical layered structure with fewer skin holes. That of the latter extended deeply into the interior with a net-shaped Ti-Si phase, cracks, and holes. Addition of MgO to Cr effectively improved the castability and changed the reaction zone to the typical layered structure. However, slender holes occurred along the mold wall. The overall area around the holes was contaminated by Si and Mg. Probably, this resulted from a reaction of forsterite with Ti. The reactivity difference between Qu and Cr was not related to the fired strength of mold.

Dental Casting Investment↗

PubMed1999

[Determination of normal temperature properties of refractory die material compatible with slip casting core of sintered titanium powder].

OBJECTIVE: The refractory die is the precondition for developing slip casting core of sintered powder. This study is to determine the normal temperature properties of the refractory die material compatible with slip casting core. METHODS: to mix the die material at five different ratios (8/1, 7.5/1, 7/1, 6.5/1, and 6/1) and measure their solidification time with self-manufactured Vicker's needle; to prepare five cylindrical specimens (phi 10 x 15 mm) in different drying time for determining their compressive strength, and then to let another five specimens fire at 1000 degrees C four times for measuring the residual compressive strength at room temperature. RESULTS: The setting time was 16.25 minutes (7.5/1), and the lower the powder-liquid ratio, the longer the setting time. The normal compressive strength was 25.32 MPa (drying 24 hours), while the longer the drying time, the higher the compressive strength achieved (P < 0.01). The residual compressive strength was 24 MPa. CONCLUSION: The normal temperature properties of the refractory die material meet the demand of slip casting core of sintered powder.

Compressive Strength↗

PubMed1999

[Determination of high temperature compressive strength and refractory degree of die material compatible with slip casting core of sintered titanium powder].

OBJECTIVE: The refractory die is the precondition for developing slip casting core of sintered powder. This study is to determine the high temperature properties of the refractory die material compatible with slip casting core. METHODS: To prepare three cylindrical specimens (phi 10 x 15 mm) and determine their compressive strength at 1000 degrees C: to make four specimens in flat-topped cone for determining the practical refractory degree by decreasing the pressing temperatures in a sequence of 1420, 1400, 1350 and 1100 degrees C. RESULTS: The compressive strength of this material was 17.8 MPa at 1000 degrees C. Its practical refractory degree was higher than 1100 degrees C. CONCLUSION: The high temperature properties of the refractory die material that we developed meet the demand of slip casting core of sintered powder.

Compressive Strength↗

PubMedDate not supplied

Comparisons of precision of fit between cast and CNC-milled titanium implant frameworks for the edentulous mandible.

PURPOSE: The purpose of this study was to investigate and compare the precision of fabrication in repeatqdly produced computer numeric controlled (CNC)-milled frameworks with consventional castings, and to analyze the distortion from application of different veneering materials. MATERIALS AND METHODS: Twenty identical titanium frameworks were fabricated by means of a CNC milling technique for the same master model. Five conventional frameworks were cast as a control group to the same model. The frames were measured with regard to fit in a coordinate measuring machine linked to a computer. Measurements were made during different stages of handling of the titanium framework, and after veneering materials had been applied. RESULTS: The CNC frameworks showed a statistically better fit and precision of fabrication compared to conventional castings (P < .05). The application of veneering material did not statistically affect the fit of the titanium frameworks (P > .05). CONCLUSION: It is possible to fabricate implant-supported frameworks by means of the present CNC technique with a very high precision and repeatability.

Acrylic Resins↗

PubMedDate not supplied

Implant-supported laser-welded titanium and conventional cast frameworks in the partially edentulous law: a 5-year prospective multicenter study.

PURPOSE: This study evaluated and compared the clinical performance of laser-welded titanium fixed partial implant-supported prostheses with that of conventional cast frameworks in the partially edentulous jaw. MATERIALS AND METHODS: Forty-two patients provided with Brånemark system implants were arranged into two groups. Twenty-one patients (group A) were provided with a conventional cast ceramometal framework in one side of the jaw and a laser-welded titanium framework with low-fusing porcelain in the other side. In group B, 21 patients received a titanium framework prosthesis to replace a conventional implant prosthesis. Clinical and radiographic data were collected for 5 years. RESULTS: Four implants and one titanium framework were lost during the follow-up period. The two framework designs did not show any significant differences with regard to implant or prosthesis survival (P > .05). Few clinical complications were observed. In group A, marginal bone loss after 5 years was similar for both prosthesis designs, with an average of 0.1 mm and 0.3 mm in the maxilla and mandible, respectively. Basically, no bone loss was observed on average in group B. Furthermore, no significant relationship was observed between marginal bone loss and placement of prosthesis margin or prosthesis design. CONCLUSION: Except for an insignificant tendency toward a slightly higher incidence of small chips of porcelain veneers, laser-welded titanium frameworks presented an overall similar clinical performance as conventional cast frameworks in partial implant situations after 5 years.

Adult↗

PubMed2003

[A study on microstructures and heat reaction zone of laser-melted and cast post-keepers].

OBJECTIVE: In order to introduce the laser welding technology into root-cap making, this study compared the surface characters and internal structures of laser-melted and cast post-keeper to provide experimental data for clinical application of the technique. METHODS: Using untreated keeper as the control group, the surface characters and metallographic structures of the keepers were examined by stereomicroscope, metallographic microscope and SEM, and element analysis were conducted with EPMA. RESULTS: The laser-melted post-keeper basically kept the original smooth and the internal structure of the keeper, the heat reaction zone was extremely small and elements diffused mutually around the fusion zone obviously. While in the cast post-keeper, the surface was rough and had an oxide-layer. The internal structure changed and a fusion band formed between the base alloy and the keeper, but element diffusion was limited to the fusion zone. CONCLUSION: Compared with casting, laser welding technique demonstrated less influence on the surface and internal structure of the keepers.

Dental Alloys↗