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At least 703 records · Page 39Linked to original sources
PubMed1999

Healing of open stump wounds after vascular below-knee amputation: plaster cast socket with silicone sleeve versus elastic compression.

OBJECTIVE: To assess the effect of a plaster cast socket on the healing of open wounds and on temporary prosthesis fitting after below-knee amputation because of arterial occlusive disease. DESIGN: Randomized controlled trial. SETTING: Rehabilitation center, university hospital. PATIENTS: All included patients had undergone recent (in the previous 3 months) below-knee amputation because of arterial disease and initially had an open stump. Patients were randomly assigned to two groups of 28 subjects each. The sizes of the amputation scars were 8 to 24 cm2. Ischemia of the stump was eliminated as a probable cause of delayed wound healing by the inclusion criterion of transcutaneous oxygen tension (TcPO2) of >35 mmHg. The average age in group I (the experimental group) was 65.2 +/- 12.4 (SD) years and in group II (the control group) 66.8 +/- 10.8 years (not significant). INTERVENTION: A plaster cast (supracondylar-type) socket was fitted on the stumps of group I patients, interposed with a silicone sleeve. The patients were gradually trained to wear this cast for up to 5 hours a day. They were provided with elastic compression bandages for the remainder of the time. Patients in group II wore elastic compression bandages, which were only removed for dressing changes. MAIN OUTCOME MEASURES: Time required for stump healing, length of time between amputation and ability to walk wearing a contact socket, and length of hospital stay. RESULTS: Group I had a quicker average healing time (71.2 +/- 31.7 [SD] days compared to the control group's 96.8 +/- 54.9 days) and a shorter average length of hospital stay (99.8 +/- 22.4 days compared to the control group's 129.9 +/- 48.3 days). CONCLUSION: Use of a plaster cast socket leads to more rapid healing of the open stump and to a shorter hospitalization. If there is no stump ischemia, this plaster cast technique is safe.

Aged↗
PubMed1999

Inhibitory casting decreases a vibratory inhibition index of the H-reflex in the spastic upper limb.

OBJECTIVE: To test the hypothesis that application of an inhibitory cast to the spastic upper limb will decrease a vibratory inhibition index (VII) of the H-reflex in the spastic upper limb. DESIGN: Prospective, nonrandomized, open-label trial. SETTING: University tertiary care center. PARTICIPANTS: Eight adults with upper limb spasticity. INTERVENTION: Fiberglass cast application spanning the wrist to the upper arm. MAIN OUTCOME MEASURE: The amplitude of the H-reflex with and without continuous 60Hz vibration to the tendon of the flexor carpi radialis was measured, and the VII was calculated using the formula: [H-reflex amplitude (vibrated)/H-reflex amplitude (control)] x 100%. RESULTS: Mean VII decreased from baseline (70.7) on day 1 (67.6, p = .699), day 2 (55.9, p =.066), and day 3 (43.5, p = .033) of casting, and increased on day 4 (89.9, p = .146) after removal of the cast. CONCLUSION: Findings lend support to the idea that during application of an inhibitory cast motor neuron excitability is decreased in the spastic upper limb.

Adult↗
PubMed1998

Comparison of the results of short-term rigid and semi-rigid cast immobilization for the treatment of grade 3 inversion injuries of the ankle.

In this prospective, randomized study, short-term immobilization with semi-rigid (Soft Cast) and rigid (Scotchcast Plus) synthetic cast materials were compared for the functional treatment of acute grade 3 lateral ligament injuries of the ankle. Degree of ligament injury was assessed by clinical criteria. Duration of immobilization was 2 weeks for both groups and home physiotherapy was started thereafter. Fifty-seven patients completed the study and both materials were found to be equally effective in providing a stable ankle at the end of 6 weeks follow-up. Soft Cast group had better range of motion and could walk better at 2 weeks, but these differences diminished at 6 weeks. With the Soft Cast, patient satisfaction was higher, need for a support for walking was less and return to work was earlier. When combined with the reduced cost of application, Soft Cast is the material of choice for the initial short-term immobilization for the functional treatment of acute ankle ligament injuries.

Adolescent↗
PubMed1997

One clinical visit for a multiple implant restoration master cast fabrication.

The making of a one-piece, long-span, implant-supported prosthesis with conventional procedures frequently has difficulties associated with the accuracy of fit. This article presents a clinical and laboratory procedure for making an accurate implant working cast that facilitates fabrication of the casting on the master cast. The procedure demonstrates the process of sectioning and rejoining of the resin between the transfer copings and then pouring the impression by first joining the analogs alone with impression plaster, sectioning it, and rejoining it again to stabilize the analogs, and finally, using dental stone to pour the impression. Clinical, radiographic, and laboratory (optical microscope) measurements for one clinical implant restoration confirm the accuracy of fit of this one prosthesis made with this procedure. Its advantage is that it can allow fabrication of the final casting on the cast, thereby eliminating the clinical time necessary to obtain repetitive solder indexes, and thus minimizing inconvenience to the patient.

Calcium Sulfate↗
PubMed1998

A method for true coordinate three-dimensional measurement of casts using a measuring microscope.

Exact 3-dimensional measurements are more useful for researchers and clinicians than are relative distance measurements. Through the use of a measuring microscope and a personal computer, the technique presented in this article provides meaningful and accurate (0.005 mm) 3-dimensional measurements of casts in true coordinates (x, y, z). By fabricating the master cast with reference landmarks, leveling the casts before measurement, removing the cast between repeat measures, and mathematically rotating the data points, this technique places all the landmarks in a standardized reference plane that allows for the comparison of dimensional changes between different casts.

Computer Simulation↗
PubMed1998

The fit of cast and premachined implant abutments.

STATEMENT OF PROBLEM: There is insufficient information regarding the adaptation of abutments to implants. PURPOSE: This study assessed the adaptation of premachined, cast, and laboratory modified premachined abutments to implants at two sites: abutment/implant interface and screw to screw seat. MATERIAL AND METHODS: Six combinations of abutments and implants were studied: CeraOne abutments joined to Nobel Biocare implants; STR (Implant Innovations Inc.) abutments joined to 31 implants; Cast UCLA (31) abutments subjected to porcelain firing cycles and joined to 31 implants; Cast UCLA abutments subjected to porcelain firing cycles and joined to Nobel Biocare implants; UCLA premachined abutments cast with gold palladium alloy and subjected to porcelain firing cycles (later joined to 31 implants); and UCLA premachined abutments joined to 31 implants. Each group contained five assemblies. RESULTS: The adaptation of abutments to implants was closer and the amounts of contact larger for assemblies with premachined and laboratory modified premachined abutments than for those with cast abutments. CONCLUSION: The finishing of custom-made abutments requires further refinement.

Analysis of Variance↗
PubMed1999

Occlusal refinement of mounted casts before crown fabrication to decrease clinical time required to adjust occlusion.

STATEMENT OF PROBLEM: An inordinate amount of time is often required to adjust the occlusion of a newly fabricated crown. PURPOSE: This study determined whether the procedure of "cast adjustment" significantly decreases the time necessary to clinically adjust the occlusion of a newly fabricated crown. MATERIAL AND METHODS: Thirty-eight crowns were fabricated by a commercial dental laboratory for patients of senior dental students at the University of the Pacific School of Dentistry. After master casts were returned from the laboratory and then mounted on semiadjustable articulators by the students, the cases were divided randomly into 2 groups: (1) the control group, for which no further work was performed before fabrication of the restoration; and (2) the experimental group, in which casts were occlusally adjusted by a certified laboratory technician until there was at least 1 cusp tip to flat surface centric contact on each posterior tooth in maximum intercuspation position. After the crowns were delivered, the students filled out a survey. One question on the survey asked the student for the time required to adjust the occlusion on the crown. RESULTS: Of the 19 crowns in the control group, 6 crowns required more than 1 hour for occlusal adjustment. Of the 19 crowns in the experimental group, 1 crown required more than 1 hour for occlusal adjustment. CONCLUSION: Performing a "cast adjustment" before fabricating a single unit casting can significantly decrease the chance of a lengthy clinical occlusal adjustment.

Centric Relation↗
PubMed1999

Accelerated toxicity testing of casting alloys and reduction of intraoral release of elements.

STATEMENT OF PROBLEM: Short-term (72-168 hours) in vitro testing of dental casting alloys for cytotoxicity may not reflect in vivo biocompatibility. An accelerated test for evaluation of dental casting alloy cytotoxicity could help screen newly developed alloys more rapidly and accurately. PURPOSE: This study evaluated a method of accelerating alloy cytotoxicity by short-term conditioning of alloys. Cytotoxicity and mass release of these conditioned alloys were compared with alloys conditioned for 10 months or unconditioned alloys. The hypothesis was that a short-term conditioning procedure could be developed that would give cytotoxicity and mass release values similar to alloys exposed to a biologic solution for 10 months. MATERIAL AND METHODS: Dental casting alloys were conditioned in either saline, cell-culture medium, or a saline/bovine serum albumin (BSA) solution for 168 hours before standard in vitro cytotoxicity testing. Eight types of casting alloys with a range of nobilities (98% to 0%) were tested (n = 6). Controls were Teflon (Tf). Conditioned alloys were placed in direct contact with Balb/c fibroblasts for 72 hours, and cell viability was measured by succinic dehydrogenase activity (MTT method) relative to Tf controls. Elements released into the conditioning solutions were measured by atomic absorption spectroscopy. The cytotoxicities of conditioned alloys and total mass released were compared with unconditioned alloys (0 month) and alloys that were exposed to cell culture medium for 10 months. ANOVA and Tukey multiple comparison intervals (alpha =. 05) were used to compare mass released and cytotoxicity. RESULTS: Conditioning for 168 hours altered the cytotoxicity of the alloys. The saline/BSA conditioning solution reduced cytotoxicity of the alloys compared with unconditioned alloys, except for the Ni-Cr alloy. Other conditioning solutions were not as uniform in their effects, some increasing toxicity, others decreasing it. Overall, the saline/BSA solution was the most effective at changing alloy cytotoxicity from the unconditioned (0 month) toward the 10-month values. Mass loss during saline/BSA conditioning most closely approximated 10-month loss for most alloys. CONCLUSION: Conditioning of casting alloys appeared to be a useful method for predicting long-term cytotoxicity with a short-term in vitro test, but all conditioning solutions were not equivalent.

Animals↗
PubMed1999

Cytotoxicity of dental casting alloys pretreated with biologic solutions.

STATEMENT OF PROBLEM: Short-term (72-168 hours) in vitro tests are used to evaluate the cytotoxicity of dental casting alloys. The ability of these short-term tests to predict long-term in vivo cytotoxicity has been questioned. A procedure to accelerate the testing of casting alloys would be useful in predicting longer-term alloy cytotoxicity. PURPOSE: This study hypothesized that preconditioning casting alloys by soaking in a biologic liquid would change subsequent cytotoxicity by removing some elements. Preconditioning may be 1 method of accelerating short-term in vitro tests. MATERIAL AND METHODS: Dental casting alloys were exposed to either saline, cell culture medium, or a saline/bovine serum albumin (BSA) solution for 72 hours before standard in vitro cytotoxicity testing. Six types of alloys were tested (n = 6): 5 Au-Ag-Cu-Pd alloys (single phase) and 1 Ag-Pd-Cu alloy (multiple phase). Teflon (Tf) samples served as a control. After preconditioning, alloys were placed in direct contact with Balb/c fibroblasts for 72 hours, after which cell viability was measured by succinic dehydrogenase activity (MTT method) relative to Tf controls (100% = no toxicity). Elements released into the preconditioning solutions were measured by atomic absorption spectroscopy. Cytotoxicities of preconditioned alloys and amounts of elemental release were compared with unconditioned alloys. RESULTS: A preconditioning time of 72 hours was sufficient to change the cytotoxicity of the tested alloys. The alloys that were more cytotoxic initially became less cytotoxic after preconditioning. For all the alloys tested, except the Ag-Pd-Cu multiphase alloy, preconditioning with either the saline or the saline/BSA solution caused an increase in cellular activity, therefore the preconditioned alloys were less cytotoxic. The cell culture medium preconditioning solution had a variable effect, causing increased or decreased cellular activity depending on the alloy treated. CONCLUSION: Preconditioning of casting alloys decreased subsequent cytotoxicity. However, not all preconditioning solutions are equivalent. A preconditioning strategy may be useful in accelerating the short-term cytotoxicity test toward a longer-term result.

3T3 Cells↗
PubMed2003

Grindability of cast Ti-Cu alloys.

OBJECTIVE: The purpose of the present study was to evaluate the grindability of a series of cast Ti-Cu alloys in order to develop a titanium alloy with better grindability than commercially pure titanium (CP Ti), which is considered to be one of the most difficult metals to machine. METHODS: Experimental Ti-Cu alloys (0.5, 1.0, 2.0, 5.0, and 10.0 mass% Cu) were made in an argon-arc melting furnace. Each alloy was cast into a magnesia mold using a centrifugal casting machine. Cast alloy slabs (3.5 mm x 8.5 mm x 30.5 mm), from which the hardened surface layer (250 microm) was removed, were ground using a SiC abrasive wheel on an electric handpiece at four circumferential speeds (500, 750, 1000, or 1250 m/min) at 0.98 N (100 gf). Grindability was evaluated by measuring the amount of metal volume removed after grinding for 1min. Data were compared to those for CP Ti and Ti-6Al-4V. RESULTS: For all speeds, Ti-10% Cu alloy exhibited the highest grindability. For the Ti-Cu alloys with a Cu content of 2% or less, the highest grindability corresponded to an intermediate speed. It was observed that the grindability increased with an increase in the Cu concentration compared to CP Ti, particularly for the 5 or 10% Cu alloys at a circumferential speed of 1000 m/min or above. SIGNIFICANCE: By alloying with copper, the cast titanium exhibited better grindability at high speed. The continuous precipitation of Ti(2)Cu among the alpha-matrix grains made this material less ductile and facilitated more effective grinding because small broken segments more readily formed.

Carbon Compounds, Inorganic↗
PubMed2001

Porcelain adherence to dental cast CP titanium: effects of surface modifications.

OBJECTIVES: A reaction layer forms on cast titanium surfaces due to the reaction of the molten titanium with the investment material. Such a layer prevents strong adhesion between titanium and porcelain. This study characterized the effects of surface modifications on cast titanium surfaces and titanium-ceramic adhesion. METHODS: ASTM grade II CP titanium was cast into an MgO-based mold. Castings were devested by sandblasting with alumina particles, and subjected to surface modification by immersion in one of the following solutions: (1) 35% HNO3-5% HF at room temperature for 1min; (2) 50% NaOH-10% CuSO4 x 5H2O at 105 degreesC for 10min; (3) the NaOH-CuSO4 solution followed by the HNO3-HF solution; (4) 50% NaOH-10% NaSO4 at 105 degreesC for 10 min; (5) the NaOH-NaSO4 solution followed by the HNO3-HF solution; and (6) 50% NaOH solution at 105 degreesC for 10min. Surfaces only sandblasted with alumina were used as controls. Specimen surfaces were characterized by XRD and SEM/EDS, and hardness-depth profiles were determined. All specimens were sandblasted with 110 microm alumina particles before porcelain firing. An ultra-low-fusing porcelain (Vita Titankeramik) was fused on the titanium surfaces. The titanium-ceramic adhesion was characterized by a biaxial flexure test, and area fraction of adherent porcelain (AFAP) was determined by X-ray spectroscopy. RESULTS: EDS analyses revealed a substantial amount (13-17 wt%) of Al on the control, and specimens modified with Methods 2, 4, and 6. XRD revealed residual stress in the titanium surfaces and corundum on the control, and Methods 2, 4, and 6 specimens. A new Ti(Cu, Al)2 phase was identified on the titanium surfaces modified by immersion in 50% NaOH-10% CuSO4 x 5H2O aqueous solution. Reduced residual stress was observed on Method 1, 3, and 5 specimens. No corundum peaks were detected on these specimens. Compared to the control, significantly lower (P < 0.05) hardness values were found for Methods 1-3 and Method 5 specimens at 20 microm below the surfaces and for Method 1-5 specimens at 50 microm below the surfaces. Significantly higher (P < 0.05) AFAP values were found for surfaces modified with Methods 2-6 compared to the control and Method 1, and no significant differences were found among Methods 1-6, and between control and Method 1. SIGNIFICANCE: Based on the results from the present study, porcelain adherence to cast CP titanium can be improved by the caustic baths used in the study.

Dental Casting Investment↗
PubMed2003

Stump/socket pressure profiles of the pressure cast prosthetic socket.

OBJECTIVE: The aim was to evaluate stump/socket interface pressure in amputees wearing a socket developed by a pressure casting system.Design. Five unilateral transtibial amputees wore a pressure cast socket and walked at a self-selected speed. BACKGROUND: The socket produces equally distributed pressure at the stump/socket interface, deviating from the conventional belief that pressure varies in proportion to the pain threshold of different tissues in the stump. METHODS: The socket was fabricated while the subject placed his stump in a pressure chamber. Pressure was applied while he adopted a normal standing position. A specially built strain gauged type pressure transducer was used for measuring pressure distribution. Pressure and gait parameters were measured simultaneously while the subjects were standing and walking. RESULTS AND CONCLUSION: The pressure cast technique was able to provide comfortable fitting sockets. A hydrostatic pressure profile was not evident during standing or gait. Results also showed that no standard pressure profile for the pressure cast socket was observed. This was expected as no rectifications were done on the pressure cast socket. Pressure profiles at 10%, 25% and 50% of gait cycle did not correlate with the pressure profiles previously proposed. RELEVANCE: The hydrostatic theory is an attractive concept in socket design as it produces a stump/socket pressure profile that is evenly distributed. Furthermore, it is a method that is easily implemented, independent of a prosthetist's skill and experience and reduces manufacturing time. However, there is still controversy surrounding the efficacy of this hydrostatic theory.

Adult↗
PubMed1997

Dentists' opinions on aspects of cast titanium restorations.

OBJECTIVES: The purpose of this paper was to study dentists' opinions regarding aspects of the clinical use of cast titanium restorations. METHODS: Since 1988 more than 10,000 cast titanium units of crowns and fixed partial dentures have been produced by the only dental laboratory that produces cast titanium restorations in Norway. A questionnaire on the clinical behaviour of such restorations was mailed to all 72 dental practitioners who were recorded in the computer file of this laboratory. RESULTS AND CONCLUSION: In the opinion of the 64 dental practitioners who completed the questionnaire, cast titanium is a useful supplement to conventional casting alloys, particularly because of its favourable cost. It has a satisfactory clinical behaviour, although there may be some problems related to technical and aesthetic aspects.

Attitude of Health Personnel↗
PubMed2002

Comparative evaluation of casting retention using the ITI solid abutment with six cements.

OBJECTIVE: The purpose of this study was to test the retention of metal copings fabricated to fit on the one-groove, one flat-sided solid titanium abutment using six different cements. MATERIALS AND METHODS: Ten hollow screw 3.8 mm ITI implants were mounted in acrylic resin blocks. A solid titanium abutment was placed on each implant and torqued at 35 Ncm. Prefabricated burn-out caps were placed on the titanium abutment and wax loops added to the occlusal surface to allow for subsequent retention testing. All plastic caps were embedded in phosphate-bonded investment and cast with noble alloy. Castings were inspected for surface irregularities using a stereomicroscope at 10x magnification. The six cements were: 1) eugenol-free zinc oxide (Temp Bond NE); 2) zinc-oxide eugenol (IRM); 3) zinc phosphate (Hy-Bond); 4) resin-modified glass ionomer (Protec Cem); 5) zinc polycarboxylate (Durelon) and 6) 10-methacryloyloxydecyl dihydrogen phosphate resin (Panavia 21). After cementation, implant-abutment-casting assemblies were stored for 24 h in 100% humidity. Samples were subjected to a pull-out test using an Instron universal testing machine at a crosshead speed of 0.5 mm/min. The load required to de-cement each coping was recorded and mean values for each group calculated. Means and standard deviations of loads at failure were analyzed using ANOVA and a Tukey studentized test. Statistical significance was set at P < or = 0.05. RESULTS: The mean values (+/- SD) of loads in kilograms at failure (n = 10) for the various cements were as follows: Temp Bond 3.18 (+/- 1.1) (Tukey group D), IRM 9.25 (+/- 3.83) (Tukey group CD), HY-Bond 10.9 (+/- 6.52) (Tukey group C), Protec Cem 18.98 (+/- 6.23) (Tukey group B), Durelon 23.55 (+/- 4.29) (Tukey group B) and Panavia 21, 36.53 (+/- 8.1) (Tukey group A). Means with the same letter in the Tukey grouping are not significantly different. CONCLUSIONS: The retention values of castings cemented to ITI solid abutments have not been reported in the literature. Within the limitations of this in vitro study, the results do not suggest that one cement type is better than another, but they do provide a ranking order of the cements in their ability to retain the castings. This ranking is somehow different than that obtained when the same cements are used on natural teeth. The material and surface characteristics of the implant abutment are likely responsible for this difference. Cement retention values obtained from studies that use teeth as abutments may be misleading when used in cement-retained implant-supported crowns. It is at the clinician's discretion to use a certain type of cement, based on the situation at hand.

Analysis of Variance↗
PubMed2003

A preliminary report on a computer-assisted dental cast analysis system used for the prosthodontic treatment.

To accomplish computerized 3D morphological analyses of maxillary and mandibular casts with malocclusions on the same co-ordinate system, a new reference co-ordinate located on soft tissue has been proposed consisting of the top of maxillary bilateral tubercles and incisive papilla on the maxillary cast. To test the validity of this co-ordinate system, the angles of the occlusal plane in this system were examined on 10 subjects with normal occlusion. In addition, to analyse maxillary and mandibular casts on the same co-ordinate system, a bite block was made under the intercuspal position. The maxillary cast was measured by 3D measuring system, then, the bite block was placed on maxillary casts, and measured similarly. To examine the position reproducibility of this method, 3D co-ordinates of the apex of the buccal cusp of the mandibular pre-molar in five bite blocks were determined. The angles formed of the occlusal plane were 1.3 +/- 1.3 degrees and 0.2 +/- 1.1 degrees on the sagittal and frontal base plane, respectively. This co-ordinate system had enough stability to replace the occlusal plane. By the measurement of bite blocks, the co-ordinates of the mandibular cusp tips were determined within the deviation of 0.2 mm.

Dental Casting Technique↗
PubMed2002

Treatment of pressure ulcers by serial casting in patients with severe spasticity of cerebral origin.

OBJECTIVE: To assess the effectiveness of serial casting in the treatment of pressure ulcers caused by severe spasticity. DESIGN: Case series. SETTING: A clinic for the rehabilitation of persons with neurologic disorders. PATIENTS: Nine patients with 11 pressure ulcers resulting from severe cerebral spasticity, the ulcers being intractable to conventional management because of repeated friction and/or inaccessibility. INTERVENTION: Serial casting of the limb(s) with the pressure ulcer(s), with either fenestration or a cast arch providing access to the wound. MAIN OUTCOME MEASURES: Improved healing of pressure ulcers, as quantified with the National Pressure Ulcer Advisory Panel classification system. RESULTS: Within a mean of 4.6 weeks, 7 ulcers healed completely and 4 improved markedly. The casting caused no complications. Moreover, extension deficits improved markedly in all patients (105 degrees +/- 27 degrees to 17 degrees +/- 10 degrees ). CONCLUSION: Serial casting may be a valuable tool in the treatment of pressure ulcers at the extremities of patients with severe cerebral spasticity.

Adult↗
PubMed2002

The influence of tray type and other variables on the palatal depth of casts made from irreversible hydrocolloid impressions.

STATEMENT OF PROBLEM: There are conflicting data regarding the effect of various factors on the palatal depth of casts made from irreversible hydrocolloid impressions. PURPOSE: This study examined the influence of tray type, water temperature, pouring technique, and stone expansion on the palatal depth of casts. MATERIAL AND METHODS: Irreversible hydrocolloid impressions were made of a model under simulated oral conditions. Palatal depth was measured relative to a reference plane with a microscope. The reference planes were standardized by subjecting the data to three 2-dimensional mathematic rotations. A 2-factor analysis of variance (alpha=.05) was used to determine whether differences existed among tray types and among palatal locations. RESULTS: The palatal depth of the casts increased approximately 0.06 mm compared with the master model with all but 2 variables. Statistical testing revealed that increased depth was not attributable to water temperature (52 degrees F or 72 degrees F) or tray type (custom resin, perforated metal, metal rimlock, or rimlock with built-up palate). Custom resin tray impressions poured with a lower expansion stone and perforated tray impressions inverted onto a base made from the same mix of stone resulted in casts with palatal depths most similar to that of the master model (P<.001). CONCLUSIONS: Casts with palatal contours of comparable accuracy were obtained with the use of a stock metal or customized tray and the use of differing water temperatures to mix the impression material.

Acrylic Resins↗
PubMed2003

Dimensional changes of one-piece frameworks cast from titanium, base metal, or noble metal alloys and supported on telescopic crowns.

STATEMENT OF PROBLEM: The dimensional accuracy of 1-piece frameworks cast from commercially pure titanium and used to accommodate supporting telescopic crowns has not been demonstrated. PURPOSE: To compare dimensional changes incurred in frameworks cast from commercially pure titanium, a cobalt-chromium alloy, and a noble metal (gold) alloy. MATERIAL AND METHODS: This study was based on 2 different models, both prepared to receive telescopic crowns: 1 with 4 dies, designed to measure dimensional changes of the castings in the horizontal plane; and another with 2 dies, designed to measure dimensional changes in the vertical plane. As variables for the 2-die models, the palatal shape (16- and 20-mm radius) as well as the palatal depth (20-mm radius with the smallest palatal depth of 8 mm, 16-mm radius with flat palate and palatal depth of 10 mm, 16-mm radius with greatest palatal depth of 16 mm) were studied. Ten specimens each were fabricated from a commercially pure titanium, a cobalt-chromium alloy, and a gold alloy. All castings were fabricated under standardized conditions. All measurements were taken with a computer-controlled measuring microscope at the margins of the simulated telescopic crowns; these served to calculate the ideal midpoint from which the distances between the telescopic crowns were measured. The positional relation of the telescopic crowns was determined in horizontal and vertical directions. The measurements of the cast models were compared with measurements of the original model. The distances between the dies and the angles of the chosen telescopic crowns were calculated in fractions of millimeters and the angles were measured in degrees. The Kruskal-Wallis test and the Mann-Whitney U test were used for statistical analysis. The level of significance was alpha=5%. RESULTS: With the following exceptions, none of the 3 alloy types showed significantly different results. With the 4-die model, all 3 alloys showed significant variations from the original model for chosen lengths (P=.001). For those lengths, the dimensional accuracy of the noble metal alloy was approximately 99.9% of the length of the original; for the 2 other alloys, an average value of 99.4% was determined. With the 2-die models the calculated angle was significantly different from the original model for all alloys (P=.001 or.000), independent from the palatal vault and depth. Significant differences from the original model were also found for the distance between the 2 telescopic crowns with all alloys for the 2-die model with a 16-mm depth palatal vault and a 16-mm radius (P=.001,.006, or.009). CONCLUSIONS: Within the limitations of this study, the significant different dimensional changes both for the 4-die models and the 2-die models did not depend on the type of alloy. The 2-die models demonstrated significant dimensional changes resulting from the palatal geometry of the corresponding test models; the 4-die models demonstrated a tendency to contract toward the geometric center.

Chromium Alloys↗