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Evaluation of the fracture resistance of a wrought post compared with completely cast post and cores.

The intraradicular fracture of a post and core presents a difficult and often unrestorable situation. Attempts to prevent this problem involved the use of materials with increased physical properties. The use of a preformed wrought post with a core cast to it may provide a more fracture-resistant foundation. This investigation compared a commercially available noble alloy-wrought post that had a gold core cast to it with completely cast specimens from three different alloys. A standard pattern was designed to simulate a post and core that would be used in a tooth of limited length and canal space. Patterns were cast and fixed to custom holding devices. Each specimen was subjected to a shearing force until catastrophic failure in a universal testing machine. Significant differences were noted among the groups.

Analysis of Variance↗

A secondary lingual casting for removable partial dentures.

This article describes a technique for constructing a nickel chromium alloy lingual casting that reinforces a removable partial denture against heavy anterior occlusion. The metal can be cast into a thin secondary casting, and it is easily etched and bonded to the resin anterior teeth and associated base. This type of lingual casting has the potential to provide a simple and effective solution to the problem of repeated fracture or displacement of anterior teeth in many restorations.

Cementation↗

Clinical success of cast metal posts and cores.

The topic of posts for endodontically treated teeth has received considerable attention in the literature, but there is sparse in vivo research and certain information from in vitro investigations is contradictory. A retrospective study of 1273 endodontically treated teeth in the practices of nine dentists in general practice indicated an inordinately high failure rate with cast posts and cores compared with alternate systems of coronoradicular stabilization. However, a closer evaluation of the data in this study indicated that almost half of the cast posts were half the desired length or less. The indications for the cast post and core are discussed and the specific causes of failure are reviewed. Additional research is needed to compare the success rate of securely seated cast posts and cores with alternate methods of coronoradicular stabilization.

Dental Alloys↗

Effect of adhesive luting agents on the marginal seating of cast restorations.

This study determined the effect of new adhesive luting agents on the marginal seating of cast restorations. Standardized preparations were completed on freshly extracted premolars, impressions were made, and complete metal veneer crowns were cast with a base metal alloy. The castings were placed on their respective teeth and the extent of marginal opening was recorded. They were then assigned to a luting agent group: glass ionomer cement (GI), polycarboxylate cement (PC), microfilled BIS-GMA composite resin with NPG-GMA/PMDM dentinal bonding agent (GMA + NPG), microfilled BIS-GMA/phosphate ester composite resin (GMA/PE), or zinc phosphate cement (ZP). The castings were cemented and marginal openings remeasured. ANOVA revealed that the cement groups were similar before cementation (p 0.35) but were different after cementation (p < 0.0001). Tukey's multiple comparisons test identified statistically similar groups that were different from other groups and ranked them from lesser to greater marginal opening: (GI, ZP, PC) (GMA/PE, GMA + NPG).

Adhesives↗

Internal porosity of cast titanium removable partial dentures: influence of sprue direction and diameter on porosity in simplified circumferential clasps.

OBJECTIVE: The behavior of molten titanium in molds of complicated shape is still insufficiently understood; consequently, definite spruing criteria are not yet available for titanium RPD frameworks. This study investigated the influence of sprue design on porosity in pressure-cast titanium circumferential clasps. METHODS: The patterns of 90 circumferential clasps were sprued with three directions (0, 30 and 60 degrees , as measured between the sprue and the symmetry plane of the clasp assembly) and three sprue diameters (1.5, 2.0 and 2.5mm). CPTi was cast in a one-chamber pressure casting machine. Pore number and size were assessed on radiographs of the castings. Statistical analysis was done by two-way analysis of variance (ANOVA), followed by Fisher's PLSD post hoc test. RESULTS: The porosity in lingual arms increased significantly with increase of sprue diameter and sprue angle, while the porosity in minor connectors had an inversely proportional distribution. Very low porosity, uninfluenced by sprue design, was found in buccal arms. In conclusion, internal porosity in titanium circumferential clasp arms can be minimized through sprue design: the 0 degrees sprue direction produced the least porosity, while for the 30 and 60 degrees directions, 1.5mm diameter sprues produced lower porosity than 2.0 and 2.5mm diameter sprues. SIGNIFICANCE: In this study, the lowest porosity in titanium circumferential clasp arms was obtained with sprues attached perpendicularly to the minor connectors, regardless of sprue diameter. Conventional sprue directions produced significantly higher porosity in clasp lingual arms, the amount of porosity increasing with sprue diameter.

Analysis of Variance↗

Prediction of permanent deformation in cast clasps for denture prostheses using a validated nonlinear finite element model.

OBJECTIVES: Permanent deformation is one of the most common mechanical complications that affect denture clasps. This can lead to loss of retention and stability of the prosthesis. The purpose of this study was to apply and validate a nonlinear finite element model for permanent deformation prediction in cast denture clasps. Such a model can enhance the process of design optimization and contribute to minimizing the possibility of this problem. METHODS: Cast clasps made from Ti-6Al-7Nb, Co-Cr and Type IV gold alloys were loaded in three different directions (outside, inside and outside inclined 30 degrees ), and the resulting permanent deformation values were recorded. Nonlinear finite element analysis simulations based on the maximum distortion energy criterion for yielding, were conducted for clasp models that were reproduced according to the dimensions of each experimental specimen. Linear regression analysis for the results of the experiment and simulation was performed to verify the validity of the mathematical models. RESULTS: Deflections required to produce specific amounts of permanent deformation were in close agreement with those recorded experimentally. The R2 value for all bending tests was 0.985 and the linear regression equation expressed in micrometers was [DeflectionFEA=0.976 (DeflectionReal)+34]. SIGNIFICANCE: Permanent deformation behavior in the cast clasps with a relatively wide range of deflections (0-2 mm) can be predicted using the proposed model, which shall enhance the design optimization process of cast clasps for denture prostheses.

Dental Alloys↗

Closed manipulation and casting of distal radius fractures.

Closed reduction and cast treatment of distal radius fractures renders satisfactory results in fractures that are reducible and stable and do not re-displace in plaster in the first 2 weeks following reduction. Intra-articular and unstable fractures have a high risk for re-displacement in plaster and therefore represent a contraindication for cast treatment. A fracture that re-displaces in plaster despite perfect casting technique is most probably an unstable type that requires skeletal fixation. A fracture that re-displaces in a non-molded, loose, or over-padded cast because of insufficient technique is, however, in the author's view, the only clinical situation in which re-manipulation is worth the effort. The tolerable amount of residual deformity has been radiographically defined by Fourrier et al in an analysis of 64 malunions of the distal radius and correlated the functional impairment with the residual deformity of the distal radius. They concluded that the lower limits of deformity, at which symptoms are likely to be present, area radial deviation of 20-30 degrees, a sagittal tilt of 10-20 degrees, and a radial shortening of 0-2 mm. In addition, experimental evidence suggests that a sagittal tilt of 20-30 degrees should be viewed as a pre-arthrotic condition. Although these figures are useful for decision making, acceptance of deformity when treating fractures conservatively varies individually according to the age, osteoporosis, and functional demands of the patient. Anatomic restoration, however, should remain the primary goal of conservative management.

Casts, Surgical↗

Shear bond strengths of polymethyl methacrylate to cast titanium and cobalt-chromium frameworks using five metal primers.

STATEMENT OF PROBLEM: Poor chemical bonding of a denture base resin to cast titanium frameworks often introduces adhesive failure and increases microleakage. PURPOSE: This study examined the shear bond strengths of a denture base resin to cast pure titanium, Ti-6Al-4V, and a cobalt-chromium alloy using various adhesive primers. MATERIAL AND METHODS: Disks (6.0 mm diameter, 2.5 mm thick) were cast of the 3 alloys. The disk surfaces were grit-blasted with 50 microm alumina and treated with 5 different metal primers (Metal Primer II ¿MP]; Cesead Opaque primer ¿OP]; Meta Base ¿MB]; experimental primer ¿EP]; Siloc bonding system ¿SI]). A denture base resin (Palapress Vario) was then applied on the disks with hole-punched sticky tape (bonding area of 5.0 mm) and a Teflon (PTFE, New Age Industries Inc, Willow Grove, Pa.) ring (6.0 mm diameter x 2.0 mm thick). Specimens without primer were also prepared as controls. All specimens were immersed in 37 degrees C water and thermocycled up to 2,000 cycles. Shear bond strength values were determined at a crosshead speed of 0.5 mm/min. Data were statistically analyzed using 3-way ANOVA, followed by 1-way ANOVA and the Scheffé multiple range test. RESULTS: Primers significantly (P <.05) improved shear bond strengths of denture base resin to all metals, among which no significant differences were found. Specimens primed with OP, MP, and EP showed higher bond strengths than did those primed with MB. After thermocycling, the bond strengths of MB and SI decreased substantially; MB showed the least durability (22.8% to 35.5% decrease) among the primers. CONCLUSION: The application of 5 primers significantly improved the shear bond strengths of a denture base resin to cast CP titanium, Ti-6Al-4V, and Co-Cr alloy. OP and MP primers exhibited greater bond strength and durability than did MB and SI.

Analysis of Variance↗

Wettability of elastomeric impression materials and voids in gypsum casts.

Numerous factors are involved in making an accurate void-free dental artificial stone cast or die. The relationship of the wettability of an elastomeric impression material and its interaction with the gypsum slurry is an important factor. This study examined the relative "pourability" of several impression materials by counting the number of resultant voids in artificial stone casts containing 48 point angles. Those elastomers that exhibited the lowest contact angle with water produced artificial stone casts with the fewest voids. Surfactants applied to the impression material significantly reduced the number of voids in artificial stone casts, as did modified elastomers designated by the manufacturer as hydrophilic.

Calcium Sulfate↗

Mechanical properties of laser-welded cast and wrought titanium.

This study evaluated the mechanical properties of laser-welded cast and wrought titanium base and compared them with those of a brazed type IV casting gold alloy. Ultimate tensile strength, 0.2% yield strength, and percent elongation were recorded for joined and unjoined bars of the previously mentioned materials. Sections of titanium bars were laser-welded, and gold alloy bars were brazed. Both joining methods significantly reduced the ductility of the material. The strength of the cast gold alloy was superior to that of titanium. However, the strength of the laser-welded titanium equaled that of the brazed gold alloy, which suggests that dental restorations made of cast and wrought titanium would satisfy ordinary clinical requirements.

Analysis of Variance↗

1998 Judson C. Hickey Scientific Writing Award. Use of a flexible cast for the indirect fabrication of provisional restorations.

Efficient fabrication of a clinically acceptable provisional restoration for a fixed partial denture is an important part of treatment success. Fabrication of provisional restorations that uses the indirect technique produces accurate fitting provisional restorations without the chemical and thermal irritation associated with direct fabrication. With a typodont model, an indirect method is presented that uses an elastic cast for fabrication of multiple unit provisional restorations for fixed partial dentures. The cast is available within 6 minutes of impression making, can be trimmed with a sharp scalpel, and provides flexibility that allows easy separation of the acrylic provisional from the cast. The cast can also be used to evaluate the clinical acceptability of the preparations before impression making. This method has also been successfully used for the fabrication of acrylic provisional restorations for onlay preparations.

Acrylic Resins↗

Low molecular weight heparin (Innohep) as thromboprophylaxis in outpatients with a plaster cast: a venografic controlled study.

INTRODUCTION: The aim of this study was to investigate the incidence of deep vein thrombosis (DVT) in patients immobilized in plaster cast and the possible efficacy of prophylaxis with low molecular weight heparin (LMWH). MATERIAL AND METHODS: The study was a randomized, assessor-blinded, open multicenter (three centers) study. All patients over 18 years of age with planned plaster cast on a lower extremity of at least 3 weeks were eligible for participation. Written informed consent was obtained from 300 patients and they were randomized to either 3.500 IU anti-Xa of tinzaparin (Innohep) subcutaneously once daily or no prophylaxis. On the day the cast was removed, ascending unilateral venography was performed. Two experienced radiologists, unaware of treatment, assessed the pictures independently. The radiologist had to obtain consensus as to whether DVT was present or not. RESULTS: 300 patients were included (148 in the treatment group and 152 in the control group). Ninety-five were subsequently withdrawn. DVT was diagnosed in 10/99 patients in the treatment group and in 18/106 patients in the control group. This difference is not significant (P=.15, chi(2) test) and the odds ratio was 0.55 (95% confidence interval=0.34-1.26). CONCLUSION: DVT in legs after plaster casting is a big problem, with an incidence of almost 20%. An effective prophylactic regime is required. Once-daily dose of 3.500 IU anti-Xa of tinzaparin was not sufficient.

Adolescent↗

Disinfection procedures: their effect on the dimensional accuracy and surface quality of irreversible hydrocolloid impression materials and gypsum casts.

OBJECTIVES: This study primarily investigated the effect of disinfection procedures (Perform and sodium hypochlorite) on the dimensional accuracy and surface quality of four irreversible hydrocolloid impression materials and the resultant gypsum casts. The antibacterial efficacy of the procedures was also studied. METHODS: Dimensional accuracy was determined from the mean percentage deviation of six measurements taken from casts made from disinfected impressions compared with corresponding measurements from the master model and controls. Statistical analysis of data was determined by analysis of variance. Surface quality was determined using a stainless steel test block in accordance with ISO 1563. RESULTS: The dimensional accuracy of the impression materials tested were of a comparable standard following disinfection. The surface quality of casts taken from Blueprint Cremix impressions were unaffected by the disinfection procedures. The remaining impression materials studied showed greater surface deterioration on casts following disinfection with sodium hypochlorite than immersion in Perform. All disinfection procedures selected proved appropriate for antibacterial purposes. SIGNIFICANCE: Individual analysis of impression materials is required to determine their suitability to a given disinfection protocol.

Alginates↗

Variability of the geometry of the human common carotid artery. A vessel cast study of 31 specimens.

The carotid artery is of special interest both for the pathologist because of its frequent depositions and for the fluid mechanic because of its complex flow properties. However, current knowledge of its geometry is insufficient. Therefore, a vessel cast study was undertaken and a method to fabricate vessel casts was developed. At post mortem the arteries are excised and filled with a resin at the proper transmural pressure. Thirty-one vessel casts of the carotid artery were performed and the following selected geometric parameters of these vessel casts were measured: the diameters of the main branches of carotid bifurcation (common, internal and external arteries) and the angles between internal, external and common carotid arteries. The geometric parameters vary considerably and may contribute to a corresponding variability in local hemodynamics.

Adult↗

Failure of cast immobilization for thumb ulnar collateral ligament avulsion fractures.

To determine if small avulsion fractures of the thumb ulnar collateral ligament (UCL) with minimal (< or = 2.0 mm) displacement can successfully be treated by cast immobilization, the authors reviewed 9 patients with minimally displaced fractures initially treated by casting. Despite immobilization within an average of 2 days of the initial injury (range, 0-6 days), a minimum of 6 weeks of immobilization in a cast, and adequate rehabilitation, all 9 patients had persistent thumb pain, especially with activities requiring strong pinch. After undergoing open reduction and internal fixation, the patients had relief of thumb pain and pinch strength improved from 36% of the contralateral side to 89% (p < .01). Grip strength increased from 77% to 93% (p < .05), but the ranges of motion of the thumb metacarpophalangeal and interphalangeal joints were not significantly altered. Minimally displaced UCL avulsion fractures frequently have significant rotation that prevents successful fracture healing even with prompt cast immobilization.

Adolescent↗

Functional limitation immediately after cast immobilization and closed reduction of distal radius fractures: preliminary report.

The majority of research on distal radius fractures consists of retrospective, descriptive studies of patients with unstable fractures requiring fixation. The purpose of this investigation was to report on impairments in flexibility, grip strength, and motor control and on the presence of swelling and atrophy immediately after cast immobilization of closed reductions of simple distal radius fractures. Sixteen adult subjects from Kaiser Permanente Medical Center, San Francisco, entered the study, and 13 completed it. At the initial evaluation, upper extremity ranges of motion, grip strength, forearm circumferences, two-point discrimination, and motor reaction times were measured on the uninvolved side. The same measurements were taken on the affected side within 48 hours after cast removal. All but one subject worked throughout the casting period. There were significant postcasting impairments in forearm rotation (40% deficit in pronation and supination); wrist flexion, extension, and radial and ulnar deviation (50% reduction in all motions); grip strength (-32 kg, or approximately 24% of the strength of the unaffected side); and forearm circumference (-1.1 cm) and wrist circumference (+1.5 cm). Patients complained of awkwardness of the involved hand. These measured impairments immediately after immobilization of simple radius fractures were greater than the reported impairments in patients after reduction of radius fractures with fixation 6 to 27 months after injury. To prevent long-term disability and recover flexibility, strength, and function, patients with simple distal radius fractures should be referred to a hand, occupational, or physical therapist for evaluation, education, and treatment after immobilization. Longitudinal studies are needed to quantify long-term functional recovery with regard to the type of fracture and the degree of impairment measured immediately after casting.

Adult↗

Adhesive bonding of super-elastic titanium-nickel alloy castings with a phosphate metal conditioner and an acrylic adhesive.

The purpose of the current study was to evaluate the bonding characteristics of super-elastic titanium-nickel (Ti-Ni) alloy castings. Disk specimens were cast from a Ti-Ni alloy (Ti-50.85Ni mol%) using an arc centrifugal casting machine. High-purity titanium and nickel specimens were also prepared as experimental references. The specimens were air-abraded with alumina, and bonded with an adhesive resin (Super-Bond C & B). A metal conditioner containing a phosphate monomer (Cesead II Opaque Primer) was also used for priming the specimens. Post-thermocycling average bond strengths (MPa) of the primed groups were 41.5 for Ti-Ni, 30.4 for Ti and 19.5 for Ni, whereas those of the unprimed groups were 21.6 for Ti, 19.3 for Ti-Ni and 9.3 for Ni. Application of the phosphate conditioner elevated the bond strengths of all alloy/metals (P < 0.05). X-ray fluorescence analysis revealed that nickel was attached to the debonded resin surface of the resin-to-nickel bonded specimen, indicating that corrosion of high-purity nickel occurred at the resin-nickel interface. Durable bonding to super-elastic Ti-Ni alloy castings can be achieved with a combination of a phosphate metal conditioner and a tri-n-butylborane-initiated adhesive resin.

Adhesives↗

Geometry of the human common carotid artery. A vessel cast study of 86 specimens.

The carotid artery is of special interest for the pathologist because of its frequent depositions, and for the fluidmechanician because of its complex flow properties. However, there is a distinct lack in current knowledge of its geometry. Therefore, a vessel cast study was undertaken. At post mortem, the arteries are excised and filled with a special resin at the proper transmural pressure. Eighty-six vessel casts of the carotid artery were performed, and some etiological factors of atherosclerosis, such as age, sex and disease, were collected. The following selected geometric parameters of these vessel casts were measured in this study: the diameters of the main branches of carotid bifurcation (common, internal and external arteries), and the angles between internal, external and common carotid arteries. The averaged geometric parameters and their variability over 86 vessel casts of the carotid artery were investigated. Furthermore, the relationship between these measured parameters and the etiological factors age, sex and disease was analyzed. The geometric parameters varied considerably, presumably contributing to a corresponding variability in the local hemodynamic and distribution of the atherosclerotic lesions.

Aged↗