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PubMed1996

Comparison of the in vitro fatigue resistance of an acrylic resin removable partial denture reinforced with continuous glass fibers or metal wires.

PURPOSE: The fatigue resistance of heat-polymerized acrylic resin test specimens reinforced with continuous glass fibers or metal wire was investigated. MATERIALS AND METHODS: Test specimens in the shape of maxillary removable partial dentures were reinforced with one of the following: (1) circular steel wire (cross-sectional diameter, 1.0 mm); (2) semicircular steel wire (cross-sectional diameter, 1.0 x 2.0 mm); or (3) continuous unidirectional E-glass fibers. Ten specimens were fabricated for each test group. The specimens were tested by a constant force flexural fatigue test at a force of 180 N while immersed in 37 degrees C water. The number of loading cycles required to generate a fatigue fracture and the position of the fracture were measured. RESULTS: Results showed that the test specimens, which were either unreinforced or reinforced with metal wires, fractured after 13,197 to 39,237 loading cycles. For the glass fiber-reinforced test specimens, the fracture did not coincide with the region of the strengthener but with the opposite side of the test specimen after 1,239,298 loading cycles. The position of the fracture showed a statistically significant variation between the test groups (P < .001). CONCLUSIONS: This study suggests that the fatigue resistance of acrylic resin removable partial dentures reinforced with glass fibers are superior to those removable partial dentures reinforced with conventional metal wire.

Analysis of Variance↗
PubMedDate not supplied

Fracture resistance of fiber-reinforced PMMA interim fixed partial dentures.

PURPOSE: To compare different fiber reinforcements on fracture toughness of interim polymethyl methacrylate materials and then use the best combination to determine the optimal position for fiber placement in an interim 3-unit fixed partial denture (FPD). MATERIALS AND METHODS: In the first stage of the study, five groups of notched fracture toughness specimens were fabricated and loaded to failure (Instron): (1) unreinforced (control); (2) reinforced with pre-impregnated silanized E-glass fibers (Fibrestick); (3) cold plasma-treated woven polyethylene fibers (Ribbond triaxial); (4) pre-impregnated silanized plasma-treated woven polyethylene fibers (Construct); and (5) 1.0-mm-diameter stainless steel wire. In the second stage, the optimal position (occlusal, middle, or cervical third of pontic) for reinforcement with glass fibers (regimen 2) was tested by loading a 3-unit FPD to failure. All groups were compared with analysis of variance (alpha < 0.05). RESULTS: The fracture toughness (in MPam(1/2)) for each reinforced group (Fibrestick 2.74 +/- 0.12, Construct fibers 2.59 +/- 0.28, Ribbond triaxial 2.13 +/- 0.20, and orthodontic wire 1.66 +/- 0.09) was statistically greater (p< 0.05) than for the unreinforced group (control = 1.25 +/- 0.006). Fracture loads for FPDs were greatest when the fiber reinforcements were placed in the cervical third (cervical = 1165 N). CONCLUSIONS: The use of fiber and, to a lesser extent, orthodontic wire is an effective method to reinforce interim restoration resins.

Analysis of Variance↗
PubMed2005

Structural resistance in immature teeth using root reinforcements in vitro.

The purpose of this study was to evaluate in vitro the efficacy of root reinforcements by light-cured composite resin or zirconium fiber post in simulated immature non-vital teeth. Fifty-six bovine incisors teeth were used for this study. The crown of each tooth was removed in the medium third to obtain a standard length of 30 mm. The specimens were divided into four groups (n = 14): G1) the root canals were instrumented and enlarged to simulate immature non-vital teeth and were reinforced with a light-cured composite resin using a translucent curing post (Luminex system); (G2) the specimens were instrumented, enlarged and they received root reinforcement with zirconium fiber post; G3 (positive control): they received similar treatment to the G1 and G2 groups, but did not receive root reinforcement; G4 (negative control): the roots were not weakened and did not receive reinforcement. Every tooth was submitted to compressive force using an Instron testing machine with an angle of 45 degrees at a speed of 1 mm min(-1) until the fracture. The results showed a markedly increased resistance to fracture in the G1 and G2 (122.38 and 122.08 kg f, respectively). Among the results of G1 and G2 there was not any significant difference (P > 0.05) but they were significantly different from the control groups (P < 0.05). The conclusion is that the use of root reinforcements with zirconium fiber post or composite resin can increase significantly the structural resistance of the weakened teeth, decreasing the risk of the fracture.

Animals↗
PubMed1999

Ceramic whisker reinforcement of dental resin composites.

Resin composites currently available are not suitable for use as large stress-bearing posterior restorations involving cusps due to their tendencies toward excessive fracture and wear. The glass fillers in composites provide only limited reinforcement because of the brittleness and low strength of glass. The aim of the present study was to reinforce dental resins with ceramic single-crystalline whiskers of elongated shapes that possess extremely high strength. A novel method was developed that consisted of fusing silicate glass particles onto the surfaces of individual whiskers for a two-fold benefit: (1) to facilitate silanization regardless of whisker composition; and (2) to enhance whisker retention in the matrix by providing rougher whisker surfaces. Silicon nitride whiskers, with an average diameter of 0.4 microm and length of 5 microm, were coated by the fusion of silica particles 0.04 microm in size to the whisker surface at temperatures ranging from 650 degrees C to 1000 degrees C. The coated whiskers were silanized and manually blended with resins by spatulation. Flexural, fracture toughness, and indentation tests were carried out for evaluation of the properties of the whisker-reinforced composites in comparison with conventional composites. A two-fold increase in strength and toughness was achieved in the whisker-reinforced composite, together with a substantially enhanced resistance to contact damage and microcracking. The highest flexural strength (195+/-8 MPa) and fracture toughness (2.1+/-0.3 MPa x m(1/2)) occurred in a composite reinforced with a whisker-silica mixture at whisker:silica mass ratio of 2:1 fused at 800 degrees C. To conclude, the strength, toughness, and contact damage resistance of dental resin composites can be substantially improved by reinforcement with fillers of ceramic whiskers fused with silica glass particles.

Ceramics↗
PubMedDate not supplied

Foam-reinforced elderly human tibia approximates young human tibia better than porcine tibia: a study of the structural properties of three soft tissue fixation devices.

BACKGROUND: Because there is an insufficient supply of young human knees, an alternative is needed for evaluating anterior cruciate ligament reconstructions. The authors determined whether an elderly human tibia reinforced with foam is a better substitute for a young human tibia than a porcine tibia in this study of the tibialfixation of a soft tissue anterior cruciate ligament graft using 3 devices. HYPOTHESIS: A foam-reinforced elderly human tibia more closely approximates the performance of a young human tibia than porcine tibia. STUDY DESIGN: Biomechanical study. METHODS: Failure mode, stiffness, yield, and slippage were determined for a double-looped tendon graft fixed with either an interference screw, WasherLoc, or tandem washers in young human tibiae, foam-reinforced tibiae from elderly humans, and porcine tibiae. RESULTS: The stiffness and yield of interference screw and WasherLoc fixation in foam-reinforced tibiae more closely approximate those in young human tibiae than in porcine tibiae. Slippage of all combinations of tibiae and fixation devices was similar CONCLUSIONS: A foam-reinforced human tibia more closely approximates the performance of a young human tibia than that of porcine tibia in this study. CLINICAL RELEVANCE: Fixation devices should be tested in foam-reinforced tibiae from elderly humans rather than tibiae from large farm animals when the supply of young human knees is insufficient.

Adolescent↗
PubMedDate not supplied

Increased burst pressure in gastrointestinal staple-lines using reinforcement with a bioprosthetic material.

BACKGROUND: Leakage at an anastomosis is a major and often catastrophic complication of gastrointestinal (GI) surgery. Staple-line reinforcement with one of the several materials commercially available has been utilized to reduce the incidence of this complication. The bioprosthetic material, small intestinal submucosa (SIS, Surgisis((R)); Cook, Inc., Bloomington, IN) has found widespread applications in surgery. However, its ability to improve the durability of staple-lines in GI surgery in terms of burst pressure has not been documented. We hypothesized that SIS reinforcement of staple-lines in healthy living GI tissue would increase durability, as determined by leak rates at increased intraluminal pressures, compared to unreinforced staple-lines. METHODS: Two healthy Yorkshire-Cross pigs were subjected to midline laparotomy and underwent small intestinal division (n=28) with GIA stapling devices. Half of the staple-lines were reinforced with SIS. The staple-lines were then exposed to increased intraluminal pressures by means of a constant-rate dye solution infusion, until staple-lines exhibited visible leakage of the dye solution. The intraluminal pressure was recorded at the time of visible leakage. RESULTS: Staple-lines reinforced with SIS had significantly better durability as determined by analysis of variance and Kaplan-Meier survival calculations, with respect to leak rate as a function of intraluminal pressure (P<0.003). The mean burst pressure of the unreinforced staple-lines was 53 mmHg, while those staple-lines reinforced with SIS had a mean burst pressure of 83 mmHg. CONCLUSION: Reinforcement of stapled GI anastomoses with SIS significantly increases anastomotic burst pressure. These findings suggest a role for this material in GI surgery.

Anastomosis, Roux-en-Y↗
PubMed1973

Effects of reinforcement on children's academic behavior as a function of self-determined and externally imposed contingencies.

This experiment was designed to compare the effects of contingent reinforcement under conditions of self-determined and externally imposed performance standards. A major purpose was to examine the maintenance of self-imposed performance standards over time. Children in one contingent reinforcement condition self-determined their academic performance standards. The same performance standards were externally imposed upon children in a second contingent reinforcement condition who were yoked to subjects in the first condition. Children in a no-reinforcement control condition performed in the absence of external reward. Behavioral productivity of the self-determination condition was greater than that of the no-reinforcement condition. Further, no attenuation of the efficacy of contingent reinforcement occurred when performance standards were self-determined rather than externally imposed. Over six sessions, children became progressively more lenient in their self-imposed performance demands in the absence of social surveillance.

Journal Article↗
PubMed1974

Sociometric and disruptive behavior as a function of four types of token reinforcement programs.

Children in a first-grade classroom were divided into four groups. Baseline measures of disruptive classroom behavior were taken on a well-behaved and disruptive child in each group. Following baseline, four types of token economies were simultaneously introduced and rotated every 10 days within a Latin Square design. The token economies were: (1) individual reinforcement determined by individual performance; (2) group reinforcement determined by the behavior of the most disruptive child; (3) group reinforcement determined by the behavior of the least disruptive child; (4) group reinforcement determined by the behavior of a randomly chosen child. The token economies were compared on their effectiveness in changing target behavior, preference by the targets, ease of use, and cost. Additionally, sociometric responses were taken on questions of responsibility, friendship, and funniness. Results showed a significant decrease of inappropriate behavior for the disruptive children and no difference between the effectiveness of the four types of token economies in producing behavior change. However, there were other differences that indicated that the system in which group reinforcement was determined by a randomly selected child would be desirable for most teachers. Results also showed changes in the sociometric status of the disruptive children. As predicted, disruptive children were rated as more responsible when they were in the group reinforcement determined by the most disruptive child in the group token economy. Using behavior modification techniques indirectly to change sociometric status is suggested as offering a new potential technique for behavior change agents.

Behavior Therapy↗
PubMedDate not supplied

Self-reinforcement.

Self-reinforcement in operant situations generally refers to those arrangements in which the subject delivers to himself a consequence, contingent on his behavior. However, it is noted that the definition of all other types of reinforcement make its delivery contingent on the subject's behavior. What is actually at issue is the agent who defines whether or not the response required for reinforcement has been met. In self-reinforcement, the subject himself defines this. In the laboratory, this requirement is machine-defined; in school examinations, it is teacher-defined; and in many clinical self-control situations, it is also independently defined. A reinforcement contingency presupposes such independence, absent in self-reinforcement. Implications for research and practice are discussed and alternative formulations are offered.

Journal Article↗
PubMed1977

Effects of a token reinforcement system on journal reshelving.

A token reinforcement program involving two levels of token value and backup reinforcers to increase journal reshelving behavior in a large university library was experimentally evaluated. Results showed that instructions (in which signs asked users to reshelve journals) had no impact. By contrast, token reinforcement contingent on reshelving behavior led to a marked increase in journals reshelved. A return to instructions-only conditions, when data were corrected for library usage, showed an increase in unreshelved journals over the token reinforcement period, though the increase was not to baseline levels. For the next 11 months, library staff maintained a modified token program. Follow-up data collected after that interval showed that number of unreshelved journals remained markedly lower than levels at baseline and the first instructions-only period, though they were slightly higher than at the token reinforcement period. Token reinforcement of the variety employed in this study constitutes an efficient, economical means of changing the behavior of library users who fail to reshelve books and journals.

Journal Article↗
PubMed1995

An analysis of the reinforcing properties of hand mouthing.

Hand mouthing often has been described as a stereotypic response that is maintained by nonsocial (automatic) reinforcement; however, data supporting this conclusion can be found in relatively few studies. This series of studies presents an experimental analysis of conditions associated with the maintenance of hand mouthing. In Experiment 1, a functional analysis was conducted for 12 individuals who engaged in chronic hand mouthing, to determine whether the behavior is usually maintained independent of social contingencies. Results obtained for 10 subjects were consistent with an automatic reinforcement hypothesis; the remaining 2 subjects' hand mouthing was maintained by social-positive reinforcement. Based on these results, Experiment 2 was designed to identify the specific reinforcing properties of hand mouthing. Each of 4 subjects was provided with a toy that substituted for hand mouthing, and preference for a specific topography of toy manipulation (hand-toy contact or mouth-toy contact) was measured. Results indicated that hand stimulation was the predominant reinforcer for all subjects. Experiment 3 provided an extension of Experiment 2 in that the same responses were measured across a variety of toys presented to each of 5 subjects. Results again indicated that hand stimulation was the predominant reinforcer for all subjects. Implications of these results are discussed with relevance to treatment.

Adult↗
PubMed1962

Nonconsumption of the reinforcer under drug action.

Cats were trained to respond on a multiple discriminative schedule, with milk as reinforcement. Two subjects did not immediately consume the reinforcer when they were injected with 6 mg of methylphenidate before the experiment. This observation could be repeated in one of the subjects under various conditions of reinforcement and various doses of the drug. Control experiments showed that under normal conditions the same cats never ignored the reinforcer. The modification induced by the drug in the relationship between behavior and the reinforcement is discussed in its bearing on the notion of reinforcer.

Journal Article↗
PubMed1967

Reinforcement of least-frequent sequences of choices.

When a pigeon's choices between two keys are probabilistically reinforced, as in discrete trial probability learning procedures and in concurrent variable-interval schedules, the bird tends to maximize, or to choose the alternative with the higher probability of reinforcement. In concurrent variable-interval schedules, steady-state matching, which is an approximate equality between the relative frequency of a response and the relative frequency of reinforcement of that response, has previously been obtained only as a consequence of maximizing. In the present experiment, maximizing was impossible. A choice of one of two keys was reinforced only if it formed, together with the three preceding choices, the sequence of four successive choices that had occurred least often. This sequence was determined by a Bernoulli-trials process with parameter p. Each of three pigeons matched when p was (1/2) or (1/4). Therefore, steady-state matching by individual birds is not always a consequence of maximizing. Choice probability varied between successive reinforcements, and sequential statistics revealed dependencies which were adequately described by a Bernoulli-trials process with p depending on the time since the preceding reinforcement.

Journal Article↗
PubMed1968

Differential reinforcement and stimulus control of not responding.

Pigeons were trained to respond with equal variable-interval reinforcement in the presence of a white key and also a white key with a vertical line. They were then trained not to respond to the vertical line by extinguishing the response or by reinforcing its non-occurrence at various frequencies. During training, the rate of key-pecking in the presence of the white key, maintained by a constant variable-interval schedule of reinforcement, depended on the frequency of reinforcement in the presence of the line. When lines of different orientations were presented in a generalization test, birds trained with extinction responded more to other orientations than to the vertical line, whereas those trained with high frequencies of reinforcement for not responding tended to respond equally at all line orientations. Intermediate frequencies of reinforcement gave mixed results.

Journal Article↗
PubMed1971

Matching to relative reinforcement frequency in multiple schedules with a short component duration.

Three pigeons performed on two-component multiple variable-interval variable-interval schedules of reinforcement. There were two independent variables: component duration and the relative frequency of reinforcement in a component. The component duration, which was always the same in both components, was varied over experimental conditions from 2 to 180 sec. Over these conditions, the relative frequency of reinforcement in a component was either 0.2 or 0.8 (+/-0.03). As the component duration was shortened, the relative frequency of responding in a component approached a value equal to the relative frequency of reinforcement in that component. When the relative frequency of reinforcement was varied over conditions in which the component duration was fixed at 5 sec, the relative frequency of responding in a component closely approximated the relative frequency of reinforcement in that component. That is, the familiar matching relationship, obtained previously only with concurrent schedules, was obtained in multiple schedules with a short component duration.

Journal Article↗
PubMed1971

Second-order schedules and the problem of conditioned reinforcement.

Thirteen pigeons were exposed to a variety of second-order schedules in which responding under a component schedule was reinforced according to a schedule of reinforcement. Under different conditions, completion of each component resulted in either (1) the brief presentation of a stimulus also present during reinforcement (pairing operation), (2) the brief presentation of a stimulus not present during reinforcement (nonpairing operation), or (3) no brief stimulus presentation (tandem). Brief-stimulus presentations engendered a pattern of responding within components similar to that engendered by food. Patterning was observed when fixed-interval and fixed-ratio components were maintained under fixed- and variable-ratio and fixed- and variable-interval schedules. There were no apparent differences in performance under pairing and nonpairing conditions in any study. The properties of the stimuli presented in brief-stimulus operations produced different effects on response patterning. In one study, similar effects on performance were found whether brief-stimulus presentations were response-produced or delivered independently of responding. Response patterning did not occur when the component schedule under which a nonpaired stimulus was produced occurred independently of the food schedule. The results suggest a reevaluation of the role of conditioned reinforcement in second-order schedule performance. The similarity of behavior under pairing and nonpairing operations is consistent with two hypotheses: (1) the major effect is due to the discriminative properties of the brief stimulus; (2) the scheduling operation under which the paired or nonpaired stimulus is presented can establish it as a reinforcer.

Journal Article↗
PubMed1971

The reinforcement of four interresponse times in a two-alternative situation.

Pigeons pecked for food in a two-key procedure. A concurrent variable-interval variable-interval schedule of reinforcement for two classes of interresponse times was arranged on each key. A visual stimulus set the occasion for potential reinforcement of the four operant classes: shorter and longer interresponse times on left and right keys. In Exp. I, the relative frequency of respones on a key equalled the relative frequency of reinforcement on that key. In Exp. II, the relative frequency of an interresponse time equalled the relative reciprocal of its length. In Exp. III, the relative frequency of an interresponse time was a monotonically increasing function of its relative frequency of reinforcement. These functions relating the relative frequency of an interresponse time to its relative length and to its relative frequency of reinforcement were the same as if there had been no second key. Also, the distribution of responses between keys was independent of the relative frequency of an interresponse time on either key. Experiment IV replicated Exp. I except that choices between keys were controlled by a stimulus that signalled the availability of reinforcement on the right key. A comparison of Exp. I and IV suggested that the relative frequency of an interresponse time on one key generally was independent of behavior on the other key, but that the number of responses per minute on a key did depend on behavior on the other key.

Journal Article↗
PubMed1972

Aversive aspects of a fixed-interval schedule of food reinforcement.

The key pecking of pigeons was reinforced according to a fixed-interval schedule of reinforcement. The pigeons were also given the opportunity to attack a restrained target pigeon. The attack rates during the sessions of fixed-interval reinforcement were higher than during the operant level sessions in four of the five pigeons. Most attack occurred during the post-reinforcement pause in key pecking. It was suggested that a fixed-interval schedule of positive reinforcement possesses aversive properties, the most aversive of which are located during the post-reinforcement pause.

Journal Article↗