Visual pop-out in infants: Evidence for preattentive search in 3- and 4-month-olds.

The present experiment tested for preattentive visual search in 3- and 4-month-old infants using stimulus features described by Treisman and Souther (1985) as producing visual "pop-out" effects in adults. Infants were presented with two visual arrays to the left and right of midline. One array comprised homogeneous elements, while the other had a discrepant element embedded in it. On the basis of previous research, we expected infants to fixate the array containing the embedded discrepant element. The pattern of fixation indicated detection of the embedded discrepant element for both age groups, but only with stimuli shown to elicit visual pop out in adults. This asymmetry in detection is consistent with the presence of preattentive visual search in infants as young as 3 months.

A comparison of the tensile strength of four prosthodontic adhesives.

PURPOSE: This study compared the in vitro tensile bond strength of four prosthodontic adhesives to sandblasted base-metal alloy. MATERIALS AND METHODS: Alloy cylinders were bonded end-to-end with the various adhesives, thermocycled, stored for 28 days, and subjected to a tensile load. RESULTS: Mean tensile bond strengths obtained were: Panvia = 42.3 MPa, Metabond = 31.1 MPa, All-Bond = 28.06 MPa, and F21 = 18.5 MPa. Statistical analysis showed significant differences (P < .05) in mean bond strengths between the adhesive systems. CONCLUSION: Under the conditions of this study, the Panavia system showed the strongest mean tensile bond strengths.

Evaluation of strain at the terminal abutment site of a fixed mandibular implant prosthesis during cantilever loading.

PURPOSE: Cantilever lengths from 10 mm to 20 mm have been empirically recommended for Brånemark fixed mandibular implant prostheses. However, functional stresses generated within the framework and at the crestal bone associated with various cantilever lengths have not been well researched. The purpose of this investigation was to evaluate the strain generated within an implant-supported prosthesis and on a simulated bone surface during functional cantilever loading. MATERIALS AND METHODS: A symmetrical mandibular fixed-implant framework supported by six Nobelpharma 7.0 x 4.0-mm abutments and 15.0 x 4.0-mm fixtures was fabricated. The fixtures were embedded in a simulated bone matrix of polymethyl methacrylate resin. Fourteen different arrangements of active supporting abutments were tested during 15 lb unilateral static cantilever loading 7 mm, 14 mm and 20 mm distal to the terminal abutments. T-rosette strain gauges were placed immediately distal to the terminal abutment site on the right side of the framework and on the corresponding simulated bone surface. RESULTS: There was no difference in framework microstrain as abutment number and arrangement were varied. Microstrain distal to the terminal abutment increased significantly with increasing cantilever length. Distal abutment microstrain increased 213% (63 mu epsilon to 197 mu epsilon) when cantilever length was increased from 7 mm to 14 mm and an additional 55% (197 mu epsilon to 306 mu epsilon) when cantilever length was increased from 14 mm to 20 mm. Overall, microstrain increased 306% when cantilever length was increased from 7 mm to 20 mm. Microstrain on the framework was always tensile (positive). Microstrain at the simulated bone reached higher maximum levels than on the framework (-588 mu epsilon versus 314 mu epsilon) and was compressive in nature (negative). In contrast to framework microstrain, microstrain at the simulated bone site varied dramatically with changes in abutment arrangement. Strains observed at the simulated bone surface increased dramatically as the distance to the adjacent active abutment increased or as the anterior-posterior span of abutments decreased. Distal abutment microstrain also increased significantly at the bone site as cantilever length increased, however, percent increases were less (7 mm to 14 mm, 55%; 14 mm to 20 mm, 30%; 7 mm to 20 mm, 101%). CONCLUSIONS: The results of this study indicate that an optimum biomechanical environment should exist when cantilever spans exceeding 7 mm are planned regardless of the number of supporting abutments. Strain transmitted to the crestal bone can be decreased by maximizing the number and anterior-posterior spread of supporting fixtures while minimizing the distance between the distal abutment and its adjacent abutment.

Evaluation of three impression techniques for osseointegrated oral implants.

The purpose of this in vitro investigation was to determine the accuracy of gypsum casts produced from impressions made with polyether, polyether and impression plaster, or polyether and acrylic resin for the fabrication of osseointegrated implant prostheses. Strain gauges were attached to a master framework to determine the passivity of fit of the framework to sample casts made by the three impression techniques. Strain values were statistically compared by one way analysis of variance and Duncan's multiple range test. A statistically significant difference was found between the three impression techniques tested (p < 0.05). The results of this investigation revealed that none of the impression techniques resulted in an absolutely passive framework fit. However, of the techniques tested, the polyether alone resulted in the closest duplication of the master cast.

Comparison of the adhesive strength of a BIS-GMA cement to tin-plated and non-tin-plated alloys.

This study compared the tensile bond strengths of two base metal alloys and two noble metal alloys, tin-plated and non-tin-plated, with an adhesive resinous cement. Two tin platers were compared for their effectiveness in enhancing the composite resin-to-metal bond. Cylinders of the alloys were bonded end to end with the adhesive cement, thermocycled for 24 hours, stored in distilled water for 27 days, and tested for tensile bond strength. The mean bond strengths and mode of failure were recorded, and scanning electron micrographs were recorded for subjective evaluation. Significant differences were demonstrated between the non-tin-plated and the tin-plated noble alloys and base metal alloys.

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.

Secondary sewage treatment versus ocean outfalls: an assessment.

Simplified models have been developed to obtain order of magnitude estimates of the oxygen demand of municipal and industrial wastes and of their potential eutrophication effects in the marine environment. The models have been applied to assess two major corrective actions that might be considered for such pollution problems-secondary sewage treatment and ocean outfalls. It is concluded that the arguments for secondary sewage treatment as the proper corrective action are not compelling and that the problem should be reexamined with appropriate scientific and engineering evaluations. One goal of such scientific evaluations should be a more thorough understanding of the life histories of possible trace contaminants and pathogens which may have long biological, chemical, or geological retention times in the marine environment.

Nitrogen, phosphorus, and eutrophication in the coastal marine environment.

The distribution of inorganic nitrogen and phosphorus and bioassay experiments both show that nitrogen is the critical limiting factor to algal growth and eutrophication in coastal marine waters. About twice the amount of phosphate as can be used by the algae is normally present. This surplus results from the low nitrogen to phosphorus ratio in terrigenous contributions, including human waste, and from the fact that phosphorus regenerates more quickly than ammonia from decomposing organic matter. Removal of phosphate from detergents is therefore not likely to slow the eutrophication of coastal marine waters, and its replacement with nitrogen-containing nitrilotriacetic acid may worsen the situation.