Market Power and Cartel Formation: Theory and an Empirical Test

Antitrust enforcement makes it difficult to test theories of cartel formation because most attempts to form cartels are blocked. However, federal laws allow U.S. produce growers to operate marketing cartels through devices called marketing orders. These cartels use quantity controls and quality standards to raise prices on fresh produce. Some growers have adopted marketing orders and others have not. This paper develops and tests a positive theory of the adoption of marketing orders. The theory suggests that growers in a region are more likely to adopt a marketing order if the demand for fresh produce is inelastic, the growers’ market share in the fresh market is large, there are barriers to entry and expansion, the fraction of the output the growers ship to the fresh market is not too large or too small, growers are homogeneous, and large cooperatives exist. Probit analyses support these hypotheses.marketing order; cartel; collusion; empirical; agriculture

The effect of surface conditioning on the bond strength of resin composite to amalgam

OBJECTIVES: This study evaluated the effect of different surface conditioning methods on the tensile bond strength (TBS) and integrity of the amalgam-resin composite interface, using commercially available restoration repair systems. METHODS: One hundred and sixty Gamma 2 amalgam specimens were stored in artificial saliva for 2 weeks and then randomly assigned to one of the following conditioning groups (n=20/group): Group 1: air abrasion, alloy primer and 'Panavia 21', Group 2: air abrasion and 'Amalgambond Plus', Group 3: air abrasion and 'All-Bond 3', Group 4: diamond bur, alloy primer and 'Panavia 21', Group 5: diamond bur and 'Amalgambond Plus', Group 6: diamond bur and 'All-Bond 3', Group 7: silica coating technique, and Group 8: non-conditioned amalgam surfaces (control group). Subsequently, resin composite material was added to the substrate surfaces and the amalgam-resin composite specimens were subjected to TBS testing. Representative samples from the test groups were subjected to scanning electron microscopy and surface profilometry. The data was analysed statistically with one-way ANOVA and post hoc Tukey's tests (α=0.05). RESULTS: The mean TBS of amalgam-resin composite ranged between 1.34 and 5.13MPa and varied with the degree of amalgam surface roughness and the type of conditioning technique employed. Significantly highest TBS values (5.13±0.96MPa) were obtained in Group 1 (p=0.013). CONCLUSION: Under the tested conditions, significantly greater tensile bond strength of resin composite to amalgam was achieved when the substrate surface was conditioned by air abrasion followed by the application of the Panavia 21 adhesive system. CLINICAL SIGNIFICANCE: Effecting a repair of an amalgam restoration with resin composite via the use of air abrasion and application of Panavia 21 would seem to enhance the integrity of the amalgam-resin composite interface. Clinical trials involving the implementation of this technique are indicated to determine the usefulness of this technique