The purpose of this study was to investigate how differences in dental implant and screw materials affected screw loosening. Screws (pure titanium; Ti4S, titanium alloy; TiAS), blocks (Y-TZP; ZrB, pure titanium; Ti4B) and plates (Y-TZP; ZrP), representing abutment screws, implant bodies and superstructures, respectably, were used. Plates were fastened to blocks by screws using a torque of 20 N•cm, and the loosening torque was measured after cyclic loading. Tests was performed on 13 specimens per group, with four groups for loading at the eccentric point (9 mm from screw center) and one group at the centric point (3 mm from screw center). In eccentric point tests, Ti4S screws led to significantly more loosening than TiAS screws (p<0.01). The block material had no effect. For ZrB-Ti4S, there was no difference in loosening before and after the centric point tests. More loosening occurred for eccentric point than for centric point tests (p<0.05).

We examine the coalition-proof equilibria of a participation game in the provision of a public good and study which Nash equilibria are achieved through the cooperative behavior of agents. We investigate the coalition-proof equilibria under strict and weak domination. We show that, under some incentive condition of agents, (i) a profile of strategies is a coalition-proof equilibrium under strict domination if and only if it is a Nash equilibrium that is not strictly Pareto-dominated by any other Nash equilibrium and (ii) every strict Nash equilibrium for non-participants is a coalition-proof equilibrium under weak domination.

This paper examines the relationship between coalition-proof Nash equilibria based on different dominance relations. Konishi, Le Breton, and Weber (1999) pointed out that the set of coalition-proof Nash equilibria under weak domination does not necessarily coincide with that under strict domination. We show that, if a game satisfies the conditions of anonymity, monotone externality, and strategic substitutability, then the set of coalition-proof Nash equilibria under strict domination contains that under weak domination. The above three conditions are met by standard Cournot oligopoly games and participation games in a mechanism producing a public good.

In this study, we provide the conditions for efficient provision of a public good in a participation game in which a non-negative integer number of units of the public good can be provided. In the case in which at most one unit of the public good can be provided, we provide refinements of Nash equilibria at which agents choose only a Nash equilibrium with an efficient allocation and provide sufficient conditions for cost-sharing rules that guarantee the existence of a Nash equilibrium with an efficient allocation. In the case of a multi-unit public good, we provide a necessary and sufficient condition for the existence of a Nash equilibrium with an efficient allocation and prove that Nash equilibria are less likely to support efficient allocations if the participation of many agents is needed for efficient provision of the public good in the case of identical agents.

Most studies on buyer-supplier relationship have focused on the nature of interfirm relationships from the viewpoint of the assembler of managing suppliers as partners. The flip side of this relationship, that is, the supplier's customer strategy and performance, has rarely been considered or examined. The purpose of the paper is to provide a simple game theoretical model explaining buyer-supplier relationships and show what factors determine the number of trading partners. We investigate buyersupplier relationships from the viewpoint of suppliers. We show that when the supplier is able to determine the number of trading partners, the optimal number of trading partners is small for the supplier if the supplier's bargaining power with its trading partners is weak, the economy of scope concerning the supplier's variable costs is significant, and its sunk investment has a firm-specific nature. The result might be consistent with the formation of Japanese buyer-supplier networks.