Which type of pharmaceutical agent binds to another agent's receptor site, preventing the other agent from binding there and causing its desired effect?

For a left lateral chest projection with accurate positioning, the

1. SID is set at 40 inches (102 cm). 2. humeri are positioned vertically. 3. shoulders, posterior ribs, and posterior pelvic wings are aligned perpendicular to the image re-ceptor (IR). 4. midsagittal plane is aligned perpendicular to the IR. a. 1 and 3 only b. 2 and 4 only c. 2 and 3 only d. 3 and 4 only

According to Wilson et al. (1984), what percentage of patients never return to the office for periodontal maintenance?

A) 10 B) 23 C) 34 D) 45 E) 59