Screening and enrolling subjects in a randomized clinical trial involving implant dentures

When planning and budgeting for a clinical trial, researchers have few references to help them estimate how many volunteers will need to be screened, how long the screening process may take, and how much it may cost to enroll sufficient qualified subjects. The purpose of this study was to analyze the time and costs involved in recruiting, screening, and enrolling subjects for a randomized clinical trial examining patient satisfaction with mandibular dentures retained by 1 or 2 implants.

Data collected included age and sex of volunteers, recruiting sources, length of time and costs of recruiting and screening volunteers, and reasons for inclusion or exclusion. Results were analyzed using Pearson chi-square tests.

We estimated that we would need to screen 180 volunteers over a period of 4 years at an estimated total cost of CAN$47,664.00 to enroll 86 subjects. Instead, we had to screen 220 volunteers at a direct cost of $63,324.81. We excluded 28% of volunteers, while 32% declined participation and 40% agreed to participate in the study. Volunteers were most commonly excluded because of technical problems with their existing dentures, while they were most likely to decline participation because of perceived surgical risks with implants. Those who agreed to participate most commonly cited anticipation of a more secure mandibular denture as their reason for enrolling.

We had to screen more volunteers at a higher cost than anticipated, with only 40% of those screened meeting inclusion criteria and agreeing to participate in the trial.