Having open communication is a key to avoiding organizational or interpersonal problems at work.  What can you do shen there is silence among some employees?  Are your employees just not speaking up or is it just in thier personality not to?

Here are a few ways to create a work environment with a commitment to open communication and how to break the silence. (Creating a Great Place to Work from Business Week)

Spend the day out of the office:   Meet with employees in their own departments.  Actually take the time to see your workers in their element rather than yours.  

Have an employee orientation:  New employees should have an extensive training and "getting to know you" period.  Have a strict plan in place to make them feel welcomed.

Company wide meetings:  This way everyone is in the same place hearing the same thing.  Everyone is then on the same page.

Keep open lines of varying communication:  Have multiple ways for your employees to communicate to their managers and bosses.  Some personality types like face to face conversations while others express themselves better in writing.