Your office actually needs someone to come in and refresh your employer's management skills.
In the first place, as hourly employees, you are generally supposed to be paid for the time that you spend attending a training session. Although there can be exceptions, such as in cases where the training is voluntary, outside regular work hours, and unrelated to your job, none of these criteria appear to apply in your situation.
Secondly, your employer's approach links training with a form of punishment, namely the lack of pay. It makes far more sense for employers to actively support and encourage employee training, development, and growth. Your employer's action has encouraged little more than resentment.
In addition, by failing to advise the employees up-front that they will not be paid for attending the session, your employer has also undermined his own credibility and trust. From this point, the employees are going to be suspicious of any actions that he may take, no matter how supportive they may appear to be.
You and your associates should meet with your employer to discuss this entire situation. It sounds like there is a need for more wide-open communication...or, since this is a dental office, open-wide communication.
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