What are the CDC Recommendations Related to How Fingernails Should be Maintained?

The CDC states that fingernails should be kept short and smooth. The edges should be filed smooth too allow thorough cleaning and prevent glove tears. The CDC also recommends to  not wear artificial fingernails or extenders when having direct contact with patients at high risk (e.g. those in intensive care units or operating rooms). Use of artificial nails is usually not recommended. 

Source: Center for Disease Control and Prevention (CDC), Infection Prevention Checklist for Dental Setting: Basic Expectations for Safe Care, Page 6, https://www.cdc.gov/oralhealth/infectioncontrol/faq/hand.htm