The Dental Timeline is a feature that has been included in MacPractice Generation 9 (Builds 9.0 and greater). The Chart History button allows you to cycle through each visit/procedure date to review the progression of a patient's chart over time.
The Dental Timeline is assembled by each treatment's procedure date present on the Chart. You can use the "Chart History" drop down to choose a date you wish to review, or you can cycle through the dates by using the arrow buttons.
It is important to note that newly charted procedures will default to a procedure date of the New Patient Date field, located in the Patient Tab.