HIPAA's Security Rule treats data availability as a security property, not just an operational one. A backup that runs nightly but cannot actually restore is, under that rule, indistinguishable from no backup.
For dental, the failure mode is specific: practice-management databases (Dentrix, Eaglesoft, Open Dental) and imaging libraries (DEXIS, Carestream, sensor vendor archives) often live in different storage tiers, with different schemas, and frequently with vendor-specific consistency requirements. A "files backed up" green check in a generic backup console can hide a Dentrix database that will refuse to attach on restore, or a DEXIS image vault whose index is out of sync.
Backup verification in this sense is a restore-test, end to end. The artifact you want to show an auditor is a log of the most recent successful verified restore for each protected system, what was restored, against what dataset, and who or what authorized the test.