Your breadcrumb markup is indeed valid, but it has an additional nesting level, in comparison with the markup, which makes Google as an example.
Look, your markup for the last piece, All-On-4, looks like:
"name": "Dental Implants > All-On-4"
item an extra type. But look, how Google does it:
"name": "Science Fiction",
item is just an
URL, without aditional nesting level.
I realized in many cases: nesting often makes Google not (fully) understand structured data. Earlier i thought it would be the best practice to make single JSON-LD snippet for the whole web document. Earning more experience with the subject i begun to create extra snippets for every important data type - own snippet for breadcrumb, own snippet for aggregatedRating and so on.
I don't say, you should do the same (own snippet for every data type) - but i'm pretty sure: avoiding nesting, specially on places like here, where you can go without, helps Google better understand your markup.