This is Doctor Spark, DOS (the only name she will now go by, now and forever), at the very end of her "initiation" into the Equestria Dental Clinic conducted by Doctor Dash, DHD. After having her resistance quashed, her will broken, her identity deconstructed and rebuilt from the ground up, and her mind fully perfected for her one true purpose- after all the knowledge and skills and wisdom and dogma was installed into her brain; after the full rubber uniform, mask and gloves was applied to her body; after she performed her first ever braces application on herself while in the throes of pure pleasure- she confirms to Doctor Dash her commitment to the Clinic and her role/specialization in it, as she gives her thick, permanent technomagical braces one last initial tightening with the power of her horn. Feeling endless pleasure and bliss, which will never cease.

She is the third clinician, after Doctor Rarity and then Doctor Dash, as well as the first orthodontist. She will be applying her wares and affixing her tools onto the teeth of several pony patients every single day, for years to come.

Eventually, once a couple more brainwashed ponies join that department working under her, she is fittingly retitled Head Orthodontist.

Originally posted by KinkyRainbowDash within a larger doodle stream sketch page in these places:
https://twitter.com/krds_cloud/status/1445016737641074691
https://www.furaffinity.net/view/44001928/

Originally posted by me, with much more very fun (lewd) writing that you should definitely check out, in these places:
https://twitter.com/sqwrrkpon/status/1445222553585270785
https://www.furaffinity.net/view/47111811/