Dr. Salazar Kagan

In Diary of a Wimpy Kid: Ugly Truth
In the middle of his first appointment with Greg, Greg accidentally bites down on his finger during some oral x-rays. As a result of his anger from his bit finger, he prescribed a headgear to Greg which he didn't need. The next day, Greg couldn't find his headgear. The headgear was later stolen by Manny Heffley, which Greg considers to be a blessing.

Appearances

 * Diary of a Wimpy Kid'' (online) (As Dr. Alcazar)
 * The Wimpy Kid Do-It-Yourself Book
 * Diary of a Wimpy Kid: The Ugly Truth
 * Diary of a Wimpy Kid: Double Down (Mentioned)
 * Diary of a Wimpy Kid: Big Shot (Cameo)

Trivia

 * Dr. Kagan's appearance is quite identical to Chirag Gupta's father. The only difference is the presence of his moustache.
 * It's mentioned in the second book that Greg brushes his teeth at least four or five times, so despite his eating and drinking habits, he takes pretty good care of his teeth (for the most part at least).
 * Even though Dr. Kagan is a long-term, trusted dentist for Frank, he might not be a very responsible professional, since he promptly made Greg go upon a treatment he did not seem to actually need, just to punish him for - accidentally - biting and annoying him.