While on a trip to the dentist's office, a paranoid Ben grows uneasy over the dentist's odd behavior and goes into hiding, but when his suspicions prove right, and the dentist transforms into the monstrous Toothache, Ben must pull himself together if he is to save the day!
The Tennyson trio arrives at the dentist office, Ben keeps trying to make up excuses for them to leave. Gwen tells Ben that he liked this dentist the last time they visited. Ben states that Gwen has nothing to worry about because of her perfect teeth. Ben tries everything he can to not go to the dentist, but Max explains that this is something they have to do, and there's no easy way around it. The trio enters the dentist office.
Ben has a daydream of the dentist being evil. Ben transforms into Jetray to fight off Tooth ninja. Jetray gets caught by an X-ray vest, and is approached by the evil dentist.
Gwen snaps Ben out of his daydream, and the hygienist (who's name is Jen) walks in asking who's going first. Ben begs for Gwen to go first, and she does. The lady tells Gwen that Dr. Pang will be with her shortly, but the music in the dentist office begins to start acting up. Ben doesn't like the sound of the music, he believes that Gwen might be in trouble. Ben leaves to go use the restroom, he checks on Gwen and notices that she's fine. Ben walks into the restroom, and soon Dr. Pang walks in as well. Pang starts panicking. Ben notices that Dr. Pang is out there. Dr. Pang's reflection begins talking to him. Telling him that all sweets should go away. The refection tells him that they should let "him" do it, referring to Toothache. Ben decides to tell Max. He blast throw the wall using Heatblast.
Dr. Pang walks in to the room where Gwen is at, and checks her teeth. He notices that Gwen has a cavity forming. That causes him to almost transform, but he able to resist. He tells her that she has a start of a little cavity. Gwen gets mad and starts throwing a tantrum, telling Pang that she brushes two times a day, and occasionally brushes three times.
Heatblast runs through the door telling Max that they have to save Gwen. Max questions why he's Heatblast, and that he's not getting out of this appointment. Ben tells him that he isn't trying to get out, and that the dentist is saying the weirdest things to himself in the bathroom. Max questions how does he know that, and how did he even get outside. Gwen continues to complain about having a cavity, Dr. Pang steps out trying to fight the monster inside, but he transforms into Toothache. The transformation scares Jen. Ben admits that he might've overreacted a bit, but then Jen runs out telling them that there is a monster. Heatblast and Max burst into the room where Gwen and Toothache are. The monster grabs Gwen, and they run off. Ben times out, and Max attempts to call the authorities to look for the monster, max questions what it was, and Jen tells them that it was Dr. Pang.
Jen explains that Dr. Pang has been acting differently since returning from his last trip. He brought back a plant that he believed to be the cure of all cavities. The plant needed to be tested, but he tested it on himself, causing him to transform into a monster. Max asks if she knows how they can get him back to normal. She tells them that if she could get close enough to him, she could calm him down. Toothache runs through the city, with Gwen on top of him, destroying things, looking for sweets. Max, Ben, and Jen runs through the city looking for them. They notice a lot of wreckage. Ben notices that the monster destroyed an ice cream truck. They also notice that he wrecked a candy store. Ben transforms into Four Arms in anger. He runs through the town, noticing that it destroyed a churro cart, and goes Omni-kix. A little girl comes by asking if he would like to by some cookies, but Ben thinks for a second, and asks for some sweet cookies. Toothache and Gwen follows a trail of cookies, and is lead to an ally way, where Four Arms trapped them. Ben follows the monster onto a building, and the monster traps him in a tooth cage. Gwen and Toothache travels up a building, which is the headquarters of a cookie company. Ben throws a flag pole at the cookie monster, causing it to drop Gwen. Omni-Kix Four Arms rocket punch allowed him to catch Gwen. Max runs towards Gwen, who landed safely. He asks where Ben and Dr. Pang are. Gwen tells them that they are heading towards the top of a cookie headquarters, and tells them that they have to stop Ben before it's too late. Max tells Gwen that she has to get over the cavity problem. Ben uses a Dr. Smoothy flag pole to launch himself up to the top of the building Toothache is climbing. The two fight each other, but before Toothache finishes off Ben, he hears music, and transforms back human. It's revealed to be Jen playing the calm music. Max goes to comfort Ben. Dr. Pang comes and apologizes for putting them through all of that trouble.
Later on, Jen checks Ben's teeth, and tells him the status on his teeth. She thanks him for helping Dr. Pang, and tells him that he is also recovering. Jen pulls out a giant drill, ready to fix a few problems in his teeth, but Ben runs away. Max comes in asking if he needs to go get him, but she tells him that Ben's teeth are great, and she doesn't want him to start slacking off. Max things, feeling that they forgot something, then later Gwen is seen still wrapped around Omni-Kix Four Arms hand.
It is revealed that Ben's dentist, Dr. Pang wanted to find a cure for cavities so he used an experiment that would transform his body into a dangerous tooth monster.
Dr. Pang: Pull it together, Pang. Ben: Pang? Dr. Pang: There's nothing wrong. You're just tired. That's all.
Dr. Pang: Hm. Oh, dear, it's, uh...(Chuckles) You've got the start of a little cavity. Gwen: What?! No way! I brush twice everyday! On occasion, I brush three times. Dr. Pang: I-It's no big deal. It's not uncommon for someone your age to develop a cavity. Gwen: I'm 10 years old!
Heatblast: Grampa, we have to save Gwen! Max: Why are you Heatblast? You're not getting out of this appointment. Heatblast: I'm not trying to get out of a checkup. That dentist is in the bathroom right now saying the weirdest stuff. To himself! Max: How do you know that? And how did you even get outside? Heatblast: Ok, I may have blasted a giant hole in the wall of the bathroom.
Ben: He wrecked an ice cream kart! Max: We have to find Dr. Pang, fast, before people really get hurt. Jen: Look! (Points at a destroyed candy store) Ben: [Gasp] A candy shop. That's it! [Slams the Omnitrix and turns into Four Arms]