Happy New Year Teeth
The large text of the ad reads:
This basically just means “happy New Year,” but the 呀 on the end is a modal particle you hear a lot in Shanghai. It adds a tone of playfulness, possibly childishness.
The pun is on 好牙, which refers to “good teeth.” (The two-character word for “tooth” or “teeth” is 牙齿). And since it’s an ad for dental services, the pun on good teeth is quite appropriate.
But do you see where the 口 component of 呀 (the modal particle) is actually a tooth? That’s the characterplay aspect. But the weird thing is that if you take away the 口, what’s left actually does literally mean “tooth.”