That's not entirely true about the Marines. The Marines do have specialty jobs other than infantry and those are equally important to the mission. However, the USMC is a department of the Navy. Because of that, Dental Specialists for Marines typically come from the Navy. Its the same with Marine Corps Medics. They are Navy Corpsmen.
If by training, you mean combat training, then yes. With the right MOS, you may never have to fire a weapons besides in basic training in the Army. In the Marines, if you have a non-infantry MOS, you go to boot camp and then MCT (Marine Combat Training) instead of Infantry School. There you will learn how to be proficient in combat should the situation ever arise.
The standard combat training is not widely different between branches. Although the Army has a wider possibility for advanced combat training. The famous rigorous paths to Airbourne, Rangers, Special Forces, etc. Once you're at that level, no Devil Dog is going to talk down to you.
Dental training in the army is pretty standard. There's no way to say its only "for girls". You'll get a specialty that you can take outside the Army. If you do well, you can transition pretty quickly to becoming a hygienist in the civilian world. Also, with the GI bill, you can go to school to become a dentist afterward.