Orthotropics youtube channel has some good videos explaining the how and why of deep bites, and how they often result in partially erupted 2nd molars. I don't have the links right now(just google Orthotropics deep bite to find out), but here's my attempt at explanation.

My understanding regarding your case is that it all stems from the tongue. Check right now, where is your entire tongue, especially the sides of it? My guess is that the tongue, lacking sufficient intermolar width to stick to the palate without touching any teeth, is lightly sticking between your molars in the back. After a long time, imagine what that does...It pushes the 2nd molars on the mandible and the maxilla inwards, intruding them. As a result, your incisors overerupt to close the bite. And when you put your teeth together (without the tongue between the teeth) to check what your occlusion is, you got a deep bite. I recall Mike Mew saying that a lot of deep bite patients don't rest(ie resting oral posture) in a deep bite, but they rest with their tongue in between their molars and their incisors not in a deep bite position. It's only when an orthodontist asks them to bite together do you get that deep bite showing.

So the cause is ultimately a lack of lateral space causing your tongue to precipitate all these issues. I don't know about why your father/brother don't have the deep bite if they have the same intermolar width; it might be just that malocclusion is highly individual and manifests itself in different ways...or that explanation might just be a cop out, like how the orthodontists cop out and attribute almost everything to genetics.

Anyway, if you're going to get treatment as opposed to just mewing, you should be careful with how your orthodontist addresses the issue. Conventional orthodontics would usually address the incisor overeruption as the root of the problem, and push the upper incisors upwards and the mandible downwards, increasing lower facial height unfavorably(an unavoidable consequence, the textbooks say). An orthotropist(or orthodontist who follows similar principles) would move the upper incisors forward and upwards and bring the mandible up to meet it at a class I occlusion, and expand the maxilla/mandible so that the tongue can fit in the palate and the molars can fully erupt.

Another option other than orthotropics/orthodontics/mewing is a palate expander. It would help you gain lateral space to get your tongue out from between your teeth. And that could, if you fix your tongue posture and teeth close together, etc, allow your molars to fully erupt. Also, instead of the palate expander, devices like the DNA and ALF would help you with your lateral space and deep bite as well.

Hope that made sense and gave you some guidance on the cause/treatment, please let me know if you have any questions - and do seek other opinions and explanations and do your own research too. I'm not sponsoring any treatment, just spreading information.

@qwerty135

Hey, I think what you said makes sense. My tongue is bigger in surface area than my families, so that might explain the lack of lateral space.

And, also, I am getting treatment to fix it. Its invisalign, and what suprised me is it moves the incisors on top up and forward a bit and the bottoms once to meet it, just like you said.

My only thing is, my 2nd molars do not move, up or down, and they do not even touch. I cannot maintain good resting occlusion as my jaw tends to loose stability as they do not even touch because my molars below have not erupted.

Would tongue posture encourage my lower arch to widen? And potentially aid in the eruption of these teeth so that I get closer to normal development. I did not get proper answers and, I need to know because if yes, that would mean ditching my retainers (I am halfway through treatment).

@jawshrunk123

You don’t really need the lower arch to expand to get your lower molars to erupt...they are intruded because you tongue hangs out between the upper and lower arches. So, if the upper arch expands to a point where the tongue can fit in the upper palate, the lower molars will erupt even without much increase in expansion of the lower arch. The lower arch fits the upper arch, so once you expand the upper arch the lower arch will slowly expand to meet it(chewing gum/food for 1 hour or so a day helps with this).

So, your real question should be how to expand the upper arch, I think. Mewing can help, but I’m not going to advise you on removing retainers, etc due to liability issues. Do your research please. I know it depends on your starting point in IMW. Progress and Greensmoothies have had success expanding around 10 mm starting from intermolar widths lower than yours, just through mewing. But if you don’t fix tongue posture properly and remove your retainer, it could lead to crowding/relapse. So again, please do your research and come to a knowledgeable decision. And don’t worry too much, it can erupt at any age, so time is not an issue.

Overbite deep bite is caused by low tongue posture so much that the lower molars intrude hence the incisors overerupt to compensate for that and complete the bite. 

You can't get your molars in contact because you have short molars so your need to use your jaw muscles to keep them in contact 

Mew with chin tuck and gap between your molars so will slowly erupt to fix your bite

@qwerty135

Will the molars erupt at any age????? I'm 17 having a deep bite my molars are really short and how much time will they take to erupt fully and cure my deep bite 

Posted by: @jawshrunk123

@qwerty135

Hey, I think what you said makes sense. My tongue is bigger in surface area than my families, so that might explain the lack of lateral space.

And, also, I am getting treatment to fix it. Its invisalign, and what suprised me is it moves the incisors on top up and forward a bit and the bottoms once to meet it, just like you said.

My only thing is, my 2nd molars do not move, up or down, and they do not even touch. I cannot maintain good resting occlusion as my jaw tends to loose stability as they do not even touch because my molars below have not erupted.

Would tongue posture encourage my lower arch to widen? And potentially aid in the eruption of these teeth so that I get closer to normal development. I did not get proper answers and, I need to know because if yes, that would mean ditching my retainers (I am halfway through treatment).

Typically these type of problems arise from lack of sagittal growth, not transverse, so your small IMW shouldn't of have been an issue. Either way, I doubt your tongue is that wide, you just never had good tongue posture so your tongue is now too small to fit in.

I have 35mm ICW and 50mm IMW and I still can't fit my tongue without narrowing it first neither in the back nor especially in the front. Try to just narrow your tongue and then widen it once it's inside your upper arch, also try to focus on the front more than the back contrary to what this site constantly advises. It's much more important to expand front maxilla than rear maxilla so you can comfortably rest your tongue for mewing.

Would tongue posture encourage your lower arch to widen? Yes. Both widening of the upper arch or the lower arch causes the other arch to widen as well, especially in the back.

Widening your arch won't help your molars erupt though. As I said before, I already have 50mm IMW from 37mm and my third molars on my lower arch are still erupting slowly while my upper third molars are just stuck up there.

I think the only thing that will "provoke" your molars to erupt is to put various forces on them, like chew with them lightly in all kinds of ways, like what kids with itching teeth do.