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Dentistry/Hyrax problem expansion?


QUESTION: 2013-12-21

Dear Doctor Randolph Myerson

My name is Domingos Savio, I am 49 years old and I live in Brazil. I would like to ask you some explanation over a problem I had during a Sarpe surgery.
I was recently diagnosed with transverse maxillary constriction with posterior crossbite.
(Class I Malocclusion on Left), and the doctor recommended me a surgically assisted rapid palatal expansion.
Once the surgery was done, and just one week after it and during the activation of the Hyrax, the result was a serious asymmetric expansion on the right side, with strong pain close to my ear and leaving me with a visible asymmetry on my right cheek.
The left side, with more serious crossbite almost didn����ove.

I was told the problem happened because there was a blockage of the zygomatic bone on the left side, preventing the Hyrax from working properly, making the right side to expand  excessively, causing the asymmetry.

The orthodontist was forced to work on the Hyrax to reduce the asymmetry and eliminate the facial deformity I was with.
He told me he managed to keep the minimum expansion that occurred on the left side, and at the same time he pulled the right side back to a satisfactory position.
Well, from my understanding and view of the facts, I remember all the doctor actually did was to untighten the Hyrax, working on the only screw, in order to reduce the excess of asymmetry on the right side.

My question for you is exactly about the possibility of the adjustment the doctor claimed he did.  
In practice, there being only one screw to turn on the Hyrax, allowing only two movements, to tighten up or untighten, and only four bands as levers connecting the main body of the Hyrax to the teeth, do you think it����possible to adjust one side independently from the other, or any action done on this screw, will directly affect the sides simultaneously?

I appreciate and thank you for your help
My best regards
Domingos Savio

ANSWER: Domingos,
You pose a very thoughtful question. Yes it is possible.  Just as a problem with the zygomatic bone may have resulted in uneven responses to the forces produced by the hyrax, it is quite possible that the occlusal forces of your bite can result in uneven responses to those same forces produced by the appliance.  I am referring to the effect of your bite on the changes in your maxillary dental arch.

---------- FOLLOW-UP ----------

QUESTION: 2013-12-22

Dear Dr. Myerson

Thank you for your reply.
I would just like to debate with you something really confusing for me.
I easily understand when you say the problem with the zygomatic bone may have resulted in uneven responses to the forces produced by the Hyrax.

Talking a little bit about the structure of the Hyrax and its possible movement.
Considering there is only one screw on the Hyrax, and this screw once activated, will open sideward the four arms with equal force and simultaneously to both sides, causing the expansion (in a bilateral surgery like mine).
In case of a blockage on one side (in my case it happened on the left side), the Hyrax force will still be the same on the four arms, but with some resistance on the left side, the major force will be thrown to the other side (my right side), causing the asymmetry. If it is not correct, please tell me.
I think it is pretty much has to do with the laws of Physics, right?

Based on this, the only point I really cannot understand is how the doctor may execute adjustments on each side independently using only one screw. His option was to turn the key to open and close the Hyrax, and any progress during the opening, with symmetrical or asymmetrical result, must have the same equal and proportional progress during the closing.
Could you, please, explain how to act on the only screw to reduce the excess of opening on the right side, leaving the left side with the minimum opening it had?

I hope I made myself clear, I understand it may be a little tricky, specially for someone not expert.
I thank you once more and apologize for any inconvenience.

Best regards
Domingos Savio

As I explained before, there may be other forces involved here.  It is not simply the laws of physics working.  There are also biological forces which may alter how the teeth and supporting bone respond to the forces created by the expansion or contraction of the appliance.  The side that was appropriately expanded may be properly in synch with the corresponding teeth of the lower jaw and this may help to stabilize that side while the over-expanded side is un-expanded with the reversal of the hyrax adjustments. That remains to be seen and the proof of this equation will be seen in the results.


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Dr. Randolph Myerson


Please limit your inquiry to questions about orthodontics (braces) and children's dentistry. I am both an Orthodontist and a Pediatric Dentist, having been trained in both of these dental specialty fields. Orthodontics is the dental specialty that treats problems of tooth, bite and jaw alignment using braces and removable appliances. Pediatric Dentistry is the dental specialty also known as dentistry for children, which deals specifically with the dental problems of this special age group from infants to adolescents. I am also experienced in Forensic Dentistry, the application of dentistry to law enforcement and identification using dental records.


I have been in the private practice of orthodontics and pediatric dentistry for over 20 years. Prior to that I served for three years on the Cleft Palate and Cranio-facial Reconstruction team at Children''s Hospital of Philadelphia and was an Assistant Professor of Dentistry at University of Pennsylvania School of Dental Medicine. I also served as a dentist in the U.S.Air Force, stationed at Andrews AFB in Washington, DC.

I am a Fellow in the American Academy of Pediatric Dentistry, and a member of the American Association of Orthodontics, as well as a member of the American Dental Association and the Dental Society of the State of New York.

I received my BA in Biology from Frankin & Marshall College in 1969, and my dental degree from University of Pennsylvania School of Dental Medicine in 1973. In 1978 I received both my Certificate in Orthodontics from University of Pennsylvania School of Dental Medicine, and my Certificate in Pediatric Dentistry from Children''s Hospital of Philadelphia after completing a three year Teaching Fellowship in Orthodontics and Pediatric Dentistry in 1978.

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