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Challenging age old definitions in Prosthodontics​

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Dr. Sanjay AroraDr. Sanjay Arora
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Dr. Rashida SingaporewalaDr. Rashida Singaporewala
Dr. Rashida Singaporewala, is a renowned Cosmetic Dentist, heading a leading chain of dental centres-Signature Smiles. Apart from Cosmetics, Botox & Implants, her most important area of focus remains-Dental occlusion, Neuro – Muscular Dentistry and Cranio-Sacral Dentistry. She has fast emerged as a sought after keynote speaker on the subject. Temporo Mandibular Disease, today fast being recognised as the most important disorder, in causation of several body disorders, is mastered by her. This places her formidably amongst the best “Full Mouth Rehabilitation Dentists “ in the country.

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“Overjet definition is wrong in literature throughout”

Random Thoughts
This article I am putting some random thoughts and tips together gained over last 2 decades in practice and almost quarter of a century spent with dental textbooks. Hope it may benefit some, inspire some and make some thinkers. A few of you may not agree, write to me at I also give a call for a scientific board/ consensus club where contentious issues of science, mainly occlusion can be discussed and joint statement of that board could be made available to all. All are invited to online fb group, “Think Club Occlusion”. I propose such a discussions under leadership of such stalwarts like Dr. Kumarswamy or Dr. Kanir Bhatia. And who better to conduct than Famdent.

Prosthodontics, T-Scan, Prosthodontics Treatment in Delhi India Quite by accident, while I was training a young exceptionally intelligent Dentist, I discovered that the definition of “overjet” is wrong in Dentistry. To my mind even Dawson has erred. If you disagree or want to discuss, please write to me. While I was discussing with her ill effects of “overjet” (will explain below), she inspite of being gifted with an exceptional “IQ”, although agreed with need of “zero overjet”, unlike what literature wants 2mm overjet. But she would not get –how a 2mm overjet would destroy a bite? Almost for a year I wrote her off. A year later a similar discussion and I discovered that she was right too all the while. The overjet taught to her throughout and cemented by Dawson’s book was the place she was coming from. When I saw those was left dumb founded.

Did I misunderstand, what is overjet?

Thanks to her I dig into the literature. Here’s my conclusion- either I am completely wrong or textbooks just missed this one including Dawson. Overjet is variably described as:

The projection of the upper anterior and/or posterior teeth beyond their antagonists in a horizontal direction-Farlex Partner Medical Dictionary © Farlex 2012 as given in medical dictionaries.

Clinical Cases in Orthodontics

By Martyn T. Cobourne, Padhraig S. Fleming, Andrew T. DiBiase, Sofia Ahmad, , page 13 describe it as above, except it says from upper palatal surface to lower labial surface.

It further goes on to define the goal of Orthodontic treatment as “ To create 2-4mm overjet”, this part I am going to take up next.

“The horizontal projection of maxillary teeth beyond the mandibular teeth, usually measured parallel to the occlusal plane. When not otherwise specified, the term is generally assumed to refer to central incisors and is measured from the labial surface of the lower central incisors to the palatal surface of the upper central incisors at the level of the upper incisor edge. Unique conditions may sometimes require other measuring techniques. Notice he defines, distance between surfaces, but at the incisal edge”.—Mosby’s Dental Dictionary, 2nd edition. © 2008 Elsevier.

Prosthodontics Treatment in Delhi India, TMJ Treatment In IndiaHe says 1-3mm overlap is recommended. This to my mind is close to definition of overjet but not perfect. How much should be the overjet I will discuss in next section.

Reproduced from power point/pdf by Brian Laumer, which is apparently a part of Dawson’s book.

As given in Dawson’s book apparently, a reproduction by Brian Palmer. The sentence that describes Overjet is “Overjet is a horizontal measurement”. At the Incisal edge of upper tooth seems to be erroneous and arbitrary call. A definition must be complete in all aspects.

The Book “Euro-Qual Program: Toward a Quality System for European Orthodontic …edited by GeaHeege”, describes overjet almost similarly but elaborately and specifies incisal edge of upper teeth to labial surface of lower teeth, as the measuring points. This does not seem to my mind coming from any basis.

Now you can clearly see that literature for almost two centuries of rapid development of science has not stuck to rigor in defining what is overjet and no consensus or disagreement exists on these definitions. This is against the scientific principles.

Also medicine unlike other basic sciences has discouraged “theorists” or “ logic thinkers” and I have seen authors writing their possible explanations hidden in overdetailed articles for the fear of criticism. This sometimes may lead to confusion and not aid in development of science. Fundamentally two types of thinking exists-

  • Inductive (Leonardo da vinci, Albert Einstein, Heddy Lamarr-famous Hollyood superstar Aishwarya of 50’s whose technology today runs Bluetooth, Wi-Fi, CDMA and Torpedo locking on targets. Many inductive thinkers or theorists like these listed here were discredited in our history of medicine and science and not paid heed to in their times. Even Einstein did not escape this abuse. And was thrown out of Germany by Nobel Laureates.
  • Deductive or the ones who go into detailed studies and trails.

    These thinkers do a great service by checking reality painstakingly but may be unkind to brothers from the Inductive group. Lets not forget major science came from former and development came from latter. The scope of the second is limited to the scope of study and is narrow mostly with less room for imagination and thinking.

Case in point here is the three inventors named above and scores others. Hence I recommend a balanced emphasis on studies should be given. The concept of “peer review is far overstretched as where would one have gotten peers of Einstein or Leonardo or Heddy who was not even a scientist. Peer incidentally means equal- these scientists were way above. Next article I will write on similar blunders in medicine and dentistry in an article titled “Strange History of Medicine.”

So coming back to the point, apologies for straying away to establish context, to my mind the definition of Anterior overjet should be

“Minimum horizontal distance between lower labial surface and upper palatal surface. “ in maximum intercuspation position.

This of course would not be valid when distances are large and maxillary incisors over proclined lets say to 45 degrees and above. That may be categorized as more or less a form of open bite. More

T-Scan, Prosthodontics Treatment in Delhi India Minimum distance (blue black line) between two surfaces-labial and palatal of lower and upper incisors would be the “Overjet“ and not the line at the Incisal edge of upper- proposed to be adopted as the definition by Dr. Sanjay Arora. important parameter would be the “ Right overjet recommended” that I would take up next.

How much should be the overjet?

Orthodontic and Prosthodontics literature has variably recommended an overlap of 1-3mm. If above definition of Overjet is accepted then overlap should be “Zero” mm as any overlap produces the possibility of forward movement of lower jaw with disclusion being guided by the posterior cusps. If it is Zero then disclusion would be instantaneous leading to immediate separation/disclusion- which will be vertical in nature in posteriors, leading to no or minimal rubbing of the posterior cuspal inclines. This would else be destructive to bite.

Next article would take up redefining “Anterior guidance”, which to my opinion has been erroneously described in literature as something that involves disclusion on protrusion. The same is true about canine guidance. Such movements of disclusion never take place in any jaw cycle. At best they are ways to test presence of guide planes. Only T-Scan can currently decipher this disclusion that has to be in microseconds. It is the incursion that has to be focused on and not excursion that is almost forceless.

Next article would also look at forces with which anterior teeth should meet at “rest” and “motion”, in order to avoid wear of anteriors.