15/01/2021
One Newton is defined as that force necessary to provide a mass of one kilogram with an acceleration of one metre per second per second. One newton is equal to a force of 100,000 dynes in the centimetre-gram-second (CGS) system, or a force of about 0.2248 pound in the foot-pound-second (English, or customary).Guess what is human bite force ?
1100 to 1800 Newtons in the second molar region.
This amplifies the significance of considering the role of masticatory muscles in smile designs with crowns .
One can not neutralize the anomalous forces that destroy the enamel of teeth completely but can lessen the amount by understanding and respecting these forces of nature unique to each individual.
The compressive strength of enamel (384 MPa) and dentin (297 MPa) and the fracture strength of a natural tooth (molar = 305 MPa; premolar = 248 MPa) offer excellent mechanical standards to select the optimal strength for posterior composite resins.
Now imagine if you are grinding off the enamel what chance does filling or crown have to last ....
( 1 MPa 1000000 newton/square meter.)
Therefore TMJ analysis,Placement of teeth in arch,analysis of contacts of opposing teeth ,and Facebow transfer of all this has to be the first step
to correct treatment planning.
That is what your dentist does.
Patients are these days concerned with life long warranty of crowns and implants.Well let's share some facts.
Compressive
Zirconia .900Mpa to 1600
Ceramic 350 to 550 Mpa
Composite 250 to 350 Mpa.
Tensile strength is a measurement of the force required to pull something such as rope, wire, or a structural beam to the point where it breaks. The tensile strength of a material is the maximum amount of tensile stress that it can take before failure, for example breaking.
Tensile strength
Enamel 20MPA
Dentin 40Mpa
Dental ceramics 20 to 50 Mpa
Zirconia 330Mpa
Composite 50 to 90 Mpa
Teeth are subjected to compression and tension while eating and is worse for night grinders or in bruxism.
The comfort of muscles is more in materials whose strengths are matching the natural enamel.
Muscles tend to become hyperactive in aberrant contacts which interfere in the centric placement of TMJ .The function of muscle is to place the condyle in the socket as designed by anatomy.Any interference will be grinded off with time.
The masticatory muscle bite force is dynamic .It is measured in static usually but now the study of dynamics is possible.Muscle forces determine joint loads, but the objectives governing the mix of muscle forces involved are unknown. Masticatory muscle forces exerted during static biting are consistent with objectives of minimization of joint loads (MJL) or muscle effort (MME).
It is now known that the Electromyography of Masticatory muscles show that bite related parameters depends upon the food and the time related factors depend chewing cycles.The bite forces reach a peaks and dips in accordance to closing and opening of jaws.
So in a nutshell as a dentist we try and work out a balance when we rehabilitate the Masticatory unit of the body.
Believe me it is working on creating a harmious symphony.
Marketing is another field altogether.Much easier.....
