occlusion

[drkooks]

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i have some doubts in released papers

• in longitudinal section of premolar enamel thickest in occlusal third...

according to key ..why ???why not the middle

• in right lat excrusion , MB cusp of max right first molar passes through which groove in mand right 1st molar

lingual according to key....i thought it is central groove as it move
from MB groove ...can someone explain

 

[Streetwolf]

i have some doubts in released papers

• in longitudinal section of premolar enamel thickest in occlusal third...

according to key ..why ???why not the middle

• in right lat excrusion , MB cusp of max right first molar passes through which groove in mand right 1st molar

lingual according to key....i thought it is central groove as it move
from MB groove ...can someone explain

1. Because the enamel isn't in the middle of the tooth... Maybe you are confused on the plane of section? If you look straight ahead at a tooth (not looking down on it) and cut it into thirds so that the entire bottom of the tooth was a third, the entire middle of the tooth was a third, and the entire top of the tooth was a third, then the top would be the occlusal third. That's where the enamel is thickest.

2. In max intercuspation the MB cusp of #3 is the balancing cusp. It doesn't sit in a fossa. The ML cusp sits in the central fossa of #30 (mand right first molar). Furthermore during right lat excursion the buccal cusp would move even more buccally which means it gets further from the mandibular tooth. If however you meant either (1) left molar or (2) left lat excursion then I'd go with lingual grove because that particular side of the arch would be moving toward the lingual.

 

[Ibanez]

/quote drkooks i have some doubts in released papers

• in longitudinal section of premolar enamel thickest in occlusal third...

according to key ..why ???why not the middle


The answer is OCCLUSAL THIRD.

Enamel is thickest at CUSP TIPS
In accordance to the functional needs... ENAMEL PROTECTS the underlying tissues from the occlusal forces/stresses. THE DIRECT VERTICAL FORCES OCCUR AT CENTRIC OCCLUSION. (occlusal surface; "THICK" enamel provides RESISTANCE to occlusal forces)

For horizontal component there's PDL, gingival fibers which justify the need for thinner enamel covering the MIDDLE/cervical thirds; contact area in premolars cf. OCCLUSAL third.)

Therefore there's a greater need for thick enamel in the occlusal third.

• in right lat excrusion , MB cusp of max right first molar passes through which groove in mand right 1st molar

lingual according to key....i thought it is central groove as it move
from MB groove ...can someone explain


1. Well MESIOBUCCAL cusp of MAXILLARY MOLARS is a GUIDING CUSP (and not supporting)

2. MB cusp occludes in the BUCCAL GROOVE in CENTRIC OCCLUSION (/max intercuspation);

3 During the LATEROTRUSIVE movement...

3.1 The buccal incline of mandibular counterpart moves over the lingual incline of MB cusp.

3.2 Therefore the path of MB cusp is limited to traversing the buccal groove (/Group function occlusion; Mutually protective occlusion; Canine guided/protected occlusion)
and thereafter the MB disoccludes (is in the air and never reaches the central groove in an ideal group function occlusion)

4. I feel the there's a mistake in the question, it should be MESIO-LINGUAL CUSP of MAXILLARY molars...

Because:

1. ML cusp of max. molars traverses the lingual groove of mand counterpart in laterotrusive movements.

2. The working/supporting cusps follow the CUSP FOSSA relationship
(cf. guiding cusps which follow CUSP EMBRASURE relationship).

The cusp fossa relationship is the classically tested on NBDE.



Your questions are ANSWERED... (to the best of MY ability 😛).

Mayank. 😎

 

[skabbaraju]

1. Because the enamel isn't in the middle of the tooth... Maybe you are confused on the plane of section? If you look straight ahead at a tooth (not looking down on it) and cut it into thirds so that the entire bottom of the tooth was a third, the entire middle of the tooth was a third, and the entire top of the tooth was a third, then the top would be the occlusal third. That's where the enamel is thickest.

2. In max intercuspation the MB cusp of #3 is the balancing cusp. It doesn't sit in a fossa. The ML cusp sits in the central fossa of #30 (mand right first molar). Furthermore during right lat excursion the buccal cusp would move even more buccally which means it gets further from the mandibular tooth. If however you meant either (1) left molar or (2) left lat excursion then I'd go with lingual grove because that particular side of the arch would be moving toward the lingual.

Both the answers have some mistakes, but remember Max. lingual and Mand. Buccal cusps are working cusps and the others are supporting.
Again, how can Right Max.buccal cusps move more buccally wr.t the mand.teeth on a right later excursion? as explained by streetwolf.?

 

[Ibanez]

Ah shoot!

 

[Ibanez]

And what about my explanation, Mr. Sravan? 😛

Mayank.

 

[skabbaraju]

And what about my explanation, Mr. Sravan? 😛

Mayank.

I need to brush up on this a li'l more but it still does not seem right to me. (atleast part of it)
Cusp-Fossa relationship is for Working cusps (marginal ridge - fossa as well)
Cusp-Embrasure relationship is for supporting cusps.

 

[Ibanez]

I need to brush up on this a li'l more but it still does not seem right to me. (atleast part of it)
Cusp-Fossa relationship is for Working cusps (marginal ridge - fossa as well)
Cusp-Embrasure relationship is for supporting cusps.

Nevermind, if you do not know about "Cusp Fossa Vs. Cusp Embrasure" read my reply to 32pearls' "DA Qs rel 96"

I have given the rules (my rules) for posterior contact relationship.

Mayank. 8)

 

[Streetwolf]

Both the answers have some mistakes, but remember Max. lingual and Mand. Buccal cusps are working cusps and the others are supporting.
Again, how can Right Max.buccal cusps move more buccally wr.t the mand.teeth on a right later excursion? as explained by streetwolf.?

Sorry I answered the question at 2:30am after 7 hours of being in the preclinic. So I will change my answer haha.

The MANDIBULAR teeth move laterally so the buccal cusp of the maxillary tooth will move lingually relative the mandibular tooth it occludes with.

Therefore the MB cusp of #3 will travel through the BUCCAL groove of #30. I still think the question should say ML cusp.

 

[skabbaraju]

Nevermind, if you do not know about "Cusp Fossa Vs. Cusp Embrasure" read my reply to 32pearls' "DA Qs rel 96"

I have given the rules (my rules) for posterior contact relationship.

Mayank. 8)

I looked at that post and thats great information.
But I am still not sure if my terminology is wrong or yours.
Max.palatal cusps and Mand. Buccal cusps are working/non-supporting cusps and viceversa. You specified that they are supporting cusps.?
Could you or someone else please clarify.?
I appreciate it.

 

[Ibanez]

I looked at that post and thats great information.
But I am still not sure if my terminology is wrong or yours.
Max.palatal cusps and Mand. Buccal cusps are working/non-supporting cusps and viceversa. You specified that they are supporting cusps.?
Could you or someone else please clarify.?
I appreciate it.

Mr. Raju


BULL Never Works [... but guides]
(Buccal Upper and Lingual Lower) /My Rule 3


PS I was wrong there...

 

[skabbaraju]

Mr. Raju

Your terminology is definitely WRONG.

Remember as a rule, BULL Works... (Buccal Upper and Lingual Lower) /My Rule 3


PS I wonder if you've ever tried/skimmed through DA section of released papers... More than 50% Qs deal with CONTACT RELATIONSHIP... and if you use WRONG terminology you'll lose some easy marks there.

Thats right, its been a while since i did DA. I was thinking that supporting cusps are non-working and thats wrong. But otherwise, the terms are:
The working cusps are also called supporting or holding cusps
Non-working cusps are also called balancing, guiding cusps. (BULL)

 

[Ibanez]

Thats right, its been a while since i did DA. I was thinking that supporting cusps are non-working and thats wrong. But otherwise, the terms are:
The working cusps are also called supporting or holding cusps
Non-working cusps are also called balancing, guiding cusps. (BULL)

I was wrong there!
I need to re-do occlusion again. 😛

Regards,
Mayank. 😀

 

[Streetwolf]

Working cusps are also known as supporting cusps or functional cusps.
Non-functional cusps are also known as guiding cusps or balancing cusps.

This comes straight from my DA slides.

 

[Ibanez]

Working cusps are also known as supporting cusps or functional cusps.
Non-functional cusps are also known as guiding cusps or balancing cusps.

This comes straight from my DA slides.

I know I was wrong !
A big Mix-up with words "supporting"; "guiding" and "working".
Thank you for re-stating it.

--> So now my ( 😛) BULL DOESN'T WORK BUT GUIDES! (my bull is NON FUNCTIONAL 😛)

--> WHAT WORKS... ALSO HOLDS and SUPPORTS ! (the occlusion, that is...)


Hope I don't mess them up again...

Regards,
Mayank. 😀

PS Now I should be morally castrated... 😛

 

[Streetwolf]

Yeah it's confusing haha, you'd think support would be similar to guidance but no!

Yeah and we learned that the BULL rule was for the balancing cusps.

 

[Ibanez]

uh huh, so the BULLs NEVER WORK :