In a prior post, I discussed how the mystery of the dots was solved for me. I explained that I subscribe to the philosophy of the Dawson Academy and the Pankey Institute: “Lines in the front, dots in the back.”
I showed that the dots in the back are just the supporting cusp occluding in the opposing tooth’s central fossa or marginal ridge (mesial or distal). Any other dots found should be eliminated as they may represent an occlusal prematurity.
Okay, so what about the “lines in the front?” The lines are left by articulating paper as the anterior teeth guide the mandible through protrusive and lateral excursive movements. Let’s dig deeper…
(1) Anterior Guidance Protects the Posterior Teeth In Lateral Function
Remember the term, “group function?” The idea is that the posterior teeth on the working side all come into contact in lateral movement. On the contrary, if you believe in concept of anterior guidance, you want that lateral guidance to come from the anterior teeth, not the posterior teeth. Why?
The further posterior you travel , the greater the occlusal forces on teeth. This is so because the posterior molars function like a Class 2 lever, just like a nutcracker.
You crack the nuts closer to the fulcrum, where you’re maximum mechanical advantage resides. Well the same principles of physics apply to teeth, hence why our teeth that are designed for the greatest crunching (molars) are located in the posterior. Anterior teeth receive less stress because they are the furthest from the TMJ, which is the fulcrum. Lateral forces can be harmful because they are received off the central axis of the tooth. Thus the theory goes that if any teeth are going to receive harmful lateral loads, it is best for the anterior teeth to handle it.
(2) Anterior Guidance is Determined by the Anterior Teeth Contours
So in anterior guidance, the anterior teeth guide the mandibular movements from maximum intercuspation. Whether or not maximum intercuspation is also centric relation is irrelevant for our purposes in this discussion. For more discussion on centric relation, see my post here.
Anyway, if you think about it, those lines left by the articulating paper in protrusive and lateral movements are highly dependent upon the contours of the anterior teeth. To be more specific, anterior guidance is dependent upon the contours of the lingual surfaces of maxillary anterior teeth and facial surfaces of mandibular anterior teeth.
Imagine central and lateral incisors with undercontoured crowns. Imagine short, worn clinical crowns. Damaged, missing, or altered contours of anterior teeth may shift the protrusive and lateral guidance to posterior teeth, which may suffer more wear and tear since the guidance of the mandible will be on teeth with higher forces.
(3) Incisal Edge Position is Key
The lingual surfaces of maxillary anteriors and the facial surfaces of mandibular anteriors are important, but the position of the incisal edges is of special consideration.
If your incisal edges are too far forward, you will have phonetic and esthetic problems. The edges can interfere with the lip, certain speech sounds may be compromised, etc.
If your incisal edges are too far backward, you will interfere with the normal envelope of function.
The light blue shape represents the path of the mandible in profile.
Your teeth will excessively grind on each other and cause damage. The effects of this can be catastrophic, from bulky maxillary veneers that keep popping off, to bulky maxillary crowns that wear away the mandibular teeth.
The position of the incisal edges will determine whether or not the anterior guidance is in harmony with the envelope of function. During the motions of the jaw during function, the moment the teeth leave contact and re-enter contact is based solely on where the incisal edges are in relation to each other, between arches.
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If you’re interested in how this applies to occlusal adjustment, I have an e-book available for download: “The TMJ and Occlusal Adjustment”
I also recommend my favorite book on occlusion,“Functional Occlusion: From TMJ to Smile Design” by Pete Dawson.
