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Animated Tutorial of the Temporomandibular System
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How excess vertical dimension provided by the NTI can be straining to a joint. 
While the occlusal scheme provided by the NTI (anterior midline point stop) allows for minimal muscular parafunctional intensity, the vertical dimension created by the NTI's Discluding Element modifies the degree of condylar translation. 

In the example to the right, the contraction of the left inferior belly of the LP advances/translates its condyle while the temporalis' maintain incisal contact on the Discluding Element.  An excessive vertical dimension created by the Discluding Element (flashing yellow in the example) allows for further condylar translation, thereby exposing the condyle and disc to compaction and strain.

The therapeutic goal with NTI protocol is to allow for minimal muscular parafunctional intensity (made possible by preventing posterior and canine contacts), and minimal joint strain (made possible by minimal condylar translation).

This patient reported a continual discomfort in the left TMJ upon right excursive movement.  The practitioner's intent was to prevent canine and posterior occluding, but simultaneously allow for excessive translation of the left condyle.  Reduction of the tip of the lower canine and of the Discluding Element resolved the patient's symptoms.
In the example above on the right, the Discluding Element has been reduced until there is canine contact in excursive position, which is still allowing joint strain and discomfort.  It's not so much that the NTI that is made poorly, but the lack of insight of how and when the pain is being caused in the joint.  The NTI is just a pre-fabricated piece of plastic.  You don't specifically need an NTI device to provide the desired therapeutic outcome, just a device that follows the therapeutic protocol that the device's design is a part of.  In the example above, it's the excessive length of the occluding canine(s) (which is causing the excessive translation in excursive movement) that is the problem.  Just as obvious posterior interfereces can prevent optimal centric condylar position, so can canine "interferences" (or Discluding Elements that are too high) prevent optimal condylar position in excursive.  The remedy is to perform an "equilibration" of the lower canine.
Next:  Clenching in a protrusive position can cause/perpetuate facial/sinus symptoms and cervical tension.
1. Introduction of normal function versus parafunction
2. The simultaneous combination of condylar rotation and translation
3. Normal unilateral activity and effect of a Lateral Pterygoid muscle
4.  Parafunctional clenching activity of the Temporalis
5.  How various occlusal schemes alter Temporalis clenching intensity
6.  The maximum clenching intensity occurs in the musculoskeletally stable position
7. How "canine rise" serves to diffuse parafunction
8. Working posterior interference causes non-working side joint strain during occluding
9. Non-working posterior inference causes non-working side joint and disc strain and CLASS III complications
10. Comparing the NTI's occluding scheme with other occluding schemes.
11. How excess vertical dimension provided by the NTI can be straining to a joint
12. Clenching in a protrusive position can cause/perpetuate facial/sinus symptoms and cervical tension.
13. The  Parafunctional Nature of Articulators