Custom Fabrication of an NTI-type device
James P. Boyd, DDS

Regardless of the occlusal scheme, the therapeutic goal of an NTI appliance, whether it has been retrofitted from a prefabricated matrix, or custom fabricated, is to prevent the occluding scenarios that allow for near maximal temporalis contraction.  Since both posterior and canine occluding allow for maximal temporalis contraction the therapeutic goal of an NTI-type appliance is to prevent posterior and/or canine occluding in all parafunctional movements.

This requires that the practitioner establish what the full range of parafunctional range-of-motion is.  The difficulty here is that the patient will typically claim, "I don't go that far excursively/protrusively".  When asked why, they respond, "Because it hurts to do that".  The reality of the situation is that it hurts because they do that (a parafunctional sleep disorder).

The steps for custom fabrication of an NTI-type device:

1.  Take impressions and pour a model of the maxillary  and mandibular arches.

2.  Using .06" thick plastic sheeting for vacuum forming,  make a "suck-down" of the entire
     model (referred to here as a "stint").

3.  With the stint still adapted to the maxillary model,  articulate the two models to confirm
     where on the maxillary model the mandibular central incisors occlude.   Mark the stint to
     indicate this location.  The Discluding Element (DE) on the stint will be centered over the
     incisal embrasure between the mandibular centrals.

4.  Using orthodontic acrylic in a damp, doughy stage,  form a DE on the warm stint at the
     mark made in #3 above.   Some examples of the DE can be  seen at:
      http://www.DrJimBoyd.com/NTI_Tutorial_page_22.html  (example photos using the technique described here)
       http://www.drJimBoyd.com/NIGHTTIME_NTI_DEVICE.html

5.  Regardless of the degree of overjet, the DE  must be extended lingually enough so that the
     incisal edges of the mandibular incisors contact the DE, thereby maintaining disclusion of
     the posterior teeth.

     5a.  Occasionally, with large overjets, the orientation of the lower incisors will not allow the
            DE to be able to contact the mandibular incisors perpendicular to their long axis.
            DO NOT increase the height of the DE to create a perpendicular contact in this
            scenario.  It is preferable to maintain the occlusal surface of the DE parallel to the
            maxillary occlusal plane.

6.  Depending on the alignment of the maxillary incisors, cut away the stint from the model to
     include as many anterior incisors as necessary for adequate retention (lateral to lateral is
     recommended).

7.  Direct re-line the custom matrix on the internal lingual surface with a small amount of
     acrylic.  This is a critical step and ensures stability and enhanced retention.

For clinical application, refer to:
General NTI protocol
Typical protocol for Patient Selection, Diagnosis and Delivery
NTI Fabrication and Trouble-Shooting