James P. Boyd, DDS
Having observed the development of
varying degrees of AOBs using an NTI, I'd like to present another
hypothesis for you...
The phenomenon is somewhat new to dentistry, and traditional models to explain the occurrence of an AOB resulting from NTI use tend to incorporate "off the shelf" TMD assumptions that don't particularly apply.
The development of an AOB with NTI use is typically seen in a patients who have three factors in common:
--minimal incisal overlap;
--long term history of symptoms, particularly headache;
--significant resolution of symptoms.
The patient typically has had headaches "since they can remember". It might take a bit of prodding to discover this.
The patient's chronic clenching typically initiates during adolescence. During the clench, the LPs are contracting (because they reflexively do so the instant the teeth touch so as to provide immediate disclusion) and obviously, so are the elevators. If the mandible were to continue its growth, the chronic tension of the elevator's sling (masseter and medial pterygoid and the force of the temporalis) plus the anterior pull of the LPs on the condyles may tend to "stunt" the potential growth of the ramus in a vertical and distal sense. Meanwhile the compartment of the fossa can continue to develop, with the ceiling of the fossa and posterior wall of the fossa both growing "away" from the stabilized condyle (dentistry use the term "stabilized condyle" when the clenching overwhelms the attempts of the LPs to disclude the teeth).
The result is a condyle that is slightly down and forward on the eminence (because the fossa space has enlarged superiorly/posteriorly), in the presence of a normal-length LP. The LP is not in an adaptive tensed posture, as dentistry usually observes in symptomatic people, because it hasn't been involved in having to avoid interferences during closure, or contacting with contralateral resistance as it does during excursive parafunction. Whereas the experienced CR manipulation practitioners can romance the mandible back to CR (as they coax the LP to "relax"), there's no relaxing for the LP to do in this example.
The condylar position of the chronic tension headache patient without TMD isn't going anywhere...unless...
The use of an NTI "frees up" and allows the elevator's natural tendency to brace the condyles against the eminence in accordance with the direction of their pull, which is up and forward (the same concept as Okeson's "musculoskeletally stable" position, and Dawson's CR). So the elevators begin to exert an influence on the condyles to migrate to the MS/CR position. However, the direction of that movement is resisted by normal resting length of the LP. In order for that movement to occur, the LP must "remodel" to a a new resting length. So weeks must pass for the LP to slightly "stretch and grow", thereby letting the condyle seat more posterior/superior. Typically, at the patient's 2 week NTI reveal, all is well. Maybe the 4-week is all WNL as well. But sometimes, at a 6-month checkup, an AOB has developed.
You can't simply have the patient discontinue with the NTI in order to close the anterior bite (first of all, the patient will want to know why you'd want them to such a thing as that...they'd don't remember ever feeling this good
and want to know why you're so nervous and concerned). In order
for the occluding scheme to return, the LP would have to assume a
chronically contracted and somewhat contorted posture to simultaneously
advance and
un-rotate the condyle. Many practitions
have reported their ability to manually get the
patient's incisors back to their original orientation, by adding the
elevating rotation to the patient's chin. There are no jaw
elevator muscles that can replicate that ability. The
bottom line is, you can't ask the LP to assume a
parafunctional/pathologic posture to provide a constant orthognathic
exercise.
Many times, the newly developed initial posterior contacts (typically the palatal cusps of the max. 2nd molars and the DB cusps of the mand. 2nd molars) can be reduced, only to have these interferences re-appear a few weeks later. Did the molars supraerupt? Of course not, and neither did the 1st molars, or bicuspids. The condyle seated a bit more because it could once the interferences to do so had been eliminated.
Finally, what about supraeruption? That is typically the one of the first assuptions, and is the simplest to demonstrate its non-existance.
Here's a clincial example, following one-year of continual nightly NTI use.
The primary indicator of potential AOB developement exists: minimal incisal overlap upon initiation of treatment.
Did only those second molars erupt? While the tonge prevented the others from doing so?
Hand-held models can demonstrate the lack of tooth movements :
The factors of the development of an AOB and a couple insights:
--minimal incisal overlap; This is the best warning sign. For example, in the presense of a class III, anterior edge-to-edge patient, the tiniest condylar shift will separate the incisal edges. Whereas, someone with a 60% incisal overlap can have a considerable change in condylar position, and not develop an AOB at all. The occurrence of condylar seating is probably far more common than is reported, but the degree of initial incisal overlap has hidden that fact.
--long term history of symptoms, particularly headache;
--significant resolution of symptoms. An insightful informed consent speech includes the phrase: "In the presence of success, your jaw may achieve it's optimal and intended position, meaning your teeth may not fit together then the way they do today. The vast majority of the time, it doesn't happen, but if it does, the vast majority of those times requires simple reshaping some of the bumps of your back teeth".
The phenomenon is somewhat new to dentistry, and traditional models to explain the occurrence of an AOB resulting from NTI use tend to incorporate "off the shelf" TMD assumptions that don't particularly apply.
The development of an AOB with NTI use is typically seen in a patients who have three factors in common:
--minimal incisal overlap;
--long term history of symptoms, particularly headache;
--significant resolution of symptoms.
The patient typically has had headaches "since they can remember". It might take a bit of prodding to discover this.
The patient's chronic clenching typically initiates during adolescence. During the clench, the LPs are contracting (because they reflexively do so the instant the teeth touch so as to provide immediate disclusion) and obviously, so are the elevators. If the mandible were to continue its growth, the chronic tension of the elevator's sling (masseter and medial pterygoid and the force of the temporalis) plus the anterior pull of the LPs on the condyles may tend to "stunt" the potential growth of the ramus in a vertical and distal sense. Meanwhile the compartment of the fossa can continue to develop, with the ceiling of the fossa and posterior wall of the fossa both growing "away" from the stabilized condyle (dentistry use the term "stabilized condyle" when the clenching overwhelms the attempts of the LPs to disclude the teeth).
The result is a condyle that is slightly down and forward on the eminence (because the fossa space has enlarged superiorly/posteriorly), in the presence of a normal-length LP. The LP is not in an adaptive tensed posture, as dentistry usually observes in symptomatic people, because it hasn't been involved in having to avoid interferences during closure, or contacting with contralateral resistance as it does during excursive parafunction. Whereas the experienced CR manipulation practitioners can romance the mandible back to CR (as they coax the LP to "relax"), there's no relaxing for the LP to do in this example.
The condylar position of the chronic tension headache patient without TMD isn't going anywhere...unless...
The use of an NTI "frees up" and allows the elevator's natural tendency to brace the condyles against the eminence in accordance with the direction of their pull, which is up and forward (the same concept as Okeson's "musculoskeletally stable" position, and Dawson's CR). So the elevators begin to exert an influence on the condyles to migrate to the MS/CR position. However, the direction of that movement is resisted by normal resting length of the LP. In order for that movement to occur, the LP must "remodel" to a a new resting length. So weeks must pass for the LP to slightly "stretch and grow", thereby letting the condyle seat more posterior/superior. Typically, at the patient's 2 week NTI reveal, all is well. Maybe the 4-week is all WNL as well. But sometimes, at a 6-month checkup, an AOB has developed.
You can't simply have the patient discontinue with the NTI in order to close the anterior bite (first of all, the patient will want to know why you'd want them to such a thing as that...they'd don't remember ever feeling this good
and want to know why you're so nervous and concerned). In order
for the occluding scheme to return, the LP would have to assume a
chronically contracted and somewhat contorted posture to simultaneously
advance and
un-rotate the condyle. Many practitions
have reported their ability to manually get the
patient's incisors back to their original orientation, by adding the
elevating rotation to the patient's chin. There are no jaw
elevator muscles that can replicate that ability. The
bottom line is, you can't ask the LP to assume a
parafunctional/pathologic posture to provide a constant orthognathic
exercise. Many times, the newly developed initial posterior contacts (typically the palatal cusps of the max. 2nd molars and the DB cusps of the mand. 2nd molars) can be reduced, only to have these interferences re-appear a few weeks later. Did the molars supraerupt? Of course not, and neither did the 1st molars, or bicuspids. The condyle seated a bit more because it could once the interferences to do so had been eliminated.
Finally, what about supraeruption? That is typically the one of the first assuptions, and is the simplest to demonstrate its non-existance.
Here's a clincial example, following one-year of continual nightly NTI use.
The primary indicator of potential AOB developement exists: minimal incisal overlap upon initiation of treatment.
Did only those second molars erupt? While the tonge prevented the others from doing so?
Hand-held models can demonstrate the lack of tooth movements :
The factors of the development of an AOB and a couple insights:
--minimal incisal overlap; This is the best warning sign. For example, in the presense of a class III, anterior edge-to-edge patient, the tiniest condylar shift will separate the incisal edges. Whereas, someone with a 60% incisal overlap can have a considerable change in condylar position, and not develop an AOB at all. The occurrence of condylar seating is probably far more common than is reported, but the degree of initial incisal overlap has hidden that fact.
--long term history of symptoms, particularly headache;
--significant resolution of symptoms. An insightful informed consent speech includes the phrase: "In the presence of success, your jaw may achieve it's optimal and intended position, meaning your teeth may not fit together then the way they do today. The vast majority of the time, it doesn't happen, but if it does, the vast majority of those times requires simple reshaping some of the bumps of your back teeth".