The K test and the condylar test by almuzian

1. The K Test and the Condylar Test
DR. HENRI P. PETIT, DR. MICHEL CHATEAU, 1984
Orthodontists need precise, routine tests to measure progress. Insufficient or
nonexistent progress may go unnoticed, and sometimes aggravation of the initial
problem or iatrogenic adaptation may occur. If these are not discovered immediately,
the opportunity to make a proper and timely correction may be lost. This is true for
all treatment modalities, but especially for so-called functional appliances. Since
1956, Dr. Michel Chateau has been using two tests 1 to detect problems and follow
progress in orthodontic and orthopedic cases in daily practice.
The K test helps in checking progress of correction in the vertical dimension. The
condylar test was designed to measure progress of orthopedic correction in the
sagittal or anteroposterior direction.3
K Test
Looking at the patient or at the lateral cephalometric radiograph from the right side,
the upper and lower incisor crowns in occlusion form an inverted "K".
The important sign to look for when following progress in vertical correction of a
deep bite is whether the vertical overlap improves. A simple way to measure this is:
with the patient's teeth in occlusion, place a thumbnail underneath and touching the
incisal edges of the upper centrals, and contacting the labial surface of the lower
incisors (Fig. 1 A). Holding the finger in position, ask the patient to open the jaw
slightly. The height of the labial surface above the nail represents the amount of
vertical overlap (Fig. 1B), and is easily measured (Fig. 1C).
"K" = 3mm means that, in occlusion, the upper incisors overlap the lowers by 3mm.
"K" = 0mm means that the occlusal edges of upper and lower incisors are in the
same occlusal plane. In open bite cases, the widest opening is measured and
recorded with a negative sign. An opening of 4.3mm is recorded as "K" = - 4.3mm.
The precision of the K test has been established by successive measurements. It
was found to be
±0.2mm for open bites and ±0.5mm for severe deep bites. Precision in deep bite
cases is slightly improved by substituting a pencil with a flat eraser at the end for
the thumbnail. We use a Faber-Castelli "jet eraser" and notch the tip of the cylinder-
shaped eraser (Fig. 2).
If a K test with a negative sign (open bite) does not improve with time, it means
that the tongue problem responsible for the open bite has not been corrected. To
obtain a measurable open bite correction, the High Proglossia Syndrome (associated
with a tongue postured upward and forward) must be totally corrected.
If a K test does not reveal improvement in a deep bite in a functional treatment case,
either an improper appliance is being used or a proper appliance is not being used
as prescribed.
Condylar Test
The main therapeutic action of a monobloc or activator in Class II cases is forward
growth of the mandible activated by protraction of the mandible.3-4 Wearing such a

2. device induces a habit of mandibular protraction, which generally lasts for several
hours after the removal of the appliance, increases with time, and is often unnoticed
by the patient. If a practitioner unaware of this orthopedic conditioning checks a
Class II patient a few weeks or months following the start of protraction therapy and
simply asks him to bring the mandible backward, the answer often is, "I cannot". In
fact, the patient only believes that he cannot, or he may be confused. Very often
when you ask a patient to move the mandible backward, he will move it forward--
moving the upper jaw backward.
If this practitioner, still unaware of the orthopedic basic principle, accepts this
artificial protraction and believes that the correction of the retrognathic mandible has
been accomplished, he will probably discontinue the functional protraction appliance.
A few days later, when the protraction habit has been lost, the mandible reverts to
Class II and the practitioner talks about relapse or concludes that functional
orthopedics does not work. What happened was just a false temporary forward
positioning of the mandible.
How could such disastrous case management and unscientific conclusions be
prevented? The simplest way is with the condylar test ( Fig. 3 ) designed by Dr.
Chateau in 1949.1 The basis for the condylar test is that the relationships within a
given temporomandibular joint do not change much with time. In fact, under normal
conditions the amount of sagittal movement the mandible is allowed to express with
the guidance of the TMJ is almost a constant within a two-to-three-year period.
Moreover, the possible anteroposterior movement, which we call condylar expression,
seems to be a good reference measurement to evaluate the effect of orthopedic
therapy in an anteroposterior problem.
Since we are measuring the displacement of the mandible in relation to the skull,
any fixed point of reference on the maxilla can be used. Two measurements are
necessary to define the sagittal condylar expression. The first one measures the
distance between the fixed point (skull) and the mandibular point when the
mandible is in its most retracted position. The second measures the distance
between the same fixed point (skull) and the mandibular point when the mandible is
in its most protracted position. Dr. Chateau makes these measurements from the
most anterior surface of the most protruded upper central incisor to the
corresponding point on the lower incisor, using a simple caliper such as the plastic
vernier from Unitek (#807-010), which has a central rod protruding from one end
the exact amount of the opening between the jaws on the other end. Dr. Petit
always measures the mesial aspects of the right upper and lower incisors, using a
new caliper he designed. The caliper has a horseshoe-shaped occlusal sheet that
helps in the orientation of the measuring rod and in the consistency of the vertical
positioning of the rod on the incisors.
To measure the sagittal condylar expression clinically, the patient is seated
comfortably and the mandible is gently manipulated backward and downward to its
most retruded position, avoiding the
guidance of the teeth. At the first occlusal contact, the closing movement is stopped
and the plastic end of the caliper is applied to the labial surface of the upper central
incisor with the caliper held parallel to the occlusal plane. The tip of the rod is
moved into contact with the lower incisor. The caliper is removed from the mouth
and the measurement is read on the vernier scale. In deep bite cases, the patient is

3. asked to open the jaw so that there is no more than 2mm overbite during
measurement.
To measure the most anterior position (maxiprotraction), the patient is seated in a
more erect position and is asked to move the mandible as far forward as possible.
The plastic end of the caliper is placed against the labial surface of the lower incisor,
with the caliper again held parallel to the occlusal plane, and the rod is moved into
contact with the labial surface of the upper incisor. The caliper is removed from the
mouth, and this measurement is read on the vernier scale.
When the measurements are recorded on the patient's chart, we suggest using the
letter "V" to represent the upper incisor reference point. In a Class II case, the
recording might be:
December 14, 1983: 7.0 V 3.0mm
Adding the two measurements gives us the sagittal condylar expression of 10mm on
that date.
In a severe Class II, in which the patient cannot reach the upper incisors with the
lower in maxiprotraction, the recorded measurements might look like this:
December 11, 1983: 12.6 - 3.0mm V
If the measurements were added in this case, the distance from the most anterior
position to the upper incisor would be counted twice, and the sagittal condylar
expression would be erroneous. The correct measurement is 9.6mm.
Clinical Notes
The measurement in the most posterior position is identical to the measurement of
the overjet plus the thickness of the incisal edge of the upper incisor (about 2.4mm).
This measurement is quite valid and often preferable to the usual measurement of
overjet.
The sagittal condylar expression averages around 10mm in patients age 8 to 14, and
tends to decrease slightly to around 9mm in adults. It is often less in deep bite cases
and more in cases of generalized abrasion of the occlusal surfaces or in Class III.
We have recently noticed that the sagittal condylar expression increases during any
active functional treatment. We have measured condylar expressions reaching
13.8mm during treatment with Chateau three-piece appliances, and even 14.2mm
during treatment with Herbst appliances and H. Petit reciprocal masks. The sagittal
condylar expression returns to normal after completion of the therapy, if the initial
"normal" measurement was not a reading of a restricted condylar expression, which
can be more fully expressed during activator therapy.
We have also recently noticed that Class II, division 2 cases with severe deep bite
have a poorly expressed condylar expression that can be permanently increased with
orthopedic treatment.
Using the Condylar Test
If a Class II patient with a retrognathic mandible measures 7 V 3mm (for a sagittal
condylar expression of 10mm) at the start of treatment, and measures 2.4 V 5mm
(for a sagittal condylar expression of 7.4mm) after a few months of hyperprotraction
with a functional appliance and/or heavy extraoral forces on a reciprocal mask, we
know for sure that there is something wrong. The condylar expression cannot have
been diminished by the treatment, although it could have been increased. We must
conclude that at least one of our measurements is incorrect. In the example given, it

4. is likely that the first measurement (2.4mm) is erroneous. It corresponds to the
thickness of the edge of the upper incisor, simulating a total correction of the
retrognathic mandible. The patient is bringing the mandible forward so that the
incisors touch. This may be a newly acquired habit, or for reasons of esthetics or
comfort. In such cases, the skeletal Class II problem has not been corrected; there
is just an artificial progliding posture of the mandible.
The condylar test enables the orthodontist to follow the true evolution of correction
of the skeletal Class II problem and the labial tipping of the upper incisors. We
cannot consider these dentofacial deformities fully corrected unless the condylar test
reads something like 2 V 8mm. If one wants to have a slight overcorrection, we
suggest stopping treatment when the condylar test reads something like 0 V
10.5mm.
If the "good looking" occlusion with correct interdigitation of all the teeth is achieved
only through a forward displacement of the condyles, a centric occlusion/centric
relation disharmony is created, and one can usually notice the presence of this
"double occlusion" or "Sunday bite" by observing a degree of infraclusion
(Christensen effect) in the bicuspid and molar areas. In that case, it is mandatory to
persevere in the correction of the dental Class II by hyperprotraction or any other
orthodontic means, including extractions and a multibanded technique, until centric
occlusion and centric relation coincide.
The condylar test must be measured at each appointment in treating a skeletal or
dental Class II with functional orthopedics. It is the only practical way of knowing if
treatment is progressing according to plan; or, more important, if treatment is not
progressing according to plan.
Reasons for Lack of Progress
If the measurements of successive condylar tests do not demonstrate any progress,
one might suspect that the deep bite has not been controlled or corrected (see K
test). After 10 years of experience with these tests, we have observed that, in the
case of any overbite, the condylar test measurement in the most posterior position
of the mandible cannot be smaller than the K test measurement. This clinical
observation, made by Dr. Chateau in 1964,3 can be explained by the fact that the
plane of the lingual aspect of the upper incisors is about 45º to the occlusal plane.
Therefore, if the anterior occlusal interference of the deep bite is not eliminated, the
incisors will receive a traumatic signal during protraction that stops forward
mandibular growth. This hypothesis has been confirmed by the experimental studies
of Petrovic, 5 who added the "incisor sensors" at the right end of his cybernetic
model describing the control process of mandibular growth.
A second possible reason for lack of progress in treatment of skeletal Class II
problems with functional appliances is related to a lack of appreciation for the lingual
etiological syndrome (as described in the notes accompanying the K test).
Mouthbreathing is sometimes the cause of the tongue problem, because it prevents
strong opposition of the jaws and the transmission of functional forces to the
skeletal bases through one or two interposed appliances. This, in turn, prevents the
correction of the deep bite and also dramatically changes the functional effect of the
protraction. Either the protraction is not accomplished, to avoid the incisor sensor of
Petrovic, or the direction of the forced protraction is modified into a more downward
direction, which is much less powerful. Mouthbreathing appears to be a cause of

5. failure in treatment of Class II problems without deep bite, and a double cause of
failure when deep bite is present.
An additional reason for lack of progress can be related to the biological incapacity
of some specific condylar structures to actually "grow" bone (growth potential) in
response to orthopedic stimulation. This rarely happens before age 14, but can be
expected in adults. There is a considerable difference between growth and condylar
adaptation, which can happen much later, but is more limited in potential. Direct
growth enhancement is generally excellent at age 7 or 8, if the patient is serious
about treatment and wears the orthopedic devices regularly.
Problems in functional treatment can be related to the FMA angle. Although we have
had some success with FMA angles of 30º and even 35º, it is easier and more
reliable to treat patients with lower angles, since this means that the gonion is low,
the ramus is well developed, and the condylar cartilage is working well, at least to
age 14. Dr. Petit has designed a minor surgical procedure, which-- associated with
tongue surgery, ENT treatment, and vertical pull extraoral force-- can change the
prognosis of long face syndromes. It is called angular bilateral corticotomy and
requires some special intraoral appliances for correct control of the post-surgical
adaptation.
Significance of the Condylar Test
The condylar test alone does not prove an increase in growth during Class II
treatment. It is simply a relative measurement of the anterior and posterior limits of
movement of the condyle, using the upper and lower incisor teeth as points of
reference. Changes in the condylar test measurements may be related to:
 1. an increase or decrease in mandibular growth,
 2. an increase or decrease in the anteroposterior growth of the maxilla, and
 3. a modification in the labiolingual inclination of the upper or lower incisors.
The condylar test enables an evaluation of the stage of orthopedic correction of a
patient whose treatment was started elsewhere. Such treatment cannot be
considered to be finished until the maxiprotraction reading reaches at least 8mm.
The test is also an excellent differential diagnosis
tool to avoid the common error of mistaking a Class II patient with the mandible
postured forward for a Class I or Class III; and it is useful in an appreciation of the
evolution of individual growth and development without orthopedic treatment, and in
the early diagnosis of an ongoing relapse following active treatment.
The condylar test and the K test are helpful in monitoring progress at each
appointment for orthopedic and orthodontic treatments and during the accelerated
heavy force mask therapies.