The k test and the condylar test by almuzian
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The k test and the condylar test by almuzian

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The k test and the condylar test by almuzian The k test and the condylar test by almuzian Document Transcript

  • 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 tests1 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. 1A). 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 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 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 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 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.