Registration of the Seated Condylar Position (SCP/CR): Part II: Technique: The Two-Piece Wax Bite Registration

The purpose of this paper is to present the technique for registration of the Seated Condylar Position (SCP)/Centric Relation (CR) position of the condyles: a two-piece wax bite registration with deprogramming and no mandibular manipulation


Introduction
From the results of previous investigations it can be concluded that the following four pre-requisites must be completed in order to: The four pre-requisites for accurate registration of the SCP/CR are: 1) Neuromuscular deprogramming; 2) Mandibular closure without deflection/tooth contact; 3) Voluntary muscle contraction: NO mandibular manipulation; 4) Two-piece registration incorporating a hard anterior stop.
Each of these four elements is essential to achieve more complete condylar seating when registering the SCP/CR.

Neuromuscular Deprogramming
Clinical mandibular manipulation is unreliable in determining the seated condylar position because of the effects of the neuromusculature, which is consistent with Calagna's [1] statement that "there is no known scientific method available to determine which patients require neuromuscular conditioning."To study the dental arch and condyle positional changes between the IP/MIC/CO and the SCP/CR it is important to use a method that reduces or eliminates the influence of the occlusion on the musculature.Only then can the condyles be accurately seated.
Eliminating the influence of the neuromusculature on condylar seating and accurately registering the SCP/CR as a reference allows for a determination of the dental inter-arch relationship and occlusion-dictated condylar position in three spatial planes.The identification and full extent of deflective occlusal contacts and resultant condylar displacement may be hidden by guarding of the neuromusculature.Thus, it is recommended that subjects (both symptomatic and asymptomatic) be deprogrammed prior to occlusal and condylar position evaluations.Deprogramming for both asymptomatic and symptomatic subjects prior to the registration of the SCP/CR eliminates the subject's neuromuscular response to the habitual occlusion.
Neuromuscular deprogramming is the key to reproduciblilty [2]- [23].Deprogramming allows location of the SCP/CR and occlusal analysis that correlates condylar position with tooth contacts (Figure 1).Splint therapy has proven to be Williamson [14] utilized condylar position instrumentation with true hinge axis recordings and studied the effect of full-time wear of a full-coverage upper stabilization splint on the location of the mandibular hinge axis in both asymptomatic and symptomatic subjects.He found that the axis moves anterior-superiorly with deprogramming, and that the axis locations following two different periods of stabilization splint wear were highly reproducible.Williamson concluded that "with relaxed musculature [e.g., deprogramming] the hinge axis location is highly reproducible." However, in a busy dental practice it is often not practical to deprogram numerous patients with stabilization splint wear for 2 wks. to 3 mos.prior to registration of the SCP/CR.The usefulness of an adjunct deprogramming procedure which separates the posterior teeth, deprograms the neuromusculature, and eliminates premature occlusal contacts/tooth interferences that guide the mandible into maximum intercuspation (IP/MIC/CO) is dependant, in part, upon its ease of fabrication, cost-effectiveness, and minimal patient compliance required for effectiveness.Slavicek [9] and Dawson [51] advocate having the patient bite on cotton rolls for deprogramming prior to registering the SCP/CR.However, a soft material that can be distorted by tooth indentations is not as effective in deprogramming as a hard occlusal stop.Therefore, the anterior jig advocated by Lucia [18] [20] [52], the leaf gauge advocated by Long [21], Williamson [42], Woeffel [23] and others [6] [12] [13] [19] [22], and the anterior flat plane jig utilized by Calagna [11], Karl and Foley [15], and Greco and Vanarsdall [24] are examples of registration techniques incorporating more effective anterior deprogrammers which separate the posterior teeth, deprogram the neuromusculature, and prevent deflective occlusal contacts that guide the mandible into the IP/MIC/CO.
An important registration consideration is that if the condyles have been displaced out of the fossae for an extended period of time, as with orthdontic appliances that displace the mandible anteriorly and vertically in an attempt to "stimulate condylar growth," it has been shown that it takes a year or more of consistent splint wear for the condyles to seat, due to scar tissue buildup in the retro-discal area over the duration of mandibular displacement appliance use.

Thus it is difficult and time consuming to deprogram these patients and register
the SCP/CR when the condyles have been displaced out of the fossae by forward positioning appliances [53] [54]. is a conditioned reflex reinforced and stored in the masticatory muscles at every swallow, adjusting masticatory muscle activity to guide the mandible and lower dental arch unerringly into its ICP.These muscle adjustments compensate for the continually changing internal and external factors that affect the mandible's entry into the ICP," masking the DAD between the IP and the SCP [61].

Mandibular Closure without Deflection/Tooth Contact
Occlusal contacts on a small number of teeth are inefficient functionally and create discomfort (both physical and psychic) causing the subject to subconsciously shift the mandible to an IP/MIC/CO position where contact between the upper and lower teeth is maximized.
The neuromuscular response to the habitual occlusion has been described in the occlusion literature as the neuromuscular protective mechanism by Hannam

Voluntary Muscle Contraction: NO Mandibular Manipulation
The clinician is NOT "manipulating" or "guiding" the mandible into the seated position.The PATIENT'S OWN musculature (temporalis, masseter, internal pterygoid-(sup head), and external pterygoid) seats the condyles.The clinician does NOT push the chin back in an attempt to "guide" the mandible into the SCP.
As soon as the clinician pushes on the patient, the reciprocal reaction is that the patient will push back.
The clinician is merely assuring that the mandible is passively rotating/in the rotational phase of closure (0 -25 mm of opening) and the mandible is not protruding.
The importance of voluntary muscle contraction in condylar seating cannot be overemphasized.
McMillen [65] used pantographic tracings to prove the importance of muscle tonicity in positioning the condyles in their superior-most position.In this study the true hinge axis was recorded and with the hinge axis instrument still in place, the subject was placed under general anesthesia and given succinylcholine.The condyles dropped from the seated position and vertical mandibular manipulation applied during anesthesia to the angles of the mandible was insufficient to reposition the condyles to their original seated position in the glenoid fossae.
Thus with general anesthesia and a hinge axis recording of the SCP the investigators could not seat the condyles fully with mandibular manipulation alone.
They concluded that voluntary muscle contraction is necessary to fully seat the condyles superiorly into the seated position.

Two-Piece Registration Incorporating a Hard Anterior Stop
The neuromuscular protective mechanism/proprioceptive guidance is also why it is not accurate to attempt to register the SCP/CR with a one-piece registration.
Williamson [42] utilized a leaf gauge anteriorly (hard anterior stop) with posterior tooth separation (no posterior contact) when registering the SCP/CR and concluded that the SCP/CR is a muscle determined position, not an operatorguided position.From clinical experience, as soon as the clinician pushes on the patient, the reciprocal reaction is that the patient will push back.
Calagna [11] evaluated four neuromuscular conditioning techniques-the insertion of cotton rolls, and deprogramming with either the myomonitor, an anterior jig, or a maxillary biteplane.He found that deprogramming with the maxillary biteplane revealed a condylar displacement that was, on average, twice the displacement found with the other three methods, all of which found comparable displacements.Greco and Vanarsdall [24] found that the function of the masseter and temporalis muscle muscles significantly decreased after the patient wore a Hawley biteplane or superior repositioning splint 8 hours per day for 2 weeks.Karl and Foley [15], utilizing deprogramming and condylar position instrumentation, found a larger discrepancy between the SCP/CR and the IP/MIC/CO than had been reported previously by using a hard anterior flat plane jig for deprogramming prior to registering the SCP/CR.They also found that while there was an 18% chance of detecting a condylar displacement of more than 2 mm in either the horizontal (AP) or the vertical (SI) planes with the Roth two-piece wax registration technique alone, this percentage more than doubled (to 40%) with the addition of a hard anterior deprogramming appliance prior to registration of the SCP/CR.They concluded that deprogramming provides a registration of condylar position that reveals a greater condylar displacement from the IP/MIC/CO than a registration taken without prior deprogramming.Johnston and Huffman [66] deprogrammed 92 orthodontically treated subjects and 83 controls with full-time wear of a full-coverage upper stabilization splint and found that the mean DAD for both groups, as measured from articulated study models, was slightly higher than that found in previous studies.They attributed this finding to "unmasking the discrepancy with splint wear." Deprogramming, accurate registration of the SCP/CR, articulator-mounted study models, and condylar position instrumentation are required to determine condylar position and the associated dental arch displacement accurately in three dimensions.
To seat the condyles to the most orthopedically-stable joint position, the registration technique utilizes: 1) Neuromuscular deprogramming; 2) Mandibular closure without deflection/tooth contact; 3) Voluntary muscle contraction: NO mandibular manipulation; enough to include the first molar and second premolar teeth, and it does not extend too far buccally to be distorted by the cheek nor too far anteriorly to interfere with the anterior section of wax (Figure 3).

The Procedure
1) The subject is seated in the dental chair and positioned at a 45-degree angle to the floor.
2) The subject is instructed to bite continually with a moderate pulsating biting force (5 seconds clench, 5 seconds relax) on a wooden tongue depressor for 5 to 10 minutes to modify the neuromuscular engram.The wax registration of the Figure 3.The two-piece wax bite registration taken after deprogramming and with no mandibular manipulation.
SCP is taken immediately following deprogramming.
3) The anterior section of wax (4 thicknesses) is softened in a water bath at 135 degrees Fahrenheit, then placed and held against the maxillary anterior teeth with one hand.The operator places the thumb of the free hand lightly on the chin while the middle and index fingers lightly contact the angle of the mandible bilaterally.No pressure is applied to the chin: just assure that subject is in the repeatable rotational phase of closure (<25 mm).
The subject is then instructed to "Close lightly on your back teeth" and is allowed to close without protrusion on a reproducible mandibular arc until approximately 3 mm of posterior vertical separation/clearance is observed between the upper and lower posterior-most teeth.The subject is instructed to hold this position.The anterior section of wax is chilled with air, hardened to the point where it can be removed without distortion, and is then removed.The anterior section is cooled in cold water and trimmed to allow passive indexing of the mandible into the SCP position.The subject is NOT permitted to close the teeth together into intercuspation (the IP) until the registration is completed.
4) The posterior section (two thicknesses) is heated in the water bath until it is completely soft (would offer no resistance to closure) and then placed across the upper molars and supported with the fingers on the buccal surfaces.While holding the posterior section in place, the chilled anterior section is replaced on the upper anterior teeth without contacting the posterior section.This can be supported with the same hand that is holding the posterior section.7) It is recommended that the maxillary position in three planes is registered with a facebow (EZ-bow R or ear bow) for orientation of the maxillary cast in the articulator.

Common Dental Arch Characteristics of Casts Accurately Articulated in the SCP/CR
From the two-part study conducted by this author on 596 asymptomatic [44] and 596 symptomatic [45] subjects, the following findings were reported.2) Measure the condylar displacement between the SCP/CR and the IP/MIC/CO (Figure 6).
Generally discrepancies between the SCP/CR and the IP/MIC/CO have the appearance of HORIZ/AP discrepancies when observed intra-orally (DAD), giving the impression that they are also HORIZ/AP discrepancies at the joint  [71] and correction of the HORIZ/AP inter-arch discrepancy is rather tied to vertical control treatment mechanics that attempt to seat the condyle with treatment (to improve/decrease the vertical CD).
3) Convert the lateral cephalogram, a common plain film taken in orthodontics for skeletal and dental analysis, from the IP/MIC/CO to SCP/CR, thus displaying the actual DAD and maxillo-mandibular relationship present (Figure 7).
5) Treatment plan orthognathic surgical cases, in which it is absolutely critical to achieve full condylar seating when repositioning the skeletal elements/segments.

Conclusion
The ability to more reliably register the SCP/CR has important ramifications for dental correction.Dental and orthodontic treatment goals can be quantified (mm) with measurable criteria, allowing for more accurate diagnosis, more precise treatment planning, more efficient treatment mechanics, improved treatment

Figure 1 .Figure 2 .
Figure 1.Deprogramming allows location of the SCP/CR and occlusal analysis that correlates condylar position with tooth contacts.

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and proprioceptive guidance by Roth[10] [62] [63][64].Thus the occlusal position observed intra-orally (the IP/MIC/CO) is an accomodated mandibular postion with condylar displacement (CD).As soon as the upper and lower teeth approach close contact, the neuro muscular protective mechanism/proprioceptive guidance is elicited.Subjects subconsciously occlude in the IP/MIC/CO, avoiding the initial occlusal contact and closing into maximal tooth contact (the IP/MIC/CO), leading the clinician to perceive that it is the patient's actual occlusion.This is also the mechanism that prevents clinicians from observing most DAD's intra-orally.Tooth position and the occlusal surfaces of the teeth dictate condylar position at the end of closure.Suffice it to say, deflective occlusal contacts/interferences require condylar displacement (CD) to achieve the IP/MIC/CO.Thus the occlusal position observed intra-orally is an accommodated mandibular position with condylar displacement and condylar position is determined by the dentition at the IP as a result of deflective contacts.It is therefore necessary to keep the posterior teeth separated (by 2.5 -3 mm) when registering the SCP/CR in order to prevent triggering this mechanism, which guides the mandible into a position that results in maximal tooth contact (the IP/MIC/CO).The posterior section of the bite registration, be it wax, impression material, ZOE, or other bite registration material, must offer no resistance to closure.

4 ) 1 )
A two-piece registration incorporating a hard anterior stop.The advantages of this technique are: Allows mandibular closure without dental interference (avoids posterior tooth contact and possible mandibular deflection); 2) Allows patient's own mandibular elevator muscles to seat the condyles: no mandibular manipulation is utilized (thus not as technique sensitive as other "manipulation" technics).The bite registration is taken immediately after neuromuscular deprogramming (relaxation).A 2-piece wax registration incoporating anterior resistance (a hard anterior stop) and no posterior resistance generates activity of the mandibular elevator muscles and avoids posterior tooth contact, allowing condylar seating in a reproducible musculo-skeletal position without dental interference or deflection.No attempt is made to direct mandibuar closure or influence positioning of the mandibular condyles.The wax bite is taken with Blue Bite Registration Wax (AD2 Advanced Dental Designs, Moreno Valley, CA https://www.ad2usa.com/800.232.2849,Great Lakes Dental Technologies, Tonawanda, NY https://www.greatlakesdentaltech.com/800.828.7626)within the hinge axis rotation phase of closure (<25 mm) and is prepared in two sections.The anterior section is made by folding over the softened wax to form 4 layers (more, in case of anterior open bite).The anteroposterior dimension of the anterior wax section is dictated by the overjet (AP difference in upper to lower incisor teeth anteriorly), and the width should include both the upper and lower anterior teeth (cuspid to cuspid).The posterior section is two layers thick.The antero-posterior dimension is trimmed wide

F 5 ) 6 )
The mandible is allowed to close into the SCP as above with the free hand.The lower anterior teeth should index into the hardened anterior section of wax without any (anterior) slide into the indentations.As the subject closes into the hardened anterior section, he/she is instructed to "close lightly on your back teeth and hold."The condyles seat as the subject closes into the hardened anterior stop and the posterior teeth hinge closed without resistance and without posterior tooth contact.Observe that lower incisors index into same indentations in the anterior wax section.The posterior section is chilled with air.When the posterior section has hardened sufficiently to avoid distortion upon removal, both wax sections are removed and cooled in cold water.The 2-piece wax record is inspected to ensure the absence of cusp penetration through the wax.It is then trimmed with a sharp scalpel blade to the incisal edge for cusp tip indexing for articulator mounting the lower dental cast into the SCP.

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How are Dental Casts Articulated in the SCP/CR Utilized in Dental Correction?Dental casts articulated accurately in the SCP/CR are utilized to: Diagnose the exact/actual inter-arch discrepancy (dental arch displacement/DAD) in the SCP.Articulating dental casts in the SCP/CR reveals the magnitude (mm) of the actual discrepancy to be corrected.For example, is the dental inter-arch relationship a Class 1 or Class 2? If Class 2, is it a 3 mm, 5 mm, or 7 mm Class 2 in the horizontal (AP) plane?In dental correction, knowledge of the magnitude (mm) of the actual discrepancy (DAD) to be addressed is essential when: a) Restoring the dentition with multi-unit restorations.b) Restoring posterior occlusal stability with tooth restoration or occlusal adjustment.c) Treating mandibular dysfunction.d) Treating patients with complete denture prosthetics.e) Treating patients orthodontically.f) Positioning the condyles during orthognathic surgery.Caveat: an observation from articulating dental casts in the SCP [44] [45]: the majority of Class 2 subdivision cases (presenting as Class 2 unilaterally in the IP/MIC/CO) are actually a half cusp (3.5 mm) Class 2 on the apparent Class 1 side and a full cusp (7 mm) Class 2 on the Class 2 side when the condyles are seated.These cases are often a mandibular apical base retrusion and asymmetry with lower dental midline toward the more Class 2 side.A maxillary skeletal asymmetry is rarely present.

Figure 5 .
Figure 5. Characteristics of dental casts articulated in the SCP/CR.

Figure 6 .
Figure 6.3D assessment of condylar displacement between the SCP/CR and the IP/MIC/CO with dental instrumentation and condylar graph recordings.

Figure 7 .
Figure 7. Converting the lateral cephalogram, a common plain film taken in orthodontics for skeletal and dental analysis, from the IP/MIC/CO to the SCP/CR demonstrates the actual DAD and maxillo-mandibular relationship present.