RCP in Dentures (Basic) - Gothic Arch Tracing

This is a step guide for obtaining the retruded contact position (rcp) in patients for complete denture cases with the use of a Gothic Arch Tracing system.

Gothic arch tracing is a device for taking very accurate measurements of the vertical dimension and centric relation for edentulous cases. An adjustable ball bearing strikes against a metal plate on the opposing, giving an adjustable reference point for determining the proper vertical dimension and centric relation.  

Please note: This is only used for OVD and CR jaw relationship, all other features for complete dentures require a separate upper bite rim on a solid base for the provision of obtaining orientation, facial and smile features of the patient. (please see bite registration guide for further information)

If Gothic Arch Tracing is not a option there are other methods with bite blocks that could be used:

• Asking the patient to push there tongue to the posterior border of the upper
• Tilting the head backwards
• Stretch and relax the mandible
• Swallow and close

The beauty of Gothic Arch Tracing is that it eliminates guess work and you can accurately find the CR and OVD utilizing the best articulator in the world, the patient.    
The first stage of any denture case is: Patient details & history, denture history, E/O & I/O examinations, diagnoses, prognosis, treatment options and a treatment plan.

Step 1: Primary imps, Secondary special tray imps and construction of Gothic Arch Tracing.
Step 2: Measure the old OVD, RVD, FWS
Step 3: Obtain new OVD
Step 4: Find CR
Step 5: Orientation, facial & smile features

Centric Relation
The relationship of the mandible to the maxilla with the condyles in the most superior position, regardless of tooth position.

Step 1: Primary imps, Secondary special tray imps and construction of Gothic Arch Tracing.
A primary impression is needed for a special tray to be constructed. In order for this system to work correctly a Gothic Arch Tracing system should only be constructed after a secondary impression from a special tray. There are various types of Gothic Arch tracing, I will talk about the one I have used.

What does Gothic Arch Tracing look like?
Maxilla:
The maxilla will have a solid base plate with a metal flat plate attached with wax, within the palate region. The flat plate is then covered with a type of marking material – crayon, articulating paper or permanent pen marker.

Mandible:
The mandible will have a solid base plate with metal bar mounted in the pre molar region across the LRHS to the LLHS of the ridge, in the middle of the metal bar there will be an adjustable ball bearing or stylus sticking up right as a screw and is finger tight. The space underneath the metal bar will allow the patients tongue to sit comfortably and controlled underneath.

The ball bearing (stylus) on the lower will dictate the OVD and CR by touching the metal plate on the upper and acting as a pen to trace the patients CR by achieving various movements.  
The main aim is to utilize the patients instead of manually forcing a patient into CR jaw relationship , science and technology will allow the patient without knowing to indicate the CR for us.
Please see photos below:

How to use Gothic Arch Tracing System:

• Obtain patients old overall vertical dimension (OVD), resting vertical dimension (RVD) and find the free way space (FWS), by using a Willis gauge or place a dot with a pen on the patients nose and chin and use a measuring device to measure the distance (Fig 1).
  (please see bite registration in dentures clinical guide: Step 3 – Register the bite for more info on Willis gauges)
  
• Place both upper and lower base plates into the patients mouth (Fig 2,3)
  

• Make sure the patients tongue sits underneath the metal plate
• Adjust the ball bearing by using your fingers to turn the screw in the ball bearing (Fig 4)
  
• Make sure the ball bearing on the lower is touching the flat metal plate on the upper (Fig 5)
  
• Measure the OVD to either match, increase or decrease to old measurements with a Willis gauge or measuring device and turning the ball bearing screw on the lower to dictate the measurement (Fig 6)

Once OVD has been achieved, the tracing of CR is started by asking the patient to preform the following movements (make sure you are standing in front of the patient)

• Make sure the screw is tight and not loose, with a permanent mark the metal flat plate (tracing plate) (Fig 7)
• Ask the patient to advanced the mandible in a protrusive position and back into the most retrousive position. (Move lower jaw forwards and backwards)
• Repeat several times to create an accurate reproducible path on the tracing plate on the upper (Fig 8)
• Ask the patient to move the mandible in the most lateral position to the left hand side and repeat to right hand side(Move lower jaw side to side) (Fig 8)
• Repeat several times to create an accurate reproducible path on the tracing plate on the upper (Fig 8)
• Once this has been achieved the metal flat plate (tracing plate) on the upper should have various tracing marks as show below. (Fig 8)
• The tracing measurements should create a arrow on the tracing plate, the point of which all of the arrows meet is the centric relation of the patient (Fig 9)
• With the use of plastic with a small hole or a centric pin receiver, attach the CPR onto the tracing plate on the upper with wax and make sure the open hole is exactly over the point of which all of tracings measurements meet. (Fig 10)
• The centric pin receiver will act as a lock and the ball bearing will act as a key and go into this hole and lock together. This will set the patient to go into their natural centric relation that might unnatural or unknown to the patient at the time. (Fig 11)
• Once the ball bearing has been locked into place, use bite registration paste around lock the upper and base plate together. (Fig 12)
  
  

Please note: This is only used for OVD and CR jaw relationship, all other features for complete dentures require a separate upper bite rim on a solid base for the provision of obtaining orientation, facial and smile features of the patient. (please see bite registration guide for further information)
This has now been completed and can be sent to the laboratory for articulating and fabrication of a try in.

My personal experience:
I have done many Gothic Arch Tracing to obtain OVD and CR, from my experience it works, after a while you begin to become quick at this stage (8 minutes my last timing) but it relies on patient co operation and not every case is the same, some patients get used to it and some cannot.

Many factors contribute, for instance overtime denture wearers who traditionally had class 1 jaw relationship have worn the same dentures for many years and now their jaw relationship is class 3. This is due to gradually over time wearing down the plastic of the anterior and posterior teeth over time. This is also accelerated if dentures are loose and causing the patient to bite in a different pattern.

Slowly overtime, the dentures are worn down from it’s original jaw relationship position and after main years of daily of training at night and through out the day, the patients muscles of the face, anatomy of the arches and condyles of the TMJ have adjusted and now accommodate a class 3 jaw relationship.
In extreme cases like this, you may have to slowly bring the jaw relationship back e.g class 3 into a class 3 edge to edge jaw relationship first and then another set of dentures set to class 1 jaw relationship.

The beauty of Gothic Arch Tracing is that it eliminates guess work and you can accurately find the CR and OVD utilizing the best articulator in the world, the patient.

Images of gothic arch tracing were taken from:
www.ptcdental.com 
www.dentistrytoday.com/prosthodontics/prosthetics/1718--sp-108641534
Accessed on the 12th May 2020.

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