CE: Simplified Accurate Denture Records by Dr. Leif Stromberg

 

How to determine and record VDO and centric relation

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Abstract
This course covers essential concepts for successfully fabricating tissue-supported complete dentures, including vertical dimension of occlusion (VDO) and centric relation (CR). It offers practical techniques such as using phonetics to determine VDO and using the gothic arch tracing device to accurately determine CR and record VDO and CR.

 

Learning objectives
After completing this course, readers should be able to:

1. Understand the definitions and clinical significance of VDO and CR in complete denture fabrication.
2. Discuss a simplified technique for accurately locating and recording CR using the gothic arch tracing device.
3. Compare the differences between vertical dimensions of rest, speech and occlusion, and their roles in denture fabrication.
4. Implement procedures for recording accurate VDO and CR using simplified techniques.

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Introduction
Achieving predictability and success in fabricating tissue-supported complete dentures requires a thorough understanding of key elements, such as determining and recording vertical dimension of occlusion (VDO) and centric relation (CR). This continuing education course addresses concepts and techniques applicable to all types of tissuesupported complete dentures, including digital, implantretained and traditional analog approaches. The course covers three common challenges encountered during denture fabrication and offers practical strategies for effective resolution.

Challenges addressed:

• Determining a clinically acceptable vertical dimension of occlusion.
• Precisely locating centric relation.
• Accurately recording vertical dimension of occlusion and centric relation.

This course is designed to help dentists develop skills to confidently manage complexities of complete denture fabrication, enhancing both the success and predictability of outcomes. After adjusting the aesthetic wax rim (as covered in part 3A of this course series), proceed with determining and recording VDO and CR.


VDO and its clinical significance
An adequate VDO is crucial for achieving predictable success with removable tissue-supported complete dentures. This course discusses VDO by focusing on its definition, significance, and challenges involved with its determination and accurate recording.

Three important vertical dimensions will be defined and discussed in relation to complete denture fabrication:

• VDO
• vertical dimension of speech
• vertical dimension of rest

VDO definition: VDO refers to the vertical distance between two selected points on the patient’s face, one commonly on the tip of the nose (on the maxilla) and the other on the chin (on the movable mandible), when the mandible is in its fully closed position and the teeth are occluding in maximal intercuspal position (Figs. 1, 12).

Clinical significance of VDO for complete dentures: For edentulous patients, establishing an adequate VDO is important for maintaining health, harmony, balance and functionality of the stomatognathic system, as well as for clear and comfortable speech.

Physiological considerations for VDO (muscle length and eruptive forces of teeth): For an edentulous patient with no teeth to occlude, the dentist must determine the appropriate positions for the replacement teeth to reestablish an acceptable VDO (Fig. 2).

Muscle length: The length of the mandibular elevator muscles—the masseter, temporalis and medial pterygoid muscles—is a primary determinant of VDO. These muscles play a critical role in establishing VDO through their length and tonicity (Figs. 1, 2). Together, these factors determine the amount of space between the alveolar ridges available for erupting teeth.

Eruptive force: During the eruption of natural teeth, a constant eruptive force causes the teeth to continue erupting until they encounter an equal opposing force. Typically, the opposing force is provided by the erupting teeth on the opposing arch. This dynamic equilibrium guides the eruption and positioning of teeth within the oral cavity, ultimately contributing to the establishment of VDO.

Establishing VDO in edentulous patients: For edentulous patients, the dentist determines the VDO. This establishes the space between the alveolar ridges to accommodate the prosthetic restorations (Fig. 2).


Vertical dimension of speech: definition and importance
The vertical dimension of speech refers to the vertical distance between two selected points on the face, typically on the tip of the nose and the chin, when the mandible is in its most closed position during speech. The vertical dimension of speech measurement is very important for determining VDO.

The most closed position the mandible assumes during speech occurs when “S” sounds are spoken, such as when counting from 60 to 70 or saying six and seven when counting from one to 10 (Fig. 3).

The “S” position represents the most closed position the mandible assumes during speech and the closest the mandibular teeth come to contacting the upper teeth while speaking. It is important to note the upper and lower teeth should not make contact during speech. The VDO must be slightly more closed than the vertical dimension of speech, which is crucial when determining the patient’s VDO (Fig. 4).

Vertical dimension of rest: definition and importance
The vertical dimension of rest (VDR) refers to the vertical distance between specific facial landmarks, typically the tip of the nose and the chin, when the mandibular muscles are in minimal contraction. This measurement is taken when the mandible is naturally positioned and at rest while the individual is seated or standing in a neutral posture.

At the vertical dimension of rest, the mandibular elevator muscles are in a state of minimal contraction, and the mandibular depressor muscles are similarly at rest. In this balanced state, the elevator and depressor muscles are in equilibrium.

The vertical dimension of rest is typically greater (more open) than the vertical dimension of speech, which, in turn, is greater (more open) than the VDO (Fig. 5).

While the vertical dimension of rest can serve as a rough guideline for determining VDO, relying solely on this measurement can lead to inconsistent and unreliable results. This is because the vertical dimension of rest naturally fluctuates because of normal changes in muscle tonicity throughout the day.

Using the vertical dimension of rest to establish VDO may result in an excessively open and unacceptable VDO, leading to the teeth contacting when speaking. This would indicate an inadequate VDO, as the teeth should remain apart during speech.


Why is VDO important for complete dentures?
An adequate VDO is important for patient function and comfort with complete dentures. An excessively opened VDO can lead to muscle strain, soreness of denture-supporting tissues, fractured restorations and imbalances in the stomatognathic system.

If the VDO is increased (opened) to an unacceptable dimension by lengthening the prosthetic teeth beyond an acceptable dimension, the mandibular elevator muscles become overstretched, placing stress on the stomatognathic system. This imbalance can potentially cause far-reaching effects on various areas (Fig. 6), such as:

1. Muscle activity: Stretched elevator muscles will attempt to return to their original length, leading to efforts to intrude (tooth movement in an apical direction) the lengthened teeth.
2. Tissue-supported dentures: For complete dentures with an excessively opened VDO, these intrusion forces can cause soreness in the denture-supporting tissues. Because the denture teeth cannot be intruded, the pressure is transferred to the denture-supporting tissues, often causing tissue discomfort, inflammation and, in some cases, alveolar bone loss.
3. Implant-supported restorations: With implant-supported edentulous restorations, an excessively open VDO can lead to the restoration breaking or implant failure. This occurs as the muscles attempt to return to their original length by intruding teeth.

Dentists may tell a patient with ill-fitting dentures: “It will take a couple of days to get used to them.” However, it is crucial to recognize that adapting to pathology has undesirable side effects (Fig. 6).


Understanding CR and its importance in removable prosthodontics
Centric relation is the relationship between the mandible to the maxilla when the heads of the condyles of the mandible and the articular disks of the temporomandibular joints are correctly oriented in the glenoid fossae of the temporal bones. In CR, the condyles are fully seated on the disks in the glenoid fossae (Fig. 7).

One of the primary goals of complete denture occlusion is to fabricate dentures so that when the mandible closes in CR, all posterior teeth contact uniformly in maximum intercuspation (Fig. 8).

CR is an unstrained, comfortable, stable and physiologic maxillomandibular relationship. It is not muscle-supported and is a clinically useful, repeatable mandibular position. CR enhances the function and stability of complete dentures, contributing to improved patient outcomes.


Techniques for locating CR for patients with complete dentures:

• Bilateral mandibular manipulation method: This method for locating CR is highly valuable for guiding the mandible to CR and verifying the accuracy of this position. However, with this method, it can be very challenging to successfully record CR with movable tissue-supported baseplates (Fig. 9). When baseplates are stabilized with implant retention, the bilateral mandibular manipulation method can often be used successfully for locating and recording CR.
• Tongue to the roof of the mouth method: This method is often inaccurate as it positions the heads of the condyles posteriorly and inferiorly to the CR position (Fig. 10).
• Use of the gothic arch tracing device: This method is recommended for precisely locating and accurately recording CR for complete denture fabrication.

Recording verticentric VDO and CR
Accurate records are essential for predictability and success of complete dentures. The verticentric record, which is a simultaneous recording of VDO and CR, is typically made using wax rims or a gothic arch tracer (Fig. 11). An accurate verticentric recording allows the master casts to be mounted on the articulator with precise VDO and CR, allowing for effective denture creation.

Phonetics (the vertical dimension of speech) is the preferred method for determining VDO. Because no single method for determining VDO works for all patients, it is advisable to employ multiple methods and compare the results. These methods include:

1. Position the patient upright. Then, insert a comfortable and retentive maxillary record base with an adjusted wax rim or the patient’s existing maxillary denture. If needed, secure it with denture adhesive.
2. Place reference marks on the patient’s nose and chin using a Sharpie extra fine point permanent marker (Fig. 12). Measure the distance between these marks with a Boley gauge (Fig. 13). The marks can be wiped off the patient’s skin at the end of the appointment with alcohol after the verticentric record has been made.
3. Instruct the patient to lick their lips, swallow, relax their jaw and let their lips lightly touch. The mandibular elevator muscles should exhibit minimal contraction activity. Measure and record the distance between the reference points to determine the vertical dimension of rest.
4. Instruct the patient to repeat “mmm-mmm” or “Emma” several times, keeping their facial muscles relaxed and gently bringing their lips together. Measure and record the distance between the reference points again to determine the vertical dimension of rest.
5. Use phonetics to measure and record the distance between the reference points while the patient makes “S” sounds. Examples include counting from 60 to 70, saying six and seven when counting from one to 10, and saying “Mississippi” several times. The vertical dimension of speech measurements are usually less than the vertical dimension of rest measurements.
6. Measure and record the distance between the reference points while the patient is wearing the old dentures and is closing in maximum intercuspation. This is the VDO with the existing dentures.

Guide for determining VDO
The vertical dimension of rest is greater (more open) than the vertical dimension of speech, which is greater (more open) than the VDO (Fig. 5).

• Using the vertical dimension of speech measurement (phonetics): Close the vertical dimension of speech measurement by 3 mm at nose/chin measurement to determine VDO. This is the preferred method for determining VDO for an edentulous patient.
• Using vertical dimension of rest measurement: Close the vertical dimension of rest measurement by 3–5 mm at nose/chin measurement to determine VDO.
• Using VDO measurement with the existing dentures: Copy or adjust the VDO as appropriate.

The determined VDO should be verified at the wax try-in approval appointment before the dentures are processed.


Using a gothic arch tracing device
Centric relation can be accurately located with a gothic arch tracer, provided the patient does not have temporomandibular disorder (TMD).

The gothic arch tracer setup includes:

• A horizontal tracing plate on an upper baseplate
• A bar with an adjustable vertical pin on a lower baseplate (Fig. 14)

Benefits of the gothic arch tracing device:

• Ease of recording CR and VDO.
• Precise location and accurate recording of CR. The tracing indicates the precise location of CR.
• Easy and accurate VDO adjustment using the pin to the patient’s VDO.
• Stability. Vertical forces applied through the pin and tracing plate securely seat the upper and lower baseplates on the alveolar ridges during record-making (Fig. 11).

Components of the gothic arch tracing device for edentulous patients:

• Tracing plates
• Bars, vertical threaded pins, and nuts to secure the pins to the bars
• Clear (transparent) plastic disks that are centric relation stops
• An ink marking pen, such as a Marks-A-Lot permanent marker

Acquiring a gothic arch tracer kit:

• Dental laboratories often supply the kit to the dentist.
• Kits are available through leemarkdental.com
• Kits may be available for purchase online from Amazon or eBay.

Recording verticentric

1. Set the vertical pin: Adjust the vertical pin (raise or lower) to the patient’s VDO (Fig. 11). This ensures the verticentric record will capture the determined VDO for the case.
2. Ink the tracing plate: Paint the upper tracing plate with black ink, such as a Marks-A-Lot permanent marker (Fig. 15).
3. Record mandibular border movements: With the tracing device in the patient’s mouth, instruct the patient to move their mandible forward, backward and laterally several times. The clinician may gently guide these movements but should never force them.
4. Record the tracing: The pin traces the mandibular movements on the inked tracing plate, forming an arrow. The arrow’s point indicates CR (Figs. 16–17).

Verticentric is the simultaneous recording of CR and VDO. With the gothic arch tracer, the mandible is in CR when the point of the vertical tracing pin is on the point of the arrow. The vertical pin is set to the patient’s VDO. Verticentric will be accurately recorded in this position, and the record will be sent to the dental laboratory to mount the case on an articulator.


Making the verticentric record:

1. A small clear plastic disk with a center hole is placed on the tracing plate with the bevel around the hole facing out. The hole is precisely positioned over the point of the arrow, which represents CR, and the disk is attached to the tracing plate with sticky wax (Figs. 18–19).
2. The baseplates with the gothic arch tracing device are replaced in the patient’s mouth with the clear plastic disk in place on the tracing plate.
3. The patient’s mandible is guided until the vertical pin goes into the hole in the center of the disk. This assures the clinician the patient’s mandible is in CR.
4. With the mandible in CR and the jaws at the patient’s VDO, record the relationship of the baseplates using a firm bite registration material, such as Regisil Rigid Bite Registration Material (a polyvinyl siloxane [PVS] material) (Figs 18–22).

This systematic approach ensures the accurate recording of VDO and CR, facilitating the fabrication of successful complete dentures.


Conclusion
Key elements for denture predictability and success covered in this course are:

• Determining an acceptable VDO for edentulous restorations.
• Accurately locating CR for the edentulous patient.
• Using simplified procedures to accurately record VDO and CR for edentulous restorations.

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