Quartz 4

L4 Base Rim MMr

17 min read

Complete Dentures1

Preclinical

Info

The procedures discussed are typically performed during the second and third clinical appointments for complete denture treatment. The fabrication of the base and rim is a laboratory step following the secondary impression appointment. While shade and mold selection are part of the third clinical visit, they are not detailed here as they will be covered in a subsequent lecture on tooth arrangement.

Maxillo-Mandibular Relations

Note

Understanding the spatial relationships between the upper and lower jaws is critical for fabricating functional and stable complete dentures. The goal is to determine and record a reproducible jaw position that can serve as a reference point throughout the fabrication process.

Historically, there has been significant confusion in dental literature regarding terminology. Terms like centric relation and centric occlusion have been used interchangeably to describe different phenomena, such as the first point of tooth contact, maximum intercuspation, or the condyle’s position in the fossa. To establish scientific rigor, a consensus on terminology was necessary, leading to the classification of jaw relationships into vertical and horizontal dimensions.

Clinical Steps Overview2

  1. Examination
    • Review existing prosthesis
    • Extra —& Intra oral examination
  2. Primary Impression
  3. Secondary Impression (with border moulding)
  4. Base & Rim and MMR and Facebow
  5. Trial insertion
  6. Insertion
  7. Review

Maxillo-Mandibular Relationships3

Temporomandibular Joint

  • Hinge type synovial joint that connects the mandible to the rest of the skull:

A More Specific Term

The TMJ is a ginglymoarthrodial joint, reflecting its dual functions of rotation (ginglymoid) and translation (arthrodial).

  • Provides an articulation between the mandibular fossa and articular tubercle of the temporal bone, and the condylar process of the mandible.
  • Is atypical of a synovial joint in that its articular surfaces are lined by fibrocartilage rather than hyaline cartilage.
  • The joint allows a range of movements of the lower jaw:
    • Translational movements (protrusion/retraction and lateral deviation)
    • Rotational movements (elevation/depression).

Envelope of Mandibular Motion4

Opening 50 – 60 mm
Lateral 10 – 12 mm
Protrusive 8 – 11 mm
Retrusive ~ 1 mm

AbbreviationFull Term
RCPRetruded Contact Position
HMaximum Hinge opening
ICPIntercuspal Position (CO)
PrMaximal Protrusion
PRest Position
OMaximum Opening

Posselt 1952

In the dentate mouth, the teeth define the superior border of the diagram, while the TMJ anatomy defines the retruded path.

  • The movement from RCP to the hinge arc limit (H) is a pure hinge (rotational) movement of the condyle.
  • The movement from the hinge arc limit (H) to maximum opening (O) involves both rotation and translation of the condyle.

Goal for Complete Dentures

For edentulous patients, the Retruded Contact Position (RCP) and Intercuspal Position (ICP) should coincide. This ensures that maximum intercuspation occurs along the most reproducible posterior path of mandibular closure.

Vertical Jaw Relationships56

  • Rest Vertical Dimension → The postural position of the mandible when an individual is resting comfortably in an upright position and the associated muscles are in a state of minimal contractual activity

Measurement

RVD is measured between two arbitrary points on the face, such as subnasale (base of the nose) and soft tissue menton (most inferior point of the chin). A Willis face guide is an ideal tool for this. If using skin dots, choose areas with minimal mobility.

  • Occlusal Vertical Dimension
    • The distance between two selected anatomic or marked points (usually one on the tip of the nose and the other on the chin) when in maximum intercuspal position

Info

An appropriate OVD is crucial for optimal aesthetics and functions like speech, mastication, and swallowing.

  • Interocclusal Clearance
    • The distance between the occluding surfaces of the maxillary and mandibular teeth when the mandible is in a specified position; i.e. rest position. = RVD - OVD

Also Known As...

This is commonly known as the Freeway Space. It typically ranges from 2 to 5 millimeters.

Horizontal Jaw Relationships789

  • Retruded Contact Position
    • Contact of a tooth or teeth along the retruded path of closure; initial contact of a tooth or teeth during closure around a transverse horizontal axis.

Clinical Aids & Techniques

  • ==Leaf Gauge: A leaf gauge (multiple 0.1 mm polyester strips) can be placed between the anterior teeth to help deprogram the muscles and allow the patient to stabilize their jaw at this first point of contact.==
  • ==Manipulation Technique (Operator Behind Patient): The operator places the fifth fingers behind the angle of the mandible, fourth fingers in front of the angle, third fingers on the inferior border, and index fingers submentally. Thumbs are placed lateral to the symphysis. This directs the condyles antero-superiorly. The patient is guided to open and close on the hinge axis to relax the muscles.==
  • ==Manipulation Technique (Operator in Front of Patient): The operator uses index fingers to stabilize the lower record base and guides the mandible with thumbs on the chin.==

  • Intercuspal Position

  • Eccentric Jaw Relations

    • Protrusive Jaw Relation
    • Left & Right Jaw Relations

  • Intercuspal Position → The complete intercuspation of the opposing teeth independent of condylar position

Average Ranges of Motion from ICP

  • ==Retrusion: 0.5 - 2 mm==
  • ==Lateral Excursions: 10 - 12 mm==
  • ==Protrusive Movement: 5 - 11 mm==
  • ==Maximum Opening: 40 - 70 mm== [!warning]

Abnormal values may indicate temporomandibular dysfunction.

  • Eccentric Jaw Relations
    • Protrusive Jaw Relation
      • A registration of the mandible in relation to the maxillae when both condyles are advanced in the glenoid fossae – takes advantage of the Christensen Phenomenon

As the jaw protrudes, the posterior teeth separate. This separation can be recorded with registration material to set the condylar guidance on an articulator.

  • Left & Right Jaw Relations

    A registration of the positional relationship of opposing teeth or arches made in either a right or left lateral position of the mandible

Condylar Movements

During a left lateral excursion, the left (working) condyle rotates while the right (non-working) condyle translates down and forward along the articular eminence. These records are used to set the lateral condylar guidance on an articulator.

Laboratory Fabrication of Occlusal Rims10111213

Protect Master Casts

The master casts are part of the final mold for processing the dentures, so they must not be damaged during baseplate fabrication.

  1. **Block out undercuts on master casts with baseplate wax

Tip

Minimal wax is used to block out undercuts on the tissue surface of the cast (e.g., labial of the maxilla, lingual of the mandible). This ensures the baseplate can be removed without damaging the cast, while not compromising its fit.

** 2. Survey alveolar ridges on casts

  • ==Maxillary Cast: Dots are placed on the incisive papilla, canine eminences, and the center of the posterior ridge.==
    • ==Mandibular Cast: Dots are placed on the alveolar ridge at the midline, canine eminences, and the center of the retromolar pad.==
    • Lines are drawn connecting these points and extended onto the land area of the cast to serve as a guide for rim placement.
  1. Apply separating medium to bearing areas on cast (Use vaseline or alginate separating medium)
  2. Fabricate baseplates
  3. Attach wax rims to baseplates using survey lines and average height measurements as a guide

Fabricate Baseplates141516

Polylux light-curing box
Palatray light-curing tray material

Baseplates can also be made from other materials, including self-curing acrylic or 3D-printed resin.

Rim Specifications1718

  1. Attach Wax Rim:
    • A preformed wax rim is softened in warm water.
    • It is contoured to the baseplate, using the survey lines as a guide:
      • ==Maxilla: 2/3 of the rim should be buccal and labial to the survey line.==
      • ==Mandible: The rim should be centered over the survey line.==
    • The rim is attached to the baseplate using heated yellow sticky wax.
Maxillary RimMandibular Rim
Width 8 mm anteriorly,
10 mm posteriorly		Width 8 mm anteriorly,
10 mm posteriorly
2/3 of width Buccal & Labial to survey line on castBuccal width equals lingual width
15 mm high anteriorly,
tapering to 13 mm posteriorly		14 mm high anteriorly and parallel to crest of the residual ridge

Boley gauge

Figure of eight caliper

  1. Attach wax rims to baseplates using survey lines and average height measurements as a guide

Recording Jaw Relationships1920

Info

Accurate jaw relation records are essential for reducing chair time at the delivery appointment and creating stable, comfortable prostheses.

  1. Check extension, retention and stability of upper and lower occlusal rims
  • ==Extension: The baseplate periphery should be about 2 mm short of the resting sulcus depth. It should not be displaced when the cheek or lip is gently stretched. The posterior border extension can be checked by marking it with an indelible marker and transferring it to the tissue.==
    • ==Stability: Ensure all 3D printing supports are removed. The baseplate should not rock or displace when pressure is applied with one finger on either side, anteriorly or posteriorly.==
  1. Establish facial contour and occlusal plane by shaping the upper rim
  2. Maxillary facebow record
  3. Determination of vertical dimension of occlusion by modifying the mandibular rim only
  4. Registration of centric and eccentric relations at accepted vertical dimension
  5. Mark midlines, smile line and canine lines on rims
  6. Tooth selection

2. Establish Facial Contour & Occlusal Plane21

The maxillary occlusal rim is adjusted first to establish aesthetics and the plane of occlusion.

  • ==Lip Support: The rim’s contour provides support for the lips and cheeks. Proper support reduces the depth of the nasolabial fold and vertical wrinkles. The vermilion borders of the lips should be clearly visible. An average nasolabial angle of approximately 90 degrees indicates adequate lip support.==
  • ==Phonetics: When making **

Deficient contour
Overclosed

Correct contour
Correct OVD

Anterior RegionPosterior Region
Height• relation to upper lip (shape & age)
• existing denture as reference
• interpupillary line
• curve of the lower lip		• Parallel to Camper’s plane (ala-tragal line)
• compensating curve
Width• lip support (aesthetics)
• lower ridge		• buccal corridor
• neutral zone

Camper’s Plane
Occlusal Plane

Cephalometric analysis shows that the occlusal plane more closely parallels a line from the inferior border of the tragus to the inferior border of the ala.
Sharab et al, 2023

Occlusal plane too low
Occlusal plane reversed

3. Facebow Record22232425262728

Earbow
Kinematic

A facebow is an instrument that records the relationship of the maxilla to the hinge axis of rotation of the mandible

Types of Facebows

  • ==Kinematic (e.g., Dentatus): More accurate, as it locates the patient’s true terminal hinge axis. Requires a hinge axis locator and may involve tattooing reference points on the skin.==
  • ==Arbitrary (e.g., Whip Mix): Simpler and more common. It uses anatomical landmarks like the external auditory meatus as a reference, assuming a constant relationship to the true hinge axis. It is self-centering and considered sufficiently accurate for complete denture fabrication.==

The Importance of Occlusion29

Understanding the correct relations between the static and functional dental contacts is key to good clinical practice in restorative dentistry. The articulator’s primary function is to work as if it was a patient in-absence.

The Articulator30

The articulator is defined as “a mechanical instrument that represents the temporomandibular joints (TMJs) and jaws, to which maxillary and mandibular casts may be attached to simulate some or all mandibular movements” (Academy of Denture Prosthetics 1977).

Articulator – a mechanical instrument that represents the temporomandibular joints and jaws, to which maxillary and mandibular casts may be attached to simulate some or all mandibular movements.

TypeSynonymDescription
Class INon-adjustableA simple holding instrument capable of accepting a single static registration; vertical motion is possible
Class IISemi-adjustableAn instrument that permits horizontal as well as vertical motion but does not orient the motion to the temporomandibular joints
Class IIISemi-adjustableAn instrument that simulates condylar pathways by using averages or mechanical equivalents for all or part of the motion; these instruments allow for orientation of the casts relative to the joints and may be arcon or non-arcon instruments
  • ==Arcon: The condylar housing is on the upper member and the condylar ball is on the lower member, mimicking human anatomy. - Non-Arcon: The condylar housing is on the lower member and the condylar ball is on the upper member.==
Class IVFully adjustableAn instrument that will accept 3D dynamic registrations; these instruments allow for orientation of the casts to the temporomandibular joints and simulation of mandibular movements

4. Occlusal Vertical Dimension – Pre-extraction Evaluation31

  • Measurements of intra-oral dimensions
    • Measuring the distance between points marked by the treating clinician with tattoo dots
    • Measuring the distance between maxillary and mandibular fixed landmarks
    • Fabricating the denture(s) on pre-existing mounted diagnostic casts
  • Profile tracing
    • Fabricating a template that traces the profile of the lower third of the face
  • Cephalometric approach
    • Pre-extraction and post-extraction cephalometric radiographs are obtained. The latter with the occlusal rims in place which are adjusted accordingly
  • Pre-extraction phonetics
  • Pre-extraction photographs
  • Oro-facial device
    • Measures the angle between the Frankfort plane and the border of the mandible

4. Occlusal Vertical Dimension - Post-extraction Evaluation32

The OVD is not an immutable reference, but rather a dynamic dimension within a zone of physiological tolerance.
Vertical changes in the OVD have biological, biomechanical, aesthetic, and three-dimensional (3D) functional implications.

Among the most commonly accepted techniques to determine the OVD in edentulous patients are:

  • Morphological or facial proportions

    • External appearance of the face
    • Conformation of nasolabial folds
    • Harmony between lower third and the other thirds of the face (Turner & Fox, 1928)
    • Distance from outer corner of eye to labial commissure was equal to distance from base of nose to chin [Willis Face Guide] (Willis, 1930)

  • Phonetic methods

    • ==Use of the Closest Speaking Space with sibilant

  • Physiological

    • Freeway space (interocclusal clearance) should average 3mm (Niswonger, 1934)

  • Phonetic methods

    • Pronunciation of certain sounds should identify the smallest vertical dimension of pronunciation (Silverman, 1951)
    • Use of “s” sound based on fact that jaw had a memory of the vertical and horizontal position of “S” sound phonation (Pound, 1951)

  • Salivary swallowing (Shanahan, 1955)

  • Cephalometric (Pyott and Schaeffer, 1954)

Calamita et al, 2019

As none of these techniques has been shown to be sufficiently consistent and accurate to be used alone, the clinician should understand their principles and make use of an association of them to ensure greater accuracy in accordance with the patient’s case requirements.

5. Registration of Centric and Eccentric Relations33

  • Place a V-shaped notch bilaterally on the occlusal surface of the wax rim in the area of the second premolar
  • The notches should be 1 – 1.5 mm deep with no undercuts and have their horizontal axes angled posteriorly at about 45° to the midline
  • Lubricate the occlusal surfaces of the mandibular teeth with Vaseline
  • Apply a thin film of PVS adhesive to posterior occlusal surfaces of maxillary rim and allow to dry
  • Apply layer of Regisil to posterior occlusal surfaces of maxillary rim and close articulator pin onto the incisal guide

Verification

After the registration paste sets, the rims are removed from the mouth and reassembled to check for any interferences or inaccuracies in the record, particularly in the posterior regions.

Modified Procedure for Technique Class3435

Rationale for Modification

For the purposes of this technique class, the procedure is modified for time management. The preclinical course is abbreviated to 7 weeks, compared to a traditional 22-week course. Therefore, students will be provided with a 3D printed replica of a suitable lower complete denture and will only fabricate the upper denture.

Verify Articulator settings

  • Set incisal guide pin to zero (dark circle on pin flush with upper member of articulator)
  • Set condylar guidance to 25°
  • Set Bennett angle to 0°
  • Lock articulator in centric position

Adjust the occlusal rims

Todo

Instead of the standard procedure of adjusting the mandibular rim, students will adjust the upper occlusal rim to achieve even contact against the provided 3D-printed lower denture at the correct OVD.

  • Check that maxillary base fits the maxillary cast on the articulator
  • Adjust facial and occlusal contours of maxillary rim as follows:
    • The labial surface of the maxillary rim should be approximately parallel to the incisal pin
    • The occlusal level of the maxillary rim should be parallel to the occlusal plane with the incisal pin about 1.5 mm open (off the incisal guide table)
    • The distal ends of the rim should be clear of their respective retromolar pads
    • Cut a step in the anterior occlusal surface of the maxillary rim from the palatal to allow anterior overlap and reduce the posterior occlusal surface, distal to the canine teeth, so that the posterior rim just contacts the cusp tips of the opposing teeth, and the articulator pin is in contact with the incisal guide
  • Mark the centreline, smile line and canine line on the maxillary rim

6. Marking of reference lines3637

7. Tooth Selection

To be continued

But in the meantime:

Review

Journal of Oral Rehabilitation
Journal of Oral Rehabilitation 2017 44: 896–907

Determination of occlusal vertical dimension for complete dentures patients: an updated review

M. N. ALHAJJ*†, N. KHALIFA*‡, J. ABDUO§, A. G. AMRAN† & I. A. ISMAIL

Summary

A highly recommended reference on this topic is the comprehensive review by Calamita et al. (2019). The key finding of this review is that no single method for determining OVD is consistently accurate enough to be used in isolation. Clinicians should use a combination of several techniques to arrive at a clinically acceptable OVD.

*
*Department of Oral Rehabilitation, Faculty of Dentistry, Khartoum University, Sudan, †Department of Prosthodontics, Faculty of Dentistry, Dhahar, Yemen, ‡Department of General and Specialist Dental Practice, College of Dental Medicine, University of Sharjah, Sharjah, UAE, §Restorative Section, Melbourne Dental School, Melbourne University, Australia and †Department of Periodontics, Faculty of Dentistry, Thamar University, Dhahar, Yemen

Footnotes

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