As was pointed out in Chapter 1, failure of removable partial dentures can usually be attributed to factors that result in poor stability. These can result from inadequate diagnosis and failure to properly evaluate the conditions present. This results in failure to prepare the patient and the oral tissues properly before the master cast is fabricated. The importance of the examination, the consideration of favorable and unfavorable aspects relative to movement control, and the importance of planning the elimination of unfavorable influences cannot be overemphasized (see Chapter 2).

As was mentioned earlier, for complex treatment, two appointments are often required. The first will likely include a preliminary oral examination (to determine the need for management of acute needs), a prophylaxis, full-mouth radiographs, diagnostic casts, and mounting records if baseplates are not required. The follow-up appointment includes mounting of the diagnostic casts (when baseplates and occlusion rims are needed), a definitive oral examination, review of the radiographs to augment and correlate with clinical findings, and arrangement of additional consultations when required. Following collection and synthesis of all patient and clinical information, including surveying of the casts, a treatment plan (often with options) is presented.

Oral Examination

A complete oral examination should precede any treatment decisions. It should include visual and digital examination of the teeth and surrounding tissues with a mouth mirror, explorer, and periodontal probe, vitality tests of critical teeth, and examination of casts correctly oriented on a suitable articulator. Clinical findings are augmented by and correlated with a complete intraoral radiographic survey.

During the examination, the objective to be kept foremost in mind should be the consideration of possibilities for restoring and maintaining the remaining oral structures in a state of health for the longest period of time. This is best accomplished by an evaluation of factors that generate functional forces and those that resist them. The stability of tooth and prosthesis position is the goal of such an evaluation. The following sequence of examination allows attention to be paid to aspects of each of these critical features of evaluation for removable partial denture service.

Sequence for Oral Examination

An oral examination should be accomplished in the following sequence: visual examination, pain relief and temporary restorations, radiographs, oral prophylaxis, evaluation of teeth and periodontium, vitality tests of individual teeth, determination of the floor of the mouth position, and impressions of each arch.

1. Relief of pain and discomfort and caries control by placement of temporary restorations. A preliminary examination is conducted to determine the need for management of acute needs and whether a prophylaxis is required to conduct a thorough oral examination. It is advisable not only to relieve discomfort arising from tooth defects but also to determine as early as possible the extent of caries, and to arrest further caries activity until definitive treatment can be instituted. If tooth contours are restored with temporary restorations, the impression will not be torn on removal from the mouth, and a more accurate diagnostic cast may be obtained.

2. A thorough and complete oral prophylaxis. An adequate examination can be accomplished best with the teeth free of accumulated calculus and debris. Also, accurate diagnostic casts of the dental arches can be obtained only if the teeth are clean; otherwise the teeth reproduced on the diagnostic casts are not a true representation of tooth and gingival contours. Cursory examination may precede an oral prophylaxis, but a complete oral examination should be deferred until the teeth have been thoroughly cleaned.

3. Complete intraoral radiographic survey (Figure 12-1). The objectives of a radiographic examination are (a) to locate areas of infection and other pathosis that may be present; (b) to reveal the presence of root fragments, foreign objects, bone spicules, and irregular ridge formations; (c) to reveal the presence and extent of caries and the relation of carious lesions to the pulp and periodontal attachment; (d) to permit evaluation of existing restorations as to evidence of recurrent caries, marginal leakage, and overhanging gingival margins; (e) to reveal the presence of root canal fillings and to permit their evaluation as to future prognosis (the design of the removable partial denture may hinge on the decision to retain or extract an endodontically treated tooth); (f) to permit evaluation of periodontal conditions present and to establish the need and possibilities for treatment; and (g) to evaluate the alveolar support of abutment teeth, their number, the supporting length and morphology of their roots, the relative amount of alveolar bone loss suffered through pathogenic processes, and the amount of alveolar support remaining.

4. Impressions for making accurate diagnostic casts to be mounted for occlusal examination. The casts preferably will be articulated on a suitable instrument. The importance of accurate diagnostic casts and their use will be discussed later in this chapter.

5. Examination of teeth, investing structures, and residual ridges. The teeth, periodontium, and residual ridges can be explored by instrumentation and visual means. Recording of relevant patient history and clinical data on diagnosis charts is important to document features important to clinical presentation. These can be recorded on electronic or paper charts for future reference (Figures 12-2 and 12-3).

Figure 12-1 Complete intraoral radiographic survey of remaining teeth and adjacent edentulous areas reveals much information vital to effective diagnosis and treatment planning. The response of bone to previous stress is of particular value in establishing the prognosis of teeth that are to be used as abutments.

Figure 12-2 A, Diagnosis record for recording pertinent data.B, Treatment record chart for recording treatment plan and treatment progress.

Figure 12-3 Simple working chart. Restorations for individual teeth, crowns, and fixed partial dentures to be made may be marked on the chart and checked off as completed during mouth preparations.

Visual examination will reveal many of the signs of dental disease. Consideration of caries susceptibility is of primary importance. The number of restored teeth present, signs of recurrent caries, and evidence of decalcification should be noted. Only those patients with demonstrated good oral hygiene habits and low caries susceptibility should be considered good risks without resorting to prophylactic measures such as the restoration of abutment teeth. At the time of the initial examination, periodontal disease, gingival inflammation, the degree of gingival recession, and mucogingival relationships should be observed. Such an examination will not provide sufficient information to allow a definitive diagnosis and treatment plan. For this purpose, complete periodontal charting that includes pocket depths, assessment of attachment levels, furcation involvement, mucogingival problems, and tooth mobility should be performed. The extent of periodontal destruction must be determined with appropriate radiographs and use of the periodontal probe.

The number of teeth remaining, the location of the edentulous areas, and the quality of the residual ridge will have a definite bearing on the proportionate amount of support that the removable partial denture will receive from the teeth and edentulous ridges. Tissue contours may appear to present a well-formed edentulous residual ridge; however, palpation often indicates that supporting bone has been resorbed and has been replaced by displaceable, fibrous connective tissue. Such a situation is common in maxillary tuberosity regions. The removable partial denture cannot be supported adequately by tissues that are easily displaced. When the mouth is prepared, this tissue should be recontoured or removed surgically, unless otherwise contraindicated. A small but stable residual ridge is preferable to a larger unstable ridge for providing support for the denture. The presence of tori or other bony exostoses must be detected and their presence in relation to framework design must be evaluated. Failure to palpate the tissue over the median palatal raphe to ascertain the difference in its displaceability as compared with the displaceability of the soft tissues covering the residual ridges can lead to a rocking, unstable, uncomfortable denture and to a dissatisfied patient. Adequate relief of the palatal major connectors must be planned, and the amount of relief required is directly proportionate to the difference in displaceability of the tissues over the midline of the palate and the tissues covering the residual ridges.

During the examination, not only each arch but also its occlusal relationship with the opposing arch must be considered separately. A situation that looks simple when the teeth are apart may be complicated when the teeth are in occlusion. For example, an extreme vertical overlap may complicate the attachment of anterior teeth to a maxillary denture. Extrusion of a tooth or teeth into an opposing edentulous area may complicate the replacement of teeth in the edentulous area or may create occlusal interference, which will complicate the location and design of clasp retainers and occlusal rests. Such findings subsequently will be evaluated further by careful analysis of mounted diagnostic casts.

A breakdown of the fee may be recorded on the back of this chart for easy reference if adjustments or substitutions become necessary because of changes in diagnosis as the work progresses.

6. Vitality tests of remaining teeth. Vitality tests should be given particularly to teeth to be used as abutments and those having deep restorations or deep carious lesions. This should be done through both thermal and electronic means.

7. Determination of the height of the floor of the mouth to locate inferior borders of lingual mandibular major connectors. Mouth preparation procedures are influenced by the choice of major connectors (see Figure 5-6). This determination must precede altering contours of abutment teeth.

The fee for examination, which should include the cost of the radiographic survey and the examination of articulated diagnostic casts, should be established before the examination is performed and should not be related to the cost of treatment. It should be understood that the fee for examination is based on the time involved and the service rendered, and that the material value of the radiograph and diagnostic casts is incidental to the effectiveness of the examination.

The examination record should always be available in the office for future consultation. If consultation with another dentist is requested, respect for the hazards of unnecessary radiation justifies loaning the dentist the radiograph for this purpose. However, duplicate films should be retained in the dentist’s files.

Diagnostic Casts

A diagnostic cast should be an accurate reproduction of all the potential features that aid diagnosis. These include the teeth locations, contours, and occlusal plane relationship; the residual ridge contour, size, and mucosal consistency; and the oral anatomy delineating the prosthesis extensions (vestibules, retromolar pads, pterygomaxillary notch, hard/soft palatal junction, floor of the mouth, and frena). Additional information provided by appropriate cast mounting includes occlusal plane orientation and the impact on the opposing arch; tooth-to-palatal soft tissue relationship; and tooth-to-ridge relationships both vertically and horizontally.

A diagnostic cast is usually made of dental stone because of its strength and the fact that it is less easily abraded than is dental plaster. Generally the improved dental stones (die stones) are not used for diagnostic casts because of their cost. Their greater resistance to abrasion does, however, justify their use for master casts.

The impression for the diagnostic cast is usually made with an irreversible hydrocolloid (alginate) in a stock (perforated or rim lock) impression tray. The size of the arch will determine the size of the tray to be used. The tray should be sufficiently oversized to ensure an optimum thickness of impression material to avoid distortion or tearing on removal from the mouth. The technique for making impressions is covered in more detail in Chapter 15.

Purposes of Diagnostic Casts

Diagnostic casts serve several purposes as an aid to diagnosis and treatment planning. Some of these are as follows:

1. Diagnostic casts are used to supplement the oral examination by permitting a view of the occlusion from the lingual, as well as from the buccal, aspect. Analysis of the existing occlusion is made possible when opposing casts are occluded, as is a study of the possibilities for improvement by occlusal adjustment, occlusal reconstruction, or both. The degree of overclosure, the amount of interocclusal space available, and the possibilities of interference with the location of rests may also be determined. As was stated previously, opportunities for improvement of the occlusal scheme, by occlusal adjustment or occlusal reconstruction, are best evaluated by analysis and modification of mounted diagnostic casts. Such procedures often include diagnostic waxing to determine the possibility of enhancing the occlusion before definitive treatment is begun (Figure 12-4). In other words, diagnostic casts permit the dentist to plan ahead to avoid undesirable compromises in the treatment being given a patient.

2. Diagnostic casts are used to permit a topographic survey of the dental arch that is to be restored by means of a removable partial denture. The cast of the arch in question may be surveyed individually with a cast surveyor to determine the parallelism or lack of parallelism of tooth surfaces involved, and to establish their influence on the design of the removable partial denture. The principal considerations in studying the parallelism of tooth and tissue surfaces of each dental arch are to determine the need for mouth preparation: (a) proximal tooth surfaces, which can be made parallel to serve as guiding planes; (b) retentive and nonretentive areas of the abutment teeth; (c) areas of interference with placement and removal; and (d) esthetic effects of the selected path of insertion. From such a survey, a path of placement may be selected that will satisfy requirements for parallelism and retention to the best mechanical, functional, and esthetic advantage. Then mouth preparations may be planned accordingly.

3. Diagnostic casts are used to permit a logical and comprehensive presentation to the patient of present and future restorative needs, as well as of the hazards of future neglect. Occluded and individual diagnostic casts can be used to point out to the patient (a) evidence of tooth migration and the existing results of such migration; (b) effects of further tooth migration; (c) loss of occlusal support and its consequences; (d) hazards of traumatic occlusal contacts; and (e) cariogenic and periodontal implications of further neglect. Treatment planning actually may be accomplished with the patient present, so that economic considerations may be discussed. Such use of diagnostic casts permits justification of the proposed fee through the patient’s understanding of the problems involved and of the treatment needed. Inasmuch as mouth rehabilitation procedures are frequently lengthy and often irreversible, there must be complete accord between dentist and patient before extensive treatment is begun, and financial arrangements must be consummated during the planning phase.

4. Individual impression trays may be fabricated on the diagnostic casts, or the diagnostic cast may be used in selecting and fitting a stock impression tray for the final impression. If wax blockout is to be used in the fabrication of individual trays, a duplicate cast made from an irreversible hydrocolloid (alginate) impression of the diagnostic cast should be used for this purpose. The diagnostic cast is too valuable for purposes of future reference to risk damage resulting from the making of an impression tray. On the other hand, if oil-based clay blockout is used, the diagnostic cast may be used without fear of damage.

5. Diagnostic casts may be used as a constant reference as the work progresses. Penciled marks indicating the type of restoration, the areas of tooth surfaces to be modified, the location of rests, and the design of the removable partial denture framework, as well as the path of placement and removal, all may be recorded on the diagnostic cast for future reference (Figure 12-5). Then these steps may be checked off the worksheet as they are completed. Areas of abutment teeth to be modified may first be changed on the duplicate diagnostic cast by trimming the stone cast with the surveyor blade. A record is thus made of the location and degree of modification to be done in the mouth. This must be done in relation to a definite path of placement. Any mouth preparations to be accomplished with new restorations require that restored teeth be shaped in accordance with a previously determined path of placement. Even so, the shaping of abutment teeth on the duplicate diagnostic cast serves as a guide to the form of the abutment. This is particularly true if the contouring of wax patterns is to be delegated to the technician, as it may be in a busy practice.

6. Unaltered diagnostic casts should become a permanent part of the patient’s record because records of conditions existing before treatment are just as important as are preoperative radiographs. Therefore diagnostic casts should be duplicated, with one cast serving as a permanent record and the duplicate cast used in situations that may require alterations to it.

Figure 12-4 A, Following mounting of the diagnostic casts, tooth arrangement for the mandibular occlusal plane requirements can be accomplished. B, Following placement of the maxillary anterior teeth in an ideal position, diagnostic arrangement of occlusion results in a space posterior to surveyed crown #27. If such a finding were objectionable, alternative arrangements could be investigated. This is not possible unless a diagnostic workup is completed. C, Occlusion of the mandibular removable partial denture will be enhanced by improving the maxillary posterior occlusal plane of the super-erupted molars.

Figure 12-5 Proposed mouth changes and design of the removable partial denture framework are indicated in pencil on the diagnostic cast in relation to the previously determined path of placement. This serves as a means of communicating with the patient and as a chair-side guide to tooth modification.

Mounting Diagnostic Casts

For diagnostic purposes, casts should be related on an anatomically appropriate articulator to best understand the role occlusion may have in the design and functional stability of the removable partial denture. This becomes increasingly important as the prosthesis replaces more teeth. If the patient presents with a harmonious occlusion and the edentulous span is a tooth-bound space, simple hand articulation is generally all that is required. However, when the natural dentition is not harmonious and/or when the replacement teeth must be positioned within the normal movement patterns of the jaws, the diagnostic casts must be related in an anatomically appropriate manner for diagnosis. This means placement of the maxillary cast in a position relative to the opening axis on the articulator, which is similar to the position of the maxilla in relation to the temporomandibular joint of the patient (Figure 12-6). The mandibular cast is then placed beneath the maxillary cast in a horizontal position dictated by mandibular rotation without tooth contact, at a minimal vertical opening.

Figure 12-6 Use of the facebow makes possible the recording of the spatial relationship of the maxillae to some anatomic reference points and transference of this relationship to an articulator.

The Glossary of Prosthodontic Terms* describes an articulator as a mechanical device that represents the temporomandibular joints and jaw members, to which maxillary and mandibular casts may be attached. Because the dominant influence on mandibular movement in a partially edentulous mouth is the occlusal plane and the cusps of the remaining teeth, an anatomic reproduction of condylar paths is probably not necessary. Still, movement of the casts in relation to one another as influenced by the occlusal plane and the cusps of the remaining teeth, when mounted at a reasonably accurate distance from the axis of condylar rotation, permits a relatively valid analysis of occlusal relations. This is more anatomically accurate than a simple hinge mounting.

It is better that the casts be mounted in relation to the axis-orbital plane to permit better interpretation of the plane of occlusion in relation to the horizontal plane. Although it is true that an axis-orbital mounting has no functional value on a nonarcon instrument because that plane ceases to exist when opposing casts are separated, the value of such a mounting lies in the orientation of the casts in occlusion. (An arcon articulator is one in which the condyles are attached to the lower member as they are in nature, the term being a derivation coined by Bergström from the words articulation and condyle. Many of the more widely used articulators such as the Hanau H series, Dentatus, and improved Gysi have the condyles attached to the upper member and are therefore nonarcon instruments.)

Sequence for Mounting Maxillary Cast to Axis-Orbital Plane

The initial steps allow recording of the maxilla–temporomandibular joint (TMJ) relationship:

1. Identify the anterior and posterior reference points for the facebow (e.g., external auditory meatus, orbitale).

2. Prepare the bite fork and occlusion rim.

3. Place the bite fork centered to the arch, indexing it to the teeth with wax or elastomer.

4. Place the facebow over the bite fork rod anteriorly.

5. Place the bow evenly into the ears posteriorly.

6. Secure the bow anteriorly.

7. Position the bow anteriorly to the third point of reference (establishes the horizontal plane).

8. Secure the bite fork vertical rod, then the horizontal rod (holding the bow securely to prevent torque).

9. Release the bow anteriorly to allow spread, and disengage from the ears.

10. Remove the fork downward and out of the mouth with the attached bow.

11. Carefully check the security of the attachments.

The next steps allow transfer of the recorded relationship to the articulator:

1. Position the posterior reference points on the articulator (usually a posterior attachment point).

2. Secure the posterior points by securing the bow anteriorly.

3. Vertically relate the secured bow to the articulator anterior reference point.

4. Seat the maxillary cast into the bite fork registration (wax or elastomer).

5. Close the articulator and check clearance for mounting plaster (modify the cast as needed).

6. Mount with low-expansion plaster.

The facebow is a relatively simple device used to obtain a transfer record for orienting a maxillary cast on an articulating instrument. Originally, the facebow was used only to transfer a radius from condyle reference points, so that a given point on the cast would be the same distance from the condyle as it is on the patient. The addition of an adjustable infraorbital pointer to the facebow and the addition of an orbital plane indicator to the articulator make possible the transfer of the elevation of the cast in relation to the axis-orbital plane. This permits the maxillary cast to be correctly oriented in the articulator space comparable with the relationship of the maxilla to the axis-orbital plane on the patient. To accommodate this orientation of the maxillary cast and still have room for the mandibular cast, the posts of the conventional articulator must be lengthened. The older Hanau model H articulator usually will not permit a facebow transfer with an infraorbital pointer.

A facebow may be used to transfer a comparable radius from arbitrary reference points, or it may be designed so that the transfer can be made from hinge axis points. The latter type of transfer requires that a hinge-bow attached to the mandible should be used initially to determine the hinge axis points, to which the facebow is then adjusted for making the hinge axis transfer.

A facebow transfer of the maxillary cast, which is oriented to the axis-orbital plane in a suitable articulator, is an uncomplicated procedure. The Hanau series Wide-Vue 183-2, all 96H2-0 models, the Whip-Mix articulator (Whip-Mix Corp, Louisville, KY), and the Dentatus model ARH (Dentatus USA, New York, NY) will accept this transfer. The Hanau earpiece facebow models 153 and 158, the Hanau fascia facebow 132-2SM, and the Dentatus facebow type AEB incorporate the infraorbital plane to the articulator. None of these are hinge axis bows; they are used instead at an arbitrary point.

The location of the arbitrary point or axis has long been the subject of controversy. Gysi and others have placed it 11 to 13 mm anterior to the upper third of the tragus of the ear on a line extending from the upper margin of the external auditory meatus to the outer canthus of the eye. Others have placed it 13 mm anterior to the posterior margin of the center of the tragus of the ear on a line extending to the corner of the eye. Bergström has located the arbitrary axis 10 mm anterior to the center of a spherical insert for the external auditory meatus and 7 mm below the Frankfort horizontal plane.

In a series of experiments reported by Beck, it was shown that the arbitrary axis suggested by Bergström falls consistently closer to the kinematic axis than do the other two. It is desirable that an arbitrary axis is placed as close as possible to the kinematic axis. Although most authorities agree that any of the three axes will permit transfer of the maxillary cast with reasonable accuracy, it would seem that the Bergström point compares most favorably with the kinematic axis.

The lowest point on the inferior orbital margin is taken as the third point of reference for establishing the axis-orbital plane. Some authorities use the point on the lower margin of the bony orbit in line with the center of the pupil of the eye. For the sake of consistency, the right infraorbital point is generally used and the facebow assembled in this relationship. All three points (right and left axes and infraorbital point) are marked on the face with an ink dot before the transfer is made.

Casts are prepared for mounting on an articulator by placing three index grooves in the base of the casts. Two V-shaped grooves are placed in the posterior section of the cast and one groove in the anterior portion (Figure 12-7).

Figure 12-7 The base of the cast has been prepared for mounting by placing three triangular grooves to allow indexing when mounted. The grooves are prepared with a 3-inch stone mounted in a laboratory lathe.

An occlusion rim properly oriented on a well-fitting record base should be used in facebow procedures involving the transfer of casts representative of the Class I and II partially edentulous situations. Without occlusion rims, such casts cannot be located accurately in the imprints of the wax covering the facebow fork. Tissues covering the residual ridges may be displaced grossly when the patient closes into the wax on the facebow fork. Therefore the wax imprints of the soft tissues will not be true negatives of the edentulous regions of the diagnostic casts.

For purposes of illustration, a facebow using the external auditory meatus as the posterior reference point, the Whip-Mix Facebow technique (DB 2000, Whip-Mix Corp, Louisville, KY), will be shown. The facebow fork is covered with a polyether, polyvinyl siloxane or a roll of softened baseplate wax with the material distributed equally on the top and on the underneath side of the facebow fork. Then the fork should be pressed lightly on the diagnostic casts with the midline of the facebow fork corresponding to the midline of the central incisors (Figure 12-8). This will leave imprints of the occlusal and incisal surfaces of the maxillary casts and occlusion rim on the softened baseplate wax and is an aid in correctly orienting the facebow fork in the patient’s mouth. The facebow fork is placed in position in the mouth, and the patient is asked to close the lower teeth into the wax to stabilize it in position. It is removed from the mouth and chilled in cold water and then replaced in position in the patient’s mouth. An alternative method of stabilizing the facebow fork and recording bases is to enlist the assistance of the patient.

Figure 12-8 Orienting the facebow fork to the maxillary cast and occlusion rims will avoid displacing the occlusion rim in the mouth through patient closure or another uneven force. Polyvinyl siloxane material has been evenly distributed around the facebow fork, and care is exercised to position the fork to be centered at the mid-incisal position without any fork extension posterior to the record base, which could cause discomfort.

If an earpiece facebow is to be used, the patient should be reminded that the plastic earpieces in the auditory canals will greatly amplify noise. With the facebow fork in position, the facebow toggle is slipped over the anterior projection of the facebow fork (Figure 12-9). The patient can assist in guiding the plastic earpieces into the external auditory meatus. The patient can then hold the arms of the facebow in place with firm pressure while the operator secures the bite fork to the facebow. This accomplishes the radius aspect of the facebow transfer.

Figure 12-9 The horizontal toggle clamp of the Whip-Mix earpiece facebow (1) is slid onto the shaft of the facebow fork protruding from the patient’s mouth. The patient then helps guide plastic earpieces into the external auditory meatus and holds them in place while the operator tightens three thumb screws (2) and centers the plastic nosepiece (3) securely on the nasion. The horizontal toggle clamp is positioned and secured near (but not touching) the lip. The T screw (4) on the vertical bar is tightened. note: Extreme care should be exercised not to tilt the facebow out of position when tightening.

If an infraorbital pointer is used, it is placed on the extreme right side of the facebow and angled toward the infraorbital point previously identified with an ink dot. It is then locked into position with its tip lightly touching the skin at the dot. This establishes the elevation of the facebow in relation to the axis-orbital plane. Extreme care must be taken to avoid any slip that might injure the patient’s eye.

With all elements tightened securely, the patient is asked to open, and the entire assembly is removed intact, rinsed with cold water, and set aside. The facebow records not only the radius from the condyles to the incisal contacts of the upper central incisors, but also the angular relationship of the occlusal plane to the axis-orbital plane.

The facebow must be positioned on the articulator in the same axis-orbital relation as on the patient. If an arbitrary-type facebow is used, the calibrated condyle rods of the facebow ordinarily will not fit the condyle shafts of the articulator unless the width between the condyles just happens to be the same. With a Hanau model 132-25M facebow, the calibrations must be reequalized when in position on the articulator. For example, they have read 74 (mm) on each side of the patient but must be adjusted to read 69 (mm) on each side of the articulator. Some later model articulators have adjustable condyle rods and may be adjusted to fit the facebow. It is necessary that the facebow be centered in either case. Some facebows are self-centering, as is the Hanau Spring-Bow (Whip-Mix Corp, Louisville, KY).

The third point of reference is the orbital plane indicator, which must be swung to the right so that it will be above the tip of the infraorbital pointer. The entire facebow with maxillary cast in place must be raised until the tip of the pointer contacts the orbital plane indicated. The elevation having thus been established, for all practical purposes the orbital plane indicator and the pointer may now be removed because they may interfere with placing the mounting stone.

An auxiliary device called a cast support is available; it is used to support the facebow fork and the maxillary cast during the mounting operation (Figure 12-10). With this device, the weight of the cast and the mounting stone are supported separately from the facebow, thus preventing possible downward movement resulting from their combined weight. The cast support is raised to supporting contact with the facebow fork after the facebow height has been adjusted to the level of the orbital plane. Use of some type of cast support is highly recommended as an adjunct to facebow mounting.

Figure 12-10 Facebow fork support used to maintain the fork and cast in position while mounting.

The keyed and lubricated maxillary cast is now attached to the upper arm of the articulator with the mounting stone, thus completing the facebow transfer (Figure 12-11). Not only will the facebow have permitted the upper cast to be mounted with reasonable accuracy, it also will have served as a convenient means of supporting the cast during mounting. Once mastered, its use becomes a great convenience rather than a time-consuming nuisance.