Louis Blatterfein

Comparison of the fidelity of radiographs of mandibular condyles made by different techniques.

Abstract The radiograph is an important aid in the diagnosis of temporomandibular joint problems. A marked difference of opinion exists in the interpretation of radiographs produced by various techniques. To establish some common basis for agreement, a study of the morphology of the condyle of the temporomandibular joint was undertaken. Temporomandibular joints of cadavers were radiographed and dissected. The dissections revealed a startling variation in the form of condyles and many instances of pathologic aberrations. Radiographs of the temporomandibular joints were made by three commonly used techniques to correlate the morphology of condyles with their radiographic appearance. All three techniques (Atco, Updegrave and Lindblom) failed to provide a meaningful depiction of the three-dimensional appearance of condyles with irregular forms. Tomography was used to obtain radiographic information of greater diagnostic value. The Polytome H machine uses a hypocycloidal (twisting, pretzel-like) movement to provide radiographs of predetermined sections of structures. All structures other than the thin section desired are blurred out by the hypocycloidal movement of the machine. Tomographs were made of patients with temporomandibular joint problems in conjunction with conventional radiographs for diagnostic study and comparative evaluation. The tomographs provided evidence of condyle and glenoid fossa irregularities that were undetectable by the usual radiographs. When tomographs are made of both sides and in the open and closed positions, valuable clinical information about intercondylar symmetry and the comparative symmetry of condylar movement is provided. Tomography was used on cadavers to determine the fidelity of (1) conventional radiographs and (2) tomographic radiographs in relation to the gross structures they are expected to depict. Comparisons were made of radiographs of the in situ condyles that were obtained by the three one-plane techniques. No significant differences were observed in the radiographs obtained. Comparisons were made of in situ one-plane radiographs with the ideally angulated radiographs of the enucleated condyle. A fair degree of fidelity of the in situ radiographs was observed. However, both radiographs depicted only maximum contours of the condyle and failed to reveal irregularities in contour when asymmetry or pathologic aberrations are present. Comparisons were made of in situ one-plane radiographs with ideally angulated radiographs of the serial cuts of the enucleated condyle. Some degree of fidelity of the in situ radiographs was observed when a symmetrical condyle was sectioned. Lack of fidelity was noted when condylar irregularity was present. Comparisons were made of individual radiographs of a tomographic series with the corresponding ideally angulated radiographs of the condyle section depicted. A fair degree of fidelity of the radiographic image of the tomographic radiograph was observed. However, tomographic radiographs exhibit some magnification and are not as sharp and clear as conventional radiographs.

The use of the semiprecision rest in removable partial dentures

Abstract The requirements of retainers for removable dentures are more effectively fulfilled with a deep rest retainer than with a shallow rest design. A deep rest retainer may be of the precision or the semiprecision type. In designing a semiprecision rest, four aspects of it must be taken into consideration: (1) the occlusal form, (2) the proximal form, (3) the gingival floor form, and (4) the proximal surface placement. When a semiprecision rest is used, primary retention can be attained by either a lingual arm or a spring device. If a lingual arm is used, the degree of retention can be augmented by modifying the contour of the lingual surface of the abutment casting. Possible modifications are an exaggerated undercut contour, a horizontal groove, and a dimple in a casting. Various spring devices can be used depending on whether the deep rest is placed on the proximal surface adjacent to the edentulous area or on the proximal surface away from the edentulous region. All types of preparations for abutment castings should have a full shoulder on the proximal surface that is to receive the deep rest. The shoulder should turn into the buccal and lingual contours of the preparation. The wax patterns of the abutment castings should have proximal surfaces that are parallel to each other and have enough bulk to permit milling of the selected form of semiprecision rest. The lingual surface should have its greatest contour close to the gingival margin of the tooth on the half that is to be contacted by the rigid section of the lingual arm. The greatest contour of the other half of the lingual surface should be closer to the occlusal surface. Impressions for the construction of a semiprecision removable partial denture can be made in rubber or silicone elastic materials in conjunction with plaster. The technique used varies depending on the arrangement of the remaining teeth. The two main arrangements encountered are (1) a free-end ridge on one side and a tooth-bounded ridge on the opposite side, and (2) bilateral free-end edentulous ridges. In both situations, the ridge areas are registered by the elastic material in a spaced custom-made tray, and the seats for the abutment castings are registered in plaster or rapid-setting artificial stone.

A loading impression technique for semiprecision and precision removable partial dentures

The rationale of designing a seimprecision or precision distal-extension removable partial denture and the justification of ridge loading in distal-extension ridge impression techniques have been presented. The effectiveness of existing impression techniques in securing firm seats for abutment castings, accurate border extension of the denture base, and loading of the ridge mucosa has been evaluated. A technique has been described that overcomes the limitations of existing impression techniques for semiprecision and precision distal-extension removable partial dentures.

Rebasing procedures for removable partial dentures

Abstract Partial dentures cannot be successfully rebased by a routine standardized technique. Critical clinical factors determine the procedure followed. These factors are: (1) the type of denture bases present on the partial denture, (2) the degree of ridge resorption under the denture bases, (3) the accuracy of the border extension of the denture bases, (4) the occlusion of the artificial teeth on the denture bases, and (5) the presence of framework rotation. A consideration of these factors dictates the classification of partial dentures requiring rebasing into seven definite groups requiring supplements to a general basic technique. The supplements that are added to the basic technique according to changes observed are: (1) the border supplement, (2) the spacing supplement, (3) the framework supplement, and (4) the occlusion supplement. The problems encountered in each group of the classification are analyzed, and procedures incorporating the various required supplements are described.

A new approach to partial denture design for unilaterally remaining lower teeth.

Abstract The usual types of removable partial dentures do not function adequately in mouths where one or a few lower teeth remain on only one side and where there are edentulous regions anterior and posterior to the teeth. The amount of rotation around framework fulcrums of sections of the denture base varies greatly. This uneven movement may cause excessive resorption of the ridge on the side opposite the remaining teeth. Fulcrum points or areas of the framework on a horizontal plane must be eliminated to permit a uniform vertical movement of the base. This objective can be accomplished by eliminating occlusal rests and the engaging points of stress-breaking devices. The natural tooth contours are modified by crowns to allow continuing contact of the framework and abutment teeth during function and following ridge resorption. Crowns placed on abutment teeth are contoured to have surfaces 4 to 5 mm. long that are parallel to each other in a vertical direction. These surfaces are contacted by metal bands that encircle the crowns. The contacts are 0.5 mm. in diameter, and they are made at the center of the 2.5 mm. wide metal bands. Space is established 1 mm. occlusal to and gingival to the area of contact. This space permits rotation without causing excessive torque on the abutment teeth. Contact is established after the initial rotation. The amount of space is determined by such clinical factors as the condition of ridges, crown heights, root lengths, and periodontal evaluation of the remaining teeth. The crowns may be constructed of gold or porcelain on metal. No attempt is made to attain primary retention. Occlusal displacement is counteracted by the stabilizing effect of the framework and patient training in proper tongue position. Since this type of prosthesis functions similar to a complete denture, it should be constructed only in conjunction with a complete upper denture. Acrylic resin teeth are used on the upper denture and porcelain teeth on the lower one. The teeth of the upper denture that oppose the crowns are set out of contact. Dentures of this type were constructed for 19 patients over a 2 year period. Observations on the patients were made at 6 month intervals. The observations were on patient reaction, tissue condition, stability, periodontal condition and mobility of abutment teeth, retention, maintenance of occlusion, and ridge resorption. The results were generally favorable with good patient acceptance and satisfaction. The long-term potential of the procedure requires further clinical study and observation. Information on length of time that abutment teeth can be retained, the magnitude of ridge resorption, and the relationship of ridge resorption to tooth extrusion must be secured before a final evaluation of the procedure can be made.

The planning and contouring of acrylic resin veneer crowns for partial denture clasping

Abstract Crowns on abutment teeth that are to be clasped must be properly planned and contoured for maximum clasp function. Ideal clasp positioning is used as a basis for establishing functional contour. The typical circumferential clasp contacts a proximal surface and usually the buccal and lingual surfaces. The body of a clasp should be located with its inferior edge approximately halfway between the gingival margin and the occlusal surface of the tooth. To permit this positioning, the height of contour (survey line) of the proximal surface should be somewhere in the gingival half of the tooth. The flexible section of a clasp arm lies in the far zone and should be positioned at the gingival margin. For this positioning, the survey line in the far zone should be at the junction of the middle and gingival thirds. The rigid section of a clasp arm lies in the near zone and joins the body to the flexible section. It should be placed midway between the gingival margin and occlusal surface. To allow for this positioning, the survey line should be somewhere in the gingival half of the near zone. If these contours are constructed on an acrylic resin veneer crown abutment, the undercut necessary for clasp retention will be entirely of acrylic resin. Repeated insertions and removals will wear away the undercut with the ultimate loss of clasp retention. To prevent this undesirable wear, the undercut providing primary retention must be constructed entirely in metal rather than acrylic resin. If crowns are to be constructed with these contours, modifications in routine procedure must be adopted. They must be contoured in relation to one another. A master cast is obtained with dies of the prepared teeth in correct relation to one another. Wax patterns of crowns are surveyed and contours corrected to give ideal survey lines. Windows for acrylic resin veneers are carved in the patterns. In the near zone, these windows are carved as far occlusally and gingivally as possible. In the far zone, their gingival outlines are carved slightly occlusal to the survey line that is ideally located at the junction of the gingival and middle thirds. Crowns are cast, again surveyed for correct contour, and the veneers are processed. The veneers are checked on the surveyor for overcontouring. If clasping retention is desired in the near zone rather than the far zone, the wax patterns are contoured differently. In the near zone, the survey line should be at the junction of the gingival and middle thirds. In the far zone, the survey line can be anywhere in the gingival half. When windows for acrylic veneers are carved, in the far zone the windows are cut as far occlusally and gingivally as possible. In the near zone, the gingival outlines of the windows are cut slightly occlusal to the survey line located at the junction of the gingival and middle thirds. The crowns are then completed from these patterns.