FIXED PROSTHODONTICS HENRY
E. EBEL, SAMUEL
Clinical metal
E. GUYER,
procedures
WILLIAM
for improving
LEFKOWITZ,
Section editors
veneered
crowns
Jaime Pietrokovski, Hebrew University,
C.D., MS.,* and Saul Sorin, Dr.Odont.** Hadassah Faculty of Dental Medicine, Jerusalem,
Israel
lhe d esign and preparation of the window for the labial and proximal surfaces of a veneered metal crown are essentially routine laboratory procedures. However, clinical experience indicates that optimal esthetic effects and maximum retention of the veneering material can only be achieved when the dentist is well acquainted with the laboratory procedures and is able to recognize technical errors and make the appropriate corrections.1-3 This article describes a step-by-step chairside procedure for properly reshaping and adjusting the laboratory prepared window during the try-in phase of the cast restoration. PREPARATION When preparing an anterior tooth for a veneered metal crown, special care is necessary to achieve an optimum esthetic result. In addition to careful attention to the size, shape, and color of the entire restoration, the metallic frame should not be visible to the observing eye. On the facial and proximal surfaces of the prepared tooth, a deep preparation, in the form of a shoulder or chamfer, is necessary to provide enough space for the porcelain or acrylic resin veneering material. This chamfer or shoulder preparation must follow the contour of the gingival crest and should extend uniformly at least 0.5 mm. into the sulcus, so that the gingival margin of the veneering material is located inside the gingival sulcus (Fig. 1) . The veneer material should cover the entire window, conceal the metal, and produce a veneered crown which is harmonious, in color and form, with the adjacent Supported in part by a grant from the Joint Hadassah School of Dental Medicine, Jerusalem. *Senior **Clinical
Lecturer, Lecturer,
Department Department
Research Fund of The Hebrew University,
of Oral Rehabilitation. of Oral Rehabilitation.
503
504
Pietrokouski
and Sorin
J. Prosthet. Dent. November, 1975
Fig. 1. Left central incisor after reduction for a veneered metal crown. The chamfer PIreparation is parallel to the gingival crest contour at the buccal and proximal aspects of the tooth.
Fig. 2. The metal casting after its return from the dental laboratory for the try-in. collar covers the chamfer preparation and is the only guideline for the technician the level of the veneer window.
The gingival to determine
Fig. 3. Try-in of the crown in the patient’s mouth. Note the evidence of gold at the center of the labial surface. The gold will be visible in the finished crown if not corrected at this stage.
teeth. For optimum contour and shade, an acrylic resin veneer needs a square butt joint I mm. thick, extending proximally to include the full depth of the embrasure. Because proper adjustment depends on the extent and exactness of the shoulder or chamfer, it is obvious that the correct design and preparation of the window must begin with the accurate preparation of the tooth. In the absence of an adequate preparation, which should extend deep into the mesial and distal interproximal spaces, carving and reproducing the three-dimensional contour of natural teeth become difficult. The usual result is a flat veneer, so typical of artificial teeth. The technician, in an attempt to correct for the lack of a proper interproximal preparation, has to make the metal margins heavier than necessary. The final restora-
Volume 34 Number 5
Improving
Fig. 4. The displayed gold collar of the gingival margin. Fig. 5. The metal the labial aspect.
crown
after
is reduced
completion
with
veneered
metal
crowns
a No. 6 bur to a level flush with
of the reduction.
The gold collar
Fig. 7. The complete veneered metal crown all surfaces which are visible to the eye.
in the patient’s
mouth.
the crest
is invisible
Fig. 6. The veneered crown returned to the master cast. Note the diminished collar on the labial surface when compared with the collar in Fig. 2. The acrylic
width
505
from
of the
resin covers
tions, especially short ones, lose any resemblance to natural teeth. They also impinge on the interdental papillae and constitute a potential source of periodontal disease. Usually, the technician casts these cervical margins in a slightly bulkier form than necessary, because the extra thickness of the metal ensures a better and denser casting and protects the integrity of the margins during subsequent handling. Therefore, after checking the fit, the contact areas, and the form and occlusal anatomy of the crown, the cervical margin usually has to be reduced to preserve the space for the interdental papillae, even if it does not cause blanching of the gingivae. An overcontoured shoulder may also adversely affect the facial anatomy of the veneer, which is important for esthetic reasons and gingival health (Figs. 2 and 3).
506
J. Prosthet. Dent. November, 1975
Pietrokouski and Sorin
Fig. 8. The metallic retainer. This will plastic material.
band has been reduced from the contact area to the gingival crest for a allow for a satisfactory esthetic result when the window is covered by the
Fig. 9. The clinical be detected
aspect of the finished fixed partial denture on the mesial aspect of the veneered metal crown.
after
insertion.
No metal can
ADJUSTtNG THE WtNDOW Adjustment of the thickness of metal at the gingival margin should be made in the mouth with a No. 6 round bur at low speed. Shortening and reshaping of this margin level with and parallel to the curvature of the free gingiva, without lacerating it, will clearly mark the exact relation of the gingiva to the cervical margin of the gold frame (Figs. 4 and 5). Unless visibility of the gold is not critical, as in lower and posterior restorations, this demarcation line is not the finish line of the veneering material. It is only a guideline for the technician to cut back the metal about 0.5 mm. This will ensure that the metal margin of the shoulder will be subgingival and that no gold will be visible. Reducing the margin will be part of the over-all refinement by the technician before he applies the veneering material. If necessary, the incisal length of the casting is also adjusted directly in the mouth, according to the length of the adjacent teeth and the esthetic requirements of the patient. At this stage, unless already done in wax, the refinement will also include the maximum extension of the window, both mesially and distally, so that no metal will be visible interproximally (Figs. 6 to 9) .
DEPTH OF WINDOW To
facilitate
proper
contouring
and
shade,
the entire
inner
aspect
of the veneer
window, which is mainly a retentive area, must allow for a thickness of at least 1 mm. of the veneering material. Though such space must be provided during the preparation of the tooth, the dentist should check this space before finishing the restoration. Most dentists will leave the choice of adequate retentive elements on the facial surface of the veneer to the discretion of the laboratory personnel. Loops and/or beads, distributed over the entire inner surface and attached to the mesial and distal cervical corners of the casting, provide satisfactory retention for the veneering
Volume 34 Number 5
Improving
veneered
metal
crowns
507
material. For obvious reasons, these retaining elements have to be inserted in the waxing stage, and their position cannot be changed after casting.4p 5 However, only after the window outline has been finally approved during the try-in phase can the reverse bevel be prepared. This bevel, required for acrylic resin veneers, is the groove which the technician cuts along the entire periphery of the veneer, completely surrounding it, and by which the veneering material is most effectively retained.G SUMMARY Satisfactory design and preparation of the veneer window presuppose that a perfect or a near-perfect preparation of the tooth has been made. The window is not just a cutout and is not the responsibility of the laboratory technician. Whenever optimum gingival health, a satisfactory esthetic result, and a longlasting restoration are desired, it is worthwhile to carefully check and, if necessary, adjust the veneer window directly in the mouth before the veneer is added. This is especially important in restorations that extend below the gingival margin. References 1. Cohen, L. A.: The Acrylic Faced Cast Gold Crown, J. PROSTHET. DENT. 1: 112-124, 1951. 2. Long, A. C.: Acrylic Resin Veneered Crowns: The Effect of Tooth Preparation on Crown Fabrication and Future Periodontal Health, J. PROSTHET. DENT. 19: 370-380, 1968. 3. Johnson, J. F., Phillips, R. W., and Dykema, R. W.: Modern Practice in Crown and Bridge Prosthodontics, Philadelphia, 1969, W. B. Saunders Company, p. 343. 4. Weinberg, L. A.: Atlas of Crown and Bridge Prosthodontics, St. Louis, 1965, The C. V. Mosby Company, pp. 83-87. 5. Dykema, R. W., Johnson, J. F., and Cunningham, D. M.: The Veneered Gold Crown, Dent. Clin. North Am., Nov., 1958, p. 653. 6. Miller, A. J.: Inlays, Crowns and Bridges. An Atlas of Clinical Procedures, Philadelphia, 1962, W. B. Saunders Company, p. 127. DR.
PIETROKOVSKI
TUFTS UNIVERSITY SCHOOL OF DENTAL MEDICINE ONE KNEELAND ST. BOSTON, MASS. 02111 DR. SORIN THE HEBREW UNIVERSITY HADASSAH SCHOOL OF DENTAL MEDICINE P. 0. Box 499 JERUSALEM, ISRAEL
E. EBEL, SAMUEL
Clinical metal
E. GUYER,
procedures
WILLIAM
for improving
LEFKOWITZ,
Section editors
veneered
crowns
Jaime Pietrokovski, Hebrew University,
C.D., MS.,* and Saul Sorin, Dr.Odont.** Hadassah Faculty of Dental Medicine, Jerusalem,
Israel
lhe d esign and preparation of the window for the labial and proximal surfaces of a veneered metal crown are essentially routine laboratory procedures. However, clinical experience indicates that optimal esthetic effects and maximum retention of the veneering material can only be achieved when the dentist is well acquainted with the laboratory procedures and is able to recognize technical errors and make the appropriate corrections.1-3 This article describes a step-by-step chairside procedure for properly reshaping and adjusting the laboratory prepared window during the try-in phase of the cast restoration. PREPARATION When preparing an anterior tooth for a veneered metal crown, special care is necessary to achieve an optimum esthetic result. In addition to careful attention to the size, shape, and color of the entire restoration, the metallic frame should not be visible to the observing eye. On the facial and proximal surfaces of the prepared tooth, a deep preparation, in the form of a shoulder or chamfer, is necessary to provide enough space for the porcelain or acrylic resin veneering material. This chamfer or shoulder preparation must follow the contour of the gingival crest and should extend uniformly at least 0.5 mm. into the sulcus, so that the gingival margin of the veneering material is located inside the gingival sulcus (Fig. 1) . The veneer material should cover the entire window, conceal the metal, and produce a veneered crown which is harmonious, in color and form, with the adjacent Supported in part by a grant from the Joint Hadassah School of Dental Medicine, Jerusalem. *Senior **Clinical
Lecturer, Lecturer,
Department Department
Research Fund of The Hebrew University,
of Oral Rehabilitation. of Oral Rehabilitation.
503
504
Pietrokouski
and Sorin
J. Prosthet. Dent. November, 1975
Fig. 1. Left central incisor after reduction for a veneered metal crown. The chamfer PIreparation is parallel to the gingival crest contour at the buccal and proximal aspects of the tooth.
Fig. 2. The metal casting after its return from the dental laboratory for the try-in. collar covers the chamfer preparation and is the only guideline for the technician the level of the veneer window.
The gingival to determine
Fig. 3. Try-in of the crown in the patient’s mouth. Note the evidence of gold at the center of the labial surface. The gold will be visible in the finished crown if not corrected at this stage.
teeth. For optimum contour and shade, an acrylic resin veneer needs a square butt joint I mm. thick, extending proximally to include the full depth of the embrasure. Because proper adjustment depends on the extent and exactness of the shoulder or chamfer, it is obvious that the correct design and preparation of the window must begin with the accurate preparation of the tooth. In the absence of an adequate preparation, which should extend deep into the mesial and distal interproximal spaces, carving and reproducing the three-dimensional contour of natural teeth become difficult. The usual result is a flat veneer, so typical of artificial teeth. The technician, in an attempt to correct for the lack of a proper interproximal preparation, has to make the metal margins heavier than necessary. The final restora-
Volume 34 Number 5
Improving
Fig. 4. The displayed gold collar of the gingival margin. Fig. 5. The metal the labial aspect.
crown
after
is reduced
completion
with
veneered
metal
crowns
a No. 6 bur to a level flush with
of the reduction.
The gold collar
Fig. 7. The complete veneered metal crown all surfaces which are visible to the eye.
in the patient’s
mouth.
the crest
is invisible
Fig. 6. The veneered crown returned to the master cast. Note the diminished collar on the labial surface when compared with the collar in Fig. 2. The acrylic
width
505
from
of the
resin covers
tions, especially short ones, lose any resemblance to natural teeth. They also impinge on the interdental papillae and constitute a potential source of periodontal disease. Usually, the technician casts these cervical margins in a slightly bulkier form than necessary, because the extra thickness of the metal ensures a better and denser casting and protects the integrity of the margins during subsequent handling. Therefore, after checking the fit, the contact areas, and the form and occlusal anatomy of the crown, the cervical margin usually has to be reduced to preserve the space for the interdental papillae, even if it does not cause blanching of the gingivae. An overcontoured shoulder may also adversely affect the facial anatomy of the veneer, which is important for esthetic reasons and gingival health (Figs. 2 and 3).
506
J. Prosthet. Dent. November, 1975
Pietrokouski and Sorin
Fig. 8. The metallic retainer. This will plastic material.
band has been reduced from the contact area to the gingival crest for a allow for a satisfactory esthetic result when the window is covered by the
Fig. 9. The clinical be detected
aspect of the finished fixed partial denture on the mesial aspect of the veneered metal crown.
after
insertion.
No metal can
ADJUSTtNG THE WtNDOW Adjustment of the thickness of metal at the gingival margin should be made in the mouth with a No. 6 round bur at low speed. Shortening and reshaping of this margin level with and parallel to the curvature of the free gingiva, without lacerating it, will clearly mark the exact relation of the gingiva to the cervical margin of the gold frame (Figs. 4 and 5). Unless visibility of the gold is not critical, as in lower and posterior restorations, this demarcation line is not the finish line of the veneering material. It is only a guideline for the technician to cut back the metal about 0.5 mm. This will ensure that the metal margin of the shoulder will be subgingival and that no gold will be visible. Reducing the margin will be part of the over-all refinement by the technician before he applies the veneering material. If necessary, the incisal length of the casting is also adjusted directly in the mouth, according to the length of the adjacent teeth and the esthetic requirements of the patient. At this stage, unless already done in wax, the refinement will also include the maximum extension of the window, both mesially and distally, so that no metal will be visible interproximally (Figs. 6 to 9) .
DEPTH OF WINDOW To
facilitate
proper
contouring
and
shade,
the entire
inner
aspect
of the veneer
window, which is mainly a retentive area, must allow for a thickness of at least 1 mm. of the veneering material. Though such space must be provided during the preparation of the tooth, the dentist should check this space before finishing the restoration. Most dentists will leave the choice of adequate retentive elements on the facial surface of the veneer to the discretion of the laboratory personnel. Loops and/or beads, distributed over the entire inner surface and attached to the mesial and distal cervical corners of the casting, provide satisfactory retention for the veneering
Volume 34 Number 5
Improving
veneered
metal
crowns
507
material. For obvious reasons, these retaining elements have to be inserted in the waxing stage, and their position cannot be changed after casting.4p 5 However, only after the window outline has been finally approved during the try-in phase can the reverse bevel be prepared. This bevel, required for acrylic resin veneers, is the groove which the technician cuts along the entire periphery of the veneer, completely surrounding it, and by which the veneering material is most effectively retained.G SUMMARY Satisfactory design and preparation of the veneer window presuppose that a perfect or a near-perfect preparation of the tooth has been made. The window is not just a cutout and is not the responsibility of the laboratory technician. Whenever optimum gingival health, a satisfactory esthetic result, and a longlasting restoration are desired, it is worthwhile to carefully check and, if necessary, adjust the veneer window directly in the mouth before the veneer is added. This is especially important in restorations that extend below the gingival margin. References 1. Cohen, L. A.: The Acrylic Faced Cast Gold Crown, J. PROSTHET. DENT. 1: 112-124, 1951. 2. Long, A. C.: Acrylic Resin Veneered Crowns: The Effect of Tooth Preparation on Crown Fabrication and Future Periodontal Health, J. PROSTHET. DENT. 19: 370-380, 1968. 3. Johnson, J. F., Phillips, R. W., and Dykema, R. W.: Modern Practice in Crown and Bridge Prosthodontics, Philadelphia, 1969, W. B. Saunders Company, p. 343. 4. Weinberg, L. A.: Atlas of Crown and Bridge Prosthodontics, St. Louis, 1965, The C. V. Mosby Company, pp. 83-87. 5. Dykema, R. W., Johnson, J. F., and Cunningham, D. M.: The Veneered Gold Crown, Dent. Clin. North Am., Nov., 1958, p. 653. 6. Miller, A. J.: Inlays, Crowns and Bridges. An Atlas of Clinical Procedures, Philadelphia, 1962, W. B. Saunders Company, p. 127. DR.
PIETROKOVSKI
TUFTS UNIVERSITY SCHOOL OF DENTAL MEDICINE ONE KNEELAND ST. BOSTON, MASS. 02111 DR. SORIN THE HEBREW UNIVERSITY HADASSAH SCHOOL OF DENTAL MEDICINE P. 0. Box 499 JERUSALEM, ISRAEL
