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Selecting facings for pontics
SELECTING J. MARVIN Medical
FACINGS
REYNOLDS,
College
Richmond,
FOR
PONTICS
B.S., D.D.S.*
of Virginia,
School
of Dentistry,
Vu.
exist as to the type of facings that should be used for pontics in fixed prosthetics and whether these facings should be porcelain or acrylic resin. The facings in common use are: (1) the flatback facing, (2) the Trupontic facing,? (3) the long pin facing, (4) the reverse pin facing, and (5) the sanitary facing. These facings are used in combination with gold alloy to complete the pontics. The object of this article is to review the properties of porcelain, acrylic resin, and gold as related to their use in pontics. The characteristics of each type of facing will be discussedso that the optimum biomechanical design can be achieved in the pontics for fixed prosthesis.
D
IFFERENCES OF OPINION
MATERIALS
The object of a pontic is the restoration of a missing tooth and the maintenance of oral function in a biologic, physiologic, and esthetic manner. The pontic must be constructed of materials that will be compatible with the surrounding tissues and have a form that will ensure proper sanitation and stimulation of the mucosa. Porcelain is superior to other materials in duplicating the appearance of natural teeth and in maintenance of color. Porcelain is resistant to abrasion, dimensionally stable, and insoluble in the oral fluids. However, the elastic limit of porcelain is so low that fractures occur from extremely small shearing and impact forces. Much experience, care, and skill is required in the handling, blending, and fabrication of porcelain. Acrylic resin is resilient in nature and easy to fabricate. Acrylic resin does not permit the precise control of color and light refraction as does porcelain,l and it absorbs oral fluids and tends to be unclean in areas of stasis.2 Acrylic resin falls far short in its ability to resist wear and abrasion and is unfavorably tolerated by the soft tissues. *Associate Professor, Department of Crown and Bridge Prosthodontics. +Columbus Dental Mfg. Co., Columbus, Ohio. 746
\‘olume 14 Numbe1- 1
POXTICS
747
Gold alloy provides the best strength to withstand and resistance to wear and satisfies all other requirements
the stresses of occlusion except those of esthetics.
BASIC
SELECTING
FACINGS
FOR
CONSIDERATIONS
The best biologically acceptable material is glazed porcelain.1-4 Dense, highly polished gold and porcelain with an overglaze are next in preference. Acrylic resin is the least desirable.lJ When all factors are considered, a porcelain facing in combination with a gold backing creates.,the best pontic in most circumstances from biologic and mechanical standpoints, iMany acrylic, resin facings are used. This is of doubtful merit. Commercial dental laboratories favor resin facings because they require less care and skill during construction and fabrication of fixed dental prostheses. Some dentists encourage the use of resin for the same reason. Resin facings also are used as a means of minimizing breakage which reduces the tedious task of replacing broken facings. CAUSESOFFRACTURES
Facings fracture from several causes. Some of these are: (1) insufficient gold to rigidly resist occlusal forces, (2) improper treatment of the incisal (occlusal) edge, (3) use of a gold alloy that is too soft, and (4) blows originating from extraoral sources. Facings rarely fracture from external forces” but may do so when the backing distorts under function. Replacement of broken facings is a difficult task. The possibility of fracture of porcelain facings is anticipated by some dentists so an interchangeable type is used. Alterations to porcelain facings are often kept at a minimum which may actually increase the incidence to fracture. Fractures are reduced by proper modifications when interchangeable facings are used. Facings break because basic principles of good design are violated. Potential errors should be corrected before they occur by incorporating thorough diagnosis, treatment planning, and construction in conjunction with a knowledge of the design attainable for each facing. Such procedures virtually eliminate the problem of broken facings. METALBACKINGS
The metal backing must be made strong enough to withstand the forces to which the pontic will be subjected so that a porcelain facing may serve as long as the fixed prosthesis is functional. The backing must have sufficient bulk, distribution, strength, hardness, and the correct shape to resist distortion in function without distracting from the appearance of the facing by undue display of gold. A properly formed backing prevents shearing forces from being transmitted to the facing and thus eliminates failures due to breakage. Of course, no material or design is completely immune from failure.6 DESIGN
OF FACINGS
Certain facings lend themselves to better design than others. Facings that are inserted into the backing from a horizontal direction can be modified on all six
J. Pros. Dew July-Au&, 1964
REYNOLDS
748
surfaces. This is not true of facings that are inserted from the occlusal surface. Oral environmental conditions7 influence the type of facings that can be used and the modifications that can be made. Certain conditions must be evaluated before a facing is selected. These are: (1) the location of the prosthesis, (2) the amount of overlap of the opposing teeth, (3 ) the width of the edentulous ridge.
Fig.
Fig.
Fig.
3.-Long
pin
facings.
A,
1.-A
2.-A
flatback
Trupontic
facing.
facing.
The Dentists’ Supply Company, Products Corp., Pasadena, Calif.
York,
Pa.
B,
Harmony
Dental
Volume Number
THE
14 4
SELECTING
FLATBACK
FACINGS
FOR
PONTICS
749
FACING
The flatback facing (Fig. 1) is the nearest of all facings to being interchangeable when it is used with a minimum of alteration. The incisal edge cannot be beveled to allow for metal protection because of the incisal path of insertion. As a result, the facing must be positioned slightly short of the occlusal plane. In maxillary restorations when there is little horizontal overlap of the teeth, it is difficult to provide enough thickness of metal in the incisal third of the backing without rotating the facing labially. As the vertical overlap increases, the entire facing must he placed labially to provide the required bulk in the backing. The use of this facing should generally be limited to incisors where the incisogingival space is adequate, a normal horizontal overlap of opposing teeth exists, and when incisal clearance can be established to protect the porcelain from positive biting forces. THE
TRUPONTIC
FACING
The Trupontic facing (Fig. 2) is also classified as interchangeable. It can be used successfully in many instances provided proper modifications are made. However, the modifications automatically remove the facing from the easily replaceable variety. It is inadvisable to select Trupontic facings on the basis of the interchangeable feature. Additional strength is attained in the backing when the occlusal edge is beveled and the lingual slope is hollow ground. The labial convexities and angles are difficult to shape and contour properly without displaying gold.* This factor reduces the usefulness of the Trupontic facing for anterior restorations. Normal width and plenty of occlusogingival space is needed to use this facing successfully. The Trupontic facing is acceptable for maxillary posterior restorations that have sufficient interarch space in the edentulous region. THE
LONG
PIN
FACING
Of the commercially manufactured varieties, the long pin facing (Fig. 3) can be adapted to the largest number of situations. It is particularly indicated where the available vertical space is short. Excellent contour can be developed from the esthetic and mechanical standpoints. Medium fusing porcelain can be added to the ridge lap surface by an uncomplicated technique when there is adequate space. 4 The addition is adapted and refined in the bisque state before glazing. The long pin facing is contraindicated in the maxillary dental arch when the opposing teeth have little horizontal overlap and a large amount of vertical overlap. In these situations the incisal edges of the mandibular teeth will be located in such a manner that the pins will have to be shortened to the point that they are nearly worthless for retention. The width of the edentulous space must be greater than that between the retention pins. THE
REVERSE
PIN
FACING
The reverse pin facing (Fig. 4) is fabricated from a porcelain denture tooth by means of a special porcelain drill press. 2 This technique seems to have eliminated
J. Pros. Den. July-Aug., 1964
REYNOLDS
Fig.
Fig.
B.-Sanitary
facings.
4.-A
reverse
pin facing.
A, Columbus Dental Mfg. Co., Columbus, Dental Products Corp., Pasadena, Calif.
Ohio.
B
and
C, Harmon)
or at least reduced many of the problems that have been associated with the use of commercially manufactured porcelain facings, especially the interchangeable types. Excellent design and esthetics can be attained when using this facing in the anterior part of the mouth. Many molds and shades are available. Retention is secured over the entire lingual surface of the facing instead of by one or two pins or posts. Great variation is possible when an overlapped or tilted arrangement of teeth is desired. This facing seems to work nicely even where the opposing occlusal surfaces closely approximate the residual ridge. Porcelain can be added to the ridge lap surface. The reverse pin facing satisfies the requirements as well or better than most other facings. The use of this facing is encouraged. THE
SANITARY
FACING
The sanitary facing (Fig. 5) is not intended for use when esthetics is important. The sanitary facing provides porcelain on the ridge contact surface of the pontic and is not indicated when the edentulous space is extremely narrow in width
Volume Number
14 4
SELECTING
FACINGS
FOR
and length. This facing should be used in the lower to the first bicuspid.
PONTICS
7.51
dental arch, especially posterior
SUMMARY
The five porcelain facings that are most commonly used in fixed prosthesis have been reviewed. The use of porcelain facings in combination with gold alloy backings is encouraged. Emphasis is placed on attaining the optimal biomechanical design. The reverse pin facing can be adapted to the greatest number of situations, followed by the long pin facing. Regardless of the facing used, the proper contour and form of the entire pontic must be developed. REFERENCES
1. Smith, G. P.: Objectives of a Fixed Partial Denture, J. PROS. DEN. 11~63-473,1961. 2. Shooshan, E. D.: The Reverse Pin-Porcelain Facing, J. PROS. DEN. 9:284-301, 1959. 5. Allison, J. R., and Bhatia, H. L. : Tissue Changes Under Acrylic and Porcelain Pontics, J. D. Res. 37:66-67, 1958. 4. Tyhnan, S. D., and Tylman,. S. G.: Theory and Practice of Crown and Bridge Prosthodontics, ed. 4, St. LOUIS, 1960, The C. \i. Mosby Co. D. Digest 43:16-20, 5. Smith, FG3!5, and Potter, H. R.: The Pontic in Fixed Bridgework, 6. Wilson, W.‘H., and Lang, R. L.: Practical Crown and Bridge Prosthodontics, New York, 1962, McGraw-Hill. 7. Harmon, C. B. : Pontic Design, J. PROS. DEN. 8 :496-503, 1958. 8. Johnston, J. F., Phillips, R. W., and Dykema, R. W.: Modern Practice in Crown and Bridge Prosthodontics, Philadelphia, 1960, W. B. Saunders Co. MEDICAL COLLEGE OF VIRGINIA SCHOOL OF DENTISTRY WOOD MEMORIAL BLDG. RICHMOND 19. VA.
FACINGS
REYNOLDS,
College
Richmond,
FOR
PONTICS
B.S., D.D.S.*
of Virginia,
School
of Dentistry,
Vu.
exist as to the type of facings that should be used for pontics in fixed prosthetics and whether these facings should be porcelain or acrylic resin. The facings in common use are: (1) the flatback facing, (2) the Trupontic facing,? (3) the long pin facing, (4) the reverse pin facing, and (5) the sanitary facing. These facings are used in combination with gold alloy to complete the pontics. The object of this article is to review the properties of porcelain, acrylic resin, and gold as related to their use in pontics. The characteristics of each type of facing will be discussedso that the optimum biomechanical design can be achieved in the pontics for fixed prosthesis.
D
IFFERENCES OF OPINION
MATERIALS
The object of a pontic is the restoration of a missing tooth and the maintenance of oral function in a biologic, physiologic, and esthetic manner. The pontic must be constructed of materials that will be compatible with the surrounding tissues and have a form that will ensure proper sanitation and stimulation of the mucosa. Porcelain is superior to other materials in duplicating the appearance of natural teeth and in maintenance of color. Porcelain is resistant to abrasion, dimensionally stable, and insoluble in the oral fluids. However, the elastic limit of porcelain is so low that fractures occur from extremely small shearing and impact forces. Much experience, care, and skill is required in the handling, blending, and fabrication of porcelain. Acrylic resin is resilient in nature and easy to fabricate. Acrylic resin does not permit the precise control of color and light refraction as does porcelain,l and it absorbs oral fluids and tends to be unclean in areas of stasis.2 Acrylic resin falls far short in its ability to resist wear and abrasion and is unfavorably tolerated by the soft tissues. *Associate Professor, Department of Crown and Bridge Prosthodontics. +Columbus Dental Mfg. Co., Columbus, Ohio. 746
\‘olume 14 Numbe1- 1
POXTICS
747
Gold alloy provides the best strength to withstand and resistance to wear and satisfies all other requirements
the stresses of occlusion except those of esthetics.
BASIC
SELECTING
FACINGS
FOR
CONSIDERATIONS
The best biologically acceptable material is glazed porcelain.1-4 Dense, highly polished gold and porcelain with an overglaze are next in preference. Acrylic resin is the least desirable.lJ When all factors are considered, a porcelain facing in combination with a gold backing creates.,the best pontic in most circumstances from biologic and mechanical standpoints, iMany acrylic, resin facings are used. This is of doubtful merit. Commercial dental laboratories favor resin facings because they require less care and skill during construction and fabrication of fixed dental prostheses. Some dentists encourage the use of resin for the same reason. Resin facings also are used as a means of minimizing breakage which reduces the tedious task of replacing broken facings. CAUSESOFFRACTURES
Facings fracture from several causes. Some of these are: (1) insufficient gold to rigidly resist occlusal forces, (2) improper treatment of the incisal (occlusal) edge, (3) use of a gold alloy that is too soft, and (4) blows originating from extraoral sources. Facings rarely fracture from external forces” but may do so when the backing distorts under function. Replacement of broken facings is a difficult task. The possibility of fracture of porcelain facings is anticipated by some dentists so an interchangeable type is used. Alterations to porcelain facings are often kept at a minimum which may actually increase the incidence to fracture. Fractures are reduced by proper modifications when interchangeable facings are used. Facings break because basic principles of good design are violated. Potential errors should be corrected before they occur by incorporating thorough diagnosis, treatment planning, and construction in conjunction with a knowledge of the design attainable for each facing. Such procedures virtually eliminate the problem of broken facings. METALBACKINGS
The metal backing must be made strong enough to withstand the forces to which the pontic will be subjected so that a porcelain facing may serve as long as the fixed prosthesis is functional. The backing must have sufficient bulk, distribution, strength, hardness, and the correct shape to resist distortion in function without distracting from the appearance of the facing by undue display of gold. A properly formed backing prevents shearing forces from being transmitted to the facing and thus eliminates failures due to breakage. Of course, no material or design is completely immune from failure.6 DESIGN
OF FACINGS
Certain facings lend themselves to better design than others. Facings that are inserted into the backing from a horizontal direction can be modified on all six
J. Pros. Dew July-Au&, 1964
REYNOLDS
748
surfaces. This is not true of facings that are inserted from the occlusal surface. Oral environmental conditions7 influence the type of facings that can be used and the modifications that can be made. Certain conditions must be evaluated before a facing is selected. These are: (1) the location of the prosthesis, (2) the amount of overlap of the opposing teeth, (3 ) the width of the edentulous ridge.
Fig.
Fig.
Fig.
3.-Long
pin
facings.
A,
1.-A
2.-A
flatback
Trupontic
facing.
facing.
The Dentists’ Supply Company, Products Corp., Pasadena, Calif.
York,
Pa.
B,
Harmony
Dental
Volume Number
THE
14 4
SELECTING
FLATBACK
FACINGS
FOR
PONTICS
749
FACING
The flatback facing (Fig. 1) is the nearest of all facings to being interchangeable when it is used with a minimum of alteration. The incisal edge cannot be beveled to allow for metal protection because of the incisal path of insertion. As a result, the facing must be positioned slightly short of the occlusal plane. In maxillary restorations when there is little horizontal overlap of the teeth, it is difficult to provide enough thickness of metal in the incisal third of the backing without rotating the facing labially. As the vertical overlap increases, the entire facing must he placed labially to provide the required bulk in the backing. The use of this facing should generally be limited to incisors where the incisogingival space is adequate, a normal horizontal overlap of opposing teeth exists, and when incisal clearance can be established to protect the porcelain from positive biting forces. THE
TRUPONTIC
FACING
The Trupontic facing (Fig. 2) is also classified as interchangeable. It can be used successfully in many instances provided proper modifications are made. However, the modifications automatically remove the facing from the easily replaceable variety. It is inadvisable to select Trupontic facings on the basis of the interchangeable feature. Additional strength is attained in the backing when the occlusal edge is beveled and the lingual slope is hollow ground. The labial convexities and angles are difficult to shape and contour properly without displaying gold.* This factor reduces the usefulness of the Trupontic facing for anterior restorations. Normal width and plenty of occlusogingival space is needed to use this facing successfully. The Trupontic facing is acceptable for maxillary posterior restorations that have sufficient interarch space in the edentulous region. THE
LONG
PIN
FACING
Of the commercially manufactured varieties, the long pin facing (Fig. 3) can be adapted to the largest number of situations. It is particularly indicated where the available vertical space is short. Excellent contour can be developed from the esthetic and mechanical standpoints. Medium fusing porcelain can be added to the ridge lap surface by an uncomplicated technique when there is adequate space. 4 The addition is adapted and refined in the bisque state before glazing. The long pin facing is contraindicated in the maxillary dental arch when the opposing teeth have little horizontal overlap and a large amount of vertical overlap. In these situations the incisal edges of the mandibular teeth will be located in such a manner that the pins will have to be shortened to the point that they are nearly worthless for retention. The width of the edentulous space must be greater than that between the retention pins. THE
REVERSE
PIN
FACING
The reverse pin facing (Fig. 4) is fabricated from a porcelain denture tooth by means of a special porcelain drill press. 2 This technique seems to have eliminated
J. Pros. Den. July-Aug., 1964
REYNOLDS
Fig.
Fig.
B.-Sanitary
facings.
4.-A
reverse
pin facing.
A, Columbus Dental Mfg. Co., Columbus, Dental Products Corp., Pasadena, Calif.
Ohio.
B
and
C, Harmon)
or at least reduced many of the problems that have been associated with the use of commercially manufactured porcelain facings, especially the interchangeable types. Excellent design and esthetics can be attained when using this facing in the anterior part of the mouth. Many molds and shades are available. Retention is secured over the entire lingual surface of the facing instead of by one or two pins or posts. Great variation is possible when an overlapped or tilted arrangement of teeth is desired. This facing seems to work nicely even where the opposing occlusal surfaces closely approximate the residual ridge. Porcelain can be added to the ridge lap surface. The reverse pin facing satisfies the requirements as well or better than most other facings. The use of this facing is encouraged. THE
SANITARY
FACING
The sanitary facing (Fig. 5) is not intended for use when esthetics is important. The sanitary facing provides porcelain on the ridge contact surface of the pontic and is not indicated when the edentulous space is extremely narrow in width
Volume Number
14 4
SELECTING
FACINGS
FOR
and length. This facing should be used in the lower to the first bicuspid.
PONTICS
7.51
dental arch, especially posterior
SUMMARY
The five porcelain facings that are most commonly used in fixed prosthesis have been reviewed. The use of porcelain facings in combination with gold alloy backings is encouraged. Emphasis is placed on attaining the optimal biomechanical design. The reverse pin facing can be adapted to the greatest number of situations, followed by the long pin facing. Regardless of the facing used, the proper contour and form of the entire pontic must be developed. REFERENCES
1. Smith, G. P.: Objectives of a Fixed Partial Denture, J. PROS. DEN. 11~63-473,1961. 2. Shooshan, E. D.: The Reverse Pin-Porcelain Facing, J. PROS. DEN. 9:284-301, 1959. 5. Allison, J. R., and Bhatia, H. L. : Tissue Changes Under Acrylic and Porcelain Pontics, J. D. Res. 37:66-67, 1958. 4. Tyhnan, S. D., and Tylman,. S. G.: Theory and Practice of Crown and Bridge Prosthodontics, ed. 4, St. LOUIS, 1960, The C. \i. Mosby Co. D. Digest 43:16-20, 5. Smith, FG3!5, and Potter, H. R.: The Pontic in Fixed Bridgework, 6. Wilson, W.‘H., and Lang, R. L.: Practical Crown and Bridge Prosthodontics, New York, 1962, McGraw-Hill. 7. Harmon, C. B. : Pontic Design, J. PROS. DEN. 8 :496-503, 1958. 8. Johnston, J. F., Phillips, R. W., and Dykema, R. W.: Modern Practice in Crown and Bridge Prosthodontics, Philadelphia, 1960, W. B. Saunders Co. MEDICAL COLLEGE OF VIRGINIA SCHOOL OF DENTISTRY WOOD MEMORIAL BLDG. RICHMOND 19. VA.