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Partial coverage retainers: A critical evaluation
FIXED
P.ARTIAL
PARTIAL
COVERAGE
DENTURES
RETAINERS:
A Critical
Evaluation
WILLIAM H. PRUDEN,11,D.D.S. P(aterson, N. J.
calling for re-examination of the “full coverage” craze, which was in full force, was published in 1957.l Many advantages to maintaining sound, healthy buccal and labial enamel were cited, and the esthetic and contouring problems of the full crown retainers were pointed out. At the time, I could not have agreed more. More recently, full coverage has been widely condemned as wanton destruction o:i tooth structure. However, the real reason for the recent swing away from using as many full coverage restorations might be the number of crowns we see with nlonanatomic form, faulty contours, and poor marginal fit buried beneath the g:ingiva. The resultant poor esthetics and/or unhealthy soft tissue response has b’een a major concern of dentistry in recent years. Articles published since 1957s-6* have initiated a resurgence of interest in partial coverage retainers. After attending many clinics on the subject of partial coverage in which the use of parallel pins for additional retention was emphasized, one cannot help wondering if the pendulum is not swinging back in an unhealthy manner. The partial coverage retainers, if prepared and used as sometimes advocated, will create other problems for the future. We are told that Black’s principles of cavity preparation are obsolete. However, a thin occlusal wafer of gold, thinly b’eveled, is not an adequate retainer for a fixed prosthesis, regardless of the number of pins that are used. We have all had the sickening experience of a thin inlay margin in heavy occlusion being “work hardened” with subsequent cement breakdown, leakage, and recurrent caries. Sometimes this is not detected until the pulp is involved. It seems too much to expect that .020 inch pins alone will give adequate resistance form to a fixed partial denture, or that a thin bevel or slice would provide adequate bulk and strength for a solder joint. Perhaps we should re-evaluate some of the preparation designs being advocated before we become too enthusiastic about partial coverage restorations.
A
N ARTICLE
COMPARISON
OF PREPARATIONS
The pin-ledge preparations in Fig. 1 are of sound design because, in addition tla the well-placed pinholes, there are seats to resist shearing stress on the pins Read before the American *Personal communication:
Academy of Restorative Dr. Arvin Mann, 1964. 545
Dentistry
in Chicago.
546
PRUDEN
J. Pros. Den. May-June, 1966
Fig. L-Casts of pin-ledge preparations. The definite seats for the pins will protect the castings from shearing stresses. The groove connecting the incisal seats will produce a virtual “I-beam” in the casting, and add strength and rigidity. The lateral bevels when connected to the cingulum contour will form a U-shaped bar with sufficient bulk and strength to receive a solder joint.
and horizontal grooves which will produce “I-beams” and give rigidity to the casting. The U-shaped marginal ridges and the cingulum contours (at least 1 mm. in thickness) connect these beams and give bulk and added strength to the casting. One of the preparations in Fig. 2 will accommodate only a very thin occlusal surface and has a fine bevel of minimal support to act as a solder wing. The other preparation in Fig. 2 also covers the occlusal surface completely but provides for additional thickness and strength as well as resistance form on the pulpal floor and in the two distinct boxes. The boxes are finished with hand instruments for increased retention. Reverse-margin trimmers are Ad to prevent any tendency of the casting to spread. We have been told that pin placement at the tip of a cusp is incorrect, but the sectioned teeth in Figs. 3 and 4 seem to indicate that pulpal proximity is not a factor in one pin placement or the other. In fact, the properly placed pin on the buccal cusp of a premolar is no closer to the pulp than the gold of a shoulder preparation would be for a veneer crown, and the pin involves far less bulk of metal. The preparations in Fig. 2 were made on very young premolars and extracted for orthodontic reasons before the apices of the roots were completely formed. If
Volume 16 Number 3
PARTIAL
COVERAGE RETAINERS
547
Fig. 2.-The boxes and occlusal groove (above right, below left) will give additional resistance form and strength-giving bulk to the gold casting over the thin pin-retained casting for the other tooth. The longer the span, the more important this resistant bulk of metal becomes. The pins should be used merely to add retention.
Fig. 3.-This tooth was sectioned large pulp in this young tooth.
to show that the two 2 mm. pins do not threaten
the
these teeth can be prepared without pulpal exposure, any teeth upon which we would be making preparations are favorable risks. Partial coverage retainers are certain to be condemned at the next swing of the pendulum, and this will be no more valid than today’s criticism of the full coverage retainers.7rs Many dental meetings feature panel discussions on the relative merits of full versus partial coverage restorations. These presentations are popular, perhaps
J. Pros. Den. May-June, 1966
548
Fig. (.-When the teeth in Fig 2 are ground down from the occlusal surface, the pulp is exposed before the four 2 mm. pinholes are eliminated, left. The pinholes of the same 2 mm. length in the other tooth are eliminated before the pulp is reached, tight. This is due to the two holes being started near the height of the cusp so the pulp has adequate clearance.
because of the controversy. The claims that partial coverage is a return to the dark ages, which will set dentistry back years, and the claims that full coverage is wanton destruction may be sensational, but they hardly contribute to the advancement of our profession. DIAGNOSIS
It seems reasonable to concern ourselves with proper diagnosis and meticulous execution of properly designed retainers, rather than to pit one type of retainer against another. After all, retainers are our tools like our high-speed instruments, our hydrocolloid conditioner, or the articulator we use. We should use all of our tools. If dentistry is the fine profession we feel it is, we must tailor our treatment plans to the specific needs of our individual patients rather than to fit our patients to our favorite method of treatment or to any current fad. REFERENCES
Pruden. K. C.: Abutments and Attachments in Fixed Dentures, J. PROS. DENT. 7:502-510, ‘1957. Kahn, A. E. : Partial Ve rsus Full Coverage, J. PROS. DENT. 10:167-178, 1960. Karlstrom, S. : Pinledge Retainer, D. Abst. 3:581, 1958. Sanell, C., and Feldman, A. J.: Horizontal Pin Splint for Lower Anterior Teeth, J. PROS. DENT. 12:138-15 i;, 1962. Courtade, G. L., Sanell, C:, and Mann, A. W.: The Use of Pins in Restorative Dentistry. Part I. Parallel Pm Retention Obtained Without Using Paralleling Devices, Part II. Paralleling Instruments, J PROS. DENT. 15:502-516; 691-703, 1965. 6. Shooshan, E. D.: Pin Ledge Castin g Technique-Its Application in Periodontal Splinting, D. Clin. North America. DD. 1189-206,1960. 7. Miller, L6F, and Feinberg, E: L Full Coverage Restorations ; J. PROS. DENT. 12:317-325, 8. Miller, I. F.‘: Fixed Deatal Prosthesis, J. PROS. DENT. 8483-495, 1958. 44 CHURCH ST. PATERSON, N. J.
P.ARTIAL
PARTIAL
COVERAGE
DENTURES
RETAINERS:
A Critical
Evaluation
WILLIAM H. PRUDEN,11,D.D.S. P(aterson, N. J.
calling for re-examination of the “full coverage” craze, which was in full force, was published in 1957.l Many advantages to maintaining sound, healthy buccal and labial enamel were cited, and the esthetic and contouring problems of the full crown retainers were pointed out. At the time, I could not have agreed more. More recently, full coverage has been widely condemned as wanton destruction o:i tooth structure. However, the real reason for the recent swing away from using as many full coverage restorations might be the number of crowns we see with nlonanatomic form, faulty contours, and poor marginal fit buried beneath the g:ingiva. The resultant poor esthetics and/or unhealthy soft tissue response has b’een a major concern of dentistry in recent years. Articles published since 1957s-6* have initiated a resurgence of interest in partial coverage retainers. After attending many clinics on the subject of partial coverage in which the use of parallel pins for additional retention was emphasized, one cannot help wondering if the pendulum is not swinging back in an unhealthy manner. The partial coverage retainers, if prepared and used as sometimes advocated, will create other problems for the future. We are told that Black’s principles of cavity preparation are obsolete. However, a thin occlusal wafer of gold, thinly b’eveled, is not an adequate retainer for a fixed prosthesis, regardless of the number of pins that are used. We have all had the sickening experience of a thin inlay margin in heavy occlusion being “work hardened” with subsequent cement breakdown, leakage, and recurrent caries. Sometimes this is not detected until the pulp is involved. It seems too much to expect that .020 inch pins alone will give adequate resistance form to a fixed partial denture, or that a thin bevel or slice would provide adequate bulk and strength for a solder joint. Perhaps we should re-evaluate some of the preparation designs being advocated before we become too enthusiastic about partial coverage restorations.
A
N ARTICLE
COMPARISON
OF PREPARATIONS
The pin-ledge preparations in Fig. 1 are of sound design because, in addition tla the well-placed pinholes, there are seats to resist shearing stress on the pins Read before the American *Personal communication:
Academy of Restorative Dr. Arvin Mann, 1964. 545
Dentistry
in Chicago.
546
PRUDEN
J. Pros. Den. May-June, 1966
Fig. L-Casts of pin-ledge preparations. The definite seats for the pins will protect the castings from shearing stresses. The groove connecting the incisal seats will produce a virtual “I-beam” in the casting, and add strength and rigidity. The lateral bevels when connected to the cingulum contour will form a U-shaped bar with sufficient bulk and strength to receive a solder joint.
and horizontal grooves which will produce “I-beams” and give rigidity to the casting. The U-shaped marginal ridges and the cingulum contours (at least 1 mm. in thickness) connect these beams and give bulk and added strength to the casting. One of the preparations in Fig. 2 will accommodate only a very thin occlusal surface and has a fine bevel of minimal support to act as a solder wing. The other preparation in Fig. 2 also covers the occlusal surface completely but provides for additional thickness and strength as well as resistance form on the pulpal floor and in the two distinct boxes. The boxes are finished with hand instruments for increased retention. Reverse-margin trimmers are Ad to prevent any tendency of the casting to spread. We have been told that pin placement at the tip of a cusp is incorrect, but the sectioned teeth in Figs. 3 and 4 seem to indicate that pulpal proximity is not a factor in one pin placement or the other. In fact, the properly placed pin on the buccal cusp of a premolar is no closer to the pulp than the gold of a shoulder preparation would be for a veneer crown, and the pin involves far less bulk of metal. The preparations in Fig. 2 were made on very young premolars and extracted for orthodontic reasons before the apices of the roots were completely formed. If
Volume 16 Number 3
PARTIAL
COVERAGE RETAINERS
547
Fig. 2.-The boxes and occlusal groove (above right, below left) will give additional resistance form and strength-giving bulk to the gold casting over the thin pin-retained casting for the other tooth. The longer the span, the more important this resistant bulk of metal becomes. The pins should be used merely to add retention.
Fig. 3.-This tooth was sectioned large pulp in this young tooth.
to show that the two 2 mm. pins do not threaten
the
these teeth can be prepared without pulpal exposure, any teeth upon which we would be making preparations are favorable risks. Partial coverage retainers are certain to be condemned at the next swing of the pendulum, and this will be no more valid than today’s criticism of the full coverage retainers.7rs Many dental meetings feature panel discussions on the relative merits of full versus partial coverage restorations. These presentations are popular, perhaps
J. Pros. Den. May-June, 1966
548
Fig. (.-When the teeth in Fig 2 are ground down from the occlusal surface, the pulp is exposed before the four 2 mm. pinholes are eliminated, left. The pinholes of the same 2 mm. length in the other tooth are eliminated before the pulp is reached, tight. This is due to the two holes being started near the height of the cusp so the pulp has adequate clearance.
because of the controversy. The claims that partial coverage is a return to the dark ages, which will set dentistry back years, and the claims that full coverage is wanton destruction may be sensational, but they hardly contribute to the advancement of our profession. DIAGNOSIS
It seems reasonable to concern ourselves with proper diagnosis and meticulous execution of properly designed retainers, rather than to pit one type of retainer against another. After all, retainers are our tools like our high-speed instruments, our hydrocolloid conditioner, or the articulator we use. We should use all of our tools. If dentistry is the fine profession we feel it is, we must tailor our treatment plans to the specific needs of our individual patients rather than to fit our patients to our favorite method of treatment or to any current fad. REFERENCES
Pruden. K. C.: Abutments and Attachments in Fixed Dentures, J. PROS. DENT. 7:502-510, ‘1957. Kahn, A. E. : Partial Ve rsus Full Coverage, J. PROS. DENT. 10:167-178, 1960. Karlstrom, S. : Pinledge Retainer, D. Abst. 3:581, 1958. Sanell, C., and Feldman, A. J.: Horizontal Pin Splint for Lower Anterior Teeth, J. PROS. DENT. 12:138-15 i;, 1962. Courtade, G. L., Sanell, C:, and Mann, A. W.: The Use of Pins in Restorative Dentistry. Part I. Parallel Pm Retention Obtained Without Using Paralleling Devices, Part II. Paralleling Instruments, J PROS. DENT. 15:502-516; 691-703, 1965. 6. Shooshan, E. D.: Pin Ledge Castin g Technique-Its Application in Periodontal Splinting, D. Clin. North America. DD. 1189-206,1960. 7. Miller, L6F, and Feinberg, E: L Full Coverage Restorations ; J. PROS. DENT. 12:317-325, 8. Miller, I. F.‘: Fixed Deatal Prosthesis, J. PROS. DENT. 8483-495, 1958. 44 CHURCH ST. PATERSON, N. J.