BAR
ATTACHMENTS
FOR
OVERDENTURES
ods have been presented. Two of these methods require no additional materials or equipment other than those routinely found in the dental laboratory. The third method requires only a twist drill, screw tap, and implant screws. These alternative techniques should be considered when planning for bar attachments to nonparallel abutments because of their simple design, readily available components, and relatively inexpensive approach.
7. Trabert KC, Caputo AA, Abou-Rass M. Tooth fracture-A comparison of endodontic and restorative treatments. J Endodont 1978;4:341-45. 8. Marquardt GL. Dolder bar joint mandibular overdenture: A technique for nonparallel abutment teeth. J PROSTHET DENT 1976;36:101-11. 9. Mensor MC Jr. Attachments for the overdenture. In: Brewer AA, Morrow RM, eds. Overdentures. 2nd ed. St Louis: CV Mosby Co, 1980:20851. 10. Matsuo E, Shimegi S. Screw-retained dental prostheses. Chicago: Quintessence Publishing Co, 1981:16-44, 89-97. 11. Mensor MC Jr. Attachments for overdentures. In: Rudd KD, Morrow RM, Rhoads JE, eds. Dental laboratory procedures: Removable partial dentures. Vol 3. 2nd ed. St Louis: CV Mosby Co, 1986:577-616. 12. Ruemping DR, Lund MR, Schnell RJ. Retention of dowels subjected to tensile and torsional forces. J PROSTHET DENT 1979;41:159-62. 13. Standlee JP, Caputo AA, Collard EW, Pollack MH. Analysis of stress distribution by endodontic posts. Oral Surg 1972;33:952-60. 14. Render PJ, Jennings DE. Simplified bar-clip attachment for an overdenture patient with divergent roots. J PROSTHET DENT 1989;61:127-8. 15. Farish SM, Pansch JL, Sherwood RL. Prosthetic management of unparallel titanium plasma-sprayed screw implants. J PROSTHET DENT 1989;61:129-32. 16. Dykema RW, Goodacre CJ, Phillips RW. Johnston’s modern practice in fixed prosthodontics. 4th ed. Philadelphia: WB Saunders Co, 1986: 364-78. 17. Shillingburg HT, Hobo S, Whitsett LD. Fundamentals of fixed prosthodontics. 2nd ed. Chicago: Quintessence Publishing Co, 1981: 143-59. 18. Rosensteil SF, Land MF, Fujimoto J. Contemporary fixed prosthodontics. St Louis: CV Mosby Co, 1988:198-217.
Our special thanks to Dr. Jeanne Hansen-Bayless for her clinical contributions and to Mr. Kenneth Kemple for his laboratory support. REFERENCES 1. Crum RJ, Rooney GE. Alveolar bone loss in overdentures: A 5 year study. J PROSTHET DENT 1978,40:610-13. 2. DeFranco RL. Overdentures. In: Winkler S, ed. Essentials of complete denture prosthodontics. 2nd ed. Littleton, Massachusetts: PSG Publishing Co, 1988:384-402. 3. Crum RJ. Rationale for the retention of teeth for overdentures. In: Brewer AA, Morrow RM, eds. Overdentures. 2nd ed. St Louis: CV Mosby Co, 1980:3-11. 4. Renner RP. Complete dentures: A guide for patient treatment. New York: Masson Publishing USA, 1981:257-71. 5. Preiskel HW. Precision attachments in prosthodontics: Overdentures and telescopic prostheses. Vol2. Chicago: Quintessence Publishing Co, 1985:243-306,360-51. 6. Caputo AA, Standlee JP. Biomechanics in clinical dentistry. Chicago: Quintessence Publishing Co, 1987:178-80.
he design Change-xi
of a two-part Shi,
DDSa
The Fourth Military China
Ji-hua
Chen,
Reprint requests to: DR. DOUGLAS B. EVANS 11350 WOODRIDGE FOREST SAN ANTONIO, TX 78249
acid-etched PhD,b
and
Medical University, Stomatological
He-ying
resin-bonded
fixed
YuanC
Hospital, Xian, The People’s Republic of
A new framework design is presented for resin-bonded, acid-etched, fixed partial dentures. This innovative design divided the restoration into two parts, each with a separate path of insertion. The preparation of abutment teeth required minimal reduction and the pontic could not be displaced during function. Thirty-five patients with missing posterior teeth have been treated with this imaginative approach and after approximately 2 years, there have been no debonding failures. (J PROSTHET
DENT1992;68:11-15.)
abrication of the first acid-etched, solid resinbonded fixed partial denture (FPD) in 1980 at the University of Maryland introduced a new era in conservative tooth rep1acement.l Several investigators have reported results
aProfessor, Prosthodontic Department. “Doctor, Prosthodontic Department. “Technician-in-charge, Prosthodontic Department. 10/l/35254 THE
JOURNAL
OF PROSTHETIC
DENTISTRY
on bonding between the restoration and abutment teeth. These include the appropriate treatment of the castings and tooth enamel, improvement in the design of the FPD framework, and tooth preparation. To improve retention of the FPD to the enamel of the abutment, authors have suggested the preparation of grooves, boxes, three-quarter or complete crowns, inlays, onlays, and pins in the abutment, including expansion of the wings.ss6 Clinically, the framework design must observe the basic 11
SHI,
Fig. 2. When model is inclined to lingual line or red line on facial surface is lower.
Fig. 1. Guideline or blue line when path of insertion from vertical direction only.
AND
YUAN
surface, guide-
is
principles of retention and resistance form, such as near parallel or g-degree taper opposing walls, a single path of insertion, maximum tooth coverage, and vertical stops.7 When these guidelines and the appropriate use of newer techniques such as composite resin luting agents and sandblasted or electrolytically etched inner surfaces of cast wings are applied, the resin-bonded prosthesis is a permanent restoration and a valuable asset in the dentist’s armamentarium.s The abutment preparations were not all conservative, but certain approaches were aggressive to ensure a vertical path of insertion. Unfortunately, of all the preparations the best retention form or the natural undercuts of abutment were not used. The greater bond between the resin and metal rather than between the resin and enamel9 was not adequately exploited. In this article, a new design is described to use the natural undercuts of abutments by changing the path of insertion of the FPD. When the undercuts of the abutments are identified with a surveyor, the path of insertion is concomitantly determined. The undercuts on lingual or facial surfaces may be modified by altering the path of insertion. If only the lin-
12
CHEN,
Fig. 3. Path of insertion is altered by inclining model to facial surface. There is no undercut on lingual surface red line.
gual or facial surface was considered, the undercuts of two abutments of an FPD could be lowered to 1 mm above the gingival tissue, which is ideal for the abutment. However, if a resin-bonded FPD could be inserted simultaneously from both facial and lingual directions, the abutment preparations could be finished with only minimal tooth reduction, retaining the abutment’s natural undercuts. Figs. 1 through 4 demonstrate that varying paths of insertion allow the use of different undercuts of the abutment. When the path of insertion was in a vertical direction (Fig. l), the undercut or blue line was near the occlusal one third of the axial surface. When the path of insertion was from a facial direction and ended at the center of proximal (Fig. 2) and then switched to a lingual direction (Fig. 3) to finish the tracing of the guideline, the underscored undercuts (red line) of the same tooth were lower than those resulting from insertion in a single vertical direction. The red and blue lines in Fig. 4, A, in a facial view
JULY
1992
VOLUME
68
NUMBER
1
TWO-PART
RESIN-BONDED
FPD
Fig.
Fig. Fig. Fig. Fig.
5. 6. 7. 8.
4. Two guidelines
completed;
Occlusal view of lower part of wax pattern. Upper part of wax pattern (pink wax) and lingual-occlusal Lingual view of partially finished FPD. Buccal view of finished wax pattern.
and in Fig. 4, B, in a lingual view revealed the two types of undercuts resulting from two directions with a single, specific direction for the path of insertion. According to this design, a two-part resin-bonded FPD could be inserted from both the lingual and the facial directions simultaneously.
THE
JOURNAL
OF PROSTHETIC
facial view (A) and lingual
DENTISTRY
view (B).
view of lower part.
The abutment preparation for the two-part resin-bonded FPD is different from that of the traditional FPD because the undercuts on lingual, facial, and proximal surfaces do not require reduction. The other principles in the designing of a two-part framework, such as vertical occlusal stops and maximum coverage of the wings of an FPD, were the
13
SHI,
Fig. Fig.
9. Two parts of wax pattern attached 10. Finished cast restorations.
CHEN,
AND
YUAN
to main sprue.
inserted from two different paths of insertion (Fig. 11). The restoration was finished except for the inner surface of the four wings, the surface of the lower pontic, and the surface of the upper pontic that contacts with the lower pontic. The unpolished areas of the two parts were then sandblasted. A thin layer of chemically cured composite resin cement was used on the inner surface (intaglio) of the wings and on the surface of the lower pontic. The two parts were then inserted simultaneously. When the wings were bonded to the etched enamel, the two parts of the pontic were also bonded to each other.
DISCUSSION Fig. 11. Inserting model.
two-part
fixed
partial
denture
on
same as those used for the routine resin-bonded FPD, or “Maryland bridge.” Figs. 5 through 10 describe a step-by-step introduction to the two-part resin-bonded FPD made on a model, with a proximal undercut near the missing tooth that was restored. Figs. 5 and 6 illustrate the wax formulation of the twopart FPD including two rests, two wings, and a half-round ring pontic, from facial and lingual directions, respectively. The pontic of this part was narrower than was originally intended. When the wax pattern became completely cold, the upper section was increased dimensionally. A separating fluid is suggested so that the upper part does not adhere to the lower part. The upper part also has two wings on the same side of the abutments. The finished upper part must have a suitable contact with the opposing teeth, including a functional and anatomic form. Figs. 7 and 8 show the upper part from lingual and facial surfaces, respectively. The wax patterns were attached to the main sprue individually (Fig. 9), invested, and cast with a nonprecious alloy. The finished cast restorations are displayed in Fig. 10 and were 14
The bonds between composite resins and human enamel have been verified by various authors since Buonocorel” introduced the theory in 1955. The resin-bonded acidetched FPD has also been acknowledged as a permanent restorations but there have been numerous failures because of debonding at the interface of the wings and ename1.s Nevertheless, to ensure a single, specific path of insertion, the undercut of the abutment is commonly reduced. In the design of two-part resin-bonded FPD (TFPD), besides the bonding strength of tbe composite resin cement to enamel or to the “main retention” of the FPD, there are retentive forces created from maintaining the undercut. The undercut can provide a major portion of the retention during function. The question arises whether the bonding between the two parts of the pontic can withstand the occlusal forces during function. In fact, because the upper pontic engages the lower pontic as a man rides on a horse saddle, the lower pontic is secured tightly in the upper pontic. A more convincing fact is that the bonding strength of the composite resin cement to the sandblasted alloy surfaces is two to three times greater than the bond strength of the composite resin cement to etched enamel.g The greater bond strength of composite resin cement to alloy has been exploited in this innovative design. Nevertheless, further JULY
1992
VOLUME
68
NUMBER
1
TWO-PARTRESIN-BONDEDFPD
research is indicated to investigate the bond strength between the “two-part pontics.” The two-part resin-bonded, acid-etched FPD was especially useful if the undercuts of abutments were excessive and the patient could not endure tooth preparation. In addition, the upper and lower parts of the TFPD might have greater retentive strength than the retention created by the bond strength of resin to enamel, the critical retention force of a conventional resin-bonded FPD. The chief disadvantage of the new design was the complex formulation of the wax-up and precise casting technique.
SUMMARY Anew framework was designed for the resin-bonded, acid-etched FPD so that the natural undercuts of the abutments were used for retention of the FPD. This new design (TFPD) divided the conventional Maryland FPD into an upper and lower “pontic” part, each with a separate path of insertion. The two insertion directions were different so the pontic parts could not be displaced during function. Thirty-five patients have had missing teeth replaced with a TFPD since 1988 in the prosthodontic department. The results of the clinical testing have been extremely encouraging because, in the 35 pairs of TFPDs-the oldest in service 23 months and the most recent 4 months-there has been no debonding at the enamel surfaces or at the interfaces between the two-part pontics.
Resin-bonded David Israel
Madjar, Defense
Forces
cast coverage
REFERENCES 1. Simonsen R, Thompson V, Barrack G. Etched cast restorations: ciinical and laboratory techniques. Chicago: Quintessence Publishing Co, 1983:169. 2. Kishimoto M, Shillingburg HT, Duncanson MG. Influence of preparation features on retention and resistance. Part II. Three-quarter crowns. J PROSTHET DENT 1983;49:168-92. 3. Pegorro LF, Barrack G. A comparison of bond strength of adhesive-cast restoration using diierent designs, bonding agents, and luting resins. J PROSTHFX DENT 1987;57:133-8. 4. Burgess JO, McCartney JG. Anterior
retainer design for resin-bonded acid-etched 6xed partial dentures. J PROSTHET DENT 1987;61:433-6. 5. W&shire WA. Resin bonded fixed partial dentures utibziig additional pin retention. Quintessence Int 1986;17:343-7. 6. Meiers JC, Meetz HK. Design modifications for etched-metal, resinbonded retainers. Gen Dent 1985;33:41-4. I. Barrack G. Recent advances in etched cast restorations. J PROSTHET DENT 1984;52:619-26. 8. Williams VD, Thayer
KE, Denehy GE, Bayer DB. Cast metal, resinbonded prostheses: a lo-year restrospective study. J PROSTHET DENT 1989;61:436-41. 9. Simonsen R, Thompson V, Barrack G. Etched cast restorations: cliicai and laboratory techniques. Chicago: Quintessence Publishing Co, 198341-56. 10. Buonocore MG. A simple method of increasing the adhesion of acrylic filling material to enamel surfaces. J Dent Res 1955;34:849-53. Reprint requests to: DR. JI-HUA CHEN PROSTHODONTIC DEPARTMENT STOMATOLOGICAL HOSPITAL FOURTH MILITARY MEDICAL UNWERS~~Y XIAN 710032 CHINA
for fractured
posterior
teeth
DMD,a and Irit Divon-Kupershmidt, DMDb Center for Oral and Dental Medicine, Tel Hashomer, Israel
Enamel-dentin fracture without pulpal involvement of intact posterior teeth demands restoration of form and function while preserving as much sound tooth material as possible. A partial-coverage restoration cast in nonprecious metal and air-abraded and bonded to the tooth by an adhesive resin is suggested. The strong bond of the adhesive resin to the enamel and dentin of the tooth and to the airabraded metal allows for simple fabrication of a cast partial coverage that requires only minimal tooth preparation. (J PROSTHET DENT 1992,68:15-18.)
-
\
The views expressed herein are private ones of the authors and do not necessarily reflect those of the Medical Corps, Israel Defense Forces. *Major, Israel Defense Forces, Department of Prosthodontics and Maxillofacial Prosthetics. bCaptain, Israel Defense Forces, Department of Prosthodontics and Maxillofacial Prosthetics. 1Q/1/35787 THE
JOURNAL
OF PROSTHETIC
DENTISTRY
T
raumatic forceful closure of teeth after a blow to the chin often leads to crown or crown and root fracture of one or more intact teeth. The indirect trauma mechanism applies a sudden, rapid load to the teeth, causing cuspal fracture and exposure of dentin with or without pulpal involvement1-3 (Figs. 1 and 2). Salis et a.l.,4 in an in vitro study, found that when dynamic forces are applied to in15
ATTACHMENTS
FOR
OVERDENTURES
ods have been presented. Two of these methods require no additional materials or equipment other than those routinely found in the dental laboratory. The third method requires only a twist drill, screw tap, and implant screws. These alternative techniques should be considered when planning for bar attachments to nonparallel abutments because of their simple design, readily available components, and relatively inexpensive approach.
7. Trabert KC, Caputo AA, Abou-Rass M. Tooth fracture-A comparison of endodontic and restorative treatments. J Endodont 1978;4:341-45. 8. Marquardt GL. Dolder bar joint mandibular overdenture: A technique for nonparallel abutment teeth. J PROSTHET DENT 1976;36:101-11. 9. Mensor MC Jr. Attachments for the overdenture. In: Brewer AA, Morrow RM, eds. Overdentures. 2nd ed. St Louis: CV Mosby Co, 1980:20851. 10. Matsuo E, Shimegi S. Screw-retained dental prostheses. Chicago: Quintessence Publishing Co, 1981:16-44, 89-97. 11. Mensor MC Jr. Attachments for overdentures. In: Rudd KD, Morrow RM, Rhoads JE, eds. Dental laboratory procedures: Removable partial dentures. Vol 3. 2nd ed. St Louis: CV Mosby Co, 1986:577-616. 12. Ruemping DR, Lund MR, Schnell RJ. Retention of dowels subjected to tensile and torsional forces. J PROSTHET DENT 1979;41:159-62. 13. Standlee JP, Caputo AA, Collard EW, Pollack MH. Analysis of stress distribution by endodontic posts. Oral Surg 1972;33:952-60. 14. Render PJ, Jennings DE. Simplified bar-clip attachment for an overdenture patient with divergent roots. J PROSTHET DENT 1989;61:127-8. 15. Farish SM, Pansch JL, Sherwood RL. Prosthetic management of unparallel titanium plasma-sprayed screw implants. J PROSTHET DENT 1989;61:129-32. 16. Dykema RW, Goodacre CJ, Phillips RW. Johnston’s modern practice in fixed prosthodontics. 4th ed. Philadelphia: WB Saunders Co, 1986: 364-78. 17. Shillingburg HT, Hobo S, Whitsett LD. Fundamentals of fixed prosthodontics. 2nd ed. Chicago: Quintessence Publishing Co, 1981: 143-59. 18. Rosensteil SF, Land MF, Fujimoto J. Contemporary fixed prosthodontics. St Louis: CV Mosby Co, 1988:198-217.
Our special thanks to Dr. Jeanne Hansen-Bayless for her clinical contributions and to Mr. Kenneth Kemple for his laboratory support. REFERENCES 1. Crum RJ, Rooney GE. Alveolar bone loss in overdentures: A 5 year study. J PROSTHET DENT 1978,40:610-13. 2. DeFranco RL. Overdentures. In: Winkler S, ed. Essentials of complete denture prosthodontics. 2nd ed. Littleton, Massachusetts: PSG Publishing Co, 1988:384-402. 3. Crum RJ. Rationale for the retention of teeth for overdentures. In: Brewer AA, Morrow RM, eds. Overdentures. 2nd ed. St Louis: CV Mosby Co, 1980:3-11. 4. Renner RP. Complete dentures: A guide for patient treatment. New York: Masson Publishing USA, 1981:257-71. 5. Preiskel HW. Precision attachments in prosthodontics: Overdentures and telescopic prostheses. Vol2. Chicago: Quintessence Publishing Co, 1985:243-306,360-51. 6. Caputo AA, Standlee JP. Biomechanics in clinical dentistry. Chicago: Quintessence Publishing Co, 1987:178-80.
he design Change-xi
of a two-part Shi,
DDSa
The Fourth Military China
Ji-hua
Chen,
Reprint requests to: DR. DOUGLAS B. EVANS 11350 WOODRIDGE FOREST SAN ANTONIO, TX 78249
acid-etched PhD,b
and
Medical University, Stomatological
He-ying
resin-bonded
fixed
YuanC
Hospital, Xian, The People’s Republic of
A new framework design is presented for resin-bonded, acid-etched, fixed partial dentures. This innovative design divided the restoration into two parts, each with a separate path of insertion. The preparation of abutment teeth required minimal reduction and the pontic could not be displaced during function. Thirty-five patients with missing posterior teeth have been treated with this imaginative approach and after approximately 2 years, there have been no debonding failures. (J PROSTHET
DENT1992;68:11-15.)
abrication of the first acid-etched, solid resinbonded fixed partial denture (FPD) in 1980 at the University of Maryland introduced a new era in conservative tooth rep1acement.l Several investigators have reported results
aProfessor, Prosthodontic Department. “Doctor, Prosthodontic Department. “Technician-in-charge, Prosthodontic Department. 10/l/35254 THE
JOURNAL
OF PROSTHETIC
DENTISTRY
on bonding between the restoration and abutment teeth. These include the appropriate treatment of the castings and tooth enamel, improvement in the design of the FPD framework, and tooth preparation. To improve retention of the FPD to the enamel of the abutment, authors have suggested the preparation of grooves, boxes, three-quarter or complete crowns, inlays, onlays, and pins in the abutment, including expansion of the wings.ss6 Clinically, the framework design must observe the basic 11
SHI,
Fig. 2. When model is inclined to lingual line or red line on facial surface is lower.
Fig. 1. Guideline or blue line when path of insertion from vertical direction only.
AND
YUAN
surface, guide-
is
principles of retention and resistance form, such as near parallel or g-degree taper opposing walls, a single path of insertion, maximum tooth coverage, and vertical stops.7 When these guidelines and the appropriate use of newer techniques such as composite resin luting agents and sandblasted or electrolytically etched inner surfaces of cast wings are applied, the resin-bonded prosthesis is a permanent restoration and a valuable asset in the dentist’s armamentarium.s The abutment preparations were not all conservative, but certain approaches were aggressive to ensure a vertical path of insertion. Unfortunately, of all the preparations the best retention form or the natural undercuts of abutment were not used. The greater bond between the resin and metal rather than between the resin and enamel9 was not adequately exploited. In this article, a new design is described to use the natural undercuts of abutments by changing the path of insertion of the FPD. When the undercuts of the abutments are identified with a surveyor, the path of insertion is concomitantly determined. The undercuts on lingual or facial surfaces may be modified by altering the path of insertion. If only the lin-
12
CHEN,
Fig. 3. Path of insertion is altered by inclining model to facial surface. There is no undercut on lingual surface red line.
gual or facial surface was considered, the undercuts of two abutments of an FPD could be lowered to 1 mm above the gingival tissue, which is ideal for the abutment. However, if a resin-bonded FPD could be inserted simultaneously from both facial and lingual directions, the abutment preparations could be finished with only minimal tooth reduction, retaining the abutment’s natural undercuts. Figs. 1 through 4 demonstrate that varying paths of insertion allow the use of different undercuts of the abutment. When the path of insertion was in a vertical direction (Fig. l), the undercut or blue line was near the occlusal one third of the axial surface. When the path of insertion was from a facial direction and ended at the center of proximal (Fig. 2) and then switched to a lingual direction (Fig. 3) to finish the tracing of the guideline, the underscored undercuts (red line) of the same tooth were lower than those resulting from insertion in a single vertical direction. The red and blue lines in Fig. 4, A, in a facial view
JULY
1992
VOLUME
68
NUMBER
1
TWO-PART
RESIN-BONDED
FPD
Fig.
Fig. Fig. Fig. Fig.
5. 6. 7. 8.
4. Two guidelines
completed;
Occlusal view of lower part of wax pattern. Upper part of wax pattern (pink wax) and lingual-occlusal Lingual view of partially finished FPD. Buccal view of finished wax pattern.
and in Fig. 4, B, in a lingual view revealed the two types of undercuts resulting from two directions with a single, specific direction for the path of insertion. According to this design, a two-part resin-bonded FPD could be inserted from both the lingual and the facial directions simultaneously.
THE
JOURNAL
OF PROSTHETIC
facial view (A) and lingual
DENTISTRY
view (B).
view of lower part.
The abutment preparation for the two-part resin-bonded FPD is different from that of the traditional FPD because the undercuts on lingual, facial, and proximal surfaces do not require reduction. The other principles in the designing of a two-part framework, such as vertical occlusal stops and maximum coverage of the wings of an FPD, were the
13
SHI,
Fig. Fig.
9. Two parts of wax pattern attached 10. Finished cast restorations.
CHEN,
AND
YUAN
to main sprue.
inserted from two different paths of insertion (Fig. 11). The restoration was finished except for the inner surface of the four wings, the surface of the lower pontic, and the surface of the upper pontic that contacts with the lower pontic. The unpolished areas of the two parts were then sandblasted. A thin layer of chemically cured composite resin cement was used on the inner surface (intaglio) of the wings and on the surface of the lower pontic. The two parts were then inserted simultaneously. When the wings were bonded to the etched enamel, the two parts of the pontic were also bonded to each other.
DISCUSSION Fig. 11. Inserting model.
two-part
fixed
partial
denture
on
same as those used for the routine resin-bonded FPD, or “Maryland bridge.” Figs. 5 through 10 describe a step-by-step introduction to the two-part resin-bonded FPD made on a model, with a proximal undercut near the missing tooth that was restored. Figs. 5 and 6 illustrate the wax formulation of the twopart FPD including two rests, two wings, and a half-round ring pontic, from facial and lingual directions, respectively. The pontic of this part was narrower than was originally intended. When the wax pattern became completely cold, the upper section was increased dimensionally. A separating fluid is suggested so that the upper part does not adhere to the lower part. The upper part also has two wings on the same side of the abutments. The finished upper part must have a suitable contact with the opposing teeth, including a functional and anatomic form. Figs. 7 and 8 show the upper part from lingual and facial surfaces, respectively. The wax patterns were attached to the main sprue individually (Fig. 9), invested, and cast with a nonprecious alloy. The finished cast restorations are displayed in Fig. 10 and were 14
The bonds between composite resins and human enamel have been verified by various authors since Buonocorel” introduced the theory in 1955. The resin-bonded acidetched FPD has also been acknowledged as a permanent restorations but there have been numerous failures because of debonding at the interface of the wings and ename1.s Nevertheless, to ensure a single, specific path of insertion, the undercut of the abutment is commonly reduced. In the design of two-part resin-bonded FPD (TFPD), besides the bonding strength of tbe composite resin cement to enamel or to the “main retention” of the FPD, there are retentive forces created from maintaining the undercut. The undercut can provide a major portion of the retention during function. The question arises whether the bonding between the two parts of the pontic can withstand the occlusal forces during function. In fact, because the upper pontic engages the lower pontic as a man rides on a horse saddle, the lower pontic is secured tightly in the upper pontic. A more convincing fact is that the bonding strength of the composite resin cement to the sandblasted alloy surfaces is two to three times greater than the bond strength of the composite resin cement to etched enamel.g The greater bond strength of composite resin cement to alloy has been exploited in this innovative design. Nevertheless, further JULY
1992
VOLUME
68
NUMBER
1
TWO-PARTRESIN-BONDEDFPD
research is indicated to investigate the bond strength between the “two-part pontics.” The two-part resin-bonded, acid-etched FPD was especially useful if the undercuts of abutments were excessive and the patient could not endure tooth preparation. In addition, the upper and lower parts of the TFPD might have greater retentive strength than the retention created by the bond strength of resin to enamel, the critical retention force of a conventional resin-bonded FPD. The chief disadvantage of the new design was the complex formulation of the wax-up and precise casting technique.
SUMMARY Anew framework was designed for the resin-bonded, acid-etched FPD so that the natural undercuts of the abutments were used for retention of the FPD. This new design (TFPD) divided the conventional Maryland FPD into an upper and lower “pontic” part, each with a separate path of insertion. The two insertion directions were different so the pontic parts could not be displaced during function. Thirty-five patients have had missing teeth replaced with a TFPD since 1988 in the prosthodontic department. The results of the clinical testing have been extremely encouraging because, in the 35 pairs of TFPDs-the oldest in service 23 months and the most recent 4 months-there has been no debonding at the enamel surfaces or at the interfaces between the two-part pontics.
Resin-bonded David Israel
Madjar, Defense
Forces
cast coverage
REFERENCES 1. Simonsen R, Thompson V, Barrack G. Etched cast restorations: ciinical and laboratory techniques. Chicago: Quintessence Publishing Co, 1983:169. 2. Kishimoto M, Shillingburg HT, Duncanson MG. Influence of preparation features on retention and resistance. Part II. Three-quarter crowns. J PROSTHET DENT 1983;49:168-92. 3. Pegorro LF, Barrack G. A comparison of bond strength of adhesive-cast restoration using diierent designs, bonding agents, and luting resins. J PROSTHFX DENT 1987;57:133-8. 4. Burgess JO, McCartney JG. Anterior
retainer design for resin-bonded acid-etched 6xed partial dentures. J PROSTHET DENT 1987;61:433-6. 5. W&shire WA. Resin bonded fixed partial dentures utibziig additional pin retention. Quintessence Int 1986;17:343-7. 6. Meiers JC, Meetz HK. Design modifications for etched-metal, resinbonded retainers. Gen Dent 1985;33:41-4. I. Barrack G. Recent advances in etched cast restorations. J PROSTHET DENT 1984;52:619-26. 8. Williams VD, Thayer
KE, Denehy GE, Bayer DB. Cast metal, resinbonded prostheses: a lo-year restrospective study. J PROSTHET DENT 1989;61:436-41. 9. Simonsen R, Thompson V, Barrack G. Etched cast restorations: cliicai and laboratory techniques. Chicago: Quintessence Publishing Co, 198341-56. 10. Buonocore MG. A simple method of increasing the adhesion of acrylic filling material to enamel surfaces. J Dent Res 1955;34:849-53. Reprint requests to: DR. JI-HUA CHEN PROSTHODONTIC DEPARTMENT STOMATOLOGICAL HOSPITAL FOURTH MILITARY MEDICAL UNWERS~~Y XIAN 710032 CHINA
for fractured
posterior
teeth
DMD,a and Irit Divon-Kupershmidt, DMDb Center for Oral and Dental Medicine, Tel Hashomer, Israel
Enamel-dentin fracture without pulpal involvement of intact posterior teeth demands restoration of form and function while preserving as much sound tooth material as possible. A partial-coverage restoration cast in nonprecious metal and air-abraded and bonded to the tooth by an adhesive resin is suggested. The strong bond of the adhesive resin to the enamel and dentin of the tooth and to the airabraded metal allows for simple fabrication of a cast partial coverage that requires only minimal tooth preparation. (J PROSTHET DENT 1992,68:15-18.)
-
\
The views expressed herein are private ones of the authors and do not necessarily reflect those of the Medical Corps, Israel Defense Forces. *Major, Israel Defense Forces, Department of Prosthodontics and Maxillofacial Prosthetics. bCaptain, Israel Defense Forces, Department of Prosthodontics and Maxillofacial Prosthetics. 1Q/1/35787 THE
JOURNAL
OF PROSTHETIC
DENTISTRY
T
raumatic forceful closure of teeth after a blow to the chin often leads to crown or crown and root fracture of one or more intact teeth. The indirect trauma mechanism applies a sudden, rapid load to the teeth, causing cuspal fracture and exposure of dentin with or without pulpal involvement1-3 (Figs. 1 and 2). Salis et a.l.,4 in an in vitro study, found that when dynamic forces are applied to in15
