- Email: [email protected]
A simplified procedure for stabilizing pontics
DENTALTECHNOLOGY
Kenneth D. Rudd
A simplified procedure for stabilizing pontics Cary P. Inzerello, CDT, a and Robert W. Rudd, DDS, MS, CDT b Lackland Air Force Base, Texas, and Peterson Air Force Base, Colorado A simplified technique is described for use when waxing pontics to a f'txed partial denture which ensures accurate pontic placement without attaching the pontic to the retainers until late in the fabrication process. This technique allows easy access to the proximal contours and margins of the retainers and to proximal and gingival contours of the pontic while maintaining an accurate occlusal relationship. (J Prosthet Dent 1997;78:405-7.)
During fabrication o f a fixed partial denture (FPD), there are situations when it is desirable to work with the pontic individually, then relate it at a later step to the retainer patterns or castings. Faucher x described a technique that requires cementation o f a die pin lingual to the edentulous area o f a cast to accomplish this purpose. McMordie et al. 2 suggested using 0.7 mm plastic pins inserted into parallel-sided holes to support the pontics during laboratory procedures. This article describes a simplified procedure that uses commonly available materials when waxing pontics to an FPD. This procedure ensures accurate pont~c placement without attaching the pontic to the retainers until late in the fabrication process. This procedure allows easy access to the proximal contours and margins o f the retainers and to proximal and gingival contours o f the pontic, while maintaining a consistent relationship among the components. Tapered pins are used that ensure a snug fit into the prepared hole in the cast.
Fig. 1. Post hole that was drilled just lingual to crest of ridge.
PROCEDURE
The working cast and dies are made in the usual manner. Any plastic post pattern and a corresponding size bur will work with this procedure, however, tapered pins ensure a snug fit o f the post to the cast. The size o f the bur used will be dictated by the size o f the post. The post should fit snugly in the hole made by the bur. Some suggested bur and post sizes are presented in Table I. 1. Prepare a working cast in the usual manner. 2. Drill a hole just lingual to the crest o f the edentulous ridge where the pontic will be placed (Fig. 1). The hole should not interfere with the pontic tissue contact area. It should be 5 mm deep and should parallel the path o f insertion o f the abutment retainers. (Attaching a handpiece to a surveyor or using a milling
The opinions or assertions expressed herein are the views of the authors and are not to be construed as reflecting those of the United States Air Force Dental Service or the Department of Defense. aMaster Sergeant, United States Air Force, NCOIC, McKown Dental Laboratory, Lackland Air Force Base. bColonel, United States Air Force, Dental Corps, and Director, Area Dental Laboratory, Peterson Air Force Base. OCTOBER 1997
Fig. 2. Corresponding sized post is placed in hole. machine may be helpful in establishing the proper path o f insertion.) 3. Place the post into the hole (Fig. 2). Make sure the post is seated snugly in the shaft to ensure there is no movement toward the ridge or laterally. (If the tip o f the post prevents it from seating completely, cut offa small amount o f the tip so it does seat solidly into the hole.) Cut the other end o f the post so it does not interfere with the occlusion, but otherwise leave it as long as possible. 4. Wax the abutment retainers and pontic to full contour as usual and incorporate the exposed part o f the THF JOURNAL OF PROSTHETIC DENTISTRY
405
THE JOURNAL OF PROSTHETIC DENTISTRY
INZERELLO AND RUDD
Table I. Suggested posts and corresponding bur sizes Bur size
1/2
700 701
Fig. 3. Completed full contour wax-up of individual retainers and pontic.
Fig. 4. Proximal view of individual pontic shows post placement.
5.
6. 7.
8.
post into the pontic (Fig. 3). Create appropriate proximal contact areas between the pontic and the retainers. (The contact areas should be the size of the anticipated connectors. The contact will stabilize the pontic against rotation and latcral movement.) I f a veneer is to be applied, cut back the wax pattcrn appropriately. (The post will maintain the vertical relationship between the pontic and the ridge. A piece of 18 gauge wax may be added to the lingual to aid in handling the pontic during veneer application and to assist in stabilizing the pontic in investment during soldering.) Finish the margins of the retainers (Fig. 4). The pontic may be attached to one or both retainers at this time, or the units may be cast separately and soldered later. Attach sprues, invest, cast, and finish as normal. The post is removed during the finishing stage, after the pontic is attached to the retainers.
DISCUSSION This procedure allows many options and can be applied in various situations. The pontic may be joined to 406
Post size
JS pins (JS Plastic Pins ASDI, Stockholm, Sweden) 90 Endowel (Stariite Endowel Posts, Star Dental Mfg. Co. Inc., Conshohocken, Pa.) 80 Endowel (Starlite Endowel Posts, Star Dental Mfg. Co. Inc.) 100 Endowe] (Starlite Endowel Posts, Star Dental Mfg. Co. Inc.)
the retainers before casting, or it may be cast separately and soldered before veneer application. The esthetic veneer may be applied after casting but before soldering. When the pontic is cast as a separate unit, the post will stabilize the pontic during waxing and porcelain application before indexing from the cast for post soldering. As an aid to nonrigid connector fabrication, the retainer housing the keyway component is cast as usual and fitted to the working cast. With this procedure, the pontic is waxed, attached to the key component, and cast. The key component is fitted to the keyway component. The remaining retainer with the rigid connector is waxed, cast, and fitted at this time, then soldered to the pontic. This procedure can help ensure an accurate relationship between the key and keyway components of the connector. When the retainers must be made of one alloy, for example, type 111 gold alloy, and the pontic of another alloy, such as a ceramic metal for porcelain veneering, this procedure allows separate construction of the pontic, with porcelain application, followed by post soldering. Sometimes long-span FPDs are difficult to manage without distortion during wax-up, cut back, investing, or casting procedures. Fabrication of the pontics separately from the retainers may control stresses and expansion factors during the investing and casting procedures. For long-span FPDs, it may be desirable to use two or more parallel posts for the pontics. During fabrication of resin retained, etched metal FPDs, particularly when a refractory cast method is used, it is difficult to develop the proximal contours of the wings and the tissue surface of the pontic. The abutment wings and pontic can be completely contoured before they are attached to one another by using this procedure. SUMMARX A procedure is described that allows waxing an FPD pontic separate from the retainers and attaching it at some point after the initial wax-up stage. This procedure may be used to substantially increase the flexibility of standard fabrication procedures. Although it adds an VOLUME 78 N U M B E R 4
INZERELLO AND RUDD
THE JOURNAL OF PROSTHETIC DENTISTRY
extra step to the fabrication process, it can improve access to interproximal margins and contours during the waxing stage, uses readily available materials, and can actually save time.
2. McMordie R, Cloetta CL, Bullard JT. Technique for fabrication of individualized ceramo-metal pontics. J Prosthet Dent 1980;44:220-3.
Reprint requests to: DR. ROBERTW. RUDD
675 CARVEDTERRACE COLORADOSPRINGS,CO 80919
REFERENCES
10/1/84581
1. Faucher RR. A system for localizing pontics, l Prosthet Dent 1984;52:6437.
N o t e w o r t h y Abstracts of the Current Literature
I n vitro study o f m a n d i b u l a r implant-retained overdentures: The influence o f stud attachments on load transfer to the i m p l a n t a n d soft tissue. Ichikawa T, Hofiuchi M, Wigianto R, Matsumoto N. IntJ
Prosthodont 1996;9:394-9. P u r p o s e . This study investigated the occlusal stress distribution, using static and dynamic loads, to the implant and soft tissue for an implant-supported overdenturc. Material and Methods. An acrylic resin model was fabricated that simulated a mandibular edentulous ridge. Two Apaceram implants (Type-S, Pentax, Tokyo, Japan) were placed bilaterally in the canine regions. These implants were placed vertical to the ridge and held in place with a resin cement. Four strain gauges were attached to the mesial, distal, buccal, and lingual sides o f the resin surface around the implant on the fight side. A load cell transducer was placed beneath the right molar ridge area. The acrylic resin model was covered with a 2 mm thickness ofpolysulfide rubber to simulate the oral mucosa. Next, an acrylic resin denture was fabricated on the mandibular model. Four different types o f attachments were prepared to connect the implant to the overdenmre. The same overdenture was used with each attachment mechanism. The first attachment was a magnetic attachment (type M). A second modified magnetic system (type D) had a 1 m m thick silicone layer placed between the magnet and the acrylic resin base. The third type was a customfabricated ball attachment (type B). Silicone was also placed between the attachment and the denture base. For the final "attachment," there was no retainer (type S). This type had no retainer attachment and was not allowed to contact the acrylic resin base. A loading apparatus was used to apply dynamic and static occlusal loads to the occlusion rim at the molar regions bilaterally. There were three loading sites: right, center, and left. A static load o f 500 N and a dynamic load with a 20 gm metal rod, dropped from a height o f 30 mm, were used. Each measurement was made seven times to allow a recovery o f 5 minutes between measurements. Results. For static load, a significant difference in stress was found among connecting structures when the load was applied to each site. The strain at the mesial and distal regions were tensile, regardless o f the type o f connecting structure used. The absolute value o f the buccolingual strain was less than the mesiodistal strain. The loading sites were less affected by the strains when using the type S attachment. For dynamic load, the least stress transferred to the molar ridge occurred with the type S attachment, and the most stress transferred occurred with the type M attachment. Conclusions. For this in vitro model, when the static load was applied, significant differences in stress at the molar region and strains around the implant were generated between the connecting structures. Occlusal stresses were concentrated around the implant, especially distally. During dynamic load application the influence o f connecting structures was not as great as it was during static load application. Optimal stress distribution was found when the modified magnetic attachment was used. 24 references.--DL Dixon
OCTOBER 1997
407
Kenneth D. Rudd
A simplified procedure for stabilizing pontics Cary P. Inzerello, CDT, a and Robert W. Rudd, DDS, MS, CDT b Lackland Air Force Base, Texas, and Peterson Air Force Base, Colorado A simplified technique is described for use when waxing pontics to a f'txed partial denture which ensures accurate pontic placement without attaching the pontic to the retainers until late in the fabrication process. This technique allows easy access to the proximal contours and margins of the retainers and to proximal and gingival contours of the pontic while maintaining an accurate occlusal relationship. (J Prosthet Dent 1997;78:405-7.)
During fabrication o f a fixed partial denture (FPD), there are situations when it is desirable to work with the pontic individually, then relate it at a later step to the retainer patterns or castings. Faucher x described a technique that requires cementation o f a die pin lingual to the edentulous area o f a cast to accomplish this purpose. McMordie et al. 2 suggested using 0.7 mm plastic pins inserted into parallel-sided holes to support the pontics during laboratory procedures. This article describes a simplified procedure that uses commonly available materials when waxing pontics to an FPD. This procedure ensures accurate pont~c placement without attaching the pontic to the retainers until late in the fabrication process. This procedure allows easy access to the proximal contours and margins o f the retainers and to proximal and gingival contours o f the pontic, while maintaining a consistent relationship among the components. Tapered pins are used that ensure a snug fit into the prepared hole in the cast.
Fig. 1. Post hole that was drilled just lingual to crest of ridge.
PROCEDURE
The working cast and dies are made in the usual manner. Any plastic post pattern and a corresponding size bur will work with this procedure, however, tapered pins ensure a snug fit o f the post to the cast. The size o f the bur used will be dictated by the size o f the post. The post should fit snugly in the hole made by the bur. Some suggested bur and post sizes are presented in Table I. 1. Prepare a working cast in the usual manner. 2. Drill a hole just lingual to the crest o f the edentulous ridge where the pontic will be placed (Fig. 1). The hole should not interfere with the pontic tissue contact area. It should be 5 mm deep and should parallel the path o f insertion o f the abutment retainers. (Attaching a handpiece to a surveyor or using a milling
The opinions or assertions expressed herein are the views of the authors and are not to be construed as reflecting those of the United States Air Force Dental Service or the Department of Defense. aMaster Sergeant, United States Air Force, NCOIC, McKown Dental Laboratory, Lackland Air Force Base. bColonel, United States Air Force, Dental Corps, and Director, Area Dental Laboratory, Peterson Air Force Base. OCTOBER 1997
Fig. 2. Corresponding sized post is placed in hole. machine may be helpful in establishing the proper path o f insertion.) 3. Place the post into the hole (Fig. 2). Make sure the post is seated snugly in the shaft to ensure there is no movement toward the ridge or laterally. (If the tip o f the post prevents it from seating completely, cut offa small amount o f the tip so it does seat solidly into the hole.) Cut the other end o f the post so it does not interfere with the occlusion, but otherwise leave it as long as possible. 4. Wax the abutment retainers and pontic to full contour as usual and incorporate the exposed part o f the THF JOURNAL OF PROSTHETIC DENTISTRY
405
THE JOURNAL OF PROSTHETIC DENTISTRY
INZERELLO AND RUDD
Table I. Suggested posts and corresponding bur sizes Bur size
1/2
700 701
Fig. 3. Completed full contour wax-up of individual retainers and pontic.
Fig. 4. Proximal view of individual pontic shows post placement.
5.
6. 7.
8.
post into the pontic (Fig. 3). Create appropriate proximal contact areas between the pontic and the retainers. (The contact areas should be the size of the anticipated connectors. The contact will stabilize the pontic against rotation and latcral movement.) I f a veneer is to be applied, cut back the wax pattcrn appropriately. (The post will maintain the vertical relationship between the pontic and the ridge. A piece of 18 gauge wax may be added to the lingual to aid in handling the pontic during veneer application and to assist in stabilizing the pontic in investment during soldering.) Finish the margins of the retainers (Fig. 4). The pontic may be attached to one or both retainers at this time, or the units may be cast separately and soldered later. Attach sprues, invest, cast, and finish as normal. The post is removed during the finishing stage, after the pontic is attached to the retainers.
DISCUSSION This procedure allows many options and can be applied in various situations. The pontic may be joined to 406
Post size
JS pins (JS Plastic Pins ASDI, Stockholm, Sweden) 90 Endowel (Stariite Endowel Posts, Star Dental Mfg. Co. Inc., Conshohocken, Pa.) 80 Endowel (Starlite Endowel Posts, Star Dental Mfg. Co. Inc.) 100 Endowe] (Starlite Endowel Posts, Star Dental Mfg. Co. Inc.)
the retainers before casting, or it may be cast separately and soldered before veneer application. The esthetic veneer may be applied after casting but before soldering. When the pontic is cast as a separate unit, the post will stabilize the pontic during waxing and porcelain application before indexing from the cast for post soldering. As an aid to nonrigid connector fabrication, the retainer housing the keyway component is cast as usual and fitted to the working cast. With this procedure, the pontic is waxed, attached to the key component, and cast. The key component is fitted to the keyway component. The remaining retainer with the rigid connector is waxed, cast, and fitted at this time, then soldered to the pontic. This procedure can help ensure an accurate relationship between the key and keyway components of the connector. When the retainers must be made of one alloy, for example, type 111 gold alloy, and the pontic of another alloy, such as a ceramic metal for porcelain veneering, this procedure allows separate construction of the pontic, with porcelain application, followed by post soldering. Sometimes long-span FPDs are difficult to manage without distortion during wax-up, cut back, investing, or casting procedures. Fabrication of the pontics separately from the retainers may control stresses and expansion factors during the investing and casting procedures. For long-span FPDs, it may be desirable to use two or more parallel posts for the pontics. During fabrication of resin retained, etched metal FPDs, particularly when a refractory cast method is used, it is difficult to develop the proximal contours of the wings and the tissue surface of the pontic. The abutment wings and pontic can be completely contoured before they are attached to one another by using this procedure. SUMMARX A procedure is described that allows waxing an FPD pontic separate from the retainers and attaching it at some point after the initial wax-up stage. This procedure may be used to substantially increase the flexibility of standard fabrication procedures. Although it adds an VOLUME 78 N U M B E R 4
INZERELLO AND RUDD
THE JOURNAL OF PROSTHETIC DENTISTRY
extra step to the fabrication process, it can improve access to interproximal margins and contours during the waxing stage, uses readily available materials, and can actually save time.
2. McMordie R, Cloetta CL, Bullard JT. Technique for fabrication of individualized ceramo-metal pontics. J Prosthet Dent 1980;44:220-3.
Reprint requests to: DR. ROBERTW. RUDD
675 CARVEDTERRACE COLORADOSPRINGS,CO 80919
REFERENCES
10/1/84581
1. Faucher RR. A system for localizing pontics, l Prosthet Dent 1984;52:6437.
N o t e w o r t h y Abstracts of the Current Literature
I n vitro study o f m a n d i b u l a r implant-retained overdentures: The influence o f stud attachments on load transfer to the i m p l a n t a n d soft tissue. Ichikawa T, Hofiuchi M, Wigianto R, Matsumoto N. IntJ
Prosthodont 1996;9:394-9. P u r p o s e . This study investigated the occlusal stress distribution, using static and dynamic loads, to the implant and soft tissue for an implant-supported overdenturc. Material and Methods. An acrylic resin model was fabricated that simulated a mandibular edentulous ridge. Two Apaceram implants (Type-S, Pentax, Tokyo, Japan) were placed bilaterally in the canine regions. These implants were placed vertical to the ridge and held in place with a resin cement. Four strain gauges were attached to the mesial, distal, buccal, and lingual sides o f the resin surface around the implant on the fight side. A load cell transducer was placed beneath the right molar ridge area. The acrylic resin model was covered with a 2 mm thickness ofpolysulfide rubber to simulate the oral mucosa. Next, an acrylic resin denture was fabricated on the mandibular model. Four different types o f attachments were prepared to connect the implant to the overdenmre. The same overdenture was used with each attachment mechanism. The first attachment was a magnetic attachment (type M). A second modified magnetic system (type D) had a 1 m m thick silicone layer placed between the magnet and the acrylic resin base. The third type was a customfabricated ball attachment (type B). Silicone was also placed between the attachment and the denture base. For the final "attachment," there was no retainer (type S). This type had no retainer attachment and was not allowed to contact the acrylic resin base. A loading apparatus was used to apply dynamic and static occlusal loads to the occlusion rim at the molar regions bilaterally. There were three loading sites: right, center, and left. A static load o f 500 N and a dynamic load with a 20 gm metal rod, dropped from a height o f 30 mm, were used. Each measurement was made seven times to allow a recovery o f 5 minutes between measurements. Results. For static load, a significant difference in stress was found among connecting structures when the load was applied to each site. The strain at the mesial and distal regions were tensile, regardless o f the type o f connecting structure used. The absolute value o f the buccolingual strain was less than the mesiodistal strain. The loading sites were less affected by the strains when using the type S attachment. For dynamic load, the least stress transferred to the molar ridge occurred with the type S attachment, and the most stress transferred occurred with the type M attachment. Conclusions. For this in vitro model, when the static load was applied, significant differences in stress at the molar region and strains around the implant were generated between the connecting structures. Occlusal stresses were concentrated around the implant, especially distally. During dynamic load application the influence o f connecting structures was not as great as it was during static load application. Optimal stress distribution was found when the modified magnetic attachment was used. 24 references.--DL Dixon
OCTOBER 1997
407