A technique to ensure the reproducibility of a cast post and core Haitem MM. Naas, BDS,a Mohammad Hossein Dashti, DMD,b Roxana Hashemian, DDS,c and Nedda Y. Hifeda, BDSd School of Dental Medicine-Boston University, Boston, Mass The post-and-core pattern duplication technique is a simple, cost-effective, and accurate method of ensuring the reproducibility of a cast post and core. An acrylic resin pattern is fabricated for an endodontically treated tooth. The post portion of the pattern is duplicated with a polyvinyl siloxane impression material in the lower compartment of a container. The core portion is then duplicated with a polyether impression material in the upper compartment. After the original pattern has been retrieved, the duplicate resin pattern is fabricated in the provided space. This technique will improve efficiency if damage or loss of the pattern or the actual cast post and core occurs. (J Prosthet Dent 2014;112:1585-1587)
The advantages of a cast post and core over a prefabricated system include a reduced incidence of microleakage,1 inherent strength due to the unity of the post and the core segments, and antirotational features.2 In addition, because the cast post can be adapted to an existing, properly shaped, endodontically treated canal, the need to remove additional dentin is less.3 Fabricating a pattern for a cast post and core can be done directly or indirectly.4,5 For the indirect technique, an elastomeric impression of the endodontically treated tooth is made, a stone cast is poured, and the pattern is fabricated by the dental technician.6 In the direct technique, an acrylic pattern resin is used directly on the endodontically treated tooth to form a pattern.7 Although the direct technique results in a pattern that can be invested and cast without any alterations, in the case of accidental damage or a loss, the pattern needs to be remade. The aim of this article was to describe a simple and practical technique for ensuring the reproducibility of a cast post and core.
a
TECHNIQUE 1. Fabricate a pattern with a plastic pin (Spee-Dee Plastic Pins; Pulpdent Corp) and acrylic pattern resin (Pattern resin; GC America Inc) by following the standard protocol (Fig. 1).7 2. Select a 2-compartment plastic container with a square cross section (28 mm wide, 28 mm long, 62 mm high). 3. Heat a piece of sticky wax (Sticky Wax 00625; Kerr Corp) (8 mm in diameter and 40 mm in length) and attach it perpendicularly to the middle of another piece of sticky wax of similar dimensions. 4. Draw an orientation mark on 1 side of the container (the upper and the lower compartments) with a permanent marker (Sharpie; AP) and suspend the sticky wax assembly in the lower compartment (Fig. 2). 5. Inject a medium-body polyvinyl siloxane impression material (Aquasil Ultra LV; Dentsply Intl) into the lower compartment until it is filled, which encompasses the entire vertical and covers the lower portion of the horizontal sticky wax.
Resident, Department of Post-graduate Prosthodontics. Clinical Associate Professor, Department of Post-graduate Prosthodontics. c Clinical Instructor, Department of General Dentistry. d Resident, Post-graduate Endodontics, Department of Endodontics. b
Naas et al
6. After the recommended setting time, remove the 2-piece sticky wax and fill the space with light-body polyvinyl siloxane from the same manufacturer. 7. Gently immerse the post portion of the resin pattern in the impression
1 Endodontically treated tooth with original post-and-core pattern.
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Volume 112 Issue 6 material up to, but not including, the core portion. 8. Close the top cover of the container, align the marks on the side (Fig. 3), and inject a light-body polyether impression material (Dimension Penta H; 3M ESPE) through a predrilled
hole on the top of the upper compartment until filled. After the recommended setting time, separate the upper compartment from the container and retrieve the original pattern (Fig. 4). 9. Fabricate the duplicate pattern in the same manner as the original and
make certain that the post length is measured and marked on the plastic pin to avoid perforation of the silicone mold. For the core portion, cut the plastic pin 2 mm shorter than the height of the core of the original pattern and avoid any possible interference
2 Lower compartment of duplication flask, showing sticky wax assembly in position.
3 Duplication flask with original post-and-core pattern being duplicated.
4 Duplication flask, showing mold of post in lower and mold of core in upper compartment.
5 Post and core patterns. Original pattern is shown on left and duplicate pattern is on right.
6 Cast post and cores. Sequence is same as in Figure 5.
7 Cast post and cores, showing notch on duplicate cast on right.
The Journal of Prosthetic Dentistry
Naas et al
December 2014
1587 CONCLUSION The cast post-and-core pattern duplication technique is a simple, costeffective, and accurate method of ensuring the reproducibility of the pattern. This will reduce any stress and inconvenience that results from damage or loss of the pattern or the actual cast post and core.
REFERENCES
8 Periapical radiograph of original cast post and core. with the top portion of the mold on closure. Fill the mold of the core portion with the resin, and close the 2 compartments completely. Retrieve the duplicate pattern after complete polymerization (Fig. 5).
DISCUSSION The fit of the cast post and core made from the original pattern should closely match the one made from the duplicate pattern. This can be verified both visually and radiographically (Figs. 6-9). This technique can be valuable in a restorative practice. The process of duplication can be performed up to the mold production stage and saved in the patient’s file until the completion and cementation
Naas et al
9 Periapical radiograph of duplicate cast post and core. of the original cast post and core. In the event of a loss, mishandling, or a miscast, a duplicate cast post and core can be made and delivered to the patient with minimal inconvenience. This is particularly important for those patients with unfavorable physical or psychological conditions, or those with limited time and availability. Although other elastomeric impression materials may be used for the duplication process, polyvinyl siloxane is the material of choice for the post portion of the resin pattern because of its dimensional stability and elastic recovery.8 Regardless of the material selection, the material used for the upper compartment must be chemically different from that used in the lower compartment to avoid any bonding between them.
1. Geramipanah F, Rezaei SM, Sichani SF, Sichani BF, Sadighpour L. Microleakage of different post systems and a custom adapted fiber post. J Dent Tehran 2013;10: 94-102. 2. Hemmings KW, King PA, Setchell DJ. Resistance to torsional forces of various post and core designs. J Prosthet Dent 1991;66:325-9. 3. Morgano SM, Milot P. Clinical success of cast metal post and cores. J Prosthet Dent 1993;70:11-6. 4. Al-Omari W, Zagibeh A. The retention of cast metal dowels fabricated by direct and indirect techniques. J Prosthodont 2010;19: 58-63. 5. Schneider R. A one-appointment procedure for cast post and core restoration. J Prosthet Dent 1994;71:420-2. 6. Lau VM. The reinforcement of endodontically treated teeth. Dent Clin North Am 1976; 20:313-28. 7. Shillingburg HT, Sather DA, Wilson EL, Cain JR, Mitchell DL, Blanco LJ, et al. Fundamentals of fixed prosthodontics. 4th ed. Quintessence; 2012. p. 214-25. 8. Chew CL, Chee WW, Donovan TE. The influence of temperature on the dimensional stability of polyvinyl siloxane impression materials. Int J Prosthodont 1993;6:528-32. Corresponding author: Dr Haitem M. M. Naas Boston University School of Dental Medicine 13 Pompeii Street, No. 1 Boston, MA 02119 E-mail: [email protected] Copyright ª 2014 by the Editorial Council for The Journal of Prosthetic Dentistry.
The advantages of a cast post and core over a prefabricated system include a reduced incidence of microleakage,1 inherent strength due to the unity of the post and the core segments, and antirotational features.2 In addition, because the cast post can be adapted to an existing, properly shaped, endodontically treated canal, the need to remove additional dentin is less.3 Fabricating a pattern for a cast post and core can be done directly or indirectly.4,5 For the indirect technique, an elastomeric impression of the endodontically treated tooth is made, a stone cast is poured, and the pattern is fabricated by the dental technician.6 In the direct technique, an acrylic pattern resin is used directly on the endodontically treated tooth to form a pattern.7 Although the direct technique results in a pattern that can be invested and cast without any alterations, in the case of accidental damage or a loss, the pattern needs to be remade. The aim of this article was to describe a simple and practical technique for ensuring the reproducibility of a cast post and core.
a
TECHNIQUE 1. Fabricate a pattern with a plastic pin (Spee-Dee Plastic Pins; Pulpdent Corp) and acrylic pattern resin (Pattern resin; GC America Inc) by following the standard protocol (Fig. 1).7 2. Select a 2-compartment plastic container with a square cross section (28 mm wide, 28 mm long, 62 mm high). 3. Heat a piece of sticky wax (Sticky Wax 00625; Kerr Corp) (8 mm in diameter and 40 mm in length) and attach it perpendicularly to the middle of another piece of sticky wax of similar dimensions. 4. Draw an orientation mark on 1 side of the container (the upper and the lower compartments) with a permanent marker (Sharpie; AP) and suspend the sticky wax assembly in the lower compartment (Fig. 2). 5. Inject a medium-body polyvinyl siloxane impression material (Aquasil Ultra LV; Dentsply Intl) into the lower compartment until it is filled, which encompasses the entire vertical and covers the lower portion of the horizontal sticky wax.
Resident, Department of Post-graduate Prosthodontics. Clinical Associate Professor, Department of Post-graduate Prosthodontics. c Clinical Instructor, Department of General Dentistry. d Resident, Post-graduate Endodontics, Department of Endodontics. b
Naas et al
6. After the recommended setting time, remove the 2-piece sticky wax and fill the space with light-body polyvinyl siloxane from the same manufacturer. 7. Gently immerse the post portion of the resin pattern in the impression
1 Endodontically treated tooth with original post-and-core pattern.
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Volume 112 Issue 6 material up to, but not including, the core portion. 8. Close the top cover of the container, align the marks on the side (Fig. 3), and inject a light-body polyether impression material (Dimension Penta H; 3M ESPE) through a predrilled
hole on the top of the upper compartment until filled. After the recommended setting time, separate the upper compartment from the container and retrieve the original pattern (Fig. 4). 9. Fabricate the duplicate pattern in the same manner as the original and
make certain that the post length is measured and marked on the plastic pin to avoid perforation of the silicone mold. For the core portion, cut the plastic pin 2 mm shorter than the height of the core of the original pattern and avoid any possible interference
2 Lower compartment of duplication flask, showing sticky wax assembly in position.
3 Duplication flask with original post-and-core pattern being duplicated.
4 Duplication flask, showing mold of post in lower and mold of core in upper compartment.
5 Post and core patterns. Original pattern is shown on left and duplicate pattern is on right.
6 Cast post and cores. Sequence is same as in Figure 5.
7 Cast post and cores, showing notch on duplicate cast on right.
The Journal of Prosthetic Dentistry
Naas et al
December 2014
1587 CONCLUSION The cast post-and-core pattern duplication technique is a simple, costeffective, and accurate method of ensuring the reproducibility of the pattern. This will reduce any stress and inconvenience that results from damage or loss of the pattern or the actual cast post and core.
REFERENCES
8 Periapical radiograph of original cast post and core. with the top portion of the mold on closure. Fill the mold of the core portion with the resin, and close the 2 compartments completely. Retrieve the duplicate pattern after complete polymerization (Fig. 5).
DISCUSSION The fit of the cast post and core made from the original pattern should closely match the one made from the duplicate pattern. This can be verified both visually and radiographically (Figs. 6-9). This technique can be valuable in a restorative practice. The process of duplication can be performed up to the mold production stage and saved in the patient’s file until the completion and cementation
Naas et al
9 Periapical radiograph of duplicate cast post and core. of the original cast post and core. In the event of a loss, mishandling, or a miscast, a duplicate cast post and core can be made and delivered to the patient with minimal inconvenience. This is particularly important for those patients with unfavorable physical or psychological conditions, or those with limited time and availability. Although other elastomeric impression materials may be used for the duplication process, polyvinyl siloxane is the material of choice for the post portion of the resin pattern because of its dimensional stability and elastic recovery.8 Regardless of the material selection, the material used for the upper compartment must be chemically different from that used in the lower compartment to avoid any bonding between them.
1. Geramipanah F, Rezaei SM, Sichani SF, Sichani BF, Sadighpour L. Microleakage of different post systems and a custom adapted fiber post. J Dent Tehran 2013;10: 94-102. 2. Hemmings KW, King PA, Setchell DJ. Resistance to torsional forces of various post and core designs. J Prosthet Dent 1991;66:325-9. 3. Morgano SM, Milot P. Clinical success of cast metal post and cores. J Prosthet Dent 1993;70:11-6. 4. Al-Omari W, Zagibeh A. The retention of cast metal dowels fabricated by direct and indirect techniques. J Prosthodont 2010;19: 58-63. 5. Schneider R. A one-appointment procedure for cast post and core restoration. J Prosthet Dent 1994;71:420-2. 6. Lau VM. The reinforcement of endodontically treated teeth. Dent Clin North Am 1976; 20:313-28. 7. Shillingburg HT, Sather DA, Wilson EL, Cain JR, Mitchell DL, Blanco LJ, et al. Fundamentals of fixed prosthodontics. 4th ed. Quintessence; 2012. p. 214-25. 8. Chew CL, Chee WW, Donovan TE. The influence of temperature on the dimensional stability of polyvinyl siloxane impression materials. Int J Prosthodont 1993;6:528-32. Corresponding author: Dr Haitem M. M. Naas Boston University School of Dental Medicine 13 Pompeii Street, No. 1 Boston, MA 02119 E-mail: [email protected] Copyright ª 2014 by the Editorial Council for The Journal of Prosthetic Dentistry.
