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A simple technique to facilitate investment flow through screw access channels
A simple technique to facilitate investment flow through screw access channels Paul E. Quinlan, BA, BDent Sc, MSc, MSa University of Texas Health Science Center at San Antonio, San Antonio, Texas
Air bubble entrapment can be a problem when metal frameworks are cast.1 When implant frameworks are cast, for example, an air bubble may form within the screw access channel of the wax pattern during the investment procedure (Fig. 1). The entrapped bubble will prevent investment from fully surrounding the wax pattern, resulting in a casting that is unusable due to obliteration of the screw access channel. A procedure is described that enhances flow of investment through the screw access channel of the wax pattern.
PROCEDURE 1. Attach the completed wax pattern to the crucible former. 2. Cut a strip of waxed dental floss (Johnson and Johnson, New Brunswick, N.J.) approximately 6 inches in length, and tie a knot at one end. 3. Thread the floss, knot first, through the access channel so that the knot is located beneath the framework, close to the crucible former. 4. Attach the casting ring to the crucible former, taking care not to trap the floss beneath the ring (Fig. 2). 5. Slowly pour investment (Beauty-Cast; Whip Mix, Louisville, Ky.) around the pattern until the investment reaches the outer edge of the abutment or gold cylinder (Fig. 3, A). 6. Withdraw the floss through the access channel; the investment material will adhere to the floss and be removed with it (Fig. 3, B). 7. After removing the floss, cover the remainder of the wax pattern with investment, and fill the casting ring. This procedure encourages the flow of investment through the screw access channel by breaking the surface tension of the investment, thereby reducing the risk of air bubble entrapment within the wax pattern. The procedure neither reduces the risk of air bubble formation around other parts of the pattern (especially not the portion that interfaces with the implant) nor reduces bubble formation due to other causes.2 When the floss is withdrawn, care should be taken not to disturb the invested pattern, as it is possible to detach the wax pattern from the supporting sprue formers. a
Teaching Assistant, Department of Periodontics. J Prosthet Dent 2002;88:112-3.
112 THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 1. Screw access channel obliterated due to air bubble blockage during investment procedure.
Fig. 2. Wax pattern attached to crucible former in casting ring with floss placed in access channels.
Fig. 3. A, Investment filling casting ring to edge of UCLA abutment, and floss in place in access channel. B, Floss is pulled through access channel, breaking surface tension and carrying investment with it as it is withdrawn. VOLUME 88 NUMBER 1
QUINLAN
THE JOURNAL OF PROSTHETIC DENTISTRY
REFERENCES 1. Johnson A. The effect of five investing techniques on air bubble entrapment and casting nodules. Int J Prosthodont 1992;5:424-33. 2. Lacy AM, Mora A, Boonsiri I. Incidence of bubbles on samples cast in a phosphate-bonded investment. J Prosthet Dent 1985;54:367-9. Reprint requests to: DR PAUL E. QUINLAN 11 CASTLEKNOCK GREEN CASTLEKNOCK DUBLIN 15, IRELAND E-MAIL: [email protected]
Noteworthy Abstracts of the Current Literature
Copyright © 2002 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2002/$35.00 ⫹ 0 10/4/123847
doi:10.1067/mpr.2002.123847
Cooperation and competition between dentists and denturists in Finland. Tuominen R. Acta Odontol Scand 2002;60:99-102.
Purpose: In several countries (Canada, New Zealand, and Denmark) denturists can fabricate both complete and removable partial dentures, while in some American states and Finland, denturists can fabricate only complete dentures. This study investigated the cooperation between dentists and denturists in Finland, especially in relation to the perception of competition between the 2 groups. Material and methods. A sample of 350 private practitioners and 253 denturists was taken from the Finnish Dental Association and the Association for Special Dental Technicians in Finland, respectively. Sixty-eight percent of both groups returned completed questionnaires that dealt with competition and cooperation between the 2 health care providers. Questions were similar for both groups but were customized for denturists to reflect the nature of their work. Collected data were organized in 3 tables: personal and practice characteristics, percent distribution of perceived competition, and odds ratios for the background factors for probability of cooperation. Results. Survey responses indicated that fewer dentists referred their patients to denturists (26.2%) than denturists referred their patients to dentists (94.1%). Professionals who did make referrals received significantly more referrals in return than those who did not refer patients (60.7% vs. 16.7% of dentists, and 90.0% vs. 44.4% of denturists). Fifty-six percent of denturists saw themselves in competition with dentists, while only 29% of dentists saw themselves in competition with denturists. There was more cooperation between dentists and denturists in rural areas or small-town settings than in urban areas. Denturists who were younger or who worked fewer hours referred more patients to dentists. Conclusion. The author concluded that cooperation between dentists and denturists is common in Finland. The fact that the denturists’ service is limited to complete dentures may explain their willingness to cooperate with dentists. 23 References.—RP Renner
JULY 2002
113
Air bubble entrapment can be a problem when metal frameworks are cast.1 When implant frameworks are cast, for example, an air bubble may form within the screw access channel of the wax pattern during the investment procedure (Fig. 1). The entrapped bubble will prevent investment from fully surrounding the wax pattern, resulting in a casting that is unusable due to obliteration of the screw access channel. A procedure is described that enhances flow of investment through the screw access channel of the wax pattern.
PROCEDURE 1. Attach the completed wax pattern to the crucible former. 2. Cut a strip of waxed dental floss (Johnson and Johnson, New Brunswick, N.J.) approximately 6 inches in length, and tie a knot at one end. 3. Thread the floss, knot first, through the access channel so that the knot is located beneath the framework, close to the crucible former. 4. Attach the casting ring to the crucible former, taking care not to trap the floss beneath the ring (Fig. 2). 5. Slowly pour investment (Beauty-Cast; Whip Mix, Louisville, Ky.) around the pattern until the investment reaches the outer edge of the abutment or gold cylinder (Fig. 3, A). 6. Withdraw the floss through the access channel; the investment material will adhere to the floss and be removed with it (Fig. 3, B). 7. After removing the floss, cover the remainder of the wax pattern with investment, and fill the casting ring. This procedure encourages the flow of investment through the screw access channel by breaking the surface tension of the investment, thereby reducing the risk of air bubble entrapment within the wax pattern. The procedure neither reduces the risk of air bubble formation around other parts of the pattern (especially not the portion that interfaces with the implant) nor reduces bubble formation due to other causes.2 When the floss is withdrawn, care should be taken not to disturb the invested pattern, as it is possible to detach the wax pattern from the supporting sprue formers. a
Teaching Assistant, Department of Periodontics. J Prosthet Dent 2002;88:112-3.
112 THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 1. Screw access channel obliterated due to air bubble blockage during investment procedure.
Fig. 2. Wax pattern attached to crucible former in casting ring with floss placed in access channels.
Fig. 3. A, Investment filling casting ring to edge of UCLA abutment, and floss in place in access channel. B, Floss is pulled through access channel, breaking surface tension and carrying investment with it as it is withdrawn. VOLUME 88 NUMBER 1
QUINLAN
THE JOURNAL OF PROSTHETIC DENTISTRY
REFERENCES 1. Johnson A. The effect of five investing techniques on air bubble entrapment and casting nodules. Int J Prosthodont 1992;5:424-33. 2. Lacy AM, Mora A, Boonsiri I. Incidence of bubbles on samples cast in a phosphate-bonded investment. J Prosthet Dent 1985;54:367-9. Reprint requests to: DR PAUL E. QUINLAN 11 CASTLEKNOCK GREEN CASTLEKNOCK DUBLIN 15, IRELAND E-MAIL: [email protected]
Noteworthy Abstracts of the Current Literature
Copyright © 2002 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2002/$35.00 ⫹ 0 10/4/123847
doi:10.1067/mpr.2002.123847
Cooperation and competition between dentists and denturists in Finland. Tuominen R. Acta Odontol Scand 2002;60:99-102.
Purpose: In several countries (Canada, New Zealand, and Denmark) denturists can fabricate both complete and removable partial dentures, while in some American states and Finland, denturists can fabricate only complete dentures. This study investigated the cooperation between dentists and denturists in Finland, especially in relation to the perception of competition between the 2 groups. Material and methods. A sample of 350 private practitioners and 253 denturists was taken from the Finnish Dental Association and the Association for Special Dental Technicians in Finland, respectively. Sixty-eight percent of both groups returned completed questionnaires that dealt with competition and cooperation between the 2 health care providers. Questions were similar for both groups but were customized for denturists to reflect the nature of their work. Collected data were organized in 3 tables: personal and practice characteristics, percent distribution of perceived competition, and odds ratios for the background factors for probability of cooperation. Results. Survey responses indicated that fewer dentists referred their patients to denturists (26.2%) than denturists referred their patients to dentists (94.1%). Professionals who did make referrals received significantly more referrals in return than those who did not refer patients (60.7% vs. 16.7% of dentists, and 90.0% vs. 44.4% of denturists). Fifty-six percent of denturists saw themselves in competition with dentists, while only 29% of dentists saw themselves in competition with denturists. There was more cooperation between dentists and denturists in rural areas or small-town settings than in urban areas. Denturists who were younger or who worked fewer hours referred more patients to dentists. Conclusion. The author concluded that cooperation between dentists and denturists is common in Finland. The fact that the denturists’ service is limited to complete dentures may explain their willingness to cooperate with dentists. 23 References.—RP Renner
JULY 2002
113