Fabrication of a simple ball-socket attachment

Dental technology DANIEL H. GEHL and S. HOWARD PAYNE, Associate Editors

Fabrication of a simple ball-socket attachment Joseph T. Quinlivan, D.D.S.*

State University of New York at Buffalo, School of Dentistry, Buffalo, N. Y.

T h e s e ball and socket attachments are designed for use in endodontically treated roots to attach an overlay denture. The male part is a ball-type extension from a cast post and cap. The female part is a resin dome which becomes incorporated in the denture base? The attachment encloses an elastic " O " ring and has an inner surface which provides a smooth socket to receive the male casting. The elastic " O " ring provides some retention for the overlay denture. This design allows for a direct transfer of vertical forces to the tooth root, but it reduces some of the torque that would be transmitted by pivotal movement of a denture having a more restrictive type of attachment (Fig. 1). METHODS AND MATERIALS Any competent machine, shop staff can produce the jig shown in Fig. 2. Aluminum stock may be used for everything but the ~ 6 inch rod insert with the ball ends; stainless steel is suggested for durability. (Noncorrosive metals must be selected since the jig will be under water in a pressure pot while the acrylic resin parts are being fabricated.) A silicone rubber, such as Acra-Sil,t is used to make an elastic mold for the male attachment.

The mold. 1. Fill the % inch well in the cylindrical insert, for the base of the jig, with a bubble-free mix of silicone rubber. 2. Insert the cylinder in an uptight position in the jig, and tighten the setscrew. 3. Orient the ~ ~ inch rod insert with the larger ball end down, and gradually adjust it in the bridge of the jig until it is embedded up to its shoulder in silicone. This setscrew is also tightened (Fig. 3, A). Read before The Carl O. Boucher Prosthodontic Conference, Columbus, Ohio. *Associate Professor, Department of Removable Prosthodontics. tZahn Dental Mfg. Company, Inc., New York, N. Y. 222

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Fig. 1. (A) A completed casting in a mandibular cuspid. The neck and ball extension make up the male portion of the attachment. (B) The female portion, which is incorporated in the denture base, consists of a resin dome with an elastic "0" ring.

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Fig. 2. The jig is made from aluminum stock, % inch thick and 1 ~ inch square. The bridge is made from ~v~ inch stock and is % inch high, and it is attached to the base with screws from the bottom. A stainless steel rod insert, ~6 inch in diameter and 1 ~2 inch long, fits a hole in the bridge and is held by a thumbscrew. A cylindrical aluminum insert, % inch in diameter and ~ inch thick, fits a hole in the base and is held by a thumbscrew. There are chambers of different sizes in the upper and lower aspects of this insert.

4. W h e n the silicone has set c o m p l e t e l y , loosen the setscrews, c a r e f u l l y r e m o v e the cylindrical insert w i t h its elastic m o l d , a n d e x a m i n e it for flaws. W i t h c a r e in h a n d l i n g , q u i t e a few p a t t e r n s c a n be m a d e in the s a m e m o l d . W h e n the m o l d b e c o m e s d a m a g e d , a n o t h e r c a n be m a d e easily by r e p e a t i n g these f o u r steps.

The male pattern. 1. Fill the elastic m o l d w i t h a c o l d - c u r i n g acrylic resin m o n o m e r . C a r e m u s t be

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Fig. 3. (A) An elastic mold is made in the larger chamber of the aluminum insert for the base. This well is filled with silicone rubber, and the male end of the stainless steel insert for the bridge is inserted to the level of its shoulder. (B) The elastic mold is filled with cold-curing acrylic resin. (C) The cured acrylic resin pattern teased from the mold. (D) The male resin pattern after the excess has been trimmed.

Fig. 4. (A) The elastic "O" rings used in making the female dome. (B) The elastic rings in place on the female end of the stainless steel insert. The smaller well of the aluminum insert has been filled with cold-curing acrylic resin. (C) The acrylic resin, with the enclosed elastic rings, upon recovery from the mold. (D) The trimmed acrylic resin dome. The smaller elastic has been removed. The larger elastic was removed and a fresh one put in its place. The original is held too securely when the resin cures around it. exercised to avoid e n t r a p m e n t of air. (A hypodermic syringe a n d b l u n t needle work well to accomplish this.) 2. Dust the m o n o m e r with fine-grained polymer powder; gravity will allow it to settle to the base of the mold. Fill the mold to excess. 3. Dust on polymer until no free m o n o m e r is left (Fig. 3, B). 4. Place the insert in a pressure pot filled with w a r m water; set the pressure at 25 p.s.i, for 20 minutes. 5. Remove the p a t t e r n by teasing it from the mold (Fig. 3, C ) . 6. Finish the p a t t e r n by g r i n d i n g the excess acrylic resin to the level of the neck (Fig. 3, D ) . This male p a t t e r n becomes the extension-post portion of the p a t t e r n to be cast a n d cemented to the root.

Female portion. 1. O r i e n t the ~ 6 inch rod insert with the smaller ball e n d down. 2. Place a n elastic ligature (Alastik A-1 No. 406-011 ~) over the ball end onto ~Unitec Mfg. Company, Monrovia, Calif.

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the neck and follow with an elastic separator (Alastik S-1 No. 406-081") placed in a similar fashion (Fig. 4, A). 3. Place the cylindrical insert for the base on the bench with the ~ inch diameter depression facing upward. 4. Fill this depression with fine-grained cold-curing acrylic resin in the same manner as that employed in making the male pattern. (The author uses tooth-colored resin to give a sharp color contrast with the denture base.) 5. Orient the cylindrical insert into the base of the jig, and hold it in place with its setscrew. 6. Gradually lower the ~ 6 inch insert with its elastic " O " rings into the resin until the smaller " O " ring is just covered. Now tighten the setscrew (Fig. 4, B). 7. Place the jig in a pressure pot containing water, and apply 25 p.s.i, air pressure for 90 minutes. 8. Loosen the setscrews, and recover the resin housing (Fig. 4, C). 9. Trim the excess resin away to uncover the top surface of the smaller " O " ring. 10. Remove both " O " rings using a small instrument, such as a 3S Hollenbeck carver, t 11. Replace the larger elastic (Alastik S-I) in the resin housing with another of the same using a wooden applicator stick or blunt instrument. The smaller elastic controls size reduction in the resin housing. This provides mechanical retention of the larger elastic to prevent accidental dislodgment (Fig. 4, D). In clinical use, the elastics are changed at six-month intervals as retention decreases. With practice, the removal and replacement of the " O " ring can be accomplished in less than a minute. The author wishes to thank Mr. Melford Diedrick, Director of Medical Illustration at State University, for the illustrative material accompanying this article. *Unitec Mfg. Company, Monrovia, Calif. tPremier Dental Products Company, Philadelphia, Pa. Reference 1. Quinlivan, J. T.: An Attachment for Overlay Dentures, J. PROSTHET. DENT. In press. STATE UNIVERSITYOF NEW YORKAT BUFFALO DEPARTMENTOF REMOVABLEPROSTHODONTICS SCHOOLOF DENTISTRY ROOM G30A, CAPEN HALL BUFFALO, N. Y. 14214