Attachment fixation of the overdenture: Part II M e r r i l l C. M e n s o r , Jr., D . D . S .
San Mateo, Galif.
I t is impossible to overemphasize the need for simple attachments for overdenture fixation. Such simple attachments as the nonresilient Gerber,* the Intr0fix,~ or the Bona cylinder* can perform the primary function of positional fixation adequately and relatively inexpensively. Only the desire for fine resilient movement justifies using a highly sophisticated and expensive attachment like the resilient Gerber. There is a need for simple systems such as t h e H a d e r bar unit~" and the H a d e r bar joint, which offer easy serviceability and laboratory fabrication using plastic patterns (Fig. 1). T h e overall cost is low, because both systems can be cast directly. The snapper or the rider of a bar unit can be made of resin picked up in the mouth or processed in the laboratory. The most important consideration is the attachment stabilization of the overdenture and not necessarily the choice of attachment. SELECTION OF A T T A C H M E N T S Manufacturers or inventors n a m e d the various attachment groups such as the Gerber Stud Attachment and the Dolder Bar Unit.~ A c o m p e n d i u m known as the E M Attachment Selector~ presents 30 points of information about each a t t a c h m e n t ? This selector and the E M Gauge~ provide a simple colorcode method of choosing attachments from mounted diagnostic casts. 2 In the making of an overdenture only the stud, the bar, and some of the accessory attachments are of interest. S T U D (PRESSURE B U T T O N ) A T T A C H M E N T S Most of the stud-type attachments, also considered snap fasteners, are simple in concept. However, Read before the Academy of Denture Prosthetics, Washington, D.C. *Cendres and Metaux S.A., Biel, Switzerland. ~'Metaux Precieux S.A.,~Neuch~tel, Switzerland. ~Bell International, Burlingame, GaliL
16
many, such as the resilient Gerber, seem to be complicated upon initial examination. Like any device each system requires careful study and compliance with the manufacturer's recommendations. T h e simpler the attachment the easier it is to use, except for the Rothermann* series, Some stud attachments, such as the Gerber, are resilient and have a spring return. Others, such as the Dalbo* cylinder, are tissue resilient; still others, such as the Introfix, are nonresilient. The resilient attachments can be unidirectional or multidirectional, and may involve both the bar and the telescopic stud attachments. A compensating factor in resilient attachments allows the tissue rather than the tooth to support the denture base entirely. Resilient studs. Resilient attachment systems perform a compensatory function and act as a safety valve in the event of an overload. No two resilient attachment systems should oppose each other unless one is locked out of function, such as in the case of the attachments in a mandibular prosthesis, where the maxillary prosthesis receives additional support from the palatal coverage. This situation arises when two overdentures oppose each other or a mandibular restoration opposes a natural dentition. It is essential to allow for movement to achieve maxium tissue contact of the denture base under m a x i m u m load. I n the well developed denture base careful positioning of the attachments makes the need for a resilient system questionable. No attempt should be made to equilibrate, establish permanent records, or reline without locking the resilient attachments out of function. Otherwise the base w{ll move and incorrect markings of the interferences will be produced. The primary function of the retained root is the retention and positional or directional orientation of the restoration. When a dentist uses an inadequate technique or lacks the ability to develop a well fitting *Metaux Precieux S. A., NeuehStel, Switzerland.
JANUARY 1978
VOLUME39
NUMBER 1
AITACHMENT FIXATION OF THE OVERDENTURE: PART II
Fig. 1. The Hader bar joint can be used as a joint or unit; the plastic pattern is a simple and an inexpensive method of bar fabrication and pattern length is sufficient to handte most large span demands. denture base, the resilient attachment allows some leeway in the patient's acceptance of the prosthesis by allowing more base contact and support during function. Nonresilient studs. The nonresilient stud attachments are effective when interocclusal space is limited. They are essential when the teeth are stable or when the dentist does not desire movement of the overdenture. Ancrofix. The Ancrofix* (Fig. 2) is a resilient pressure-button system that consists of four parts: a solder base, a replaceable retention head, a housing with four lamellae to activate, and a teflon ring to allow the lamellae to function. The overall height of the unit is 3.2 mm. The advantages of the Ancrofix are: 1. Tinfoil spacers can provide tissue resilience during fabrication. 2. The attachment allows rotational movement, and flattening the knob on top of the male post deactivates it. The components are replaceable, and it is easy to adjust the retention, thereby giving the attachment an indefinite life. 3. The solder base is interchangeable with the Introfix attachment, allowing exchange of attachments. The button can be picked up in the mouth with resin or processed in the laboratory. 4. There is no clinically significant torque to the support tooth when the denture base is developed properly. 5. The attachment system is simple and inexpensive. The disadvantages of the Ancrofix system are: *Metaux Precieux S.A., Neuchhtel, Switzerland.
THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 2. A line drawing of Ancrofix shows a threaded stud section and housing with four lamellae surrounded b y a teflon ring; the male unit is replaceable, and has a hemispherical knob (arrow) that permits rotational movement or provides rigid fixation after reduction. The height of the attachment is 3.2 mm. 1. Use of more than one attachment requires a paralleling mandrel for attaining proper alignment. 2. Improper base development and overtightening of attachments can torque the teeth. 3. Repositioning the attachment during rebasing can damage the teflon ring. This attachment is ideal for removable partial dentures and overdenture fixation. BAR ATTACHMENTS
Bar attachments are of two types: bar units and bar joints. They provide fixation for an overdenture and splinting for the remaining teeth. Bar units, as the name implies, offer rigid fixation for an overdenture, whereas bar joints permit some degree of rotational a n d / o r resilient movement. Bar units. The selection of a bar unit depends upon the space available, the shape and curvature of the ridge, and the type of defect that is to be replaced. Bar units are ideal for replacing a gross tissue defect and supporting an overdenture. It is possible to convert a bar joint to function as a bar unit by bending it into a shape other than that supplied by the manufacturer. The primary functions of bar units are splinting and carrying the appliance positionally. Most laboratory-fabricated bars, such as the Gaerny or Steiger-Boitel bars, are considered bar units. 3. + The height available, the type of occlusal surface, and the type of denture tooth are the only factors that limit their size, position, and design.
17
MENSOR
Fig. 3. The Dolder bar can and should be bent to conform to the ridge; the rider should be segmented to fit the straight sections.
Fig. 4. Bar fixation can be provided for markedly divergent teeth by using a Schubiger attachment. The bar is soldered on the coping for the weakest tooth, and the attachment is placed on the strongest tooth for future salvage or conversion to stud fixation. The usual bar attachment splints two or more teeth together. Most prefabricated bars are made of high-strength alloy and consequently size plays no part in selection for short-term applications. If only splinting is considered, theoretically a long-reach splint, i.e., one between a molar and a canine, requires a bar with a larger cross section than a cuspid-to-cuspid splint. This usage has led to a rule, according to which the cross section is in direct proportion to the length Of the span. This rule i s more important with respect to the laboratoryfabricated bar than to the commercially available prefabricated bar because of the difference in the type of alloy used (except in the instance of nonprecious metals). The major consideration in selecting proper bar size is the space available to assure rigidity of the splint. It is always desirable to select the largest possible size for the space without disturbing the vertical relationship, occlusion, or the contour of the prosthesis. 18
The number of abutments and their location, as well as the dimension of the bar, control the splinting effect and the strength of the restoration. Properly designed bar restorations have retention, adjustment, and wear in the attachment portion, eliminating wear on the bar and the need for a bar of larger diameter. A bar of large diameter is necessary only when there is a need to span a long edentulous space, which will subject the bar to greater forces. The Dolder bar is the one most often mentioned in discussions of the bar system. Preiskel 5' 6 discussed the Dolde r bar joints and units in the second edition of his book. An in-depth review of Dolder's writing indicates that it is possible to bend the Dolder bar system and shape it to approach the configuration of any ridge (Fig. 3). 7-~Both the inventor, Dolder,* and the manufacturers recommend this broad application of the system. Technically any bending, cutting, or soldering of bar attachments requires annealing followed by heat treatment to restore the alignment of the crystalline structure and the original strength to the alloy. Cutting, bending, and soldering produce a weaker bar than bending alone because the solder joint has a different crystal structure. A few representative bars will be discussed. Dolder bar unit. The Dolder bar unit has a church window profile that contrasts to the egg shape of the joint. It consists of the bar and a rider with retention mesh. The unit, which is rigid, is available in both a standard size, 4.65 mm in height, and a micro-size, 3.6 m m in height. This bar can be joined to divergent teeth by using the Schubiger, VK, or Kurer systems (Fig. 4).t The advantages of the Dolder bar unit are: 1. It is possible to segment rider sections and adjust them for retention. 2. The bar and rider are available in two sizes. 3. The rider makes a good frictional fit. The disadvantages of the Dolder unit are: 1. It is too bulky in all dimensions. 2. Retention in the denture complicates rebasing or positioning. 3. It is very expensive. 4. T h e bulk has a negative effect on the esthetic results. Although the Dolder bar unit is used for overdentures it is not recommended highly because of its bulk, cost, and esthetic problems. *Dolder, E. J.: Personal communication. Z/irich, Switzerland, 1963. ~Union Broach Co., Long Island City, N. Y. JANUARY 1978
VOLUME 39
NUMBER 1
ATTACHMENT FIXATION OF THE OVERDENTURE: PART II
Fig. 5. The Hader bar can be incorporated on individual crowns for stud type fixation. This bar has been reduced in length and height and made part of the casting, incorporating the coping and the dowel. The cross-section measurement is 1.9 ram. H a d e r bar. T h e H a d e r bar consists of the following prefabricated plastic forms: Keyholeshaped 5 cm plastic bar sections, a 1.9 m m bar (which comprises the greatest bulk), processing clips, a series of resilient plastic rider clips 5 m m long by 4 m m high, and a rider seater tool (Fig. 5). T h e unique features of this system are that the bars can be cast in any restorative alloy or nonprecious alloy and the riders can be serviced by the patient (Fig. 6). It is the least expensive of the bar joint systems, and there is no torque to the teeth. The advantages of the H a d e r bar are: 1. Preformed plastic bars allow fabrication in any alloy. 2. The patient or the dentist can replace the retention. 3. It is possible to pick up a metal rider with resin and substitute it for the plastic rider for more retention if needed. 4. T h e assembly technique is simple. T h e disadvantages of the H a d e r bar are: 1. T h e rider is too bulky occluso-gingivally in contrast to a metal clip. 2. The rider retention decreases too rapidly. 3. There is no tension adjustment; addition of metal riders is necessary to increase tension. The H a d e r bar can be r e c o m m e n d e d for overdentures because of the resin bar pattern as well as the riders. T h e rider clips provide m i n i m u m retention but serve as good intermediate training clips until substitution with metal riders. Riders have single sleeve and multiple sleeve configurations. Multiple sleeve riders, such as the Ackermann,* the C . M . , t and the Baker,~ are short segments. T h e y allow m a x i m u m contouring of the *Metaux Preeieux S.A., Neuch~tel, Switzerland. tCendres and Metaux S.A., Biel, Switzerland. ~Baker Dental, Carteret, N. J. THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 6. The Replaceable plastic rider on completed casting referred to in Fig. 5. Note that the "bar" position is lingual of the crown, which reduces bulk and allows space for teeth. bar to follow the shape of the ridge and permit the dentist to increase retention by the n u m b e r of riders used rather than by the tension of a single sleeve rider such as the Dolder bar rider, which generally is used in straight segments. T h e Dolder bar rider can be sectioned to serve as a multiple sleeve system when desired. In addition a wrought bar such as the Dolder has better physical characteristics than a cast gold-alloy bar, and its use requires far less expenditure of time and material than fabrication of a cast and precision-milled bar. BAR C O M P A R E D T O S T U D F I X A T I O N T h e splinting of two or more teeth with a bar produces stability similar to that obtained with rigid stud-type a t t a c h m e n t when the overdenture is in place. T h e question that arises immediately is that, if the denture base is so well developed that the bar serves only as a fixation device, what is the end difference in splinting between the stud prosthesis and the bar prosthesis? Theoretically there is no difference, but the stud type allows independent movement. If one tooth is especially weak the strong tooth can serve as the fulcrum point for m o v e m e n t of the weaker tooth in the prosthesis. W h e n using bar units and joints the bar often splints in more than one plane. Instead of the prosthesis moving one tooth, all or none move under a functional load with bar fixation. A stronger and a weaker tooth can be splinted with the result that the stronger tooth strengthens the weaker tooth, and the weaker tooth weakens the stronger tooth. AUXILIARY ATTACHMENTS Auxiliary attachments for overdentures consist of the variously sized screws that retain bars or secondary copings that carry bars, and the pawl connectors that provide or increase the retention of bar units. Screws offer two advantages: (1) they 19
MENSOR
plunger, a stainless steel spring, a n d a recessed screw. A d v a n t a g e s of the M i n i - P r e s s o m a t i c are: 1. This unit is less b u l k y t h a n the Pressomatic, a n d it provides the same "click" retention. 2. It is designed to be cast to the rider. 3. T h e p l u n g e r a n d the spring, b e i n g replaceable, give the c o n n e c t o r a n indefinite service life. A d i s a d v a n t a g e of the M i n i - P r e s s o m a t i c is t h a t its very small size necessitates m e t i c u l o u s care in assembly a n d service, for it is impossible to rectify any d a m a g e to the t h r e a d housing. SUMMARY
Fig. 7. Mini-Pressomatics are the smallest of the pawl connectors and provide excellent "click" retention for short bar units, crowns, and overdentures. The facial view shows the access screw and the image shows the pawl plunger. provide r e m o v a b l e b a r fixation splinting with the aid of secondary copings on the roots, a n d (2) they hold a b a r in place on divergent teeth. PAWL CONNECTORS Pressomatic.* T h e Pressomatic is a p a w l connector t h a t is a v a i l a b l e in two lengths, 2.2 m m or 3 ram, a n d in two p l u n g e r configurations, flange or r o u n d stud. T h e Pressomatic, which has a d i a m e t e r of 2.6 m m , consists of a housing, a plunger, a nylon cushion, a n d a recessed locking screw. T h e s e connectors can be soldered in or cast to the b a r or rider. A d v a n t a g e s of the Pressomatic are: 1. These connectors p r o v i d e a positive seat a n d retention for the riders t h a t is verified b y the "click" sound w h e n they are seated. 2. T h e y give the b a r system a n indefinite service life because the r e t e n t i o n elements are replaceable. D i s a d v a n t a g e s of the Pressomatic are: 1. T h e a t t a c h m e n t increases the b u l k buccolingually. 2. Assembly requires skilled t e c h n i c a l assistance. M i n i - P r e s s o m a t i c . * T h e M i n i - P r e s s o m a t i c is a p a w l c o n n e c t o r t h a t can increase the r e t e n t i o n of a b a r unit (Fig. 7). It is only 1.75 m m long a n d has a 3.2 m m diameter. It consists of an alloy shell, a stud
*Metaux Precieux S.A., Neuch~tel, Switzerland.
20
M a n y a t t a c h m e n t systems of the b a r or stud t y p e increase the stability of a n overdenture. W h e n selecting an a t t a c h m e n t it is essential to consider the skill of the d e n t i s t - l a b o r a t o r y t e a m as well as the dexterity of the p a t i e n t a n d to use the easiest system that will still i m p r o v e stabilization. G e n e r a l l y simplicity in design, ease of m a i n t e n a n c e , a n d m i n i m u m leverage should be p a r a m o u n t considerations in selection. Use of a guide such as the E M G a u g e a n d of the E M A t t a c h m e n t Selector significantly reduces the confusion in selecting a t t a c h m e n t s a n d increases the w o r k i n g a r m a m e n t a r i u m for stabilizing an o v e r d e n t u r e . ' REFERENCES 1. Mensor, M. C., Jr.: Classification and selection of attachments. J PROSTHETDENT 20:494, 1973. 2. Matsuo, E.: ASC 52. Tokyo, 1970, Ishiyaku Shupan Company. 3. Gaerny, A.: Removable closure of the interdental space. Chicago, 1972, Die Q uintessenz Buch-Und ZeitschriftenVerlag. 4. Steiger, A. A., and Boitel R. H.: Precision Work for Partial Dentures. Ziirich, 1959, Berichthaus, pp 135-139. 5. Preiskel, H. W.: Precision Attachments in Dentistry. London, 1968, Henry Kimpton, pp 117, 143, 150, 156. 6. Preiskel, H. W.: Precision Attachments in Dentistry, ed 2. London, 1973, Henry Kimpton, p 113. 7. Dolder, E. J.: Die Steg-Gelenk-Prothese in Unterkiefer. Dtsch Zahnaerztl Z 14:11, 1959. 8. Dolder, E. J.: The barjoint mandibular denture. J PROSTHET DENT 11:694, 1961. 9. Dolder, E. J.: Steg-Prothetik. Heidelberg, 1966, Alfred Hfithig. Reprint requests to: DR. MERRILL C.
MENSOR
i00 SOOTHELLSWORTH,aTE. 509 SANMATEO,CAUF.94401
JANUARY 1978
VOLUME 39
NUMBER 1
San Mateo, Galif.
I t is impossible to overemphasize the need for simple attachments for overdenture fixation. Such simple attachments as the nonresilient Gerber,* the Intr0fix,~ or the Bona cylinder* can perform the primary function of positional fixation adequately and relatively inexpensively. Only the desire for fine resilient movement justifies using a highly sophisticated and expensive attachment like the resilient Gerber. There is a need for simple systems such as t h e H a d e r bar unit~" and the H a d e r bar joint, which offer easy serviceability and laboratory fabrication using plastic patterns (Fig. 1). T h e overall cost is low, because both systems can be cast directly. The snapper or the rider of a bar unit can be made of resin picked up in the mouth or processed in the laboratory. The most important consideration is the attachment stabilization of the overdenture and not necessarily the choice of attachment. SELECTION OF A T T A C H M E N T S Manufacturers or inventors n a m e d the various attachment groups such as the Gerber Stud Attachment and the Dolder Bar Unit.~ A c o m p e n d i u m known as the E M Attachment Selector~ presents 30 points of information about each a t t a c h m e n t ? This selector and the E M Gauge~ provide a simple colorcode method of choosing attachments from mounted diagnostic casts. 2 In the making of an overdenture only the stud, the bar, and some of the accessory attachments are of interest. S T U D (PRESSURE B U T T O N ) A T T A C H M E N T S Most of the stud-type attachments, also considered snap fasteners, are simple in concept. However, Read before the Academy of Denture Prosthetics, Washington, D.C. *Cendres and Metaux S.A., Biel, Switzerland. ~'Metaux Precieux S.A.,~Neuch~tel, Switzerland. ~Bell International, Burlingame, GaliL
16
many, such as the resilient Gerber, seem to be complicated upon initial examination. Like any device each system requires careful study and compliance with the manufacturer's recommendations. T h e simpler the attachment the easier it is to use, except for the Rothermann* series, Some stud attachments, such as the Gerber, are resilient and have a spring return. Others, such as the Dalbo* cylinder, are tissue resilient; still others, such as the Introfix, are nonresilient. The resilient attachments can be unidirectional or multidirectional, and may involve both the bar and the telescopic stud attachments. A compensating factor in resilient attachments allows the tissue rather than the tooth to support the denture base entirely. Resilient studs. Resilient attachment systems perform a compensatory function and act as a safety valve in the event of an overload. No two resilient attachment systems should oppose each other unless one is locked out of function, such as in the case of the attachments in a mandibular prosthesis, where the maxillary prosthesis receives additional support from the palatal coverage. This situation arises when two overdentures oppose each other or a mandibular restoration opposes a natural dentition. It is essential to allow for movement to achieve maxium tissue contact of the denture base under m a x i m u m load. I n the well developed denture base careful positioning of the attachments makes the need for a resilient system questionable. No attempt should be made to equilibrate, establish permanent records, or reline without locking the resilient attachments out of function. Otherwise the base w{ll move and incorrect markings of the interferences will be produced. The primary function of the retained root is the retention and positional or directional orientation of the restoration. When a dentist uses an inadequate technique or lacks the ability to develop a well fitting *Metaux Precieux S. A., NeuehStel, Switzerland.
JANUARY 1978
VOLUME39
NUMBER 1
AITACHMENT FIXATION OF THE OVERDENTURE: PART II
Fig. 1. The Hader bar joint can be used as a joint or unit; the plastic pattern is a simple and an inexpensive method of bar fabrication and pattern length is sufficient to handte most large span demands. denture base, the resilient attachment allows some leeway in the patient's acceptance of the prosthesis by allowing more base contact and support during function. Nonresilient studs. The nonresilient stud attachments are effective when interocclusal space is limited. They are essential when the teeth are stable or when the dentist does not desire movement of the overdenture. Ancrofix. The Ancrofix* (Fig. 2) is a resilient pressure-button system that consists of four parts: a solder base, a replaceable retention head, a housing with four lamellae to activate, and a teflon ring to allow the lamellae to function. The overall height of the unit is 3.2 mm. The advantages of the Ancrofix are: 1. Tinfoil spacers can provide tissue resilience during fabrication. 2. The attachment allows rotational movement, and flattening the knob on top of the male post deactivates it. The components are replaceable, and it is easy to adjust the retention, thereby giving the attachment an indefinite life. 3. The solder base is interchangeable with the Introfix attachment, allowing exchange of attachments. The button can be picked up in the mouth with resin or processed in the laboratory. 4. There is no clinically significant torque to the support tooth when the denture base is developed properly. 5. The attachment system is simple and inexpensive. The disadvantages of the Ancrofix system are: *Metaux Precieux S.A., Neuchhtel, Switzerland.
THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 2. A line drawing of Ancrofix shows a threaded stud section and housing with four lamellae surrounded b y a teflon ring; the male unit is replaceable, and has a hemispherical knob (arrow) that permits rotational movement or provides rigid fixation after reduction. The height of the attachment is 3.2 mm. 1. Use of more than one attachment requires a paralleling mandrel for attaining proper alignment. 2. Improper base development and overtightening of attachments can torque the teeth. 3. Repositioning the attachment during rebasing can damage the teflon ring. This attachment is ideal for removable partial dentures and overdenture fixation. BAR ATTACHMENTS
Bar attachments are of two types: bar units and bar joints. They provide fixation for an overdenture and splinting for the remaining teeth. Bar units, as the name implies, offer rigid fixation for an overdenture, whereas bar joints permit some degree of rotational a n d / o r resilient movement. Bar units. The selection of a bar unit depends upon the space available, the shape and curvature of the ridge, and the type of defect that is to be replaced. Bar units are ideal for replacing a gross tissue defect and supporting an overdenture. It is possible to convert a bar joint to function as a bar unit by bending it into a shape other than that supplied by the manufacturer. The primary functions of bar units are splinting and carrying the appliance positionally. Most laboratory-fabricated bars, such as the Gaerny or Steiger-Boitel bars, are considered bar units. 3. + The height available, the type of occlusal surface, and the type of denture tooth are the only factors that limit their size, position, and design.
17
MENSOR
Fig. 3. The Dolder bar can and should be bent to conform to the ridge; the rider should be segmented to fit the straight sections.
Fig. 4. Bar fixation can be provided for markedly divergent teeth by using a Schubiger attachment. The bar is soldered on the coping for the weakest tooth, and the attachment is placed on the strongest tooth for future salvage or conversion to stud fixation. The usual bar attachment splints two or more teeth together. Most prefabricated bars are made of high-strength alloy and consequently size plays no part in selection for short-term applications. If only splinting is considered, theoretically a long-reach splint, i.e., one between a molar and a canine, requires a bar with a larger cross section than a cuspid-to-cuspid splint. This usage has led to a rule, according to which the cross section is in direct proportion to the length Of the span. This rule i s more important with respect to the laboratoryfabricated bar than to the commercially available prefabricated bar because of the difference in the type of alloy used (except in the instance of nonprecious metals). The major consideration in selecting proper bar size is the space available to assure rigidity of the splint. It is always desirable to select the largest possible size for the space without disturbing the vertical relationship, occlusion, or the contour of the prosthesis. 18
The number of abutments and their location, as well as the dimension of the bar, control the splinting effect and the strength of the restoration. Properly designed bar restorations have retention, adjustment, and wear in the attachment portion, eliminating wear on the bar and the need for a bar of larger diameter. A bar of large diameter is necessary only when there is a need to span a long edentulous space, which will subject the bar to greater forces. The Dolder bar is the one most often mentioned in discussions of the bar system. Preiskel 5' 6 discussed the Dolde r bar joints and units in the second edition of his book. An in-depth review of Dolder's writing indicates that it is possible to bend the Dolder bar system and shape it to approach the configuration of any ridge (Fig. 3). 7-~Both the inventor, Dolder,* and the manufacturers recommend this broad application of the system. Technically any bending, cutting, or soldering of bar attachments requires annealing followed by heat treatment to restore the alignment of the crystalline structure and the original strength to the alloy. Cutting, bending, and soldering produce a weaker bar than bending alone because the solder joint has a different crystal structure. A few representative bars will be discussed. Dolder bar unit. The Dolder bar unit has a church window profile that contrasts to the egg shape of the joint. It consists of the bar and a rider with retention mesh. The unit, which is rigid, is available in both a standard size, 4.65 mm in height, and a micro-size, 3.6 m m in height. This bar can be joined to divergent teeth by using the Schubiger, VK, or Kurer systems (Fig. 4).t The advantages of the Dolder bar unit are: 1. It is possible to segment rider sections and adjust them for retention. 2. The bar and rider are available in two sizes. 3. The rider makes a good frictional fit. The disadvantages of the Dolder unit are: 1. It is too bulky in all dimensions. 2. Retention in the denture complicates rebasing or positioning. 3. It is very expensive. 4. T h e bulk has a negative effect on the esthetic results. Although the Dolder bar unit is used for overdentures it is not recommended highly because of its bulk, cost, and esthetic problems. *Dolder, E. J.: Personal communication. Z/irich, Switzerland, 1963. ~Union Broach Co., Long Island City, N. Y. JANUARY 1978
VOLUME 39
NUMBER 1
ATTACHMENT FIXATION OF THE OVERDENTURE: PART II
Fig. 5. The Hader bar can be incorporated on individual crowns for stud type fixation. This bar has been reduced in length and height and made part of the casting, incorporating the coping and the dowel. The cross-section measurement is 1.9 ram. H a d e r bar. T h e H a d e r bar consists of the following prefabricated plastic forms: Keyholeshaped 5 cm plastic bar sections, a 1.9 m m bar (which comprises the greatest bulk), processing clips, a series of resilient plastic rider clips 5 m m long by 4 m m high, and a rider seater tool (Fig. 5). T h e unique features of this system are that the bars can be cast in any restorative alloy or nonprecious alloy and the riders can be serviced by the patient (Fig. 6). It is the least expensive of the bar joint systems, and there is no torque to the teeth. The advantages of the H a d e r bar are: 1. Preformed plastic bars allow fabrication in any alloy. 2. The patient or the dentist can replace the retention. 3. It is possible to pick up a metal rider with resin and substitute it for the plastic rider for more retention if needed. 4. T h e assembly technique is simple. T h e disadvantages of the H a d e r bar are: 1. T h e rider is too bulky occluso-gingivally in contrast to a metal clip. 2. The rider retention decreases too rapidly. 3. There is no tension adjustment; addition of metal riders is necessary to increase tension. The H a d e r bar can be r e c o m m e n d e d for overdentures because of the resin bar pattern as well as the riders. T h e rider clips provide m i n i m u m retention but serve as good intermediate training clips until substitution with metal riders. Riders have single sleeve and multiple sleeve configurations. Multiple sleeve riders, such as the Ackermann,* the C . M . , t and the Baker,~ are short segments. T h e y allow m a x i m u m contouring of the *Metaux Preeieux S.A., Neuch~tel, Switzerland. tCendres and Metaux S.A., Biel, Switzerland. ~Baker Dental, Carteret, N. J. THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 6. The Replaceable plastic rider on completed casting referred to in Fig. 5. Note that the "bar" position is lingual of the crown, which reduces bulk and allows space for teeth. bar to follow the shape of the ridge and permit the dentist to increase retention by the n u m b e r of riders used rather than by the tension of a single sleeve rider such as the Dolder bar rider, which generally is used in straight segments. T h e Dolder bar rider can be sectioned to serve as a multiple sleeve system when desired. In addition a wrought bar such as the Dolder has better physical characteristics than a cast gold-alloy bar, and its use requires far less expenditure of time and material than fabrication of a cast and precision-milled bar. BAR C O M P A R E D T O S T U D F I X A T I O N T h e splinting of two or more teeth with a bar produces stability similar to that obtained with rigid stud-type a t t a c h m e n t when the overdenture is in place. T h e question that arises immediately is that, if the denture base is so well developed that the bar serves only as a fixation device, what is the end difference in splinting between the stud prosthesis and the bar prosthesis? Theoretically there is no difference, but the stud type allows independent movement. If one tooth is especially weak the strong tooth can serve as the fulcrum point for m o v e m e n t of the weaker tooth in the prosthesis. W h e n using bar units and joints the bar often splints in more than one plane. Instead of the prosthesis moving one tooth, all or none move under a functional load with bar fixation. A stronger and a weaker tooth can be splinted with the result that the stronger tooth strengthens the weaker tooth, and the weaker tooth weakens the stronger tooth. AUXILIARY ATTACHMENTS Auxiliary attachments for overdentures consist of the variously sized screws that retain bars or secondary copings that carry bars, and the pawl connectors that provide or increase the retention of bar units. Screws offer two advantages: (1) they 19
MENSOR
plunger, a stainless steel spring, a n d a recessed screw. A d v a n t a g e s of the M i n i - P r e s s o m a t i c are: 1. This unit is less b u l k y t h a n the Pressomatic, a n d it provides the same "click" retention. 2. It is designed to be cast to the rider. 3. T h e p l u n g e r a n d the spring, b e i n g replaceable, give the c o n n e c t o r a n indefinite service life. A d i s a d v a n t a g e of the M i n i - P r e s s o m a t i c is t h a t its very small size necessitates m e t i c u l o u s care in assembly a n d service, for it is impossible to rectify any d a m a g e to the t h r e a d housing. SUMMARY
Fig. 7. Mini-Pressomatics are the smallest of the pawl connectors and provide excellent "click" retention for short bar units, crowns, and overdentures. The facial view shows the access screw and the image shows the pawl plunger. provide r e m o v a b l e b a r fixation splinting with the aid of secondary copings on the roots, a n d (2) they hold a b a r in place on divergent teeth. PAWL CONNECTORS Pressomatic.* T h e Pressomatic is a p a w l connector t h a t is a v a i l a b l e in two lengths, 2.2 m m or 3 ram, a n d in two p l u n g e r configurations, flange or r o u n d stud. T h e Pressomatic, which has a d i a m e t e r of 2.6 m m , consists of a housing, a plunger, a nylon cushion, a n d a recessed locking screw. T h e s e connectors can be soldered in or cast to the b a r or rider. A d v a n t a g e s of the Pressomatic are: 1. These connectors p r o v i d e a positive seat a n d retention for the riders t h a t is verified b y the "click" sound w h e n they are seated. 2. T h e y give the b a r system a n indefinite service life because the r e t e n t i o n elements are replaceable. D i s a d v a n t a g e s of the Pressomatic are: 1. T h e a t t a c h m e n t increases the b u l k buccolingually. 2. Assembly requires skilled t e c h n i c a l assistance. M i n i - P r e s s o m a t i c . * T h e M i n i - P r e s s o m a t i c is a p a w l c o n n e c t o r t h a t can increase the r e t e n t i o n of a b a r unit (Fig. 7). It is only 1.75 m m long a n d has a 3.2 m m diameter. It consists of an alloy shell, a stud
*Metaux Precieux S.A., Neuch~tel, Switzerland.
20
M a n y a t t a c h m e n t systems of the b a r or stud t y p e increase the stability of a n overdenture. W h e n selecting an a t t a c h m e n t it is essential to consider the skill of the d e n t i s t - l a b o r a t o r y t e a m as well as the dexterity of the p a t i e n t a n d to use the easiest system that will still i m p r o v e stabilization. G e n e r a l l y simplicity in design, ease of m a i n t e n a n c e , a n d m i n i m u m leverage should be p a r a m o u n t considerations in selection. Use of a guide such as the E M G a u g e a n d of the E M A t t a c h m e n t Selector significantly reduces the confusion in selecting a t t a c h m e n t s a n d increases the w o r k i n g a r m a m e n t a r i u m for stabilizing an o v e r d e n t u r e . ' REFERENCES 1. Mensor, M. C., Jr.: Classification and selection of attachments. J PROSTHETDENT 20:494, 1973. 2. Matsuo, E.: ASC 52. Tokyo, 1970, Ishiyaku Shupan Company. 3. Gaerny, A.: Removable closure of the interdental space. Chicago, 1972, Die Q uintessenz Buch-Und ZeitschriftenVerlag. 4. Steiger, A. A., and Boitel R. H.: Precision Work for Partial Dentures. Ziirich, 1959, Berichthaus, pp 135-139. 5. Preiskel, H. W.: Precision Attachments in Dentistry. London, 1968, Henry Kimpton, pp 117, 143, 150, 156. 6. Preiskel, H. W.: Precision Attachments in Dentistry, ed 2. London, 1973, Henry Kimpton, p 113. 7. Dolder, E. J.: Die Steg-Gelenk-Prothese in Unterkiefer. Dtsch Zahnaerztl Z 14:11, 1959. 8. Dolder, E. J.: The barjoint mandibular denture. J PROSTHET DENT 11:694, 1961. 9. Dolder, E. J.: Steg-Prothetik. Heidelberg, 1966, Alfred Hfithig. Reprint requests to: DR. MERRILL C.
MENSOR
i00 SOOTHELLSWORTH,aTE. 509 SANMATEO,CAUF.94401
JANUARY 1978
VOLUME 39
NUMBER 1
