a.   Cosmetic Appearance

d. Patient Comfort

Figs. 1-5:  This case was restored in 1960.  The 15-year X-Rays show very little changes around the lower right lateral incisor, even though a cantilever pontic contains the female for the attachment! Note how the restorations are built on three-dimensional full shoulder preparations—that is, the shoulders relate to each other, the gingival and the bone.  This arrangement is the ideal setup for the maintenance of periodontal health.

   Fig. 6-10:  A growth and development abnormality prevented the formation of most of this patient's teeth.  The case was restored with precision attachment cases for both arches in 1963 and is still in the mouth after 39 years!  Note that only four abutment teeth in the upper arch have carried the entire arch during this period, with minimal changes in the  1991 X-Rays.              

             Figs. 11-13:  This case is one of the most famous cases ever restored by Dr. Elliot Feinberg, having been constructed on the weakest abutments imaginable.  The lower left cuspid was so mobile that a periodontist refused to treat it and advised its extraction.  In 1976, however there were no osseointegrated implants in the United States.  The only other option was a lower denture--the worst restoration imaginable. A heroic attempt was made to save these teeth..  Endodontics, three dimensional full shoulder preparations, and a splinted temporary fixed anterior bridge/clasp partial worn for several months allowed these teeth regain health and stability.  A precision attachment case was then able to be fabricated.  The case lasted for 17 years until the patient’s death from severe pulmonary disease.  The before X-Rays, 5 year and 10 year X-Rays are shown here.       

 

Fig. 14-16: This lower arch precision attachment case was constructed in 1970 (before osseointegrated implants) using a single molar abutment.  One tooth that is saved vastly improves the function and comfort of a lower removable restoration. Note how the 5 and 10 year X-Rays of the molar show negligible changes despite carrying the load of an entire arch!

The success of these extreme cases demonstrates why the average precision attachment case--one with adequate abutment roots and periradicular bone--can have an excellent prognosis for success. 

Fig. 17-20:  The average precision attachment case is an anterior fixed bridge with a posterior partial denture. This case was fabricated in 1983.  No other dentistry except relining the partial has been done since. X-Rays taken in 2000  show very minimal changes in the underlying bone during the past 17 years.

Basic Fundamentals for the Abutment Teeth

 Before the precision attachment case can be made, the abutment teeth must be properly prepared to minimize biomechanical factors that can interfere with success.  The teeth should be prepared with full shoulder preparations, because full shoulders offer the following advantages1:

Definite Finishing Line
Repeatable Fit
Less Sensitivity
Greater Area for Embrasure Spaces
Elimination of Oversized Teeth Buccolingually
Ease of Parallelism
Decrease of Leverage on the Prepared Teeth
Elimination of Sites of Future Erosion

             

The full shoulder preparations should exhibit three-dimensional architecture—that is, they should relate to each other, the gingiva and the underlying bone.  The fixed bridgework fabricated on the abutment teeth must also follow sound principles of biomechanics.  The architectural requirements for fixed bridgework include narrow bucco-lingual diameters, adequate embrasure spaces, anterior teeth with proper length and cingulum anatomy, solid and passive fit, and adequate occlusion at the correct vertical dimension.  

In every case at least two attachments should be placed in crowns that are splinted to other teeth in order to help distribute the forces. Auxiliary attachments may be used on single teeth (usually posterior) for additional support and retention.  The only exception is placement of attachments in single canines that have long roots and good bone support.  In posterior edentulous cases, cross arch splinting of the remaining anterior teeth that includes two strategic attachments is the ideal choice.2

The importance of accurate impressions and models cannot be over-emphasized.  Precision attachments must be used in a precise manner.  Great care must be taken to ensure precision at every step, as the entire chain can only be as strong as the weakest link.  Even a small error can compromise the ultimate success.  Precision attachment cases must fit with precision—the abutments must be stable and the frameworks must fit properly against the tissue without rock.

The Free Moving Attachment

The Feinberg Classification for Precision Attachments3 categorizes attachments on the basis of function, rather than on structure (i.e. intracoronal, extracoronol, anchor, ball and socket etc.).  According to this classification, attachments fall into two categories: 

A.    Rigid (mechanical locking action that includes clasps, lingual arms, springs and ball & sockets)

B.     Passive (free moving, stress-breaking action)

Fig.21 :An attacment can be used as a rigid connector or as a passive connector.  The top two partials use lingual arms and springs to rigidly retain the partial.  Only the bottom partial is a passive connector  It uses the path of insertion as a retentive mechanism to allow free-moving stress breaking action.

A free moving attachment has several advantages over rigid connectors:

 

 

Elimination of destructive “locking” forces to the abutment teeth.

Stress breaking action results in decreased lateral forces on the abutment teeth during function.

Physiologic stimulation of the abutment teeth encourages longevity.

Physiologic stimulation of the edentulous ridges results in firm, ; healthy tissue and less tendency to resorb

 

  Rigid connectors apply lateral forces to the abutment teeth that are ultimately destructive.  Teeth are designed to withstand vertical forces, but they cannot always tolerate lateral forces. Thomas Forde, in The Principles and Practice of Oral Dynamics 7 theorizes that vertically directed forces drive the hydraulic system of dentitional blood supply to the periodontal structures, whereas rocking or rotational forces disrupt the dentitional blood supply, causing “force-induced mouth degeneration” and loss of teeth.

In gripping the abutment teeth, a clasp acts as an orthodontic appliance, torquing teeth laterally.  A typical clasp case will necessitate moving the clasp to adjacent teeth as abutments are lost, with a full denture as the eventual result.

By using the path of insertion as the retentive mechanism, a passive attachment can function as a true stress breaker.  The path of insertion is different from the pull of the muscles, the action of the tongue and gravity, so the partial cannot be dislodged during function. However, it can move in a vertical direction slightly to release the forces.  The result is physiologic stimulation  of the abutment teeth and the edentulous ridges.  Clinical experience has shown that this physiologic stimulation results in increased longevity of the abutment teeth4, even when a few teeth are required to carry the load of an entire arch. The stimulation of the edentulous ridge also prevents the bone resorption that typically reduces tissue support for the prosthesis.  The tissue under a well-fitting precision attachment partial is typically healthy and firm.  There is surprisingly little wear of passive attachments, even after many years of function.  While the prosthesis may require relining or alteration of the occlusion to compensate for changes, it is rarely necessary to adjust or replace the attachments.4

The Double-Tilt Path of Insertion

The path of insertion is designed in two planes—a “double tilt”:

1.   The master model is secured to the surveyor table of the parallelometer.. The model is placed with the occlussal plane approximately parallel to the table with the anterior teeth facing forward.

2.    The heel of the model (posterior) is raised between ten and fifteen degrees to provide an anterior-posterior tilt.

It is advisable to survey the double tilt when creating the wax-ups so that the boxes for the attachments will be correct.

 

The Sterngold Latch Attachment

The empirical evidence for precision attachments was gleaned largely from cases designed with Sterngold’s #7 Attachment.  The attachment, conceived in 1906 and patented by the Sterngold company in 1921, is no longer on the market.  However, the attachment itself is less important than how the attachment is used.  Cases fabricated with the Poveromo attachment using the basic principles of passive, free moving design have been successful.  The Poveromo attachment,

(Fig. 22   left), however, has nowhere near the precision fit of the #7 attachment.  The Poveromo male contains a screw that controls its retention inside the female that is highly susceptible to breakage.

Fig. 23:  The Sterngold male and female (left) are 6mm in height and much smaller in width than the #7, which is 7mm in height.  The #7 attachment is no longer manufactured.  The Stern Latch is depicted below (Fig.  )

 

The Sterngold Latch Attachment5 is similar in design to the #7, except that it is smaller, both in width and length.  Unlike the #7, it contains a dimple (the “latch”) for retention, but this feature can easily be deactivated. The Latch Attachment is machined to a high degree of precision fit—perhaps higher than the #7 attachment.  During the last decade of manufacturing, the molds that were used to make the #7 attachment became worn, resulting in inconsistent fit of the attachments.  Males did not fit females with the same degree of accuracy as in the past and often had to be rubber wheeled or sandblasted if they were too tight. 

 

Precision fit allows any male out of the box to fit an existing female with an exact degree of accuracy.  As a result, the males and females can be easily  replaced if breakage occurs.  Even if the entire partial is lost a new one can be fabricated without remaking the fixed bridgework that contains the females.  (See Figs. 48-53, below)..

The Latch attachment can be used in the same manner as #7 attachment, with one exception.  Because the #7 attachment was large enough, the buccal flange of the male was typically removed and replaced with a spring wire that was soldered to the framework.  The spring wire was rarely used, but served an “insurance policy” in the event that an error occurred in the path of insertion (double tilt).  If the partial dislodged too easily, the spring wire was activated to increase frictional adaptation against the vertical plate of the female. 

Fig: 25  A half-round spring wire replacing the buccal flange of the #7 male.

The Latch Attachment cannot be altered to accommodate a spring wire.  However, a spring wire can be soldered next to the attachment.  It is prudent to eliminate the use of the spring wire entirely when using the latch attachment.  If necessary, a spring wire can always be added to the partial with acrylic. 

     The following two cases demonstrate that the latch attachment can be used in the same manner as the #7 attachment.   

Figs. 26-33: In the first case, the teeth are prepared with full shoulders using a three-dimensional approach.  Endodontics and osseous surgery were performed to create health. Temporary restorations are equally important in creating health, providing comfort and proper function.  Because temporaries serve as a blue print for the final restoration it is critical that they include a temporary clasp partial..  Patients who wear a clasp partial deeply appreciate the comfort of a precision attachment case and have no difficulty adjusting to wearing a bar across the palate.  The castings are fit individually and soldered before the master impression is taken.  It is important that the master impression be precise when working with precision attachments.  Seating castings into an overall impression can introduce error if they are not placed precisely or if they move during pouring.  To avoid this problem an impression is taken with a tray simulating the partial and connected to the castings with acrylic.  The entire apparatus is removed in one piece.  Note that a coping was placed on tooth #4 and attachments were placed in #3 and #5.  This avoids fabricating a unilateral partial, which cannot function properly. 

       In the second case (below, Figs. 34-41   ), the patient is wearing a clasp partial that fits over an underlay coping.  This tooth will be extracted.

Advantages of Precision Attachments (Part II)

In addition to Cosmetic Appearance, Maintainable Periodontal Health, Longevity of the Abutment Teeth and Patient Comfort, precision attachment cases have several other key advantages:

e. Questionable Teeth do not affect Case Longevity

f.  Natural Tooth and/or Implant Abutments can be used

g.  Precision Attachment Partial Dentures are easily adapted to future changes

Diagnosis:  Precision vs. Fixed Restorations

      Diagnosis must take into account contingency plans for problems that might occur tomorrow.  Patients are entitled to the treatment option that has the best chance of success rather than a treatment option that the dentist knows how to do best.  Often the patient is only offered the choice of fixed bridgework.  Practitioners either do not know how to make a good attachment case or they believe fixed bridgework is better because they are afraid that the patient will not like wearing a removable partial denture.  Too often fixed bridgework is created questionable posterior teeth.  When those teeth fail, the patient ends up with a second rate clasp case.   Because patients are often reaching financially to have sophisticated dentistry, they should have the option a first rate attachment case at the start.

However, if an attachment case is made and a questionable posterior abutment fails, the case does not have to be remade.  The crown is added to the partial denture with acrylic and the patient continues with the case in the same manner.  When this treatment option is properly presented to patients, most patients are quite amenable to treatment.   Patients are told that an attachment case replaces missing structures better than fixed bridgework, so their lips and cheeks will be better supported.  The partial is worn 24 hours a day to prevent collapse of the musculature and the occlusion.  It is only removed for hygiene. 

The Treatment of Questionable Posterior Teeth

Single posterior teeth can be added to an attachment case with the following connectors, depending on their prognoses:

1. A full attachment.  This option is best suited to teeth that have adequate roots and  good bony support.  It is important to recognize that the use of four or more attachments may increase the difficulty of inserting the partial denture.

2. A rest.  The best rest is the box surveyed for the full attachment.

3. An underlay coping.  This option is best suited to questionable teeth--teeth that are not     expected to survive long term.  The coping can be surveyed for parallelism at the same time the boxes are surveyed for the attachments.  The partial is designed to fit over the coping with acrylic.  When the tooth is lost, the overlay housing is simply filled in with acrylic.



Figs. 42-47:   This case with four attachments was completed in 1975.  Note that the upper left molar has a short root shaped like a nail instead of having curves like a screw.  This type of abutment has a questionable prognosis for fixed bridgework.  The X-Rays, however, show very few changes in 25 years as a result of the action of the attachment.  Very often questionable teeth last far longer with attachment cases than they would with fixed bridgework.

   

Figs. 48-50: This patient had an attachment case in 1984 and moved away (above, left) . After 14 years, something happened  to the partial and it was lost.  A dentist convinced the patient that he should have fixed bridgework, even though the patient originally understood that the attachment case option was superior to fixed bridgework because the poor root structure of the posterior molars. The dentist made a fixed bridge for the upper right that promptly decayed.  A unilateral clasp partial was made for the upper left.  A fixed bridge with female attachment was made for #5 and 6 and a coping was made to cover the remaining upper right posterior molar. 



Figs. 51-53:  A new partial was made using the original females on the left side and the new female on the right side. The upper right molar (#2) was treated with an underlay coping and the partial sits on top of it.  The original restoration on this tooth contained a female attachment.  The upper right lateral (#7) was left as a cantilever pontic.  Should it become necessary in the future, the two bridges can be splinted by removing adjacent porcelain and connecting the metal substructures with a single overlay (telescopic) bridge.  

Using Implants for Precision Attachment Cases

Dentistry is very akin to engineering.  Bridgework in the mouth or across the river are engineered structures.  Those structures must be designed to withstand the forces or they will fail.  One of the most famous engineering failures is the collapse of the Tacoma-Narrows Bridge, built in 1940. The builders did not realize that the structure was improperly designed to withstand crosswinds of more than 42 miles per hour.   “Engineering design”. says Henri Petroski, has as its first and foremost objective the obviation of failure” 8.

Osseointegrated implants are quite strong.  Unlike natural teeth, which are connected to the bone by the periodontal ligament, implants are fused to the bone, much like cementing a screw in concrete.  Implant supported fixed bridgework has enjoyed a high degree of success.  No matter how strong the fixtures seem; however, they will fail if they are overloaded with forces.  Case design must take into account these factors:

A.                Foundation support.  This support consists of the placement and number of fixtures, the angle of the fixtures, the length of the fixtures and the quality of the bone they are placed in. 

B.                Force Distribution.  Malocclusion and neuromuscular habits can be sources of destructive forces.

C.                Systemic Factors.  Systemic diseases, genetic conditions and oral hygiene can have a tremendous effect on the bony support.  It has been shown that the bone around implants continually undergoes remodeling.  “As a rule”, says implant expert Tomas Albrektsson, the weakest part of the osseointegrated bone-to-implant complex is the bone itself”9.

The following example shows how mechanical overloading of implants can lead to failure.  This patient had fixed bridgework placed that failed.  The long span of bridgework, poor bone and inadequate length of bone contributed to the failure of the second molar implant.   A history of malocclusion and bruxism may also have contributed to the failure.   Fixed bridgework in this case was clearly the wrong choice of dental restoration:  (Figs. 54-59)



A common misconception is that implants make attachments obsolete.  If attachments work so well on the weakest of natural teeth, imagine how they can work with osseointegrated implants!   Because this case was screw-retained, it was easily removed  and converted to an attachment case.  The patient has been functioning properly and is quite happy:

 



The rationale for using implants with attachments is that fixed bridgework cannot be done for the following reasons:

1.                 Anatomical Problems:  Most of the anatomical problems encountered for placing implants are in the posterior regions of the mouth.  Inadequate bone under the sinus or above the mandibular nerve may make it impossible to place implants of adequate length in the posterior regions of the mouth.

2.              Bone Grafts:  The prognosis for success is lower when bone grafts are required for implant placement and the duration of treatment is much longer.   Candidates for these procedures should be patients who understand the risks and are willing to accept them in order to have fixed bridgework.

3.                 Bone Quality:  The bone in some areas of the mouth may have poor quality for the placement of implants.  The lowest quality bone (Type IV) is typically found in the upper posterior maxilla.

4.                 Fixed Bridgework with Cantilevers may be inappropriate. Branemark’s studies have proven that four or five implants in the anterior region can be used with cantilevers to create a successful case.  However a cantilever fixed bridge may be the wrong choice for the following reasons:

a. Anatomical deficiencies require support that fixed bridgework cannot deliver.

b  Bicuspid occlusion is inadequate for neuromuscular comfort, esthetics, or function.

c. The patient has been comfortable with an attachment case in the past.

d. The patient does not want too many implants placed.  Patients who do not want the extra surgery and expense of multiple implants are often receptive to the placement of three implants.

 

5.                 Patients Choose Implants to Avoid Wearing Dentures.  Implants can usually be placed in the upper and lower anterior regions of the dental arches.  The placement of just three implants is enough to make a fantastic attachment case—an anterior fixed bridge and a precision attachment posterior partial denture. 

An implant- supported precision attachment partial denture is far superior to an implant-supported full denture for the following reasons:

a.            Superior Comfort and Self-Esteem.  The posterior bar can be made thin and only covers a small area of the palate, while a denture usually covers the entire palate.  The patient wearing an attachment case has anterior teeth that do not come out, unlike the patient wearing a denture. He or she doesn’t feel bad looking in the mirror when removing a posterior partial denture for hygiene. 

b.            Superior Function.  Unlike a denture, the posterior bar of an attachment case frees the tongue for normal speech and allows taste buds on the anterior palate to function normally.  An attachment case doesn’t have the anterior-posterior movement that an implant supported denture might have.

c.            Increased Longevity.  A precision attachment case does not place lateral forces on implants, which can be destructive to implants as well as natural teeth.  Implants are not indestructible and if overloaded they can fail. A denture connected to implants, however, is usually locked in place.

d.            Both Natural and Implant Abutments Can Be Used. Single posterior teeth that remain from a previous attachment case can be left intact, and used as part of the new attachment case!  Unlike fixed bridgework, a precision attachment partial denture can link both implant and natural abutments because of the stress-breaking action of the attachment case. 

e.            Patients Avoid Wearing Dentures.    A denture that rests on tissue can only exert 10 to 15% of the force of a patient with natural teeth6.  Although the placement of implants may making wearing a denture easier, most people don’t want to go through the surgery and expense unless they are going to get rid of the denture.  Patients who wore an attachment case prior to wearing a denture know the difference between the two, and they are thrilled that they can have the same exact case by placing only three implants. 



Figs. 60-62:  This case was completed in 1993.  Three implants were used to create a fixed anterior bridge and a precision attachment partial denture.  Few changes have occurred in the X-Rays during a ten year period.

 



Figs. 63-66: This patient wore upper and lower attachment cases for over 20 years before the upper attachment case failed.  The patient is still wearing the lower attachment case, completed in 1980s. It is amazing that this case has lasted so long with such poor roots and bone for the foundation! The patient is thrilled that the placement of only 3 implants has enabled her to have the same type of attachment case that she wore all those years.    

Planning for the Future

            Success is forseeing failure.  “If a designer overlooks just one way his structure may fail”, says engineering expert Henri Petroski, “all may be for naught”.  Ultimate success depends on having a contingency plan in the event that something does go wrong. 

      It is wise to consider what may happen to the teeth around any implants that might be placed.  An implant restoration might be successful for many years, but it may become useless if the adjacent teeth are lost in the future. Future medical conditions, anatomical problems and financial constraints (such as retirement fixed incomes) may make it impossible to place additional implants. 

      Atttachments can be used as a contingency plan for implants.

Figs. 67-73:  In this case the patient’s lost upper anterior teeth were replaced with temporary clasp partial while implants were being placed.  When the implants were uncovered, the case was checked out with acrylic and one of the estheticone abutments had to be repositioned lingually. .  X-Ray examination reveals bone loss and weak posterior bridges that will probably be lost in the future.  At that time it is unlikely that the patient will want to have additional implants due to advancing age, diabetes, and retirement status.  It will be even less likely that the patient will want to have sinus lift surgery and bone grafts to place posteriorimplants. As a result, two attachments were placed in the anterior implant fixed bridge.  When the posterior teeth are lost, the anterior bridge will not have to be touched.  A posterior precision attachment case can easily be made at that time. 

Compensating for Changes

            One of the reasons that Attachment Cases enjoy such a high degree of longevity is that they can compensate for changes as they occur.  The partial denture can be altered to compensate for:

A.       Tissue Remodeling (by relining the partial denture)

B.       Occlusal Wear (by adding new occlusion with acrylic or composite)

C.       Esthetic Changes (by replacement of teeth)

To Summarize, the Precision Attachment is the Rolls-Royce of Dental Restorations.  When properly used, precision attachments promote oral health, patient comfort, esthetics, and case longevity for both natural teeth and implant abutments. 

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Articles
	The Precision Attachment Case is the Rolls Royce of Dental Restorations
	The Use of CAPTEK for Full Coverage Restorative Dentistry
	The Value of Continuing Education
	A Short History of Modern Dentistry
	Successfull Precision Attachment Removable Partial Dentures
	Using the Path of Insertion to Retain a Partial Denture
	A Technique for Making Full Coverage Temporaries on Teeth with Insufficient Clinical Crowns
	Adobe Required Artices:
	Depth Guide Technique for Anterior Full Coverage Restorations
	Attachment Retained Partial Dentures
	Redistribution of Leverage for Anterior Teeth
	Electronic Surgery for Improved Esthetics
	Stern Latch Information