precision attachments (2021)

Precision attachment
(Attachment in over denture)
An attachment is a connector consisting of two or more components. One component is
connected to a tooth, tooth root, or an implant and the other component is connected to a
prosthesis. Precision attachments, allow prosthesis to combine the advantages of fixed &removable restorations. The precision attachment denture has long been considered the highest form of partial denture therapy. It combines a fixed &removable prosthodontics in such a way as to create the most esthetic partial possible. It also has the reputation of lasting far longer than the conventional partial.
The precision attachment partial should differ only in the means of its retention when compared to the clasp-retained partial denture. The only reason for utilizing this mechanical device is to replace the visible clasp arm. All other functions of the partial can be performed by conventional means if they are understood &the partial is constructed to the highest standards.
Attachments are rigid or resilient connectors that redirect the forces of occlusion. They are stress attenuators &absorbers. Their function is to protect &preserve soft tissue &bone, as well as provide retention &cosmetic alternatives.
Implants are devices that are rigidly fixated to bone. This characteristic differentiates from natural teeth. Their long term success depends on bone characteristic, occlusal relationships &loading forces as well as the types of attachments selected.
Treatment planning options from two to ten implants are presented. Various precision &semi-precision attachment cases are used along with numerous types of resilient &non-resilient bar units, joints, studs, magnets, screw, &various accessory attachments. The quantity &quality of available bone, various ridge relationships, number of implants placed &the anterior-posterior spread are affecting the results. Treatment plans are presented using attachments &implants in a variety of removable or fixed prosthetics approaches of missing teeth &oral structures.
There are number of attachments available now. At the same time, attachments are being used in all manner of restorative procedures, from partial dentures to implant-based prostheses. No single attachment is perfect for every application, it is critical that the appropriate attachment be utilized for each individual case situation. By analyzing study model &x- rays, the clinician can make several important determinations, each of which will influence final attachment selection.

1. Available inter-arch space.
2. Crown root ratio and alignment of the roots.
3. Type of coping.
4. Vertical space available.
5. Number of teeth present.
6. Amount of bone support.
7. Location of abutments.
8. Location of the strongest abutments.
9. Whether the overdenture is a tooth supported or tooth tissue- supported.
10.The type of the opposing dentition whether it is complete denture, overdenture, fixed appliance or natural dentition.
11.The maintenance problems and the cost.
12.Clinical experience and personal preference.
Indication of the attachment are:
1. Fixed bridge work intra-coronal attachment on non-parallel abutments.
2. Partial denture.
3. Over-denture.
4. Unilateral or bilateral free end denture.
5. Implant prostheses.
Diagnostic procedures:
Space will almost always be a major consideration &a problem for precision attachment selection &use; therefore, a diagnostic wax-up &set up is essential for every case, regardless of what is found in the opposing arch, this diagnostic positioning of teeth on bases that will allow verification in the mouth must be done so that tooth position can be evaluated both by the clinician &the patient. The final position of all teeth& the denture base, must be known to ensure that the space requirements of the attachment system under considerations can be met. When insufficient space is available, either the system selected or the oral environment must change, through surgeries, orthodontics or tooth modification. The clinician will need up-to-date. Comprehensive catalog of attachment system that indicates all dimensions of each unit. In choosing all attachment system, the laboratory must have experience with the chosen system or be willing to experiment a long with the clinician.
The pick-up impression:
The clinician must develop a technique for making a final impression for the RPD frame work that includes picking up the completed fixed components from the mouth in such a way that the position of the units remains accurately related to the remainder of the reminder of the mouth, having the actual crowns on the master cast allows precise positioning of the attachment components, a task that may not be possible when working on a stone replica of the crown, due to the probable fracturing of thin projections of stone. It also allows the master cast to be used as a milling cast to provide a stable platform for milling metal surfaces of the fixed components. This procedure will require a custom impression tray &an impression made with a relatively rigid material. Usually silicone or a polyether, the fixed units will have to be completely retentive on the tooth because of the inherent fit of the casting, or, if there is a potential for movement during the master impression, they will have to be temporarily cemented to keep them from moving. The cementing medium for this procedure must be one that will allow the unit to be removed from the mouth with the final impression, since replacing a unit in an elastic materials runs the risk of creating an inaccurate relationship. When the impression is removed from the mouth &is found to be acceptable, resin dies that have been made previously are placed into each fixed unit & the impression is boxed &poured. These dies are made with an autopolymerizing resin, with a retentive wire projection to lock them into the dental stone of the master cast. The completed crown is lubricated &the resin is added up to the margin. A wire that has been serrated is inserted into the resin mass, &the resin is allowed to set. The portion of the wire that protrudes from the crown is bent into some retentive form to retain it in the stone. The crown must seat completely on the resin die with the margin protected &be easily removed from the cast as needed, this is particularly true if the crown has a porcelain butt margin. The master cast must always be poured in improved stone to gain maximum resistance to fracture &abrasion.
Classification of precision attachments:
There are many different types of prefabricated attachments available &they are usually classified on :
1) Basis of location :
A. Extra-coronal.
B. Intra-coronal.
2) Based primarily on the function of the attachments:
A. Rigid: any attachment employing a mechanical locking action with the use of clasps, lingual arms, springs, ball &sockets etc.
B. Passive: an attachment that provides a free movement of the male when the abutment teeth are exposed to excessive forces.
3) Based on shape &form:
A. Stud.
B. Bar.
C. Magnetic attachment.
Intracoronal Attachments
An intra-coronal attachment is one which is contained within the normal contours of the crown portion of a natural tooth. The placement of the attachment requires that the abutment tooth be restored with a full or partial coverage (3/4) crown. Intra-coronal attachment are made with a key (patrix) &key way (matrix) mechanism, the matrix fits within the contours of a crown &the patrix is a part of the RPD framework. The patrix engages the vertical walls built within the contours of the crown &resists dislodgement by a torsional resistance of the metal.
Advantages:
1. Improve aesthetic outcomes.
2. Improve leverage management.
3. It have a rigid connection that does not require indirect retainers.
Disadvantages:
1. It required extensive preparation of an abutment tooth in order to obtain space for the matrix mechanism.
2. Aggressive crown preparation make the younger individual with large pulp chamber is contra-indicated.

Extracoronal Attachment
Extracoronal attachments are positioned entirely outside the crown contour of the tooth. The advantages of this type of attachment are that the normal tooth contour can be maintained, minimal tooth reduction is necessary and the possibility of devitalizing the tooth is reduced. Also, the path of insertion is easier for patients with limited dexterity. It is more difficult to maintain hygiene with extracoronal attachments and patients need to be instructed on the use of hygiene accessories such as proxi brushes etc. Keeping the underside of the attachment area clean, greatly improves the tissue response .


This group of images shows the extracoronal attachment components and the aesthetics of the removable partial denture when viewed from the buccal aspect.
Rigid attachments
Advantages:
• - Reduction of the load on the edentulous ridge during function and parafunction.
• - Minimum tipping of the abutment teeth when subjected to lateral forces.
Disadvantages:
• - Applied forces and movements of the denture are transmitted almost entirely to the abutment teeth.
Rigid attachments should be used whenever possible because they place lower demands on the edentulous ridge during function and parafunction, and require fewer repairs than do non-rigid attachments.
Non-rigid attachments
Advantages:
• - Reduced effect of tipping force on the abutment teeth (principle of shortening).
Disadvantages:
• - Greater stress on the tissues supporting the denture (ridge resorption)
• - Greater tipping of the teeth under lateral Forces.
There is no universal or ideal design is available, so if attachments are used, they should be selected from group with the most suitable characteristics for the task required. However, the principle concern is always the distribution of forces to maintain remaining alveolar ridges &teeth in an optimal state of health &to provide the patient with improved comfort &function.
Stud attachments:
Most of the stud attachments are simple in design, consisting of a male stud type that is soldered to a base. The base is a coping covering the prepared tooth stump, usually having a post extending into an endodontically treated root canal. Fixation is achieve by a female housing that is either embedded in the acrylic of an overdenture or soldered to a substructure in the overdenture. The female housing can be rigidly attached to the male &classified as a non-resilient attachment. It could also be designed with a spring load or some other engineered style to provide for a controlled movement &therefore be classified as a resilient attachment. Stud attachments are divided into two groups:
A. Extraradicular stud attachment in which the male element projects from the root surface of the preparation or implant.
B. Intraradicular stud attachment in which the male element forms part of the denture base &engages a specially produced depression within the root contour or implant.
Radicular and intraradicular stud type attachments are connected to a root preparation. Some stud type attachments are directly cemented to the prepared root without requiring a cast coping. Stud type attachments may promote improved or easier oral hygiene and enhance the crown-root ratio due to the low profile. The image at the right shows such an attachment utilized with an implant.
Bar attachment:
The purpose of the bar attachment are splinting of the abutment teeth &retention &support of the prosthetic appliance. Bar attachment are of two types bar units &bar joints. Bar unit have rigid fixation where there is no movement between the bar & overlying sleeve &therefore can be classified as tooth borne. Bar unit permit rotational movement between sleeve &bar, utilizing more of the residual ridge for support