|Year : 2014 | Volume
| Issue : 2 | Page : 176-181
Selection of attachment systems in fabricating an implant supported overdenture
D Krishna Prasad, D Anupama Prasad, Manan Buch
Department of Prosthodontics and Crown and Bridge, A B Shetty Memorial Institute of Dental Sciences, Nitte University, Mangalore, Karnataka, India
|Date of Web Publication||16-Sep-2014|
D Krishna Prasad
Department of Prosthodontics and Crown and Bridge, A B Shetty Memorial Institute of Dental Sciences, Nitte University, Deralakatte, Mangalore - 575 018, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Dental specialists today are facing a major influx of completely edentulous patients and patients with generalized compromised teeth who ask for cost-effective full mouth rehabilitation. The choice of overdenture as a treatment modality is significantly less expensive and is within the reach of many patients who are on a limited financial support. Various types of attachment systems are currently available to restore implant-supported over-denture. Clinicians have selected various attachment systems based on factors such as durability, patient demand, cost-effectiveness, technical simplicity, and retention. The decision-making process to select certain types of attachment system still remains unclear. This article explains about various attachment system available, their advantages and disadvantages and their use in different clinical conditions.
Keywords: Attachment system, full mouth rehabilitation, over-denture
|How to cite this article:|
Prasad D K, Prasad D A, Buch M. Selection of attachment systems in fabricating an implant supported overdenture. J Dent Implant 2014;4:176-81
|How to cite this URL:|
Prasad D K, Prasad D A, Buch M. Selection of attachment systems in fabricating an implant supported overdenture. J Dent Implant [serial online] 2014 [cited 2019 Dec 11];4:176-81. Available from: http://www.jdionline.org/text.asp?2014/4/2/176/140905
| Introduction|| |
Dental specialists in their day to day practice come across many edentulous patients with compromised maxillary and mandibular ridges. In such conditions, it is very challenging for the specialist to fabricate prosthesis which has good retention and which can ultimately fulfill patient's expectations. To overcome such situations, Osseo integrated implant supported over dentures are gaining popularity among clinicians. Implant supported overdentures are considered as one of the best options for replacement of missing teeth due to their added advantages as well as they are not very expensive and are within the reach of many patients who are on limited financial support.
Attachments are considered as pillars of implant supported overdentures. Different clinical situations demand different types of attachment systems to serve better. It is very important for the clinician to have a good knowledge about different attachment systems, their advantages and disadvantages, indications and contraindications for achieving long lasting stable results. To select a proper attachment, one should first understand the mechanical properties and the load distribution characteristics of different attachment systems.
Types of attachment systems
Various types of attachment systems are available, and different manufacturers provide different variety of attachment designs, but mainly there are four types of attachment assemblies which are commonly used  [Figure 1].
This article mainly deals with mentioned attachment systems in brief, their advantages and disadvantages, indications and contraindications, and discussion of various clinical studies which compares various attachments in different clinical scenarios.
Before going into details of individual attachments systems, one should understand the basics of various attachments system and their mechanical and load distribution properties. Almost all the attachment systems available show the different level of resiliency. It is associated with the movement between the abutment and prosthesis in predetermined directions. More resilient the attachment, more will be movement and more stress distribution on the residual ridges and less stress concentration on implant. Various movements allowed by resilient attachments are  [Figure 2].
| Types of attachments based on resiliency|| |
Attachments based on resiliency are classified as shown below into six types: 
- Rigid nonresilient attachment: In such attachments, no movement is seen between the abutment and implant. It is recommended only when sufficient implants are available. They are rigid and do not provide any relief to the supporting implants
- Restricted vertical resilient attachment: Such attachments will not allow any lateral tipping or rotary movements. They provide 5-10% of relief to the supporting implants by allowing vertical movements of the attachments
- Hinge resilient attachment: They resist lateral tipping and rotational forces. They provide 30-35% of load relief to the supporting implants
- Combination resilient attachment: They allow unrestricted vertical and hinge movements. They provide 45-55% of load relief to the supporting implants by uniformly transferring masticatory forces to the residual ridges
- Rotary resilient attachment: They allow vertical, hinge, and rotation movements. They provide 75-85% of load relief to the supporting implants
- Universal resilient attachment: Almost all kinds of movements are permitted. They provide 95% of load relief to the supporting implants.
| Criteria for selecting attachments|| |
- Available bone
- Patients prosthetic expectation
- Patients economical status
- Clinical expertise of specialist
- Availability of skilled technician.
| Factors influencing the design and resiliency level of the attachment assembly|| |
The design and resiliency level of the attachments assembly are influenced by the following aspects  [Figure 3].
| Stud attachments|| |
Stud attachments are one of the oldest attachment systems in use. They can be divided into two groups: 
- Extraradicular, in which male component projects from the implant
- Intrardicular, in which the male component is a part of denture base.
Ball attachment, Locaters, O-ring attachments, Extracoronal Resilient Attachment (ERA) attachments are the most commonly used in implant supported over-denture. ERA attachments are rigid attachments and are best suitable for parallel implants. Ball attachments are considered as the most simplest type of attachments for clinical application with implant-supported overdentures. But, the main drawback of this system is that the O-rings gradually loose retention, and must be replaced periodically. 
If implants are nonparallel and they have angulations >15°, stud attachments cannot be used.  To overcome this disadvantage, locaters were developed (Zest Anchors, Escondido, CA, USA) in 2001. ,, All other stud attachments provide vertical and hinge movements, but locators are classified as universal hinge. The major areas to be considered while aligning stud attachments are its relation to one another and to the path of insertion of the denture.
Advantages of locator attachment system are
- Can be used in cases of limited inter-arch space
- Can accommodate inter implant angulations up to 40°.
Locator attachments provide dual retention, one is mechanical and another is frictional. The nylon male head is slightly oversized than its female component which provides frictional fit. The outer margin of attachment engages the shallow undercut area on abutment to provide outer mechanical attachment. Locator attachments are used without an inner retention feature when they are aimed to correct implant angulation. ,,
Disadvantages of using locator attachments are
- They cannot be used in cases where rigid restoration is required
- Regular replacement of male nylon part due to constant wear and tear.
| Bar and clip attachments|| |
Bar and clip type attachments are mainly of two varieties
- Bar joint (resilient) ,
- Single sleeve
- Multiple sleeves
- Bar unit (nonresilient). 
It is now proven fact that bar type of attachments provides good retention and stability. ,, The disadvantages of this attachment system are:
- Vertical dislodgement, bar type attachments show maximum stress generation around implants
- Fabrication is technique sensitive
- Higher cost
- Maintenance of hygiene is difficult which can lead to problems like mucosal irritation
- Frequent loosening of retentive clips. 
The ideal length of a single bar should be minimum of 20-22 mm to accommodate two clips. Hence, while placing implants one should keep this aspect in mind. Shorter bar attachments cannot provide adequate retention and support. 
Hader bar is classified as hinge resilient attachment, and it provides mechanical snap retention. Plastic clips are recommended than metal clips.
Advantages of metal clips are
- They are more resistant to wear
- Smaller bar dimensions can be used. 
Disadvantages of metal clips are
- Removal of metal clips is difficult as compared to plastic clips
- Metal clips require more chair side time.
Dolder bar is another type of bar attachments. They are classified as combination resilient attachments as they allow vertical and hinge movements. Due to its adjustability, it is easy to control the retention provided by the bar. It is best-indicated when patient has adequate inter-arch space, and minimum resiliency and maximum retention is required.
Factors that influence the flexibility of the bar
- Length of the bar between the two implants
- Height of the bar
- Physical properties of the alloy
- Magnitude of the masticatory loads.
Application of anterior-posterior distance rule
Anterior-posterior distance rule is applicable in determining the length of cantilever bar extension. A line is drawn through the center of most posterior and most anterior implants on each side of the arch. The distance between these two lines is known as the anterior-posterior spread. In general, the distal cantilever should not exceed more than half of the anterior-posterior distance.
| Magnetic attachments|| |
Magnets which are commonly used in implant dentistry are made up of mainly aluminum-nickel-cobalt metals. They are classified as universally resilient attachments as they allow all the movements of the prosthesis. These are not very successful to provide retention because the magnetic forces of attraction generated to provide retention were weaker as compared to retention provided by mechanical attachments like ball and bar attachments. Another problem is that these magnetic attachments get corroded in saliva on long-term use.  To overcome this, newer generation magnets were developed which is made up of rare earth elements such as samarium and neodymium.  These have improved properties as compared to conventional magnets. ,
The advantages of magnetic attachments are
- Magnetic attachments are shorter compared to mechanical attachments so can be used in cases of reduced inter-arch space 
- They can be used in moderately nonparallel abutments since they do not follow a particular path of insertion 
- Laboratory procedures associated with castings are not necessary
- They are more resilient and allow for free movement of the prosthesis.
- Attachment needs to be removed before taking magnetic resonance imaging because it causes streaking 
- When numbers of implants are relatively few, retention is not as good as when ball attachments are used
- Least retention 
- Heating during sterilization leads to decrease in retentive forces in long-term use. 
| Telescopic attachments|| |
Telescopic crowns have been used since years to connect teeth to overdenture, but their use as implant supported overdenture is limited. They provide rigid attachment hence can be used for immediate loading. But the disadvantage is that due to its design they require adequate inter-arch space to be used, in cases where sufficient inter-arch space is not present it cannot be used. The syncone system is an innovative type of telescopic attachments which is mainly indicated in immediate loading cases. 
The syncone system has prefabricated titanium abutments and corresponding gold retainers which come in 4-6° taper. The abutments can correct angulations by 15° and can rotate 360° for precise alignment. Gold retainers fit on titanium abutments and provide excellent retention, and retention improves over time due to the settling phenomena. 
Advantages of telescopic crown techniques
- Excellent immobilization of the restoration
- Flexibility of design
- Easy maintenance of oral hygiene
- Syncone system has virtually wear resistant attachments
- Can also be used on angulated abutments.
| Discussion|| |
Various attachment systems are available, and they vary from one another in their ability to provide retention. It is documented that not only attachment type but also position of implants in the jaw influences the retention and stability of the prosthesis.
An in vitro study was done to evaluate the retention and stability of two simulated implant supported overdenture, and it was also compared between four different types of attachments (Ball, O-ring, Locator, ERA attachments). The results showed that the vertical retention and horizontal stability of the implant increased with its distal placement up to second premolar. Antero-posterior stability also increased with distal placement of implants. Comparison among different attachments showed that ball attachment produces the highest level of retention and stability followed by Locator, O-ring, and ERA attachments. 
A study was done to evaluate patient satisfaction and masticatory efficiency of a single implant retained overdenture using locators as stud attachment and magnetic (Magfit) attachment. Locator attachment showed slightly better chewing efficiency than Magfit attachments, but there was no statistical significant difference between both the attachments. 
Various in vitro and vivo studies have concluded that the ball and O-ring attachments transfer less stresses to implant bone interphase as compared to bar and clip attachment. ,,,
Although ball attachments are considered relatively simple and resilient but their specific design may influence the free movement of ball attachment and can make them less resilient.  Studies evaluating wear induced retentive changes have shown that ball attachments have lost their initial retentive force by 32-50%. In contrast to that magnetic attachments showed loss of retention due to wear by only 1.7-5.3%. This is despite microscopic corrosion seen in stainless steel magnetic case. 
A finite element analysis study was done to evaluate the stress distribution around the implant supporting mandibular overdenture using ball/O-ring and magnetic attachment. Results showed that as the diameter of the attachment increased, there was an increase in stress in the cortical bone around the implant. The results were constant for both the attachments and it was concluded that if larger diameter attachments are used then implants with greater width will help to reduce stresses on the cortical bone. 
A clinical study was done using locator attachments in atrophic mandible to evaluate its success and advantages over other attachments. Locator attachments were placed in inter canine region, and patient was evaluated after prosthesis fabrication. The locator attachment gave very pleasing results with very good retention and stability.  A study done also concluded that locator attachments provide better hygiene maintenance and help to maintain healthy soft tissue around implants. 
Another study recommended usage of locator system as the problems associated with these prostheses are usually simple to resolve.  A laboratory study was conducted to evaluate the influence of inter implant divergence on the retention characteristics of locator attachments. Total ten pairs of locators were evaluated with inter implant divergence of 0°, 10° and 20°. The results showed that there was no change or decrease in retention of locators with increase in inter-implant angulations up to 20°. The nylon Locator patrices showed wear defects of similar type, and magnitude in the scanning electron microscopy images, regardless of inter implant angulation. 
Study was done to evaluate complications associated with ball, bar, and locator attachments in implant supported overdenture. The main focus of study was to evaluate complications associated with prosthesis fabrication and implant failures. Results concluded that locator attachments provided best results without any failures followed by bar and ball attachments. 
One basic concept should be kept in mind while planning an implant supported overdenture that, patients with resorbed ridges are candidates for bars and telescopic copings as they offer good stability and patients with minimal resorption are good candidates for stud or magnetic attachments.
Various studies have done to compare different attachment systems for implant supported over denture. By analyzing these studies, one can come to the conclusion that locators have superior properties as compared to any other attachment system available. In situations of limited inter-arch, space locator attachments provide excellent retention and stability which is the primary goal of any prosthetic treatment. In most of the clinical condition, locators provide satisfactory results. No discomforts to the patients have been noted on long-term use of these attachments.
Syncone attachments have proved to have satisfactory retention and stability with minimal postoperative complications. Hence, in conditions like patient has good inter-arch space to accommodate telescopic attachments, syncone should be our first choice as an attachment.
| Conclusion|| |
To provide a successful treatment, the clinician should have a thorough knowledge of various attachments available, their use in various clinical situations, their advantages and disadvantages. Selection of attachment should be based on proper diagnosis of intraoral structures and various factors such as bone type and inter-arch space which are important for successful results. While using any particular type of attachment system clinician should try to fulfill all the necessary requirements which are essential for stable results for successful esthetic and functional rehabilitation.
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[Figure 1], [Figure 2], [Figure 3]