Haroon Rashid1 , Ayesha Hanif2 , Fahim Vohra3 , Zeeshan Sheikh4
1. Assistant Professor, Department of Prosthodontics,Ziauddin College of Dentistry, Karachi, Pakistan.
2. Clinical Lecturer, Department of Prosthodontics, Ziauddin College of Dentistry, Karachi, Pakistan.
3. Assistant Professor, Department of Prosthetic Dental Science, King Saud University, Riyadh, Saudi Arabia.
4. Post-doctoral Fellow, Faculty of Dentistry, University of Toronto, Ontario, Canada.
Corresponding author: “Dr Nosheen Zehra” Nosheen_zehra130@hotmail.com
How to CITE:
Rashid H, Hanif A, Vohra F, Sheikh Z. Implant Over Dentures: A Concise Review of The Factors Influencing The Choice of The Attachment Systems. J Pak Dent Assoc 2015; 24(2):63-69.
Provision of implant over-dentures (IODs) has become a popular treatment modality for edentulous patients. Oral rehabilitation carried out using dentures supported by endosseous implants greatly improves oral function and majority of the problems associated with the dentures i.e. poor stability and retention may be solved. Good success rates have been reported regardless of the attachment system used for the IODs however; the maintenance and complications may be influenced by the use of different attachment systems and other factors. The aim of the current paper is to briefly review the attachment systems used for IODs and the factors influencing their selection. Chair-side pickup Impression technique for mandibular implant over-denture is also briefly described.
1. Implant retained over dentures. 2. Implant retained prosthesis. 3. Implant attachment systems 4. Chair-side pickup impression.
Over-dentures are defined as,”removable dental prosthesis that cover and rests on one or more remaining natural teeth, the roots of natural teeth, and/or dental implants”1. It may also be termed as an overlay denture, overlay prosthesis, superimposed prosthesis, hybrid prosthesis, a crown and sleeve prosthesis, superimposing denture and a biological denture1.
The concept of retaining teeth/roots of the terminal dentition for the provision of an overdenture dates back to more than 100 years2,3. It was first described in 1950’s that the residual alveolar bone undergoes resorption which continues to progress after tooth extraction compromising support for a conventional dentures to be provided. The analysis of several longitudinal studies confirmed that the resorption was progressive, irrevocable and continuous4,5. The rate of resorption is the greatest in the first six months after tooth extraction however; it slows down due to several biological and mechanical factors4.
Overdenture abutments, whether a retained root or an implant, have shown to preserve alveolar bone height7,8 and stabilize dentures, particularly the mandibular ones9. Retained roots are cost effective than implants, with no requisite of an invasive therapy, and therefore should be considered by general practitioners as a useful platform for over dentures, particularly for older individuals10. From physiological viewpoint, the roots provide not only a periodontal ligament to support the teeth, but also directional sensitivity, tactile sensitivity to load, dimensional discrimination,7,11,12 and gives an individual a sense of not being edentulous13. Dental implants provide adequate retention and stability for overlying prosthesis however; the individual is deprived of tactile sensitivity14.
Dental implant therapy is considered the treatment of choice for edentulous patients10. IODs have gained worldwide acceptance and improve the quality of life for edentulous patients. IODs although retentive and stable,require good maintenance of the prosthesis and implant retentive components6. Continued research related to IODs has resulted in multiple options and combinations for IOD attachment systems with varying success. The aim of the current paper is to briefly review the attachment systems used for IODs and the factors influencing their selection. Chair-side pickup Impression technique for mandibular implant over-denture is also briefly described. The treatment of the patient described in the current paper was carried out at the department of prosthodontics, college of dentistry,Ziauddin University, Karachi.
In the early days, only bare teeth with questionable prognosis as a whole were used as abutments for over dentures. Recently, the use of implant abutments for overdenture use has increased. The use of sub-mucosal roots with magnets is also still in use 15,16.
When using naturally retained bare teeth, it is aimed that canines and second premolars are preserved on both sides of the arches. Teeth are prepared in a dome shape, 2-3 mm above the gingival level, with the dome converging occlusally. To cope up with certain disadvantages of bare teeth such as caries progression, attrition of the abutment teeth, metal copings (short and long) were used over the dome shaped prepared teeth. Sub-mucosal root retention helps to reduce the possible oral hygiene obligations for the patients but delays residual ridge resorption. Being submerged, they escape the sequelae of poor oral hygiene by being isolated from the oral cavity.
With advancements in implant dentistry, implant supported over-dentures are gaining wide popularity. Along with implant abutments, sub-mucosal vital tooth retention and use of magnets are also commonly used. For many years, osseointegrated implant-supported overdentures have been used in the rehabilitation of the edentulous jaws particularly the lower ones, offering promising results 17,18,19.
Literature states that the IODs should become the first choice of care for the edentate mandibles20,21. This is a lucrative option but simultaneously, has been questioned for the fact that wide number of the edentate patients are poor and cannot afford the cost of implant therapy 22,23.
Attachment System for IODs
IODs come with a variety of attachment systems including the bar and clip attachment systems or a range of individual, abutment-based attachments called stud attachments (ball, magnets, and resilient stud attachments such as Locators [Zest Anchors], ERA [Sterngold], and non resilient stud attachments such as Ankylos Syncone [DENTSPLY Implants])24,25,26,27,28. Fabrication of an IOD over these systems is costly; require clinical expertise and signification chair-side time18.
Factors Influencing Selection of the Attachment Systems
Selecting the most apposite system for an individual is dependent on a variety of factors29. These factors are identified during the treatment and planning phase of the therapy. Following are the factors that influence the selection:
a) Implant site:
The location of the placed implant in reference to the bone and the pontics will guide the selection of the type of attachments. However; the selection should ideally be decided during the phase of treatment planning. For ample retention, it is highly recommended that the implants are placed as parallel as possible30,31,32. Where parallelism cannot be achieved, a bar designed is favored. Bar design is also preferred in cases where the unfavorable location of the anatomic structures such as, prominent mental foramen or the knife-edge ridge, precludes the ideal placement of the implants33,34,35,36.
b) Cross arch stabilization:
Bars are indicated in patients with shallow vestibules and resorbed ridges. The bar helps to resist the lateral loading and provides stabilization37. The stability of the prosthesis is also improved and cantilever design may be provided with one to two teeth distal to the most posteriorly placed implant38. The cases where denture stability is not a concern and retention is the only requirement, individual attachments should be used which offer promising results.
c) Prosthesis extent:
When the patient demands the prosthesis to be of the minimal size, custom designed milled bars is the attachment system of choice39. These types of restorations require ideal implant placement. The size of the prosthesis may be limited while keeping in mind the principles of anterior-posterior spread and cross arch stabilization. This also minimizes the lateral loads on the implants38. Fabricating a denture using the neutral zone technique will also determine the horizontal space availability for the prosthesis39. Neutral zone is the area of the minimal conflict i.e. the potential denture space; “that space in the edentulous mouth vacated by the natural dentition and dental supporting tissues and bound by the tongue medially, and the lips and cheeks laterally”40,41,42.
d) Sore spots:
It is established that the patients who are prone to soft-tissue sore spots, for instance xerostomic patients, are reportedly more comfortable with a bar, since the denture can rest entirely on the bar without impingement of the soft tissues43. With individual attachments, the denture is supported by the mucosa and the compressive forces acting on the mucosa cause may cause soreness in patients who are prone to it44.
e) Patient’s Oral Hygiene:
Dentures retained over bars are capable of gathering more debris and hence make such patients more susceptible to mucosal inflammation and peri-implantitis 44,45,46,47,48,49,50,51. Unless the patient commits to the meticulous oral hygiene measures52, the bar attachments should be denied in patients with poor oral hygiene.
f) Treatment Costs:
Bar attachments are costly as compared to the stud abutments in most of the scenarios35,53. Cost is one of the major decisive factors in the selection of the attachment system. Patients may be upgraded to the bars and a new over denture may be fabricated if the financial condition of the patient has improved and other factors are considered. Yet, in every case, the selective treatment option must follow the appropriate guidelines maximizing the welfare of the patient and the options should never be merely dependent on patient’s finances.
g) The Restorative Space:
Restorative space is the space which is available for prosthesis restoration. In general, this space is bounded by the planned occlusal plane, the denture bearing tissues, facial tissues i.e. the lips, cheeks and the tongue54. When planning an implant overdenture, considerations should be given to the adequate space available for the denture base, denture teeth, and the attachment system of the implant. The freeway space, phonetics and aesthetics must also be considered. The minimum space requirement for implant supported over-dentures with Locator attachment system is 8.5mm of vertical space and 9 mm of horizontal space55. Ideally, for maxillary implant overdentures, 13-14mm of vertical space is required for dentures which are supported by bars and 10-12mm for the over-dentures supported with individual attachments56.
h) The Aesthetic Space:
This is defined as “the space between the ridge crest and the corresponding lips at rest”29. Prosthesis supported by the individual attachment systems will require less aesthetic space compared o the bar counterparts. The measurement of the aesthetic space helps the dentist in determining the space allowed for a particular type of the attachment system of an over-denture.
i) Ease of Fabrication and Repair:
Bar supported removable prosthesis require manual dexterity for the fabrication and repair compared with the removable prosthesis supported by individual studs 24,57,58,59,60. Many a times, the attachment systems are chosen without the proper consideration given to the aforementioned factors. This eventually leads to a failed prosthesis with patient dissatisfaction.
j) Resilience Difference:
Another factor documented that influences the selection of the attachment system for implant-retained over-dentures, is the difference of resilience between the implant and the oral mucosa61,62. Furthermore, this difference should be considered while taking the impression of the implant and tissue retained over-dentures.
k) The Attachment System:
IODs supported with bars or balls offer good survival rates and patient’s appreciation levels with a denture retained with implants are better as compared to a conventional complete denture63. The use of magnets for retaining over-dentures is also described in the literature however; their success rates have been limited”1.64. The limited success of magnets is mainly due to corrosion of the magnets caused by saliva and partly because of less retentive forces achieved as compared to other attachment systems. Bar and ball attachment systems offer better mechanical retention and have many differences between them. Table 1 outlines the differences between the attributes of bar and ball attachment systems 65,45,66,49,67.
Chair Side “Pick-Up” Impression Technique for IODs
The selected attachment can be incorporated into the denture either chair-side or in the laboratory. Chair-side pick-up technique allows for passive in-vivo pick up of the attachment, furthermore, attachments are picked-up under mucosal compression allowing for even load distribution during function68,69. The technique requires manual dexterity but simultaneously provides the incorporation of the attachments into a pre-fabricated denture. Direct chair-side attachment incorporation also avoids laboratory cost and a further denture delivery visit. Usually resilient, non-splinted, prefabricated attachments are utilized.
Abutments are selected with an appropriate gingival height (Figure 1), which is obtained by measuring the vertical distance from the implant collar to the highest
point of soft tissue circumferentially. Another important factor for abutment selection is the available space in occlusion in the denture. The suitable abutments are torqued at 25Ncm and housings are placed over the overdenture abutments after placing a spacer to avoid acrylic block-out (Figure 2, Figure 3). The prefabricated complete denture prosthesis is hollowed at the location of abutments for the housing to be incorporated, (Figure 4) and is checked intra-orally. The denture preparation results in two open windows lingual to the mandibular anterior denture teeth. The abutment housings are placed on to verify and check the full seating of the final prosthesis and ensure there is not interference either from the
attachments or the housings. Auto-cure denture base acrylic resin is mixed and placed into the housing space and the denture is seated in position. The patient is made to bite in centric occlusion and the acrylic resin excess
on the polished surface of the denture is cleared. On complete setting of acrylic resin, the prosthesis is removed and any defect in the reline/pick up, is filled extra-orally using the auto cure acrylic (Figure 5). The prosthesis after the final finishing and polishing is ready to be delivered (Figure 6).
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