Sum

mer

201

4

Implant Overdenture Attachments: Selection and Application

As patient awareness of implant dentistry increases, expectations of benefits realized from dental implant therapy also increase. At the heart of implant overdenture performance is the attachment system used to facilitate prosthesis retention, support and stability during functional and parafunctional activity. With ever­advancing technology driving implant overdenture attachment development, the practitioner’s ability to follow and understand subtle improvements in this area is critical to patient well­being. This issue of Prosthodontics Newsletter represents a synopsis of information important to implant overdenture attachment systems.

Bar or Stud Attachments: Which Work Better?

A t tachments for implant-re-tained overdentures can be divided into 2 groups: bars

and studs. Trakas et al from Tufts University, Massachusetts, reviewed the literature on the attachment systems’ impact on implant sur-vival rate, marginal bone loss, soft tissue complications, retention, stress distribution, space require-ments, maintenance complications and patient satisfaction—factors necessary for successful outcome and long-term prognosis.

Implant survival rate: Bone quality and quantity, arch mor-phology, and implant length are more important to im plant success than the type of at tachment used.

Marginal bone loss: Although some evidence exists that mean bone loss values appear higher in patients with ball attachments, no significant difference in mean bone loss has been found between patients with ball and with bar attachments.

Soft tissue com-plications: Some published evi dence shows that magnet-type attachments are associated with a higher plaque index, but neither attach-ment appears to affect peri-implant soft tissue.

Retention: Bars and clips ap -pear to provide more retention. Discrepancies in results exist be -tween in vitro studies and clinical experience. However, both types supply sufficient retention for the typical patient.

(continued on next page)

➤ Choosing the Best Technique for Incorporating Attachments

➤ Rotational Freedom of Overdenture Attachments

➤ Comparison of Overdenture Attachment Systems

➤ Locator vs Bar Attachments: Patient Satisfaction

Insi

de t

his

Issu

e

M. Patrick Pedlar, BSc, ddS, MSd, Frcd(c) B. larry Pedlar, ddS, MSd, FacP

Restoring the Natural Appearance of Teeth310 Plains Road East • Burlington, Ontario L7T 4J2

Tel: 905-632-1882 • Fax: 905-632-1351 • www.RestorativeDentistry.ca e-mail: patrick@drpedlar.com

Certified Specialists in Prosthodontics: Crowns • Veneers • Bridges • Implants • Dentures • Aesthetic Reconstructive Dentistry

A Professional Courtesy of:

Stress distribution: Ball attach-ments more evenly distribute stress, transferring minimal stress to the implants under vertical forces. Rig id designs and cantilever bars increase the force transmitted to implants.

Space requirements: Although bar and stud attachments have similar vertical dimensions, some bar attachments require specific distances between implants due to limitation of bar length and exces-sive stress on longer cantilevered segments.

Maintenance complications: No definitive evidence exists as to whether bar or stud attachments require more maintenance. Most maintenance issues arise during the first year in service.

Patient satisfaction: Because there is no difference between the bar or ball attachment methods, the authors concluded that both mechanisms seemed to satisfy most pa tients more than did the magnet attachment method.

Comment

Treatment planning decisions should be based on many factors, including cost-effectiveness, avail-able bone, expected level of oral hygiene, interimplant distance, maxillomandibular relationship and patient expectations. Either attachment may be a good choice for an individual patient.

Trakas T, Michalakis K, Kang K, Hirayama H. Attachment systems for implant retained overdentures: a literature review. Implant Dent 2006;15:24­34.

Choosing the Best Technique For Incorporating Attachments

The use of implant-re tained overdentures to treat the edentulous mandible is now

the standard of care, but no single technique has proven superior in all situations. Bidra et al from the University of Connecticut Health Center reviewed the advantages and disadvantages of various tech-niques to incorporate attachments in implant-retained prostheses.

The choice of final impression meth od determines subsequent clinical and laboratory procedures, dictat ing the method of attachment in corporated into the overdenture. Overdentures may be fabricated concurrent to 3 different stages of treatment, and attachments can be included using either a direct or an indirect technique.

These 3 options create 7 different techniques:

➤ tissue-level impression, record base stage, direct technique

➤ tissue-level impression, denture insertion stage, direct technique

➤ tissue-level impression, denture insertion stage, indirect technique

➤ abutment-level impression, base stage, indirect technique

➤ abutment-level impression, denture processing stage, indi-rect technique

➤ implant-level impression, record base stage, indirect technique

➤ implant-level impression, den-ture processing stage, indirect technique

Factors influencing technique choice are shown in Table 1. Tis sue-level impressions may be fa vored to in -corporate attachments after the definitive denture has been fabri-cated; implant-level im pressions may be needed when issues with implant placement arise or pros-thetic space needs to be reassessed before attachment system selection.

2

Bar or Stud Attachments: Which Work Better? (continued from front page)

TM

ProsthodonticsNewsletterTM

Table 1. Factors affecting choice of technique for incorporating attachments for implant-retained partial and complete overdentures

1. Choice of prosthetic design (splinted vs unsplinted abutments) 2. Chronology of implant placement with respect to prosthesis 3. Number and position of implants 4. Angulations of implants 5. Prosthetic space availability 6. Choice of attachment system 7. Need for processed denture bases 8. Complexity of maxillomandibular relationships 9. Changes in tissues after implant surgery10. Operator preference11. Availability of inventory for prosthetic components12. Cost

The direct technique gives the clini-cian intra-oral control of the proce-dure and immediate confirmation of accurate seating but requires increased chair time and is contra-indicated in several scenarios, such as changes in soft tissue morphol-ogy after implant surgery as well as improper implant positions and angulations.

Comment

Each technique has advantages and disadvantages. A successful clinical outcome requires the clini-cian to have broad, specialized knowledge of the rationale for and likely result of decisions made dur-ing the process.

Bidra AS, Agar JR, Taylor TD, et al. Tech ­niques for incorporation of attachments in implant­retained overdentures with unsplinted abutments. J Prosthet Dent 2012;107:288­299.

Rotational Freedom of Overdenture Attachments

S tudies highlighting their ad -vantages to treat the edentu-lous mandible have supported

the acceptance of implant-re tained removable prostheses, but the abut-ment selection’s impact on freedom of rotation has not been extensively studied. Rotation at the implant is a double-edged sword: too much rotation during mastication may lead to a loss of prosthesis retention from compression of the posterior denture-bearing mucosa; too little rotation may create un even stress concentration on the implant, po -

tentially compromising the bony structure around it.

To determine levels of resistance to rotation, Chen et al from the Uni-versity of Washington de signed an in vitro study that subjected the components of 3 commonly used types of stud-resilient matrices to the expected levels of rotation in clinical use. Components of the most and least retentive versions of 3 attach-ment systems, as defined by the manufacturers, were studied:

➤ ERA (metal jacket and black ny lon patrix)

➤ Locator (metal housing and black processing patrix and spacer)

➤ O-ring (retainer ring and regu-lar red O-rings for processing)

Each attachment system and reten-tion level was tested with a single implant system and a 2-attachment parallel implant system (Figure 1). Regardless of attachment system or number of implants, rotational freedom was greater for the Locator system than it was for the ERA. Among the least retentive compo-

nents, the O-ring provided the most rotation, followed by the Locator and the ERA. One-implant systems al lowed significantly greater rota-tion than did 2-implant systems.

Comment

Of the attachment systems tested in this study, the O-ring with the least retentive component would be the choice of a clinician who wishes to use a prosthesis with the greatest degree of rotational freedom.

Chen I-C, Brudvik JS, Mancl LA, et al. Free-dom of rotation of selected overdenture attachments: an in vitro study. J Prosthet Dent 2011;106:78­86.

Comparison of Overdenture Attachment Systems

To date, no consensus exists re garding the ideal number of implants to treat the eden-

tulous mandible or the best choice of attachment mechanism between the implants and the denture base. To evaluate 3 mandibular implant overdenture treatments for pros-thesis retention and stability, peri-implant tissue response, pa tient satisfaction and preference, and complication rate, Burns et al from Virginia Commonwealth University conducted a crossover clinical trial of 30 adults (mean age, 58.9 years).

The participants had adequate bone quantity to minimally accommodate 4 3.75-mm diameter im plants. After successful integration, the patients randomly received overdentures using 1 of 3 attachment systems:

Summer 2014

3

Figure 1. Differences in retention among attachments (n = 15); horizontal bar represents no significant difference.

8

10

6

4

2

0Most retentive Least retentive

1 attachment2 attachments

➤ an independent O-ring attach-ment using 2 implants (2I)

➤ a bar attachment using 2 im -plants (2B)

➤ a bar attachment using 4 im -plants (4B)

After 12, 24 and 36 months, pa -tients received a different attach-ment system; all patients received each of the 3 attachment systems for either 1 or 2 12-month periods.

Tested with a force gauge, the 4B attachment system demonstrated the greatest retention with no dif-ference in stability. Prob ing depth was greatest for the 4B attach-ment, while gingival and plaque indices were most favorable for the 2I attachment. Other parameters, including supporting tissue, keratin-ized tissue and attachment level, were equivalent for all 3 systems. Patients with the 2I and 4B attach-ments provided more favorable answers to masticatory ability and denture complaint questionnaires. In general, more patients found the 2I system preferable, followed by the 4B and the 2B; however, none of the differences reached statistical significance.

Comment

Increased retention demonstrated by the 4B attachment system did not translate to increased patient prefer-ence. The systems’ equivalence sug-gests that the choice of design for mandibular implant overdentures should be made with patient input on an individualized basis.

Burns DR, Unger JW, Coffey JP, et al. Ran­domized, prospective, clinical evaluation of prosthodontic modalities for mandibular implant overdenture treatment. J Prosthet Dent 2011;106:12­22.

Locator vs Bar Attachments: Patient Satisfaction

Studies have shown no differ-ence in patient satisfaction with mandibular overdentures

retained by ball, bar or magnet at -tachments. While ball attachments are easily replaceable, bar attach-ments have demonstrated better stability. Locator attachments com-bining the best results of both sys-tems may provide an alternative.

Cordaro et al from Eastman Dental Hospital, Italy, compared treat-ment results and quality of life in 39 edent ulous patients (age range, 49–81 years; mean age, 62 years) re ceiving mandibular overdentures retained by either Locator attach-ments or milled bars. The patients were divided into 2 groups:

➤ Locator group (n = 19): over-denture retained by the Locator attachment system

➤ Bar group (n = 20): overden-ture retained by computer-aided design/computer-aided manufac-turing (CAD/CAM) milled bars

Three independent dentists evalu-ated implants for peri-implant soft tissue health, implant mobil-ity and implant success. Patients completed a 9-item questionnaire to measure their perception and attitude toward their implant-sup-ported prostheses.

The Locator group had less plaque but more sites with bleeding on probing. General satisfaction, abil-ity to chew, ability to speak, sta-bility, comfort, appearance, pain

around implants and pain on gin-giva were not significantly different for the 2 groups. Regarding ease of cleaning, patients showed a sig-nificant preference for the Locator attachment. The independent dentists found significantly better results for the Locator attachment in retention, oral hygiene and soft tissue condition.

Comment

The primary difference in clinical performance between Locator and bar attachments for mandibular overdentures relates to hygiene maintenance. Patient satisfaction was very high in both groups.

Cordaro L, di Torresanto VM, Petricevic N, et al. Single unit attachments improve peri­implant soft tissue conditions in man dibular overdentures supported by four implants. Clin Oral Implants Res 2013;24:536­542.

4

TM

ProsthodonticsNewsletterTM

Digital prosthodontics

Do you or your staff have any questions or comments about Prosthodontics Newsletter? Please write or call our office. We would be happy to hear from you.

© 2014

In the Next Issue

Our next report features a discussion of these issues and the studies that analyze them, as well as other articles exploring topics of vital interest to you as a practitioner.