Effects of Implant Angulations and Attachment Configurations on the Retentive Forces of Locator Attachment–Retained Overdentures Bulent Uludag, DDS, PhD1/Serdar Polat, DDS, PhD2/Volkan Sahin, DDS, PhD3/Ali Alper Çomut, DDS, PhD4 Purpose: The aim of this study was to evaluate the effects of different implant angulations and attachment configurations on the retentive forces of locator attachment–retained overdentures over a simulated time period of 6 months. Materials and Methods: Two acrylic resin models (models 1 and 2) were fabricated to represent an edentulous mandible. In model 1, the midline implant (in the central region) was vertical and the other two implants (in the canine regions) were 20 degrees divergent from the midline, reaching a total divergence of 40 degrees. In model 2, all three implants were vertically oriented, perpendicular to the occlusal plane and parallel to each other. Three-point vertical pull-out forces were employed in a universal testing machine at a constant crosshead speed of 50 mm/min after overdenture construction and a simulation of 6 months of repeated insertions/removals of the overdenture. Locator attachments with different male combinations and bar and clip attachments were tested in model 1. Clear locator attachments and bar and clip attachments were tested in model 2 and served as controls. Results: The initial retentive forces of all attachments in both models ranged from 26.58 to 62.05 N, whereas the initial retentive forces of the attachments for only model 1 ranged from 49.58 to 62.05 N. The highest retention value was recorded for clear green locator attachments and the lowest for hader bar yellow clip attachments. Locator attachments showed higher retention values than hader bar yellow clip attachments. Conclusion: All attachment systems demonstrated a decrease in retention over time. Locator attachments provided better retention than hader bar yellow clip attachments. The highest retention values were obtained when green male locators were used in combination with male attachments. Int J Oral Maxillofac Implants 2014;29:1053–1057. doi: 10.11607/ jomi.3401 Key words: implant-retained overdenture, locator attachments, retention

B

ar and clip and stud attachments represent two different types of attachment systems for implantretained overdentures.1 Implants can be splinted with a bar and the overdenture retained with a bar and clip, or the implants may stand alone and retain the overdenture with stud attachments.2 The choice of attachment system depends on the amount of retention required, arch morphology, patient expectations,

1Professor,

Prosthodontics, Ankara University, Faculty of Dentistry, Ankara, Turkey. 2 Assistant Professor, Prosthodontics, Gazi University, Faculty of Dentistry, Ankara, Turkey. 3Associate Professor, Prosthodontics, Kirikkale University, Faculty of Dentistry, Kirikkale, Turkey. 4 Assistant Professor, Prosthodontics, New York University, New York, New York, USA. Correspondence to: Bulent Uludag, Prosthodontics, Ankara University, Faculty of Dentistry, Besevler, 06500 Ankara, Turkey. Email: [email protected] ©2014 by Quintessence Publishing Co Inc.

cost, soft tissue pain,1–3 and load distribution to the implants and their surrounding tissues. Implant angulation also plays an important role in the selection of attachments.4 Some clinicians state that bar and clip attachments should be used when implants are angulated.5 The use of stud attachments has typically been limited to implants with less than 10 degrees of divergence.6 Angulation is less critical with fixed implant prostheses or when a superstructure bar is used to retain an overdenture.7 However, bar and clip attachments need more restorative space, are initially more expensive, and are technically more complex than stud attachments.8,9 Moreover, some studies have shown that many spherical attachment systems can function appropriately with nonparallel implants.10,11 Locator attachments have recently come into widespread use and are now available from several implant manufacturers. Locator attachments are designed to provide correct seating and adequate retention of implant-supported overdentures.12 The locator attachment system is self-aligning, does not require splinting, has dual retention (inner and outer), and has been The International Journal of Oral & Maxillofacial Implants 1053

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Uludag et al

a

b

a

b

Figs 1a and 1b   Locator attachments and bar-clip attachments in model 1.

Figs 2a and 2b   Locator attachments and bar-clip attachments in model 2.

shown to have the lowest profile height of all attachment systems tested.4,13 Unlike other attachments, the locator attachment uses a straight abutment and relies on the male component, which lies within the removable prosthesis and includes a nylon liner, to resolve any problems related to angulation.7 Depending on the axial divergence between the implants, dualretention inserts (inner stud and external retention) can be used, or inserts with only external retention can be selected for extended use. Standard locator male components (clear, pink, and blue) will permit up to 10 degrees of divergence for a single implant and 20 degrees between implants, and the extended-range locator male components (green, orange, red, gray) can accommodate up to 40 degrees of divergence between implants.7 Locator attachments benefit from minimal height requirements (3.7 mm) and a larger cross section, which adds strength.4 Numerous articles have reported on mandibular overdentures with bar and clip and stud attachments,2,14–18 and others have reported on the retention forces of locator attachment systems.4,19,20 Locator attachments have been shown to provide significantly higher retentive forces compared to ball and magnet attachments for overdentures subjected to vertical and oblique dislodgment forces.19 Also, white male locators provided higher retentive forces compared to hader bar metal clips, and pink male locators provided higher retentive forces compared to magnet attachments.20 However, a previous study reported the greatest loss of retention force of overdentures for green male locators, followed by white male locators and hader bar yellow clips subjected to 20 consecutive pulls.4 Studies have shown that retention is influenced by attachment type and design,21,22 component wear,23,24 and implant angulation.10 Predictably, retention has been shown to have a great impact on patient satisfaction.19 The aim of the present study was to evaluate the effects of implant angulations and attachment configurations on the retentive forces of locator attachment– retained overdentures over a simulated time period of 6 months. The null hypothesis was that the retentive forces of the locator attachment–retained overdentures were not influenced by differences in implant angulations and attachment configurations.

MATERIALS AND METHODS Test Materials

Two models of an edentulous mandible were fabricated from acrylic resin (PL-2, Vishay Intertechnology). The arch configuration was adapted from a mandibular cast of an edentulous patient. A silicone mold (Speedex, Coltene/Whaledent) of the mandibular cast was obtained to duplicate the cast in wax models (Poliwax, Bilkim Kimya). Three tapered ScrewVent implants (3.75 × 13 mm, Zimmer Dental) were embedded in the interforaminal region of each wax model using a surveyor (Ney Surveyor, Dentsply). The orientations of the inclined implants were verified through the use of 20-degree angled abutments (Tapered Screw-Vent, Zimmer Dental). In model 1, the midline implant, positioned in the central region, was vertical, and the other two implants, positioned in the canine regions, diverged from the midline by 20 degrees each, reaching a total divergence of 40 degrees. In model 2, all three implants were vertically oriented, perpendicular to the occlusal plane and parallel to each other. The implants were placed at the crestal bone level. The implants were placed 11 mm apart from each other.25 Three impression copings were screwed onto the implants. A pickup impression of the wax model was obtained using a silicone mold (Speedex, Coltene/Whaledent). The wax was removed with hot water and the implant surfaces were cleaned with a steam cleaner (Triton SL, Bego); then the models were poured in acrylic resin (PL-2, Vishay Intertechnology) (Figs 1 and 2). Colors of the male locator attachment components represent the degree of retention according to the manufacturer (Zest Anchors): clear 22.26 N, pink 13.34 N, blue 6.67 N, green 17.75 N, orange 28.83 N, red 4.42 N, and gray 0 N. A single hader bar yellow clip was shown to provide a mean retentive force of 14.12 ± 2.94 N.4 Locator attachments with different male combinations (central locator male/lateral locator males) (22.26 N/17.75 N, 13.34 N/17.75 N, 6.67 N/17.75 N, 22.26 N/4.42 N, 13.34 N/4.42 N, 6.67 N/4.42 N) and hader bar yellow clips (estimated mean retentive force of 28 N) were tested in model 1. Locator attachments with clear male components (central locator male/lateral locator

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males) (22.26 N/22.26 N) and hader bar yellow clips (estimated mean retentive force of 28 N) were tested in model 2 and used as controls (Table 1, Fig 3).

Pull-out Tests

The overdentures were attached to the models, and each model was screwed to the base of a universal testing machine (Fig 4). Three 10-cm metal chains were hooked to each overdenture and connected to the head of a universal testing machine (LRX, Lloyd Instruments Ltd)18 set at a constant crosshead speed of 50 mm/min to approximate the speed of the movement of the denture away from the ridge during mastication.19,20 A three-point vertical pull was employed to measure direct retention against a vertically (axially) directed dislodgment force parallel to the path of insertion. Ten measurements were performed, and the mean of the measurements was recorded as the retention value at insertion. To simulate repeated insertions and removals of the overdenture over a 6-month period (assuming three daily removals and insertions of the overdenture for the purpose of hygiene26), each overdenture was pulled out 540 times. Ten additional measurements were performed, and the mean of these measurements was recorded as the retention value after the simulation of 6 months of use. Statistical comparisons were made using repeated analysis of variance and the Tukey B post hoc test, with the level of significance set at P < .05.

RESULTS The mean retention values of the different attachment combinations are presented in Table 2. The initial retentive forces of all the attachments (models 1 and 2) ranged from 26.58 to 62.05 N; the initial retentive forces of the attachments for only model 1 ranged from 49.58 to 62.05 N. The highest retention value was recorded for the A1 pair of locator attachments (62.05 ± 5.11 N) (P < .0001) and the lowest was seen for the hader bar yellow clips (28.51 ± 0.92 N) (P < .0001). Locator attachments (nonsplinted attachments) showed higher retention values than bar and clip attachments (splinted attachments). Among the locator attachments, the A6 pair had the lowest average retention value (49.58 ± 1.27 N). All attachments showed a decrease in retention between the initial and the final pull-out tests. The lowest retention value at 6 months was observed in the control group with the B1 pair of locator attachments (38.95 ± 1.41 N). In comparison to the locator attachment with a retentive force of 22.26 N, the locator attachment with a retentive force of 17.75 N, when used with other locator attachments of different retentive

Table 1  Locator Attachments with Different Male Combinations Tested in Models 1 and 2 Model/ overdenture

Implant Angulation Mean retentive force of location (deg) the male attachment(s)

Model 1 (test) A1

Central Lateral

0 20

22.26 N* 17.75 N/17.75N*

A2

Central Lateral

0 20

13.34 N* 17.75 N/17.75 N*

A3

Central Lateral

0 20

6.67 N* 17.75 N/17.75 N*

A4

Central Lateral

0 20

22.26 N* 4.42 N/4.42 N*

A5

Central Lateral

0 20

13.34 N* 4.42 N/4.42 N*

A6

Central Lateral

0 20

6.67 N* 4.42 N/4.42 N*

A7

Central Lateral

0 20

Bar and clips (28 N)†

Model 2 (control) B1

Central Lateral

0 0

B2

Central Lateral

0 0

22.26 N* 22.26 N* Bar and clips (28 N)†

*Mean retentive forces provided by the manufacturer (Zest Anchors). †Mean retentive force provided by Evtimovska et al.4

A1

A2

A3

A4

A5

A6

A7

B1

B2

Fig 3   Internal views of overdentures.

forces, had higher initial retentive values, as well as higher retentive values at 6 months. Compared to the other attachments tested, the A6 pair of locator attachments exhibited significantly less reduction in retention from the initial values to the 6-month values (19.52%), whereas the B1 pair of locator attachments exhibited significantly more reduction from the initial values to the 6-month values (28.29%). The hader bar yellow clips in model 2 exhibited the lowest rate of reduction from initial values to 6-month values (12.03%). The hader bar yellow clips in model 1 exhibited rates of reduction similar to those seen for the locator attachments (22.09%). The International Journal of Oral & Maxillofacial Implants 1055

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Fig 4   Model in the universal testing machine.

Table 2  Mean Retentive Values (Means ± Standard Deviations) of the Different Attachment Combinations Male locator combination

Initial retention

Retention at 6 mo

Reduction of P retention values* (%)

A1

62.05 ± 5.11 49.64 ± 3.14 < .001

20.00

A2

60.11 ± 1.59 47.49 ± 1.13 < .001

20.99

A3

60.21 ± 1.08 47.21 ± 0.97 < .001

21.59

A4

51.61 ± 2.30 40.43 ± 0.88 < .001

21.66

A5

50.41 ± 1.64 40.28 ± 0.44 < .001

20.09

A6

49.58 ± 1.27 39.90 ± 1.43 < .001

19.52

A7

28.51 ± 0.92 22.21 ± 1.39 < .001

22.09

B1

54.32 ± 3.47 38.95 ± 1.41 < .001

28.29

B2

26.58 ± 0.77 23.38 ± 1.19 < .001

12.03

*Initial vs 6 months.  A = Model 1 overdentures; B = model 2 overdentures.

DISCUSSION The effects of implant angulations and attachment configurations on the retentive forces of locator attachment–retained overdentures over a simulated time period have not yet been reported. This study therefore examined the retention of three-implant–supported mandibular overdentures retained by different pairs of male locator attachments and compared the retention provided to that provided by male locators with a retentive force of 22.26 N or hader bar yellow clip attachments. The null hypothesis was that the retentive forces of the locator attachment–retained overdentures were not influenced by differences in implant angulations and attachment configurations. The use of attachments should enhance the retention and stability of implant-retained overdentures. Initial retention values may indicate clinical predictability and performance and facilitate patient acceptance of a prosthesis. Forces of 20 N are considered sufficient for

overdentures in edentulous mandibles.1 In the present study, retentive forces ranged from 22.21 to 62.05 N, which is in agreement with the literature. In contrast to studies by Petropoulos et al18 and Naert et al,14–16 which found that the bar and clip design was better than ball and magnet attachments for retaining overdentures, the present study found that locator attachments had higher retentive forces compared to hader bar yellow clip attachments. Savabi et al17 compared the retentive forces of different color caps on ball attachment systems; green caps had significantly higher retention values than pink and white caps, both of which performed similarly. Sadig19 found that locator attachments provided the greatest level of retention for implant-supported overdentures, followed by ball and magnet attachments. Chung et al20 compared the retention of different attachment systems; white male locator attachments provided higher retentive forces (28.95 ± 0.78 N) than hader bar metal clips (24.15 ± 3.40 N), and pink male locators provided higher retentive forces (12.33 ± 1.28 N) than magnet attachments. The initial retentive forces of all the locator male attachment combinations tested in the present study ranged from 49.58 ± 1.27 N to 62.05 ± 5.11 N, which exceed the retentive forces of the hader bar/yellow clip attachments, which provided retentive forces ranging from 26.58 ± 0.77 N to 28.51 ± 0.92 N. In an in vivo study, Wilfried et al13 demonstrated that locator attachments lost 75.5% of their retentive capacity over time as a result of wear of the male locator part; however, the same study suggested that, overall, the locator attachment system required more maintenance compared to ball attachments. Evtimovska et al4 reported the greatest loss of retentive force of the overdentures with a pair of green male locator attachments, with a mean loss of 11.05% ± 4.94% of retentive force over time, followed by a pair of white male locators (mean loss of 8.60% ± 4.42%) and hader bar yellow clips (mean loss of 6.50% ± 3.59%); however, the difference between the white male locators and the hader bar yellow clips was not significant. In the current study, the highest mean loss of retentive force was seen with the B1 pair of locator attachments (28.29%), and the smallest loss of mean retentive force was seen with the hader bar yellow clips in model 2 (12.03%). The hader bar yellow clips in model 1 exhibited rates of reduction similar to those of the locator attachments (22.09%). All the tested male locator attachments showed similar mean retentive force loss values, ranging from 19.52% to 21.66% over a simulated time period of 6 months, except for the B1 pair of locator attachments (28.29%). One study reported an 11.05% ± 4.94% mean retentive force loss with green male locator attachments placed onto two implants with 40 degrees of divergence that were subjected to multiple pulls.4 However,

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Uludag et al

in the current study the mean retentive force loss ranged from 20% to 21.59% for the attachment combinations A1, A2, and A3, which incorporated green male locator attachments on three implants with 40 degrees of divergence. The difference between these mean retentive force loss values can be explained by the different number of pulls to which the locator attachments were subjected. Because the current study did not simulate the conditions of the oral cavity, further studies should be conducted to evaluate retention during function in the oral environment.

CONCLUSION Within the limitations of this study, the following conclusions were drawn. 1. All attachment systems had retention values greater than 20 N, which should be sufficient for retention. 2. All attachment systems demonstrated a decrease in retention over time. 3. Locator attachments provided better retention than hader bar/yellow clip attachments. 4. The best retention was obtained when at least one green male locator was used in the male attachments. 5. The decrease in retention can be reduced by using a combination of different locator male attachments.

ACKNOWLEDGMENTS The authors reported no conflicts of interest related to this study.

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5. Misch CH. Contemporary Implant Dentistry, ed 3. St Louis: Elsevier, 2008:297. 6. Banton B, Henry M. Overdenture retention and stabilization with ball-and-socket attachments: Principles and technique. J Dent Technol 1997;14(7):14–20. 7. Schneider AL, Kurtzman GM. Restoration of divergent free-standing implants in the maxilla. J Oral Implantol 2002;28(3):113–116. 8. Sadowsky SJ. Mandibular implant-retained overdentures: A literature review. J Prosthet Dent 2001;86:468–473. 9. Burns DR. Mandibular implant overdenture treatment: Consensus and controversy. J Prosthodont 2000;9:37–46. 10. Gulizio MP, Agar JR, Kelly JR, Taylor TD. Effect of implant angulation upon retention of overdenture attachments. J Prosthodont 2005;14:3–11. 11. Wiemeyer AS, Agar JR, Kazemi RB. Orientation of retentive matrices on spherical attachments independent of implant parallelism. J Prosthet Dent 2001;86:434–437. 12. Alsiyabi AS, Felton DA, Cooper LF. The role of abutment-attachment selection in resolving inadequate interarch distance: A clinical report. J Prosthodont 2005;14:184–190. 13. Wilfried KK, Peer WK, Sinsa H, Bilan AN, Wilfried W. A Comparison of three different attachment systems for mandibular two-implant overdentures: One-year report. Clin Implant Dent Relat Res 2010;12:209–218. 14. Naert IE, Gizani S, Vuylsteke M, van Steenberghe D. A randomised clinical trial on the influence of splinted and unsplinted oral implants in mandibular overdenture therapy. A 3-year report. Clin Oral Investig 1997;1:81–88. 15. Naert I, Gizani S, Vuylsteke M, van Steenberghe D. A 5-year randomized clinical trial on the influence of splinted and unsplinted oral implants in the mandibular overdenture therapy. Part I: Peri-implant outcome. Clin Oral Implants Res 1998;9:170–177. 16. Naert IE, Gizani S, Vuylsteke M, van Steenberghe D. A 5-year prospective randomized clinical trial on the influence of splinted and unsplinted oral implants in the mandibular overdenture: Prosthetic aspects and patient satisfaction. J Oral Rehabil 1999;26:195–202. 17. Savabi O, Nejatidanesh F, Yordshahian F. Retention of implantsupported overdenture with bar/clip and stud attachment designs. J Oral Implantol 2013;39:140–147. 18. Petropoulos VC, Smith W, Kousvelari E. Comparison of retention and release periods for implant overdenture attachments. Int J Oral Maxillofac Implants 1997;12:176–185. 19. Sadig W. A comparative in vitro study on the retention and stability of implant-supported overdentures. Quintessence Int 2009;40:313–319. 20. Chung KH, Chung CY, Cagna DR, Cronin RJ Jr. Retention characteristics of attachment systems for implant overdenture. J Prosthodont 2004;13:221–226. 21. Doukas D, Michelinakis G, Smith PW, et al. The influence of inter implant distance and attachment type on the retention characteristics of mandibular overdentures on 2 implants: 6-month fatigue retention values. Int J Prosthodont 2008;21:152–154. 22. Williams BH, Ochiai KT, Hojo S, et al. Retention of maxillary implant overdenture bars of different designs. J Prosthet Dent 2001;86:603–607. 23. Rutkunas V, Mizutani H, Takahashi H. Influence of attachment wear on retention of mandibular overdenture. J Oral Rehabil 2007;34:41–51. 24. Gamborena JI, Hazelton LR, NaBadalung D, et al. Retention of ERA direct overdenture attachments before and after fatigue loading. Int J Prosthodont 1997;10:123–130. 25. Celik G, Uludag B. Photoelastic stress analysis of various retention mechanisms on 3-implant retained mandibular overdentures. J Prosthet Dent 2007;97:229–235. 26. Besimo CH, Guarneri A. In vitro retention force changes of prefabricated attachments for overdentures. J Oral Rehabil 2003;30:671–678.

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Effects of implant angulations and attachment configurations on the retentive forces of locator attachment-retained overdentures.

The aim of this study was to evaluate the effects of different implant angulations and attachment configurations on the retentive forces of locator at...
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