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 Table of Contents  
Year : 2020  |  Volume : 17  |  Issue : 1  |  Page : 37-42

Effect of bollard coping and locator attachment on implant stability and patient satisfaction in single implant assisted mandibular overdenture (in-vivo study)

1 Department of Removable Prosthodontics, Faculty of Dentistry, October 6 University, October 6 City, Egypt
2 Department of Removable Prosthodontics, Faculty of Dentistry, Al-Azhar University, Cairo, Egypt

Date of Submission26-Oct-2019
Date of Acceptance30-Jan-2020
Date of Web Publication20-Jun-2020

Correspondence Address:
Ahmad M. Shoeib
Lecturer of Removable Prosthodontics, Faculty of Dentistry, Al-Azhar University, Cairo
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/tdj.tdj_49_19

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This study was performed to evaluate the effect of bollard coping and locator attachment on immediately loaded single implant retained complete mandibular overdenture.
Patients and methods
Twenty completely edentulous patients were selected from the Outpatient Clinic, Prosthodontics Department, Faculty of Dental Medicine, Al Azhar University. For each patient complete maxillary and mandibular conventional complete denture were constructed. The patients were divided into two equal groups: group I: patients were treated by single implant assisted mandibular overdenture retained with a new design (bollard coping); group II: patients were treated by single implant assisted mandibular overdenture retained with locator attachment. The bollard coping retention was achieved by engagement of the undercut in the bollard coping to the chemical-curing silicone soft liner in the denture. The locator attachment retention was achieved by the mechanical interlock between the attachment and the metal housing in the denture. The stability of implants was measured by using the Osstell implant stability quotient (ISQ) system and patient satisfaction was evaluated by using a questionnaire. Measurements were taken at baseline, 3, 6, and 12 months after implant insertion. Independent t-test was used for comparison between groups while the comparison of within each group by time was done by one-way analysis of variance followed by post-hoc Tukey test.
Patient satisfaction and ISQ values results showed higher values in group I than group 2 without any statistically significant difference. ISQ values in both groups over time showed a statistically significant difference between the baseline and 6 and 12 months, between 3 and 12 months, and between 6 and 12 months values. There were statistically nonsignificant difference resulted from the comparison of 3 and 6 months values.
There was an increase in the ISQ, and retention values for both groups during the follow-up period, but the difference was statistically insignificant between the two groups.

Keywords: bollard coping, implant overdenture, implant stability, locator attachment, patient satisfaction

How to cite this article:
Ismael MH, El-Haddad DF, Shoeib AM, Quassem MA. Effect of bollard coping and locator attachment on implant stability and patient satisfaction in single implant assisted mandibular overdenture (in-vivo study). Tanta Dent J 2020;17:37-42

How to cite this URL:
Ismael MH, El-Haddad DF, Shoeib AM, Quassem MA. Effect of bollard coping and locator attachment on implant stability and patient satisfaction in single implant assisted mandibular overdenture (in-vivo study). Tanta Dent J [serial online] 2020 [cited 2020 Oct 20];17:37-42. Available from: http://www.tmj.eg.net/text.asp?2020/17/1/37/287100

  Introduction Top

Most of complete denture patients are not satisfied with a lower complete denture. Patients frequently complain of looseness and social embarrassment due to movement of the prosthesis during function [1]. This is because the mandibular dentures cover less surface area than maxillary prostheses, therefore they are subjected to a lower magnitude of adhesive and other retentive forces [2]. Mandibular single-implant overdentures are a successful treatment option for early loading protocol of implants with different diameters and different attachment systems [3]. A systematic review failed to demonstrate any significant risk differences for implant survival between one or two implants mandibular overdenture regarding the outcomes of as patient satisfaction [4].

Many attachment systems have been used with implant supported overdenture, which are mainly classified into single attachments, splinted anchorage systems (bars) and telescopic crown [5]. The use of locator attachment seems to have a favorable effect on implant stability and marginal bone around immediately loaded single implant mandibular overdenture after a considerable time of function [6]. The retention value of the locator attachment depends on the patrix, which is composed of a metallic cap with a replaceable nylon element, and its cross-sectional strength is obtained through its dual retention feature (inner and outer). This attachment employs mechanical and frictional forms of retention, since the insert section of the nylon male component is slightly oversized compared to the inner ring of the female abutment [7]. Locator attachment had widespread and international use as a low-profile attachment for implants supporting overdentures, which develop more favorable stress distribution in the peri-implant area, with less damage to the osseo integrating implants and overdentures. It offers several advantages including; dual retention, self-aligning, compensation for a misaligned implant, and availability of different levels of retentive forces obtained from the nylon male inserts [8].

The Bollard is a new resilient telescopic attachment employed in implant supported overdentures. Bollard coping consist of a metal coping with 6° convergence and a retention cap, to form an undercut. The Bollard coping is screwed to the implant abutment. Silicon is placed in the denture with retention achieved by engagement of the silicon to the undercut in the Bollard coping [9]. The use of Bollard coping in implant supported overdentures is indicated as it achieved more implant stability than the conventional telescopic crown and showed simpler fabrication technique [10]. Bollard coping attached dentures, each supported by only two implants placed in the canine region were better than bar-retained and ball-retained implant-supported mandibular dentures with similar characteristics regarding the peri-implant conditions, functional or total loss of implants, alterations of denture materials, as well as functional and esthetic parameters of the dentures [9].

  Aim Top

The purpose of this study was to evaluate the effect of bollard coping and locator attachment on immediately loaded single implant assisted complete mandibular overdenture as regard patient satisfaction, implant stability.

  Patients and Methods Top

Twenty male completely edentulous patients aged between 50 and 60 years were selected from the Clinic of Removable Prosthodontics, Faculty of Dental Medicine, Al-Azhar University Cairo, Boys. Patient inclusion criteria for immediate loading were done according to American College of Prosthodontics. First, Angel's class I jaw relation; second, patient with normal tongue size and behavior; third, patient with adequate inter-arch space (about 8.5 mm between the soft tissues and the occlusal plane); fourth, patients that did not require preprosthetic surgery [11]. Exclusion criteria were either local as the presence of lesions, unhealed extraction sites, bruxism, history of bone grafting techniques at site of intended implant placement, or systemic disorders as hemophilia, head and neck radiation or chemotherapy [12]. Patients participated in the study were divided into two equal groups:

  1. Group I: patients were treated by single implant assisted overdenture retained with bollard attachment.
  2. Group II: patients were treated by single implant assisted overdenture retained with locator attachment.

Prosthetic phase

The whole study procedure and time was explained to the patients, then a written consent was obtained from the patients according to the ethical committee of faculty of Dental Medicine, Al-Azhar University. History taking, and clinical examination was done on each patient. Each patient had a complete denture which was fabricated by conventional protocol. After denture insertion, any necessary adjustment of denture and occlusion was carried out. The teeth were set with bilateral balanced occlusion concept. Cone beam computerized tomography was taken for assessment the bone quality and dimensions at implant site, surgical guide stent was fabricated to assist implant insertion at its planned site. Implants with 12 mm length and 3.5 mm diameter (Sky Implant System, Bredent, UK) were selected to be placed the parasymphyseal area of the mandible slightly lateral to the midline and immediately loaded [13].

Implant placement

Midcrestal incision was made using blade no. 15, then full thickness mucoperiosteal flap was reflected and elevated. The surgical stent was placed to drill the implant site using the pilot drill, then the subsequent drills were used to widen the implant site. The implant was screwed in place using hand torque controller at 20 Ncm 2.

Attachment placement

The attachment (bollard or locator) was screwed on the implant using hand torque controller at 20 Ncm. and then the flap edges were repositioned and sutured. In the bollard attachment group, the implant position in the fitting surface of the lower denture was prepared to have a round shape cavity that allows a minimum thickness of silicon by 1 mm. Then a thick coat of bonding agent (Multisil Primer; (Sika, Chino, California, USA) is applied to the prepared surface and left to dry at air for 3 min. The cavity was filled with chemical-curing silicon soft liner and denture inserted immediately into the mouth. Patient was instructed to close in centric relation during setting of the silicone until full setting after 2 min [Figure 1]. For the locator attachment group, block-out spacers were placed over the head of locator attachment. Then, the metal housings were placed over their attachments. A marking paste was placed to the intaglio surface of the over denture and inserted into the mouth to mark areas into which the metal housings will be picked up. The marked areas were relieved by using acrylic bur, and the lower denture was tested intraorally to ensure enough clearance during the maximum intercuspation. The housing was connected intraorally using autopolymerized acrylic resin (cold cure acrylic; Acrostone, Heliopolis, Cairo, Egypt) through direct pick-up procedure. The excess polymerized acrylic resin contacting the locator abutment was trimmed to avoid transfer any additional stresses to the implants during function [Figure 2]. Antibiotic (amoxicillin 875 mg with clavulanic acid 125 mg, and metronidazole 500 mg) were taken twice daily for at least 7 days and analgesic (diclofenac sodium 75 mg) were prescribed for all patients after surgery.
Figure 1: Bollard attachment.

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Figure 2: Locator attachment.

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Implant stability test

Implant Stability was measured by Osstell ISQ device (Osstell, W&H, Osterreich, Austria). A small piezoelectric transducer screwed to an implant and the tip of the Osstell device is kept close to the transducer in buccolingual and mesiodistal directions. The device produces electromagnetic pulses which causes the transducer to vibrate, the amount of resonance frequency values of the transducer is calculated automatically converted into an arbitrary scale called implant stability quotient (ISQ) and shown on the device display. The ISQ values range from 1 to 100 [14].

Patient satisfaction

For each patient the following questioner used for assessment of patient satisfaction. each question taking score from 1 to 10 [15]:

  1. How do you rate the appearance of your denture?
  2. How do you rate the quality of expression and phonetics?
  3. How do you rate the quality of your mastication?
  4. How do you rate the removal and insertion of your denture?
  5. How comfortable is your denture?

Statistical analysis

Measurements at the follow-up were carried out at insertion, 3, 6, and 12 months of functional loading. Data was collected, tabulated, and statistically analyzed by SPSS 20 (SPSS, Chicago, USA) for windows. The data distribution of normality was done by using Kolmogorov–Smirnov test. The test showed normal distribution of data and independent t-test was used for comparison between groups while the comparison of within each group by time was done by one-way analysis of variance followed by post-hoc Tukey test.

  Results Top

Effect of different attachment on implant stability quotient values

The mean ISQ values found for both the group I and group II are showed in [Table 1]. Independent t-test showed statistically nonsignificance difference at insertion and at 3, 6, and 12 months [Table 1].
Table 1: Mean IS1 values for group I, group II

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Effect of time on implant stability quotient values

Regarding ISQ values in both groups, there was a significant difference between the baseline values and 6 and 12 months values. There was a significant difference between 3 and 12 months values, also there was a significant difference between 6 and 12 months values but there was no significance resulted from the comparison of 3 and 6 months values [Table 2].
Table 2: Change on implant stability quotient values by time (P≥0.05)

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Patient satisfaction

The values of patient satisfaction regarding appearance, phonetics, mastication, removal, and comfort showed no statistical difference between the two groups at insertion and at 3, 6, and 12 months [Figure 3].
Figure 3: Stacked column of patient satisfaction and stability data in group I, group II.

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  Discussion Top

Completely edentulous patients represent a challenge for prosthodontists to offer them a satisfactory and retentive prosthesis. The implant-retained overdenture for the mandible has been shown to be a highly successful prosthetic treatment because of its relative simplicity, minimal invasiveness and economy and improve retention, stability, better function, and overall satisfaction for the patients [16]. A meta-analysis showed that single implant supported overdenture is an alternative treatment option for edentulous mandible which has a comparable result regarding patient satisfaction and implant survival rate than the two-implant supported overdenture treatment. In addition, it can save the cost and the time of the treatment [17].

The implants were immediately loaded in this study because it was reported that immediate loading of implants in anterior mandible shorten the treatment time and show comparable clinical success with the delay loading approach [18], since the high degree of primary stability at implant insertion is considered to be a key prerequisite for obtaining a successful osteo integration as shown in a systematic review [19]. Osstell ISQ device was used in this study as it is highly reliable, easy utilized, and measurements are repeatable and reproducible, and noninvasive technique [20].

Primitive methods such as percussion and mobility testing by application of lateral forces with mirror handles have been used to determine primary stability. More recent methods have involved measuring cutting torque resistance and insertion torque values, both of which lack repeatability. Reverse torque test is invasive and destructive, hence impractical in a clinical setting. Other techniques such as the Periotest and dental fine tester were primarily developed for use on natural teeth and are subjected to several variables, and hence questionable for accuracy and reliability [21].

Readings were taken immediately before prosthesis placement to measure the initial stability of the implants, then at 3, 6, and 12 months, so that any change in the implant's stability can be attributed to the attachment design being utilized [6].

The results of this study revealed an increase in the ISQ value of both groups at the end of the follow-up period. This agrees with Karakoca-Nemli et al. [22] in which the ISQ value of a stable osseointegrated implants increases with time, which indicate an increase in the bone-implant contact area. The increase in ISQ can be attributed to the nature of bone, in which bone remodeling whether it is bone deposition or bone resorption, is induced by bone stimulations. According to Koyama et al. [23] when functional loading has been initiated, the bony structures adapt to the load by improving the quality of the bone and replacing preexisting and necrotic woven bone with mature viable lamellar bone. Frost [24] reported that if implant loading does not exceed physiologic threshold of bone adaptation, the bone quality increases. This shows that the load induced by the bollard coping and the locator is within the physiologic threshold of bone.

When the two groups compared together during the same period, numerically implant stability was higher in bollard group than locator group but this difference was statistically nonsignificant, this is due to the resiliency of both attachments. However, the bollard attachment gave higher values because of the silicon used for retention. Which gave higher resiliency, better stress distribution, and acted as a shock absorber. So, the physiologic occlusal force on the implant and bone lead to bone remodeling and increase the quantity of bone surrounding the implant and thus increase in implant stability. This was supported by Federick and Caputo [25] in which the resilient attachment provides the most equitable stimulated occlusal forces to the implants. Krennmair et al. [26] found that resilient and nonsplinted attachments had no deteriorating effect on implant survival rate and peri-implant condition.

The results of this study showed higher values of patient satisfaction with the bollard attachment group with no statistically significant difference with the locator group. This may be explained that the locator system shows higher maintenance frequency due to nylon's high rate of deformation and damage [27]. These results are similar to Akca et al. [28] who indicated that the main concern about the locator attachment when compared to other retentive systems is its need for replacement in a reduced time-frame.

  Conclusion Top

There was an increase in the ISQ values for both groups during the follow-up period, however, the new attachment Bollard increased implant stability more than the conventional locator attachment during the same follow-up period but statistically the difference was non-significant.

There were higher values of patient satisfaction with patients treated by the new attachment Bollard group than the conventional locator group but statistically the difference was nonsignificant.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2]


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