The aim of this study was to evaluate the self-aligning overdenture attachment system by comparing its oral health–related quality of life (OHRQL) with a traditionally used ball attachment system. In this randomized, within-subject crossover trial, 25 edentulous subjects each received 2 mandibular implants, and were then assigned to receive either self-aligning or traditional ball attachments. After 3 months, all subjects were switched to the second attachment type. The OHRQL was evaluated for both of the treatments using the short form of the Oral Health Impact Profile (OHIP-14). A subanalysis among subjects with below-average space available for attachment placement was also performed. Wilcoxon signed-rank test was used to compare differences between groups. Scores on the OHIP-14 physical disability domain were significantly better for the self-aligning attachment system (P = .049). Among subjects with below-average attachment space, functional limitation, psychological discomfort, physical disability, psychological disability, and total OHIP-14, scores were significantly better for the self-aligning attachment system (P = .041, P = .047, P = .048, P = .026, and P = .005, respectively). The self-aligning attachment system for 2-implant–retained mandibular overdentures is equal or superior to traditional ball attachments in all domains of the OHIP-14.
Edentulous patients frequently experience problems with conventional mandibular dentures. Endosseous implants have been shown to be a valuable rehabilitation for these patients.1 Moreover, the McGill Consensus Statement on overdentures recommends that an overdenture retained by 2 implants is the treatment of choice for the edentulous mandible.2 Therefore, the impact of implant-retained overdentures on patient satisfaction and quality of life are essential outcomes requiring further investigation.3–9
A wide variety of commercially available attachment systems are used to connect implants to mandibular overdentures, either by splinting or unsplinting the implants. The anatomic situation of the mandible, desired level of retention, hygiene maintenance capability, parallelism of the implants, and cost considerations are important factors in choosing the appropriate overdenture attachment type.10,11
For unsplinted implants, the most common attachment used is the ball attachment.12 This attachment system is a practical, effective, and relatively low-cost prosthetic concept.12,13 Recently, a self-aligning overdenture attachment system that maintains a vertical and hinge resiliency has been introduced for unsplinted implants. It is a useful alternative when the interarch distance or the height of the denture is inadequate for processing traditional ball attachments.11,14
Previous studies have shown that mandibular overdentures retained by 2 implants provide significant enhancement in stability, retention, patient satisfaction, and quality of life over complete dentures.3–8,12,15–20 However, no significant difference in patient satisfaction has been reported for various attachment types,20–23 except for a few studies of magnetic attachments.24,25 Also, there is a lack of studies evaluating self-aligning attachment in terms of oral health–related quality of life (OHRQL). The purpose of this study was to compare the effect of the recently introduced self-aligning attachment system with the traditional ball attachment system on OHRQL. The null hypothesis was that there would be no differences between the 2 types of attachment systems in patients with adequate space for traditional attachment placement, and that the self-aligning attachment system would give better results in cases of reduced space for attachment placement.
Materials and Methods
A randomized, within-subject crossover trial was conducted at the Istanbul University Department of Removable Prosthodontics. Thirty edentulous patients seeking implant-retained mandibular overdentures during a 6-month period were invited to participate in this clinical trial. Inclusion criteria were the ability to read and sign the informed consent document and sufficient bone height (as determined by panoramic radiography) for the placement of 4.5 mm wide and 13 mm long dental implants in the interforaminal region of the mandible. Exclusion criteria included any systemic disease that was likely to compromise implant surgery.26 The study was approved by the university institutional review board. Twenty-seven edentulous patients between the ages of 44 and 74 years fulfilled the inclusion criteria and were enrolled after providing informed consent.
All edentulous subjects received two 4.5 × 13 mm endosseous dental implants (Osseospeed, Astra Tech AB, Mölndal, Sweden) in the interforaminal region; the same oral surgeon performed the implant surgery according to the guidelines of the manufacturer.27 After 1 week of healing, sutures were removed and prosthodontic procedures were performed by the same prosthodontist.
Conventional maxillary and mandibular dentures were fabricated using a conventional prosthetic method that included balanced articulation with anatomically shaped acrylic resin teeth (Enigma, Davis Schottlander & Davis, Tonawanda, NY) and maximum extension of the denture base using functional impression methods.28 The dentures were inserted 4 weeks after surgery, taking care to avoid any contact of the mandibular dentures with the implants. After 2 weeks of function, healing abutments (Zebra Healing Abutments, Astra Tech AB) were unscrewed and gingival heights were measured using a depth gauge (Astra Tech AB) (Figure 1). Two subjects were excluded from the study because self-aligning abutments for their gingival heights were not available. The final 25 edentulous subjects (16 men, 9 women; mean age = 57.3 years), which corresponded to a power of 0.80 (P = .05), were randomly assigned to 2 groups using a lottery method. Self-aligning abutments (Locator, Astra Tech AB) were screwed into the implants in 13 subjects and were connected to the dentures by matching self-aligning attachments using a chair-side processing method.14 The remaining 12 subjects received ball abutments (Ball Abutments, Astra Tech AB), and matching ball attachments were used to connect the implants to the denture using a previously described direct-processing technique.29 After 3 months of function, the attachment types and abutments (Figure 2) were changed to the other system in all subjects. Because the same denture bases were used, analogous occlusion, denture-base extension, and occlusal vertical dimension were maintained. Following the early loading protocol used in previously studies, the implants in both groups were connected to the mandibular overdentures 6 weeks after surgery.30–32
To determine the available space for attachment placement, the distance from the tip of the 2 central incisors to the corresponding intaglio surface of the mandibular dentures was measured using a gauge (Alma gauge, Davis Schottlander & Davis) (Figure 3) before attachment connection.
The short-version Oral Health Impact Profile (OHIP-14) was used to compare the effect of attachment systems on subjects' quality of life. The OHIP is a disease-specific measure of an individual's perception of the social impact of oral disorders on his or her well-being. Its validity and reliability have previously been established.3,33 The full-length OHIP consists of 49 questions covering 7 domains: functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability, and handicap.33 The OHIP-14, a shorter and patient-friendly version, consists of 14 questions in the same domains.34 Responses for each item are on a 5-point Likert scale (0 = “never” to 4 = “very often”). Lower scores represent higher OHRQL. All subjects completed the OHIP-14 after functioning for 3 months with each attachment type. A Turkish version of OHIP-14 that had previously been determined to be valid and reliable was used in this study.35
The statistical analysis was performed using statistical software (NCSS 2007 and PASS 2008, NCSS, Kaysville, Utah). In a paired analysis, each subject's OHIP-14 responses for the self-aligning attachments were compared with the subject's responses for the ball attachments using a Wilcoxon signed-rank test. Internal consistency was assessed using Cronbach's reliability coefficient α among all 14 items.
No significant difference was observed in total OHIP-14 scores between the two attachment systems (Table 1). Comparison of subdomains of the OHIP-14 showed that scores on the physical disability domain were significantly better for the self-aligning attachment system than the ball attachment system (P = .049). No significant difference was observed in the other OHIP-14 domains.
The average value obtained from the Alma gauge was 11.08 mm. Among the 13 subjects with below-average attachment space, functional limitation, psychological discomfort, physical disability, psychological disability, and total OHIP-14 scores were significantly better for the self-aligning attachment system (P = .041, P = .047, P = .048, P = .026, and P = .005, respectively) (Table 2). Among the 12 subjects with above-average attachment space, no significant difference between the 2 attachment systems was observed (P > .05). Internal consistency for the 14 questions using Cronbach's α was established as 0.835, meaning that the reliability of the Turkish version of OHIP-14 was high.
The null hypothesis that there would be no differences between the 2 types of attachment systems in patients with adequate space for traditional attachment placement and that the self-aligning attachment system would give better results in cases of reduced space for attachment placement was accepted. In subjects with below-average attachment space, the self-aligning attachments had significantly better total OHIP-14 scores than ball attachments, while the physical disability domain was significantly better for self-aligning attachment in all subjects, indicating more comfortable use from self-aligning abutments. The OHIP-14 physical-disability domain contains questions about interruption of meals and poor diet due to the overdenture's retention and stability. Anecdotally, subjects reported higher satisfaction with the retention and stability of self-aligning abutments, giving them more confidence. Studies specifically comparing the retention and stability of these 2 attachment types should be done to confirm this result.
In cases of insufficient vertical space in the lower overdentures, the overdentures had to be overcontoured, which may have restricted tongue space after embedding the ball attachments. This might explain the worse OHIP-14 scores for ball attachments. Anecdotally, 3 subjects with below-average attachment space who first received self-aligning attachments reported dissatisfaction when switched to ball attachments and wanted the self-aligning attachments back. However, no subject reported dissatisfaction with the self-aligning attachments.
The self-aligning attachment system arose out of a need for a shorter abutment in conditions with minimal vertical dimension or interocclusal space, where embedding of the matrix of a ball attachment or the bar retainer is not possible.11,14 The current study demonstrates improved quality of life with the self-aligning attachment system in subjects with low interocclusal space. One disadvantage of the current self-aligning attachment system is that it cannot accommodate as wide a range of gingival heights as the traditional ball attachment system. This is why 2 subjects were excluded from this study.
This study has 2 major limitations. First, a validated Turkish version of the OHIP-EDENT was not available at the time of the study, and therefore the Turkish OHIP-14 had to be used for assessing the OHRQL. The OHIP-EDENT is a modified shortened version of the OHIP that has been shown to be more reliable than the OHIP-14 for edentulous patients.9 Second, when the study group was subdivided based on attachment space, the power of the analysis dropped to 0.43, making interpretation of these results difficult. However, the results from this study will be valuable for sample-size estimation in future trials to confirm these results.
Within the limitations of this study, it can be concluded that self-aligning attachments for mandibular overdentures retained by 2 attachments are comparable to ball attachments in OHRQL and may be superior in cases of reduced space for attachment placement. Larger studies are needed to confirm this latter result.