Influence of Denture Cleansers on the Retention Loss of Attachment Systems Retained Implant Overdenture

Background This study aimed to evaluate the effects of different denture cleansing solutions (DCSs) on the retention of Locator and Locator R-Tx attachment systems of implant retained overdentures (IRO). Methods Two part acrylic resin blocks were fabricated, upper part contained metal housing and plastic inserts and lower part contained implant analogs and abutments. Eighty pink plastic inserts (40/attachment, 10/solution) were immersed in Corega, Fittydent, sodium hypochlorite, and water for a time simulating upto 1-year of clinical usage. Acrylic blocks were held on a universal testing machine for a pull-out test to record the dislodgement force. Measurements were conducted after 6 months (T1) and 12 months (T2). One-way ANOVA followed by Tukey's HSD test was used to analyze the results (α = 0.05). Results For both attachments, retention significantly decreased after immersion in different solutions at T2 (P < 0.001). Locator R-Tx attachment in NaOCl showed a significant decrease in retention compared with other solutions at T1. At T2, there was a significant decrease in retention for all DCS compared with water (P < 0.001). Locator R-TX showed higher retention values per solution compared to Locator attachment (P < 0.001). In terms of retention loss %, NaOCl recorded the highest (61.87%) loss, followed by Corega (55.54%) and Fittydent (43.13%), whereas water demonstrated the best retention (16.13%) in both groups. Conclusion Locator R-TX has better retention with different DCS immersion. The loss of retention varied with different types of DCS and NaOCl recorded the highest retention loss. Therefore, denture cleanser selection must be guided by the type of IRO attachment.


Introduction
Implant-retained overdentures (IROs) are an efective treatment option for edentulous patients [1]. IRO was developed to improve overdenture retention, stability, support, and chewing ability, as well as to preserve the surrounding bone and enhance patient satisfaction by utilizing various retentive attachment systems [2,3]. Attachment selection is guided by the amount of retention needed, jaw anatomy, complexity of the case, implant alignment, vertical and horizontal prosthetic space, and patient compliance for recall appointments in order to perform adequate maintenance [3].
Te most common attachment system in dental practice is the Locator ® attachment system (Zest Anchors, Inc., Escondido, CA), which is a stud-type attachment and was designed to make restorative treatment with implantsupported overdentures easier [4,5].
Compared with the ball and bar attachments, this system is relatively simple to fabricate and has shown clinically superior results in terms of postplacement prosthodontic complications and hygiene [6,7]. Furthermore, Locator attachments have resiliency that helps distribute loads more evenly between the supporting dental implants and denturebearing surfaces. Tese attachments have grown in popularity since their inception in 2001 owing to their ease of use and modest space requirements, as indicated by clinical reports of their use in situations where prosthesis space was restricted [6,7].
Locator attachments can be used to replace existing ball abutments, particularly in patients who experience rapid wear of ball abutment components [8]. Moreover, these attachments have a rotational pivoting design, with the male component providing a resilient connection to the denture without retention loss. Te full rotational movement of the denture cap over the male component enhances retention.
Other factors contributing to the popularity of Locator attachments include excellent retention, small device dimensions (especially height), and durability of the components [9,10].
Among all available stud systems, locators have the lowest profle, with a height of 2.5 mm [5,11]. A titanium nitride coated cylindrical abutment with internal and external undercuts makes up the Locator "female" matrix, while the "male" is composed of a metallic housing with interchangeable plastic patrices [12]. Te plastic inserts come in a variety of colors that correspond to diferent retention values. According to the manufacturer, a 10°variation between the direction of insertion of the plastic insert and the central axis of the matrix abutment is acceptable. As a result, these are advocated in cases where the interimplant angles range from 0°to 20°. When interimplant angles surpass 20°, an "extended-range" type of insert is recommended [12]. Te Locator attachment has a dual retention strategy that combines inner and outer frictional modes to produce three distinct retention strengths, depending on the color of the plastic insert [13]. Te overdenture seating of Locator attachment has a limited pivoting capability and wide coronal geometry [14].
Te Locator ® R-TX abutment system incorporates various enhancements over the original Locator abutment, in addition to a design that aids patient care. Tis innovative design allows for mobility in all axes, minimizing the amount of load placed on the implant and supporting bone [14]. According to the manufacturer, the Locator R-TX has an improved angle correction and pivot function, and is, therefore, recommended for implant angular discrepancies of upto 60°(maximum 30°per implant) [14,15]. Tis is a signifcant advancement over the previous Locator attachment system, which only allowed a 40°diversion between implants, when used with extended-range inserts.
In case of misaligned implants, the pivoting capacity of Locator R-TX system helps prevent damage to the retention inserts [14]. Locator R-Tx has internal hex abutment with an initiative hex pressure, presenting signifcantly less space for food/plaque accumulation and the absence of a principal stud inside the retention plastic inserts. However, there is no consensus regarding their long-term performance [14]. IRO demands rigorous hygienic care; adequate denture hygiene can help in the prevention as well as treatment of oral infections in edentulous patients [16]. Although brushing has been deemed insufcient for thorough denture cleaning, it remains one of the most prevalent methods of denture cleaning [17]. Furthermore, the ability of elderly patients to manually clean their dentures is often compromised [18]. Terefore, commercial denture cleansing solutions (DCSs) are often recommended for efective denture care [19,20]. However, denture cleansers can have adverse consequences on overdentures and might cause deterioration of the denture base material, bleaching of acrylic resin, corrosion of metal, and destruction of temporary and soft lining substances if used incorrectly [21][22][23][24].
A previous study reported that DCSs are efective in controlling Candida infection, plaque deposition, and staining of dentures [24]. DCS may have a negative impact on prosthetic components, leading to loss of retention [21]. Nguyen et al. studied the infuence of fve DCS on Locator attachment retention and found a signifcant reduction in retention with sodium hypochlorite (NaOCl) and Eferdent, while Listerine increased the retentive value [23]. Other materials such as sodium bicarbonate-sodium perborate tablets and gel containing sodium laureth sulfate increased the retention of attachments. However, there was no signifcant change in retention using sodium bicarbonate [19].
Only a few investigators have studied the efects of DCS on the retention of the Locator attachments in the past. Moreover, the efect of DCS on the newly introduced Locator R-TX has not yet been investigated. Te aim of this study was to evaluate the efects of diferent DCS on the retention of two commercially available attachment systems. Te null hypothesis of our study was that DCS does not afect the retention of Locator and Locator R-TX attachment systems.

Specimen Preparation.
Te sample size was calculated using the G * Power, version 3.0.10. (Franz Faul, Universitat Kiel, Germany) software. Using one-way ANOVA, a medium efect size of f � 0.4 (Cohen, J. 1988. Statistic power analysis in the behavioral sciences, Hillsdale, NJ: Erlbaum), 80% power, and at a 0.05 signifcance level (i.e., 95% confdence interval), the total required sample size of 10 specimens per group was needed to evaluate the efects of DCS on the retention of the Locator R-TX attachment in comparison with the Locator attachment system according to study design as shown in Figure 1. Figure 2 shows the rubber insert (a and b), metal housing (c and d), and two acrylic blocks (e). To examine the retention of the two systems, two acrylic blocks were prepared (one for each system). Each block was composed of two compartments. Upper compartment contained the metal housing, and lower compartment contained the implant analog of 3.7 mm diameter and abutments for each system (Zimmer Biomet, USA). Tese acrylic embedded implant analogs (one per attachment type) were immersed in three diferent DCS (Corega, Fittydent, and NaOCl; n � 10 for each subgroup) and tap water (control group) for varying time intervals to simulate 6 (T1) and 12 (T2) months of clinical usage (Table 1).
For preparing the acrylic blocks, a plastic mold (5 × 3.5 × 5 cm) with the requisite dimensions was produced, and molten wax was poured into it. Tereafter, a wax guide pin was used to position the implant analog in the middle of the wax block, perpendicular to the foor, with 3 mm of the implant analog visible above the wax surface using a dental surveyor. Te wax block with the implant analog was fasked and treated using the traditional water bath method. Te retrieved acrylic block was fnished and tested for implant analog position after polymerization. In order to ensure an accurate ft of the upper compartment into the lower compartment, a groove of 4 mm (L) × 4 mm (W) × 3 mm (D) was made on both sides of the implant as an index to meet an opposing elevation in the metal housing block. Te surface of the acrylic block was coated with Vaseline separating medium to create the acrylic component with the attachment. Molten wax was poured over the top of the acrylic block with the implant, using a plastic mold. Tis wax block was fasked and acrylized in the same manner as the preceding block.
Te Locator and Locator R-TX abutments were then ftted into their respective implant analogs, followed by the metal housing. Te metal housing was picked up by the upper block, which was attached with an autopolymerized acrylic resin. Te upper and lower pieces were separated after polymerization and verifed for a perfect ft, with no interference and positive ft indices.

Denture Cleanser Preparation and Immersion Protocol.
Te types and compositions of the denture cleansers used in this study are summarized in Table 1. Each attachment system was randomly separated into four groups based on the immersion solutions: Corega, Fittydent, NaOCl, and water as a control group (n � 10 each). According to the manufacturer's instructions, ten pink plastic inserts per denture cleanser solution were placed in perforated plastic bags and immersed in 125 ml of each cleanser, simulating 12 months of immersion (Table 1).

Study design and specimen grouping
Acrylic resin blocks containing Locator attachment (N=4) Acrylic resin blocks containing Locator R-TX attachment (N=4) Light retention plastic insert attachment (N=40) Light retention plastic insert attachment (N=40) Load-to-dislodgment force (N) was recorded at 6 months (T1) and 12 months (T2) of immersion simulation Figure 1: Flowchart of study design and specimen grouping.

Testing Procedures, Data Collection, and Statistical
Analysis. Te load-to-dislodgment force (N) was recorded at 6 months (T1) and 12 months (T2) of immersion simulation. A Locator Core Tool was used to remove the processing inserts. Tereafter, Locator patrices were carefully placed into the metallic housings in the upper mounting using a Locator Core Tool with medium retention (pink) plastic inserts for each Locator type. Te force experienced by the load cell during a single seating/unseating cycle was monitored to ensure proper attachment engagement. Te load-to-dislodgment force was measured using an Instron universal testing machine (INSTRON 5965 US) with a 50 mm/min crosshead speed and a preset repeating insertion-removal cycle (N). All testing procedures were conducted and monitored by a single technical operator who was an expert in operating the equipment. Finally, data were collected, tabulated, computed, and statistically analyzed.

Statistical Analysis.
Descriptive analyses were performed using means and standard deviations. Data were tested for normality using the Kolmogorov-Smirnov and Shapiro-Wilk tests. All values showed a parametric (i.e., normal) distribution. A paired t-test was performed to test for diferences between water, Corega, Fittydent, and NaOCl across the two time points T1 and T2 in the Locator and Locator R-TX groups. Student's t-test was used to test for diferences between Locator and Locator R-TX attachment groups at each time point separately (T1 and T2). ANOVA and Tukey's multiple comparison test were performed to test for diferences between water, Corega, Fittydent, and NaOCl in the two study groups at 6 months and 12 months. Statistical signifcance was set at P < 0.05. All statistical analyses were performed using SAS statistical software package, version 9.4 (SAS Institute Inc., Cary, NC, USA).

Results
Te means, standard deviations, and statistical signifcances of retention for the two types of Locator attachments for each DCS are summarized in Table 2 and Figure 3.  (Tables 3  and 4), Locator R-TX showed a signifcant decrease in retention in NaOCl compared to water, Corega, and Fittydent at T1, while there was no signifcant diference in retention of water vs. Corega and Corega vs. Fittydent at T2. Overall, there was a signifcant decrease in retention in all DCS compared to water (P < 0.001). No signifcant diferences of retention were observed between Corega and Fittydent or Corega and NaOCl. In term of retention, Fittydent recorded the lowest values (38.86%), followed by Corega (34.28%) and NaOCl (30.5%), and water showed the best retention among all groups (−3.39%).
Upon intergroup comparison between the Locators (Table 5 and Figure 4), water immersion at T1 showed no signifcant diferences between the two attachment groups (P � 0.266), while Locator R-TX showed signifcantly greater retention when compared with the Locator system for all solutions at both recall times (P < 0.001).

Discussion
IRO requires meticulous hygiene maintenance for improved lifespan and durability. Denture wearers are instructed to follow home care measures in order to maintain healthy oral mucosa. Te method of hygiene may afect the overdenture attachment and retention. Tis study tested the efect of diferent DCS on the retention of the Locator and Locator R-TX attachment systems after a simulated period of upto 1 year of clinical usage [25,26].
In this study, two types of attachments were evaluated using four types of DCS. Te efect of DCS on the Locator R-TX attachments of the IRO has not been investigated to date. Our results showed that when selecting a cleaning solution, it is important to consider which cleaning solution will result in the best long-term retention when used with a specifc attachment system. For removable dental prostheses wearers, diferent denture cleansers and cleaning methods were recommended to prevent microbial adhesion and subsequently prevent denture stomatitis occurrences [19,27]. Efervescent denture cleansers (Corega and Fittydent) are most commonly used due to their efcacy in decreasing C. albicans adhesion in addition to its ability in removing light stains and debris loosing from denture surfaces [19,20]. On the other hand, NaOCl is one of the most common used disinfectant solutions with its efectiveness in reducing C. albicans adhesion due to its fungicidal properties [19]. Due to the diferent compositions and immersion times of denture cleansers, the clinical use might afect the properties of denture base resin as well as attachment systems; therefore, these representative cleansing solutions were selected in the present study.
Te null hypothesis that DCS will not afect the retention of the attachment systems was rejected. After a simulated period of 12 months, a signifcant decrease was observed in the peak load-to-dislodgement force of both attachment systems. It was observed that the loss of retention values in Locator attachments immersed in NaOCl solution was much higher than that in the other cleansers at all time intervals, which is consistent with the fndings of multiple previous studies [22,23,28]. It was previously reported by Evtimovska et al. that cleaning IRO with NaOCl signifcantly decreased the retentive values of the Locator attachments International Journal of Biomaterials 5 [29]. According to Kürkcüoglu et al. [28], NaOCl altered the surface morphology of the plastic attachments, resulting in porosities and cracks. However, no signifcant diference was found in the efect of water and NaOCl on the retentive value of pink plastic inserts [28]. Furthermore, in our study, when all cleansing solutions were compared with water, Corega    Te data obtained from this study demonstrate that water afects the retention of Locator attachments, but has no impact of the retention of Locator R-TX attachments. Tis may be attributed to the diferences in design between the two attachments. Further studies are needed to confrm the direct relationship between the denture attachment design and retention [30]. Hypochlorite solutions have been shown to exhibit bactericidal and fungicidal efects on the organic constituents of the plaque matrix. Because of its bleaching and deteriorating efects on acrylic resins, NaOCl may be the most efective denture immersion solution with antifungal activities in the market [5,18]. However, the soaking time should not exceed 10 minutes [18]. Due to lack of literature on the Locator R-TX attachment, the results of the current study should be interpreted with caution until further investigations confrm our fndings.
It has been reported that patients with IRO remove their prostheses at an estimated speed of 50 mm/min; therefore, the same speed was selected for the pull-out test in the current study [2,23,28]. In addition, a one-pull test was performed based on the recommendations of previous studies [23,29,31], which revealed that a signifcant loss of retention occurs after the frst separation of attachments and abutments. Te simulation immersion times in our study were selected based on previous studies conducted to test the retention values of IRO [2,23,28].
According to the fndings of the present study, frequent replacement of attachments is crucial when using NaOCl as a cleansing agent. Since NaOCl was observed to gradually reduce the retention of Locator attachments, it should not be used as a regular denture cleanser. Tis is the primitive study on R-TX so the results should be explained with cautions to implement clinically. Due to the variations between efects of denture cleanses with time (long-term use), the type of cleanser is considered regardless the attachment type. Additionally, the resin surface properties must considered as the denture cleansers afected the resin surface properties and has adverse efects on the color and esthetics [32]. Tis is considered a point for further studies with long durations and diferent denture cleansers. When more fndings are reported in future studies, this will be more benefcial in  International Journal of Biomaterials usage of rubber insert for long time with appropriate amount of retentions and decrease the need for periodic rubber inserts replacement. Tis in vitro study had some limitations. First, the plastic inserts were immersed in the cleansers for a maximum of 12 months simulation period, although longer immersion times might result in more changes. Second, the attachments were not tested in a realistic oral environment or with natural occlusal forces. Tis may have concealed certain efects of the denture cleansers on the attachments. Terefore, further in vivo studies are recommended to evaluate the clinical retention loss diferent attachment systems after using diferent denture cleansers.

Conclusions
Within the limitations of present study, the following conclusion could be drawn: (1) Te retention of the Locator as well as Locator R-TX attachment systems decreased with immersion in all types of DCS. (2) R-TX attachments showed higher retention values compared to the Locator attachments with all types of DCS. (3) Te lowest retention values for both attachments were recorded after immersion in NaOCl. (4) Due to the varying efects of DCS on the diferent attachment systems, the selection of denture cleanser should be based on the clinician's recommendation. In addition, periodic replacement of that the plastic inserts is recommended to improve long-term denture retention.

Data Availability
Te data used to support the fndings of this study are available from the corresponding author upon request.

Conflicts of Interest
Te authors declare that they have no conficts of interest.