# Retentive Behavior of Locator versus Ball Attachments on Parallel versus Non-Parallel Implants
## 2 Materials and Methods  
Two bone level implants each (BLT Bone Level Tapered 4.1 \(\times\) 12 mm RC, Straumann, Basel, Switzerland) were embedded in polyurethane resin (SikaBiresin, Sika, Bad Urach, Germany) to resemble a two-implant mandibular interformanil patient situation with either parallel orientation or 12\({}^{\circ}\) divergence (Figure 1). Either locators (ZEST Dental Solutions, Carlsbad, CA--group locator) or ball attachments (CLIX, Hader Solutions and Distribution, Swords, Ireland--group Clix) with 3 mm gingiva height could be attached to the implants with a torque of 35 Ncm according to the implant manufacturer's protocol.  
After positioning female attachment components for locator and ball attachments, respectively, a counterpart (simulated prosthesis) was fabricated using the same polyurethane resin (SikaBiresin; Figure 2a) and a bar-shaped mold made from silicone impression material (Optosil, Kulzer GmbH, Hanau, Germany) and resembling a bar-like structure. Each assembly was positioned in a custom-made high-precision jig (Bacherlschmiede, Wallmunchen, Germany), allowing for well-controlled vertical movement (Figure 2b), which could then be mounted on a universal testing machine (Z020, Zwick/Roell, Ulm, Germany). The assemblies were separated three times by controlled vertical force application at a crosshead speed of 2 mm/s [5; 6; 7; 10]. After three separation cycles, the female retentive plastic parts were changed, and a total of five repetitions were carried out.  
Figure 1: Model situation with either two parallel implants (**a**) or with the left implant angled at approximately 12\({}^{\circ}\) (**b**).  
For the locator abutments (Figure 3a), the female parts could only be positioned in alignment with the male part, while in the Clix group, the female parts could be aligned with the male part (Figure 3b) but also be aligned in such a way that a common path of insertion was achieved (Figure 3c). For locator abutments, female inserts with 0.7 kg (blue, extra light), 1.4 kg (pink, light) and 2.3 kg (white, regular) retention force were used. For Clix abutments, female plastic inserts with 8 N (white) and 12 N (yellow) retention force were used.  
In the second part of the study, the retentive surfaces of the locator and ball abutments were determined by surface scanning [17] using a manual video machine (Sylvac Visio 300, Sylvac SA, Yverdon-les-Bains, Switzerland). The resulting 3D models were then imported into CAD software (SolidWorks 2022, Dassault Systemes, Velizy-Villacoublay, France). The CAD software allowed for directly measuring the total surface area of the male components as well as the surface parts used for retention by applying the software's weight properties calculation tool.  
Statistical analysis (R version 4.3.2, The R Foundation for Statistical Computing, Vienna, Austria; www.R-project.org) was based on Shapiro-Wilk tests, Levene tests, analyses  
Figure 3: Two female locator components positioned on the model with angulated implants (**a**). Two female components attached in line with the implants and ball abutments (**b**). Female ball attachment parts aligned for achieving a common path of insertion (**c**).  
Figure 2: Antagonist structure (simulated prosthesis) with two female locator attachment parts (**a**) and the assembly positioned in a universal testing machine for simulating prosthesis removal (**b**).  
of variance (ANOVA), [PERSON]'s Honest Significant Difference tests and Welch _t_-tests with the level of significance set at \(p\) < 0.05.