{'fraction_non_alphanumeric': 0.03036458890195659, 'fraction_numerical': 0.017320645782102, 'mean_word_length': 5.129750982961992, 'pattern_counts': {'":': 0, '<': 2, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
A comparative biomechanical study of original and compatible titanium bases: evaluation of screw loosening and 3D-crown displacement following cyclic loading analysis

PURPOSE This study evaluated screw loosening and 3D crown displacement after cyclic loading of implant-supported incisor crowns cemented with original titanium bases or with three compatible, nonoriginal components. MATERIALS AND METHODS A total of 32 dental implants were divided into four groups (n = 8 each): Group 1 used original titanium bases, while Groups 2-4 used compatible components. The reverse torque value (RTV) was evaluated prior to and after cyclic loading (1,200,000 cycles). Samples (prior to and after cyclic loading) were scanned with a microcomputed tomography (micro-CT). Preload and postload files were superimposed by 3D inspection software, and 3D crown displacement analysis was performed using root-mean-square (RMS) values. All datasets were analyzed using one-way ANOVA and Tukey’s post hoc analysis. RESULTS Significant variations were observed in the postload RTV, depending on the titanium base brand (P < .001). The mean postload RTVs were significantly higher in Groups 1 and 2 than in the other study groups. While evaluating 3D crown displacement, the lowest mean RMS value was shown in the original Group 1, with the highest RMS value occurring in Group 4. CONCLUSION Within the limitations of this in vitro study and under the implemented conditions, it was concluded that the manufacturer brand of the titanium base significantly influenced screw loosening following the fatigue test and influenced 3D crown displacement after cyclic loading.


INTRODUCTION
The connection between a dental implant and a titanium base is a clamped joint. The stability of this joint depends on multiple factors, including the ma-chining accuracy/tolerance profile, component uniformity, material properties, abutment screw type, and implant-abutment connection type. [1][2][3][4] Components produced by different manufacturers are made with different machining microtolerances, resulting in design/dimensional accuracy discrepancies. 5 Misfit can be defined as a 3D gap between a titanium base and an implant 6,7 and can lead to micromotion, 8 causing wear of the mating surfaces 9 and screw loosening. 1,4,10 Thus, an indicator of implant-abutment connection stability is maintenance of the reverse torque value (RTV) during cyclic loading. 11 Several studies have investigated abutment axial displacement following cyclic loading 12 and 3D-crown displacement following screw tightening. 13 However, no previous study has investigated the influence of oblique (30°) cyclic loading on 3D anterior crown displacement when cemented with different brands of titanium bases. Thus, it was hypothesized that embedment and wearing of mating surfaces lead to abutment together with crown 3D displacement during cyclic loading.
Titanium bases are versatile prosthetic components for implants. 14 From one perspective, different material (zirconia, lithium disilicate, porcelain fused to metal) single-or multi-unit restorations can be cemented with bases. Conversely, a reliable connection with implants can be achieved. 15 The use of nonoriginal prosthesis components in dental implants has become popular for economic reasons.
This study aimed to compare biomechanical properties of original and compatible titanium bases. The initial study objective was to compare the postload RTV for varying titanium base groups. The secondary objective was to compare 3D-central incisor shaped crown displacement following cyclic loading of varying titanium base groups.
The first null hypothesis was that no differences would be identified in the postload RTV of various titanium base groups. The second null hypothesis was that no differences would be found in 3D crown displacement among different titanium base groups.

MATERIALS AND METHODS
A total of 32 internal-conical connection, with six indexing slots and commercially pure grade 2 titani-um implants (3.5 × 11 mm Ankylos® C/X (Dentsply® Implants Manufacturing GmbH, Hanau, Germany)), were divided into four groups (n = 8 each) according to the manufacturer of the titanium base: (1) Ankylos® titanium base/X (Dentsply® Implants Manufacturing GmbH, Hanau, Germany); (2) Arum® titanium base with a regular pilar (Doowonid Co., Ltd., Daejeon, Korea); (3) IPD titanium base with a 1 mm gingival height Prior to the experiment, each implant/titanium base/crown complex was scanned using an X-ray microtomography SkyScan 1275 (Bruker MicroCT, Kontich, Belgium) to create a baseline. Scanning parameters were standardized at a tube voltage of 80 kV with a tube current of 125 μA using an aluminum filter.
Each sample was scanned at a total angle of 180° and five frames/0.2° rotation. After postcyclic loading, micro-CT micrographs were reobtained for each sample.
All images were collected as a 3D model and exported into an STL file.
To smooth the 3D models, the Mesh Doctor command was used (Geomagic Wrap®; 3D Systems, Rock Hill, SC, USA). All 3D analyses were performed with the 3D inspection software Geomagic® Control X™ (3D Systems, Rock Hill, SC, USA). The preload STL file was used as a reference dataset. The implant was split from the entire surface and used for best-fit alignment as a reference body (Fig. 2). To ensure that 3D crown displacement was measured equivalently between groups, each crown was cropped precisely above the titanium base. During 3D analysis, distances between surfaces of the preload and postload crowns were calculated as the RMS values for quantitative evaluation of the overall crown displacement. 13 The RMS value was calculated using the following equation: where X 1, i is the measuring point i on the reference data, X 2, i is the measuring point i on the postload data, and n is the total number of measuring points per specimen. The RMS value demonstrates congru-

RESULTS
In the present study, all samples survived 1,200,000 loading cycles. Table 1 shows the means, standard deviations, and percentages of initial and postload RTV. ANOVA results demonstrated that there was a significant variation among the initial and postload RTV means for the titanium base groups (P < .001).
All RTVs were lower than the insertion torque, both prior to and after mechanical cycling. The smallest decrease in initial RTV was observed in Group 2. The smallest decrease in postload RTV mean was also observed in Group 2, while the most marked decrease

DISCUSSION
The null hypothesis that no significant difference would be found in postload RTV between original and three generic titanium bases following dynamic loading was rejected. The null hypothesis that no significant differences would be found in 3D crown displacements following dynamic loading among different titanium base manufacturer brands was also rejected.
This study showed that the Group 1 (original) and Group 2 titanium bases exhibited lower postload RTV loss than Groups 3 and 4. In previous work, several authors found that original abutments presented lower values for screw loosening than non-originals. 1,11,17 In addition, previous studies also found significant variations in the mean micro gap at the implant/abutment interface, 18,19 leakage, 20,21 and rotational misfit 2 between the original and other manufacturer brand abutment groups.
The loading scenario was 30° to the implant long axis. Due to nonaxial loading, the upper and lower titanium base connection parts acted as a lever. 22 Loss of RTV and crown/titanium base displacement can be explained by embedment relaxation ('settling' effect) 23  This study, however, contains several limitations.
A higher GH of the titanium base may increase loading on the implant/titanium base joint due to a higher vertical cantilever. In our study, the lowest GH was J Adv Prosthodont 2022;14:70-7 A comparative biomechanical study of original and compatible titanium bases: evaluation of screw loosening and 3D-crown displacement following cyclic loading analysis The Journal of Advanced Prosthodontics 0.7 mm, and the highest was 1.3 mm. However, we assume that the effect of GH was minimal because in another study, a significant difference in postload RTV was found only between GHs of 1.5 and 5.5 mm across abutment groups after 50,000 75 N loading cycles. 31 Another limitation of this study is that the predominant factors (i.e., screw properties, titanium base surface properties, design, machining tolerance) that caused screw loosening and crown displacement in each group were not clarified. Clinical research is required to evaluate RTV and any displacements in vivo. Because this study was conducted with a specific implant manufacturer in vitro, the results may not provide generalized conclusions that apply to other manufacturers' implants and titanium bases. However, periodic retightening of the titanium base screw should be used as a routine procedure in dental practice.

CONCLUSION
Within the limitations of this in vitro study, it can be concluded that the manufacturer brand of the titanium base significantly influenced screw loosening and 3D crown displacement following fatigue testing. According to the results, the selection of the titanium base manufacturer is important for long-term stability of implant/titanium base/crown complex.