Dental Medium rearview: Structural and torque changes in implant components of different diameters subjected to mechanical fatigue

Structural and torque changes in implant components of different diameters subjected to mechanical fatigue
Get rights and content




To evaluate torque maintenance and structural damage in implant components of different diameters subjected to a fatigue challenge.


Thirty 10-mm-long, morse taper connection, titanium dental implants and their corresponding one-piece abutments were divided into three groups (n = 10) according to implant diameter: 4.3 mm (I4.3), 3.5 mm (I3.5), and 2.9 mm (I2.9). The implants were placed into a load-bearing fixture simulating bone tissue (modified G10), and the abutments were screwed into the implants to a final torque of 20 Ncm for the I4.3 and I3.5 and 15 Ncm for I2.9. The torque was secured by a digital torque meter. Cone-beam computed tomography (CBCT) scans were acquired and post-processed (e-Vol DX software) for all implant/abutment sets before and after subjecting them to fatigue in 37 °C distilled water (2 million cycles, constant load and frequency). The removal torque was measured using the same digital torque meter to calculate the difference in torque before and after fatigue.


I2.9 showed substantial structural deformation compared with the other implant diameters (I3.5 and I4.3). However, the experimental groups did not show statistical differences for abutment loosening.


Implants smaller than 3.5 mm in diameter have a higher probability of structural deformation than standard-diameter implants. The association between tomographic scans and e-Vol DX software showed satisfactory consistency with the direct assessment using the digital torque meter, offering an additional tool to evaluate implant component loosening and structural deformations.



Narrow-diameter implants (NDIs) are recommended in cases of limited available three-dimensional bone to adequately place standard-diameter implants (SDIs), mainly in lower incisors and upper lateral incisor areas. NDIs seem to be an alternative to avoid additional surgery procedures, such as bone grafting, showing faster case resolution and lower costs for the patient [1], [2], [3].

Compared to SDI treatments, patients treated with NDIs may experience some complications, mainly in the components, such as loosening the screw or the solid abutment (one-piece abutment) and fracturing the component or the retaining screw [4], [5]. These complications corroborate the ISO standard [6], which defines failure as material yielding, permanent deformation, loosening of the implant assembly, or fracture of any implant component.

Implants with a diameter of ≤ 3.75 mm were classified as NDIs [7], showing promising results in short-term survival rates compared to SDIs [8], [9], [10], [11], [12]. Yet, complications involving NDIs have been associated with reduced resistance [13], [14], mainly involving components with smaller dimensions [5], [15], and component fracture has been reported as the primary failure cause for NDIs with abutments screws [16]. Besides the increased fracture risk due to the smaller diameter, NDIs can compromise rehabilitation because of bone overload [5].

Studies [17], [18], [19], [20] have used cyclic fatigue as the method of choice to simulate the clinical challenge. However, fatigue parameters are significantly diverse. Quek et al., 2005 [15] used 5 × 106 cycles, a 2–15 Hz frequency range, and the ISO-standard [6] recommended load. Other studies used 5 × 105 [18], [20], [21] and 106 (1000,000) cycles [16], but load and frequency are recurrent variations in the studies.

Cone-beam computed tomography (CBCT) scans are widely used in dental practice, including implant dentistry [22]. Yet, high-density metal structures affect the contrast of CBCT scans, resulting in artifacts that lead to diagnostic errors and incorrect CBCT scan interpretations [23], [24]. Nevertheless, new dedicated dental software using algorithms to process the acquired scans reduces or even eliminates the harmful effects of metal structures during CBCT image processing [25], [26]. The e-Vol DX software (CDT Software, São José dos Campos, SP, Brazil) allows the visualization of complex anatomical structures with reduced artifacts, importing and manipulating DICOM files and standardizing images to analyze volumes acquired from different sources [27], [28]. Therefore, CBCT scans can be a viable alternative to assist in implant dentistry diagnosis.

Therefore, considering the relevance of torque changes and structural damage of implant components subjected to a fatigue challenge and the use of new dedicated imaging resources, the present study evaluated the following hypotheses: (1) NDI-abutment sets (2.9 mm and 3.5 mm in diameter) present greater torque and structure changes than the SDI-abutment set (4.3 mm in diameter) after fatigue; and (2) the algorithm used in e-Vol DX software for CBCT scans can assess implant component displacement, producing a similar and comparable response to using the digital torque meter.


Section snippets

Materials and methods

Thirty 10-mm-long, morse taper connection, titanium dental implants (Ti-6Al-4 V) (Unitite, SIN – Sistema de Implante, São Paulo, Brazil) and their corresponding abutments (Micro-Mini Straight Abutment, SIN – Sistema de Implante, São Paulo, Brazil) were divided into three groups (n = 10) according to the implant diameters: 2.9 mm (I2.9), 3.5 mm (I3.5), and 4.3 mm (I4.3).

The support blocks (Fig. 1) for simulating the supporting bone tissue consisted of two materials with different elastic moduli: 


Table 1 presents the initial and final (post-fatigue) torque values and the measurements between the BS and LW (before and after fatigue). Data for the difference in torque between groups failed in the normality test (Shapiro-Wilk), therefore, Kruskal-Wallis one-way ANOVA was used to analyze the data, which showed no statistical difference among the experimental groups (p = 0.6). Based on torque results (Table 1, Tf - Ti), and considering that component loosening was defined as ≥ 20% Ti


Narrow-diameter implants have been increasingly relevant in clinical practice to reduce patient exposure to bone grafting procedures. The present study partially confirms the first hypothesis that narrow-diameter implants (NDI: I2.9 and I3.5) [7] exhibit greater torque and structural changes than the control group of standard-diameter implants (SDI: I4.3) when subjected to fatigue. Relevant structural alterations (fracture and bending) occurred in 70% of the I2.9 specimens, but the I3.5 samples 


This study concluded that morse taper implants with a diameter smaller than 3.5 mm have a higher probability of failure and structural deformation than implants with larger diameters. In addition, using CBCT scans associated with e-Vol DX software to evaluate potential misfits between implants and their components was consistent with traditional torque assessment (digital torque meter) in vitro.


The authors would like to thank Capes do Brasil (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Finance Code 001) and SIN - Sistema de Implante, São Paulo, Brazil for partially supporting this study.


References (42)