The Effect of Repeated Torque in Small Diameter Implants with Machined and Premachined Abutments

Abstract

Background: Detorquing value is an important factor in the amount of preload stresses during abutment screw fastening. This study evaluated the percentage of detorque values in two‐piece machined titanium and premachined cast abutments in small diameter implants. Materials and Methods: Three groups of five samples were evaluated. Group 1 (G1), machined titanium abutments, group 2 (G2), premachined cast straight abutments that cast with gold‐palladium, and group 3 (G3), premachined angled cast abutments that cast with the same alloy, were angled before casting. Each abutment was torque to 24 Ncm according to the manufacturer's instructions and detorqued five times. The means of detorquing and torquing values in all groups were recorded. The mean of detorque in each group as a percentage of the toque value was calculated. The data for all groups were compared and calculated using analysis of variance (ANOVA) and t‐test. Results: Mean detorque values in G1, G2, and G3 were 88.1 ± 1.69, 93.1 ± 2.68, and 80.9 ± 4.95%, respectively. The ANOVA showed significant differences in mean of applied detorque (p < .001) and torque (p = .06) tightening among different groups. G2 had significantly greater detorque values (p < .05). No significant differences were found between G1 and G2. Surprisingly, abutment screw fracture occurred in three samples of G3. Conclusions: G3 showed significant percentage torque reduction (p < .05) and exhibited abutment screw fracture during evaluation. G2 presented the lowest torque reduction. Screw fracture occurred only in G3.

Influence of Abutment Type and Esthetic Veneering on Preload Maintenance of Abutment Screw of Implant‐Supported Crowns

“…According to the SEM images (Fig ), the abutments cast in gold alloy (groups GC and GR) exhibited less expressive irregularities than the titanium abutments (groups TiC and TiR). The irregularities between the mating surfaces may have caused preload loss to fit the components, which resulted in reduced detorque value, as also demonstrated by Burguete et al…”

“…According to the SEM images (Fig 2), the abutments cast in gold alloy (groups GC and GR) exhibited less expressive irregularities than the titanium abutments (groups TiC and TiR). The irregularities between the mating surfaces may have caused preload loss 9,13 to fit the components, which resulted in reduced detorque value, as also demonstrated by Burguete et al 8 According to Koke et al 24 this characteristic is inherent to the machining process, since castable abutments are required for titanium casting, which may increase misfit. 22,28 The same results were observed by Byrne et al 14 and Kano et al 11 who demonstrated better fit and higher torque maintenance for machined abutments than for castable abutments.…”

“…The screw can be compared with a spring stretched and kept between the threads by friction. Any external force that may cause slippage between the threads decreases the tension generated in the screw, named preload . At the first stage, the higher the preload, the higher the resistance to loosening .…”

“…Any external force that may cause slippage between the threads decreases the tension generated in the screw, named preload. 8,9 At the first stage, the higher the preload, the higher the resistance to loosening. 10,11 At the second stage, a preload below a critical level means any external force or vibration may lead to complete loosening.…”

Original vs. non‐original abutments for screw‐retained single implant crowns: An in vitro evaluation of internal fit, mechanical behaviour and screw loosening

“…However, the preload should not be too large and should be within the elastic limit to prevent the screw from yielding or breaking. Previous studies have demonstrated that the ideal preload is 60%–75% of the elastic limit of the material used for fabrication of the abutment screw (Kim et al., ; Saboury, Neshandar Asli & Vaziri, ; Sella et al., ). The effect of retightening after applying the initial tightening torque has been evaluated as a method to increase joint stability (Siamos, Winkler & Boberick, ).…”