Differential effects of abutment contamination within an internal hexagonal connection on preload formation and...

The purpose of this in vitro study was to quantitatively evaluate the effect of surface contamination within an internal hexagonal implant-abutment connection on preload formation and preload loss under cyclic loading conditions.

Internal hexagonal implant-abutment assemblies were divided into three groups according to the degree of surface contamination: no contamination (CT0), partial contamination (CT3), and extensive contamination (CT6). Reverse torque values were measured after initial tightening to assess preload formation (pre-RTV). Specimens were then subjected to cyclic loading, after which post-loading reverse torque values were recorded (post-RTV), and absolute torque loss (ΔRTV) was calculated. Surface alterations were qualitatively assessed using scanning electron microscopy (SEM). Statistical analyses were performed to compare torque-related outcomes among groups.

Pre-RTV were significantly lower in the contaminated groups than in the uncontaminated control (P < .001), with no significant difference between CT3 and CT6. After cyclic loading, post-RTV decreased progressively with increasing contamination (P < .001). ΔRTV was significantly greater in CT6 than in CT0 and CT3 (P < .001), whereas no significant difference was observed between CT0 and CT3. SEM revealed localized surface wear at line angles in contaminated specimens, whereas uncontaminated specimens exhibited minimal surface alteration.

Surface contamination within an internal hexagonal implant-abutment connection adversely affects joint stability through two distinct mechanical stages. While the presence of contamination primarily compromises initial preload formation, extensive contamination accelerates preload loss under cyclic loading. These findings suggest that even subtle contamination, often overlooked clinically, may have meaningful implications for implant-abutment stability.