Purpose: To examine how saline and acidic environments affect the mechanical integrity of narrow single-body titanium (Ti) implants for oral rehabilitation. Materials and Methods: A total of 30 Ti-base alloy implants (2.5-mm diameter) were placed into a polyacetal holder and coupled to a stainless steel prosthetic cap for fatigue testing in the three different environments as follows: (1) dry air, (2) saline solution (pH at 7.6), and (3) lactic acid solution (pH at 3.4). The fracture surfaces were analyzed using a scanning electron microscope (SEM). Also, finite element analysis (FEA) was carried out to estimate the maximum von Mises stresses. Results: The fatigue resistance was higher in the group tested in dry air (60%), followed by saline solution (30%) and lactic acid (10%). Regardless of the environment, the FEA showed that fractures occurred at the same areas with highest stress concentration. SEM analyses revealed two distinct failure regions that both had fatigue streaks: fatigue and overload. A high incidence of secondary cracks was also noticed on the specimens exposed to the solutions. Conclusions: Both saline and acidic solutions significantly affect the fatigue resistance of narrow dental implants. Critical regions of the narrow implants were also susceptible to cracks and plastic deformation, which should be taken into consideration when planning for an oral rehabilitation.