Risk factors associated with screw loosening in CAD-CAM custom abutments: A 6-year retrospective study

Custom abutments made by using computer-aided design and computer-aided manufacturing (CAD-CAM) are often used for implant-supported prostheses. However, studies on screw loosening of implant prostheses using custom abutments are lacking.

The purpose of this retrospective study was to investigate the risk factors of screw loosening in implant-supported prostheses using custom abutments made with CAD-CAM.

Clinical charts, radiographic images, and CAD custom abutment design file data were collected and analyzed retrospectively. The study included 255 patients with 401 dental implants, and the follow-up duration was 6 years. Age, sex (male/female), type of unit (single-unit or multiunit), location of the implant (maxilla or mandible and anterior, premolar, or molar tooth), type of antagonist, and experience of the prosthodontist were reviewed, and implant angulation (mesiodistal and buccolingual), location of the screw access hole (mesiodistal and buccolingual distances from center), and attrition status (none, localized, or generalized) were measured by using a CAD file. The frequencies and percentages of risk factors were evaluated with the Fisher exact test, and the Bonferroni correction was used as a post hoc test. Multiple logistic regression with the Firth method was performed to calculate the odds ratios and their confidence intervals (α=.05).

Screw loosening showed a correlation with the severity of attrition (P<.001). Single-unit prostheses had a higher risk of screw loosening than multiunit prostheses (P<.001). Experience of the prosthodontist (P<.001). Buccolingual angulation of the implant and abutment significantly influenced the incidence of screw loosening (P<.05). Age, sex, location of the implant, type of antagonist, mesiodistal implant angulation, and buccolingual and mesiodistal location of the screw access hole did not significantly influence the incidence of screw loosening (P>.05).

The degree of attrition, buccolingual angulation of the implant and abutment, type of unit, and experience of the prosthodontist (>3 years or <3 years) were risk factors in the incidence of screw loosening.