title: Elongation and preload stress in dental implant abutment screws.
abstract: A common problem associated with dental implant restorations is loosening of screws that retain the prosthesis to the implant. A method was developed to determine initial preload on UCLA-type abutment screws by measuring elongation after applying known tightening torques with a digital torque gauge. Loosening torque was also measured after tightening to 32 N-cm torque for gold alloy abutment screws and 20 N-cm for titanium abutment screws. Gold alloy and titanium abutment screws were each used to secure a gold UCLA hexed abutment to a titanium implant. Stresses and forces were calculated from the elongation measurements for three regions of each screw. Elongation of the screws after applying the manufacturer's recommended tightening torques were within the elastic range. Induced stresses were 57.5% and 56% of the yield strengths for gold alloy and titanium, respectively. Tightening of screws beyond recommended levels may be possible without producing plastic deformation. At manufacturer's recommended torques, mean preload was 468.2 (+/- 57.9) N using gold alloy screws and 381.5 (+/- 72.9) N with titanium screws.
authors.affiliation: Department of Oral Sciences, Minnesota Dental Research Center for Biomaterials and Biomechanics, School of Dentistry, Minneapolis, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Haack
authors.forename: R L
authors.initials: RL
authors.lastname: Sakaguchi
authors.forename: T
authors.initials: T
authors.lastname: Sun
authors.forename: J P
authors.initials: JP
authors.lastname: Coffey
mesh_terms: D000044:Dental Abutments; D015921:Dental Implants; D017268:Dental Prosthesis Retention / Q000295:instrumentation*; D003799:Dental Stress Analysis / Q000379:methods*; D004548:Elasticity; D006047:Gold Alloys; D006801:Humans; D016014:Linear Models; D011475:Prosthesis Failure; D013314:Stress, Mechanical; D014025:Titanium
chemical_list: D015921:Dental Implants; D006047:Gold Alloys; D014025:Titanium