Mechanical Complications Troubleshooting

01 — Failure Modes

The four common mechanical complications

Most technical complications cluster into four presentations. Each has typical causes; nearly all share occlusal overload or an under-torqued/ill-fitting interface as a root contributor.

Most common

Screw loosening

Among the most frequent technical complications (~5-year rates high)
Causes: under-torque, settling, occlusal overload, misfit, non-axial load
Often presents as mobility/rotation without fracture
Usually retrievable and correctable

Less common

Screw fracture

Often follows repeated loosening ignored over time
Causes: fatigue, overload, cantilevers, parafunction
Requires fragment retrieval; risk of damaging internal threads
Replace with new screw; correct the driver of failure

Veneer

Ceramic chipping / fracture

Frequent in veneered restorations; fracture of veneering material
Causes: overload, framework support, firing/processing, parafunction
Minor chip → polish/repair; major → remake
Monolithic materials reduce chipping risk

Retention

Decementation / loss of retention

Cement-retained crowns: loss of retention
Causes: short/over-tapered abutment, poor cement, contamination
Recement after thorough cleaning, or improve retention form
Consider converting to screw-retained if recurrent

02 — Decision Pathway

Interactive complication selector

Start from what the patient presents with. Tap the problem to see the likely cause and a stepwise management protocol.

Tap the presenting mechanical problem.

Step 1 — What is the presenting problem?

LOOSENING

Screw loosening

Mobile/rotating restoration, screw intact.

FRACTURE

Screw fracture

Fragment retained in the implant.

CHIP

Ceramic chipping / fracture

Veneer chipped or fractured.

RETENTION

Decementation

Cemented crown loose / dislodged.

▾

03 — Quick Reference

Complication → cause → action → prevention

A consolidated troubleshooting matrix. In every case, re-evaluate the occlusion as a likely contributor.

Complication	Likely cause	Action	Prevention
Screw loosening	Under-torque, settling, overload, misfit	Inspect screw; retorque to spec; adjust occlusion	Correct torque, passive fit, protective occlusion
Screw fracture	Fatigue from repeated loosening / overload	Retrieve fragment; replace with new screw	Address loosening early; reduce cantilevers
Ceramic chip / fracture	Overload, framework support, processing, bruxism	Minor: polish/repair; major: remake	Adequate support, monolithic materials, nightguard
Decementation	Short/over-tapered abutment, poor cement	Clean & recement; or improve retention form	Adequate height/taper; consider screw-retained

Reference

Sources & clinical disclaimer

For licensed clinicians — educational use only. This algorithm summarizes published complication data and is not a substitute for individual clinical judgment, examination, or the standard of care in your jurisdiction. Torque values and retrieval tooling are system-specific — follow manufacturer instructions.

Pjetursson BE, Thoma D, Jung R, et al. A systematic review of the survival and complication rates of implant-supported fixed dental prostheses (FDPs) after a mean observation period of at least 5 years. Clin Oral Implants Res. 2012;23(Suppl 6):22–38.
Jung RE, Zembic A, Pjetursson BE, et al. Systematic review of the survival rate and the incidence of biological, technical, and aesthetic complications of single crowns on implants reported in longitudinal studies with a mean follow-up of 5 years. Clin Oral Implants Res. 2012;23(Suppl 6):2–21.
Sailer I, Mühlemann S, Zwahlen M, et al. Cemented and screw-retained implant reconstructions: a systematic review of the survival and complication rates. Clin Oral Implants Res. 2012;23(Suppl 6):163–201.

Last reviewed: June 2026 · Next review due: June 2027 · Version 1.0