Risk Factors Associated with Occlusal Overload

Several biomechanical and prosthetic factors can predispose implants to overload and compromise long-term success; they include the following:

Parafunctional Habits

Parafunctional habits (such as bruxism and clenching) are strongly associated with increased prosthetic and biologic complications in implant-supported restorations.⁴ The magnitude of occlusal forces may vary according to the site and the physical characteristics of these patients, ranging from 100-250 N in the anterior region to 300-800 N in the posterior region.⁴ In some patients, parafunctional activity may generate forces exceeding 800 N in the molar area.^4,22

Patients with parafunctional habits not only exhibit greater occlusal loads but also increased contact frequency and duration.^11,23,24 The absence of periodontal ligament-mediated proprioception may further exacerbate parafunctional loading in patients with implant-supported restorations.¹¹ Many studies have linked bruxism with peri-implant marginal bone loss, implant fracture, and eventual implant failure.^4,11,25,26

Cantilevers

Cantilevers are commonly linked to the generation of non-axial/lateral forces, subjecting the closest supporting implants to bending movements.^4,11,27 They are therefore associated with biomechanical complications such as screw loosening, screw and framework fractures, prosthetic failure, and peri-implant bone loss.²⁸

An increase in the length of the cantilever exponentially increases the stresses on the supporting implant-bone interface (Figure 6).⁴ A maximum cantilever length of 15 mm in the mandible and 12 mm in the maxilla has been suggested for a full arch implant-supported fixed prosthesis; however, more conservative recommendations advocate limiting distal cantilevers to 7-8 mm to minimize complications.^4,9,28

Image Source: AI-generated image

Image Source: AI-generated image

Figure. 6 Increase in the length of the cantilever exponentially increases stresses at the bone-implant interface.

Poor Bone Quality

Bone quality is a critical factor affecting implant stability and success. Poor bone quality (e.g., Type IV) coupled with occlusal overload presents an increased risk of biomechanical complications and implant failure.^4,5,29

Temporomandibular Disorders

Existing TMJ dysfunctions/disorders may influence occlusal harmony and should be resolved prior to the fabrication of the definitive restorations.³⁰

Poor Patient Compliance

Long-term success of implant restorations depends on the patient’s adherence to maintenance protocols, including oral hygiene practices and regular professional follow-up.³¹

Other Contributing Factors

Additional risk factors include an insufficient number of implants,⁴ incorrect distribution of implants, narrow-diameter and/or short/ultrashort implants, ridge deficiencies, improper implant design (decreased thread height, increased thread width),¹⁴ suboptimal passive fit of the prosthetic framework,¹⁴ improper prosthetic design, undesirable distribution of occlusal contacts, premature contacts, steep cuspal inclines, wide occlusal tables, improper loading time, and non-axial loading.^4,9,32