Abstract
BACKGROUND AND AIM:
Compromised
fit between the contact surfaces of screw-retained implant-supported
fixed dentures (IFDs) is thought to create uncontrolled strains in the
prosthetic components and peri-implant tissues, thus evoking biological
and technical complications such as bone loss, screw loosening,
component fractures and, at worst, loss of implants or prostheses. The
aim of this systematic review was to evaluate the impact of marginal
misfit on the clinical outcomes of IFDs, and to elucidate definition and
assessment methods for passive fit.
MATERIALS AND METHODS:
A
systematic review of the literature was conducted with a PICO question:
"For partially or complete edentulous subjects with screw-retained
IFDs, does the marginal misfit at the implant-prosthesis interfaces have
an impact on the clinical outcomes?". A literature search was performed
electronically in PubMed (MEDLINE) with the help of Boolean operators
to combine key words, and by hand search in relevant journals. English
written in vivo studies published before August 31, 2016 that reported
on both clinical outcome and related implant prosthesis misfit (gap,
strains, torque) were selected using predetermined inclusion criteria.
RESULTS:
The
initial search yielded 2626 records. After screening and a subsequent
filtering process, five human and five animal studies were included in
the descriptive analysis. The selected studies used different methods to
assess misfit (linear distortion, vertical gap, strains, screw torque).
While two human studies evaluated the biological response and technical
complications prospectively over 6 and 12 months, the animal studies
had an observation period < 12 weeks. Four human studies analysed
retrospectively the 3 to 32 years' outcomes. Screw-related complications
were observed, but biological sequelae could not be confirmed. Although
the animal studies had different designs, bone adaptation and implant
displacement was found in histological analyses. Due to the small number
of studies and the heterogenic designs and misfit assessment methods,
no meta-analysis of the data could be performed.
CONCLUSIONS:
The
current literature provides insufficient evidence as to the effect of
misfit at the prosthesis-implant interface on clinical outcomes of
screw-retained implant-supported fixed dentures. Marginal gaps and
static strains due to screw tightening were not found to have negative
effects on initial osseointegration or peri-implant bone stability over
time. Based on two clinical studies, the risk for technical
screw-related complications was slightly higher. While the degree of
tolerable misfit remains a matter of debate, the present data do not
imply that clinicians neglect good fit, but aim to achieve the least
misfit possible. Conflict of interest statement: The authors declare no
conflict of interest. The review was conducted as part of the 2016
Foundation of Oral Rehabilitation Consensus Conference on "Prosthetic
Protocols in Implant-based Oral Rehabilitation".
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