Internal vs. external connections for abutments/reconstructions: a systematic review.
OBJECTIVE
The objectives of the review were (1) to evaluate the accuracy of implant-level impressions in cases with internal and external connection abutments/reconstructions, and (2) to evaluate the incidence of technical complications of internal and external connection metal- or zirconia-based abutments and single-implant reconstructions.


METHODS
A MEDLINE electronic search was conducted to identify English language publications in dental journals related to each of the two topics by inserting the appropriate keywords. These electronic searches were complemented by a hand search of the January 2009 to January 2012 issues of the following journals: Clinical Oral Implants Research, The Journal of Prosthetic Dentistry, The International Journal of Prosthodontics, The International Journal of Periodontics and Restorative Dentistry, The International Journal of Oral Maxillofacial Implants, Clinical Implant Dentistry and Related Research.


RESULTS
Seven in vitro studies were included in the review to evaluate the accuracy of implant-level accuracy. No clinical study was found. There was no study that directly compared the influence of internal and external implant connections for abutments/reconstructions on the accuracy of implant-level impressions. All in vitro studies reported separately on the two connection designs and they did not use same protocol and, therefore, the data could not be compared. Fourteen clinical studies on metal-based abutments/reconstructions and five clinical studies on zirconia-based abutments/reconstructions satisfied the inclusion criteria and, therefore, were included in the review to evaluate the incidence of technical complications. The most frequent mechanical complication found in both implant connection design when employing metal abutments/reconstructions was screw loosening.


CONCLUSIONS
Implant-level impression accuracy may be influenced by a number of variables (implant connection type, connection design, disparallelism between multiple implants, impression material and technique employed). Implant divergence appears to affect negatively impression accuracy when using internal connection implants. Based on the sparse literature evaluating the incidence of technical complications of metal or zirconia abutments/reconstructions, it was concluded that: The incidence of fracture of metal-based and zirconia-based abutments and that of abutment screws does not seem to be influenced by the type of connection. Loosening of abutment screws was the most frequently occurring technical complication. The type of connection seems to have an influence on the incidence of the screw loosening: more loose screws were reported for externally connected implant systems for both types of materials. However, proper preload may decrease the incidence of such a complication.
Division of Postgraduate Prosthodontics, Tufts University, School of Dental Medicine, Boston, MA, USA. sgracis@dentalbrera.com
Stefano
S
Gracis
Konstantinos
K
Michalakis
Paolo
P
Vigolo
Per
P
Vult von Steyern
Marcel
M
Zwahlen
Irena
I
Sailer
D001863:Bone Screws; D059605:Dental Implant-Abutment Design; D003758:Dental Implantation, Endosseous; D015921:Dental Implants; D003761:Dental Impression Technique; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D006801:Humans; D008670:Metals; D003765:Models, Dental; D011183:Postoperative Complications; D015040:Zirconium
D015921:Dental Implants; D008670:Metals; D015040:Zirconium; C028541:zirconium oxide