Supervisors info:
Συκαράς Νικήτας, Επίκουρος Καθηγητής Τομέα Προσθετολογίας,Γούσιας Ηρακλής, Επίκουρος Καθηγητής Τομέα Προσθετολογίας, Πελεκάνος Σταύρος, Επίκουρος Καθηγητής Τομέα Προσθετολογίας
Summary:
Introduction: Tooth replacement with implants is considered a well-documented
therapeutic solution in prosthodontic treatment. A "successful" implant is
defined as an osseointegrated dental implant that is prosthetically restored
resulting in a functional and aesthetic outcome.
Different types of complications may appear both in regards to the implants and
the prosthetic restoration. Biological complications refer to the peri-implant
tissues whereas mechanical failures may refer to the implant body or affect the
complex structure of the prosthetic restoration.
Occlusal overloading and non-axial forces are responsible for the appearance of
mechanical complications in implant-supported restorations. Implants should be
placed in the ideal position, where implant connection is located at or near
the center of the tooth it replaces. Implant placement is nowadays advocated to
be prosthetically-driven in order to achieve the optimum positioning. However,
the final clinical position is often different from the ideal, resulting in the
development of intra-coronal cantilevers.
Aim: The aim of the present study is to investigate the correlation between the
three-dimensional structure of the implant restoration and the positioning of
the supporting implant.
Material and methods: The dimensions of the implant-supported restorations and
their components were measured and correlated with clinical parameters, which
determine the clinical performance and functional success of the restorations.
The following clinical parameters were analyzed: (a) implant dimensions, (b)
abutment characteristics, (c) implant restoration design and (d) occlusal
contacts.
The dimensions of 49 posterior implant-supported cemented restorations and
their corresponding components were recorded. The restorations were inserted in
18 patients at the postgraduate clinic of Prosthetic Dentistry of Dental School
of National and Kapodistrian University of Athens. The following parameters
were recorded: (1) implant diameter and length, (2) abutment diameter, (3)
abutment height, (4) crown length(mesial-distal), (5) crown
width(buccal-lingual/palatal), (6) crown height, (7) occlusal table area, (8)
intra-coronal cantilevers, (9) opposite side crown length, width and area and
(10) distance between the implant center and the restoration center.
During the second phase of the study, an interocclusal bite record was made
utilizing a special recording device: T-scan III Pressure Management
System(Tekscan Inc). The recorded data were analyzed in order to specify the
magnitude and exact point where maximun occlusal force was applied.
Results: The results of the correlation estimation between different parameters
are the following:
1. Moderate positive correlation between implant diameter and crown width
2. Moderate positive correlation between implant diameter and abutment diameter
3. High positive correlation between abutment height and crown height
4. Low negative correlation between implant length and crown height. The
average crown/implant ratio was 0,9, whereas when the implant length was <10mm
the estimated ratio was found 1,28.
5. Moderate positive correlation between crown's area and opposite crown's
area. The restoration's area:opposite crown's area(implant supported
restorations) ratio was 1:1,016 and the restoration's area:opposite crown's
area(natural teeth) ratio was 1:0,89.
The intra-coronal cantilever's maximum level was 6,35mm (lingual/palatal
cantilever) and the maximum level of the distance between implant center and
restoration center was 3,65mm. The center of the implant was placed at the same
section(5th section) with the center of the restoration in 68% of the included
restorations. Based on the recording of the exact point of maximum occlusal
force's application, intra-coronal cantilever was developed in 71% of the
premolar's restorations and in 82% of the molar's restorations. Finally, there
was no correlation between the percentace of occusal force and the implant
diameter, whereas the correlation with the occlusal unit's area was low
negative and non-statistically significant.
CONCLUSIONS: Survival and success of implant-supported restorations are
affected by all the clinical parameters which were examined. Discrepancies were
observed despite the appropriate treatment planning and prosthetically driven
implant placement. The aforementioned discrepancies do not necessarily
correlate with restorations' malfunction and failure.
Occlusal forces play a predominant role even in cases where the prostheses
fulfill the requirements of the optimum design. For this reason, control of
force's magnitude and orientation during the restoration's construction and
insertion and frequent follow-up appointments are fundamental for its
successful clinical performance.
Keywords:
Implants, Implant-supported restorations, Intra-coronal cantilever, Ideal implant position, Occlusal contacts
