  
A 10-Year Prospective Clinical and Biomechanical
Study of the Implant and Restorative System Manufactured by Biomedical
Implant Technology Inc.
Clinical
From November, 1992 to October, 1999 a total
of 172 consecutive patients with 235 independent metal-ceramic prostheses
(single to full edentulous restorations) supported by 863 implants
were evaluated for a period of eight years, with one group receiving
the two-piece device in a two-stage procedure while the second group
received a two-piece device in a one-stage procedure. Implants which
did not osseointegrate failed during within three months of the
normal healing period before the restorative phase (two-stage 91.1%
and one-stage 89.1% success rate). With the exception of maxillary
anterior single restorations, all other prostheses were screw retained.
For the two-piece device, one crown was lost after four years due
to a fractured abutment screw, the crown was restored with a new
abutment screw. No other prosthetic complications were observed.
Only two implants failed after insertion of the final prosthesis
and did not affect the overall restoration. The overall prosthetic
complication for the follow-up period was <1%. Eight year Kaplan-Meier
life table analysis of the implant and restoration survival indicates
no significant difference in survival between the two-stage and
the one-stage procedures (over 99 %).
Since October 1999, another prospective clinical
study of 420 one-piece non-submergible, implantable device achieved
osseointegration and were able to support a total of 120 fixed restorations.
32 out of 58 single implant restorations were screw-retained crowns
and the remaining 26 single crowns were cemented. 62 other restorations
were supported by multiple implants and all were screw retained.
No prosthetic complication was observed in this three years period.
Biomechanical
Biomechanical studies indicate that this standardized
abutment configuration has a retentive force of 56.0 kgF (SD 12.2kgF)
and a minimum resistant force of one million cycles at 200 N loaded
on a 14 mm crown, 2.5 mm from the implant axis at 30º inclination.
Pull-out tests were performed to evaluate the retentive strength
of the splinted prefabricated copings cemented onto the modified
hex abutment and also the custom round abutment copings. The splinted
coping cast from prefabricated components produced the highest retentive
strength (98.86 Kgf, SD 13.85 Kgf). The retentive strength obtained
from the custom cast round coping was only 43.61 Kgf, SD 8.04 Kgf.
Dynamic, functional comparative analysis of screw retained versus
cement retained prosthesis oscillating at 24º at 0.02 Hz at
15 kg resulted in the following: the cement group failed on average
at 2.6 M cycles (SD=2.27M cycles) for n=20, and screw retained samples
failed at 2.17 M cycles (SD=1.27M cycles) when n=18 (P>0.05).
A comparative study of (A) straight abutment with an angulated crown
versus (B) straight crown with an angulated abutment shows that
arrangement (A) typically ran out well over 20 million cycles while
arrangement (B) failed on average at 2.6 million cycles for the
same given load. The result of this experiment shows that arrangement
(A) is at least 7 times more stable than arrangement (B). A mathematical
vector analysis of the two specimens indicated that arrangement
(A) has a torque of 122kg.mm at the abutment-implant interface,
while arrangement (B) has a smaller torque of 112kg.mm. These biomechanical
tests support the usefulness of this type of abutment.
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