n a recent article, Dr.
Carl Misch72
and coworkers state that the Maestro System from BioHorizons:
...is designed on a scientific tenet
that prescribes increasing surface area where the
mechanical stresses are the highest and bone quality
(strength) is the lowest.72
According to Misch's theory, varying the number of
threads, overall lengths and surface textures of four
different implant designs [Fig. 64]
will compensate for corresponding differences in density
and strength of four bone categories (D1–D4).
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| Fig.
64: Maestro System Implants |
Fig.
65: SEM of a Maestro D4 implant. Source: Steri-Oss®
Flyer. The HA coating adheres only to the peaks and
valleys of the square thread pattern. |
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| The Flaw
in Misch's Theory |
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When
planning an implant-supported restoration, it is impossible
to determine the precise amount of mechanical stress that
will be applied to the prosthesis, given such variables as
the musculature of the patient (e.g. male
vs. female), parafunctional forces (e.g.
bruxing, clenching), occlusion (e.g.
lateral interferences, premature contacts, wide occlusal tables,
long-span fixed bridges), and the angle of implant
placement, which determines the direction of occlusal forces.
A sounder approach is to
plan maximum use of available bone by selecting the longest
possible implant with the greatest number of threads and
the most effective surface, regardless of bone quality.
For example, if a 13mm long, 4mm diameter "D4" HA-coated
implant works well in quality 4 bone, a 16mm long implant
in a wider diameter will carry a greater load and reduce
more stress within the bone, provided there is available
bone to accommodate it. Furthermore, the "fine pitch" thread
design and HA coating recommended by Misch72
for quality 4 bone [Figs. 64-65]
would be even more effective in distributing occlusal forces
in dense quality 1 or 2 bone than the Maestro System's "D1"
implant, which has fewer threads and lacks HA or TPS coating.
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| Prospective
Clinical Research VS. Misch's Theory |
|
Fig. 66: VA Study Results:
Survival (%) of HA-Coated Implants in Different Qualities
of Bone73.
HA Micro-Vents®,
HA Bio-Vents®
& HA Screw-Vents®
combined. |
A
long-term, prospective clinical study by the U.S. Department
of Veterans Affairs (VA study) includes over 1700 HA-coated
Micro-Vent® ledge-type
implants, Bio-Vent®
cylinder implants and Screw-Vent®
threaded implants that vary in lengths from 7mm to 16mm and
diameters from 3.25mm to 4.5mm.65
After three years in function, there was only a 2% difference
in clinical success between type 1 bone (98%) and type 4 bone
(96%).73
Failure to use preoperative antibiotics in about 40% of the
cases accounted for a 3% lower success rate, and smoking also
increased the failure rate more than 2%.73
The maxillary posterior arch
consists of either Type 3 or 4 bone, according to Misch.74
The VA study documented a 3-year success rate of 96% for
Bio-Vent HA-coated cylinders, 17% of which were used in
sinus elevation procedures, and 97.5% success for Micro-Vent
HA-coated ledge-type implants, 20% of which were used in
sinus elevation procedures.73
Overall three-year success of 392 implants in the maxillary
posterior arch was 96%, with no statistically significant
difference in success or bone loss related to the use of
non-threaded cylinders vs. implants with threads and ledges
[Fig. 66].73
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