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“RULES OF 10”
Figure 1: Failure of fixed and removable implant prosthesis
(acrylic fracture)
Figure 2: Failure of fixed and removable implant prosthesis
(framework fracture)
of common limitations associated
with dental implant therapy for the
edentulous mandible.
The commonly prescribed IRO and
ISFP prostheses are based upon denture
fabrication techniques that utilize
methyl methacrylate “acrylic”
resin chemistry and cross-linked denture
teeth. These materials serve as
the functional substrate and esthetic
foundation of the implant-based
prostheses for the edentulous mandible.
Support for the acrylic-veneered
prosthesis has commonly been provided
by gold-based dental alloy frameworks
and, more recently, computer
numeric controlled (CNC)-milled titanium
or chromium-cobalt frameworks.
The functional stresses — impact and
imposed bending — endured by the
esthetic veneer must be supported by
and transmitted through the framework
and the components to the supporting
implants. The data for IRO
and ISFP prostheses suggests that
the incidence of complications with
these prosthetic components is greater
than the failure of the implants 11
(Figs. 1, 2). The materials, designs, and
techniques used in the production of
implant-supported prostheses for the
treatment of mandibular edentulism
require further consideration.
One hypothesis to explain the
prosthetic failures and complications
associated with the IRO and ISFP is
that the mechanical environment
established by implant placement
is inadequate to permit proper construction
of a robust and resilient IRO
or ISFP prosthesis. Three different
factors are essential to defining this
mechanical environment (Fig. 3). One
is the magnitude of forces — specifically,
bending moments, which are
dependent on the magnitude of the
load and the length of any cantilever.
The second is the resistance of the
prosthesis (of a defined material)
against these relatively high and
repetitive loads. The third factor is the
biology of bone and its innate ability
to respond to loading environments.
The aim of this report is to provide
simple rules for treatment planning
dental implant therapy in the edentulous
mandible that both acknowledge
and control the mechanical environment.
This ultimately influences the
success of both the endosseous dental
implants and the prosthesis, and can
offer lasting success for treatment of
mandibular edentulism.
In order to provide a conceptual
framework to manage the treatment
of mandibular edentulism using dental
implants, the three aforementioned
factors affecting implant and prosthesis
longevity have been addressed
and are embodied in three “rules” for
treatment planning. For any IRO or
ISFP, there must be a minimum of
10 mm of alveolar dimension (inferior/
superior) and a minimum of 10 mm of
interocclusal (restorative) dimension
measured from the soft tissue ridge
crest to the occlusal plane. Additionally,
for an ISFP, the anterior/posterior
distribution of implants (commonly
referred to as “A-P spread”) must be
greater than 10 mm. Together, these
three rules are referred to as the “Rules
of 10.” This report will provide the rationale
to support these general rules
and illustrate their application in the
treatment of mandibular edentulism.
Rule No. 1: Inferior/superior
dimension of the mandible must
be ≥10 mm
This rule states that the minimum alveolar
dimension sufficient to support
an IRO or ISFP must be equal to that
required to use implants of approximately
10 mm in length.
The use of implants of 10 mm or less
in length for ISFP is well defined and
successful. More than a decade ago,
Brånemark and co-workers 12 compared
the outcome of ISFP treatment using
implants of greater than 10 mm and
less than 10 mm after 10 years. The
outcome with different lengths of
3.75 mm machined surface implants
revealed no difference in implant
survival after 10 years. In a more
recent 5-year prospective evaluation,
Gallucci and others 13 confirmed a
high (100 percent) implant survival
rate associated with treatment of
mandibular edentulism using ISFP
supported with four, five, or six
implants of between 8 mm and 16 mm.
In all cases, implant failures occurred
before loading. A recent evaluation of
119 patients rehabilitated with four
implants to support mandibular ISFP
revealed a 99.1 percent success rate. 14
There is little information that indicates
the use of longer implants improves
the survival of implants placed in the
parasymphyseal edentulous mandible.
It has also been suggested that
longer implants may be required to
resist the function of long cantilever
prostheses. There is little clinical data
to support or refute this notion. A
three-dimensional (3-D) finite element
model demonstrated that implant
length had no appreciable effect on
stress distribution at the bone/implant
interfaces when loaded by a cantilever
prosthesis, suggesting that implant
length does not dictate survival. 15
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