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The replacement of missing teeth has been one of the primary goals
of Dentistry since ancient times. As anyone who wears a full lower
denture can attest, the lack of solid teeth with which to
chew considerably lowers the quality of one's life, both from
a nutritional and a socio-psychological standpoint. However,
until recently, replacement teeth could only be held in place
by resting upon the gum tissue and/or supported by existing teeth.
Due to the remarkable advances in the understanding of bone physiology
and biomechanics, dental implants have now come to the forefront of
modern Dentistry. Dental Implantology now addresses many of the heretofore
vexing problems encountered in providing a solid dentition for chewing,
with highly predictable and dramatic results.
Dental implants are used as support for the replacement of missing
teeth. There are two basic types of dental implants: the superiosteal
implant, and the root-form implant.
SUBPERIOSTEAL IMPLANTS
The subperiosteal implant is a custom made metal framework
which lies directly over the lower jaw bone, but underneath the
gum tissue. Usually four or five metal posts will protrude through
the gum, which hold a full lower denture in place. Although still
widely accepted, this technique has become less common due primarily
to advances in root-form implants.
ROOT-FORM IMPLANTS
A root-form implant, as the name implies, is analogous to the root
of a tooth. It is usually a titanium cylinder which is placed directly
into the upper or lower jaw bone. A typical root-form implant has
internal threads which allow a screw-type post to be threaded into
the implant. This post, or abutment, protrudes through the gum
tissue upon which the replacement tooth or teeth are anchored.
An implant with its abutment component may be used to support a
single replacement tooth, or several implants may be used to support
multiple teeth, including a full upper or lower arch of teeth.
Root-form implants, in contrast to the subperiosteal, are directly
integrated into the bone itself, which anchors them very solidly.
They are highly predictable, and it has recently been reported
that the success rate of dental implants has now surpassed the
success rate of root canal treatment, at approximately 97%.
Missing Tooth
Missing Tooth replaced with implant and crown
PROCEDURE
There are two phases of treatment involved in the replacement of
teeth using root-form implants: First, the placement of
the implant itself, secondly, uncovering and loading of
the implant.
Implant placement: Implant placement is a surgical
procedure, normally performed under local anesthesia. A small
hole is made in the jaw bone inside the mouth which is the exact
size of the implant to be used. The implant is then carefully
threaded all of the way into the hole, until the top of the implant
is flush with the bone. Next, a cap screw is fitted over the
top of the implant to prevent ingress of tissue into the internal
threads, and the gum is stitched over the implant, usually covering
it completely. About one week later the stitches are removed,
and the implant is left alone for a period of usually three to
six months. During this time, osseointegration occurs. That is,
the bone heals tightly around the implant.
Implant uncovering and loading: After the implant
is deemed to be integrated (the time frame varies, usually depending
on the location in the mouth and bone density), the cover screw
is removed from the implant through a small opening which is
made in the gum tissue, exposing the implant (i.e. uncovering)
(also done under local anesthesia.) Once the cover screw is removed
a healing cap is threaded into the implant body which protrudes
above the gumline. The gums are allowed to heal around this "healing
abutment" for about one to two weeks. After the gums are
healed, the implant is ready to have a permanent abutment placed,
upon which the actual replacement tooth or teeth can be supported.
The placement of functional teeth supported by the underlying
implant is referred to as loading of the implant. Depending upon
the individual circumstances, steps in the process may be omitted,
or added.
ADVANTAGES
In cases involving the replacement of a single tooth, an implant
supported replacement tooth does not require "cutting down" the
adjacent teeth as would be necessary to fabricate a bridge (a bridge is
an artificial tooth or teeth connected to crowns on adjacent teeth,
and permanently cemented.) In this instance, the implant acts as
a new root for the replacement tooth, without affecting any other
teeth, because it stands by itself.
In cases involving multiple teeth, the use of implants often
obviates the necessity to rely upon the remaining teeth and gum
tissue for support and retention of a partial denture. ( a "partial" is
a removable appliance, usually composed of a substructure which clasps
onto remaining teeth.) This is particularly advantageous when replacing
several back teeth, because the support for chewing would otherwise
be borne primarily by the underlying gum tissue.
When all of the teeth in the lower arch are missing, dental implants
present their most striking advantage. Although it is usually still
necessary to wear a lower denture, which replaces both the missing
teeth and compensates for the shrinkage in the gums and jawbone,
a lower denture supported and held in place by implants, in contrast
to a conventional tissue borne denture, is SOLID. Almost invariably,
patients can expect to eat almost anything, and speak without fear
of dislodgement of the denture. Predictably, this leads to an overall
improvement in a person's nutrition, social function, and enhancement
in the quality of life in general.
Since conventional full upper dentures seem to be well tolerated
by most people, implants are often not necessary. In contrast to
lower plates, (which have an amazing propensity for dislodgement
at inopportune moments and only provide at best 25% chewing efficiency)
upper plates are held in place by vacuum. This usually keeps them
stable and comfortable most of the time.
DISADVANTAGES
Dental implant placement is primarily dependent upon the degree and
character of available bone in the area of the mouth for the proposed
implant. Often, the amount or density of the bone is deemed insufficient
to provide for predictable implant longevity. Fortunately, almost
all of these barriers have been overcome by the multitude of new
bone-grafting techniques which we have employed with considerable
success. However, adding new bone can also lengthen the treatment
process.
The presence and/or location of nerves or other anatomic structures
may entail a risk which outweighs the potential benefit.
Habits such as smoking, or diseases such as diabetes adversely affect
the statistical predictability of success.
Risks involving any type of surgery are always present, in particular,
post-operative infection, however we have found these incidences
to be rare.
General: the above information is intended as a simplistic
overview of dental implantology, and the indications for their
use must be evaluated on an individual basis.
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