Download 11. Dental implants

AN OVERVIEW OF IMPLANTS
A. INTRODUCTION
What I hope to do with this handout, is to introduce you to the tangle of implant
dentistry. For a number of reasons, this is a difficult task. Difficult, because of the very
nature of implantology and its evolution over the years.
First of all, even a definition is difficult. Just about anything you put into a patient can be
considered an implant; so first we must narrow our scope. Implants in this context
refers to artificial devices used to replace the supporting structures of the dentition.
The rational for placing implants is straight forward enough. Through their lifetimes
some people will lose teeth and along with them, the supporting dental alveolus. From
the simple single tooth to the fully edentulous situation, the process is the same. The
tooth is lost and the bone slowly follows. Conventional prosthetic rehabilitation;
therefore, needs to deal with a progressively deteriorating situation. In some cases, this
proves unsatisfactory, and the dentist will search for solutions.
There is a general rule in clinical dentistry that goes like this: The fewer ways to do
something, the more likely is success. The corollary, of course, is also true: The more
ways there are to accomplish a given objective, the less likely that any given technique
will work. Let us cast our eye then on a short list of jaw reconstructive and dental
implant techniques:
(please do NOT try to memorize this list)
A. Ridge augmentation:
1) Autogenous
bone - split rib
- iliac crest
- cortical blocks
- particulate cancellous
- superior border
- inferior border
- interpositional
- visor +/- graft
cartilage
2) Allogeneic
bone - demineralized
- deantigenized
- deproteinated
- freeze dried
B. Subperiosteal
C. Endosteal
3) Xenogeneic
bone -demineralized
- deproteinated
- freeze dried
4) Alloplastic
silastic
proplast
hydroxylapatite
- Calcitite
- Durapatite
blocks
particles
collagen impregnated
mixed with bone
mixed with blood
1) cast frameworks
2) ramus frames
3) plus bone grafts
1) vitreous carbon
2) crystal saffire
3) stainless steel
- blades
- screws
- pins
4) titanium
- screws
- cylinders
- blades
and on and on................
The problem is obvious...... over the decades implantology has encompassed an
enormous range of materials and techniques, some of which worked better than others.
Until very recently , there was little science. The recent revolution in implant dentistry
has occurred as a direct result of the reversal of that trend.
B. BASIC SCIENCE
Over the last forty years, a Swedish group, headed by Professor P.I. Branemark has
pioneered and developed a reliable, scientifically proven system of replacing teeth for
the virtual lifespan of the patient. Interestingly enough this was a rather serendipitous
discovery. Dr. Branemark's training was as an orthopaedic surgeon and the lab he was
working in was the Institute for vital microscopy. Their interest was in placing metal
boxes with glass windows into rabbit legs and then peering into the windows with
microscopes in order to watch the bone heal. These boxes were placed as carefully as
possible, the observations were made over a period of time and when the experiment
finished, the animal sacrificed and the boxes removed for use in another animal. One
of the problems was that the boxes corroded and influenced healing, so various
materials were tested in order to minimize this effect. As it turned out, the titanium
boxes were impossible to remove and in actual fact, the bone broke around them before
they would loosen their grip on the bone. They had to be literally cut out of the bone.
Realizing the potential value of this discovery, Dr. Branemark looked for applications of
this technology. In this way, the modern era of dental implants was begun.
Over the last forty years, the Swedish group and then other groups throughout the world
performed extensive laboratory and clinical testing of the system. The end result was
presented to the North American market in the early 1980's and this changed clinical
dentistry. What these studies did was debunk the pseudo-science and poor track
record of the previous systems and replace them with scientifically and clinically proven
alternatives. Along the way, these studies redefined implants in a number of ways.
What then, made these new implants different from the old ones? Distinctions lay in a
number of key areas:
Material:
titanium
Technique: minimally traumatic surgery
Healing:
unloaded (or minimally loaded) bone healing (3 to 6 months)
The combination of these three critical factors led to the enormous success of this
system. The newer systems on the market represent modifications and adaptations of
the basic principles.
C. PROVIDING THE SERVICE
What then is modern implant dentistry all about? Essentially it boils down to a series of
nine basic steps:
1. Diagnosis
2. Treatment Plan
3. Preliminary procedures:
a. Non-surgical procedures include
b. Surgical intervention
4. Primary Surgery
5. Primary Healing
6. Secondary Surgery
7. Secondary Healing
8. Prosthesis Fabrication
9. Follow Up
1. Diagnosis: As in all clinical dentistry, the diagnosis is the most critical step. From a
systemic health point of view you want to rule out things like uncontrolled diabetes,
renal disease or metabolic bone disease. These significantly reduce the success of
implants. All of the usual questions regarding systemic health and the patient's ability to
withstand one or more surgical procedures also have to be answered.
From an oral point of view, the patient needs to have enough bone to support the
fixtures. In the maxilla this is particularly important in the posterior where the maxillary
sinus sweeps into the alveolus. In the mandible the main consideration is the height of
the canal in the bone and the antero-posterior position of the mental foramen. In
addition to absolute height; width and configuration of the bone is critical. The bone
must support the implant in height as well as circumferentially. The status of the
occlusion is also very important, specifically intra- and inter-arch relationships. This
issue is all the more important in partially edentulous cases. The following is a check
list of issues that require attention as part of the diagnostic process:
Patient's chief complaint: which teeth does he or she want replaced and how
(fixed vs removable)
History of chief complaint: how long have the teeth been missing, the present
status of prostheses or the history of previous attempts, reason for the loss
of teeth, etc.
Medical history: medications, allergies (particularly to metals), conditions,
radiotherapy, smoking, etc.
Examination findings:
General: number of teeth, Class I, II or III, oral hygiene, caries, periodontal disease,
overbite / overjet, canine rise vs group function occlusion, gingivitis, mucosal changes,
mouth opening, status of current appliances, vertical dimension, lip to tooth
relationships, height of the smile line, TMJ and muscle of mastication status, etc
Local: ridge shape, height and width, gingival width, thickness and condition,
restorative and periodontal status of the adjacent and opposing teeth, mesial to distal
width of the edentulous space, open bite vs overeruption of opposing teeth, crossbite,
etc.
Radiographic general: Presence or absence of pathoses (infection, cysts, tumours,
impacted teeth, etc), TMJ status, periodontal and restorative status, etc.
Radiographic local: ridge shape, height and width, gingival, thickness, restorative
and periodontal status of the adjacent and opposing teeth, root resorption, mesial to
distal width of the edentuous space, open bite vs overeruption of opposing teeth, root
proximity to the proposed implant site, proximity of adjacent structures (sinus, floor of
nose, incisive canal, inferior alveolar canal, mental nerve), etc.
The patient's degree of compliance with your instructions can also be assessed at this
time. If a patient is unwilling to follow the necessary steps in the diagnostic stage, he
will be unlikely to help you maintain the finished product. Considering the time and cost
involved, this is a key consideration.
2. Treatment Plan: The treatment plan is based on diagnosis (systemic health, bone
volume, etc.) and the patient's needs (fixed vs. removable and costs)
The two basic approaches in the fully edentulous situation are fixed bridgework or clip
retained overdenture. The cost differences is important (approx. $8 to 10,000 vs.
approx. $4 to 5,000), fixed bridgework requires much more bone to support it, especially
in the maxilla, and much more dexterity to maintain it.
In the partially edentulous situation, the situation is much more complex. This is a
function of having to take into account the current restorative, periodontal and occlusal
status of the existing dentition. All of these factors must be optimized prior to
proceeding and the costs can significantly add up.
3. Preliminary procedures:
a. Non-surgical procedures include: periodontal therapy for adjacent teeth,
restorative dentistry, occlusal adjustment, orthodontics to move, upright or torque teeth,
TMJ therapy and so on.
b. Surgical intervention: this may include periodontal surgery for adjacent teeth or
the removal of pre-existing pathoses (such as infected teeth, impacted teeth, cysts,
tumours, soft tissue masses, etc.). Preliminary surgery may also include bone or soft
tissue graft augmentation of implant sites. The most common sites for bone
augmentation include the posterior maxilla with sinus lift procedures and onlay
procedures for the anterior maxilla and mandible (both vertical and horizontal
augmentation). Soft tissue grafting is required in order to increase attached gingiva or
to improve ridge contour short of bone grafting. The most complex cases may require
transposition of the inferior alveolar nerve or mental foramen or orthognathic surgery to
alter the relationship of the jaws.
4. Primary Surgery: The primary surgery is the placement of the implants in the bone.
A generous flap is raised, holes (appropriate to the system) are drilled in the bone the
implants (titanium or titanium alloy) are screwed or tapped into place. The drilling
MUST be carried out in a minimally traumatic fashion, most importantly avoiding
overheating and killing of bone cells (critical temperature is 47'C) When the implants
are in place, the flap is closed and the patient sent home. The key to successful
surgery is the precise placement of the implant in the position and orientation required
to support the eventual prosthesis. This requires accurate diagnostic wax mock-ups
and the fabrication of appropriate surgical splints.
5. Primary Healing: The most critical factor in the immediate post-op period is the
NON-loading of the implants. At the time of surgery, The mucosa is closed with the
implants either buried or minimally exposed and the implants are virtually ignored for
two to six months (depending on location, implant system, quality and quantity of bone,
etc.). During that time the patient may wear his or her old denture if it is accurately
relined to fit the healing ridge. It is during this period of quiescence in the bone that the
process of osseointegration occurs. Viable bone will grow up to and fuse with the
implant structure. If immediately over-loaded, the interface with tissue will be fibrous and
the implant will ultimately fail.
6. Secondary Surgery: At the completion of the prescribed primary healing time,
buried implants are uncovered through gingival incisions and transmucosal healing
abutments are placed. The gingival tissue is then carefully adapted by sutures to the
implants and again minimally loaded.
7. Secondary Healing: This two to three week period of time allows formation
epithelial hemi-desmosomal attachment to the titanium surface.
8. Prosthesis Fabrication: A careful impression technique transfers the positions and
orientations of the implants to the working model and the ultimate restoration is waxed,
cast and processed in multiple steps.
9. Follow Up: Following insertion of the restoration, the patient must be followed over
the years for potential loosening of implants (rare) and for routine maintenance of the
teeth. This may include occlusal adjustment, replacement of teeth, cleaning, tightening,
etc. Because the implants systems will stay with the patient for the rest of their lives, a
commitment to lifelong maintenance must be made by both the patient and the
restorative dentist.