Whole Dental Arch Implant Reconstructions
The following principals apply to reconstructing a whole arch of teeth (example upper jaw -maxilla or lower jaw-mandible).
A hybrid prosthesis is a whole set of teeth on either 4 or 5 implants in the lower jaw, or 6-8 implants in the upper jaw. It is screwed into place, and is not removable, except by your dentist. It is referred to as a hybrid because on top of the implants there is a metal or zirconium bar or “superstructure” which is screwed into the implants and distributes the bite forces across the implants. On top of the superstructure are set the teeth, either in acrylic, zirconia, or porcelain, and along these are the gums or gingiva. The pink gingiva is fabricated from either acrylic, porcelain or composite resin. The beauty of the Hybrid prosthesis is it allows a whole set of teeth on a smaller number of implants, properly positioned in the dental arch, therefore distributing the bite forces. Another big advantage is normally when a person loses all their teeth in a whole dental arch, the gums and bone have very irregular contours, due to years of periodontal bone and gum loss. The hybrid prosthesis makes up for this esthetically by replacing lost gums and bone via the superstructure and gingival replacement. When designed properly, with enough implants to distrubute the bite forces the long-term success with these is high, usually 98-99% or higher after 20 years. I addition, they are highly functional and esthetic when designed properly.
Crown and Bridge Prosthesis:
This refers to a situation where the implants are placed precisely where the teeth used to be, and the subsequent teeth on top of them are made up of bridge work, just like dental work on teeth. It usually requires more implants per arch and may be more costly. The higher cost comes from more implants, and the fact that the prosthesis is typically all porcelain. The advantages of this type of prosthesis are several.
They are very similar to your original teeth, and how they emerge from the gingiva (gums), which mentally and esthetically can be very nice, the prosthesis is broken up in several different components, which may make it easier for the dentist to deliver, and if a tooth ever chips or breaks, just that section needs to be replaced. Another advantage is the skills required for your dentist to fabricate this are similar to what they do for placement of tooth supported crowns and bridges. This prosthesis cannot be done when there has been excessive bone loss in the areas where the teeth used to exist.
An overdenture refers to a “removable” prosthesis that snaps onto implants. In the lower jaw – usually 2 or 4 implants are used to stabilze the denture. In the upper jaw either 2, 4 or 6 implants are used to stabilize the denture. With only 2 implants in the upper jaw – the palatal portion of your denture must remain. If placing 4 or 6 implants – the palatal portion of the denture can be removed. This improves the quality of eating significantly – via better taste and tactile sensitivity.
It not only keeps your denture much more stable, the implants themselves help prevent vertical bone loss of the jawbone – which prematurely ages people with dentures.
The advantage of a “removable” overdenture over a “fixed” hybrid prosthesis is a lower cost for prosthesis fabrication, and often a decreased surgical fee because of the need for less implants.
Maxillary Hybrid (Upper Jaw):
When you lose all our upper teeth, or are about to lose them, this usually is the prosthesis (set of teeth) of choice. The teeth can be removed in stages so you always have a fixed bridge during treatment, often supported by a combination of teeth and implants. We have also developed techniques so that even if we take all the teeth out at once, we oftencan place implants, register their positition with a laser digital scanner, and from that design and mill a beautiful provisional prosthesis delivered later that day, or the next morning.
The final prosthesis typically will have 6-8 implants. There are two key engineering principals. One is the number of implants is more than 4. 6-8 implants provide wide arch support, and longevity. The other is you place the majority of implants in the molar area with only 2-4 in the incisor and or canine area. By placing the implants posteriorly, this puts the large bite forces of the molars on top of the implants, preventing prosthesis fracture, or implant overload. Often sinus lifts are done for the posterior molar implants so large (13-16 mm long) implants can be placed, with large surface area to handle these bite forces. It also keeps the implants away from the 4 front upper teeth, so they can be positioned on the prosthesis for maximum esthetics, speech, and hygiene.
One other advantage of a hybrid prosthesis on 6-8 implants -is longevity -in the face of changing oral hygiene. As patients get older, their dexterity and ability to clean may become compromised. If a patient develops gum disease (peri-implantitis) around one of these implants years later, it can be cut out from the prosthesis, and the remaining implants can typically support it.
Mandibular Hybrid (lower jaw)
The same principles apply as with the upper jaw- a superstructure sits on the implants and the teeth and artificial gums (gingiva) are put on the prosthesis.
However, the lower jawbone is anatomically much different. It is very dense, and therefore 4-5 implants will support a whole arch of teeth. 5 implants has been the standard for 40 years, however people with smaller bite forces, and if the teeth are not planned to extend to the molars, often 4 will suffice. Bone grafting is rarely needed in the lower jaw to place 4 or 5 implants for a fixed hybrid prosthesis. This is because the implants are placed in the anterior one half of the lower jaw, from the1st premolar forward, staying anterior to the inferior alveolar nerve.. For this reason the 5 implants for the lower hybrid are placed in front of this nerve – basically from the 1st premolar forward. The molar teeth are cantilevered off of the 5 implants. The strong superstructure prevents fracture.
Also, hygiene with the lower hybrid is very easy. Since the lower lip covers up the lower jawbone and part of the gums, a space can be left between the lower gingiva and the underside of the prosthesis. This makes cleaning this relatively easy.
The lower fixed hybrid was the very original implant prosthesis developed in Sweden by Branemark in the mid 1960’s. It has the most data on longevity, and basically is the most maintenance free implant supported prosthesis in existence – when properly designed.