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Biological Width - Dental Implantts
Biological Width - Dental Implants
The phenomenon of the establishment of a zone of biological width has been with use for many years in dentistry. In its most simplified form, biological width is defined as the distance necessary for a healthy existence of bone and soft tissue from the most apical extent of a dental restoration. In a more complex form, the definition states that there must not be any encroachment of a restorative margin within two millimeters of the bone that surrounds the tooth...
The problem is not the restoration per se, but rather, the bacteria which will always find shelter in the interface between the restorative margin and the tooth structure. The presence of bacteria and their associated toxins within approximately 2mm of the boney margin will cause and inflammatory response in the soft tissue and an eventual apical migration of the entire periodontal complex (gingiva, periodontal ligament and bone).
The purpose of this paper is to discuss the phenomenon of biological width as it pertains to dental implants and to look at any contributing factors in the re-establishment of biological width that may be attributed to dental implants alone.
Observations regarding bone loss around healthy dental implants
From the beginning of the Brånemark work, it was noticed that there would almost always be a loss of crestal bone around a dental implant. This bone usually stabilized at the first thread of the 7implant. The loss was attributed to function, loading and other normal stages of implant use, but there was really never any proof about what was happening.
The Brånemark implant was a two stage implant which was initially placed below the crest of bone and subsequently uncovered and attached to a restoration or an abutment. It was noted that no bone loss occurred under most circumstance before the second stage surgery. In every case, after second stage surgery, bone loss would occur to about the level of the first thread of the implant or approximately 2mm. Researchers did not understand this second stage bone loss, but it appeared self limiting and was therefor accepted as normal.
It is interesting to note that some other systems, such as the one stage ITI system, did not experience this bone loss. It was thought that this lack of bone loss might have something to do with the surface of those implants, however, when those implants were used in a two stage procedure, they suffered the same or greater bone loss at second stage surgery and attachment.
Many researchers and clinicians were still puzzled by this bone loss and offered different theories as to why it might occur and how it might be prevented. Dr. Carl Misch was sure that this bone loss was due to functional loading and the inability of the various implant designs to properly distribute the functional forces within bone. His theories lead to a new design of dental implants. Some groups, like the Nobel Biocare researchers, felt that this was just a reflection of the positioning of the threads and felt that bone would always be lost to the first thread of any implant. They proved themselves wrong with their first attempt at a wide diameter implant which had the first thread right at the top of the implant (so now the bone loss moved down to the third or fourth thread) and then with their conical implant, they proved themselves disastrously correct (The conical implant had a smooth conical top which extended for about 3mm. It was totally countersunk in bone and the bone loss always resulted in 3mm or more. In this case, it was the polished collar which just would not allow for the connection of the boney interface.).
What truly accounts for biological width relative to dental implants?
When an implant is placed at or below the crest of bone and is then covered with a soft tissue barrier to prevent any ingress of bacteria, the bone level will remain in a virtual steady state. We do see some instance of cupping or bone loss around covered implants, but this is fairly less common and may be due to aggressive countersinking or damaging of the bone at the time of insertion. It might also be due to altered healing responses in patients with poor healing factors such as smoking.
When an implant is exposed to the outside world, there is a connection of some sort of abutment or prosthetic to the implant. This connection will harbor bacteria and the body reacts to this bacteria by attempting to establish a zone of biological width. Bone and soft tissues will recede from the bacterial laden gap usually to about the two millimeter mark which usually coincides with the first thread of a threaded implant. Once this biological width has been re-established, the system returns to a steady state.
Implants that are placed in a one stage procedure such that the top of the implant is at least 2mm above the crest of bone should not show any significant bone loss at restoration attachment and during ensuing function. The biological steady state is established in these situations right from the initial surgery and should be completely maintainable unless there is a significant loss of the attached gingiva. In this sense, any implant may be used as a one stage implant and may be used to prevent additional bone loss at restoration hook-up and subsequent functional loading.