Planning General considerations Planning for dental implants focuses on the general health condition of the patient, the local health condition of the
mucous membranes and the jaws and the shape, size, and position of the bones of the jaws, adjacent and opposing teeth. There are few health conditions that absolutely preclude placing implants and there are certain conditions that can increase the risk of failure. Those with poor oral hygiene, heavy smokers and diabetics are all at greater risk for a variant of
gum disease that affects implants called
peri-implantitis, increasing the chance of long-term failures. Long-term steroid use,
osteoporosis and other diseases that affect the bones can increase the risk of early failure of implants. Nevertheless, a systemic study published in 2016 concluded that dental implants installed in the irradiated area of an oral cavity may have a high survival rate, provided that the patient maintains oral hygiene measures and regular follow-ups to prevent complications.
Biomechanical considerations The long-term success of implants is determined in part by the forces they have to support. As implants have no periodontal ligament, there is no sensation of pressure when biting so the forces created are higher. To offset this, the location of implants must distribute forces evenly across the prosthetics they support. Concentrated forces can result in fracture of the
bridgework, implant components, or loss of bone adjacent the implant. The ultimate location of implants is based on both biologic (bone type, vital structures, health) and mechanical factors. Implants placed in thicker, stronger bone like that found in the front part of the
bottom jaw have lower failure rates than implants placed in lower density bone, such as the back part of the
upper jaw. People who
grind their teeth also increase the force on implants and increase the likelihood of failures. The design of implants has to account for a lifetime of real-world use in a person's mouth. Regulators and the dental implant industry have created a series of
tests to determine the long-term mechanical reliability of implants in a person's mouth where the implant is struck repeatedly with increasing forces (similar in magnitude to biting) until it fails. When a more exacting plan is needed beyond clinical judgment, the dentist will make an acrylic guide (called a stent) prior to surgery which guides optimal positioning of the implant. Increasingly, dentists opt to get a
CT scan of the jaws and any existing dentures, then plan the surgery on
CAD/CAM software. The stent can then be made using
stereolithography following computerized planning of a case from the CT scan. The use of CT scanning in complex cases also helps the surgeon identify and avoid vital structures such as the
inferior alveolar nerve and the sinus.
Bisphosphonate drugs The use of bone-building drugs, like
bisphosphonates and
anti-RANKL drugs, requires special consideration with implants because they have been associated with a disorder called
medication-associated osteonecrosis of the jaw (MRONJ). The drugs change
bone turnover, which is thought to put people at risk for death of bone when having minor oral surgery. At routine doses (for example, those used to treat routine
osteoporosis) the effects of the drugs linger for months or years but the risk appears to be very low. Because of this duality, uncertainty exists in the dental community about how to best manage the risk of BRONJ when placing implants. A 2009 position paper by the
American Association of Oral and Maxillofacial Surgeons discussed that the risk of BRONJ from low dose oral therapy (or slow-release injectable) as between 0.01 and 0.06 percent for any procedure done on the jaws (implant, extraction, etc.). The risk is higher with
intravenous therapy, procedures on the lower jaw, people with other medical issues, those on steroids, those on more potent bisphosphonates and people who have taken the drug for more than three years. The position paper recommends against placing implants in people who are taking high-dose or high-frequency intravenous therapy for cancer care. Otherwise, implants can generally be placed and the use of bisphosphonates does not appear to affect implant survival. Additional precaution can be taken by administering pentoxifylline and
tocopherol both pre-operatively and post-operatively. Moreover, patients taking bisphosphonates present a higher risk of implant failure in comparison to patients not taking this class of drugs. at a precise
torque so as not to overload the surrounding bone (overloaded bone can die, a condition called osteonecrosis, which may lead to failure of the implant to fully integrate or bond with the jawbone). • Tissue adaptation: The
gingiva is adapted around the entire implant to provide a thick band of healthy tissue around the healing abutment. In contrast, an implant can be "buried", where the top of the implant is sealed with a cover screw and the tissue is closed to completely cover it. A second procedure would then be required to uncover the implant at a later date.
Timing of implants after extraction of teeth There are different approaches to placement dental implants after tooth extraction. The approaches are: • Immediate post-extraction implant placement. • Delayed immediate post-extraction implant placement (two weeks to three months after extraction). • Late implantation (three months or more after tooth extraction). An increasingly common strategy to preserve bone and reduce treatment times includes the placement of a dental implant into a recent extraction site. On the one hand, it shortens treatment time and can improve aesthetics because the soft tissue envelope is preserved. On the other hand, implants may have a slightly higher rate of initial failure. Conclusions on this topic are difficult to draw, however, because few studies have compared immediate and delayed implants in a scientifically rigorous manner. In the early stages of implant development (1970−1990) implant systems used a two-stage approach, believing that it improved the odds of initial implant survival. Subsequent research suggests that no difference in implant survival existed between one-stage and two-stage surgeries, and the choice of whether or not to "bury" the implant in the first stage of surgery became a concern of soft tissue (
gingiva) management. When tissue is inadequate, deficient or mutilated by the loss of teeth, adjacent bone or gingiva, implants are placed and allowed to osseointegrate, then the gingival flat is surgically placed around the healing abutments. The downside of a two-stage technique is the need for additional surgery and compromise of circulation to the tissue due to repeated surgeries. The choice of one or two stages now centers around how best to reconstruct the soft tissues around lost teeth.
Additional procedures to augment deficient bone in implant site For an implant to
osseointegrate, it needs to be surrounded by a healthy quantity of bone. In order for it to survive long-term, it needs to have a thick healthy soft tissue (
gingiva) envelope around it. It is common for either the bone or soft tissue to be so deficient that the surgeon needs to reconstruct it either before or during implant placement.
Hard tissue (bone) reconstruction Bone grafting is necessary when there is a lack of bone. It also helps to stabilize the implant by increasing survival rates of the implant and decreasing marginal bone level loss. While there are always new implant types, such as short implants, and techniques to allow compromise, a general treatment goal is to have a minimum of in bone height, and in width. Alternatively, bone defects are graded from A to D (A=10+ mm of bone, B=7–9 mm, C=4–6 mm and D=0–3 mm) where an implant's likelihood of osseointegrating is related to the grade of bone. To achieve an adequate width and height of bone, various bone grafting techniques have been developed. The most frequently used is called
guided bone graft augmentation where a defect is filled with either natural (harvested or
autograft) bone or
allograft (donor bone or synthetic bone substitute), covered with a semi-permeable membrane and allowed to heal. During the healing phase, natural bone replaces the graft, forming a new bony base for the implant. Orthodontic extrusion or orthodontic implant site development can be used in selected cases for vertical/horizontal alveolar augmentation.
Soft tissue (gingiva) reconstruction The
gingiva surrounding a tooth has a 2–3 mm band of bright pink, very strong attached mucosa, then a darker, larger area of unattached mucosa that folds into the cheeks. When replacing a tooth with an implant, a band of strong, attached gingiva is needed to keep the implant healthy in the long-term. This is especially important with implants because the blood supply is more precarious in the gingiva surrounding an implant, and is theoretically more susceptible to injury because of a longer attachment to the implant than on a tooth (a longer
biologic width). When an adequate band of attached tissue is absent, it can be recreated with a soft tissue graft. There are four methods that can be used to transplant soft tissue. A roll of tissue adjacent to an implant (referred to as a palatal roll) can be moved towards the lip (buccal),
gingiva from the palate can be transplanted, deeper
connective tissue from the palate can be transplanted or, when a larger piece of tissue is needed, a finger of tissue based on a blood vessel in the palate (called a vascularized interpositional periosteal-connective tissue (VIP-CT) flap) can be repositioned to the area. Additionally, for an implant to look esthetic, a band of full, plump gingiva is needed to fill in the space on either side of implant. The most common soft tissue complication is called a
black triangle, where the
papilla (the small triangular piece of tissue between two teeth) shrinks back and leaves a triangular void between the implant and the adjacent teeth. Dentists can only expect 2–4 mm of papilla height over the underlying bone. A black triangle can be expected if the distance between where the teeth touch and bone is any greater. can only be used when there is an edentulous area adjacent to healthy teeth that can be moved orthodontically into the edentulous site and generate healthy bone volume for implant placement. Orthodontic tooth movement can generate new bone. This is because of the fibres of the
periodontal ligament (PDL) surrounding the teeth and attached to the alveolar bone, the stretched fibres in the PDL stimulate the
osteoblasts depositing new
alveolar bone. For instance, the orthodontic forced eruption of hopeless teeth can augment the bone vertically and eliminate or reduce the amount of
bone graft required prior to implant placement. Similarly, where there is a bone-deficient
edentulous (toothless) site, it is possible to move the healthy adjacent teeth into this area, closing the edentulous space and simultaneously creating an implant site with enough bone adjacent to where implant placement was originally planned. ==Recovery==