Dental implants, also known as endodontic dental implants, are surgical components that interface with the jawbone, their basic role being to support future crowns, bridges and dentures. The process by which modern implants are fixed into the bone is called osseointegration and consists of the formation of bone tissue around the implant thus increasing its stability and integration into the body. A variable amount of time is required for healing and completion of osseointegration before future dentures can be attached to implants.
The success rate depends on the patient’s overall health and the medication they are taking.
Masticatory forces must also be assessed. If the value of these forces is too high or not evenly distributed, the integrity of the implant may be affected.
Planning the position and number of implants is essential for long-term treatment success because the biomechanical forces created during mastication can be significantly increased.
The position of implants is determined by the position and angle of adjacent teeth. Following extractions and as the years go by, the bone resolidifies and some surgery is required before implants can be inserted.
These are bone augmentation and sinus lifts, which can artificially recreate the bone and space needed for the implants to integrate properly.
Once the implants have been inserted and the osseointegration has been awaited, prosthetic treatment can begin, which can be carried out using two types of prosthesis: a fixed prosthesis or a removable, mobile prosthesis. For both types of prosthetic restorations, an implant-retained bridge is required. With fixed prostheses the crown is cemented over the abutment or screwed on. In the case of removable dentures, a different system will be created whereby it can be removed.
The risks and complications of implant therapy fall into several categories. One of them concerns those that occur during surgery (excessive bleeding or nerve damage).
The next category of complications occurs in the first 6 months after implant insertion (infection and improper osseointegration), and the long-term ones concern peri-implantitis and chewing problems.
Studies show that an implant made with healthy and well-integrated tissues can have a survival rate in the first 5 years of 98% and a lifetime for prosthetic restorations of about 10-15 years.
The main use of dental implants is to support dentures. Implants are used and indicated for both single tooth missing cases and cases where all teeth are missing and the patient is totally edentulous.
At the same time, implants can be combined with other operations apart from edentulous restorations. Thus, they can be used in orthodontics to anchor teeth and can also be used in highly complex surgeries to correct facial deformities. In this case, implants are used to anchor a facial prosthesis that will replace part of the face.
Implant restoration of single tooth edentulousness
If the patient has only one missing tooth and the space is between two teeth, it is possible to choose either to insert an implant and then a crown on the implant, the restoration being independent and not affecting the neighboring teeth, or to make a dental bridge whereby the teeth neighboring the edentulous space will serve as support for a false crown. A major disadvantage in this case is that the abutment teeth will have to be ground down and, in each case, devitalized in order to make the treatment possible. Moreover, the bone at the site of the extracted tooth will resorb over time. For these reasons, with the evolution of technology and the promotion of minimally invasive procedures on teeth, specialists recommend implants.
Restoring extensive edentulousness with implants
If there are several missing teeth on the arch, one of the recommended treatments is to have a bridge on implants. For example, if 3 neighboring teeth are missing, you may choose to insert two implants and make a false crown between them. In this way, 2 implants can support 3 teeth. These bridges are similar to conventional bridges except that the abutment teeth will no longer be the natural teeth, but will be represented by implants.
Implant-supported restoration of total edentulousness
If the patient is totally edentulous, it is possible to opt for the insertion of a variable number of implants depending on the case and the possibilities, followed by the creation of a fixed or removable prosthesis on these implants. This treatment is far superior to conventional total dentures, with much better support, stability and retention. This type of prosthesis also greatly increases the patient’s quality of life.
Use of mini-implants in orthodontic treatment
Dental implants are used in patients with orthodontic needs as a temporary anchorage device to facilitate orthodontic tooth movement by providing an additional anchorage point. In order for the teeth to move, a force must be applied in the direction of the desired movement. This stimulates cells in the periodontal ligament resulting in bone remodeling, removing bone in the direction of tooth movement. To generate force on a tooth, an anchorage point is needed. Usually, implants designed to facilitate orthodontic treatment are small and do not fully integrate so they can be easily removed at the end of treatment.
Another type of mini-implants are those that provide fully or partially edentulous patients with transitional dentures that can be loaded immediately while the permanent restorations are being worked on. There have been many clinical studies on the use of these mini-implants as definitive restorations, but the success rate of the treatments is short-lived.
The material of choice from which implants are made is titanium, available in 4 grades, depending on the amount of carbon, nitrogen, oxygen and iron.
Planning for implant insertion focuses on both the general health of the patient and the condition of the tissues around the implant site.
There are few health conditions that absolutely prevent implant placement, although there are some relative conditions that increase the risk of failure. Poor oral hygiene, smokers and diabetics are at greater risk of developing peri-implantitis, increasing the risks of long-term failure.
Long-term steroid use and diseases such as osteoporosis or other bone diseases can also significantly increase the risk of failure.
Some studies have focused on the possible negative effect radiotherapy may have on implants, but it has been concluded that under conditions of strict oral hygiene and regular check-ups, the success rate of implants in radiotherapy is good.
The long-term success of implants is determined by the masticatory forces that they have to withstand. As patients have no periodontal ligament, they do not feel any pressure during mastication resulting in higher forces.
To compensate for this inconvenience, the placement of implants must distribute all forces evenly over the dentures they support. Excessive forces can lead to fracture of dentures, implant components or resorption of bone adjacent to the implant.
The final location of implants is based on both biological factors (bone type and surrounding structures) and mechanical factors.
Implants placed in denser bone, such as in the mandible, have a much lower failure rate than those placed in the jaw. People with bruxism exert constant and strong pressure on their teeth, which increases the possibility of failure.
Effects of bisphosphonate medication
Bisphosphonates belong to a class of drugs used in the preventive and curative treatment of bone disorders. Special care is needed in patients using this type of medication as the insertion of implants in such patients increases the risk of osteonecrosis. The success rate increases the lower the dose of bisphosphonates.
Stages of implant insertion
In summary, the placement of most implant systems involves five basic steps:
- Creation of the flap which is done through an incision in the gum to create a direct approach to the bone.
- Drilling at high speed: After exposing the bone, the primary hole is drilled, which must be done extremely precisely and at very high speed under cooling to prevent burning or pressure necrosis of the bone
- Low speed drilling: the primary hole is enlarged using progressively wider cutters
- Implant placement: the implant screw is screwed into the previously prepared site.
- Suture: The gum will be sutured to completely cover the implant, and then the implant will be expected to osseous-integrate. The next session consists of uncovering the implant and applying the healing cap.
Implants, depending on the time of tooth extraction, can be placed:
- Immediately after extraction (2 weeks-3 months after extraction)
- Late (3 months or more after extraction)
An increasingly common strategy for preserving bone and reducing treatment times includes placing an implant in a site where an extraction has recently been performed. On the one hand, it shortens treatment time and may improve the aesthetic consideration, and on the other hand implants may have a higher initial failure rate.
After placing an implant, the internal components are covered with either a healing bridge or a cover screw.
If the healing abutment is chosen first, the surrounding gingival mucosa is fitted around the abutment. The cover screw sits flush with the implant and is designed to be completely covered by the mucosa. After a period of osseointegration a second surgery will be required to reflect the mucosa and place the healing bridge.
In the early years of implant use, systems were built to use the two-stage technique, which was thought to increase the chances of implant integration.
For an implant to integrate it must be surrounded by a healthy amount of bone. To survive in the long term, it must have a thick shell of healthy soft tissue around it. Sometimes, however, the bone or soft tissue may be deficient, so the practitioner must restore it before or during implant treatment.
Procedures that target bone are called sinus lift and bone augmentation.
- Bone addition is necessary when the bone is resorbed so that the implant cannot be inserted. It also helps to stabilize the implant by increasing the integrity of the implant. Although there are new types of implants such as short implants and techniques to replace bone addition, a general goal is for the implant to be a minimum of 10mm long and 6mm wide to last over time. To achieve adequate bone width and height, various bone addition techniques have been developed. The most commonly used technique is guided bone augmentation and targets defects that need to be filled either with natural, harvested or autograft bone or by allograft (synthetic bone) covered by a semi-permeable membrane. During the healing phase, the natural bone replaces the graft forming a new bone base for the implant.
There are 3 procedures used in practice to facilitate the integrity of implants in the case of resorbed bone:
- Sinus lift
- Lateral alveolar augmentation – increasing the width
- Vertical alveolar augmentation – increasing height
At the same time, there are other more invasive procedures for larger bone defects such as mobilization of the inferior alveolar nerve to allow placement of a fixation device, using iliac crest or another large source of bone and microvascular bone graft. The final decision about which bone addition technique is best is based on an assessment of the degree of vertical and horizontal bone loss, each classified as mild (2-3mm), moderate (4-6mm) and severe (more than 6mm).
When a tooth is replaced with an implant it is necessary that the gum around the implant is healthy and attached well to the bone. This will help the implant to integrate well and last for the long term.
This is very important as there is less blood supply to the gum surrounding an implant, making it more susceptible to injury. If the gum is not properly attached, a soft tissue graft can be surgically implanted.
The most common soft tissue complication following implant insertion is shrinkage of the interdental papilla (the tissue between 2 neighboring teeth). Thus, there will be a small unsightly gap between the implant and the adjacent teeth.
The prosthetic phase begins once the implant is well embedded in the bone. Even in the case of loading less than 3 months later, many practitioners will initially opt to place temporary teeth until osseointegration is confirmed. The prosthetic stage of implant restoration requires equal technical expertise to the surgical stage because of biomechanical considerations, especially when multiple teeth are to be restored.
One can choose between immediate (when the implants are inserted), early (1-12 weeks after implant insertion) and late (more than 3 months) prosthetic loading. For an implant to be stable, bone must grow around it. Based on this biological process, it was thought that prosthetic loading of an implant during the osseointegration period would lead to movements that would prevent osseointegration and thus increase the failure rate. However, further research suggests that the initial stability of the implant in the bone is the most important factor in osseointegration, even more important than a variable healing period. As a result, the time allowed for healing is typically based on the density of the bone in which the implant is placed rather than the healing time.
After placement, implants should be sanitized in the same way as a natural tooth to remove any traces of bacterial plaque.
As the gingiva is less vascularized, care should be taken to floss.
Implants will lose bone at a similar rate to natural teeth. For example, in the case of periodontal disease, implants will lose bone similar to natural teeth.
Dental crowns that cover the teeth should normally last around 10 years, on a case-by-case basis, depending on the masticatory forces applied to them and the type of material they are made of.
A mouth irrigator can be used for cleaning around implants. However, as with natural teeth, the most important thing is brushing, which should be done twice a day.
Peri-implantitis is a condition that can occur in implants due to bacteria or plaque. This condition initially develops as a reversible reaction called peri-implantitis mucositis, but if left untreated it can progress to an irreversible form of peri-implantitis, leading to implant failure.
Treatment of peri-implantitis consists of mechanical debridement, antimicrobial irrigation and the use of antibiotics.
Surgery may also be performed to remove bacteria, assess, smooth the implant or decontaminate its surface. Unfortunately, there is not enough evidence to know exactly which of the methods listed above is most effective.
Risks and complications
- During surgery
Implant placement is surgery and carries the normal risks of any operation, such as infection, excessive bleeding and necrosis of the tissue flap around the implant. Nearby anatomical structures such as the inferior alveolar nerve, maxillary sinus and blood vessels may also be compromised. If the mucosa of the maxillary sinus is perforated by the implant, long-term sinusitis is rare. Another risk is the inability to place the implant in healthy bone, compromising the primary stability of the implant and resulting in osseointegration failure.
- In the first 6 months after surgery
Primary implant stability refers to the stability of a dental implant immediately after implantation. If this stability is sufficient, immediate loading with the prosthetic component may be chosen, although if this is done too early, there is the possibility of a higher failure rate.
As time goes by, bone tissue forms around the implant and the stability will become secondary, which is different from the initial stability because it results from the continuous process of bone regeneration.
When this healing process is complete, mechanical stability becomes biological. Primary stability is essential for successful surgery, and if it is insufficient, there is a possibility of increased implant mobility.
- Immediate postoperative risks
- Infection. Antibiotics reduce the risk of infection by 33%.
- Excessive bleeding
- Failure of integration
An implant is checked between 8 and 24 weeks to determine if it is integrated. There are significant variations in the criteria used to determine implant success, with the most commonly cited implant criteria being no pain, mobility, infection, gingival bleeding, or peri-implant bone loss greater than 1.5 mm.
Dental implant success is related to the skill of the operator, the quality and quantity of bone available, and the patient’s oral hygiene, but the most important factor is the primary stability of the implant.
Integration failure is rare, especially if the dentist’s or surgeon’s instructions are followed closely by the patient. Immediate loading implants may have a higher failure rate due to immediate loading after trauma or extraction.
Osseointegration failure occurs more frequently when a patient suffers from general disease or has a reticent behavior when it comes to oral hygiene.
Long-term complications resulting from restoring teeth with implants relate to the patient’s risk factors. There are risks associated with appearance, including a high smile line, poor gum quality and missing papillae, difficulty in matching the shape of natural teeth that may have uneven contact points or unusual shapes, missing bone, unrealistic patient expectations or poor oral hygiene.
Risks may be related to biomechanical factors, where the position of the implants does not support the teeth in the same way as natural teeth did. Similarly, tooth grinding, lack of bone or small diameter implants increase failure rates. Finally, there are risks due to manufacturing errors, whereby the implants themselves can fail due to fracture or loss of retention in the crowns they are supposed to support.
Long-term failures are due to loss of bone around the implant, the main causes being peri-implantitis and mechanical failure of the implant. Because there is no tooth enamel on an implant, it does not fail due to decay as with natural teeth.
While large-scale, long-term studies are rare, several studies estimate long-term (five to ten years) survival of implants.
Initially, all crowns were attached to teeth with screws, but recent advances have allowed crowns to be placed on dental cement posts, which is similar to placing a crown on a natural tooth. The likelihood has been created that the cement can escape from under the crown during cementing and become trapped in the gum, increasing the risk of peri-implantitis, but there is no evidence that the condition occurs more frequently with cemented crowns than with screw-retained crowns.
Complications vary depending on the type of implant and prosthetic restoration thus:
Implant supporting a single crown (after 5 years)
- Implant survival: 96.8%.
- Crown survival:
- metal-ceramic: 95.4%
- ceramic: 91.2%
- Peri-implant: 9.7% to 40%
- Peri-implant mucositis: 50%
- Implant fracture: 0.14%
- Loosening of screw or pontic: 12.7%
- Screw or pontic fracture: 0.35%
Implants supporting a fixed denture
- Progressive but still functional vertical bone loss (Peri-implantitis): 8.5%
- Failure after the first year 5% after 5 years, 7% after 10 years
Incidence of fracture at:
- 5 years: 13.5% to 30.6%.
- 10 years: 51.9%
- 15 years: 66.6%
Implants supporting a removable denture
- Retention reduction: 33%
- Fracture 16-19%