Placement of dental implants is a surgical procedure and carries the normal risks of surgery including infection, excessive bleeding and necrosis of the flap of tissue around the implant. Nearby anatomic structures, such as the inferior alveolar nerve, the maxillary sinus and blood vessels, can also be injured when the osteotomy is created or the implant placed. Even when the lining of the maxillary sinus is perforated by an implant, long term sinusitis is rare. An inability to place the implant in bone to provide stability of the implant (referred to as primary stability of the implant) increases the risk of failure to osseointegration.
Bone loss (peri-implantitis) on implants over 7 years in a heavy smoker
Recession of the gingiva leads to exposure of the metal abutment under a dental crown.
Black triangles caused by bone loss between implants and natural teeth
Fracture of an implant and abutment screw is a catastrophic failure and the fixture cannot be salvaged.
Fracture of an abutment (all-zirconia) requires replacement of the abutment and crown.
Fracture of abutment screws (arrow) in 3 implants required removal of the remainder of the screw and replacement.
Dental cement under the gingiva causes peri-implantitis and implant failure.
First Six Months
Primary Implant Stability
Primary implant stability refers to the stability of a dental implant immediately after implantation. The stability of the titanium screw implant in the patient’s bone tissue post surgery may be non-invasively assessed using resonance frequency analysis. Sufficient initial stability may allow immediate loading with prosthetic reconstruction, though early loading poses a higher risk of implant failure than conventional loading.
The relevance of primary implant stability decreases gradually with regrowth of bone tissue around the implant in the first weeks after surgery, leading to secondary stability. Secondary stability is different from the initial stabilization, because it results from the ongoing process of bone regrowth into the implant (osseointegration). When this healing process is complete, the initial mechanical stability becomes biological stability. Primary stability is critical to implantation success until bone regrowth maximizes mechanical and biological support of the implant. Regrowth usually occurs during the 3–4 weeks after implantation. Insufficient primary stability, or high initial implant mobility, can lead to failure.
Immediate Post-Operative Risks
- Infection (pre-op antibiotics reduce the risk of implant failure by 33 percent but do not affect the risk of infection).
- Excessive bleeding
- Flap breakdown (less-than 5 percent)
Failure to Integrate
An implant is tested between 8 and 24 weeks to determine if it is integrated. There is significant variation in the criteria used to determine implant success, the most commonly cited criteria at the implant level are the absence of pain, mobility, infection, gingival bleeding, radiographic lucency or peri-implant bone loss greater than 1.5 mm.
Dental implant success is related to operator skill, quality and quantity of the bone available at the site, and the patient’s oral hygiene, but the most important factor is primary implant stability. While there is significant variation in the rate that implants fail to integrate (due to individual risk factors), the approximate values are 1 to 6 percent.
Integration failure is rare, particularly if a dentist’s or oral surgeon’s instructions are followed closely by the patient. Immediate loading implants may have a higher rate of failure, potentially due to being loaded immediately after trauma or extraction, but the difference with proper care and maintenance is well within statistical variance for this type of procedure. More often, osseointegration failure occurs when a patient is either too unhealthy to receive the implant or engages in behavior that contraindicates proper dental hygiene including smoking or drug use.
The long-term complications that result from restoring teeth with implants relate, directly, to the risk factors of the patient and the technology. There are the risks associated with esthetics including a high smile line, poor gingival quality and missing papillae, difficulty in matching the form of natural teeth that may have unequal points of contact or uncommon shapes, bone that is missing, atrophied or otherwise shaped in an unsuitable manner, unrealistic expectations of the patient or poor oral hygiene. The risks can be related to biomechanical factors, where the geometry of the implants does not support the teeth in the same way the natural teeth did such as when there are cantilevered extensions, fewer implants than roots or teeth that are longer than the implants that support them (a poor crown-to-root ratio). Similarly, grinding of the teeth, lack of bone or low diameter implants increase the biomechanical risk. Finally there are technological risks, where the implants themselves can fail due to fracture or a loss of retention to the teeth they are intended to support.
From these theoretical risks, derive the real world complications. Long-term failures are due to either loss of bone around the tooth and/or gingiva due to peri-implantitis or a mechanical failure of the implant. Because there is no dental enamel on an implant, it does not fail due to cavities like natural teeth. While large-scale, long-term studies are scarce, several systematic reviews estimate the long-term (five to ten years) survival of dental implants at 93–98 percent depending on their clinical use. During initial development of implant retained teeth, all crowns were attached to the teeth with screws, but more recent advancements have allowed placement of crowns on the abutments with dental cement (akin to placing a crown on a tooth). This has created the potential for cement, that escapes from under the crown during cementation to get caught in the gingiva and create a peri-implantitis (see picture below). While the complication can occur, there does not appear to be any additional peri-implantitis in cement-retained crowns compared to screw-retained crowns overall. In compound implants (two stage implants), between the actual implant and the superstructure (abutment) are gaps and cavities into which bacteria can penetrate from the oral cavity. Later these bacteria will return into the adjacent tissue and can cause periimplantitis. As prophylaxis these implant interior spaces should be sealed.
Criteria for the success of the implant supported dental prosthetic varies from study to study, but can be broadly classified into failures due to the implant, soft tissues or prosthetic components or a lack of satisfaction on the part of the patient. The most commonly cited criteria for success are function of at least five years in the absence of pain, mobility, radiographic lucency and peri-implant bone loss of greater than 1.5 mm on the implant, the lack of suppuration or bleeding in the soft tissues and occurrence of technical complications/prosthetic maintenance, adequate function, and esthetics in the prosthetic. In addition, the patient should ideally be free of pain, paraesthesia, able to chew and taste and be pleased with the esthetics.
The rates of complications vary by implant use and prosthetic type and are listed below:
Single Crown Implants (5-year)
- Implant survival: 96.8 percent
- Crown fracture: a) metal-ceramic: 95.4 percent, all-ceramic; 95.4 percent (cumulative rate of ceramic or veneer fracture: 4.5 percent)
- Peri-implantitis: 9.7 percent up to 56 percent
- Implant fracture: 0.14 percent
- Screw or abutment loosening: 12.7 percent
- Abutment screw fracture: 0.35 percent
Fixed complete dentures
- Progressive vertical bone loss but still in function (Peri-implantitis): 8.5 percent
- Failure after the first year 5 percent at five years, 7 percent at ten years
- Incidence of veneer fracture at:
- 5-year: 13.5 to 30.6 percent
- 10-year: 51.9 percent (32.3 to 75.5 percent with a confidence interval at 95 percent)
- 15-year: 66.6 percent (44.3 to 86.4 percent with a confidence interval at 95 percent)
- 10-year incidence of framework fracture: 6 percent (2.6 to 9.3 percent with a confidence interval at 95 percent)
- 10-year incidence of esthetic deficiency: 6.1 percent (2.4 to 9.7 percent with a confidence interval at 95 percent)
- prosthetic screw loosening: 5 percent over five years to 15 percent over ten years
The most common complication being fracture or wear of the tooth structure, especially beyond ten years with fixed dental prostheses made of metal-ceramic having significantly higher ten-year survival compared those made of gold-acrylic.
Removable Dentures (overdentures)
- Loosening of removable denture retention: 33 percent
- Dentures needing to be relined or having a retentive clip fracture: 16 to 19 percent