By: Dr. Jim Grisdale
Implant supported restorations have become a preferred treatment option for the rehabilitation of both completely and partially endentulous patients. However, in spite of a very high success rate with osseointegration of dental implants, they are not free of complications. Implant complications have been categorized into the following two types:
• Biological
• Bio mechanical
Biological complications include a failure to osseointegrate (early failure) and peri-implant disease (late failure). Technical complications can include abutment screw loosening, fracture, abutment fracture, implant body fracture and a fractured prosthesis.
Picture 1: Early Failure Picture 2: Peri-implantitis-Bone Loss
BIOMECHANICAL COMPLICATIONS
I – Abutment Screw Loosening or Fracture
Following the successful osseointegration, forces within the oral cavity are transferred to the implant restoration/prosthesis, the screw joint and the surrounding bone. A screw joint is defined as two parts which are held together by a screw. When torque is applied to a screw within a joint, a force is developed within the screw referred to as ‘preload’. Preload is developed when the torque applied to the screw places the shank of the screw under tension. If the elastic recovery of the screw is exceeded by overtightening or excessive forces on the joint, the screw will either loosen or fracture. This problem is found more often to occur with prosthetic screws compared to abutment screws and is more often associated with single implant restorations compared to multiple units. Occlusion frequently plays a significant role in screw loosening or fracture. Occlusal factors include the type of prosthesis and the opposing arch; i.e. implant versus natural teeth versus denture; and fixed or removable prosthesis. The best way to reduce the incidence of screw loosening or fracture is to maximize the joint clamping forces (manufacture recommendation) and to minimize joint separating forces including excursive contact, non-passive frameworks and parafunctional habits. It has been recommended to retighten the screw after a period of approximately 10 minutes after the initial recommend tightening tongue to overcome the settling effect and prevent premature screw loosening.
Pictures 1 and 2: Fractured Abutment Screw
When a screw fractures, retrieval can be very difficult depending on the depth of the fractured portion and whether the fractured portion is loose or tightly bound within the abutment or implant. Different methods of retrieval have been advocated including a dental explorer, hand scaler, ultrasonic scaler, round burr or end cutting burr in reverse mode in the hand piece and a groove cut into the screw head to provide purchase for removal with a flat head screwdriver. A more promising solution to the removal of a fractured screw is a screw retrieval kit supplied by most implant companies.
Picture 1: Fractured Prosthesis Screws Picture 2: Restoration Screw Fracture
II – Abutment Loosening Or Fracture
The screw joint stability of the abutment to implant interface involves the following three critical factors: (1) adequate preload; (2) the precision of fit between the abutment and the implant interface; and (3) the basic anti-rotational characteristics of the abutment to implant interface. The abutment screw length is shorter than the receptor site within the implant permitting the receptor site within the implant to be machined and permit the abutment screw to tighten the abutment avoiding the risk of “bottoming out” before the screw is completely tightened. The stress which is caused by the retaining screws of prosthesis with a non-passive fit may result in constant tension on the implant and predispose it to fracture. Methods of retrieval of fractured abutment screws are the same as above, however in the event the internal threads of the implant body are altered as a result of fractured screw removal, the implant itself will require removal and replacement. The best option is a fixture removal kit provided by many of the implant manufacturers.
Picture 1: Abutment Screw Inside Dislodged Crown
BIOLOGICAL
I – Early Failure (Failure To Osseointegrate)
The most common complications associated with early failure include improper implant selection, overheating bone + 47°C, placing implants in immature bone, contamination of the implant body, infection and pre-mature loading. Due to a lack of osseointegration or only limited osseointegration a reversal tool from the manufacturer will usually suffice to remove the implant body. Otherwise a fixture removal kit will need to be used to remove the implant body.
II – Late Failure (Peri-implant Disease)
Peri-implant disease is comprised of peri-mucositis and peri-implantitus. Peri-mucositis is a reversible disease if treated at an early stage. However untreated peri-mucositis may proceed to irreversible peri-implantitus. The incidence of peri-implant diseases has been suggested to be as much as 47%. Peri-implant diseases share many factors in common with periodontal disease. Peri-implant mucositis has been defined as presenting with inflammation of the soft tissues; probing pocket depths of less than 4 mm with bleeding on probing, and/or suppuration. On the other hand, peri-implantitus presents with inflammation of the soft tissue, probing pocket depths greater than 4 mm with bleeding, suppuration, radiographic evidence of bone loss and progressive loss of supporting bone beyond biologic bone remodeling. The inflammatory cell infiltrate tends to be more severe in the implants versus the natural dentition. In the case of peri-implantitus, if bone loss is minimal (7/3 threads) one can proceed with conservative treatment as for peri-mucositis. However, if bone loss is progressing or advanced, surgical intervention including a regenerative component is preferable. A bone collector instrument can be employed to harvest autogenous bone to be used in the regenerative procedure; e.g. Auto Bone Collector (Hiossen Implants). In the case of a failed implant or mobility, non-retrievable or a fractured implant body explantation is recommended using a fixture removal kit and replacement with the new implant at the appropriate time.
Picture 1: Fractured Implant
CONCLUSION
Implant complications are frustrating for both the clinician and the patient and most often present a challenge to the clinician occasionally involving the inconvenience, time and expense of replacing the implants and the prosthesis. The incidence of technical complications is generally low however the incidence of implant disease is unfortunately increasing with the global increase in the number of implants being placed.
Dr. Jim Grisdale
Hiossen Faculty Member