Cold welding is characterized as the bonding and adhesion process between two metallic components, such as the implant–cover screw, implant–healing abutment, or implant-final abutment. The phenomenon of cold welding can pose an unexpected complication, wherein clinicians encounter difficulties in separating the interconnected components, presenting a highly challenging scenario. Unfortunately, there is currently no universally effective technique to successfully separate the components, with efforts often leading to damage of the implant internal threads or fracture leading to implant removal. The incidence of this complication has been reported to range from 0.5%–8%. (Figure 1)
Etiology: [1] [2] [3]
Numerous factors may contribute to the predisposition of cold welding complications, including variations in implant type, internal versus external connection, and differences in screw head design, material, and diameter. (Figure 2) While the literature provides limited discussion on this complication, various case reports highlight local issues that can exacerbate the risk, such as:
- Application of excessive torque and preload to the cover screw or abutment.
- Manufacturing errors in either of the two components
- Presence of bone debris and dried blood on implant component surfaces, leading to the development of a blood fibrin “glue.”
These factors collectively underscore the complexity of preventing and managing cold welding incidents, necessitating careful consideration and awareness during clinical procedures.
Treatment Options:
When confronted with cold welding clinical situations, clinicians are presented with various treatment options, which may include:
- Separation of the Cold-Welded Components: This involves attempting to carefully separate the cold-welded components. Techniques such as applying controlled force, using specialized instruments, or introducing modifications to weaken the bond may be employed to facilitate successful separation.
- Submerging the Implant – Restore with Conventional Prosthetics: Submerging the affected implant and subsequently restoring the area with conventional prosthetics is an option. This approach allows for the creation of a new restoration while leaving the cold-welded implant in place, minimizing the need for complete removal.
- Implant Removal with Re-insertion of an Implant: The clinician may opt for complete implant removal. After removal, a new implant can be re-inserted.
The selection of the most suitable treatment option depends on the specific circumstances of each case, and clinicians should carefully assess the feasibility and potential risks associated with each approach to make informed decisions.
Management – Separation Of Implant Components: [4] [5]
When confronted with the task of separating components without damaging internal implant threads, various approaches and instruments can be employed, with the specific method depending on the type of implant connection present. [6]
Cover Screw:
- Reverse Torque Wrench (Maximum – 40-50 N/cm): Employing a reverse torque wrench within the specified torque range can help loosen and facilitate the removal of the cover screw without causing damage to the internal threads
- Ultrasonic Scaler: this instrument maybe used to vibrate and remove a cover screw in counter-clockwise direction: The application of an ultrasonic scaler to induce vibrations can assist in breaking the coldwelded bond, making it easier to remove the cover screw.
- Prepare Screw Access Slot Cover Screw with Reverse Torque: Creating a screw access slot on the cover screw and applying reverse torque can provide an alternative method for separating the components.
- Apply Crushed Ice over the Cover Screw to Shrink the Screw Threads: Placing crushed ice over the cover screw can cause contraction, potentially aiding in the loosening of the threads and facilitating the removal process.
- Drill Through the Center of Cover Screw with Carbide (High Speed + Round Bur): Using a drill with a carbide tip, such as a high-speed round bur, to carefully drill through the center of the cover screw can disengage the body, allowing for the subsequent removal of the threaded screw.
Abutment (Healing):
Modification of Healing Abutment (i.e., Two-Parallel Sides) and Removal with Rongeurs/Extraction Forceps:
Modifying the healing abutment, particularly by creating two parallel sides, facilitates its removal using rongeurs or extraction forceps. This modification enhances grip and maneuverability during the removal process.
Abutment (Final):
Use of Hemostats or Forceps to Rotate the Implant from the Implant Body:
Employing hemostats or forceps to carefully rotate the implant from the implant body aids in the separation of the abutment during the final stage. Proper placement of the instrument at the most occlusal aspect enhances the fulcrum force, facilitating controlled and effective rotation. Care should be exercised as this procedure may lead to a fracture of the implant neck.
It is crucial for clinicians to exercise precision and choose the appropriate instruments for each step, considering the specific characteristics of the abutment and implant type. Careful execution of these techniques can help ensure successful component separation without compromising the integrity of the internal implant threads.
Cold Welding Prevention: [7] [8]
In the literature, certain implant systems, such as Astra and Straumann, have been reported to exhibit a higher incidence of cold welding complications, primarily attributed to the morse taper design of these systems. Various techniques have been advocated to mitigate the risk of cold welding:
- Lubrication Applied on Threads of Implant Components (Water-based Petroleum Jelly or Antibiotic Ointment): Application of lubrication, such as water-based petroleum jelly or antibiotic ointment, on the threads of implant components helps reduce friction and may decrease the likelihood of cold-welding during assembly and disassembly.
- Irrigation (Chlorhexidine) of the Internal Implant Threads Prior to Abutment Placement: Prior to abutment placement, irrigation of the internal implant threads with chlorhexidine serves to cleanse and prepare the surfaces, potentially minimizing the risk of cold welding.
- Verification of Accurate Insertion Torque: Applying hand torque pressure torque within the range of 10-15 N/cm for cover screws and healing abutments ensures appropriate insertion torque. For final abutments, manufacturer recommended torque should be utilized.
- Verification of Accurate Torque Wrenches: To prevent excessive torque, ensuring the precision and accuracy of torque wrenches used during implant procedures is vital for preventing excessive torque application. Regular calibration and adherence to manufacturer specifications contribute to reliable torque delivery and help minimize the risk of cold-welding complications.
These preventive measures aim to enhance the overall success of implant procedures and reduce the incidence of cold welding, particularly in systems with morse taper designs.
Conclusion
Effectively managing cold-welding complications presents a significant challenge for practicing clinicians. The intricacies involved in separating components can vary widely across cases, and thus, a universal solution is not feasible for the diverse clinical scenarios that may be encountered. This article aims to tackle the inherent challenges associated with cold-welding complications and provides a range of approaches to navigate the complexities inherent in the diverse clinical situations.
References
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[2] Satterthwaite J, Rickman L. Retrieval of a fractured abutmentscrew thread from an implant: a case report. Br Dent J2008;204:177-180.
[3] Balshi TJ. An analysis and management of fractured implants:a clinical report. Int J Oral Maxillofac Implants 1996;11:660-666.
[4] Healing abutment Does Not Unscrew: safest way to removeit without damaging the Implant Threads? Available from:www.osseonews.com
[5] Norton MR. Assessment of cold welding properties of the internal conical interface of two commercially available implant systems. J Prosthet Dent. 1999 Feb;81(2):159-66.
[6] Meisberger EW, Bakker SJ, Cune MS. Temperature rise during removal of fractured components out of the implant body: an in vitro study comparing two ultrasonic devices and five implant types. Int J Implant Dent. 2015;1(1):7.
[7] Krishna, R., R. Kejrival, and J. Suma. “Retrieval of Cold Welded Dental Implant Cover Screw Using a NewTechnique.” Int J Implantol Clin Res 6.3 (2015): 69-72.
[8] Arshad M, Mahgoli HA, Rasouli K, Refoua S. A novel technique to retrieve cold-welded implant abutment: A case series. Clin Case Rep. 2019 Aug 16;7(10):1854-1857.