A dental implant provides a permanent foundation for a replacement tooth, consisting of an implant body placed in the jawbone and a prosthetic part above the gum line. Connecting the implant body to the artificial tooth (crown or bridge) is the implant screw, which can be an abutment screw (connecting the abutment to the implant body) or a fixation screw (securing the restoration directly). When this screw fractures, the prosthetic tooth is no longer securely attached. This mechanical complication requires a precise procedure to retrieve the broken fragment without damaging the rest of the implant system.
Why Implant Screws Break and When Removal is Indicated
Implant screws are engineered from durable materials but can fail due to mechanical stresses. The most frequent cause of fracture is metal fatigue, resulting from repeated, cyclical chewing forces. Excessive occlusal load, often from teeth grinding (bruxism), accelerates this fatigue. Poorly fitting prosthetic components, where the crown or bridge does not seat properly, also concentrate stress onto the screw, leading to fracture.
Inadequate torque during initial placement is another factor, as an under-tightened screw is more likely to loosen and fracture. Removal of the broken fragment is mandatory when it causes prosthetic instability, such as a loose or detached crown or bridge. Intervention is also indicated if the fragment compromises the implant seal, which could lead to chronic inflammation or bacterial ingress. Early intervention is necessary to prevent further damage to the implant fixture or surrounding bone.
Specialized Tools and Techniques for Retrieval
Retrieval begins with conservative techniques to minimize damage to the implant’s internal threads. If the fragment is accessible and slightly mobile, a dental professional first uses a fine-tipped probe or explorer. They gently engage the fragment’s edge and rotate it counter-clockwise. This initial approach often succeeds because the tensile forces holding the screw disappear upon fracture, leaving the fragment relatively loose.
If simple rotation fails, the next step is using ultrasonic vibration, typically applied with a specialized scaler tip. High-frequency vibration disrupts debris or binding forces locking the fragment in place. This non-invasive method often loosens the fragment enough for removal with a probe or aspiration tool, avoiding mechanical contact with the internal threads.
For deeply lodged or resistant fragments, dedicated retrieval kits are necessary. These kits use specialized reverse-torque instruments that cut a pilot hole into the center of the broken screw. A reverse-threaded tap or drill embeds itself into the fragment, allowing the instrument to grip the piece. Applying reverse rotation with a motor unscrews the fragment from the implant body. A more aggressive technique, coring, uses a trephine bur to cut away the fragment and surrounding implant material, but this risks damaging the implant fixture and is reserved for fragments that cannot be grasped.
Factors Determining Procedural Difficulty
The complexity and success of retrieval are heavily influenced by several variables specific to the implant. The position in the mouth is a major factor, as posterior molar areas present greater difficulty due to limited visibility and access compared to anterior implants. Limited visibility often necessitates advanced visual aids, such as an operating microscope, to enhance precision.
The depth and orientation of the fracture also matter, as fragments broken deep within the fixture are harder to engage than those near the access opening. Implant system design plays a role; older external connection implants may allow easier access than modern internal connection designs, which feature deeper mating surfaces. Furthermore, proximity to vital anatomical structures, such as the inferior alveolar nerve or maxillary sinus, limits the force and types of rotary instruments that can be safely used. These constraints require extreme caution and often extend the time needed for safe removal.
Post-Removal Considerations and Restoration
After successful removal of the fractured fragment, the remaining implant fixture requires a thorough assessment. The internal threads must be meticulously checked for damage caused during the fracture or retrieval process. This assessment often involves passing a specialized thread tap through the implant channel to clean and potentially re-form any minor thread deformation.
If the implant fixture and threads are intact, the site is cleaned, and a new, correctly torqued screw secures the replacement restoration. If the internal threads are compromised or the implant body is cracked, the fixture is deemed non-restorable. In this scenario, the damaged implant must be surgically removed (explantation). Following explantation, the resulting bone defect often requires bone grafting to repair the site and rebuild adequate volume. A healing period of several months is then required before a new dental implant can be considered for placement.