Different Methods to Salvage the Fractured Abutment Screws and Potential Reasons of Abutment Screw Loosening: A Narrative Review

ABSTRACT

Dental implant restoration is a popular therapy for replacing lost teeth and regaining human masticatory function. However, studies have shown prosthetic problems like implant fracture, screw loosening, and screw fracture. Abutment screw loosening is the second most common reason for implant-supported restoration failure after loss of osseointegration, especially in single implant restorations. This literature review aims to synthesize data on screw loosening reasons and salvage methods.

INTRODUCTION

Osseointegrated implant-supported prostheses, particularly titanium endosteal implants, are a reliable treatment for missing teeth. However, they face challenges such as mechanical issues, which can affect the prosthesis’ longevity and success.[1] Dental procedures can cause anxiety and pain, making pain control and assurance crucial during and after implant surgery.[2] Mechanical and biological factors are crucial in determining prosthesis longevity and success. Issues like abutment screw fracturing, incorrect placement methods, biomechanical overload, and manufacturing mistakes can lead to failures. Screw mechanics are complex, with abutment screw fractures common and loosening being the second most common issue.[3]

NUMEROUS VARIABLES HAVE BEEN PROPOSED AS POTENTIAL CAUSES OF LOOSENING ABUTMENT SCREWS

Abutment screw loosening is influenced by factors like preload, settling effect, coefficient of friction, screw material, connection geometry, number and diameter, and restoration design. Preload should be 65% of the breaking strength or 75% of the yield strength. The settling effect occurs when rough spots flatten under pressure, decreasing forces. To prevent loosening, screws should be tightened after insertion and regularly.[4,5]

Screw material, connection geometry, and restoration design can impact screw loosening in implants. Wider implants increase stability and reduce stress on the abutment screw. The design of the restoration and occlusion table can also reduce screw loosening. Strategies like narrowing the buccolingual dimensions or shifting the occlusal contact region can help reduce strain on abutments.[6,7,8] Factors increasing and decreasing the load to screw depicted in [Table 1].[9]

Table 1.

Factors increasing and decreasing the load to screw[9]

Increasing factors	Decreasing factors
IA separation due to micromovement	Design which locks with friction and no flat surface between IA
Torque inadequacy	Torque should be adequate
IA mismatch	Less COF between IA
Off-axis load	Axial load
Less number and size of implants	More number and width of implant
Cantilever increased	Reduced cantilever
Sharp cusp and large occlusal table	Flattened cusp and narrow occlusal table
External hex connection	Internal hex connection

RISK-BASED EXAMINATION AND DIAGNOSIS

After diagnostic and examination procedures, a gross plan must be created using basic instruments and modifications. Stiff instruments like scalers, sickle explorers, and endodontic explorers can be used to extract broken fragments, but caution is advised as they can damage the implant’s internal threads.[10] Flexible devices like endo-files should be used sparingly. An ultrasonic scaler can loosen the screw if a hand instrument is unable to move the fractured portion. Moderate risk involves screw modification using rotating tools, while high risk involves deliberate implant modification.[11,12,13] Successful implant restoration depends on effective screw and implant retrieval techniques [Tables 2 and 3].

Table 2.

Screw retrieval techniques[14,15,16,17,18,19,20]

Lumen Technique	Applicator tip squeezed between implant and screw
Reverse Torque	Applying torque in the opposite direction of the insertion
Piezoelectric Scaler	Using ultrasonic vibrations to loosen the screw
Cotton Driver	Employing a cotton-tipped instrument to grip and remove the screw
IMZ Retrieval Kits	Specialized toolkits designed for screw extraction
Screw Modification	Altering the screw or implant to facilitate removal (e.g., creating a slot, using a trephine)
Ultrasonic Instrumentation	Using ultrasonic energy to loosen or remove the screw

Table 3.

Summary of implant modification techniques and researchers for recovering damaged dental implants

Researcher(s)	Technique	Specific Method
Fauvell et al.[14]	Lumen Technique	Applicator tip in apical direction
Satterwaite and Rickman[15]	Endodontic File	Curved-tip file for thread extraction
Patel et al.[16]	Ultrasonic Instrumentation	High-powered magnification and coaxial light
McGlumphy and Yilmaz[17]	Washer Technique	Using washers to engage and provide preload
Gupta et al.[18]	Post and Core	Creating a custom post and core for implant restoration
Harshakumar et al.[19]	Ti Post and Core	Using titanium post and core with acrylic resin pattern
Lee JH et al.[20]	Modified Scissors	Using modified scissors to extract implant remnants
Shah and Lee[21]	Cast Post and Laser Welding	Replacing locator abutment screws with cast post and laser-welded attachments

Dental implant screws have improved due to engineering literature’s study of screws. A strong bond between implant and abutment is crucial for proper operation and stability. Abutment screw loosening is more common in external hex designs due to limited engagement and a short fulcrum point.[22,23] Techniques to reduce screw loosening include achieving ideal screw joint preload and adding antirotational devices. Internal hex connectors have less screw loosening due to long wall engagements, unified body, and flexibility.[24,25]

CONCLUSION

Proper treatment planning, occlusal scheme awareness, torque adjustments, and recall visits can reduce abutment screw loosening and fracture, preventing implant placement-related screw breakage.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.