A Case Study on Custom Cast Post: An Alternative for Fractured Abutment Screw in Implant

Introduction

Implantology is a progressive specialty in the present era of dentistry. Dentists can replace one or more missing teeth and improve both the aesthetics and function in a long-standing manner, thereby satisfying the desire of the patient.

Though implants are made of materials with properties close to the body tissues, implants are susceptible to various biological and mechanical problems, which include screw loosening, screw fractures, cement failures, loss of osseointegration, progressive marginal bone loss, adverse soft tissue reactions, sensory disturbances, etc.¹ Screw fractures are the common complications noticed in clinical practice. As there is a chance of damage to the implant during the removal of the fractured screw, a high degree of manual dexterity is needed and thus it is a challenging task for an implantologist^_.2

Literature has described different methods for the removal of a broken screw, but the knowledge, ability, and meticulous skills of the clinician play a vital role to overcome these complications. The present case study describes one of the methods that can be used to manage the fractured screw complication and to restore it in a functional and aesthetically satisfactory manner.

Case Presentation

A 26–year–old female visited the department of periodontology with a complaint of loosening of the implant-supported crown. The patient’s history revealed that the implant was placed one year back to 15 and the prosthesis was given 6 months after the placement of the implant. The patient noticed a slight movement of the crown one month back which gradually increased.

On examination, a cement-retained Porcelain fused metal (PFM) crown with a loosened abutment was noticed and a fractured crown or implant was absent, hence a hole was drilled into the PFM crown using a diamond round bur. But unfortunately while tightening the screw using the ratchet with a one-quarter turn, the abutment screw was broken (Figure 1A and 1B).

Radiograph revealed a well-integrated implant with a small abutment screw fragment present exactly at 1/3rd of the implant.

The clinician tried to remove the broken fragment retained in the fixture using explorers, spoon excavators, cavitron (ultrasonic scaler), and low-speed handpiece but all these methods were unsuccessful.

Finally, the screw fragment was broken into pieces and internal threads were eliminated using an airotor with carbide tungsten bur (Figure 2).

A custom-made post and core were fabricated by direct technique and sent to the laboratory. Later it was cemented on the implant and an impression was made for crown fabrication (Figure 3A, 3B, 3C, and 3D).

The crown was placed and the results were acceptable both for the patient and the clinician (Figure 4)

Discussion

The present clinical implant complication is one of the most common situations a dentist has to deal with implant prostheses.¹ Dental implant complications are divided into biological and hardware-related complications. Biological complications relate to soft and hard tissue surrounding the implant and hardware complications related to the implant and prosthetic components of restorations.

The abutment is connected to the fixture with the help of an abutment screw. The primary reason for screw fracture is screw loosening which can be aggravated by non-axial movements that can occur during prosthetic loading or due to parafunctional habits like bruxism or an ill-fitting superstructure. Overloading can also result in screw loosening which is closely linked to the screw fracture.

Other possible reasons can be a defect in the screw itself or over torqued on insertion or improper abutment placement which results in increased stress. Reduced interocclusal distance and inefficiency of the operator can also act as a risk factor for fracture of the abutment screw.³

Seetoh and coworkers tested three systems. In every system, there were failures of at least one component, either the abutment, the abutment screw, and/or the implant neck.

Significant differences were noted among these systems. Thus various abutment fixture connection designs can also affect fracture resistance.⁴

Jung et al., (2008) reported that prosthetic screw loosening has an incidence rate of 6.7% and the rate of prosthetic screw fracture is 3.9%. ^5,6

The fractured screw segment inside the implant must be removed otherwise the implant will lose its ability to retain the prosthesis and the existing prosthodontic restoration can no longer be used.⁴ Retrieval of fractured abutment screw is a difficult process and need a high level of manual dexterity. It is an even more complex procedure in cement-retained crowns compared to screw-retained crowns. In cement-retained crowns, the crown has to be removed with judicious force with the help of a straight elevator or a crown remover.³

Treatment options for the management of this condition include

1. Retrieving the screw with a screw retrieval kit

2. Fracture of the screw using tungsten carbide bur and removal

3. Fracture of the screw with bur and post-space preparation in the implant

4. End of the bur or spoon excavator is made into a chiseled form and the screw head is engaged and removed.

5. Counterclockwise rotation with a sharp dental explorer or a probe.^{7, 9}

In the present case scenario, the conventional technique such as custom-made cast post which is used for natural teeth to retain a core restoration and crown and also to redistribute stresses down onto the root was used as a successful compromise option for replacing fractured implant abutment screw.

Conclusion

The rehabilitation of a fractured abutment screw in an implant is a complicated and vital step that is performed to prevent further fracture of other implant components. This simple non-invasive technique of custom cast post fabrication can be performed on the patient which has a satisfactory and excellent result.

Conflict of Interest

None