Removal of broken screws on implant abutment by digital guide plate: A case report and literature review

Abstract

Implant restoration is currently the most mainstream method for repairing missing teeth. With the increasing number of plantings, various planting complications begin to be paid attention to. Among them, there are many reports of disability phenomena such as loose and broken abutment screws and broken top screws, which cause the implant to fail or fail to function. In recent years, with the development of computer-aided software and its application in the field of oral treatment, digital guide plates based on 3D printing of oral CBCT scanning data are widely used in oral implants. Therefore, we explore the application prospect of post-core crown restoration after removing broken screws from the implant abutment with a digital guide plate. We reported a case of upper right first molar implant abutment screws broken, which were removed by a digital guide plate and customized turning bur. The resin-matrix ceramics crown post core was prepared, and then the occlusal force was tested by the T-ScanIII system. It provides a reference for the application of digital guide plates in special cases such as broken screws of implant abutment.

Introduction

Implant restoration is currently the most mainstream method for repairing missing teeth. ¹ The implant neck configuration influenced the strain distribution and magnitude in the cortical bone and cancellous bone tissues. ² In dental crowns the multilayer structure with functional elasticity gradient modifies the stress distribution in the restoration. ³ The use of resin composite can attenuate the stress magnitude on the cement layer, and the use of acrylic resin can attenuate the stress magnitude on the connector region. ⁴ With the increasing number of plantings, various planting complications begin to be paid attention to. ⁵ Due to many factors such as abnormal occlusal stress, periodontal diseases, and poor masticatory force, implant restoration may have some complications, including abutment fracture, implant fracture, abutment screw fracture, etc.^{6 –9} In recent years, with the development of computer-aided software and its application in the field of oral treatment, digital guide plates based on 3D printing of oral CBCT scanning data are widely used in oral implants. ¹⁰ In this study, we reported a case in which the screw of the implant abutment was broken and could not be removed intact. A digital guide plate and customized turning bur were used to remove residual screws in implants, and then post-core bonding was prepared, and resin-matrix ceramics was made digitally to restore abutment shape.

Case report

This report has been approved by the ethical review of XX Hospital (KS20220624001). The patient signed the informed consent form. A 63-year-old male patient was admitted to our hospital due to the crown loss of the right upper posterior tooth implant 1 week. The patient reported that 5 years ago, the upper right first molar was implanted and restored after being extracted due to caries, and the implant crown fell off after accidentally chewing hard objects 1 week ago. He had a history of hypertension and diabetes for many years and a history of smoking for more than 40 years. Intraoral examination showed that the smooth collar of the bare implant, gingival coverage, exposed broken end of the screw, and no obvious loosening of the implant was found in the upper right first molar position (Figure 1(a)). Cone beam computer tomography (CBCT, NewTomVGi, Italy) showed that there was the right upper first molar implant (4.1 mm × 10 mmSP, Straumann, Switzerland), the mesial neck absorption was 0.5 mm, and the occlusal relationship was normal. Therefore, he was diagnosed with a dentition defect of the right upper posterior teeth and a broken screw of the implant abutment. Combined with the basic situation of patients, a digital guide plate and customized turning bur were used to remove the remaining screws, post-core bonding was prepared, and resin-matrix ceramics were used to restore the abutment shape.

Figure 1.

Digital surgical guide fabrication and broken screw removal: (a) intraoral photos of implant superstructure after falling off, (b) Erbium laser resection of overlying gingiva, (c) complete exposure of implant after resection, (d) design bur feeding direction, (e) digital surgical guide plate forming, and (f) the broken screw is removed with the aid of a digital surgical guide.

First, the digital guide plate was made and the screws are removed. Erbium laser (M021-3AF/3, Fotona, Slovenia) was used to remove hyperplastic gingival tissue and fully expose the implant neck edge (Figure 1(b) and (c)). The intraoral scanner (3shape, Denmark) was used to scan the upper and lower jaws, which were imported into the guide plate design software (3shape, Denmark) together with CBCT data. The diameter of the abutment screw of the implant was 2 mm. To avoid implant damage, we selected a retention pin with a diameter of 1.5 mm for simulation. After positioning the entry angle, the STL format file was generated, and then the digital guide plate was printed in 3D (Figure 1(d) and (e)). An extended turning bur was used (# 1557, MANI, Japan) with a working blade diameter of 1.5 mm and a total length of 25 mm. The speed of the low-speed electric motor (ROSE CLINC3, China) was 4000 rpm. The turning bur passed through the custom guide ring and began to grind out the broken screws left in the implant. Each depth was controlled within 1–2 mm. Take out the bur when working for no more than 20 s each time. Flush with normal saline solution in large quantities to flush the formed debris at the target position and to cool. After the screws were completely removed (Figure 1(f)), a large amount of flushing was continued to remove the debris in the implant generated by preparation.

Secondly, post-core design and resin-matrix ceramic restoration were carried out. After the abutment screws were removed, the model was prepared with silicone rubber (Figure 2(a)), and the pure titanium post core was designed. After intraoral try-on, post-core bonding was carried out with glass ionomer (Figure 2(b) and (c)). After bonding, the excess and spilled adhesive should be removed as much as possible to prevent the residual adhesive from stimulating the tissues around the implant. After post-core bonding, a silicone rubber model was made for crown restoration. The patient used resin-matrix ceramics (LT A2 Elchon, China) for crown restoration. After the crown was made, try it on in the mouth and blend it. After the whole mouth cleaning treatment, the final bonding fixation was completed with resin binder (Figure 2(d)–(f)).

Figure 2.

Design of post-core and restoration of a resin-matrix ceramic crown: (a) post core silicone rubber impression, (b) the pure titanium post and core are made and the model is tried on, (c) post core in oral trial and bonding, (d) making resin matrix ceramic crown, (e) wear the crown, adjustment, and bonding, and (f) after completing the repair, X-ray imaging is performed.

After the repair was completed, the patient underwent an occlusion test. He first used occlusion paper (40 µm, Boshi, Germany) for the median, left lateral, and right lateral occlusion. The patient was in the median position, and the occlusal contact point can be observed. The occlusal area and the number of contact points of the upper right first molar were smaller than those of the contralateral teeth with the same name (Figure 3(a)). Subsequently, occlusion analysis was performed using T-scanIII Digital Occlusion Analysis System (T-scan Novus System, tekscan, USA). When he underwent median occlusion and reached the maximum bite force, the bite force on the left and right sides accounted for 55.9% and 44.1%, respectively. The center of the occlusal moment was located slightly ahead of the center. Among them, the bite force of the upper right first molar was less than that of the opposite teeth with the same name, and the initial contact time of the upper right first molar was later than that of other teeth (Figure 3(f) and (g)). One year later, the patient was reexamined. Because he usually had the habit of drinking strong tea, tea spots can be seen adhering to the tooth surface (Figure 3(b)). After supragingival scaling and sandblasting (Figure 3(c) and (d)), the patient underwent T-scanIII bite force test. The bite force of the upper right first molar was enhanced, but it was still less than that of the opposite teeth with the same name, achieving the expected restoration purpose (Figure 3(h)). After 1 year, no further absorption of bone tissue around implants was found (Figure 3(e)).

Figure 3.

Postoperative images: (a) postoperative occlusal paper point photo, (b) 1 year after the operation, tea spots attached to the tooth surface, (c) 1 year after the operation, the tooth surface morphology after supragingival scaling, (d) bite photograph 1 year after operation, (e) 1 year after the operation, X-ray imaging, (f) T-scan: The right upper first molar is not contacted, while the other teeth are contacted, (g) T-scan: Full contact of median occlusion, and (h) 1 year after the operation, T-scan image of complete contact of median occlusion.

Discussion

In implant-supported single crown or multi-unit bridges, the 5-year incidence of abutment or screw fracture is between 0.3% and 0.8%. ¹ Although the probability of occurrence is not high, once it occurs, it is often forced to replace the implant because of difficulty in taking out or damaged implant in the process of taking out, which is regarded as a complication with serious consequences. ⁹

When the abutment screw breaks, there are generally four ways to take it out. (1) Ultrasonic oscillation: ultrasonic equipment was used to oscillate the broken end of the abutment screw, and screw it out counterclockwise after loosening; (2) Screw take-out kits: Many planting brands have their screw take-out kits; (3) Slotting method: firstly, slotting the screw section with the emery turning bur for preparing teeth on the adjacent surface, and then turning it out with a screwdriver; (4) Direct grinding and removing method: free hand operation with diamond ball drill destroys the central screw and takes it out. For these four types of methods, the first three are mostly used in cases where the screw section is higher or flush with the implant. For cases where the broken end of the screw is located in the implant, the three methods are often difficult to remove smoothly and without damage. In the fourth method, the free hand method may cause uncertain complications to the internal structure of the implant and even the soft tissue around the implant.^5,11 Recently, it has been reported that the post-core crown is converted to the post-core crown after screw grinding, but these studies have directly removed broken screws and internal threads of implants by free hand.^9,12,13 In this case report, we tried to remove residual screws under the guidance of customized digital guide plates. We aimed to remove the broken screw in a less damaging way and repair it again like a post-core crown. Compared with the traditional replanting and freehand operation, this method has less damage, saves more time and cost, avoids surgery, and relieves patients’ pain.

In this case, a mixed support guide plate was used. Considering that the operating end is located at the free end, to strengthen the stability of the guide plate, the guide plate is extended to the canine on the opposite side. This allows clinical procedures to be carried out in a pre-designed direction and depth and maximally prevents damage to the implant’s internal structure when residual screws are worn out. At the same time, it can reduce the vibration of the implant during operation, thus reducing the damage to the stability of the implant and protecting the soft tissue around the implant. ¹⁴ From the degree of mandibular tooth wear and T-scan III data, it can be judged that the occlusal force of the patient is large, and the old restoration may be broken due to excessive bearing force of abutment screws caused by occlusal interference. Therefore, reducing the occlusal stress of implant prosthesis becomes the key to preventing re-fracture.

In this case, resin-matrix ceramics were selected in the process of crown restoration mainly because of their good physical and chemical properties. Resin-matrix ceramics have physical hardness and wear resistance closer to natural teeth, and better adhesion and machinability.^{15 –17} Although its hardness is not as good as that of glass ceramics and zirconium ceramics, considering the problems of neck bone absorption and retention force of post and core after the broken implant screw, in this case, it is proposed to reduce the closing and lateral bite force of resin- matrix ceramics in the design, to offset the risk of re-breaking caused by the poor bite. In the blending process, the contact area and contact height of resin-matrix ceramics are intentionally reduced, resulting in a bite without contact and a bite with light contact. This is also to protect the stability and safety of implants.

In the bite force test, the traditional bite paper will be interfered with by subjective factors such as bite paper thickness, and saliva secretion of patients and operators. ¹⁸ Therefore, the T-scanIII occlusion analyzer was used for occlusion analysis in this case. The advantage of T-scanIII includes that it can dynamically analyze the occlusal process, and can give the relative strength of each tooth and the sequence of contact between each tooth. Because the implant and bone tissue are rigidly combined, the occlusal stress is directly transmitted to the alveolar bone surface. Because there is a small amount of bone resorption at the proximal and middle end of the implant in this case, the occlusion was accurately adjusted under the guidance of T-scan III. Therefore, the initial contact time of the implant was slightly later than that of the natural tooth, to protect the implant during occlusion.

The method used in this case still has some shortcomings. First of all, to minimize the damage to the implant, it is impossible to prepare a complete pile channel shape inside the implant. Therefore, the anastomosis between a customized post-core and an implant is problematic. Secondly, although it has been considered that the implant is a gingival horizontal implant, the spilled adhesive can be removed to the maximum extent during post-core bonding, but there may still be residual adhesive affecting the implant. It is necessary to observe the situation around the implant through long-term follow-up. Additionally, to obtain less bearing capacity for implants, we use resin-matrix ceramics for restoration. However, due to the lack of hardness and wear resistance of resin-matrix ceramics, the prosthesis may crack in the long term. Finally, the three-dimensional finite element analysis of the post crown in our study is on the implant. In future study, 3D finite element analysis needs to be conducted on the different interfaces of the material to investigate its durability for the design.

Conclusion

This case report described a case in which a broken abutment screw could not be removed in a non-destructive manner. Digital guide plate technology was used as a guide, the broken screws were removed and then the post-core crown was repaired. To prevent the tooth from breaking again, the crown was made of resin-matrix ceramics, and then the occlusal force was accurately adjusted by a T-scanIII occlusal analyzer. During the 1-year follow-up, the patient can use it normally without adverse reactions such as crown breakage, peri-implant inflammation, and bone resorption around implants, thus achieving the purpose of expected restoration.