A revolution in the research and technology of implants during the last two decades has made the replacement of missing teeth with endosseous implants the standard care, and an implant-supported prosthesis is the first line of treatment and long-lasting rehabilitation [1]. Dental implants have recorded high success rates over 97% over 10 and 75% over 20 years [2]. There is an infrequent occurrence with multi center studies and several meta-analyses indicating 93% survival rates of dental implants [3,4]. However, there is still apaucity of data in the literature regarding follow-up of implants in function for at least 5 years or more [5,6]. Failures due to loosening or fractures of the prosthetic and abutment screws, as well as implant fractures can occur [7], mandating immediate implant removal [8]. This extends and complicates the therapeutic process, and jeopardizes the attempts of the clinician to achieve satisfactory function and esthetics [3-7]. For the patient, this usually involves further cost and additional procedures [9]. Few data are still available in the literature concerning the removal of failed dental implants and evidence is still focused primarily on case reports or trials with a limited number of patients [10]. The decision-making plan should be aimed at assisting and simplifying the process of selecting the appropriate alternative once a failure has occurred [11]. The aim of this work was to supply dental community with an up to date about implant failure by focusing on when, why and how to remove?

Implant failures are classified into: Early ones occuring from weeks to few months after placement caused by factors that interfere with normal healing process or by an altered healing response, and Late failures arising from pathologic processes that involve a previously osteo-integrated implant [12]. Implant failures can generally be categorized as shown in (Figure 1) [13].

Figure 1: Classification of implant failures [13].

The most prevalent diagnostic criteria for defective implants are as follows:-

Clinical Signs of Early Infection

Signs of infection which occur during the early stage of healing are more critical than if they occur at a later stage. Early infection can lead to disruption in the implant's osseointegration into the surrounding bone. Swelling, fistulas, suppuration, early/late mucosal dehiscence and osteomyelitis during the healing period (3-9 months) are the most common complications seen, suggesting implant failure [14].

Clinically Distinct Movement

Several forms of mobility have been defined as: (1) rotational mobility; (2) lateral or horizontal mobility; and (3) axial or vertical mobility [15]. Even, minus distinct radiographic bone changes, clinically evident implant movement may be present. Mobility is therefore the cardinal sign of implant failure [16].

Radiographic Signs of Failure

Two well-distinct radiographic images may be present in implant failure. First, the entire implant is covered by a thin perifixtural radiolucence. This implies the lack of direct interaction with the bone implant and likely a loss of stability. The second is an increased median loss of bone. If suspected perifixtural radiolucency or severe marginal bone loss is detected, it is recommended that the prosthesis structure is removed and the implants are tested for stability. The required radiographic detection of implant failure is accompanied by clinically observable mobility after framework removal [17].

Dull Sound at Percussion

A muted sound is representative of soft tissue encapsulation on percussion. A definite sound of crystallization suggests that osseointegration is successful [16].

Bleeding On Probing

Bleeding on probing was an indicator of the condition of peri-implant tissue. However, recent findings suggest that it cannot be used to discriminate between a healthy and diseased peri-implant state and it has no scientific evidence to support it [18].

No or Loss of Osseointegratuion

Early failure happens before or at abutment insertions and is attributed to loss of osseointegration [19]. As implants fail to integrate, when cylindrical implants are used, the morbidity of failure is minimal. In this case a re-attempt at implant placement with a larger diameter implant or a bone graft followed by an implant will allow successful osseointegration (Figure 2). When non cylindrical implants are used, more trauma is caused on removal; this can lead to severe hard and soft tissue loss. Multiple operations can involve reconstruction of these defects (Figure 3). For this purpose, the placement of non-cylinder implants should be avoided [19].

Figure 2: a- Implant provisional in place, b-Occlusal view of implant with provisional restoration removed – note health of soft tissue. c- Impression coping attached and failing cylindrical implant being removed. d- Implant removed and remaining wound which usually heals without incident.

Figure 3: a-Non cylindrical failed Implants needed removal, b- Surgical wound from removal of non-cylindrical implant, c- Removed failing non-cylindrical implant, and c- Ridge contour following loss of hard and soft tissue after removal of non-cylindrical implants that have failed.

Late Failure

Occurring after occlusal loading, after inserting implant-prosthesis and it is related to any process that may affect the maintenance of previously established osseointegration [20] like:-

Peri-Implantitis

It is the main biological complication and is characterized as a pathological disorder that occurs in tissues around functionally loaded dental implants, characterized by mucosal inflammation and progressive marginal bone loss [21]. It is the primary cause of late implant failure [22]. Late failures have been demonstrated to be specifically linked to peri-implantitis (Figure 4) [23].

Figure 4: Intra-oral view of implants with progressive bone loss following perimplantitis.

Fibrous Down Growth (Encapsulation)

The implant that has lost integration will suffer from the entire implant body's fibrous downgrowth (Figure 5). This tissue serves as a shield against bone-to-implant interaction and replaces osseointegration [24]. Until implant placement, it is mandatory to thoroughly debride the implant socket and meticulously remove all soft tissue. Proper instrumentation would enable the clinician to enter the apex of the socket of the implant and be sharp enough to perform curettage on the osseous walls of the socket (Figure 6 a). After complete tissue removal, chemical modification is the next step (Figure 6 b). In addition, laser sterilization of the inflamed soft tissue surrounding the failed implant can help increase tissue tone during healing (Figure 6 c) [25].

Figure 5: Radiograph showing total integration loss and fibrous encapsulation.

Figure 6: a- Slade Blade socket curette (Paradise Dental Technologies) is used to remove fibrous soft tissue from the residual implant socket, b- Cotton pellets soaked with 60% citric acid used to detoxify an implant socket, and c- Laser sterilization of soft-tissue flap during implant removal to facilitate healing.

Positional Failures

Poor treatment preparation and/or poor surgical execution are responsible for the most common form of failure. With careful treatment preparation, proper site creation, the use of surgical guides and a thorough understanding of the restorative aspects of implant dentistry by the surgeon, this form of failure can easily be prevented. Malposition of the implant can lead to biomechanical problems to the screw joint or in severe situations to the implant itself due to overload (Figure 7 a,b) [26,27].

Figure 7: a- Malpositioned implants with a severely lingually inclined implant axis, And b- Occlusal view of the same case.

Biomechanical Failures

Possible causes of implant fractures include bruxism, large occlusal forces, and mechanical trauma, decreased implant diameters, material fatigue and advanced bone loss, leading to decreased mechanical support around the implant [28]. More recent fracture data was released by analyzing 19,087 implants in 8,501 patients. In 70 implants (0.4 percent) and 57 patients, fractures were observed. Less data is available with respect to zirconia implants [29]. These types of failures vary from screw loosening to implant components and implant breakage. Screw loosening was an often reported problem with implant supported restorations and when screws are cross-threaded, the implant may be weakened and when too much force is applied, the screw may break [30]. It is difficult to remove when screws are cross-threaded and broken and can make the implant unusable (Figure 8 a,b).

Breakage of Implants and Implant Components

This can also occur often due to poor treatment planning and exposing implants to excessive forces (Figure 9 a,b) [31]. The implant shown in Figures 9 a and b was treatment planned as a single implant in an incomplete dentition and a terminal tooth. The implant was connected to the tooth causing decay on the tooth, and eventually the implant to fracture under the load [31]. These types of failures can be avoided with proper treatment planning, a good understanding of screw joint mechanics and knowledge of the implant system used [19].

Figure 9: a. Restoration of the implant along with the broken implant portion, and b. Radiograph of implant supporting restoration in Figure 9a. Note that the implant has broken (red arrow) and the rest seat on the restoration has caused decay on the adjacent tooth (yellow arrow).

The factors that could cause implant fixture fractures were assessed in a study. The research included patients who from 2007 to 2015 encountered implant fixture removal due to implant fixture fracture at Seoul National University Bundang Hospital. Crown /implant ratio (Figure 10), implant fracture duration, clinical symptoms before implant fracture, broken implant treatment, and the effectiveness and survival rate of replacement implants were retrospectively analyzed. The findings showed that in 12 patients, 13 implants were fractured. The mean ratio of crowns/implants was 0.83:1. Screw loosening in five implants, marginal bone loss in five implants, and the involvement of peri-implant diseases in five implants were the clinical signs prior to fracture. All the broken implants were removed and re-implanted at 12 out of the 13 sites. In two patients, parafunction was observed: one with bruxism and one with attrition due to a heavy chewing habit. There were some clinical signs before the fracture of the implant. Therefore, if these clinical symptoms are observed, appropriate treatments can be taken before more serious complications result [32].

Figure 10: The method of measuring the crown/implant ratio = A/B.

Once the decision for the removal of an implant has been made, the selection of the appropriate removal technique should be addressed. The selected option should be fast, as minimally traumatic as possible and cost-effective for patient and dentist [10]. Once the decision for the removal of an implant has been made, you can select one of the following techniques:-

Trephine Burs

Implants with any degree of bone loss or mobility are removed using forceps through destroying osseointegration. However, the flap is raised and the bone around the implant is removed using a thin surgical bur etc. for implants with no bone loss and high osseointegration, and then removed with forceps. Several companies offer kits for the removal of implants. The implant can be removed by affecting only the bones around the implant by using a trephine bur that matches the diameter of the implant. Kits provided by some companies destroy osseointegration in a unique way. Osseointegration is lost when a strong reverse torque is applied by the operator after firmly attaching the package to the implant hex motor. Proper use of such kits minimizes trauma and permits implant removal [32]. As trephine burs is commonly regarded as a standard approach, it is therefore still a very popular technique for removing failed implants. Such burs occur in various diameters and should be selected to be just slightly larger than the actual diameter of the implant in order to eliminate the remaining bone as little as possible. With optimum water cooling, a cutting speed varying between 1,200 and 1,500 rpm is recommended to prevent overheating and thermal necrosis [33]. However, trephine burs can only be used if no less invasive alternative methods are applicable. Since complications such as mandible fractures and osteomyelitis have been identified in case reports, the local anatomy should be carefully examined, including conventional and cone-beam radiology if appropriate [34]. The use of CAD/CAM-generated surgical guides, which can also be used for guided explanation, has recently been identified as a new approach to trephine bur removal. The authors concluded that 3D guided surgery could be more precise and less invasive [35]. There are few case series and case reports evaluated this process [36]. This procedure allows for a less painful surgical approach for the removal of the failed implants compared with trephine burs. The authors point out that it is also possible to find blood vessels and nerves in close proximity to implants which can be affected. The devices operate at frequencies ranging from 24.000 to 29.500 Hz, which apparently allows for a precise and selective cutting in order to conserve sensitive structures [36]. Basically, with a diamond coated insert connected to a piezoelectric unit, a circumferential osteotomy is performed. The implant bone interface is thus destroyed by ultrasonic waves; however, intermittent application mode and adequate saline solution cooling is also compulsory. The osteotomy is performed as close as possible to the implant surface in order to remove only the least necessary amount of bone. In combination with broken and mal positioned implants, the technique was mainly identified. Compared with trephine bur procedure, better postoperative bone healing was observed [33]. Note that when piezo surgery is applied to patients with pacemakers, care must be taken. While no significant side effects were seen in an in vitro sample, further evidence was still needed [37].

Clinical Case Report for Re Moving Broken Abutment Screw off The Implant Fixture Inside

A male patient 70 old year asked Department of Periodontology to remove the implant fixture at second molar region of left mandible (Figure 11).

Figure 11: Preoperative panoramic X-ray image showing implant of #37 area shows the broken abutment screw off the implant fixture inside (yellow arrow).

The patient was diagnosed with a broken abutment screw inside the implant fixture via clinical and radiographic examination, and with the consent of the patient, an implant removal was scheduled. Block and infiltration anesthesia were administered on the surgical site. Upon anesthesia, intra crevicular and crestal incisions were followed using #12 and #15 blades. The full thickness flap elevation on the alveolar ridge crest secured a direct line of sight of the exposed implant. Trephine bur (Biomet, Warsaw, IN, USA) with 6mm outer diameter and 5mm inner diameter was placed on top of the implant fixture to make sure that it fits inside the bur. In a panoramic X-ray image, the depth of the implant fixture was measured and its inclination was compared to the adjacent teeth. Based on these, the implant fixture and surrounding bone were drilled at low speeds under saline irrigation using trephine bur. In order not to damage the alveolar bone, the loosen implant fixture was removed with caution by a dental elevator (Hu-Friedy, Chicago, IL, USA) and root forceps (Hu-Friedy, Chicago, IL, USA). The guided bone regeneration using the Osteon II 0.5 g (particle size 0.5∼1.0mm; Genoss, Suwon, Korea) and 10 x 20mm collagen membrane was added to the commonly shaped implant removal socket for the implant reinstallation. Interrupted suture was given for primary closure on the spot after properly positioning the buccal and lingual flap (Figure 12).

Figure 12: Conventional removal method applied on #37 region. a) Preoperative state showing a gingival defect. b) Removing implant by a trephine bur, elevator, and root forceps. c. Removal of the implant and the surrounding alveolar bone. d) and e) Immediate grafting of bones and collagen membrane on the implant removal socket. f) Suture for a primary wound closure.

The full removal of the implant after the procedure was checked by the Periapical X-ray picture (Figure 13). Two weeks after the surgery, the patient showed normal healing phase as the stitches were removed. Two months after the surgery, completely cured soft tissues of the surgical site were verified; thus reinstallation of an implant was planned and carried out four months later (Figure 14) [38].

Figure 13: Periapical X-ray image. (a) Implant fixture with a fractured abutment screw. (b) Implant removal site filled with a bone grafting material.

Figure 14: Postoperative X-ray panoramic picture. Implant reinstallation On #37 region four months after implant removal.

Dental implants that are mobile or have little residual bone to implant contact may usually be removed with tools, including levers, elevators, and/or forceps, which are often used for tooth extraction (Figure 15). If the threads oppose no resistance, rotating movements are not even required [10].

Figure 15: A combined solution to a clinical case using forceps (d) (minute residual bone) and the reverse screw technique (e). (a,b) Clinical preoperative condition. (c) X-ray. Yellow arrows indicating the extent of a bone defect (d) Implant removal (c,f) with a forceps by counterclockwise rotation. (e) Implant removal (c,g) with the reverse screw technique. (f,g) Showing both implants after removal.

The removal of a single dental implant using an Er, Cr: YSGG-laser [39] was mentioned in one case study. The procedure was identified as similar to piezo-surgical interventions, as the laser system achieves a circumferential destruction of the bone-implant interface. The laser generates pulsed photons, which absorbed by water leading to micro explosions and destruction on the surrounding target tissue. This procedure is described as the hydrokinetic effect and leads to clean cuts without any thermal damage. The approach could theoretically be less invasive compared to other methods, as stipulated by the authors [39]. Optimal hemostatic control was stated as a further benefit of laser surgery, thus promoting good visualization and thus speeding up the intervention. Another in vitro study on human mandibles used the same laser and compared it to the conventional trephine approach [40]. The quantity of the removed bone, length of the operation, and morphological changes on the surface of the bone were the parameters evaluated. These procedures were performed on six implants in each group (length: 12 mm; diameter: 5 mm). The findings showed about half of the bone extracted by the laser relative to the trephine bursa (0.302 vs. 0.519 cm3). Trephine burs were more than twice as fast as the laser for the duration of the operation (17.2 vs. 44.1 s). The authors found well-defined bone edges without any thermal alteration when examining morphological bone alterations in the laser sample, whereas the trephine bur group with some micro cracks showed irregular bone formations. In conclusion, compared with trephine burs, laser surgery demonstrated a less invasive and painful intervention; however, the operation was more time consuming. While laser surgery has already been developed in the fields of periodontology and implant dentistry and some preliminary data seem promising, further research is needed before this technique can be widely recommended [40].

Counter-Torque Ratchet Technique

In order to remove failed implants, the counter-torque ratchet technique (CTRT) is stated to be the least damaging technique [33]. The implementation of this technique helps the surrounding bone to remain more or less undamaged. So far, two separate modalities of CTRT have been described:-

• In order to loosen the fixture, the first alternative needs an intact implant connection. A fitting abutment or extraction instrument for involvement is put in or on the implant hereby. Via a counterclockwise torque, the removal is completed [41]. Different factors are listed that influence this technique. First, because of the higher leverage, it is easier to remove an implant with an internal connection than implants with external connections. Second, because of the different bone-to-implant contact, the different implant thread shapes, namely, buttress, square, V-shaped, and reverse buttress, can affect the removal. It is defined that square threads have the highest bone-to-implant contact and are therefore more difficult to remove. Next, the body shape of the implant influences the removal of the implant. It is stated that tapered implants are removed more easily than parallel implants. Finally, the anti-rotational design of certain implants, especially found in apical implants [42].
• The second choice is the reverse screw (RST) procedure, which is primarily used for the removal of broken and damaged implants. In the latter, a screw is inserted into the damaged implant counterclockwise to grip the damaged implant. Then, to eliminate the device as a whole, counter-torque-wise force is applied [33]. Force is applied before the resistance decreases, and the implant can be quickly unscrewed without force. During this first unscrewing process, some authors also suggest cooling the bone with saline, stating that high friction can increase bone temperature [43].

A counter-torque procedure was tested by some authors to remove transitional orthodontic implants [44]. Thirty-one orthodontic mini implants with a diameter of 1.8 mm have been removed using a revised ITI torque driver using CTRTT. Twenty-six of these implants with torque ranging from 11 to 23 N cm were removed intact. At the bone level, the remaining implants fractured at torques of between 27 and 35 N cm and could not be removed by CTRT. The counter-torque method was defined by Anitua ET alusing the osseointegrated implants BTI explantation kit (BTI Biotechnology Institute, Vitoria, Spain) [45]. Again, the goal of this technique is again to remove the implant as atraumatic as possible in order to ensure the possibility of a second implantation best possible. For a total of 91 implants, the authors evaluated 42 patients. Seventy-eight CTRT-only implants were eliminated, while 13 implants still required a combination of trephine bursa and BTI. Another study of 81 patients and 158 non-mobile implants scheduled for explanation found that 139 implants with 146 N cm torque were removed without bursal adjunctive use [46]. Again, it was appropriate to use 19 interventions with trephine burs and a higher torque of 161 N cm. Initial removal torques greater than 200 N cm, broken implants and fractured prothetic components were indicators for the use of trephine burs. For plasma-sprayed implants, the removal torque was statistically significantly lower than for other surfaces. For the removal of acid-etched and sand-blasted implants, the highest torque was established. For the decision to use the CTRT method alone, four millimeters of remaining osseointegration was defined as a critical amount. A combination of CTRT and a bone-cutting procedure, such as trephine burs or piezo, is recommended for the removal of implants with greater osseointegration [47]. As recommended by Anitua [45], Figure 16 shows clinical cases of implant removal using the reverse screw technique. Clinicians should, in any event, be aware of potential implant fractures, especially in narrow implants [33]. Several CTRT sets are currently on the market. As recommended by Anitua [45], (Figure 16) indicates clinical cases of implant removal with the reverse screw technique. Clinicians should, in any event, be aware of potential implant fractures, especially in narrow implants [33]. There are currently numerous CTRT sets on the market.

Figure 16: Illustration showing the reverse screw technique. (a) Preoperative X-ray showing advanced peri-implantitis in Region 38 (white arrow). (b) Removal of the three-piece temporary cemented bridge. (c) Abutment disconnection. (d) I Trephine bur is used to remove the first 2 cm of bone-to-implant contact (not needed in this case) if necessary; (II) the screw is applied and cut counterclockwise into the implant; (III) torque is applied counterclockwise until the implant is loosened and unwinded. (e) Implants removed from Area 38. (f) Post-operation site (green arrow). (g) (IV) The socket has been kept in good condition and ready for regeneration and/or for a new implant (V) [45].

The concept behind this method is to cause a distinct bone-implant interface thermo-necrosis in order to be able to remove the implant after osseo disintegration at a low counterclockwise torque in order to be as mechanically atraumatic as possible. Thermal-related osteonecrosis is a disease that results in local bone death via loss of blood supply and primary or secondary bone cell death [48]. The authors used an ultra-high frequency mono-polar electro surgery device for 15 s in a mal positioned implant in one study explaining the respective technique [49]. One week later, it was possible to remove the implant with a 30 N counter torque ratchet. With this approach, the authors' main concern was the growth of mucosal and prolonged osteonecrosis. Temperatures above 56 °C to 70 °C are known to be detrimental to bone tissues in the literature, primarily due to the transformation of alkaline phosphatase [50]. In their studies, Eriksson and Albrektsson stated that bone heated to a temperature ranging from 44 ° C to 47 ° C would already cause thermal necrosis for more than 1 min [51]. A more recent study reported 47 ? as critical temperature for the development of thermal osteonecrosis in bone. Although some dentists (also by heating implants using blunt diamond burs without water supply) have promising and anecdotally documented and performed, obviously more research needs to be done in this field to allow for a credible clinical justification of this approach [49].

The success of dental implants is difficult to predict as it depends on various bio-mechanical factors. It is difficult to assess whether the various modifications in the latest implants deliver improved performance so it is well established that the failure can occur even under best care. It is often said 'An implant in the wrong position will always integrate'. Unfortunately failure to integrate is usually not as difficult to manage as an improperly positioned implant which may affect function and esthetics of the prosthesis. Proper care preparation and a sound understanding of the restorative aspects of dental implants, biomechanics and forces put on implant restorations and components will prevent most of the failures, except for loss of integration [52]. Implant failure is a multifactorial phenomenon and the management protocol for complications and implant failure is affected by the detection of potential etiological factors. When a diagnosis is established and possible etiologic factors identified, the causative agent should be eliminated and treatment attempted as soon as possible [53]. In the case of implant fractures, the safest treatment choice is the complete removal of the broken implants and the insertion of new implants. More importantly, dental surgeons should be aware about the factors that prevent implant fractures [54].

Few data are still available in the literature as regards the removal of failed dental implants and evidence is still based primarily on case reports or studies with a limited number of patients, so the following conclusions can be drawn [10]:

• Early and late implant failure normally have different causes and can be treated in different ways.
• Peri-implantitis shows to be the main reason for late implant failure.
• The best-known procedure for implant removal tends to be Trephine burs.
• Due to its low invasiveness, the CTRT approach alone or combined should be the first option for the clinician.
• The defect type of the bone at the failed implant is crucial for the choice of the removal method and the subsequent treatment.
• Implantation in previously failed sites irrespective of an early or late failure have high success rates.

Authors declare no conflicts of interest.

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