Implant placement in the mandibular posterior area is relatively predictable and a simple procedure if enough bone exists. However, though it rarely happens, cases of accidental implant displacement into the marrow space of mandibular body have been continuously reported.1–7 Severe implant displacement can first violate the inferior alveolar nerve (IAN); the subsequent surgical procedure for implant retrieval can secondarily injure the IAN. Therefore, adequate evaluation of the patients' status and establishment of an optimal strategy for removal of the implant fixture should be emphasized.
In the present report, our patients and those of other institutes were investigated to analyze the pattern and outcomes of the treatment for dental implant displacement into the mandibular bone marrow cavity.
A 68-year-old woman was referred by a private dental clinic for the removal of a displaced implant fixture that was located lingually to the IAN in the body of the mandible (Figures 1 and 2). Six days later, the previous site of implant preparation was enlarged with a round bur. The fixture was carefully engaged with an impression coping and removed under the local anesthesia. Hypoesthesia was improved but not completely resolved at 13 months after the surgery.
A 59-year-old woman with hypertension and history of recurring thyroid carcinoma was referred by a local clinic for removal of an accidentally displaced implant fixture during the surgery at the mandibular second molar (Figures 3 and 4). Several hours after the initial accident, the lateral corpus of the mandibular body was decorticated, after which the buccally and inferiorly displaced fixture was removed (Figure 5). Hypoesthesia was mostly reversed after 8 months; the patient had mild persistent hypoesthesia.
A 34-year-old woman with osteoporosis history (1 year of bisphosphonate medication) was referred by a private clinic. One week before the referral, accidental displacement happened during immediate implantation after extraction of the right first and second molars (Figures 6 and 7). The patient complained of hypoesthesia on the right lower lip. The implant was removed via a lateral window under general anesthesia (Figure 8). Hypoesthesia was improved after 3 months.
A 61-year-old woman experienced accidental implant displacement into the marrow space during surgery (Figures 9 and 10). The site of implant preparation (mandibular second molar) was enlarged with a round bur. The fixture was engaged with an impression coping and removed successfully. Hypoesthesia was almost completely reversed at the 6-month follow-up.
A 67-year-old man was referred by a private dental clinic. As with the four previous cases, the practitioner felt the sudden drop of the implant during final engagement of the fixture to the bone (Figures 11 and 12). The patient complained of severe hypoesthesia. Six days later, under general anesthesia, the IAN was visualized via lateral decortication, and the lingually located implant was removed (Figure 13). The cortical bone was replaced with a microplate. Hypoesthesia was slightly reversed but persistent at 3 months after the surgery.
Literature review with the current cases
Only 7 articles and 10 patients were identified in previously published literature.1–7 Therefore, including our 5 cases, 15 cases were investigated. Most cases involved women, and there was no specific age predisposition. Only 3 patients had been diagnosed with osteoporosis. The locations of displaced implants are listed in Table 1.
Ø indicates diameter; L, length of the implant fixture; Mn, mandible; HTN, hypertension; IAN, inferior alveolar nerve; Ca, carcinoma. Empty boxes indicate the lack of information from the reports.
The direction of the surgical approach could be classified largely into two categories of approach: crestal or lateral. The majority of cases (n = 10) used the lateral approach. Because of insufficient information in previous publications, we could find only two articles mentioning hypoesthesia after implant removal.4,6 Including our cases, hypoesthesia was observed in 47% of total cases (n = 7/1; Table 2).
In most previously published articles, authors suggested that osteoporosis is the first possible reason for accidental implant displacement to the mandibular marrow space (so-called “mandibular sinus”) during surgery.2,3,6,7 All patients in the previous reports were women of 50 years of age or older, except for the first reported case of implant displacement (age 36).1 However, including the author's current cases, only 3 patients had clear documentation of a history of osteoporosis. Even in articles suggesting osteoporosis as the most probable risk factor of accidental mandibular implant displacement, there was no evidence of osteoporosis in presented cases.4,7 According to the systemic review, the association between osteoporosis and implant failure cannot be supported by evidence.12 In most cases presented, other implants were successfully installed near the problematic site or opposite side of the implant displacement.1,3,4,6,7 A possible explanation is a local insufficiency of the trabecular bone in the mandibular posterior areas. In previous reports' description at the time of implant displacement, the implant lost its resistance suddenly and displaced inferiorly during the tightening of the healing screw,1 placement of a driver to healing screw,2 or final positioning of the implant with a hand wrench.3 Sometimes, attempt to remove the implant has resulted in further displacement.1 It had been reported that mandibular basal bone had lower volume and fewer trabeculae patterns than did the crestal alveolar bone,9 and the posterior mandible had a large percentage of low-density medullary space.10 In our five cases, there was nearly no cancellous bone in the mandibular marrow space. These facts mean that a possible reason for implant displacement during surgery is the lower density of the trabecular bone in the posterior mandible rather than systemic osteoporosis in patients. Therefore, even without a history of osteoporosis, patients can possibility experience accidental implant displacement at the final stage of implant fixation.
The case series showed that displaced implants were located more lingual than buccal. It was easy to approach the implant that was located more buccally or was superiorly positioned relative to the IAN. In eight cases with lingually displaced implants, four cases experienced hypoesthesia. These suggest that lingual displacement of the implant needs a more careful approach to prevent additional IAN damage. In two cases with lingual displacement, we used crestal hole enlargement where we could successfully engage the displaced fixture with impression coping. However, in our experience, exploration of the implants inside the marrow cavity can result in secondary nerve damage.
The crestal approach is simple and can be performed under local anesthesia but has limited vision, a small operation field, and potential problems in future implant fixation and risk of further displacement. On the contrary, the lateral approach can give sufficient operation field and vision, ensuring the safe handling of the displaced implants but needing more extensive surgery. Therefore, we recommend the lateral approach in cases with a deeply displaced implant into the mandibular bone marrow space. If the implant is not deeply displaced and located above the IAN, it can be removed after enlargement of the drill hole, ensuring the safe removal of the fixture. The schematic presentation of the procedure is shown in Figure 14.
Accidental implant displacement into the mandibular bone marrow space occurred mostly in women above 50 years of age. However, there was no clear evidence of association with osteoporosis. It is reasonable to suggest that fewer and lower trabeculae in the posterior mandible would be associated with implant displacement during fixture placement. It is recommended to remove the displaced implants through the lateral approach rather than a crestal approach, especially when the implant is deeply displaced relative to the IAN.
The authors declare that they have no conflict of interest.