Displacement or migration of dental implants into anatomical cavities has been reported, and displacement into the maxillary sinus is considered to be the most common type.1,2 However, displacement of dental implants within the mandibular body is considered to be an unusual occurrence.3,4
Dental implants can be displaced into the mandibular body or the submandibular space in case of lingual perforation.5 Displacement within the mandibular body may be attributed to bone marrow defects.
Simple bone cysts and focal osteoporotic bone marrow defects (FOBMDs) may be identified intraoperatively or on radiographs.6 However, they may be less discernible on images acquired by routine panoramic radiographic techniques than those acquired by 3-dimensional radiographic techniques such as computed tomography. Osteoporosis can cause loose marrow, which might be a risk factor for poor primary stability.
Although there have been a few reports regarding the displacement of dental implants into the mandibular body, surgical procedures for its treatment are not well described.3,5 Piezoelectric osteotomy might be a good option for the retrieval of displaced implants with minimum removal of the local bone. This report presents an instance of displacement of an implant into the osteoporotic mandibular body and its removal by minimally invasive trapezoidal osteotomy using a piezoelectric device.
A woman in her mid-seventies was referred from a local dental clinic for the removal of a displaced implant in the right posterior mandible. On initial panoramic radiographs, no significant radiolucency was observed around the displaced implant, which made the implant seem to have been displaced into a cavity rather than within the bone. An implant in the right mandibular second molar region was observed in the middle of the mandibular body, and cone-beam computed tomography (CBCT) images confirmed the exact position of the displaced implant (Fig. 1).
To minimize the extent of removal of the local bone at the site of displacement, a trapezoidal osteotomy line was planned with a piezoelectric device (Mectron S.p.A., Carasco, Italy), as shown in the schematic drawing in Figure 2. Two oblique osteotomy lines were designed starting from the mesiodistal tips of the previous implant placement hole (Fig. 3A).
On complete trapezoidal osteotomy, the cortical wall could be removed; it was temporarily placed in a saline-soaked gauze. A loose blood clot was removed, on which, the platform of the displaced implant could be seen (Fig. 3C). The implant, 4 mm in diameter and 8 mm in length, was extracted (Fig. 3C). After this, the trapezoidal cortical block was replaced into its original position (Fig. 3D), and primary closure was performed. The wound healed uneventfully, and no neurological complications were noted.
The demand for dental implant restorations in elderly patients is increasing, which necessitates special considerations.
Osteoporosis leads not only to bisphosphonate-related osteonecrosis but also to poor bone quality. Osteoporosis is a rather common disease, which causes decreased bone mass and strength. In terms of implant survival, patients with osteoporosis do not exhibit any statistically significant differences compared with healthy subjects. It has been reported that postmenopausal estrogen status might be a risk factor for implant failure in the maxilla, but not in the mandible.7
In a study investigating the influence of skeletal and local bone densities on implant stability, the mean resonance frequency analysis (RFA) value of the control group was reported to be higher compared with that of the osteoporosis group, which implies that general bone density might affect the alveolar bone density.8 Therefore, although the survival rate of dental implants in patients with osteoporosis is almost comparable with that in normal patients, efforts to optimize primary stability should be pursued.8
The patient investigated in this report had been diagnosed with osteoporosis, and, although routine panoramic radiography findings revealed no radiolucency-like FOBMDs, the trabecular pattern in the mandibular region was observed to be sparse in the CBCT images. During retrieval of the displaced implant, nothing but a blood clot was observed under the cortical layer. Microscopically, confirmation of the existence of a hematopoietic marrow composed of erythroid, monocytic, granulocytic, and lymphocytic cells, and megakaryocytes associated with fatty marrow are required for the diagnosis of this lesion.9,10
Panoramic radiography can be used for the screening of osteoporosis, but not for its diagnosis.11,12 Taguchi et al12 reported that osteoporosis can be identified with high accuracy based on images of the inferior cortical border of the mandible. The hallmark of osteoporotic change is the erosion of the inferior cortical layer of the mandible.11,12
Eroded mandibular cortices might be correlated with an increased risk of osteoporosis. However, they showed no correlation with osteoporotic fractures.13
According to the normal anatomical features of the posterior mandible, the trabecular patterns in this region may be invisible, and the removal of the cancellous bone in the posterior mandible of cadavers was found to have no effect on the radiographic findings.14 In the case presented here, displacement had occurred although no bone marrow defects were present in the mandibular body, which indicates that inadvertent placement might cause such displacement even in the absence of anatomical variation.
Although such displacement may be attributed to overworked drill holes, it might occur even in cases where the tooth preparation is accurate. In cases with bone marrow defects or cavities such as simple bone cavities, when the final thread of an implant is screwed in at a depth greater than the thickness of the mandibular cortical bone at the crest, the implant might be displaced into the cavity because of the sudden loss of primary stability; this could happen especially in cases of flapless implantation, because the exact vertical position of the implant cannot be easily confirmed during placement.
The clinical applications of piezoelectric devices are increasing with technical advances in their design. As seen in our case, previously formed holes at the alveolar crest can act as the means for surgical access to the displaced implant. Placing 2 oblique osteotomy lines starting from the largest perimeter of the hole makes it possible to reach the implant without unnecessary bone reduction. With a rotary instrument, the osteotomy line would have been wider, resulting in greater injury to the alveolar bone of the patient. Because of minimal bone loss along the osteotomy line, the detached trapezoidal bony lid can be easily repositioned in its previous place after implant removal, without the necessity for additional fixation.
Although such an intraoperative complication is quite rare, special attention should be paid during implant placement in elderly patients with osteoporosis because of the possibility of FOBMDs, which might cause implant displacement during placement; however, it should be noted that such displacements might occur despite seemingly normal trabecular conditions.
Preoperative CBCT for the evaluation of bone density might prevent such complications. Modification of surgical procedures might be effective in reducing the incidence of such displacement, and avoiding countersink preparation might afford the implant greater retention. It is advisable to avoid countersinking in cases where poor primary stability is expected. In fact, countersinking, especially in bones of types III and IV, can jeopardize the cortical bone thickness at the alveolar crest. Therefore, avoiding countersinking during implant placement will enhance the initial stability because of the blockage of the collar in the cortical bone.15
Selection of appropriate implants can also be beneficial in increasing the primary stability, for which, wide-diameter implants could be the implants of choice.15 Undersized preparation is another option for achieving greater primary stability.16,17 In a prospective study for evaluating the effect of undersized preparations in patients with poor bone quality, no significant differences were found in the mean RFA values between patients who underwent standard drilling and those who underwent undersized drilling.17
The author claims to have no financial interest, directly or indirectly, in the products or information listed in this article.
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