Bone reabsorption associated with silicone implants in mentoplasty : a clinical case report

For many years, silicone implants were used in reconstructive and esthetic surgeries, especially in cases in which the facial profile of patients presented deficiencies in the inferior third of the face. This material proved to be successful in most aspects. However, several complications were well reported in the literature, as the case of bone reabsorption in the region of the mandibular chin. In this article, the authors present two clinical cases of bone reabsorption from the anterior cortex of the chin associated with silicone implants and discuss the etiology, complications, and treatment plan. ■ ABSTRACT


INTRODUCTION
The pillar of face surgery is the quest for harmony through remodeling of tissue contours.Towards this goal, several alloplastic materials are used.The materials currently available in the market largely vary in density, remodeling, tissue reaction, reabsorption, migration, incidence of infections, extrusion rate, and the ease of removal 1 .
Aspects, such as low toxicity, carcinogenic potential, satisfactory bioactivity to prevent organ rejections, and sufficient stability to support the physiological environment and to avoid changes in the receptor site, would be crucial to achieve the success and longevity of the treatment 2 .
The advantages of silicone implants include a lower risk for sensory loss and the possibility to be removed, if the result is unsatisfactory; conversely, the disadvantages include asymmetry, malposition, hematoma, seroma, infection, mobility, extrusion, and bone reabsorption 3 .
When removal of the implant material is required owing to any of the aforementioned reasons, lip ptosis might occur owing to the lack of insertion of the chin muscle of the mandible; in these cases, the best option would be to perform mentoplasty via basilar osteotomy 4,5 .
However, care should be taken while suturing the chin muscle so that lip ptosis does not occur, regardless of the technique used.

OBJECTIVE
In this article, the authors present two clinical cases of bone reabsorption of the anterior cortex of the chin associated with silicone implants and discuss the etiology, complications, and treatment plan.

Case 1
Patient D.S., a 53-year-old woman with leukoderma, was sent for evaluation of a radiolucent lesion in the chin region.This was observed by the endodontist after requesting a computed tomography (CT) scan to evaluate the fracture of a tooth in the chin region.During the anamnesis, the patient was reported to have silicone chin implants for almost 38 years, without any complaint in the region.
During the extra-oral examination, no changes, such as lip ptosis, pain upon palpation, or any sensitivity change in the region of the inferior lip (dysesthesia), were observed.During the intra-oral examination, no changes were observed in the color of the mucous membranes

Case 2
Patient J.J.J., a 29-year-old woman with leukoderma, was referred by the orthodontist for evaluation of a class II facial tooth deformity and temporomandibular disorders.During the anamnesis, the patient was reported to have been submitted to rhinoplasty and silicone implantation in the chin region ~10 years ago.During the intra and extra-oral clinical examinations, no change was observed on the mucous membrane or skin in the chin region; there were also no paresthesia, dysesthesia, and pain upon palpation.
After requesting for preoperative imaging examinations (CT), a hypodense lesion extending from the region of teeth 33 to 43 (Figures 3 and 4) was observed, with expansion of the vestibular cortex.The results of the percussion and thermal pulpal vitality tests were positive in all teeth close to the lesion.Based on the tomographic and clinical findings, the diagnostic hypothesis of bone reabsorption related to silicone implant was obtained.
The proposed treatment was removal of the silicone prosthesis associated with mentoplasty via basilar osteotomy.
shape of the implant or its positions.In other reports, the etiology was related to the pressure exerted by large implants, subperiosteal placement, and implant hardness 1,4 .
Besides producing a significant defect with potential damages to underlying structures, such as tooth roots and nerves, bone reabsorption may also be responsible for the loss of chin projection.Radiographically, reabsorption seems to occur 12 months after placing the implants; however, there are reports of bone reabsorption at 2 months follow-up [5][6][7] .
Of all regions, the chin seems to be the most affected owing to the thickness of the vestibular cortex and the great tension exerted by the chin muscle; conversely, bone reabsorption is rare in other regions, such as in the zygomatic region owing to the bone density and minimum muscle tension exerted by the facial muscles against this bone 8 .
Patients with class II facial tooth deformities (long lower third of the face and lip incompetence) seem to be more predisposed to bone reabsorption in implants installed in the chin owing to the fact that this hyper-function takes pressure and to the migration of the implant superiorly on the thinner bone, which predisposes the reabsorption.In addition, implants are more sensitive to be placed in these patients for esthetic purposes 4,9 .
In case of severe reabsorption, implant removal should be considered.Serious distortions of the soft tissues have been reported after its removal 10 .Owing to this, mentoplasty should be performed via basic osteotomy in the same surgical time as a prophylactic measure to avoid residual deformities 10 .In both the cases reported above, these were the treatments used.
Basilar chin osteotomy is a procedure that offers many advantages over other techniques for chin augmentation, e.g., better contour of the soft tissues by the maintenance of the mandibular base, predictability, versatility in three-dimensional correction, and maintenance of the joined mobile pedicle that allows better viability of the osteotomized segment 10 (Figure 5).

DISCUSSION
The first reports of failure related to alloplastic implants were described by Robinson 6 in 1972 in which 12 of 14 patients submitted to acrylic and silicone implantations presented bone reabsorptions of up to 5 mm.In this article, reabsorption was attributed to the

Figure 1 .
Figure 1.Three-dimensional computed tomography reconstruction image demonstrating an extension of the injury.

Figure 2 .
Figure 2. Sagittal tomographic section showing bone reabsorption in the proximity of the root of tooth 33.

Figure 4 .
Figure 4. Axial section showing bone reabsorption and three-dimensional reconstruction of the implant extension.