Infected Silicone Chin Implant After Implant-Supported Jaw Rehabilitation: Case Report and Literature Review

The chin is an important component to determine the facial profile.¹  The importance of the chin may be noted when the chin is smaller or greater than the ideal size.²  Microgenia is the appropriate term for the isolated underdevelopment of the chin. This term is different from micrognathia, which refers to underdevelopment of the mandibular body and ramus, or retrognathia, when the patient has an underdeveloped/malpositioned ramus, with class II malocclusion and only horizontal deficiency.³ 

Four basic options are available to acquire a more prominent chin: surgical placement of an alloplastic implant, bone osteotomy with chin advancement, injectable fillers, and augmentation with autologous fat.^2,4  Augmentation of the chin with autologous fat or soft tissue fillers is not permanent, thus many patients prefer surgical techniques that show lasting results.²  Both genioplasty and implant placement offer advantages and disadvantages and have different indications and possible complications.² 

Augmentation of the chin with an implant is a simple procedure, and a good choice for horizontal microgenia in patients with good chin symmetry and normal vertical chin height.²  The solid materials often used are Gore-Tex (expanded polytetrafluorethylene; W.L. Gore & Associates Inc., Flagstaff, AZ), Medpor (high-density porous polyethylene; Porex Industries, Fairburn, GA), Mersilene (nonabsorbable polyester fiber; Ethicon, Somerville, NJ), Silastic (solid silicone elastomer; Michigan Medical Corporation, Santa Barbara, CA) and silicone (polydimethylsiloxane).^5,6 

Silicone was first used for chin augmentation in the early 1950s.⁶  Until today, it is the most commonly used material for implants, because it causes less adhesion of soft tissue, which facilitates the implant insertion or removal as necessary.⁷  However, some complications could occur with this material, such as infections, oral incompetence, implant displacement, damage of the mental nerve, and bone resorption as the most disturbing complication.^6,7 

Bone resorption, also called bone erosion, was first described by Robinson and Shuken in 1969.⁸  The classification for chin-implanted bone erosion was introduced by Robinson,⁹  based on the amount of resorption (depth) compared to the implant size used, analyzed on lateral cephalograms, as follows: I: Any resorption up to one-third of the added implant dimension; II: Resorption between one-third and one-half of the added implant dimension, or approximately 3–5 mm; III: More than 50% of the implant dimension, or 5 mm. Later, another classification method was introduced by Guyuron et al¹⁰  based on the depth of bone invaded: 1: Cortical; 2: up to 3 mm; 3: 3 to 5 mm; 4: over 5 mm.

This paper presents the case of a silicone chin implant that showed bone resorption and became infected possibly due to the nonideal placement of dental implants.

A 67-year-old female patient with a two-year history of recurring pain, purulent secretion, erythema, and edema in the chin reported multiple unsuccessful attempts of antibiotic therapy. The medical history revealed that the patient had undergone a surgical procedure for placement of a silicone chin implant 25 years previously due to her dissatisfaction with the esthetics of her chin. The patient had undergone further surgery for placement of 6 dental implants in the mandible for subsequent prosthetic rehabilitation 2 years ago, and 6 months after implant placement, the patient perceived a change in her occlusion, with mobility of implant-supported denture and difficulty in eating. Upon returning to the prosthodontist, the implant-supported denture was removed, along with one of the dental implants, which was located in the region of tooth #26, precisely where the silicone ulceration was seen. However, the recurring episodes of inflammation and local infection continued.

No abnormalities were seen during extraoral examination. The intraoral examination revealed dehiscence in the alveolar mucosa and anterior portion of the mandible, with consequent exposure of the silicone implant near the dental implant at the region of tooth #27, which exhibited mobility and a purulent secretion (Figure 1).

The lateral radiograph (cephalogram) revealed bone resorption in the region of the mandibular symphysis and new bone formation in the region below the silicone implant (Figure 2a). The panoramic radiograph revealed bone resorption around the dental implants in regions of teeth #s 22 and 27 (Figure 2b). Cone-beam computerized tomography (CBCT) revealed the well-defined edges of the silicone implant, formation of a narrow bone layer around the base of the silicone implant, bone erosion in the mandibular symphysis region, and close contact between the silicone implant and dental implants in regions of teeth #s 23 and 27 (Figure 2c, d, and e). Bone erosion was observed in the prototyped model (Figure 2f).

The diagnostic hypothesis was that the nonideal positioning between dental implant position and silicone implant led to infection of the silicone implant. The patient was submitted to surgery for removal of the silicone chin implant and the dental implant at the position of tooth #27. Intraoral access was achieved by a low biangular trapezoidal incision from the distal portion of tooth position #27 to the distal portion of tooth position #21, exposing the mental nerves for complete visualization and avoidance of injury (Figure 3a). The mucoperiosteal flap was reflected for complete access to the silicone implant, which was subsequently removed along with the dental implant in region of tooth position #27 (Figure 3b, c, and d). Laminated burs were used for surgical debridement of the bone tissue under abundant irrigation with saline solution (Figure 3e). When the procedure was finished, suturing was performed with resorbable 4.0 Vycril (polyglactin 910; Ethicon Johnson & Johnson) (Figure 3f). A compression bandage was placed on the chin and maintained for 3 days.

The patient returned for the 2-month follow-up evaluation with no complaints of pain, good healing of the surgical wound, and no signs or symptoms of infection (Figure 4a and b). The radiographic evaluation revealed an image compatible with new bone formation in the region of the removed implant, without bone abnormalities (Figure 4c and d).

After this situation, the patient agreed to stay without the prominent chin and a new implant-supported rehabilitation was proposed.

The cosmetic augmentation of the chin (genioplasty) is performed to correct a profile deficiency resulting from soft tissue atrophy or mandibular retrusion. Autogenous materials, such as bone or cartilage grafts, have been used for this purpose, but these implants tend to have donor-site morbidity, a greater tendency toward resorption, and loss of the esthetic outcome over time.^5,11  Compared to osteotomy, chin implant surgery is considered to be faster, simpler, safer, and less invasive, and it offers significant predictability with the use of digitally created analogues based on computerized tomograms; this type of surgery also results in less postoperative ecchymosis and edema.^5,12 

Silicone was the first material used in facial implants. This substance stimulates the formation of a surrounding fibrous capsule, which facilitates its removal, if necessary.⁶  However, several complications may arise with any type of facial implant, such as migration or displacement, extrusion, foreign body reaction, bone resorption, ulceration, heterotopic bone formation, and infection.^1,11–14 

A chin implant can be inserted in the symphysis or parasymphysis region;^3,11  also, it may be placed in the subperiosteal or supraperiosteal region.⁵  Especially in implants placed in the subperiosteal region, it is not uncommon to observe formation of a thin layer of new bone around the implant,¹¹  as presented in the case report.

Bone resorption below a silicone chin implant is often attributed to some possible etiologies like inadequate implant positioning, soft tissue pressure on the implant, subperiosteal placement, oversized prosthesis, hypercontraction of the mentalis muscle to overcome lip incompetence,⁶  and foreign-body reaction by giant cells on the implant.¹  The hypothesis of mentalis muscle causing overpressure is widely accepted since bone erosion is not seen in implants placed in the region of the cheek bone or nasal dorsum.¹³  However, some authors support subperiosteal insertion, creating a pocket that will prevent inferior displacement of the implant.⁵ 

Theoretically, the greater the degree of retrogenia or microgenia and the larger the implant size, the greater the muscle activity and consequently the greater the bone resorption.⁵  Thus, thicker implants lead to greater bone resorption.⁶  Therefore, a chin implant could be contraindicated for patients with lip incompetence and labial tension due to the force applied to the implant and, consequently, the mandibular symphysis.¹⁵ 

There are reports of less erosion when the implant is placed in a lower portion of the mandible, where the bone is denser and the pressure of the mentalis muscle is not as pronounced, when the implant is located supraperiosteally, or when the implant is fixed with screws.^12,13  The adequate screw fixation prevents movement of the implant; this technique eliminates any gaps between implant and bone, minimizes capsule formation, and decreases the risk of bone resorption.⁵  In the related case, no screws were found, which may have contributed to the exacerbated resorption found in imaging studies and proximity with dental implants.

In the present case, heterotopic bone formation was found around the silicone implant and bone resorption occurred below it (Figure 2a, c–f), which agrees with findings described in the literature.^1,11–13,15  In such cases, a medium degree of erosion is generally found and is considered benign and self-limiting, occurring up to approximately 12 months.⁶  Sciaraffia et al evaluated 15 patients who had submitted to silicone chin implant insertion at least 1 year after the surgical placement. Bone erosion was found in 14 of the 15 patients; nevertheless, 80% of them presented less than 2 mm of erosion.⁷  However, controversy still remains regarding whether resorption continues/increases over time or is only seen during the first few months after implantation.⁵  This bone resorption can cause exposure of the dental roots and subsequent pain.^11,16 

The material used for the implant can affect the incidence of infection, as porous materials offer a niche for bacteria. With nonporous materials, such as silicone, infection is rare and, when it does occur, can often be treated with local measures without the need for implant removal. Nonporous implants have low complication rates (2% to 3%), with 1.7% reported to be due to infection and the need for implant removal in only 0.62% of cases analyzed.¹⁵  Local erythema, ulceration, pain, and migration of the implant to distant sites have been described after placement of a silicone implant.¹⁴  There are reports of silicone implant infection manifested as cellulitis, abscess, maxillary sinus drainage, and osteomyelitis.¹¹ 

In the present case, mucosa ulceration was found in the region of the silicone implant, along with pain, local erythema, and purulent secretion. The close contact between the silicone implant and dental implants in regions of teeth #s 23 and 27 (Figure 2c–e), and the previous presence of dental implant in the region of tooth position #26 may be the cause of infection of the silicone implant. When the dental implant is placed in the alveolar bone, a process of osseointegration occurs by bone remodeling, with bone resorption and new bone formation. In addition, the prosthetic connection of the implant remains in contact with the oral environment through saliva and biofilm. Considering that the dental implant was placed in close contact with the silicone implant, osseointegration did not occur on its entire surface, favoring bacterial proliferation and, consequently, infection of the chin implant. This is a rare occurrence, with no previous cases reported in the literature thus far.

The radiographic examination revealed absence of bone tissue to support the dental implants (Figures 2a and b), and computed tomography (Figures 2c–2e) showed close contact between the dental implants and silicone implant, adversely affecting both. In the panoramic radiograph, the silicone implant overlapped with the mandibular symphysis, making it difficult to identify. Polo⁶  reported the importance of lateral cephalograms to determine the presence of a chin implant and to detect bone resorption at early stages, as observed in the image examinations presented in the case report.

The classification systems of bone resorption are based on evaluation of lateral cephalograms.^9,10  Unfortunately, the initial X ray of the patient before placement of the chin implant was not available for the authors to compare with the current condition and thus allow classification as proposed by Robinson⁹  and Guyuron et al.¹⁰  Thus, we can emphasize the importance to prospective monitoring individuals submitted to chin implants with lateral radiographs and to achieve a baseline radiograph immediately after surgery, to compare the 2 moments and consider if early removal of an implant is necessary or not.

As reported in a previous study, many people involuntarily do not report on their medical history forms having had a chin implant.⁶  Therefore, the present paper warns dental professionals, mainly oral surgeons, on the need to perform a discerning physical examination and obtain a detailed patient history, as well as to employ precise imaging examinations to achieve a diagnosis and the best treatment plan.

Abbreviations

CBCT:

cone-beam computerized tomography

The authors report no conflicts of interest.