Bone Changes With Silicone Chin Implants: Clinical Case, Review, and Considerations for Technique Modification

Abstract

Background:

Bone resorption has been imputed to silicone chin implants as the cause of the reported bone changes with chin augmentation. Bone remodeling is complex. Both neo-ossification and bone resorption can occur.

Methods:

A literature review was performed on bone complications of silicone chin implants and bone remodeling with periosteal manipulation. Available data from plastic surgical and dental literature, alongside a case observation showing neo-ossification 10 years after implantation, were analyzed and used to explain patterns of bone changes around chin implants.

Results:

Periosteal elevation induces bone formation. Spur-like neo-ossification with silicone chin implants is caused by subperiosteal implant placement. Our case describes such neo-ossification 10 years after silicone chin implantation. The pressure of an implant on bone can cause limited bone resorption. The pressure of an implant trapped under a forming bone shelf can cause significant bone resorption in rare cases.

Conclusions:

Previously reported mandibular bone resorption ascribed to silicone chin implants has been overwrought. Bone formation is more common with silicone chin augmentation. We propose surgical modifications to limit bone complications of chin implants based on the reviewed literature. Surgical approaches to periosteal elevation and implant insertion and consideration of alternate biomaterials to silicone chin implants may improve outcomes of chin augmentation.

Takeaways

Question: What is the relationship between chin implants and bone changes such as resorption and neo-ossification?

Findings: Literature review and a case observation showed that both neo-ossification and bone resorption can occur under specific conditions. Subperiosteal implant placement leads to spur-like bone formation, which in turn can lead to implant entrapment leading to pressure-induced bone resorption.

Meaning: Chin implant placement must consider the relationship of the implant to the periosteum and its osteogenic response to elevation.

INTRODUCTION

Solid silicone implants have been used in cosmetic procedures since the 1960s. Silicone was the first to reach widespread use and is considered to be one of the safest implant materials.^1,2 There have been multiple reported cases of long-term bone resorption with silicone implants in chin augmentation.^3–8 It has been suggested that the pressure from the implant causes these bone changes. However, both bone resorption and edge neo-ossification have been associated with silicone chin implants. The purpose of this review was to analyze the current medical and dental literature to better understand how implant placement and periosteal elevation induce bone changes. We describe a case of a spur-like bone formation above the silicone chin implant and the possible physiology surrounding its formation.

MATERIALS AND METHODS

This study is a narrative review designed to investigate the literature behind complex bone remodeling and its relationship with periosteal elevation and silicone chin augmentation in dental and facial plastic surgery literature over the past 60 years, from 1960 to 2020. A literature review was conducted on peer-reviewed articles covering the above subjects. We searched the literature for articles that met our criteria to answer the research question, “do silicone chin implants cause bone resorption or neo-ossification?” After exhausting alloplastic implant literature within plastic surgery and otolaryngology, we discovered that greater insight into periosteal response was found within dental/maxillofacial literature. The animal studies on bone remodeling further served to reinforce clinical observations. Thus, the authors followed clues from one field to another, evaluating all disciplines. (See table, Supplemental Digital Content 1, which displays a review of studies investigating effects of implants on bone changes, http://links.lww.com/PRSGO/D846.) Each author independently performed the literature review and data abstraction. Databases queried included Google Scholar, PubMed, Medline, and EBSCO. Keywords included chin augmentation, silicone chin implant, bone resorption, bone neo-ossification/formation, periosteal elevation, and silicone biocompatibility. There were no exclusion criteria. The literature search was completed in September 2023.

RESULTS

The analyzed literature covered implant-related bone changes, silicone chin implant bone complications, and dental implant–related periosteal elevation and its effect on bone remodeling. A total of 29 relevant articles were analyzed. Of the 29, 17 were case series, 6 were systematic reviews, 5 were case reports, and 1 was an abstract. Of the 29 studies, 14 were animal studies, 12 were patient studies, and 3 were basic science studies.

We present the case of a 61-year-old woman with growing lateral chin fullness and asymmetry after a chin augmentation with a silicone implant at least 10 years prior. The patient reported progressive swelling over the right lateral chin and sensory symptoms of the right lower lip. Four years after the initial surgery, the patient presented to the surgeon who performed the chin augmentation, complaining of asymmetry. The physician suggested that the implant had shifted in position. After 10 years of increased swelling and asymmetry, the patient presented to the senior author. Clinical examination found right lateral chin fullness and a palpable nodule (Fig. 1). Intraoperatively, a bony shelf was discovered arising from the mandible just below the mental nerve and wrapping around the superior half of the silicone implant (Fig. 2). (See Video 1 [online], which displays a video of bone growth over a silicone implant placed 10 years prior in a 61-year-old woman.)

Fig. 1.

Clinical presentation of right chin fullness and asymmetry and result postresection. A, Right chin fullness and visual asymmetry. B, Nine months post bony growth resection.

Fig. 2.

Neo-ossification laterally and over the right side of the silicone implant in chin. A, Right-sided bone growth (blue arrow) over silicone implant (yellow arrow). B, Endoscopic view with implant removed: bone “shelf” and convex bone on the deep side of the implant. C, Resected bone edge below the mental nerve.

Video 1. displays a video of bone growth over a silicone implant placed 10 years prior in a 61-year-old woman.

Download video file ^{(1.9MB, mp4)}

The left side of the mandible was normal. The implant was removed, and the bony shelf measuring 2.2 cm × 0.5 cm and 0.1 cm was trimmed with rongeurs and osteotomes (Fig. 2C). (See Video 2 [online], which displays a video of bone growth after removal of the silicone implant, showing the “shelf-like” growth of bone.) There was no evidence of bone remodeling or resorption below the implant. The right side of the implant was trimmed, and the implant was replaced. Histological examination showed benign compact bone without active inflammation. At the 9-month follow-up, the edema resolved (Fig. 1B). The collected information was Health Insurance Portability and Accountability Act of 1996 compliant, and informed consent was obtained from the patient.

Video 2. displays a video of bone growth after removal of the silicone implant, showing the “shelf-like” growth of bone.

Download video file ^{(2.1MB, mp4)}

DISCUSSION

Chin augmentation with silicone implants has been utilized since the 1960s with few complications due to silicone’s high biocompatibility.^1,2,7 Complications included infection, implant shifting resulting in visual asymmetry, bone changes, and nerve injury.⁹ Bone changes associated with solid silicone implants have been mostly described as resorption.^3–8

The first case series of bone resorption beneath chin implants was reported in 1969 by Robinson and Shuken³ with a follow-up in 1972.⁴ The implants were all placed subperiosteally. Both resorption of 3–5 mm and “spur-like subperiosteal bone formation beginning to grow over the edges of the implant” were noted. Lateral radiographs were used for evaluation and measurement.

Jobe et al⁵ in 1973 presented a case of 3 mm of mandibular bone resorption underneath a silicone rubber implant measured again on a lateral radiograph. They failed to mention the bony spurs on both sides of the implant visible on the same radiograph. Jobe et al in 1973, and then with Lilla et al⁶ in 1976, also found that silicone placed on the rabbit skulls caused calvarial bone flattening. Bone resorption was irrespective of the periosteal relationship to the implant.⁶

More dramatic findings of inferior spur-like bone formation around the implant and bone resorption below were described by Peled et al¹⁰ in 1986. Nine of 12 children with Down syndrome augmented with polydimethylsiloxane (silicone rubber) chin implants had these findings of resorption.¹⁰ Lateral radiographic examples provided by the author did not clearly differentiate new bone formation from bone resorption.

Most recently, in 2018, Sciaraffia et al⁷ evaluated patients a median of 5 years after subperiosteal chin augmentation with silicone implants. Lateral chin radiography found 14 of 15 patients with up to 2.0 mm of bone resorption. Curiously, they found no correlation between follow-up time and depth of resorption.

The most dramatic cases of bone changes due to silicone chin implants were documented with mandibular computed tomography scans and described by Abrahams and Caccres⁸ in 1998. Two patients presented with bone erosion extending to the periapical space of a tooth. Similar to other reports, there was evidence of new bone formation around the implants and spur-like bone growths inferior to the implants.⁸ We assume that the implants were placed intraorally with subperiosteal incision superiorly and dissection from superior to inferior, leaving the inferior periosteum intact. This assumption is based on the nature of neo-ossification inferiorly.

Pressure on bone-inducing bone resorption is well demonstrated in animal models. Pearson and Sherris¹¹ elegantly demonstrated that higher pressure results in more bone resorption in dog mandibles. Periosteal elevation did not make a difference. Wellisz et al¹² suggested that implant size has a greater effect in the rabbit mandible model, finding greater bone erosion with thicker than thinner silicone implants.

It is likely that in addition to describing bone resorption, these publications are also describing a process of neo-ossification of elevated periosteum. All of these cases demonstrate a predominance of spur-like bone growth either superior or inferior to the implant.

A case similar to ours with bone formation around a silicone chin implant was presented by Johnson¹³ in 2008. The patient had an 11-year progressive growth of bone on the right side of the implant.¹³ Unilateral right neo-ossification, like in our case, may be due to better subperiosteal elevation on the right side of the chin than the left side by a right-handed surgeon. The left-side dissection is more awkward when the surgeon remains on the patient’s right side, thus limiting effective periosteal elevation on the left. This observation applies to the submental approach to the chin.

In our case, we documented new bone forming from the superior shelf where the elevated periosteum remained intact with the bone and blood supply. Inferiorly, the periosteum was disconnected from the bone to accommodate implant insertion and, consequently, no neo-ossification was observed.

A good source of understanding of periosteal manipulation and its interaction with bone formation is gleaned from distraction osteogenesis literature. As early as 1966, Bassett and Ruedi¹⁴ had shown that osteoprogenitor cells in the periosteum can be differentiated into osteoblasts with mechanical strain. The first histological proof of bone induction by periosteal distraction was provided by Schmidt et al¹⁵ in 2002. The periosteal distraction creates an artificial space between the cortical bone and periosteum where new bone formation occurs.¹⁶ The periosteum has a strong ability of osteogenesis through its inner layer. The outer layer is formed by collagen fibers, blood vessels, and nerves, thus providing nutrition and sensation. The inner layer consists of osteoblasts responsible for bone creation and growth.^17,18

Dental implant research has further contributed to a greater understanding of the subject matter. Dental implants require a certain amount of peri-implant bone, whether with bone graft augmentation or the use of bone substitute material in combination with spacers, called guided bone regeneration. However, most bone augmentation procedures are combined with periosteal elevation. It is the periosteal elevation that is believed to be the significant source of bone augmentation in dental implant procedures.

The osteogenic potential of the periosteum after elevation off the bone with a titanium mesh was demonstrated by Kessler et al¹⁹ in 2007 and Tudor et al²⁰ in 2010. The mechanical tension on the periosteum stimulated the mesenchymal stem cells to differentiate into osteoblasts resulting in subperiosteal bone formation.^19,20

More recently, Lutz et al²¹ in a pig model elegantly demonstrated with cross-sectional histology new bone formation with periosteal elevation around a projected osseointegrated screw. Elevated periosteum suspended above bone by an osseointegrated screw resulted in supracortical bone formation on the cortical bone and under the periosteum in animal models and observed in mandibular resections. Furthermore, when an implant (polydioxanone) was placed around the screw as a periosteal shielding device, spur-like bone formation occurred similar to the reports of chin implants above. No bone resorption was evident below the implants. The robust bone regeneration starts at the limit of periosteal elevation off the bone and progresses away from there toward higher elevated periosteum (Fig. 3).

Fig. 3.

Progression of periosteal osteogenesis. A. Torn periosteum with no initial osteogenesis. B, Beginning of osteogenesis. C, Progression of osteogenesis with fibrous separation between periosteum and cortical bone. D, Complete spur/shelf-like osteogenesis. E, Depiction of bone erosion.

Bone remodeling is complex. Pressure on bone can induce bone resorption.¹¹ Bone force loading encourages bone formation.²² Subperiosteal bone formation can entrap an implant below it and place pressure on it. With pressure, bone remodeling can occur and encourage the progression of periosteal osteogenesis.^19,20 At the same time, the pressure exerted by the implant on the bone below can induce bone resorption. The case reports by Abrahams and Caccres⁸ in 1998 demonstrate the concurrent phenomena of osteogenesis and resorption with silicone chin implants.

Reported cases of bone resorption from silicone chin implants described above may not have accurately represented the real bone changes that occurred. The spur-like bone formation at the site of periosteal elevation creates a higher bone plateau around the implant. The central valley around the plateau thus may not represent true bone resorption but an illusion of resorption. Studies attributing the distance between the high point of the spur and the low point of the valley below the implant may not be accurately measuring the amount of bone resorption if any even occurred.

The literature review indicates that periosteal elevation is the source of bone formation. A silicone implant shields the full-thickness formation of bone, instead creating spur-like projections around the implant. This bone can serve to compress the silicone implant. In turn, implant pressure on bone can create bony erosion. This seems to occur less prominently with porous implants.¹²

CONCLUSIONS

Interaction of an implant with bone remodeling can be complex. To limit periosteal osteogenesis with chin implants, limiting subperiosteal dissection and placing a portion of the implant supraperiosteally may be useful. This entails central periosteal sparing and lateral subperiosteal dissection.

Because tight entrapment of the implant and pressure under the periosteum can lead to greater osteoneogenesis, we suggest considering reducing the entrapment with the wide periosteal release. This needs to be balanced with limiting implant mobility which raises infection risk. Another approach includes a submental inferior approach to chin implant insertion that will avoid the reported cases of periapical bone erosion of the transoral superior approach.

Perhaps, it is a consideration of biomaterials that would minimize bone complications of chin implants. Minimally porous expanded polytetrafluoroethylene or very porous polyethylene implants allow tissue ingrowth. Bone growth into the implant instead of applying greater force on its surface can reduce the pressure on the implant and possible bone erosion below it.

Our case report served as an impetus to answer the questions about osteoneogenesis with silicone chin implants. The exploration of the science of periosteal elevation can guide the clinician in balancing the choices of surgical approaches and biomaterials.

DISCLOSURES

The authors have no financial interest to declare in relation to the content of this article. This study was funded by the Skin Cancer and Reconstructive Surgery Foundation.