Bone resorption under chin implants: The orthodontist's role in its diagnosis and management
2016; Elsevier BV; Volume: 151; Issue: 1 Linguagem: Inglês
10.1016/j.ajodo.2016.06.035
ISSN1097-6752
Autores Tópico(s)dental development and anomalies
Resumo•Bone erosion can occur under chin implants.•A patient may be unaware of it.•An orthodontist could radiographically diagnose it in the initial evaluation. Alloplastic chin implants have been a valuable treatment modality for the correction of microgenia. Their use has provided satisfactory esthetic results by improving facial balance. However, bone resorption under these implants can occur. Case reports of 4 patients with the incidental radiographic finding of the presence of chin implants are presented. All 4 subjects had lateral cephalograms and panoramic x-rays taken as part of their orthodontic evaluation. One had a normal mandibular symphyseal contour, and 3 had bone resorption under the implants. One subject had severe resorption. In addition to panoramic and cephalometric x-rays, the subject with severe resorption also had magnetic resonance imaging and computerized tomography as part of the evaluation workup. Alloplastic chin implants have been a valuable treatment modality for the correction of microgenia. Their use has provided satisfactory esthetic results by improving facial balance. However, bone resorption under these implants can occur. Case reports of 4 patients with the incidental radiographic finding of the presence of chin implants are presented. All 4 subjects had lateral cephalograms and panoramic x-rays taken as part of their orthodontic evaluation. One had a normal mandibular symphyseal contour, and 3 had bone resorption under the implants. One subject had severe resorption. In addition to panoramic and cephalometric x-rays, the subject with severe resorption also had magnetic resonance imaging and computerized tomography as part of the evaluation workup. Microgenia is often called chin retrusion or recessive chin, and it is the most frequently found type of chin deformity, occurring mostly in the sagittal plane.1Matarasso A. Elias A.C. Elias R.L. Labial incompetence: a marker for progressive bone resorption in silastic chin augmentation.Plast Reconstr Surg. 1996; 98: 1007-1014Crossref PubMed Scopus (54) Google Scholar Chin retrusion can be determined cephalometrically2Steiner C.C. Cephalometrics in clinical practice.Angle Orthod. 1959; 29: 8-29Google Scholar, 3Rickets R.M. Esthetics, environment and the new law of lip relation.Am J Orthod. 1968; 54: 272-289Abstract Full Text PDF PubMed Scopus (245) Google Scholar, 4Legan H.L. Burstone C.J. Soft tissue cephalometric analysis for orthognathic surgery.J Oral Surg. 1980; 38: 744-751PubMed Google Scholar or clinically by evaluation of the patient's facial profile or lateral facial photos.5Gonzalez-Ulloa M. Quantitative principles in cosmetic surgery of the face (profileplasty).Plast Reconstr Surg Transplant Bull. 1962; 29: 186-198Crossref PubMed Scopus (118) Google Scholar In 1934, Aufricht6Aufricht G. Combined plastic surgery of the nose and chin: résumé of twenty-seven years' experience.Am J Surg. 1958; 95: 231-236Abstract Full Text PDF PubMed Scopus (13) Google Scholar reported the use of autogenous nasal hump bone for chin augmentation. Hofer7Hofer O. Die osteoplastiche verlaengurung des unterkiefers von eiselberg bei mikrogenie.Disch Zahn Mund Kieferheilkd. 1957; 27: 81-85Google Scholar performed an externally approached osseous genioplasty with a horizontal osteotomy to advance a receding chin on cadavers in 1942. Converse8Converse J.M. Restoration of facial contour by bone grafts introduced through the oral cavity.Plast Reconstr Surg. 1950; 6: 295-300Crossref Scopus (68) Google Scholar used intraorally inserted bone grafting in the 1950s to advance the chin, and in 1957 Trauner and Obwegeser9Trauner R. Obwegeser H. Surgical correction of mandibular prognathism and retrognathism with consideration of genioplasty.Oral Surg. 1957; 10: 677-689Abstract Full Text PDF PubMed Scopus (658) Google Scholar developed an intraoral approach for a sliding osteotomy of the chin. Alloplastic biomaterials have been used for implant prostheses. Silicone (polydimethylsiloxane) was first used for chin augmentation procedures in the early 1950s by Brown et al10Brown J.B. Fryer M.P. Randall P. Lu M. Silicones in plastic surgery.Plast Reconstr Surg. 1953; 12: 374-376Crossref Scopus (55) Google Scholar and by Millard.11Millard D.R. Chin implants.Plast Reconstr Surg. 1954; 13: 70-74Crossref Scopus (23) Google Scholar Proplast (Vitek, Houston, Tex) was introduced in 1977 by Dann and Epker12Dann J.J. Epker B.N. Proplast genioplasty: a retrospective study with treatment recommendations.Angle Orthod. 1977; 47: 173-185PubMed Google Scholar but was later recalled from the market because it was associated with potential complications. Other alloplastic materials later introduced include Mersilene mesh, a polyester fiber sheeting (Ethicon, Somerville, NJ); Gore-Tex, expanded polytetrafluoroethylene (W. L. Gore & Associates, Flagstaff, Ariz); Medpor, porous high-density polyethylene (Porex Surgical, College Park, Ga); and Silastic, a medical-grade silicone rubber (Dow Corning, Midland, Mich).13Gürlek A. Firat C. Aydogan H. Cehlik M. Ersöz-Öztürk A. Kalmç H. Augmentation mentoplasty with diced high-density porous polyethylene.Plast Reconstr Surg. 2007; 119: 684-691Crossref PubMed Scopus (14) Google Scholar Although silicone has been reported to be widely used among surgeons treating this condition, the use of diced polyethylene in a surgicel oxidized cellulose mesh (Johnson & Johnson, Somerville, NJ) was advocated by Gurlek et al,13Gürlek A. Firat C. Aydogan H. Cehlik M. Ersöz-Öztürk A. Kalmç H. Augmentation mentoplasty with diced high-density porous polyethylene.Plast Reconstr Surg. 2007; 119: 684-691Crossref PubMed Scopus (14) Google Scholar whereas Mersilene mesh has been the option for others.14Gross E.J. Hamilton M.M. Ackerman K. Perkins S.W. Mersilene mesh chin augmentation. A 14 year experience.Arch Facial Plast Surg. 1990; 1: 183-189Crossref Scopus (39) Google Scholar Bone resorption, at times also called bone erosion, is a risk associated with the use of allopastic chin implants. It was first described by Robinson and Shuken15Robinson M. Shuken R. Bone resorption under plastic implants.J Oral Surg. 1969; 27: 116-118PubMed Google Scholar in 1969. Bone resorption under the implant's surface in contact with the mandible is a high risk and occurs quite often.1Matarasso A. Elias A.C. Elias R.L. Labial incompetence: a marker for progressive bone resorption in silastic chin augmentation.Plast Reconstr Surg. 1996; 98: 1007-1014Crossref PubMed Scopus (54) Google Scholar Despite this fact, chin implant placement by plastic, facial, and maxillofacial surgeons is frequent. According to the American Society of Plastic Surgeons, 18,136 alloplastic chin augmentation procedures were performed in the United States during 2014.16ASPS 2014 Plastic Surgery Statistics Report. Available at: http://www.plasticsurgery.org/Documents/news-reresources/statistics/cosmetic-procedure-trends-2014.pdf. Accessed on August 16, 2015.Google Scholar Procedural data and statistics have been gathered by the American Society of Plastic Surgeons for several years and reported to the public since 2005. Possible etiologies of bone resorption are inadequate implant positioning, soft tissue pressure on the implant, subperiosteal placement, oversized prosthesis selection, implant compactness and firmness, sex, and age.15Robinson M. Shuken R. Bone resorption under plastic implants.J Oral Surg. 1969; 27: 116-118PubMed Google Scholar Hypercontraction of the mentalis muscle to overcome lip incompetence has been shown by Matarasso et al1Matarasso A. Elias A.C. Elias R.L. Labial incompetence: a marker for progressive bone resorption in silastic chin augmentation.Plast Reconstr Surg. 1996; 98: 1007-1014Crossref PubMed Scopus (54) Google Scholar as a possible etiologic factor and lip incompetence as a marker for progressive bone resorption under chin implants. According to them, patients with obtuse labiomental angles have greater resorption than do those with acute angles.1Matarasso A. Elias A.C. Elias R.L. Labial incompetence: a marker for progressive bone resorption in silastic chin augmentation.Plast Reconstr Surg. 1996; 98: 1007-1014Crossref PubMed Scopus (54) Google Scholar Classification and prevalence of bone resorption (erosion) have been addressed in the past. In 1972, Robinson17Robinson M. Bone resorption under plastic chin implants: follow-up of a preliminary report.Arch Otolaryngol. 1972; 95: 30-32Crossref PubMed Scopus (48) Google Scholar introduced a classification for chin implant bone erosion based on the amount of resorption (depth) compared with the size of the implant used, as observed on lateral skull radiographic views (Table I). An alternate classification method was later introduced by Guyuron et al18Guyuron B. Michelow B.J. Willis L. Practical classification of chin deformities.Aesthetic Plast Surg. 1995; 19: 257-264Crossref PubMed Scopus (31) Google Scholar based solely on the depth of bone invaded (Table II).Table IRobinson classification system of bone resorptionI.Any resorption up to a third of the added implant dimension, or approximately 3 mmII.Resorption between a third and a half of the added implant dimension, or approximately 3-5 mmIII.More than 50% of the implant dimension, or 5 mm Open table in a new tab Table IIGuyuron classification system of bone resorption1.Cortical2.Up to 3 mm3.3-5 mm4.Over 5 mm Open table in a new tab In a retrospective study, Friedland et al19Friedland J.A. Coccaro P.J. Converse J.M. Retrospective cephalometric analysts of mandibular bone absorption under silicone rubber chin implants.Plast Reconstr Surg. 1976; 57: 144-151Crossref PubMed Scopus (78) Google Scholar used lateral cephalograms to determine the incidence of bone resorption under chin implants. Over 50% of their sample had bony erosion. A dental computed tomography (CT) software program (DentaScan; General Electric, Milwaukee, Wis) has been recently used for the evaluation of mandibular erosion arising from silastic implants.20Abrahams J.J. Caceres C. Mandibular erosion from silastic implants: evaluation with a dental CT software program.Am J Neuroradiol. 1998; 19: 519-522PubMed Google Scholar The purpose of this report was to create awareness among orthodontists about the existence of chin implant-related bone erosion among adults seeking our services. It will also benefit readers by suggesting management alternatives once diagnosed. Four patients were used to describe the cephalometric and panoramic radiographic findings of varying degrees of bone erosion induced by surgically positioned chin implants. Lateral cephalograms and panoramic x-rays of 4 subjects with incidental findings of alloplastic chin implants are presented, and magnetic resonance images and CT scans were also available for 1 subject. The images were evaluated for implant position related to the anatomy of the chin, presence and size of the bone defect, and relationship of the defect to the root apices. Four surgeons placed the implants, and the implants' compositions varied in the sample. Consent to use the radiographs and images was obtained from all 4 subjects. A 39-year-old woman, whose lateral cephalogram showed a small 0.45-cm silicone chin implant, had a normal mandibular symphyseal bony contour. The mandible and chin area as observed in her panoramic dental x-ray were also unremarkable. When the radiograph was obtained, the implant had been in place for 10 years and had been placed by surgeon 1. The patient was asymptomatic. A normal bone pattern was observed, with no radiographic evidence suggesting possible mandibular bone erosion under the implant (Fig 1). A 32-year-old woman had a medium-sized implant of approximately 0.7 cm. The type of biomaterial used was unknown. When the radiograph was taken, the implant placed by surgeon 2 had been in place for 17 years. An elongated, C-shaped concavity superior, posterior, and inferior to the implant of approximately 3.0 mm and penetrating deeper than the cortex was observed in her initial lateral cephalogram (Robinson grade I, Guyuron grade 2). Her panoramic radiograph showed a subtle symmetric radiolucency in the parasymphyseal region of the mandible (Fig 2). A 32-year-old woman had a large, 0.9-cm silicone implant. When the radiograph was obtained, the implant placed by surgeon 3 had been in place for 10 years. A rounded C-shaped concavity mostly posterior and inferior to the implant of approximately 0.5 cm and penetrating almost into the internal portion of the lingual symphyseal cortex was observed in her routine initial lateral cephalogram (Robinson grade II, Guyuron grade 3). Her panoramic radiograph showed a mild radiolucency in the mandibular body, elliptical in shape, which included the parasymphyseal region and extended from the right to the left premolar areas (Fig 3). A 33-year-old man had an extra-large Mersilene mesh chin implant, measuring approximately 5.0 cm in length and with 1.4 cm in the anterior projection. The implant placed by surgeon 4 had been in place for 10 years. A rounded C-shaped concavity located posterior to the implant, measuring approximately 0.7 cm in depth, and with significant intrasymphyseal penetration, was observed in his routine initial lateral cephalogram (bone erosion: Robinson grade III, Guyuron grade 4). The erosive area was close to the apices of the teeth. His panoramic radiograph showed a large elliptical lucent lesion with well-defined, thin, sclerotic borders. The lesion was located in the right and left bodies of the mandible and in the parasymphyseal mandibular region, and was close to the anterior dentition (Fig 4). His anteroposterior cephalogram showed a radiolucent spherical area in the parasymphyseal region of the mandible. The patient underwent axial and coronal magnetic resonance imaging (Fig 5) and a CT scan of the head (Fig 6). Axial magnetic resonance images showed the implant as an oblong T1 and T2 hypointense structure resulting in erosion of the buccal cortex of the mandible and marked thinning of the medullar space. The accompanying CT image through the same level, using bone window settings, demonstrated how the buccal cortex and medullar space were completely eroded at this level. The lingual cortex was severely thinned. Endodontic evaluation of the mandibular incisors, canines, and premolars was performed. All teeth were vital. The surgeon who placed the implant was consulted. Removing the implant was considered but not performed because the procedure had a high risk of soft tissue disfigurement at the chin. Six months after orthodontic treatment was started on this patient in preparation for a mandibular advancing osteotomy, he sustained a mandibular fracture, and several mandibular teeth were completely avulsed as a result of trauma to the mandible in a car accident. The orthognathic correction for this patient is on hold, pending prosthetic rehabilitation.Fig 5T1 axial and coronal magnetic resonance image of the head of patient 4. Arrows point towards the chin implants and also delineate periphery of areas of resorption, thus visually aiding the reader in their identification.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Fig 6CT scan (bone window) of the head of patient 4. Arrows point towards the chin implants and also delineate periphery of areas of resorption, thus visually aiding the reader in their identification.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Four patients with alloplastic chin implants are presented, 3 of whom have varying degrees of bone erosion under the prostheses, and 1 has a normal bony contour (Table III). The bony defects varied from 3 to 7 mm in depth. The erosive areas and the superior aspect of the implant were close to the mandibular anterior teeth in 2 subjects, those with the greatest amount of erosion. The greatest amount of erosion that occurred in 1 subject extended posteriorly into the premolar area. The CT scan performed on the subject with the deepest concavity and the greatest bone loss did not show any periapical lesions on the dentition. Endodontic evaluation of patient 4 was negative. He had the implant with the largest anterior projection among the 4 reported: 1.4 cm thick. Patients 3 and 4 were referred back to their surgeons for evaluation of the bony defects and disposition regarding the implants before orthodontic treatment. Both surgeons opted not to remove the implants. Patient 2 could not contact her surgeon, who practices in another country.Table IIIPatient dataPatientAge (y)SexTime from placement (y)Surgeon's identification numberImplant materialImplant size (AP projection at midline)Robinson bone erosion classificationGuyuron bone erosion classification139F101Silicone0.45 cmNormalNormal232F172Unknown0.7 cmGrade IGrade 2332F103Silicone0.9 cmGrade IIGrade 3433M104Mersiline mesh1.4 cmGrade IIIGrade 4F, Female; M, male; AP, anteroposterior. Open table in a new tab F, Female; M, male; AP, anteroposterior. Alloplastic implants have been in use for 5 decades. Despite their well-known associated risk of bone erosion (resorption), they are still frequently used. Bone erosion presents risks to adjacent structures: ie, teeth. There is a high incidence of progressive bone resorption associated with chin implants, often appearing as soon as a few months after placement of the implant.15Robinson M. Shuken R. Bone resorption under plastic implants.J Oral Surg. 1969; 27: 116-118PubMed Google Scholar, 17Robinson M. Bone resorption under plastic chin implants: follow-up of a preliminary report.Arch Otolaryngol. 1972; 95: 30-32Crossref PubMed Scopus (48) Google Scholar Bone erosion is a progressive condition with multiple negative outcomes. According to the American Society of Plastic Surgeons, 18,136 chin implants were placed in the United States during 2014 and 26,924 during 2000; thus, approximately 337,500 chin implants could have been placed over a 15-year period.16ASPS 2014 Plastic Surgery Statistics Report. Available at: http://www.plasticsurgery.org/Documents/news-reresources/statistics/cosmetic-procedure-trends-2014.pdf. Accessed on August 16, 2015.Google Scholar Extrapolation of these figures indicates that currently close to half a million people with chin implants could be living in the United States. A ratio of close to 50 persons with chin implants per orthodontist is possible. There is a high possibility for us as clinicians to orthodontically examine a patient with a chin implant, and underlying bone erosion could be present. Many people involuntarily do not to report on their medical history forms having had a chin implant. Others might opt to withhold the information. Lateral cephalograms appear to be the optimal tool in determining the presence of a chin implant, and we, as orthodontists, might be seeing them as incidental findings during our initial evaluation of these patients. As clinicians, we are in an excellent position to detect the associated bone resorption at an early stage. Use of the classification systems of bone erosion associated with chin implants as observed in lateral cephalograms could be a beneficial tool in determining the potential optimal time to consider their removal. If a chin implant is removed during an early stage of bone resorption, this measure could avoid further progression of the bony erosive process and other possible sequelae: damage to the dental neurovascular bundle of teeth adjacent to the erosive process (loss of vitality), tooth loss, mandibular fractures, decreased soft tissue chin prominence, and facial disfigurement. Radiographic follow-up of chin implants does not seem to be recommended on a regular basis by the surgeons placing them. With high esthetic demands, subjects with chin implants could seek orthodontic treatment, and their presence could be an incidental finding. Others might have the implants placed after orthodontic treatment but might consult with us eventually during adulthood. An adequate medical history at this time and a lateral cephalogram might prove to be of great value. Orthodontists radiographically detecting chin implants should consider certain guidelines in the management of these patients. Ideally, all persons undergoing a chin implant procedure should have a baseline lateral head x-ray (or a cephalogram) performed immediately after the operation. Once there is radiographic evidence of a chin implant, any bone erosion should be classified. If there is a normal bony contour without evidence of erosion, the orthodontist should consider risk counseling to the patient, because of the legal implications of the finding: knowing and not informing. If there is radiographic evidence of erosion, the orthodontist should inform the patient. A consultation and evaluation with the surgeon regarding the benefits or contraindications for implant removal should be considered. I believe that Robinson grades I and II and Guyuron grades 2 and 3 erosion stages seem to be the most appropriate times to consider early removal of an implant. Based on data herein reported, prospective monitoring of mandibular symphyseal bone erosion as observed in lateral radiographs in subjects with alloplastic chin implants is recommended. A management algorithm for patients with chin implants has been developed. The use of a standardized management strategy for all persons with implants, regardless of the biomaterial used, is presented. This proposed protocol is summarized and described in the flow chart in Figure 7. Depending on the depth and extent of the defect, a CT scan, cone-beam CT, or DentaScan (General Electric) might be in order. When the defect is close to the dental root apices, an endodontic consultation to determine tooth vitality is essential. Loss of sensory and vascular supply leading to pulpitis, or even pulp necrosis and periapical pathology, could later develop. Some chin implants are designed with wings extending posteriorly and laterally. In addition to other risks already addressed, this type of design could also present a risk of mental nerve impairment, depending on initial positioning or eventual displacement from where it was initially placed. To reduce this risk, securing the implant with screws might be a surgical option. Chin disfigurement after the removal of an alloplastic chin implant has been addressed since 1984 by Snyder21Snyder G.B. Augmentation mentoplasty.in: Goldwyn R.M. The unfavorable result in plastic surgery: avoidance and treatment. 2nd ed. Little, Brown, Boston1984: 651-668Google Scholar and Goldwin.22Goodwin R.M. Comments on augmentation mentoplasty.in: Goldwyn R.M. The unfavorable result in plastic surgery: avoidance and treatment. 2nd ed. Little, Brown, Boston1984: 669Google Scholar It was later addressed by Cohen et al,23Cohen S.R. Mardach O.L. Kawamoto Jr., H.K. Chin disfigurement following removal of alloplastic chin implants.Plast Reconstr Surg. 1991; 88: 62-70Crossref PubMed Scopus (30) Google Scholar who also reported adverse facial changes on 10 patients after alloplastic chin implant removal. Physical findings on these 10 women, aged 23 to 62 years, included dimpling and pogonial bunching. They further stated that these "bizarre" soft tissue deformities, once established, are most likely uncorrectable. They recommended immediate osseous genioplasties after the implants were removed. The procedure involved in a genioplasty is more invasive and time-consuming than the placement of a chin implant, and is most often performed in a hospital. Some inherent risks are associated with this procedure, and it could have a longer recovery time. Nonetheless, a sliding genioplasty vs a chin implant should be considered as a treatment option for those with microgenia. Matarasso et al1Matarasso A. Elias A.C. Elias R.L. Labial incompetence: a marker for progressive bone resorption in silastic chin augmentation.Plast Reconstr Surg. 1996; 98: 1007-1014Crossref PubMed Scopus (54) Google Scholar and Friedland et al19Friedland J.A. Coccaro P.J. Converse J.M. Retrospective cephalometric analysts of mandibular bone absorption under silicone rubber chin implants.Plast Reconstr Surg. 1976; 57: 144-151Crossref PubMed Scopus (78) Google Scholar recently readdressed the issue regarding the merits of alloplastic implants vs autogenous augmentation with orthognathic surgery. This issue has been debated for several decades. Orthodontists should inform their patients who need chin augmentation of the 2 available treatment options. As orthodontists, we are in a privileged position for the early detection of progressive bone erosion under chin implants. In those with mild erosion, removal of the implant might be the best option. If so, the immediate use of endogenous or exogenous bone grafting to cover the defect, followed by an advancing genioplasty, might be an option. Observation and follow-up could also be wise decisions. Orthodontists evaluating adults considering orthodontic treatment who have previously had chin augmentation with alloplastic implants are in a unique position to detect bone erosion (resorption) under the prostheses. If detected early enough, further progression of this process could be avoided. Prevention of potential dental damage or loss is another possibility. Adverse facial esthetic changes could also be prevented. An algorithm for the management of patients with chin implants has been developed. A team approach between the orthodontist and the plastic surgeon in the evaluation process of this situation could also be the first step for the orthodontist in establishing a new professional relationship. Research related to this topic, including minimally invasive corrective treatment alternatives, is indicated.
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