The long-term risks and complications of bovine-derived xenografts: A case series.

The frequency of dental implant related surgeries that involve soft tissue and bone augmentation procedures has increased significantly. Bovine-derived substitutes have been by far the most commonly used xenografts in dentistry. Albeit literature is replete with clinical studies in favor of bovine-derived graft materials, bibliographical data reporting on risks and clinical complications is scarce. Clinical impression and concern for patient safety led to the report we have provided. The aim of the present case series was to raise awareness on the long-term risks and late clinical complications of bovine-derived graft materials. Patients were referred to a private practice due to bone augmentation complications. Demographics, significant medical and dental findings are reported. Complications included sinus and maxillary bone pathoses, displacement of the graft materials, oroantral communications, implant failure, foreign body reactions, encapsulation, chronic inflammation, soft tissue fenestrations and associated cysts. Bovine-derived graft materials were not biodegradable. Resolution of the associated lesions and symptoms was achieved after the removal of the bone graft materials. The surgical removal of the xenograft materials may require advanced clinical skills because of the different configurations clinicians might encounter of the non-resorbed and migrated particles. The authors' concern is that patient morbidity may not be reduced with xenografts, due to the inherent risks and associated complications. Clinicians seeking to provide functional and esthetic outcomes should be aware of the complications of the bovine-derived graft materials. The long-term safety of xenografts and their potential association with disease are valid concerns.

INTRODUCTION

Esthetics is an inseparable part of today's dental treatment; however, consistency of results, reliability of treatment modalities, and long-term prognosis require scientific approaches to therapeutic procedures. The optimal dental solution recognizes the long-term well-being of the patient.[1] All treatment planning must have proven scientific basis that will predict what lies ahead for the patient in years to come.

The frequency of dental implant-related surgeries that involve soft-tissue and bone augmentation surgical procedures has increased significantly.[2] Bovine-derived substitutes are by far the most commonly used xenograft in dentistry.[345] However, bibliographical data reporting on clinical complications are scarce and the long-term safety is rarely addressed in dental literature; the risk of bovine spongiform encephalopathy (BSE). Reported complications have included as follows: acute and chronic sinusitis, maxillary fungus ball, material displacement, immune reactions, chronic inflammation, foreign body reaction,[678910] and the risk of disease transmission (variant Creutzfeldt–Jakob disease).[1112]

Dental literature is replete with clinical studies in favor of anorganic bovine bone as grafting material. Nevertheless, a close evaluation of published papers in favor of bovine-derived graft materials reveals wide variation in the study designs, creating conditions for erroneous conclusions from the methods used.[11] Often, the use of broad or vague definitions and errors in analytical models can be noted.[11] Recently, Kim et al. concluded that the long latency period to manifestation of the disease (1 to over 50 years) in xenograft-infected patients provides a framework for discussing possible long-term risks of the xenografts.[12]

The purpose of the present case series was to raise awareness on the long-term risks and late complications of bovine-derived xenografts. Concern for patients led to the report we have provided. Without anticipating potential failure, any immediate success is limited to initial satisfaction and ignores the far greater elements of the problematic outcome yet to occur.

CASE REPORTS

All patients were provided with the written informed consent and the Health Insurance Portability and Accountability Act documents. Identity of the patient and health-care providers have been excluded from the study. Primary ethical approval was obtained by the competent local authority. Patients were referred to a private practice due to bone augmentation complications. Patients’ demographic, significant medical and dental findings are reported. The following descriptions are the overviews of the affected patients.

Case 1

Patient 1 was a 60-year-old female with no significant medical history. Approximately 2 years before her visit, the left lateral incisor extraction site was xenografted. Clinical evaluation revealed localized soft-tissue inflammation associated with edema and pain. At palpation, a mobile mass could be detected. Surgical exposure revealed a mass of encapsulated xenograft particles that was removed. Treatment consisted of autogenous bone augmentation and soft-tissue grafting [Figure 1].

Figure 1

Clinical photography from the baseline to final result (a-c). Notice the chronic inflammation, edema, and gingival fenestration (arrow) caused by bovine-derived bone particles at baseline (a). Resolution of gingival fenestration and chronic inflammation after removal of bovine-derived biomaterials (c). Periapical radiograph (d). Surgical removal of the encapsulated bovine-derived biomaterials (e-h). Autogenous bone blocks graft surgery (i). Implant placement (j and k). Autogenous connective tissue graft (l). Periapical radiograph at 5-year follow-up (m)

Case 2

Patient 2 was a 52-year-old female with no significant medical history. The full edentulous maxilla was restored with nine dental implants following bone augmentation procedures. Five years after what was considered to be a successful treatment, facial edema was associated with pain and discomfort, migrating bovine bone particles and peri-implantitis. After the removal of the bovine bone particles, pain and edema were eliminated. Subsequently, the implants were removed [Figure 2].

Figure 2

Smile, frontal, and occlusal photographs (a-c). Surgical removal of bovine-derived bone biomaterials (d-f). Nonresorbed bovine-derived bone particles (g)

Case 3

Patient 3 was a 59-year-old male with a medical history of angina, hypercholesterolemia, aortic valve stenosis, and periodontal disease. Medications included rosuvastatin calcium (40-mg tablet, once daily), nitroglycerin (0.4 mg, sublingual), ticagrelor (90 mg, twice a day), acetylsalicylic acid (81 mg, once every other day), and coenzyme Q10 (300 mg daily). Seven years after bovine bone sinus grafting, the displacement of the graft particles was associated with sinus and maxillary bone pathologies. After surgical debridement, bony defects were repaired using the autogenous bone. Histopathological examinations revealed segments of fibrous and granulation tissue containing a mixed chronic inflammatory cell infiltrates composed of lymphocytes and plasma cells. Occasional macrophages were also seen. Fragments of thin, cystic-type epithelium were noted. The periphery of the cyst walls was compressed and well hyalinized. Large collections of pink amorphous necrotic debris containing cholesterol clefts were detected. No specific microorganism was encountered. No evidence of malignancy was observed in the sections studied [Figure 3].

Figure 3

Radiographic evaluation of the cystic lesions associated with bovine bone particles (*), scattering of the particles can be observed (a-c). Surgical removal of bovine-derived xenografts (arrow) and associated cyst (d-i)

Case 4

Patient 4 was 87-year-old male with a medical history of hypertension, hypercholesterolemia, osteoarthritis, asthma, and periodontitis. Medications included acetylsalicylic acid (81 mg, once every other day), pravastatin sodium, balsalazide, valsartan, and allopurinol. The patient's otolaryngologist diagnosed him with bovine bone associated left maxillary sinusitis 13 years after sinus elevation. The thickening of the maxillary sinus mucous membrane was detected. The presence of mucoid material had opacified 80% of the sinus. The left nasal fossa including the left middle meatus was also affected and diagnosed with inflammatory/rhinitis. The right ostiomeatal unit areas were clear. The surgical debridement of the maxillary sinus was performed and resulted in significant improvement [Figure 4].

Figure 4

Misleading periapical radiograph of what was considered to be a successful sinus lift (a). Bovine-derived biomaterial view from the transversal sections of the computed tomography scan (b and c). Frontal sections of computed tomography scan (d-i). Transversal sections of the computed tomography scan (j-o). Notice the opacification (+) of the left maxillary sinus. Note the unhealed access window previously performed for sinus lift procedure (arrow) and the scattered bovine-derived xenograft particles (*)

Case 5

Patient 6 was a 31-year-old female with no medical history. Three years before her visit, the maxillary right lateral incisor was grafted with bovine-derived bone materials followed by implant placement. The migration of the bone particles was associated with the soft-tissue fenestration adjacent to an intact neighboring periodontium. Notably, the change in soft-tissue color and texture associated with the encapsulated bovine bone was observed. Bovine bone particles were removed and autogenous connective tissue grafts were inserted. Gingival fenestration resolved and esthetic outcome was achieved [Figure 5].

Figure 5

Clinical photographs and periapical radiograph at baseline of the improper dentistry (a-d). Note gingival fenestration associated with bovine-derived biomaterials (c). Surgical removal of bovine-derived bone particles and insertion of connective tissue graft (e). Photography of the achieved esthetic outcome and resolution of gingival fenestration (f). Periapical radiograph at 10-year follow-up (g). Final results (h-i)

DISCUSSION

The long-term safety of xenografts and their potential association with disease transmission are valid concerns. Dental literature has rarely addressed the clinical risks and complications of anorganic bovine bone as a grafting material. However, the scarce literature on complications does not mean that such events are unusual. Often, the “negative” findings are not published or are not being submitted for publication. Ignoring the negative outcomes is worrisome as it skews the scientific literature. “Negative” data can be statistically more trustworthy than positive data.[13] However, regardless of being positive or negative, publication of interesting results would create a more unbiased scientific endeavor.[14] The present report was conceived with the safety of patients in mind.

The major concern of the present report was the late complications extending from 2 to 13 years after what was considered to be a successful treatment outcome. Adverse effects in the present case series report included sinus and maxillary bone pathoses, displacement of the graft materials, oroantral communications, implant failure, foreign body reactions, encapsulation, chronic inflammation, soft-tissue fenestrations, and associated cysts. The bovine bone xenograft is not biodegradable. Mordenfeld et al. provided evidence of deproteinized bovine bone particles not biodegraded after 10 years.[15] Later on, in a human histological and histomorphometrical study, Mordenfeld et al. detected particles of deproteinized bovine bone showing no significant size change at 11 years.[16] Ayna et al. showed the presence of residual bovine bone particles in humans after 14 years.[17] Moreover, Traini et al. reported residual particles of anorganic bovine bone after 20 years in a human clinical and biological performance assessment.[18] In accordance with our observations, foreign body reactions to anorganic bovine bone have also been reported.[8] Histologically, the bovine bone particles have been intimately associated with multinucleated giant cells along with lymphocytes, plasma cells, and histiocytes.[8] The present consecutive case series evidenced encapsulation of the material, clinical signs, and reactions proper of foreign body reactions. The authors’ concern is that patient morbidity may not be reduced with xenografts, due to the inherent risks and associated complications.

Although clinicians have interpreted osteoclastic activity around bovine bone particles positively,[1920] it may be of concern to patients’ safety as well. Osteoclasts are the only cells capable to degrade the bone matrix by resorption, a required process for bone morphogenesis during development and continual repair of the skeleton (bone remodeling).[2122] The unique specialized attachment to bone matrix is facilitated by integrin receptors such as osteopontin.[23] The detection of osteoclasts in contact with the bovine bone particles and/or allografts[24] could indicate the presence of proteins in the surface of the “deproteinized” graft particles. Studies have demonstrated the presence of proteins in “anorganic” bovine bone xenografts such as growth factor-β, bone morphogenetic protein, and collagens.[252627] Interactions of residual proteins within bovine bone particles and the host cell receptors could elicit acute and chronic immune reactions, as well as disease transmission. These findings raise doubt concerning the ability of manufactures to obtain consistently anorganic bovine bone. Bovine bone encephalopathy (BSE) prion inactivation by anorganic bovine bone manufacturing processes has yet to be proven.[1112] BSE is a type of transmissible spongiform encephalopathies caused by prion proteins. Prions are well known for their resistance to conventional chemical and physical decontamination methods,[2829] and the heat treatment used for anorganic bovine bone material preparation (300°C for Bio-Oss®, 1100°C for PepGen P-15®) has not proven to inactivate BSE prion.[12] Chronic inflammation of the soft tissue associated with the bovine bone was evidenced in the present report. The inflammatory processes resolved after the removal of the bovine bone materials. The plausibility of bovine-derived bone substitutes in producing immune reactions is present.

Sinusitis, scattering of the graft materials, or wound dehiscence are not unusual when xenografting is performed.[30] Chirilă et al. reported 4.3% occurrence of acute maxillary sinusitis in patients who underwent sinus lift with the use of a combination of xenograft (Cerabone, Botiss biomaterials GmBhH, Gerlingen, Germany or Gen-Os, Osteobiol, Tecnoss Dental, Torino, Italy) and autogenous bone. The clinical signs were headache, locoregional pain, cacosmia, inflammation of the oral buccal mucosa and rhinorrhea, or unilateral nasal discharge.[31] Chronic sinusitis and related symptoms (mucopurulent nasal drainage, facial pain and/or pressure, nasal congestion, and foul smell) have been shown to develop in patients following implant placement and sinus lift.[32] Interestingly, Scolozzi et al. demonstrated association between deproteinized bovine bone (Bio-Oss) substitute and development of fungus ball in the maxillary sinus.[9] Fungus ball represents the most common form of fungal infection involving paranasal sinuses, encountered in 28.5% of patients suffering from chronic maxillary sinusitis. The frequent causative agent is Aspergillus fumigatus.[9] All 13 cases with fungus ball had received anorganic bovine bone. This form of sinusitis typically affects healthy adults.[9] Similar to the present report, resolution or improvement of the symptoms was achieved by removal of the bone graft material.

Sivolella et al.[33] and McCrea[34] have reported a total of three cases of cysts associated with dental implants. The reported cases developed nasopalatine duct cystic lesions.[3435] Cystic lesions associated with bovine bone particles have not been reported in the dental literature. In the present paper, we identified a bovine bone associated cyst 7 years after grafting. The periphery of the cyst wall was well-hyalinized with amorphous necrotic debris.

Autogenous transplants were the treatment of choice for patients that required surgical reconstruction of the tissues after the removal of the xenograft materials. Intraoral soft and hard donor tissue areas share biological, biochemical, and embryological similarities with intraoral recipient sites that enhance transplant vascularization and incorporation. Furthermore, transplants of autogenous origin have a healing and incorporation period shorter when compared to alternatives. Although quantities may be limited, autogenous transplants remained the “gold standard” for the restoration of intraoral tissues volume without immune reactions.[3536]

Dentistry has experienced periods of major excitement followed rapidly by severe disappointments. Ioannidis and Trikalinos provided evidence that the paradoxical events are in part the result of many research teams working in the same field with massive experimental data being produced.[37] Therefore, each team may prioritize pursuing and disseminating its most impressive “positive” results. Frequently, clinicians misled by the overwhelming amount of positive results use vague concepts and conclusions, not clearly substantiated, to develop therapies with disappointing long-term results. The term to describe this phenomenon of rapidly alternating extreme research claims and extremely opposite refutations is known as “Proteus Phenomenon.”[37] “Negative” results are useful and should be disseminated for the science endeavor.[38] Immediate esthetic outcomes are a crucial factor influencing dentistry, which is undeniable of interest to clinicians and patients.[39] However, research and science are about revisiting accepted knowledge, expressing doubt, and positing new questions for consideration. Clinicians seeking to provide functional and esthetic outcomes should be aware of the clinical complications of the bovine-derived graft materials. The surgical removal of the xenograft materials may require advanced clinical skills due to the different configurations clinicians might encounter of the nonresorbed and migrated particles.

CONCLUSION

The long-term safety of xenografts and their potential association with disease are valid concerns. The bovine bone xenograft is not biodegradable. Complications in the present case series included sinus and maxillary bone pathologies, displacement of the graft materials, implant failure, foreign body reactions, encapsulation, chronic inflammation, soft-tissue fenestrations, and associated cysts. Resolution or improvement of the associated lesions was achieved by the removal of the bone graft materials. Long-term clinical evaluations are needed to identify the biological complications of xenografts that are used extensively in dentistry.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patients have given their consent for their images and other clinical information to be reported in the journal. The patients understand that names and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.