Bone Augmentation Techniques Research Articles

PR599: The “Sandwich” bone augmentation technique

PR599: The “Sandwich” bone augmentation technique

Cortical Bone Repositioning Technique for Horizontal Alveolar Bone Augmentation: A Case Series.

The objective of this study was to present a novel procedure for cortical bone repositioning (CBR) that maintains a secure space under the periosteum by replacement of the lateral cortex via fixation, employing titanium screws. Seven systemically healthy patients presenting with horizontal alveolar bone defects in radiographs and CT images were enrolled for CBR technique for horizontal alveolar bone augmentation. A lateral cortical bone block was cut in the defects and freed from the original bony surface. A screw was inserted into the block, and the block was placed laterally to allow fixation. The block was checked for adequate stability, and the flap was closed after creation of periosteal releasing incisions to ensure tension-free closure. There were no complications, and 16 implants were placed uneventfully. Preoperative bone width in the defect area was 3.28 mm; the postoperative 4-month bone width in the same area was 6.46 mm. The mean implant stability quotient (ISQ) at placement was 68. At the secondary operation for changing to a healing abutment, the mean ISQ was 72. All patients were functionally and esthetically rehabilitated with implant-supported dentures. CBR technique is a simple procedure without the use of any biomaterials or devices. The main advantage of this technique in comparison to autogenous grafts is the lack of donor site issues. This technique has the possibility of inducing the patient's regenerative ability for bone healing.

Trends in Surgical Management of Anterior Shoulder Instability: Increased Utilization of Bone Augmentation Techniques†.

The purpose of this study is to evaluate the trends in surgical management for anterior shoulder instability in the U.S. Military. A retrospective analysis of military service members undergoing arthroscopic or open shoulder stabilization from 2012 to 2015 within the U.S. Military Health System was conducted. Demographic and surgical variables were extracted from the medical record. Chi-square and linear regression analysis were performed to identify temporal trends by surgical procedures and concomitant surgery. Associations between demographic variables and surgical procedure were evaluated using logistic regression analysis with odds ratios and 95% confidence intervals. Eight thousand five hundred and eighty nine surgeries were performed for anterior shoulder instability. The arthroscopic Bankart procedure remained the dominant surgical procedure over time (n = 8177, 95.2%), whereas the open Bankart procedure (n = 172, 2.0%) demonstrated a diminishing trend, which was significant on univariate analysis (p = 0.0009), but not statistically significant on linear regression (p = 0.12). Additionally, there was a significant trend toward increased utilization of the Latarjet procedure over the period studied (n = 33, 1.7% - n = 81, 3.56%) (p = 0.009). During the same time period, concomitant superior labrum anterior/posterior repairs decreased (n = 980, 11.4%; p = 0.0045), whereas rates of biceps tenodesis (n = 741, 8.6%; p = 0.05) increased significantly. When analyzing patient age as a continuous variable, increasing age was associated with a significantly higher likelihood of arthroscopic treatment (odds ratio 1.02, 95% confidence interval 1.00-1.03, p = 0.05). The rate of performing an arthroscopic Bankart repair has remained relatively stable as the dominant surgical procedure for shoulder instability in the military patient population. There was a significant trend of increased use of the Latarjet procedure, which likely reflects the recognition of bone loss through use of preoperative advanced imaging and computed tomography with three-dimensional reconstructions. Additionally, there was a significant decrease in adjacent superior labrum anterior/posterior repairs over the study period, followed by a corresponding rise in biceps tenodesis. Level of evidence: level IV.

Effect of Deproteinized Bovine Bone Mineral at Implant Dehiscence Defects Grafted by the Sandwich Bone Augmentation Technique.

The aim of this study was to compare the amount of radiographic horizontal buccal bone thickness (BBT) at implant dehiscence defects grafted with the sandwich bone augmentation (SBA) and modified sandwich bone augmentation (MSBA) techniques. Compared to the SBA technique, the MSBA approach involved an additional outer layer of deproteinized bovine bone mineral (DBBM) to maintain the space for bone regeneration for longer periods. A total of 19 patients, each with a buccal implant dehiscence defect, were recruited. The control group was treated with SBA technique (n = 10), while the test group was treated with MSBA technique. Cone beam computed tomography (CBCT) scans, taken at three time points (before and immediately after implant surgery, and 6 months post-treatment) were used to assess the BBT at the implant platform (-1.8 mm), the rough-smooth junction (0 mm), and 2, 4, 6, 8, and 10 mm apical to the rough-smooth junction. At 6 months postsurgery, the mean BBT in control and test groups was 1.69 ± 0.38 mm and 2.55 ± 0.21 mm, respectively. Mean BBT was significantly greater in the test group at 2, 4, 6, and 8 mm apical to the rough-smooth junction. There was no statistical difference in the mean BBT at the implant platform, the rough-smooth junction, and 10 mm apical to the rough-smooth junction between the two groups (P > .05). Within the limitations of this study, it was concluded that the additional layer of DBBM enhanced BBT along the implant, except at the smooth collar.

The Use of Poly-d,l-lactic Acid (PDLLA) Devices for Bone Augmentation Techniques: A Systematic Review.

Poly-d,l-lactic acid (PDLLA) has been proposed in dentistry for regenerative procedures in the form of membranes, screws, and pins. The aim of this review was to evaluate the efficacy of bone augmentation techniques using PDLLA devices. A literature search was carried out by two independent and calibrated reviewers. All interventional and observational studies assessing the efficacy of bone augmentation techniques using PDLLA devices were included. Six studies were included. The relevant variability of design and methods impeded any qualitative or quantitative comparison. Ease of handling, absence of a re-entry phase, moldability of foils, and good soft-tissue response were appreciated characteristics of PDLLA devices. Some drawbacks such as the risk of membrane exposition, a prolonged adsorbability, and a tendency to a fibrous encapsulation of the PDLLA devices have been described, although the clinical significance of these findings is unclear. Clinical data about PDLLA devices for bone regeneration are very scarce and heterogenous. Well-designed randomized controlled trials comparing the use of PDLLA foils and pins with conventional membranes for bone regeneration are strongly encouraged in order to understand the real clinical benefits/drawbacks of this technique.

Full-Mouth Rehabilitation with Calvarium Bone Grafts and Dental Implants for a Papillon-Lefèvre Syndrome Patient: Case Report

Papillon-Lefèvre syndrome (PLS) is a rare autosomal recessive disorder of keratinization associated with palmoplantar keratoderma and severe periodontitis resulting in complete edentulism in late adolescence. The pathognomonic dental features of PLS are pathologic migration, hypermobility, and exfoliation of the teeth without any signs of root resorption. It has been suggested that an effective way to treat PLS patients presenting early in the disease progression is extraction of the erupted primary dentition or hopeless permanent teeth followed by antibiotic coverage with periodontal therapy for the remaining teeth. Unfortunately, studies have shown that this regimen only temporarily delays the progression of periodontal disease and does not prevent further tooth loss and bone destruction in the long term. Post-tooth loss, atrophic ridges make conventional prosthodontic rehabilitation quite challenging, and more recently, implant-supported prostheses have been considered as a viable alternative. In a PLS patient, implant placement is complicated by inadequate bone volume; thus, bone augmentation techniques or the use of short implants is often considered. When large volumes of bone are required, parietal calvarium bone can be used to predictably reconstruct severe defects. A PLS patient aged 21 years presented a chief complaint of ill-fitting conventional complete dentures. The patient had severely atrophic ridges, requiring significant bone augmentation for an implant-supported prosthesis. The present case is the first example of bone augmentation using autogenous calvarium parietal graft followed by endosseous implant placement and prosthetic restoration in a PLS patient.

Return to Sports After Shoulder Stabilization Surgery for Anterior Shoulder Instability.

Young athletes continue to experience traumatic shoulder instability and are often plagued by recurrent instability, limiting their return to sport. The purpose of this paper was to review return to sport in athletes after shoulder stabilization surgery for anterior shoulder instability. Athletes managed nonoperatively demonstrate unacceptably high rates of recurrent instability and are less likely to successfully return to sport. Operative management includes capsuloligamentous repair (arthroscopic versus open) and bone augmentation techniques. While modern arthroscopic techniques have provided favorable outcomes, open techniques have demonstrated lower recurrence rates among young collision athletes. A subset of athletes continue to experience recurrent instability, leading to further investigation of concomitant pathologies, which may put patients at risk of failure following Bankart repair. Bony augmentation procedures remain favorable for patients with glenoid bone loss; however, what constitutes critical bone loss in the decision between anterior labral repair versus bone augmentation has recently been questioned. Operative management of anterior shoulder instability provides superior results, including lower recurrent instability and return to sport. Future research on patient-specific risk factors may aid surgical decision-making and optimization of outcomes.

The protective effect of platelet released growth factors and bone augmentation (Bio-Oss®) on ethanol impaired osteoblasts

BackgroundChronic alcohol consumption is a known limiting factor for bone healing. One promising strategy to improve bone augmentation techniques with Bio-Oss® in oral and maxillofacial surgery might be the supportive application of platelet-concentrated biomaterials as platelet-released growth factor (PRGF). To address this matter, we performed an in vitro study investigating the protective effects of PRGF and Bio-Oss® in ethanol (EtOH) treated osteoblasts. MethodsThe SAOS-2 osteosarcoma cell line, with and without EtOH pretreatment was used. The cell viability, proliferation and alkali phosphatase activity (ALP) after application of 0%, 5% and 10% PRGF and Bio-Oss® were assessed. ResultsThe application of PRGF and Bio-Oss® in EtOH impaired osteoblasts showed a significant beneficial influence increasing the viability of the osteoblasts in cell culture. The synergistic effect of Bio-Oss® and 5% PRGF on the proliferation of osteoblasts was also demonstrated. Bio-Oss® only in combination with PRGF increases the alkaline phosphatase (ALP) activity in EtOH pretreated cells. ConclusionsThese results indicate that the simultaneous application of PRGF and Bio-Oss® inhibits EtOH induced bone healing impairment. Furthermore, in the cells, PRGF induced a protective mechanism which might promote bone regeneration.

Alternative Fixation in Osteoporotic Fractures

Purpose of Review The goal of this paper is to review the current available literature in alternative fixation in osteoporotic fractures, including the roles of locking plates, polyaxial screws, bone augmentation techniques, arthroplasty, and implant coating, as well as the role of co-managed care.

Transalveolar Osteotomy of the Mandibular Canal Wall for the Treatment of Severely Atrophied Posterior Mandible

Treatment of severe bone atrophy of the posterior mandible requires an advanced surgical bone augmentation technique. This report describes a minimally invasive approach for a residual alveolar height less than 5mm. A retrospective case series was conducted in a single private dental clinic. Outcome variables were dental implant survival rate, intraoperative complications, occurrence of neurosensory disturbances, and marginal bone loss. Descriptive analysis was performed for patients' demographic data, postoperative healing, and implant details. Kaplan-Meier method was used to assess the implant survival rate. The mean age of the 19 patients was 60±13years. Twenty-eight implants (5.5mm long) were placed in a residual alveolar bone height of 4.5±0.6mm. The implant survival rate was 96% at 5-year follow-up. Extra-short implants and transalveolar preparation of the inferior alveolar cortical bone could be a safe and effective treatment of severe mandibular atrophy.

Platelet-Rich Fibrin (PRF) in Implants Dentistry in Combination with New Bone Regenerative Flapless Technique: Evolution of the Technique and Final Results.

Most common techniques for alveolar bone augmentation are guided bone regeneration (GBR) and autologous bone grafting. GBR studies demonstrated long-term reabsorption using heterologous bone graft. A general consensus has been achieved in implant surgery for a minimal amount of 2 mm of healthy bone around the implant.A current height loss of about 3-4 mm will result in proper deeper implant insertion when alveolar bone expansion is not planned because of the dome shape of the alveolar crest. To manage this situation a split crest technique has been proposed for alveolar bone expansion and the implants’ insertion in one stage surgery. Platelet-rich fibrin (PRF) is a healing biomaterial with a great potential for bone and soft tissue regeneration without inflammatory reactions, and may be used alone or in combination with bone grafts, promoting hemostasis, bone growth, and maturation.AimThe aim of this study was to demonstrate the clinical effectiveness of PRF combined with a new split crest flapless modified technique in 5 patients vs. 5 control patients.Materials and methodsTen patients with horizontal alveolar crests deficiency were treated in this study, divided into 2 groups: Group 1 (test) of 5 patients treated by the flapless split crest new procedure; Group 2 (control) of 5 patients treated by traditional technique with deeper insertion of smaller implants without split crest. The follow-up was performed with x-ray orthopantomography and intraoral radiographs at T0 (before surgery), T1 (operation time), T2 (3 months) and T3 (6 months) post-operation.ResultsAll cases were successful; there were no problems at surgery and post-operative times. All implants succeeded osteointegration and all patients underwent uneventful prosthetic rehabilitation. Mean height bone loss was 1 mm, measured as bone-implant most coronal contact (Δ-BIC), and occurred at immediate T2 post-operative time (3 months). No alveolar bone height loss was detected at implant insertion time, which was instead identified in the control group because of deeper implant insertion.ConclusionThis modified split crest technique combined with PRF appears to be reliable, safe, and to improve the clinical outcome of patients with horizontal alveolar crests deficiency compared to traditional implanting techniques by avoiding alveolar height-loss related to deeper insertion of smaller implants.

Bone augmentation as an adjunct to dental implant rehabilitation in patients with diabetes mellitus: A review of literature.

The aim of the present article is to review the success of bone augmentation performed as an adjunct to dental implant rehabilitation in patients with diabetes mellitus. A literature review was conducted in PubMed on this topic, which yielded a total of 102 publications. For inclusion, publications had to be human studies, written in English language and should report on the success of bone augmentation as an adjunct to dental implant rehabilitation in diabetic patients. After screening the titles and abstracts, 11 full texts publications were obtained, of which seven were included in the review. These studies provided data on various bone augmentation techniques such as sinus floor elevation (SFE), guided bone regeneration (GBR), and onlay bone grafting. Even though the current review revealed that there are not many studies reporting data relevant to the analyzed topic, the data obtained suggests that; (1) staged GBR technique should be considered more feasible and predictable for bone augmentation, (2) clinicians must take meticulous care when planning and conducting SFE, and (3) block bone augmentation technique should be avoided.

Bone Augmentation of the Edentulous Maxilla for Implant Placement: A Systematic Review.

Multiple bone augmentation techniques are available to allow implant placement in the atrophic maxilla. However, questions remain, regarding which methods are most predictable and have the best dental implant survival rate (SR) in grafted bone. The aim of this systematic review was to evaluate literature from the last 30 years to determine predictability of bone grafting of the edentulous maxilla for implant placement as well as for implant SR. A systematic review was performed of studies conducted during the period 1980 to 2014, specifically focusing on the edentulous maxilla and bone grafting. Surgical techniques discussed in the publications included were guided bone regeneration (GBR), sinus augmentation, onlay bone grafting, nasal floor grafting, and Le Fort I interpositional grafting. All identified articles were evaluated and screened to meet strict inclusion criteria of at least 10 patients, complete maxillary edentulism, 1-year follow-up, and information regarding implant SR. A total of 974 articles were identified with electronic and manual searches. On further evaluation of the titles and abstracts, 44 articles were excluded. Full texts of the articles that met the inclusion criteria were reviewed, of which 40 articles were included in the systematic review. For onlay bone grafting, 16 studies were included and analyzed, and the weighted mean implant SR was 85.2%. For the GBR technique, two studies were included, with a reported SR ranging from 96.1% to 100%. For Le Fort I interpositional grafting, 11 studies were included, with a weighted mean SR of 89.6%. For the sinus augmentation technique, 12 studies were investigated and the weighted mean SR was 91.5%. For the combination technique, six studies were analyzed and the weighted mean SR was 93.6%. All five treatment modalities discussed-onlay bone grafting, GBR, Le Fort I interpositional grafting, maxillary sinus augmentation, and/or nasal floor inlay grafting or the combination approach-can be successfully used to augment edentulous maxillary ridge with high implant SRs.

Modern implant dentistry based on osseointegration: 50years of progress, current trends and open questions.

In the 1960s and 1970s, implant-supported prostheses based on subperiosteal or blade implants had a poor reputation because of questionable clinical outcomes and lack of scientific documentation. The change to a scientifically sound discipline was initiated by the two scientific pioneers of modern implant dentistry, Professor P. I. Brånemark from the University of Gothenburg in Sweden and Professor André Schroeder from the University of Bern in Switzerland. Together with their teams, and independently of each other, they laid the foundation for the most significant development and paradigm shift in dental medicine. The present volume of Periodontology 2000 celebrates 50years of osseointegration. It reviews the progress of implant therapy over the past 50years, including the basics of implant surgery required to achieve osseointegration on a predictable basis and evolving innovations. The development of bone-augmentation techniques, such as guided bone regeneration and sinus floor elevation, to correct local bone defects at potential implant sites has increased the indications for implant therapy. The paradigm shift to moderately rough implant surfaces resulted in faster and enhanced bone integration and led to improvements in various treatment protocols, such as immediate and early implant placement in postextraction sites, and made various loading protocols possible, including immediate and early implant loading. In the past 15 years, preoperative analysis and presurgical planning improved as a result of the introduction of three-dimensional imaging techniques. Hereby, cone-beam computed tomography offers better image quality with reduced radiation exposure, when compared with dental computed tomography. This opened the door for digital planning and surgical modifications. Over the last 50years this evolution has facilitated tremendous progress in esthetic outcomes with implant-supported prostheses and improved patient-centered outcomes. This volume of Periodontology 2000 also discusses the current trends and open questions of implant dentistry, such as the potential of digital implant dentistry in the surgical and prosthetic field, the trend for an increasing average age of implant patients and the related adaptations of treatment protocols, and the second attempt to establish ceramic implants using, this time, zirconia as the implant material. Finally, some of the hottest controversies are discussed, such as recent suggestions on bone integration being a potential foreign-body reaction and the evidence-based appraisal of the peri-implantitis debate.

Interventions for Dental Implant Placement in Atrophic Edentulous Mandibles: Vertical Bone Augmentation and Alternative Treatments. A Meta-Analysis of Randomized Clinical Trials.

The purpose of the current study is to assess which vertical bone augmentation techniques are most effective for restoring atrophic posterior areas of the mandible with dental implants and compare these procedures with alternative treatments. Electronic literature searches in PubMed (MEDLINE), Ovid, and the Cochrane Library were conducted to identify all relevant articles published up to July 1, 2015. Eligibility was based on inclusion criteria, and quality assessments were conducted. The primary outcome variables were implant and prosthetic failure. After data extraction, meta-analyses were performed. Out of 527 potentially eligible papers, 14 randomized clinical trials were included. Out of these 14 studies, four trials assessed short implants (5 to 8 mm) as an alternative to vertical bone augmentation in sites with a residual ridge height of 5 to 8 mm. No statistically significant differences were found in implant (odds ratio [OR]: 1.02; 95% confidence interval [CI]: 0.31 to 3.31; P = 0.98; I2: 0%) or prosthetic failure (OR: 0.64; 95% CI: 0.21 to 1.96; P = 0.43; I2: 0%) after 12 months of loading. However, complications at treated sites increased with the augmentation procedures (OR: 8.33; 95% CI: 3.85 to 20.0; P <0.001; I2: 0%). There was no evidence of any vertical augmentation procedure being of greater benefit than any other for the primary outcomes (implant and prosthetic failure). Short implants in the posterior area of the mandible seem to be preferable to vertical augmentation procedures, which present similar implant and prosthetic failure rates but greater morbidity. All the vertical augmentation technique comparisons showed similar intergroup results.

Is Alveolar Ridge Split a Risk Factor for Implant Survival?

There is a paucity of studies that have assessed the long-term outcomes of the alveolar ridge split (ARS). This study evaluated the intraoperative and postoperative complications and assessed the placed dental implant and prosthesis. A retrospective study of the ARS was conducted in a single private dental clinic. The predictor variable was the ARS technique (1 stage vs 2 stages). The primary outcome was the dental implant survival rate. Secondary outcomes were intraoperative complications, marginal bone loss, prosthetic complications, and prosthesis success rate. Descriptive analysis was performed for patients' demographic data, implant details, and prosthetic complications. The Kaplan-Meier method was used to assess implant survival rate and prosthesis success rate. Twenty patients (mean age, 55 ± 6yr) had a mean follow-up time of 5years. Delayed implant placement was performed when the residual alveolar bone width was narrower than 3mm. No intraoperative or postoperative complications were reported. The survival rate of the 31 implants was 100% and the prosthesis success rate was 96.8%. The ARS is an effective technique for horizontal bone augmentation in the mandible. Delayed dental implant placement when the alveolar bone width is narrower than 3mm could minimize the risk of buccal wall fracture.

Bone regeneration using bilayer bone augmentation around dental implants: A preliminary study by micro-CT in dogs.

The purpose of this preliminary study was to compare the effects of the bilayer bone augmentation technique (BBA) for the treatment of dehiscence-type defects around implants and evaluate the role as a membrane of the xenogenic bone positioned as the outer layer in the BBA technique using a micro-computed tomography (micro-CT). Four standardized dehiscence defects were prepared on each mandible bilaterally in 3 dogs and 1 implant was placed per defect, where each defect was treated with autograft (AB), xenograft (XB), BBA technique, or negative control without a membrane. Two months post-regenerative surgery, sectioned bone blocks were obtained. The image acquisitions were then scanned by micro-CT. Bone volume (BV), horizontal bone width (HBW) and vertical bone height (VBH) were measured through the analyses program. The BV were 11.08 mm3, 10.42 mm3, 8.1 mm3, and 7.01 mm3 in XB, BBA, control, and AB group in sequence of high value, respectively. HBW were 1.33 mm, 1.3 mm, 1.06 mm, and 1.03 mm in XB, BBA, AB, and control group, respectively. VBH were 4.88 mm, 4.85 mm, 4.74 mm, and 4.67 mm in XB, BBA, AB, and control group, respectively. However, there was no significant difference between the 4 groups. VBH tended to be higher in sequence of control, AB, BBA, and XB group (p for trend <0.05). The results showed the usefulness of the BBA technique involving mechanical support for prolonged space maintenance of xenogenic bone, for the treatment of dehiscence-type defects around implants. However, further studies with a larger sample size are required to confirm the results.

Full mouth implants rehabilitation of a patient with ectodermal dysplasia after 3-Ds ridge augmentation. A clinical report

A 22-year-old female presented with hypodontia and severe atrophy of alveolar ridge associated with ectodermal dysplasia, was treated with 3Ds bone augmentation technique and full mouth implants rehabilitation. Bone blocks harvested from the retro molar area to construct adequate bone volume at posterior maxilla and mandible. The vertical and horizontal bone augmentation allowed proper implant placement according to prosthetically-driven implant placement concept. Ten implants were placed. Six in the maxilla and four implants were inserted in the mandible. A cement-retained full mouth metal ceramic FPDs were fabricated. The outcome of the treatment showed that dental implants placed in bone block grafts should be considered as a good treatment modality for patients with ectodermal dysplasia. It also, provided the patient with a prosthesis that enhanced the patient function and esthetics.

Ridge Expansion by Flapless Split Crest and Immediate Implant Placement: Evolution of the Technique.

Various treatment strategies and techniques have been proposed to perform alveolar bone augmentation; most common are guided bone regeneration, split crest, and autologous bone grafting. All of these techniques are reported to possess bone regenerative properties of osteoinduction and osteoconduction in relation to regenerated bone survival. Split crest resulted to be one of the most reliable bone augmentation techniques. In this study, we describe a new flapless-modified split crest technique on 4 patients to optimize the bone regeneration with bone augmentation implant insertion in 1 single stage. The rationale of this technique is to obtain a proper buccal cortex expansion preserving its vascular supply and avoiding periosteal elevation for better cortical bone preservation. The main advantages of this technique consist in a single surgical stage without donor sites, vascular periosteal preservation of vestibular cortical walls, preservation of alveolar bone height avoiding bone loss after implant kit drilling, and preservation of proper cortical thickness on both sides, thereby saving periosteal nourishment on the vestibular side. Indication for this technique could be extended to almost every implant insertion for alveolar height saving at drilling time for implant insertion, because of the alveolar crest shape.

The Risk of Prion Infection through Bovine Grafting Materials.

Bovine-derived grafting materials are frequently used in a variety of bone augmentation techniques. The aim of this paper is to assess the unique safety issue of bovine-derived grafting materials that is rarely addressed in dental literature: risk of bovine spongiform encephalopathy (BSE). The validity of the current BSE diagnostic methods, surveillance and epidemiological trends in affected countries, and BSE infectivity in bovine bone before and after manufacturing processing were reviewed and analyzed. Prion screening has significant limits. Humans are not safe from the infection of prion disease of other species. Prions can and do break the species barrier. There is evidence there may be tens of thousands of infectious carriers in the western countries alone. This raises concern about the potential for perpetuation of infection via medical procedures. The limited ability to screen prions within the animal genome, along with a long latency period to manifestation of the disease (1 to over 50 years) in infected patients, provides a framework for discussing posible long-term risks of the xenografts that are used so extensively in dentistry. We suggest abolishing the use of bovine bone.