Faculty Bibliography

The complex and patient-unique geometry of posterior all-ceramic dental crowns represents a particularly interesting set of challenges to understanding stress concentration and fracture evolution in response to loading. A series of numerical and physical experiments, with both single cycle and fatigue loading, show that geometry profoundly influences the stress concentration and fracture initiation and propagation. In stylized crowns with uniform axial wall height, stresses concentrate beneath the indenter. As the height of the axial wall increases, loads to cause failure increase linearly. In crowns with variation in axial wall height around the periphery, stresses concentrate both beneath the indenter and at the margin of the core ceramic. The magnitude of the stress concentration at the margin is directly related to the amount of variation in axial wall height around the periphery of the crown. Anatomically correct veneered zirconia core crowns subjected to single-cycle loads, fracture in areas of greatest stress concentration identified by finite element models. Fractures and stress concentrations that occur in response to single-cycle loading are important indicators of initiation sites for fatigue failure. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008

Thick bioceramic coatings like plasma sprayed hydroxyapatite have been shown to increase the overall tissue response and biomechanical fixation of dental implants. However, the presence and potential fracture of a bone-coating-metallic substrate interface at long times after implantation led these implants to fall from favor in clinical practice. The purpose of this study was to evaluate the biomechanical fixation and biological response of Ca- and P-based, 20-50 nm thickness bioceramic deposition on a previously alumina-blasted/acid-etched Ti-6Al-4V implant surface in a dog model. Cylindrical alumina-blasted/acid-etched (AB/AE) (Control, n = 16), and Nanothickness bioceramic coated AB/AE(Nano, n = 16) implant surfaces were surgically placed in dogs proximal tibia and remained for 2 and 4 weeks in vivo. Following euthanization, the implants-in-bone were mounted in epoxy and pullout at a 0.5 mm/min rate. Following mechanical testing, the specimens were decalcified and processed (Hematoxylin and Eosin) for standard transmitted light microscopy evaluation. Percent bone-to-implant contact (BIC) to the pulled out implant surface was determined through computer software. Statistical analyses were performed by one-way ANOVA at 95% level of significance and Tukey's post-hoc multiple comparisons. No significant differences in pullout force were observed (p > 0.88): 2W Control (212.08 +/- 42.96 N), 2W Nano (224.35 +/- 42.97 N), 4W Control (207.07 +/- 42.97 N), and 4W Nano (190.15 +/- 45.94 N). No significant differences in %BIC were observed (p > 0.94): 2W Control (72.66 +/- 8.51), 2W Nano (69.44 +/- 8.51), 4W Control (70.44 +/- 8.51), and 4W Nano (69.11 +/- 9.09). It is shown that 20-50 nm thickness bioceramic depositions onto previously alumina-blasted/acid-etched substrates did not improve the biomechanical fixation and the BIC at early implantation times, and studies concerning shorter and longer implantation times are recommended for confirmation or before a conclusion can be made.

BACKGROUND: Evaluation of long-term outcomes of free-muscle transfer for smile restoration is overdue. Arguments for and against free-muscle transplantation in children are considered, and the debate on the influence of the growing skeleton on muscle function is revisited. This study evaluated the fate of free-muscle transfer over long follow-up periods in pediatric patients. METHODS: Thirty-two children with follow-up of 5 years or longer who received a free-muscle transfer for smile restoration were reviewed. To better analyze the effect of time, patients were classified into groups based on the length of follow-up: group A, 5 to 6 years; group B, 7 to 10 years; group C, 11 to 15 years; and group D, more than 15 years. Patients were videotaped at three stages: preoperatively, 2 years after free-muscle transfer, and at the last follow-up visit. Four independent observers graded patients' videotapes using a five-category scale ranging from poor to excellent. Panelists were asked to comment on any noticeable craniofacial disharmony with growth. RESULTS: All patients exhibited improved function and symmetry at 2 years after free-muscle transfer (averaged scores, p < 0.0001). A positive effect of time was seen in the long-term evaluation; observers' scores (p < 0.0001) and motor units on electromyography (p = 0.001) showed further improvement. No significance was found when comparing measured outcomes among the four follow-up groups, indicating that despite the growing skeleton, muscle function was maintained over time. CONCLUSIONS: These clinical data support the use of free-muscle transfer for smile restoration in children. The transplanted muscle appears to grow harmoniously with the craniofacial skeleton, and muscle function and aesthetic outcomes improved over time

BACKGROUND: The versatility of the temporalis muscle justifies its wide popularity in reconstructive craniomaxillofacial surgery. In late facial paralysis, results of neural reconstructive techniques such as cross-facial grafting or mini-hypoglossal-to-facial nerve transfer are partial at best. In this series, the authors have used a segmental temporalis transfer, the 'mini-temporalis,' to augment the function attained with neural microsurgery. The aim of this present study was to present the experience of the authors' center with the use of the mini-temporalis as an adjuvant to facial nerve microsurgery for smile restoration. METHODS: Data were collected from 31 patients who underwent mini-temporalis transfer for smile restoration. In all patients, the mini-temporalis was used to augment the results of neural reconstructive techniques. Opting for the mini-temporalis related to a variety of reasons, after preoperative evaluation was weighed against the advantages and disadvantages of different reconstructive strategies on individual bases. Aesthetic and functional outcomes were evaluated by a panel of five independent observers using a five-category scale ranging from poor to excellent. RESULTS: All patients observed a follow-up longer than 3 months. Of 31 patients, 61.3 percent achieved excellent or good results and 29 percent achieved moderate results. All patients demonstrated an increase in the observers' scores after mini-temporalis transfer in comparison with the scores granted preoperatively or after neural microsurgery. Highly motivated patients committed to postoperative motor reeducation exhibited the best results. CONCLUSION: The clinical data presented support the use of mini-temporalis transposition in association with facial nerve microsurgery as a valuable alternative to free muscle transfer in selected cases

BACKGROUND: Tissue engineering is often limited by the time required for culture expansion of cells necessary for scaffold seeding. Cell cycle regulators control entry and exit into the cell cycle and as such regulate cellular proliferation rates. The authors hypothesized that transient alteration in cell cycle regulators can be utilized as a means to accelerate stem cell proliferation. METHODS: Mesenchymal stem cells were harvested from wild-type mice and mice deficient in the cell cycle regulator p21. Wild-type cells were treated with small interfering RNA against p21 in two- or three-dimensional cultures in vitro. Cellular proliferation and the potential for cellular differentiation into the bone or fat lineage were assessed. RESULTS: Mesenchymal stem cells treated with small interfering RNA targeting p21 demonstrated a significant decrease in p21 protein and mRNA expression 96 hours after treatment. They also proliferated significantly faster than control cells (2.5 to three times) in both two- and three-dimensional culture. Similarly, cells harvested from p21-deficient mice demonstrated a significant acceleration in cellular proliferation. Inhibition of p21 expression was not associated with significant changes in spontaneous cellular differentiation. However, transient p21 inhibition promoted both osteoblastic and adipogenic differentiation when cells were exposed to differentiation medium. CONCLUSIONS: Transient inhibition of the cell cycle regulator p21 results in significant acceleration of mesenchymal stem cell proliferation without promoting spontaneous cellular differentiation. Exposure to differentiation medium results in increased cellular differentiation toward the osteoblast and fat lineage. Manipulation of cell cycle regulators may represent a novel means by which stem cell proliferation can be accelerated, thereby decreasing the time required for scaffold synthesis in tissue engineering.

Background: Ectopic beats are frequently associated with morphologic repolarization alterations of ensuing sinus beats. Less is known about repolarization duration alterations of post-ectopic sinus beats. In one patient who developed long QT and torsades de pointes upon exposure to a class III antiarrhythmic drug, and was later genotyped as being a carrier for long QT syndrome (LQTS) type 1, review of a pre-drug Holter monitor study revealed marked QT prolongation of post-ectopic sinus beats. In wondering whether this might be a common clue to "concealed" unexpressed LQTS, we realized that we must first characterize the range of post-ectopic QT prolongation present in normals. Prolongation beyond the upper limit of this range might then raise suspicion of possible LQTS and alter the antiarrhythmic drug selection process for the suppression of atrial fibrillation or other arrhythmias. Methods: Accordingly, we assessed the presence/degree of repolarization prolongation following premature ectopic impulses in 166 subjects with normal conduction intervals and normal repolarization on their resting 12-lead ECG, 75 of whom had no known associated cardiovascular disorder of any kind. That is, in our subjects, the maximal prolongation of the QT interval of the sinus beat following isolated ventricular and atrial premature complexes was characterized. Results: QT prolongation is common in post ectopic sinus beats. However, in our subjects the uncorrected QT interval of post-ectopic sinus beats never exceeded 480 ms in duration [which was much shorter than that seen (510-590 ms) in our gene carrier]. CONCLUSIONS: The QT interval in normal subjects may prolong following premature complexes but not to a value in excess of 480 ms.

The fundamental aspects of damage initiation and accumulation in one-piece zirconium oxide endosseous dental implants remain to be investigated. Aims: This study tested the null hypothesis that there is no influence on mouth-motion fatigue reliability and failure modes between as-received and after full crown preparation on one-piece ceramic implants. Methods: Forty-eight one-piece Y-TZP ceramic implants (Nobel Biocare, Goteborg, Sweden) were utilized. All specimens were embedded in acrylic resin exposing the first two threads at 30 degrees angulation with respect to the vertical axis (as per ISO specification 14801). Full crown preparations were performed following prosthodontic guidelines for half of the specimens. As-received and prepared specimens were distributed among three step-stress profiles based on the specimens ultimate fracture strength. Specimens were step-stress fatigued until failure or survival. A master Weibull curve was generated from the data and the reliability for completion of a mission of 50,000 cycles at 600 N load calculated. Results: No differences between the groups' reliability was observed. Failure mode for both groups was similar, where cracks initiated mainly at the tensile bending side of the second thread's internal diameter. The low Weibull modulus (<1) indicates that fatigue (<150,000 cycles) did not influence failure. Failure depended upon the applied load. Conclusion: Crown preparation did not influence the reliability of the one-piece ceramic implant. The null hypothesis was accepted. Fatigue did not influence the life time of ceramic implants at loads under 600 N. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008