Faculty Bibliography

OBJECTIVE: To evaluate the effects of clinically relevant variables on the maximum principal stress (MPS) in the veneer layer of an anatomically correct veneer-core-cement-tooth model. METHODS: The average dimensions of a mandibular first molar crown were imported into CAD software; a tooth preparation was modeled by reducing the proximal walls by 1.5 mm and the occlusal surface by 2.0 mm. 'Crown systems' were composed by varying characteristics of a cement layer, structural core, and veneer solid, all designed to fit the tooth preparation. The main and interacting effects of proximal wall height reduction, core material, core thickness, cement modulus, cement thickness, and load position on the maximum stress distribution were derived from a series of finite element models and analyzed in a factorial analysis of variance. RESULTS: The average MPS in the veneer layer over the 64 models was 488 MPa (range = 248-840 MPa). MPS increased significantly with the addition of horizontal load components and with increasing cement thickness. In addition, MPS levels varied as a function of interactions between: proximal wall height reduction and load position; load position and cement thickness; core thickness and cement thickness; cement thickness and proximal wall height reduction; and core thickness, cement thickness and proximal wall height reduction. CONCLUSION: Rational design of veneered structural ceramics must consider the complex geometry of the crown-tooth system and integrate the influence of both the main effects and interactions among design parameters

PURPOSE: Cancer stem cells are found in many tumor types and are believed to lead to regrowth of tumor mass due to their chemoresistance and self-renewal capacity. We previously demonstrated small subpopulations of cells in retinoblastoma tissue and cell lines that display cancer stem cell-like activities, including expression of stem cell markers, Hoechst dye exclusion, slow cycling, and self-renewal ability. Identifying factors regulating stem cell proliferation will be important for selectively targeting stem cells and controlling tumor growth. Wingless and Int1 (Wnt) signaling is an essential cellular communication pathway that regulates proliferation and differentiation of non-neoplastic stem/progenitor cells in the retina and other tissues, but its role in cancer stem cells in the retinal tumor retinoblastoma is unknown. In this study, we investigated whether the Wnt pathway activator lithium chloride (LiCl) regulates proliferation of retinoblastoma cancer stem-like cells. METHODS: The number of stem-like cells in Weri and Y79 retinoblastoma cell line cultures was measured by 5-bromo-2-deoxyuridine (BrdU) pulse-chase, immunohistochemistry, and quantitative polymerase chain reaction (PCR) for stem cell marker genes. The cell lines were sorted into stem-like and non-stem-like populations by fluorescence-activated cell sorting (FACS), using an antibody against the stem cell marker ATP-binding cassette, subfamily G, member 2 (ABCG2). Activated Wnt signaling was measured in the sorted cells by western blotting and immunolocalization of the central mediator beta-catenin. RESULTS: LiCl increased the number of stem-like cells, measured by BrdU retention and elevated expression of the stem cell marker genes Nanog, octamer transcription factor 3 and 4 (Oct3/4), Musashi 1 (Msi1), and ABCG2. Sorted ABCG2-positive stem-like cells had higher levels of beta-catenin than ABCG2-negative non-stem cells, suggesting elevated canonical Wnt signaling. Furthermore, stem cell marker gene expression increased after small interfering RNA (siRNA) knock-down of the Wnt inhibitor secreted frizzled-related protein 2 (SFRP2). CONCLUSIONS: These results indicate that the cancer stem-like cell population in retinoblastoma is regulated by canonical Wnt/beta-catenin signaling, which identifies the Wnt pathway as a potential mechanism for the control of stem cell renewal and tumor formation in retinoblastoma tumors in vivo.

OBJECTIVE: this study aimed to histomorphologically and histomorphometrically evaluate the in vivo response to three variations in the resorbable blasting media (RBM) surface processing in a rabbit femur model. STUDY DESIGN: screw root form implants with 3.75 mm in diameter by 8 mm in length presenting four surfaces (n=8 each): alumina-blasted/acid-etched (AB/AE), bioresorbable ceramic blasted (TCP), TCP + acid etching, and AB/AE + TCP were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The implants were placed at the distal femur of 8 New Zeland rabbits, remaining for 2 weeks in vivo. After sacrifice, the implants were nondecalcified processed to 30 micro m thickness slides for histomorphology and bone-to-implant contact (BIC) determination. Statistical analysis was performed by one-way ANOVA at 95% level of significance considering implant surface as the independent variable and BIC as the dependent variable. RESULTS: SEM and AFM showed that all surfaces presented rough textures and that calciu-hosohate particles were observed at the TCP group surface. Histologic evaluation showed intimate interaction between newly formed woven bone and all implant surfaces, demonstrating that all surfaces were biocompatible and osseoconductive. Significant differences in BIC were observed between the AB/AE and the AB/AE + TCP, and intermediate values observed for the TCP and TCP + Acid surfaces. CONCLUSION: irrespective of RBM processing variation, all surfaces were osseoconductive and biocaompatible. The differences in BIC between groups warrant further bone-implant interface biomechanical characterization.

Patients who present for alloplastic jaw angle augmentation have 2 potentially troublesome choices. The use of a silicone implant can mean unpredictable motion, and if the lower pterygomasseteric sling is breached during implant placement, the masseter insertion will ride up without anything to which to adhere. When the patient bites down, a bulge will be present.The porous alternative even has a ledge made to go under the gonial angle, which if not removed, guarantees violation of the pterygomasseteric sling and an implant that is longer than the muscle can cover. The inferior muscle insertion is disrupted and is left to ride up serendipitously.This article presents 5 instances of these issues in which one case required a revision via a modified Risdon approach to access the uncovered material which stuck out beyond the high riding masseter.The basic aim of this article is to advocate the need to maintain the pterygomasseteric sling, and describe the consequences of the failure to do so

BACKGROUND: During cleft palate repair, levator sling palatoplasty with tensor veli palatini tendon transection significantly improves speech results. However, the procedure may pose a risk to eustachian tube function. This study assesses the impact of three types of palatoplasty techniques on eustachian tube function: no tensor transection, tensor transection alone, and a new addition to the palatoplasty technique, tensor tenopexy. METHODS: A retrospective review was conducted of all patients undergoing cleft palate repair at two institutions between 1997 and 2001. Three cleft palate repair groups were studied: no tensor transection (n = 64), tensor transection alone (n = 31), and tensor tenopexy (n = 52). The percentages of patients requiring myringotomy tubes at each year of age were compared among the three groups. RESULTS: By 7 years of age, there was a significantly decreased need for myringotomy tubes in patients who underwent no tensor transection compared with patients who underwent tensor transection alone (38 percent versus 61 percent, respectively; p = 0.05), as well as for patients who underwent tensor tenopexy compared with patients who underwent tensor veli palatini tendon transection (23 percent versus 61 percent, respectively; p < 0.001). Also, by the age of 7, there was a trend toward a decreased need for myringotomy tubes in patients who underwent tensor tenopexy compared with patients who underwent no tensor transection (23 percent versus 38 percent, respectively; p = 0.11). CONCLUSIONS: No tensor transection and tensor tenopexy significantly decrease the need for myringotomy tubes compared with tensor transection alone. There is a small decrease in the need for myringotomy tubes when comparing tensor tenopexy with no tensor transection

BACKGROUND: Mobius syndrome is a disorder characterized by developmental impairment of cranial nerve VII, VI, often XII, and other cranial nerves. Facial reanimation in such patients restores the ability of some motion and of limited emotional expression. In one-fourth of these patients, hypoglossal involvement results in severe speech impairment due to tongue atrophy and lack of voluntary mobility. Bilabial incompetence due to facial paralysis further deteriorates speech capability. Direct tongue neurotization has been used by the senior author (J.K.T) to improve tongue function and speech intelligibility in patients with Mobius syndrome. This study presents the senior author's experience with the technique as a component of multistage facial reanimation procedures. METHODS: Data collection was performed by retrospective review on six patients with Mobius syndrome who underwent direct tongue neurotization. In addition, each patient was videotaped for 30 minutes preoperatively and postoperatively according to a standardized protocol. RESULTS: Four independent investigators scored speech intelligibility in each patient using a standardized grading system. The results showed considerable improvement in speech intelligibility and articulation. Higher improvement was noted in patients with partial bilateral hypoglossal involvement than in patients with complete unilateral involvement of the hypoglossal nerve, as well as in younger ages. No difference was noted between sexes. CONCLUSIONS: To the authors' knowledge, this is the first study presenting the effect of direct tongue neurotization on speech intelligibility in patients with Mobius syndrome. Tongue neurotization has therefore an important role in restoring the ability of these patients to communicate and obtain the potential to develop normal social skills

AlloDerm has been used as a tissue supplement in conjunction with the pectoralis major muscle to provide full coverage over an implant in breast reconstruction. While this method of reconstruction has shown promising results there is little known on the relationship of AlloDerm size and potential immediate expansion volume. A retrospective chart review was completed evaluating all tissue expander or primary implant reconstructions using AlloDerm. Data recorded included: The type/size of implant/expander, dimensions of the AlloDerm used, initial fill volume, number of expansions and time period of expansion. Statistical analysis was completed with a linear regression model. AlloDerm was used on 49 patients (72 reconstructions). Thirty-four patients (50 reconstructions) underwent reconstruction with a tissue expander and 15 patients (22 reconstructions) underwent a single stage reconstruction with a permanent implant. The tissue expander volume filled (cc) could be predicted by 5 x surface area of AlloDerm (cm(2)) - 12 (R(2) = 0.62) and 80 x height of AlloDerm (cm) - 15 (R(2) = 0.59). The tissue expanders could be filled to an average of 75% of total size and required three to four injections in the postoperative period to reach full expansion. Obviously, a requirement for maximal implant expansion is an appropriate skin sparing mastectomy. There is a mathematical relationship between fill volume and surface area as well as height of AlloDerm used in breast reconstruction. This analysis provides a guideline for immediate implant expansion to surgeons using AlloDerm in reconstructive breast surgery