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Resinous denture base fracture resistance: effects of thickness and teeth

Choi, Mijin; Acharya, Varun; Berg, Robert W; Marotta, Joshua; Green, Chad C; Barbizam, Joao V; White, Shane N
Purpose: Fracture is a frequent complication of resinous prostheses. The purpose of this study was to evaluate the effect of thickness on flexural strength of a resinous prosthesis containing a prosthetic tooth. Materials and Methods: Beam-shaped specimens 65-mm long, 12-mm wide, and 1, 2, 3, 4, or 6 mm in thickness were made from high-impact strength polymethyl methacrylate denture base material, each containing a resin-based molar prosthetic tooth at the center of the beam. A group of 3-mm-thick specimens without a prosthetic tooth (n = 7) were also made. Specimens were aged artificially, loaded in three-point flexure, examined fractographically, and analyzed. Results: The 1- and 2-mm-thick beams underwent considerable deformation at low loads. Maximum loads varied considerably from 0.6 kg (1-mm beams) to 38 kg (6-mm beams). The 3-, 4-, and 6-mm beam groups all underwent brittle fracture, with mean relative flexural strengths of approximately 73 MPa. Denture teeth reduced the relative flexural strength of resin beams by 0.7x. Fracture initiation sites were generally at tiny surface defects, but did not directly involve denture teeth. Denture resin fracture toughness was 3.2 MPa m1/2, and modulus of rupture was 104 MPa. Conclusion: Denture teeth substantially decreased the strength of resinous beams. Increased thickness markedly increased the load-bearing capacity of resinous beams containing denture teeth. Beams less than 2 mm in thickness with denture teeth were weakened substantially more than comparable beams of 2 mm or more in thickness. Surface finish was of critical importance. Fracture toughness was calculated fractographically, facilitating future forensic examination of clinically failed resinous prostheses. Int J Prosthodont 2012;25:53-59.
PMID: 22259797
ISSN: 0893-2174
CID: 157638

Ocular-Orbital Prosthesis: Use Of Staged Custom-Conformers For Modeling Of Anophthalmic Socket And Impression-Making

Chapter by: Hanna, Chad S; Choi, Mijin
in: Clinical & Educational Scholarship Showcase by
[New York NY : NYU College of Dentistry. NYU Academy of Distinguished Educators], 2011
pp. 20-20
ISBN: n/a
CID: 151831

Saliva Diagnostics Integrate Dentistry into General and Preventive Health Care [Editorial]

Choi, M
ISSN: 0893-2174
CID: 155133

Clinical Cases in Prosthodontics

Jahangiri, Leila; Moghadam, Marjan; Choi, Mijin
Hoboken : John Wiley & Sons, 2010
Extent: 274 p.
ISBN: 9781282774414
CID: 2420522

A model for an integrated predoctoral implant curriculum: implementation and outcomes

Jahangiri, Leila; Choi, Mijin
The implementation of an implant dental curriculum in U.S. dental schools has been consistently increasing from 33 percent in 1974 to 97 percent in 2004. Among these, only 51 percent have clinical components implemented. A survey of students conducted in 2004 at New York University College of Dentistry (NYUCD) showed an inadequacy in clinical implant restoration experience by graduation. This prompted the development of an extensive dental implant curriculum at NYUCD to meet the needs of the dental students. This report addresses the challenges in implementing such a curriculum and describes a step-by-step approach to develop a program that encompasses didactic, simulation, and patient care components. In 2005, a fully integrated predoctoral implant curriculum was initiated. In 2008, nearly all of the NYUCD students (91.8 percent) completed implant restorations/prosthesis on patients. An assessment revealed a 30 percent increase in students' positive perceptions of the implant curriculum. Based on our experiences at NYUCD, it is recommended that an implant curriculum become part of the core predoctoral curriculum and be integrated throughout the four years of dental education. This article reports on a model for a pre-doctoral implant curriculum, which includes planning, curriculum implementation, program management, and post-implementation stages. Using this model, dental schools can develop implant education for their students that is adapted to their institutional missions, priorities, and resources
PMID: 18981209
ISSN: 0022-0337
CID: 153410

An alternative technique for fabrication of an occlusal device

Choi, Mijin; Holden, Jason; Tung, Francis
Several methods have been described for fabrication of occlusal devices, but many require complex and time-consuming laboratory procedures. In this article, an alternative fabrication method for a hard occlusal device while maintaining the articulation of the cast is described
PMID: 18544135
ISSN: 1532-849x
CID: 153409

Assessment of teaching effectiveness in U.S. Dental schools and the value of triangulation

Jahangiri, Leila; Mucciolo, Thomas W; Choi, Mijin; Spielman, Andrew I
The routine evaluation of teaching effectiveness is important in improving faculty, departmental, and institutional efforts. There are three main categories of assessments: those performed by students, peers, and self. Although each category is independently valid, a collection of data from all three categories leads to a more comprehensive outcome and a creation of a triangulation model. The purpose of this study was to identify commonly used methods of assessing teaching effectiveness and to suggest the use of a triangulation model, which has been advocated in the literature on performance assessment as an optimal approach for evaluating teaching effectiveness. A twelve-question survey was sent to all U.S. dental schools to identify evaluation methods as well as to find evidence of triangulation. Thirty-nine out of fifty-seven schools responded. The majority of the schools used student evaluations (81 percent) and peer reviews (78 percent). A minority of schools reported using self-evaluations (31 percent). Less than one in five dental schools reported using all three strategies to achieve triangulation (19 percent). The three most commonly used evaluation methods ('performed routinely') were all in the student evaluation category. Less than half of the schools routinely evaluated clinical teaching effectiveness by any means (42 percent). In conclusion, dental schools should implement a triangulation process, in which evaluation data are obtained from students, peers, and self to provide a comprehensive and composite assessment of teaching effectiveness
PMID: 18519601
ISSN: 0022-0337
CID: 153021

Ultrasound detection of submerged dental implants through soft tissue in a porcine model

Culjat, Martin O; Choi, Mijin; Singh, Rahul S; Grundfest, Warren S; Brown, Elliott R; White, Shane N
STATEMENT OF PROBLEM: Current methods of measuring soft tissue thickness over potential dental implant sites and locating submerged implants may be imprecise or invasive. PURPOSE: The purpose of this study was to develop and demonstrate proof of the concept of a customized ultrasound imaging system in locating and measuring the depth of implants submerged beneath soft tissue. MATERIAL AND METHODS: A complete ultrasound system, including a customized soft tissue-matched transducer, transceiver, and digital signal processing algorithms, was created for the specific application of detecting dental implants anchored in bone beneath soft tissue. The system was used to locate implants placed in cancellous bone and measure overlying soft tissue depth in a porcine model. Ten measurements were made on each porcine model by manually moving the transducer laterally over the soft tissue surface. Data were analyzed with descriptive statistics. RESULTS: The mean signal-to-noise ratio, SNR (standard deviation), from the bone surfaces, was 19.1 (4.6) dB, and the mean SNR from the implant surfaces was 36.6 (2.2) dB, resulting in a mean difference of 17.5 dB, or x56.2, in average signal power between the bone and implant surfaces. Consequently, implants were easily and accurately (+/-0.2 mm) located beneath at least 5 mm of soft tissue. Likewise, soft tissue depths over bone and implants were accurately measured and were within the corresponding caliper tissue measurement error (+/-0.5 mm). CONCLUSIONS: The specialized ultrasound imaging system located and measured the depth of implants placed in bone submerged beneath soft tissue in a porcine model
PMID: 18319093
ISSN: 0022-3913
CID: 153408

Effects of varied dimensions of surgical guides on implant angulations

Choi, Mijin; Romberg, Elaine; Driscoll, Carl F
STATEMENT OF PROBLEM: Fabrication of a proper surgical guide is critical for success of implant restorations. The effects of the dimensional factors of the surgical guide on implant placement have not been studied. PURPOSE: The purpose of this study was to determine the effect of varied dimensions (diameter, length, and distance between the underside of the surgical guide and the implant recipient site) of a surgical guide on the accuracy of implant angulation. MATERIAL AND METHODS: In this in vitro study, 240 implant recipient sites were randomly prepared using varied dimensions of a surgical guide. The varied dimensions of the surgical guide's channel and distance were: channel diameter (2, 3, 4, or 5 mm), channel length (6 or 9 mm), and distance between the underside of the surgical guide and the simulated implant recipient site (2 or 4 mm). From these varying dimensions and distances, 16 combinations of dimensions and distances were tested. For each combination, 15 simulated implant recipient site (SIRS) specimens were prepared. The deviated angulation (DA) from the midpoint of the top surface of the 1- x 1-inch simulated implant recipient site (each simulated implant recipient acrylic block contained 5 SIRS of 1 x 1 inch), in the right-to-left (DA(RL)) and front-to-back (DA(FB)) directions, were measured in degrees using a protractor. The data was analyzed using factorial analysis of variance and Tukey's HSD test (alpha=.05). RESULTS: The DA(RL) , in degrees, at a channel length of 9.0 mm (2.33 +/- 1.27) was significantly smaller than at a channel length of 6.0 mm (3.0 +/- 1.42, P =.0001). The DA(RL) , in degrees, at a distance of 4.0 mm (2.13 +/- 1.16) was significantly smaller than at a distance of 2.0 mm (3.16 +/- 1.39, P =.0001). Also, a significant interaction for DA(RL) was found between diameter and distance ( P <.05). For DA(FB) , the varying diameters ( P <.05), lengths ( P =.0001), and distances ( P =.0001) showed significant differences. The DA(FB) at a channel length of 9.0 mm (2.56 degrees +/- 1.51) was significantly smaller than that at 6.0 mm (3.82 degrees +/- 1.87). Significant interactions found for DA(FB) were: diameter by length ( P =.0001), diameter by distance (F=4.547, P =.004), and length by distance (F=11.512, P =.001). CONCLUSION: Within the limitations of this study, the results suggest channel length as the primary controlling factor in minimizing deviated angulations
PMID: 15523335
ISSN: 0022-3913
CID: 153404

Fabrication of a custom eyelid implant prosthesis: a clinical report

Choi, Mijin; Driscoll, Carl F
Patients with lagophthalmos are often treated with a stock gold weight that has been implanted in the upper eyelid. This relatively simple surgical technique does not, however, always produce the desired result. This article describes a technique for the fabrication of a custom eyelid implant prosthesis for patients who present with a non-functioning and unaesthetic eyelid implant
PMID: 15210005
ISSN: 1059-941x
CID: 153402