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Biomedical subjects

J M Leary

Publications and source records attributed to J M Leary.

At least 19 recordsLinked to original sources
PubMed1996

Influence of post dimension on stress distribution in dentin.

Stress distribution studies can be helpful in determining the appropriate diameter and length of endodontic posts for specific teeth in select occlusal relationships. This study selected the finite element method to predict distribution of stresses in dentin of an endodontically treated tooth restored with cast post and cores with various post dimensions. Peak dentinal shear stresses occurred adjacent to the post at mid-root. Peak shear stresses were elevated as the length of the post decreased. Peak dentinal tensile stresses occurred in the gingival third of the facial root surface, whereas peak dentinal compressive stresses were evident in the gingival third of the lingual root surface. The distribution of tensile and compressive stresses was not affected with variation in the dimensions of the posts.

Computer Simulation↗
PubMed1996

Effect of ultrasonic vibration on post removal in extracted human premolar teeth.

The purpose of this study was to determine the effectiveness of ultrasonic vibration in removing Paraposts from extracted teeth. Paraposts were cemented in mandibular premolars to a depth of 9 mm with zinc phosphate cement and the teeth placed in four groups. Group 1 received no vibration. Group 2 received vibration for 4 min, group 3 received vibration for 12 min, and group 4 received vibration for 16 min. Tensile forces were applied to the posts and mean dislodgment forces compared. The mean force (kg) required to dislodge the Parapost in group 1 was 24.92 +/- 1.64 SEM; in group 2, 25.01 +/- 1.80; in group 3, 24.08 +/- 2.29; and in group 4, 12.41 +/- 2.60. There was a significant difference between group 4 and groups 1 to 3 (p = 0.0003). Results of this study indicate that 16 min ultrasonic vibration is an effective method for removing Paraposts from human premolar teeth.

Analysis of Variance↗
PubMed1995

Management of the clinical curriculum in which students direct rather than perform the laboratory stages of restorations.

At the University of Iowa, senior dental students direct rather than perform laboratory construction of clinical prosthodontic work. This report highlights the fundamentals of a successful curriculum based on this concept. One critical component of the curriculum involves teaching the process of self-evaluation of laboratory work as well as the evaluation of work received from a commercial laboratory. Instructors teach students how to evaluate a product in the sophomore preclinical curriculum. A computerized evaluation form, developed by the prosthodontic faculty, allows assessment of the students' laboratory work in addition to self-evaluation. To incorporate patient care into the appraisal process, a modified preclinical evaluation framework is used during the junior clinical clerkship. This expanded framework takes into consideration patient treatment factors such as degree of difficulty, diagnosis and treatment planning, use of infection control, and students' understanding of patients' comprehensive treatment plan. In the senior clinic, the students' ability to direct the construction of a prosthesis is enhanced by the unique diversity of faculty within the Department of Family Dentistry at the University of Iowa. This department unites private practice dentists with academicians and general practitioners with specialists.

Communication↗
PubMed1994

Effect of polyethylene fiber reinforcement on the strength of denture base resins polymerized by microwave energy.

This study investigated the effect of addition of polyethylene fibers on the transverse strength, deflection, and elastic modulus of two denture base acrylic resins polymerized by microwave irradiation. Specimens of each resin, Lucitone 199 and Acron MC, were fabricated with 0.0%, 0.5%, 1.5%, and 3.0% fiber loading. Specimens were tested with use of a three-point flexure apparatus with an Instron universal testing machine after storage in water for 10 days at 37 degrees C. The results showed that polyethylene fibers significantly decreased the transverse strength of Acron MC resin and slightly increased the transverse strength of Lucitone 199 resin at a loading of 0.5% by weight. Fiber loading did not significantly affect the deflection and the elastic modulus of either material.

Acrylic Resins↗
PubMed1992

Evaluation of the fracture resistance of a wrought post compared with completely cast post and cores.

The intraradicular fracture of a post and core presents a difficult and often unrestorable situation. Attempts to prevent this problem involved the use of materials with increased physical properties. The use of a preformed wrought post with a core cast to it may provide a more fracture-resistant foundation. This investigation compared a commercially available noble alloy-wrought post that had a gold core cast to it with completely cast specimens from three different alloys. A standard pattern was designed to simulate a post and core that would be used in a tooth of limited length and canal space. Patterns were cast and fixed to custom holding devices. Each specimen was subjected to a shearing force until catastrophic failure in a universal testing machine. Significant differences were noted among the groups.

Analysis of Variance↗
PubMed1992

Pontic design and localized ridge augmentation in fixed partial denture design.

The endpoint of fixed prosthesis design is an esthetic and functional pontic that is compatible with soft-tissue health. In the posterior segment, where esthetics is not as critical, a sanitary pontic form is most compatible with function and hygiene. In the maxillary anterior region, a properly contoured modified ridge-lap pontic design constructed of glazed porcelain most readily fulfills both the esthetic and physiologic requirements. Although the ovate pontic form may satisfy esthetic demands to a greater degree, this is often at the expense of underlying soft-tissue health. In maxillary edentulous regions, ridge deformities may preclude a good pontic fit and esthetic result and dictate the need for surgical augmentation of the collapsed ridge. Selection of the appropriate surgical procedure and graft material depends on the nature and extent of the defect and availability of donor tissue. The subepithelial graft employing the tunnel approach is appropriate when augmentation in only a labial dimension is necessary. When the employing the trapdoor approach or full thickness gingival onlay graft may be employed. In large defects, sequential grafting procedures may be necessary to achieve the desired result. An esthetic and functional result can be attained through proper execution of an appropriate surgical technique and adherence to the principles of proper pontic design.

Alveolar Ridge Augmentation↗
PubMed1992

Methylphenidate and seizure frequency in brain injured patients with seizure disorders.

BACKGROUND: Psychostimulant drugs such as methylphenidate are increasingly being used in patients with traumatic brain injury or other brain injuries for a variety of cognitive and behavioral problems. However, there is some reluctance among clinicians and family members to use methylphenidate in brain injured patients because of warnings of seizure occurrence, which are prominently reported by the product labeling included in the Physicians' Desk Reference. METHOD: We retrospectively studied the use of methylphenidate in 30 consecutive patients with active seizure disorders. We compared the seizure frequency in the 3 months before and after methylphenidate with the seizure frequency during methylphenidate treatment, using the Wilcoxon signed-rank test. RESULTS: Overall, the findings demonstrated a trend toward a lesser incidence of seizures in patients during methylphenidate treatment. Only 4 patients had greater seizure frequency during methylphenidate treatment, and 3 of these 4 were receiving tricyclic antidepressants. CONCLUSION: Methylphenidate can be safely used in brain injured patients, even those at high risk for seizures, as it was associated with a trend toward reduction (rather than increase) in seizure frequency in this population.

Adult↗
PubMed1991

Vertical root fracture and relative deformation during obturation and post cementation.

There are several speculated etiologies of vertical root fractures such as pressure exerted during post placement and excessive forces during lateral condensation. However, there are no reports comparing these two forces by use of the same measurement system. This study determined and compared on single-rooted teeth (1) the amount of strain to the root that occurs during obturation and post cementation and (2) the incidence of incomplete and complete vertical root fractures occurring during the aforementioned procedures. Canals of 32 extracted maxillary central incisors were step-back prepared. Teeth were randomly divided into negative and positive controls and experimental groups. The amount of root distortion was recorded with a strain gauge during each of the following procedures: (1) lateral condensation, and (2) lateral condensation plus cementation of a cast gold post. Relative deformations were compared statistically. Teeth were examined by transillumination and stereomicroscopy for incomplete and complete fractures and compared among groups. Data showed significantly more relative deformation with placement of a post and loading than with obturation alone. The accumulation of strain from both procedures did not significantly increase incidence of vertical root fractures. The results indicate that stresses from cementation of posts is more likely to cause relative deformation of roots.

Cementation↗
PubMed1989

An evaluation of porcelain strength and the effect of surface treatment.

This investigation evaluated the flexural strengths of five porcelains commonly used in the all-porcelain margin technique and the effect of surface treatment on the flexural strength. Thirty samples were made by using each of five different porcelain margin systems. The five porcelain groups were subdivided into groups of 10 each to allow the evaluation of three surface treatments. A three-point flexural test was used to test the specimens on a universal testing machine. Crystar shoulder porcelain with distilled water as the binder was significantly stronger than the other porcelains tested, and porcelain treated with an overglaze was stronger than porcelain treated with autoglaze or autoglaze and polish.

Dental Casting Technique↗
PubMed1989

Load transfer of posts and cores to roots through cements.

This study evaluated differences in load transfer when cast posts are fixed to roots with different cements. Cast posts and cores were cemented with 40 endodontically prepared teeth by using four different cement mediums. The load exerted on the root surface through the post was evaluated using a strain gauge. The increased flexure after cementation was statistically analyzed. In conclusion, there was load transfer from post to root structure when posts were cemented, but no difference was found between cementation mediums.

Cementation↗
PubMed1988

Immediate fixed partial dentures.

This technique offers immediate fixed partial denture replacement of dentition lost in either an anterior or posterior location. It allows modification of the preextraction tooth or the diagnostic wax-up. Because the provisional restoration is made indirectly, the extraction site is not contaminated. Postoperative comfort and function for the patient is achieved.

Denture Design↗
PubMed1988

Management of dental patients with bleeding disorders: review and update.

Management of the dental patient who has a bleeding disorder requires an understanding of the normal hemostatic system and the patient's specific coagulation defect. This patient group can receive quality comprehensive dental care, provided appropriate preoperative planning and evaluation with the patient's physician or hematologist is accomplished. Emphasis should be placed on providing appropriate replacement therapy before the dental procedure, selection of conservative treatment approaches, and use of local hemostatic measures to facilitate hemostasis.

Blood Coagulation Disorders↗
PubMed1987

An evaluation of post length within the elastic limits of dentin.

Posted teeth were evaluated to determine the reinforcement capabilities of various post lengths. The results suggest that as internal tooth structure is removed from the tooth the tooth becomes weaker, that teeth with posts do show more reinforcement than nonposted teeth with the same manipulation characteristics, and that some load transfer appears to exist with cemented posts.

Cementation↗
PubMed1986

Multiple cast post and cores for severely worn anterior teeth.

A technique has been presented to simplify the fabrication of multiple direct post and core patterns. When combined with techniques for indirect provisional restorations, this technique merely requires the fabrication of an additional plastic template to form the direct core patterns.

Acrylic Resins↗