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Biomedical subjects

W C Shellhart

Publications and source records attributed to W C Shellhart.

11 recordsLinked to original sources
PubMed1997

Effective orthodontics: achieving objectives, avoiding misadventures.

The authors outline four principles that should be considered when planning orthodontic tooth movement. They suggest that dentists have clear treatment objectives, know the force requirements to achieve those objectives, choose the best equipment to provide the needed forces and prevent unwanted tooth movement during treatment. To illustrate use of these principles, the authors refer to a sample treatment scenario. They also provide a mnemonic device to help dentists recall these principles.

Dental Stress Analysis↗
PubMed1996

Lip adaptation to simulated dental arch expansion. Part 1: Reliability and precision of two lip pressure measurement mechanisms.

Understanding the influence of lip and tongue pressure on tooth position requires a reliable method of measuring pressure. A transducer with a beam mechanism has been used extensively in the past. A transducer with a diaphragm mechanism has been recently introduced. Comparative in-vivo tests of these transducers have not been published. The purpose of this study was to investigate transducer reliability and precision. Transducers were placed intraorally in 22 subjects, and two lip pressure measurements were recorded. Paired t-tests and interclass correlations were used to evaluate repeatability and reliability. The error of the method was analyzed for each transducer type. Both transducer types produced measurements that were repeatable and reliable. The error was smaller for the diaphragm transducer. The diaphragm transducer is more precise.

Adaptation, Physiological↗
PubMed1996

Lip adaptation to simulated dental arch expansion. Part 2: One week of simulated expansion.

An increase in resting lip pressure and the resulting disruption of the intraoral pressure equilibrium may be responsible for the poor stability found with orthodontically expanded dentitions. Passive expansion strategies seek improved stability by altering lip pressure, thus creating a new equilibrium. One of these strategies has been shown to alter pressure favorably. However, pressure changes associated with conventional expansion need to be studied before conclusions regarding the superiority of passive expansion can be drawn. The purpose of this study was to examine lip pressure changes after 1 week of simulated conventional expansion. Twenty-two subjects agreed to wear a mandibular expansion-simulating stent full-time for 1 week. Resting pressure was measured in the midline and right canine areas. Midline lip pressure decreased significantly after 1 week. Resting pressure was measured in the midline and right canine areas. Midline lip pressure decreased significantly after 1 week while pressure in the canine area did not change significantly. This finding suggests an adaptive response that varies according to anatomic location.

Adaptation, Physiological↗
PubMed1995

Equilibrium clarified.

Understanding the concept of equilibrium is crucial to understanding the mechanics of tooth movement. The purpose of this article is to clarify the concept of equilibrium. This concept is most clearly understood when the clinician focuses on the appliance. Understanding the forces acting to deform the appliance readily translates to knowledge of the forces acting on the teeth. Knowing the forces that act on the teeth allows the clinician to predict tooth movement more accurately.

Acceleration↗
PubMed1995

Reliability of the Bolton tooth-size analysis when applied to crowded dentitions.

The Bolton tooth-size analysis is widely taught and used in orthodontics. However, its reliability has not been documented. The purpose of this study was to evaluate the reliability of the analysis when performed with needle-pointed dividers and a Boley gauge. Four clinicians measured the teeth on 15 sets of casts with two instruments at two sessions. The measurements were used to calculate tooth-size excess. To evaluate the measurement error, the difference between the two analyses made by the same investigator on the same set of casts was calculated. More of the same-investigator analyses were significantly correlated when the Boley gauge was used than when the needle-pointed dividers were used. Between-investigator analyses revealed significant correlations for each measurement session with both instruments. Every investigator was found to have at least one measurement error for each analysis and with each instrument that was as large as a clinically significant result of a Bolton analysis. The results of this study demonstrate that clinically significant measurement errors can occur when the Bolton tooth-size analysis is performed on casts with at least 3 mm of crowding. The Boley gauge demonstrated a higher frequency of significantly correlated repeated measures and thus may be somewhat more reliable for this analysis than the needle-pointed dividers.

Cuspid↗
PubMed1992

Effects of bisphosphate treatment and mechanical loading on bone modeling in the rat tibia.

Bisphosphonate treatment has been shown to decrease endosteal bone formation and increase periosteal bone apposition in the rat tibial diaphysis. This study tested the hypothesis that the increase in periosteal apposition is a compensatory attempt to maintain skeletal mass appropriate for the mechanical load. Twenty-four rats were divided into four groups. In two of the groups, one hindlimb in each rat was immobilized with a sling device to increase the mechanical load on the opposite limb. Daily injections of dichloromethylene bisphosphonate (Cl2MBP) were given at 10 mg/kg to one immobilized group and one mobile group. The other two groups were given daily injections of normal saline. Fluorescent bone labels were administered at two-week intervals. All rats were killed after ten weeks of treatment, and calcified tibial cross sections were prepared for fluorescence microscopy. Bone dimensions and periosteal and endosteal apposition rates were calculated. When compared with saline controls, Cl2MBP treatment decreased endosteal apposition rate in all tibias. Periosteal apposition rate was increased with Cl2MBP treatment in all tibias except the unloaded limb of immobilized rats. The Cl2MBP-induced increase in periosteal apposition rate was greatest in loaded limbs and was proportional to the relative amount of body weight supported.

Animals↗
PubMedDate not supplied

Oral findings in fragile X syndrome.

This study compares the oral findings in fragile X syndrome individuals to those of normal age-matched patients. Sixteen fra(X) males (mean age 22 10/12 years) had a low caries rate (decayed, missing and filled surfaces (DMFS) = 12.3) and minimal intraoral hard or soft tissue disease. Rate of malocclusion, as determined by the first permanent molar classification of Angle, was not significantly different from that of matched subjects. Fra(X) subjects had a significantly higher occurrence of malocclusion as compared to matched subjects using crossbite and openbite as criteria. Palatal dimensions of fra(X) subjects did not differ significantly from those of the matched sample. The fra(X) males also demonstrated significantly more severe occlusal wear of their teeth than the matched sample.

Adolescent↗
PubMedDate not supplied

Efficacy and safety of intravenous ketamine for the severely handicapped.

The severely and profoundly mentally and physically handicapped dental patient predominates in the institutional setting today. Many patients still require restorative dentistry, periodontal treatment, and an occasional tooth extraction. In terms of enabling treatment to be performed by the institutional dentist, intravenous agent can be effective but can be accompanied by substantial risks in this population. The anesthetic ketamine was evaluated as a sedative agent for dental treatment in this study.

Adolescent↗
PubMedDate not supplied

General anesthesia and fragile X syndrome: report of a case.

A case report of an 11-year-old Caucasian boy with the fragile X syndrome is presented. The fragile X syndrome is a form of X-linked mental retardation with a connective tissue component that involves mitral valve prolapse. Antibiotic prophylaxis, electrocardiographic abnormalities, and special anesthetic management considerations are elements of treating patients with fragile X syndrome. The patient received morphine sulfate and scopolamine as a preoperative premedication. Ketamine was also administered intramuscularly prior to induction to gaseous anesthetic. Pancuronium was used to facilitate nasotracheal intubation. A wandering atrial pacemaker and progressive hypocapnia, both of which were managed without complication, were the only problems encountered in the anesthetic procedure.

Anesthesia, Dental↗