Biomedical subjects

Keith Horner

Publications and source records attributed to Keith Horner.

4 recordsLinked to original sources

PubMed2006

A mathematical model for simulating the bone remodeling process under mechanical stimulus.

OBJECTIVES: Among the current mathematical models for bone remodeling, few can consider bone resorption due to overload. The objective of this paper is to develop a new bone remodeling model which can simulate both underload and overload resorptions that often occur in dental implant treatments. METHODS: Based on the traditional model, a new mathematical equation relating the density change rate with mechanical stimulus has been developed. The new equation contains an additional quadratic term which can produce reduction in bone density at high load levels. In addition, to fully exploit the characteristics of this model, a range of different bone remodeling behaviors were studied under the load cases with both constant and varying stress magnitudes. Finally, the model was applied in conjunction with the finite element method to a practical case of dental implant treatment. RESULTS: The FE analysis results showed that bone resorption at the neck of the implant occurred due to occlusal overload but then resorption stopped after some time before reaching the coarse threads. Meanwhile, the density of the bone deeper into the mandible increased slightly due to the additional mechanical stimulus provided by the occlusal load. This phenomenon is observable in some clinical situations. SIGNIFICANCE: The new model can describe the bone overload resorption, a feature which is absent in most of the current models. And by simulating the dental implant treatment using FE method, the ability of the new mathematical model to simulate overload bone resorption has been clearly demonstrated.

Biomechanical Phenomena↗

PubMed2006

Mandibular morphological changes in low bone mass edentulous females: evaluation of panoramic radiographs.

OBJECTIVE: The objective of this study was to evaluate morphological changes of the mandible in osteopenic and osteoporotic edentulous females. STUDY DESIGN: Fifty-two female edentulous patients underwent panoramic radiography and dual-energy x-ray absorptiometry of the lumbar spine and femoral neck. Measurements of the gonial angle, antegonial angle, antegonial depth, antegonial index (AI), and mental index (MI) were performed. Patients were classified as normal (T-score > -1.0), osteopenic (T-score of -1.0 to 0 -2.5), or osteoporotic (T-score < -2.5). RESULTS: The gonial angle did not show differences among the three categories of skeletal bone status (P > .05). The antegonial angle was significantly smaller in individuals with low bone mass (P < .05). The antegonial depth was significantly greater in osteoporotic (P < .05) and osteopenic individuals (P < .05). The AI and MI were significantly smaller in individuals with low bone mass (P < .05); however, after age adjustment there were no differences among the groups (P > .05). CONCLUSIONS: Edentulous females with low bone mass have a deeper antegonial region. The thickness of the cortical mandibular bone is highly influenced by age.

Absorptiometry, Photon↗

PubMed2004

The effect of ovariectomy on mandibular cortical thickness in the rat.

OBJECTIVES: The purpose of this study was to investigate the effects of long-term oestrogen deficiency on mandibular cortical thickness in ovariectomized rats. METHODS: Twelve female rats either underwent ovariectomy or received a sham-operation. One year later images of the left side of the mandible were made using a standardized radiographic protocol. Manual measurements were made of the lower mandibular cortical thickness at three locations. The mean cortical thickness was also assessed using a specially developed image analysis program by placing points at three positions, identical to those used for the manual measurements, and additionally at 20 points evenly distributed along the mandibular cortex. RESULTS: The mean mandibular cortical thickness of the ovariectomized mandibles was significantly less than that of the sham-operated rats, measured using the computer image analysis (p=0.016, 95% CI=0.125, 0.016) and measured manually (p=0.011, 95% CI=0.0218, 0.1309). When 20 computational points were used, the mean mandibular cortical width of the ovariectomized rats was significantly less than that for the control rats (p=0.016, 95% CI=0.127, 0.018). CONCLUSIONS AND CLINICAL IMPLICATIONS: Long-term oestrogen deficiency in ovariectomized rats decreased the mandibular cortical thickness. If our result is applicable to human studies, a considerable duration of oestrogen deficiency may be necessary before a reduction of mandibular cortical bone loss can be observed. Because mandibular cortical bone is resistant to resorption, the value of clinically determined mandibular cortical thickness measurements as a method of detecting patients at risk of osteoporosis may have a reduced importance in younger postmenopausal patients.

Animals↗

PubMed2002

Detecting patients with low skeletal bone mass.

OBJECTIVES: The object of this study was to determine the relative usefulness of clinical and radiographic indices in the diagnosis of patients with low skeletal bone mass amongst 135 healthy perimenopausal women, aged 45-55 years, attending for routine dental treatment. METHODS: Bone mineral density was measured for the spine and femoral neck, using dual energy X-ray absorptiometry. Each patient's osteoporosis status was calculated according to the WHO criteria for Caucasian women. Each patient received a dental panoramic tomogram, and the width of the inferior mandibular cortex (mental index, (MI)) was measured. The body mass index (BMI) and simple calculated osteoporosis risk estimation (SCORE) indices were calculated. RESULTS: The SCORE index was a significant factor in predicting low bone mass, but with the weight of the patient being the only significant constituent factor. MI, BMI and SCORE indices were significantly correlated with skeletal bone density. When the logistic regression model included MI, BMI and SCORE indices, all three variables were significant predictors of low skeletal bone mass. CONCLUSIONS: A thinning of the mandibular cortices (MI<3mm) in a normal perimenopausal female is associated with low skeletal bone mass. If, in addition, the patient is underweight (BMI is below 20kg/m(2)) or has a high SCORE index (> or =6) then this increases their risk of osteoporosis.

Absorptiometry, Photon↗