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Biomedical subjects

P W Ngan

Publications and source records attributed to P W Ngan.

18 recordsLinked to original sources
PubMed1997

Longitudinal evaluation of growth changes in Class II division 1 subjects.

Longitudinal records from the Ohio State University Growth Study were used to compare the skeletal growth changes between Class II division 1 and Class I female subjects between ages 7 and 14. Tensor analysis was used to determine the yearly growth rate and direction. No significant difference was found in cranial base dimension between the Class I and Class II subjects. In Class II subjects, the maxilla (S-N-A) was found to be normally related to the cranial base. However, mandibular position (S-N-B and S-N-Pog) was found to be significantly more retrusive in Class II when compared with Class I subjects. Mandibular length (Ar-Gn) and corpus length (Go-Gn) were found to be shorter in Class II subjects. The ratio of PFH to AFH was found to be smaller in Class II subjects. This is particularly apparent during the pubertal growth period. The y-axis and mandibular plane angle were more open in Class II subjects which also contributed to the retrusive position of the mandible. Maxillo-mandibular difference (A-N-B) between Class I and II subjects was present at age 7 and persisted through puberty, maintaining a greater angle of convexity (A-N-Pg) in Class II subjects. These results suggest that Class II malocclusion can be detected early. The majority of the Class II cases showed mandibular skeletal retrusion or a combination of horizontal and vertical abnormalities of the mandible rather than maxillary protrusion. These skeletal differences remain through puberty without orthodontic intervention. Individual variations were found within each type of malocclusion.

Adolescent↗
PubMed1997

Treatment response and long-term dentofacial adaptations to maxillary expansion and protraction.

The purpose of this article is to summarize the short-term and long-term results of the authors' clinical prospective study on the treatment of Class III malocclusion using the protraction facemask. An attempt is made to answer questions pertaining to this treatment modality. Twenty patients with skeletal Class III malocclusion were treated consecutively with maxillary expansion and a protraction facemask. A positive overjet was obtained in all cases after 6 to 9 months of treatment. These changes were contributed to by a forward movement of the maxilla, backward and downward rotation of the mandible, proclination of the maxillary incisors, and retroclination of the mandibular incisors. The molar relationship was overcorrected to Class I or Class II dental arch relationship. The overbite was reduced with a significant increase in lower facial height. The treatment was found to be stable 2 years after removal of the appliances. At the end of the 4-year observation period, 15 of the 20 patients maintained a positive overjet or an end-to-end incisal relationship. Patients who reverted back to a negative overjet were found to have excess horizontal mandibular growth that was not compensated by proclination of the maxillary incisors. A review of the literature showed that maxillary expansion in conjunction with protraction produced greater forward movement of the maxilla. Maxillary protraction with a 30 degrees forward and downward force applied at the canine region produced an acceptable clinical response. The reciprocal force from maxillary protraction transmitted to the temporomandibular joint did not increase masticatory muscle pain or activity. Significant soft tissue profile change can be expected with maxillary protraction including straightening of the facial profile and better lip competence and posture. However, one should anticipate individual variations in treatment response and subsequent growth changes. Treatment with the protraction facemask is most effective in Class III patients with a retrusive maxilla and a hypodivergent growth pattern. Treatment initiated at the time of initial eruption of the upper central incisors helps to maintain the anterior occlusion after treatment.

Adaptation, Physiological↗
PubMed1997

Masticatory muscle pain before, during, and after treatment with orthopedic protraction headgear: a pilot study.

Protraction headgear has been used in conjunction with a palatal expansion appliance to correct Class III malocclusion with maxillary deficiency and/or mandibular prognathism. In general, 800 gm of orthopedic force is used to protract the maxilla, and 75% of this force is transmitted to the temporomandibular joint (TMJ) area via the mandible. The effect of this heavy intermittent force on the TMJ has not been reported in the literature. The objectives of this study were to determine the level of masticatory muscle pain and EMG activity in patients treated with maxillary protraction headgear. Ten patients with skeletal Class III malocclusion whose treatment plan called for maxillary protraction headgear treatment participated in this study. Nocturnal masticatory muscle activity was determined using a portable electromyographic (EMG) recording device. Subjects wore the EMG device 14 nights before treatment, 14 nights during treatment, and 14 nights 1 month after active treatment. Masticatory muscle pain level was determined by muscle palpation, scored on a scale of 0 to 3 each period, according to the method of Gross and Gale. The examiner followed a sequence outlined by Burch to examine the masticatory muscles. Results showed no significant differences for masticatory muscle activities before, during, and after treatment. Only a few patients experienced level 1 masticatory pain during treatment. None of the patients experienced masticatory muscle pain 1 month after treatment. These results demonstrate no significant increase in masticatory muscle activity or muscle pain associated with orthopedic treatment using maxillary protraction headgear.

Adolescent↗
PubMed1991

Interleukin 1 beta and prostaglandin E are involved in the response of periodontal cells to mechanical stress in vivo and in vitro.

Cytokines are local mediators released by cells of the immune system in response to stimulation by a variety of agents. These polypeptides may interact directly or indirectly with bone cells. The objectives of this study were (1) to localize prostaglandin E (PGE) and the cytokine interleukin-1 beta (IL-1 beta) in the periodontal ligament after the application of mechanical force to teeth in vivo and (2) to determine the effects of mechanical stress or IL-1 beta (or the two in combination) on PGE synthesis and bone resorption by fibroblasts in the human periodontal ligament (PDL). In 24 female cats, one maxillary canine was tipped distally by 80 gm force for 12 hours, 24 hours, or 7 days. PGE and IL-1 beta were localized immunohistochemically in serial jaw sections, and semiquantitation of cellular-staining intensity was done by microphotometry. Unstressed periodontal ligament cells stained mildly for PGE and IL-1 beta, but the staining intensity increased significantly in sites of tension. Human periodontal ligament fibroblasts were preincubated with mechanical stress and/or IL-1 beta in the presence or absence of indomethacin for 1 hour. Then the media were replaced by BGJb (Fitton-Jackson modification) medium (GIBCO), and incubation was continued for 4, 8, or 24 hours in conditioned media. PGE concentrations in conditioned media were determined by radioimmunoassay, and bone-resorbing activity in conditioned media was assessed by 45Ca release from prelabeled neonatal mouse calvaria. The conditioned media derived from cells stimulated by mechanical stress plus IL-1 beta caused significantly more bone resorption than the conditioned media obtained from cells that had been treated by each factor alone. The addition of indomethacin did not inhibit bone resorption completely. These results demonstrate that periodontal ligament cells respond to mechanical stress by increased production of PGE, and that IL-1 beta enhances this response.

Adolescent↗
PubMed1991

Grafted and ungrafted labial gingival recession in pediatric orthodontic patients: effects of retraction and inflammation.

The purpose of this retrospective study was to determine changes in recession and other periodontal factors after orthodontic treatment of malocclusions. Twenty patients with preorthodontic labial recession on one or more mandibular central incisors were studied. Ten patients had received autogenous gingival grafts in the area of recession prior to orthodontics, while ten received no graft. The teeth presenting recession had been retruded from a preorthodontically prominent arch position. Moderate inflammation of marginal tissues and fair-to-poor oral hygiene were maintained by the patients. Statistically significantly less gingival recession was found in both groups after orthodontic treatment than was found pretreatment. The results of this study indicated that labial recession tends to decrease with retrusion of mandibular incisors even when moderate inflammation and fair-to-poor oral hygiene persist. Preorthodontic gingival grafting did not further decrease the postorthodontic gingival recession.

Adolescent↗
PubMed1990

Bone-resorbing activity and prostaglandin E produced by human periodontal ligament cells in vitro.

Human periodontal ligament (PDL) cells were derived from healthy premolars extracted for orthodontic treatment and were utilized for in vitro experiments in passages 4-6. Human PDL cells were seeded in tissue culture tubes and incubated with interleukin-1 alpha (IL-1 alpha), IL-1 beta, tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), indomethacin, parathyroid hormone (PTH), or their combinations, for 1 h. The medium was then replaced with serum-free BGJb medium and incubated for 24 h without further additions. Prostaglandin E (PGE) concentrations in the conditioned media (CM) were measured by radioimmunoassay, and bone-resorbing activity was measured using 45Ca-labeled neonatal mouse calvariae. The results of this study indicated that (1) unstimulated cultured PDL cells produced PGE, and PDL CM stimulated bone resorption; (2) cytokine-treated (IL-1 alpha, IL-1 beta, and TNF-alpha) PDL cells had increased production of PGE and bone-resorbing activity compared to unstimulated PDL cells; (3) indomethacin completely inhibited PGE production from unstimulated PDL cells but only partially inhibited bone-resorbing activity, indicating that PDL cells produced nonprostaglandin bone-resorbing factor(s); (4) IFN-gamma did not change PGE or bone-resorbing activity production by cytokine-stimulated PDL cells; and (5) PTH treatment of PDL cells in addition to cytokines (IL-1 alpha, IL-1 beta, and TNF-alpha) had additive effects on the production of bone-resorbing activity and synergistic effects on PGE production compared to cytokine treatment alone.

Animals↗
PubMed1990

Wire-bending test as a predictor of preclinical performance by dental students.

Traditional Dental Aptitude Test and academic grade point average have been shown to be poor predictors of clinical performance by dental students. To refine predictors of psychomotor skills, a wire-bending test was given to 105 freshmen at the beginning of their dental education. Grades from seven restorative preclinical courses in their freshman and sophomore years were compared to scores on wire bending and the three traditional predictors: GPA, academic aptitude, and perceptual aptitude scores. Wire-bending scores correlated significantly with six out of seven preclinical restorative courses. The predictive power for preclinical performance was doubled when wire bending was added to traditional predictors in stepwise multiple regression analysis. Wire-bending scores identified students of low performance. These preliminary results suggest that the wire-bending test shows some potential as a screening test for identifying students who may hae psychomotor difficulties, early in their dental education.

Adult↗
PubMed1989

Total child patient care--aspects of paediatric dentistry and orthodontics.

Various factors have combined to create a situation in which paediatric dentistry is undergoing considerable change. These include the declining prevalence of caries, the refinement of preventive measures and the rapid development of new materials and techniques. The result is a shift in emphasis away from a purely conservative, restorative approach towards a concept of total child care. This requires the practitioner to consider total treatment planning in which there will be phases of preventive, restorative and orthodontic treatment appropriate to each child patient. Correct application of these skills, modified by the application of advancing technology, will ensure that children so treated will grow to value and appreciate good dental health.

Child↗
PubMed1988

Immunohistochemical assessment of the effect of chemical and mechanical stimuli on cAMP and prostaglandin E levels in human gingival fibroblasts in vitro.

These were evaluated by: (1) a combined immunohistochemical-microphotometric procedure (IH) and (2) conventional radiometric assays. Human gingival fibroblasts were in the sixth passage, grown and maintained in Dulbecco minimal essential medium (DMEM) supplemented with 10 per cent horse serum. For chemical and hormonal stimuli, cells (2 x 10(4] were seeded on tissue-culture chamber/slides, and incubated with graded doses of either parathyroid hormone (PTH) or prostaglandin E2 (PGE2) for assessment of their adenosine-3',5'-monophosphate (cAMP) levels, and with indomethacin or colchicine for their effect on PGE levels. For mechanical stimuli, cells (1 x 10(6] were seeded on culture dishes with a flexible plastic membrane and stretched for 5, 30, 60 or 120 min by placing the membrane over a convex surface and weighting the dish cover. After freeze drying, cells were stained by an immunoperoxidase technique for either cAMP or PGE, using monoclonal antibodies. The staining intensity of fibroblasts was determined at 600 nm wavelength. Per cent light absorbance of 15 cells in each slide was measured and the results tested by analysis of variance. The gingival fibroblasts responded to the drugs and hormones in a dose- and time-related fashion. Stretching significantly increased their synthesis of PGE with concomitant increase in cAMP. The IH results were compared with the radiometric assays to confirm the validity of this technique; both assays were valid for describing the quantitative responses of these cells to the stimuli. In particular, the IH method could localize those intracellular sites which demonstrated chances in relative cAMP and PGE concentrations in response to hormonal stimuli.

Colchicine↗
PubMed1988

Orthodontic treatment of the primary dentition.

Five patients were treated for corrections of problems in the primary dentition. Anterior and posterior crossbite, deep overbite malocclusion, and overbite malocclusion were treated with simple removable orthodontic appliances. Early orthodontic treatment for these patients helped resolve any functional problems that could interfere with later growth and development, such as health and function of the TMJ complex.

Activator Appliances↗
PubMed1988

Neurotransmitters, cytokines, and the control of alveolar bone remodeling in orthodontics.

This article described research aimed at testing the hypothesis that tissue remodeling during orthodontic tooth movement is modulated, at least in part, by factors derived from the nervous and vascular (immune) systems. Specifically, the neurotransmitters SP and VIP and the cytokines IL-1 alpha and IL-1 beta were localized immunohistochemically in paradental tissues of cat canines that had been treated by the application of an 80 g tipping force for 1 hour to 14 days. Increased staining (concentrations) of these agents were found in areas of PDL tension and compression at different time periods. Moreover, administration of SP and IL-1 beta to human PDL fibroblasts in vitro for 1 to 60 minutes resulted in significant increases in the levels of the intracellular "second messenger" cAMP, as well as of PGE2, a plasma membrane-associated fatty acid believed to serve as a local regulator of bone cell activity. Taken together, these results tend to support the hypothesis that neurotransmitters and cytokines play a regulatory role in orthodontic force-induced alveolar bone remodeling. Consequently, determination of the cytokine synthetic activity by leukocytes of orthodontic patients may inform about their alveolar bone remodeling potential.

Alveolar Process↗
PubMed1981

Evaluation of fluoride prophylaxis pastes.

The fluoride (F) uptake from two commercial prophylaxis pastes and a newly formulated prophylaxis paste was compared. The enamel fluoride uptake of 26 extracted sound human molars was measured using an acid etch biopsy method. The F uptakes in ppm (mean +/- SEM) for the control prophy pastes (C), Zircate treatment paste (Z), an APF paste (Nuppro,A), and a new experimental paste (N) were 1145 +/- 65,1245 +/- 72,1857 +/- 296, and 1841 +/- 321, respectively. The enamel biopsy depths in micrometers (mean +/- S.D.) for the control, Zircate APF pastes, and Newpaste were 6.64 +/- 1.75, 7.4 +/- 2.32, 6.55 +/- 2.23 and 7.69 +/- 1.80. The Newpaste appeared to give a significantly higher fluride uptake than Zircate and control pastes, but was very similar to an APF paste.

Aluminum Silicates↗