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Biomedical subjects

M S Cooke

Publications and source records attributed to M S Cooke.

At least 37 records · Page 2Linked to original sources
PubMed1997

Effect of training and experience on cephalometric measurement errors on surgical patients.

The aim of this study was to quantify and compare the cephalometric measurement errors (interexaminer errors) between two orthodontic residents and two oral and maxillofacial surgical residents with differing years of experience. It was hypothesized that the measurement errors would differ between observers with different training backgrounds and experience and that this would lead to significant disagreements in the cephalometric assessment of patients to receive combined orthodontic and orthognathic surgical treatment. Thirty cephalograms were used in the evaluation. Each examiner independently digitized all cephalograms twice. Common cephalometric skeletal and dental variables, 18 angular and 9 linear, were measured. Interexaminer errors were calculated using two-sample t tests for every pair of examiners. The interexaminer error was large in both landmark identification and in angular and linear measurements. The amount of error did not depend on training or experience but probably on individual conception of landmark definition and perception of landmark location. Methods to limit interexaminer measurement errors are described.

Adult↗
PubMed1996

Quantitative determination of cyclobutane thymine dimers in DNA by stable isotope-dilution mass spectrometry.

In order to understand the role of UV-induced DNA lesions in biological processes such as mutagenesis and carcinogenesis, it is essential to detect and quantify DNA damage in cells. In this paper we present a novel and both highly selective and sensitive assay using capillary gas chromatography (GC) combined with mass spectrometry (MS) for the detection and accurate quantitation of a major product of UV-induced DNA damage (cis-syn cyclobutadithymine). Quantitation of the cyclobutane thymine dimer was achieved by the use of an internal standard in the form of a stable 2H-labeled analogue. Both isotopically labeled and nonlabeled dimers were prepared directly from their corresponding monomers. Each was identified as their trimethylsilyl ether derivative by GC-MS. Calibration plots were obtained for known quantities of both nonlabeled analyte and internal standard. Quantitation of cis-syn cyclobutadithymine was demonstrated in DNA exposed to UVC radiation over a dose range of 0 to 3500 J m-2. Under the conditions used, the limit of detection was found to be 20-50 fmol on column (equivalent to 0.02-0.05 nmol dimer per mg DNA). The results of the present study indicate that capillary GC-MS is an ideally suited technique for selective and sensitive quantification of cis-syn cyclobutadithymine in DNA and hence UV-induced DNA damage.

Animals↗
PubMed1995

Comparative cephalometric errors for orthodontic and surgical patients.

The aim of this study was to quantify and compare the reproducibility (intraexaminer method error) of cephalometric measurements in two groups of adult patients: one group with minor skeletal disharmonies and the other with severe skeletal disharmonies. It was hypothesized that errors were greater for subjects displaying severe morphologic deviations. The samples comprised two groups: 30 pretreatment cephalograms of patients planned for comprehensive orthodontic treatment and 30 cephalograms of patients additionally planned for orthognathic surgery. Two reference points and 28 cephalometric landmarks were defined and digitized by one examiner on two occasions 1 week apart. In total, 30 angles and 9 distances were studied. Reproducibility was expressed as the angular or linear differences between the two series of recordings. Two sample t tests were performed. In general, no significant differences in landmark location and measurement were found between the orthodontic and surgical patient groups. It was concluded that extreme variations in skeletal morphology do not effect the accuracy of cephalometric evaluation.

Adult↗
PubMed1994

Effects of cephalometric landmark validity on incisor angulation.

An experimental cephalometric study on the accuracy of independently locating eight landmarks and the subsequent effects on the maxillary (ILs/NL) and mandibular (ILi/ML) incisor angulation was carried out on 30 dry skulls. The true location of each landmark was marked with a steel ball glued onto the skulls. Two additional steel balls were used as reference markers. A purpose-designed skullholder was made to assure a firm and reproducible positioning of the skulls in the cephalostat. Six series of cephalograms were recorded. One reference series with all the steel balls, four series each with a single steel ball marker removed, one at a time, from each jaw and one series with all the steel ball markers removed, except the reference markers. The combined method error in relocating and replacing the steel ball markers, repositioning the skulls into the skull holder, and digitizing, was low. From the first series, the true position of the palatal plane (NL), the maxillary incisor line (ILs), the mandibular plane (ML) and the mandibular incisor line (ILi) were assessed. From series 2 to 5, each of the landmarks without the steel ball markers was estimated. The accuracy of each landmark was then assessed relative to the true cephalometric plane and its perpendicular. On average, the accuracy was high for all the landmarks except posterior nasal spine (PNS), which was estimated 1.2 mm too far anteriorly (p < 0.05). The standard deviations of the accuracy of the dental and skeletal landmarks were similar, being 1.4 to 2.4 mm. The maxillary incisors were proclined 1.1 degrees (p < 0.05) by the estimates of incision superior (Is).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Validity of cephalometric landmarks. An experimental study on human skulls.

Cephalometric landmark validity (the difference between the estimated landmark and the true landmark) has surprisingly not previously been comprehensively evaluated, and no previous study has examined the validity of cephalometric angles and distances. The aim of this study was to investigate the validity of 15 commonly used skeletal and dental cephalometric landmarks, and the subsequent effects on 17 angles and distances. Small steel balls were glued on to 30 Chinese dry skulls to represent the true anatomical landmarks. The skulls were mounted in a purpose-designed skull holder and two cephalograms recorded of each skull, one with and one without the steel balls on the landmarks. Validity was expressed as the difference in the measurements between the assessments made with and without the steel ball markers. Measurements were made relative to X and Y co-ordinates which were constructed from reference points (steel balls) glued intracranially to the skulls. Seven out of the 10 skeletal landmarks and all five dental landmarks, were found to be non-valid along the X or the Y axes (P < 0.05). The standard deviations of the validity errors were large, being 1.0-2.5 mm, along at least one axis, for eight of the skeletal landmarks and three of the dental landmarks. Four of the cephalometric angles (SNA, SN/MnP, MxP/MnP, and LI/MnP) and three of the distances (N-Me, MxP-Me, and lower incisor edge to APg) were also found to be invalid (P < 0.05). The validity errors were greater for angles involving dental landmarks and for angles dependent on four landmarks compared to those dependent on three. The standard deviations of the validity errors for the skeletal angles ranged from 0.9 to 1.8 degrees, except for ANB (0.4 degrees), and for the dental angles from 3.2 to 5.8 degrees.

Adult↗
PubMed1994

Head posture and cervicovertebral anatomy as mandibular growth predictors.

In this study, the separate and the combined influence of head posture and cervicovertebral anatomy on mandibular growth direction was analysed. The subjects, 20 boys and 16 girls, were a subsample of 12-year-old Chinese children in Hong Kong, all with initial and 2-5-year follow-up lateral cephalometric radiographs recorded in natural head position (NHP). Postural variables were measured in terms of craniovertical, craniocervical, and cervicohorizontal angulations. Morphological variables of the craniocervical junction region were measured in terms of intervertebral space and atlantoaxial dimensions. Mandibular growth was estimated as the direction of displacement of prognathion in relation to the sella nasion line when superimposing on stable cranial base structures. The data were analysed with a multiple regression model, separately for boys and girls. In both sexes the height of the atlas dorsal arch showed a statistically significant correlation (P < 0.01) with mandibular growth direction (boys r = 0.54 and girls r = 0.62), while the craniovertical angulation correlated significantly only for the boys (NSL/VER r = 0.59, P < 0.01; C1/VER r = 0.49, P < 0.05). However, atlas dorsal arch height (DORS C1) combined with cervicohorizontal angulation (OPT/HOR) in girls and with craniovertical angulation (NSL/VER; C1/VER) in boys, displayed a significantly (P < 0.05) increased correlation (r = 0.76 and 0.71, respectively). Combination of atlas morphology and head posture predicts mandibular growth direction better than either variable alone.

Analysis of Variance↗
PubMed1994

Esthetic treatment of severe tetracycline staining with orthodontics and veneers: a case report.

This case history describes and illustrates the excellent esthetic results now clinically possible when fixed appliance orthodontic therapy is combined with porcelain veneers to treat severe tetracycline staining and crowding. Because the patient also presented with a bimaxillary protrusion and a displaced maxillary midline, the treatment options also illustrate the dilemma between ideal, but prolonged, treatment options and quicker, but compromised, alternatives. The excellent final result accepted the initial protrusion but corrected the midline. A long-span bonded multistrand wire functioned as semipermanent retention.

Adult↗
PubMed1993

Effect of head posture on cephalometric sagittal angular measures.

The definitions of cephalometric landmarks include relative terms that are dependent on the orientation of the head (e.g., lowest, most posterior) and head orientation differ widely during cephalometry (e.g., Frankfort plane horizontal, natural head posture). The purpose of this study was to quantify the effect of head posture changes on the commonly used sagittal angular measures SNA, SNB, and SNPogonion (SNPg). The sample comprised 30 Chinese skulls. Cephalograms were taken in a purpose designed skull holder with the Frankfort plane horizontal and at +10 degrees, +20 degrees, +30 degrees, -10 degrees, -20 degrees, and -30 degrees. A geometric grid was used to locate the deepest landmarks, and the landmarks were digitized followed by computer superimposition on the S-N line. To compare the values of the SNA, SNB, and SNPg angles in the different head postures, t tests were used. Head (skull) posture changes produced significant effects on the cephalometric values even at +/- 10 degrees of tilting. Overall, the angles were underestimated by approximately 1 degrees. In general, the angular differences and their standard deviations increased as the skull rotation increased with most of the differences for the SNB and the SNPg angles being clinically significant and also statistically significant at the 0.1% level. It was concluded that head posture needs to be standardized during cephalometry. Changes in posture significantly affect the location of some landmarks and the subsequent data obtained.

Asian People↗
PubMed1993

Two-stage incisor transplant and orthodontic space redistribution.

This report describes a complex case with unerupted upper anterior teeth and other dental anomalies requiring the two-stage incisor transplantation technique in conjunction with two phases of orthodontic treatment. The case illustrates the benefits of careful planning and of limiting treatment goals to the needs and perceptions of the patient. The final result also emphasizes the aesthetic dental improvements now possible with a multidisciplinary approach.

Child↗
PubMed1992

Incisor spacing: a sequential orthodontic restorative treatment approach.

For those patients presenting with one or more missing incisors, a sequential technique utilizing specific arch wires to level and align the irregular incisor teeth may be used. Auxiliary coil springs are then fitted to redistribute the space prior to the preparation of a prosthesis, the fabrication of which is facilitated by parallel and upright abutments. The space obtained allows esthetically proportioned pontics. Two cases that illustrate this technique are presented.

Anodontia↗
PubMed1991

Cephalometric errors: a comparison between repeat measurements and retaken radiographs.

This study compares landmark location errors in cephalometric radiography (when re-measuring radiographs) and radiographic errors (when retaking the radiograph). The samples comprised 32 remeasured and re-digitized radiographs and a further series of 22 retaken radiographs drawn from the same overall sample of 12-year-old Chinese children in Hong Kong. All radiographs were recorded in natural head posture with the lips in light contact. The relative size of the errors were assessed by calculating the 'error percentage' for both selected dento-skeletal and soft tissue profile measures. It is suggested that this index is clinically more meaningful than the usually used 'method error'. It expresses the variance of the method error (me2) as a percentage of the variance of the measurement under study (standard deviation2). This error percentage was found to be doubled, on average, for measurements on the retaken radiographs. In general, measures with most landmarks in the mid-sagittal plane showed the least increase in percentage error. The results suggest that errors arising from retaking cephalometric radiographs may effectively be greater than those usually reported. The Frankfort plane, the functional occlusal plane and the incisor long axes displayed poor reproducibility. For the soft tissues the lips served as poor angular landmarks and relatively acute angles with short 'arms' also displayed large errors.

Analysis of Variance↗
PubMed1991

Proportional analysis of the facial profile in natural head position in Caucasian and Chinese children.

A proportional analysis of the facial soft tissue profile in natural head position involving 11 indices (ratios), was applied to 80 Caucasian, and 80 Chinese male and female 12-year-old children in Hong Kong. The analysis is based on the true horizontal and the porion vertical, and has the advantage that its foundation lies on a more stable (less growth affected) region of the head compared to profile soft tissue landmarks. Measurements were made on cephalograms recorded in natural head position. Male subjects were larger than the females for most of the horizontal measurements, but for both population samples the vertical measurements displayed virtually no significant intersex differences at 12 years. No very significant intersex differences were found for the proportional indices. Ethnic differences were mainly found with the horizontal measurements. Relative to the porion vertical the Caucasian children were more protrusive over soft tissue nasion, nose tip, and sulcus labialis superior, whilst the Chinese displayed more protrusion over the lower lip and sulcus labialis inferior. Ethnic proportional differences relative to nasion were combined with a shorter porion-nasion distance in the Chinese as compared with the Caucasian children. The sella-nasion line was found to be more forwards-upwards inclined in Chinese than Caucasian children. It was concluded that a proportional soft tissue profile analysis, based on natural head position, is a useful method for the comparison of ethnic population groups. This study amplified ethnic differences previously reported by Cooke (1986) and Cooke and Wei (1989).

Asian People↗
PubMed1990

Five-year reproducibility of natural head posture: a longitudinal study.

Natural head posture (NHP) is being increasingly used as the logical reference position for the evaluation of craniofacial morphology. The basic premise underlying its use is that the long-term clinical reproducibility (variability) of NHP is significantly less than the variability of conventional intracranial reference planes with respect to the vertical. This study reports the results of a 5-year longitudinal study evaluating the reproducibility over time of NHP lateral cephalometric radiographs. The subjects were 126 randomly selected Chinese children in Hong Kong who were first assessed at the age of 12 years. Thirty subjects were recorded after 5 years. NHP reproducibility deteriorated over time but showed signs of stabilizing after 1 to 1 1/2 years. The method error was 1.93 degrees after 1 to 2 hours, 2.34 degrees after 3 to 6 months, and 3.04 degrees after 5 years. The individual variability of NHP reproducibility also increased over time. The standard deviation of the SN/vertical angulation was 2.61 degrees after 1 to 2 hours, 3.16 degrees after 3 to 6 months, and 4.20 degrees after 5 years. Further longitudinal data are required to determine whether NHP reproducibility continues to deteriorate after 5 years. After 5 years, however, the variance of NHP (9.24 degrees [= 3.04(2)]) remains significantly less than the variance of intracranial reference planes to the vertical (25 degrees to 36 degrees).

Cephalometry↗
PubMed1990

Combined orthodontic and restorative correction of severe anterior open bite.

This article describes a multidisciplinary approach to the treatment of a severe skeletal anterior open bite, complicated by severe chronological enamel hypoplasia, in a 12-year-old southern Chinese girl. Correction of the open bite, of which the cause was unknown, involved the extraction of all first permanent molars and provisional repair of the wafer-thin enamel to permit bonding of fixed orthodontic brackets. Several phases of maxillary and mandibular fixed appliance therapy followed. As the open bite resolved, further restorative treatment was performed. The result was stable 3 years after the end of retention. This case demonstrates the benefits of well-planned, integrated, multidisciplinary treatment.

Cephalometry↗
PubMed1989

A comparative study of southern Chinese and British Caucasian cephalometric standards.

A comprehensive cephalometric comparison between unselected Chinese and Caucasian 12-year-old male children in natural head posture finds the intracranial reference planes to slope down more caudally in the Chinese. By superimposing on true vertical, the degree of prognathism in the Chinese becomes apparent. Significant intergroup differences are highlighted for both selected dentoskeletal and soft tissue profile variables.

Asian People↗