Trends in Academic Dentistry and Oral Health Research Funding by Gender.

INTRODUCTION: Dental and oral health researchers compose a small share of the research workforce, and within this group female researchers form a much smaller share than male researchers. Additionally, a majority of full-time faculty appointments at dental schools are held by men, with women making up only 39% of full-time appointments. These factors suggest that there could be disparities between men and women in obtaining research funding. OBJECTIVE: The focus of our study was to determine whether there are gender differences in award funding obtained from the National Institute of Dental and Craniofacial Research or the National Institutes of Health (NIH). METHODS: NIH administrative data were analyzed by focusing on Research Project Grants (RPGs), the primary and most commonly used mechanism to support investigator-initiated research projects. Analyses involved 1 or 2 of the following variables: number of unique applicants or awardees, fiscal years 2007 to 2016, average age of unique applicants, awardee's degrees, awardee's age at first R01, and award rates. RESULTS: About two-thirds of RPG applicants and awardees were men. Although there were significantly more male applicants and awardees, there was no significant difference in award rate by gender, and there was no significant award rate variation through time or by degrees. The average ages of RPG applicants were similar for genders for all degrees, except that male dentists and PhD-dentists applying to the National Institute of Dental and Craniofacial Research were older and male MDs and PhD-dentists from dental schools applying to the NIH were older. CONCLUSIONS: This study demonstrated that men in the dental/oral health workforce submit more applications and receive more NIH awards than do women; however, there was no difference in award rates between women and men and no difference in ages by gender at which the first R01 awards are received. KNOWLEDGE TRANSFER STATEMENT: Analyses of the implications of this study by the academic dentistry and oral health community could lead to establishing opportunities to expand the representation of women in dental and oral health research. Increasing the number of applications submitted by women may help achieve an equitable balance of grantees in the workforce.

Radiometric classification of alveolar bone health.

A radiograph-based classifier for discrimination between normal and diseased alveolar bone was developed. The alveolar bone health of dry mandibles was rated, by consensus of two trained observers, as normal or diseased. Bitewing radiographs of mandibular quadrants were digitized and regions of interest (ROIs) of the alveolar bone between the first and second permanent molars outlined. Gray-scale histograms for the ROIs were computed, and a classifier based on these histograms was developed. Two observers (independently) used only the classifier to rate the bone as being normal or diseased. These ratings were compared with the original ratings of trained observers who viewed and scored the actual alveolar bone. The sensitivity (the ability to detect diseased alveolar bone), specificity (the ability to detect normal alveolar bone), and accuracy were 0.90 or greater, indicating good agreement with subjective visual assessments of dry mandibles. These results suggest that this procedure may be applicable for evaluations of bone health in humans.

Automated classification of periodontal disease using bitewing radiographs.

The feasibility of applying a prototype, computer-based pattern recognition system to the objective classification of periodontal disease using dental radiographs was tested. Twenty-nine observer-classified bitewing radiographs, representing seven individuals with varying grades of periodontal disease, were selected. The radiographs were digitized using a computer-controlled TV camera. Mathematical features of these radiographs were interactively extracted using a digital image processing system (International Imaging Systems Model 75 and System/575). The features extracted from these radiographs included the brightness levels of cortical and trabecular bone and ratios of bone-loss to linear-crown height. Twenty-eight mathematically defined features (variables) were determined for each radiograph. Stepwise linear discriminant analysis used these features to classify subjects based on the presence and extent of periodontal disease. This pattern recognition system was able to grade periodontal disease in our test series with percentages of correct classifications ranging from 78.8% to 91%. This technology is particularly applicable to the development of morbidity and activity indices for periodontal diseases.

Spatial resolution and angular alignment tolerance in radiometric analysis of alveolar bone change.

This pilot study was undertaken to determine the effect of x-ray beam alignment and spatial resolution on quantification of alveolar bone using radiometric techniques. Six (6) dry mandibles were radiographed at 70 kVp, 10 mA, 0.6 seconds using D-speed film, with a bone chip (2.64, 4.10, or 6.07 mg) present or absent at 7 x-ray beam alignments (0 degree, 2 degrees horizontal, 2 degrees vertical, 4 degrees horizontal, 4 degrees vertical, 6 degrees horizontal, 6 degrees vertical). This resulted in 28 radiographs per mandible. Radiographs were digitized using 50- and 200-microns pixel spatial resolution. Image gray levels were standardized using a simple look-up table shift. Regions of interest (ROIs) were positioned on the alveolar bone where the bone chips had been placed. Cumulative percent histograms (CPH) were calculated for those ROIs. Regression analysis was used to evaluate the relationships between CPH changes and bone chip size as x-ray beam angulation and spatial resolution was varied. The resulting R2 values for angulation ranges of 0 degree to 1.4 degrees, 1.5 degrees, to 2.4 degrees, and 2.5 degrees to 5.5 degrees were: 0.983, 0.941, 0.891 for 50-microns pixel images and 0.869, 0.909, and 0.774 for 200-microns pixel images. We conclude that 50-microns pixel spatial resolution is apparently superior to 200-microns pixel images if radiometric data is to be evaluated. With 50-microns pixel spatial resolution, alignment variations up to 5 degrees may be acceptable in clinical studies, depending on the magnitude of bone change that is to be detected.

Periodontal disease morbidity quantification. I. Optimal selection of teeth for periodontal bone loss surveys.

The assessment of alveolar bone loss with bite-wing radiographs is attractive because bite wings are relatively convenient, inexpensive, and available. The choice of teeth used influences the validity of global bone loss assessments based on partial mouth measurements. The objective of this study was to validate periodontal bone loss indices based on a few teeth. The mandibular posterior teeth were considered as a basis for abbreviated indices. The optimum number of teeth included was evaluated, and the utility of abbreviated indices was determined experimentally. The teeth from 75 skulls were measured from the cemento-enamel junction (CEJ) to the alveolar bone at six locations per tooth. The subsets of teeth which best represent the average whole mouth bone loss were found with all-possible-subsets regression analysis. Bone loss data from 179 prehistoric skulls were used to test the validity of selected teeth indices. Bone loss measurements from the mandibular posterior areas were representative of full-mouth bone loss measurements. Mandibular second premolars plus any other mandibular posterior teeth were the optimal combination of tooth for an abbreviated index. This subset is suitable for use with bite-wing radiographs.

Comparison of 5 protocols based on their abilities to use data extracted from digitized clinical radiographs to discriminate between patients with gingivitis and periodontitis.

BACKGROUND: This study was undertaken to compare 5 digital analytic protocols for their abilities to extract data from digital clinical radiographs and discriminate between patients with gingivitis and periodontitis. METHODS: Five digital-image analysis protocols were compared for their abilities to discriminate between two groups of 24 patients each. One group was diagnosed with healthy gingiva (or gingivitis) and the second with periodontitis. These groups were previously evaluated in published studies that used fractal and morphologic analyses. Pre-existing clinical radiographs for each patient were digitized and regions of interest (ROIs) were placed on interdental bone in mandibular posterior quadrants. The 5 protocols used were: 1) MGB: a median filtration to remove high-frequency noise, a Gaussian filtration to remove low-frequency noise, binarization of the resulting image, and quantification of the black pixels; 2) MGBS: the same protocol as MGB except for a skeletonization of the binary image and a quantification of the skeleton's pixels; 3) GBS: Gaussian filtration, binarization (thresholding on the mean pixel value) of the resulting image, skeletonization, and quantification of the pixels of the skeleton; 4) NS: normalization, skeletonization, and quantification of the skeleton's pixels; and 5) S: a variation of NS, except normalization was not used. The resulting values for the 2 patient groups were compared with Mann-Whitney U tests and effect likelihood-ratio test. RESULTS: For digitized radiographs, the mean gray-scale value (+/- standard deviation) for gingivitis patients was 183.22 +/- 18.53 and for periodontitis patients 181.26 +/- 17.20. Mann-Whitney U tests resulted in the following P values for these protocols: MGBS <0.01; S <0.01; GBS <0.01; NS <0.01; and MGB <0.83. Effect likelihood-ratio tests indicated that only MGBS and S significantly contributed to models containing the other factors. CONCLUSIONS: Small variations to protocols affected the strength of the discrimination between the gingivitis and periodontitis groups. While there is potential for morphologic analysis to be used to discriminate between patients with gingivitis and periodontitis, a robust technique was not identified.

A comparison of 2 patient populations using fractal analysis.

This study was undertaken to demonstrate that the fractal dimensions calculated using digitized non-standardized, clinical radiographs of mandibular alveolar bone from a population of patients diagnosed with periodontitis are statistically different from fractal dimensions calculated from another population diagnosed as having gingivitis or healthy gingiva. The fractal dimension was calculated using a public domain fractal analysis program distributed by the National Institutes of Health (NIH). Fractal dimensions were calculated from digitized clinical radiographs for 29 patients diagnosed with healthy gingiva and/or gingivitis and 32 patients diagnosed with periodontitis and compared. To estimate the reproducibility of the technique, we recalculated the fractal dimension from images of the gingivitis patients 3 months after the original calculations and compared them to the originals. A 2 sample, 2-tailed Student t test showed the gingivitis data group to be different from the periodontitis data group (P = 0.0012). The original gingivitis and repeat gingivitis groups fractal dimension calculation were the same and analysis showed the two data sets were not significantly different (P = 0.99). We found that: 1) fractal dimensions could be used to distinguish between gingivitis and periodontitis patient groups; 2) fractal dimensions could be calculated from non-standardized clinical radiographs; and 3) fractal dimensions for gingivitis patients were reproducible over a 3-month period.

Periodontal disease morbidity quantification. II. Validation of alveolar bone loss measurements and vertical defect diagnosis from digital bite-wing images.

Quantitative alveolar bone loss evaluation by digital processing of dental radiographs was performed. More than 20 contrast and edge enhancement techniques were applied to bite-wing radiographs of adult molar teeth and the results subjectively evaluated. Wallis space variant image enhancement was selected as the most promising candidate for improved visualization of the cemento-enamel junctions and alveolar crests. Seventy-three skulls were radiographed, the films digitized, and enhancement performed on the digital images. Alveolar bone loss measurements from skulls (truth) were compared with those from the original radiographs, unprocessed digital images, and enhanced digital images. The average intraclass correlation coefficient for two observers was 0.83 for radiographs, 0.86 for digital images, and 0.91 for enhanced images. The intraclass correlation coefficient between the 2 sets of dry skull measurements made by two additional observers was 0.88. Means and 95% confidence limits were determined for differences between measurements from dry skulls and radiograph-based images. In the worst case for measurements from enhanced images, the mean difference from truth was -0.40 mm with a 95% confidence interval from -0.54 to -0.25 mm. Receiver operating characteristic (ROC) analysis was used to determine the utility of radiograph-based images for the diagnosis of vertical defects. The ability of two observers to diagnose vertical defects on dry skulls was also tested. All methods of vertical defect diagnosis, including the identification of vertical defects on dry skulls, had relatively low diagnostic performance. Image processing technology has considerable potential in periodontal disease studies for quantitative evaluations of alveolar bone height. The diagnosis of vertical defects using current definitions and techniques is problematic, with considerable room for improvement.

Relationships between longitudinal changes in radiographic alveolar bone height and probing depth measurements: data from postmenopausal women.

BACKGROUND: The relationship between loss of radiographic alveolar bone height and probing attachment loss has been studied by a number of investigators, with mixed results. Recent studies have found weak correlations and have suggested that the relationship between bone loss and attachment loss is complex, perhaps because changes in bone height and attachment level are separated in time. METHODS: The 85 patients in this report were part of a prospective estrogen replacement interventional study. All patients were in good oral health at entry and received annual oral prophylaxis as part of the study. Standard probing measurements were made with a pressure-sensitive probe at 6 sites on each tooth. Vertical bite-wing radiographs were taken of each patient, radiographs were digitized, and 6 linear measurements (corresponding to probing site measurements) were made from the cemento-enamel junction to the alveolar crest. These procedures were performed at baseline and at annual intervals; this study reports results after 2 years. Data were analyzed both by individual site and by averaging identical sites from all measured teeth for each patient. RESULTS: Very weak direct relationships between change in alveolar bone height and change in attachment level were found in both the site data (r2=0.0022; P = 0.189) and the patient average data (r2=0.031; P= 0.104). CONCLUSIONS: The changes in these patients were probably due to systemic changes in bone health rather than to periodontal disease. However, the weak correlations between changes in attachment level and bone height are similar to recent studies of periodontal disease. Our results support suggestions in the literature that the link between changes in attachment and alveolar bone height is complex, perhaps because changes in the 2 tissue types are separated by a considerable time delay.

Comparison of morphological measurements extracted from digitized dental radiographs with lumbar and femoral bone mineral density measurements in postmenopausal women.

BACKGROUND: We set out to determine whether morphologic measurements extracted from digitized images of bite-wing radiographs correlated with lumbar and femoral bone mineral density (BMD) measurements in 45 postmenopausal women who had no or only mild periodontal disease (no probing depths >5 mm). METHODS: Lumbar spine and femoral BMDs were determined by dual-energy x-ray absorptiometry. Vertical bite-wing radiographs were taken and digitized. Crestal and apical regions of interest (ROIs) were drawn on the digital images of the maxillary and mandibular alveolar bone on the patient's right and left sides. For each patient, a single morphologic measurement was made for each of 8 ROIs. Correlation analysis was performed to determine the strengths of the relationships between the morphologic measurements made at the 8 locations and between these morphologic measurements and BMD measurements. RESULTS: The correlations (r) between the morphologic operator (MO) measurements and lumbar spine and femoral BMDs were weak (mean r = 0.02, range = 0.32 to -0.26) and not statistically significant, with no clear trends discernible. Correlations between MO measurements made at the 8 alveolar sites were also weak (mean r = 0.05, range = 0.35 to -0.38) and not statistically significant. CONCLUSIONS: The MO measurements used in this study were weakly correlated with lumbar spine and femoral BMDs, with no clear trends discernible in this population of postmenopausal women with no or mild periodontal disease.

Alveolar bone height and postcranial bone mineral density: negative effects of cigarette smoking and parity.

BACKGROUND: Our objective was to test the association between cemento-enamel junction, alveolar-crest distance (CEJ-AC, as measured on digitized vertical bite-wing radiographs) and postcranial bone mineral density (BMD) relative to clinical, dietary, and demographic variables. METHODS: Data were collected in a cross-sectional study of 134 postmenopausal women. CEJ-AC distances were determined from digitized vertical bite-wing radiographs. Lumbar spine and proximal femur BMDs were determined from dual-energy x-ray absorptiometric scans. Correlation analysis and Student t tests were used to identify those variables most associated with CEJ-AC distance. The selected variables were modeled with a backward stepwise regression analysis, with CEJ-AC distance as the dependent variable. RESULTS: Parity (number of pregnancies to term), cigarette smoking, and the interaction of lateral spine BMD with cigarette smoking were independent predictors of CEJ-AC distance (P < or =0.05). Statistical models containing these variables accounted for 19% of the variation in CEJ-AC distances. CONCLUSIONS: CEJ-AC distance in postmenopausal women is the result of a complicated interaction of many effects, including but not limited to, parity, cigarette smoking, and skeletal BMD.

Objective and subjective evaluations of Kodak Ektaspeed Plus dental x-ray film.

A new dental x-ray film, Kodak Ektaspeed Plus (Eastman Kodak Co., Rochester, N.Y.), was compared with Kodak Ektaspeed and Ultraspeed films. The comparison was based on objective measures (film contrast, speed, and fog levels) and subjective appraisals (film graininess and appearance). Ektaspeed Plus had higher contrast than Ektaspeed and in general similar contrast to Ultraspeed. Ektaspeed Plus was faster than Ektaspeed. Films were stored in various locations and base + fog determinations were made during a 16-week period. Ektaspeed Plus and Ultraspeed films were generally stable within this period. There were no meaningful differences in fog buildup based on storage location. Ektaspeed Plus had the least rate of buildup. Ektaspeed demonstrated the greatest rate of buildup and the greatest sensitivity to environmental factors. Periapical exposures were made of the molars of a manikin. These radiographs were subjectively assessed by three observers. The Ektaspeed Plus film was judged to appear less grainy than the Ektaspeed and to have a pleasing appearance. On the basis of the evaluations performed in this initial investigation, it was concluded that Ektaspeed Plus was superior to Ektaspeed film and was superior or equivalent to Ultraspeed film for dental radiography.

The effect of image variations on fractal dimension calculations.

OBJECTIVES: We used digitized dental radiographs of alveolar bone to test the hypothesis that the fractal dimension, as calculated with the program "ImageFractal" was independent of variations in X-ray exposure, beam alignment, and region of interest placement. STUDY DESIGN: The radiographic data set consisted of 72 radiographs digitized with 200 microns pixels. Radiographs were obtained with the use of three time settings and two alignments. Rectangular regions of interest were placed on each digital image over the interdental bone between the mandibular first and second molars on six hemimandibles. Each of six hemimandibles had identical copies of a unique region of interest placed on every image in its series. New regions were made 3 months later. A fractal dimension was computed from each region of interest with the caliper method included in ImageFractal, a public domain program available through National Institutes of Health. The resulting fractal dimensions were evaluated with two repeated measures analysis of variance. RESULTS: No significant differences were found between the fractal dimensions calculated for baseline images and those from overexposed and underexposed images, from images with 4 to 6 degrees of alignment variations, or from repeat regions of interest. CONCLUSION: The results support the hypothesis that fractal dimensions derived from digitized dental radiographs are not affected by variations in exposure or small variations in alignment and imply an absolute region of interest placement may not be necessary. However, caution should be used with the use of the fractal dimension to discriminate among alveolar bone variations until further research is performed.

Morphologic operations used to distinguish between two patient populations differing in periodontal health.

OBJECTIVES: This study was conducted to determine whether morphologic operation procedures applied to digitized, non-standardized, clinical radiographs of mandibular alveolar bone could be used to distinguish between a population of patients diagnosed with periodontitis and a population of patients either diagnosed with gingivitis or having healthy gingivae. STUDY DESIGN: Two groups, one consisting of 29 patients who either had healthy gingivae or had been diagnosed with gingivitis and the other consisting of 32 patients who had been diagnosed with periodontitis, were compared. Pre-existing clinical radiographs were digitized, and for each patient three to six regions of interest were placed on an image of the mandibular posterior region of the interdental bone. The regions of interest were processed under two morphologic-operations protocols, and a mean density (referred to as an MO number) was calculated for each patient. With paired t-tests, the resulting MO numbers for the two groups were compared. RESULTS: The two populations were statistically different (p < 0.05). CONCLUSION: The results of this study indicate that morphologic operations have the potential to differentiate between patient groups differing in periodontal health.

Three-dimensional dental imaging by spiral CT. A progress report.

OBJECTIVE: To demonstrate the feasibility of using spiral computed tomographic data for three-dimensional image acquisition, display, and segmentation of dental structures and lesions and to demonstrate the feasibility of metal artifact suppression. STUDY DESIGN: Isolated extracted teeth, a dry mandible, cadaver mandible, and cadaver head were scanned and reconstructed using spiral computed tomography data. Algorithms for metal artifact reduction including extended attenuation range and interpolation of missing projections were applied. Volumetric rendering was performed to synthesize images comparable to conventional intraoral dental radiographs. Serial examinations were obtained by spiral computed tomographic tomography, registered by surface matching, and interval change determined by three-dimensional subtraction. RESULTS: Metal artifact reduction was successful in markedly reducing the streaks and star patterns that usually accompany metallic restorations and intraoral appliances. Voxel sum images were comparable to dental radiographs. Image segmentation could successfully isolate dental structures, and simulated lesions could be detected through three-dimensional subtraction. CONCLUSION: The results demonstrate the feasibility of spiral volumetric computed tomography for quantitative study of oral hard tissues in the presence of metal restorations.

Spatial resolution in radiometric analysis of enamel loss. A pilot study.

This pilot study was undertaken to determine whether spatial resolution affects radiometric analyses aimed at detecting progressive enamel loss. Four teeth were weighed, attached to a positioning device, and evaluated with radiography. A 1 mm strip of enamel was removed from each tooth, and the teeth were weighted again and reexamined by radiography. This process was repeated five times until 1/2 mm of dentin was removed. The radiographs were digitized twice with 59 and 200 microns pixels at 8 bits, providing two series of images with the optical densities converted into 256 gray levels. Each series of images was adjusted for contrast variation. Regions of interest were drawn on the crowns, and cumulative percent histograms (CPHs) were calculated. Within a series of CPHs enamel reduction resulted in shifts in the CPHs that were directly proportional to the amount of enamel removed. CPH shifts associated with the smaller 59 microns pixels accounted for 68% of the variation in weights caused by enamel reduction, whereas the shifts associated with the larger 200 microns pixels accounted for 50%. The results indicate that pixel size does affect radiometric determinations of enamel reduction.

The effect of region of interest variations on morphologic operations data and gray-level values extracted from digitized dental radiographs.

OBJECTIVE: To determine the correlations among morphologic operations (MO) values and the correlations among gray-level values for regions of interest (ROIs) placed at various locations on digital images of alveolar bone for 45 patients. STUDY DESIGN: As part of a larger study, up to 7 vertical bite-wing radiographs were taken and digitized for each of 45 patients. Sets of 2 rectangular ROIs were placed on the digitized images of interdental alveolar bone at 4 locations for each patient. The ROIs (1 crestal and 1 apical) were placed between second premolars and first molars in all 4 dental quadrants. Gray-level values were measured, and MO analysis was performed on each ROI. Descriptive statistics were calculated and correlations determined. RESULTS: Paired correlations (such as apical vs crestal, left vs right, maxillary apical vs mandibular apical) of MO values were weak (r = 0.01-0.21), but corresponding correlations for gray-level values were relatively strong (r = 0. 60-0.92). CONCLUSION: MO values varied with ROI location considerably more than did gray-level values. Additionally, ROI size and shape apparently affected MO data. Accurate placement and documentation of ROIs appear to be critical considerations in analyses that use MOs.

Interactive segmentation of cerebral gray matter, white matter, and CSF: photographic and MR images.

Digital photography of postmortem brain slices was compared with magnetic resonance imaging (MRI) for morphological analysis of human brain atrophy. In this study, we used two human brains obtained at autopsy: a cognitively defined nondemented control (70-yr-old male) and a demented Alzheimer's disease (AD) subject (82-yr-old female). For each of two brains, interactive manual image segmentation was performed by two observers on two image sets: (a) four coronal T1-weighted MR images (5 mm slices); and (b) four digitized photographic images from comparable rostrocaudal levels. Microcomputer image analysis software was used to measure the areas of three segmented cerebral compartments--gray matter (GM), white matter (WM) and CSF--for both image types. Resegmentation error was defined as the absolute difference between the areas derived from two segmentation trials divided by the value from trial 1 and multiplied by 100. This yielded the percent difference between the area measurements from the two trials. We found intra-observer agreement was better (error rates 1-18%) than inter-observer agreement (3-70%) with best agreement for WM and least for CSF, the smallest object class. MRI overestimated GM area relative to digitized photographs in the control but not the AD brain. The results define limitations of manual image segmentations and comparison of MRI with pathologic section photographic images.

Interpretation of base-metal dentinal radiopacities: survey results.

A survey was conducted to determine the familiarity with base metal dentinal radiopacity. The results show that although 91% of the respondents had observed this phenomenon, only 6% could correctly identify its cause. Despite the general misunderstanding concerning its cause, 48% of the respondents considered this radiopacity when making a diagnosis and providing treatment. To limit confusion, a standard term is suggested so this feature can be more consistently identified and properly considered in making diagnoses and in formulating treatment plans.

Digital enhancement of radiographs: can it improve caries diagnosis?

Unlike traditional radiographs, digital images are electronically alterable and offer the potential for enhancing diagnostic information. The authors conducted a small-scale study to examine differences in clinicians' diagnoses of caries using traditional radiographs and digitized images vs. microscopic diagnosis. Two general dentists and one oral-maxillofacial radiologist scored the images for caries. This study suggests that digital enhancements may aid some clinicians in caries diagnosis.