Digital image processing. II. In vitro quantitative evaluation of soft and hard peri-implant tissue changes

Accuracy evaluation of cone beam computed tomography applied to measure peri-implant bone thickness in living patients: an ex vivo and in vivo experiment

OBJECTIVES

This study aims to study the accuracy of cone beam computed tomography (CBCT) for measuring peri-implant bone thickness in living patients via a novel visualization method (NVM).

MATERIAL AND METHODS

The validity of the NVM was verified ex vivo by measuring the same peri-implant bone thicknesses in bovine ribs by using raw postoperative CBCT (clinical measurement, CM), the visualized fused images obtained using the NVM (visualized fused measurement, VF), and hard tissue sections (gold standard measurement, GS). The NVM was applied by deconstructing the postoperative CBCT model into the Model_post-bone and Model_implant and replacing it with bone from preoperative CBCT and standard implant models, respectively. In vivo, 52 implants were included, and the VF of each implant was obtained using data processing methods similar to those used ex vivo. Then, we compared the results of CM and VF.

RESULTS

Ex vivo, the VF was similar to GS, while CM usually underestimated the peri-implant bone thickness, especially at the implant shoulder (P < 0.01). In vivo, on CBCT, areas with a peri-implant bone thickness of 0-0.50 mm were not visible, while those with a thickness of 0.50-1.00 mm were occasionally visible. There was less underestimation of bone along the implant long axis.

CONCLUSIONS

Thin peri-implant bones could be completely underestimated on CBCT. CBCT scans alone are insufficient to warrant surgical intervention. Our NVM facilitates the accurate visual assessment of implant dimensions.

CLINICAL RELEVANCE

The thickness of peri-implant bone could be completely underestimated when thinner than 1.0 mm in living patients. Familiarity with these confusing CBCT results may help clinicians and patients avoid further unnecessary evaluation, misdiagnosis, and invasive treatment.

Quantitative analysis of bone density in direct digital radiographs evaluated by means of computerized analysis of digital images

OBJECTIVES

minimal density variations of mineralized tissues can be reliably detected with quantitative image subtraction analysis. The aim of this study was to evaluate quantitative variations of in vitro mineral density by varying the exposure time of direct digital radiographs using a computer assisted densitometric image analysis (CADIA) program.

METHODS

in a human mandibular segment a three-wall periodontal defect was created mesial to a molar. Bone chips were created from the marrowbone of the same mandible with masses of 1 to 5 mg. A triplicate radiograph of the defect was taken as a baseline for seven different exposure times. The bone chips were inserted into the defect and another triplicate series of radiographs for the seven exposure times were taken as follow-up images. The images were analysed using CADIA software to detect variations in bone density.

RESULTS

the results of CADIA revealed increased density when the size of the inserted bone chip increased. The 2 mg chip was underestimated owing to mass reduction during insertion. The regression line of the CADIA values was consistent with the weight of the bone chips of 1, 3, 4 and 5 mg. The exposure time f6 (0.178 s) showed the best correlation with the bone chip weight. Loss of information in the images occurred when the exposure time exceeded the sensor's latitude.

CONCLUSIONS

CADIA analysis is a reliable and sensitive tool for detecting subtle bone density variations. More reliable results are obtained with increased exposure time; however, excessive exposure should be avoided.

A robust generalized fuzzy operator approach to film contrast correction in digital subtraction radiography

Digital subtraction radiography requires close matching of the contrast in each pair of X-ray images to be subtracted. Previous studies have shown that nonparametric contrast/brightness correction methods using the cumulative density function (CDF) and its improvements, which are based on gray-level transformation associated with the pixel histogram, perform well in uniform contrast/brightness difference conditions. However, for radiographs with nonuniform contrast/ brightness, the CDF produces unsatisfactory results. In this paper, we propose a new approach in contrast correction based on the generalized fuzzy operator with least square method. The result shows that 50% of the contrast/brightness errors can be corrected using this approach when the contrast/brightness difference between a radiographic pair is 10 U. A comparison of our approach with that of CDF is presented, and this modified GFO method produces better contrast normalization results than the CDF approach.

Non-Invasive Method to Measure the Length of Soft Tissue From the Top of the Papilla to the Crestal Bone

BACKGROUND

In order to verify the results of interdental papilla regeneration, various methods of measuring the length of the papilla have been introduced. Invasive methods, such as bone probing under local anesthesia, might cause discomfort to the patients and possibly damage the delicate gingival unit. The purpose of the present study was to validate a method of measuring the length of the interdental papilla non-invasively, using radiopaque material and a periapical radiograph.

METHODS

This study involved 142 interproximal papillae in 40 patients with chronic periodontitis. The distance between the radiopaque material and most coronal portion of the crestal bone was measured (radiographic length of papilla, RL). Bone probing at the interdental papilla was performed after local anesthesia (bone probing length, BPL). After flap elevation, the actual length of the papilla was measured (actual length of papilla, AL). A correlation analysis was performed between AL-RL and AL-BPL using Pearson's correlation coefficients.

RESULTS

The correlation between AL-RL and AL-BPL was 0.903 and 0.931, respectively, both of which showed significance at the 0.01 level.

CONCLUSION

The results of this study suggest that the noninvasive method using a radiopaque material and periapical radiograph could be utilized to measure the length of the interdental papilla.

Healing, post-operative morbidity and patient perception of outcomes following regenerative therapy of deep intrabony defects

AIM

This prospective multicenter randomized controlled clinical trial was designed to compare the clinical outcomes of papilla preservation flap surgery with or without the application of enamel matrix derivatives (EMD). This article reports on early healing events, post-operative morbidity and patient perceptions of the surgical outcomes.

MATERIAL AND METHODS

One hundred and seventy-two patients with advanced chronic periodontitis and at least one intrabony defect of > or =3 mm were recruited in 12 centres in seven countries (European Research Group on Periodontology (ERGOPERIO)). Papilla preservation flaps were used to obtain access and primary closure. After debridement, and root conditioning, EMD was applied in the test subjects, and omitted in the controls. Healing was monitored 1, 2, 3, 4, 6 and 12 weeks after surgery. During the first 12 weeks of healing, supracrestal soft-tissue density was evaluated with a computer-assisted densitometric image analysis system (CADIA) using underexposed radiographs taken on a subset of 34 patients. Patient perceptions were evaluated with a questionnaire immediately after the procedure, at suture removal 1 week later and at 1 year.

RESULTS

Subjects reported little intraoperative or post-operative pain or discomfort for both test and controls. Twenty-four percent of controls and 30% of tests (p=0.64) reported a degree of interference with daily activities for an average of 3 and 3.5 days, respectively. Post-surgical edema was noted in 25% of tests and 28% of controls. Wound dehiscence in the interdental portion of the flap was uncommon (14% of tests and 12% of controls at week 1) and of limited size. Root sensitivity was the most frequent post-operative adverse event: it affected 45% of test and 35% of controls (p=0.55). Up to 6 weeks post-operatively, soft-tissue densities were significantly higher in subjects treated with EMD with respect to controls. One year after completion of the surgery, patients reported high levels of satisfaction with the outcomes. The most frequently reported benefits included the ability to preserve a tooth/dentition and to maintain/improve chewing ability. The cost and need for frequent follow-ups were cited as significant drawbacks.

CONCLUSIONS

This study portrayed the early healing events, pain, discomfort and adverse events of papilla preservation flap surgery and the 1-year patient perceptions of the benefits and disadvantages of periodontal surgery in intrabony defects. Earlier gains in soft-tissue density were observed following application of EMD. In terms of patient-centered outcomes, however, both procedures performed in a similar manner.

Image processing and analysis program for measurement of bone density changes in reference and follow-up standardized extraoral oblique lateral cephalometric radiographs of the mandible

OBJECTIVES

The aim of this study was to develop an image processing and analysis program for peri-implant bone density measurements of the mandible using extraoral radiographs, which includes a correction for the variable projection of the soft tissues of the face.

METHODS

The measurement procedure is based on pairs of reference and follow-up extraoral oblique lateral cephalometric radiographs (OLCRs) of patients with endosseous implants in the anterior part of the atrophic edentulous mandible. The procedure consists of image acquisition, correction for radiographic variation using an aluminium wedge (i.e. film exposure and development) and transformation of the grey values into aluminium-equivalent values. After correction for variation in the projection of the soft tissues of the face using internal calibration fields, the actual peri-implant bone density measurements are performed.

RESULTS

The soft tissue projection correction significantly reduces the variation between radiographs owing to the position of the soft tissues.

CONCLUSIONS

It is concluded that the described image processing and analysis program, in combination with extraorally made OLCRs, is a valuable technique for measurement of peri-implant bone density changes of the mandible. With minor adaptations, the program can be used for other semi-edentulous patients.

In vitro calibration and validation of a digital subtraction radiography system using scanned images

OBJECTIVES

To calibrate and validate a digital subtraction radiography system using scanned images for quantification of alveolar bone changes by means of computer-assisted densitometric image analysis (CADIA) in vitro.

MATERIALS AND METHODS

Noise levels were determined using 10 standardized periapical radiographs of the same lower molar region in a human dry skull. For validation of the system, radiographs were taken before and after bovine bone particles in measures with increments of 2 mg weighing from 2 to 20 mg were added into each socket of three dry skulls. Radiographs were developed and scanned into a computer with a flatbed scanner. After digitization, the images were subjected to alignment, normalization and subtraction. Appropriate regions of interest (ROIs) were selected and their CADIA values were calculated for the determination of noise levels, and correlations between the CADIA values and the actual bone mass were performed.

RESULTS

When the threshold value was 7, the percentage of pixels deviating from the set threshold value was small (0-11.3%). There were statistically significant correlations between the actual bone mass and the CADIA value for anterior sockets (p<0.001, r2=0.89) and posterior sockets (p<0.001, r2=0.9). For pooled data of both anterior and posterior sockets, the correlation was also statistically significant (p<0.001, r2=0.88).

CONCLUSIONS

A high and statistically significant correlation between the actual bone mass and CADIA value was obtained, which suggests that the system could be suitable for the detection of small alveolar bone changes.

Clinical, radiographic and biochemical assessment of IL-1/TNF-alpha antagonist inhibition of bone loss in experimental periodontitis

OBJECTIVES

To assess clinical, radiographic, and biochemical markers as diagnostic indicators of disease activity by comparing ligature-induced bone loss in the presence or absence of IL-1/TNF-alpha antagonist inhibition of bone loss in a primate model.

MATERIAL AND METHODS

6 animals with a naturally-occurring gingivitis were evaluated over a 6-week time period following the placement of silk ligatures and initiation of a soft diet. Three animals received intrapapillary injections of soluble receptors (blockers), capable of blocking the biologic activity for both IL-1 and TNF-alpha, and 3 animals received vehicle (control) injections. Injections were given 3X per week over the course of the study. Clinical assessments included a gingival index and quantification of gingival crevicular fluid (GCF) levels. Collected GCF samples were then used in the biochemical assessment of pyridinoline (PYD) and bone alkaline phosphatase (BAP). Radiographic assessment was made using computer-assisted subtraction radiography to measure both bone density (CADIA) values and linear changes in crestal bone height.

RESULTS

Significant (p<0.01) changes using both radiographic measures occurred between 2 and 4 weeks following initiation of disease in this model. The use of the blockers significantly (p<0.01) reduced the levels of radiographic bone loss by approximately 50% over that found in the control sites. Both biochemical markers showed the greatest increase during the first two weeks of the study with PYD levels increased 35-fold over baseline levels after 1 week. This difference in response was significantly (p<0.05) greater than the levels found in the non-ligated teeth or in the ligated teeth receiving blockers injections. BAP levels showed significant increases in ligated teeth compared to non-ligated teeth, but failed to show any significant differences between animals treated with vehicle and those treated with IL-1/TNF antagonists. In contrast to these radiographic and biochemical effects, there were no significant differences detected between animals treated with antagonists and the control group for any of the clinical measures.

CONCLUSIONS

The results of this study demonstrate that both subtraction radiography and PYD crevicular fluid levels can detect relative differences in periodontal disease progression, while BAP crevicular fluid levels cannot.

Treatment of peri-implantitis by local delivery of tetracycline. Clinical, microbiological and radiological results

The purpose of this study was to investigate the clinical, microbiological and radiological effects of peri-implantitis therapy by local delivery of tetracycline. In 25 partially edentulous patients, 30 implants with radiographic evidence of circumferential bone loss, and peri-implant probing depths > or =5 mm were treated with polymeric tetracycline HCl-containing fibers. Clinical and microbial parameters were recorded at baseline, and 1, 3, 6, and 12 months (M) after treatment. Standardized radiographs were obtained at baseline, M3, and one year after treatment. Two patients were discontinued from the study after 180 days because of persisting active peri-implantitis with pus formation. The remaining subjects showed a significant decrease of mean peri-implant probing depth from 6.0 to 4.1 mm (M1, P<0.001), which was maintained over 12 months. In comparison to baseline, the bleeding tendency was significantly reduced after one month, and thereafter (P<0.001). No significant recession of the mucosal margin was noted. The radiologically determined distance from the shoulder of the implant to the bottom of the bony defect decreased slightly, but not significantly, from 5.2 to 4.9 mm. At M1, M3 and M6, mean total anaerobic cultivable bacterial counts were significantly lower than at baseline (P<0.001). A significant decrease in frequency of detection was noted for Prevotella intermedia/nigrescens, Fusobacterium sp., Bacteroides forsythus, and Campylobacter rectus (P<0.01). Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and Eikenella corrodens had very low baseline frequencies that could not be significantly suppressed further. In conclusion, therapy of peri-implantitis by local delivery of tetracycline had a positive effect on clinical and microbiological parameters.

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.

Radiographic and digital imaging in periodontal practice

This review defines terms such as accuracy, validity, and reliability, which are used to describe the quality of methods for taking x-rays and for analyzing digital images. Values for these parameters are described for techniques of taking standardized x-rays such as ear-rod fixation and fixation by use of teeth with a dental impression. In addition, values are given for linear measurements on digitized images and for quantitative image subtraction. Differences are addressed between quantitative subtraction with a reference ramp and relative subtraction using the computer-assisted densitometric image analysis (CADIA) system. The relationship between radiographic bone height and clinical attachment level is also discussed. Finally, present and future use in the periodontal office of linear radiographic measurements on digital images and digital subtraction is discussed.

Evaluation of tetracycline fiber therapy with digital image analysis

The aims of the present study were to assess radiographically the effects of scaling/root planing combined with antibiotic therapy using tetracycline fibers (TCF): (I) on alveolar bone density and linear descriptors and (II) on supracrestal soft tissue density. 19 subjects with generalized adult periodontitis (with at least 20 teeth present, at least 4 teeth with pockets >4 mm and bleeding upon controlled force probing) and high cultural counts of Porphyromonas gingivalis were recruited from a pool of 57 patients. The full mouth treatment group (FT) consisted of 10 patients, who underwent a full mouth supra-gingival scaling and prophylaxis treatment and were instructed to rinse 2x daily with a 0.1% chlorhexidine solution. 1 week later, tetracycline-hydrochloride-containing fibers (Actisite periodontal fiber) were applied around all teeth. After 7-12 days, the fibers were removed and all teeth were scaled and root planed under local anaesthesia. The chlorhexidine rinsing continued for another 2 months. In 9 subjects (local treatment group LT), 2 teeth with periodontal lesions with pocket probing pepth (PPD) > or =5 mm were treated by placement of tetracycline fibers, which remained in place for 7 to 12 days. Upon removal of the fibers, scaling and root planing was performed on these 2 teeth, while the rest of the dentition remained untreated, and no chlorhexidine rinse was applied. 2 of the untreated teeth revealing similar periodontal lesions were chosen to represent sites affected by untreated periodontitis (NT). In this group, a limited local treatment was performed (2 teeth) with the inherent potential for recolonization from the untreated pocket sites. Standardized periapical radiographs were obtained from the 4 monitored sites within each patient at baseline (before treatment) and 2 and 6 months thereafter. One radiograph was exposed in a standard way for bone assessment. The second radiograph was underexposed, at about a 1/5 of the original exposure time to allow the evaluation of soft tissue. Mean changes in the linear parameters and changes in density (CADIA) observed at multiple sites within each patient and treatment group were used as the best estimate of treatment outcome. Over the observation period of 6 months, a significant difference in bone height changes was found between the untreated sites (median loss -0.29 mm) and the sites from full-mouth treated patients (median gain 0.24 mm, p=0.008). When comparing the baseline to the 6 months radiographs, a loss in bone density was observed for the untreated group (median=-2.13 CADIA). Both treatment groups revealed a gain in density (median=1.58 and 2.43 CADIA for the locally and the full-mouth treated groups, respectively). Differences in density were significant, both between the nontreated and locally treated sites (p=0.026) and between the nontreated sites and the sites from the full mouth treated patients (p=0.002). The analysis of the soft tissues showed a similar pattern of changes in density to those seen in the bone defect. At 2 months, there was a tendency for loss in density for the nontreated group (median=-0.17 CADIA) that continued over the 6 month period (median=-0.31 CADIA). A significant increase in density was observed for the full-mouth treated sites (median=1.57 and 0.64 CADIA for the 2 and 6 months radiographs, respectively). A significant increase was also observed for the locally treated group when compared to the untreated sites (median=0.13 and 0.10 CADIA for the 2 and 6 months radiographs, respectively). Comparing untreated sites with full-mouth treated sites, a significant difference was observed for CADIA measurements (p<0.001). No significant difference was observed comparing locally treated and untreated sites (p=0.24). It was concluded that scaling and root planing combined with TCF therapy can result in increased bone density and alveolar bone height. Full-mouth treatment seemed to result in more pronounced gains compared to local tre

Computer-assisted densitometric image analysis of digital subtraction images: in vivo error of the method and effect of thresholding

The aim of the present study was to assess the in vivo error of the method as well as the effect of thresholding when obtaining and evaluating standardized periapical radiographs for computer-assisted densitometric image analysis (CADIA). Twenty healthy volunteers participated in an experimental gingivitis study in which neither mechanical nor chemical plaque control was performed for 21 days. Two pairs of standardized periapical radiographs were taken at days 0 (baseline) and 21 (follow-up), one from a maxillary area (15 volunteers) and one from a mandibular molar/premolar area (17 volunteers). Each baseline radiograph was digitized and its image displayed on a monitor. The follow-up radiograph was then superimposed and digitized as well. After gray level correction, subtraction radiographic images were produced. The difference in gray level between the baseline and the follow-up image was calculated within each region of interest (ROI) at each picture point (pixel). In bone ROI, changes in density reflected the amount of change due to methodological errors plus the basic bone remodeling over 3 weeks. For gingival ROI, changes in density reflected the methodological error plus a possible change in soft tissue density during the experimental gingivitis. Within all of the ROI, some pixels indicated a change in gray level. A change in gray level was then thresholded; i.e., only changes >5 and then >10 gray levels were registered and used for calculation of the CADIA values. With a threshold of 5, 44/45 maxillary bone ROI and 60/66 mandibular bone ROI showed a change in density, while 41/45 maxillary gingiva ROI and 26/66 mandibular gingiva ROI indicated a change in density. With a threshold of 10, 16/45 maxillary bone ROI and 12/66 mandibular bone ROI indicated a change in density, while 13/45 maxillary gingiva ROI and 1/66 mandibular gingiva ROI indicated a change. The amounts of changes in density calculated in the various ROI were low even when applying no threshold, ranging from -0.279 to 0.621. Applying a threshold of 5, the CADIA values ranged from -0.234 to 0.727. With a threshold of 10, the changes in density ranged from -0.318 to 0.133. In vivo, CADIA of standardized radiographs indicated change in density due to methodological errors. Application of thresholds may avoid false-positive diagnoses. When applying CADIA in clinical research, the range of change to be expected due to methodological limitations as well as the threshold for true change should be evaluated. These thresholds may differ in various areas of the mouth, i.e., bone or gingival, maxillary/mandibular, anterior/posterior ROI.

Accuracy of quantitative digital subtraction radiography for determining changes in calcium mass in mandibular bone: an in vitro study

The aim of this in vitro study was to determine the accuracy of digital subtraction radiography (DSR) to detect small changes in calcium mass in alveolar bone adjacent to tooth roots. In each of 4 dried porcine mandible segments, one interproximal and one buccal "defect" region was defined adjacent to a premolar root. A series of cortical and cancellous bone slices with a 50 microns--stepwise increasing thickness (0-5000 microns) were attached to the mandible segments covering the respective "defect" region. Standardized radiographs were quantitatively assessed for density changes using DSR. After dissolving each bone slice in hydrochloric acid, its calcium concentration was photometrically determined. For each bone slice, the mean calcium mass covering a single pixel of the subtraction image was calculated. The Wilcoxon signed-rank test and the Mann-Whitney U-test were used for statistical analysis (alpha = 0.05). A strong linear correlation (r2 = 0.86-1.00; p < or = 0.001) was found between the thickness of the bone slices and their calcium mass. Cortical bone showed a 3.5 times higher mean calcium mass/pixel than cancellous bone. Furthermore, a strong linear correlation (r2 = 0.63-1.00; p < or = 0.001) was found between the mean calcium mass per image pixel and the radiographic density changes. Neither the bone type nor the "defect" localization had a significant influence on radiographic density changes caused by changes in calcium mass. A change in mean calcium mass per image pixel of 0.1-0.15 mg was necessary to be detected by DSR. In conclusion, this study revealed a high accuracy of DSR to detect small changes in calcium mass in alveolar cortical and cancellous bone.

Quantitative digital subtraction radiography for the determination of small changes in bone thickness: an in vitro study

OBJECTIVE

The objective of this study was to determine the ability of quantitative digital subtraction radiography to detect small changes in bone thickness adjacent to tooth roots.

STUDY DESIGN

A series of cortical or cancellous bone slices with a 50 microm-stepwise increasing thickness were attached to 4 porcine mandible sections covering buccal and interproximal "defect" regions. Standardized radiographs were quantitatively evaluated for radiographic density changes with the use of digital subtraction radiography. Furthermore, all radiographs were conventionally evaluated by 10 clinicians. The Wilcoxon signed-rank test and the Mann-Whitney U test were used for statistical analysis (alpha = 0.05).

RESULTS

A high linear correlation was found between the actual thickness of bone slices and radiographic density changes (cortical bone: r2 = 0.89 to 0.99; cancellous bone r2 = 0.61 to 0.86, p < or = 0.001). A certain increase in bone thickness caused a 3 times higher increase in radiographic density for cortical bone than for cancellous bone (p < or = 0.05). The detection limits of digital subtraction radiography were 200 microm for cortical and 500 microm for cancellous bone, whereas the detection limits of conventional radiography were 600 microm and 2850 microm, respectively.

CONCLUSIONS

This in vitro study demonstrated a very high correlation between the objective, quantitative assessment of subtle changes in alveolar bone by digital subtraction radiography and the true changes in bone thickness.

Effect of the NSAID flurbiprofen on remodelling after periodontal surgery

The aim of the present experiment was to assess the effect of the administration of the NSAID flurbiprofen (Froben) on tissue healing after periodontal surgery. Sites from patients with the same treatment modality (modified Widman flap) but receiving a placebo drug and sites within each patient not exposed to surgery served as controls. Nineteen patients suffering from moderate to severe periodontal disease were recruited and they signed informed consent forms. These patients required periodontal surgery as assessed at the periodontal re-evaluation. The sites chosen for the study were all diagnosed with PPD > or = 5 mm and were bleeding on probing. During the healing phase 10 patients received 50 mg Froben 3 times per day for 30 d whereas 9 patients received a placebo drug. Two sites with PPD > or = 5 mm after initial therapy and bleeding on probing served as surgical sites, whereas 2 similar sites were not exposed to surgery. The study design was set up double-blind. The radiographic examination consisted of 2-4 standardized vertical bitewings obtained at the periodontal re-evaluation (BL) at 1, 3 and 6 months post-surgically for digital subtraction and computer assisted densitometric image analysis (CADIA). The regions of interest analysed were mesial or distal crestal sites. Minimal remodelling activity was observed radiographically after periodontal surgery in both patient groups. There were no statistically significant differences between the four groups of sites regarding the mean changes in density when analysing the pairs of radiographs 0-1, 0-3, 0-6 months. A frequency analysis was performed to list the number of sites with different ranges of density change. No differences in the distributions of the numbers of sites were observed when comparing the 4 site groups (Kolmogorov-Smirnov, p > 0.05). A significant reduction of the probing pocket depth and a significant amount of clinical attachment gain was noted at the surgically treated sites irrespective of whether the patients had used flurbiprofen or placebo. Whereas the pathways leading to bone resorption in periodontally diseased sites have been shown, in other studies, to be influenced by NSAID, the results of the present study could not justify general administration of Froben for the purpose of reduction of bone resorption after periodontal surgical procedures in patients with adult periodontitis.

Particulate bioglass as a grafting material in the treatment of periodontal intrabony defects

The present clinical trial was designed to evaluate the effects of a bioactive glass, Perioglas, in the treatment of periodontal intrabony defects. 20 patients, 23-55 years of age (44 sites), with intrabony defects completed the 1-year study. Teeth with furcation involvement were excluded. After completion of initial therapy, defects were randomly assigned to either a test or control procedure. Following flap reflection, root planing and removal of chronic inflammatory tissue in both groups, the test defects were restored with the bioactive glass particulate material. Mucoperiosteal flaps were replaced, sutured and a periodontal dressing was used. All the patients received postoperative antibiotics and analgesics and were seen at 1 week for suture removal. Follow-up was then carried out weekly and at 3 months, 6 months, 9 months and 1 year post-surgery. Plaque score, bleeding score, probing pocket depth (PPD), probing attachment level (PAL) and gingival recession were recorded at baseline, 3 months and 1 year. Standardised radiographs for computer-assisted densitometric image analysis (CADIA) were taken at baseline, immediately post-operatively and at 1 year. The CADIA data showed a significant increase (F-ratio: 15.67, p < 0.001) in radiographic density and volume between the defects treated with the Perioglas when compared to those treated with surgical debridement only. PPD and PAL showed significant improvements in both experimental and control sites, with a greater trend to improvement in the experimental sites. It was concluded that this bioactive glass is effective as an adjunct to conventional surgery in the treatment of intrabony defects.

Evaluation of a dental subtraction radiography system

The aim of this in vitro study was to evaluate the ability of a dental subtraction radiography system to quantitatively detect differences in density between radiographic image pairs. Four periapical radiographs were taken of the upper first permanent molars on five human skulls using the Digora radiographic imaging system. The 4 images were a "baseline" image and 3 containing test objects consisting of either 0.5, 1 or 2 mm thick aluminium cylinders, 2.5 mm in diameter. Semi-automated image processing software was used to "warp" the 3 images with test objects into the same geometric/density registration as the corresponding baseline image using a process called patch minimization. "Difference" images were than produced and their contrast stretched. For regions of interest, with and without test objects present, the difference in density between the baseline and "test object" images was calculated using a reference aluminium step wedge. The test objects were clearly visible in all the "difference" images. The mean difference between the actual and estimated volume of the test object was 0.31 (95% CI [-0.55, 1.17]) mm3 Al. There was a strong association (r = 0.83) between the actual and estimated aluminium volumes. It is concluded that this system provides adequate precision for clinical evaluation.

Digital image ratio: a new radiographic method for quantifying changes in alveolar bone. Part II: Clinical application

As reported in a previous paper (1) we have developed a new technique, Digital Image Ratio (DIR), which theoretically avoids some of the drawbacks of quantitative digital substraction radiography. DIR allows the direct computation and visualization of bone-mass-ratio changes. This second paper describes the use of DIR analysis to examine 20 sites in 8 patients undergoing regenerative periodontal therapy. Standardized reproducible radiographs of these 20 sites were taken before and 12 months after surgery. Ten experimental sites were treated with bone graft substitutes (natural coral or natural coral+collagen), and 10 control sites by debridement alone. None of the experimental sites had a density ratio below 1, where 1 indicates no change. The error was +/- 0.07 (0.93-1.07). The experimental sites showed an 18% mean increase in bone density (1.18), which increased to 23% (1.23) for sites filled with natural coral alone. All the control sites had values close to 1.00 (1.00 +/- 0.07) except for 3 sites, which showed a 9-15% loss of bone density. It is thus possible to compare and quantify the changes in experimental and control sites in the same patient using the percentage gain or loss of bone density. This demonstrates that DIR is suitable for clinical applications, and can be used in clinical analysis when bone changes are expected.

Histogram-matching and histogram-flattening contrast correction methods: a comparison

OBJECTIVES

To compare the results or two methods of histogram matching and two methods of histogram flattening for their ability to correct for contrast variations in digital dental images.

METHODS

A custom-built, aluminium stepwedge with 0.1, 0.5 and 1.0 mm steps was placed over Ektaspeed films and exposed for 0.06, 0.12 and 0.25 s, respectively. Radiographs were digitized at 50 microns spatial resolution and 12-bit contrast resolution. Contrast corrections were performed using Rüttimann et al.'s algorithm (1986) for one method of matching (RM) and flattening (RF) and Castleman's algorithm (1979) for the other method of matching (CM) and flattening (CF). Mean pixel grey-scale values were determined for each step. The 0.12 s exposure was considered to be the target image exposure. Absolute differences in pixel grey-scale values between the target images and the modified images were determined.

RESULTS

The median values of the absolute differences in pixel grey-scale values between the target images and the contrast corrected images were: CM = 4.3; RM = 4.1; CF = 70.2 and RF = 70.2.

CONCLUSION

Castleman's and Rüttimann's matching algorithms perform equally well in correcting digital image contrast. Histogram flattening was less effective.

Accuracy in detecting bone lesions in vitro with conventional and subtracted direct digital imaging

OBJECTIVE

To implement direct digital imaging (DDI) in subtraction radiography and compare the accuracy of conventional and subtracted DD images in detecting small bone lesions in vitro.

METHODS

Alveolar bone defects were produced in a section of a pig mandible, with slow-speed burs 0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.4 mm in diameter. Standardized DD images were subtracted and displayed in black and white, contrast-enhanced and pseudo-colour transformed formats. 370 pairs of slides taken directly from the computer monitor were evaluated by eight observers.

RESULTS

The area P(A) under the ROC curve with DDI was 0.67 +/- 0.1. This was significantly lower (p < 0.001) than any of the three modes of subtraction radiography (mean P(A) = 0.88 +/- 0.09). The detection of small lesions (bur diameter 0.6 mm) was significantly better (p < 0.001) with contrast enhancement. Observer agreement was smaller for DDI (chi = 0.22 +/- 0.09) compared with the subtraction images (mean chi 0.64 +/- 0.13) (p < 0.001).

CONCLUSION

The diagnostic characteristics of the DDI system were significantly improved by digital subtraction with image processing.

Successful bone fill in late peri-implant defects using guided tissue regeneration. A short communication

Severe loss of peri-implant supporting bone traditionally leads to the removal of the affected implant, but this may not be necessary in all cases. This paper presents a novel treatment approach aimed at the successful regeneration of bone lost to peri-implantitis using guided tissue regeneration (GTR). Four years after implant placement two patients presented with severe peri-implant tissue breakdown. Clinical signs of disease included bleeding on probing, suppuration, increased probeable pocket depth (4 to 9 mm) and a decreased level of clinical attachment (2 to 10 mm). Radiographic analysis revealed 2.6 to 7.1 mm loss of supporting bone. Treatment of these lesions included raising flaps, wound debridement, and rinsing with sterile saline and 0.2% chlorhexidine digluconate. Subsequently, ePTFE membranes were adapted around the necks of the implants and the flaps sutured around the necks of the implants, allowing for transmucosal healing. Both patients were placed on a 10-day antibiotic regimen and instructed to rinse twice daily with a 0.12% chlorhexidine solution. They were reevaluated every 3 weeks at which time professional plaque control was performed. After 4 1/2 and 6 1/2 months, respectively, the membranes required removal due to infection. The radiographic analysis 1 year after membrane removal revealed 1.5 to 3.6 mm of bone gain. As a result of regenerative therapy the implants in both these patients were successfully maintained. It can be concluded that implants with severe loss of bone resulting from peri-implantitis need not always be extracted. A potential approach for the treatment of peri-implant bone destruction is GTR therapy using strict attention to good antimicrobial therapy.