Long-term stability of jaw bone tuberosities formed by "guided tissue regeneration"

The aim of the present study was to evaluate whether bone tuberosities produced by GTR on the lateral surface of the mandibular ramus in rats are stable on a long-term basis. Thirty male 6-month-old albino rats of the Wistar strain were used in the study. Tissue flaps were elevated on the lateral aspect of the mandibular ramus. The periosteum was preserved (P+) on one side of the jaw while the bone was denuded (P-) on the other. A rigid, non-porous oval-shaped teflon capsule was placed on both sides with its opening facing the ramus. Six months following surgery, 10 rats were sacrificed and prepared for histology while the remaining 20 rats were subjected to a second operation during which the capsules were removed. Standardized radiographs, taken immediately before and after removal of the capsule and after 3, 6, 9 and 12 months, were subjected to planimetric measurements and subtraction radiography. Ten animals were sacrificed and prepared for histological analysis after 6 months following removal of the capsules and the remaining 10 animals after 12 months. Histology revealed that at 6 months after the placement of the capsules, 17 were completely filled with new bone. The remaining 3 capsules which were displaced exhibited only partial bone fill. The radiographic analysis revealed that after 6 months 98.6 +/- 7.6% (mean +/- SD) in average of the cross-sectional area created by the capsules was filled with new bone. Within 3 months after removal of the capsules a slight resorption of the new bone had occurred, thereby reducing the area of the bone tuberosities by 4 to 8%. No further resorption of the bone tuberosities took place from 3 to 12 months. These observations indicating that new bone produced by GTR is stable on a long-term basis, may question the general belief that non-functional bone will resorb over time.

Dot probe performance in two specific phobias

OBJECTIVES

The present study applied MacLeod, Mathews & Tata's (1986) dot probe attentional deployment methodology to individuals with specific phobias.

DESIGN

Attentional deployment towards spider-related, blood-related, positive, negative, and neutral words was examined.

METHOD

Individuals with either spider phobia (N = 13) or blood/injury phobia (N = 14) and non-anxious controls (N = 14) completed the dot probe attentional deployment task.

RESULTS

Individuals with specific phobias did not demonstrate an attentional bias towards phobia-related stimuli relevant to their particular fears.

CONCLUSION

Semantic-based information processing paradigms may not be sufficiently potent to demonstrate biased performance towards threatening stimuli in individuals with mild specific phobias who are otherwise healthy.

Behaviour of approximal carious lesions assessed by clinical examination after tooth separation and radiography: a 2.5-year longitudinal study in young adults

This study aimed to record and monitor over a 2.5-year period the occurrence of cavitation and lesion depth progression in approximal surfaces with radiographic caries at baseline. In total, 66 approximal sites (in 29 students), where at least one of the contacting surfaces had radiographic caries, were selected to take part in the study. A clinical examination undertaken before and after tooth separation in order to assess the presence/absence of cavitation was repeated every sixth month. To monitor lesion progression bite-wing radiographs were taken every sixth month, too. After each series of examinations, surfaces judged to be prone for disease progression were referred to operative caries treatment. In surfaces with radiographic dentinal caries at baseline the cavitation prevalence following tooth separation found at the various recall examinations ranged from 20 to 44%. In surfaces with radiographic enamel caries at baseline this prevalence ranged from 4 to 8% at the various recall examinations. In dentinal lesions found with an intact surface at baseline, the risk of cavitation development during the first 1.5-year period was assessed to be up to 22%. After this period no new cavitations were found in previously intact dentinal lesions. In intact enamel lesions the risk of cavitation formation was found to be 3% during the first 1-year period. After this period no new cavitations developed in previously intact enamel lesions. Three of 7 lesions, which showed radiographic caries progression from the outer one third to the inner two thirds of the dentine during the observation period, had intact surfaces at baseline. On the basis of these results it is recommended to re-examine carefully intact, dentinal lesions by repeated clinical examination after tooth separation and by radiography about 1-1.5 years after baseline.

A two-film versus a four-film bite-wing examination for caries diagnosis in adults

The aim of this study was to compare the caries diagnostic outcome of a two-film and a four-film routine bite-wing examination undertaken in an adult population. A digital bite-wing examination using two and four films, respectively, was performed in 174 patients. The radiographs from the two examinations were assessed jointly by 2 observers for the number of imaged surfaces in the area from the distal surface of the canine to the distal surface of the third molar and for the detection of carious lesions. Significantly more surfaces were available for examination by the four-film than by the two-film examination. Overlapping surfaces were recorded in 14 and 10%, respectively, of the surfaces imaged by the two-film and four-film set. The prevalence of primary enamel and dentinal caries was 6.8% with the two-film and 5.6% with the four-film method. In 1, 684 surfaces only imaged by the four-film method caries was detected in 20 surfaces. If these extra lesions were added to the number of lesions found by the two-film method the total disease prevalence using the last-mentioned method would increase by 2 per thousand. The majority (92-99%) of all recorded lesions were detected in surfaces located between the occlusal surface of the first premolar and the mesial surface of the third molar. The little additional diagnostic outcome obtained by the use of four instead of two films did not seem to match the extra resources (double patient charge and radiation dose, and extended scan/developing and recording time for the dentist) connected to the four-film method. Thus, it may be recommended that a routine bite-wing examination undertaken in young adults should be performed with only two films: one in each side of the mouth, placed behind the premolars and the first and second molars.

Differential DNA binding activities of the transcription factors AP-1 and Oct-1 during light-induced apoptosis of photoreceptors

The activity of transcription factors like AP-1 and Oct-1 is critical for the regulation of gene expression. Whereas Oct-1 mainly regulates the expression of housekeeping genes, AP-1 is often involved in cellular responses to external stimuli and plays an essential role in the regulation of light-induced apoptosis of mouse retinal photoreceptors. In this study, we investigated AP-1 and Oct-1 DNA binding activity and AP-1 complex composition in the mouse retina during light-induced photoreceptor apoptosis. AP-1 DNA binding activity was low in dark-adapted animals but was transiently elevated within 12 h after exposure of mice to apoptosis-inducing levels of white fluorescent light. Maximal AP-1 activity was found 6 h after light-exposure. Antibody interference analysis at 6 h after damaging light exposure and under normal light conditions revealed that the major fraction of AP-1 consists of c-Fos/JunD heterodimers in both situations. In contrast to AP-1, Oct-1 DNA binding activity was maximal in dark-adapted animals and was reduced during photoreceptor apoptosis. Transient induction of AP-1 (c-Fos/JunD) and inactivation of Oct-1 may be crucial events for light-mediated apoptosis of retinal photoreceptors.

Comparison of microscopy and radiography as gold standards in radiographic caries diagnosis

OBJECTIVES

To compare the effect of the choice of gold standard on the diagnostic outcome of approximal caries detection in original and compressed digital radiographs.

METHODS

116 extracted teeth radiographed with a storage phosphor system constituted the original images. These images were compressed at 1:20 and 1:33 with the JPEG irreversible compression standard. Five radiologists scored the three sets of images for the presence of approximal caries on a five-rank confidence scale. The radiographic scores were validated by stereomicroscopy (the true gold standard). The individual ROC areas for the five observers were used to select the worst (obsworst) and the best (obsbest) performer: Their scores in the original images were used as the second and third 'gold standards' for the remaining observers. Mean ROC areas for the three observers with the three types of images were calculated using these two new 'gold standards'. Differences between the ROC areas when using microscopy, obsworst, and obsbest as the 'gold standard' were compared.

RESULTS

The mean ROC areas in the original images were 0.66, 0.74 and 0.91 using the true gold standard and obsbest and obsworst as the 'gold standards' respectively. The difference between the true gold standard and obsworst was statistically significant (P < 0.001). The mean ROC areas using the true gold standard decreased with increasing compression whereas they were constant or increased using obsworst and obsbest as 'gold standards', respectively.

CONCLUSIONS

Accuracy in approximal caries diagnosis was significantly higher when an observer was the 'gold standard' than when the true gold standard was obtained by microscopy. Paradoxically, the compressed, degraded images were more accurate than the originals when an observer was the 'gold standard' while they were less accurate with the true gold standard. Thus, results obtained using observers' scores from the radiographs which are being evaluated, as validation for the presence of caries may mislead the clinician.

Patient discomfort and cross-infection control in bitewing examination with a storage phosphor plate and a CCD-based sensor

OBJECTIVES

The aim was to compare a CCD-based sensor and a storage phosphor plate with respect to patient discomfort and the efficacy of a simple cross-infection control procedure in connection with a posterior bitewing examination.

METHODS

130 patients accepted to have one posterior bitewing of the left and right side taken with two digital radiography systems, the Digora phosphor plate and the Trophy RVG XL, CCD-based sensor system. The patients assessed their feeling of discomfort after the examination on a 100-mm. Visual Analogue Scale (VAS). Microbiological samples were taken from the RVG sensor and cord and from the Digora envelope, plate and scanner during examination of 14 patients. The samples were plated and incubated anaerobically, and the colony-forming units counted.

RESULTS

Median VAS score for discomfort was 20 min for Digora and 32 min for the RVG sensor (P < 0.001). Median total counts of cultivable bacteria were low (< 20), the majority being catalase-positive, Gram-positive cocci and Gram-positive rods, presumably skin bacteria. Only the samples taken from the enveloped Digora plate and the rubber tube coated RVG sensor immediately after exposure yielded large numbers of oral bacteria.

CONCLUSION

The phosphor plate was less unpleasant than the CCD sensor. Cross-contamination posed a minor problem for both systems when a simple, standard hygiene procedure was followed.

Dental students' ability for three-dimensional perception of two-dimensional images using natural stereopsis: its impact on radiographic localization

OBJECTIVES

To investigate the ability of dental students to perceive 2D images in 3D using natural stereopsis and to evaluate whether the use of stereovision influences their interpretation of radiographic depth, with particular reference to intra-oral radiographs of third molars compared with scanograms.

METHODS

Seventy-two dental students (37 from sixth semester and 35 from fourth semester) who had all completed a course in the use of the buccal-object rule participated in the study. Lectures in 3D perception were given to the sixth semester students. They were trained in 3D perception using a 'single image colour field' stereogram and classical stereograms of circles. Both semester students diagnosed nine scanograms and nine intra-oral radiographs for: (1) the position of the crown of an impacted third molar in relation to the second molar and (2) root deviations in the bucco-lingual plane. The sixth semester students recorded whether they were able to achieve a 3D image in these cases.

RESULTS

Five students could not achieve a depth image from the training stereograms. Fifty-six per cent agreed on which two objects in the circles were nearest to the viewer and which were most distant, whereas 38% agreed on the opposite. Root deviation was a more difficult diagnostic task than crown position, and the sixth semester students made significantly more correct diagnoses than the fourth semester students (P < 0.001). Irrespective of semester, there was no significant difference between number of correct diagnoses of crown alignment in intra-oral radiographs and scanograms (P = 0.57), whereas root deviations were diagnosed significantly more accurately from the intra-oral radiographs (P < 0.001).

CONCLUSIONS

Most dental students can be taught to use natural stereovision to achieve a 3D image from two radiographs at different angles. 3D image is achieved equally well from intra-oral radiographs with a free-hand tube shift and scanograms. Those students who achieved a 3D image in a particular case, made more correct diagnoses than those who could not.

Development of a system for craniofacial analysis from monitor-displayed digital images

OBJECTIVES

To develop a program for clinical craniofacial analysis directly on monitor-displayed digital images.

METHODS

The program was developed in VisualBasic (Microsoft, Redwood WA, USA), using Access (Microsoft) database, for landmark identification analysis and data storage. It runs on Windows95 (Microsoft).

RESULTS

The following established cephalometric analyses were included in the program: Bjork, Down, Frontal, Jarabak, Occlusogram, Rickett and Tweed. In addition, an orthodontist can simply define his own analyses. If he wants to identify a particular landmark, he clicks on its name at the top of the screen, and the definition including a drawing will be shown. If specified in the analysis selected, reference lines or templates are drawn using the identified landmarks. Soft tissues can be drawn either freehand or using the 'soft tissue detection' that generates an outline from the grey-level histogram. The program has been implemented at the Royal Dental College and at the Department of Maxillofacial Surgery and at the Cleft Palate Centre, Aarhus University Hospital.

CONCLUSION

A program (PorDiosW) has been developed which has facilitated cephalometric analysis from digital lateral and frontal skull radiographs and digital photographs. The program has been successfully applied in patients with cleft lip and palate and other developmental craniofacial anomalies before and after surgery.

Retinal degeneration in the rd mouse in the absence of c-fos

PURPOSE

Apoptosis is the final common death pathway of photoreceptors in light-induced retinal degeneration and in several animal models for retinal dystrophy. To date, little is known about gene regulation of apoptosis in the retina. The expression of the immediate early gene c-fos is upregulated concomitant with apoptosis in light-induced photoreceptor degeneration and in the rd mouse, an animal model for inherited retinal degeneration. In a recent study it was shown that c-Fos is essential for light-induced apoptosis of photoreceptors in vivo. To determine whether c-Fos is also involved in the apoptotic pathway of inherited retinal degeneration, rd/rd, c-fos -/- double-mutant mice have been generated.

METHODS

Double-mutant mice (rd/rd, c-fos -/-) were crossbred from c-fos+/- mice and rd/rd mice. Their genotype was determined by polymerase chain reaction analysis of genomic DNA. Wild-type control mice and homozygous rd mice were killed at 2-day intervals from postnatal day (P)9 through P21. Double-mutant mice were killed at postnatal days P9, P11, P13, P15, and P21. To determine levels of apoptosis in the retina, eyes were enucleated and processed for light microscopy and in situ nick-end labeling. Total retinal DNA was extracted from isolated retinas for DNA fragmentation analysis.

RESULTS

Morphologic, histochemical, and biochemical analyses showed that the time course of apoptosis and the outcome of photoreceptor degeneration in rd/rd, c-fos-/- double-mutant mice was indistinguishable from that in rd mice carrying functional c-fos.

CONCLUSIONS

These data suggest that in contrast to its role in light-induced photoreceptor degeneration, c-Fos is not essential for apoptosis in the rd mouse.

Apoptotic cell death in retinal degenerations

Apoptosis is a regulated mode of single cell death that involves gene expression in many instances and occurs under physiological and pathological conditions in a large variety of systems. We briefly summarize major features of apoptosis in general and describe the occurrence of apoptosis in the retina in different situations that comprise animal models of retinitis pigmentosa, light-induced lesions, histogenesis during development, and others. Apoptosis can be separated into several phases: the induction by a multitude of stimuli, the effector phase in which the apoptotic signal is transmitted to the cellular death machinery, the excecution period when proteolytic cascades are activated, and the phagocytic removal of cellular remnants. Control mechanisms for retinal apoptosis are only beginning to be clarified. Potential apoptotic signal transducers were investigated in our laboratory, including metabolites of arachidonic acid and downstream mediators of signaling molecules such as transcription factors. Work in our laboratory revealed an essential role of the immediate-early gene product c-Fos in light-induced apoptosis. c-Fos is a member of the AP-1 family of transcription factors and, together with other members of this family, it may regulate apoptosis in the central nervous system. Expression of the c-fos gene in the retina can be evoked by light exposure and follows a diurnal rhythm. Future studies will have to clarify how light can control the expression of specific genes, and specifically, the role of c-fos and other genes of retinal apoptosis including potential target genes and signaling pathways.

Evaluation of a new radiographic technique: outcome following removal of mandibular third molars

OBJECTIVE

To compare the effect on outcome of third molar removal of pre-operative radiographic assessment by two different techniques.

METHODS

Two hundred and sixty three patients were allocated prior to surgery to one of two diagnostic groups. One hundred and thirty-seven were examined by the Scanora and 126 by a panoramic plus three intra-oral radiographs. Ten oral surgeons recorded their operating time in minutes. Postoperative pain was recorded 4 h after the operation by the patients on a Visual Analog Scale (VAS). The following clinical parameters were recorded at the 1-week postoperative examination: alveolitis, bleeding, and swelling related to the operation area, and any other complications such as paresthesia, nausea and trismus.

RESULTS

There was no significant difference in operation time between the two groups of patients (t-test; P > 0.82) nor in the frequency of immediate postoperative pain (chi 2-test; P > 0.5). There were no statistically significant differences in pain score between patients who experienced pain in the two groups (P = 0.10). Sixty-four patients experienced one or more postoperative complications, but the differences between the two groups were not statistically significant (chi 2-test; P > 0.05). There were no significant differences between the surgeons in the number of patients they operated on who experienced pain (chi 2-test; P = 0.18) or who developed complications (chi 2-test; P = 0.27).

CONCLUSION

There are no adverse effects on the rate of postoperative complications when surgeons with little experience with it base their diagnosis and treatment plan on Scanora compared with conventional radiography.

Evaluation of a new radiographic technique: diagnostic accuracy for mandibular third molars

OBJECTIVE

To compare the accuracy of Scanora with that of traditional panoramic and intra-oral radiography for the assessment of impacted mandibular third molars.

METHODS

Two hundred and fifty-four patients referred for removal of impacted or partly erupted third molars were randomly allocated to one of two groups; 133 were examined by the Scanora system and 121 by a panoramic plus a series of three intra-oral radiographs. The radiographs were read by a trained oral radiologist and her diagnoses validated against the surgeons' findings at operation.

RESULTS

There was agreement about the state of tooth eruption in 71.4% of Scanora and 74.4% of conventional examinations and about tooth position in 77.2 and 69.7% respectively (P < 0.05). The number of roots was assessed more accurately by Scanora (82.7% agreement) than by conventional (71% agreement) examination (P < 0.05). There was agreement about the root morphology in 70.4% of Scanora and 62.4% of conventional examinations. In 12% of the patients, the roots were in very close contact with the canal determined by the surgeon. In approximately 50% of these cases, the close contact to the canal was found by radiography with no significant differences between the methods.

CONCLUSION

The Scanora method was more accurate when validated against the surgeons' findings for the position and number of roots of ectopic mandibular third molars while both methods were equally accurate in demonstrating the relation between the roots and the inferior alveolar nerve.

[HPETE, an arachidonic acid metabolite, induces apoptosis in rat retina in vitro]

BACKGROUND

Apoptosis is a gene-regulated mode of cell death which gains increasing importance in retinal pathologies such as retinitis pigmentosa, retinal detachment and proliferative vitreoretinopathy. A better understanding of the regulation of apoptosis could imply the means to reduce photoreceptor cell death and thereby provide therapeutic strategies to influence the time course of retinal diseases. Previous studies in our laboratory demonstrated that light induces apoptosis in the rat retina in vivo as a function of light dose. In several cell systems, oxidative stress including oxygenated metabolites of arachidonic acid (AA) was found to evoke apoptosis. We have observed a light-elicited release of AA and the subsequent formation of its metabolites in the rat retina. Therefore, AA and its metabolites appeared to be suitable candidates for the induction of apoptosis during light exposure.

MATERIALS AND METHODS

Isolated rat retinas were incubated for 60, 120 and 180 min, respectively, with and without the addition of 30 mumol 5S-hydroperoxyeicosatetraenoic acid (5-HPETE). Retinas were then processed for light- and electron microscopy and examined for the morphological signs of apoptosis. The rate of apoptosis in the outer nuclear layer was assessed quantitatively.

RESULTS

5S-HPETE induces apoptosis of photoreceptors in the rat retina in vitro. Quantitative analysis revealed a significant increase in the rate of apoptosis of 5S-HPETE-treated retinas when compared to untreated controls.

CONCLUSION

Arachidonic acid metabolites released upon light exposure may represent messenger candidates for apoptosis in the retina.

In vitro analysis of the accuracy of subtraction radiography and computed tomography scanning for determination of bone graft volume

PURPOSE

This study evaluated the accuracy of digital subtraction radiography (DSR) and three-dimensional computed tomography (3D CT) for determination of bone graft volume in the maxillofacial region.

MATERIALS AND METHODS

Standardized bone defects were made on the top of the alveolar ridge in 10 dry pig mandibles. To resemble the clinical situation, a bone block was harvested from the symphyseal region of the mandible and fixed in the defect. True bone graft volume was determined by the water displacement technique (VOL I) and correlated to direct measurements by calipers (VOL II). The mean gray value of the bone graft as imaged by DSR was correlated to the directly measured thickness. Furthermore, VOL I was correlated to the 3D CT of the bone graft (VOL III) and to the 3D CT with the bone graft fixed in the defect (VOL IV).

RESULTS

There was a strong correlation between VOL I and VOL II (r = .95), whereas there was a poorer correlation between mean gray level in DSR and measured bone thickness (r = .63). A strong correlation was also registered between VOL I and VOL III (r = .97) and VOL I and VOL IV (r = .97).

Reproducibility of cephalometric landmarks on conventional film, hardcopy, and monitor-displayed images obtained by the storage phosphor technique

The aim of the present study was to evaluate and compare the reproducibility of cephalometric landmarks on (1) conventional films, and images acquired by storage phosphor digital radiography both on (2) hardcopy and (3) monitor-displayed versions. The material consisted of 19 cephalograms for each image modality. The phosphor plates were scanned in an image reader and the 10-bit normalized, raw data digital images were converted to 8-bit TIFF images for PC monitor-display. The digital hardcopies were produced in a laser printer. Six observers were asked to record 21 cephalometric landmarks on each conventional film, hardcopy, and monitor-displayed image. For the films and hardcopies, the landmark co-ordinates were recorded via a digitizing tablet. For the monitor-displayed images, the co-ordinates were recorded directly from the monitor using a dedicated Windows-based cephalometric program. Reproducibility was defined as an observer's deviation (in mm) from the mean between all observers. Differences between the image modalities and between the observers were tested by two-way analysis of variance for each landmark. There was a statistically significant difference between the reproducibility of film, hardcopy and monitor-displayed images in 11 of the 21 landmarks. There was no unequivocal trend that one modality was always the best. For a full cephalometric recording (the sum of all 21 landmarks), the monitor-displayed images (mean = 25.3 mm) had a lower precision than film (P < 0.005) and hard-copy (P < 0.02). There was no significant difference between film (mean = 21.8 mm) and hardcopy (mean = 22.8 mm). The lower reproducibility seen for the monitor-displayed images is most probably of little clinical significance.

GTR therapy of intrabony defects using 2 different bioresorbable membranes: 12-month results

This prospective split-mouth study was designed to compare the clinical and radiographic healing results in intrabony periodontal defects 12 months after GTR therapy with 2 different bioresorbable barriers. The study comprised 25 healthy patients with one pair of contralaterally located intrabony defects with a probing pocket depth of > or = 6 mm and radiographic evidence of angular bone loss of > or = 4 mm. The 2 defects of each patient were randomized for treatment either with polylactic acid (PLA) membranes or with polyglactin-910 (PG-910) membranes. The patients received systemic doxycycline (100 mg/d) for 11 days postoperatively. One blinded examiner recorded the following clinical parameters using a pressure calibrated probe at baseline and after 12 months: papillary bleeding index (PBI), gingival recession (REC), probing pocket depth (PPD), and probing attachment level (PAL). The vertical relative attachment gain (V-rAG) was calculated as a % of the PAL gain related to the maximum possible attachment gain (expressed by the intraoperatively measured depth of the osseous defect). Geometrically standardized intraoral radiographs were quantitatively evaluated for bone changes (density, area) in the defect region using digital subtraction radiography (DSR). Clinical and radiographic data were statistically analyzed using the Wilcoxon-signed-rank test (alpha=0.05). Postoperative membrane exposures occurred in 9 PLA and 13 PG-910 treated sites. After 12 months of healing, both barrier types provided significant PPD reductions and PAL gain [median (25/75 percentile)]: deltaPPD [PLA: 3.0 (2.0/4.0) mm; PG-910: 3.0 (2.0/4.5) mm]; deltaPAL [PLA: 3.0 (2.5/4.0) mm; PG-910: 2.0 (1.0/4.0) mm]. V-rAG amounted to 60% in PLA sites and 54% in PG-910 sites. DSR revealed significant bone density gain after 12 months. 58.3% of the initial defect area in PLA sites and 54.0% of the initial defect area in PG-910 sites showed bone density gain. Neither clinical nor radiographic data revealed any significant difference between the 2 barrier types after 12 months. In conclusion, this 12-month study demonstrated that PLA and PG-910 membranes provided similar favorable regeneration results in deep intrabony periodontal defects.

Discrimination between restorative dental materials by their radiopacity measured in film radiographs and digital images

The aim of this study was to investigate the possibility of differentiating between various dental restorative materials by means of their radiopacity. Ten extracted molars and ten canines/anterior teeth were selected for the study. In the molar group a class II cavity and in the canines/anterior teeth group a class III cavity were cut by airrotor. The cavities were coated with vaseline before filling with five molar- and three anterior tooth restorative materials in the following sequence: for molars: amalgam, light-cured composite, glass ionomer cement, reinforced glass ionomer cement and light-cured composite. After each filling sequence radiographs were taken of the teeth on conventional film (Ektaspeed Plus) and by two digital systems: a storage phosphor plate (Digora) and a ccd-based sensor (Sidexis). Density was measured in the films with a densitometer in three areas of "air", in three areas of the class II fillings and one area of the class III fillings. The same areas were measured in the digital images where the program calculated automatically the mean grey shade values. The density values obtained from the filling areas were taken as a proportion of the values obtained from the areas of "air". Statistically significant differences in material density when related to "air" density (Wilcoxon's test) were observed between all materials in film (p < 0.01 for molars and p < 0.02 for canines/anterior teeth). For Digora only half of the materials differed significantly which was also the case for the Sidexis system (none of the CF materials were significantly different). In conclusion, the molar filling materials could be distinguished with a high probability in film while the two digital systems were less reliable. The results may be useful in forensic dentistry.

Light-induced cell death of retinal photoreceptors in the absence of p53

PURPOSE

Cell death by apoptosis is essential for normal development and tissue homeostasis, and it is involved also in a variety of pathologic processes. Apoptosis is the final common pathway of photoreceptor cell death in retinal dystrophies and degeneration. So far, little is known about genes regulating apoptosis in the retina. The tumor-suppressor gene product p53 is a potent regulator of apoptosis in numerous systems. However, p53-independent apoptotic pathways also have been described. In this study the authors investigated the role of p53 in the light-induced apoptosis of retinal photoreceptors using mice lacking p53.

METHODS

Free-moving p53-/- and p53+/+ mice were dark adapted and were exposed to 8,500 or 15,000 lux of diffuse, cool, white fluorescent light for 2 hours. Animals were killed before and immediately after light exposure or at 12 hours in darkness after light exposure. Eyes were enucleated and processed for light and electron microscopy and histochemistry (TdT-dUTP terminal nick-end labeling method). Isolated retinas were subjected to the extraction of total retinal DNA. Electroretinogram (ERG) recordings were performed at all time points.

RESULTS

Morphologic, biochemical, histochemical, and ERG analysis showed that the retinas of untreated p53-/- mice and wild-type control mice were structurally and functionally indistinguishable. After exposure to diffuse white fluorescent light, light-induced photoreceptor cell death was analyzed and was found to be the same in both groups of mice.

CONCLUSIONS

These data suggest that light-induced apoptosis of photoreceptors is independent of functional p53.