digital radiograph or radiovisiography was first described in 1987 and was commercially introduced by trophy radiologie in collaboration with mouyen12 in 1993 .
three systems are employed for radiovisiography : the ccd sensor ( charge - coupled device ) , cmos sensor ( complementary metallic oxide sensor ) , and psps ( psps  phosphor storage plate  optical plate ) ; the latter includes the digora , digident , denoptix and den ortix systems11 .
however , some doubts remain in the use of radiovisiography based on the optical plate system as to the durability of the plate3 , image quality according to the processing delay1,2,14 , and storage conditions10 .
no study has yet investigated the influence of utilization of opaque cases on the quality of digital image .
this ex vivo study evaluated the quality of digital radiographic images obtained with the digora system according to the processing delay and maintenance of optical plates in either opaque ( supplied with the system ) or transparent protective plastic cases during this period .
the study was conducted on a dry human mandible fixed on an acrylic resin base .
a plastic tube was fixed frontally to the mandible to standardize the position of the x - ray source , thus standardizing the vertical and horizontal angles ( figure 1 ) .
a groove was prepared on this resin base to standardize the position of the optical plate .
radiographs were obtained from the mandibular molar region by utilization of optical plates with an x - ray unit ( gnatus model xr 6010 ; gnatus , ribeiro preto , sp , brazil ) set at 60 kvp and 10 ma , with open tube , total filtration of 1.5 mm al , exposure time of 0.3 s , and optical plate of the digora system ( soredex , orion corporation , finland ) .
two groups were constituted for x - ray exposure : in group a , the optical plate was inserted and sealed in the opaque plastic case supplied by the manufacturer and kept as such until processing ; in group b , the optical plate was stored in a transparent plastic case ( figure 2 ) .
the optical plates were processed in the digora scanner immediately and 5 , 60 and 120 min after x - ray exposure , and were transferred to the computer for analysis of digitized images .
analysis was performed directly on the computer screen by three examiners using the digora for windows software .
the images were analyzed as to brightness , contrast and resolution of tooth structures ( enamel , dentin , root and pulp cavity ) and periapical structures ( periodontal space , cortical bone , alveolar bone ) , which received scores 0 to 2 , as follows : 0- poor image quality ; 1- good image quality ; 2- excellent image quality .
data were submitted to the kruskal - wallis non - parametric test , and comparison of results between opaque and transparent cases were submitted by the mann - whitney test .

 table 1 presents the scores assigned by examiners to the images , according to processing delays and utilization of opaque or transparent plastic cases .
there was statistically significant difference ( p<0.05 ) regarding the processing delays , namely immediate , 5 and 60 min with utilization of opaque case ( table 2 ) .
this difference was observed between the 120-min delay and the other periods ( table 3 ) .
no statistically significant difference ( p>0.05 ) was observed among processing delays with utilization of transparent case ( table 4 ) .
comparison of results between opaque and transparent cases did not reveal significant differences ( p>0.05 ) ( table 5 ) .
10.05882 ; chi - square with 3 degrees of freedom ; probability = 0.018072 ( significant ) u=5.00000000;exact probability = 0.150794 ; normal approximation : z=1.96396101 ; probability = 0.04953461 hc= 5.164999 ; chi - square with 3 degrees of freedom ; probability = 0 .
digital radiography was introduced to dental practice with a view to replace the conventional radiography due to the shorter exposure to radiation , achievement of high - quality images , possibility of adjustments with aid of software , and comparable reliability to conventional radiography , for both endodontic diagnosis and treatment3,57 , 
  the main disadvantage of the optical plate system is the need of additional time for processing and possible loss of quality when the sensitized optical plate is exposed to light . some authors have emphasized that , after exposure to x - ray , the optical plates should be processed within 1 h in order to avoid loss of image quality1,2 .
other authors believe that the plates can be processed within 6 h if stored in appropriate cases10 . in the present study , a processing delay of 120 min caused a mild reduction in image quality , yet without compromising the quality of diagnosis ( table 1 ) .
it should be highlighted that the images were not altered as to the brightness and contrast provided by the system , being analyzed as produced on the computer screen .
together with the digora system , the manufacturer supplies opaque plastic cases that offer protection against contamination and the deleterious effect of light . images of optical plates maintained in the original opaque cases after exposure to x - ray maintained their image quality up to 120 min ( table 2 ) , with significant difference between the 120- min processing delay and the other periods ( table 3 ) .
when the optical plates were maintained in transparent cases , there was also a progressive reduction of image quality ( table 1 ) , which was more accentuated at 120 min ( table 4 ) , though without statistical difference among periods .
this is due to the fact that the optical plate protected with transparent cases is subjected to the continuous action of light , with progressive loss of image quality .
however , images obtained with optical plates protected with both opaque and transparent cases and with processing delays of up to 120 min provided good quality for diagnosis .
the findings of the present study revealed that the processing delay of 120 min for the digora system caused a reduction in image quality , yet without interfering with the quality of diagnosis .
the opaque case supplied by the system 's manufacturer provided better protection to the optical plate than the transparent case .
 this ex vivo study evaluated the quality of digital radiographic images obtained with the photostimulable phosphor plate system ( digora ) according to the processing delay and maintenance of optical plates in either opaque ( supplied with the system ) or transparent protective plastic cases during this period . 
 five radiographs were obtained from the mandibular molar region of a dry human mandible using optical plates . 
 these plates were placed in the protective plastic cases before obtaining the radiographs and were processed immediately or after processing delays of 5 , 60 and 120 min , when the case was removed . 
 the results revealed a reduction in image quality when processing was delay 120 min compared to the other times . 
 the opaque case provided better protection to the sensor than the transparent case . in conclusion , 
 a 120-min processing delay for the digora system caused a reduction in image quality , yet without interfering with the quality of diagnosis . 
 the opaque case supplied by the system 's manufacturer provided better protection to the optical plate than the transparent case . 