OOOOEVolume 107, Number 4 Abstracts e31

proportional to the radiation dose. TLD measurements were alsoused for comparison.

Results: The Tru-Align™ instrument reduced the skin-sur-face area dose by a factor of almost 5 when compared with roundcollimation. These measurements indicate a reduction of radia-tion exposure at the periphery of the circular collimation areafrom 0.0708 mGy (with round collimation) to 0.0026 mGy (withTru-Align).

The Tru-Align instrument was easy to use. However, incertain instances, the perimeter of the rectangular collimator wasnot large enough to completely cover the sensor, and this resultedin unexposed areas at the sensor periphery (i.e., cone-cuts). Themeasurements obtained indicate that OSL dosimeters have a 5 to20% higher sensitivity when compared with TLD’s.

Conclusions: The Tru-Align™ reduced radiation exposure atthe points studied by a factor of almost 5, gave perfect alignment,and was easy to use; however, it did not allow complete coverageof the usable area of the sensor. The InLight dot dosimeters hada high level of sensitivity, a wide range of measuring capabilitiesin the low dose range, and a fast and relatively simple readout ofsamples.

TOMOGRAPHIC, RADIOGRAPHIC AND MICRO-SCOPIC EVALUATION OF PERIAPICAL REPAIR AFTERROOT CANAL TREATMENT Silva FWGP1, Leonardo MR1,Wu MK2, Silva LAB1, 1Department of Pediatric Clinics, Pre-ventive and Social Dentistry, University of Sao Paulo, Brazil;2ACTA - Vrije Universiteit, Amsterdam, Netherlands

Background: Computed tomography (CT) scans are cur-rently used to detect periapical lesions; however, direct compar-ison of periapical disease repair evaluated by periapical radio-graphs or CT scans with microscopic evaluation has not beenperformed.

Objectives: The aim of this study was to use CT scans andperiapical radiographs to evaluate periapical disease repair afterroot-canal treatment in dogs’ teeth and compare both techniqueswith the gold standard microscopic evaluation.

Methods and Materials: The animals were divided accordingto the endodontic treatment performed into 3 groups: Group 1(single visit) - endodontic treatment in teeth without chronicperiapical disease (CPD) (n�12), Group 2- (single visit)- end-odontic treatment in teeth with CPD (n�12) and Group 3-endodontic treatment in teeth with CPD using calcium hydroxideas a root canal dressing (n�12). The Group 4 (control) consistedof teeth with CPD without treatment (n�12). The measurementof the lesions before and after the root canal treatment wereperformed to calculate the percent rate reduction of the CPD.Radiographic, tomographic and microscopic evaluations wereperformed by blind examiners using NIH ImageJ software.

Results: 45 days after CPD induction there was discontinuityof the lamina dura and CPD in all teeth from groups 2, 3, and 4evaluated by tomography and radiography. Radiographically,180 days after root canal treatment, there was no periapical lesionin 25% of teeth from group 3 and all teeth from group 1, withthese groups being significantly different from groups 2 and 4(p�0.01). The highest reduction in the CPD size was observedfor group 3 (p�0.05). According to the tomographic results, therewas reduced size of the CPD in groups 2 and 3, also with thehigher decrease in group 3. However, in all groups the periapicallesions presented larger mesio-distal extension compared with

radiography, both 45 days after CPD induction and 180 days after

root canal treatment. One hundred eighty days after root canaltreatment, CPD areas measured using CT scans were similar tothose obtained with microscopic evalution (p�0.05) but largerthan those obtained using conventional periapical radiographs.

Conclusion: CT scans and microscopic measurements ofremanescent periapical disease after root canal treatment pre-sented similar values but were larger in mesio-distal extensioncompared with conventional periapical radiographs.

CHARACTERIZATION OF THE MICROSTAR DOT OSLDOSIMETERS FOR MAXILLOFACIAL DOSIMETRYSTUDIES Valiyaparambil JV, Mallya SM, Section of Oraland Maxillofacial Radiology, University of ConnecticutSchool of Dental Medicine, Farmington CT

Introduction: Thermo-luminescent dosimeters (TLD) are themost widely used point dosimetry systems in the medical anddental field for personnel dosimetry, dose assessment and radio-biological studies. TLDs are small in size volume, can be usedover a wide dose range, are resilient to environmental changesand are reusable. However, their use requires costly equipmentand the processes for annealing, readout and calibration whichare cumbersome. Optically stimulated luminescent dosimeters(OSLD) have been in use for personnel dosimetry for more thana decade. Recently, OSL dosimeters (MicroStar dot dosimeters,Landauer Inc.) have been introduced for point dose measure-ments. OSL dots overcome many of the limitations of TLDchips—they do not require an annealing process, provide quickreadouts, are reusable immediately and are sensitive to radiationover a broad dose range. Moreover, they are environmentallystable and have a unique identification number to allow forefficient and accurate tracking of dose.

Objectives: This study examined the basic characteristics ofOSL dots in point dosimetry. We determined the linear doseresponse and angular dependence of OSL dots to low ionizingradiation from a dental x-ray unit.

Materials and Methods: MicroStar dosimeters were exposedto an x-ray beam (70kVp, 7mA) and the relationship between themeasured dose and radiation exposure times was determined. Todetermine the angular dependence, the angle of the incident x-raybeam was varied from 0°, 45°, 90°, 135° angles. The absorbeddoses were determined using the MicroStar reader.

Results: The MicroStar Dot OSL dosimeter was remarkablylinear in its response to x-ray dose delivered (0.26 to 1.15 mGy).A change of 45°, 90° and 135° in angle of the incident beamresulted in variations of 4%, 15% and 7% in the measured dose,respectively.

Discussion: The MicroStar dot OSL dosimeter is a relativelynew dosimetry system that has been introduced for point dosim-etry. These dosimeters are linear in the range of radiation expo-sures from dental radiographic examinations. The convenience ofhandling, reproducible readouts of absorbed doses and immediatereusability make OSL dosimeters an economical alternative toTLD in maxillofacial dosimetry studies.

EFFICACY OF RECTANGULAR COLLIMATORS FOR IN-TRAORAL RADIOGRAPHY Zhang W1, Abramovitch K1,Thames W1, Leon I-L1, Colosi DC2, Goren AD2, 1RadiologySection, Department of Diagnostic Sciences, Univ. of TexasDental Branch at Houston, Houston, TX., 2Department ofGeneral Dentistry, School of Dental Medicine, SUNY Stony

Brook, NY

OOOOEe32 Abstracts April 2009

Background: Rectangular collimation for intraoral radiogra-phy significantly reduces patient exposure to ionizing radiationand is recommended by the American Dental Association (ADA)and the National Center for Radiation Protection (NCRP). Con-sequently, various types of rectangular collimation instrumentsare being devised, but the efficiency and accuracy of theseinstruments have not been evaluated.

Objectives: This study is designed to compare the operatingefficiency and technical accuracy of three different types ofrectangular collimation; Type I: “free-hand” alignment of thecollimator, Type II: mechanical interlocking alignment, Type III:magnetic alignment

Methods and Materials: For Type I collimation, a Rinn XCP(Dentsply, Elgin, IL) unit was used with a Planmeca Intra rect-angular collimator which is aligned with the Position IndicatingDevice (PID) of the X-ray unit. For the Type II collimation, aPlanmeca Intra rectangular collimator was modified to mechan-ically interlock and align to the aiming ring of a Rinn XCPinstrument. The Tru-Align instrument was used for the magneticType III collimation. Thirty-three sophomore dental and first yeardental hygiene students were recruited to test the collimators.IRB approval was obtained for their participation. An 18 expo-sure full mouth series (FMS) of radiographs excluding centralincisor views was taken on DXTTR phantoms. The series con-sisted of nine identical views per right or left side. Photostimu-lable phosphor (PSP) plates were used for image capture. Eigh-teen students exposed one side of the DXTTR with Type I“free-hand” collimation and the other side with Type II directinterlocking collimation. Fifteen students exposed one side withType I collimation and the other side with Type III magneticcollimation. The time taken to expose each half of the FMS was

measured. To determine the user friendliness of the collimation

types, a question survey using a 5-point rating scale was com-pleted by each student. Technique errors were measured by thenumber of views with placement errors, projection geometryerrors and cone cuts, and by the total surface area of cone cuts perhalf FMS. These errors were evaluated by experienced radiologictechnologists. The Student’s t-test or the signed rank test wasused to determine statistical difference between the differentcollimator types.

Results: Compared with Type I, Type II collimation signif-icantly shortened the time required to finish a 9 exposure halfFMS (31.03 min vs. 37.14 min, p�0.007) and it was judgedmuch easier to use (score 4.07 on 5 point scale, p�0.0001), butType II generated significantly more placement errors (3.76/9 vs.2.94/9, p�0.04) and more cone cut errors (1.29/9 vs 0.47/9,p�0.008), although total cone cut area per half FMS and projec-tion error were similar to Type I (p�0.42, and 0.65, respectively).Compared with Type I, Type III was judged easier to use (score4.27 on 5 point scale, p�0.0001), but Type III generated signif-icantly more cone cuts (5.4/9 vs 1.2/9, p�0.0002) and a muchlarger total cone cut area per half FMS (1088.83 mm2 vs. 50.25mm2, p�0.0001). The time taken to complete the half FMS, andthe placement and projection errors were comparable (P�0.10,0.52, and 0.65, respectively).

Discussion: This study demonstrated that Types II and IIIcollimations are more user-friendly. Type II collimation has ashorter operating time compared with Type I. Type II and IIIcollimation have increased cone cut errors. The heavier weight ofthe Type II collimator is likely to cause the placement error, andthe relatively small window of Type III may contribute to thecone cut error. Further optimization of the design of these instru-

ments is expected to improve their performance and utility.