Comparison of radiography and scintigraphy in the diagnosis of dental disorders in the horse

Scintigraphy, with (99m)Technetium methylenediphosphonate (Tc-99m-MDP) and Tc-99m-labelled leucocytes, was compared to radiography in the diagnosis of dental disease in the horse in a prospective case-controlled study, compri sing 30 horses with clinical signs of dental disease and 30 control horses. In each case, right and left lateral, ventral and dorsal soft tissue and b one phase scintigraphic images were obtained after i.v. injection of 1 GBq/ 100 kg bwt Tc-99m-MDP, using a gamma camera. The same views were acquired i n 10 horses with clinical signs of dental disease and 12 control horses aft er injection of Tc-99m-labelled leucocytes. Standard radiographic projectio ns of the paranasal sinuses and of the apices of the maxillary and mandibul ar teeth were obtained. The scintigraphs and radiographs were assessed subj ectively by 2 board-certified surgeons and one board-certified radiologist, with extensive experience of equine radiology, from who the clinical histo ry was withheld. Sensitivity, specificity and kappa, as a measure of agreem ent, were calculated for the different methods. Bone phase images were also scored subjectively on a scale from 0 to 3 on the basis of isotope uptake over the teeth. Regions of interest were defined over the teeth, and normal teeth compared to diseased counterparts. Total scintigraphic counts were r elated to the age of the animal and to the disease process. Differences in density ratios between left and right teeth were evaluated using the Mann-W hitney Test. Dental disease was confirmed in 22 horses at surgery or postmortem examinat ion. Horses with dental disease showed a significant increase in scintigrap hic activity over the affected tooth compared to the contralateral tooth, w ith a typical pattern for different diseases. The sensitivity of scintigrap hy with Tc-99m-MDP proved to be excellent (95.5%), whereas the specificity was moderate (86.4%), In contrast, radiography had excellent specificity (9 5.0%) and a low sensitivity (51.5%), The greatest sensitivity and specifici ty were achieved by evaluating radiographs and scintigrams together. The ob jective scintigraphic density ratios were found to be significantly differe nt between diseased and control horses. The results of this study suggest t hat, if a density ratio of 1.5 or greater between a suspected diseased toot h and its contralateral number is regarded as abnormal, only 1% false posit ive diagnoses and 20% false negative diagnoses will occur. In contrast, sci ntigraphy with Tc-99m-labelled leucocytes was not very successful, due to t he lack of anatomical detail provided by this technique, which made identif ication of the diseased tooth impossible. Accurate radiographic interpretat ion of dental disease presents difficulties, both in terms of missed diagno ses and mistaken diagnoses. Scintigraphy complements radiographic examinati on of dental structures by providing information important for accurate dia gnosis and is, therefore, conceived to be essential for selection of the ap propriate treatment for dental disease.