How to Utilize Advanced Imaging in the Management of Equine Dental Cases

1. Introduction

Equine dental cases are challenging. All cases require a complete and thorough oral examination that often leads to routine radiographic imaging in order to establish a diagnosis. In selective cases, more advanced diagnostic imaging such as nuclear scintigraphy (NM), computed tomography (CT), or magnetic resonance (MR) imaging enhance the clinician/surgeon’s ability to clearly define the problem and plan treatment. Sensitivity and specificity of radiography for dental disease ranges from 52 to 69% and 70 to 90%, respectively.^1,2  While radiographs are the most common and easily accessible imaging modality utilized in equine dentistry, accurate interpretation is difficult due to the complexity and summation of anatomic structures. Radiography is often the only imaging modality available and frequently yields an immediate diagnosis. On the contrary, further advanced imaging may be required in patients that are recalcitrant to medical therapy, require extensive surgical intervention, or have a disease that involves more than one tooth. As a general practitioner, it is important to understand the limitations of radiography to clearly diagnose equine dental disease. Advanced imaging may be employed to better characterize the extent and exact location of the abnormality, thus allowing a more effective treatment. 

2. Materials and Methods

Advanced Diagnostic Modalities

A complete physical and oral examination must be completed prior to performing any imaging in patients with suspected dental disease. A proper oral examination must include the use of a mouth speculum, a light source, and a dental mirror or oroscope on a properly restrained and sedated horse. It is nearly impossible to have an accurate diagnosis from an oral examination without the appropriate instrumentation. If dental-related disease is suspected, a complete series of skull radiographs is the next step in the course of confirming a diagnosis prior to advanced imaging.³

When deciding whether to perform advanced imaging in dental cases, it is important to realize that NM, CT, and MR do not guarantee a precise diagnosis. On the contrary, advanced imaging is acceptable to perform even on cases where a fairly confident diagnosis has been made through other modalities. Dental disease can be perplexing to diagnose and treat with the potential for complications. Performing invasive dental surgery without an accurate diagnosis and complete understanding of the pathological process can lead to long-term complications such as chronic oro-nasal, -sinus, and -cutaneous fistulas that are extremely difficult to resolve. It is the authors’ opinion that invasive surgical treatment of dental related disorders not be performed until there is confidence in the diagnosis. Advanced imaging can only strengthen a clinician’s confidence in a diagnosis, resulting in a well-constructed and precise treatment regime for the horse. While advanced imaging is significantly more expensive compared to other diagnostic tools, the financial cost of inaccurate diagnoses and/or treatment can oftentimes result in higher overall costs to the owner and morbidity to the horse.

Prior to referral for advanced diagnostic imaging, it is important to understand the differences between NM, CT, and MR and their advantages and disadvantages (Table 1).
 

3. Results

Nuclear Scintigraphy

Nuclear scintigraphy images reflect physiologic rather than anatomic structure and are highly sensitive to bone turnover.⁴ The sensitivity and specificity of scintigraphy has been reported at 95% and 86%, respectively.¹ When radiographs and scintigrams were concurrently evaluated, the sensitivity and specificity for detection of dental disorders increased to 97.7% and 100%, respectively.¹ One advantage to NM is the ability to perform imaging in the sedated standing horse. This is obviously better for the horse by avoiding general anesthesia. However, since NM does not provide multiplanar images, anatomical understanding is challenging and fails to improve the diagnosis of secondary disease such as sinusitis or fistulas. At $400 to 700 for a focused exam of the skull in cases of suspected dental disease, the authors feel that NM should be reserved for cases where CT or MR imaging are not available, general anesthesia must be avoided, or where an accurate diagnosis is unobtainable by either modality.

Computed Tomography

Computed tomography has played a pivotal role in the diagnosis and effective treatment of equine dental and sinonasal disorders.^5-9 Computed tomography acquires radiographic skull images in the transverse plane and a complete examination can be performed in approximately 15 min. Postacquisition reconstructed images can then be made in any plane or into three-dimensional images for surgical planning and owner/client education. New software can even allow 3-D printers to construct scaled down versions of the skull or dental tissues. Computed tomography allows for evaluation of the skull without anatomic superimposition and provides excellent contrast and spatial resolution. For these reasons, CT provides a more accurate assessment of the extent and physical features of diseases of the skull than conventional radiographs. Both soft tissues and bone can be imaged with CT. However, the soft tissue contrast resolution of MR imaging is superior to CT. An important function of CT is the measure of tissue attenuation (radiopacity) in Hounsfield units (Table 2). This can help differentiate pure fluids from soft tissue masses. Common CT features of dental disease include widening of the periodontal space, tooth root lysis/blunting, tooth crown or root fragmentation, alveolar bone sclerosis, and apical tooth root gas.^5,8

Computed tomography imaging has traditionally been performed with the horse under general anesthesia. More recently, a handful of imaging facilities around the world allow CT examinations to be performed in the standing sedated horse. This technique is becoming increasingly popular. 
 

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