Infundibular caries of the equine maxillary cheek teeth is an important disorder that can lead to dental fracture or apical infection. Treatment by removing food debris and carious dental tissue from affected infundibulae using high-pressure abrasion with aluminium hydroxide micro-particles, followed by filling the cleaned defect with endodontic restorative materials is a recommended treatment. However, although anecdotally considered a successful treatment option, there is currently no objective evidence to support this claim. Forty maxillary cheek teeth (CT) that contained 55 infundibulae with caries (mainly grade 2) were extracted post-mortem from 21 adult horses. Five of the CT were sectioned prior to treatment to facilitate visual examination of the carious infundibulae. The remaining carious infundibulae were cleaned using high-pressure abrasion with aluminium hydroxide particles and five CT were sectioned to assess the efficacy of this cleaning process. The remaining 30 CT containing 39 carious infundibulae were then filled with a composite restorative material. The efficacy of this restoration was assessed by computed tomography imaging followed by direct visual examination after sectioning the teeth. Only 46% (18/39) of restored infundibulae, all with shallow (mean 9.6 mm deep) defects, were fully cleaned of food debris and carious material, and filled with restorative material to their full depth. Of these 18, 11 had peripheral defects around the restoration, leaving just 18% (7/39) of restorations without any gross defects. The remaining 54% (21/39) of infundibulae (mean depth of infundibular caries defect, 18.3 mm) still contained food debris and/or carious material in more apical locations, with infundibulae with the deepest caries defects being the least effectively cleaned. The findings of this study indicate that high-pressure micro-particle abrasion is only effective in cleaning food debris from shallow, carious CT infundibulae and consequently, the majority of subsequent infundibular restorations are imperfect.