3.12).Maxillary upper fourth premolar in dogPerpendicular to film (Figure 3.13): too short.Perpendicular to teeth (Figure 3.14): too long.Split the difference (Figure 3.15).Figure 3.9 By “splitting the difference” between the two positions, the images will be closer to the actual size of the structures, minimizing distortion. The radiographic aid is placed with the green stick perpendicular to the film and the red stick perpendicular to the tooth (root). The beam is aimed midway between the two sticks.Figure 3.10 Mandibular incisors/canines: beam perpendicular to film.Figure 3.11 Mandibular incisors/canines: beam perpendicular to teeth (roots).Figure 3.12 Mandibular incisors/canines: split the difference.Figure 3.13 Maxillary premolars/molars: perpendicular to film.Figure 3.14 Maxillary premolars/molars: perpendicular to teeth (roots).Maxillary incisors/canines in catPerpendicular to film (blue positioning guide).Perpendicular to teeth (red positioning guide).Split the difference (Figure 3.16).
When positioning the beam, make sure it is aimed directly over the tooth (maxillary fourth premolar) or at midline (mandibular or maxillary incisors and canines for symmetry) (Figure 3.17). Adjust beam (laterally or obliquely for canines or mesially or distally for premolars) to “move” the superimposed apices away from each other (Figure 3.18).
Hint. Maxillary incisors and canines: on most dogs and cats (not brachycephalic breeds), aim the beam perpendicular to the ventral aspect of the nasal fold (or haired portion of muzzle just under the nares); in most cases, the positioning will closely approximate the correct beam alignment (Figure 3.19). Position the beam initially based on the nares, and confirm the angle.
Figure 3.15 Maxillary premolars/molars: split the difference.
Figure 3.16 Maxillary incisors/canines in cat: positioning aids illustrating perpendicular to the film (blue) and perpendicular to the teeth roots (red); split the difference with the beam.
Figure 3.17 Maxillary canines in dog: beam aimed initially at midline; roots of canines will be superimposed over premolar roots.
Figure 3.18 Maxillary canines in dog: adjust beam away from midline to separate image of canine apex from premolars.
Figure 3.19 In most dogs (not brachycephalic) and even some cats, by aiming the beam perpendicular to the ventral aspect of the nasal fold, the positioning will be adequate (approximates the split the difference position).
Challenging Radiographs
Dog: maxillary canine apex (Figure 3.20).Place sensor/film centered at the second premolar and palpate apex of canine tooth.Aim beam towards palpated apex, slight oblique off midline (see Figure 3.18).
Differentiation of mesial (towards the front of the tooth) and palatal roots of the upper fourth premolar (Figure 3.21).Shift the generator tube distally (towards the back of the tooth) to image the entire tooth without superimposition of the distal root over the first molar.Classically called SLOB (same lingual/opposite buccal) [4]. This means that the root that is more lingual (or palatal) will be imaged in the same direction. The root that moves in the opposite direction as the tube is the buccal root.If the distal root of the upper fourth premolar is imaged well (distal tube shift), the palatal root will move distally (the same direction as the tube) in comparison to the buccal root. The palatal root is in the middle of the distal and mesial roots (Figure 3.21).
Dog: maxillary molars.Place sensor/film lengthwise palatally, lined up with the two molars.Aim beam from above and slightly behind, almost directly aimed at film (Figure 3.22).
Dog: mandibular first premolars. It is challenging to place sensor far enough rostral in the intermandibular space for true parallel image.Intraoral: with sensor/film in place, aim beam from a position below (ventral) and rostral; this will “push” the image onto the film (Figure 3.23).
Dog: mandibular second and third molars.Pull the patient’s tongue out to allow the sensor/film to slide by the oral soft tissues.Position sensor/film further caudally, but also dorsally. Usually the caudal aspect of the sensor/film is angled and above the rostral half of the sensor/film (keep in place with perm roller).Figure 3.20 Maxillary canine apex in dog: aim beam towards palpated apex, slight oblique off midline.Figure 3.21 (a) Standard beam positioning for the upper fourth premolar and its radiograph. (b) Beam position with distal tube shift and SLOB technique radiograph showing the palatal root in the middle.Figure 3.22 Maxillary molars in dog: place sensor/film lengthwise palatally, lined up with the two molars. Aim beam from above and slightly behind, almost directly at film.Figure 3.23 Mandibular first premolars in dog: with sensor/film in place intraorally, aim beam from a position below (ventral) and rostral. This will “cast the shadow” or “push” the image onto the film.Figure