How to Manage Maleruptions of Upper Fourth Premolars in the Miniature Horse

Maleruption of the upper fourth premolars may rarely occur in the miniature horse. Monitoring the eruption process with regular oral and radiographic exams, managing the occlusal contacts, and treating any periodontal disease will help to ensure that these teeth remain in the upper arcades as functional teeth.

1. Introduction

Miniature horses are prone to class III malocclusions (MAL3) [1] caused by maxillary brachygnathism. With the shortened maxilla, they are prone to crowding of the upper premolars and molars. The upper fourth premolars (108/208) [2] are the last cheek teeth to erupt into the arcade. When crowding occurs during the eruption process, these teeth tend to rotate at 90° on their long axis, with the buccal aspect of the tooth facing in a mesial direction.

Minimal information is available in the literature that documents this type of maleruption. In 2004, a case report [3] was written that documented this type of rotation in a 5.5-yr-old miniature horse in which a left nasal discharge had developed as a sequel to periodontal disease. The purpose of this paper is to document this type of malocclusion in a younger (5.5 yr) and older (11 yr) miniature horses. With monitoring and preventative dental care, these teeth can be functional. As a general rule, once an apical abscess and sinus discharge develops, the prognosis for that tooth is very poor, with the only viable/realistic option being extraction. Management of this type of maleruption should include the following: (1) radiographic monitoring (extraoral and intraoral views), (2) oral examinations (intraoral mirror and/or intraoral camera), (3) occlusal reduction of any irregularity/step, and (4) subgingival scaling and local antibiotic treatment of any deep periodontal pockets (greater than ≈7 - 12 mm). The optimal goal is to have these teeth remain functional without a need for extraction.

2. Materials and Methods

Regular Oral Examinations

Frequent oral examinations are very important when monitoring any maleruption case. The upper fourth premolar in a miniature horse erupts at ≈5 - 5.5 yr of age. Other horses (Arabians, Quarter Horses, etc.) [4] have eruptions of 108 and 208 at 4 - 4.5 yr of age. When dealing with a miniature horse that has a potential maleruption, it is important to have frequent oral exams during the process. Monitoring should be done for any retained or displaced deciduous caps (508/608) that may be inhibiting movement (Fig. 1). One should watch for any developing periodontal pockets as the tooth rotates into position (Figs. 2 and 3). One should measure the depth of the periodontal pocket with a periodontal probe [a]. On follow-up exams, one should determine if the pocket is increasing in size. Watch for periodontal disease in the neighboring teeth; particularly 107 and 207. The periodontal pockets tend to develop at the interproximal space between 107/108 and 207/208. The food tends to pocket in the spaces between the enamel transverse ridges because of the uneven surface.

Figure 1. Malerupted 208 with a retained and displaced deciduous cap (608 RD).

Figure 2. 108 actively rotating as it erupts. Note the developing periodontal pocket (5.5 yr old).

Figure 3. 208 rotated into the dental arcade with a periodontal pocket at the interproximal space of 207/208 (11.0 yr old).

Radiographic Monitoring

Frequent radiographic monitoring is necessary during active eruption. Radiographic evaluation for this type of problem is best evaluated with a combination of extraoral and intraoral views. The extraoral views would include a dorsal ventral (DV) view and an open-mouthed right and left dorsal oblique (R/L D OBL). The DV view in a miniature horse may be taken with a film distance of 40 - 50 cm at 70 - 74 kV and 0.75 - 1.0 mAs. The beam should be focused at the rostral aspect of the facial crest (Fig. 4). The open mouthed dorsal oblique view is taken at 30° dorsal to the lateral position and focused on the rostral aspect of the facial crest (Figs. 5 and 6). A speculum with elastic straps on the side works well to hold the cassette on the imaging side and for a non-obstructed view on the camera side (radiograph machine) [b]. The film distance is also at 40 - 50 cm with 64 - 68 kV and 0.60-.070 mAs.

Figure 4. A dorsal ventral (DV) view with the X-ray beam centered at the rostral aspect of the facial crest.

The intraoral view is challenging in the miniature horse. Special small flexible cassettes are available in multiple sizes including 2.5 × 7 and 3 × 6 in (Fig. 7) [c]. A bisecting angle technique [5] is used with a film distance of 30 - 40 cm at 50 - 60 kV and 0.50 - 0.60 mAs. Because the cassette is smaller to fit in the mouth of the miniature horse, it becomes more challenging to get the whole molar and premolar imaged. However, the view is especially important to evaluate the impact of the maleruption(s) on 107 and/or 207.

Occlusal Reduction

With this type of malocclusion, there is the potential for a severe "step" to develop on an upper arcade. In the younger (≈5.5 yr old) miniature horse, problems may occur with the 107 and 207 as they become displaced and or mesially "tipped" forward at the coronal aspect (Figs. 8 and 9). In the older miniature horse (11 yr old), the enamel transverse ridges of 108/208 and the distal crown of 107/207 contribute to the step (Figs. 3 and 10). Painful buccal lacerations may develop as a consequence. If a MAL3 is present, the lower second premolars (306/ 406) may develop a step that will also need periodic attention. These steps should be reduced and maintained in stages. The active maleruption may need to be addressed every 2 - 4 mo. Once the mal-erupted tooth is in place, occlusal reduction of the step(s) may still be necessary as often as two to three times per year (Fig. 11).

Figure 5. A left dorsal oblique (L D OBL) view. The X-ray beam is angled 30° dorsal from the lateral position and centered on the rostral aspect of the facial crest.

Figure 6. L D OBL positioning. A speculum [b] with elastic straps allows for (1) an unobstructed radiographic view, (2) a method of handling the cassette "hands free," and (3) an opened mouth view.

Figure 7. Intraoral cassettes [c] for miniature horses.

Figure 8. The distal aspect of 107 develops into a step as 108 mal-erupts.

Figure 9. As 208 erupts, 207 is displaced in a buccal and mesial direction. Note the 306 overgrowth as a result of the MAL3 occlusion.

Subgingival Scaling and Antibiotic Treatment of Periodontal Pockets

The severity of periodontal disease that develops from this type of maleruption is the determining factor as to whether or not the tooth will survive. If periodontal disease progresses, it can lead to exfoliation through loss of periodontal ligament and/or alveolar bone [6]. The periodontal disease could also lead to an endodontic lesion (class 2 lesion) [7]. A root abscess could develop as a result of the endodontic lesion and lead to a sinus infection with nasal discharge. The goal of treating the periodontal disease is to prevent the above scenarios and to maintain the tooth as a functional unit for mastication.

The first line of defense for periodontal disease in the equine patient is to maintain occlusal equilibration. If a periodontal pocket persists on follow-up examination (more than ≈7 - 12 mm deep), more aggressive treatment must be instituted. The basic goals of periodontal treatment involve (1) subgingival cleaning, (2) creating a barrier for future food contamination, and (3) local placement of antibiotics.

The concept of subgingival cleaning is to remove any decayed cementum and sucular epithelium [6]. A piezoelectric ultrasonic scaler (Figs. 12 and 13) is easily adapted to the equine patient for this purpose.

A portable pressurized water tank can be implemented with this unit to make it mobile [d].

CaCO3 and CaSO4 hemihydrate [f] when mixed with sterile water, can be used to form a temporary barrier to food accumulation. In addition, CaSO4 has the ability to augment and/or accelerate regeneration of bony defects [8,9]. This mixture can also be used with an antibiotic such as metronidazole for a sustained release of antibiotic within the periodontal pocket.

3. Results

Regular Oral Examination

A thorough oral examination allows for a more comprehensive understanding of the dental pathology. Figure 14 shows the active eruption of 108 as it becomes malpositioned within the dental arcade. The red numbers and arrows point to the corresponding pulp horns (PHs). The 90° rotation becomes evident as noted by the 1 and 2 PHs starting to angle into a mesial orientation within the alveolus. Normally these two PHs are located buccally. In addition, it can be noted that the mesial (M) and distal (D) infundibulums (INFs) are shifting into a palatal (P) and buccal (B) orientation, respectively (blue letters and arrows). Figure 15 shows the same structures in an older miniature horse once the tooth has shifted into place within the arcade. It can be noted that a thinning of the enamel transverse ridges has developed leading to a near exposure of the 1 and 2 PHs. The INFs have become malpositioned within the normal tooth anatomy. These changes are possibly a result of stresses to the developing tooth during the abnormal eruption process.

Figure 10. Three months after occlusal reduction of the "step" (STP) formed by 207 and 208 (11.0 yr old).

Figure 11. Occlusal reduction of 207 and 306 (5.5 yr old).

Radiographic Monitoring

DV View

The DV view is probably the most informative view when monitoring the active maleruption in the younger miniature horse (5.5 yr). Figure 16 shows how a retained deciduous tooth (608 RD) affects the eruption process. The apical aspect of the developing tooth is deviated toward the midline as it tries to find a place within the arcade. Figure 17 shows the same patient ≈8 wk later. It is evident that 208 has been aided in the eruption process by the removal of 608. Also, there appears to be a crowding effect with 107 that is developing since the previous radiographs were taken. Figure 18 shows a DV radiograph of an older miniature horse with the M and D margins marked with red arrows.

Figure 12. (Left) Solid tip. (Right) Hollow tip (piezoelectric ultrasonic scaler).

Figure 13. Piezoelectric ultrasonic scaler and pressurized water tank

Figure 14. Active maleruption of 108 as it rotates into the dental arcade.

Figure 15. Post rotation of 108 in an older (11.0 year old) miniature horse.

D OBL View

The D OBL is a strong compliment to the intraoral view in miniature horses with a fourth premolar maleruption. The D OBL view is useful in the evaluation of the apical portion of the reserve crown.

In Fig. 19 the R D OBL view shows how the apical half of 108 is displaced caudally (and possibly misshapen). Figure 20 is the R D OBL view of an older miniature horse. The malerupted 108 has fully erupted into the normal location; however, crowding is evident with the mesial aspect of 109.

Figure 16. Retained deciduous cap (608 RD).

Figure 17. Eight weeks after removal of 608 RD.

Figure 18. Mesial and distal margins of 108 and 208 (11.0 yr old).

Intraoral View

The intraoral view (IO) is challenging in a 200-lb miniature horse. This is because of the limited space within the oral cavity coupled with the fact that the teeth are close to the same size as that of a full-size horse. The IO view does give critical information pertaining to the coronal portion of the tooth. In the younger miniature horse with the active mal-eruption (Fig. 21), the overlap/displacement of the M aspect of 108 and the D aspect of 107 is evident as the tooth tries to position itself. In the older miniature horse, the IO view (Fig. 22) shows how the crowding is still present even after repositioning has occurred.

Occlusal Reduction

Occlusal reduction in the event of a maleruption should focus on removing obstructions that would inhibit the normal eruption process. In addition, the reduction/equilibration should make the patient more comfortable by removing sharp enamel points and steps that cause buccal lacerations.

Figure 23 shows the removal of 608 that was depicted in Fig. 1. Figure 10 shows the 8-wk follow-up exam of the step reduction performed on the 11-yr-old miniature horse. Figure 11 shows an additional reduction being performed after ≈8 wk on the 200 arcade of the 5.5-yr-old miniature horse. Note the healing of the buccal lacerations between the initial exams (Figs. 8 and 9) and the follow-up exams (Figs. 10 and 11).

Subgingival Scaling and Antibiotic Treatment of Periodontal Pockets

If the periodontal pockets have not shown any evidence of healing on the follow-up exam, more aggressive therapy is warranted. The piezoelectric ultrasonic scaler is well suited for this purpose. Other options would include using a high-speed bur or hand instruments [6]. The scaler tip of the piezo-electric can be made either with a solid or hollow tip. The hollow tip allows water to spray out through the center and is designed for periodontal treatment. The solid tip is typically used for endodontic procedures.

Figure 19. Right dorsal oblique view (R D OBL; 5.5 yr old).

Figure 20. Right dorsal oblique view (R D OBL; 11.0 yr old).

Figure 21. Right intraoral view (5.5 yr old).

Figure 22. Right intraoral view (11.0 yr old).

The 5.5-yr-old miniature horse had an ≈23-mm periodontal pocket at the palatal aspect of the 107/108 interproximal space (Fig. 2). The piezoelectric ultrasonic scaler is used to remove the decayed cementum, food, and inflamed sulcular epithelium (Figs. 24 and 25). Figure 26 shows the periodontal pocket after cleaning/scaling. CaCO3 and CaSO4 hemihydrate (1.5 tbsp) is mixed with metronidazole (2 g) and formed into a moist pliable "puddy." The formulation is placed at the sight of the periodontal pocket using a cement spatula [g] (Fig. 27) and firmly packed into the pocket using an amalgam plugger [h] (Fig. 28). Figure 29 shows the 23-mm periodontal pocket of the 5.5 yr old, filled with the CaCO3, CaSO4 hemihydrate, and metronidazole. Figure 2 is from the 11-yr-old miniature horse with a 25-mm periodontal pocket at the palatal aspect of 207/208. Figure 30 is an intraoral photograph of the same pocket immediately after treatment.

4. Discussion

When evaluating and treating periodontal disease associated with a maleruption, several questions remain to be answered. What role does the eruption process play in the rotational force of the upper fourth premolar? How frequently should these cases be monitored? What treatments should be instituted? What is the definition of a successful management?

Figure 23. Removal of 608 RD (previously noted in Fig. 1).

Eruption and Rotational Force

On first impression, it might seem that by rotating the fourth upper premolar at 90° on its axis, the tooth will fit more easily into the dental arcade. In reality, the opposite is true, because typically, the occlusal surface of the crown is ≈10% wider (palatal to buccal) than in length (mesial to distal).

The anatomy of the enamel transverse ridges may play a role in the rotational force. As the premolar starts to malerupt because of limited space, the enamel transverse ridges may "catch" on the palatal distal aspect of the third premolar (107/207). The appearance of this happening is evident with the IO photograph of the exposed crown of 107 in the 5.5yr-old miniature horse (Fig. 2).

The direction of force with the eruption process may contribute to the rotation. The radiographs from the 5.5-yr-old miniature horse (Figs. 16, 19, and 21) show the apical one half of the fourth premolar shifting caudal and toward the midline of the skull. This angular displacement could explain the misguided "rotational" eruption.

Figure 24. Piezoelectric ultrasonic scaler with a hollow tip.

Figure 25. Subgingival scaling of a periodontal pocket.

Figure 26. Periodontal pocket after subgingival scaling.

Figure 27. Placement of CaCO3, CaSO4, and metronidazole using a cement spatula [8].

Monitoring Frequency

The interval between examinations, radiographs, occlusal equilibrations, and treatments is variable and case dependent. A younger horse that is at the stage of active maleruption should be monitored frequently. An older horse with an eruption pattern that is more stable may not need to be monitored as frequently. Guidelines may range between 6 and 12 wk for younger horses and two to three times per year for older horses.

Treatment Options

With this type of maleruption, the health of the neighboring periodontium is the determining factor as to whether or not the rotated tooth will become a functional unit within the arcade. Occlusal equilibration (OE) and the reduction of steps (odonto-plasty [OD]) will help to control a majority of the periodontal disease. On re-examination after OE/ OD, all persistent periodontal pockets should have some type of subgingival cleaning, scaling, and su-cular curettage. Deep periodontal pockets should be considered for local antibiotic treatment. Different materials can be used along with the antibiotics. These materials can be used to simply occupy space [6] or to guide tissue regeneration [9].

Figure 28. Packing the CaCO3, CaSO4, and metronidazole into the periodontal pocket using an amalgam plugger [h].

Figure 29. Five and one-half-year-old miniature horse after treatment.

Figure 30. Eleven-year-old miniature horse after treatment.

Successful Management

Periodontal disease could progress and lead to exfoliation, endodontic disease, periapical abscess, and sinus infection. Successful management of a fourth upper premolar maleruption involves preventing these progressions and allowing the rotated tooth to remain, thus avoiding tooth loss and/or the need for extraction.

The author acknowledges the contributions of Stephen Galloway, DVM, Robert M. Baratt, DVM, MS, and David O. Klugh, DVM, FAVD/Equine.

Footnotes

[a] Periodontal Probe, Rena’s Equine Dental Instruments, Reno, NV 89506.
[b] Dental Speculum, Stubbs Equine Innovations, Johnson City, TX 78636.
[c] Intraoral cassettes, Diagnostic Imaging Systems, Rapid City, SD 57703.
[d] Inovadent Mini Piezon, Dr. Shipp’s Laboratories, Tucson, AZ 85741.
[e] Metronidazole tablets, USP 500 mg, PLIVA, East Hanover, NJ 07936.
[f] Bondex, Plaster of Paris, DAP, Baltimore, MD 21224.
[g] Cement spatula, Dr. Shipp’s Laboratories, Tucson, AZ 85741.
[h] Amalgam plugger, Medco Instruments, Chicago, IL 60457.