Abscessed 406

Case History:

This 3 year old QH gelding was brought to the wet lab in February 2010 to evaluate a swollen mandible with a large open abscess.  This horse was kicked by another pasture horse and shortly after a swelling in the left mandible was noticed.  This area continued to enlarge over a 2 week period before rupturing and draining purulent material.   The horse was transported to the wet lab for evaluation and treatment, two weeks after the abscess ruptured.  Fig 1 shows the open draining abscess prior to evaluation. 

The area was surgically prepped and probed for any foreign body or bone fragments.  A bone chip can be seen in the radiograph in figure 5, which was removed.  Figure 4 shows the bone chip after removal which was directly under the caudal root of the 406.  The oral cavity did not show any of signs of infection and the horse was eating normally.  The root structure of the 406 in the radiograph (fig. 5) looked normal at this time, so the abscess was flushed and treated locally along with antibiotic therapy which was to be administered orally by the owner.

The horse returned in July 2010 for follow-up evaluation.  At this time the mandible was slightly enlarged distal to the 406 and there was a drain tract presents exuding a small amount of odiferous pustular discharge (fig. 8).  Radiographs taken at this time did show an opening in the mandible distal to the caudal root of the 406 along with radiographic signs of distortion of the apical root.   The oral cavity appeared normal and the horse was eating well.

Evaluation:

Along with case history and clinical exam, radiographs confirm an infectious tract that communicates with the caudal apical root and possibly the anterior root of the 406.  This tract was not visible in radiographs taken in Feb. and there were no abnormal root formation involving the 406.  Thus, contamination and infection of the root structure of the 406 occurred shortly after trauma caused a fracture of the mandible distal to this premolar.  A dorsal ventral radiographic view (fig. 6) shows a radiolucent area on the buccal side of the 406 indicating the drain tract is positioned laterally which can also be seen clinically by the location of the exiting drain tract. The bone fragment removed in Feb. was located on the lateral side in the same location as the drain tract.  Abscesses tend to take the path of least resistance for drainage which would logically be this damaged area of bone. 

Treatment:

This apical root infection due to blunt force trauma and contamination from a wound on the lateral distal area of the mandible did not resolve with conservative medical treatment consisting of debridement and antibiotic therapy.  Even though the clinical and reserve crown of this tooth appear normal, a root canal procedure is not advisable in this 3 year old horse due the large pulp cavities and the lack of dense root structure.  This tooth was infected approximately 6 months after eruption compromising viability and further maturation of this tooth.  Obturation of the pulp cavities and sealing the apical roots would be difficult and structurally questionable for any extended period of time.  The most reasonable option for this case is oral extraction.   However, in this case, the clinical crown was fractured leaving only the distal portion of the reserve crown and root.  A 1 cm section of bone was removed distal to the 406 using a osteotome and mallet allowing access to the apical root.  A  Steinman Pin was used to loosen and repulse the remaining portion of the 406.  The distal alveolus and drain tract were debrided thoroughly with a small spoon curette and the opening was left open for drainage and aftercare flushing.  Packing the alveolus is not necessary and can delay healing.  If packs are left in place to long, complete healing around the pack can occur leaving a cavity in the arcade where food can pack causing periodontal infections.

Aftercare

The horse was sent home with instructions to flush the area daily through the opening on the outside of the mandible and also to flush the inside of the mouth out with a garden hose for 1 minute per day.  A soft feed diet was recommended for 2 weeks and the horse was prescribed oral antibiotics for 10 days. The owner is advised that drainage from the wound should decrease progressively over a 2-4 week period along with foul odor from the draining area and mouth.  Granulation of the open alveolus is fairly quick but complete healing of the skin and gingiva may take several weeks.

B.W Fletcher

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