Vitamin C requirement and deficiency
Merck explains that guinea pigs have a mutated gene for L-gulonolactone oxidase. This enzyme is involved in the synthesis of ascorbic acid from glucose, so guinea pigs of every age depend on diet for vitamin C [1][2].
According to Merck, deficiency yields defective type IV collagen, laminin and elastin. Vessels become fragile and bleed, and hemorrhage around the joints reduces joint integrity [1]. Merck also links inadequate collagen to malocclusion, because the teeth lose their anchoring [1]. The rodent oral disorders review describes scurvy in guinea pigs as showing up in the mouth as periodontal disease, gingival hemorrhage and loose teeth [3].
Merck notes that growing, lactating, pregnant and sick animals have higher requirements. These animals may show deficiency sooner than healthy ones [1]. The histories Merck flags include feeding rabbit pellets, stale pellets, or pellets made without a stable form of ascorbic acid [1].
Diagnosis and treatment of hypovitaminosis C
Per Merck, diagnosis rests on history and clinical signs. Radiographs may show enlarged long bone epiphyses and enlarged costochondral junctions [1]. The postmortem findings it lists include hemorrhage in the joints, gingiva, intestines, subcutis and skeletal muscle [1].
Merck's treatment outline is husbandry correction, vitamin C given parenterally or orally, and analgesia [1]. It gives no treatment dose on that page. The cited sources also do not describe a blood test for vitamin C status. For debilitated patients, the review adds that tube feeding, fluids, antibiotics and vitamin supplements may be needed [3].
Dental anatomy and causes of disease
Guinea pig incisors, premolars and molars all grow continuously, and opposing surfaces wearing against each other keep them at the right length [1]. The review gives the dental formula shared by guinea pigs, chinchillas, capybaras and beavers as "1/1 0/0 1/1 3/3=20" [3]. The Animals survey authors cite reported incisor growth of 1.4 to 1.9 mm per week [4]. On a rostrocaudal radiograph, normal guinea pig cheek teeth have equal crown lengths and form an open "V" at a 30 degree angle to the horizontal, according to the review [3].
Merck attributes most malocclusion and overgrowth to malnutrition, including hypovitaminosis C and low dietary fiber, and to other husbandry deficits. It also lists trauma and genetics, and notes that pulling on cage bars or wires can fracture incisors and cause misalignment [1]. The review suggests three causes of cheek tooth elongation [3]:
- anisognathia
- an abnormal incisor relationship
- the reduced chewing that processed food requires
The review argues that pelleted diets shorten chewing time and favor crushing over grinding [3]. The evidence on diet is not settled. The survey authors note that the only experimental study of diet and tooth wear in guinea pigs did not find abrasiveness significantly related to overgrowth. They add that whether vitamin D deficiency causes dental disease in this species has not been investigated [4].
As cheek teeth lengthen, the review describes a forward (mesial) shift of the mandible. Spurs form on the cheek side of the upper cheek teeth and the tongue side of the lower ones, and the incisors can develop a secondary malocclusion [3]. The survey authors note that apices extending toward the eye can lead to conjunctivitis or exophthalmos [4].
Clinical signs of dental disease
Merck describes the signs as nonspecific. They range from mild inappetence to anorexia, and include difficulty chewing or swallowing, reduced activity, weight loss and ptyalism (drooling) [1]. The review lists further presenting signs and examination findings [3]:
- general loss of condition
- changes in fecal output
- swelling along the ventral mandible
- inability to fully close the mouth
- abnormal incisor wear
- submandibular or cervical lymphadenopathy
The review adds that signs are often vague, and disease is usually advanced by the time the animal reaches a clinic [3].
In the owner survey, difficulty eating and fewer or smaller droppings were the signs significantly associated with a veterinary dental diagnosis [4]. The survey authors also cite hypersalivation ("slobbers"), reduced grooming, facial swelling and inability to perform coprophagy as reported signs [4].
Diagnosing dental disease
Merck calls for a thorough oral examination, possibly under sedation, combined with radiographs or CT [1].
The review explains why the conscious examination falls short: the oral opening is narrow and the cheek teeth sit far back. Even with good restraint and an otoscope or speculum, it calls a full examination "nearly impossible in the conscious patient" [3]. It describes examination under anesthesia with a rodent mouth gag, cheek dilators, light, mirrors, magnification and radiography [3]. Of the three standard extraoral radiographic views, the review rates the lateral and rostrocaudal views as usually most informative [3].
The review flags a pitfall with facial abscesses. Clinicians often blame a cheek tooth, but endodontic abscessation of damaged incisors is the most common cause, because guinea pig mandibular incisor apices reach the level of the premolars [3]. The survey authors note that true prevalence is often underestimated even with clinical examination [4].
None of the cited sources gives a staging or grading system for guinea pig dental disease or hypovitaminosis C.
Treatment and anesthesia
Merck describes treatment under general anesthesia. Crown heights are reduced and an appropriate occlusal angle is recreated with a dental drill and electric burr, and severely diseased, loose teeth are sometimes extracted [1]. The supportive measures it lists are analgesia, fluids, a critical care diet and husbandry changes [1].
The review recommends radiographs before leveling, because abscessed or periodontally diseased teeth will need extraction. It notes that the rostral cheek teeth are longer and need more reduction than the caudal ones [3]. For incisors, it advises against nail clippers because they can cause diagonal fractures, and it favors a burr on a high-speed handpiece [3]. For dental surgery, the review states that "opioids followed by nonsteroidal anti-inflammatory drugs (NSAIDs) are recommended" [3].
The review also reports patients whose mouths hung open after leveling because the masticatory muscles had adapted to stretching. It describes a neoprene headgear that lifts the mandible, and says ongoing research at the time suggested 12 hours a day of wear seemed sufficient to keep crowns short [3]. That observation dates from 2005.
Anesthetic notes from the review
The review covers rodents broadly but gives several guinea pig details:
- Guinea pig secretions are particularly thick, and it states atropine "should be given intravenouly or SC at a dose of 0.05 mg/kg" [3].
- A short fast may reduce aspiration risk, but prolonged food deprivation induces hepatic dysfunction [3].
- The author reports maintaining guinea pigs on 2% to 3% isoflurane through a small catheter in one nostril [3].
Recurrence, prognosis and prevention
Merck says severe or chronic dental cases typically need multiple procedures, sometimes every 4 to 6 weeks [1]. The review gives every 4 to 8 weeks when teeth keep elongating [3]. The review also says diet change alone resolves only early cases, before serious apical changes develop [3].
Extracting a continuously growing cheek tooth has lasting effects, per the review. The opposing tooth overgrows and needs lifelong trimming, and adjacent teeth can shift into a "step mouth" [3].
On diet, Merck recommends grass hay, grass-based pellets formulated for guinea pigs, and produce. It states that animals under 6 months and pregnant or lactating sows require alfalfa hay and pellets [2]. Its rule of thumb is hay equal to the animal's body size, about 1 to 2 teaspoons of pellets, and 1 to 2 cups of produce daily [2]. The high-vitamin C produce it names includes bell peppers, tomatoes, kale, parsley, beet greens and spinach. Merck also advises against adding vitamin C to drinking water, since frequent changes are needed and the taste may reduce intake [2]. The review recommends shifting recovering dental patients to hay and fresh grass to increase tooth wear [3].
The survey found that outdoor access, including runs on concrete or grass, was significantly associated with not showing dental signs [4]. Vitamin C supplementation was associated with more dental disease. The authors suggested two explanations: more knowledgeable owners both supplement and spot disease, or owners supplement animals that are already ill [4]. They state that the respondents were recruited online and were not representative, that diagnoses were owner reported, and that no animals were examined [4].
The survey authors note that clinical signs in guinea pigs are often overlooked by owners. In the survey, 17.4% of respondents did not recognize a pictured guinea pig with obviously elongated incisors as having dental disease [4].
