By David E. Hansen, DVM, FAVD, DAVDC
Fellow of the academy of Veterinary Dentistry
Diplomate of the American Veterinary Dental College
The earliest condition of the oral cavity that can cause a problem is a cleft (failure to close) palate. With the complicated and multi-staged process of development, abnormalities of the palate are sometimes experienced. As the hard and soft tissues of the palate are closing, the maxillary processes do not join at the midline at their most rostral aspect. Instead they join to the incisal area forming a "Y" shaped fusion. Complete development of this area is particularly subject to outside stimuli, but there is a possibility of hereditary involvement.
A primary palatal cleft is located at the junction of the incisal area with one or both of the maxillary processes. It may be present with a cleft lip. A more common defect is on the midline of the palate behind the incisal area involving the hard and/or soft palate and is considered a secondary cleft palate. This can be unilateral with only one side of the nasal passage exposed, or bi-lateral with both sides of the nasal passages exposed. With any form of cleft palate, a newborn cannot nurse because an effective vacuum cannot be attained. Milk that reaches the oral cavity is often aspirated into the lungs, sometimes coming out the nose. This is one of the first conditions checked for at birth and unless it is very minor, euthanasia is usually advised. Tube feeding is generally necessary to keep affected puppies alive to an age at which surgery might be an option. Potential complications are numerous and long-term management is needed. It has been suggested that asymmetrical junctions of the rugae at the median ridge may be an indication of poor migration of the left and right maxillary processes in the fetus and be a "tendency" toward cleft palate formation. It is not uncommon to find this asymmetrical pattern in parents of cleft palate puppies.
More and more frequently I am getting asked, “What’s the deal with missing teeth?” The answer depends on if the teeth are truly missing or unerupted. There are cases in which the deciduous teeth are not erupting properly. This will cause the adult teeth to become impacted and fail to erupt also. The tissue over the tooth buds is called the operculum. When the tooth is erupting, it penetrates this soft tissue which then forms the gingiva. If the operculum is too thick or tough, the teeth become impacted (Figure: 1).
This puppy was 20 weeks old and the maxilla was starting to become deformed. This is why you need to know when the deciduous teeth should be erupted. A gingivectomy procedure to expose the crowns of the affected teeth allowed them to finish erupting (Figure 2).
Figure 2: Post-gingivectomy
This can also happen to the adult teeth (Figure 3a to 3f).
Trauma to the maxilla of a growing puppy can result in missing teeth. Some tooth buds may re-absorb and not be present or may be buried, but still develop and cause problems later. This is a dental radiograph of a 14-month-old dog that was bitten on the muzzle by his dam at 8 weeks of age (Figure 4). The first 2 premolars are not present, but the maxillary canine tooth developed within the bone and was causing the dog to sneeze and snort.
If a tooth fails to erupt it can develop into a dentigerous cyst. This is because the cells that are in the gingival sulcus of an erupted tooth produce a small amount of fluid to flush out the sulcus around the tooth. When the tooth fails to break thru, the fluid has nowhere to go, so the increase in pressure will cause bone destruction and eventually swelling, as the cyst gets larger. This is a 20-month-old dog with a dentigerous cyst of the mandible, due to an unerupted lower first premolar (Figure 5a and b). A visual observation revealed no sign of the lower right first premolar, but it is present on the dental radiograph. The white arrow indicates the unerupted lower first premolar, the black arrows the extent of the cyst.
This case and the previous case demonstrated that a missing tooth is not necessarily missing at all, but not erupted. Many times there is a missing tooth because there was never an adult tooth bud present. Missing teeth are most commonly seen in small dogs, and in some larger breeds can be considered a serious fault. Permanent teeth are more frequently missing, and if a deciduous (baby) tooth is genetically not present, the permanent associated tooth should also be absent. Generally a tooth that is truly missing can only be distinguished from an unerupted or impacted tooth by obtaining radiographs of the site. Intraoral radiographs in young animals are indicated when teeth are apparently absent It should not be assumed that the teeth are absent until proven so. Early treatment of impacted or non-erupted teeth may prevent the formation of dentigerous cysts. The formation of dentigerous cysts will result in much more tissue destruction and pain for the patient.
Developmental problems can be due to a specific inherited cause (genetic), probable genetic etiologies (theories), with a familial tendency, or due to congenital influences. Genetic describes conditions that are inherited. Congenital describes abnormalities present at birth, either inherited or due to conditions that occurred during pregnancy (e.g., infection, drugs, injury). Familial describes conditions that affect a family to an extent that is considered greater than expected by random or chance circumstance.
Missing and extra (supernumerary) teeth share a familial tendency and may be hereditary in some cases and acquired in others. A dog can have both missing and extra at the same time. (Figure 6: 2 first premolars, but no second premolar)
It is my personal observation that in the larger breed dogs, the most common missing teeth are one of the mandibular or maxillary first three premolars or the lower third molar.
As seen in the previous dental radiograph, the first premolar can have a supernumerary tooth. However, any tooth can have an additional tooth bud, resulting in a supernumerary tooth (Figure 7a, supernumerary lower right canine tooth and 7b, supernumerary upper right and left first incisors).
Retained Deciduous Teeth:
Retained deciduous teeth can also delay the eruption of the permanent teeth. Even if the permanent tooth is not delayed in eruption, it may be deflected by the deciduous tooth and can contribute to malocclusion. A general rule is that "no two teeth can occupy the same space at the same time." It can also be said that as the deciduous tooth is erupted first, it is more likely that the permanent tooth will be deflected into an abnormal position as it erupts. The extent of the deflection may lead to malocclusion if the deciduous tooth is not extracted early. If the extraction of the retained deciduous tooth is delayed until the permanent tooth is fully erupted, the tip of the crown may already be embedded in the soft tissue of the opposing arcade (Figure 8a-c). The bone surrounding the permanent tooth will also be more mature, further restricting the movement of the permanent tooth to a normal position, following extraction of the deciduous tooth. Many times early extraction of the retained deciduous tooth allows the permanent tooth to shift into the proper position as it is erupting, avoiding the need for orthodontic treatment later.
There are times when both the deciduous and permanent teeth are fully erupted and are not causing a significant malocclusion or traumatizing the soft tissue. However the periodontal ligament space between the two teeth is compromised and periodontal disease will progress until later (sometimes months to years), both teeth may be lost. This will also subject the dog to chronic infection and pain during this time.