March 1, 2007
by David Greenberg, HBSc, DDS
This case study is presented as a long term approach to a rare condition not often encountered in everyday practice.
Transposition of the maxillary canine to the central incisor position is an extremely rare phenomenon. The occurrence of all transpositions of the maxillary canine is about 0.4%. Canine to central is one of six possible maxillary anterior variations and is considered to be the only two space transposition.
The patient is a 53-year-old female in good health with no contributory medical conditions. Her initial exam was in February 1985 and at that time presented with a retained 6.3 and a gold “window” crown on the tooth in the 2.1 position. A periapical radiograph revealed a horizontally impacted 2.1 and the 2.3 as the crowned tooth. There was no apparent cyst around the 2.1 and no evidence of root resorption of the 1.1, 2.2 or 2.3. The patient was asymptomatic and had no desire to change the situation at that time.
There was no indication for removal of the impacted 2.1.
The patient continued routine dental care over the years and in February 1996 decided to change the restoration on the 2.3. As seen on the radiograph (Fig. 1) the 2.3 is tilted mesially. This presented a problem in the preparation for the Porcelain Fused to Metal crown.
The more apical the preparation, the more distal the tooth, the narrower the stump and the more difficult the path of insertion due to the mesial of the 2.2. Also a more apical margin would result in more of a “black triangle” Fortunately, a low lip line resulted in acceptable aesthetics. The photograph in Figure 2 is an 11 year follow-up. The radiograph in Figure 3 shows no significant changes in the impacted 2.3.
In July, 2002 the retained 6.3 became discoloured and mobile. A periapical radiograph showed advanced root resorption as is to be expected by 49 years of age. The patient was presented with various options including implant, “Maryland” Bridge, fixed bridge 2.2 to 2.4 and cantilever bridge 2.5, 2.4, 2.3. My recommendation was first the implant, and second, the cantilever bridge. The patient decided against the implant and to have the cantilever bridge. My decision was based on the following; 1.2, 1.1 and 2.2 are all virgin teeth and 2.4 and 2.5 were already heavily restored.
The problem of “going around the corner” because of canine guidance was not a concern. In this case, the 6.3 provided no function in lateral excursion and the final restoration provided the same group function as prior to the extraction of the 6.3. The final restoration (2.5 PFM abutment, 2.4 PFM abutment and 2.3 PFM pontic) can be seen in figures 5 & 6. Originally I had closed the space distal to the 2.5 but the patient preferred the gap and the abutment’s mesio-distal width closer to normal.
This case could have been restored several different ways at varying costs with more or less insult to the existing dentition. If the patient was born 30 or 40 years later orthodontics may have been the treatment of choice. The 1.1, 1.2, and 2.2 could have been treated with porcelain veneers but in this case I feel the aesthetics are acceptable without.
The literature on this condition is fairly sparse. The environmental or genetic cause of the transposition is not known. As an interesting side note, one of the patient’s sons had multiple odontoma in the maxillary anterior with discolouration of his existing central incisors.
I hope this case presentation has been of interest not only as a rare condition but as an example of conservative treatment.
Dr. Greenberg received his Hon. B.Sc. Physiology in 1978 from the University of Western Ontario and his DDS in 1982 from the University of Toronto. He can be reached at Kennedy Commons Dental Care, 416-752-3031.
Oral Health welcomes this original article.