6 Palatal canines
Diane, a 15-year-old girl, presents with both upper primary canines retained (Fig. 6.1). What is the cause and what treatment possibilities are there?
Diane is concerned about the size of the baby upper ‘eye’ teeth that are present and by the spaces on either side of her upper two front teeth. She is not bothered by the small space between the upper front teeth. is also slightly loose and she is worried in case it is lost, producing a big space.
Diane has been aware that the baby ‘eye’ teeth should have been lost a few years ago. Her previous general dental practitioner, who retired last year, advised her that these teeth would eventually fall out by themselves and that when the new ‘eye’ teeth came through, she would then need a brace to close the spaces between her top teeth. There is no history of trauma to areas and all other primary teeth were lost naturally. All permanent teeth have erupted on schedule.
Diane has a Class I skeletal pattern with average FMPA and lower facial height and no facial asymmetry. Her lips are competent with the lower lip at the level of the incisal third of the upper incisors.
The intraoral views are shown in Figures 6.1 and 6.2. Describe what you see.
Note in Diane’s case, the mesiodistal width of 2’s were the same as those of ’s, indicating that 2’s are smaller than average and that a tooth-size discrepancy (TSD) or Bolton discrepancy exists between the upper and lower labial segment teeth.
Between 5–14% of the population have a significant overall TSD, whereas 20–30% have a significant anterior TSD (see below). Although a TSD is most commonly due to a size anomaly of the upper lateral incisor, premolars or other teeth may also be responsible.
A tooth-size analysis, often referred to as a Bolton analysis after its developer, may also be performed. The mesiodistal width of each permanent tooth, excluding second and third molars, is measured and then the summed widths of the maxillary to mandibular teeth are compared with a standard table. This allows calculation of Bolton anterior (canine to canine) and overall (first molar to first molar) ratios as follows:
Bolton obtained an anterior ratio of 77.2 ± 1.65% and an overall ratio of 91.3 ± 1.91%. Discrepancies greater than 2SD beyond these mean values have been regarded as clinically relevant to treatment planning. Tooth-size analysis may also be undertaken using digital models; the measurements are as accurate and reliable as those obtained from plaster models.
The teeth must be proportional in size to ensure good occlusion. Rarely is a TSD of less than 1.5 mm of significance with regard to treatment planning, but where larger discrepancies exist, adjustment of the mesiodistal tooth width through either addition to the enamel (e.g. composite build-ups or porcelain veneers) or enamel removal (e.g. interdental enamel stripping/reproximation) may be required to close or open spaces in the opposing arch.