6: Palatal canines

6 Palatal canines

Summary

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?

image

Fig. 6.1 Anterior occlusion at presentation.

History

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. image is also slightly loose and she is worried in case it is lost, producing a big space.

History of complaint

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 image areas and all other primary teeth were lost naturally. All permanent teeth have erupted on schedule.

She has noticed that image has been loose intermittently for the past 18 months. It does not appear to have got looser in recent months. Diane is very keen to improve the appearance of her upper teeth.

Medical history

Diane is fit and well.

Dental history

Diane is a regular attender at her general dental practitioner but has never had any dental treatment.

Examination

Extraoral

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.

There is a slight lateral mandibular displacement to the left on closure on image.

Intraoral

image The intraoral views are shown in Figures 6.1 and 6.2. Describe what you see.

Oral hygiene is fair with mild marginal gingival erythema related to image and the upper left buccal segment teeth.
No obvious buccal swellings in the c areas but there seem to be mucosal swellings palatal to image, perhaps indicating the position of unerupted 3’s.
Slight enamel decalcification buccally on image.
image erupted.
Mild lower labial segment crowding; image very slightly mesiolingually rotated; lower buccal segments spaced.
Upper arch uncrowded; spacing in the upper labial segment.
Class I incisor relationship with a centreline shift (clinically the lower centreline was 1.5 mm to the left).
Buccal segment relationship Class I bilaterally; lingual crossbite of image with image; buccal crossbite of image with image.
image

Fig. 6.2 (A) Lower occlusal view.

image

Fig. 6.2 (B) Upper occlusal view.

image

Fig. 6.2 (C) Right buccal occlusion.

image

Fig. 6.2 (D) Left buccal occlusion.

image What are the potential causes of c’s being retained?

Absence of 3’s. This is highly unlikely (0.3% of Caucasians).
Ectopic position of 3’s – this is the most likely cause (1–2% in Caucasians with 8% of these bilateral).

image What factors are implicated in maxillary canine ectopia?

The aetiology of maxillary canine ectopia is obscure but most probably multifactorial. Possible causative factors are:

1 Genetic – palatally displaced 3 appears to result from a polygenic multifactorial mode of inheritance, with associated anomalies including incisor-premolar hypodontia and peg-shaped 2 (see below). Class II division 2 malocclusion is also associated with an increased incidence of palatal 3.
2 Crypt displacement – where the position of 3 is grossly displaced, this may be an aetiological factor.
3 3 has the longest path of eruption of any permanent tooth.
4 Arch length discrepancy – palatal displacement of 3’s has been mostly associated with an uncrowded or spaced arch. Note the spacing present in Diane’s upper arch.
5 Trauma to the maxillary anterior area at an early stage of development – this has been suggested but there is no history of trauma in this case.
6 Peg-shaped, short-rooted 2’s or absent 2’s – guidance for 3 is reduced where these features are evident, doubling the incidence of palatal impaction of 3.

Key point

Palatal displacement of 3 is more common in an uncrowded arch and is associated with small, absent or abnormal formation of 2’s and Class II division 2 malocclusion.

Note in Diane’s case, the mesiodistal width of 2’s were the same as those of image’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.

image What is the prevalence of TSD and which teeth are most commonly affected?

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.

image How would you assess for a TSD?

Quick-check method

• For anterior TSD: compare the width of the upper and lower lateral incisors; if the upper lateral incisor is not wider than the lower, a TSD exists.
• For posterior TSD: compare the width of the upper and lower second premolars; these should be about equal size.

Computational method

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:

(Sum mandibular anteriors)/(sum maxillary anteriors) × 100 = anterior ratio (%).
(Sum mandibular 6–6)/(sum maxillary 6–6) × 100 = overall ratio (%).

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.

image What are the implications of a TSD?

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.

Key point

TSD:

• May be assessed comprehensively by a Bolton analysis: mean anterior ratio is 77.2 ± 1.65%; mean overall ratio is 91.3 ± 1.91%.
• Is rarely significant if < 1.5 mm.
• Clinically significant for treatment planning if >2SD beyond Bolton mean values.

Investigations

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Jan 2, 2015 | Posted by in Orthodontics | Comments Off on 6: Palatal canines

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