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Letter to the Editor

In the study by Pirinen et al. (1996) entitled "Palatal Displacement of Canine is Genetic and Related to Congenital Absence of Teeth", the authors found evidence to support a genetic basis for the etiology of palatally impacted canines. Thus, they duly noted that their findings "...clearly indicated the genetic character of hypodontia" which "...support the hypothesis that palatally malposed canines belong to the broad spectrum of dental anomalies related to incisor-premolar hypodontia" and, later, "...the impacted canine is related to hypodontia and small and peg-shaped lateral incisors...(are)...familial and perihaps (my emphasis) genetic". These are all very cautious, valid, and scientifically correct statements which have been chosen to reflect the degree with which inferences may be drawn from their results. But other etiologic possibilities do exist, which the authors are at pains to point out. In their introduction, they note that the occurrence of maxillary canine displacement has been explained by local factors, such as lack of or excess space, by trauma, or by lack of guidance due to lateral incisor anomaly. In their present study, they neither sought nor found evidence to disprove these other suggested causes of impaction. For these reasons, the title of the article is misleading. Had the title read "Congenital Absence of Teeth is Genetic and Related to Palatal Displacement of the Canines", this would have reflected the authors' conclusions, in line with the aims, scope, design, findings, and limitations of their study and the studies of many others. It would also have been a statement that supports the findings of several of the other studies to which they refer, which suggest an alternative etiology for the displaced maxillary canine (Miller, 1963; Becker et al., 1981; Brin et al., 1986; Zilberman et al., 1990; Mossey et al., 1994). However, the impression given by the title is that palatal displacement of the canine is (apparently exclusively) genetic. On the basis of this study, this has not been proved. The article prompted Peck and Peck (1997) to quote the work of Racek and Sottner (1977, 1984), and, in their letter to the editor, they describe the Czech research as "...rigorous (my emphasis) family studies" which "...presented incontestable (my emphasis) evidence of the genetic nature of the palatally displaced canine anomaly". But Racek and Sottner themselves are more objective in their assessment, avoiding such dogmatic terminology and pointing out that "...in the complex of p)ossible cautses (my emphasis)...an important place is held by hereditary factors", conceding the possibility of other primary or contributory etiologic factors. All of the abovementioned works agree that there is a distinct genetic background to the problem, including those that have given credence to the Guidance theory. However, it remains a moot point as to whether the genetically determined lateral incisor anomalies (i.e., absent, pegshaped, small, late development, short roots, and excessive space) create the environment in which an unerupted canine is deprived of the benefit of guidance from the distal aspect of the lateral incisor root, that Broadbent (1941) believed it would normally receive. The view of Peck et al. (1994, 1995, 1997) and that proclaimed by the title of the article by Pirinen et al. (1996) is that each of the factors, including the palatal displacement of the canine, is hereditary. There is a fine difference between these two hypotheses, a difference which has yet to be resolved. Until that time, both these viewpoints must be considered credible etiologic alternatives (Becker, 1995, 1997).