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RESEARCH REPORT |
1 Department of Biostatistics, University of Aarhus, 6 Vennelyst Boulevard, DK-8000 Århus C, Denmark;
2 Department of Computer Science, School of Dentistry, University of Aarhus, Denmark;
3 Department of Orthodontics, School of Dentistry, University of Copenhagen, Denmark; and
4 Department of Community Oral Health and Pediatric Dentistry, School of Dentistry, University of Aarhus, Denmark;
* corresponding author, parner{at}biostat.au.dk
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: emergence • permanent teeth • correlation • tooth innervation
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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If emergence patterns could be interpreted biologically, it might add to the understanding of the eruption mechanism. Experimentally, it has been shown that the dental follicle plays an essential role in eruption (Marks and Schroeder, 1996), that innervation occurs in the human follicle (Christensen et al., 1993), and that denervation performed experimentally influences the process of osteoclast appearance necessary for tooth movement (Yamashiro et al., 2000). Accordingly, we hypothesized that an association exists between eruption pattern and innervation pattern.
The purpose of our present study was to examine correlations between the emergence times of different teeth in the permanent dentition on data from a large national database, using statistical methods appropriate for these types of data. In addition, we aimed to associate eruption patterns to the innervation patterns of the jaws (Kjær, 1997) and thereby possibly contribute to an understanding of the eruption process. Finally, we also wanted to assess to what extent knowledge of the emergence time of one tooth would increase the precision with which the emergence of another tooth could be predicted.
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MATERIALS & METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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For the present study, we considered tooth emergence data for children born in 1978 and with more than 11 records in the database, in total 12,642 boys and 12,095 girls. The emergence time for a given tooth, i.e., the age of the child when the tooth emerged, is known to lie in the interval determined by the age of the child at the last visit prior to emergence and the age at the first visit after emergence. Such data are called "interval-censored data" (see Lindsey and Ryan, 1998, for a review on the analysis of interval-censored data). When pairs of emergence times are considered, the data on each child are a pair of interval-censored observations, and the pair of emergence times is therefore known to lie only in a two-dimensional interval, i.e., a rectangle in the plane.
In earlier studies, we showed that the distribution of emergence times is approximately Gaussian (Parner et al., 2001), and that the joint distribution of two emergence times indeed follows approximately a two-dimensional Gaussian distribution (Parner, 2001). Both of these papers used non-parametric methods for interval censoring, which requires only a minimum set of assumptions. This approach may be viewed as a generalization of the empirical distribution function to interval-censored data, and the appropriateness of Gaussian distribution can therefore be assessed. In the present analysis, the likelihood function for two emergence times was derived as the product of the probabilities of the observed rectangles based on a two-dimensional Gaussian distribution. We then obtained maximum likelihood estimates of the means, standard deviations, and correlations by maximizing the likelihood function. Standard errors of the means, standard deviations, and correlations were calculated as the inverse of minus the matrix of second numerical derivatives of the log-likelihood function.
We used standard results about multivariate Gaussian distributions to derive the effect on the variance of the distributions of emergence times for a given tooth when the emergence times of other teeth were taken into account (Mardia et al., 1979, page 64). If the emergence time of just one other tooth were accounted for, the variance would thus be reduced by a factor equal to 1 minus the squared correlation coefficient between the two teeth. We used these results to study the effect of adjusting for the emergence times of other teeth on a reference interval for the emergence time of a given tooth.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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). Within the same side of the jaw, the correlation decreases with distance from the index tooth; for teeth in the opposite side of the upper jaw, a similar pattern is seen, since the correlation decreases with distance from the homologous index tooth. The correlations between the index tooth and the teeth in the lower jaw show the same pattern, but the correlation coefficients are generally smaller. The results for girls and boys are remarkably similar.
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In both jaws, the largest correlation between pairs of neighboring teeth is seen between the two central incisors (Fig. 2). In the upper jaw, the other neighbor correlations are around 0.8 except for the correlation between teeth which belong to different tooth groups—for example, the lateral incisors and the canines and the second bicuspid and the first molars. In the lower jaw, a similar but less pronounced pattern is seen. Again, the results for girls and boys are essentially the same.
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). The gray area in the Fig. gives a 95% reference interval for the emergence time of tooth 17 based only on information on this tooth. If the time of emergence of tooth 16 is available, the reference interval for tooth 17 is given as the interval between the two tilted lines for the particular value of x, the emergence time of tooth 16.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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In the present study, which is based on a very large dataset, it has been shown that there is a high correlation in emergence times between teeth in the dental arch that are homologous, i.e., that belong to the same group of teeth. On the other hand, there is a lower correlation in emergence times between teeth from different tooth groups. In that connection, it is worth noticing that tooth groups are innervated separately. For instance, nerve supply to molars and premolars is not the same (Kjær, 1995; Chavéz-Loméli et al., 1996). This suggests that innervation may have an important influence on emergence times. This hypothesis is supported by the relatively high correlation coefficients between teeth with the same nerve supply, while teeth from different tooth groups show lower correlation in emergence times, even though the teeth are adjacent to one another, e.g., the first molar and the second premolar. The fact that the correlation in emergence times between a given index tooth and the teeth in the same jaw segment is generally higher compared with the correlation between the same index tooth and teeth in the contralateral part of the jaw can also be explained by the pattern of innervation. Considering that the two bilateral parts of the jaw are innervated from two bilateral and different trigeminal ganglia, it is reasonable to assume a higher correlation in emergence times between teeth belonging to the same ganglion than between teeth innervated from different ganglia.
It is commonly assumed that the inferior alveolar nerve supplies all the teeth in the mandible. Recent studies, however, have shown that the inferior alveolar nerve is a large bundle of nerve fibers whose individual nerve branches grow out at different times to innervate different tooth groups (Chavéz-Loméli et al., 1996). The correlation of emergence times that is documented in the present study can thus be presumed to visualize the innervation patterns of both maxilla and mandible. That the pattern is more distinct in the maxilla than in the mandible may be related to the fact that the courses of the nerve branches are more separate in the maxilla (naso-palatine nerve to the incisors, maxillary nerve to canines/premolars, palatine nerve to molars) than in the mandible (inferior alveolar nerve with a common bundle of individual nerve branches).
General factors and local factors (e.g., caries history of the predecessors) are known to influence eruption. The present theory concerning influence from the peripheral nervous system exemplifies a general factor. The credibility of this present biological interpretation is indirectly supported by the fact that other explanations seem less consistent with the results. For instance, different types of teeth emerging about the same age do not show a particularly high correlation. Concerning the deciduous dentition, the innervation paths are similar to those of the permanent dentition, but the correlations of these emergence times have not yet been analyzed. Therefore, comparisons with similar studies in the deciduous dentition cannot be performed.
Due to the large sample size and the high precision of the estimates of correlations, results from our study could be useful in the diagnosis of the delayed eruption of permanent teeth, such as, for example, upper canines, and thus assist in the decision as to whether radiographic examination is needed. Another example could be delayed eruption of lower second molars, which is often vaguely defined as "emergence beyond the time when it should normally erupt" (Varpio and Wellfelt, 1988). Consider, e.g., the emergence of tooth 17. The 95% reference interval for the age at emergence of this tooth is (9.97, 14.67) yrs (Fig. 3
, the gray area). If we take the emergence time of tooth 16 into account, then the 95% reference limits are given by the two oblique lines in the Fig. If tooth 16 has emerged at the age of 6, the width of the 95% reference interval for tooth 17 is reduced considerably, and the improved interval becomes (10.69, 13.30). Thus, by taking the emergence time of tooth 16 into account, we have explained 69% of the biological variation of the emergence time of tooth 17. Further calculations also show that we do not gain much more in terms of reduction in the width of the reference interval by adjusting for emergence of other teeth. For example, if we simultaneously take the emergence times of teeth 11, 12, 13, 14, 15, and 16 into account, the explained variation becomes 73%, only slightly larger than when only the emergence time of tooth 16 is accounted for.
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ACKNOWLEDGMENTS |
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Received August 14, 2001; Last revision May 6, 2002; Accepted May 15, 2002
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REFERENCES |
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Christensen LR, Janas MS, Møllgård K, Kjær I (1993). An immunocytochemical study of the innervation of developing human fetal teeth using protein gene product 9.5 (PGP 9.5). Arch Oral Biol38:1113–1120.[Medline]
Garn SM, Smith BH (1980). Developmental communalities in tooth emergence timing. J Dent Res59:1178.
Garn SM, Lewis AB, Polacheck DL (1960). Interrelations in dental development. I. Interrelations within the dentition. J Dent Res39:1049–1055.
Hamano Y, Hägg U (1988). Inter-relationships among ages of emergence of teeth. A prospective longitudinal study of Swedish children from birth to 18 years. Eur J Orthod10:273–280.
Kent RL Jr, Reed RB, Moorrees CF (1978). Associations in emergence age among permanent teeth. Am J Phys Anthropol48:131–142.[Medline]
Kjær I (1995). Human prenatal craniofacial development related to brain development under normal and pathologic conditions. Acta Odontol Scand53:135–143.[Medline]
Kjær I (1997). Can the location of tooth agenesis and the location of initial bone loss seen in juvenile periodontitis be explained by neural developmental fields in the jaws? Acta Odontol Scand55:70–72.[Medline]
Lindsey JC, Ryan LM (1998). Tutorial in biostatistics methods for interval-censored data. Stat Med17:219–238.[Medline]
Mardia KV, Kent JT, Bibby JM (1979). Multivariate analysis. London: Academic Press.
Marks SC Jr, Schroeder HE (1996). Tooth eruption: theories and facts. Anat Rec245:374–393.[Medline]
Parner ET (2001). Non-parametric maximum likelihood estimation for bivariate interval censored data. Research report. Aarhus: Department of Biostatistics, University of Aarhus.
Parner ET, Heidmann JM, Væth M, Poulsen S (2001). A longitudinal study of time trends in the eruption of permanent teeth in Danish children. Arch Oral Biol46:425–431.[Medline]
Sturdivant JE, Knott VB, Meredith HV (1962). Interrelations from serial data for eruption of the permanent dentition. Angle Orthod32:1–13.
Varpio M, Wellfelt B (1988). Disturbed eruption of the lower second molar: clinical appearance, prevalence, and etiology. ASDC J Dent Child55:114–118.[Medline]
Yamashiro T, Fujiyama K, Fujiyoshi Y, Inaguma N, Takano-Yamamoto T (2000). Inferior alveolar nerve transection inhibits increase in osteoclast appearance during experimental tooth movement. Bone26:663–669.[Medline]
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