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Effect of the Birth Process on the Neonatal Line in Primary Tooth Enamel Dana Eli, DMD Haim Sarnat, DMD MS Eliezer Talmi, DMD

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Effect of the Birth Process on the Neonatal Line in Primary Tooth Enamel Dana Eli, DMD Haim Sarnat, DMD MS Eliezer Talmi, DMD PEDIATRIC DENTISTRY/Copyright © 1989 by The American Academy of Pediatric Dentistry Volume 11, Number 3 Effect of the birth process on the neonatal line in primary tooth enamel Dana Eli, DMD Haim Sarnat, DMD MS Eliezer Talmi, DMD Abstract The neonatal line is a histologic landmark in primary tooth 1980). The ultrastructural basis for the NNL was enamel corresponding to the event of birth. The average width believed to be a localized change in configuration of of the neonatal line (NNL) in primary tooth enamel of 147 enamel prisms along with possible reduction in crystal children was measured. In children with normal birth concentration (Weber and Eisenmann 1971). histories the width of the NNL was found to be 12.9 ± 4.8 \Lm. The formation and accentuation of the NNL were It was wider (18.6 ± 5.7 \un) in children born by difficult attributed to the abrupt change in the environment and operative delivery and thinner (7.6 ±1.5 \an) in children born nutrition of the newborn (Schour and Kronfeld 1938; by Caesarean section. Massler et al. 1941; Orban 1980). Noren (1984a) The data suggest that concomitant with the change from described a wider NNL in children born to diabetic intrauterine to extrauterine environment, the birth process mothers and hypothesized that the wider NNL is a itself also contributes to the width of the NNL. structural response to neonatal hypocalcemic stress (Noren 1984b). Except for the influence of maternal The incremental nature of enamel and dentin devel- diabetes, no other factors (asphyxia, low birth weight, or opment has been known and described for more than a intrauterine malnutrition) were identified as being century. Retzius (1837) reported brown lines observed associated with a wider NNL (Magnusson et al. 1978; in the enamel which were caused by periods of enamel Noren et al. 1978; Noren 1983). formation and rest — the incremental lines (striae) of The diagnostic possibilities of microscopic Retzius. The distance between the lines of Retzius was examination of enamel, using the NNL as a marker measured and found to be about 16 ^m (Schour and together with the known mean rate of enamel Hoffman 1939). deposition to determine When the very sensitive ameloblasts are subjected to the timing of noxious a noxious episode of either internal or external origin, a events, was shown by temporary change in the rhythmic enamel matrix Levine et al. (1979). A formation may occur, causing some striae of Retzius to significant association appear more prominent than normal. One such between case histories of accentuated Retzius line corresponds to the event of brain damaged children birth and is known as the "neonatal line" (NNL; Fig. 1). and histologic enamel Schour (1936) described the NNL and estimated its findings was reported distance from the dentinoenamel junction for the byjudesetal. (1985) and various teeth. He indicated the absence of the NNL in Jaffe et al. (1985a, b). teeth of unborn fetuses. By injecting sodium fluoride These studies concen- into rats, Schour and Poncher (1937) were able to trated on the identifi- estimate the average rate of enamel formation as 4 (am/ cation of any prominent 24 hr. The NNL was described as a border between the Retzius striae as a sign of prenatal enamel created during gestation and interference with the characterized by its regularity and high degree of developing fetus' tis- calcification, and the postnatal enamel created after sues, an interference Fig 1. Histologic representation which could be the cause of NN,L (arrow> in a 100^m birth which is less regular and less homogeneously , . „, sagittal ground section of a calcified (Schour 1936,1938; Massler et al. 1941; Orban of the brain damage. To primary tooth 220 EFFECT OF BIRTH PROCESS ON NEONATAL LINE: ELI ET AL. assess damage caused to the newborn during the birth TABLE1. Teeth According to Type of Delivery process, the authors assumed a width of about 8 ~m to Caesarean be normal, while any line wider than 15 ~tm was Tooth~Delivery Normal Operative Section interpreted as indicating a complicated birth or a Incisors 23 2 3 disturbance in the perinatal period (Jaffe et al. 1985a, b). Canines 62 7 1 In other studies the average NNL width in Molars 40 8 1 permanent first molars was suggested to be about 10 ~m Total 125 17 5 (Jackobsen 1975). Magnussonet al. (1978) and Nor6n al. (1978) cited 10-12 ~tm as the normal NNLwidth different regions of the tooth, 3 separate measurements microradiographic measurements of primary incisors, were made at each of the 3 different levels of the but no data concerning the measurements were anatomic crown (incisal, middle, and gingival). Mean presented. Jaffe et al. (1985a, b) indicated the need for and standard deviations were computed for each level. acquiring more accurate data regarding the NNLwidth, Thirty specimens were remeasured by another a value which could be used when the effect of the investigator with negligible discrepancies. trauma of the birth process needs to be assessed. In the present study, an attempt was made to measure accurately the average NNLwidth in children Results with normal birth histories. The effect of the birth The NNLwas identified in all teeth examined on at process on the NNLwas investigated by comparing the least 1 crown level. The microscopic evaluation of the NNLwidth in children with normal and complicated NNLshowed that it appears to be mostly straight (85% birth histories. in teeth from children born by normal delivery and 85.7% in teeth from children born by operative Materials and Methods delivery), continuous (60 and 78.6%, respectively) uniformly accentuated (78 and 57.1%, respectively). Primary teeth collected from 147 normal children significant differences were found between the 2 were examined--one tooth from each child. Normal groups. children were defined as those with no history of The mean NNLwidth in children born by normal systemic disorders related to pregnancy and/or labor delivery was found to be between 11.9 and 12.4 ~tm at the and who had birth weight not less than 2500 g. Birth various crown levels (Table 2). A significant increase histories were obtained from hospitals including type of < 0.05) in the NNLwidth in children born by operative delivery and condition of the newborn. The teeth were delivery was found for each level (Table 3). divided into 3 groups (Table 1): No significant difference (according to one-way 1. Normal delivery--125 teeth analysis of variance) was found within the values 2. Complicated (operative) delivery--17 teeth acquired for the 3 different levels of the anatomic crown (Operative delivery was determined whenever of either normal or operative delivery. Since the only active outside intervention took place, e.g., breech, data acquired for the group born by elective Caesarean forceps, or vacuumdelivery; Bensor 1982.) section were from the gingival level, this level was 3. Elective Caesarean section (no active birth chosen for comparison amongthe 3 groups (Fig 2). The process)--5 teeth. values were markedly lower (7.6 + 1.5 ~tm) for children Ground serial sections were cut sagittally in the born by elective Caesarean section. buccolingual direction (100 ~tm thick) using a low-speed TABLE2 Width of NNL(~m) in Children Born by saw (IsometT~--Buehler; Lake Bluff, Illinois) and NormalDelivery examined under a light microscope. Since the appearance of the NNLapparently can be affected by Incisors Canines Molars Level of N = 23 N = 62 N = 40 Mean* the inclination of the line relative to the plane of crown~Tooth ~ SD Y~ SD ~ SD ~ SD sectioning (Weber and Eisenmann 1971), all teeth were Incisal -- 11.3 6.1 12.2 5.1 12.1 5.1 mounted on the cutting machine and sectioned exactly (N = 4) (N = 36) (N = 40) in the mid-sagittal plane. The NNLwas identified in all Middle 11.6 6.5 12.1 7.0 16.5 9.0 12.4 7.0 specimens and its nature defined in terms of direction, (N = 6) (N = 36) (N = 4) (N = 46) continuity, and uniformity of accent. The NNLwidth Gingival 13.3 4.5 10.9 4.9 - 11.9 4.8 was measured by an eye piece (Filar~---Bausch and (N = 17) (N = 22) (N = 39) Lomb; U.S.A.), accuracy up to 0.1 ~m. To consider the Total children N = 125 effect of the different angle of the enamel rods at a No difference between groups accordig to one-way analysis of variance. PEDIATRICDENTISTRY: SEPTEMBER, 1989- VOLUME11, NUMBER3 221 TABLE3. MeanWidth of NNL(~,m) in Children Born be continuous, the lower percentage of the NNL by NormalDelivery Comparedto Children Born by identified in other studies may be due to lack of Operative Delivery appearance of the NNLin some areas of the tooth Normal Operative* crown. Levelof N = 125 N = 17 Statistical The present findings suggest that the normal NNL crown~Delivery "~ SD ~ SD Significancd width in primary teeth is about 12 ~tm. This is in Incisal 12.1 5.1 17.4 6.4 P < 0.05 agreement with Jackobsen (1975) as to the NNLwidth (N = 40) (N = 6) Middle 12.4 7.0 18.3 5.7 P < 0.05 first permanent molars and those cited by Magnussonet (N = 46) (N = 8) al. (1978) and Nor6net al. (1978) for primary incisors. Gingiva! 11.9 4.8 18.6 5.7 P < 0.05 Unlike Jackobsen (1975) who claimed that the NNL (N = 39) (N = width is highly dependent upon the distance of the Operativedelivery - breech, vacuum,forceps. section from the cusp tip, the present data demonstrate Accordingto t-test. that the level at which the sample is obtained (incisal, middle, or gingival) has little influence on the value obtained.
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