Dental outcomes of preterm infants

Abstract Follow-up of preterm infants has focused primarily on neurodevelopmental outcomes. However, the long-term effects of prematurity involve multiple systems. Dental health issues and problems related to prematurity including problems of enamel defects, delayed eruption and tooth size, and oral defects associated with oral endotracheal intubation of preterm infants are the focus of this article. Implications for long-term care and follow-up of dental concerns are also discussed. © 2003 Elsevier Inc. All rights reserved.

Dental Outcomes of Preterm Infants By Diane L. Eastman, MA, RN, CPNP

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reterm (premature) births are defined as those births occurring before 37 completed weeks of gestation.1 Within this group of births are also included very low birth weight (VLBW) births, which include all infants weighing less than 1,500 grams, and extremely low birth weight (ELBW) births, which include all those weighing less than 1,000 grams.1 The techniques required to sustain life in very small preterm infants has had some effect on oral growth and also on complications within the oral cavity from such things as endotracheal tubes. Overall, enamel defects and the effects of oral tracheal intubation are probably the most common, but other issues include delayed dentition, permanent tooth crown dimension changes, posterior cross bites, and palatal asymmetry. The pathogenesis of these defects remains unclear but are likely caused by both systemic and local causes. Relatively little long-term data are available for some of the identified problems.

Embryonic Development of the Dentition

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From the Department of Pediatrics, University of Iowa Hospital and Clinics, Iowa City, IA. Address reprint requests to Diane L. Eastman, MA, RN, CPNP, University of Iowa Hospital and Clinics, High Risk Infant Follow-up, 100 Hawkins Drive, S267, Iowa City, IA 52242. © 2003 Elsevier Inc. All rights reserved. 1527-3369/03/0303-$30.00/0 doi: 10.1053/nbin.2003.36117

evelopment of dentition begins as early as 4 weeks in utero and continues until approximately 20 years of age.2 At 2 months gestation, primary tooth development begins and permanent teeth begin to form several months before birth. Premature birth may affect those teeth that are at a critical stage of development at this vulnerable time. Teeth are formed by mineralization of a protein matrix. This process begins at about 4 months gestation and is not complete until late adolescence.2 The essential nutrients required for dental development are calcium, phosphorus, fluoride, and vitamins A, C, and D. Collagen, the protein in dentin, must have vitamin C for normal synthesis. Enamel contains keratin, a protein that requires vitamin A for its formation. Calcium and phosphorus are the basic structural material of teeth, and vitamin D is needed for calcium and phosphorus to be deposited into the protein matrix. At 40 weeks’ gestation, mineralization of deciduous incisor crowns is nearly complete, and mineralization of the other deciduous crowns has begun. Calcification of the first permanent molar crown occurs at about 28 to 30 weeks gestation and is not complete until 3 to 4 years of age.1 Formation of all anterior permanent teeth begins in utero but time to full development is highly variable.1 Maternal illness can impact tooth development and associated tooth abnormalities. Maternal diabetes, hypertension, preeclampsia, infection, and nutritional deficiencies have all been linked to size of the fetus and to oral abnormalities.3,4 Maternal smoking has also been associated with smaller birth weight and reduced dimensions of the tooth crown.1 Use of certain medications has also been associated with dental abnormalities.1 Newborn and Infant Nursing Reviews, Vol 3, No 3 (September), 2003: pp 93–98

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Enamel Defects

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namel defects are a well-studied complication of prematurity.3–5 Enamel is a hard tissue that once formed, unlike bone, does not remodel. For that reason, insults during enamel development are permanent on the tooth surface. Dental enamel formation begins during the second trimester of pregnancy and is complete by about 18 years of age.6 The major portion of the newborn’s stores of calcium and phosphorus are accumulated in the third trimester of pregnancy. Therefore, an ELBW infant will not have accumulated these stores. Enamel hypoplasia is defined as “deficient quantity of enamel resulting from developmental aberrations, and may occur in the form of pits, grooves, or larger areas of missing enamel.”6 Enamel opacity is defined as a qualitative change in the translucency of the enamel.7 The common medical complications of premature infants including surfactant-deficiency respiratory distress syndrome, asphyxia and hypoxia, hypocalcemia, renal immaturity, feeding difficulties, and infection are just some of the problems that may affect enamel formation. The biochemical cause of enamel hypoplasia is not fully understood, but growing evidence indicates it is strongly linked to calcium homeostasis.1 There are several studies that suggest a direct relationship between enamel hypoplasia in primary teeth and neonatal hypocalcemia.2,8 There are numerous pre- and postnatal problems that cause hypocalcemia in the newborn. The more premature and the lower the birth weight, the more problems with calcium homeostasis. Maternal diabetes mellitus, placental insufficiency, often related to preeclampsia, and maternal deficiency of dietary calcium and vitamin D are all in utero factors. Traumatic delivery, asphyxia, cerebral injury, and prematurity itself with deranged calcium metabolism are perinatal factors that contribute to hypocalcemia. Additional contributors to hypocalcemia include hypoxia, sepsis, and hyperbilirubinemia. The prevalence of enamel defects ranges from 43% to 96% of VLBW infants.9 –11 Seow et al reported a direct relationship between birth weight and gestational age with the greatest prevalence of enamel defects occurring in the lowest birth weight group.9 The clinical significance of enamel defects is not only esthetic, although these teeth can appear cream colored, yellow, or brown. Enamel hypoplasia is linked to plaque accumulation, dental caries, and in more severe cases, with space loss and malocclusion. In a longitudinal study by Lai et al5 there was a significant association with enamel defects and dental caries in the VLBW group that was noted on exams of the children at 44 and 52 months of age. The most dental

caries were observed in those children who had both enamel hypoplasia and opacity. Enamel defects have also been identified in the permanent dentition of children born prematurely. Pimlott et al4 found enamel hypocalcification in at least one maxillary permanent incisor in 58% of the 106 VLBW infants examined; however, the other permanent teeth were not examined. Seow12 matched 55 VLBW and 55 normal birth weight (NBW) controls at a mean age of 7.7 years for defects in enamel of permanent incisors and molars. The VLBW group had a higher percentage of enamel defects in the permanent molars (21% v 11%) and permanent lateral incisors (12% v 0%) compared with controls. Most of the defects were enamel opacities. Aine et al13 matched 32 preterm to 64 control children. The prevalence of enamel defects in preterm compared with control children was higher in both primary (78% v 20%) and permanent (83% v 36%) dentitions. Because the permanent teeth are believed to begin mineralization a few months after the preterm birth, it is hypothesized that persistent metabolic disturbances affect the mineralization and calcium homeostasis of the first few permanent teeth. Enamel defects can be both generalized or localized. Generalized defects are symmetrically distributed and likely caused by systemic illnesses associated with prematurity. As mineral stores in the preterm infant are depleted, calcium and phosphorus entering the developing tooth is insufficient for enamel formation. This theory is supported by a study of preterm children who had neonatal rickets secondary to severe osteopenia.9 In the study, every child with rickets also had severe enamel hypoplasia. A later study by the same investigators14 demonstrated that all preterm children with enamel hypoplasia also had decreased cortical mineralization of the humerus. This study demonstrated a direct relationship between enamel hypoplasia and diminished bone mineral stores. Trauma may also cause some enamel defects. Controlled studies by Seow et al9,14 demonstrated that children who had been orally intubated and required mechanical ventilation had more enamel defects on the left maxillary teeth (63% v 40%) compared with nonintubated children. A Swedish study15 of full-term infants who were intubated in the neonatal period demonstrated similar results of more defects on the left side. The process of laryngoscopy would account for this primarily left side defect. Inadvertent force is often placed on the left side as the laryngoscope is pushed more to that side to allow room to insert the orotracheal tube along a groove in the right side. Although the tube itself has been considered to be the cause of the trauma, the tube would likely cause more even distribution of force to both right and left sides.

Dental Outcomes of Preterm Infants

Oral Defects Associated with Intubation

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remature infants frequently require assisted ventilation because of respiratory insufficiency, apnea, asphyxia, and sepsis. Prolonged endotracheal intubation is often necessary for the ELBW infants. Orotracheal tubes are the preferred method of intubation for most premature infants. Orotracheal tubes are used to avoid the septal and respiratory impairments associated with nasotracheal tubes.16 Orotracheal tubes have been associated with development of acquired cleft palate, palatal grooving, alveolar grooving, primary tooth dilaceration, palatal depth and width asymmetry, crossbites, and poor speech intelligibility and nasality. Erenberg and Nowak17 reported the association between long-term use of orotracheal tubes and a higher incidence of palatal groove formation in a group of infants requiring intubation from 1 to 62 days. Alveolar grooves have been reported by a number of others.18,19 The use of “soft” ET tubes has not resulted in a reduction in palatal grooves.20,21 Multiple factors influence abnormal palate formation. The narrow elongated “preemie head” may cause a narrow high vaulted palate, made worse by head posture contributing to collapse of the palate. The ET tube may press on the midline palate and alveolar ridge, disturbing its growth. The pressure applied to the ET tube to keep it properly positioned may further affect the developing palate. Babies sucking on their ET tubes may also result in some molding of the tissues.25 Prevention of palatal groove formation has been attempted with the introduction of various appliances designed to protect the palate from increased pressure from ET and orogastric tubes. Several similar appliances have been reported in the literature.21,22 Design differences were primarily for stabilizing only the endotracheal tube or both the ET and feeding tubes. Fadavi et al23 in a randomized prospective study of 26 infants with birthweights of 540 to 1,740 grams and orally intubated from 7 to 109 days found no evidence of palatal grooving in the group who were fitted for the palatal device. Palatal grooves of 2 to 5 mm in depth developed in the control group without the palatal plate. Ginoza et al24 found the palate plate significantly diminished the degree of groove formation in a randomized trial of VLBW infants intubated for at least 5 days. Ash et al25 compared preterm infants with and without palate plates to measure changes in the palate other than groove formation. In this study of babies less than 32 weeks’ gestation, 15 nonintubated babies were used as a control group and 30 babies intubated for more than 10 days were randomly assigned to the palate plate and no palate plate groups. The palates of

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babies without plates were smaller, narrower, and deeper than nonintubated babies. There was a reduction in the narrowing and depth of the palate of those with the plate. Narrowing of the palate was not limited to intubated babies but was more extensive and persisted longer in that group. Palate plates did not restrict the lateral growth of the infant palate. The palate plate also allowed for early resolution of gum pad depression compared with the nonpalate plate group. Kopra and Davis26 found a higher incidence of oral abnormalities in two groups of LBW children ages 3 to 5 and 7 to 10 years old who had been intubated than in same age children of average birth weight who had not been intubated. In both age groups, intubated subjects had a greater incidence of high vaulted palate, palatal grooving, and posterior crossbite compared with the control group. Their speech was also judged to be less intelligible. This study is one of the few that demonstrates these defects persist into middle childhood. They concluded that a high vaulted or grooved palate may result in the tongue not meeting the palate correctly. This may adversely affect the production of normal speech sounds and contribute to hypernasality and poorer speech intelligibility. From their analysis, they also concluded that length of intubation did not influence oral defects and speech characteristics. In a more recent study by Macey-Dare et al27 of former premature and LBW infants, palatal widths, arch widths, and palatal depths were measured. The children were 8 to 11 years old at the time. The 43 premature infants had birthweights of 957 to 2,040 grams and gestational ages of 20 to 37 weeks. Intubation ranged from 1 to 58 days. The study group was compared with a control group of 50 term, normal birth weight children. Intubated children were divided into two groups: those intubated less than or equal to 15 days and those intubated for more than 15 days. There were no statistical differences between the two intubated groups at any level of measurement in this study. There were significant differences when the intubated and nonintubated groups were compared. The children who had been intubated had significantly narrower palate widths posteriorly, and palatal vaults were steeper anteriorly. The intubated group also had palatal width asymmetry with the left side consistently wider than the right. In contrast to these findings, Seow et al28 compared palate and dental arch symmetry between intubated and nonintubated groups of children. They found no significant differences in the two groups, but none of the children in the intubated group had been intubated for more than 20 days. Continued research regarding the long-term effects of intubation appears warranted from these results. In particular, persistence of effects into adolescence is important as many orthodontic interventions occur in this age group.

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Delayed Eruption and Size of Teeth

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he timing of primary teeth eruption in premature infants has not been well established. Delayed eruption has been observed in several longitudinal and crosssectional studies.29 –31 In each of these studies, the delay in tooth eruption was related to gestational age or low birth weight. Viscardi et al32 attempted to relate delayed tooth eruption to neonatal factors other than birth weight and gestational age. They followed a group of 35 infants with birth weights less than 2,500 grams and gestational age less than or equal to 36 weeks. Fourteen (40%) of this group had their first tooth erupt in the “normal” range of less than or equal to 10 months chronological age, and 21 (60%) had the first tooth erupt over 10 months of age. The late erupting group was comprised of those with birth weights ⬍1,000 grams and/or ⬍31 weeks’ gestation. Other factors appeared to be important related to nutrition. The nutritional factors that correlated significantly with tooth eruption were age when full enteral feedings were achieved, age when oral vitamin supplements were started, and average weight gain per day. They concluded that prolonged intubation for illness and inadequate nutrition were important factors affecting the timing of tooth eruption. Backstro¨ m et al33 studied the development of primary and permanent teeth in a group of preterm infants and also examined calcium, phosphorus, and vitamin D supplementation. Birth weights in the preterm group ranged from 690 to 1,930 grams and gestational ages ranged from 23 to 35 weeks. The children were followed until they reached the ages of 9 to 11 years. A control group was recruited for comparison. The corrected teething age was similar in both groups as a whole. When divided by sex, the preterm girls had significantly later tooth eruption than full-term girls. This difference was not observed between preterm and full-term boys. Preterm girls also had significantly later tooth eruption than preterm boys. Full-term boys and girls showed no differences. By 2 years of age, the median number of teeth was the same in both groups with no difference noted between the genders. The heavier the infant at 3 months chronological age, the sooner the first tooth erupted. Early vitamin D supplementation did not affect maturation of primary teeth. Permanent teeth maturation did not differ between the preterm and control groups. There was no difference between the sexes, and maturation of permanent teeth did not depend on body weight. If maturation and teething of the primary teeth was delayed at 1 year of age, it was also delayed in the permanent teeth at 9 to 11 years. The most mature permanent teeth were found in the preterm children who received vitamin D at a dose of 1,000 international units

(IU)/d; however, mineral supplementation did not affect maturation. Harila-Kaera et al1 studied the effect of preterm birth on permanent tooth crown dimensions. Three hundred twenty-eight premature black and white children and 1,804 control children were examined at 6 to 12 years of age. This study suggested decreased tooth crown dimensions in some preterm infants. One significant difference was increased crown dimensions of some permanent teeth in the white preterm boys and black preterm girls and smaller dimensions in the white girls and black boys. Differences between gender, race, and growth patterns, especially accelerated or catch-up growth, may influence the determination of permanent tooth crown dimensions.

Implications for Long-Term Care and Follow-up

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rom the literature review, it is clear that primary and permanent teeth of the preterm infant can be affected in a variety of ways. Risk factors for dental problems are linked to a number of prenatal and postnatal conditions. The dental problems discussed may, in some cases, be permanent and cannot be corrected. Some problems can be minimized with good dental care. Education of both health care professionals and parents regarding overall dental health is important not only to minimize problems but also to promote good overall health. Health care providers need to include oral health and dental care as part of a routine examination and discussion with parents. Parent education needs to focus on preventive dental care and why good dental health is important. Parents need to appreciate the link between the oral cavity and systemic health issues as well. Maternal dental care and good prenatal care must also be included in the education provided. Good dental hygiene is important for all infants and toddlers, especially for preterm infants who are at higher risk for dental problems. Parents should be given a demonstration of how to properly clean their child’s teeth, starting with the eruption of the first tooth. Teeth should be cleaned routinely after feedings and especially at bedtime. Fluoride-containing toothpaste should not be used until the child has some control of the swallowing reflex and only “pea size” amounts should be used then. Young children swallow much of the toothpaste and this may lead to systemic overexposure to fluoride and subsequent mild discoloration of developing teeth.34 Feeding practices should be assessed and monitored carefully at each follow-up visit. To prevent caries, prolonged use of bottles, especially at night, and sippy cups should be discouraged.34 Discussion with parents should begin before the first tooth has erupted. It is not uncom-

Dental Outcomes of Preterm Infants

mon to find former preterm toddlers still drinking from a bottle long after the age when they are developmentally ready to progress to a cup. Preterm infant development should be monitored closely for readiness to begin using a cup. Toddlers who are developmentally functioning at 12 to 14 months are capable of transitioning to a cup. Growth and feeding is often a problem for premature infants. Many parents are hesitant to give up the bottle fearing their child may not eat and grow as well. More frequent monitoring of growth may be needed at this time to support parents in their effort to wean to a cup. Prolonged at-will breastfeeding should also be discussed after tooth eruption has occurred since infants who fall asleep while nursing may be at a higher risk of developing caries.34 Infants should not be put to bed with a bottle containing anything other than water. Parents need to be made aware of the important role of nutrition and good dental health. A thorough diet history is important to obtain at each follow-up visit. A referral to a dietician may be needed to assist if the child eats a very small variety of foods and is not receiving the recommended daily nutrient requirements. Education regarding which high carbohydrate foods and drinks promote decay should be provided. High carbohydrate foods that should be limited include crackers, presweetened cereals, muffins, breads, cookies, potato chips, and dried fruits. Foods that are less likely to contribute to caries development are high in protein, low in carbohydrates, high in calcium, and textures that stimulate saliva secretion. Cheese, meats, eggs, and some vegetables are in this group. Sweet carbonated drinks should be avoided. Juices are high in carbohydrates and should be offered sparingly only with meals. They should not be sipped all day from a cup or bottle. There is considerable difference in the relative decay potential of the various infant formulas available on the market.35 From in vitro studies, most infant formulas cause plaque pH to decrease to less than that associated with cavity formation.36,37 This was also confirmed in vivo studies.37 Considerable differences between the different brands and types of formulas were noted when the decay potential was quantified in these studies. Soy formulas rated the highest for cariogenic potential.35 Medications used commonly in pediatrics contain sucrose. Parent education is important when prescribing or reviewing medications at each health visit. Almost all liquid antibiotics contain sucrose.34 Children receiving these medications should have their teeth cleaned after each dose. Substituting sugar-free formulations should be considered whenever possible.34 Fluoride supplementation should be prescribed as appropriate. The fluoride content in the primary water source must be determined before supplementation can be appro-

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priately prescribed. Parents need to be educated about fluoride use and the dangers of excessive fluoride intake, which can lead to a mottled discoloration of the enamel ranging from chalky white to brown staining.34 The American Academy of Pediatric Dentistry (AAPD), the American Dental Association (ADA), and other dental organizations recommend that the first dental visit should be around 1 year of age.35 Health care providers need to monitor and assess the oral cavity at each visit and recommend dental visits begin no later than 1 year of age. It is important for preterm infants who are at higher risk for dental problems to be evaluated by this time. Assisting parents to access dental services for these infants and toddlers is imperative. Promoting good oral health is an important aspect of promoting good overall health. Good dental care should be emphasized to parents of all preterm infants. At the first sign of dental abnormalities, referral to a dentist should be initiated. Before the age of 3 years, some family dentists are unwilling to see the child. In this case, a referral to a pediatric dentist should be made.

Summary

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urther long-term follow-up of VLBW babies and dental abnormalities needs to continue. There are conflicting results in outcomes in the literature. Very few of the studies performed are from the United States. Most studies were completed some years ago. This makes generalizing results to today’s population of preterm infants more tentative. Information regarding the impact of improved survival and current nutritional and feeding practices of the preterm infant and dental health is important to all who provide initial and ongoing care to this population.

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