Dental Development

Initial calcification of the primary tooth buds may be seen in the fourth month of prenatal life. In general, by the end of the sixth prenatal month, all of the primary teeth have begun to develop. The newborn infant is edentulous, with the rare exception of a mandibular central incisor. This natal or neonatal tooth tends to be quite mobile, and in the past it was thought to require immediate extraction. Recent data suggest that by the end of the neonatal period, this mobile tooth becomes quite stable and capable of normal masticatory function. This is indeed fortunate for the infant, because these neonatal teeth are frequently the only primary teeth that develop in that position (King and Lee, 1989; Cunha et al., 2001).

The sequence of eruption of human teeth may critically affect infant feeding, behavioral, and masticatory skills. Major changes in the appearance of the dentition in the oral cavity probably alter important aspects of neurobehavioral development (Wright, 2000). As an example of eruption sequence alterations, premature infants and neonates requiring prolonged orotracheal intubation have significant defects in both oral and dental structures that may persist past age 5 years, even after removal of the orotracheal tube (Fadavi et al., 1992).

The order of appearance of the teeth in the oral cavity tends to follow generalized patterns (Table 32-2). Usually the teeth erupt in pairs. A mandibular right central incisor erupts at approximately the same time as the mandibular left central incisor, at approximately 6 to 7 months of age. The mandibular teeth usually precede their maxillary counterparts; the maxillary incisors erupt approximately 1 month later than the mandibular incisors. The eruption sequence continues and is usually complete by age 2 to 2½ years. The last tooth to erupt is the deciduous second molar, called the 2-year molar because of its appearance at age 2 years.

TABLE 32–2 Eruption Sequence of the Human Dentition

From Schour I, Massler M: The development of the human dentition, JADA 28:1153, 1941. Reprinted by permission of ADA Publishing.

When completed, the primary dentition totals 20 teeth (Wright, 2000). As the toddler’s growth continues, the mandible and maxilla enlarge, causing separations, also known as diastemata, between the primary teeth (Zwemer, 1993). The diastemata increase as the primary teeth are beginning to exfoliate and the permanent or succedaneous teeth begin to erupt. The separations also permit sufficient room for the proper alignment of the permanent dentition.

The maintenance of the health and hygiene of the primary teeth is essential to avoid premature tooth loss. When primary teeth are prematurely lost as a result of decay or trauma, the space needed for the permanent tooth eruption is also lost because the natural tendency of the tooth is to tip mesially (toward the midline) in the oral cavity. Subsequently, dental malocclusions tend to occur. Finally, the primary teeth may also function as the permanent teeth if the permanent analogous tooth fails to develop (Wright, 2000).

The transition period between exfoliation of the primary teeth and eruption of the permanent teeth is called the mixed-dentition phase. This phase continues until the last primary tooth is normally exfoliated or extracted. Unlike the primary teeth, the permanent teeth normally erupt so that there is tooth-to-tooth contact.

Development of the secondary, or permanent, dentition begins at birth with calcification of the buds of the permanent first molars. The permanent dentition begins its eruption pattern with the permanent first molar, usually at approximately 6 years of age. Like their primary counterparts, the mandibular teeth usually precede the maxillary teeth, with the permanent mandibular incisors beginning to appear at approximately age 6 to 7 years. Unlike the primary dentition, where there is usually a variability of several months in the timing of eruption, the permanent teeth may vary as much as 1 to 2 years in eruption sequence. After eruption of the permanent first molars, eruption of the remaining permanent teeth then occurs in this sequence: mandibular central incisors, maxillary central incisors, mandibular lateral incisors, maxillary lateral incisors, mandibular cuspids, maxillary and mandibular first premolars, maxillary and mandibular second premolars, maxillary cuspids, and mandibular and maxillary second molars (see Table 32-2). At the completion of the eruption sequence, the permanent dentition consists of 32 teeth (Wright, 2000).

The third molars, commonly known as wisdom teeth, have the least predictable eruption sequence of any of the human dentition. They may erupt as early as age 15 to 16 years, as late as age 25 years, or not at all. Quite commonly, the third molars fail to erupt because of dental germinal pattern alterations or impactions in the soft or hard tissues. Impactions usually occur because of insufficient bony growth of the maxilla or mandible in proportion to the individual’s full dental complement.

In addition to the frequently absent third molars, two other permanent tooth forms are sometimes congenitally absent. The mandibular premolars and the maxillary lateral incisors may be congenitally absent, either singly or in symmetric pairs (Neville et al., 2002). Occasionally, a tooth that is thought to be congenitally absent is actually impacted in the soft tissues or alveolar bone.

Just as there are congenitally absent teeth, there are supernumerary or accessory teeth. The most common supernumerary tooth is the mesiodens, a conically shaped tooth consistently located in the midline between the maxillary central incisors. Other supernumerary teeth are the third premolars and fourth maxillary molars (Neville et al., 2002).

Identification of mobile primary versus transitional, or mixed, dentition can be of importance to anesthesia personnel. It is often recommended that mobile primary teeth be removed prior to airway instrumentation, as they may be at risk for dislodgment and airway obstruction. Likewise, it is important to note that newly erupted permanent teeth are often slightly mobile, with incomplete root formation. For this reason, extra care should be taken during laryngoscopy, oral airway placement, or other jaw manipulation, as immature permanent teeth may be predisposed to luxation or avulsion trauma if too great a force is placed on them.

Dental Identification

There are two principal universal dental identification systems. In both systems, the primary teeth are designated by letters, and the permanent teeth are designated by numbers. These systems differ in the way that the dental arches (mandible and maxilla) are divided. The first system uses a sequential means for identification, with the primary maxillary right second molar designated as tooth A and followed sequentially around the contralateral side of the maxilla to the left second molar, which is tooth J. The primary mandibular left second molar is tooth K, and the sequence is completed on reaching the mandibular right second molar, tooth T. Similarly, the numbering system for the permanent dentition starts with the maxillary right third molar as tooth 1 and continues to the maxillary left third molar, tooth 16. The sequence continues with the mandibular left third molar, tooth 17, and is completed with the mandibular right third molar, tooth 32 (Herlich, 1990). Both pediatric and general dentists commonly use this system of tooth identification.

The second designation system divides the dental arch into quadrants. All primary central incisors are tooth A and follow distally or posteriorly, so that all primary second molars are tooth E. To make the designation more specific, the quadrant is also named. For example, the primary maxillary right lateral incisor is designated maxillary right B. Similarly, the permanent dentition is divided into quadrants. All central incisors are tooth 1 and continue posteriorly, so that all third molars are tooth 8. This system is most commonly used by orthodontists (Fig. 32-1).

FIGURE 32-1 A, Tooth identification and sequence. B, Cast models of the primary dentition (upper) and permanent dentition (lower).

(A, From Herlich A: Dental complications of anesthesia, Prog Anesthesiol 11:250, 1990. B, From Ash MM Jr, editor: Wheeler’s dental anatomy, physiology, and occlusion, ed 7, Philadelphia, 1993, Saunders, p 2.)

Dental Anatomy and Physiology

The tooth is composed of a crown, which is usually visible for clinical examination, and a root, which is not seen during routine clinical examination. They are separated by the cementoenamel junction or cervical region of the tooth (Fig. 32-2). The cementoenamel junctions are seen more commonly in adult dentition if gingival (“gum”) recession occurs. The crown is responsible for the slicing, ripping, and grinding of foodstuffs (incisors, canines, and molars, respectively). The root structure imparts stability to the tooth in its surrounding tissues. The anterior teeth, the incisors and the canines, are single rooted with a conical shape. The posterior teeth, the premolars and molars, are multirooted and impart most of their stability by both the number of roots and the subtly divergent directions in which the roots may grow.

FIGURE 32-2 Schematic (left) and radiographic (right) views of a right maxillary molar.

(Modified with permission from Ash MM Jr, editor: Wheeler’s dental anatomy, physiology, and occlusion, ed 7, Philadelphia, 1993, Saunders, p 6.)

Surrounding the root structure of the tooth is the periodontium, which is composed of three structures as follows:

The individual teeth are composed of enamel, dentin, dental pulp, and cementum (Wright, 2000) (see Fig. 32-2). The enamel covers the external surface of the dental crown. It is the hardest substance in the human body and, unlike bone, has no living cells. When intact, enamel functions as a thermal insulator and an impervious barrier to chemicals and microorganisms.

On the internal surface of the enamel lies the dentin. It is composed of microtubules and has living cells in the dentinal structure. When tooth decay is advanced, noxious stimuli are readily transmitted via the dentinal tubules to the underlying dental pulp. The neurovascular supply of the individual teeth is contained in the dental pulp. Pain is easily elicited by many different stimuli—thermal, tactile, or liquid. The pain is transmitted from the dental pulp through the root apices to the alveolar bone and subsequently to the body’s pain receptors.

The final portion of the tooth structure is the dental cementum, which covers the external surface of the roots. Because it is not nearly as hard and impervious to the surroundings as is enamel, noxious stimuli are perceived when the cementum is exposed. The cementum is similar to the dentin of the tooth. Patients who enjoy good dental health usually do not have exposed cementum. However, with gingival and alveolar recession, root structure and its investing cementum may be exposed to the external environment.

Some morphologic differences exist between deciduous and succedaneous teeth. The most obvious difference exists in the size of the teeth in general. The deciduous teeth are significantly smaller than their permanent counterparts. With respect to the molars, the buccal-lingual dimensions are proportionately narrower. In contrast, the mesial-distal dimensions are proportionately larger.

Another difference between the sets of dentition rests in the color of the enamel. The primary teeth are milky white, or opalescent; hence, the name milk teeth. The permanent teeth, on the other hand, are significantly less “milky” because pigment absorption has occurred during their development or has been acquired during the intraoral lifetime of the tooth (Wright, 2000). Two examples are tetracycline staining (developmental) and caffeine staining (acquired).

The pulp chambers of the primary teeth are larger than the permanent teeth because of the relative thinness of the deciduous enamel and dentin (Wright, 2000). Less than meticulous dental restorations or large carious lesions may predispose the primary teeth to pulpal or endodontic therapy earlier than their permanent counterparts.

The root structures of the primary molars are more saber shaped and extend laterally beyond the crown width. This unique root structure allows adequate room for the permanent tooth bud to develop and mature until the exfoliative process is completed for the primary tooth (Wright, 2000).

Orthodontic Pathology

Teeth erupt into the alveolar processes of the maxilla and mandible and are held into bone by the periodontal membrane and gingival fibers. Together, the teeth and the jaws provide structure to the lower third of the face. In a normal bite, the maxilla and maxillary teeth are larger, which allows the maxillary arch to overlap the mandibular arch. Occlusion describes how maxillary and mandibular teeth fit together during chewing or at rest.

Malocclusion is the improper alignment of the teeth and jaws or bad bite. A skeletal malocclusion describes a malalignment between the jaws. A dental malocclusion describes the interarch relationship between the upper and lower teeth. A malocclusion may be caused by both hereditary and environmental factors. Crowding, spacing, supernumerary teeth, hypodontia, and asymmetric jaw growth are determined mostly by inheritance. Environmental factors such as thumb sucking, dental caries, premature loss of primary teeth, and trauma also can contribute to malocclusion (Mossey, 1999). An untreated malocclusion can lead to tooth decay, periodontal disease, abnormal wear of teeth, difficulty in chewing and speaking, and poor self-image.

Edward H. Angle, who is regarded as the father of orthodontics, developed a classification system for malocclusion based on the sagittal (anteroposterior) relationship of the teeth and jaws (Angle, 1899). Angle believed the upper first molars were critical to occlusion, and that the upper and lower molars should meet so that the mesiobuccal cusp of the upper molar contacts in the buccal groove of the lower molar. If this molar relationship existed and the teeth were arranged on a smoothly curving line of occlusion, then normal occlusion would result (Fig. 32-3). Angle’s classification system is as follows:

FIGURE 32-3 Angle classification system for malocclusion.

Discrepancies in the vertical or transverse dimension can also contribute to a malocclusion. An openbite or deepbite describe how teeth fit together in the vertical dimension.

Whether orthodontic treatment should occur in one or two phases of treatment is a source of controversy. Phase I, or early orthodontic treatment, may correct a problem when the patient still has primary teeth or has a combination of primary and permanent teeth. Some practitioners believe it may keep more serious problems from developing, and it may make treatment at a later age shorter or less complicated. Typically, early treatment involves the use of materials and techniques to guide or modify growth as adult teeth are erupting (Kluemper et al., 2000)

Appliances used in early treatment may be removable or fixed (cemented). They may be made of metal, ceramic, or acrylic. Examples of appliances used to address transverse discrepancies include palatal expanders, quad helixes, and transpalatal arches (Fig. 32-4). Headgear therapy may be used to treat anteroposterior discrepancies (class II or class III malocclusions) and are composed of a removable and fixed component. A lower lingual holding arch is a banded appliance used to maintain space for the eruption of permanent teeth in the mandibular arch (Fig. 32-5). Functional appliances change the position of the lower jaw to produce movement of teeth and modification of growth. Examples of functional appliances include the Twin block, Herbst appliance (Fig. 32-6), and Bionator.

FIGURE 32-4 Appliances used to address transverse discrepancies include bonded palatal expander (A), banded palatal expander (B), quad helix (C), and transpalatal arch (D).

FIGURE 32-5 A lower lingual holding arch.

FIGURE 32-6 Herbst appliance, used to change the position of the lower jaw.

Phase II or active treatment involves placement of fixed appliances (braces) or Invisalign in the permanent dentition (Boyd, 2008). Treatment times vary with several factors, including the severity of the problem being corrected, patient response to treatment, and patient compliance. Temporary anchorage devices (Fig. 32-7) are implants used to provide absolute anchorage and help move teeth (Cope, 2005). Patients use retainers to keep teeth in their new positions after treatment.

FIGURE 32-7 Temporary orthodontic anchorage devices.

Combined surgical orthodontic treatment is used to treat patients with severe malocclusions or craniofacial anomalies. Presurgical orthodontic treatment is used to prepare patients for surgery by removing dental compensations and upright teeth over basal bone (Proffit and Miguel, 1995). In a traditional orthognathic procedure, a surgical splint may be fabricated and wired to the patient’s teeth. This splint may help the surgeon determine the final position of the jaws.

Nasoalveolar molding (NAM) is a presurgical orthopedic technique used to reduce the severity of the cleft deformity in infant patients with complete unilateral or bilateral cleft lip and palate (Grayson et al., 1999). The appliance is composed of a removable acrylic plate fabricated from an intraoral impression, and a nasal stent (Fig. 32-8). The amount of acrylic is sequentially reduced to decrease the separation between the greater and lesser alveolar segments. Once the gap between the alveolar segments is 5 mm or less, the nasal stent is added to mold the nasal cartilage. Lip or nasal repair occurs at 4 to 6 months of age. Patients with NAM can present for cleft lip surgery or ear, nose, and throat procedures such as myringotomy and tubes. The NAM appliance can be left in place during inhalation induction and mask ventilation, or it can be removed before the beginning of induction. The device should be removed before airway instrumentation for a laryngeal mask airway (LMA) or endotracheal tube.

FIGURE 32-8 Nasoalveolar molding.

Facial Cellulitis

Bacterial abscess can spread from the apex of the root of the primary or permanent tooth into the surrounding alveolar bone and periosteum into deep tissue planes of the face or neck, resulting in an odontogenic facial cellulitis. Fever, dysphagia, leukocytosis, trismus, and dehydration are common physical findings. The lateral pharyngeal, retropharyngeal, masticator, buccal, submandibular, and submental spaces may be involved. Appropriate antibiotic therapy and prompt surgical drainage and extraction of the infected tooth are critical components of care.

Careful preoperative airway evaluation is critical in patients with facial cellulitis. Involvement of the masticator space or other anatomic spaces of the neck may threaten the airway. Ludwig’s angina, with bilateral involvement of the submandibular space and with associated superior displacement of the tongue base can cause airway compromise.

Clinical Settings for Pediatric Dentists

Most pediatric dental treatment occurs in the dental office without the need for psychological or pharmacologic intervention to address the child’s fear and anxiety. The hallmark of dental pain management is a kind practitioner and staff and the responsible use of adequate local or topical anesthesia, or both. For some patients, simple behavior modification techniques improve the level of cooperation in the dental chair. These techniques include the tell-show-do method and voice control for the fearful, hostile, or disruptive child. The tell-show-do technique involves explaining before the procedure, demonstrating the procedure outside of the child’s mouth, and then actually performing the procedure on the patient. This technique removes the fear of the unknown from the procedure (Lenchner and Wright, 1975). Voice control involves modulation of both the volume and tone of the dentist’s voice to achieve positive behavioral results (Wilson, 1994