Maxillary Growth

Before the age of 7, maxillary growth is primarily the result of passive displacement. After that, the maxilla grows upward and backward but is translated downward and forward relative to the cranium and cranial base. Some of the growth comes from displacement caused by growth and flexion of the cranial base. The remainder is due to resorption and appositional changes of the maxilla itself. The cranial base in effect pushes the maxilla from behind. As the maxilla moves forward and down, the sutures that attach the maxilla to the cranial base remain the same width and the processes of the maxilla grow to fill the space that has opened. As the maxilla moves forward, the anterior surfaces of the maxilla are remodeled and bone is removed from the anterior surface and nasal floor.

As transverse growth of the cranial base occurs, the midface expands. The midpalatal suture of the maxilla allows the midface to grow laterally in concert with the cranial base. Transverse growth of the maxilla accelerates at puberty. The average increase in maxillary bone width varies from 5-8 mm.⁴ Maxillary width changes occur primarily with eruption of the permanent teeth. Faster growth during puberty and a longer growth period result in adult males having greater maxillary width than adult females.

Vertical growth of the maxilla occurs primarily by apposition on the occlusal surface of the alveolus. As the alveolus is enlarged by apposition on the occlusal aspect, it is decreased by resorption on the nasal floor. Approximately one third of the increase in alveolar height is lost by this resorption. Actual vertical growth of the maxilla from infancy to puberty is in the range of 1-2 cm but net vertical growth of the maxilla is 5-6 mm. The majority of that increase is due to the increased vertical size of the permanent teeth. In terms of implant placement in children, the important consideration is that teeth and unerupted buds follow the downward migration of the maxilla; ankylosed teeth and dental implants do not.

Mandibular Growth

The mandible is projected downward and forward during growth and the chin becomes more pronounced, although it is actually a site of net resorption. The ramus is remodeled as a result of lingual and buccal cortical plate drift and permanent tooth eruption. The mandible lengthens primarily by growth of the condyle and posterior growth of the ascending ramus. Mandibular width increases mainly in the posterior. There is little change in the anterior mandibular arch after the onset of the adolescent growth spurt.

The mandible grows vertically by apposition at the dentoalveolar complex and growth at the condyle. In normal growth and development the mandible rotates minimally on a sagittal plane to maintain a normal inter-arch relationship. However, mandibles in individuals with long face or short face syndrome rotate considerably more.⁵ When more pronounced rotation occurs, eruption patterns are affected. An implant placed adjacent to one of the teeth in an abnormally rotating mandible would not move in concert with the mandible, inevitably leading to a negative relationship between the teeth and the implant. For example, in children with considerable rotation, the posterior teeth will continue to erupt to maintain the occlusal plane, but implants would not erupt and would be buried in the alveolar process.

In the developing jaw, osseointegrated implants react in much the same manner as an ankylosed primary tooth. Because they lack periodontal ligament they do not erupt or adapt to dental alveolar or facial growth.⁶ As development of the maxilla and mandible progresses, implants can become loose due to normal facial remodeling. They can also be vertically buried due to alveolar apposition. In addition, implants may not remain in appropriate and functional position relative to other teeth or oral structures as changes in the mandible and maxilla occur.

The consensus in the dental community seems to be that implant therapy should be recommended only in extraordinary cases for treatment of normally developing children who are missing teeth. For normally developing children other treatment options should be employed until skeletal craniofacial growth is complete. Chronological age is not a reliable measure of growth as there are huge differences in growth not only between the sexes but from one individual to another. Historically, several methods have been used to determine that growth has ceased. Cephalometric radiographs taken at least 6 months apart, eruption of second molars, radiographic analysis of the wrist, and the onset of menses have been used to determine whether growth has ceased. Assessment of mandibular growth based on cervical vertebrae maturation⁷ has gained acceptance. Results from analysis of cervical vertebrae maturation are consistent with results from radiographic studies of the ossification of the bones of the hand and wrist, for many years the standard for measurement of skeletal growth. Growth is considered to be complete when a radiograph shows that the second, third, and fourth cervical vertebrae have reached stage 4 of the 5-stage cervical growth maturation index.

For some children, especially those with severe oligodontia, the benefits associated with implant therapy outweigh the risks. Because these children have very few or no teeth, concerns about potential damage to existing dentition are minimal.⁸ Experience suggests that mandibular restorations supported by implants in the symphysis can be successful even in very young children. Similar positive long-term results have been reported in the literature. The author has not placed implants for permanent restoration in the maxilla because maxillary growth would most certainly lead to loosening or burial. Implants have been placed in the maxilla for temporary orthodontic anchorage but that is a separate topic not included in the scope of this chapter.

Case Reports

Case 1

A 7-year-old male with oligodontia (severe hypodontia) was referred for examination and treatment. He appeared to be a well-developed, well-nourished first-grader. His parents reported that he was functioning at grade level in school. There was no significant family history related to the oligodontia. An extraoral exam revealed a lack of lip support and an asymmetry of the mandible with the chin point deviating to the patient’s right. The left side of the mandible was underdeveloped compared to the right. The prominent chin contributed to a concave facial form. The patient had a decrease in lower third facial height and a flat mandibular plane (Figure 24-1, A). The neurological examination indicated that all cranial nerves were intact.

Figure 24-1. A, Preoperative facial view of 7-year-old male with significant underdevelopment of the lower third of the face. The right side of the mandible is more hypoplastic than the left. B, Intraoral view revealing absence of mandibular dentition and only two maxillary central incisors. C, Panoramic radiograph revealing numerous tooth buds in the maxilla and a single malformed supernumerary tooth in the mandibular symphysis. D, CT reconstruction of the mandible showing prominent genial tubercle and left and right internal oblique ridges. An absence of alveolar process is demonstrated. E, Surgical access to the posterior ilium prior to harvesting cortical cancellous bone. F, Submandibular approach to the mandible demonstrating preservation of the mental nerves bilaterally. A freeze-dried rib has been secured to the lingual surface of the mandible by 3.0 chromic sutures. G, Postoperative panograph demonstrating marked increase in the mandibular bone volume. H, Surgical guide in place at the time of implant placement. I, Four implants placed in the grafted mandibular symphysis. J, Anterior view of mandibular over-denture. K, Intaglio surface of mandibular over-denture utilizing two O-rings for retention and 2 copings for vertical support. L, Postoperative panograph demonstrating adequate bone for 13-mm implants in the mandibular symphysis. M, Patient with mandibular over-denture in place providing normalized contour to the lower third of the face. N, Mandibular over-denture in position retained by two O-rings and supported by vertical posts. O, Intraoral view of implant attachments utilized to support mandibular over-denture. Maxillary dentition not fully erupted. P, Panograph with second reconstruction utilizing original implants 9 years after implant placement. Maxillary dentition fully erupted. Q, Two mandibular bars attached to the four implants. R, Completed new bar over-denture in occlusion with fully erupted maxillary dentition. S, Facial view of patient 9 years after initial reconstruction. T, Panograph 18 years after initial implant therapy demonstrating excellent bone around the four implants. U, Facial view of patient 18 years after implant placement.

(A, B, D, and M, Reprinted with permission courtesy Montage Media Corporation © 1996. Kraut RA: Dental implants for children: creating smiles for children without teeth, Practical Periodontics & Aesthetic Dentistry 8[9]:909–913, 1996.)

In the maxilla only two central incisors were visible; no teeth were visible in the mandible and no alveolar process was found when the mandible was palpated (Figure 24-1, B). A panoramic radiograph showed numerous tooth buds in the maxilla but a complete absence of alveolus and tooth buds in the mandible (Figure 24-1, C). A computed tomography (CT) scan showed development of the internal oblique ridges bilaterally and the presence of a genial tubercle; however, a distinct lack of an alveolar process was noted. Measurement at the symphysis revealed a bone height of 3 mm (Figure 24-1, D). After discussion with the patient and his parents, a treatment plan for reconstruction of his mandible was developed. The plan called for a mandibular bone graft, placement of four implants, and construction of a removable prosthesis.

The patient was taken to the operating room and a composite bone graft was performed to augment his mandible. Once the patient was under nasal endotracheal general anesthesia, he was placed in a prone position and the right posterior ilium was exposed. Cortical and cancellous bone was harvested from the right ilium (Figure 24-1, E). The surgical site was closed and a #7 Jackson-Pratt drain was placed. The patient was turned in a supine position to facilitate a submental extraoral approach to the mandible. The left and right bodies and the symphysis of the mandible were exposed; care was taken to preserve the mental nerves as they emerged from the mental foramen. A freeze-dried cadaver rib that had been reconstituted overnight was sectioned so a single laminate of the rib could be used as a vertical strut in support of the mandibular augmentation. The rib was secured to the lingual surface of the mandible with #2 vicryl sutures (Figure 24-1, F). Stainless steel wire was not used to avoid having dissimilar metals in contact when the implants were placed. With vertical height for augmentat/>

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