The significance of late developmental crowding to early treatment planning for incisor crowding

Abstract

Incisor crowding has traditionally been attributed to discrepancies in either tooth-jaw size or interarch tooth-size ratios. Such concepts have led orthodontists to develop mixed and permanent dentition space and interarch tooth-size analyses to assist in the diagnosis of crowded dentitions. Treatment plans have emphasized the removal of 4 premolars in an attempt to stabilize the dentition. Although individuals with large teeth may tend to have more incisor crowding, several factors other than tooth size may contribute to incisor crowding, for example, altered resting or functional activity in the facial and masticatory muscles. Thus, changes in occlusion, incisor crowding-spacing, lower anterior face height, and mandibular and maxillary retrognathism or prognathism have all been induced in primates through the application of a single chronically acting, environmental impact, such as either altered tongue posture or oral respiration.1Harvold EP The role of function in the etiology and treatment of malocclusion.Am J Orthod. 1968; 54: 883-898Abstract Full Text PDF PubMed Scopus (83) Google Scholar, 2Harvold EP Chierici G Vargervik K Experiments on the development of dental malocclusions.Am J Orthod. 1972; 61: 38-44Abstract Full Text PDF PubMed Scopus (105) Google Scholar, 3Altuna G Woodside DG The relationship between lower face height and inclination of the incisor.J Dent Res. 1989; 68 ([Abstract 947]): 300Google Scholar, 4McNamara JA Experimental examination of growth of the lower jaw.Informationen aus Orthodontie und Kieferorthopadie. 1976; 8 ([German]): 219-243PubMed Google Scholar In addition, similar changes have been shown in human beings that were partially reversible after removal of the environmental impact.5Linder-Aronson S Effects of adenoidectomy on the dentition and facial skeleton over a period of five years.in: Transactions of the Third International Orthodontic Congress. Crosby Lockwood Staples, London1975: 85-100Google Scholar, 6Linder-Aronson S Woodside DG Lundstrom A Mandibular growth direction following adenoidectomy.Am J Orthod. 1986; 89: 273-284Abstract Full Text PDF PubMed Scopus (110) Google Scholar Thus, adverse neuromuscular changes, such as chronic mouth open breathing, have been associated with narrowing of both arches and lingual inclination of the incisor teeth and crowded dentitions.1Harvold EP The role of function in the etiology and treatment of malocclusion.Am J Orthod. 1968; 54: 883-898Abstract Full Text PDF PubMed Scopus (83) Google Scholar, 7Linder-Aronson S Adenoids: their effect on mode of breathing and nasal airflow and their relationship to characteristics of the facial skeleton and the dentition: a biometric, rhino-manometric and cephalometro-radiographic study on children with and without adenoids.Acta Oto-Laryngologica. 1970; ([Thesis])Google Scholar, 8Behlfelt K Enlarged tonsils and the effect of tonsillectomy: characteristics of the dentition and facial skeleton/posture of the head, hyoid bone and tongue/mode of breathing.Swed Dent J. 1990; Google Scholar, 9Woodside DG Linder-Aronson S Lundstrom A McWilliam J Mandibular and maxillary growth after changed mode of breathing.Am J Orthod Dentofacial Orthop. 1991; 100: 1-18Abstract Full Text Full Text PDF PubMed Scopus (96) Google Scholar, 10Linder-Aronson S Woodside DG Hellsing E Emerson W Normalization of incisor position after adenoidectomy.Am J Orthod Dentofacial Orthop. 1993; 103: 412-427Abstract Full Text PDF PubMed Scopus (56) Google Scholar These dentoalveolar and skeletal changes were partially or fully reversible without orthodontic therapy after removal of the chronic input8Behlfelt K Enlarged tonsils and the effect of tonsillectomy: characteristics of the dentition and facial skeleton/posture of the head, hyoid bone and tongue/mode of breathing.Swed Dent J. 1990; Google Scholar, 10Linder-Aronson S Woodside DG Hellsing E Emerson W Normalization of incisor position after adenoidectomy.Am J Orthod Dentofacial Orthop. 1993; 103: 412-427Abstract Full Text PDF PubMed Scopus (56) Google Scholar It follows that judicious orthodontic expansion procedures might be warranted to assist recovery in such cases after removal of the neuromuscular insult. We are indebted to the University of Washington for their documentation of late developmental crowding up to age 40 in orthodontically untreated as well as treated individuals. Study of untreated individuals at the University of Toronto shows that this phenomenon continues to at least age 70. Such crowding seen during the teen and adult years cannot be called tooth-jaw size discrepancy and must be neuromuscular in nature. Strong evidence supports the view that many of the crowdings we see during the mixed dentition are also neuromuscular or developmental. In a previous study9Woodside DG Linder-Aronson S Lundstrom A McWilliam J Mandibular and maxillary growth after changed mode of breathing.Am J Orthod Dentofacial Orthop. 1991; 100: 1-18Abstract Full Text Full Text PDF PubMed Scopus (96) Google Scholar of the relationship between mandibular incisor crowding and nasal mucosal swelling, cephalometric and dental cast variables from 30 male and 20 female children (8 to 13 years old) with chronic nasal mucosal swelling were compared with matched controls. These controls were orthodontically untreated and had no history of airway obstruction. The nasal mucosal swelling was confirmed with active posterior rhinomanometry and a headout volume-displacement plethysmograph. The subjects with nasal mucosal swelling had significantly (P < .001) more mandibular incisor crowding than the controls. A normalization of incisor position after adenoidectomy10Linder-Aronson S Woodside DG Hellsing E Emerson W Normalization of incisor position after adenoidectomy.Am J Orthod Dentofacial Orthop. 1993; 103: 412-427Abstract Full Text PDF PubMed Scopus (56) Google Scholar and changed mode of breathing was associated with a significant labial positioning of the incisor teeth in both jaws. In addition, Solow and Sonnesen11Solow B Sonnesen L Head posture and malocclusions.Eur J Ortho. 1998; 20: 685-693Crossref PubMed Scopus (127) Google Scholar have shown a close pattern of associations between incisor crowding and craniocervical posture. Subjects with incisor crowding in both arches had craniocervical angles that were, on average, 3° to 5° larger than subjects without crowding. The change in incisor inclination which accompanies a return from mouth to nose breathing can be partly due to changes in tongue and orbicularis oris pressures associated with the transition from an open to closed mouth posture. Lowe12Lowe A Correlations between orofacial muscle activity and craniofacial morphology in a sample of control and anterior open bite subjects.Am J Orthod. 1980; 78: 89-98Abstract Full Text PDF PubMed Scopus (65) Google Scholar has shown that the anteroposterior position of the tongue is affected when the mandible is lowered. He found that the tongue progressively protrudes with increased mandibular lowering. Thus, an alteration may occur in the differential pressure exerted by the lips and tongue on the incisors. A more labial incisor inclination and position after a change from mouth-open to the mouth-closed posture supports the concept of partial reversibility of malocclusion symptoms without orthodontic treatment. This change may provide additional space in the arches and thus assist the conservative alignment of incisor teeth without the need for premolar extraction in selected cases. Thus, some forms of incisor crowding previously attributed to tooth jaw-size discrepancy represent neuromuscular or environmental crowding that may be partially reversible without treatment and may be treated without permanent tooth removal. The differential diagnosis of incisor crowding in young subjects requires an assessment of the degree of neuromuscular impact such as nasal obstruction as a result of nasal mucosal swelling or enlarged adenoid tissue. The recognition that the skeletal and occlusal changes referred to here can be initiated by chronic environment impact and the partial reversibility of the changes raises some interesting points relative to orthodontic diagnosis and treatment planning. The use of mixed dentition and permanent dentition analyses in the diagnosis and treatment planning of incisor crowding may be invalid procedures in cases that have environmental impact as the primary cause. In such cases, narrow arch width, lingual incisor inclinations, and incisor crowding may be partially corrected by a conservative treatment approach that autorotates the mandible toward more normal lower face height relationships and modifies the transverse dimension of the arches in harmony with the new mandibular position. This concept is important in cases with excess lower face height and may also be important in short lower anterior face height cases with overclosure. Thus, in certain individual cases, a retrognathic mandible, vertical mandibular growth direction, openbite, and incisor crowding may be primarily the result of chronic environmental impact.13Lundstrom A Woodside DG Individual variation in growth directions expressed at the chin and the midface.Eur J Ortho. 1980; 2: 65-79Crossref PubMed Scopus (28) Google Scholar Such a concept requires an alteration in therapeutic approach from one that accepts dysplasia and adapts the dentition to it, to one that modifies or eliminates the environmental impact and its resultant effects on jaw position, occlusion, and tooth alignment. It also requires a changed diagnostic approach from one that measures crowding to one that evaluates the neuromuscular environment of the dentition. Hopefully, simple clinical methods for such diagnostic procedure will evolve during the coming years. Some questions to be answered are: 1.Can we develop methods for the diagnosis of neuromuscular crowding?2.How do we measure basal maxillary constriction before performing rapid maxillary expansion versus conservative ideal arch alignment?3.How do we measure dentoalveolar maxillary constriction?4.Does mandibular dentoalveolar constriction ac-company maxillary basal and/or dentoalveolar construction?5.Can a classification of maxillary and mandibular transverse dysplasia be developed?6.Does either type of arch constriction correlate with incisor crowding?