The role of biology in the orthodontic practice (Page 7)

Contemporary orthodontics is based, in the majority of cases, on transmission of mechanical forces to teeth through hard brackets (metallic, ceramic, or plastic), attached firmly to the dental crown. The list of popular orthodontic appliances in use includes the edgewise Straight Wire Appliance by Andrews in 1976 in its numerous varieties, the Begg Appliance in 1971 and its Tip-Edge version by Kesling in 1988, as well as the Speed Appliance by Hanson in 1980. In all these methods, emphasis is placed predominantly on the position of the dental crowns, while minimal attention is devoted to the dental roots and their surrounding tissues. Consequently, root resorption, dehiscences and fenestrations of the alveolar bone occur frequently in most orthodontic patients. Kaley and Phillips (1991) reported that radiographs obtained post-treatment from 200 patients treated by an 0.022 x 0.028 inch Edgewise appliance for an average of 34 months, revealed that over 90% of the maxillary central incisor roots had been resorbed to some extent, from blunting to over one quarter of their length. The percentage was nearly as high for the lateral incisors. Maxillary incisors were 4 to 5 times more likely to display severe root resorption if they had undergone torque.

The most significant situation associated with root resorption in the maxillary arch was the approximation of incisor apices against the lingual or labial plates of bone. In such cases the likelihood of severe root resorption increased by 20 times. Moreover, the degree of resorption correlated with the overall length of treatment time, and the duration of full engagement of rectangular wires in the brackets. In a study of dental radiographs of 42 patients treated by the Begg technique (Goldson and Henrickson, 1976), all subjects developed root resorption at the completion of treatment. Furthermore, a laminographic study of patients treated by this method revealed that the resorptive damage to the maxillary incisors is associated with uncontrolled tipping and subsequent round tripping of the teeth (Ten Hoeve and Mulie, 1976).

A rare opportunity to examine histologically the maxilla of a patient in the midst of treatment with a Straight Wire appliance was granted to three orthodontists (Wherbein, Fuhrmann, and Diedrich, 1995). The jaw was obtained from a 19-year old patient who had been killed in a traffic accident. At the time of her death she had completed 19 months of treatment, which included movement of molar roots into the vestibular and palatine cortical plates of bone. These authors reported on finding widespread dehiscences and fenestrations of the alveolar bone cortical plates, as well as extensive lateral, buccal, and palatine root resorption. These destructive changes were particularly pronounced in teeth that had been subjected to uncontrolled tipping, and less severe in teeth moved by translation. These histological findings could not be diagnosed by macroscopic inspection of the specimen.

Radiographic cephalometry and computed tomography were utilized in studying the maxillary and mandibular alveolar bone labial and lingual plates following incisor retraction (by controlled tipping) in patients with bimaxillary protrusion (Sarikaya et al., 2002). Comparing pre- and post-retraction records revealed that in both jaws there had been significant reductions in the width of the lingual bone as a result of treatment, with some patients demonstrating dehiscences that were not visible macroscopically or cephalometrically. It was concluded that forcing dental roots against cortical bone may cause adverse sequelae.

Concerned about the extent of tissue damage encountered by his patients who had been treated with the Edgewise and Begg appliances, De Angelis (2003) concluded that this damage, particularly root resorption, is associated with factors like the overall length of treatment time and treatment with rectangular wires that fully engage the Edgewise bracket slot. The jiggling of teeth in the sagittal, vertical, and transversal planes, as well as the round or uncontrolled tripping of teeth were also identified to contribute to this condition. In addition, root resorption can be caused by bringing dental roots into contact with the cortical plates of alveolar bone.

Page 1     Introduction

Page 2     Tissue remodelling and orthodontic tooth movement

Page 3     The age factor

Page 4     The effects of pre-existing medical conditions and the development of complications

Page 5     The etiology of tooth resorption

Page 6     The biological nature of an optimal orthodontic force

Page 7     How to move teeth without resorbing their roots

Page 8     Summary