[Orthodontic fixed retainer: fix or not fix? that is the question].

Orthodontic fixed retainer is widely used, as an orthodontic retention appliance, for nearly four decades. It answers the need for prolonged retention with minimum patient compliance. The effectiveness of fixed retainers was compared to other retention devices in several studies, and was found as effective as removable appliances. But, further high quality research is still needed. A bonded fixed retainer was suspected as an obstacle that impedes the patient's ability to keep satisfactory oral hygiene. But research failed to prove the influence of fixed retainers on periodontal health or white spot lesion occurrence as clinically significant. The definite downsides of fixed retainer are the risk of retainer breakage, and unwanted tooth movements. A typical tooth movement can appear even without a retainer breakage, including a change of torque of a mandibular incisor or skewing of the anterior mandibular arch segment. Both the dentist and the orthodontist are encouraged to be familiarized with these possible side effects, recognized them as soon as possible, and consider changing the retention protocol, when appropriate.

[Are you afraid of open bite?].

Treatment of open bite malocclusion is a challenge for both the orthodontist and the patient. The key to successful treatment are careful evaluation, that leads to correct diagnosis and treatment plan, as well as meticulous cooperation on behalf of the patient. There are many treatment options starting with follow up and orofacial myofunctional therapy, and concluding with orthosurgical correction. The tendency to relapse and reopening the bite must be emphasized to the patient before initiation of the orthodontic treatment. It is highly recommended in indicated cases to include orofacial myofunctional therapy in combination with the orthodontic treatment. New modalities of treatment give great promise for the future, and enable us to intrude posterior teeth using skeletal anchorage. However, it is still unknown whether these new treatment modalities will give better stability for open bite correction.

Prediction of premolar tooth lengths based on their panoramic radiographic lengths.

OBJECTIVE: Establishing a linear regression model for the determination of first premolar lengths based on panoramic radiographs. MATERIALS AND METHODS: The real lengths of 112 first premolars extracted for orthodontic reasons were measured and compared with their panoramic lengths. The teeth were divided into four groups according to their intraoral quadrant locations (T14, T24, T34, T44) and regression analysis was conducted for each group. RESULTS: A linear regression model for the prediction of tooth length (mm) based on the panoramic length was established (P < 0.0001): For group T14 the predicted length = (panoramic length x 0.698) + 2.61. For group T24 the predicted length = (panoramic length x 0.5056) + 7.844. For group T34 the predicted length = (panoramic length x 0.5075) + 9.282. For group T44 the predicted length = (panoramic length x 0.436) + 11.298. CONCLUSION: Prediction of all first premolar lengths using their panoramic images is both feasible and reliable.

Dynamics of tissue changes found after mechanical loading of the rat incisor. I. A three-dimensional longitudinal study of the morphologic aspects.

A three-dimensional morphometric method was used to evaluate progressive changes in shape and size of recovering dental and periodontal tissues after orthodontic loading. In 35 female rats weighing 212 +/- 4 gm, loads of 19.7 +/- 1.6 gm generated by closed-coil springs were applied for 2 weeks to the shortened lower left incisor. The rats were killed in groups of five at 0, 1, 3, 5, 7, 9, and 10 weeks (groups 0-w to 10-w) after the springs were removed. A group of rats with normal incisors (group C-1) and one with five incisors that had been continually shortened for 10 weeks (group C-2) served as controls for groups 0-w and 10-w, respectively. Width, area, and volume of the tooth and enamel-bordering periodontal ligament (e-PDL) and cementum-bordering PDL (c-PDL) were measured. After 2 weeks of loading (group 0-w), the volume of the compressed e-PDL had decreased by 22%, and the volume of the stretched c-PDL had increased by 72%, suggesting that bone apposition lags behind the rate of tooth movement. During the recovery period, the dental and periodontal parameters tended toward a gradual return to control (C-2) values, although at the end of 10 weeks many still lagged significantly behind the controls. Recovery was slowed by repeated reversals at different sites in the various groups. The ability of the preloaded incisor to adjust to changes in occlusal function was lastingly impaired.