Temporomandibular joint dysfunction and flat lateral guidances: a clinical association.

Temporomandibular joint alterations have been associated with abnormal mandibular movements in the open/close cycles and in the laterotrusive border movements. The quantitative analysis of these movements could allow a better or earlier diagnosis for patients and offer some insight into the pathophysiology of the disorder. Maximum opening and mandibular laterotrusive border movements were studied and measured in a group of 165 patients with a considerable lateral deviation (equal to or greater than 5mm) in maximum opening. Movements were directly performed by the patients and recorded with a mandibular kinesiography. The slope of the lateral guidance (frontal plane projection) was measured in the first millimeters of motion and started from the maximum intercuspal position. On average, slopes were significantly flatter on the same side with the opening deviation. These slopes were significantly flatter than previously published physiologic ranges, whereas contralateral slopes were similar to normal references. The results may be explained by a correlation between the insufficient lateral protection and a temporomandibular mandibular joint dysfunction (ipsilateral low mobility).

Assessment of facial form modifications in orthodontics: proposal of a modified computerized mesh diagram analysis.

A modified computerized mesh diagram analysis enables rapid, easy, and independent quantifications of facial size, shape, and head position. A lateral cephalometric radiograph is traced, positioned in natural head position (NHP) according to the NHP registered on a lateral photograph, and superimposed by the standard grid of rectangles determined by the patient's upper face height and face depth. The patient's tracing is compared with a reference tracing of a norm. The two tracings are registered at nasion in NHP, and the size difference of the patient's mesh rectangles from the norm is quantified by a size normalization. The shape discrepancies are evaluated by calculating relevant displacement vectors for each cephalometric landmark, and a global difference factor. This computerized method provides a rapid graphic evaluation of the patient's sagittal and vertical discrepancies and can also be applied to determine the effects of orthodontic therapy and/or growth on the skeletal and dental relationships in a single patient.

Relative position of porion and tragus in orthodontic patients.

In order to assess the relationship between the hard (porion-orbitale) and soft (tragus-orbitale) tissue Frankfurt planes, the relative positions of porion, orbitale, and tragus were evaluated on cephalometric radiographs. A 5-mm radiopaque disk was fixed on the right tragus of 160 white orthodontic patients (65 males aged 7 to 28 years, and 95 females aged 7 to 36 years), and a pre-treatment lateral cephalometric radiograph was taken. In every film the positions of orbitale, porion, and tragus were digitized, and the linear distances between the points, as well as the position of tragus relative to the skeletal structures, were calculated. The linear distances porion-orbitale and tragus-orbitale progressively increased with age, with a low variability in all age classes. The linear distances were always larger in the males than in the females. The tragus was always lower and more anterior than the porion, with vertical distances ranging from 1.2 to 19.8 mm. When the porion-tragus distance was expressed as a percentage of the porion-orbitale distance, the variability decreased. In the age classes, mean percentage horizontal projections from porion ranged from 18 to 23% of the porion-orbitale distance, mean percentage vertical projections ranged from 8 to 15%. Unfortunately, sample variability was large, and, in a single patient, the position of tragus relative to the skeletal structures could be predicted only with a large approximation.

Head posture and cephalometric analyses: an integrated photographic/radiographic technique.

A photographic technique for natural head posture (NHP) recording that can be associated to standard radiographic exposures is presented. It allows the evaluation of radiographs, according to both the standard intracranial references and NHP. On the NHP photograph, the angle between the soft tissue nasion-pogonion line and the true vertical is calculated, and this value is used to rotate the standard radiograph around the Bolton point. The technique has been applied to 40 private orthodontic patients (24 females and 16 males, aged 7 to 20 years, mean 12.9 years). The hard tissue Frankfurt plane in NHP showed a wide variation: 80% of the patients had orbitale lower than porion (mean angle -6 degrees relative to the ground), 20% had orbitale higher than porion (mean angle 4 degrees). The position of this plane in NHP seemed to be different in the two sexes, with more males having the Frankfurt plane going upwards than females. The soft tissue Frankfurt plane (tragus-orbitale) in NHP was directed upwards (head extended) in 53% of patients. The two Frankfurt planes were never coincident in all subjects; the tragus was always lower and more anterior than porion. On average, the angle tragus-orbitale-porion was about 6 degrees. In young orthodontic patients NHP is therefore highly variable, gender dependent, and cannot be deduced from mean population values. Nevertheless, the evaluation of head position should be performed in each young patient before and during the treatment, to verify how the combined effects of therapy and growth act.