A re-investigation of the relationship between head posture and craniofacial growth.

This investigation was designed to repeat classic studies into the associations between head posture and growth as a single unified study using up-dated methods for gathering and analysing the data. The material comprised the cephalometric radiographs of 59 children (34 males and 25 females) recorded in natural head posture (self-balance position), at the beginning and end of a period of observation during which no treatment was performed (mean age at initial radiograph 11.76 years, mean interval between radiographs 3.52 years). Correlation analysis (corrected for multiple inference and adjusted for dependency between the variables) showed the strongest associations to be between growth direction of the face and the change in posture. No association was found between growth (direction or magnitude) and pre-observation posture. The most prominent associations were between the change in cranio-cervical posture (CCP) and variables representing the growth directions of the mandible (r = 0.72, P < 0.0001); anterior maxilla (r = 0.49, P < 0.001); posterior cranial base (r = 0.45, P < 0.01); temporomandibular joint (r = 0.56, P < 0.001); and the change in postural height of the tongue (r = 0.54, P < 0.0001). These findings do not support the hypothesis of a causal relationship between initial posture and subsequent facial growth. Instead, they indicate that it is the change in posture that is primarily linked to the growth direction of the face. The patterning of the correlations and the inter-relationships between the main growth variables suggest that this linkage arises from the coordinated changes that occur in the postures of the mandible and tongue. These coordinated postural changes appear to determine the growth direction of the mandible and, at the same time, influence CCP, possibly via an effect on pharyngeal patency.

Natural reference structures in the human mandible: a systematic search in children with tantalum implants.

SUMMARY: The purpose of this study was to locate stable natural reference structures (NRS) in the mandible as seen on lateral cephalometric radiographs. The material consisted of pairs of serial radiographs of 34 children (15 males and 19 females aged 8.7-14.3 years at the initial radiograph, with a mean interval of 4.1 years between radiographs). Each child had three Björk type tantalum implant markers in the left side of the mandible. The pairs of radiographs were converted to digital image format, superimposed, and registered using stable implants. Potential NRS were located by visual examination of the superimposed images. The morphological and spatial stability of these potential NRS were tested using automated computer-based analysis employing cross-correlation. NRS were located in each subject (range 4-15 NRS). The number of NRS was statistically significantly correlated with age at the initial radiograph (r(rank) = 0.39, P = 0.02) but not with the interval between the radiographs (r(rank) = 0.21, P = 0.23). Two groups of NRS were found: a small group of amorphous bony condensations and prominent trabeculae mainly in the body and ascending ramus, and a larger group of nine anatomical structures consisting of neurovascular canals and bony striae close to the endocortical surface of the inferior cortex. Two bony structures previously reported as stable (the inner inferior contour of the symphysis and prominent trabeculae within the symphysis) were generally found to drift, presumably because of gradual differential remodelling, making them unreliable as NRS. Based on these findings, two alternative methods are proposed for accurate mandibular superimposition.

Myths and realities in orthodontics.

Comprehensive orthodontic treatment typically comprises an initial phase of alignment over a period of four to six months, followed by vertical, transverse and antero-posterior corrections, space closure, finishing and detailing to enhance dental and facial aesthetics and function. Each course of treatment involves a series of decisions and alternatives relating to objectives, appliance design and treatment mechanics. In recent years there has been increasing interest in short-term approaches to treatment with more limited objectives and the avoidance of phases traditionally considered integral to successful treatment. In this review the veracity of accepted truths in orthodontics are discussed; specifically, the importance of initial molar relationship, final incisor relationship, the merits of orthodontic extractions, anticipated treatment times, the value of modern fixed appliance systems, the importance of torque expression and the relative merits of bonded retainers and inter-proximal reduction are considered.

Specialist orthodontics in the General Dental Service.

This study investigated treatment times and treatment standards produced by 10 specialist orthodontic practitioners working in the General Dental Service (GDS) in England. Twenty cases from each practitioner, consecutively completed with two-arch fixed appliance therapy, were selected and assessed to evaluate treatment times and treatment standards. Observer-generated timings were recorded to provide values for the time taken by these practitioners to perform the various component activities associated with fixed appliance orthodontic therapy. These timings were then pooled to produce an 'average' value for each procedure. Treatment time was assessed retrospectively by applying these average times to the appropriate appointments, as documented on the patient's record card. The treatment duration, number of visits, appliance type and extraction regime were also recorded. Treatment standards were assessed by applying the weighted Peer Assessment Rating Index (PAR Index) to pre- and post-treatment study casts. Relationships between each of these variables were investigated using multiple regression analysis. No relationship was found between treatment time and PAR score change. Predictors of treatment time were the number of visits, and more interestingly, the use of extra-oral forces. However, no useful predictors of the treatment standard were found. On the basis of this sample, it appears that when specialist orthodontic practitioners in the GDS provide two-arch fixed appliance therapy: treatment is completed, on average, in 3-5 hours of chairside time, in 20 visits, spread over 22 months; they provide a high standard of treatment, as assessed by the PAR Index, to a caseload of patients in need to treatment.

Indelible bond location marks: an avoidable aesthetic hazard.

An increasingly popular method of aiding the precise placement of bonded brackets is to identify the long axis and centre of the crown with small pencil marks. A case is reported where marks placed with a soft pencil in the centre of the etched enamel have led to the inclusion of pigment deep in the enamel surface which has proved impossible to remove.

Unerupted premolars--an alternative approach.

These two cases illustrate variations of an alternative technique for moving unerupted teeth into the mouth. Previously described techniques may damage the tooth or the periodontium and the regular adjustments required can be uncomfortable and are unpleasant for the patient and the operator. The method described provides a stress free alternative which is readily acceptable to patients. Adjustments are rarely needed, but if required they usually involve repositioning a magnet in the removable appliance, a procedure carried out simply by the operator or technician using cold cure acrylic.

An evaluation of zirconium oxide brackets: a preliminary laboratory and clinical report.

A pre-production sample of zirconium oxide (ceramic) brackets was examined in this study. A laboratory investigation of the tensile/peel bond strength of the brackets was carried out using two light-cured adhesives (Prismafil and Heliosit) and one chemically-cured adhesive (Delphic). The mode of failure was also investigated using optical and scanning electron microscopy. The bond strengths achieved with Prismafil were statistically significantly (P less than 0.05) lower than Heliosit and Delphic between which no significant differences were found. All samples failed at the bracket-adhesive interface. A clinical test demonstrated the extreme ease of sliding along stainless steel and nickel-titanium archwires, and revealed a low plaque adhesion. The principal disadvantage of these brackets appears to be their off-white highly opaque appearance which in addition to giving poor aesthetics may adversely affect bond strength with light-cured adhesives.

Micro-magnetic retainers: an attractive solution to fixed retention.

The use of neodymium-iron-boron micro-magnets as a fixed retainer which does not hinder oral hygiene, is reported. A patient with persistent midline spacing treated using this method is described.

Stability of the lower labial segment following orthodontic treatment--a comparison of treatment with Andresen and Begg appliances.

This retrospective cephalometric study of Class II division 1 malocclusions investigates the effects on the lower labial segment of two forms of orthodontic treatment. Non-extraction Andresen myofunctional therapy and first premolar extraction Begg treatment are compared to the lower incisor changes found in appropriate non-extraction and first premolar extraction control groups, which also presented with Class II division 1 malocclusions. Using four angular and two linear measurements, the lower labial segment was found to procline during Andresen therapy (1-2 degrees, 1-2 mm), and on withdrawal of the appliance it retroclined by about one-half of the in-treatment proclination (0.4-0.8 degrees, 0.1-0.5 mm). During extraction Begg mechanics, the lower incisors were found to retrocline (1.3-1.5 degrees, 0.4-0.9 mm), and they continued to retrocline following removal of the appliance (0.2-3.0 degrees, 0.8-1.1 mm). In general, the variables used to measure lower incisor position demonstrated only very small changes, and were near method error. The reliability of these changes are discussed. It is considered that the axial inclination of the lower incisor in relation to the mandibular plane is the most consistent and therefore still the most useful clinical measurement of lower incisor change available from cephalometric radiographs.

The validity of two methods of mandibular superimposition: a comparison with tantalum implants.

The aim of this investigation was to examine and compare the validity of Björk's and Ricketts' methods for the superimposition of serial cephalometric radiographs of the mandible for the analysis of changes over the duration of routine orthodontic treatment in growing subjects (approximately 2 years). Pre- and posttreatment lateral cephalometric radiographs of 23 children, with tantalum markers implanted in the mandible, were studied. The differences in position of six dental and skeletal landmarks between superimposition on Björk's structures and on Ricketts' corpus axis were compared with those on the basis of the implants. A rotational effect was found for corpus axis resulting from differential movement of Xi point with growth, whereas Björk's method yielded results essentially similar to those of the implant-based superimposition. This resulted in statistically significant median differences between the two methods for all landmarks except pogonion and menton. The magnitude of the differences increased with distance from the central core of the mandible and were generally greater horizontally than vertically. Although most differences were less than 2 mm, approximately 10% of the subjects showed differences greater than 4 mm for molar and incisor landmarks. These findings suggest that, for growing subjects, Björk's method should be preferred Ricketts', which cannot be relied on to indicate the true (intramandibular) changes during orthodontic treatment in growing subjects.

Magnets and orthodontics.

The first part of this paper is a literature review of magnets and their uses in orthodontics. The biological safety of magnets is considered and a report is given of experiments carried out on rat osteosarcoma cell line UMR-106. The second part of the paper describes a case where neodynium-iron-boron magnets were used to assist eruption of an unerupted, vertically impacted upper right canine. Previously, space was available for this tooth, but it failed to show signs of eruption. Following surgical attachment of a magnet, and the use of a second magnet attached to an upper removable appliance, rapid eruption occurred producing a favourable position for bonding.