Which Way Forward? Fixed or Removable Lower Retainers

Objective: To determine whether lower lingual, canine to canine, bonded multistrand retainers prevent relapse of lower labial segment alignment following fixed appliance therapy and to compare this with lower Hawley-type removable retainers. Materials and Methods: Two groups of 29 patients were identified. Group 1 had bonded lower canine to canine multistrand retainers placed following debonding, whereas Group 2 had lower Hawley-type retainers (with acrylic labial to the incisors) fitted following debonding. Study models were taken of all patients at debonding (T1) and at least 1 year post debonding (T2). Changes in Little's index over the study period were recorded using a reflex microscope. Results: Statistically significant changes in Little's index occurred in the lower labial segment of both study groups (P = .001) over the observation period. There was no statistically significant difference in the amount of change in Little's index between the bonded and removable retainer groups (P = .13). Bonded retainers tended to be placed in older patients (P = .02). Conclusions: Relapse can occur in the lower labial segment with both fixed and removable retainers. The amount of relapse seen with both types of retainer is not statistically significantly different.

The Assessment of Crowding without the Need to Record Arch Perimeter. Part II: Crowded and Irregular Arches

A mathematically determined technique which seemed to be valid for the calculation of crowding and spacing in arches with acceptable alignment, was tested on a series of arches with varying degrees of crowding and irregularity. Upper and lower study casts of 30 individuals with sufficient malalignment and crowding to warrant orthodontic treatment with fixed appliances were examined. Models were measured by three operators, using a reflex microscope interfaced to an IBM compatible PC and a customized calculation program. The degree ofcrowdmg was compared with a ‘clinical’ assessment of each arch, in which the irregularity was measured directly using a steel ruler. Both the computer calculated and clinical values varied between observers, but the agreement between observers was better using the reflex microscope. Correlation coefficients ranged from 0·92 to 0·96 for the reflex microscope, and between 0·86 and 0·91 for the clinical assessment. Inter-observer agreement for the three operators was high: 0·93 for the reflex microscope and 0·87 where a ruler was used. This suggests that the computer program used to calculate the crowding was valid for the crowded arches under consideration.

Individualized Catenary Curves: Their Relationship to Arch Form and Perimeter

Study casts of the lower arches of 35 children in whom arch alignment was considered acceptable, were examined using a reflex microscope. Arch perimeter was calculated mathematically from a method which required measurement of the mesio-distal widths of the teeth only. This was described as the ‘overlap’ method. Arch perimeter was also calculated using individualized catenary curves for each subject. Two calculations were made, recording arch width either at the distal contact points of the first permanent molars or between their mesio-buccal cusps. Arch perimeter measured from the length of the catenary curves was consistently shorter than that calculted by the overlap method. The variation ranged from 0·02 to 4·58 mm. The catenary constructed using the distal molar contacts gave a better representation of the actual arch form: the mean discrepancy was 2·36 mm, compared with 2·86 mm with the second method where arch width was measured between mesio-buccal cusps. Both techniques for calculation of arch perimeter were heghly reproducible. The catenary curve only approximated arch form well when the arch was relatively narrow across the inter canine region. For square arches this method was unsatisfactory. It is suggested that alternative techniques would be more reliable and the overlap method desribed here is considered satisfactory.

Transverse Maxillary Arch Changes with the Use of Preoperative Orthopedics in Unilateral Cleft Palate Infants

A retrospective clinical study, using a reflex microscope, measured arch widths, palatal shelf widths, cleft widths, and palatal shelf angulation from 26 sets of plaster models of Infants' maxillary arches at birth, and at 3 and 6 months. All infants had unilateral clefts of the lip and palate. They were treated with active preoperative orthopedics until lip repair at 3 months and with a passive plate until palate repair. Cleft width significantly decreased during these periods, due to transverse growth, along with relative flattening of the palatal shelves. Arch width contracted slightly anteriorly, but remained stable posteriorly. Preoperative orthopedics may have helped these changes by removing the effects of the tongue action and allowing unrestricted growth of the palatal shelves.

The Relationship of Crowding to the Eruptive Position of the Lower Permanent Incisors

The aim of this study was to examine the positions of newly erupted lower permanent incisors and their relationship to crowding. Forty-one crowded and 37 uncrowded dental casts of children in the early mixed dentition were examined by means of digitization using a reflex microscope. Two aspects of alignment were considered: rotation and labio-lingual displacement. Rotations of the incisors were defined as deviations from ‘ideal’ predicted angles. Displacement of the incisors was measured as the distance between the most labial and most lingually placed incisors. The study showed an increase in rotations amongst the crowded sample. The result of the investigation of the relationship between crowding and displacement was inconclusive. There would appear to be significant differences between the positions of newly erupted crowded and uncrowded incisors. Crowding, however, was not the only factor causing irregularity.

The Development of a New Method of Cephalometric and Study Cast Mensuration with a Computer Controlled, Video Image Capture System. Part II: Study Cast Mensuration

A computerized system for mensuration of dental casts, developed at the Royal Berkshire Hospital in Reading was tested against a conventional manual method and a computer controlled reflex microscope. Systematic errors, calibration, and handling aspects are discussed. Results showed that the computerized system provided data which while statistically different, were clinically comparable with the same measurements carried out using conventional manual or digitizing techniques. The results indicated that future research is required with respect to object illumination for all indirect techniques.

Method Errors Recorded by Inexperienced Operators of the Reflex Microscope

The Reflex Microscope has become a standard instrument for the precision measurement of orthodontic record models. In this study, 31 individuals with no previous experience of the microscope were assessed for their precision at identifying well defined landmarks. Considerable initial variation existed in the precision of landmark identification, but despite only a limited training period, some of the novices tested achieved a high standard of precision. Mean errors were greatest in the z axis, i.e. along the axis of the eye, and astigmatism was common amongst those recording the greatest errors in this axis. A group of individuals who performed poorly initially, were retested after additional training and practice with the microscope. Method errors were significantly reduced for the majority of those retested, but the test apparatus identified two individuals for whom further measurement with the microscope would be inadvisable.