528 Reviews and abstracts Am. J. Orthod. June 1986

imum value of a single medical diagnostic radiologic examination.

The authors conclude that the dose to the face during orthodontic diagnosis and treatment is relatively low. However, they point out that radiation from natural sources accumulated over a lifetime in addition to the potential future need for medical diagnostic and/or ra- diation therapy require orthodontists to be prudent in the use of x-ray films in diagnosis of malocclusion and in the evaluation of orthodontic treatment.

Tom Zwemer

Research abstracts

In Vitro Comparison of Zinc Phosphate and Glass Ionomer Cements' Ability to Inhibit Decalcification Under Orthodontic Bands Donald J. Copenhaver Temple University, Philadelphia, 1985

Forty sets of impacted third molar teeth were banded with custom-fitted bands and cycled in a lactic acid so- lution for 4 weeks. This solution simulates an environ- ment that would be found only in patients practicing the worst oral hygiene. Each set was from the same patient. Visual, spectrophotometric and pH testing were done on the sample sets. All areas not banded showed significant decalcification after 4 weeks in the 0.10 M latic acid solution. The teeth banded with glass ionomer cement showed significantly less visible changes under dissecting microscopy ( x 10) than the zinc phosphate cemented samples. Spectrophotometric analysis con- firmed that significantly more calcium was present in solution in the zinc samples than in the glass ionomer samples. The sigfi~ificantly higher pH of the zinc phos- phate cemented sample solutions also confirmed more Ca + + ions in solution. The evidence suggests that glass ionomer cement protects the tooth surfaces from de- calcification under and adjacent to orthodontic bands significantly better than zinc phosphate cements. Fur- ther study on solubility and setting time of this new glass ionomer cement is necessary before routine clin- ical use can be considered.

The Depth of the Mandibular Antegonial Notch as an Indicator of Mandibular Growth Potential Clifford P. Singer The University of Western Ontario, London, Canada, 1985

The craniofacial characteristics and growth poten- tial of 25 orthodontically treated patients possessing

deep mandibular antegonial notches were compared with a similar group of 25 shallow notch subjects by the use of longitudinal lateral cephalometric radio- graphs.

Deep notch cases had more retrusive mandibles with a shorter corpus, smaller ramus height, and a greater gonial angle than did shallow notch cases. The lower face height in the subjects with deep mandibular notches was found to be longer and both the mandibular plane angle and facial axis were more vertically directed. During the average 4-year period examined, the deep notch sample experienced less mandibular growth as evidenced by a smaller increase in total mandibular length and corpus length, and less displacement of the chin in a horizontal direction than did the shallow notch sample.

The results of this study suggest that the clinical presence of a deep mandibular antegonial notch is in- dicative of a diminished mandibular growth potential and a vertically directed mandibular growth pattern.

A Longitudinal Study of the Occlusion and the Dental Arch Dimensions in the Cleft Lip and/or Palate Patients Athanasios E. Athanasiou Temple University, Philadelphia, 1985

The dental arch dimensions and occlusion were studied longitudinally in 72 children with unilateral cleft of the lip, alveolar process and palate (UCLP); in 34 children with bilateral cleft o ¢ the lip, alveolar process and palate (BCLP); and in 70 children with cleft of the hard and soft palate (CP). All children were surgically treated on the same time schedule and with similar surgical procedures in the Lancaster Cleft Palate Clinic. The occlusion and the dental arch dimensions were studied by means of dental casts and photographs during the time of full deciduous dentition (3-4 years of age), mixed dentition (8-9 years of age), and permanent den- tition (9-12 years of age).

Major findings were as follows: 1. The classification of occlusion showed that crossbite

was very common for both the UCLP and BCLP groups. The frequency of crossbite in these two groups was almost similar; in the CP group, the crossbite was not common.

2. In all cleft groups, a relationship between age and crossbite was not found.

3. In the UCLP group, the maxillary interdental widths and the maxillary length were significantly smaller than the normal dimensions for all ages except the intermolar width at the age of 12 years.

4. In the BCLP group, the maxillary interdental widths were significantly smaller than the normal dimen-