substantial (% = 5.5 mm.). As a result of adjustment in gonion position. the posterior facial height decreased and the mandibular plane angle increased. The increase observed in anterior facial height was negligible. The hyoid bone returned toward, but did not reach, its presurgical position. The distance between the hyoid bone and mention in- creased, which supports other findings of adaptation within the suprahyoid muscle group.

The Effect of Retraction of Maxillary Anterior Teeth Upon Lip Position Craig T. Holdaway Univrrsity of the Pacific, San Francisco, 1981

The purpose of this investigation was to determine if a reliable relationship could be established between tooth and lip retraction. The following factors were considered: (1) Age, (2) sex, (3) race, (4) length of study, and (5) lip strain.

The sample consisted of pretreatment, posttreatment, and lo-year follow-up cephalo- grams of thirty-eight patients.

The explained variation of lip-to-tooth novement at the retention period was 43 per- cent. Including a strain factor increased the explained variation to 53 percent. Explained variance increased to 77 percent and 86 percent respectively, when the retention period and retention period plus lip strain factor were considered.

The present findings indicate that a reliable relationship between incisor retraction and lip position can be established if retention time and pretreatment lip strain are taken into consideration.

The Relationship EMween Clinical Measurements of the Gingival Tii Mark McDonough University qf the Pacific. San Francisco, I981

The purpose of this study was to determine if color slides of the gingival tissue in the mandibular incisor region accurately represent this tissue clinically.

A sample of ten young, ten adolescent, and ten adult patients with varying gingival tissue heights (free gingival margin to mucogingival junction) were selected from the orthodontic clinic at the University of the Pacific School of Dentistry.

The following clinical and photographic measurements were performed on each of the thirty subjects on two separate occasions.

Clinical measurements

1. Height of the gingival tissue on the midfacial surface of the four mandibular incisors. To measure this height, two methods were used to locate the mocogingi- val junction.

2. Depth of the gingival sulcus.

Photographic measurements

1. Height of the gingival tissue measured from two color slides, one taken with retractors and one taken without.

The clinical and photographic measurements were analyzed and compared.

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Reviews and abstracts 341

Results

1. The two methods used to locate the mucogingival junction demonstrated a sig- nificant amount of variation. One method (tissue pull technique) located the mucogingival junction more apically 92 percent of the time, an average of 0.915 mm, in the lateral incisor region and 0.889 mm. in the central incisor region.

2. Of the thirty subjects tested, in only 1.5 (or 5 percent of the sample) was the gingival tissue height measured clinically equal to the gingival tissue as calculated photo- graphically from color slides. This would indicate that one cannot with certainty deduce the actual height of the gingival tissue in the mandibular incisor region from longitudinal photographic records.

The Influence of Primary Molar Extraction on the Eruption Paths of the Premolars William D. Rawlings University of the Pacijc, San Francisco, 1981

This study was designed to determine if early extraction of mandibular deciduous molars in patients treated with a lingual arch influenced the eruption paths of the premo- lars. The sample of fifty-five children, all aged 7 years 3 months or older, was divided into two groups:

1. An orthodontic treatment group, with sequential extraction of the mandibular de- ciduous molars and placement of a fixed lingual arch appliance.

2. A control group in which no orthodontic treatment or extraction of deciduous molars was performed.

Tracings of serial cephalometric radiographs were made to compare the relative posi- tions of the mandibular premolars at an early stage of development to their positions after attaining occlusal contact.

It was found that the eruption paths of the premolars in the treated and control groups did not differ at the 0.05 level of statistical significance, although the difference may be of clinical importance. Therefore, it was concluded that the extraction of the mandibular deciduous molars and the placement of a lingual arch had no significant statistical effect on the final position of the premolar teeth.

AA0 MEETING CALENDAR

1982-Atlanta, Georgia, May 2 to 5, Georgia World Congress Center 1983-Boston, Massachusetts, April 30 to May 4, John B. Hynes Center 1984-Kansas City, Missouri, May 13 to 16, Kansas City Convention Center 1985-Las Vegas, Nevada, May 5 to 9, Las Vegas Convention Center 1986-Chicago, Illinois, May IO to 14, Hyatt Regency Hotel