A validity test of cephalometric variables as a measure of clinical applicability in anteroposterior profile assessment.

Twenty-six profile silhouettes are divided by five judges into three categories: retrognathic, orthognathic, and prognathic. On the corresponding lateral cephalograms, 51 cephalometric variables are tested for profile recognition. Discriminant analysis indicates that measurements based on natural head position perform better than comparable variables based on an intracranial reference line. The soft tissue variables (SnPo'-SnTV, Po'-SnTV, ILS-SnTV) are most successful, but no single variable is totally accurate. Skeletal variables relating the maxilla to the mandible (APo, AB, NA-PoA) are more successful than those variables relating one arch to the remainder of the skull (A-FHP, B-NTV, SNA, SNB). A combination of soft tissue and dental variables (SnPo'-SnTV, SnPo'-TMe', 1u-Npo, 1l-NPo) is found to be completely successful. A methodological approach, as applied in this study, can pinpoint the cephalometric variables that are clinically more effective in describing certain facial features.

Horizontal rotation of the condyle after sagittal split osteotomy of the mandible.

Displacement of the proximal segment of the condyle such that the condyle is no longer in its correct position has been cited as a major factor in postsurgical skeletal relapse after mandibular, sagittal split osteotomy. This study examined the effects of sagittal split osteotomy on the horizontal rotation of the condyle in 16 dissected mandibles for which clamp, screw, and wire fixations were used to advance the mandible or set it back. The results showed that, after sagittal split osteotomy, horizontal rotation usually occurred, regardless of the position of the distal segment or the type of fixation used. Our finding that 82% of the condylar angles increased after surgery indicates that the lateral pole of the condyle had rotated anteriorly, while the medial pole had rotated posteriorly. There were no consistent differences in horizontal rotation between the condyles on the side where the proximal segment had been fixed first and those on the side where it had been fixed second; nor did the sizes of the original intercondylar angles affect the magnitudes of change in the postoperative intercondylar angles. The only statistically significant difference (p = 0.005) between the angles after fixation by the three different methods was between screw and wire osteosyntheses when the distal segments were in the forward position. The reason for this difference is unclear.

Bond strength of ceramic brackets under shear stress: an in vitro report.

The shear bond strength and the potential enamel damage on debonding of various currently available ceramic and stainless steel brackets were examined in vitro using extracted premolar teeth. The brackets were divided into two groups, one bonded with a new light-cured orthodontic adhesive and the other with a conventional chemically cured system. An Instron Universal testing machine was used to apply the shear stress. Mean, standard deviation, and extreme values were calculated for each group. Statistical analysis showed that the mean shear bond strength of the silane chemical bond provided by some ceramic brackets is significantly higher (p less than 0.05) than the mean of the mechanical bond of other ceramic and stainless steel brackets. There was no statistically significant difference between the mean shear bond strength of the two adhesives used. Mechanical bonds failed primarily within the adhesive itself, whereas chemical bonds failed predominantly at the adhesive-bracket interface. Single-crystal ceramic brackets tend to be more brittle than the polycrystalline ones. Strong chemical bonds can potentially lead to enamel failure on debonding.

The sagittal split osteotomy of the mandible.

Modifications of the sagittal split osteotomy of the mandible have essentially reduced the major drawbacks of the procedure, such as condyle displacement, short-term skeletal relapse, and protracted maxillomandibular fixation and mental nerve dysesthesia. These techniques have proved effective over a period of 4 years in fifty-seven patients treated.

Blood flow changes after orthognathic surgery: maxillary and mandibular subapical osteotomy.

Subapical osteotomies were performed in the left quadrant of the mandibles and maxillas of five dogs and six monkeys. Two indirect methods, the isotope fractionation (diffusible tracer) and particle distribution (nondiffusible tracer--15mu microspheres) were used to quantitate local blood flow. To examine the effect of the surgery, blood flows in the alveolar bone, mucosa, and dental pulp of the segmented left quadrant and the corresponding tissues in the right quadrant were calculated and compared. It was assumed that the blood flows to the nonoperated right quadrant could serve as the controls to those observed in the osteotomized segment. The fractional decrease in blood flows to tissues in the operated sides were similar in both experimental animals. The decrease was largest in the dental pulp, ranging from 54% to 82% on the average, and least for the mucosal tissue, ranging from 18% to 40%. Blood flows decreased by 48% to 74%, on the average, in the alveolar bone. In some animals, blood flow to mucosal tissue that served as the pedicle was actually greater than the blood flow in the corresponding tissue on the right side. After surgery, the cardiac output in the dogs averaged about 156 ml/min/kg as calculated from both the diffusible and nondiffusible data. In the monkeys in which only the microspheres were injected, the cardiac output averaged 99 ml/min/kg. The arterial blood pressure dropped 8 to 13 mm Hg on the average (dog, 108 to 100 mm Hg; monkeys, 94 to 81 mm Hg). The heart rate also decreased slightly in dogs, 158 to 139 beats/min on the average; however, it increased slightly after the surgery in the monkeys, 144 to 161 beats/min. Blood losses during surgery were replaced wtih lactated Ringer's solution and the transient decreases in blood pressure of about 20 to 35 mm Hg were not sufficient to produce any shut down of renal blood flow.