Dentoalveolar changes related to mandibular forward growth in untreated Class II persons.

The purpose of this study was to investigate dentoalveolar changes related to mandibular forward growth in persons with Class II malocclusions. The longitudinal cephalometric films of 40 subjects with untreated Class II malocclusions from mean age 8.8 to 17.8 years (before and after pubertal growth) were analyzed and compared with the Bolton norms. There was no statistically significant difference in mandibular growth between the Class II samples and the Bolton norms upon cross-sectional comparison. In the Class II subjects, forward growth of the mandible was greater than that of the maxilla by 4.36 mm on average; the dentoalveolar complex moved forward relative to the maxillary basal bone (point A) 2.16 mm and moved backward relative to the mandibular basal bone (pogonion) 2.28 mm; a strong linear relationship (almost a 1:1 ratio) existed between mandibular forward growth and dentoalveolar complex movement (r = 0.881; y = 0.976 x + 0.183). Results indicated that the effect of forward growth of the mandible, which could potentially bring the lower dentition forward, vanished into the adaptation movements of the dentoalveolar complex through intercuspal locking. Disarticulating the occlusion to minimize the effects of the adaptive mechanism and taking advantage of normal mandibular forward growth could be fundamental biological bases in treating Class II malocclusions in growing patients.

Modification of U6 spliceosomal RNA is guided by other small RNAs.

The vertebrate spliceosomal snRNAs are highly modified by pseudouridylation and 2'-O-methylation. We have identified novel conserved small RNAs that can direct addition of two methyl groups in U6 snRNA, at A47 and C77. These guide RNAs, mgU6-47 (methylation guide for U6 snRNA residue 47) and mgU6-77 contain boxes C, C', D, and D' and associate with fibrillarin. Each RNA can form a duplex with U6 snRNA positioning A47 and C77 for 2'-O-methylation. The antisense element of mgU6-77 can also position C2970 of 28S rRNA for 2'-O-methylation. Depletion of mgU6-77 from Xenopus oocytes prevents 2'-O-methylation of both C77 in U6 and C2970 in 28S; methylation can be restored by injecting in vitro transcribed mgU6-77. Thus, mgU6-77 appears to function in the 2'-O-methylation of two distinct classes of cellular RNA, snRNA, and rRNA.

Cell growth arrest and induction of cyclin-dependent kinase inhibitor p21 WAF1/CIP1 mediated by STAT1.

Signal transducers and activators of transcription (STAT) proteins can be conditionally activated in response to epidermal growth factor (EGF) and interferon (IFN)-gamma. STAT activation was correlated with cell growth inhibition in response to EGF and IFN-gamma. Activated STAT proteins specifically recognized the conserved STAT-responsive elements in the promoter of the gene encoding the cyclin-dependent kinase (CDK) inhibitor p21 WAF1/CIP1 and regulated the induction of p21 messenger RNA. IFN-gamma did not inhibit the growth of U3A cells, which are deficient in STAT1, but did inhibit the growth of U3A cells into which STAT1 alpha was reintroduced. Thus, STAT1 protein is essential for cell growth suppression in response to IFN-gamma. The STAT signaling pathway appears to negatively regulate the cell cycle by inducing CDK inhibitors in response to cytokines.

Wound healing after multisegmental Le Fort I osteotomy and transection of the descending palatine vessels.

PURPOSE: Vascular ischemia has been associated with improper soft tissue flap design, stretching of the palatal vascular pedicle, bony segmentation, transection of the descending palatal vessels, or hypotension. This study examined Le Fort I osteotomy wound healing after some of these surgical maneuvers. MATERIALS AND METHODS: Clinically analogous four-segment Le Fort I osteotomies were accomplished through circumvestibular incisions in nine adult rhesus monkeys and the animals were killed at 0, 3, 7, 14, and 28 days after surgery. Revascularization and bone healing were studied by microangiographic and histologic techniques. RESULTS: The findings indicated that the palatal mucosa or labial-buccal gingiva and mucosa provide adequate nutrient pedicles for Le Fort I osteotomies accomplished through a circumvestibular type incision. CONCLUSIONS: It was concluded that segmentalization, stretching of the vascular pedicles, or transection of the descending palatine vessels have only transitory discernible effects on revascularization and bone healing.

Biomechanical properties of small bone screws.

PURPOSE: To evaluate systematically the biomechanical properties of 13 popular screw designs, ranging from 0.8 to 2.0 mm in diameter. METHODS: Screws were characterized in terms of external, core, and drill diameter; cutting flute and head design; material; pitch, thread depth; and height of shank (unthreaded portion) and shank with plate. They were tested in standardized bone specimens (2 x 2.5cm slabs of fresh bovine femur) 1, 2, 3, and 4-mm thick. For each screw-bone thickness combination, 10 trials were conducted to determine push-out force (POF) and another 10 trials to determine insertion (IT) and maximum torque (MT) yielding a total of 1,040 tests. RESULTS: Among the 13 different screws, in 1-mm thick bone, both the lowest (108.5 N) and highest (294.9 N) POF were created by 2-mm screws (P < .001); that with the lowest POF had a long unthreaded shank and pitch, that with highest POF had a short unthreaded shank and pitch. Screws with 0.8- to 1.5-mm diameters showed no differences in POF. The 2-mm screw with the lowest POF also had the lowest MT in 1-mm thick bone compared with the other 2-mm screws (P < .001). In thicker bones (> 2 mm), two 2-mm screws showed 30% to 50% lower MT than the other same size screws (P < .001) because their head slots stripped easily. When all screws were considered together for a particular bone thickness, torque was strongly predicted by screw diameter (MT: r = .94, P < .001; IT: r = 0.92, P < .001). Screws with the same diameters varied significantly in IT because of differences in self-tapping cutting flute design. CONCLUSION: External diameter, unthreaded shank height, head slot, and self-tapping cutting flute design had the greatest impact on screw strength and efficiency in thin cortical bone. Thread depth, core diameter, and metal type did not affect performance significantly. Under these highly standardized in vitro conditions, the ideal 2-mm screw has an unthreaded shank that is as short as possible, and the pitch is about 0.8 mm. Additional aspects of a clinical situation beside holding strength must, however, be considered when choosing a screw.

Esthetic contour analysis of the submental cervical region: a study based on ideal subjects and surgical patients.

A cephalometric analysis of the submental-cervical region was carried out by examining and comparing 16 white adults who had ideal submental-cervical esthetics with 16 adult orthognathic surgery patients who were treated by submental lipectomy or liposuction and various orthognathic surgical procedures. A normative data base of the submental-cervical region was derived from the ideal subject group. The submental-cervical morphology of the preoperative patients differed significantly from the ideal subjects. The submental-cervical angle (Sm-Ce) and the submental soft tissue thickness at C point (IBM-Sm) presented the greatest disparity between the ideal subjects (118.0 degrees, 28.0 mm) and the preoperative patients (158.3 degrees, 42.1 mm, each P < .001). After surgery, Sm-Ce and IBM-Sm decreased to 132.8 degrees (P < .001) and 28.7 mm (P < .001), respectively. By the end of 6 months postoperative, the mean values of Sm-Ce and IBM-Sm were 131.1 degrees and 28.6 mm. The submental soft tissue thickness of the patients 6 months after surgery was not statistically different from the ideal subjects (each P > .05). Orthognathic surgical procedures with concomitant submental lipectomy or liposuction had a significant effect on the contour of the submental and cervical soft tissues.

[Arterial distribution and morphogenesis of human maxilla].

There are two leading hypotheses concerning maxillofacial morphogenesis in human (Fusion Hypothesis & Overlapping Hypothesis). Differing opinions about the maxillary morphogenesis lead to different concepts about the intrinsic arterial supply to the maxilla. This research was to study the arterial constitution of human maxilla so as to inquire into its morphogenetic patterns. Appropriately perfused (Pb3O4 + turpentine) infraorbital and posterior superior alveolar arteries in 9 fresh human cadavers with ages ranging from 2 days to 35 years revealed that 4 individuals' arterial systems of maxilla consisted of anterior and posterior superior alveolar arteries, but the other 5 ones consisted only of the posterior superior alveolar artery, which extending to the facial midline and supplies all the incisor and molar teeth. The results indicated that two kinds of maxillary morphogenesis patterns may exist simultaneously.

Location of the nasolacrimal canal in relation to the high Le Fort I osteotomy.

The positional relationship between the high-level Le Fort I osteotomy and the nasolacrimal canal was studied in standard posteroanterior and lateral cephalograms made of 100 adult dry skulls after orienting the Frankfort horizontal of each skull to the natural horizontal plane. The simulated high-level Le Fort I osteotomy in all of the 100 skulls was under the level of the inferior orifice of the nasolacrimal canal by a mean distance of 5.2 mm (range, 0.5 to 11.5 mm). The average distance between the canal orifice and a line which extended from the lacrimal fossa to the anterior attachment of the inferior turbinate was 0.7 mm (range, 2.0 mm medially to 3.5 mm laterally). The maxillary height was strongly correlated to the height of the infraorbital foramen (r = .59, P less than .001) and the simulated osteotomy (r = .57, P less than .001). The results indicate that the osteotomy, when made just beneath the infraorbital foramen and extending into the piriform rim at the level of anterior attachment of the inferior turbinate, will usually not jeopardize the nasolacrimal duct within its bony canal. A line drawn from the lacrimal fossa to the anterior attachment of the inferior turbinate on the anterior aspect of the maxilla is a good approximation of the course of the nasolacrimal canal.

[A study of maxillary and mandibular vasculature in relation to orthognathic surgery].

Angiography and Chinese ink perfusion were performed in 14 cadavers. It was found that the origins of arterial blood supply to maxilla and mandible in human beings are multiple. Normally, the maxilla and mandible receive not only the centrifugal blood from the alveolar arteries, but also the centripetal blood from the surrounding mucoperiosteum. This feature of jaw bone's blood supply is the important anatomic basis for the establishment of blood compensation to the moved bone segments which are nourished only by attached mucoperiostea after osteotomies have cut off the blood supply of alveolar arteries in orthognathic surgery.

[The blood supply of the jaw mucoperiostea and its significances in orthognathic surgery].

The blood supply and vascular architecture of maxillary and mandibular mucoperiostea were studied in 14 cadavers with methods of ABS resin casting mould and angiography. It was found that the arterial blood of the mucoperiostea comes from an extraskeletal blood system. The distribution of each arterial branch is limited to a certain area. These results are significant in design of incision in orthognathic surgery.

[The surface topography and ultrastructure of the human TMJ, a SEM and TEM study].

Two specimens of human temporomandibular joints were studied with scanning electron microscope and transmitting electron microscope. The whole articular surface of TMJ has an undulated or ovoid appearance. Each part of the joint has its own surfaces property. A gel-like material was found on the articular surfaces of condyle, glenoid fossa and disk. The arrangement and size of collagen fibers are also different in different parts of the joint. In many places of a specimen from a cadaver who had serious grounding on his teeth, the gel-like material has disappeared and some fibrous material has formed on the articular surface.