Maxillary canine impaction in patients with transverse maxillary deficiency.

Extensive literature exists concerning impacted maxillary canines. Tooth-size/arch-size discrepancy (lack of space) is a common etiologic factor of impacted canines. No studies exist documenting transverse maxillary deficiency as a causative factor for impacted canines. The purpose of this study was to determine whether patients with impacted maxillary canines have transverse deficiency and if other factors, such as arch length, arch perimeter, and arch form contribute to canine impaction. Fifty-seven (57) subjects with eighty-one (81) impacted maxillary canines were compared to one hundred-three (103) nonimpacted subjects. Intermolar (IM) and intercanine (IC) width, arch length (AL), arch perimeter (AP), and arch form were recorded for each subject. The experimental and control groups were compared using a Z test and Chi-square analysis. Results indicate subjects with canine impactions demonstrate profound transverse maxillary deficiency located in the anterior portion of the dental arch: No significant difference in arch form is noted between the experimental and control groups (p > 0.05).

Subjective evaluation of profile prediction using video imaging.

Video imaging has become a popular tool for predicting soft tissue profiles. However, it is important not to create false expectations with its use. The purpose of this study was to evaluate the clinical acceptability of video imaging for the prediction of soft tissue changes in mandibular advancement orthognathic surgery, and thus, to determine its suitability for patient presentation, education, and subsequent treatment planning. Simulated mandibular advancements were performed on 30 patients (21 women and 9 men) using the Dentofacial Planner Plus v1.5 software program. Two separate panels consisting of 25 laypersons and 25 dental professionals (17 orthodontists and 8 oral and maxillofacial surgeons) compared prediction images to actual posttreatment images. Overall profile predictions were found to be clinically acceptable by orthodontists and oral and maxillofacial surgeons in 87.8% of the cases and by laypersons in 95.6% of the cases. No significant differences were found among the individual facial regions graded by the dental professional panel. The results of this study suggest that video imaging is an acceptable tool for profile prediction.

Epithelial bridging of the primary palate: I. Characterization of sub-cultured epithelial cells.

Primary palatogenesis involves an intricate array of events. Cell migration, proliferation, differentiation, programmed death, and fusion occur. Prior to fusion, the morphology of the epithelium undergoes marked changes. Epithelial projections form and extend across the fusion site attaching by filopodia to the opposite prominence. By appearance, the epithelium plays a critical role in facial development. In order to monitor epithelial activities, a study was done to isolate and characterize epithelial cells derived from the primary palate. The primary palate was microdissected from day 13 Sprague-Dawley rat embryos, and the epithelium and mesenchyme were separated by enzymatic digestion with a 3% trypsin-pancreatin solution (3:1). All explants were cultured in Dulbecco's modified Eagle's medium (DMEM) and Ham's F-12 medium (1:1) supplemented with 10% fetal calf serum (FCS), 20 ng/ml epidermal growth factor (EGF), and antibiotics. Explant cells were gathered by trypsin harvesting and sub-cultured. These sub-cultured cells were further characterized. Transmission and scanning electron microscopy showed that the cells retained many morphological features observed in vivo. In passaged cells, type IV collagen, laminin, and cytokeratins were visualized by immunocytochemistry. Gel electrophoresis analysis of the water-insoluble extracts demonstrated major bands of proteins of 50 kD and 44 kD that were synthesized by the epithelial cells but not by the mesenchymal cells. These cytokeratin types are suggestive of a simple undifferentiated embryonic epithelium. The effect of all-trans retinoic acid (RA) on cell number and [3H]-proline incorporation was assessed. At [10(-4)M] and [10(-6)M] retinoic acid resulted in significant inhibition in cell proliferation and amount of proline incorporated, with the greater inhibition occurring in the mesenchymal cells. In the concentrations studied, retinoic acid has an inhibitory effect on the two differently derived cell types. This study established that sub-cultured epithelial cells maintain their phenotype and can be used to study fusion processes. Part 2 will demonstrate how the morphology of the epithelial cells can be modified to produce the changes that are observed during fusion of the primary palate.

Epithelial bridging of the primary palate: II. In vitro model mimics in vivo behavior.

Previously, Forbes et al. [J Craniofac Genet Dev. Biol, 9:271-284, 1989] and Millicovsky et al. [Am J Anat 164:29-44, 1982], demonstrated that some of the epithelial cells of the primary palate formed extensive projections, bridging the medial and lateral nasal prominences. These connections are thought to aide in the fusion process by facilitating union of the prominences, a process known as secondary fusion [Millicovsky et al., 1982]. In order to study the epithelial cell and its behavior more closely an in vitro model was established [Gibson et al.: J Craniofac Genet Dev Biol, 1989], where epithelial cells in culture were shown to produce many of the morphologic characteristics observed in vivo. In the present study, an in vitro model is discussed which reproduces the epithelial projections observed in vivo. Epithelial cells, previously characterized, were obtained from the primary palate of 13-day-old rat embryos and sub-cultured as explants. Comparisons were made with the epithelial bridging observed in vivo of two species of animals. The results indicated sub-cultured epithelium as isolated cells, at either low or high density, rarely formed bridges. Primary cultures of epithelial explants also infrequently formed projections. However, sub-cultures of epithelial explants, plated as small clusters of cells with intervening spaces between cell groups, demonstrated extensive epithelial bridging. Epithelial projections did not form from cells that were directly attached to the plastic culture dish; only superficial, elevated cells formed projections. Significantly, the connections that occurred between explants did not attach to the plastic substratum. Instead, they appeared as line connections suspended by the medium. With time, the number of projections increased and epithelial cells could be seen along the projections forming an epithelial bridge. This study established a model of epithelial bridging in vitro for analysis of a process which has been shown to be an integral part of primary palate fusion.

Reduced epithelial surface activity is related to a higher incidence of facial clefting in A/WySn mice.

The epithelial surfaces of the facial primordia were evaluated by scanning electron microscopy (SEM) during primary palatogenesis in two genetically related mouse strains, the A/J and the A/WySn strains. These two strains were selected because the reported frequency of spontaneous cleft lip with or without cleft palate [CL(P)] in the A/J strain approximates 0%, whereas the spontaneous frequency of CL(P) in the A/WySn strain is 20-30%. The embryos were examined prior to (two to six tail somites), during (seven to ten tail somites), and after (ten to 14 tail somites) primary palate fusion. During fusion, epithelial surface activity (characterized as cellular debris, dissociated cells, cellular projections, and epithelial bridging) was more pronounced in A/J embryos. A/WySn embryos with spontaneous cleft lip exhibited a marked deficiency in epithelial activity when compared to their normal littermates. No discernible differences were detected in the facial morphology, with the exception of the distal end of the medial nasal prominence, which appeared longer in the A/J strain. This study suggests that the degree of epithelial surface activity at the putative site of fusion and the relative length of the medial nasal prominence may account for the observed differences in facial clefting of the two strains. Face shape, related to prominence divergence, was similar in the two strains and could not explain the higher incidence of clefting observed in the A/WySn strain.

Repair of surgical clefts of the hard palate in beagles.

The biological responses to the repair of palatal clefts has been evaluated principally by monitoring craniofacial growth. Little is known about the regenerative ability of the repaired palate. In the present study, 18 Beagle pups (51 to 58 days old) were assigned to one of three groups: (1) control group, having no surgery; (2) cleft group, having a surgically created cleft of the posterior hard palate (mean bony measurement: 3.1 x 11.7 mm) at 8 weeks of age; and (3) repaired group, same as group 2, and followed by soft-tissue closure at 12 weeks of age. Craniofacial growth was monitored by cephalometric and dental cast measurements. Records were taken at 6-week intervals. Animals were sacrificed either 16 or 28 weeks after time of cleft creation. Routine histologic examination and histochemical detection of alkaline phosphatase activity were performed to examine the quality and extent of soft-tissue repair and bone formation. Analysis of the cleft palate group revealed that the size of the bony cleft increased with time. The histologic examination demonstrated at 24 weeks of age (12 weeks after the repair) active reduction of medial margin of the bony palate as evidenced by osteoclastic activity. At 36 weeks of age, neither osteoblastic nor osteoclastic activity was detected. The mean dimensions of the bony cleft, in the cleft group at 36 weeks, were 7.9 x 18.8 mm. In the repaired group, partial bone repair occurred. However, no consistency was seen in predicting extent or location of repair. Histochemical detection of alkaline phosphatase activity indicated that the repaired group had greater amounts of new bone formation. In some sites, suture regeneration was seen. As with the amount of bone formation, the amount of suture regeneration was variable. This study revealed that the presence of a cleft inhibits osteoblastic activity along the margin of the cleft, and there is limited potential for regeneration of the palate subsequent to the repair.

The effects of force magnitude on a sutural model: a quantitative approach.

In an effort to quantify the biologic effects of an orthodontic tensile force, the rat interpremaxillary suture was investigated as a model for the periodontal ligament and expanded in vivo with a helical spring across the maxillary incisors. Three levels of force were used: light (50 to 75 g), medium (150 to 175 g), and heavy (250 to 300 g). Thymidine labeling and histologic studies after 12 hours and 1, 2, and 4 days of force delivery are described (n = 48 rats), as are biochemical studies after 2 and 4 days including a 6-hour organ culture (n = 32). The percentage of labeled cells increased significantly in all force groups at 1 day, followed by a rapid decline at 2 days, to a value at 4 days not significantly different from the controls. Biochemical studies showed significant increases in proline incorporation and alkaline phosphatase activity after 2 days of heavy force application. Histologic examinations showed obvious tissue changes beginning by day 1 and involving increases in suture width, vascularity, size and number of cells, amount of osteoid production, and changes in suture morphology. The experimental system was convenient, inflammation-free, and appeared to be reliable as evidenced by characteristic, synchronous tissue and autoradiographic changes in all experimental sutures through 4 days.

The morphologic and biochemical effects of tensile force application to the interparietal suture of the Sprague-Dawley rat.

The purpose of this study was to correlate the histologic and biochemical responses of the interparietal suture to a range of tensile forces. Stainless steel spring implants, calibrated to generate expansive forces from 50 to 250 g, were placed across the interparietal suture in 85 female Sprague-Dawley rats. After experimental periods from 2 hours to 14 days, the interparietal sutures were evaluated by radiography, histology, and biochemistry. An in vivo/in vitro system was used for the biochemical analysis; total protein, proline incorporated, percent collagen, and alkaline phosphatase activity were measured. The radiographs and histology showed that in vivo suture expansion was achievable with 50 to 70 g of force, but the heavier forces showed greater sutural opening, more cellular proliferation, and more bone formation. This increased biologic response by the heavier forces was substantiated by an increase in sutural protein and alkaline phosphatase activity but not in percent collagen. It was concluded that changes in the total protein content of the suture were not primarily caused by proliferation of osteogenic cells and fibroblasts but due to an influx of transudate. In contrast, the increase in incorporation of 3H-proline and alkaline phosphatase activity correlated with the observance of bone formation. This study indicated a positive correlation between the magnitude of tensile forces and osteogenic response.

Inhibition of secondary cartilage of the intermaxillary suture in Sprague-Dawley rats following the enucleation of maxillary molars.

A single craniofacial suture can undergo several morphologic transformations during its development. From 3 to 7 weeks of age, the intermaxillary suture of the rat is synchondrotic in character, featuring secondary cartilage; at later times, this suture is syndesmotic in character, featuring a fibrous tissue interface. Since intermittent mechanical stimulation has been reported to initiate secondary cartilage formation, a study was done to determine if the functioning dentition were responsible for secondary cartilage formation in the intermaxillary suture of the rat. Twenty-two female Sprague-Dawley rats were used. At 3 weeks of age, prior to eruption, the maxillary molars were enucleated from nine animals. Body weights were recorded weekly. Animals were sacrificed weekly from 4 to 7 weeks of age. One hour prior to sacrifice, each rat was injected with [35S]sulfate at a dosage of 2 microCi/g body weight. The tissues were evaluated by light microscopy and autoradiography. In the experimental group, the midpalatal suture did not undergo the normal synchondrotic transformation. Instead, this suture remained fibrous with negligible metachromatic staining. In the control animals, the peak period of [35S]sulfate incorporation was 4 weeks of age and was five times greater than in the experimental group. The primary stimulus for the initiation of secondary cartilage formation in the midpalatal suture of the rat was molar function. Also, functioning molars were found to be important in the maintenance of the palatal bone.