[Histological changes in the circum-maxillary sutures during alternate maxillary expansions and constrictions in a rat model].

OBJECTIVE: To investigate changes in the circum-maxillary sutures during alternate maxillary expansions and constrictions in a rat model. METHODS: Twenty-two male Sprague-Dawley rats (6 weeks old) were used and divided into three groups. In maxillary expansion (ME) group (n=9), an expander was activated for 5 d, and then sacrificed. In alternate maxillary expansions and constrictions (Alt-MEC) group (9 animals), an alternate expansion and constriction protocol (5 d expansion and 5 d constriction for one cycle) was conducted for 2.5 cycles (25 d total), and then sacrificed. The control group comprised 4 animals with no appliances used, each of two sacrificed on day 5 and day 25, respectively. Circum-maxillary sutures (mid-palatal, maxillopalatine, premaxillary, zygomaticotemporal, and frontonasal suture) in each group were characterized histologically. RESULTS: Histological findings of circum-maxillary sutures: in control group, the normal sutures were divided into 5 zones, the center was polygon mesenchyme zone, the lateral was mature chondrocyte zone, the next lateral was bone tissue. In ME group, the mid-palatal suture was expanded after ME, the fibre and connective tissue were extracted and invaded into cartilage zone. Osteoblast hyperplasia and new bone formation occurred. The orientation of the new bone trabecula was consistent with force. The osteoclast appeared in some area. Findings of other sutures were similar with those of control group, osteogenesis was active in some area without obvious reconstruction in Alt-MEC group, mid-palatal suture and other sutures in some area were widened after Alt-MEC with much more osteoblast hyperplasia and new bone formation. Fibre and connective tissue were extracted, distorted or even broken. Sutures in some areas were narrowed with osteoblast cytopenia and osteoclast hyperplasia. Fibre and connective tissue compressed because of the different force and orientation. Osteoclast count results showed that compared with the control group, the number of the osteoclast was increased only in the palatal suture in ME group (P<0.05). Other sutures did not show obvious changes (P>0.05). In Alt-MEC group, the numbers of the osteoclast in circum-maxillary sutures were the most, and had statistical significances (P<0.05). CONCLUSION: These RESULTS suggested that circum -maxillary sutures were actively reconstructed after Alt-MEC. while only midpalatal suture had active reaction after ME.

Comparative characterization of maxillary expansion and alternate maxillary expansions and constrictions in rats.

The purpose of this study was to evaluate whether the cranial and circumaxillary sutures react differently to maxillary expansion (ME) and alternate maxillary expansions and constrictions (Alt-MEC) in a rat model. Twenty-two male Sprague-Dawley rats (6 weeks old) were used and divided into three groups. In ME group (n=9), an expander was activated for 5 days. In Alt-MEC group (9 animals), an alternate expansion and constriction protocol (5-day expansion and 5-day constriction for one cycle) was conducted for 2.5 cycles (25 days total). The control group comprised 4 animals with no appliances used, each of two sacrificed on day 5 and day 25 respectively. Midpalatal suture expansion or constriction levels were assessed qualitatively and quantitatively by bite-wing X-rays and cast models. Distances between two central incisors and two maxillary first molars were measured on cast models after each activation. Circumaxillary sutures (midpalatal, maxillopalatine, premaxillary, zygomaticotemporal and frontonasal suture) in each group were characterized histologically. Results showed that midpalatal suture was widened and restored after each expansion and constriction. At the end of activation, the widths between both central incisors and first molars in Alt-MEC group were significantly larger than those in ME group (P<0.05). Histologically, all five circumaxillary sutures studied were widened in multiple zones in Alt-MEC group. However, only midpalatal suture was expanded with cellular fibrous tissue filling in ME group. Significant osteoclast hyperplasia was observed in all circumaxillary sutures after alternate expansions and constrictions, but osteoclast count increase was only observed in midpalatal suture in ME group. These results suggested that cranial and circumaxillary sutures were actively reconstructed after Alt-MEC, while only midpalatal suture had active reaction after ME.

[Influence of the mandibular second premolar extraction on the angulation of the mandibular third molar].

OBJECTIVE: To compare the angular changes in the developing mandibular third molars in the mandibular second premolar extraction and non-extraction cases and to determine whether the mandibular second premolar extraction causes favorable rotational changes in the angulations of the developing mandibular third molars and benefits its later eruption. METHODS: Pretreatment and posttreatment panoramic radiographs were taken from 45 subjects who had been treated by the extraction of the mandibular second premolars and 48 subjects who had been treated without extraction. The horizontal reference plane was used to measure and compare the changes in the angulations of the developing mandibular third molars. RESULTS: The mean uprighting of the mandibular third molars seen in the extraction group was (5.9±2.5) degrees on the right side and (8.0±3.4) degrees on the left side following treatment. For the nonextraction group the mean uprighting was (1.8±2.4) degrees on the right side and (1.5±2.1) degrees on the left side. There was a statistically significant difference between the groups (P<0.05). CONCLUSION: Mandibular second premolar extraction might be a helpful procedure on the angulations of the developing mandibular third molars.

[Temporomandibular joint osteoarthrosis in patients receiving orthodontic treatments: a clinical investigation].

OBJECTIVE: To investigate the clinical characteristics of temporomandibular joint osteoarthrosis (TMJOA) in patients with malocclusion before orthodontic treatment and evaluate the radiographic changes of temporomandibular joint during treatment. METHODS: Complete clinical recordings of 10,032 patients referring to the Orthodontic Department of Peking University School and Hospital of Stomatology from January 1998 to December 2003 were reviewed in present study. Patients with a history of previous orthodontic treatment, jaw surgery, facial trauma or systemic diseases which could potentially involve temporomandibular joint were excluded. The detection rate of TMJOA was calculated and its association with the possible risk factors of age, gender and malocclusion classifications was analyzed using the method of chi-square and multivariate logistic regression analysis. The clinical and radiographic characteristics were investigated and the radiographic findings before and after treatment were compared to evaluate the orthodontic effect on the articular bony structures. RESULTS: The detection rate of TMJOA in 10,032 patients before orthodontic treatment was 1.6% (159/10,032) and significantly higher in females (1.9%, 124/6,409) than in males(1.0%, 35/3,623)(chi-square = 13.925, P < 0.01).The detection rate increased positively with age (chi-square = 136.381, P < 0.01). Multivariate logistic regression analysis showed that patients with Angle II malocclusion were 1.683 times more likely to suffer from TMJOA compared with patients with Angle I malocclusion(Wald chi-square = 9.007, OR = 1.683, P < 0.01), while there was no significantly difference between the patients with Angle III and I malocclusion. Among the 85 TMJOA patients who finished their orthodontic treatments, 63 patients (74.1%, 63/85) maintained stable articular bony structure and the remaining 9(10.6%, 9/85) and 13 (15.3%, 13/85) patients showed recovering and deteriorating signs respectively according to the radiographs. CONCLUSION: The detection rate of TMJOA associated with age, gender and malocclusion classifications. Stable articular bony structure was maintained in the majority of the TMJOA patients (74.1%, 63/85) during the orthodontic treatments.

Buccal mucosa cell damage in individuals following dental X-ray examinations.

The aim of the present study was to monitor genotoxic and cytotoxic effect of X-ray on exfoliated buccal mucosa cells and investigate the association between the effects and the accumulated absorbed doses of oral mucosa. 98 participants' buccal mucosa cells were collected before and 10 days after different series of dental radiographs performed. Cytological preparations were successively dyed with the methods of Feulgen and fast-green, and analyzed under a light microscope. Micronuclei (MN)and other cells were scored. Accumulated absorbed dose of buccal mucosa was estimated with the method of anthropomorphic phantom and dosimeter chips. The dose rang was 0.18-3.54 mGy. A significant difference in the rate of MN cell was found before and after X-ray examinations (P = 0.008) as well as in the rates of Pyknotic (p < 0.001) and Karyolytic cell (p = 0.0021). When only the patients whose mucosa absorbed dose is lower than 1 mGy was analyzed, significant differences were not found except for Karyolytic cells (p = 0.0313). There was a correlation between the accumulated does and the change rate (ρ = 0.25, p = 0.0118). The frequency of micronuclei cells in buccal mucosa may be increased when a series of dental radiographs including a CBCT examination was performed.

Craniofacial morphology of Chinese patients with bilateral temporomandibular joint osteoarthrosis.

OBJECTIVE: To evaluate the morphological features of craniofacial structures in young patients affected by bilateral temporomandibular joint osteoarthrosis (TMJOA). METHODS: Forty-three males and 189 females aged 15 to 25 years who had lateral cephalograms and temporomandibular joint (TMJ) radiological examinations were included. They were classified into a TMJOA group and a control group, according to TMJ bony status. Thirty-two variables from lateral cephalogram were analysed by t test to evaluate the cranial and dentofacial differences between the two groups. RESULTS: TMJOA group showed a shorter posterior ramus height and shorter condyles, smaller SNB angle and larger ANB angle, smaller facial plane angle and larger angle of convexity, steeper mandibular plane angle and more vertical y-axis. CONCLUSION: Bilateral TMJOA is associated with dentofacial alterations characterised by a tendency toward retrognathism and shorter mandibles. However, the cause-and-effect relationship is yet to be clarified.