Chinese Journal of Dental Research, 01/2008

Tooth formation is a complex and dynamic process in which epithelial- mesenchymal interactions play a pivotal role in regulating tooth morphogenesis and subsequent development. Regeneration of a biocompatible tooth has been studied for many years with various results, but has never been totally satisfactory. Recent achievements from stem-cell biology, tissue engineering, bionics, developmental and molecular/cellular biology have made stem-cell-based tooth regeneration a novel approach that will hopefully replace missing teeth and metal implants in the foreseeable future. To avoid the legal and ethical dilemmas regarding the use of embryonic cells for therapeutic and clinical applications, the optimal approach towards clinical tooth regeneration should be mediated by multipotent postnatal stem cells. Here, this review outlines the potential candidate cells and their performances in postnatal stem-cell-based tooth regeneration. Keywords: tooth regeneration, postnatal stem cell, epithelial-mesenchymal interaction, odontogenesis

Objective: To evaluate the particular expression of Shh and its receptor patched (Ptch) involved in mouse embryonic craniofacial development. Methods: The expression patterns of Shh pathway genes during murine embryonic craniofacial development were investigated by applying in-situ hybridization studies of whole-mount and sections, immunohistochemistry, and reverse transcription polymerase chain reaction analysis. Results: Shh was expressed in the mouse embryo at 11 and 12.5 days postcoitum (dpc); Ptch was expressed at 11, 12.5, and 14.5 dpc, but expression patterns were different. SHH protein could also be detected at 11, 12.5, and 14.5 dpc, confirming the gene expression studies. Conclusion: Shh and Ptch expression patterns are characterized. The data suggest that Shh and Ptch are involved during craniofacial development and their roles may vary. Keywords: immunohistochemistry, in-situ hybridization (ISH), maxillofacial region development, Shh, Ptch

Objective: To evaluate the effect of different particulate nanofiller fractions on the surface microhardness of short glass-fibre reinforced semi-IPN polymer matrix composite resin. Methods: Experimental composite resin (FC) was prepared by mixing 22.5 wt% of short Eglass fibres (3 mm in length) to 22.5 wt% of resin matrix with various weight fractions of nanofillers (0, 10, 20, 30, 40, 50 wt%) and then 55 wt% of silane-treated silica filler was gradually added using a high-speed mixing machine. Three filling composite resins (Z250, Grandio and Nulite), resin-modified glass ionomers (Fuji II LC), amalgam (ANA 2000), fibre-reinforced composite (FRC; everStick and Ribbond), and prefabricated ceramic filling insert (Cerana class 1) were tested in this study. Enamel and dentine were used as controls. The specimens (n = 3 per group) were polished and water-stored at 37°C for 24 h before testing. A universal testing machine was used for testing Vickers microhardness. All results were analysed statistically with one-way analysis of variance (ANOVA). Results: ANOVA revealed that nanofiller fraction had a significant effect (P 0.05) on the Vickers microhardness of the short-fibre composite resin. No statistically significant difference was found between FC composite resin and conventional filling composite resins (Nulite and Z250) (P > 0.05). Ribbond FRC had a lower surface microhardness than everStick FRC (P 0.05). Conclusion: The use of high nanofiller fraction with short-fibre fillers in IPN polymer matrix yielded increased surface microhardness. Keywords: surface microhardness, nanofillers, fibre composite resin, filling materials

Objective:To investigate the effect of condylar reconstruction by autogenous coronoid process graft on mandibular growth. Methods: Eighteen growing goats were randomly divided into group A (n = 10) and group B (n = 8). Each animal underwent right condyle removal and was treated by coronoid process graft. Three-dimensional computerised tomography was performed at different intervals. Animals in group A were used for mandibular measurements at 48 weeks postoperatively. Animals in group B were sacrificed at 24 and 48 weeks postoperatively for histological observation. Results: No difference was found in ramus height, mandibular height, and mandibular length between the two sides. The neocondylar size increased significantly, whereas there was a significant reduction of ramus width on the operated side. A well-organised fibrocartilage was seen at the neocondylar surface over time. Conclusion: This study suggests that a neocondyle reconstructed by autogenous coronoid process has the potential to grow under temporomandibular joint functional stimuli. Therefore, this technique may serve as an alternative method for condylar reconstruction in growing individuals. Keywords: temporomandibular joint, mandibular condyle, reconstruction, coronoid process, growth

Objective: To investigate the effect of dental treatments on the glycaemic control of type 2 diabetes. Methods: At baseline, 105 patients with poorly controlled type 2 diabetes (glycated haemoglobin HbA1c >= 8%) were recruited. Dental treatments were provided and the subjects were reviewed at three-monthly intervals. At 12 months, 83 patients remained in the treatment group. Sixty type 2 diabetic patients who had not received any dental treatment during the past 12 months were recruited into the comparison group. Results: The HbA1c level of the treatment group subjects decreased from 9.0% at baseline to 8.1% at evaluation (paired t-test; p 0.001). The reduction was higher than that in the comparison group over the same period, 0.9% versus 0.3% (t-test; p 0.01). Analysis of covariance showed that receipt of dental care was related to a reduction in HbA1c level (p = 0.001). Conclusion: Provision of dental treatment and maintenance of good oral health contribute to an improvement in glycaemic control in patients with type 2 diabetes. Keywords: diabetes mellitus, dental treatment, Chinese, Hong Kong, clinical trial

Objective: To investigate the prevalence and clinical characteristics of temporomandibular disorders (TMD) in a population prior to orthodontic treatment and to evaluate the possible risk factors for TMD. Methods: Clinical documentations and radiographs of 9,909 patients with malocclusions were retrospectively reviewed. All the patients were from the Orthodontic Department of Peking University School and Hospital of Stomatology during January 1998 to December 2003. The prevalence of TMD was calculated and the clinical characteristics were investigated. The association between the prevalence and the potential risk factors including aging, gender and malocclusion classifications was analysed using the method of chi-square and multivariate logistic regression analysis. Results: The prevalence of TMD was 8.6% in this population and statistically higher in females (9.5%) than in males (7.0%) (χ2 = 18.125, P 0.01). The prevalence had a positive association with age and increased in adolescence and young adulthood (χ2 = 157.503, P 0.01). Patients with Angle II malocclusion were more likely to suffer TMD than patients with Angle I malocclusion (odds ratio [OR] = 1.445, P 0.01). Conclusion: Aging, female gender and Angle II malocclusion were risk factors for the occurrence of TMD in the population. Keywords: temporomandibular disorders, orthodontics, risk factor

Objective: To explore effective reconstruction of the defects of tongue following total glossectomy with extended vertical lower trapezius island myocutaneous flap. Methods: Eleven patients with advanced squamous cell carcinoma of the tongue were treated with glossectomy and repaired with extended vertical lower trapezius island myocutaneous flap based with the transverse cervical artery for the defect of tongue. The size of the skin paddle varied from 8 cm * 6 cm to 9 cm * 7 cm. Results: No major flap failure and no shoulder dysfunction occurred. All of the patients had uneventful postoperative courses and began to intake food perorally 8 to 15 days postoperatively. The patients were followed for 8 to 26 months (average 20.6 months). The function of the tongue for speech and swallowing were satisfactory. Conclusion: The extended vertical lower trapezius island myocutaneous flap was suitable for reconstructing total tongue defects following ablation of advanced tongue cancer. Keywords: tongue cancer, trapezius myocutaneous flap, reconstruction

Objective: To assess the oral health status and oral hygiene habits of undergraduate dental students in India and to analyse the influence of dental education on their oral health status. Methods: The target population comprised all first-, second-, third- and fourth-year students at a private dental college, among which 281 students participated in this study with 75.5% response rate. Clinical examination was conducted by two trained examiners according to the methodology recommended by World Health Organization oral health surveys (1997). Bivariate analysis and analysis of variance tests were performed on the data. Results: Mean decayed, missing or filled teeth score was found to be highest (1.70) for the first-year students and lowest (1.03) for the second-year students, with gingival bleeding prevalence rates of 19% and 20% respectively. As the study year progressed there was a constant improvement in their oral health. Conclusion: Oral health was significantly improved for fourth-year students compared with first-year students, implying that constant exercise and growing knowledge in the field of the profession reflects a growing capability to perform an adequate self-assessment of dental state, oral hygiene habits and oral health condition. Keywords: caries, periodontal status, dental students, oral hygiene habits

Objective: To investigate the effect of soft drink on human salivary pH. Methods: Thirty healthy volunteers were included in this study. Cola, orange or lemon soft drinks were consumed (200 ml per day) by each participant for 3 days. Saliva was collected 10 min before drinking, immediately after, and at 30 and 60 min after drinking, and the pH of the saliva was measured. Results: The pH of saliva collected immediately and 30 min after the consumption of all three types of drink was significantly lower than that of saliva collected before consumption (except for the lemon group between before and 30 min after consumption). There is no pH difference between the saliva collected before and 60 min after consumption of the three drinks (P > 0.05). Conclusion: Soft drink intake can reduce salivary pH. Therefore, frequent consumption of soft drinks could be a high risk for dental erosion. Keywords: saliva, pH, soft drink

Nowadays, oral implants are routinely used for rehabilitation of the edentulous mandible as this procedure is often considered uncomplicated, especially when limiting implant placement to the symphyseal area. Nevertheless, a case of nerve disturbance in the anterior mandible after the implant placement is described. Therefore, surgical, radiographic and anatomic considerations are reviewed in order to encounter the risks for neurosensory disturbance and haemorrhage. It is clear that preoperative radiographic planning of oral implant placement in the anterior mandible should pay attention to the mandibular incisive and lingual canals, besides the mental one, to avoid any neurovascular complications. Keywords: dental implant, surgical complications, neurovascular, anterior mandible

Renal cell carcinoma (RCC) is the third most frequent infraclavicular tumour to metastasise to the extracranial region of the head and neck. Metastasis occurs in about 15% of patients with RCC, but only 1% of the patients have metastasis confined to the head and neck. This paper reports three cases of RCC with metastases to the unilateral parotid, the bilateral parotid and the paranasal sinuses. The clinical behaviour and radiographic appearance are reviewed, and the treatment options are also discussed. Keywords: renal cell carcinoma, metastasis, head and neck