Chinese Journal of Dental Research, 02/2008

The quality of clinical and research work on temporomandibular disorders (TMD) has increased rapidly in the last 30 years, especially in the last 20 years in China. The current status of clinical work and basic research achievements on TMD in China were surveyed. In addition, the establishment of the Chinese Society of TMD and Occlusion, the problems in TMD treatment and prospects of TMD clinical and research work in China are introduced and discussed. Keywords: China, research, temperomandibular disorders, treatment

Congenital agenesis of permanent and/or primary teeth is one of the most common orofacial developmental disorders. Although environmental factors can also affect tooth agenesis, genetic factors play a more important role. It can be classified into nonsyndromic and syndromic hypodontia. MSX1, PAX9, DLX1, DLX2, Activin beta-A, Activin receptor types IIA and IIB, and SMAD2 have been considered related to the former. Syndromic congenitally missing teeth is related to ectodermal dysplasias, Van der Woude syndrome and other syndromes. In this article, we will review the molecular genetic mechanisms of congenitally missing teeth. Keywords: congenitally missing teeth, hypodontia, mechanisms, molecular genetics

Sports medicine is related to serious sport-related diseases and injuries, and dental care has been included in the medical services for the Olympic Games since 1932. For a host country organising the Olympic Games, it is very important to understand what dental care should be offered during the games, how many dentists are needed and what kind of specialists should be available. The data regarding dental care from previous Olympic Games a re helpful to estimate the need for dental services in 2008. The protocol for preparing for medical care at the 2012 Olympic Games has been published. However, no detailed information about the guidelines for dental services at the Olympic Games was found from previous data. It is critical for the host city to have guidelines for organising and training the dental team. A guideline and protocol is important for dental diagnostics and treatment during the Olympic Games. The detailed guidelines for dental care at the 2008 Olympic Games are presented in this study. Different parts of these guidelines establish the prescripts for the following: types of dental treatments offered in the 2008 Olympic Games, participants in dental care, equipment and staff for dental care, x-ray examinations, mouthguard programme, working time and after-hours dental service, venue medical care and dental service, and data collection. The prescripts presented formed the protocol for the dental service in the 2008 Olympic Games, and it is planned to provide data to help with future events.

Objective: A prediction model was developed to simulate an underexposed radiograph to that which is optimally exposed. The objective of the study was to evaluate if radiographic landmarks were equally observed in lateral cephalometric radiographs processed with and without the prediction model. Methods: Using a digital imaging system (Orthopantomograph®OC-100D), test radiographs of a human skull phantom covered with simulated soft tissue were obtained using different exposure settings. The optimal radiograph was subsequently established. The under-exposed raw data radiographs were then processed in two sets. In one set, the radiographs were first simulated from the optimally exposed raw data radiograph using the prediction model and then processed with the default settings of the proprietary softwa re that was used to control the imaging system used. In the second set, the radiographs were processed only with the default settings of the proprietary softwa re. Two monitors were employed to simultaneously display the radiographs. Six observers subjectively compared the fourteen most frequently used landmarks on both radiographs. Results: Compared with the non-predicted radiographs, in the predicted radiographs subjective impression of the radiographic landmarks was more frequently considered the same or better than the optimal radiographs. The difference was statistically significant. Conclusion: The subjective impression of the landmarks in the predicted radiographs is better than that in the non-predicted radiographs. Keywords: cephalometry, dental radiography, digital dental radiography, image processing, radiography

Objective:To investigate the displacement and stress distribution of maxillary anterior teeth during retraction using the finite element method. Methods: A three-dimensional finite element model of six maxillary anterior teeth with a straight wire appliance on intermaxillary bone was established in ANSYS 8.1. Retractions in two typical force directions were simulated: case 1 simulated routine anterior tooth retraction by a force of 150 g applied between the anterior hook of 2.0 mm and the first molar tube; case 2 simulated anterior tooth retraction by a force of 150 g between the anterior hook of 4.0 mm and the implant 10.0 mm towa rds the gingiva from the first molar tube. Results: This finite element model was highly realistic for the simulation of orthodontic tooth movement. In case 1, lateral incisors showed controlled lingual crown tipping movement, while central incisors and canines showed lingual crown tipping movement. Stress concentration was found close to the cervix and root apex of each tooth. In case 2, the displacement and stress level was much higher. Central incisors and canines still showed lingual crown tipping movement while lateral incisors showed bodily retraction and intrusion. In the coronal direction, the lateral incisor root tipped mesially, while the canine root tipped buccally. Stress distribution on central incisors and canines was similar to that in case 1, but the maximum principal stress on labial and lingual surfaces of lateral incisors was mostly compressive stress. Conclusion: During routine anterior tooth retraction by sliding mechanics, the crown of anterior teeth tends to tip lingually. Retraction force passing near the centre of resistance of six anterior teeth makes their displacement and stress distribution more uniform, but their translation is still undetectable. Loading on lateral incisors is greater than that on other teeth and stress concentration at its lingual apex should be considered. Keywords: anterior tooth retraction, biomechanics, orthodontics, sliding mechanics, threedimensional finite element

Objective:To compare the arch expansion effect between the Quad Helix (QH) palatal expansion appliance and the rapid palatal expansion (RPE) appliance. Methods:The sample consisted of 27 cleft lip and palate children who required palatal expansion as part of their orthodontic treatment: 13 were treated with the QH and 14 with the RPE. Dental casts were taken before treatment and at the end of the retention period after expansion. Inter-canine width, inter-molar width, and palatal depth were measured in each cast. In addition, occlusal radiographs were obtained before and 2 weeks after expansion to evaluate sutural separation by the appliances. Results: Posterior crossbites were corrected in all patients following expansion. Both the QH and the RPE groups produced significant increases in inter-canine width (2.11 mm and 3.08 mm, respectively) and maxillary inter-molar width (3.49 mm and 4.80 mm, respectively). Neither the QH nor the RPE group demonstrated a significant change in palatal depth (-0.50 mm and -0.46 mm, respectively). The ratio of skeletal change to total expansion was greater in the RPE group (0.30) than that in the QH group (0.18). Conclusion: It was suggested that both the QH and the RPE appliances were capable of expanding the maxillary dentition and alveolar process, and were equally capable of correcting posterior crossbites. RPE was more effective in the midpalatal suture separation. Keywords: cleft lip and palate, palatal expansion, quad helix, rapid palatal expansion

Objective: To compare the percentage of gutta-percha filled area (PGFA) in the root canals filled with warm vertical condensation (WVC), Obtura II, ultrasonic lateral condensation (ULC), and cold lateral condensation (CLC). Methods: Four groups (total 80) of extracted human teeth with single root were instrumented. The prepared canals were randomly divided into four groups (n = 20). Groups 1, 2, 3 and 4 were obturated with CLC, WVC, Obtura II, and ULC, respectively. Horizontal sections were cut at 3, 6 and 9 mm from the apical foramen (AF) of each tooth. The cross-sectional areas of the canal and gutta-percha were measured using an image-analysis program, and the PGFA was calculated. Results: The PGFAs in both the WVC and Obtura II groups were significantly higher than those of CLC (P 0.05). There was no difference in the PGFA between the WVC and Obtura II groups (P > 0.05). A significant difference between ULC and CLC in PGFA was only observed at 3 mm from the AF of the root. Conclusion: WVC and Obtura II produced significantly higher PGFAs than those produced using ULC and CLC techniques Keywords: gutta-percha filled area, root canal obturation, warm gutta-percha

Objective: To describe a technique of fabricating a positioning template with silicone materials intraorally for dental colorimeters and assess the reproducibility of this technique under in vivo condition. Methods: The template was fabricated using silicone materials. A 5 mm punch was used to create a circular opening on the labial side of the template. The elastic touch probe of the colorimeter was then placed in the opening to check if there was any space between the touch probe and the template. If so, the space was filled with light body silicone material. An in vivo study was performed to assess the reproducibility of this technique. The L*, a*, b* values of 36 anterior teeth were measured by two examiners. Intra- and inter-examiner reproducibility were assessed by calculating intra-class correlation coefficients (ICCs) and the limits of agreement. Results: The results of ICCs showed that the colorimeter with the silicone template had better intra-/inter-examiner reproducibility than without the silicone template. Furthermore, the limits of agreement of the colorimeter with template showed a narrower measuring range compared with the colorimeter without the template. Conclusion:With the use of the template, repositioning of the colorimeter or spectrophotometer for each colour measurement can be precise. This kind of template enables clinicians to evaluate colour changes of teeth and restorations consistently. This technique is convenient and timesaving, and it may be helpful when using other hand-held colorimeters or spectrophotometers for colour evaluation. Keywords: silicone material, positioning template, colorimeter, spectrophotometer, colour measurement

Objective:To investigate the influence of two new generations of light-emitting diode (LED) curing lights with different curing modes on the temperature rise in resin composite samples during their polymerisation. Methods: Bluephase C8 and Bluephase 16i (Ivoclar Vivadent) LED curing units with different curing programmes (high intensity programme [HIGH], low intensity programme [LOW], and soft-start programme [SOF]) were used for two types of resin composite polymerisation (Tetric Ceram, Tetric EvoCeram; Ivoclar Vivadent). The temperature was measured and recorded at the beginning and at the end of illumination using the ELV Pyroscan (ELV Elektronik) thermometer. Results: Regardless of the resin composite material used, there was a statistically significant difference between the temperature rise in polymerisation with Bluephase C8 and Bluephase 16i LED curing lights under the LOW programme (P = 0.022) and SOF programme (P = 0.033). However, no statistically significant difference was found in polymerisation with Bluephase C8 and Bluephase 16i LED curing lights under the HIGH polymerisation programme. Conclusion: Results from this study showed that the polymerisation programme, not the type of curing light used, was related to the rise in temperature. Keywords: LED curing unit, polymerisation curing mode, temperature

In the present case report, a rare congenital fistula of the accessory parotid gland is discussed, including aetiology, methods and imaging for diagnosis and treatment options. Keywords: accessory parotid gland, fistula, salivary gland fistula

A case of sclerosing polycystic adenosis involving the sublingual gland in a 60-yearold Chinese female is presented. Keywords: sclerosing polycystic adenosis, sublingual gland

Presented are two case reports of the ra re congenital anomaly Hallermann-Streiff Syndrome. One patient received dental treatment and cytogenetic examination for primary aetiological investigation. Keywords: Hallermann-Streiff syndrome