Chinese Journal of Dental Research, 01/2009

The use of fibre-reinforced composite (FRC) technology in clinical dentistry may solve many of the problems associated with a metal alloy substructure such as corrosion, toxicity, complexity of fabrication, high cost and aesthetic limitation. There are societies where the use of FRC has become common such as in the U.S., Finland, Belgium and the Netherlands. However, the widespread use of this material is still limited. This article briefly presents background and clinical applications of FRC in dentistry.

Objective: To investigate the effects of superhydrophobic modification of hydroxyapatite on the adhesion of Streptococcus mutans and calcium dissolution. Methods:The surface of hydroxyapatite (HAP) discs were modified with a self-assembling film of fatty acids (FAs), CH3(CH2)n-1COOH in ethanol, with different carbon chain lengths (n = 1, 2, ... , 16) for 12 hrs to obtain superhydrophobicity. The water contact angle on the surface of the modified HAP discs was measured to determine the superhydrophobicity. The superhydrophobically modified HAP discs were coated with human saliva, incubated in a S. mutans suspension for 24 hrs and the amount of the bacterium bound to the HAP disc surface was measured as colony-forming units. The HAP discs modified with FAs with different carbon chain length were also examined for their resistance to acid by immersing in an artificial caries demineralisation solution for 12 hrs. The calcium dissolved in the demineralisation solution was measured by atomic absorption spectroscopy. Further, the resistance of superhydrophobically modified HAP discs to acid was examined by the same method at 1, 8, 24 and 48 hrs. Results: The contact angle increased significantly with the increase of the FA carbon chain length, and the surfaces of the modified HAP discs became superhydrophobic (contact angle larger than 150 degrees) when the FA carbon chain length was 12 or more. The amount of bacteria that adhered to the superhydrophobically modified HAP discs was significantly less than the control group (P 0.05). The calcium dissolved from the FA-modified HAP discs into the demineralisation solution was dramatically decreased when the FA carbon chain length was 12 or more. The superhydrophobically modified HAP discs had less calcium dissolved into the demineralisation solution compared with the control (non-modified) for up to 48 hrs (P 0.01). Conclusion: HAP discs were easily superhydrophobically modified by FAs. The superhydrophobic modification efficiently reduced both the oral bacterial adhesion to the surface of the modified HAP discs and calcium dissolving from the modified HAP discs. This is likely to be of significant interest in caries prevention. Keywords: acid erosion, bacterial adhesion, hydroxyapatite, superhydrophobicity

Objective: To explore the risk factors of children with a high decayed, missing and filled surfaces (DMFS) score compared with children with no caries. Methods: Seven kindergartens in Conghua, located in suburban Guangzhou in Southern China, were selected. A total of 401 3- to 4-year-old children were examined for dental caries status, developmental defect of enamel (DDE) and visible plaque index (VPI). Data on children's oral health behaviour, parents' oral health knowledge, attitude and behaviour and other related information were collected by a structured questionnaire completed by their parents. A total of 120 children (30%) with the highest DMFS score (DMFS >= 7) and all 118 caries-free children were chosen for a case-control analysis to explore the risk factors. Results: In bivariate analysis, age at start of tooth brushing, frequency of tooth brushing, frequency of sweet food consumption, pacifying children with sweet food, bottle feeding with sugary drinks, having visited a clinician, VPI, family income, parents'education level, parents' tooth brushing habit, and parents' oral health knowledge and attitude were associated with caries experience in the children. The results of logistic regression analysis showed that the factors associated with high DMFS score were VPI, frequency of sweet food consumption, family income, parents' oral health attitude and having visited a clinician. Conclusion: The results of this study suggest that brushing teeth in an effective way, controlling sugar consumption and educating parents to have a more positive attitude toward oral health are important components in caries prevention among children in Southern China. Keywords: caries, epidemiology, risk assessment

Objective:To evaluate the reliability of the deep plane cervicofacial flap to repair large defects of the cutaneous face and neck. Methods: Nine patients with malignant tumours were treated with extensive resection. The large defects of the cutaneous face and neck were repaired using deep plane cervicofacial flaps based on the superficial musculoaponeurotic system. The subjects were seven male and two female patients, ranging in age from 56 to 74 years (mean 68.2). The size of the defects ranged from 4 × 3 to 10 × 8 cm (mean 6.1 × 5.9 cm). Results: Apart from mild facial contour deficiency following minor flap necrosis in one patient, excellent functional and cosmetic outcomes were acheived with good skin colour and texture matching in all patients. The follow-up periods ranged from 6 to 18 months (mean 10.7) and all of the patients were still alive without recurrence. Conclusion:The deep plane cervicofacial flap is reliable with excellent vascularity. Moreover, it is easy to harvest, compatible with the principles of oncologic resection and the method of choice for repairing major defects of the cutaneous face and neck following tumour resection. Keywords: cervicofacial flap, face and neck defects, reconstruction, rotation flap, superficial musculoaponeurotic system (SMAS)

Objective: To compare three flowable composites (Esthet-X flow, Beautifil flow and Filtek Z350) with a hybrid composite (Z100), and two temporary filling materials (Cavit and IRM) as intra-orifice filling materials to prevent coronal microleakage. Methods: Root canal treatments were performed on 104 extracted human single-rooted premolars. Three millimetres of coronal gutta-percha was replaced by one of the six filling materials to seal the intra-orifice. After thermocycling (5°C to 55°C) for 750 cycles and immersion in Indian dye for 5 days, the teeth were evaluated for dye penetration along canal walls. The data were analysed with the Kruskal-Wallis test and the Mann-Whitney U test. Results: All of the three flowable composites sealed the intra-orifice of root canals as well as Z100, but significantly better than Cavit and IRM. There was no significant difference among the three flowable composites, or between Cavit and IRM. Conclusion: Flowable composites are ideal intra-orifice seals. Keywords: coronal leakage, flowable composite, intra-orifice seal

Objective: To evaluate the diagnostic accuracy of the panoramic radiograph in judging the relationship between the impacted mandibular third molar (IMTM) and the inferior alveolar canal (IAC) by cone-beam computed tomography (CBCT) and give guidelines for using radiological examinations before IMTM extraction. Methods: A total of 1735 IMTMs on panoramic radiographs were analysed and classified into three classes according to the relationship between the IMTMs and the IAC. A total of 126 IMTMs superimposing on the canal partially or touching the canal in line on panoramic radiographs were examined by CBCT. Nine radiographic signs were observed by two radiologists respectively and multivariate logistic regression analysis was performed. Results: 8.7% of IMTMs have superimposition or a linear touching relationship with the IAC on panoramic radiographs. Of these IMTMs, 52.4% impinged and broke the IAC in CBCT images. Two radiologic signs on panoramic radiographs, including interruption of the radiopaque border of the canal (P = 0.009), and interruption of the alveolar lamina dura and periodontal space (P = 0.007), were statistically significant in predicting the impingement of the IAC. Conclusion: Panoramic radiography can be used to screen out high-risk cases of inferior alveolar nerve injury before the IMTM extraction. Those IMTMs superimposing the canal partially or touching the canal in line on panoramic radiographs should be examined by CBCT further. Two features on panoramic radiographs, including interruption of the alveolar lamina dura and periodontal space, and interruption of the radiopaque border of the canal, were more valuable than other signs to predict impingement and interruption of the IAC wall. Keywords: cone-beam computed tomography, impacted mandibular third molar, inferior alveolar canal, panoramic radiography

Objective: To assess debris and smear layer remaining following canal preparation with ProTaper hand-operated rotary instruments and stainless steel K-files. Methods: Sixty freshly extracted single-rooted mandibular premolars due to orthodontic treatment were randomly assigned to three groups of 20 premolars each. The canals were prepared by a rotary or manual ProTaper system using a crown-down technique, or by stainless steel K-files using a step-back technique. After each instrument, the root canals were flushed with 2 ml of a 5.25% NaOCl solution and at the end of instrumentation with 2 ml of a 5.25% NaOCl and 5 ml of distilled water. The amount of debris and smear layer were evaluated at the apical, middle and coronal regions by scanning electron microscopic photomicrographs and the data were analysed separately using Walloon's test. Results: In the coronal and middle thirds, both ProTaper groups achieved better results than the K-file group, and there was no significant difference between the two ProTaper groups. In the apical third, no significant difference for debris and smear layer was found among the three groups. Conclusion: Under the conditions of the present study, ProTaper hand-operated and rotary instruments resulted in relatively good cleaning in the coronal and middle thirds, but there was no difference among the three instruments in the apical third. Keywords: canal preparation, cleanliness, nickel-titanium (NiTi), scanning electron microscope (SEM)

Objective: To evaluate the effect of surface conditioning methods on the bond strength of a self-developed dental CAD/CAM composite resin material (polymethylmethacrylate/nano SiO2-ZrO2) and dentine, and to select appropriate resin cements from three resin luting agents. Methods: A total of 210 cylindrical composite resin blocks were divided into 7 groups (n = 30) and treated by 7 different surface conditions: (1) no treatment, (2) etching with phosphoric acid and application of adhesive agent, (3) silane coupling agent (S), (4) etching with hydrofluoric acid (HF) and silanisation, (5) sandblasting (Sa), (6) Sa + S, and (7) Sa + HF + S. Each group was further divided into three subgroups for application of three resin cements (RelyX ARC, Panavia F, or Variolink II) to bond the treated composite blocks and dentine. Subsequently, the shear bond strengths were measured and the failure mode examined. The composite surface treatments of 400-grit silicon carbide paper, PA, HF, Sa and Sa + HF were examined with a scanning electron microscope to determine the effect of these conditions. Results: For the same resin cement, the three sandblasting treatment groups showed the highest bond strengths except for the Sa + S and Sa group when using Variolink II. For the same surface treatment, there were no differences among the three resin cements. After sandblasting treatment, the occurrence of adhesive failures at the composite-luting cement interface was greatly reduced. Sandblasting presented the greatest topographical relief with evident irregular morphological change. Conclusion: Sandblasting treatment was the main factor responsible for improving the bond strength of indirect composite resin and dentine. Keywords: CAD/CAM, composite resin, dentine, shear bond strength, surface treatment

The aim of this case report is to describe a rare case of a five-rooted maxillary second molar that had two separated buccal roots and three separated palatal roots, each containing one independent root canal. The case report demonstrates that anatomical variations in the maxillary second molar should be taken into consideration during endodontic treatment, coupled with application of advanced techniques such as endodontic microscopy and cone-beam computed tomography to increase the ability of clinicians to treat difficult cases. Keywords: anatomical variations, cone-beam computed tomography, maxillary second molar, root canal anatomy, root canal therapy

Two clinical case reports are presented to illustrate the anatomical variation found in the human mandibular canine. In the first case, the mandibular canine has one root and two root canals. In the second case, the mandibular canine has two distinct roots. Both were treated with conventional endodontic treatment. Keywords: canal anatomy, endodontic treatment, mandibular canine

Central giant cell granuloma (CGCG) is a benign lesion that affects children and young adults. Surgery is the traditional treatment of CGCG. However, calcitonin and intra-lesional steroid were used in this case with good results. In this case report, an 18-year-old Saudi girl presented with a recurrent CGCG and was treated with 6, weekly intralesional injections of steroid that gave very good results. Keywords: giant cell granuloma, steroids, surgical excision