The ball mill as a means of investigating the mechanical failure of dental materials

Objective: The main purpose of this paper is to present a new method of predicting clinical performance using mechanical loading in a ball mill. Methods: A series of four experiments (two involving a hybrid composite and one each on orthodontic brackets and bands) is described in which the ball mill was used to subject specimens to mechanical fatigue. Results: A reproducibility study using composite beam specimens showed no significant difference between the Mean Survival Time (MST) in all the three experimental runs (P = 0.42). When subjected to thermal cycling, the MST of the cycled group was 155.0 min compared to 247.0 min fur the control group (P < 0.01). The MST of untreated and sandblasted brackets was 7.9 h and 14 h respectively (P < 0.01). There is also a significant difference (P < 0.001) in the MST of sandblasted bands when compared to the untreated bands. Conclusions: The ball mill proved to be a convenient and reproducible means of producing mechanical fatigue and may be useful in predicting the clinical performance of dental materials. This record was migrated from the OpenDepot repository service in June, 2017 before shutting down

Cutting efficiency of dental burs - A pilot study

Objectives: This study aim to evaluate the cutting efficiency of tungsten carbide burs (TC) and rotary diamond instruments by measuring their rake angle and visual examination of their cutting surfaces respectively, using scanning electron microscopy (SEM). Materials and Method: 60 short and long head pear-shaped TC and 18 round rotary diamond instruments that had been used to prepare than 5 and > than 10 cavities were selected from the 3rd & 4th year dental students, Dental Faculty, University of Malaya. 12 cylindrical and flame rotary diamond instruments were also selected from the 5th year students. The rake angle of TC was measured and surfaces of diamond instruments were evaluated using Field Emission Scanning Electron Microscope (FESEM). Each test group comprised of 10 samples and new burs constituted the control group. The data were analysed descriptively and statistically using Two-way ANOVA, SPSS version 12. Results: The rake angles of control, than 5 groups were significantly higher compared to > than 10 groups, p than 10 teeth showed blunt and dislodged diamond particles. Conclusions: The rake angle of TC is significantly lower and diamond instruments showed blunt diamond particles after cutting > than 10 preparations

Adjunctive buccal and palatal corticotomy for adult maxillary expansion in an animal model

Objective: This study aimed to explore the usefulness of adjunctive buccal and palatal corticotomy for adult maxillary expansion in an animal model using cone-beam computed tomography (CBCT). Methods: Twelve adult sheep were randomly divided into two groups (each n = 6): a control group, where no treatment was administered, and a treatment group, where buccal and palatal corticotomy-assisted maxillary expansion was performed. CBCT scans were taken before (T1) and after (T2) treatment. Differences in all transverse dental and alveolar dimensions, alveolar width at crest level, hard palate level, horizontal bone loss, interdental cusp width and inter-root apex were assessed using Wilcoxon signed-rank and Mann-Whitney U-tests. Kruskal-Wallis tests and pairwise comparisons were used to detect the significance of differences among the inter-premolar and inter-molar widths. Results: CBCT data revealed significant changes in all transverse dental and alveolar dimensions. The mean interpremolar alveolar width showed an increase of 2.29 to 3.62 mm at the hard palate level, 3.89 to 4.38 mm at the alveolar crest level, and 9.17 to 10.42 mm at the buccal cusp level. Dental changes in the vertical dimension were not significant. Conclusions: Our findings based on an adult animal model suggest that adjunctive buccal and palatal corticotomy can allow for both skeletal and dental expansion, with the amount of dental expansion exceeding that of skeletal expansion at alveolar crest and hard palate levels by two and three folds, respectively. Therefore, this treatment modality is potential to enhance the outcomes of maxillary expansion in adults

Dental students' perception towards effective clinical feedback and assessment

Supervised practice in the dental clinic is one of the teaching tools in preparing a good dental practitioner. Teachers who are efficient in helping students learn in these settings improve this process. The ability to impart good feedback and carry out proper assessment is an important measure of effectiveness. Objective: The purpose of this study was to investigate the perception of students from the Faculty of Dentistry, University of Malaya towards effective clinical feedback and assessment from the staff of the Dept. of Conservative Dentistry. Method: A 4-point Likert-type scale questionnaire was formulated according to Myers, 1977 (J.Dent.Edu 41:68-76). Aspects of clinical feedback and assessment in the questionnaire include:- 1) the ability to be critical in assessing students' work, 2) the usage of criterion-based assessment and 3) the manner in which feedback are given to students. One hundred and sixty dental students from Year IV and V participated in this survey. Results: Generally, student responses showed that assessment and clinical feedback were carried out by staff. The data were subjected to two statistical procedures; exploratory factor analysis and Rasch rating scale analysis. Factor analysis indicated that all 3 constructs were clearly measured by the items in the questionnaire. Rasch rating scale analysis revealed logit values of -0.78 and -0.18 for the usage of criterion-based assessment when assessing students' clinical work. The highest logit value of 0.45, 0.37 and 0.34 were for the third construct; the students would like feedback be given privately and with a view to helping them improve their clinical performance. Conclusion: Students place great emphasis on the manner feedback is given and assessment is conducted of their clinical performance

Fatigue of dental composites

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Surface reproduction of elastomeric materials: viscosity and groove shape effects

Objective: To evaluate the effect of viscosity and type of grooves on surface detail reproduction of elastomeric impression materials. Methods: Express putty/light-, Impregum medium- and heavy/light-bodied and Aquasil medium- and putty/light-bodied elastomeric impression materials were chosen for this study. Five impressions were made using a cylindrical aluminum reference block with U- and V- shaped grooves and to produce 35 master dies. Each master die was immersed in distilled water at 370 C for 5 minutes prior to the impression making on moist surfaces. Surface topography of the dies and impressions were captured using Alicona Imaging System. The mean difference in depth between the master dies and its corresponding impressions were analysed using two-way ANOVA, p=.01. Results: The lowest mean difference in depth for U- and V-shaped grooves was obtained from the Express putty/light group. The highest mean difference in depth for U- and V-shaped grooves was obtained from Impregum medium, Aquasil medium, Impregum�· heavy/light and Impregum heavy/light groups respectively. Two-way ANOVA indicated that there was a significant difference in the effect of materials (p < .01) and grooves (p < .01). Conclusion: Express putty/light-bodied elastomeric material produced the best surface detail, and U-shaped groove showed better surface detail reproduction than V-shaped groove

Thermocycling as a means of inducing mechanical fatigue in dental composites

The effect of thermocycling on the fatigue behaviour of 5 commercially available dental composites; P50(P)1, Silux Plus(S)2, Heliomolar(H)3, Clearfil Photo Posterior-light activated(CLA)4 and Clearfil Posterior-chemically activated(CC)5 was investigated. One hundred and ten rectangular bar specimens were prepared for each materil and divided into 11 groups of 10 each. Test groups 1-6 were subjected to 0, 250, 500, 750, 1000 and 1000 thermal cycles respectively. Each thermal cycle consisted of 1 minute immersion time of 50 seconds per change. The control groups 7-11 were stored in distilled water at 370c for the equivalent time to complete 250, 500, 750, 1000 and 10000 thermal cycles respectively. All specimens were subjected to a 3 point bend test and loaded at a crosshead speed of 1mm/min on a an Inston Testing Machine. The flexural strength of all materials decreases with the number of cycles and length of water storage except for CC where the flexural strength increases during the earlier stages of thermocycling and water storage. The lowest flexural strength was observed in groups 6 and 11. One way analysis of varience showed that Group 1 was significantly different from groups 6 and 11 (P<.05), however the thermally cycled and water storage groups were not different from each other for all materials tested. The decrease in flexural strength of all materials in the water storage groups (7-11) when compared to the 24 hour group (1) is related to weakening of resin-filler interface bu hydrolysis. While the decrease of the thermally cycled groups can be attributed to debongding of matrix-filler due to variation in coefficient of thermal expansion. It can be concluded that thermal changes does not reduce the flerxural strength of composites

Optimization of pre-transplantation conditions to enhance the efficacy of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are considered a potential tool for cell based regenerative therapy due to their immunomodulatory property, differentiation potentials, trophic activity as well as large donor pool. Poor engraftment and short term survival of transplanted MSCs are recognized as major limitations which were linked to early cellular ageing, loss of chemokine markers during ex vivo expansion, and hyper-immunogenicity to xeno-contaminated MSCs. These problems can be minimized by ex vivo expansion of MSCs in hypoxic culture condition using well defined or xeno-free media i.e., media supplemented with growth factors, human serum or platelet lysate. In addition to ex vivo expansion in hypoxic culture condition using well defined media, this review article describes the potentials of transient adaptation of expanded MSCs in autologous serum supplemented medium prior to transplantation for long term regenerative benefits. Such transient adaptation in autologous serum supplemented medium may help to increase chemokine receptor expression and tissue specific differentiation of ex vivo expanded MSCs, thus would provide long term regenerative benefits

Advancing stem cell therapy from bench to bedside: lessons from drug therapies

The inadequacy of existing therapeutic tools together with the paucity of organ donors have always led medical researchers to innovate the current treatment methods or to discover new ways to cure disease. Emergence of cell-based therapies has provided a new framework through which it has given the human world a new hope. Though relatively a new concept, the pace of advancement clearly reveals the significant role that stem cells will ultimately play in the near future. However, there are numerous uncertainties that are prevailing against the present setting of clinical trials related to stem cells: like the best route of cell administration, appropriate dosage, duration and several other applications. A better knowledge of these factors can substantially improve the effectiveness of disease cure or organ repair using this latest therapeutic tool. From a certain perspective, it could be argued that by considering certain proven clinical concepts and experience from synthetic drug system, we could improve the overall efficacy of cell-based therapies. In the past, studies on synthetic drug therapies and their clinical trials have shown that all the aforementioned factors have critical ascendancy over its therapeutic outcomes. Therefore, based on the knowledge gained from synthetic drug delivery systems, we hypothesize that by employing many of the clinical approaches from synthetic drug therapies to this new regenerative therapeutic tool, the efficacy of stem cell-based therapies can also be improved

Microleakage testing

Microleakage testing has been used to determine the possible clinical performance of a restorative material. Many microleakage testing materials have been developed and performed through the years. There has been no agreement as to which testing methodology would give the most accurate results. Attempts have been made to simulate the oral conditions and to give a more quantitative representation of micro leakage. The different micro leakage testing methodologies are presented in this paper