Reza Vahid Roudsari

The influence of auxiliary features on the resistance form of short molars prepared for complete cast crowns

STATEMENT OF PROBLEM Several factors exist which result in crown preparations that are less than ideal. In these situations, the clinician should find a practical way to overcome the lack of resistance of the compromised tooth preparation. PURPOSE The purpose of this study was to evaluate the effect of different auxiliary features on the resistance form of crowns with reduced axial wall height and increased total occlusal convergence. MATERIAL AND METHODS An Ivorine tooth was prepared on a milling machine with 22 degrees of total occlusal convergence (TOC), 3.0 mm of occlusocervical height, and a chamfer finish line (Group Ctrl). The crown preparation was subsequently modified to include proximal grooves (Group Grv), and reduced TOC from 22 to 4 degrees in the cervical 1.5 mm (Group Rdc). Ten standardized metal dies were fabricated for each group. Cobalt-chromium copings were fabricated for all specimens. The metal copings were cemented onto their corresponding metal dies with zinc phosphate cement. The resistance of each specimen was evaluated when force was applied at a 45-degree angle to the long axis of the die with a universal testing machine in a buccal to lingual direction. The maximum force (newtons) was applied before coping dislodgment was measured. Data from the 3 groups were compared with a 1-way ANOVA (α=.05) and a Post Hoc Bonferroni test. RESULTS The mean (SD) force needed to dislodge crowns with proximal grooves was 156.75 (30.96) N and for those with reduced TOC, it was 221.06 (27.02) N, Both were effective in increasing the resistance form of the original shape (P=.002 and P<.001 respectively). The reduced TOC increased the resistance significantly more than the proximal grooves (P<.001). CONCLUSIONS Within the limitations of this in vitro study, crown preparation modifications enhanced the resistance form; however, the reduction in cervical TOC proved to be more effective than proximal grooves.

Fracture toughness of heat cured denture base acrylic resin modified with Chlorhexidine and Fluconazole as bioactive compounds

PURPOSE This study investigated the impact of incorporating Chlorhexidine and Fluconazole as bioactive compounds on the fracture toughness of conventional heat cured denture base acrylic resin material (PMMA). MATERIALS AND METHODS 30 single edge-notched (SEN) samples were prepared and divided into three groups. 10% (mass) Chlorhexidine and 10% (mass) Diflucan powder (4.5% mass Fluconazole) were added to heat cured PMMA respectively to create the two study groups. A third group of conventional heat cured PMMA was prepared as the control group. Fracture toughness (3-point bending test) was carried out for each sample and critical force (Fc) and critical stress intensity factor (KIC) values measured. Data were subject to parametric statistical analysis using one-way ANOVA and Post hoc Bonferroni test (p=0.05). RESULTS Fluconazole had no significant effect on the fracture toughness of the PMMA while Chlorhexidine significantly reduced the KIC and therefore affected the fracture toughness. CONCLUSION When considering addition of a bioactive material to PMMA acrylic, Chlorhexidine will result in reduced fracture toughness of the acrylic base while Fluconazole has no effect.

Film thickness of dentin desensitizing agents on full crown preparations: Influence of product and gravity.

OBJECTIVE To determine the thickness of resin layer formed when dentin desensitizing agents are applied to teeth prepared for full crown restorations. DESIGN In vitro measurements of resin layer thickness. METHODS AND MATERIALS Forty caries-free human premolar teeth were prepared as for a full metal-ceramic crown restoration with a retention groove placed mesiobuccally. Stratified allocation created five groups of eight teeth, which were treated with various desensitizing agents. Four teeth within each group were treated upright, and four were treated while inverted, resulting in a total of 10 experimental groups. Teeth were sectioned and resin layer thickness measured under an environmental scanning electron microscope at certain sites across the section. RESULTS Analysis was carried out using three-way analysis of variance. On flat tooth surfaces, light-cured resins (Prime & Bond and Seal & Protect) formed layers of 16.2 ± 8.9 μm and 23.4 ± 10.6 μm, respectively. More concave sites had significantly thicker layers (p<0.05) than flat or convex sites. At the internal shoulder angle, mean thicknesses were 84.1 ± 27.8 μm and 104.3 ± 56.6 μm, respectively. At the retention groove, figures were 86.6 ± 3.13 μm and 136.2 ± 72.0 μm. Differences between these two resins were not significant (p>0.05). Light-cured resins formed significantly thicker layers on inverted samples at the occlusal indentation only (p=0.004), with a mean of 66.9 ± 21.6 μm; upright samples had a mean of 36.6 ± 12.4 μm. Self-activating resins (Pain-Free Desensitizer, Viva Sens, and Gluma Desensitizer) formed no consistent layers. CONCLUSION Within the limitations of this in vitro study, light-cured resins consistently pooled in convex areas of crown preparations. A great portion of retention grooves can potentially become occluded by resin. The self-activating products tested did not form significant layers.

The aetiology and management of labial and vertical migration of maxillary incisors: 'do you catch my drift?'.

Labial and vertical migration of maxillary incisors is a common complaint seen in general and specialist practices alike. Tooth movement in the aesthetic zone may cause significant concern to the patient, and a challenging management case for the dental team. This paper describes the aetiology, stabilisation and management of such cases.

Clinical scenario-based assessments to measure reasoning in complex cases: Are we fully realising their potential in specialty training?

Planning the management of complex cases requires years of structured training, with experienced gained both by attending joint/multidisciplinary clinics and through managing patients needing interdisciplinary care. Together, these reinforce basic skills and develop high-order thinking. It is crucial, however, that the development of these advanced planning skills can be measured, so as to assess the progress of trainees and the effectiveness of training programmes. Here, the validity, reliability and consistency of a clinical, hypodontia case-based structured assessment tool of clinical reasoning and higher-order thinking is tested.