Saudi Dental Journal 2007;19(SI)-Abstr.081

Orthodontic textbooks, articles and academic presentations explain most labial orthodontics (LaO) biomechanical principles. However, lingual orthodontic (LiO) are rarely introduced or discussed at the same level. In this article, the author compares between Labial Orthodontics (LaO) and Lingual Orthodontics (LiO) from a biomechanical, theoretical and practical standpoints. Differences between labial and lingual techniques have a great impact on the biomechanical, theoretical and practical principles. The most important difference (between the convention labial orthodontic technique and the lingual one) is because of the differentiation of brackets positions.
Insertion of brackets lingually may look far more esthetic. However, the small distances with narrow parameters within "the working area" of lingual technique make biomechanical principles more complicated, especially when first, second and third orthodontic movements are discussed. What's more, the distance between points of forces and centers of resistances are smaller in lingual technique than in labial one, what affects the moment's values, potential torque manipulation and load deflection ratio "of  wires" that becomes higher in lingual technique, what makes getting an optimal low orthodontic forces more difficult in lingual orthodontics technique. Also, changing of brackets positions in lingual technique may affect tooth position and change torque values far more conspicuous than what takes place in labial technique.
In summary, it's recommended that orthodontist be aware of lingual technique biomechanically, theoretically and practically to be able to manipulate, avoid the side effects and get the best results.

Saudi Dental Journal 2007;19(SI)-Abstr.082
 

Objective: The aim of this study was to evaluate the effects of food-simulating liquids on flexural strength and hardness of composites and polyacid-modified composite restorative materials.
Materials and Methods: Four composites [Two hybrids, Spectrum TPH (STPH) and Tetric Ceram (TC); one packable, Tetric Ceram HB (TCHB); one flowable, Tetric Flow (TF)] and one polyacid-modified composite [Compoglass F (CGF)] were used for this study.  Flexural strength specimens (25 x 2 x 2 mm) and hardness specimens (2 mm thick, and 5 mm diameter) were prepared according to manufacturer^'s recommendations. After light polymerization, the specimens were removed from their molds and conditioned for one week at 37˚C as follows: (1) Air (control), (2) distilled water, (3) 0.02 M lactic acid, (4) Heptane, (5) 50% ethanol-water solution. After conditioning, flexural strength testing was carried out using Shimadzu Autograph Measuring Unit and microhardness testing was carried out on MHT-1 Vickers microhardness. Data were analyzed using ANOVA and post-hoc Tukey HSD tests at a significance level 0.05.
Results: The flexural strength of all restoratives was not affected after conditioning in heptane. With the exception of Spectrum TPH, The flexural strength of all restoratives conditioned in ethanol-water solution was found significantly decreased than that conditioned in water and lactic acid. In all conditioning mediums used, Spectrum TPH had the significantly highest flexural strength and Compoglass F had the lowest. With the exception of Tetric Flow, no significant change in surface hardness was noted with conditioning of all other restoratives in water, lactic acid, and heptanes. However, the surface hardness of all materials was significantly deteriorated after conditioning in ethanol-water solution. 
Conclusion: Ethanol-water solution was found the only food-simulating liquid which had a significant deterioration effect on flexural strength and hardness of all materials tested at the same time. Despite flexural strength values of all composites tested; specially the more recent composites, TCHB&TF; was also reduced with conditioning in water and lactic acid, but still exceeded the minimum flexural strength limit of ISO for polymer-based restorative materials.

Saudi Dental Journal 2007;19(SI)-Abstr.083

The purpose of this study was to evaluate both the effects of immersion in different chemical disinfectant solutions and the type of repair material on the transverse strength of repaired heat-polymerized acrylic resin. A total of 110 rectangular specimens (65 × 10 × 3 mm) of heat-polymerized acrylic resin (Triplex) were fabricated. After polymerization, the specimens were polished, then stored in distilled water at 37 º C for 1 week. The specimens were divided into 11 groups (n=10) coded A to K. Specimens of Group A remained intact (control). The specimens of Groups C to F and Groups H to K were immersed in the following chemical disinfectant solutions (1%, 2.5%, and 5.25% sodium hypochlorite and 2% glutaraldehyde, respectively) for 10 minutes. The specimens of all groups except those of Group A were sectioned in the middle to create 10 mm gaps and repaired with the same resin (Groups B to F) and autopolymerizing acrylic resin (Groups G to K). The specimens of Groups C to F and Groups H to K were again immersed in the disinfectant solutions in the same sequence. The transverse strength (N/mm2) was tested for failure in a universal testing machine, at a crosshead speed d of 5 mm/min. Two-way analysis of variance (ANOVA) was performed to evaluate the effects of both the disinfectant solutions and repair materials on the transverse strength of repaired specimens. All data were statistically analyzed using one-way analysis of variance followed by Tukey's test at 95% confidence level. The repaired specimens treated with/without disinfectant solutions showed similar (P>.05) transverse strength values. No differences (P>.05) were detected among the repaired specimens either with heat-polymerized or auto-polymerizing acrylic resins. The intact specimens showed transverse strength values (86.9±11.8) significantly higher (P<.05) than the values of the repaired specimens. Among the repaired specimens, transverse strength was not affected after immersion in the disinfectants for the immersion period tested (10 min). The repair material either, heat-polymerized or autopolymerizing acrylic resins had no effect on the transverse strength of the repaired acrylic resin specimens. The clinical implication seems that all immersion solutions evaluated in this study could be safely applied in everyday practice for the disinfection of dentures before repairing procedures.

Saudi Dental Journal 2007;19(SI)-Abstr.084

Objective: The aim of this study was to compare failure patterns of different types of resin luting cements using scanning electron microscopic after Push-out test.
Materials and Methods: Thirty extracted human premolars were endodontically treated. The tested materials/group were as follow: Group 1: Excite DSC + Multicore flow (Ivoclar-Vivadent), Group 2: Excite DSC + Variolink II (Ivoclar-Vivadent) and Group 3: RelyX Unicem, Self-Adhesive Universal Resin Cement (3M ESPE). Posted roots were sectioned perpendicularly to the long axis of the tooth in mesiodistal direction into sections considering the different root regions (cervical, middle and apical). Push-out test was performed and the failure was evaluated using a scanning electron microscope at different magnifications.
Results: Among the tested materials, Group 1 (Excite DSC + Multicore flow) achieved the highest interfacial strength (18.23 MPa) and the lowest was for RelyX Unicem (Group 3) which had 9.31 MPa. Type of failure patterns among the tested groups for Excite DSC+ MCF; (Group 1) and Excite DSC + Variolink II (Group2) had 66.10% and 93.18% of failure for type 1 (post only), respectively. For Group 3 RelyX Unicem had 36.58 % of failure Type 1 (post only), 34.14 % of failure Type 2 (adhesive between resin cement and root canal dentin) and 29.26 % of failure Type 3 (mixed).
Conclusion: Multicore flow with ExiteDSC achieved the highest interfacial strength.

Saudi Dental Journal 2007;19(SI)-Abstr.085