Aim: To measure the proportion of post-channel circumference in dentine and examine the minimum residual dentine thickness of proximal root walls in the coronal, middle and apical thirds of post channels prepared in oval roots with parallel and tapered twist drills.
Methodology: Forty extracted human single-rooted teeth were instrumented and filled with gutta percha and sealer. The sample was divided into 2 groups; Group 1 (n=20) for preparation of parallel post channels and Group 2 (n=20) tapered post channels by two operators. Prepared roots were sectioned horizontally and digital images measured for the proportion of post-channel circumference in dentine and the minimum residual dentine thickness (RDT) with Image software. The data were analyzed by independent t-tests and One Way ANOVA.
Results: Overall, the proportion of post channel circumference contained within dentine ranged from 79% to 89%. At the apical level, the mean proportion of post-channel contained in dentine was greater for parallel than tapered post preparations (P=0.015).  The incidence of minimum RDT <0.5 mm was significantly higher in roots prepared for tapered than parallel posts (P=0.02). Roots prepared by operator 2 had a significantly higher incidence of minimum RDT <0.5 mm than those prepared by operator 1 (P=0.02).
Conclusions: Tapered posts may not be inherently safer than parallel sided posts and operator philosophy greatly influences the balance of post fit and preservation of RDT.
Saudi Dental Journal 2007;19(SI)-Abstr.056

057.Effect of different curing technique  on the mechanical properties of provisional(temporary) crowns and bridges restorations

Several factors may affect final properties of any material, the provisional crowns and bridges restorations, affected by the type of the acrylic resin, heating time and temperature, and the water immersion time and heating temperature. This investigation evaluated the effects of pressure and heat on the surface hardness and elastic modulus (transverse strength) of ALIKE auto polymerized acrylic resin material. Specimens were grouped into: Group I (Self cure), Group II [Minimasure (water and pressure)], Group III (Heat cure). This study demonstrated that raising temperature and pressuring during polymerization increase strength and stiffness of autopolymerizing resin. Moreover, resin polymerized in the pressured condition showed higher strength than that of polymerized in the dry condition. The pressured condition produced greater hardness than the non-pressured, but the difference became less at higher temperature. But ANOVA (P<0.05) and Tukey's post-hoc tests for the surface hardness demonstrated no significant differences among three conditions.  Whereas, the results indicated a statistically significant difference among the test groups for transverse strength (elastic modulus), and transverse modulus increased with increasing curing temperature. Raising temperature and pressuring during polymerization increase strength and stiffness of autopolymerizing resin. The transverse strength increased with increasing curing temperature, Comparison between dry and pressure showed that the dry condition produced higher strength than the pressure conditions. A Pearson correlation coefficient was also applied between the hardness Shore D of the materials and the E-Modulus, Maximum force, Elongation at max Force, Force at break, Elongation at break. When hardness was correlated with all groups combined, no significant correlation was found at the 0.05 level (2-tailed). The only significant correlation were observed between Force at break and Maximum force (r = 0.99703493) and correlation was highly significant at the 0.01 level (2-tailed) between  Elongation at max Force, and Elongation at break (r = 0.99999793).

Saudi Dental Journal 2007;19(SI)-Abstr.057

Surface roughness of materials attributes to the differences in the size and content of filler particles. Different methods have been used to finish and polish resin composite restorations, but celluloid strips (matrix) are more efficient and the choice of most clinicians. The aim of this investigation was to compare and measure the average surface roughness (Ra, μm) of five resin composites with different filler types, loading and different matrix set against two different celluloid strips (matrix). The composite resins were mixed according to manufacturer's instructions and placed into a Teflon mould. The specimens were prepared by using Teflon moulds measuring 6 mm internal diameter by 3 mm height. The composites were compacted into the mould with a plastic spatula. Specimens of each composite material were divided into three groups according to the surface finishing methods used. Group 1(control): The composite was filled to the mould surface, compacted and finished by a plastic spatula. Group 2: The composite was filled to the mould a polythene sheet was placed over the composite surface and pressed flat with a cover glass. Group 3: The composite was filled to the mould a celluloid strip was placed over the composite surface and pressed flat with a cover glass. All group's specimens were light irradiated with 500 mW/cm² for 40s pulse curing light. After polymerization, the specimens were stored in distilled water at 37°C until the first analysis of surface roughness, carried out after 24 hours. The roughness of each specimen was calculated with Taylor-Hobson (Leicester, England) using five intervals within each stylus transverse to calculate Ra, Rmax, and Rz. Analysis of variance (ANOVA) with Tukey's post-hoc test at P < 0.05 was used to test the statistical significant. Group 3 shows no statistical differences even though there were slight differences in the mean values for Ra. The smallest values for all roughness parameters were Venus and Definite.

Saudi Dental Journal 2007;19(SI)-Abstr.058

059.Changes in dentists selection of treatment in response to the modification of the public payment system

DR. HASSAN S. HALAWANY
College of Dentistry, King Saud University,Riyadh, Saudi Arabia

 
Background: This study evaluates the impact of modifying the payment system of the governmental insurance coverage on dentist's selection of treatment with publicly insured children compared to their treatment selection with privately insured children in the sate of Michigan.

Methods: Two groups of dentists were followed in two periods of observation. The first group (76 pediatric dentists and 4,173 general practitioners) was followed in the first 27 months period of observation before the start of the modified payment system (from October 1, 1997 until December 31, 1999). The second group (83 pediatric dentists and 4,481 general practitioners) was followed in the 27 months period after the start of the modified payment system (from October 1, 2000 until December 31, 2002). The study compared the service mix (restorations, stainless crowns, pulp therapy, and extraction) of these dentists with 772,375 children (two control groups (publicly insured children with regular payment system, and privately insured children) and one treatment group (publicly insured children with the modified payment system).

Results: Dentists did not change their service mix (not more than 2% for any treatment category) with the two control groups between both periods of observation. However, they changed their service mix significantly with the treatment group, where they selected more restorations than other categories, despite the increase in the selection of extraction with older age groups.

Conclusion: Dentists changed their pattern of treatment selection with publicly insured children after modifying the payment system of the governmental coverage, be closer to their patterns of selection with privately insured children.
Saudi Dental Journal 2006;18(SI)-Abstr.059

Saudi Dental Journal 2007;19(SI)-Abstr.060