Chromian spinel is a widespread accessory mineral in ultramafic rocks of the Penjwen ophiolite, occurring in two modes; fresh grains in dunite rocks that crop out in the eastern part and altered grains in serpentinized peridotites in the western part of the Penjwen ophiolite. Unaltered grains are generally primary phase optically and chemically homogeneous with uniform high Cr# at ~ 0.72 and low Mg# at 0.3. High-Cr#, low-Al2O3, low-TiO2 chromites have the geochemical characteristic of chromites preserved in arc lavas and specifically overlap the field of chromites in boninites. . The cores of altered spinel grains from serpentinized harzburgite appear to retain their original igneous chemistry and are similar to fresh chromian spinel grains. The outer rim of these grains shows different degrees of alteration. Four criteria characterized the alteration process of Cr-spinel in serpentinised peridotite rocks of the Penjwen ophiolite. First, optical inhomogeneity on the scale of micrometers; chromian spinel is deep reddish brown in thin section, but opaque due to replacement by magnetite along cracks and grain boundaries. Second, chemical zonation with a decrease in Mg, Al, and Cr, increase in Fe and significant modification of minor elements (Si, Ti and Mn) towards the fractures and grain margins. Third, significant amount of SiO2¬ analyzed in Cr-spinel. Although Si does not go into the crystal structure of spinel, the microprobe analysis detected sub ordinary amount of SiO2. This suggests the presence of submicroscopic silicate phase situated at the vacancy of dissolution elements (Mg, Al, and Cr). Fourth, Ferritchromite rims and chlorite aureoles. Altered spinels deviate from primitive Cr-spinel, by sharp increase in Fe# and Cr#. The chemical changes reflect hydrothermal metamorphic reactions between spinels and the surrounding serpentinized silicate matrix.

ينتشر معدن الكرومايت بصورة واسعة في صخور الفوق قاعدية لمعقد بنجوين الافيولايتي و تتواجد بنمطين الأول الكرومايت الخالي من التحلل والمتواجد ضمن صخور الدانايت المنكشفة في الجزء الشرقي من المعقد , في حين الحبيبات المتعرضة للتحلل تظهر في صخور البيروداتايت المتعرضة لعملية السربنتنة و تنكشف في الجزء الغربي من المعقد . يتميز الكرومايت الغير متحلل باحتفاظه بالخصائص المعدنية الأصلية و تجانس صفاته البصرية و الكيميائية فضلاً عن امتلاكه لمحتوى عالي من الكروم (Cr # ~ 0.72). أظهرت الدراسة اقتصار عملية التحلل على حواف الحبيبات في الكرومايت المتحلل دون نواته . أذ تبين وجود أربعة مظاهر تحلل مختلفة : الأول عدم التجانس البصري بمقياس المايكرون إذ يظهر المعدن بلون احمر غامق مع حافة معتمة أو غامقة اللون بسبب إحلال المغنيتايت على الحافة وعلى طول التشققات .ثانياً التمنطق الكيميائي للمعدن مع نقصان في محتوى عناصر Cr, Al & Mg و زيادة في نسبة Fe مع تغيرات في محتوى العناصر الثانوية Mn, Ti, Si . ثالثاً وجود كمية منSiO¬¬2 بالرغم من ان السليكا لا تدخل في التركيب البلوري للمعدن إلا أن التحليل بواسطة المجهر الالكتروني الدقيق سجل وجود كميات من ثاني اوكسيد السليكون الذي يمكن تفسيرها بوجود أطوار معدنية للسليكا في الفراغات الناجمة من إذابة عناصر Cr, Al & Mg . رابعاً وجود حافة من معدن الكروماتايت الحديدي محاط بهالة من معدن الكلورايت . التغييرات الكيميائية لمعدن الكرومايت تعكس تفاعلات تحولية لمحاليل حرمائية بين الكرومايت الماكمائي و القاعدة السليكاتية للسربنتين .

Chemistry --- accessory --- chromian --- spinel --- serpentinites --- Penjwen --- ophiolite --- rocks --- Zagros thrust zone --- تغييرات --- معدن الكرومايت --- صخور السربنتين --- ضمن معقد بنجوين --- الافيولايتي – نطاق --- زاكروس --- الزاحف – شمال شرق العراق

The aim of this study was to determine the effect of storagetime on shear bond strength of three composite resin, twoutilize total etch technique and one utilize self etching bondingagent.One hundred twenty maxillary and mandibular molarswere used in this study. The teeth were prepared by cutting theocclusal enamel with diamond bur to expose dentin and groundwet with silicone carbide papers. The specimens were thendivided into three groups and stored in distilled water.Scotchbond Multipurpose Plus was used in the first groupand a stainless steel round mould, with a central hole of 4mm in diameter and 2 mm in height was used to build up thecomposite Z100. The composite resin was inserted in two increments,each one was light cured for 40 seconds. This gro-upis divided into four subgroups each of ten according to thestorage time (one day, fifteen days, three months and six months)then stored in distilled water accordingly.The same procedure was repeated in the second and thirdgroups. The composite used in the second group was Tetricwith Excite bonding agent. In the third group, Definite compositeand its bonding agent Etch and Prime was used.The bond strength was measured and the data were statisticallyanalyzed. Z100 composite had the greatest shear bondstrength followed by Tetric and Definite. One day and fifteendays storage time for all types of composite had greater shearbond strength than the three months and six months storagetime.In conclusion there was a gradual decrease in bond strengthwith increased storage time up to six months irrespectiveof the type of composite.

Composite resin --- dental bonding --- storage time

Aim: To evaluate the surface roughness of three different types of light activated composite resin using (Sof-Lex) – polishing system, a profilometer study. Materials and Methods: A total of 30 resin com-posite disks were prepared from three different types of composite resin include 3 – groups. Group I: 10 specimens were prepared from light activated nano hybride (Tetric n – Ceram, Ivoclar – Vivadent – Liechtenstein). Group II: 10 specimens were prepared from light activated microhybride composite resin (Arabesk – Voco, Germany). Group III: 10 specimens were prepared from light activated poly-glas composite resin (Solitaire – 2, Heraeus, Kulzer, Germany). The resin blocks finished and polished using (Sof – Lex) polishing system. The specimens were analyzed for surface roughness using “Pro-filometer”. Results: Tetric n – Ceram composite resin showed the lowest roughness average (0.112 μm) followed by Arabesk composite (0.150 μm), Solitaire – 2 composite resin showed the highest roughness average (0.341 μm). Conclusions: Tetric n– Ceram (nano-hybride) was the best polished composite resin, showed the least roughness average.

Surface roughness --- composite resin --- profilometer

Aim: To measure the temperature rise induced by a light emitting diode (LED) curing unit and byquartz tungsten halogen (QTH) curing unit using two types of composite resin XRV Herculite andVenus. Materials and Methods: Forty extracted non–carious single canal premolars were cleaned andbisected longitudinally. Class V preparations were cut on the buccal surfaces. The teeth were dividedinto four groups; each of ten. The teeth in the first and second groups were restored with XR–Herculitecomposite resin. The teeth in the third and fourth groups were restored with Venus composite resin.The composite resin in the first and third groups were polymerized using QTH curing unit “Astralis”for 40 seconds; the light intensity was 502 mW/cm2. The distance between the tip of the light and thecomposite was 3 + 1 mm. The composite resin in the second and fourth groups was polymerized usingLEDs “Ultra–Lite 200 E plus” curing unit for 20 seconds; the light intensity was 536 mW/cm2 usingthe same distance as the first and third groups. The temperature rise at the pulpal wall was recorded byplacing a thermocouple on the pulpal wall directly under the restoration. Results: The lowesttemperature rise during LED irradiation with Venus composite resin followed by LED irradiation withXRV Herculite composite resin. Whereas QTH curing units with XRV Herculite composite resinproduced higher values, QTH curing units with Venus composite resin produced the highesttemperature rise. Conclusion: The temperature rise of LED curing units and QTH curing units used inthis study was under the limits that affect the integrity of the dental pulp.

Composite resin --- heat generation --- pulp damage

The aim of this study was to evaluate the common errors that may occur during crown and bridge construction. Four hundred stone models were used in this study for fabrication of 265 bridges and 135 single crown. The total number of units was 1141. Four main parameters were evaluated for each stone model: General informa-tion about the case, the condition of the stone model, the type of impression mater-ial and the prepared abutment tooth. The result of this study showed that 33.7% of the models were one unit and 48.7% of the models were 2–4 units and the remaining 17.5% of the models were more than five units, 8.7% of the models were without opposing arch. Alginate impression materials were used in 95% of the cases and only 5% of the cases elastomeric impression material were used. The finishing line was absent in 19.7% of the cases. Enough tooth reduction was done in 61.3% of the cases and 16.3% of the cases showed too much tooth reduction while 22.4% of the cases the tooth reduction was not enough. In order to avoid these errors continuous education courses and journal club are highly recommended.

Dental models --- dental impression techniques --- dental communication