Correct alignment of pedicle screws is imperative in multilevel instrumentation. However, there has been no report addressing the technical aspects of this subject. If the head diameter of a pedicle screw is D, the head height is H, and the convergence angle of the screw being inserted is alpha, then the distance between the extension line of the medial borders of the inserted screw heads and the insertion point of the adjacent screw (A) is described by the following formula: A = 1/2Dcos alpha- Hsin alpha If an L3 pedicle screw (D=13 mm, H=15 mm) is to be inserted with a convergence angle of 14 degrees after the insertion of L4 and L5 screws, its insertion point should be 3.6 mm medial to the extension line of the centers of the L4 and L5 screws and 2.7 mm lateral to the extension line of their medial borders for all screw heads, so it can be aligned in the coronal plane. In order to achieve the best alignment, a pedicle screw is inserted between the extended line of the centers and that of the medial borders of the inserted adjacent screw heads. For the routine range of convergence angles, it is essential to move the entry point medially toward the extended line connecting the medial borders of the inserted adjacent screw heads.
Head

No abstract available.
Head*

The purpose of this study was to evaluate the abrasion resistance of surface penetrating sealant which was applied on a composite resin restoration and to provide proper time to reapply sealant on composite resin surface. Two hundred rectangular specimens, sized 8 x 3 x 2 mm, were made of Micronew (Bisco, Inc., Schaumburg, IL, U.S.A) and divided into two groups; F group (n = 10) was finished with coarse and medium grit of Sof-Lex discs and BisCoverwas applied B group (n = 190) after finishing with discs. B group was again subdivided into nineteen subgroups. From B-1 group to B-18 group were subjected to toothbrush abrasion test using a distilled water-dentifrice slurry and toothbrush heads. B-IM group was not subjected to toothbrush abrasion test. Average surface roughness (Ra) of each group was calculated using a surface roughness tester (Surfcorder MSE-1700: Kosaka Laboratory Ltd., Tokyo, Japan). A representative specimen of each group was examined by FE-SEM (S-4700: Hitachi High Technologies Co., Tokyo, Japan). The data were analysed using cluster analysis, paired t-test, and repeated measure ANOVA. The results of this study were as follows; 1. Ra of F group was 0.898 +/- 0.145 microm and B-IM group was 0.289 +/- 0.142 microm. Ra became higher from B-1 group (0.299 +/- 0.48 microm) to B-18 group (0.642 +/- 0.313 microm). 2. Final cluster center of Ra was 0.361 microm in cluster 1 (B-IM ~ B-7), 0.511 microm in cluster 2 (B-8 ~ B-14) and 0.624 microm in cluster 3 (B-15 ~ B-18). There were significant difference among Ra of three clusters. 3. Ra of B-IM group was decreased 210.72% than Ra of F group. Ra of B-8 group and B-15 group was increased 35.49% and 51.35% respectively than Ra of B-IM group. 4. On FE-SEM, B-IM group showed the smoothest resin surface. B-8 group and B-15 group showed vertically shallow scratches, and wide and irregular vertical scratches on composite resin surface respectively. Within a limitation of this study, finished resin surface will be again smooth and glazy if BisCover would be reapplied within 8 to 14 months after applying to resin surface.
Head

The purpose of this study was to evaluate the abrasion resistance of surface penetrating sealant which was applied on a composite resin restoration and to provide proper time to reapply sealant on composite resin surface. Two hundred rectangular specimens, sized 8 x 3 x 2 mm, were made of Micronew (Bisco, Inc., Schaumburg, IL, U.S.A) and divided into two groups; F group (n = 10) was finished with coarse and medium grit of Sof-Lex discs and BisCoverwas applied B group (n = 190) after finishing with discs. B group was again subdivided into nineteen subgroups. From B-1 group to B-18 group were subjected to toothbrush abrasion test using a distilled water-dentifrice slurry and toothbrush heads. B-IM group was not subjected to toothbrush abrasion test. Average surface roughness (Ra) of each group was calculated using a surface roughness tester (Surfcorder MSE-1700: Kosaka Laboratory Ltd., Tokyo, Japan). A representative specimen of each group was examined by FE-SEM (S-4700: Hitachi High Technologies Co., Tokyo, Japan). The data were analysed using cluster analysis, paired t-test, and repeated measure ANOVA. The results of this study were as follows; 1. Ra of F group was 0.898 +/- 0.145 microm and B-IM group was 0.289 +/- 0.142 microm. Ra became higher from B-1 group (0.299 +/- 0.48 microm) to B-18 group (0.642 +/- 0.313 microm). 2. Final cluster center of Ra was 0.361 microm in cluster 1 (B-IM ~ B-7), 0.511 microm in cluster 2 (B-8 ~ B-14) and 0.624 microm in cluster 3 (B-15 ~ B-18). There were significant difference among Ra of three clusters. 3. Ra of B-IM group was decreased 210.72% than Ra of F group. Ra of B-8 group and B-15 group was increased 35.49% and 51.35% respectively than Ra of B-IM group. 4. On FE-SEM, B-IM group showed the smoothest resin surface. B-8 group and B-15 group showed vertically shallow scratches, and wide and irregular vertical scratches on composite resin surface respectively. Within a limitation of this study, finished resin surface will be again smooth and glazy if BisCover would be reapplied within 8 to 14 months after applying to resin surface.
Head

No abstract available.
Head

No abstract available.
Head*

No abstract available.
Head and Neck Neoplasms* ; Head*

No abstract available.
Head Impulse Test* ; Head*

No abstract available.
Head and Neck Neoplasms* ; Head*

STATEMENT OF PROBLEM: Implant screw loosening has been remained a problem in implant prosthodontics. The time needed to insert screw driver into abutment screw head should be shortened for the purpose of decreasing the chair time. PURPOSE: The purpose of this study was to investigate the effects of the design of abutment screw driver on the amount of time for insertion of screw driver into abutment screw head. MATERIAL AND METHODS: Hexagonal and rectangular types of abutment screw drivers were used. The original abutment screw drivers were modified by grinding acute angle of the screw driver tip (modified drivers). Group 1 : hexagonal type abutment screw and original driver Group 2 : hexagonal type abutment screw and modified driver Group 3 : rectangular type abutment screw and original driver Group 4 : rectangular type abutment screw and modified driver UCLA lab analogues were located in acrylic resin block. The angulations of them were 0 and 20 degrees. The times needed for insertion were measured. Group 1 and 3 were used as controls. RESULTS: 1. Group 2 showed shorter insertion time than group 1, regardless of implant angulations (p<.05). 2. Group 4 showed shorter insertion time than group 3, regardless of implant angulations (p<.05). CONCLUSION: Modified abutment screw drivers required less amount of time to insert screw driver into abutment screw head. Modification of abutment screw driver was beneficial.
Head* ; Prosthodontics