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Flexural strength of various fiber posts
Nearly 58% of the dentists’ working time was spent in some degree of trunk flexion, with flexion of 30° occurring almost 45% of the time. Hygienists’ working time was spent in similar positions. Dentists spent at least 86% of the time with their necks flexed at least 30° degrees, with 51% of the time at 60°. The data for hygienists were comparable to those of dentists. Some degree of elevation of the left shoulder (abduction) was noted for more than 50% of the dentists’ time but only 25% for the right shoulder. Hygienists’ left shoulders were abducted 45% of the time and right shoulders 34% of the time. Discussion.—Both dentists and dental hygienists spent at least half their working time in positions where their necks were flexed 60° or more, their trunks were flexed 30° or more, and at least 1 shoulder was abducted. These static positions require high muscle forces, which lead to high compression loads on the joints. Prolonged flexed or abducted joint postures can produce muscle pain in the neck, shoulder, and lower back, rotator cuff syndrome in the shoulder, and low back pain or disorder.
Clinical Significance.—Studies were conducted to design dental equipment that would minimize the occupational stresses of providing dental care. Observing the postural contortions of both dentists and dental hygienists in a clinical setting reveals harmful habits for both. What combination of properly designed equipment, coupled with muscle strengthening exercise and proper posture, will ease these strains?
Marklin RW, Cherney K: Working postures of dentists and dental hygienists. Calif Dent Assoc J 33:133-136, 2005 Reprints available from RW Marklin, Dept of Mechanical and Industrial Engineering, Marquette Univ, PO Box 1881, Milwaukee,WI 53201-1881
Operative Dentistry Flexural strength of various fiber posts Background.—Crown or root fracture is the most severe type of failure of restorations with intraradicular retention because it requires tooth extraction. The root fracture index with cast metallic posts is about 2% to 4%. Fiber posts have an elasticity modulus (E) closer to that of dentin (20 GPa for posts versus 18 GPa for dentin) than is seen with either cast posts and prefabricated metallic posts (E of 200 GPa) or ceramic posts (E of 150 GPa). Thus, stresses are absorbed and uniformly distributed to the remaining root structure rather than concentrated. Among the types of fiber posts developed are carbon fiber, quartz fiber, and glass fiber posts. The clinical requirements of most importance for root canal posts are a high flexural strength value
300 Dental Abstracts
and an E value close to the value of dentin. With excessively flexible fiber posts, fractures can result from force applied to the interface between post, resin, and dentin. The flexural strength of 8 types of fiber posts was assessed by means of the 3-point bending test. Methods.—Representatives of 1 type of carbon fiber post, 1 carbon/quartz fiber post, 1 opaque quartz fiber post, 2 translucent quartz fiber posts, and 3 glass fiber posts were tested. Eighty samples were distributed into 8 groups of 10 each for testing with use of the 3-point bending test. The groups were G1 (C POST), G2 (AESTHETI-POST), G3 (ASTHETI-PLUS), G4 (LIGHT-POST), G5 (D.T. LIGHT-POST),
G6 (PARAPOST WHITE), G7 (FIBREKOR), AND G8 (REFORPOST). The average values obtained for each group were analyzed statistically. Results.—The highest flexural strength value was obtained by the G2 and G3 groups. The strengths of G1 and G3 were similar, and those of G1, G4, G5, G6, and G7 were statistically similar. The lowest flexural strength value was recorded for the G8 group. Discussion.—The differences in composition of the various posts may not be a significant factor in determining flexural strength values, as all had approximately the same E value. Two of the 4 quartz fiber posts had higher flexural strength. Aspects such as integrity, size, density, distribution of the fibers, and nature of the bond between matrix and fibers may be more important in determining flexure strength values.
Clinical Significance.—Modulus of elasticity closely approximating that of dentin is the great virtue of fiber posts in preventing root fracture. Excessive flexibility, however, can lead to fracture of the restoration.
Galhano GÁ, Valandro LF, de Melo RM, et al: Evaluation of the flexural strength of carbon fiber-, quartz fiber-, and glass fiber-based posts. J Endodont 31:209-211, 2005 Reprints available from GÁP Galhano, School of Dentistry, Dept of Dental Materials and Prosthodontics, São Paulo State Univ at São José dos Campos, Av Francisco José Longo, 777, CEP: 12245-000, São José dos Campos, Brazil; e-mail: grazielagalhano@yahoo .com.br
Fatigue loading tests Background.—For clinical success in restoring endodontically treated premolars it is essential to have posts with a flexibility close to that of tooth structure, resin cement with a favorable C-factor for the root canal, and proper mechanical properties and adhesive strength to both the post and the root canal well. Fatigue testing was developed to assess post-and-core restorations, measuring the breaking or fracturing of a material caused by cyclic or repeatedly applied loads less than the yield limit, usually revealed as minute cracks that then tear and rupture. An analysis of the influence of fatigue loading on the quality of the cement layer between quartz coated carbon fiber posts and the root canal focused on 2 adhesive resin composite cements (chemical-cured Panavia 21 and dual-cured RelyX-ARC) and 1 resin-modified glass-ionomer cement (RelyX).
the proximal cemento-enamel junction. Endodontic treatment was carried out, then post-and-core restorations with a post length of 6 mm were prepared for each tooth. Posts were cemented directly into the root canal, an adhesive was applied, and the posts were then built up with a core build-up composite (Table 1). Half the specimens in each group were exposed to 106 load cycles of loading nearly perpendicular to the axial axis and half were maintained as controls. Sections were obtained from each specimen at the apical, medial, and coronal locations; these were parallel, transverse root sections measuring 1.5 mm in thickness (Fig 1). These were then evaluated with the scanning electron microscope (SEM) to determine the integrity of the cement layer (Fig 3). The push-out test was used to assess the retention strength of the cemented post sections.
Methods.—The single-rooted human maxillary premolars used had the coronal sections removed at the level of
Results.—None of the specimens developed separation of the post-and-core restorations from the roots as a
Volume 50 • Issue 5 • 2005 301
Clinical Significance.—Studies were conducted to design dental equipment that would minimize the occupational stresses of providing dental care. Observing the postural contortions of both dentists and dental hygienists in a clinical setting reveals harmful habits for both. What combination of properly designed equipment, coupled with muscle strengthening exercise and proper posture, will ease these strains?
Marklin RW, Cherney K: Working postures of dentists and dental hygienists. Calif Dent Assoc J 33:133-136, 2005 Reprints available from RW Marklin, Dept of Mechanical and Industrial Engineering, Marquette Univ, PO Box 1881, Milwaukee,WI 53201-1881
Operative Dentistry Flexural strength of various fiber posts Background.—Crown or root fracture is the most severe type of failure of restorations with intraradicular retention because it requires tooth extraction. The root fracture index with cast metallic posts is about 2% to 4%. Fiber posts have an elasticity modulus (E) closer to that of dentin (20 GPa for posts versus 18 GPa for dentin) than is seen with either cast posts and prefabricated metallic posts (E of 200 GPa) or ceramic posts (E of 150 GPa). Thus, stresses are absorbed and uniformly distributed to the remaining root structure rather than concentrated. Among the types of fiber posts developed are carbon fiber, quartz fiber, and glass fiber posts. The clinical requirements of most importance for root canal posts are a high flexural strength value
300 Dental Abstracts
and an E value close to the value of dentin. With excessively flexible fiber posts, fractures can result from force applied to the interface between post, resin, and dentin. The flexural strength of 8 types of fiber posts was assessed by means of the 3-point bending test. Methods.—Representatives of 1 type of carbon fiber post, 1 carbon/quartz fiber post, 1 opaque quartz fiber post, 2 translucent quartz fiber posts, and 3 glass fiber posts were tested. Eighty samples were distributed into 8 groups of 10 each for testing with use of the 3-point bending test. The groups were G1 (C POST), G2 (AESTHETI-POST), G3 (ASTHETI-PLUS), G4 (LIGHT-POST), G5 (D.T. LIGHT-POST),
G6 (PARAPOST WHITE), G7 (FIBREKOR), AND G8 (REFORPOST). The average values obtained for each group were analyzed statistically. Results.—The highest flexural strength value was obtained by the G2 and G3 groups. The strengths of G1 and G3 were similar, and those of G1, G4, G5, G6, and G7 were statistically similar. The lowest flexural strength value was recorded for the G8 group. Discussion.—The differences in composition of the various posts may not be a significant factor in determining flexural strength values, as all had approximately the same E value. Two of the 4 quartz fiber posts had higher flexural strength. Aspects such as integrity, size, density, distribution of the fibers, and nature of the bond between matrix and fibers may be more important in determining flexure strength values.
Clinical Significance.—Modulus of elasticity closely approximating that of dentin is the great virtue of fiber posts in preventing root fracture. Excessive flexibility, however, can lead to fracture of the restoration.
Galhano GÁ, Valandro LF, de Melo RM, et al: Evaluation of the flexural strength of carbon fiber-, quartz fiber-, and glass fiber-based posts. J Endodont 31:209-211, 2005 Reprints available from GÁP Galhano, School of Dentistry, Dept of Dental Materials and Prosthodontics, São Paulo State Univ at São José dos Campos, Av Francisco José Longo, 777, CEP: 12245-000, São José dos Campos, Brazil; e-mail: grazielagalhano@yahoo .com.br
Fatigue loading tests Background.—For clinical success in restoring endodontically treated premolars it is essential to have posts with a flexibility close to that of tooth structure, resin cement with a favorable C-factor for the root canal, and proper mechanical properties and adhesive strength to both the post and the root canal well. Fatigue testing was developed to assess post-and-core restorations, measuring the breaking or fracturing of a material caused by cyclic or repeatedly applied loads less than the yield limit, usually revealed as minute cracks that then tear and rupture. An analysis of the influence of fatigue loading on the quality of the cement layer between quartz coated carbon fiber posts and the root canal focused on 2 adhesive resin composite cements (chemical-cured Panavia 21 and dual-cured RelyX-ARC) and 1 resin-modified glass-ionomer cement (RelyX).
the proximal cemento-enamel junction. Endodontic treatment was carried out, then post-and-core restorations with a post length of 6 mm were prepared for each tooth. Posts were cemented directly into the root canal, an adhesive was applied, and the posts were then built up with a core build-up composite (Table 1). Half the specimens in each group were exposed to 106 load cycles of loading nearly perpendicular to the axial axis and half were maintained as controls. Sections were obtained from each specimen at the apical, medial, and coronal locations; these were parallel, transverse root sections measuring 1.5 mm in thickness (Fig 1). These were then evaluated with the scanning electron microscope (SEM) to determine the integrity of the cement layer (Fig 3). The push-out test was used to assess the retention strength of the cemented post sections.
Methods.—The single-rooted human maxillary premolars used had the coronal sections removed at the level of
Results.—None of the specimens developed separation of the post-and-core restorations from the roots as a
Volume 50 • Issue 5 • 2005 301