- Email: [email protected]
Stress analysis for nonrigid connectors on FPDs with pier abutments
origin than merely calcium phosphates. Milk and fluoridated milk have possibly increased remineralization in artificial caries-like lesions as well. Although long-term exposure to milk risks demineralization through a decline in pH as bacteria ferment the lactose, it is important to see the effect of rinsing with milk after an acidic challenge. Mineral water was less effective, although the results still reached significance in the current study. Mineral water has a lower content of calcium, phosphate, and fluoride, but may influence rehardening by dental tissues by increasing the oral clearance of citric acid and raising the intraoral pH.
Clinical Significance.—The role of saliva in remineralizing enamel surfaces softened by acidic beverages has been documented. Reported here, rinsing with a fluoride solution, milk, or water were all beneficial in increasing oral clearance of the acid solution, hastening restoration of surface microhardness.
Wiegand A, Mu¨ller I, Schnapp JD, et al: Impact of fluoride, milk and water rinsing on surface rehardening of acid softened enamel. An in situ study. Am J Dent 21:113-118, 2008 Reprints available from A Wiegand, Clinic for Preventive Dentistry, Periodontology and Cariology, Univ of Zurich, Plattenstr 11, 8032 Zurich, Switzerland; e-mail: [email protected]
Prosthodontics Stress analysis for nonrigid connectors on FPDs with pier abutments Background.—A pier abutment- supported fixed partial denture (FPD) may be needed to replace missing teeth. Restoring two missing teeth and an intermediate pier abutment using a rigid FPD is not advised. The pier abutment can function as a fulcrum, permitting tensile forces to develop between the retainer and the abutment (Fig 1). The result can be extrusive forces and possible loss of retention for the restoration. Higher debonding rates accompany the use of rigid FPDs with pier abutments compared to shorter span prostheses. The proposed alternative is nonrigid connectors. Using the finite element method (FEM), the stress distribution within complex structures can be calculated, allowing investigators to assess the effect of parameter variations after the model has been accurately defined. The FEM was used to evaluate various placement options and thereby determine the ideal placement of a nonrigid connector for a pier abutment FPD. Methods.—A five-unit metal ceramic FPD with a pier abutment using rigid or nonrigid connectors was depicted in a three-dimensional cross-section FEM model (Table 1). The connector locations were at the mesial region of the second molar, the distal or mesial region of the second premolar, or the distal region of the canine. The canine, second premolar, and second molar served as abutments. The model included a supporting periodontal ligament and alveolar bone, both cortical and trabecular. For each abutment a 50-N static vertical occlusal load was applied to the cusp and stress distribution was analyzed. The type of load was also varied, with loading of all cusps simulating maximum centric occlusion contacts, loading of the canine simulating a single anterior contact, and loading of the
50
Dental Abstracts
Fig 1.—Schematic illustration of pier abutment acting as fulcrum. Blue, Anterior loading situations; red, posterior loading situations. (Courtesy of Oruc S, Eraslan O, Tukay HP, et al: Stress analysis of effects of nonrigid connectors on fixed partial dentures with pier abutments. J Prosthet Dent 99:185-192, 2008.)
second molar simulating posterior contact. The von Mises stress values were analyzed for the various conditions. Results.—All of the models demonstrated areas of maximum stress concentration at the loading areas and had the highest stress values at the connectors and cervical regions of the abutment teeth, particularly the pier abutment.
Table 1.—Design Configurations of Five-unit FPDs Evaluated (Courtesy of Oruc S, Eraslan O, Tukay HP, et al: Stress analysis of effects of nonrigid connectors on fixed partial dentures with pier abutments. J Prosthet Dent 99:185-192, 2008.) Design Type Rigid/Nonrigid
R MPosterior DPier MPier DAnterior
Rigid Nonrigid Nonrigid Nonrigid Nonrigid
Location of Nonrigid Connector
Not applicable Mesial to posterior terminal abutment Distal to pier abutment Mesial to pier abutment Distal to anterior terminal abutment
Stress concentrations were also noted at the root surface and apical tooth locations. The minimum stress concentrations were at the nonrigid connector with terminal loading. The rigid and nonrigid connector designs and their placement influenced stress distribution. Discussion.—Both the presence and the location of a nonrigid connector affected the distribution and value of stress on these FPDs with a pier abutment. Because the connectors are where the greatest concentrations of stress were located in these FPDs, placing nonrigid connectors in these areas would be the best choice. The minimum stress concentration area for the pier abutments was in the distal region.
Clinical Significance.—The solution to a common prosthodontic problem often involves a fixed five-unit prosthesis between cuspid and second molar with second bicuspid pier abutment. In this study the FEM was used to aid design by examining stress patterns developed with rigid versus nonrigid connectors and to decide where best to locate a nonrigid connector.
Oruc S, Eraslan O, Tukay HP, et al: Stress analysis of effects of nonrigid connectors on fixed partial dentures with pier abutments. J Prosthet Dent 99:185-192, 2008 Reprints available from O Eraslan, Univ of Selcuk, Faculty of Dentistry, Dept of Prosthodontics, 42079 Kampus, Konya, Turkey; fax: 90 332 2410062; e-mail: [email protected]
Research Photodynamic therapy added to endodontic treatment Background.—Endodontic treatment is designed to eliminate as many pathogens as possible from the root canal system. Photodynamic therapy (PDT) is a novel approach that combines a nontoxic photosensitizer (PS) and a light source to kill pathogenic microbes. The excited PS reacts with molecular oxygen, yielding a highly reactive oxygen species that injures and eventually kills microorganisms. The PS possesses a significant cationic charge that quickly binds and penetrates the bacterial cell and is highly selective in killing microorganisms but sparing host mammalian cells. Studies have pitted PDT against the oral bacteria that cause periodontitis, peri-implantitis, and caries. Its use against endodontic infection with bioluminescent bacteria was studied ex vivo, specifically using PDT with polyethyleneimine (PEI) chlorine conjugate (PEI ce6) and fiberoptic-delivered red light. PDT used after conventional endodontic therapy produced significantly more killing and less bacterial growth. The combination was tested in a clinical trial in patients who needed endodontic therapy. Methods.—Twenty patients aged 21 to 35 years in Sa˜o Paulo, Brazil, had symptoms of necrotic pulp and periapical periodontitis. A single practitioner was responsible for all procedures. Microbiological samples from 20 anterior teeth were obtained after their root canals were accessed, demonstrating the initial contamination status of the root canal; after endodontic therapy was performed; and after PDT was used. The process was repeated and samples
obtained again a week later. Initially the root canal was accessed after installing a rubber dam and irrigating the area with 5 mL of 2% chlorhexidine solution. Three paper points were deposited in a sterile bottle of fresh Moller’s viability medium Go ¨ teborg anaerobic (VMGA) III transport medium (first sampling). The canal was irrigated with 1 mL of 2.5% sodium hypochlorite solution, then an endodontic needle was used to apply 10 mL of 3% hydrogen peroxide solution between each file. A final irrigation with 5 mL of 17% ethylenediaminetetraacetic acid (EDTA) was used to remove the antimicrobial agent, then 3 paper points were applied to yield the second sample of microbiological status. The photosensitizer (0.5 mL) was deposited in the root canal using the endodontic needle, then the diode laser plus optical fiber was used to irradiate the canal for 240 seconds, for a total energy of 9.6 J. Each patient was treated with a new fiber. Irrigation with 10 mL of sterile saline solution was then performed to remove the photosensitizer. Three paper points were used to dry the canal and provide the third microbiological sample. The canals were filled with calcium hydroxide paste and dressed with restorative material. The canals were sampled a week later to analyze recolonization status, then each patient had a second endodontic treatment and PDT. Conventional sealing techniques were used to close the root canals at this time. Results.—All patients began the study with necrotic pulp and periapical lesions, with infection confirmed by
Volume 54
Issue 1
2009
51
Clinical Significance.—The role of saliva in remineralizing enamel surfaces softened by acidic beverages has been documented. Reported here, rinsing with a fluoride solution, milk, or water were all beneficial in increasing oral clearance of the acid solution, hastening restoration of surface microhardness.
Wiegand A, Mu¨ller I, Schnapp JD, et al: Impact of fluoride, milk and water rinsing on surface rehardening of acid softened enamel. An in situ study. Am J Dent 21:113-118, 2008 Reprints available from A Wiegand, Clinic for Preventive Dentistry, Periodontology and Cariology, Univ of Zurich, Plattenstr 11, 8032 Zurich, Switzerland; e-mail: [email protected]
Prosthodontics Stress analysis for nonrigid connectors on FPDs with pier abutments Background.—A pier abutment- supported fixed partial denture (FPD) may be needed to replace missing teeth. Restoring two missing teeth and an intermediate pier abutment using a rigid FPD is not advised. The pier abutment can function as a fulcrum, permitting tensile forces to develop between the retainer and the abutment (Fig 1). The result can be extrusive forces and possible loss of retention for the restoration. Higher debonding rates accompany the use of rigid FPDs with pier abutments compared to shorter span prostheses. The proposed alternative is nonrigid connectors. Using the finite element method (FEM), the stress distribution within complex structures can be calculated, allowing investigators to assess the effect of parameter variations after the model has been accurately defined. The FEM was used to evaluate various placement options and thereby determine the ideal placement of a nonrigid connector for a pier abutment FPD. Methods.—A five-unit metal ceramic FPD with a pier abutment using rigid or nonrigid connectors was depicted in a three-dimensional cross-section FEM model (Table 1). The connector locations were at the mesial region of the second molar, the distal or mesial region of the second premolar, or the distal region of the canine. The canine, second premolar, and second molar served as abutments. The model included a supporting periodontal ligament and alveolar bone, both cortical and trabecular. For each abutment a 50-N static vertical occlusal load was applied to the cusp and stress distribution was analyzed. The type of load was also varied, with loading of all cusps simulating maximum centric occlusion contacts, loading of the canine simulating a single anterior contact, and loading of the
50
Dental Abstracts
Fig 1.—Schematic illustration of pier abutment acting as fulcrum. Blue, Anterior loading situations; red, posterior loading situations. (Courtesy of Oruc S, Eraslan O, Tukay HP, et al: Stress analysis of effects of nonrigid connectors on fixed partial dentures with pier abutments. J Prosthet Dent 99:185-192, 2008.)
second molar simulating posterior contact. The von Mises stress values were analyzed for the various conditions. Results.—All of the models demonstrated areas of maximum stress concentration at the loading areas and had the highest stress values at the connectors and cervical regions of the abutment teeth, particularly the pier abutment.
Table 1.—Design Configurations of Five-unit FPDs Evaluated (Courtesy of Oruc S, Eraslan O, Tukay HP, et al: Stress analysis of effects of nonrigid connectors on fixed partial dentures with pier abutments. J Prosthet Dent 99:185-192, 2008.) Design Type Rigid/Nonrigid
R MPosterior DPier MPier DAnterior
Rigid Nonrigid Nonrigid Nonrigid Nonrigid
Location of Nonrigid Connector
Not applicable Mesial to posterior terminal abutment Distal to pier abutment Mesial to pier abutment Distal to anterior terminal abutment
Stress concentrations were also noted at the root surface and apical tooth locations. The minimum stress concentrations were at the nonrigid connector with terminal loading. The rigid and nonrigid connector designs and their placement influenced stress distribution. Discussion.—Both the presence and the location of a nonrigid connector affected the distribution and value of stress on these FPDs with a pier abutment. Because the connectors are where the greatest concentrations of stress were located in these FPDs, placing nonrigid connectors in these areas would be the best choice. The minimum stress concentration area for the pier abutments was in the distal region.
Clinical Significance.—The solution to a common prosthodontic problem often involves a fixed five-unit prosthesis between cuspid and second molar with second bicuspid pier abutment. In this study the FEM was used to aid design by examining stress patterns developed with rigid versus nonrigid connectors and to decide where best to locate a nonrigid connector.
Oruc S, Eraslan O, Tukay HP, et al: Stress analysis of effects of nonrigid connectors on fixed partial dentures with pier abutments. J Prosthet Dent 99:185-192, 2008 Reprints available from O Eraslan, Univ of Selcuk, Faculty of Dentistry, Dept of Prosthodontics, 42079 Kampus, Konya, Turkey; fax: 90 332 2410062; e-mail: [email protected]
Research Photodynamic therapy added to endodontic treatment Background.—Endodontic treatment is designed to eliminate as many pathogens as possible from the root canal system. Photodynamic therapy (PDT) is a novel approach that combines a nontoxic photosensitizer (PS) and a light source to kill pathogenic microbes. The excited PS reacts with molecular oxygen, yielding a highly reactive oxygen species that injures and eventually kills microorganisms. The PS possesses a significant cationic charge that quickly binds and penetrates the bacterial cell and is highly selective in killing microorganisms but sparing host mammalian cells. Studies have pitted PDT against the oral bacteria that cause periodontitis, peri-implantitis, and caries. Its use against endodontic infection with bioluminescent bacteria was studied ex vivo, specifically using PDT with polyethyleneimine (PEI) chlorine conjugate (PEI ce6) and fiberoptic-delivered red light. PDT used after conventional endodontic therapy produced significantly more killing and less bacterial growth. The combination was tested in a clinical trial in patients who needed endodontic therapy. Methods.—Twenty patients aged 21 to 35 years in Sa˜o Paulo, Brazil, had symptoms of necrotic pulp and periapical periodontitis. A single practitioner was responsible for all procedures. Microbiological samples from 20 anterior teeth were obtained after their root canals were accessed, demonstrating the initial contamination status of the root canal; after endodontic therapy was performed; and after PDT was used. The process was repeated and samples
obtained again a week later. Initially the root canal was accessed after installing a rubber dam and irrigating the area with 5 mL of 2% chlorhexidine solution. Three paper points were deposited in a sterile bottle of fresh Moller’s viability medium Go ¨ teborg anaerobic (VMGA) III transport medium (first sampling). The canal was irrigated with 1 mL of 2.5% sodium hypochlorite solution, then an endodontic needle was used to apply 10 mL of 3% hydrogen peroxide solution between each file. A final irrigation with 5 mL of 17% ethylenediaminetetraacetic acid (EDTA) was used to remove the antimicrobial agent, then 3 paper points were applied to yield the second sample of microbiological status. The photosensitizer (0.5 mL) was deposited in the root canal using the endodontic needle, then the diode laser plus optical fiber was used to irradiate the canal for 240 seconds, for a total energy of 9.6 J. Each patient was treated with a new fiber. Irrigation with 10 mL of sterile saline solution was then performed to remove the photosensitizer. Three paper points were used to dry the canal and provide the third microbiological sample. The canals were filled with calcium hydroxide paste and dressed with restorative material. The canals were sampled a week later to analyze recolonization status, then each patient had a second endodontic treatment and PDT. Conventional sealing techniques were used to close the root canals at this time. Results.—All patients began the study with necrotic pulp and periapical lesions, with infection confirmed by
Volume 54
Issue 1
2009
51