The Alteration Of Infeted Root Canal Wall Before And After Root Canal Preparation: A Electron Microscopic And Histomorphological Study

Objective: To investigate the characteristics of infected root canal and the structure changes of canal wall dentine after hand instrument preparation; the structure changes of canal wall dentine after hand instrument preparation followed by Nd:YAG laser irradiation. To provide experimental foundation for the effectiveness of root canal treatment.Methods: (1) Specimen collection: Sixty single root human teeth with periapical periodontitis were randomly divided into five groups as infected root canal group; hand instrument group; hand instrument followed by laser irradiation(50mj lOHz) group; hand instrument followed by laser irradiation( 1 OOmj lOHz) group; hand instrument followed by laser irradiation(150mj lOHz) group. Each of the first two groups was composed of fifteen teeth while each of the rest groups included ten teeth. Another twelve single root teeth extracted for orthodontic purpose served as control. (2) Treatment procedure: The root canal of teeth in group A were conventionally cleaned. The root canal of teeth in group B were treated with conventional root canal preparation. Theother three groups (C D E) were irradiated by Nd:YAG laser with different energy(50mj lOHz, lOOmj lOHz, 150mj 10Hz)for 1 minute after canal preparation. The pulp in control group was extracted. (3)Light and electron microscopic examination was conducted to observe the morphological changes of root dentinal tubules and cleaning of the surface of canal wall.Results: (1)LM observation: the control group: The dentinal tubules adjacent to pulp surface lined up in order and regularity, and slighted curved; Infected root canal group: The dentinal tubules adjacent to pulp surface lined up in disorder and irregularity, and the dentinal tubules curved like curly hair, hand instrument group: The dentinal tubules adjacent to pulp surface lined up in order and regularity, and slighted curved. (2) SEM observation: the control group: the dentinal tubules in cross section lined up in order and regularity. The surface of canal wall was clean without dirt. Clear dentinal tubule orifices could be seen; infected root canal groups: the dentinal tubules in cross section lined up in disorder and irregularity. The normal structure of dentinal tubules was destroyed; The surface of canal wall was covered by a layer of irregular dirt over the dentinal tubule orifices; hand instrument group: After conventional preparation the dentinal tubules in cross section lined up in order and regularity. But the dentinal tubule orifices were covered by smear layer. The surface of canal wall was covered by a lotof irregular debris. Most of dentinal tubule orifices was covered by smear layer; hand instrument followed by laser irradiation(50mj lOHz) group: the dentinal tubules in cross section lined up in order and regularity. Some of dentinal tubule orifices were open without smear layer; The surface of canal wall have was not fused. Some of dentinal tubule orifices were exposed; Hand instrument followed by laser irradiation( 1 OOmj lOHz) group: the dentinal tubules in cross section lined up in order and regularity. Some of dentinal tubule orifices were fused and entirely sealed. Some of dentinal tubule orifices were partially sealed; The surface of canal wall was clean and fused. The size of most dentinal tubule orifices was decreased; hand instrument followed by laser irradiation(150mj lOHz) group: the dentinal tubules in cross section lined up in order and regularity. Dentinal tubule orifices were entirely sealed. The surface of the fused layer was uneven; The surface of canal wall was fused apparently. Some scattered crystalloid materials were present.Conclusion: (1) The dentinal tubules adjacent to surface of canal wall of necrotic pulp tissue lined up in disorder and irregularity. (2) The smear layer is present on the wall of root canals after hand instrument preparation. (3) After hand instrument preparation, the irradiation of laser (50mj 1 OHz) for 1 minute on the wall of root canals can remove smear layer partially. (4) After hand instrume...