Short-term periradicular tissue response to mineral trioxide aggregate (MTA) as root-end filling material
http://endodonticsjournal.com/articles/135/1/Short-term-periradicular-tissue-response-to-mineral-trioxide-aggregate-MTA-as-root-end-filling-material/Page1.html
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Published on 12/28/2008
N. Economides, O. Pantelidou, A. Kokkas & D. Tziafas
Department of Endodontology, School of Dentistry, Aristotle University of Thessaloniki, Greece.
Aim.
The aim of the present study was to evaluate the short-term response of periradicular tissues to MTA when used as a root-end filling material in ideal tissue conditions.
Conclusions.
MTA is a biocompatible material that stimulates periradicular tissue repair at the root-end situation; however, the nature of the newly formed tissues requires further elucidation.
Department of Endodontology, School of Dentistry, Aristotle University of Thessaloniki, Greece.
Aim.
The aim of the present study was to evaluate the short-term response of periradicular tissues to MTA when used as a root-end filling material in ideal tissue conditions.
Conclusions.
MTA is a biocompatible material that stimulates periradicular tissue repair at the root-end situation; however, the nature of the newly formed tissues requires further elucidation.
Introduction - Materials and methods.
N. Economides, O. Pantelidou, A. Kokkas & D. Tziafas
Department of Endodontology, School of Dentistry, Aristotle University of Thessaloniki, Greece.
Introduction.
Recent research in endodontics has been focused on the ability of various techniques and filling materials to enhance optimal tissue healing. Root-end filling materials designed to stimulate hard and soft tissue repair in the periradicular tissues are highly recommended (Friedman1991, Guttman & Harrison1994).Mineral trioxide aggregate (MTA) is a relatively new material with numerous clinical applications in endodontics (Torabinejad & Chivian1999). It has been reported to stimulate healing of the periradicular tissues to almost normal preoperative status, when used as a root-end filling material. Experimental studies in infected dog teeth and healthy monkey teeth showed less inflammation with the MTA than with amalgam (Torabinejad et al.1995, Torabinejad et al.1997), whilst formation of a cementum-like matrix was also observed. Nevertheless, the mechanism controlling periradicular tissue healing and hard tissue repair needs to be elucidated further.
The aim of the present study was to evaluate the short-term response of periradicular tissues to MTA, when used as a root-end filling material in optimal tissue conditions, i.e. root-end resection in healthy dog teeth.
Materials and methods.
Two healthy dogs, 15 and18 months of age, were used in the present study. The animals were anaesthetized with pentothal (20 mg kg_1body weight) and intubated with a cuffed endotracheal tube before beginning the experimental procedures. All procedures were conducted in accordance with the protocol outlined by the General Secretariat of Research and Technology in Greece regarding the recommended Standard Practices for Biological Investigations.
Twenty-four root canals of single- and double-rooted premolars were divided equally into four groups that were treated sequentially so that observation periods of 1week (right teeth of the first animal), 2 weeks (right teeth of the second animal), 3 weeks (left teeth of the second animal) and 5 weeks (left teeth of the first animal) were created.
The teeth were opened through occlusal access cavities and the pulps were removed with barbed broaches. The root canals were then cleaned and instrumented to the apical delta with the step-back technique to a size 40 master apical file. The canals were irrigated with 1% sodium hypochlorite before the use of each instrument. After instrumentation, the canals were dried with paper points and obturated with laterally condensed gutta-percha and Roth 801root canal sealer (Roth International Ltd, Chicago, IL, USA). The access cavities were filled with amalgam.
At the same session, a full-thickness triangular muccoperiosteal flap was raised to gain access to the periradicular tissues of the teeth. The cortical bone was removed with a size 6 round bur in a low-speed hand piece using sterile saline spray. After apical resection, root-end cavities were prepared to a depth of 3 mm using a size 2 round bur followed by a size 34 inverted cone bur in a low-speed hand piece with the use of copious sterile saline spray. Eight root-end cavities were filled with IRM (Dentsply Detrey GmbH, Konstanz, Germany) and 14 with ProRoot MTA (Dentsply Simfra, Paris, France). The materials were mixed according to the manufacturer’s instructions and placed in the cavities using an MTA carrier. Light pressure was then applied to the MTA using wet cotton pellets. The surgical flaps were sutured with absorbable gut sutures, and the animals maintained on standard diet.
The animals were killed using an overdose of pentothal and the jaws were immediately dissected and fixed in 10% buffered formalin solution. Radiographs were taken of all operated teeth. Blocks, including one root and the surrounding alveolar bone each, were cut after demineralization in 5%trichloroacetic acid and the specimens were embedded in paraffin. Longitudinal sections, 7 mm thick passing through the root apex, were stained with haematoxylin and eosin. The tissue responses were evaluated by light microscopy at postoperative periods of 1, 2, 3 and 5 weeks.
Two of the canals, filled with MTA for 2 and 3 weeks, were analysed with scanning electron microscopy (JEOL JSM-840A). After fixation, the soft tissue was removed by mechanical means. The specimens were immersed in 1% sodium hypochlorite solution for 4 h and dehydrated in alcohol. The surface structure and composition of the resected roots, MTA and the newly formed calcified deposits were evaluated.
Department of Endodontology, School of Dentistry, Aristotle University of Thessaloniki, Greece.
Introduction.
Recent research in endodontics has been focused on the ability of various techniques and filling materials to enhance optimal tissue healing. Root-end filling materials designed to stimulate hard and soft tissue repair in the periradicular tissues are highly recommended (Friedman1991, Guttman & Harrison1994).Mineral trioxide aggregate (MTA) is a relatively new material with numerous clinical applications in endodontics (Torabinejad & Chivian1999). It has been reported to stimulate healing of the periradicular tissues to almost normal preoperative status, when used as a root-end filling material. Experimental studies in infected dog teeth and healthy monkey teeth showed less inflammation with the MTA than with amalgam (Torabinejad et al.1995, Torabinejad et al.1997), whilst formation of a cementum-like matrix was also observed. Nevertheless, the mechanism controlling periradicular tissue healing and hard tissue repair needs to be elucidated further.
The aim of the present study was to evaluate the short-term response of periradicular tissues to MTA, when used as a root-end filling material in optimal tissue conditions, i.e. root-end resection in healthy dog teeth.
Materials and methods.
Two healthy dogs, 15 and18 months of age, were used in the present study. The animals were anaesthetized with pentothal (20 mg kg_1body weight) and intubated with a cuffed endotracheal tube before beginning the experimental procedures. All procedures were conducted in accordance with the protocol outlined by the General Secretariat of Research and Technology in Greece regarding the recommended Standard Practices for Biological Investigations.
Twenty-four root canals of single- and double-rooted premolars were divided equally into four groups that were treated sequentially so that observation periods of 1week (right teeth of the first animal), 2 weeks (right teeth of the second animal), 3 weeks (left teeth of the second animal) and 5 weeks (left teeth of the first animal) were created.
The teeth were opened through occlusal access cavities and the pulps were removed with barbed broaches. The root canals were then cleaned and instrumented to the apical delta with the step-back technique to a size 40 master apical file. The canals were irrigated with 1% sodium hypochlorite before the use of each instrument. After instrumentation, the canals were dried with paper points and obturated with laterally condensed gutta-percha and Roth 801root canal sealer (Roth International Ltd, Chicago, IL, USA). The access cavities were filled with amalgam.
At the same session, a full-thickness triangular muccoperiosteal flap was raised to gain access to the periradicular tissues of the teeth. The cortical bone was removed with a size 6 round bur in a low-speed hand piece using sterile saline spray. After apical resection, root-end cavities were prepared to a depth of 3 mm using a size 2 round bur followed by a size 34 inverted cone bur in a low-speed hand piece with the use of copious sterile saline spray. Eight root-end cavities were filled with IRM (Dentsply Detrey GmbH, Konstanz, Germany) and 14 with ProRoot MTA (Dentsply Simfra, Paris, France). The materials were mixed according to the manufacturer’s instructions and placed in the cavities using an MTA carrier. Light pressure was then applied to the MTA using wet cotton pellets. The surgical flaps were sutured with absorbable gut sutures, and the animals maintained on standard diet.
The animals were killed using an overdose of pentothal and the jaws were immediately dissected and fixed in 10% buffered formalin solution. Radiographs were taken of all operated teeth. Blocks, including one root and the surrounding alveolar bone each, were cut after demineralization in 5%trichloroacetic acid and the specimens were embedded in paraffin. Longitudinal sections, 7 mm thick passing through the root apex, were stained with haematoxylin and eosin. The tissue responses were evaluated by light microscopy at postoperative periods of 1, 2, 3 and 5 weeks.
Two of the canals, filled with MTA for 2 and 3 weeks, were analysed with scanning electron microscopy (JEOL JSM-840A). After fixation, the soft tissue was removed by mechanical means. The specimens were immersed in 1% sodium hypochlorite solution for 4 h and dehydrated in alcohol. The surface structure and composition of the resected roots, MTA and the newly formed calcified deposits were evaluated.
Results.
The short-term periradicular tissue reactions are summarized in Table 1.
Retrograde filling with MTA.
Both, soft tissue and thin layers of hard tissue, were observed in contact with MTA (Figs 1-5). The most characteristic reaction was the presence of soft tissue over the MTA retrograde fillings in all observations periods. Basophilic spindle-shaped or polygonal cells with large nuclei and a few collagen fibres were consistently found around or in close proximity to the MTA surface, 1week postoperatively (Fig.1). Fibroblasts and collagen fibres arranged parallel to each other were observed in all specimens after 2 weeks (Fig. 2). The roots filled with MTA for 3or5 weeks had thick fibrous capsules (Figs 3and4).
Thin layers of hard tissue were observed over all MTA fillings at 2-, 3- or 5-week observation periods (Figs 3- 5). At the 2-week observation period, hard tissue was seen mainly over the exposed dentine surfaces at the level of the apical resection. Traces of calcified matrix were also noticed at the interface between fibrous connective tissue and the MTA filling material after 3- 5 weeks (Figs 3 and 4).
The surface structure of hard tissue and the calcified matrix deposits over the MTA-filled roots were further examined by SEM in two roots treated for 2 and3 weeks. Thin layers of calcified matrix, revealing a homogenous surface structure of well-organized crystal deposits, were seen over the resected dentine and the exposed MTA surface (Fig. 5).
The periradicular tissues in four specimens filled with MTA displayed inflammation at all observation periods. The inflammation was scored as moderate-to-severe in only one specimen at the 3-week observation period (Fig. 3). The predominant inflammatory cells were macrophages and lymphocytes. New bone at the site of the resected apices was evident in all MTA-filled roots after 2-5 weeks.
Retrograde filling with IRM.
Relatively few collagen fibres were seen over the IRM fillings, regardless of the observation period. Six out of the eight roots had inflammatory reactions and those were scored as moderate-to-severe in three cases. Bone formation was found at the site of the resected apices in three IRM-filled roots. None of the specimens revealed hard tissue formation over the IRM filling material.
Retrograde filling with MTA.
Both, soft tissue and thin layers of hard tissue, were observed in contact with MTA (Figs 1-5). The most characteristic reaction was the presence of soft tissue over the MTA retrograde fillings in all observations periods. Basophilic spindle-shaped or polygonal cells with large nuclei and a few collagen fibres were consistently found around or in close proximity to the MTA surface, 1week postoperatively (Fig.1). Fibroblasts and collagen fibres arranged parallel to each other were observed in all specimens after 2 weeks (Fig. 2). The roots filled with MTA for 3or5 weeks had thick fibrous capsules (Figs 3and4).
Thin layers of hard tissue were observed over all MTA fillings at 2-, 3- or 5-week observation periods (Figs 3- 5). At the 2-week observation period, hard tissue was seen mainly over the exposed dentine surfaces at the level of the apical resection. Traces of calcified matrix were also noticed at the interface between fibrous connective tissue and the MTA filling material after 3- 5 weeks (Figs 3 and 4).
The surface structure of hard tissue and the calcified matrix deposits over the MTA-filled roots were further examined by SEM in two roots treated for 2 and3 weeks. Thin layers of calcified matrix, revealing a homogenous surface structure of well-organized crystal deposits, were seen over the resected dentine and the exposed MTA surface (Fig. 5).
The periradicular tissues in four specimens filled with MTA displayed inflammation at all observation periods. The inflammation was scored as moderate-to-severe in only one specimen at the 3-week observation period (Fig. 3). The predominant inflammatory cells were macrophages and lymphocytes. New bone at the site of the resected apices was evident in all MTA-filled roots after 2-5 weeks.
Retrograde filling with IRM.
Relatively few collagen fibres were seen over the IRM fillings, regardless of the observation period. Six out of the eight roots had inflammatory reactions and those were scored as moderate-to-severe in three cases. Bone formation was found at the site of the resected apices in three IRM-filled roots. None of the specimens revealed hard tissue formation over the IRM filling material.
Table 2. Short-term periradicular tissue reactions of root ends filled with MTA and IRM.
Figure 1. Spindle-shaped or polygonal periradicular cells in direct contact with the MTA used as root-end filling materialat1postoperative week (H&E, magnification 400x).
Figure 2. Densely packed collagen fibres (arrow) in close proximity to the MTA used as root-end filling material at 2 postoperative weeks (H&E, magnification 250x).
Figure 3. Fibrous capsule (arrows) and hard tissue (arrowheads) formed in direct contact to the MTA used as root-end filling material at 3 postoperative weeks. The inflammation was scored as moderate-to-severe (H&E, magnification 40x).
Figure 4. Fibrous capsule and hard tissue (arrows) formed in direct contact to the exposed dentin surface and MTA used as root-end filling material at 5 postoperative weeks. (H&E, magnification 250x).
Figure 5. Scanning electron microscope examination at the material surface, 2 weeks after MTA used as a root-end filling material.
(a) Formation of new calcified matrix onto the MTA surface. The resected dentine surface (asterisk) (magnification 300x).
(b) Higher magnification of (a). Homogenous surface structure of well-organized crystal depositions (magnification 5000x).
Discussion - References.
Discussion.
The present data indicate that under optimal tissue conditions (in the absence of preoperative infection), apical root resection and placement of MTA creates an inflammation- free environment from the first postoperative week. Moderate-to-severe inflammation of the periradicular tissues was seen around one out of 14 MTA root-end fillings, and in three out of eight IRM-filled root ends. MTA proved to be a more favorable material in studies where MTA or amalgam was placed as retrograde filling material in infected dog teeth, 2-18 weeks postoperatively (Torabinejad et al.1995) and healthy monkey teeth, 5 months postoperatively (Torabinejad et al.1997).
The present data, indicating that MTA represents a biocompatible substrate to which formative cells can attach and produce new soft or hard tissue, are in agreement with previous data (Torabinejad et al. 1995). This study also supports previous findings that cells cultivated in vitro (Koh et al. 1998, Mitchell et al. 1999, Zhu et al. 2000), or mechanically exposed pulp cells in vivo (Tziafas et al. 2002), can be grown in intimate contact with this cement. Furthermore, these short-term observations show that early tissue healing events to MTA root-end filling material are characterized initially by fibrous connective tissue formation and secondarily by hard tissue repair.
The stimulatory effect of MTA on the biosynthetic activity of periradicular cells results primarily in stimulation of fibroblasts to lay down a fibrous connective tissue and rapid growth of periodontal ligament due to its high healing capacity. Hard tissue formation seems to be activated progressively from the peripheral root walls to the centre of the MTA. Two mechanisms could be suggested for the process leading to hard tissue formation over the MTA: either the fibrous connective tissue is calcified as the postsurgical time interval is increased or cells undergoing differentiation into hard tissue forming cells are progressively migrating between MTA surface and fibrous connective tissue, activating mineralization from the periphery of the root walls to the centre of the MTA filling. Since the nature of the hard tissue has not been specifically characterized, the mechanism for stimulating hard tissue formation over the MTA retrograde filling remains unknown. Nevertheless, it is reasonable to suggest that if activation of cementogenesis occurs after MTA placement at the apex, mineralization of previously formed connective tissue might be excluded as the main mechanism of hard tissue formation.
Based on the results of the present investigation, MTA is a biocompatible material when used in root-end cavities, stimulating repair of periradicular tissues. The nature of formative cells and newly formed hard tissue, as well as the mechanism controlling MTA-activated hard tissue formation, needs to be investigated further.
The present data indicate that under optimal tissue conditions (in the absence of preoperative infection), apical root resection and placement of MTA creates an inflammation- free environment from the first postoperative week. Moderate-to-severe inflammation of the periradicular tissues was seen around one out of 14 MTA root-end fillings, and in three out of eight IRM-filled root ends. MTA proved to be a more favorable material in studies where MTA or amalgam was placed as retrograde filling material in infected dog teeth, 2-18 weeks postoperatively (Torabinejad et al.1995) and healthy monkey teeth, 5 months postoperatively (Torabinejad et al.1997).
The present data, indicating that MTA represents a biocompatible substrate to which formative cells can attach and produce new soft or hard tissue, are in agreement with previous data (Torabinejad et al. 1995). This study also supports previous findings that cells cultivated in vitro (Koh et al. 1998, Mitchell et al. 1999, Zhu et al. 2000), or mechanically exposed pulp cells in vivo (Tziafas et al. 2002), can be grown in intimate contact with this cement. Furthermore, these short-term observations show that early tissue healing events to MTA root-end filling material are characterized initially by fibrous connective tissue formation and secondarily by hard tissue repair.
The stimulatory effect of MTA on the biosynthetic activity of periradicular cells results primarily in stimulation of fibroblasts to lay down a fibrous connective tissue and rapid growth of periodontal ligament due to its high healing capacity. Hard tissue formation seems to be activated progressively from the peripheral root walls to the centre of the MTA. Two mechanisms could be suggested for the process leading to hard tissue formation over the MTA: either the fibrous connective tissue is calcified as the postsurgical time interval is increased or cells undergoing differentiation into hard tissue forming cells are progressively migrating between MTA surface and fibrous connective tissue, activating mineralization from the periphery of the root walls to the centre of the MTA filling. Since the nature of the hard tissue has not been specifically characterized, the mechanism for stimulating hard tissue formation over the MTA retrograde filling remains unknown. Nevertheless, it is reasonable to suggest that if activation of cementogenesis occurs after MTA placement at the apex, mineralization of previously formed connective tissue might be excluded as the main mechanism of hard tissue formation.
Based on the results of the present investigation, MTA is a biocompatible material when used in root-end cavities, stimulating repair of periradicular tissues. The nature of formative cells and newly formed hard tissue, as well as the mechanism controlling MTA-activated hard tissue formation, needs to be investigated further.
References.
Friedman S (1991) Retrograde approaches in endodontic therapy. Endodontics and Dental Traumatology 7, 97-107.
Guttman JL, Harrison JW (1994) Surgical Endodontics. St. Louis: IEA Inc., 230.
Koh ET, McDonald F, Pitt Ford TR, Torabinejad M (1998) Cellular response to mineral trioxide aggregate. Journal of Endodontics 24, 543-7.
Mitchell PJC, Pitt Ford TR, Torabinejad M, McDonald F (1999) Osteoblast biocompatibility of mineral trioxide aggregate. Biomaterials 20, 167-73.
Torabinejad M, ChivianN (1999) Clinical applications of mineral trioxide aggregate. Journal of Endodontics 21, 349-53.
Torabinejad M, Hong CU, Lee SJ, Monsef M, Pitt Ford TR (1995) Investigation of mineral trioxide aggregate for root-end filling in dogs. Journal of Endodontics 21, 603-8.
Torabinejad M, Pitt Ford TR, McKendry DJ, Abedi HR, Miller DA, Kariyawasam SP (1997) Histologic assessment ofmineral trioxide aggregate as a root-end filling in monkeys. Journal of Endodontics 23, 225-8.
Tziafas D, Pantelidou O, Alvanou A, Belibasakis G, Papadimitriou S (2002) The dentinogenic activity of mineral trioxide aggregate (MTA) in short-term capping experiments. International Endodontic Journal 35, 245-54.
Zhu Q, Haglund R, Safavi KE, Spangberg LS (2000) Adhesion of human osteoblasts on root-end filling materials. Journal of Endodontics 26, 404-6.