their consequences may range from small tooth fractures to complete displacement from the socket , characterizing tooth avulsion1 . root surface and endodontic treatments attempt to increase the occurrence of repair and reduce the presence of ankylosis and resorption1 . sodium hypochlorite is employed for removal of necrotic tissues present on the root surface before replantation , followed by washing in saline10 . the use of fluoride strengths the tooth structure by formation of fluorapatite , yet it is toxic to the resorption cells in the hard tissues1,14 . the use of calcium hydroxide as a root canal dressing may avoid or limit inflammatory resorption17 due to its alkaline ph and bactericidal effect15 , and therefore it may eliminate any infection . despite such treatment possibilities , there are still many cases of root resorption , and affected teeth usually must be extracted in a mean period of 4 - 6 years13 . hence , the search for new substances that may inhibit or delay the effects of root resorption is demanding . due to the similar morphology , enzymatic properties and function of cells leading to resorption of dentin , cementum and bone , the processes of root and bone resorption thus , drugs or other substances that may inhibit bone resorption may also be effective for the treatment of root resorption . thus , the newly formed bone becomes more resistant to the action of clast cells and resorption is inhibited3,4,5,19 . gallium nitrate may act on the proton pump present on the clast membrane , on the genetic expression of protein synthesis , or even on the carbonic anhydrase present on those cells2 . bockman , et al.4 ( 1995 ) verified that low doses of gallium nitrate are enough for its activity . assuming that gallium nitrate participates in the formation of hydroxyapatite and that the processes of bone and root resorption are similar , ghazi , et al.6 , in2000 , proposed the use of a gallium nitrate solution as a root canal dressing in teeth susceptible to root resorption . the authors reported that the gallium nitrate solution was capable of diffusing through the dentinal tubules and reach the external root surface . the authors have also reported that the ideal concentration of this solution is 10 m . based on the aspects presented , the purpose of this study was to evaluate the effect of gallium nitrate solution as a root canal dressing in avulsed replanted teeth , compared to calcium hydroxide paste . thirty male wistar rats ( rattus norvegicus , albinus ) weighing approximately 250 - 300 grams were used in this investigation . the study design was revised and approved by the institutional review board on animal experimentation of bauru dental school , university of so paulo , brazil ( process # 032/2003 , october 31 , 2003 ) . the animals were anesthetized by intramuscular injection of a mixture of ketamine ( dopalen , sespo indstria e comrcio ltda , jacare , sp , brasil ) and xylazine ( anasedan , agribrands do brasil ltda , jacare , sp . brasil ) at a dose of 0.05ml/100 g of weight for each drug . asepsis of the anterior portion of the maxilla was performed with periogard ( pfizer ltda , so paulo , sp , brasil ) . the maxillary right central incisor was then extracted , simulating a case of tooth avulsion . the extracted teeth were kept dry , attached to a sheet of pink wax by their crowns for 30 minutes . the dental papillae of teeth were excised with a # 11 surgical blade ( embramac exportao e importao , ribeiro preto , sp , brasil ) for exposure of root canals . the pulp was removed through the apical foramen with a slightly curved # 15 flexofile ( dentsply- maillefer , ballaigues , switzerland ) . canals were thoroughly irrigated with 1% hypochlorite solution ( probem produtos farmacuticos e odontolgicos ltda , catanduva , sp , brasil ) using a luer look syringe and a 30x4 gauge needle . after preparation , the teeth were immersed in 50ml of 1% hypochlorite solution for 30 minutes , washed in sterile saline and then immersed in 20ml of sodium fluoride solution ( ph 5.5 ) ( pharmcia specfica , bauru , so paulo , brasil ) for 20 minutes . the sodium fluoride solution was prepared from a mixture of 0.1 m phosphoric acid ( ph 2 ) and 2% sodium fluoride ( ph 8) . root canals were further irrigated with sterile saline and filled with edta ( odahcam dentsply indstria e comrcio ltda , petrpolis , rio de janeiro , brasil ) for 3 minutes and once again washed with sterile saline . suction was performed with a 30x4 gauge needle attached to a luer look syringe and the root canals were dried with sterile absorbent paper points ( tanariman industrial ltda , manacapuru , amazonas , brasil ) . the teeth were divided into two groups according to the root canal dressing used , as follows : group i - 10 m gallium nitrate solution ( acros organics , pittsburg , usa ; cas n 13494 - 90 - 1 ) ; and group ii - calcium hydroxide paste ( s.s . the animals received a single dose of 20,000 u.i . of benzathine g penicillin via intramuscular injection . five animals in each group were killed at 15 , 30 and 60 days after replantation by anesthetic overdose . the right side of the maxilla was separated from the left through the median line with a # 15 surgical blade . the maxilla was further sectioned close to the third molar to separate the hemimaxilla containing the replanted tooth . the specimens were fixed in 10% buffered formalin for seven days and decalcified in 4.13% edta ( ph 7 ) . the specimens were then processed , embedded in paraffin , and transversally sectioned through the cervical , middle and apical tooth thirds ; 5-m sections were obtained at each 100m with a microtome , adding up to 20 sections for each specimen . the following parameters were considered for microscopic analysis : integrity of tooth structure , presence of cementum , characteristics of the connective tissue formed in the periodontal space , presence of tooth ankylosis and occurrence of inflammatory or replacement resorption . morphometric analysis was also performed , with aid of the imagelab 2000 software version 2.4 ( diracom 3 , vargem grande so sul , sp , brasil ) , specific for measuring areas and perimeters . fifteen histological sections of each study period were photographed with a digital camera ( jvc tk-1270 color video camera , tokyo , japo ) attached to a microscope ( carl zeiss , axiolab , jena , germany ) connected to a pc computer . the images were stored as figures ( tif 24 ) for analysis in the imagelab software . the perimeter of areas showing ankylosis , connective tissue formed in the periodontal space , the amount of remaining cementum and the areas of inflammatory or replacement resorption were measured . the results were organized in tables and statistically analyzed by the kruskal - wallis test at a significance level of 5% . whenever significant differences were found , the dunn 's test was used to assay individual comparisons . analysis of histological sections of specimens in group i at 15 days revealed formation of a dense connective tissue , parallel ( figure 1 ) or perpendicular to the root surface ( figure 2 ) . the presence of a periodontal ligament - like connective tissue ( perpendicular direction ) was decreased over time and was no longer observed at 60 days ( table 1 ) ( figure 3 ) . tooth ankylosis was observed in all study periods in both groups ( table 1 ) . is statistically significantly different from examination of the root surface revealed the presence of cementum covering great part of the root surface , which decreased over time in both groups ( table 2 ) . inflammatory resorption lacunae were observed in all study periods ( table 2 ) ( figure 1 and 3 ) . in group i , replacement resorption lacunae were present at 60 days , different from the 15 and 30-day periods , when no replacement resorption was observed ( table 2 ) . in group ii , replacement resorption was present at 30 and 60 days ( table 2 ) . is statistically significantly different from comparison of results obtained in groups i and ii revealed that the presence of tooth ankylosis and replacement resorption lacunae was more evident in group ii at 30 days ( p<0.05 ) . in general , no statistically significant differences were observed between groups i and ii , demonstrating a similar mechanism of action of both chemicals when used as root canal dressings ( tables 1 and 2 ) . the frequency of occurrence of root resorption in the present study groups was low , although resorption events were increasingly observed over time . this emphasizes the characteristic of gallium nitrate2,3,4,5,6,19 and calcium hydroxide7,8,16,18 in limiting the resorption process . table 2 shows the effectiveness of gallium nitrate in inhibiting replacement resorption at 15 and 30 days , since resorption was greatly increased at 60 days ( p<0.05 ) . this observation may indicate the need for placement of successive dressings , which might inhibit the occurrence of replacement resorption for a longer period . the presence of cementum could be detected on the root surface of most specimens in both groups . this suggests the efficacy of sodium hypochlorite for removal of necrotic periodontal ligament present on the root surface with no injuries to the cementum layer9 . a direct proportion between the occurrence of root resorption and the absence of cementum was also noticed ( table 2 ) . regarding the histological events occurring in the periodontal space , both groups exhibited tooth ankylosis . the occurrence of tooth ankylosis is related to the loss of epithelial rests of malassez present in the periodontal ligament as a consequence of tooth avulsion , since these cells are responsible for maintaining the periodontal space11 . the low frequency of tooth ankylosis affecting the present study groups is described in table 1 . this finding may have influenced the occurrence of replacement resorption , which is a consequence of tooth ankylosis1,12,17 . the results of this study also demonstrate discrete presence of periodontal ligament - like connective tissue at 30 and 60 days ( table 1 ) , which was considerably higher at 15 days . this may be explained by the presence of periodontal tissue remnants from the alveolar wall reaching the root surface of the replanted tooth , and not by formation of new tissue . such periodontal tissue remnants were replaced over time by a newly formed connective tissue arranged in parallel direction to the root surface . according to the present results , both gallium nitrate and calcium hydroxide were able to limit root resorption in teeth submitted to replantation , yet they did not prevent its occurrence . concerning the periodontal space , formation of a periodontal ligament - like connective tissue was not favored in any group . hence , it may be concluded that the gallium nitrate solution and calcium hydroxide paste demonstrated similar performance .
the purpose of this study was to test a gallium nitrate solution , a resorption inhibitor , employed as a root canal dressing in teeth submitted to late replantation . 
 thirty maxillary right central incisors of rats were avulsed and kept dry for thirty minutes . 
 the teeth were instrumented and the root surfaces were treated with 1% hypochlorite solution followed by application of 2% sodium fluoride . 
 thereafter , the teeth were divided into two groups according to the root canal dressing : group i , solution of gallium nitrate ; and group ii , calcium hydroxide paste . 
 the teeth were then replanted in their respective sockets . 
 the animals were killed at 15 , 30 and 60 days after replantation and the samples were processed for morphometric and microscopic analysis . 
 the results demonstrated that the gallium nitrate solution and the calcium hydroxide paste limited the root resorption , yet they did not impair its occurrence . it may be concluded that gallium nitrate solution and calcium hydroxide paste demonstrated similar performance .