amalgam is a restorative material especially suitable for classes i and ii restorations in teeth that encounter heavy chewing forces .
the advantages of amalgam restorations include resistance to wear , tolerance to a wide range of clinical placement conditions , and excellent load - bearing properties [ 13 ] . however , amalgam restorations may also present degradation in the intraoral environment due to secondary caries , fracture , marginal breakdown , and wear [ 46 ] . the traditional solution for those failures has been the complete replacement of the restorations , which may also include minor imperfections in the restorations , and replacement of defective restorations represents a major concern in dental practice , reaching up to 60% of operative dentistry interventions . consequently
, the median survival time ( mst ) of amalgam varies from 2 to 11 years , but most studies place it at over 5 years [ 810 ] .  
complete replacement of restorations has the disadvantages of being time consuming , unnecessary removal of healthy tooth tissue , enlarging preparations and restoration sizes [ 11 , 12 ] , the risk of converting the restoration to an indirect restoration , and the possibility of major injuries in pulp tissues [ 1214 ] . during the last years
, new strategies , such as repair and refinishing of localized defects , have shown improvement in the quality of the defective restorations and increased longevity of restorations with minimal intervention [ 1517 ] .
repair rather than replacement of failing restorations is a part of minimally invasive dentistry , preservation of natural tooth structure , early detection of carious lesions , nonsurgical interventions , and a modified surgical approach that includes delayed restoration and smaller tooth preparations with modified cavity designs .
the aim of this clinical trial was to assess the long - term performance of two minimally invasive clinical procedures , repair and refinishing , as treatments for localized defects of classes i and ii amalgam restorations .
the institutional research and ethical board of the dental school at the university of chile approved this randomized clinical trial ( project pri - odo-0207 ) .
fifty - two patients , 26 female ( 50% ) and 26 male ( 50% ) , were recruited at the operative dentistry clinic at the dental school , university of chile , santiago .
patients were aged 18 through 80 years ( mean age , 28.3  18.1 years ) .
a total of 160 defective restorations ( 97 class i , 63 class ii ) presenting one or more clinical features that deviated from ideal were included in the study .
the restorations ' clinical conditions ranked from bravo to charlie according to the united states public health service ( usphs)/ryge criteria ( see table 1 ) .  
patients with localized deficiencies of amalgam restorations that were clinically judged to be suitable for repair or refinishing according to usphs criteria ( table 1 ) , patients with more than 20 teeth , restorations in functional occlusion with an opposing natural tooth and at least one proximal contact area with an adjacent tooth , patients older than 18 years old , and patients who signed the consent form and completed a registration form were included in the study .   patients with contraindications for regular dental treatment based on their medical history , patients who had special aesthetic requirements that could not be solved by the alternative treatments , patients with xerostomia or who were taking medication that significantly decreased salivary flow , patients with high caries risk , and patients with psychiatric or physical diseases that interfered with tooth hygiene were excluded from the study .  
one hundred sixty defective restorations were evaluated in accordance with usphs criteria and assigned according to the following criteria.restorations with clinically diagnosed secondary caries ( charlie ) or undercontoured anatomical form defects ( bravo ) were randomly assigned to the repair or replacement group ( randomization was performed by power analysis and sample size system in pass software v. 2008 , keysville , ut , usa ) .
diagnosis of active secondary caries was made according to ekstrand 's criteria .restorations with overcontoured anatomic form , luster , or roughness defects were randomly assigned to the refinishing ( bravo and charlie ) or no - treatment group ( bravo).restorations with marginal defects ( bravo ) were randomly assigned to either the repair , refinishing , replacement , or no - treatment group .
the treatment groups were labeled ( a ) : repair ( n = 19 ) ; ( b ) : refinishing ( n = 64 ) ; ( c ) : replacement ( n = 21 ) ; ( d ) : no treatment ( n = 56 ) . restorations with clinically diagnosed secondary caries ( charlie ) or undercontoured anatomical form defects ( bravo )
were randomly assigned to the repair or replacement group ( randomization was performed by power analysis and sample size system in pass software v. 2008 , keysville , ut , usa ) .
restorations with overcontoured anatomic form , luster , or roughness defects were randomly assigned to the refinishing ( bravo and charlie ) or no - treatment group ( bravo ) .
restorations with marginal defects ( bravo ) were randomly assigned to either the repair , refinishing , replacement , or no - treatment group .  
two examiners underwent calibration exercises ( jm and ef , cohen 's kappa interexaminer coefficient 0.74 at baseline and 0.87 at five years ) .
the examiners assessed the restorations independently by direct visual and tactile examination ( mouth mirror number 5 , hu friedy mfg .
chicago , il , usa , and explorer number 23 hu friedy ) and indirectly by radiographic examination ( bite wing ) at baseline ( immediately after treatment ) and each year up to five years after treatment .
the four examined parameters were marginal adaptation ( ma ) , anatomic form ( a ) , surface roughness ( r ) , and secondary caries ( sc ) ( table 1 ) . if any difference was recorded between the two examiners , and if they did not reach an agreement , a third clinician who also underwent calibration exercises ( gm ) made the final decision .   a change from bravo to alpha
was considered an improvement , and a change from alpha to bravo represented deterioration .  

repair : carbide burs were used to explore the defective margins of the restorations , beginning with the removal of part of the amalgam restorative material adjacent to the defect . once this material was removed and the exploratory cavity preparation did not include any stained or soft tooth tissues , a dispersed - phase amalgam ( original d , wykle research , inc , carson city , nv , usa ) was used to repair the preparation .
refinishing : defective areas of the amalgam restoration were smoothed using carbide burs ( numbers 12 and 30 , brasseler usa , savannah , ga , usa ) . on the occlusal and buccal / lingual surfaces ,
silicone - impregnated points ( brownie / greenie / supergreenie , shofu dental corporation , menlo park , ca , usa ) were used for polishing .
when the proximal area was affected , the defective areas were smoothed with aluminum oxide finishing strips ( sof - lex , 3 m espe).replacement : the defective restoration was totally removed and replaced with a new amalgam ( tytin , kerr corporation , orange , ca , usa ) .
rubber dam isolation was used for this procedure.no treatment : the defective amalgam restorations did not receive any treatment.patients were recalled each year for up to five years for clinical evaluation by the same blinded examiners , applying the same criteria used at baseline .
repair : carbide burs were used to explore the defective margins of the restorations , beginning with the removal of part of the amalgam restorative material adjacent to the defect . once this material was removed and the exploratory cavity preparation did not include any stained or soft tooth tissues , a dispersed - phase amalgam ( original d , wykle research , inc , carson city , nv , usa ) was used to repair the preparation .
rubber dam isolation was used for this procedure .   refinishing : defective areas of the amalgam restoration
were smoothed using carbide burs ( numbers 12 and 30 , brasseler usa , savannah , ga , usa ) . on the occlusal and buccal / lingual surfaces ,
silicone - impregnated points ( brownie / greenie / supergreenie , shofu dental corporation , menlo park , ca , usa ) were used for polishing .
when the proximal area was affected , the defective areas were smoothed with aluminum oxide finishing strips ( sof - lex , 3 m espe ) .
replacement : the defective restoration was totally removed and replaced with a new amalgam ( tytin , kerr corporation , orange , ca , usa ) .
the results of each group in terms of degradation were analyzed by the wilcoxon nonparametric test to compare the pre- and postoperative conditions .
additionally , the performance of all groups was contrasted using the z test to determine the differences between upgrade and downgrade restoration quality .
the mst of the restorations was determined by the kaplan - meier test at each annual recall examination .
from the original cohort of 52 patients with 160 restorations , 45 patients with 108 restorations were assessed ( 67.5% ) at the fifth year ( 66 class i and 42 class ii restorations ) .
the distribution of the restorations in the groups was as follows : refinishing ( n = 46 ) , repair ( n = 11 ) , replacement ( n = 15 ) , and no treatment ( n = 36 ) .   during the five - year followup , 52 restorations ( 32.5% )
were lost to follow up due to orthodontic treatment where restorations were covered by metallic bands ( n = 3 ) , address changes or no attendance ( n = 39 ) , and restorations that presented a charlie rating during a prior study observation ( n = 10 ) . the latter were fully replaced and removed from the study .
the results are presented as percentages of alpha ratings in the different groups . after an initial improvement in all treatment groups , all groups showed a trend to downgrade during the observation period in all parameters , except in secondary caries . throughout the observation period ,
a charlie rating was observed in only a small number of restorations ( 10/160 , 6.25% ) : 3 at the first year , 2 at the second , 2 at the third , 1 at the fourth , and 2 at the fifth .
the refinishing and repair groups presented no difference in alpha - rated restorations between the baseline and the fifth - year examination regarding marginal adaptation .
in contrast , the replacement group presented more alpha - rated restorations at five years than at baseline ( p = 0.021 ) .
no - treatment group showed a reduction of alpha - rated restorations between the baseline and five - year evaluations ( p = 0.029 ) ( figure 1 ) .
the kaplan - meier test showed that the refinished and no - treatment groups showed a median survival time ( mst ) of three years for marginal adaptation after five years .
the repair and replacement groups each showed a mst of four years ( figure 8) . regarding the anatomic form parameter , the three treated groups showed no difference between baseline and five years .
no treated group showed a downgrade in alpha - rated restorations ( figure 2 ) .
all treatment groups maintained the same clinical condition as presented at baseline ( p > 0.05 ) .
no treated group showed a significant downgrade in surface roughness after five years ( p0.005 ) ( figure 3 ) .
the refinishing , replacement and no - treatment groups showed a mst of five years , and the repair group showed a mst of four years ( figure 5 ) .
the repair group showed a nonsignificant improvement in secondary caries after five years ( p = 0.157 ) , while the replacement group had a significant improvement ( p = 0.046 ) .
the refinishing ( n = 1 ) , and no - treatment groups ( n = 2 ) presented a low rate of caries lesions ( figure 4 ) .
amalgam longevity is an important issue for patients , governments , and dentists to define the cost of dental treatment .
minimal - intervention dentistry , such as repair or refinishing of localized defects of restorations , could increase the longevity of the amalgam restorations and reduce patient stress regarding treatment cost .
repair and refinishing showed a high level of clinical acceptance by patients in this study .
most of the restorations ' performance was assessed as clinically acceptable , including alpha or bravo ratings in all experimental groups .
the success of repair and refinishing allowed a significant increase in the lifetime of the original restorations with minimal intervention , as most of these procedures could be performed without dental anesthesia .   in general ,
the results show that repairing and refinishing restorations with localized defects are effective and increase the mst of the restorations .
this study showed an association between the type of treatment and prognosis , assuming clinical criteria for restoration repair instead of traditional replacement based on quality assessment and the mst of those procedures .
the choice of refinishing or repair resulted in tooth tissue preservation instead of unnecessary tooth structure removal , as in the case of the replacement group [ 17 , 19 , 20 ] .
the present study did not show a biological risk for the teeth : there were no tooth fractures , a low rate of restoration failures , and no pulp injuries .
the main reason for restoration failures is secondary caries lesions located at the margins of the restorations .
these lesions should be clinically differentiated from stained and ditched margins in order to find soft dental tissue or carious areas .
random assignation in our study was carried out after considering the types of restoration defects .
it was not possible to allocate the restorations completely randomly because there are ethical concerns with , for example , secondary caries .
additionally , some localized defects will not improve with minimally invasive treatment , for instance in the case of undercontoured restorations in the refinishing group .
only recently have a number of dental schools included restoration repair in their educational programs , which could explain why repair is not popular yet in operative dentistry .  
after five years , 96.3% of the restorations presented alpha ratings for secondary caries , with no significant differences between repair and replacement ( see case of repair figures 915 ) . according to this observation
, repair must be considered a conservative procedure and can be used safely when there is a small caries lesion with easy access .
this finding is consistent with previous research , which indicated that the presence of secondary caries is a localized process originating from the surface and not involving the entire restoration [ 2225 ]
. fifty percent of the repaired restorations had an alpha rating after 2 years in marginal adaptation .
this might be explained by the fact that other clinical conditions , such as cavity design , occlusal contacts , and bruxism , were not modified . if marginal adaptations fail , it is possible to reduce marginal discrepancies by applying other minimally invasive procedures , such as marginal flowable resins or marginal sealant , which is a practical , easy , and fast alternative to sealing the gap with pits and fissure sealant .
marginal sealants perform better than repair over time [ 11 , 17 , 19 , 20 ] .  
full replacement of restorations promotes less preservation of healthy tooth tissues and is also more time consuming than restoration repair , and yet it is the most prevalent procedure in general dental practice [ 7 , 1114 , 26 ] .
a recent study suggests that repaired restorations could outlast restorations that have been replaced , and one possible reason for this is that most of the original restoration is kept intact .
although the use of resin - based composite to repair amalgam restorations is considered an appropriate process whenever a proper surface conditioned technique is applied [ 27 , 28 ] , restorations were repaired with amalgam based on the low cost and long - term effectiveness of this material .   fifty percent of the restorations maintained alpha - rated anatomic form and surface roughness for at least 4 years in restorations that were refinished .
these two parameters were the ones that suffered the greatest deterioration over time : 30.4% and 23.9% of restorations were alpha - rated for these two parameters after 5 years , compared to 8.3% and 30.6% , respectively , in the control group ( p < 0.001 ) .  
refinishing could be considered a preventive measure because it reduces the possibility of plaque accumulation , as the restoration may achieve an anatomical form similar to the tooth , making it favorable for improvements towards restoration function and longevity [ 19 , 3032 ] .
prior to the refinishing procedure , radiographic examination is mandatory to establish the thickness of the restorations because in shallow restorations the dentin could be exposed or the mechanical properties of the restoration could be impaired .
this problem could be avoided by analyzing bite - wing radiographs in the same way that caries lesions are detected . in general , refurbishing is recommended only for improving contoured defects .
full replacement of the restoration did not present secondary caries during the study period , similar to repair . in general
, replacement showed the same trend of downgrade as observed in other groups , but it had an increased alpha rating for marginal adaptation ( greater than the refinishing and no - treatment groups ) , and it had a similar performance to the repair group . regarding secondary caries and surface roughness ,
the most relevant downgrade was observed in the no - treatment group regarding anatomic form .
this finding support the idea that it is necessary to treat small localized defects of amalgam restorations in order to prevent future damage .
for this reason , it could be considered the only parameter for which it is possible to compare the performance of the four treatments . in this context , the replacement group presented the best performance , as it was the only one that showed more alpha - rated restorations at five years than at baseline .
the no - treatment group showed a significant downgrade in the period of the study .
the present five - year clinical study supports the concept that repair treatment is as effective as total replacement of restorations with localized defects and reduces biological costs to the patient .
minimally invasive treatments of defective amalgam restorations presented similar results to the restorations that were replaced .
 replacement of dental restorations has been the traditional treatment for defective restorations . 
 this five - year prospective clinical trial evaluated amalgam restorations with localized defects that were treated by means of repair or refurbishing . 
 fifty - two patients ( 50% female and 50% male , mean age 28.3  18.1 
 years , range 1880 ) with 160 class i and class ii defective restorations were included . 
 the study focused on the application of two minimally invasive treatments for localized restoration defects and compared these with no treatment and total replacement as negative and positive controls , respectively . 
 restorations were assessed by two calibrated examiners according to modified u.s . 
 public health service criteria , including marginal adaptation , anatomic form , secondary caries , and roughness . at five years 
 , recall was examined in 45 patients with 108 restorations ( 67.5% ) . 
 the results suggest that repair treatment is as effective as total replacement of restorations with localized defects , reducing biological costs to the patient and providing new tools to the clinician . 
 refinishing restoration is a useful treatment for localized anatomic form defects . 
1. Introduction
2. Methods and Materials
3. Results
4. Discussion
5. Conclusions
6. Clinical Relevance