The lack of treatment of a deciduous tooth with irreversible pulpitis or pulpal necrosis can cause damage to the succedaneous tooth (e.g., enamel hypomineralization or hypoplasia) [32
] and produce negative impacts on the child's oral health-related quality of life (e.g., pain, missed school days and difficulty in chewing) [33
]. Therefore, teeth presenting these conditions should be extracted or subjected to root canal treatment [4
Various techniques for the endodontic treatment of deciduous teeth have been described [18
]. Traditionally, ZOE has been the material of choice for filling the root canals of deciduous teeth [36
], and until 2008 it was the only material explicitly recommended in the clinical guidelines developed by the American Academy of Pediatric Dentistry (AAPD) [2
]. In 2009, based on studies recently published, the AAPD guidelines began to cite iodoform-based pastes as suitable alternatives to ZOE [3
]. In addition, the results of a survey of diplomates of the American Board of Pediatric Dentistry and US predoctoral pediatric dental program directors conducted in 2005 showed that significantly fewer diplomates and directors advocated ZOE for root canal filling when compared to directors surveyed in 1997. This may be due to concerns about the possible detrimental effects of residual ZOE filler particles on the succedaneous teeth [20
Only two of the six studies included in the present review reported significant statistical differences between the frequency of successful cases in the test and control groups at the end of the followup period [8
]. However, in all of the studies, sample sizes were small and this may have resulted in a very low power to detect clinically meaningful treatment effects. The success rates of the two trials [8
] that included anterior teeth were similar to the success rates of the trials that included only posterior teeth. In only one study [9
] the type of tooth was considered in the analysis, and no statistically significant differences between the success rates of endodontic treatment performed in upper and lower molars were found.
One trial [8
] found that Vitapex was more effective than ZOE because it produced a greater decrease in abnormal tooth mobility and in pre-existent bone radiolucency. Furthermore, at the end of the followup period, no evidence of extruded filling material was observed in the Vitapex group whereas particles of extruded material had not changed in size in a few patients of the ZOE group. The other study [9
] concluded that both ZOE and Vitapex were 100% successful, but in the Vitapex group, six teeth needed retreatment because of complete resorption of the root canal filling material, and in the ZOE group, of the six teeth overfilled, only two showed complete resorption of the extruded material. In the same study, the success rates of ZOE and a calcium hydroxide paste were compared, and ZOE performed significantly (P
< .05) better than the root canal filling material containing calcium hydroxide.
One study found significant statistical differences between the frequency of radiographic success in the test and control groups, at the 6-month followup, but by 12 months this difference had disappeared [29
The six trials included adopted similar criteria for inclusion and exclusion of participants and used the same definition of clinical success. However, the definitions of radiographic success were so diverse that cases considered successful in one study [30
] would be classified as failures by the standards employed by two other studies [9
]. All six studies were also heterogeneous in terms of treatment techniques (i.e., number of appointments, irrigating solutions, and type of tooth restoration). In one [13
] of the studies the materials used to make the final restorations did not provide an adequate barrier against bacterial penetration and it has been shown that the absence of proper coronal sealing is associated with the failure of endodontic treatment [35
]. Pooling the results of the included studies was thus considered inappropriate.
Potential threats found to the internal validity of the studies are also worth mentioning. In clinical trials, the comparability between the test and control groups, in relation to factors other than the intervention that might influence the outcome, is crucial and is usually obtained through an adequate process of randomization in treatment allocation. Only one study properly randomized patients to treatment groups and also included just one tooth per child [8
]. However, the characteristics of the treatment groups at baseline were not described in the article, thus limiting one's ability to assess the success of the randomization process. Other features of the included studies, such as lack of masking and calibration of the examiners, may also have biased their results. Equally important is the fact that three [13
] of the selected studies had less than one year of followup.
The Cochrane review [26
], published in 2003, provided a reasonably comprehensive picture of the state of the art, but it is important, seven years out, to again raise a red flag about the lack of studies with acceptable methodological quality.
Altogether, the results of this critical appraisal of the studies indexed in the Medline database comparing ZOE with other root canal filling materials for deciduous teeth have shown that randomized clinical trials designed as recommended by the Consolidated Standards for Reporting Trials (CONSORT) [27
] are lacking in this field. Future studies should also seek to address long-term effects of treatment (i.e., damage to dental enamel or deflection of succedaneous tooth) and choose outcome measures clinically meaningful to the patients and their caregivers (i.e., premature extraction of deciduous teeth, a need for dental restoration in the successor tooth or a need for orthodontic treatment).