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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 5  »  Effect of three root canal sealers on the retentive strength of endodontic posts luted with a resin cement
Effect of three root canal sealers on the retentive strength of endodontic posts luted with a resin cement
Results - Discussion - References.



Results.
Results are shown in Figure 3. The unobturated controls had a significantly higher mean retention strength value (MRSV) than the eugenol-containing sealer group ( P = 0.017). No significant differences existed between any other groups (all groups using sealer had equivalent MRSV). Modes of failure varied appreciably between and within groups (Table 1).

Table 1. Failure modes.

Failure modes
a, Cohesive failure of post;
b, cohesive failure of cement;
c, cohesive failure of tooth;
d, failure at post-cement interface;
e, failure at cement-tooth interface.

Discussion.
Our original expectation was that unobturated controls would have higher MRSV than the eugenol-containing sealer group, and this was borne out. The failure modes observed in these two groups were clearly different (Table 1). The quality of the bond in the control group appeared to be superior, because only two of this group’s failures occurred at the tooth–cement interface. This suggested that the bond of the cement to the root canal wall dentine generally remained intact and thus was not the limiting factor in retention. Conversely, 14 of the 16 eugenol sealer samples failed cleanly at the tooth– cement interface, implying that some sealer component may have remained behind and interfered with effective dentine bonding.
The calcium hydroxide and resin sealer groups had patterns of failure between those of the control and eugenol groups, yet were not significantly different from either group in MRSV. Failures that occurred at the cement–tooth interface generally had lower retention strengths than failures at the post–cement interface, but this was not always true. Unlike the eugenol sealer samples, the resin and calcium hydroxide sealer groups frequently had small remnants of sealer and guttapercha attached to samples that failed at the cement– tooth interface (Fig. 4). These tended to occur most often in canals with more pronounced elliptical shapes. Although admittedly difficult to access and remove, these remnants may have resulted in reduced retention strength simply through decreasing the available bonding surface area.

Figure 3. Retention strength values.

Retention strength values

Figure 4. Sealer and gutta-percha remain attached to cement.

Sealer and gutta-percha remain attached to cement

Our overall results concur with those of Schwartz et al. (1998) and Boone et al. (2001), who reported no differences in post retention between eugenol-based and resinbased sealers using similar composite cements. Although our study protocol was similar to both of these studies, neither of them used unobturated controls for comparison. Burns et al. (2000) employed unobturated controls, used the same posts and cement as our study, and compared eugenol- and calcium hydroxide-based sealers. They also found no significant differences between the two sealer groups, but their unobturated controls bonded no stronger than either sealer group. Their post space preparation and post cementation were done immediately following obturation and used matching sizes of Parapost drills and posts, with MRSV considerably lower than reported in our study. Similarly, Adamian et al. (2001) found no differences between eugenol- and resinbased sealers using Paraposts with a dual cure resin cement. They also found no differences between the sealer groups and controls obturated without sealer. Their post was two sizes smaller than the one used in the present study; the MRSV were also lower.
The MRSV in our study were considerably higher than those in similar reports (Schwartz et al. 1998, Love & Purton 1998, Stockton et al. 2000, Cohen et al. 2000, Burns et al. 2000, Bergeron et al. 2001, Boone et al. 2001, Adamian et al. 2001). As examples, MRSV for AH-26/ Panavia were reported at 151.88 N (Schwartz et al. 1998) and ~245 N (Bergeron et al. 2001), whereas our MRSV for this combination was 476.02 N (48.54 kg). Similarly, Bergeron et al. found that MRSV for Roth’s 801 sealer/Panavia were ~175 N, whilst we reported 423.04 N (43.14 kg) using an equivalent combination. The other studies consistently reported lower MRSV than these two reports. The only study reporting comparable MRSV was that of Paschal et al. (1997). Whilst no two study protocols use absolutely identical methods, our finding of higher MRSV may relate to an observation made during our pilot study.
During the pilot study, size 5 Paraposts (1.25 mm diameter) were cemented in #5 Gates–Glidden drill preparation spaces (1.30 mm), but on testing, produced very low MRSV (6.8–13.6 kg). Examination of these failed specimens revealed frequent contact of the posts’ serrations against the canal walls, implying that the cement film thickness (~25 m) using this technique was inadequate. The post preparation diameter was subsequently enlarged using size 6 Gates–Glidden drills, which increased the film thickness to ~125 m (using size 5 posts). This single change resulted in the markedly higher MRSV seen in Fig. 3.
We had not anticipated that the intended 25 m cement film thickness would prove to be inadequate, so following completion of the study, we measured our post space drills and posts with an electronic digital caliper (Max-Cal, Fowler/NSK, Newton, MA, USA). We discovered that the Gates–Glidden drills were smaller than ISO specifications (size 5 drill ISO = 1.30 mm, actual diameter = 1.24 mm; size 6 drill ISO = 1.50 mm, actual diameter = 1.45 mm). The Paraposts more closely reflected the manufacturer’s stated dimension (size 5 post specification = 1.25 mm, actual diameter 1.24 mm). The cement thickness in the initial pilot study was therefore well under 5 m, and in the main study approximately 105 m.
In each investigation that reported lower MRSV, matched sets of preparation drills and posts were used, and we speculate that the intimate fit produced with matched drill and post sets may not provide adequate space for the luting agent to develop its maximal material properties. In addition to reporting much lower MRSV, Burns et al. (2000) found that 92% (47/51) of their samples, including the unobturated controls, failed at the cement–tooth interface. By comparison, our unobturated controls only failed at the cement–tooth interface in 12.5% (2/16) of samples.
The speculation that cement film thickness should be considerably increased certainly opposes generally accepted theory, although some corroborative evidence exists (Assif & Bleicher 1986, Chan et al. 1993). This issue should be examined further. We have begun a protocol, using the basic study design from this report, which will compare four thicknesses of Panavia 21, ranging between 15 m and 130 m.
In the present study, the eugenol-containing sealer group, whilst equivalent to the other sealer groups in our study, had lower MRSV than the control group. Whilst the control group did not use a clinically relevant technique, some improvement in retention with eugenolbased sealers may be possible.
One area for consideration involves the length of time that eugenol-containing materials remained in contact with dentine prior to their removal. Hume (1988) showed that the release of eugenol from ZOE into dentine occurred rapidly during the first 24 h, then decreased slowly with a detectable release still present at 2 weeks. This suggests that if removal of eugenol-containing sealer from the canal walls can be effectively accomplished immediately following obturation, MRSV might be improved to the level where failure occurs elsewhere than at the cement–tooth interface. The release pattern of eugenol after removal of eugenol-containing materials as well as the concentration of eugenol necessary to adversely affect composite polymerization, however, has not yet been established (Ganss & Jung 1998). We have therefore begun a study to compare the retention strength of posts cemented into spaces prepared immediately after obturation and at 1 and 4 weeks following obturation. This study will use the same eugenolcontaining sealer and composite cement employed in this investigation.
Another possibility is that our results are specific for Panavia 21, and that varying results might be seen with other types of cement. Many retention studies have been done comparing cement types, but very few reports have examined post retention in obturated canals. Although study methodologies differ, several reports are worth reviewing. Schwartz et al. (1998) found zinc phosphate cement to have greater MRSV than Panavia whether eugenol- or resin-based sealers were used. Using a nearly identical protocol, Bergeron et al. (2001) also reported no differences between zinc phosphate cement and Panavia 21 cements. These two studies used a different canal cleansing regimen, slightly different post design, and thinner cement film than that used in our study. Russo et al. (1999) compared the retention of cast posts luted with five different cements into canals obturated with a eugenol-based sealer. Panavia 21 and a compomer cement were more retentive than the zinc phosphate, resin-modified glass ionomer, and dual-cure composite cements tested. The time sequencing of post preparation and cementation was not stated, but appeared to be immediate.
Using the same basic protocol used in this study, we will subsequently compare the retention properties of zinc phosphate, glass ionomer, conventional BIS-GMA and/or urethane dimethacrylate cements against unobturated controls and Panavia 21.
It is also conceivable that our comparatively higher MRSV could have been at least partially due to our method of canal cleansing. Differing methods of guttapercha/ sealant removal and canal cleansing/etching may deserve further investigation. Boone et al. (2001) stated that obtaining a clean bonding substrate may be the most critical factor in achieving success with resin cements. We have planned a further study that will compare the effectiveness of several different chemical cleansing/ preparation regimens on the removal of gutta-percha and sealer remnants from canal wall dentine.

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