In vitro Results of Scanning Technique on Assessing Cement Thickness and Interfacial Nanoleakage of Luted CAD/CAM-Fabricated Fiber Posts.

BACKGROUND: Fiber posts are broadly used due to their good esthetics and elasticity close to that of dentin, which allows for uniform stress distribution within a root and lowers the possibility of nonrestorable root fractures. AIM AND
OBJECTIVES: The study assessed the layer of cement thickness and interfacial nanoleakage of luted fiber posts which were fabricated with CAD/CAM technology following direct scanning of the post space (DS) method, scanning of a polyether impression of the post space (IS), and scanning of a plaster model of the post space (MS).
METHODOLOGY: Ninety premolars were chosen randomly and were assigned to three groups according to the scanning technique. Posts were computer designed and milled from experimental fiber-reinforced composite blocks.
RESULTS: The mean and standard deviation values of cement thickness, respectively, were: DS 172 ± 39 = m; IS 199 ± 55 = m, and MS MPa 272 ± 81 = m. The fiber posts fabricated following DS technique demonstrated superior performance compared to posts fabricated upon IS and MS, in terms of the post retention. The cement thickness did not differ between DS and IS, whereas in MS group, the cement layer was significantly thicker than in the remaining two groups. The scanning technique did not influence the sealing ability, as all groups showed comparable nanoleakage.
CONCLUSION: Fiber posts fabricated following DS technique demonstrated superior performance. Furthermore, scanning technique did not influence the sealing ability, as all groups showed comparable nanoleakage. Copyright:

INTRODUCTION

Fiber-reinforced composite posts are widely used due to their good esthetics and elasticity close to that of dentin, which allows for uniform stress distribution within a root and lowers the possibility of nonrestorable root fractures. Recently, research has suggested the use of CAD/CAM-fabricated post and core restorations.[123] However, it is nearly impossible to retrieve zirconia post if fracture occurs, which leads to an irreversible tooth failure. Therefore, studies suggested the combination of prefabricated fiber post and zirconia core, as to avoid catastrophic failure caused by zirconia posts and achieve esthetic results using zirconia core. Furthermore, fiber-reinforced composite blocks were used to CAD/CAM fabricate the fiber posts for irregularly shaped or large root canals.[456] Furthermore, according to the literature, digital images of the prepared tooth required for CAD/CAM fabrication of the restoration can be obtained in three ways: by direct intraoral scanning, by scanning the impressions, or by scanning the stone models. Research has shown that both impressions and stone replicas can be digitized with high reliability.[78910] Therefore, the present study aimed to assess the performance of CAD/CAM-fabricated fiber posts into the oval-shaped root canals, fabricated using three different digital data acquisition procedure for assessing the cement thickness surrounding the post.

METHODOLOGY

Ninety human single-rooted premolars extracted due to orthodontic reasons were collected from patients upon informed consent was obtained. All roots were sealed with glass ionomer cement Fuji VII (GC, Tokyo, Japan) and stored in water at 37°C. After 1 week, oval-shaped post space preparations 10 mm in depth were made using size #6 largo burs. The roots were randomly assigned to three groups (n = 30), which differed by the digital data acquisition procedure for the fabrication of the fiber posts using CAD/CAM technology:

Group 1: Direct scanning of the post space (DS). Post space was covered with scan spray (VITA, Bad Säckingen, Germany) and scanned within Eos scanner (Sirona, Bensheim, Germany)

Group 2: Scanning of the impression of the post space (Impression Scanning, IS). Impression of the post space was made with polyether impression material in combination with silicon impression material using stainless steel impression trays (Asa Dental, Bozzano, Italy). Impression was covered with scan spray (VITA) and scanned with in Eos scanner (Sirona, Bensheim, Germany)

Group 3: Scanning the stone model of the post space (model scanning, MS). Impression was made following the same procedure as described for Group 2. Then, stone model was poured with type 4 stone. The stone model was covered with scan spray (VITA) and scanned with in Eos scanner (Sirona, Bensheim, Germany).

24 h after the cementation, six specimens per group were randomly selected. All the roots were sectioned with cutting machine (Isomet; Buehler, Lake Bluff, NY, USA) using diamond disc at slow speed (250 rpw) under water cooling. Thickness of each slice was individually measured using a digital caliper (OrteamS.r.l., Milan, Italy) with an accuracy of 0.01 mm. Digital images of all specimens were taken with a digital microscope (Nikon Shuttle Pix, Tokyo, Japan) and cement thickness around the post within each group.

Statistically significant differences in cement thickness among scanning techniques were assessed. For the assessment of statistically significant differences among root levels within impression scanning and model scanning groups, Kruskal–Wallis analysis of variance was applied, followed by Dunn's multiple range test for the post hoc comparisons, as the data were did not meet the requirement of normal data distribution.

RESULTS

Statistically significant differences in cement thickness were recorded among the scanning techniques. Significantly thicker cement layer was observed in MS group compared to DS and IS groups (P < 0.001), which demonstrated comparable cement layer thicknesses. The mean and standard deviation values of cement thickness, respectively, were: DS 172 ± 39 = m; IS 199 ± 55 = m, and MS MPa 272 ± 81 = m [Table 1]. No statistically significant differences in cement thickness emerged among the root levels in any of the groups [Table 2].

Table 1

Thickness of the cement layer surrounding the posts (μm)

Scanning technique	n	PF	Mean±SD	Median	25%	75%
DS	30	0	172±39	173	159	193
IS	30	0	199±55	190	162	222
MS	30	0	272±81	251	189	332

DS: Direct scanning, IS: Impression scanning, MS: Model scanning, SD: Standard deviation

Table 2

Thickness of the cement layer surrounding the posts (μm) by root canal level within each group

Scanning technique	Post space level	n	PF	Mean±SD
DS	Coronal	10	0	172±23
	Middle	10	0	163±22
	Apical	10	0	159±25
IS	Coronal	10	0	199±63
	Middle	10	0	201±49
	Apical	10	0	185±50
MS	Coronal	10	0	272±76
	Middle	10	0	231±81
	Apical	10	0	161±83

DS: Direct scanning, IS: Impression scanning, MS: Model scanning, SD: Standard deviation

DISCUSSION

The study showed DS technique achieved a higher retention compared to IS and MS techniques. No significant differences were found between two indirect data acquisition procedures, i.e., IS and MS procedures, in terms of postretention into the oval-shaped root canals. Lee et al. scanned stone model of the post space to custom fabricate fiber post and core restoration.[23] In the study by Liu et al.,[4] the wax pattern was prepared from the stone model of the post space was digitized to design the 30D model of fiber post and core. Chen et al.[567] scanned vinylpolysiloxane impressions taken from the die stone model to CAD/CAM fabricate fiber posts. However, no scientific information regarding the efficacy and comparison of different digital acquisition procedures of the post space in particular could be found in the literature. Direct digital scanning (DS) has been recommended as the more logical solution compared to scanning polyether impressions.[8] Moreover, significantly higher accuracy was achieved with the direct digitalization compared to the indirect digitalization of the impressions and the gypsum casts. Syrek et al.[9] also showed statistically significant superior marginal fit of the single crowns received from the direct data capturing compared to the indirect digitization. Although these studies did not investigate scanning procedures of the post spaces, results of the present study are in agreement with their findings in terms of accuracy of the direct and indirect digitalization methods. Nevertheless, according to the other authors, due to the technical features, the extraoral scanning has higher accuracy than the intraoral digitization.[10111213] Patient-related factors such as patient movement, limited intraoral space, intraoral humidity, and saliva flow could cause deviations in the intraoral scans. The mentioned patient-related factors do not apply to the direct scanning technique in the present in vitro study, as the specimens were not scanned in the intraoral environment earlier. In terms of cement thickness measured around the posts, the least accurate was MS method. Significantly, cement layer was thicker and was observed around the posts in the MS group compared to IS and DS groups, which showed comparable results. This finding is, to a certain extent, in line with the study by Güth et al.,[10] although not related to the posts, where more accurate results were achieved by the digitization of the polyether impressions compared to the digitization of the gypsum casts.

CONCLUSION

More laboratory and clinical studies need to be conducted to test the efficacy of direct and indirect digital data acquisition techniques used to scan the irregularly shaped root canals. Regarding the limitations of the current study, it should be mentioned that it was not possible in the study to take into account the mentioned patient-related factors. Therefore, fabrication of fiber posts may represent an additional option for the practitioners already working with a CAD/CAM chair-side system and also for the dental laboratories using the digital workflow. Within the limitations of this study, it can be concluded that the fiber posts fabricated by DS technique demonstrated superior performance compared to posts fabricated upon IS and MS, in terms of postretention. With regard to the thickness of the cement layer, it did not differ between DS and IS, whereas in MS group, the cement layer was significantly thicker than in the other two groups.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.