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In-vivo microbiologic evaluation of polytetrafluoroethylene and cotton as endodontic spacer materials

July 14, 2020

Filed under: Uncategorized — tntadmin @ 4:56 pm

Tina Olsson, DMD, MSD1/Daniel Chan, DDS, MS2/James D. Johnson, DDS, MS3/Avina Paranjpe, BDS, MS, MSD, PhD4

Objective: Spacers are commonly placed between the canalorifice and the temporary material between endodontic treatment appointments. This prevents the temporary restoration material from obstructing the canal orifices and allows for easy removal. Various endodontic spacers are currently used, including polytetrafluoroethylene (PTFE) tape. Previous in-vitro studies have demonstrated the advantages of using PTFE over using cotton; however, no in-vivo studies have demonstrated this.Hence, the purpose of this study was to evaluate which spacer showed less bacterial leakage between endodontic treatments.
Method and Materials: Fifty patients participated in the study and were randomly assigned to either the cotton or the PTFE group. Root canal treatments were completed in two appointments.

Cotton and PTFE spacers were collected after a2- to 4- week time interval between the first and second appointments.Samples were incubated on agar plates for 48 hours and then evaluated for presence of microbial growth. Colony forming units (CFUs) were counted for each of the samples. The results were analyzed using non parametric statistical tests.Results: Fifteen of the 24 cotton spacers and two of the 24 PTFE spacers were positive for bacterial growth. Conclusion: Cotton fibers exposed to the oral environment could potentially wick contaminants into the pulp chamber. The tendency of cotton to distort under masticatory forces may allow disruption of the temporary material’s marginal seal. Based on the results of this study, the use of PTFE is strongly recommended over cotton as an endodontic spacer material. PTFE performed better than cotton in this in-vivo microbial study. (Quintessence Int 2017;48:609–614; doi: 10.3290/j.qi.a38679)

Temporary coronal restorations and endodontic spacers are integral parts of a two-appointment endodontic procedure. The temporary restorations include materials like Cavit, IRM, amalgam, composite resin, and glass ionomer. These temporary restorative materials are
necessary to exclude debris and microbial contamination of the cleaned canals between appointments.1Endodontic spacers have traditionally been used below these temporary restorations in order to prevent restorative materials from occluding the orifices, and to aid in efficient removal of these materials. Historically,medicated cotton pellets were placed between canal orifices and temporary restorative materials as an additional antimicrobial tool.2,3 However, due to concerns to toxicity many of these medications were discontinued.Currently, intracanal medicaments and dry cotton pellet spacers are used.4 Commonly used endodontic spacers include cotton, polytetrafluoroethylene(PTFE) tape, and sponges. Alternatively, the clinician can opt to use no spacer. The properties of temporary restorative materials have been well studied.5 However, there are few studies investigating the properties of endodontic spacers. An ideal endodontic spacer should possess the following properties:
• easy to place and remove
• retain satisfactory stiffness to prevent sinking of theoverlying temporary material
• inexpensive
• not promote microbial growth.

Previous research has demonstrated that cotton was the most commonly used spacer beneath Cavit temporary restorations. 4 Advantages of cotton as a spacer include ease of removal of the temporary material without risking unnecessary removal of tooth structure, and
minimizing the chance of accidental blockage of the canal by small fragments of temporary material that could potentially be displaced during its removal. However, cotton spacers have their disadvantages as they could lead to decreased thickness of the temporary restorative materials, which ideally should be between 3.0 and 4.0 mm.6 Newcomb et al7 found that small amounts of cotton trapped between the wall of a glass tube and restorative materials could dramatically reduce the sealing quality of the temporary restorations. Furthermore, there is concern about the organic and fibrous nature of cotton that might promote wicking and bacterial uptake.8 The use of cotton pellets is therefore controversial and many practitioners have tried other materials as spacers, such as foam pellets7 and PTFE tape.9 PTFE has been gaining popularity as an endodontic spacer since it possesses many of the advantages of cotton spacers and may have the potential to overcome the disadvantages of unsatisfactory stiffness and the potential to allow microbial growth.8 A previous study demonstrated that PTFE performed better than cotton as an endodontic spacer in vitro.8 The study focused on the microbiologic evaluation of cotton and PTFE as endodontic spacers. The results demonstrated a significant difference in contamination of the cotton spacers under optimal conditions as compared to PTFE. However, the limitations of the previous study were the lack of occlusal loading and thermocycling, which would have better represented the oral environment. Currently, there are no in-vivo studies that demonstrate the effectiveness of PTFE as an endodontic spacer. An in-vivo study is therefore necessary since it would take in consideration the limitations of the previous in-vitro study. Hence, the aim of this in-vivo study was to investigate the effectiveness of two common endodontic spacers, cotton and PTFE, using microbiologic analysis. Information obtained from this in-vivo study could potentially help with developing appropriate guidelines for the selection of interim spacers.

METHOD AND MATERIALS
This study was approved by the Human Subjects Division of the University of Washington (IRB #49537). Participants Fifty subjects were enrolled for this study. These patients were scheduled for root canal treatment in the Graduate Endodontic Clinic. Specific inclusion and exclusion criteria were followed for selection of patients. The inclusion criteria were:
• patients fluent in English, allowing verbal informed consent including risks and benefits to the patients
• patients with ASA classification I or II and between the ages of 18 and 80

• patients who needed root canal treatment on first and second molars
• treated teeth had at least three intact coronal walls or full cuspal cast restorations
• included cases were treated in two steps requiring a spacer between appointments
• teeth with an endodontic pulpal diagnosis of irreversible pulpitis, necrotic, or previously initiated therapy were included. The exclusion criteria consisted of:
• patients whose endodontic treatment would becompleted in one appointment
• teeth with an endodontic pulpal diagnosis that had previously been treated
• teeth other than molars (incisors, canines, premolars)
• teeth with extensive restorations (more than one surface)
• teeth with extensive caries (more than one surface)
• teeth with any resorptions, anatomical anomalies, or perforations
• teeth with any purulent or hemorrhagic exudate from the root canal during treatment
• patients with missing opposing teeth.

Procedure and sampling Patients were randomly assigned to either the cotton or the PTFE group with the help of randomization software. The root canal procedures were performed by graduate endodontic residents. The spacers, either a sterile 2 cotton pellet or a 2.5-inch length of sterile PTFE, were assigned to the cases in a randomized manner as stated previously. Dental dam and OraSeal (Ultradent) isolation was utilized in all cases.10 The crowns of the teeth were swabbed with 6% sodium hypochlorite prior to accessing the teeth. Caries was excavated. The teeth with a missing coronal wall were restored with a glass-ionomer restoration prior to initiation of the root canal treatment in order to prevent potential leakage.

The teeth were accessed and the canals were located. Debridement was completed using hand and rotary endodontic files and 10 mL 6% sodium hypochlorite irrigation. The chamber was dried and a first sample (S1) was collected by swabbing the pulp chamber with a sterile cotton pellet after completion of debridement and before delivery of the spacer to ensure adequate disinfection of the chamber. The S1 sample was collected in a sterile Eppendorf tube containing 0.5 mL Brain Heart Infusion (BHI) broth. Calcium hydroxide(Multi-Cal, Pulpdent) was placed in the canals as an intracanal medicament. The sterile spacer (either cotton or PTFE) was placed in the access cavity with sterile cotton pliers and Cavit (3M Espe) was placed over the spacer with sterile instruments. Before discharging the patient, a bitewing radiograph was taken to make sure the thickness of the Cavit restoration was 3 to 4 mm. The S1 sample obtained from the access was vortexed for 10 seconds and the BHI broth and the cotton pellet were placed on a BHI agar plate. The agar plates were incubated aerobically for 48 hours and the colony forming units (CFUs) were then calculated.

At the second appointment, which was 2 to 4 weeks later, the Cavit was checked to make sure it was intact. It was previously determined that if the Cavit was not intact between appointments the tooth would not be considered for the study. Once the Cavit was checked the tooth was isolated again with dental dam and OraSeal, and the coronal tooth structure of all the teeth was disinfected by swabbing the crown with 6% sodium hypochlorite followed by sterile saline. The Cavit restorations were removed using aseptic techniques. The spacer was retrieved at this appointment and an S2 sample of the chamber was taken. Both samples were collected in sterile Eppendorf tubes containing 0.5 mL BHI broth and plated on BHI agar plates as stated for the S1 sample. The CFUs were counted after 48 hours of incubation. Teeth with positive S1 samples were not included in the study as this suggested contamination of the chamber before the delivery of the endodontic spacer.

Data analysis SigmaPlot 11.0 (Systat Software) was used for the analysis. Power was calculated based on sample sizes of 25 patients assigned to each treatment group. These sample sizes would provide power of 90% to detect a 1-log difference between treatment group means. A log10 transformation was performed for the counts of the samples before statistical analysis. The outcome measures were observations of CFU counts indicating a positive culture and were assessed using the chi-square test. The Wilcoxon sign-rank test was used for intragroup analysis comparing the log CFU counts in the 2-week versus the 4-week samples in both groups. The significance level was set at P < .05 for all tests.

RESULTS
One of the PTFE samples and one of the cotton samples were positive at the S1 sample and were eliminated from the study. A total of 24 samples were analyzed for each group. Microbial contamination of the cotton and PTFE spacers was evaluated 48 hours after inoculation on BHI agar plates. The number of CFUs was recorded for each S2 sample. Figure 1 demonstrates the differences between the two groups. Fifteen of the 24 cotton samples were positive for microbial growth, and two of 24 PTFE samples were positive. There was a statistically significant difference between the cotton and PTFE samples.

The samples from each of the experimental groups were analyzed for time interval, 2 weeks versus 4 weeks. In the cotton group, 10 samples belonged to the 2-week group and 14 belonged to the 4-week groups; for the PTFE group, 9 samples were retrieved in 2 weeks and the remaining in 4 weeks. There were no statistically significant differences in the intragroup analyses (cotton, P = .133; PTFE, P = .804).

DISCUSSION
Root canal therapy procedures often require more than one appointment. During the interim appointments, it is important to maintain a tight coronal seal in order to prevent bacterial leakage and recontamination.6,11 In most cases, a spacer is placed between the temporary material and the root canal orifices. This allows for easy removal of the temporary material and prevents the material from falling into the canal or/and occluding the canal orifices. Furthermore, many endodontists use cotton pellets after endodontic therapy is completed, as the spacer of choice above the gutta-percha-filled canals and beneath the temporary restorations, to facilitate the removal of the temporary restoration as well as to guide the restorative dentist to the canal orifices. However, if patients do not get a permanent restoration promptly after endodontic therapy, it could lead to loss of, or wear and abrasion of the surface of the temporary restoration; thereby reducing its thickness to below the desired 3.5 mm. This in turn could allow exposure of the entrapped cotton fibers to the oral environment and lead to the initiation of coronal microleakage from the oral cavity. Hence, this study aimed to investigate PTFE tape as alternative to cotton as a spacer. PTFE is a resin and has been used for various nonendodontic purposes, which include its use in household plumbing materials and aerospace materials because of its resistance to high temperatures and corrosion.12,13 The hydrophobicity and smooth surface of PTFE has been shown to inhibit the growth of cells and bacteria, and has proved to be antimicrobial.

These properties make PTFE an appropriate material for use in various medical and dental procedures.16-19 PTFE is used in various areas of dentistry such as restorative dentistry, ridge preservation, and implant dentistry.20-22 In endodontics, PTFE has been investigated as a spacer material. A previous in-vitro study demonstrated that PTFE performed better as a spacer.8 The present results are similar to those from the in-vitro study. However, the main differences between the previous study and the present one are the sample sizes (10 versus 24) and that the present study took into consideration the occlusal loading and thermocycling, important in order to validate the results of the in-vitro and in-vivo study. The number of contaminated PTFE and cotton samples in the previous in-vitro study was 1/10 and 9/10 respectively. The results of the present study demonstrated a statistically significant difference between the two groups. Fifteen of 24 samples from the cotton group were contaminated samples compared to two of 24 from the PTFE group. The access cavities of the spacers that tested positive for bacteria were also contaminated, as the S2 samples showed microbial growth. The possible differences between the 2-week and 4-week time interval were also analyzed. There were no statistical differences for either the PTFE or the cotton groups when the spacers were analyzed after either 2 or 4 weeks. This reiterates that Cavit is an acceptable temporary restorative material that does not allow leakage, and the results obtained were due to properties of the individual spacers. The reason for the higher number of contaminated samples in the cotton group could be that the cotton fibers were exposed to the oral environment and had a tendency to wick potential contaminants into the pulp chamber. It could also be due to the tendency of cotton to distort under masticatory forces. If the spacer is unable to maintain the integrity of the space it is holding, the overlying temporary material could sink and the marginal seal could be compromised. PTFE, on the other hand, is stiffer than cotton and when condensed well, it shrinks less than cotton under masticatory forces. Another important factor to consider is that PTFE does not adhere to the walls of the access cavity and can be easily placed and removed, in contrast to cotton, which does tend to leave fibers behind and is more difficult to remove.

The present inclusion criteria included only molars. This was to prevent introducing another variable, different coronal anatomy, into the study. Furthermore, molars with three intact walls and restored with glass ionomer were included, since this allowed analysis of spacer performance in these cases. Molars that had more missing tooth structure could have skewed the results as it would have been harder to restore these teeth and would introduce more variables into the study. Furthermore, the likelihood that the temporary restoration would not be intact between the two appointments would be higher. This could be a potential problem as it would be difficult to assess whether the contamination was from the spacer communicating with the oral environment or failure of the temporary restoration. Cavit was the temporary material of choice as the previous in-vitro study utilized Cavit.8 The thickness of Cavit was standardized to 3.5 mm based on previous studies, which suggested that this thickness was necessary to prevent leakage.6 Other studies have demonstrated that Cavit works well as a temporary restoration, and in a dye leakage study, did not allow dye to reach the pulp chamber.1,23 However, other studies have demonstrated that materials like Fermit and Duo-Temp were more effective as temporary restorative materials, although they mention that Cavit could be used as an effective temporary restoration.24,25 The S1 samples were collected to ensure that there was no contamination in the chamber prior to placing the spacer as this could contaminate the spacer and result in a false positive for the sample.

A 2- to 4-week time period between appointments was recommended, since calcium hydroxide was placed as an intracanal medicament and is recommended to be in the canals for at least 7 days for optimal efficacy.26 The results of this in-vivo study demonstrated that fewer of the PTFE samples were contaminated (2/24) in comparison to cotton samples. Based on the results of the present study, the PTFE group did better and hence the use of PTFE is recommended over cotton as an endodontic spacer material.

CONCLUSION
This study compared the effectiveness of cotton and PTFE tape used as spacer materials. This in-vivo study demonstrated that PTFE tape resulted in fewer samples that were positive for bacteria as compared to cotton. Furthermore, PTFE was easier to use and remove from the endodontic access in comparison to cotton. This information may be particularly useful for practitioners who prefer to use a spacer and a temporary restoration between appointments or after completion of root canal therapy. This information could be extended to other fields of dentistry such as dental implants, which could use PTFE over cotton.

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