Nonsurgical Root Canal Treatment (nRCT) follow-up is a vital part of the treatment plan. Despite limitations, radiographic examination is one of the most widely used methods for this purpose [1] [2] .

The optimal scenario for successful endodontic therapy should successfully combine healing/prevention of disease (apical periodontitis) and functional retention of the tooth [2] . The success of a nRCT is conditioned on the following clinical evidence: absence of pain, thoroughly filled root canal space with no radiographic evidence of periapical inflammation, and a well-restored and functional tooth. Clinical and radiographic features conventionally associated with failure of endodontic therapy include pain, periapical radiolucent lesion, fistula, and edema [3] .

The quality of the coronal restoration seems to have a greater impact on periapical status and success of the nRCT than the quality of the root filling [4] . This is because no root canal obturation technique provides a definitive coronary, lateral and apical sealing. Additionally, coronal infiltration and fracture can occur in any inadequately restored tooth [5] . Therefore, the restoration of endodontically treated teeth is an essential component of the treatment [6] .

Since the study by Ray and Trope [4] , it has become necessary to conduct similar clinical studies to confirm the validity of the results. In 2021, an 18-year follow-up study of endodontically treated teeth, found that clinically detectable not precise coronal margins predict the presence of any clinical complication with a hazard ratio almost seven times higher than endodontically treated teeth with a proper margin [7] .

The findings emphasize the importance of ensuring ongoing follow-up for the nRCT and the definitive restoration of the dental element.

The objective of this study was to evaluate the proficiency of undergraduate students in performing endodontic procedures within their clinical practice, while also establishing the success rate of nRCT. This evaluation involved both radiographic and clinical assessments of the effectiveness of nRCT procedures carried out in the undergraduate clinic of the School of Dentistry at Caxias do Sul University between 2019 and 2021. It should be noted that this clinic extends its services to low-income patients, providing them with cost-free root canal treatments and subsequent coronal restorations. Furthermore, the potential influence of the quality of coronal restorations on the outcomes of endodontic treatments was also investigated in this study.

A total of 257 teeth were endodontically treated according to the Caxias do Sul University’s data, 23 teeth from 15 patients were missing clinical records, so, the data of 234 teeth was analyzed regarding the diagnosis before nRCT and the group of teeth. The most commonly treated teeth were premolars (46.15%) (Table 1) and the most prevalent diagnosis was Chronic Apical Periodontitis (33.33%) (Table 2).

The phone numbers of 182 (88%) patients were obtained, out of a total of 207. After calling 47 patients, only 37 showed up for the follow-up appointment. Thus, we obtained a final sample of 53 endodontically treated teeth, or 21% of a

total of 257 nRCTs performed (Figure 1). The most prevalent diagnosis was Non-vital Pulp (32%), Table 3 outlines the diagnosis of the pulpal/periapical condition that has driven the teeth to endodontic treatments of the reexamined teeth, respectively.

Of the 37 patients, 59% were female and 54% were aged 36 - 59 years. 94% were Caxias do Sul residents and 100% were from the low-income group. Table 4 shows a descriptive socio-demographic analysis of the sample.

One of the 53 followed-up teeth was extracted after endodontic treatment, due to vertical root fracture.

Table 5 shows the nRCT success rate of the 52 teeth reevaluated clinically and radiographically. The teeth classified as success, being healed (n = 44) and incomplete healing (n = 7) accounted for 98% of the analyzed sample. Elements with unsatisfactory healing, classified as failure (n = 1) represented 2% of the cases. Figure 2 illustrates diagnostic periapical radiographs and the follow-up of several successful and unsuccessful cases documented in this study. Out of the 52 teeth examined, 51 (98%) achieved success, 85% deemed to be healed (Figure 2(c), Figure 2(d)) and 13% incompletely healed (Figure 2(a), Figure 2(b), Figure 2(e), Figure 2(f)). Only one tooth failed because of a large radiolucent lesion (Figure 2(g), Figure 2(h)). This tooth had definitive Class II composite resin

*Fiber and metallic posts. **Filling material exposed. GIC: Glass Ionomer Cement.

restoration with unsatisfactory adaptation and secondary caries lesion distally. This corresponded to a failure rate of 2%.

Three teeth displayed a periapical lesion healed without definitive restoration (Figure 2(d)). In these cases, all units had a Glass Ionomer Cement (GIC) restoration with satisfactory adaptation at the time of the follow-up visit.

Table 6 shows the sealing condition of the coronal restoration of the treated teeth at the follow-up visit. Among the 32 (62% of the 52 teeth evaluated) teeth definitively restored with composite resin, 11 (34% of the 32 restored teeth) exhibited inadequate marginal adaptation. Considering the seven cases with definitive cemented intra radicular posts as definitively restored, we can assume that 39 teeth (75%) were definitively restored (Table 6).

The nRCT outcomes were dichotomized. The results showed that 51 teeth were classified as successful, while only one tooth was categorized as a failure. The quality of coronal restoration was considered adequate for 33 teeth, and inadequate for 19 teeth. The Fisher Exact Test showed that there was no association between the outcome of endodontic treatment and the quality of the coronal restoration (P = 0.365) (Table 7).

The objective of this retrospective study was to clinically and radiographically

*Fisher’s Exact Test, P < 0.05.

evaluate the outcome of endodontic treatments, the restoration condition and its correlation with the outcome in teeth that were endodontically treated by undergraduate students of the Dentistry course at SD-UCS.

In this follow-up cohort study, the most prevalent teeth that underwent the follow-up appointments were maxillary premolars (n = 13) (24.53%). Endodontic treatment was most frequent in maxillary teeth (60.38%) than in mandibular dental units (39.62%). The literature [10] [11] [12] has indicated that the mandibular first molar is the tooth most commonly treated endodontically. This is because it is the first permanent tooth to erupt without a deciduous predecessor. Our results diverged from the literature, as most students in the Disciplines of Endodontics were unable to perform nRCT on permanent molars.

Of the 52 teeth that underwent the follow-up appointments, 37 (70%) had a diagnosis of non-vital pulp. Some authors have already demonstrated that this diagnosis has a worse prognosis than when there is pulp vitality [13] [14] . According to SJOGREN et al. [15] , teeth with periapical lesions present a success rate 20% lower than teeth without periapical lesions in the diagnostic radiograph. Furthermore, a better prognosis for endodontic therapy has been reported by STRINDBERG [16] for small lesions, up to 5 mm in diameter, compared to larger lesions. There seems to be a correlation between lesion size and the number of microorganisms in the root canal [17] . Another important consideration is that larger lesions also require a longer time for healing. In Figure 2(a) of this study, a large periapical lesion is observed, and in the follow-up radiograph (Figure 2(b)), taken 19 months after the completion of the endodontic therapy, incomplete healing is evident, demonstrating the need for longer follow-up periods for larger periapical lesions.

Non-vital pulp (32%) and Chronic Apical Periodontitis (26%) were the most prevalent pulpal/periapical condition diagnosis (Table 3). The records evaluated in this study indicated 14 teeth with a diagnosis of Chronic Apical Periodontitis. However, diagnostic radiographs revealed periapical lesions in 17 teeth, of which one tooth was diagnosed as Acute Apical Abscess and two teeth as Non-vital Pulp. There is a possibility that the case of acute apical abscess comes from a phoenix abscess and that the teeth with non-vital pulp were not correctly diagnosed. Phoenix abscess is a chronic apical periodontitis characterized by an acute exacerbation and appearance of clinical symptoms [18] [19] .

The overall success rate of nRCT in this study (98%) (Table 5), was considered high when compared with similar studies [20] . The students were assisted by professors during the appointments, which ensured attention to biosafety protocols, as well as a better performance of each step of the root canal treatment (disinfection of the root canals, the use of intracanal medication, obturation and coronal sealing). This fact positively impacted the success rate as well as the short follow-up period, since longer periods could yield lower success rates, especially for those dental elements with restorative failures or which were temporarily sealed. Radiographic and clinical examination techniques evidenced periapical lesion and inadequate composite resin restoration in the only case of failure reported in this study. This finding supports the studies of Ray and Trope indicating that successful endodontic treatment is more often related to definitely restored teeth [4] . Chugal et al. [14] and Safavi et al. [21] also observed successful results more frequently for teeth with a permanent restoration (amalgam, composite, crown) than for teeth with a temporary restoration; however, the differences did not reach statistical significance, which is in agreement with the results of the present study.

In four teeth, the healing was incomplete, as the lesion did not fully regress. In these cases, the lesions had larger diameters and patients showed no clinical signs other than sensitivity to palpation. According to the European Society of Endodontology [22] , these features define the success of endodontic therapy and indicate the need to maintain patient follow-up over the years. The follow-up time for all teeth was less than three years. In one out of four teeth, root canal overfilling was observed (Figure 2(f)). This endodontic failure prevents the lesion from healing. In this case, the patient was elderly and presented with Lupus, which are systemic factors that influence the healing process [11] . In two of the teeth, a six-month follow-up of the endodontic treatment was performed. One of them belonged to a young patient with no systemic conditions. Thus, the repair was favorable regardless of the established follow-up period for both teeth. These findings are aligned with the studies of HOLLAND et al. [23] , LLENA [24] and SELTZER et al. [10] . The authors state that systemic factors related to the patient’s health contributed to the outcome of the endodontic treatment. Our study corroborates the recommendations of the European Society of Endodontology [22] regarding a longer follow-up time of endodontic treatment for these cases.

This study relies on radiographic and clinical data, which presents limitations that should be considered when analyzing the results. One limitation was the evaluation of endodontic treatment success in the periapical region through periapical radiographs, instead of using CBCT, as proposed by ESTRELA et al. [2] [3] . The radiographic method was chosen for the following reasons: convenient and accessible, it is the main technique used by undergraduates at UCS-SD and matches the ALADA principle (as low as diagnostically acceptable) [25] . CBCT should only be used when an accurate diagnosis cannot be achieved through a conventional radiographic study [26] .

Another point was that the clinical sample evaluated was small (53 teeth) relating to the treated cases in the period (257 teeth), corresponding to 21% (Figure 1). Exhaustive efforts were made to contact all patients and encourage them to attend the follow-up appointment. The high proportion of dropouts, either for not showing up for the appointment (21%) or for not responding to the numerous phone calls and text messages (61%) were consistent with previous studies [13] [14] . In fact, most of the patients who attended the follow-up appointment reported other dental needs and interest in undergoing other procedures.

Our findings support the need for definitive restoration at the same appointment as root canal obturation and a long-term follow-up of endodontic treatment. The Fisher’s Exact Test was unable to identify a statistical significance between the outcome of endodontic treatment and the quality of the coronal restoration (P = 0.365). This fact may be associated with the sample size and also the low failure rate of the endodontic treatment. Studies employing a larger sample size should be encouraged to provide a correlation between the success of endodontic treatment and the restorative condition of the dental element. The main objective of the present study was to assess the performance of undergraduate students in endodontics during their clinical practice at UCS-SD. The overall percentage of nRCT success was 98%.

· The success rate of endodontic treatment performed by UCS-SD undergraduates was high (98%);

· Among the restored endodontically treated teeth (62%), 34% showed unsatisfactory marginal adaptation;

· Methodologies using a larger sample size are encouraged to analyze the correlation between the quality of the restorative condition and the success of endodontic treatment.

The authors would like to express their deepest gratitude to the undergraduates and faculty members of the Dental School of University of Caxias do Sul (UCS-SD) for the technical support in this study.

The authors declare no conflicts of interest regarding the publication of this paper.

Bartelle, G.T.B., dos Reis, D.M., Gamba, T.O. and Vier-Pelisser, F.V. (2023) Root Canal Treatment Outcome and Restorative Condition of Teeth Treated by Undergraduates—A Clinical and Radiographic Evaluation. Open Journal of Stomatology, 13, 257-270. https://doi.org/10.4236/ojst.2023.139022