This study aimed to evaluate and compare the shaping abilities and minimum dentin thickness of minimally invasive rotary instruments via micro-computed tomography. Twelve 3D-printed C-shaped canal models from a mandibular molar were divided into two groups, and root canals were prepared with either XP-endo Rise (XR) or TruNatomy (TN) systems. Pre- and post-preparation evaluations included canal volume, prepared area and minimum dentin thickness. No significant differences were found in canal volume change (XR: 22.66 ± 4.28%, TN: 23.02 ± 5.10%), prepared canal area (XR: 31.86 ± 10.72%, TN: 30.26 ± 11.59%) and minimum dentin thickness (XR: 0.30 ± 0.05 mm, TN: 0.28 ± 0.05 mm) between groups (p > 0.05). The canal volume change in the middle third was significantly higher than that in the coronal and apical thirds (p < 0.05) in both groups. In conclusion, XR demonstrated comparable shaping abilities and minimum dentin thickness to TN in preparing 3D-printed C-shaped canals.

OBJECTIVE: To compare the effects of Cervical Access Cavity (CervAC) and Traditional Access Cavity (TradAC) on root canal preparation, root canal filling, and fracture resistance in mandibular incisors.
METHODS: Twenty recently extracted and intact mandibular incisors were initially scanned using a micro-CT device. The specimens were anatomically matched to create two groups (n = 10). A wedge-shaped non-carious cervical lesion (NCCL) was created on the buccal aspect of all teeth using a double-faced segmented diamond disc. In group 1, a TradAC was prepared, whilst in group 2, access was created through the simulated NCCL using a round diamond bur 1012. After root canal preparation with Rotate instruments sizes 15/0.04, 20/0.04, and 25/0.04, the teeth were scanned again and evaluated for root canal volume and surface area, static voxels, volume of removed dental tissue, and dentine thickness. After that, the root canals were filled using the single-cone technique, teeth were restored with composite resin, and subsequently rescanned to calculate the volume of filling materials and voids. Then, the restored teeth were subjected to fracture resistance tests using a universal testing machine. Statistical comparisons between groups were performed with the Mann-Whitney test or the Student\'s t-test, with a statistical significance level of 5%.
RESULTS: Statistical comparisons indicated no significant differences between groups in terms of root canal volume, surface area, static voxels, removed root dentine, root canal filling volume, percentage of voids, or fracture resistance load (p > .05). Conversely, teeth prepared with TradAC showed a significantly higher percentage of dental tissue removed from the crown (p = .001) and a greater volume of filling material remnants in the pulp chamber (p < .001) compared to the CervAC group. A significantly lower percentage reduction in dentine thickness was observed only on the mesial aspect of root at Level 1 in TradAC group (p = .008).
CONCLUSIONS: CervAC can be considered a viable alternative approach in the presence of NCCL in mandibular incisors.

The evidence base on minimally invasive endodontic (MIE) treatment is limited. This study investigated the influence of MIE shaping on vertical root fracture (VRF) resistance and crack formation of root canal filled teeth. Human maxillary central incisors were randomized into six groups (n = 18, power = 0.9) and embedded in acrylic blocks with artificial periodontal ligaments. The root canals were either instrumented to size #40 and 0.04 taper (+MIE) or enlarged to ISO size #80 (-MIE). The canals were filled with cement-based (C) or adhesive resin-based (A) sealers in single-cone technique. The controls received no treatment or were left unfilled. After chewing simulation (staircase method, 25-150 N, 120,000×), the crack formation on the root surface was analyzed using stereomicroscope/digital imaging and classified (no defect, craze line, vertical crack, horizontal crack). Subsequently, the samples were loaded until fracture. The incidence of defects (56% vertical cracks) was not significantly different between the groups (p ≥ 0.077). VRF resistance was significantly higher in untreated teeth than in +MIE/C (p = 0.020) but did not significantly differ between the other groups (p ≥ 0.068). Minimal canal shaping did not reduce the risk of vertical root fracture and defects of root canal filled teeth.

BACKGROUND: Treating the coronal dens invaginatus (CDI) with pulp infection commonly involves the removal of invagination, which increases the risk of perforation and fracture, and compromises the tooth structure. Minimally invasive endodontic management of CDI is highly recommended. This report describes two cases of type II CDI with the application of personalized templates.
METHODS: Two cases of type II CDI, affecting the main root canal in a maxillary canine and a lateral incisor, were diagnosed. A guided endodontics (GE) approach was applied. Cone-beam computed tomography and intraoral scans were imported and aligned in a virtual planning software to design debridement routes and templates. The MICRO principle (which involves the aspects of Mechanical (M) debridement, Irrigation (I), Access cavities (C), Rectilinear routes (R), and Obstruction (O)) was proposed for designing optimal debridement routes for future applications. The templates were innovatively personalized and designed to preserve the tooth structure maximally while effectively debriding the root canal. Root canal treatment with supplementary disinfection was then performed. The follow-up of the two patients revealed favorable clinical and radiographic outcomes.
CONCLUSIONS: The GE approach could be a feasible method for preserving healthy dental structure while effectively debriding the root canal, thereby achieving successful and minimally invasive endodontic treatment for CDI.

OBJECTIVE: This study aims to establish a minimally invasive treatment using a customized digital template and a miniaturized bur for pulp canal obliteration (PCO).
METHODS: Cone-beam computed tomography (CBCT) and digital oral scans of patients diagnosed with PCO in anterior teeth were obtained. Root canal morphology was reconstructed to accurately show the location, length, and direction of obliteration. A digital template was designed and fabricated using visual design software and 3D printing technology and used as guide for the miniaturized bur and drill sleeve during calcified tissue removal. A conventional root canal treatment was performed after the lumen of the root canal was reached.
RESULTS: In both cases, the planned access cavity and glide paths were successfully established. In case 1, the deviated angle of the access cavity was 1.37°±0.07°, the deviation at the bottom of the miniaturized bur was 0.08-0.81 mm, the deviation at the tip of the bur was 0.05-1.13 mm, and difference in substance loss was 0.84-4.25 mm³. In case 2, the deviated angle of the access cavity was 3.09° ± 0.12°, the deviation at the bottom of the bur was 0.09-0.68 mm, the deviation at the tip of the bur was 0.29-0.66 mm, and the difference in substance loss was 0.55-3.79 mm3.
CONCLUSIONS: Micro-guided endodontics is a novel approach for localizing and negotiating obliterated root canals and guarantees long-term prognosis without requiring excessive hard tissue removal.
目的: 结合数字化导板技术及微创车针，建立数字化导板技术引导微创治疗钙化根管的临床方法。方法: 对于根管影像部分消失的前牙钙化患者，进行锥形束计算机断层扫描（CBCT）及数字化口腔扫描。通过三维重建技术还原根管形态，精准确定钙化的位置、长度及方向。利用可视化通路设计软件结合三维打印技术进行数字化导板的设计及制作，微创车针在导板及套管系统引导下去除根管内钙化组织，完成根管治疗。结果: 2例患牙均成功完成开髓路径的建立。病例1开髓角度偏差为1.37°±0.07°，钻针基底部的偏差为0.08~0.81 mm，钻针根尖部的偏差为0.05~1.13 mm，牙体组织去除量的偏差为0.84~4.25 mm3。病例2开髓角度偏差为3.09°±0.12°，钻针基底部的偏差为0.09~0.68 mm，钻针根尖部的偏差为0.29~0.66 mm，牙体组织去除量的偏差为0.55~3.79 mm3。结论: 数字化导板引导微创根管治疗技术可以在疏通根管内钙化组织的同时尽可能多地保留健康牙体组织，为患牙的长期留存提供保障。.

This randomized clinical trial compared postoperative pain between a minimally invasive (MP) and conventional root canal treatment protocol (CP). A total of 170 mature permanent teeth (either with vital or necrotic pulp), were randomly assigned into two groups. In the CP group, ProTaper Gold (Dentsply Sirona, Ballaigues, Switzerland) and a continuous wave of condensation technique were used, whereas, in the MP group, TruNatomy (Dentsply Sirona), ultrasonic-assisted irrigation (UI), calcium hydroxide, and a sealer-based obturation technique were used. Patients recorded preoperative and postoperative pain using a 0-10 numerical rating scale (NRS) at 4 h, 1, 2, 3, 4, 5, 6, and 7 days after instrumentation and 1 day after canal obturation, respectively. There were no significant differences in pain intensity at any time points assessed between the two groups (p > 0.05). The occurrence of moderate/intense pain after instrumentation was significantly associated with preoperative periapical index (PAI) (p = 0.017) and NRS scores (p < 0.001). Preoperative pulp status (p = 0.009) and NRS score (p = 0.006) were identified as significant factors in the occurrence of moderate/intense pain after obturation. Instrumentation unequivocally reduced pain severity for both groups. The post-endodontic pain associated with the use of MP, combined with UI, Ca(OH)2, and calcium-silicate cement, did not differ from that of CP. Preoperative pain score, PAI, and preoperative pulp status were determined to be prognostic factors for postoperative pain.

UNASSIGNED: To investigate the influence of Conventional Straight (CS) line and Modified Straight (MS) line access preparations with various restorative materials on the fracture resistance of primary molars using Finite Element Analysis (FEA).
UNASSIGNED: Three FEA models for each of the primary molars were divided into Group I- Intact tooth model; Group II- Model with CS outline and Group III- Model with MS outline. Based on the restorative material used, Group II and III were further subdivided into subgroup 1- GIC restoration, subgroup 2 - composite resin with GIC base and subgroup 3- Stainless Steel Crown (SSC). Each model was subjected to 5 different force loads directed at the occlusal surface. Maximal von Mises (VM) stresses calculated from stress distribution patterns.
UNASSIGNED: The maximum displacement, in all the models of primary molars were seen in GIC restored models in molars with both CS and MS access whereas the minimal displacement was seen in the SSC restored molars of MS group.
UNASSIGNED: In primary maxillary second molar and mandibular first and second molar with intact marginal ridges, the fracture resistance of tooth with MS outline restored with GIC base followed by Composite resin was comparable with the tooth restored with SSC and CS outline.
UNASSIGNED: Based on the results of this FEA analysis, composite restorations with MS outline would be appropriate for endodontically treated primary molars that have intact margins.

BACKGROUND: The minimally invasive endodontics could retain more peri-cervical dentin (PCD) and other important dental structures, thus realizing the minimal loss of teeth structures and preserving the strength and function of the endodontically treated tooth (ETT). The search for abnormal root canals or calcified root canals could be quite time-consuming and increase the risk of perforation.
OBJECTIVE: This study introduced a novel multifunctional 3D printing guided splint inspired by the dice, which can achieve the minimally invasive access cavity preparation and canal orifice identification.
METHODS: Data were collected from an outpatient with dens invaginatus. Cone-beam Computed Tomography (CBCT) revealed a type III invagination. The CBCT data of the patient were imported into a computer-aided design (CAD) software (Exocad 3.0; Exocad GmbH) for the 3D reconstruction of jaw bones and teeth. The dice-inspired 3D printing guided splint consists of the sleeve and guided splint. The sleeve with minimal invasive opening channel and orifice locating channel were designed with a reverse-engineering software (Geomagic Wrap 2021). The reconstructed models in the Standard Template Library (STL) format were imported into a CAD software. The design of the template was aided by the dental CAD software in Splint Design Mode. The sleeve and splint were exported into the STL files separately. A 3D printer (ProJet® 3600 3D Systems) was used to separately generate the sleeve and guided splint, and was made by stereolithography and processed in a medical resin (VisiJet M3 StonePlast).
RESULTS: The novel multifunctional 3D printing guided splint could be set in position. The opening side in the sleeve was selected and the sleeve was inserted in place. The minimal invasive opening was made in the crown of the tooth to access the pulp. The sleeve was draw out and turned to the orifice location side, and then inserted in place. The target orifice was located rapidly.
CONCLUSIONS: This novel dice-inspired multifunctional 3D printing guided splint allow dental practitioners to gain accurate, conservative, and safe cavity access from teeth with anatomical malformations. Complex operations might be carried out with less reliance on the operator\'s experience than with conventional access preparations. This novel dice-inspired multifunctional 3D printing guided splint would have a broad application in the dental field.

This study aimed to predict the fracture resistance of a mandibular first molar (MFM) with diverse endodontic cavities using finite element analysis (FEA).
Five experimental finite element models representing a natural tooth (NT) and 4 endodontically treated MFMs were generated. Treated MFM models were with a traditional endodontic cavity (TEC) and minimally invasive endodontic (MIE) cavities, including guided endodontic cavity (GEC), contracted endodontic cavity (CEC) and truss endodontic cavity (TREC). Three loads were applied, simulating a maximum bite force of 600 N (N) vertically and a normal masticatory force of 225 N vertically and laterally. The distributions of von Mises (VM) stress and maximum VM stress were calculated.
The maximum VM stresses of the NT model were the lowest under normal masticatory forces. In endodontically treated models, the distribution of VM stress in GEC model was the most similar to NT model. The maximum VM stresses of the GEC and CEC models under different forces were lower than those of TREC and TEC models. Under vertical loads, the maximum VM stresses of the TREC model were the highest, while under the lateral load, the maximum VM stress of the TEC model was the highest.
The stress distribution of tooth with GEC was most like NT. Compared with TECs, GECs and CECs may better maintain fracture resistance, TRECs, however, may have a limited effect on maintenance of the tooth resistance.

BACKGROUND: The purpose of this study was to evaluate the antimicrobial efficacy of a novel irrigation strategy using synchronized microbubble photodynamic activation (SYMPA) in a minimally prepared single canal.
METHODS: Single-canal mandibular incisors were inoculated with Enterococcus faecalis for 3 weeks and randomly allocated to 4 groups based on the irrigation protocols: (1) control (saline), (2) conventional needle irrigation (CI), (3) ultrasonic-assisted irrigation (UI), and (4) irrigation with SYMPA. The first 3 groups were instrumented to size 25.07v (WaveOne Gold Primary; Dentsply Sirona, Johnson City, TN), and the SYMPA group was minimally prepared to size 20.07v (WaveOne Gold Small, Dentsply Sirona). The apical 5 mm was resected for microbiological assessment using the culture technique (colony-forming unit), adenosine-5\'-triphosphate-based viability assay (relative luminescence units), and the percentage of live bacteria using confocal laser scanning microscopy.
RESULTS: Log colony-forming units from the UI (2.37 ± 0.66) and SYMPA (2.21 ± 0.86) groups showed a reduction compared with the control (5.16 ± 0.75) and CI (4.08 ± 1.19) groups. Relative luminescence unit reduction was significant for UI (619.08 ± 352.78) and SYMPA (415.25 ± 329.51) compared with the control (1213.2 ± 880.03) (P < .05). The percentage of live bacteria was significantly lower in the UI and SYMPA groups compared with the control and CI groups. Although higher microbial reduction was observed in SYMPA compared with UI, there was no statistical significance (P > .05).
CONCLUSIONS: SYMPA in minimally prepared canals showed significant antimicrobial efficacy. The novel irrigation strategy using SYMPA could be an effective disinfection strategy for minimally prepared root canals.