A laboratory investigation on the effect of biguanide- and pyridine-derived antiseptics on the adhesion of resin composites to dentin.

Optimal bonding of adhesive restorations to dentin is crucial to prevent microleakage and enhance the survival of root-filled teeth. The aim of this study was to investigate the effect of chlorhexidine (CHX), alexidine (ALX) and octenidine dihydrochloride (OCT) on the bond strength of resin composites to coronal dentin. Human coronal dentin specimens were treated with 2% CHX, 0.1% ALX, 0.1% OCT or saline then restored with traditional or bulk-fill resin composites. The adhesion strength between the resin and dentin was measured using the microtensile bond strength and failure mode was determined using a stereomicroscope. Treatment with ALX and OCT resulted in significantly greater µTBS compared with CHX and saline, irrespective of the resin composite used. Alexidine treatment predominantly resulted in mixed failure, while adhesive failures were frequently observed in CHX and saline-treated dentin. In conclusion, final irrigation with ALX or OCT improved the bonding of resin composites to dentin.

The Effect of Primary Root Canal Treatment on Dentinal Tubule Penetration of Calcium Silicate-based Sealers during Endodontic Retreatment.

INTRODUCTION: The aim of this study was to evaluate the effect of previous root canal treatment on dentinal tubule penetration of calcium silicate-based sealers during endodontic retreatment and to compare 2 different (commonly used and modified) tubule penetration depth measurement techniques. METHODS: The crowns of mandibular premolar teeth were removed, and root canals were prepared (ProTaper Universal; Dentsply Sirona, York, PA) and obturated using AH Plus (AH; Dentsply DeTrey, Konstanz, Germany), MTA Fillapex (MTAF; Angelus, Londrina, Brazil), and WellRoot ST (WRST; Vericom, Gyeonggi-do, South Korea); 0.1% red Rhod-2 dye (Chemodex, St Gallen, Switzerland) was added to the sealers. After storage for 3 weeks (37°C, 100% humid), the following sealer combination subgroups were created (the sealer used during the primary root canal treatment/the sealer used during the retreatment, n = 8): AH/AH, AH/MTAF, and AH/WRST; MTAF/AH, MTAF/MTAF, and MTAF/WRST; and WRST/AH, WRST/MTAF, and WRST/WRST. Green Fluo-3 dye (0.1%) was added to the sealers during retreatment. Sealer penetration depths were measured at 8 points and averaged, and the ratio of the retreatment sealer to the initial sealer was recorded as the mean tubule penetration depth ratio in the first technique, whereas the percentage of the circumferential penetration area ratios of the retreatment and initial sealers was calculated in the second technique. Statistical analyses were performed using Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests. RESULTS: The mean penetration depth of AH and MTFA was found to be higher at the coronal third region in the control groups (P < .05). Both methods showed a significant difference among the groups at the coronal and median regions (P < .05). The AH/WRST, MTAH/AH, MTAF/MTAF, MTAF/WRSTS, and WRST/WRST groups showed deeper tubule penetration (first technique, P = .01). Both techniques showed that the penetration depth of the sealers was the same at the apical region (P > .05), whereas a difference was found among the techniques at the coronal and median regions. The sealers used in the previous root canal treatment limited the penetration depth of the sealers used during the retreatment process (P < .05). When MTAF was used as the initial sealer, the penetration depth of the second sealer did not change, whereas if WRST was the initial sealer, the penetration depth of the sealers at the median and apical regions is negatively affected during the retreatment process (P < .05). CONCLUSIONS: Previous root canal treatment affects the penetration depth of calcium silicate-based sealers. The use of AH Plus and MTA Fillapex during the retreatment process showed an advantage. Both measurement techniques showed similar performances at the apical region, whereas the results varied at the coronal and midcoronal regions; therefore, a more stable sealer penetration measurement technique is still necessary.

Dentinal Tubule Penetration and Dislocation Resistance of a New Bioactive Root Canal Sealer Following Root Canal Medicament Removal Using Sonic Agitation or Laser-Activated Irrigation.

OBJECTIVE: To investigate the influence of sonic agitation or laser-activated irrigation techniques on the removal chlorhexidine (CHX) and modified triple antibiotic paste (mTAP) on the sealer penetration depth and dislocation resistance of Guttaflow Bioseal. METHODS: Single-rooted mandibular premolars (n=96) were prepared with rotary nickel titanium instruments and randomly divided into two groups (n=48) based on the intracanal medicaments used: Group 1, mTAP; Group 2, CHX gel. After 7 days, the specimens in each group were divided into three subgroups (n=16) based on the supplementary irrigation technique used to remove the medicaments: laser activated irrigation (Er, Cr: YSGG laser, Waterlase MD, Biolase Technology Inc., San Clemente, CA, USA), sonic agitation (EndoActivator, Dentslpy Sirona Endodontics, PA, USA) and syringe-and-needle irrigation (control) techniques. Canals were filled with single matched-taper gutta-percha cone and a calcium silicate-based sealer (GuttaFlow® Bioseal, Coltène/Whaledent, Langenau, Germany). At the end of three weeks, sealer penetration was investigated using confocal microscopy (n=6), and dislocation resistance was calculated by measuring the push-out bond strength (n=10). Statistical analysis was performed using three-way analysis of variance (ANOVA) and Tukey post-hoc test (P=0.05). RESULTS: Laser activated irrigation resulted in significantly higher depth of sealer penetration compared to sonic agitation and syringe irrigation (P<0.01). The average sealer penetration depths were recorded as 846.6 µm, 786.5 µm and 505 µm in the Er,Cr: YSGG laser, EndoActivator and control groups, respectively. The mean bond strength obtained in group 3 (syringe-and-needle irrigation) was significantly less than the other groups (P<0.05). The mean values were 9.08 in the Er,Cr: YSGG laser group, 8.44 in the EndoActivator group and 5.08 in the needle group. CONCLUSION: Er,Cr;YSGG laser irrigation to remove the medicaments was advantageous to other irrigation techniques in sealer penetration and dislocation resistance of the sealer.

Warm Gutta-Percha Techniques Regulate Cell Viability, Heat Shock, and Mineralized Tissue-associated Proteins of Cementoblasts.

INTRODUCTION: The aim of this study was to determine the effect of the continuous wave of condensation technique (CWCT) and the thermoplastic gutta-percha injection (TGI) technique on the messenger RNA (mRNA) expressions of heat shock proteins (HSPs) and mineralized tissue-associated proteins of the immortalized mouse cementoblasts (OCCM.30). METHODS: Crowns of human premolar teeth with single and straight canals were removed. The root canals were prepared up to the ProTaper Next X5 file (Dentsply Maillefer, Ballaigues, Switzerland) in combination with 2 mL 2.5% sodium hypochlorite solution. Roots (12 ± 2 mm height) were sterilized (121°C for 20 minutes) and placed vertically to the cell culture dishes using a tissue culture insert by opening holes according to the root diameter after the removal of 1 mm from the apex for appropriate adaptation to the petri dish surfaces. Six groups were created: control 1 (without teeth), control 2 (with teeth), AH Plus (Dentsply DeTrey, Konstanz, Germany), single-cone obturation (SC), CWCT, and thermoplastic gutta-percha injection technique (TGI). The viability of the OCCM.30 cells was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell viability experiments at 24 and 96 hours. The mRNA expression of HSP27, HSP70, and HSP90 and mineralized tissue markers (bone sialoprotein, osteocalcin, runt-related transcription factor 2, type I collagen, and alkaline phosphatase) was evaluated by real-time polymerase chain reaction. RESULTS: Reduced OCCM.30 cell viability was observed in all groups except the control groups. When the SC technique and CWCT and TGI groups were compared, it was observed that heat had a significant negative effect on cell viability (P < .05). A reduction in the mRNA expressions of HSP27, HSP70, and HSP90 was recognized in all test groups when compared with the control 1 group (P < .01). When the warm gutta-percha techniques were compared with the SC technique, a decrease in mRNA expression of HSP27 and HSP90 was noted (P < .01). The HSP70 transcript was similar in the CWCT group and the SC group. Higher HSP70 mRNA expression was observed in the TGI group compared with the SC group. In all groups except the control 1 group, bone sialoprotein, osteocalcin, runt-related transcription factor 2, type I collagen, and alkaline phosphatase mineralized tissue markers were affected, but this negative effect was higher in the heat-treated groups (P < .05). CONCLUSIONS: Within the limitations of this study, it was concluded that warm gutta-percha techniques reduced the mRNA expressions of the genes for HSPs and mineralized tissue-associated proteins of cementoblasts. Further animal studies are needed to clarify the effect of heat on the behavior of cementoblasts histologically in short- and long-term periods.

Adhesion of Two New Glass Fiber Post Systems Cemented with Self-Adhesive Resin Cements.

The aim of this in vitro study was to evaluate the adhesion strength of two new fiber post systems (FiberSite™ Post and Cytec™ Blanco Post) cemented with two different adhesive resin cements (Panavia™ SA and Maxcem™ Elite). Root canals of sixty extracted human mandibular premolars were prepared using ProTaper Universal™ rotary files (Dentsply Sirona Endodontics, York, PA, USA). The root canals were irrigated with 5.25% sodium hypochlorite (NaOCl) during instrumentation. After root canal preparation, the canals were irrigated with 2 mL of 17% EDTA (1 min), followed by 2 mL of 5.25% (5 min) NaOCI, and 2 mL saline. The root canals were dried with paper points and divided randomly into two study groups (n = 30) according to the type of post system: Group 1, FiberSite™ Post (MegaDental, Partanna, Italy); and group 2, Cytec™ Blanco Post (Hahnenkratt, Königsbach-Stein, Germany), with one of the two adhesive resin cements: Subgroup A, Panavia™ SA Cement Plus Automix (Kuraray, Osaka, Japan); subgroup B, Maxcem™ Elite (Kerr, Orange, CA, USA). Following thermocycling, the adhesion strength was evaluated using the push-out adhesion (bond) strength test. Fractographic analysis was performed using stereomicroscope. The data were analyzed using two-way analysis of variance (p = 0.05). The adhesion strength values of both the posts were significantly higher when cemented with subgroup B (Maxcem™ Elite). The highest adhesion strength value was demonstrated by group 1B (FiberSite™ post cemented with Maxcem™ Elite cement). The type of post did not have a significant impact on the bond strength values for either cement material.

Critical evaluation of fracture strength testing for endodontically treated teeth: a finite element analysis study.

OBJECTIVES: The aim of this study was to investigate whether the diameter and direction of the plunger and simulation of the periodontal ligament (PDL) affected the stress distribution in endodontically treated premolars. METHODS: A fracture strength test was simulated via finite element analysis. A base model was set up, and the following parameters were modified: plunger diameter (3 mm vs. 6 mm), plunger direction (vertical vs. 135° angular to the central fossa), and PDL simulation. The analysis was conducted using the CosmosWorks structural analysis program, and the results are presented in terms of von Mises stresses. RESULTS: The smaller plunger increased the stresses at the contact area of the crown, but the plunger diameter had no effect on the stress distribution within the root. An angular plunger direction increased stresses within the root, as well as at the buccal cusp of the crown, compared with the vertical direction. Simulation of the PDL caused higher stress accumulation, especially in the cervical region of the root. CONCLUSIONS: The plunger diameter had no effect on the stress distribution in the roots, whereas the plunger direction and PDL simulation did affect the stress distribution. More stringent standards can be established by taking such parameters into account when performing fracture testing in future studies.

Evaluation of Related Factors in the Failure of Endodontically Treated Teeth: A Cross-sectional Study.

INTRODUCTION: The aim of this study was to review the factors related to the failure and extraction of unsuccessful endodontically treated teeth. METHODS: A total of 1000 teeth treated with nonsurgical root canal therapy were analyzed, and the following information was recorded for each patient: reasons for failure and extraction, type of tooth, presence and type of coronal restoration, smoking status, age, gender, and level of education. One main reason was recorded for each failed tooth. The associations between reasons for failure, patient, and tooth were tested by using χ2 analysis. RESULTS: Of the 1000 endodontically failed teeth analyzed in this study, 28.1% (n = 281) were extracted, 66% (n = 660) were re-treated, and 5.9% (n = 59) were treated with apical surgery. Among the reasons for failure, restorative and endodontic reasons were seen most frequently (43.9%, n = 439), whereas orthodontic reasons were seldom seen (0.1%, n = 1). The most common reason for extraction was for prosthetic reasons (40.8%), and perforation/stripping was the least common (2.9%). The mandibular first molars were the most frequently extracted teeth (27.4%, n = 77). CONCLUSIONS: The most common reason for the extraction of endodontically treated teeth was for prosthetic reasons. Among the reasons for failure, restorative and endodontic reasons were the most frequently seen, and orthodontic reasons were the most seldom. The teeth that failed most frequently were mandibular first molars, and the teeth that failed least frequently were maxillary third molars. The most common reason for the extraction of failed endodontically treated teeth was for prosthetic reasons.

Effect of Different Treatment Options on Biomechanics of Immature Teeth: A Finite Element Stress Analysis Study.

INTRODUCTION: Immature teeth (IT) can be managed by using several treatment options, depending on the vitality of the tooth. The aim of this finite element stress analysis study was to evaluate the effect of different treatment procedures on the stresses in three-dimensional IT models. METHODS: Three-dimensional finite element stress analysis premolar tooth model was created as control (model 1), modified to simulate IT. Eleven models were created to simulate IT filled with (model 2) calcium hydroxide (CH), (model 3) mineral trioxide aggregate (MTA), (model 4) Biodentine (B), (models 5 and 6) MTA plug and B plug without root-filling, (models 7 and 8) MTA plug and B plug with root-filling with composite restoration, and amputation by using (model 9) CH, (model 10) MTA, and (model 11) B. Materials and structures were assumed to be homogenous and isotropic. A 300 N load was applied to the models from the functional cusps and central fossa with a 135° angle. Cosmosworks structural analysis program was used. The results were presented considering the von Mises criteria, and the scale range was limited to 0-10 + MPa. RESULTS: CH use in comparison with temporary filling increased the stresses within the root. MTA filling showed less stresses when compared with B filling. MTA and B plug increased the stresses at apical and root; however, when the roots were filled using gutta-percha and the crowns were restored with composite resin, the stresses at the coronal side of the roots were reduced. The stresses were distributed more favorably in the models simulating CH, MTA, or B amputation. Amputation by using MTA and B showed similar stresses with natural tooth model. CONCLUSIONS: CH is not a favorable dressing material for IT when compared with MTA and B. MTA or B plug increases the stresses at apical, whereas root-filling reduces the stresses within the root. Amputation by using CH, MTA, and B in combination with composite resin restoration may save both the coronal and root structure of IT.

Effects of intracanal medicaments and the remaining cavity wall on fracture strength of endodontically treated molars / Efeitos dos medicamentos intracanais e do muro de cavidade remanescente na força de fratura dos molares endodonticamente tratados

Objective: The aim of this study was to investigate the effects of the short-term intracanal application of two medicaments on the fracture strength of root-filled molar teeth with different levels of tooth structure loss. Material and Methods: Standard access cavities of totally 84 intact maxillary molar teeth were prepared in 72 teeth and were divided into 3 main groups. Standard access cavities were kept in the first group, while mesio-occlusal-distal cavities (MOD) were prepared in the second and third groups. One-half of the palatinal walls were removed in the third group. Twelve sound teeth were used in the fourth group as control. Each group was then assigned into two subgroups according to the medicament used (n=12): 2% chlorhexidine gel and calcium hydroxide. Samples were stored at 37°C and 100% humidity for 1 week. Then the teeth were inserted into a universal testing machine and vertically loaded (5 mm/min) from the occlusal surface. The data was recorded in Newtons and statistically evaluated using a Univariate ANOVA and a Tukey as post hoc test. Results: A significant difference was found among the test groups (p <0.01). No significant difference was found according to the medicament used (p>0.05), however the number of remaining walls significantly affected the fracture strength (p <0.01). The first group with access cavity showed mostly repairable fractures (60%­80%) whereas the others showed mostly nonrepairable fracture patterns s (60%­90%). Conclusion: In conclusion, the fracture strength of endodontically treated teeth is related to the structure loss rather than the intracanal medicament used. (AU)

Objetivo: O objetivo deste estudo foi investigar os efeitos da aplicação intracanal de curto prazo de dois medicamentos sobre a resistência à fratura de dentes molares preenchidos com raízes com diferentes níveis de perda de estrutura dentária. Material e Métodos: cavidades de acesso padrão de totalmente 84 dentes molar maxilares intactos foram preparadas em 72, dentes e foram divididas em 3 grupos principais. As cavidades de acesso padrão foram mantidas no primeiro grupo, enquanto as cavidades mesooclusais-distal (MOD) foram preparadas no segundo e terceiro grupos. A metade das paredes palatinas foi removida no terceiro grupo. Doze dentes de som foram utilizados no quarto grupo como controle. Cada grupo foi então atribuído em dois subgrupos de acordo com o medicamento utilizado (n = 12): 2% de gel de clorhexidina e hidróxido de cálcio. As amostras foram armazenadas a 37 ° C e 100% de umidade por 1 semana. Em seguida, os dentes foram inseridos em uma máquina de teste universal e carregados verticalmente (5 mm / min) da superfície oclusal. Os dados foram registrados em Newtons e avaliados estatisticamente usando uma ANOVA Univariada e um Tukey como teste post hoc. Resultados: uma diferença significativa foi encontrada entre os grupos de teste (p <0,01), no entanto, o número de paredes restantes afetou significativamente a resistência à fratura (p <0,01). O primeiro grupo com cavidade de acesso apresentou fracturas principalmente reparáveis (60% -80%), enquanto as demais apresentaram padrões de fratura não reparáveis (60% -90%). Conclusão: Em conclusão, a resistência à fratura dos dentes tratados endodonticamente está relacionada à perda da estrutura em vez do medicamento intracanal utilizado.(AU)

Can Degradation of Adhesive Interfaces Due to Water Storage Affect Stress Distributions? A Finite-Element Stress Analysis Study.

PURPOSE: The aim of this finite-element stress analysis (FEA) was to determine the effect of degradation due to water storage on stress distributions in root-filled premolar models restored with composite using either a self-etch (SE) or an etch-and-rinse (E&R) adhesive. MATERIALS AND METHODS: Four premolar FEA models including root filling, MOD cavity, and composite restorations were created. The cavities were assumed to be treated by SE or E&R adhesives and stored in water for 18 months. The elastic properties of the adhesive-dentin interface after 24-h and 18-month water storage were obtained from the literature and applied to the FEA models. A 300-N load was applied on the functional cusps of the models. The SolidWorks/Cosmosworks structural analysis program was used and the results were presented considering the von Mises stresses. RESULTS: Stresses in the cervical region increased over time on the load-application side of the main tooth models (SE: 84.11 MPa to 87.51 MPa; E&R: 100.24 MPa to 120.8 MPa). When the adhesive interfaces (hybrid layer, adhesive layer) and dentin were evaluated separately, the stresses near the root canal orifices increased over time in both models; however, this change was more noticeable in the E&R models. Stresses at the cavity corners decreased in the E&R model (within the adhesive layer), while SE models showed the opposite (within the hybrid layer). CONCLUSION: Change in the elastic modulus of the adhesive layer, hybrid layer, and dentin due to water storage has an effect on stresses in root-filled premolar models. The location and the level of the stresses differed depending on the adhesive used.

Evaluation of the Effect of Rotary Systems on Stresses in a New Testing Model Using a 3-Dimensional Printed Simulated Resin Root with an Oval-shaped Canal: A Finite Element Analysis Study.

INTRODUCTION: This finite element analysis study was aimed at evaluating the effects of rotary systems on stresses in photopolymerized resin root models with oval-shaped canals. METHODS: Among the data collected by computed tomographic imaging, a mandibular second premolar tooth with an oval-shaped canal was selected, recorded as Digital Imaging and Communications in Medicine, and transferred to Materialise's Interactive Medical Image Control System software. Three-dimensional modeling was performed to produce photopolymerized resin root models. Root canals were prepared by OneShape (OS; MicroMega, Besancon, France); ProTaper Universal (PTU; Dentsply Tulsa Dental, Tulsa, OK); WaveOne (WO, Dentsply Maillefer, Ballaigues, Switzerland); Mtwo (MT; VDW, Munich, Germany); Twisted File (TF; Kerr Dental, Orange, CA); ProTaper Next (PTN, Dentsply Tulsa Dental), and hand files (HFs) (control). The models were scanned (micro-computed tomographic imaging; SkyScan 1174; Kontich, Belgium), finite element analysis models were created, and stresses were calculated under 300-N loading (at a 45° angle and vertically). RESULTS: The maximum stress values were found to be higher when the roots were loaded at an angle. The range of the stress values was PTU > MT > WO > HF > PTN > OS > TF. The stresses were forwarded toward the apical area in the PTN, OS, and TF models. When loaded vertically, the highest maximum stress values were recorded in the WO model. High stress concentrations were observed at coronal, thus less stress was forwarded toward the apical, giving an advantage to the root. The range of the others was as follows: PTN ≥ PTU > MT > TF > OS ≥ HF. The TF model showed lower maximum stress values, whereas the HF model showed more homogenous stress distribution. CONCLUSIONS: Considering the stress distributions and stress values within the models, it can be concluded that oval-shaped canals prepared by HFs and WO were less likely to result in root fracture.

Effect of Root Filling on Stress Distribution in Premolars with Endodontic-Periodontal Lesion: A Finite Elemental Analysis Study.

INTRODUCTION: Endodontic-periodontal (EP) lesions require both endodontic and periodontal therapies. Impermeable sealing of the root canal system after cleaning and shaping is essential for a successful endodontic treatment. However, complete healing of the hard and soft tissue lesions takes time, and diseased bone, periodontal ligament, and tooth fibrous joints are reported to have an increased failure risk for a given load. Considering that EP lesions may affect the biomechanics of teeth, this finite elemental analysis study aimed to test the effect of root fillings on stress distribution in premolars with EP lesions. METHODS: Three finite elemental analysis models representing 3 different types of EP lesions (primary endodontic disease [PED], PED with secondary periodontic involvement, and true combined) were created. The root canals were assumed as nonfilled or filled with gutta-percha, gutta-percha/apical mineral trioxide aggregate (MTA) plug, and MTA-based sealer. Materials used were assumed to be homogenous and isotropic. A 300-N load was applied from the buccal cusp of the crown with a 135° angle. The Cosmoworks structural-analysis program (SolidWorks Corp, Waltham, MA) was used for analysis. Results were presented considering von Mises criteria. RESULTS: Stresses at the root apex increased with an increase in lesion dimensions. Root filling did not affect stress distribution in the PED model. An MTA plug or MTA-based sealer created more stress areas within the root compared with the others in the models representing PED with periodontic involvement and true combined lesions. CONCLUSIONS: Stresses at the apical end of the root increase with increases in lesion dimensions. MTA-based sealers or an MTA plug creates more stresses when there is periodontic involvement or a true combined lesion.

Comparison of different irrigation activation regimens and conventional irrigation techniques for the removal of modified triple antibiotic paste from root canals.

INTRODUCTION: The aim of this study was to compare the efficacy of irrigation activation regimens and conventional syringe irrigation technique in the removal of modified triple antibiotic paste (mTAP) from root canal walls. METHODS: Fifty-six extracted human mandibular premolars were prepared using ProTaper rotary files (Dentsply Maillefer, Ballaigues, Switzerland) up to size F4. The root canals were filled with mTAP medicament, and after 21 days, the roots were randomly assigned to 5 groups (n = 10) according to the irrigation regimens used: conventional syringe irrigation (CI), Self-Adjusting File (SAF; ReDent-Nova, Ra'anana, Israel), EndoVac (Discus Dental, Culver City, CA), EndoActivator (Dentsply, Tulsa, OK), and passive ultrasonic irrigation (PUI). In 3 teeth, mTAP was not removed (positive controls), and another 3 teeth were not filled with mTAP (negative controls). The roots were sectioned, and the amount of remaining medicament at each root half (n = 20) was evaluated at 30× magnification using a 4-grade scoring system. Data were evaluated using the Kruskal-Wallis and Mann-Whitney U tests. RESULTS: There were statistically significant differences among all experimental groups; of which, the CI group was the significantly least efficient in removing mTAP from the root canal (P < .05). At the apical and middle third, the PUI, SAF, EndoVac, and EndoActivator groups removed significantly more mTAP medicament than the CI group (P < .05); however, there were no significant differences between these groups (P > .05). The SAF and PUI showed significantly better performances in removing mTAP from the coronal third (P < .05). CONCLUSIONS: The use of irrigation activation regimens significantly improves the removal of mTAP from root canals when compared with CI.

Effect of restoration technique on stress distribution in roots with flared canals: an FEA study.

PURPOSE: The aim of this finite element analysis (FEA) study was to test the effect of different restorative techniques on stress distribution in roots with flared canals. MATERIALS AND METHODS: Five three-dimensional (3D) FEA models that simulated a maxillary incisor with excessive structure loss and flared root canals were created and restored with the following techniques/materials: 1) a prefabricated post: 2) one main and two accessory posts; 3) i-TFC post-core (Sun Medical); 4) the thickness of the root was increased by using composite resin and the root was then restored using a prefabricated post; 5) an anatomic post was created by using composite resin and a prefabricated glass-fiber post. Composite cores and ceramic crowns were created. A 300-N static load was applied at the center of the palatal surface of the tooth to calculate stress distributions. SolidWorks/Cosmosworks structural analysis programs were used for FEA analysis. RESULTS: The analysis of the von Mises and tensile stress values revealed that prefabricated post, accessory post, and i-TFC post systems showed similar stress distributions. They all showed high stress areas at the buccal side of the root (3.67 MPa) and in the cervical region of the root (> 3.67 MPa) as well as low stress accumulation within the post space (0 to 1 MPa). The anatomic post kept the stress within its body and directed less stress towards the remaining tooth structure. CONCLUSION: The creation of an anatomic post may save the remaining tooth structure in roots with flared canals by reducing the stress levels.

Influence of powdered dentin on the shear bond strength of dentin bonding systems.

This study evaluated the effect of different amounts of dentin powder (DP) mixed in Clearfil SE Bond (CSB) or Single Bond (SB) on adhesion to dentin. Human third molars (n=96) were sectioned to expose the mid-coronal dentin and divided into eight experimental groups (n=12 per group), namely, Group 1: CSB, Group 2: CSB+1.5 mg DP, Group 3: CSB+3 mg DP, Group 4: CSB+4.5 mg DP, Group 5: SB, Group 6: SB+1.5 mg DP, Group 7: SB+3 mg DP, and Group 8: SB+4.5 mg DP. Filtek Z250 composite was bonded onto dentin, and all specimens were subjected to shear bond strength test at a crosshead speed of 1 mm/min. Highest bond strength was obtained in Groups 1, 2, and 3 (15.1, 13.5, and 16.4 MPa respectively; p>0.05) and the lowest in Groups 6, 7, and 8 (5.5, 5.6, 4 MPa; p>0.05). DP addition, regardless of amount, adversely affected the bond strength of SB. Bond strength of CSB was not affected when 1.5 or 3 mg of DP was added.

The use of endodontically treated and/or fiber post-retained teeth as abutments for fixed partial dentures.

The purpose of this in vitro study was to evaluate the effect of endodontic treatment with or without fiber-post restorations on the fracture strength of abutment teeth under fixed partial dentures (FPDs). Seventy extracted premolar and canine teeth were used. Groups of fiber-post-retained and root-filled teeth were endodontically treated. The teeth were embedded in an acrylic resin perpendicular to the horizontal plane to create fixed partial dentures. The following groups were created using different abutments: (1) sound (S) canine/S premolar, (2) S canine/endodontically treated (ET) premolar, (3) ET canine/S premolar, (4) ET canine/ET premolar, (5) S canine/fiber-post-restored (FPR) premolar, (6) FPR canine/S premolar, and (7) FPR canine/FPR premolar. Each tooth was prepared for a complete-coverage full-metal crown. Impressions were taken; metal frameworks were fabricated and cemented. The samples were exposed to 5,000 cycles of thermomechanical fatigue and loaded compressively until fracture (2 mm/min). The data were statistically analyzed using (Kruskal-Wallis test, α = 0.05). No significant difference was found among the mean fracture strengths of the groups (p = 0.696). There were distinct differences in failure patterns. All of the fracture types were horizontal, and neither vertical nor non-restorable root fractures were recorded. Premolars seemed to be a critical abutment compared to canines when they were sound under FPDs. The percentage of cervical fractures was high in endodontically treated teeth when compared to post-retained groups. In case of post-debonding, the abutment fracture did not occur. When root-filled teeth are used as abutments for FPDs, fiber-post restorations or the creation of abutments from similar structures (ET/ET or FPR/FPR) results in improved conservation of root structure under loading when compared to the abutments from different structures (S/ET, ET/S, FPR/S, S/FPR).

An alternative adhesive strategy to optimize bonding to root dentin.

INTRODUCTION: This study examined the hypothesis that the shear-bond strengths of AH Plus (AH) and Hybrid Root Seal (HRS) to root dentin might be optimized by using a powdered dentin-reinforced bonding procedure. METHODS: The surfaces of root halves obtained from extracted human premolars were ground (800-grit silicon carbide paper), treated (5.25% NaOCl 17% EDTA for 5 minutes followed by distilled water) and randomly allocated into two groups according to the sealer and then into three subgroups according to bonding procedure. Dentin particles with a maximum size of 25 µm were incorporated into the adhesive of Clearfil Liner Bond 2V, and groups were created as follows: no adhesive, adhesive alone, and with powdered dentin reinforced adhesive; 3 × 3 mm high buildups were created using sealer and allowed to set (37 °C, 100% humidity, 72 hours). Shear tests were performed (1 mm/min). Data were calculated as MPa and analyzed (two-way analysis of variance, Tukey test). RESULTS: A significant difference was found between the groups (P = .000). Adhesive or reinforced adhesive had a negative effect on the shear-bond strength of AH, but they significantly increased the shear-bond strength of HRS (P = .000). HRS showed a similar bond strength with either adhesive alone or adhesive reinforced with powdered dentin. AH group was characterized by mixed failure, whereas the predominant failure type of the HRS group was cohesive failure within the sealer. CONCLUSIONS: Reinforcing adhesive resin with powdered dentin may be considered an alternative for optimizing the bonding of methacrylate-based sealers to root dentin and might affect the shear bond strength.

The effect of cavity shape and hybrid layer on the stress distribution of cervical composite restorations.

OBJECTIVES: The aim of this finite elemental stress analysis study was to evaluate the effect of cavity shape and hybrid layer on the stress distribution of the mandibular premolar tooth under occlusal loading. METHODS: The mandibular premolar tooth was selected as the model based on the anatomical measurements suggested by Wheeler. Four different mathematical models were evaluated: 1) a saucer-shaped non-carious cervical lesion restored with a composite without a hybrid layer, 2) a saucer-shaped non-carious cervical lesion restored with a composite with a hybrid layer, 3) a wedge-shaped non-carious cervical lesion restored with a composite without a hybrid layer, and 4) a wedge-shaped non-carious cervical lesion restored with a composite with a hybrid layer. A 200 N force was applied from the buccal tubercule and central fossa of the premolar tooth. The findings were drawn by the SAPLOT program. RESULTS: In models 2 and 4, the output showed that a hybrid layer acts as a stress absorber. Additionally, when the cavity shape was changed, the stress distribution was very different. CONCLUSIONS: Cavity shape and hybrid layer play an important role in stress distribution in cervical restorations.

Composite bond strength to intact enamel with current simplified adhesives.

PURPOSE: This study compared microtensile bond strength (µTBS) of six simplified adhesive systems and an etch-andrinse, one-bottle adhesive system to intact enamel. MATERIALS AND METHODS: Twenty-eight sound incisor teeth were cut at the cementoenamel junction (CEJ) under water cooling. The enamel surfaces were cleaned with pumice, randomly assigned to seven groups and treated with one of the following adhesives: Hybrid Bond (Sun Medical); AdheSE One (Ivoclar/Vivadent); One Coat 7.0 (Coltene/Whaledent); Danville Experimental (Danville Materials); Clearfil S3 Bond (Kuraray); G Bond (GC); and Prelude Total-etch (Danville Materials) as control. Composite resin (Clearfil AP-X, Kuraray) buildups were created and after 24 h, the teeth were sectioned into beams of 1.0 mm2 cross-sectional area. Each beam was tested in a microtensile tester (Bisco) at a crosshead speed of 1 mm/min. Data were calculated as MPa and analyzed by one-way ANOVA. Multiple comparisons were done using the Tukey test. RESULTS: µTBS values of adhesives to intact enamel were as follows (mean ± SD; different letters indicate statistically different groups, p < 0.05): Hybrid Bond: 15.62 ± 3.90a; AdheSE One: 17.29 ± 3.88ab; One Coat 7.0: 19.59 ± 3.95abc; Danville Experimental: 18.65 ± 5.33abc; Clearfil S3 Bond:20.89 ± 2.96bcd; G Bond: 23.49 ± 4.21cd; Prelude Totaletch: 25.79 ± 5.24d. CONCLUSIONS: Clearfil S3 Bond and G Bond showed bond strength similar to Prelude Total-etch (p = 0.064). The other simplified adhesives showed a similar performance (p = 0.239), however, µTBS values to intact enamel of these systems were lower than those obtained by Prelude Total-etch (p < 0.05).

Conservative restoration of severely damaged endodontically treated premolar teeth: a FEM study.

The aim of this finite element method (FEM) study was to test two different restorative techniques used for construction of severely damaged endodontically treated premolar teeth using Finite Element Stress Analysis Method. In this study, four types of three-dimensional (3-D) FEM mathematical models simulating (1) a sound lower single rooted premolar tooth with supporting structures; (2) a root-filled lower premolar tooth without lingual cusp, restored with resin composite; (3) a root-filled lower premolar tooth without lingual cusp restored with resin composite in combination with a polyethylene fiber which is placed circumferentially to help to create a composite lingual wall; (4) a root-filled lower premolar tooth without lingual cusp restored with resin composite in combination with a glass fiber post, were modeled. A 300-N static vertical occlusal load was applied on the node at the center of occlusal surface of the tooth to calculate stress distributions. Solidworks/Cosmosworks structural analysis programs were used for FEM analysis. The analysis of the von Mises stress values revealed that maximum stress concentrations were located at loading areas for all models. Root dentine tissue, lingual cortical bone, and apical bone structures were other stress concentration regions. There were stress concentration differences among the models at root dentine tissue. Although the distribution pattern was similar with composite resin restored tooth model, highest stress values were observed at root dentine in the model restored with post-and-core. Post structure accumulated more stress on its own body. Stress distribution patterns of sound tooth and fiber-reinforced restoration models were found as similar. The present study showed that the use of post material increased the stress values at root dentine structure while reinforcing the restoration with a fiber decreases stress transmission. Fiber-reinforced restoration provided stress distributions similar to sound tooth.