Treatment of traumatized permanent incisors with crown and root fractures: A case report

A case report of the treatment of permanent incisors with crown and root fractures is presented. A radiolucent lesion at the fracture lines was treated with calcium hydroxide in the coronal fragments for 18 months. Clinically, the teeth became firm and the radiographic results after 2 years showed healing of the lesion and hard tissue filling in the space at the fracture lines. © Munksgaard, 2001.

Effect of phosphate-bonded investments on titanium reaction layer and crown fit

This study analyzed the reaction layer and measured the marginal crown fit of cast titanium applied to different phosphate-bonded investments, prepared under the following conditions (liquid concentration/casting temperature): Rema Exakt (RE) - 100%/237°C, 75%/287°C, Castorit Super C (CS)-100%/70°C, 75%/141°C and Rematitan Plus (RP)-100%/430°C (special to titanium cast, as the control group). The reaction layer was studied using the Vickers hardness test, and analyzed by two way ANOVA and Tukey's HSD tests (α = 0.05). Digital photographs were taken of the crowns seated on the die, the misfit was measured using an image analysis system and One-way ANOVA, and Tukey's test was applied (α = 0.05). The hardness decreased from the surface (601.17 VHN) to 150 μm (204.03 VHN). The group CS 75%/141°C presented higher hardness than the other groups, revealing higher surface contamination, but there were no differences among the groups at measurements deeper than 150 μm. The castings made with CS - 100%/70°C presented the lowest levels of marginal misfit, followed by RE -100%/237°C. The conventional investments CS (100%) and RE (100%) showed better marginal fit than RP, but the CS (75%) had higher surface contamination.

Open-Flap Versus Flapless Esthetic Crown Lengthening: 12-Month Clinical Outcomes of a Randomized Controlled Clinical Trial

Background: Excessive gingival display (EGD) has a negative impact on a pleasant smile. Minimally invasive therapeutic modalities have become the standard treatment in many dentistry fields. Therefore, the aim of this study is to compare the clinical outcomes of open-flap (OF) and minimally invasive flapless (FL) esthetic crown lengthening (ECL) for the treatment of EGD.Methods: A split-mouth randomized controlled trial was conducted in 28 patients presenting with EGD. Contralateral quadrants received ECL using OF or FL techniques. Clinical parameters were evaluated at baseline and 3, 6, and 12 months post-surgery. The local levels of receptor activator of nuclear factor-kappa B ligand (RANKL) and osteoprotegerin (OPG) were assessed by enzyme-linked immunosorbent assay at baseline and 3 months. Patients' perceptions regarding morbidity and esthetic appearance were also evaluated. Periodontal tissue dimensions were obtained by computed tomography at baseline and correlated with the changes in the gingival margin (GM).Results: Patients reported low morbidity and high satisfaction with esthetic appearance for both procedures (P > 0.05). RANKL and OPG concentrations were increased in the OF group at 3 months (P < 0.05). Probing depths were reduced for both groups at all time points, compared with baseline (P < 0.05). There were no differences between groups for GM reduction at any time point (P > 0.05).Conclusions: FL and OF surgeries produced stable and similar clinical results up to 12 months. FL ECL may be a predictable alternative approach for the treatment of EGD.

Influence of abutment-to-fixture design on reliability and failure mode of all-ceramic crown systems

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evaluation of tensile tetention of Y-TZP crowns after long-term aging: Effect of the core substrate and crown surface conditioning

This study evaluated the effect of the core substrate type (dentin and composite resin) on the retention of crowns made of yttrium oxide stabilized tetragonal zirconia polycrystal (Y-TZP), submitted to three inner surface conditionings. For this purpose, 72 freshly extracted molars were embedded in acrylic resin, perpendicular to the long axis, and prepared for full crowns: 36 specimens had crown preparations in dentin; the remaining 36 teeth had the crowns removed, and crown preparations were reconstructed with composite resin plus fiber posts with dimensions identical to the prepared dentin. The preparations were impressed using addition silicone, and 72 Y-TZP copings for the tensile test were produced. Cementation was performed with a dual-cured cement containing phosphate monomers. For cementation, the crown preparation (dentin or resin) was conditioned with the adhesive system, and the ceramic was subjected to one of three surface treatments: isopropyl alcohol, tribochemical silica coating, or thin low-fusing glassy porcelain layer application plus silanization. After 24 hours, all specimens were submitted to thermocycling (6000 cycles) and placed in a special tensile testing device in a universal testing machine to determine failure loads. The failure modes of all samples were analyzed under a stereomicroscope. Two-way analysis of variance showed that the surface treatment and substrate type (alpha=0.05) affected the tensile retention results. The dentin substrate presented the highest tensile retention values, regardless of the surface treatment. When the substrate was resin, the tribochemical silica coating and low-fusing glaze application plus silanization groups showed the higher retention values.

Aesthetic rehabilitation of a complicated crown-root fracture of the maxillary incisor: combination of orthodontic and implant treatment

The aim of this paper is to present a complex rehabilitation, of fractured tooth, with implants in anterior region considering the orthodontics extrusion to clinical success. At 7 years old, the patient fractured the maxillary left central incisor and the dentist did a crown with the fragment. Twenty years later, the patient was referred to a dental clinic for orthodontic treatment, with the chief complaint related to an accentuated deep bite, and a professional started an orthodontic treatment. After sixteen months of orthodontic treatment, tooth 21 fractured. The treatment plan included an orthodontic extrusion of tooth 21 and implant placement. This case has been followed up and the clinical and radiographic examinations show excellence esthetic results and satisfaction of patient. The forced extrusion can be a viable treatment option in the management of crown root fracture of an anterior tooth to gain bone in a vertical direction. This case emphasizes that to achieve the esthetic result a multidisciplinary approach is necessary.

Biomechanical influence of crown-to-implant ratio on stress distribution over internal hexagon short implant: 3-D finite element analysis with statistical test

The study of short implants is relevant to the biomechanics of dental implants, and research on crown increase has implications for the daily clinic. The aim of this study was to analyze the biomechanical interactions of a singular implant-supported prosthesis of different crown heights under vertical and oblique force, using the 3-D finite element method. Six 3-D models were designed with Invesalius 3.0, Rhinoceros 3D 4.0, and Solidworks 2010 software. Each model was constructed with a mandibular segment of bone block, including an implant supporting a screwed metal-ceramic crown. The crown height was set at 10, 12.5, and 15 mm. The applied force was 200 N (axial) and 100 N (oblique). We performed an ANOVA statistical test and Tukey tests; p < 0.05 was considered statistically significant. The increase of crown height did not influence the stress distribution on screw prosthetic (p > 0.05) under axial load. However, crown heights of 12.5 and 15 mm caused statistically significant damage to the stress distribution of screws and to the cortical bone (p <0.001) under oblique load. High crown to implant (C/I) ratio harmed microstrain distribution on bone tissue under axial and oblique loads (p < 0.001). Crown increase was a possible deleterious factor to the screws and to the different regions of bone tissue. (C) 2014 Elsevier Ltd. All rights reserved.

Effect of crown-to-implant ratio on peri-implant stress: a finite element analysis

The aim of this study was to evaluate stress distribution in the fixation screws and bone tissue around implants in single-implant supported prostheses with crowns of different heights (10,12.5, 15 mm crown-to-implant ratio 1:1, 1.25:1, 1.5:1, respectively). It was designed using three 3-Dmodels. Each model was developed with a mandibular segment of bone block including an internal hexagon implant supporting a screw-retained, single metalceramic crown. The crown height was set at 10, 12.5, and 15 mm with crown-to-implant ratio of 1:1, 1.25:1, 1.5:1, respectively. The applied forces were 200 N (axial) and 100 N (oblique). The increase of crown height showed differences with the oblique load in some situations. By von Mises'criterion, a high stress area was concentrated at the implant/fixation screw and abutment/implant interfaces at crown-to-implant ratio of 1:1, 1.25:1, 1.5:1, respectively. Using the maxiinum principal criteria, the buccal regions showed higher traction stress intensity, whereas the distal regions showed the largest compressive stress in all models. The increase of C/I ratio must be carefully evaluated by the dentist since the increase of this C/I ratio is proportional to the increase of average stress for both screw fixation (C/I 1:1 to 1:1.25 ratio = 30.1% and C/I 1:1 to 1 :1.5 ratio = 46.3%) and bone tissue (C/I 1:1 to 1:1.25 ratio = 30% and C/I 1:1 to 1:1.5 ratio = 51.5%). (C) 2014 Elsevier B.V. All rights reserved.

Uncommon crown-root fracture treated with adhesive tooth fragment reattachment: 7 years of follow-up

Crown-root fractures account for 5% of all fractures in permanent teeth and can involve enamel, dentin, and cementum. Depending on whether there is pulpal involvement, these problems may be classified as complicated (which are more common) or noncomplicated. The treatment depends on the level of the fracture line, root length and/or morphology, and esthetic needs. Several treatment strategies are available for esthetic and functional rehabilitation in crown-root fractures. Adhesive tooth fragment reattachment is the most conservative restorative option when the tooth fragment is available and the biological width has no or minimal violation. This article reports a case of an uncomplicated crown-root fracture in the permanent maxillary right central incisor of a young patient who received treatment with adhesive tooth fragment reattachment, preserving the anatomic characteristics of the fractured tooth after periodontal intervention. The fracture line of the fragment had an unusual shape, starting on the palatal side and extending to the buccal side subgingivally. After 7 years, the attached coronal fragment remained in position with good esthetics, as well as clinical and radiographic signs of pulpal vitality, periodontal health, and root integrity, thus indicating success.

A 3-D finite element study of the influence of crown-implant ratio on stress distribution

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of the parafunctional occlusal loading and crown height on stress distribution

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of crown-to-implant ratio, retention system, restorative material, and occlusal loading on stress concentrations in single short implants

Purpose: The aim of this study was to assess the contributions of some prosthetic parameters such as crown-to-implant (C/I) ratio, retention system, restorative material, and occlusal loading on stress concentrations within a single posterior crown supported by a short implant. Materials and Methods: Computer-aided design software was used to create 32 finite element models of an atrophic posterior partially edentulous mandible with a single external-hexagon implant (5 mm wide × 7 mm long) in the first molar region. Finite element analysis software with a convergence analysis of 5% to mesh refinement was used to evaluate the effects of C/I ratio (1:1; 1.5:1; 2:1, or 2.5:1), prosthetic retention system (cemented or screwed), and restorative material (metal-ceramic or all ceramic). The crowns were loaded with simulated normal or traumatic occlusal forces. The maximum principal stress (σmax) for cortical and cancellous bone and von Mises stress (σvM) for the implant and abutment screw were computed and analyzed. The percent contribution of each variable to the stress concentration was calculated from the sum of squares analysis. Results: Traumatic occlusion and a high C/I ratio increased stress concentrations. The C/I ratio was responsible for 11.45% of the total stress in the cortical bone, whereas occlusal loading contributed 70.92% to the total stress in the implant. The retention system contributed 0.91% of the total stress in the cortical bone. The restorative material was responsible for only 0.09% of the total stress in the cancellous bone. Conclusion: Occlusal loading was the most important stress concentration factor in the finite element model of a single posterior crown supported by a short implant.

New insights on reaction pathway selectivity promoted by crown ether phase-transfer catalysis: Model ab initio calculations of nucleophilic fluorination

Crown ethers have the ability of solubilizing inorganic salts in apolar solvents and to promote chemical reactions by phase-transfer catalysis. However, details on how crown ethers catalyze ionic S(N)2 reactions and control selectivity are not well understood. In this work, we have used high level theoretical calculations to shed light on the details of phase-transfer catalysis mechanism of KF reaction with alkyl halides promoted by 18-crown-6. A complete analysis of the of the model reaction between KF(18-crown-6) and ethyl bromide reveals that the calculations can accurately predict the product ratio and the overall kinetics. Our results point out the importance of the K* ion and of the crown ether ring in determining product selectivity. While the K* ion favors the S(N)2 over the E2 anti pathway, the crown ether ring favors the S(N)2 over E2 syn route. The combination effects lead to a predicted 94% for the S(N)2 pathway in excellent agreement with the experimental value of 92%. A detailed analysis of the overall mechanism of the reaction under phase-transfer conditions also reveals that the KBr product generated in the nucleophilic fluorination acts as an inhibitor of the 18-crown-6 catalyst and it is responsible for the observed slow reaction rate. (C) 2012 Elsevier B.V. All rights reserved.