Thermal/mechanical simulation and laboratory fatigue testing of an alternative yttria tetragonal zirconia polycrystal core‐veneer all‐ceramic layered crown design

Bonfante EA, Rafferty B, Zavanelli RA, Silva NRFA, Rekow ED, Thompson VP, Coelho PG. Thermal/mechanical simulation and laboratory fatigue testing of an alternative yttria tetragonal zirconia polycrystal core‐veneer all‐ceramic layered crown design. Eur J Oral Sci 2010; 118: 202–209. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci This study evaluated the stress levels at the core layer and the veneer layer of zirconia crowns (comprising an alternative core design vs. a standard core design) under mechanical/thermal simulation, and subjected simulated models to laboratory mouth‐motion fatigue. The dimensions of a mandibular first molar were imported into computer‐aided design (CAD) software and a tooth preparation was modeled. A crown was designed using the space between the original tooth and the prepared tooth. The alternative core presented an additional lingual shoulder that lowered the veneer bulk of the cusps. Finite element analyses evaluated the residual maximum principal stresses fields at the core and veneer of both designs under loading and when cooled from 900°C to 25°C. Crowns were fabricated and mouth‐motion fatigued, generating master Weibull curves and reliability data. Thermal modeling showed low residual stress fields throughout the bulk of the cusps for both groups. Mechanical simulation depicted a shift in stress levels to the core of the alternative design compared with the standard design. Significantly higher reliability was found for the alternative core. Regardless of the alternative configuration, thermal and mechanical computer simulations showed stress in the alternative core design comparable and higher to that of the standard configuration, respectively. Such a mechanical scenario probably led to the higher reliability of the alternative design under fatigue.     

Core buildup repair using a clear matrix: a case report and clinical technique

The fracture of core buildup material is common in dental practice. This article describes a core buildup repair technique utilizing a custom matrix. This technique enables the dentist to reestablish the original contour and alignment of the broken core buildup and assures excellent crown fit in a short amount of time with a predictably successful outcome.     

�����ȫ�ɹ����޸����ٴ�Ч������

目的 探讨氧化锆全瓷冠桥修复体的修复效果,为临床应用提供参考.方法 对2008年1月至2009年6月佛山市禅城区口腔医院修复科收治的40例接受全瓷修复的患者,采用计算机辅助设计与计算机辅助制作(CAD/CAM)技术制作氧化锆全瓷冠桥修复体60件,其中上颌32件,下颌28件;前牙单冠24个,后牙单冠21个,前牙固定桥2个,后牙固定桥3个(均为3单位固定桥).分别在修复体黏结后1、3、6、12个月对患者进行随访观察,采用美国加利弗尼亚牙科学会的全瓷修复临床标准对修复体的临床效果进行评价,同时也对牙周健康状况进行评价,记录全瓷修复体牙冠的牙龈出血指数(BI)、牙周袋深度(PD)以及附着丧失(AL).结果 观察期间失访3例患者5件修复体,对剩余的37例患者55件修复体的临床观察结果显示,在黏结1个月后有2件修复体的边缘卡探针,有2颗氧化锆全瓷冠修复的牙齿出现牙龈炎.在黏结3个月后,有1个单冠出现裂纹,1例固定桥断裂,2颗牙齿出现牙龈红肿.在黏结6个月后,有1例桩核冠脱落,2颗牙齿出现牙髓炎或根尖周炎.所有复诊患者在12个月的临床观察中均未见边缘着色和继发龋,有5件修复体的颜色匹配稍差.在各时间点BI、PD和AL等指标与治疗前比较差异均无统计学意义(P＞0.05),各项指标比较差异亦无统计学意义(P＞0.05).结论 氧化锆全瓷修复体具有良好的稳定性和生物相容性,近期临床效果满意.     

The use of an existing cast post and core as an anchor for extrusive movement

PURPOSE: This article describes an original solution for a tooth with an existing cast post and core placed subgingivally. MATERIALS AND METHODS: The tooth was erupted rapidly using a simplified and easy technique that incorporates fiberotomy during the process of movement. RESULTS: The distal finish line of the core, which was subgingival before movement onset, was elevated, allowing the placement of crown margins on sound tooth structure. Clinical evaluation of the tooth after a period of 4 weeks, during which a provisional acrylic resin crown was used for retention, showed no need for corrective surgery, and fabrication of a metal-ceramic crown (Captek) was begun. CONCLUSION: When failing to place crown margins on sound tooth structure, the existence of a cast post and core in such a nonrestorable tooth may serve as an anchor in the process of rapid extrusion. Following the need to respect the biologic width and fulfill the obligatory ferrule effect circumferentially, this extrusive treatment modality was applied to meet high treatment standards.     

Alternative crown systems. Is the metal-ceramic crown always the restoration of choice?

The metal-ceramic crown system still is selected the most frequently because of its strength and versatility. The ability to select metals for color or strength for single units or fixed partial dentures gives great flexibility, but when esthetics of the anterior region are a prime concern, the all-ceramic crown is still an excellent choice. Choice of which all-ceramic system to use is dependent on the strength demands, esthetic needs, amount of tooth structure that can be preserved, and laboratory support available. Where good tooth structure remains but some color, contour, or incisal length changes are desired, the porcelain laminate veneer is an outstanding esthetic and restorative choice. When good labial tooth structure remains but lingual structure is inadequate, a partial veneer gold crown can be an excellent esthetic choice. If moderate tooth structure is lost or moderate staining is present, the Dicor crown is a superb choice. In those instances in which heavy staining is present, a foil or core system should be considered to completely block out the background colors. As the occlusal forces become more of a factor, selection of a restorative system will depend more on strength than esthetic demands. The aluminous porcelain jacket crown still offers great strength and esthetics at a reasonable price. When most of the color is on the surface of the teeth, or when there is a high translucency to the teeth, Dicor can provide very esthetic results, and the Dicor Plus crown offers the opportunity to develop intrinsic shading. When greater strength is required, selection of a foil and core system is suggested, as might be a system that provides a stronger core material, like Alceram or Inceram. These stronger core materials will render improved flexural and compressive strengths, but some increases in brightness may occur with the increased alumina content of the cores. The future in ceramic restorative dentistry may be in the computer-generated crown if ways to develop internal coloring and layered building can be developed and cost can be controlled. Ceramic crowns are best limited to the anterior region of the mouth where occlusal forces normally are less than those found in the posterior region. In selected cases, in which there is no evidence of parafunctional habits, and when the dentist and technician are well versed in functional occlusion and have maximum restorative control of the occlusion, posterior ceramic restorations will be successful. It is important to remember in these cases that porcelain is harder than enamel and very strong in compression.(ABSTRACT TRUNCATED AT 400 WORDS)     

牙冠表面形状测量造型方法

目的：建立牙冠测量造型方法,为修复体ＣＡＤ／ＣＡＭ实现奠定基础。方法：采用自制的牙冠表面形状三维测量仪和精密可调转台获得测量数据,在ＵｎｉＧｒａｐｈｉｃ软件平台上针对牙冠造型进行二次开发,通过旋转坐标轴的方法实现牙冠各面数据拼合,生成牙冠实体模型。结果：获得了上颌中切牙和下颌磨牙的计算机数据模型,逼真地再现了它们的形态。结论：牙冠测量造型方法可行。     

A finite element analysis of ferrule design on restoration resistance and distribution of stress within a root

AIM: To analyse the effect of ferrule height upon the mechanical resistance and stress distribution within a root to explain variations in the pattern of root fracture. METHODOLOGY: An extracted, intact, caries free, maxillary right central incisor was scanned by laser and then reconstructed on a computer to produce a model of the tooth and associated periodontal ligament. A simulated post/core/crown restoration was constructed on conventional tooth preparations with various ferrules. The crown was loaded with a simulated 500 N force and the simulated displacement of components and the tensile and compressive stress within the tooth structure were recorded. RESULTS: Without a ferrule preparation, the simulated crown tilted to the labial and rotated distally. With increasing ferrule height the displacement and rotation of the crown reduced in conventional and crown-lengthening models with maximum reduction occurring when the ferrule height reached 1.5 mm. In ferrule models, higher levels of tensile stress developed in internal (by a factor of 8) and mid-root palatal (by a factor of 90) dentine at the cervical margin of the preparation. With an increase in ferrule height, the area of tensile stress within the palatal mid-dentine expanded towards the cervical margin. Similar patterns and stress values were recorded for the crown-lengthening models. CONCLUSION: The study confirms that a ferrule increases the mechanical resistance of a post/core/crown restoration. However a ferrule creates a larger area of palatal dentine under tensile stress that may be a favourable condition for a crack to develop. Crown-lengthening did not alter the levels or pattern of stress within compared with conventional ferrule preparations.     

制作适合原有可摘局部义齿的基牙全冠的临床方法

目的：研究制作适合原有可摘局部义齿的基牙全冠的修复方法。方法：采取间接法制作基牙全冠，即在备牙后制取模型，并留下可摘局部义齿在技工室制作全冠。结果：做冠后，可摘局部义齿的支托与全冠紧密贴合，卡环固位良好，患者对修复效果表示满意。结论：对于需要制作基牙全冠的病例，应该依据基牙外形保存情况、牙列缺损部位的不同，选择最佳的修复方法。     

Influence of core material on fracture resistance and marginal adaptation of restored root filled teeth

Aim To investigate ex vivo the influence of direct placement core materials on the fracture strength and marginal adaptation of root filled maxillary central incisors restored with glass fibre‐reinforced posts, various core materials and all‐ceramic crowns. Methodology Forty‐eight human maxillary incisors were root filled. Posts were placed and teeth restored with composite cores and crowns (n = 8). Six core materials were examined after thermal cyclic and mechanical loading (TCML). Fracture force was determined under static loading. The marginal adaptation at the interfaces between cement‐tooth and cement‐crown were categorized as ‘intact margin’ or ‘marginal gap’ using scanning electron microscopy. Statistical analysis was undertaken with the Mann–Whitney U‐test (α = P ≤ 0.05). Results Median fracture strength varied between 204 N (low viscous experimental core) and 1094 N (Multicore). No difference in fracture resistance was found with varying viscosity of the core material. The layering technique improved the fracture performance (P = 0.059) to a minor degree. Crowns with dedicated core materials (Rebilda 1063 N; Multicore 1094 N) had a significantly higher fracture resistance than crowns with a conventional restorative material (Tetric Ceram 509 N). Significantly poorer marginal adaptation before TCML was found for the layering technique at the tooth–cement interface and for all experimental cores after TCML. At the crown–cement interface significant differences in marginal adaptation could be determined between Multicore‐layered core (P = 0.002) and Multicore‐Rebilda (P = 0.001) after TCML. Conclusions The fracture strength of post and core restorations was dependent on the core material and bonding system. Marginal adaptation was influenced by the method of application of the core material and by TCML.     

Use of CAD/CAM system to fabricate dental prostheses. Part 1: CAD for a clinical crown restoration.

The development of a computer-aided design system for a clinical crown restoration is reported. Initially, the shape of the standard crown was deformed and adapted on the die depending on the shape of the margin. Then, the measured occlusal record data were taken in the computer graphics, and the adapted crown was adjusted with these data to obtain the centric occlusion. The occlusal data were replaced with data obtained using a functionally generated path record and the occlusal interferences eliminated. The ends of the adapted crown were connected with the margin. Thus, the entire crown was efficiently designed using the computer program developed.     

Fractographic features of glass‐ceramic and zirconia‐based dental restorations fractured during clinical function

Fractures during clinical function have been reported as the major concern associated with all‐ceramic dental restorations. The aim of this study was to analyze the fracture features of glass‐ceramic and zirconia‐based restorations fractured during clinical use. Twenty‐seven crowns and onlays were supplied by dentists and dental technicians with information about type of cement and time in function, if available. Fourteen lithium disilicate glass‐ceramic restorations and 13 zirconia‐based restorations were retrieved and analyzed. Fractographic features were examined using optical microscopy to determine crack initiation and crack propagation of the restorations. The material comprised fractured restorations from one canine, 10 incisors, four premolars, and 11 molars. One crown was not categorized because of difficulty in orientation of the fragments. The results revealed that all core and veneer fractures initiated in the cervical margin and usually from the approximal area close to the most coronally placed curvature of the margin. Three cases of occlusal chipping were found. The margin of dental all‐ceramic single‐tooth restorations was the area of fracture origin. The fracture features were similar for zirconia, glass‐ceramic, and alumina single‐tooth restorations. Design features seem to be of great importance for fracture initiation.     

Additive CAD/CAM Process for Dental Prostheses

This article describes the evolution of a computer‐aided design/computer‐aided manufacturing (CAD/CAM) process where ceramic paste is deposited in a layer‐by‐layer sequence using a computer numerical control machine to build up core and fixed partial denture (FPD) structures (robocasting). Al₂O₃ (alumina) or ZrO₂ (Y‐TZP) are blended into a 0.8% aqueous solution of ammonium polyacrylate in a ratio of approximately 1:1 solid:liquid. A viscosifying agent, hydroxypropyl methylcellulose, is added to a concentration of 1% in the liquid phase, and then a counter polyelectrolyte is added to gel the slurry. There are two methods for robocasting crown structures (cores or FPD framework). One is for the core to be printed using zirconia ink without support materials, in which the stereolithography (STL) file is inverted (occlusal surface resting on a flat substrate) and built. The second method uses a fugitive material composed of carbon black codeposited with the ceramic material. During the sintering process, the carbon black is removed. There are two key challenges to successful printing of ceramic crowns by the robocasting technique. First is the development of suitable materials for printing, and second is the design of printing patterns for assembly of the complex geometry required for a dental restoration. Robocasting has room for improvement. Current development involves enhancing the automation of nozzle alignment for accurate support material deposition and better fidelity of the occlusal surface. An accompanying effort involves calculation of optimal support structures to yield the best geometric results and minimal material usage.     

Evaluation of soft-tissue alteration around implant-supported single-tooth restoration in the anterior maxilla: the pink esthetic score

Purpose: To evaluate the alterations of soft tissue around a single‐tooth implant in the anterior maxilla with a new defined pink esthetic score (PES) at the time of crown placement and 6 months post‐loading. Material and methods: According to the case inclusion criteria, 29 patients subjected to single‐tooth replacement with ITI implant‐supported restoration in the anterior maxilla were included. Assessments of soft tissue after crown placement (baseline) and at 6 months (follow‐up) were performed by two orthodontists with PES. Results: No statistically significant difference was found between the two observers. PES for the single‐tooth implant varied from 6.90 to 9.55 at 6‐month follow‐up. The scores of the mesial and distal papilla, level of soft‐tissue margin, soft‐tissue contour, soft‐tissue color and soft‐tissue texture increased significantly at follow‐up. The highest percentage of improvement in PES was found in the cases scoring 0–4 at the baseline. Conclusions: The esthetic outcome of soft tissue around the single‐tooth implant had improved significantly at follow‐up compared with baseline according to PES assessment. The results suggested that the potential for significant changes in soft‐tissue levels after restorative therapy needs to be considered for single‐implant therapy in the anterior maxilla.     

Fiber-reinforced post and core adapted to a previous metal ceramic crown

A technique to create a fiber-reinforced anatomic post and core adapted to an existing crown is described. This technique is performed with a quartz post adapted to root canal anatomy, using a core composite material. With this technique, a well-adapted anatomic post and core may be achieved in a clinical session.     

Fabricating a post and core to fit an existing crown.

This is a useful method for making a single post and core on an endodontically treated anterior tooth to fit an existing crown. It is a comparatively simple technique and gives a stable result.     

正常下颌第二前磨牙牙冠轴面外形与牙龈外形的几何关系

目的 探讨正常牙冠轴面外形与其周围健康牙龈外形的关系。方法 以下颌第二前磨牙为研究对象,在牙列模型上通过牙冠部、牙龈作３个纵断面,用曲线拟和方法得到每个断面的牙齿轴面外形及相应牙龈外形的曲线方程,以此分析两者之间 关系并计算牙冠起始外形角度,即倒凹程度的大小。结果 不同个体的牙冠轴面外形和牙龈外形有其特定的几何关系,同一断面的牙冠轴面外形曲线对应特定的牙龈外形曲线。同名牙同一断面的牙冠轴面外形之间     

Moving an ankylosed central incisor using orthodontics, surgery and distraction osteogenesis

When a dentist replants an avulsed tooth, the repair process sometimes results in the cementum of the root and the alveolar bone fusing together, with the replanted tooth becoming ankylosed. When this occurs, the usual process of tooth movement with bone deposition and bone resorption at the periodontium cannot function. If dental ankylosis occurs in the maxillary incisor of a growing child, the ankylosed tooth also cannot move vertically with the subsequent vertical growth of the alveolar process. This results in the ankylosed tooth leaving the plane of occlusion and often becoming esthetically objectionable. This report describes a 12-year-old female with a central incisor that was replanted 5 years earlier, became ankylosed, and left the occlusal plane following subsequent normal vertical growth of the alveolar process. When growth was judged near completion, the tooth was moved back to the occlusal plane using a combination of orthodontics, surgical block osteotomy, and distraction osteogenesis to reposition the tooth at the proper vertical position in the arch. This approach had the advantage of bringing both the incisal edge and the gingival margin of the clinical crown to the proper height in the arch relative to their antimeres. Previous treatment procedures for ankylosed teeth have often involved the extraction of the affected tooth. When this is done, a vertical defect in the alveolar process results that often requires additional bone surgery to reconstruct the vertical height of the alveolar process. If the tooth is then replaced, the replacement tooth must reach from the final occlusal plane to the deficient ridge. This results in an excessively long clinical crown with a gingival height that does not match the adjacent teeth.     

Three dimensional shape measurement of teeth (3). The divisional measurement method of abutment teeth

In order to improve the accuracy of the three dimensional shape measurement, the divisional measurement method, which tilts and rotates the abutment teeth was attempted. This system is composed of a high precision laser displacement meter, teeth model scanning machine and personal computer. For the measurement of a crown abutment tooth with indistinct margin lines, the measuring area was divided into four regions of the mesio-distal sides and the buccal-lingual sides. The tooth was tilted on the gonio stage +/- 30 degrees around the mesio and distal direction, rotated 180 degrees around the tooth axis, and measured divisionally. The partial data thus obtained were combined by means of the software program into the composed data. Using this method of measurement, the margin of the abutment tooth was recognizable, and the faulted data, which arose from shielding of the receiving beam, was eliminated. Overlapping data from divisional measurements were deducted and the complete data for the single abutment tooth was saved into a file. In the case of a MOD inlay abutment tooth, the divisional measurements with only rotation were carried out, since each curved wall makes nearly a square angle and sharp boundary. A couple of data sets were combined and complete data without error was obtained. Thus, measurements of abutment teeth were obtained without error. It is possible to get the basic data for the production of crown and inlay by means of CAM technique.     

The role of coronal contour in gingival health.

1. Total clinical crown contour is related to gingival health. 2. The subgingival convexity of a tooth or a restoration should extend facially or lingually no more than one half of the thickness of the gingiva. This protects the gingival crevice and promotes a knifelike free gingival margin, important in plaque control. 3. The facial and lingual surface contours should have gradual curvatures in all directions to facilitate the rubbing and cleaning function of the lips, cheeks, and tongue. 4. The interproximal contour of adjacent teeth, of the tooth contact areas, and of the teeth in relation to the gingival papilla must be such that moving tissues can rub or the patient can perform oral hygiene easily. The requirements may vary depending on the degree of gingival recession and cosmetic needs. 5. Undercontour is better than overcontour where clinical judgment is vague.     

The Use of CAD/CAM Technology for Fabricating Cast Gold Survey Crowns under Existing Partial Removable Dental Prosthesis. A Clinical Report

The fabrication of a survey crown under an existing partial removable dental prosthesis (PRDP) has always been a challenge to many dental practitioners. This clinical report presents a technique for fabricating accurate cast gold survey crowns to fit existing PRDPs using CAD/CAM technology. The report describes a technique that would digitally scan the coronal anatomy of a cast gold survey crown and an abutment tooth under existing PRDPs planned for restoration, prior to any preparation. The information is stored in the digital software where all the coronal anatomical details are preserved without any modifications. The scanned designs are then applied to the scanned teeth preparations, sent to the milling machine and milled into full‐contour clear acrylic resin burn‐out patterns. The acrylic resin patterns are tried in the patient's mouth the same day to verify the full seating of the PRDP components. The patterns are then invested and cast into gold crowns and cemented in the conventional manner.