Restoration of non-carious cervical lesions: Part II. Restorative material selection to minimise fracture

OBJECTIVE: It is still largely unknown as to what material parameter requirements would be most suitable to minimise the fracture and maximising the retention rate of the restoration of cervical non-carious lesions (NCCL). The present paper, as a first of its kind, proposes a radical approach to address the problems of material improvement, namely: numerical-based, fracture and damage mechanics materials optimisation engineering. It investigates the influence of the elastic modulus (E) on the failure of cervical restorative materials and aims to identify an E value that will minimise mechanical failure under clinically realistic loading conditions. METHOD: The present work relies on the principle that a more flexible restorative material would partially buffer the local stress concentration. We employ a "most favourable" parametric analysis of the restorative's elastic modulus using a fracture mechanics model embedded into finite element method. The advanced numerical modelling adopts a Rankine and rotating crack material fracture model coupled to a non-linear analysis in an explicit finite element framework. RESULTS: The present study shows that the restorative materials currently used in non-carious cervical lesions are largely unsuitable in terms of resistance to fracture of the restoration and we suggest that the elastic modulus of such a material should be in the range of 1GPa. We anticipate that the presented methodology would provide more informative guidelines for the development of dental restorative materials, which could be tailored to specific clinical applications cognisant of the underlying mechanical environment.     

用三种测度对楔状缺损形成因素的研究

目的探讨楔状缺损几种致病因素的作用和研究楔状缺损时所用测度的意义。方法设计了缺损侧影深度、面积和缺损体积３种测度，对横刷牙、酸蚀、力疲劳在９对双尖牙实验性楔状缺损形成过程中所起的作用进行了分析。结果证明３种因素单独作用均可致损，但缺损侧影深度间差异无显著性；而３种因素联合致损的速度与缺损程度明显增加（Ｐ＜０．００５），且缺损区牙本质和釉质的硬度显著降低（Ｐ＜０．０５）。以各实验组研究结果计算，一维测度与二维测度之间仅有低度相关，而与三维测度间有中度相关，表明用缺损深度为测度较用其面积更能代表缺损的程度。结论当样本较大且测量条件有限时，研究楔状缺损的问题仍可用一维测度；而当样本量较小，又具备较先进的三维测量设备时，用三维测度可以提高研究结果的敏感度。     

Restorative treatment of cervical lesions with resin composites: 4-year results

PURPOSE: To verify the clinical behavior of two resin-based composites with different Young's modulus (AElite Fil and Elite Flo) in the restoration of carious and non-carious cervical lesions after 48 months of clinical service. METHODS: 116 restorations with the two different materials (60 with AElite Fil and 56 with AElite Flo) were performed in 15 patients and controlled for 48 months. Retention rate and USPHS criteria were recorded at 6, 12, 24, 36 and 48 months. RESULTS: The retention rate was 66% for AElite Fil in carious and non-carious lesions and 65 and 47% for AElite Flo in carious and non-carious lesions respectively at 48 months. A decrease of quality of restorations in time was recorded with all USPHS criteria, with no statistically significant difference between materials tested.     

人工楔状缺损对牙颈部硬组织应力分布的影响

目的 分析楔状缺损患牙颈部硬组织的应力分布.方法 在下颌前磨牙沿釉牙本质界建立三角形缺损,设计楔状缺损模型,模拟侧方运动中牙齿的受力情况,对下颌前磨牙颈部硬组织行非线性接触分析.结果 斜向载荷下,釉牙本质界缺损的下颌前磨牙缺损区尖端存在明显的拉应力集中.随缺损高度的增加,应力值增大,应力集中程度也增加:应力集中区沿釉牙...     

Dyract复合充填材料与夹层技术修复楔形缺损的临床对照研究

目的：探讨Ｄｙｒａｃｔ复合充填材料在牙体修复方面替代夹层技术的可行性。方法：在同一个体上选择条件基本相同的楔形缺损患牙共３２０颗,分别采用Ｄｙｒａｃｔ复合充填材料和夹层技术充填修复,随访观察１８－２４月,并对其疗效进行比较。结果：Ｄｙｒａｃｔ组、夹层技术组分别有３、５颗修复物脱落,两组其余牙外形均完整、无缺损、表面光滑、色泽光亮 ; Ｄｙｒａｃｔ组修复物的脱落率为 １．８７％,边缘密合度失败率为１．８７％,均低于夹层技术组（ Ｐ＞ ０．０５）;两组均无牙髓病变及继发龋发生; Ｄｙｒａｃｔ总失败率为 １．８７％,低于夹层技术组（ Ｐ＞ ０．０５）２结论： Ｄｙｒａｃｔ复合充填材料具有玻璃离子复合树脂夹层技术的功效,在牙体修复方面可替代夹层技术     

Effect of root morphology on biomechanical behaviour of premolars associated with abfraction lesions and different loading types

The aim of this study was to investigate the biomechanical behaviour of maxillary premolar teeth regarding root morphology and abfraction depth, submitted to axial and oblique occlusal load. The investigation was conducted using 3D finite element analysis and strain gauge test. Sound maxillary premolar single and double root were selected for 3D model generation. The teeth were scanned for external morphology data acquisition. The 3D geometry was stored in *.STL and exported to Bio‐CAD software (Rhinoceros‐3D) to model generation. Mesh generation, mechanical properties and boundary conditions were performed in finite element software (Femap, Noran Engineering, USA). Twelve models were generated: sound tooth, 1·25 and 2·5 mm abfraction teeth. 100N compressive static load was applied: axially and 45° angle to the long axis on the palatine surface of the buccal cusp. Two strain gauges were bonded on the teeth mounted in a mechanical testing machine. Von Mises criterion showed that the double‐root teeth associated with 2·5 mm abfraction and oblique loading presented higher stress values. Axial loading associated with single‐root teeth propitiated the lowest stress rates. Double root sound 1·25 and 2·5 mm abfraction teeth associated with oblique loading showed the highest strain values (μS): 692·6, 1043·31 and 1236·14, respectively. Single root sound 1·25 and 2·5 mm abfraction teeth associated with oblique loading showed 467·10, 401·51 and 420·98 strain values, respectively. Axial loading showed lower strain rates, ranging from 136·12 to 366·91. The association of deep lesions, oblique loading and double‐root tooth promoted higher stress and strain concentration.     

楔状缺损发生的位置及其相关因素的调查研究

目的了解楔状缺损发生的情况，病损发生的部位及其相关的因素。方法对４６２例中老年人进行调查。结果该组人群楔状缺损患病率为９９．１％，病损绝大多数发生于牙齿唇、颊面，部分发生于舌侧牙颈部，好发牙齿分别为双尖牙和磨牙。病损发生的部位与刷牙及酸蚀因素无明显关系，患牙的面磨损度更重、义齿基牙率较高且功能动度增大，舌侧患病牙齿的上述症状更显著，患牙的牙周病程度较重。结论楔状缺损的发生除刷牙及酸蚀因素外还与力或力累积有关；舌侧病损的发生可能与创伤性力相关。     

楔状缺损修复体固位的实验与临床研究

作者使用在楔状缺损冠面上钻孔、玻璃离子充填缺损的方法修复楔状缺损。通过生物力学的方法测定１０颗离体牙充填物的抗拉力强度。对３２例楔状缺损患者的１３４颗牙进行了临床观察，分别用新方法与常规方法进行治疗。结果表明：本法充填固位效果比常规方法好。     

The influence of cavity design and glass fiber posts on biomechanical behavior of endodontically treated premolars

The aim of this study was to evaluate the effect of cavity design and glass fiber posts on stress distributions and fracture resistance of endodontically treated premolars. Fifty extracted intact mandibular premolars were divided into 5 groups (n = 10): ST, sound teeth (control); MOD, mesio-occlusal-distal preparation + endodontic treatment (ET) + composite resin restoration (CR); MODP, mesio-occlusal-distal + ET + glass fiber post + CR; MOD2/3, mesio-occlusal-distal + two thirds occlusal-cervical cusp loss + ET + CR; and MODP2/3, mesio-occlusal-distal + two thirds cusp loss + ET + glass fiber post + CR. The specimens were loaded on a cusp slope until fracture. Fracture patterns were classified according to four failure types. Stress distributions were evaluated for each group in a two-dimensional finite element analysis. The fracture resistance of the MODP, MOD2/3, and MODP2/3 groups was significantly lower than the ST and MOD groups (p < 0.05). The loss of dental structure and the presence of fiber post restoration reduced fracture resistance and created higher stress concentrations in the tooth-restoration complex. However, when there was a large loss of dental structure (MODP2/3), the post reduced the incidence of catastrophic fracture types.     

老年人楔状缺损临床治疗评价

目的:总结老年人楔状缺损治疗特点及最有效的方法。方法:选择60岁以上的老年人178例共452颗楔状缺损牙齿,用不同的材料进行临床治疗研究。结果:Dyract复合体与Seal&ProtectTM脱敏剂共同修复楔状缺损在临床上取得很好效果。结论:老年人楔状缺损是常见病、多发病,Dyract复合体与Seal&ProtectTM脱敏剂是一种较好的修复方法。     

牙齿楔状缺损与侧方(牙合)工作侧咬合接触关系的调查

目的研究牙颈部楔状缺损与牙齿咬合接触的关系.方法选取123名中年机关干部.用0.02mm厚的超薄咬合纸,临床检查侧方运动工作侧上颌尖牙、第一、二前磨牙、第一磨牙颊尖各斜面上及咀嚼循环各个时期中的牙齿咬合接触情况;评估接触程度.结果患楔状缺损牙齿咬合接触程度明显高于未患楔状缺损牙.上颌尖牙和前磨牙楔状缺损患牙在远中(上第一磨牙的近、远中)斜面上咬合接触程度高于未患牙,患牙在咀嚼侧方运动循环的中、末(上第一磨牙在初、中或末)期咬合接触程度增加.结论牙颈部楔状缺损的发生与牙齿的咬合接触程度加重有关.     

The influence of the sensor type on the measured impact absorption of mouthguard material

Abstract –  Mouthguards have been tested for impact energy absorption using drop-ball and/or pendulum devices. While all reports show efficiency of the mouthguard, the impact absorption abilities reported differ considerably. This difference has been attributed to differences of mouthguard material, design, and the impact force used. However, it is also possibly because of the difference in the sensors used in the experiments. The purpose of this study was to test three types of sensors and to assess which type was most appropriate for measurement of the impact absorption ability of mouthguards. A pendulum-type testing equipment and steel ball, wooden bat, baseball, field-hockey ball were used as the impact object. For all sensors or impact objects, the mouthguard decreased the impact forces. However, the absorption ability of the mouthguard varied according to the sensor or impact object. The absorbency values became smaller with the strain gauge, the accelerometer, and the load cell, respectively. With the steel ball as the impact object, 80.3% of impact absorption was measured with the strain gauge and the accelerometer but, only 62.1% with the load cell sensor. With the wooden bat, impact absorption was 76.3% with the strain gauge and 38.8% for the load cell. For the baseball ball, the absorption measurement decreased from 46.3% with the strain gauge to 4.36 with the load cell and for the field-hockey ball, the decrease in measurement values were similar (23.6% with the strain gauge and 2.43% with the load cell). It is clear that the sensor plays an important role in the measurement values reported for absorbency of mouthguard materials and a standard sensor should be used for all experiments.     

牙齿楔状缺损与侧方工作侧咬合接触关系的调查

目的研究牙颈部楔状缺损与牙齿咬合接触的关系.方法选取123名中年机关干部.用0.02mm厚的超薄咬合纸,临床检查侧方运动工作侧上颌尖牙、第一、二前磨牙、第一磨牙颊尖各斜面上及咀嚼循环各个时期中的牙齿咬合接触情况;评估接触程度.结果患楔状缺损牙齿咬合接触程度明显高于未患楔状缺损牙.上颌尖牙和前磨牙楔状缺损患牙在远中(上第一磨牙的近、远中)斜面上咬合接触程度高于未患牙,患牙在咀嚼侧方运动循环的中、末(上第一磨牙在初、中或末)期咬合接触程度增加.结论牙颈部楔状缺损的发生与牙齿的咬合接触程度加重有关.     

Restorative material for children's teeth: preferences of parents and children

The purpose of the study was to assess the preferences of parents and children regarding amalgam or tooth colored restoration material for the children's teeth and some associated factors. One hundred and 24 children aged 4 to 12 years of age (Mean age-7.3 +/- 2.4) who needed at least 1 dental restoration were selected for the study. After a dental examination, the parents were asked to complete a questionnaire requesting demographic information, preference of restoration material for their children's teeth, and influencing factors. The children were then asked to answer questions on which material they preferred and what influenced their decision. More parents preferred tooth colored restorations to amalgam restorations for their children's teeth. However, 12 percent of the parents preferred amalgam. For 40 percent of the parents, the restoration material did not matter. For most parents (76 percent), whether the tooth was primary or permanent did not influence their choice. The highest concern was given to the implications of a restoration material on the health of the body or the tooth. Half of the children preferred tooth colored restorations. For nearly 30 percent, the restoration material did not matter. Significantly, more younger children than older children noted the filling's visual prominence as an important factor (30 percent and 3 percent, respectively). Younger children were more influenced by their parents' preferences than older children. It is concluded that tooth colored restorations are preferred to amalgam by both parents and children.     

脉冲Nd:YAG激光在修复牙齿楔状缺损中的临床观察

目的评价脉冲Nd：YAG激光在修复牙齿楔状缺损中的临床效果。方法将73例患者的376颗楔状缺损牙随机分为三组，分别用激光（A组）、酸蚀（B组）、及激光＋酸蚀（C组）处理缺损区，再用光固化复合树脂充填。治疗后12个月及24个月复查并对各组的充填成功率进行统计学分析。结果激光组与酸蚀组比较无显著性差异。激光＋酸蚀组与激光组、酸蚀组比较均有显著性差异。结论脉冲Nd：YAG激光照射处理楔状缺损区可提高牙面与光固化树脂粘接力，提高充填的成功率。     

Prosthetic loading considered in the biomechanical design of removable partial dentures

The prosthetic loads in removable partial dentures are analyzed. Different clinics and laboratory methods to make retain and support are discussed. From its study is infered a therapeutic prognostic.