Unraveling the mechanical strength of biomaterials used as a bone scaffold in oral and maxillofacial defects

Three-dimensional printed natural and synthetic biomaterials have evolved as gold standards for tissue engineering scaffolds in recent trends owing to their superior role in hard tissue regeneration. The major drawback of these scaffolds is their relatively poor mechanical strength. Another key consideration in the design of the scaffolds is the difficulty in replicating the complex structural composition of hard tissues such as bones, and its structure cannot be reproduced with a single material that provides a limited range of properties. Sufficient mechanical strength is provided by the structure required for the replacement tissue. The mechanical properties of the scaffold play an important role in many applications of tissue engineering. Therefore, is it sufficient to withstand the force with only a single material used for the scaffold? There are many materials such as natural resin, synthetic resin, and polymers. They are used in combination to fulfill the function and to act as a kingpin by solving their drawbacks. The added material is not only superior in mechanical strength but also compatible with the tissues surrounding the implant, promoting cell adhesion and gradually degrading rather than intoxicating the patient. This review focuses on the various biomaterials used as scaffolds for critical size defects and the aftermath in their mechanical properties.     

机械压应力下骨硬化蛋白对成牙骨质细胞功能影响及机制的体外研究

目的 探究骨硬化蛋白（SOST）对处于机械压应力中的永生化成牙骨质细胞（OCCM-30）的功能影响及其相关的机制。方法 用不同浓度SOST培养液（0、25、50、100 ng·mL ^-1）处理细胞后依靠四点弯曲细胞力学加载器对细胞加载大小为2 000 μstrain、频率是0.5 Hz的单轴压应力6 h,用免疫印迹法检测β-连环蛋白（β-catenin）、磷酸化的细胞信号转导分子p-smad1/5/8、细胞信号转导分子smad1/5/8的蛋白水平;用碱性磷酸酶（ALP）活性检测法检测ALP活性;用荧光实时定量PCR检测核心结合蛋白因子2（Runx-2）、骨钙素（OCN）、骨涎蛋白（BSP）以及细胞核因子κB受体活化因子（RANKL）、骨保护因子（OPG）的表达。结果 p-smad1/5/8随着SOST浓度增加,呈减低的趋势,而β-catenin、smad1/5/8未有显著差异性。在仅对细胞加力时ALP活性降低,随SOST浓度升高,ALP活性逐渐发生下降,Runx-2、OCN和BSP的表达也都呈现降低趋势,RANKL的表达随着SOST增加而升高,OPG则随之下降。结论 压应力下,SOST的升高会对骨形态发生蛋白（BMP）/smad 通路产生抑制作用,对β-catenin表达未产生明显改变。外源性SOST对于BMP存在反馈性的负向调节作用。压应力下SOST对OCCM-30的矿化功能是抑制的,其机制或许是一方面利用BMP信号通路对成骨相关因子Runx2、OCN、BSP等实现下调,另一方面提高了与破牙骨质有关分子 RANKL/OPG的比率。     

Effect of poly(acrylic acid) architecture on setting and mechanical properties of glass ionomer cements

ObjectiveThis work focuses on the influence of poly(acrylic acid) (PAA) architecture (linear or branched) on setting behavior and compressive strength of glass ionomer cements (GICs).MethodsBranched and linear poly(acrylic acid)s were synthesized according to the Strathclyde methodology or by free radical polymerization. They were characterized by ¹H-NMR spectroscopy and size exclusion chromatography to determine their molecular weight and size distribution. GIC setting was characterized by oscillating rheometry and time-dependent FTIR spectroscopy. In addition, compressive strength was tested on cylindrical samples (6 × 4 mm; n = 8/cement composition) after storage in deionized water at 37 °C for one day.ResultsWe used two different routes to prepare PAA. One direct route in order to provide straightforward access to branched PAA and a two-step approach in order to get more control about the PAA molecular weight using tert-butyl acrylate (tBA) for polymerization with subsequent deprotection. Using the second approach we obtained several linear PAA of which a mixture was used in order to mimic the molecular weight and size distribution of branched PAA. This allowed the direct comparison of properties relying only on the polymer architecture. Comparing linear PAA to branched samples in general led to faster setting but at the same time decreased the compressive strength. Increasing molecular weight of branched PAA resulted in even faster GIC setting while increasing compressive strength and this correlates well with the trends reported for linear PAA in literature. Mixing of branched and linear PAA, however, turned out to be an effective way of tailoring GIC properties. Significance: our results suggest that both molecular weight and dispersity need to be considered when choosing suitable PAA architecture for obtaining specific GIC properties.     

Prevalence of oral soft and hard tissue lesions related to mechanical toothcleansing procedures

The prevalence of oral soft and hard tissue lesions related to mechanical oral hygiene procedures was recorded and correlated to toothbrushing habits and oral hygiene status in two selected samples. Fifty-one percent of 533 persons examined exhibited gingival retractions and 45% had wedge-shaped defects in the cervical area of one or several teeth. Both types of lesions were often seen in the same area, indicating a common etiologic factor. The subjects with a good oral hygiene status, as well as those who brushed more than twice daily, showed a high frequency of lesions. The various toothbrushing techniques did not, however, seem to influence the development of such lesions in the present material. Subjective symptoms were reported in a few cases only.     

The extent of slits at the interfaces between luting cements and enamel,dentin and alloy

Øilo, G. The extent of slits at the interfaces between luting cements and enamel, dentin and alloy.

Four different cements were used to assess the presence of slits at the cement/tooth or the cement/alloy interfaces using a tooth-crown model. The model consisted of ground sections of teeth and plane plates of silver/palladium alloy. The plates were fixed with bolts between two brass plates and with three different dimensions of the cement film between tooth and alloy, i.e. 50 μm, 100 μm and 200 μm. The tooth-alloy specimens were sectioned and the adaption of cements was studied with an indirect technique (replica) in a scanning electron microscope. The extent of slits was expressed as the length of all slits relative to the total length of the interface in each specimen.

The results showed that the zinc phosphate cement and poly carboxylate cement exhibited a slight to moderate tendency to formation of slits at the interfaces. The EBA cement had a small extent of slits adjacent to thin cement films, but more slits were observed with increasing film thickness. The composite resin cement had a marked tendency to slit formation independent of the cement film thickness.     

From bench to application: Current practices in tissue engineering and its realisation at maxillofacial units in Germany,Austria and Switzerland

Over the last 20 years, the highly interdisciplinary field of tissue engineering (TE) has become an established subspecialty in research facilities all over the world. Numerous methods and protocols are available for various research intentions and aims, but there are no data indicating which of these methods and resources are generally used. This study is an overview of the resources and methods that are commonly applied in TE research in general, and in the field of oral and maxillofacial surgery (OMFS) in Germany, Austria and Switzerland.The DÖSAK collaborative group for TE developed a detailed questionnaire and collected information from participating university hospitals in these three countries. We evaluated the availability of research facilities, in vitro realisation and in vivo designs for animal studies in these departments.11 units who replied, out of 35 we contacted, conducted research on bone regeneration in interdisciplinary research facilities. 10 departments used xenogeneic and alloplastic scaffolds for in vitro and in vivo applications. In this case, the most commonly utilised trademarks were Bio-Oss^® and CERASORB^®.9 units used osteoblasts (73%) and 10 proliferation assays in vitro, whereas rats served as the standard animal model for histology/immunohistochemistry in 6. All research units were interested in establishing a platform for research exchange and communication.This study shows that tissue engineering is well established and highly accepted in most participating university hospitals and research facilities. The presented data, together with data published in a foregoing paper will help arrange more readily available standardised procedures for further investigations.     

Distribution of non-collagenous dentin matrix proteins and proteoglycans, and their relation to calcium accumulation in bisphosphonate-affected rat incisors

It has been reported that multiple injections of 1-hydroxyethylidene- 1,1-bisphosphonate (HEBP) to rats prevent mineralization of incisor dentin, thereby revealing high concentrations of calcium in the non-mineralized matrix of circumpulpal dentin. To identify the molecules responsible for calcium accumulation in circumpulpal dentin matrix, rats were injected daily with HEBP (8 mg P/kg) for 7 d, and the incisors processed for various histochemical and immunohistochemical staining of non-collagenous matrices of dentin. Cuprolinic blue reactions for proteoglycans (PGs) were equally distributed in non-mineralized matrix of mantle and circumpulpal dentin layers. Dentin sialoprotein (DSP) and osteopontin (OPN) immunoreactions were found in non-mineralized circumpulpal dentin matrix, but not in mantle dentin. In normal incisors, however, predentin matrix showing significant DSP immunoreactivity was negative for Ca-GBHA reactions. HEBP-affected, non-mineralized OPN immunopositive bone matrix was also non-reactive for calcium. From these observations, neither PGs, OPN nor DSP appear to be responsible for calcium accumulation in HEBP-affected circumpulpal dentin. Stains-all reactive component, possibly dentin phosphoprotein (DPP), only showed the same distribution as that of Ca-GBHA in both HEBP-affected and normal dentin matrix, implicating a possible contribution of DPP to calcium accumulation in circumpulpal dentin and, hence, to appositional mineralization of dentin.     

牵张应力对人牙周膜细胞MMP-2表达的影响及相关信号通路的研究

目的：探讨NF-κB通路对牵张应力介导的人牙周膜细胞（HPDLCs）中MMP-2表达的影响.方法：按胶原酶消化法培养HPDLCs,分为5组：非加力对照组（A组）;12％形变率,3h组（B组）;12％形变率,6h组（C组）;12％形变率,12h组（D组）;12％形变率＋PDTC干预,12h组（E组）,通过细胞牵张应力加载系统施加机械牵张应力,结束后收集细胞提取蛋白,用蛋白印迹法检测MMP-2蛋白表达的变化.结果：B、C、D组MMP-2表达大于A组,差异有统计学意义（P＜0.05）,且随着作用时间的延长蛋白表达增加;NF-κB通路抑制剂PDTC可抑制机械牵张应力作用下牙周膜细胞MMP-2表达的增加.结论：持续机械牵张应力可诱导人牙周膜细胞MMP-2表达的增加,从而影响牙周组织细胞外基质代谢,机械牵张应力可通过NF-κB通路影响MMP-2蛋白的表达.     

Effect of staining on the mechanical,surface and biological properties of lithium disilicate

PurposeTo simulate biodegradation and wear of stained and glazed CAD lithium disilicate ceramic, and evaluate their effects on the microbial adherence and mechanical and surface properties of lithium disilicate ceramicMaterials and methods160 lithium disilicate ceramic discs were fabricated and divided in eight groups according to manual stain and glaze application with a fine paint brush (without stain and glaze; with stain and glaze) and aging procedures (no aging; wear at 30 N load, 1.7 Hz, 3 × 10⁵ cycles; biodegradation by exposure to microcosm biofilm; biodegradation + wear; biodegradation + wear). Profilometry was performed to determine the surface roughness and the wear consequences. Biaxial flexural strength test was performed, and a Streptococcus mutans adherence test was conducted to evaluate the number of colony forming units.ResultsUnaged samples with and without stain and glaze presented the lowest values of surface roughness (p < 0.001), but after aging (wear, biodegradation, or both), the samples in the stain and glaze groups were rougher than those in the no stain and glaze groups (p < 0.001). The stain and glaze groups showed the highest volume of wear after aging (p = 0.04), and had the lowest flexural strength values (p < 0.01), irrespective of the aging method. The aging method did not affect the flexural strength (p = 0.06). The number of colonies forming units was higher for biodegradation + no stain and glaze, biodegradation + wear + no stain and glaze, no aging + stain and glaze, biodegradation + stain and glaze, and biodegradation + wear + stain and glaze. The lowest values were observed for no aging + no stain and glaze.ConclusionThe staining and glazing of lithium disilicate increased the surface wear and bacterial adherence, and decreased biaxial flexural strength of the material. When exposed to S. mutans, surface roughness increased, and biodegradation favored bacterial adherence.     

Occurrence of plaque, gingivitis and caries as related to self reported frequency of toothbrushing in fluoride areas in Finland

Abstract Toothbrushing is generally recommended as one of the main means of preventing dental caries and periodontal problems. The present study was an attempt to evaluate the validity of such a claim. In three Finnish towns with low (0.2 part/10⁶), optimal (1.0 part/10⁶) and high (2.5 parts/10⁶) fluoride content in their drinking water, about 40 schoolchildren were examined in each age group of 13, 14 and 15 years. A total of 365 children were first interviewed about their oral health habits, including frequency of toothbrushing. Their teeth were then scored for visible plaque (VPI), gingival bleeding (GBI) and past caries experience (DFS). The total mean scores for the children were VPI = 43 %, GBI = 40 %, and DFS = 14.5. Girls were found to brush more often than boys. About 50 % of the girls and only 10 % of the boys reported brushing their teeth more often than once daily. Among the girls the frequency of toothbrushing significantly increased from age 13 to 15. In all groups high frequencies of toothbrushing were associated with low VPI and GBI scores. No correlation was found between the frequency of toothbrushing and the DFS scores of the children. This lack of correlation persisted also after the total material was grouped according to sex, age, and fluoride content of drinking water. The results indicate that uncontrolled toothbrushing helps to prevent periodontal disorders but has no measureable effect on dental caries.     

Healing of 400 intra-alveolar root fractures. 1. Effect of pre-injury and injury factors such as sex, age, stage of root development, fracture type, location of fracture and severity of dislocation

Abstract – This retrospective study consisted of 400 root‐fractured, splinted or non‐splinted incisors in young individuals aged 7–17 years (mean = 11.5 ± 2.7 SD) who were treated in the period 1959–1995 at the Department of Pediatric Dentistry, Eastman Dental Institute, Stockholm. Four hundred of these root fractures were diagnosed at the time of injury; and 344 teeth were splinted with either cap‐splints, orthodontic appliances, bonded metal wires, proximal bonding with composite resin or bonding with a Kevlar^® or glass fiber splint. In 56 teeth, no splinting was carried out for various reasons. In the present study, only pre‐injury and injury factors were analyzed. In a second study, treatment variables will be analyzed. The average observation period was 3.1 years ± 2.6 SD. The clinical and radiographic findings showed that 120 teeth out of 400 teeth (30%) had healed by hard tissue fusion of the fragments. Interposition of periodontal ligament (PDL) and bone between fragments was found in 22 teeth (5%), whereas interposition of PDL alone was found in 170 teeth (43%). Finally, non‐healing, with pulp necrosis and inflammatory changes between fragments, was seen in 88 teeth (22%). In a univariate and multivariate stratified analysis, a series of clinical factors were analyzed for their relation to the healing outcome with respect to pulp healing vs. pulp necrosis and type of healing (hard tissue vs. interposition of bone and/or PDL or pulp necrosis). Young age, immature root formation and positive pulp sensibility at the time of injury were found to be significantly and positively related to both pulpal healing and hard tissue repair of the fracture. The same applied to concussion or subluxation (i.e. no displacement) of the coronal fragment compared to extrusion or lateral luxation (i.e. displacement). Furthermore, no mobility vs. mobility of the coronal fragment. Healing was progressively worsened with increased millimeter diastasis between fragments. Sex was a significant factor, as girls showed more frequent hard tissue healing than boys. This relationship could possibly be explained by the fact that girls experienced trauma at an earlier age (i.e. with more immature root formation) and their traumas were of a less severe nature. Thus, the pre‐injury or injury factors which had the greatest influence upon healing (i.e. whether hard tissue fusion or pulp necrosis) were: age, stage of root development (i.e. the size of the pulpal lumen at the fracture site) and mobility of the coronal fragment, dislocation of the coronal fragment and diastasis between fragments (i.e. rupture or stretching of the pulp at the fracture site).     

Professionally defined dental treatment needs of middle-aged and older patients attending 21 general practitioners, as related to tooth retention

Data from routine examinations of 497 45–89 year old patients attending 21 South Australian general dental practitioners showed a positive association of the degree of tooth retention with the frequency of dental visits, the seeking of care for a check-up or preventive service (as opposed to a curative service) and professionally defined needs for prophylaxes and restorative care, particularly complex restorative care. Degree of tooth retention among dentate subjects was negatively related to the need for extractions, especially extractions for periodontal reasons, and to the need for denture services. The importance of using data from general dental practices as well as population-based surveys when assessing workforce requirements and when reviewing the appropriate content of undergraduate and postgraduate education programmes has been emphasized.     

Psychometric features of temporomandibular disorders patients in relation to pain diffusion, location, intensity and duration

Summary The aim of the present investigation was to assess the psychological profile of a sample of patients with temporomandibular disorders (TMD) and to compare the psychometric scores between patients with pain of different diffusion, location, intensity and duration. One hundred and ten (N = 110) patients with painful TMD fulfilled three psychometric instruments. Pain features were assessed as categorical variables as concerns its diffusion, viz., diffuse or localised, duration, viz., more or <6 months, and location, viz., joint and/or muscles. Pain intensity was scored on a 0–100 Visual Analog Scale (VAS) rating. Patients with diffuse pain showed higher psychometric scores than patients with localised pain. No significant differences were detected between patients with pain lasting from more or equal than 6 months and those with pain lasting from <6 months as well as between patients with pain localised in the jaw muscles, joints or both, even if a trend for lower scores for patients with joint pain alone was observed. Pain intensity was significantly related with anxiety (ANX), depression (DEP) and somatisation(SOM) scores. In conclusion, pain diffusion and intensity were strongly related with high levels of SOM, ANX and DEP, while no differences in psychometric scores were detected between patients with pain of different duration and location.     

A comparative study of oral health as related to general health, food habits and socioeconomic conditions of 4-year-old Swedish children

ABSTRACT An epidemiologic study of oral health, food habits and socioeconomic conditions of 187 randomly selected 4-year-old children was carried out in the city of Umeå in the north of Sweden. The findings were compared with those in an investigation performed 4 years previously in the same area. The investigation showed a decrease in caries frequency from 1967 to 1971, which might be explained by the advice which had been given at Child Health Centers. The food habits had altered, in that there was less between-meal consumption, particularly of sweets, buns, cakes and soft drinks. Also, increased consumption of fluoride tablets was noted. Multiple regression analyses confirmed the findings of the 1967 study, namely that a high frequency of sweets consumption was positively correlated with caries indexes and that children of parents with a higher educational level had lower caries indexes. It was also found that the Gingival Index was affected by the frequency of consumption of buns, cakes and soft drinks and by a high number of contacts between the teeth.     

Effect of acidic drinks on shade matching,surface topography,and mechanical properties of conventional and bulk-fill composite resins

Statement of problem

Posterior composite restorations may be negatively affected by acidic and colored drinks. Little information is available about the effect of acidic drinks on bulk-fill composite resins.