Peel bond strength of resilient liner modified by the addition of antimicrobial agents to denture base acrylic resin

In order to prolong the clinical longevity of resilient denture relining materials and reduce plaque accumulation, incorporation of antimicrobial agents into these materials has been proposed. However, this addition may affect their properties.

Objective

This study evaluated the effect of the addition of antimicrobial agents into one soft liner (Soft Confort, Dencril) on its peel bond strength to one denture base (QC 20, Dentsply).

Material and Methods

Acrylic specimens (n=9) were made (75x10x3 mm) and stored in distilled water at 37ºC for 48 h. The drug powder concentrations (nystatin 500,000U - G2; nystatin 1,000,000U - G3; miconazole 125 mg - G4; miconazole 250 mg - G5; ketoconazole 100 mg - G6; ketoconazole 200 mg - G7; chlorhexidine diacetate 5% - G8; and 10% chlorhexidine diacetate - G9) were blended with the soft liner powder before the addition of the soft liner liquid. A group (G1) without any drug incorporation was used as control. Specimens (n=9) (75x10x6 mm) were plasticized according to the manufacturers'' instructions and stored in distilled water at 37ºC for 24 h. Relined specimens were then submitted to a 180-degree peel test at a crosshead speed of 10 mm/min. Data (MPa) were analyzed by analysis of variance (α=0.05) and the failure modes were visually classified.

Results

No significant difference was found among experimental groups (p=0.148). Cohesive failure located within the resilient material was predominantly observed in all tested groups.

Conclusions

Peel bond strength between the denture base and the modified soft liner was not affected by the addition of antimicrobial agents.     

The effect of temperature changes on adaptation of resin fillings. II

In earlier laboratory investigations of thermal percolation at resinous fillings the duration of the heating periods was too long to be realistic. The aim of the present work was to investigate the effect of repeated heatings of realistic duration on the formation of marginal gaps between filling and tooth during a subsequent cooling below the minimum value in the temperature cycling process. Fillings made in extracted human teeth were studied. The brands investigated were Adaptic, Blendànt, Concise, Opotow, Sevriton Simplified, and Swedon. After closure of the initial gaps by water absorption expansion the fillings were polished and subjected to thermal cycling. The specimens were cycled between either 37° and 50° C or 37° and 60° C, the duration of each immersion in the warmer bath was 2 or 5 seconds, and the number of cycles was 1, 10, 100 or 1000. The effect of the cycling was investigated by measuring the width of marginal gaps appearing at a temperature lower than 37° C. It was found that the width of the gaps was only little affected by thermal cycling between 37° and 50° C. Cycling between 37° and 60° C increased the gap widths only with Opotow, Sevriton Simplified, and Swedon. The data indicate that thermal percolation for a number of brands may be of no clinical importance.     

A Comparison of two prosthetic methods for the treatment of Denture Stomatitis

In a case series of 30 full denture patients, two prosthetic trauma-eliminating methods recommended for treating inflammation of the mucosa beneath full maxillary dentures, were compared: (A) indirect relining with cold-curing resin; (B) repeated temporary relining with a tissue conditioner.

No significant difference in healing time was found between the two methods, nor when the patients were grouped according to resilience of the anterior alveolar process or denture wearing habits.

The study indicates that the choice between the two methods may be based upon such factors as the time required at the operating chair, access to a dental technician, etc. In certain cases the use of a tissue conditioner may be preferred in order to allow displaced soft tissues to return to normal contour before impression taking.     

Reinforcement of denture base resin with short vegetable fiber

Objectives

Short ramie fibers were selected to investigate the effect of fiber length and volume fraction on the flexural properties of ramie fiber reinforced denture base PMMA. With the aid of measured interfacial shear strength and theoretical prediction values, experimental results were well interpreted.

Methods

Interfacial properties between denture base PMMA and ramie fibers were evaluated by single fiber pull-out test. Then, chopped ramie fibers were pre-stirred with PMMA powder by a mechanical blender and then mixed with MMA liquid to fabricate composites. Two crucial influencing factors, fiber volume fraction and fiber length, were studied to clarify their effects on flexural properties of composites.

Results

With 1.5 mm fibers addition, flexural modulus of denture base PMMA rose from 2.50 to 3.46 GPa with 10 vol.% fibers, while flexural strength declined steadily with increment of fiber content. If fiber length was 3.0 mm, the modulus showed a growth to 3.5 GPa at 4 vol.% fiber content followed by a drop to 3.00 GPa at 10 vol.%, whereas fluctuation in strength was experienced. Experimental results were discussed by comparison with two theoretical models.

Significance

Short ramie fiber reinforced denture base PMMA had higher flexural modulus than neat resin, while strength was lowered due to the weak interfacial adhesion. The potential of vegetable fibers as reinforcing agents for denture base should be further investigated by strengthening the interface between cellulose and denture base PMMA.     

Influence of procedural variations during the laboratory phase of complete denture fabrication on patient satisfaction and denture quality

Objectives

To compare subjective and objective outcomes of complete dentures fabricated with standard clinical protocols, but omitted selected steps during the laboratory phase.

Materials and methods

Forty-three edentulous patients (mean age 58.1 years, SD 9.9, range 35–78), were consecutively recruited and randomly assigned to one of four groups according to selected variations of laboratory steps: Group 1 (n = 10), omission of secondary casts obtained from impressions in border moulded custom trays; Group 2 (n = 10), omission of secondary casts and face-bow articulator mounting; Group 3 (n = 10), omission of face-bow mounting; Group 4 (n = 13), no steps omitted (control). Clinical procedures for all groups were identical, and performed by senior dental students under supervision of prosthodontists, all of whom were blinded to the Group. At 1-, 4- and 12-weeks after delivery, patients rated their overall satisfaction, as well as a range of functional factors using visual analogue scales. An independent blinded prosthodontist similarly rated four domains of denture quality at the 1-week follow-up.

Results

No significant differences were noted among the groups in all aspects of patients’ assessments at all the time points (P > 0.1). There were no significant differences in prosthodontists’ ratings of denture quality in any of the domains examined (P > 0.1).

Conclusion

Selected omissions of steps (face-bow mounting and/or secondary casts) during the laboratory phase of complete denture fabrication has only a minor role, if any, in subjective and objective outcomes, contrasting with the common belief that such omissions will adversely affect outcomes.

Clinical significance

General practitioners provide most complete dentures. Many do not follow all the procedures they were taught at dental school. Our finding that omitting frequently advocated steps made no difference to patient satisfaction or to denture quality suggests that cost-effectiveness through simplifications be considered in practice and in education.     

Cyclic fatigue testing of denture teeth for bulk fracture

Objectives

Clinical experience with implant-supported dentures indicates that fracture and chipping of teeth are becoming an issue. Tooth fracture and chipping rates of approximately 2.5% per year are being experienced at one university. There has been no standardized test developed for bulk fracture or chipping of denture teeth. Such a test would aid in the development of improved teeth and in their evaluation.

Methods

Central incisor teeth were embedded in acrylic and loaded on incisal edges at 90° to their long axes. Teeth tested included ones commercially available and two sets made from improved materials designed to increase toughness. Cyclic loading was done at 5 Hz from 20 N to 135 N, 150 N, 175 N and 200 N. Data was analyzed using lifetime analysis software fit at each of the accelerated loads and then extrapolated to clinical use loads (Alta 7, Reliasoft Corp.) Clinical use loads were derived from extrapolation of probability of failure (Pf) data to 2.5% Pf.

Results

When carefully embedded, teeth could be reproducibly loaded to failure by bulk fracture involving a failure mode similar to that seen clinically. Clinical use loads were calculated to be in the range of 70 N. Results from accelerated loading could be fit to similar probability of failure distributions allowing extrapolation to clinical use loads.

Significance

This work was able to develop a clinically valid bulk fracture test for the fatigue failure of incisor denture teeth. It appears that teeth fabricated with improved materials will be expected to perform better clinically. Thus both the null hypotheses were rejected.     

Comparative Evaluation of Tensile Bond Strength between Silicon Soft Liners and Processed Denture Base Resin Conditioned by Three Modes of Surface Treatment: An Invitro Study

Soft denture liners act as a cushion for the denture bearing mucosa through even distribution of functional load, avoiding local stress concentrations and improving retention of dentures there by providing comfort to the patient. The objective of the present study was to compare and evaluate the tensile bond strengths of silicone-based soft lining materials (Ufi Gel P and GC Reline soft) with different surface pre treatments of heat cure PMMA denture base acrylic resin. Stainless steel dies measuring 40 mm in length; 10 mm in width and 10 mm in height (40 × 10 × 10) were machined to prepare standardized for the polymethyl methacrylate resin blocks. Stainless steel dies (spacer for resilient liner) measuring 3 mm thick; 10 mm long and 10 mm wide were prepared as spacers to ensure uniformity of the soft liner being tested. Two types of Addition silicone-based soft lining materials (room temperature polymerised soft lining materials (RTPSLM): Ufi Gel P and GC Reline soft) were selected. Ufi Gel P (VOCO, Germany), GC Reline soft (GC America) are resilient, chairside vinyl polysiloxane denture reliners of two different manufacturers. A total of 80 test samples were prepared of which 40 specimens were prepared for Group A (Ufi Gel P) and 40 specimens for Group B (GC Reline soft). In these groups, based on Pre-treatment of acrylic resin specimens each group was subdivided into four sub groups of 10 samples each. Sub-group I—without any surface treatment. Sub-group II—sand blasted Sub-group III—treated with Methyl Methacrylate monomer Sub-group IV-treated with chemical etchant Acetone. The results were statistically analysed by Kruscal Wallis test, Mann–Whitney U test, and Independent t test. The specimens treated with MMA monomer wetting showed superior and significant bond strength than those obtained by other surface treatments. The samples belonging to subgroups of GC Reline soft exhibit superior tensile bond strength than subgroups of Ufi Gel P. The modes of failure of all specimens were mostly adhesive in nature. Surface pre treatments by chemical means improved the bond strength between the silicone liners and denture base.     

基牙牙周损伤影响可摘局部义齿应力分布的三维有限元分析

目的 探讨三维红外扫描用于可摘局部义齿三维有限元建模的可行性,并分析基牙牙周损伤对可摘局部义齿应力分布的影响,以期为临床提供参考.方法 利用齿科非接触式红外扫描仪和Simpleware软件对下颌肯尼迪分类法Ⅱ类缺损的可摘局部义齿进行三维建模,构建正常牙槽骨组、牙槽骨吸收组和牙槽骨吸收伴牙周膜增宽组三维有限元模型.使用Abaqus有限元分析软件,研究垂直加载和颊侧45°加载条件下3组牙槽骨的应力分布.结果 垂直加载和颊侧45°加载条件下,3组模型均在义齿近中基牙和剩余牙槽嵴远中出现应力集中;牙槽骨吸收伴牙周膜增宽组近中基牙的应力最大(分别为3.57和2.50 MPa),其次为牙槽骨吸收组(分别为3.21和2.41 MPa),正常牙槽骨组最小(分别为2.63和1.79 MPa).颊侧45°加载时3组模型剩余牙槽嵴远中颊侧和远中位点上的应力值均大于垂直加载.结论 基于三维红外扫描的有限元建模方法是可摘局部义齿有限元应力分析有效的建模方式.     

Influence of high expansion dental stone used as investing medium on the changes in occlusal vertical dimension of complete dentures

Problem statementDespite advances in materials and techniques, complete dentures made of acrylic resin experience an increase in the occlusal vertical dimension (OVD) during processing. Many factors that affect the OVD of complete dentures are known. However, no study has examined the effect of using high-expansion dental stone (type V) as an investing material on the OVD.PurposeThis study investigated the effects of using a high-expansion dental stone as an investing material on changes in the OVD of complete dentures.Material and methodsTwenty sets of simulated upper and lower dentures were processed by the compression molding technique. Specimens were equally divided into 2 groups. In the dental stone type III (DST III) group, the lower, middle, and upper parts of a flask were filled with DST III. In the dental stone type V (DST V) group, the procedure was the same as in the DST III group, except that the middle layer was made of high-expansion DST V. Changes in the OVD were measured before and after denture processing. Collected data were analyzed with t-test statistics. Differences were considered statistically significant at the 95% confidence level.ResultsBoth groups showed a small increase in the OVD as a result of processing, but the OVD increase was significantly less in the DST V group compared to the DST III group.ConclusionHigh-expansion DST V can be recommended as an investing material to reduce the increase in the OVD that may occur while processing complete dentures.     

Furlow术式及改良兰式修复浅Ⅱ度腭裂的临床研究

目的对比Furlow术式及改良兰式对浅Ⅱ度腭裂的修复效果,评价这两种手术方式对于修复此类腭裂的优劣。方法 50例浅Ⅱ度腭裂患者随机分成两组,A组使用Furlow术式,B组使用改良兰式,对比两组患者的术后软腭延长长度、手术时间、术中出血量、术后3 d平均体温及术后语音改善的程度。结果两种术式在术后软腭延长长度方面,Furlow术式优于改良兰式,前者为(0.794±0.198)cm,后者为(0.118±0.076)cm,差异有统计学意义(t=15.928,P<0.001)。手术时间、术中出血量、术后3 d平均体温及术后语音改善程度,2种术式差异无统计学意义(P>0.05)。结论两种术式均可用于浅Ⅱ度腭裂的修复,但Furlow术式在延长软腭方面优势明显,对于不同类型腭裂可选用个体化修复方案。