Effect of auxiliary grooves on molar crown preparations lacking resistance form: a laboratory study.

PURPOSE: To investigate the effect of auxiliary grooves on resistance to dislodgment of crowns on compromised molar preparations lacking resistance form. MATERIALS AND METHODS: Thirty human molar teeth were randomly assigned to three groups of ten, and prepared to a height-to-width ratio of 0.3 with a total convergence of 50 degrees , and 1-mm shoulder margin. Base metal alloy copings were constructed with a 45 degrees loading platform and cemented with zinc phosphate cement under a 50 N load. Initially, resistance testing was conducted using a Universal Testing Machine (Instron) at 1 mm/min for all 30 specimens. Following crown dislodgment, Group 1 copings were recemented and retested, Group 2 had one axial groove added, and Group 3 had two axial grooves added. New copings for Groups 2 and 3 were made, cemented, and again tested for resistance. Standardized radiographs were taken prior to initial cementation and scanned into digital images. The percentage of area occupied by the pulpal chamber above the acrylic mounting (PS), and the closest distance to pulp from the preparation surface (CD) were measured. RESULTS: Recementation or the addition of one groove did not affect the dislodgment values (p > 0.05), but addition of two grooves caused a highly significant increase in resistance (p < 0.001). Regression analysis showed an inverse relationship between initial resistance values and pulpal space area. Lower resistance values were observed when the pulpal space area was large (p= 0.004). CONCLUSIONS: Crowns can be recemented without affecting resistance to dislodgment. Two grooves should be incorporated into compromised molar crown preparations to increase resistance form. Teeth with large pulps and therefore less coronal dentine have poorer resistance form, and therefore would benefit from placement of auxiliary grooves.     

The degree of zinc phosphate cement coverage of complete crown preparations and its effect on crown retention.

This investigation examined the amount of retentive area covered by cement under complete coverage crowns and its effect on retention. Sixty crowns of self-cured acrylic resin were prepared on 60 identical brass dies and were divided into six groups of 10 crowns each according to different cement applications. The results showed that retention was dependent on the amount of retentive area covered by the cement. The amount of cement in the occlusal part of the cementation space did not affect retention.     

辅助固位形对低矮磨牙全冠修复体固位力和边缘适合性的影响

目的 研究不同聚合度的沟固位形和洞固位形对低矮磨牙全冠修复体固位力和边缘适合性的影响。方法 选取70颗Nissin树脂牙,在研磨仪上预备成聚合度为20°、龈高度为2.5 mm的预备体。选择10颗作为对照组,不制备辅助固位形;另设2个实验组,每组30颗,分别制备沟固位形和洞固位形。沟固位形组又分3个小组,每组10颗,分别在近远中邻面中央制备外展度数为0°、6°和20°的沟固位形;洞固位形组同样分3个小组,每组10颗,分别在近远中邻面中央预备出外展度数为0°、6°和20°的洞固位形。常规制作金属全冠,体视显微镜下在4个轴面的牙颈部中点处测量冠黏固前后边缘间隙的大小。将黏固全冠的树脂牙牙长轴与水平面呈45°固定于特制底座上,采用万能试验机静态加载记录全冠脱离预备体时的力值。采用SAS 9.2软件进行分析。结果 0°沟固位形组、0°洞固位形组和6°洞固位形组的固位力明显大于对照组,差异有统计学意义（P<0.05）;全冠黏固后,除20°沟固位形组外的边缘浮起量与对照组无明显差异外,其余实验组均明显大于对照组（P<0.05）。结论 外展度数较小的辅助固位形可增加全冠固位力,但是辅助固位形不利于冠的就位,降低了全冠的边缘适合性;在固位力足够的情况下应尽量避免使用辅助固位形。     

A method for determining adequate resistance form of complete cast crown preparations

A diagram with various degrees of occlusal convergence, which takes into consideration the length and diameter of complete crown preparations, was designed as a guide to assist the dentist to obtain adequate resistance form. To test the validity of the diagram, five groups of complete cast crown stainless steel dies were prepared (3.5 mm long, occlusal convergence 10, 13, 16, 19, and 22 degrees). Gold copings were cast for each of the 50 preparations. Displacement force was applied to the casting perpendicularly to a simulated 30-degree cuspal incline until the casting was displaced. Castings were deformed at margins except for the 22-degree group. Castings from this group were displaced without deformation, and it was concluded that there was a lack of adequate resistance form as predicted by the diagram. The hypothesis that the diagram could be used to predict adequate or inadequate resistance form was confirmed by this study.     

不同辅助固位形提高短小磨牙全冠修复体固位效果的临床效果观察

目的：观察临床上沟固位形和钉洞固位形对短小磨牙单冠修复体固位效果的影响。方法：选取45例患者57颗需行全冠修复的短小磨牙,分别通过常规修复、沟固位形和钉洞固位形单冠修复,随访观察全冠脱落例数并进行卡方检验。结果：通过1-4年随访,常规修复17颗脱落6颗,使用沟固位形的23颗脱落2颗,使用钉洞固位形的17颗无脱落。沟固位形、钉洞固位形与常规修复方法相比脱落数差异有统计学意义(P<0.05),沟固位形与钉洞固位形之间比较差异无统计学意义(P>0.05)。结论：临床上可采用沟固位形及钉洞固位形任何一种形式来改善短冠磨牙单冠修复体固位,减少全冠脱落率。     

洞固位形外展度不同对低矮牙冠固位力的影响

目的:观察洞固位形外展度不同对低矮牙冠固位力的影响。方法:用离体牙复制出高度为3.0mm和2.5mm的金属牙体模型,然后在高度为2.5mm的离体牙模型上制备深2mm直径2.5mm大小的洞,依次控制外展度分别为4°,8°,12°,并复制金属牙体模型,在其上制作金属全冠,用玻璃离子粘固剂粘接,通过万能实验机测量记录全冠在轴向拉力作用下的粘接固位力。结果:高度为2.5mm无洞固位形组与高度为3mm组比较,固位力减小,有统计学意义(P<0.05);外展度为4°洞固位形组与2.5mm无洞固位形组比较,固位力有所增加但无有统计学意义(P>0.05);外展度分别为8°,12°洞固位形组与2.5mm无洞固位形组比较,固位力增加并有统计学意义(P<0.05)。结论:牙体高度降低,冠固位力下降,增加洞固位形后,当外展度为很小时,固位力无明显改变,当外展度适当增大时,固位力明显增大。     

全瓷冠预备体近远中向聚合度的临床研究

目的：比较不同牙位与不同年资医生全瓷冠预备体近远中向聚合度的差别,探讨临床医师轴聚角实际制备情况。方法：收集全瓷冠预备体模型462副,共765个牙。对模型进行近远中向聚合度测量和统计学分析。结果：①预备体近远中向聚合度8．1°-20．2°。②前牙组近远中向聚合度控制优于前磨牙组和磨牙组（p〈0．05）。③实习医生组近远中向聚合度控制明显差于住院医师、主治医师和主任医师各组（=P〈0．05）．结论：临床操作中全瓷冠牙体预备的近远中向聚合度远高于教科书标准。     

不同粘结材料对玻璃瓷冠修复体抗碎裂载荷影响的研究

目的 :研究不同粘结材料对前磨牙玻璃瓷冠抗碎裂载荷的影响 ,寻求理想的临床粘结方法。方法 :3 0颗拔除的正畸前磨牙随机分为 3组 ,进行标准基牙预备。轴面聚合角为 5° ,牙合面交角 13 5° ,肩台宽 1mm。制成均匀厚度为 1mm的玻璃瓷冠 ,分别由磷酸锌水门汀、玻璃离子水门汀、光固化树脂粘结于牙体上。垂直加压于人造冠直至碎裂 ,各实验组间抗碎裂载荷差异用t检验分析。结果 :光固化树脂粘结的抗碎裂载荷明显高于磷酸锌水门汀和玻璃离子水门汀粘固的抗碎裂载荷 (P <0 .0 5 )。结论 :光固化树脂粘结剂为理想的粘结材料 ,有利于提高玻璃瓷冠修复体的整体强度。     

氟保护漆处理基牙后对玻璃离子水门汀粘接强度的影响

目的 研究用氟保护漆处理基牙后是否会影响用玻璃离子水门汀粘固的金属烤瓷冠的固位.方法将40颗离体上中切牙牙冠制备成烤瓷全冠预备体,制作镍铬合金烤瓷全冠,将标本随机分为两组,实验组在粘结前涂氟保护漆,对照组不做处理,用玻璃离子水门汀粘固,24 h后检测使全冠脱位时的最大拉力值.结果 实验组和对照组烤瓷冠脱位时的最大拉力值分别为(366.176±26.536)N和(386.120±27.527)N,经统计学分析无显著性差异.结论 氟保护漆对玻璃离子水门汀粘结的金属烤瓷冠固位没有影响.     

The effect of cement thickness on the fracture strength of all-ceramic crowns

The effect of increasing cement thickness on the fracture strength of aluminous porcelain jacket crowns was investigated in this study. Thirty-three aluminous porcelain jacket crowns were divided into three groups. In Group 1, only platinum foil was used to provide cement space. In Group 2 two layers and Group 3 four layers of die spacer were painted onto the metal die before impression taking. Each crown was cemented onto a metal die with zinc phosphate cement and loaded until fracture. The maximum force to break each crown was recorded. The average fracture load was 408 N for Group 1,365 N for Group 2 and 324 N for Group 3. ANOVA (SPSS) found a significant difference (p < 0.05) between groups. A Scheffe Test revealed a significant difference between Groups 1 and 3. It was concluded that increasing the cement thickness above 70 μm reduced the fracture strength of porcelain jacket crowns.     

Effect of contact media on the diagnostic quality of electrical resistance measurements for occlusal caries

BACKGROUND: Electrical resistance measurements have been used for the diagnosis of occlusal caries. Both site and surface-specific techniques have been described, the latter more suited to clinical trials or epidemiological surveys. For surface-specific measurements the tooth is dried and a contact medium drawn along the fissure pattern to provide an electrical contact between a probe tip and the tooth surface. OBJECTIVES: Different contact media have been used and it was the aim of this study to investigate whether different contact media could influence the diagnostic accuracy and repeatability of surface-specific electrical resistance measurements. METHODS: Electrical resistance readings were taken on 99 molar teeth using saline, KY jelly, toothpaste or dental prophylaxis paste. Readings were repeated on 44 randomly selected teeth. The teeth were serially sectioned and visually examined to establish the deepest lesion if present. RESULTS: The Student t-test showed that there were statistically significant differences between readings taken with different contact media, with the exception of toothpaste and prophylaxis paste, where no difference was found. The strongest relationship between histology and resistance reading was achieved with KY jelly (r = 0.559). The optimum sensitivity and specificity achieved was 0.59 and 0.86, respectively (resistance cut-off 0.1 M(Omega)). ROC analysis showed that the diagnostic performance of saline was significantly inferior to the other contact media (P < 0.05). Limits of agreement were used to assess repeatability which were acceptable for all media except toothpaste. CONCLUSIONS: Differences were found between electronic resistance readings taken with different contact media. KY jelly was found to produce the best overall diagnostic performance and should be the standard material used for surface-specific measurements.     

The effect of delayed placement of capsulated cements on crown seating

The effect of delayed seating of a crown onto a die was determined when using capsulated zinc phosphate and glass ionomer cements. The space between the crown and the die was varied up to 60 μm, and the commencement of seating was from 30 to 210 seconds after mixing ended.
The zinc phosphate cement gave gradually increasing seating discrepancies with time, but providing 45 μm of space was present, the crown could be well seated up to 3 minutes after mixing. It is argued that this cement is particularly suitable for cementing burnishable inlays. The glass ionomer cement permitted reduced seating discrepancies compared with zinc phosphate cement when 45 μm of space was present, but gave poor results when the seating was delayed more than three minutes. The capsulated cements were clean and quick to use, and It is recommended that if there is a delay in seating, a new mix of cement shoud be prepared rather than attempting to complete cementation with an obviously setting cement.     

The effect of luting media on the fracture resistance of a flame sprayed all-ceramic crown

Objectives: This in vitro study investigated the effect of selected luting media on the fracture resistance of a flame-sprayed all-ceramic crown.

Methods: Three groups of 10 human upper premolar teeth were prepared for crowning using a standardised technique. Flame sprayed crowns were fabricated and cemented onto the preparations using zinc phosphate (ZPC), glass polyalkenoate (GPC) or composite luting cement (CLC). During crown seating, a pressure perfusion system simulated pulpal fluid outflow equivalent to 300 mm of H₂O. Compressive fracture resistance was determined for each group using a Universal Testing Machine with a crosshead speed of 1 mm min⁻¹. A group of unrestored teeth acted as a control.

Results: The fracture resistance of the groups ranked as follows: ZPC>CLCGPC=unrestored teeth. The difference between the fracture resistance of ZPC and CLC groups and the control group was statistically significant. The mode of fracture between the luted crowns and natural crowns was markedly different.

Conclusions: When tested in compression, a new, flame-sprayed all-ceramic crown, when luted in place using ZPC, GPC or CLC, could produce strengths comparable to or greater than natural unrestored teeth. The luting agent used significantly affected the recorded fracture loads.     

Effect of Surface Conditioning and Taper Angle on the Retention of IPS e.max Press Crowns

Purpose: The objective of this study was to evaluate the retentive strength of single‐unit crowns with 10° and 26° taper angles cemented using two surface conditioning methods. Materials and Methods: Thirty‐two freshly extracted sound human molars were divided into two groups (n = 16) and prepared in a standardized manner with 10° and 26° taper angles. All‐ceramic (IPS e.max Press) single crowns were fabricated for the prepared teeth. The crowns were then subdivided into two groups (n = 8), according to type of surface conditioning for the intaglio surfaces. Half the groups were HF acid etched and silanized, and the other half were conditioned with tribochemical silica coating and silanization. The crowns were cemented using adhesive cement (Panavia F 2.0). Retentive strength was measured in a universal testing machine. Results: No significant difference was found between the mean retention forces for both 10° and 26° taper angles when the crowns were conditioned either with silica coating (613 ± 190 N and 525 ± 90 N, respectively), or with hydrofluoric (HF) acid etching and silanization (550 ± 110 N and 490 ± 130 N for 10° and 26°, respectively) (p= 0.32). Conclusion: Neither the surface conditioning type, nor the taper angle affected the retentive strength of IPS e.max Press single‐unit crowns when cemented adhesively. Since silica coating and silanization did not show significant differences from HF acid gel and silanization, the former can be preferred for conditioning intaglio surfaces of glass ceramic crowns to avoid the use of the hazardous compound HF acid gel chairside.     

The effects of abutment taper, length and cement type on resistance to dislodgement of cement-retained, implant-supported restorations

PURPOSE: The purpose of this study was to compare the effect of 20 degrees and 30 degrees of total occlusal convergence (TOC), the occlusocervical dimension, and the type of cement on the tensile resistance to dislodgement of cement-retained, implant-supported restorations. MATERIALS AND METHODS: Cylindrical preparations with TOC angles of 20 degrees and 30 degrees and occlusocervical dimensions of 4 mm (S) and 8 mm (L) were made through a machining process. The cylinders had a shoulder finish line of 1.0 mm in depth. Eight impressions were made of each machined cylinder and poured in type IV dental stone, for a total of 32 dies. Die spacer was applied to each die. A master wax pattern was designed, and the 32 wax patterns were marginated, invested, and cast in type IV gold alloy (n = 8). The gold crowns were cemented with Fleck's cement (zinc phosphate cement), Temp-Bond (zinc oxide eugenol cement), Temp-Bond plus Vaseline (30% by weight), and IMProv temporary cement (acrylic/urethane cement) under a 10-kg load and placed in a humidor at 37 degrees C for 1 hour before testing. A uniaxial tensile force was applied to the crown using an Instron machine with a crosshead speed of 5 mm/min until cement failure occurred. Analysis of variance models were fit to determine the effect of TOC, occlusocervical dimension, and cement type of the restorations on the mean tensile strength. RESULTS: For each type of cement, the mean tensile strengths were significantly higher at 20 degrees of TOC and 8 mm of occlusocervical dimension compared with the other preparations. At this preparation, IMProv had the highest mean tensile resistance to dislodgement (47.7 +/- 8.4 kg), followed by Fleck's (38.2 +/- 8.8 kg), Temp-Bond (35.9 +/- 4.4 kg), and Temp-Bond plus Vaseline (8.2 +/- 2.2 kg). No statistically significant difference was observed between Temp-Bond and Fleck's zinc phosphate cement when 20 degrees of TOC and 8 mm of occlusocervical dimension was used. There was no statistical difference in the mean tensile resistance to dislodgement for Temp-Bond plus Vaseline with different preparation designs (p > 0.05) except when 20 degrees of TOC and 8 mm of occlusocervical dimension was used. The mean tensile strength was significantly different between Temp-Bond and Temp-Bond plus Vaseline for each of the 4 preparation designs (p < 0.05). Among the cements tested, IMProv exhibited higher values, which were statistically different (p < 0.05). Restorations with greater occlusocervical dimension and less TOC exhibited higher tensile resistance to dislodgement. CONCLUSIONS: Preparations with 20 degrees of TOC and 8 mm of occlusocervical dimension had significantly higher mean retentive values for all of the cements tested. Significant differences in mean tensile strength were observed, with the highest tensile resistance seen with IMProv, followed by Fleck's cement, and the lowest tensile resistance seen with Temp-Bond plus Vaseline.     

TMD患者咬合板治疗后接触变化的研究

目的:比较咬合板治疗颞下颌关节紊乱病(TMD)前后异常因素的变化情况,探讨咬合板治疗TMD的机理。方法:选取34名用咬合板治疗的TMD患者,记录其戴用咬合板后2个月时的咬合特征及临床症状,并与治疗前进行比较。结果:TMD患者治疗后的力中心距中线距离减小,闭合时间与侧方分离时间明显较治疗前缩短,早接触出现率较治疗前降低,但前伸分离时间、非工作侧干扰及前伸干扰的出现率与治疗前相比无显著性差异。结论:咬合板对于纠正力中心位置、减小早接触的发生率、缩短闭合时间及侧方分离时间具有明显的作用,能够使TMD患者的关系向着更加协调、稳定的方向发展,是其有效治疗TMD的重要机理。