Fracture strength of Class I versus Class II restored premolars tested at the marginal ridge. I. Standard preparations

Two groups of maxillary premolars with Class I cavities were prepared with one marginal ridge thickness to a width of 1.0 mm. One group was restored with amalgam and the other group with composite resin. Two groups of Class II cavities also were prepared and restored with amalgam and composite resin. The teeth in the four treatment groups were subjected to a centric load at the marginal ridge until fracture occurred. A two-factor analysis of variance revealed a statistically significant difference between the class of preparation (Class I preparations were weaker than were Class II preparations) but differences in strength between restorative materials (composite resin versus amalgam) and the interaction effect (class of preparation x restorative materials) were not found to be statistically significant (alpha = .05). A Newman-Keuls sequential range test found no statistically significant differences in strength between groups (alpha = .05). Fracture patterns were observed under scanning electron microscope. Fractures extended into the enamel and into the material in the Class I composite resin, Class I amalgam, and Class II composite resin restorations. Fractures extended only into the material in Class II amalgam restorations.     

Clinical evaluation of amalgam bonding in Class I and II restorations

BACKGROUND: Many dental practitioners are bonding amalgam to tooth structure. Although in vitro studies support this procedure, its efficacy has not been adequately confirmed in the clinical environment. METHODS: The authors placed traditional Class I and Class II bonded and unbonded amalgam restorations in 76 patients. Panavia 21 (J. Morita USA Inc.) was the bonding agent selected, and Aristaloy CR (Englehard Dental) and Tytin (Kerr Corp.) were the amalgam alloys used. Postoperative sensitivity and marginal fracture were evaluated at yearly intervals, for up to three years of clinical service. RESULTS: At the patients' appointment for polishing one to two weeks after restoration placement, and at each yearly recall appointment, the authors found no significant difference in postoperative sensitivity between bonded and unbonded restorations for either amalgam alloy (chi 2 analysis, alpha = .05). In addition, there was no significant difference between bonded and unbonded restorations for either amalgam alloy with respect to marginal fracture (analysis of variance and Tukey's contrasts at alpha = .05). Moreover, no cusp fractures were observed for either bonded or unbonded restorations. CONCLUSIONS: After three years of clinical service, amalgam bonding for traditional Class I and Class II restorations had no effect on postoperative sensitivity or marginal integrity. CLINICAL IMPLICATIONS: The merit of using adhesive bonding agents for traditional Class I and Class II amalgam restorations was not demonstrated in this three-year clinical study.     

Ⅱ类洞三明治修复方法改进的临床观察

目的：简化传统Ⅱ类洞三明治修复方法及防止充填后出现术后敏感和龈壁继发龋。方法：按纳入标准选择门诊就诊患者患牙300颗（267位患者）,随机分为实验组1、实验组2和对照组。实验组1：把树脂增强型玻璃离子充填至整个窝洞壁,光照固化后,不作酸处理、不涂粘接剂,直接充填复合树脂;实验组2：对实验组1的玻璃离子进一步树脂增强,把复合树脂一部分深入到树脂增强型玻璃离子内,另一部分露在窝洞内;对照组按传统方法充填。12个月后复诊,评价。结果：实验组复合树脂与树脂增强型玻璃离子界面间无1例出现分离现象。实验组1有4颗龈壁继发龋,1颗充填物脱落,1颗边缘密合度缺陷,1颗边缘着色,成功率92.47%;实验组2有1颗充填物脱落,1颗边缘密合度缺陷,2颗边缘着色,成功率95.79%;对照组有4颗术后敏感,4颗龈壁继发龋,1颗充填物脱落,1颗边缘密合度缺陷,2颗边缘着色,成功率86.96%。实验组2与对照组差异有统计意义（P＜0.05）,实验组1与对照组差异无统计意义（P＞0.05）。结论：实验组中复合树脂与树脂增强型玻璃离子能牢固结合。实验组1与对照组比较,能简化操作,防止术后敏感,但不能防止龈壁继发龋。实验组2与对照组比较,能简化操作,防止术后敏感和龈壁继发龋。     

Marginal ridge strength of restored teeth with modified Class II cavity preparations

This study compared marginal ridge fracture resistance in two groups of teeth restored with modified Class II cavity preparations, with control groups. The results indicated that the composite resin and dental amalgam restored teeth fractured at compressive loads that were not statistically different from those of the control (unprepared, intact) teeth. The marginal ridges of the unrestored, prepared teeth were significantly weaker.     

Marginal ridge strength in Class II tunnel restorations.

This in vitro study evaluated the compressive fracture resistance of marginal ridges of teeth with Class II tunnel preparations. Tunnel preparations were completed in extracted human bicuspid and molar teeth (bicuspids, bur size: #2, #4, #6; molars, bur size: #4, #6, #8). Control teeth in both the molar and bicuspid groups remained unprepared. Half the preparations in each group were restored with a glass ionomer cermet. After thermocycling, each marginal ridge was loaded in compression in an Instron Universal testing machine. Fracture values were compared with a two-factor ANOVA. A Dunnet post hoc test was used to compare the strength of each group to its control. Results indicated that up to a certain size, tunnel preparations could be completed without diminishing the strength of the undermined marginal ridges. Placement of a glass-ionomer cermet in the tunnel preparations restored the strength of all but the largest preparations (#6 bur in the bicuspid group) to a level which was not statistically significantly different from the controls.     

Review of bonded amalgam restorations, and assessment in a general practice over five years

This study reviewed the literature on bonded amalgam restorations and assessed the failure, marginal fracture and marginal staining behavior of 366 Permite C amalgam restorations lined with five dentin bonding resins (Scotchbond 2, Panavia Ex, Amalgambond, Amalgambond Plus, Geristore) and a polyamide cavity varnish (Barrier). The restorations were placed in the posterior permanent teeth of 190 adult patients and examined at intervals over periods of up to five years. There were five restoration failures (1.4%), usually from tooth fracture, involving Class II preparations in molar teeth. No instances of persistent pulpal sensitivity or recurrent caries were reported. The marginal deterioration of the restorations was assessed indirectly using photographs for comparison with two standard sets of enlarged color transparencies. Most of the marginal fracture and marginal staining scores were low, with little difference between the six lining materials at any period.     

Fracture strength of Class 2 amalgams with various cavity-lining materials.

This in vitro study compared the fracture resistance of class 2 amalgam restorations placed over seven materials: three resin-modified glass-ionomer cements (Fuji II LC, Vitrebond, and Vitremer), one polyacid-modified composite resin (VariGlass VLC), two conventional glass-ionomer cements (Ketac-Bond and GlasIonomer Cement), and one calcium-hydroxide material (Dycal). Eighty maxillary molars with flattened occlusal surfaces were divided into 14 experimental groups and two control (no liner) groups. One standardized class 2 amalgam cavity preparation was completed per tooth. Lining materials standardized at a thickness of 0.5 mm were placed in the approximal box portion of 10 test specimens per experimental group. Spherical amalgam was hand condensed into each cavity preparation. At 1 hour and again at 7 days, five samples from each group were fractured in compression using an Instron Universal Testing Machine. The force was directed at 10 degrees to the long axis of the tooth, 2.0 mm inside the approximal portion of the restoration. Results were analyzed using a two-way ANOVA for time and material. No statistically significant differences were found among the materials and controls at either time interval tested (P > 0.05). A statistically significant difference was found (P < 0.05) when comparing 1-hour and 7-day strengths. The 7-day specimens were more resistant to fracture than the 1-hour specimens. CONCLUSION: The fracture resistance of amalgam restorations was not affected by the presence of a material 0.5 mm thick placed in the approximal box when 3 mm of bulk of amalgam remained over it.     

Fracture resistance of teeth with Class II bonded amalgam and new tooth-colored restorations

This study compared the cuspal fracture resistance of posterior teeth restored with four different adhesive restorations. Fifty sound, maxillary human premolars were randomly divided into a control group and four experimental groups with 10 teeth in each. Specimens in the first group were intact teeth that were tested as unprepared. The remaining four groups received mesio-oclusodistal cavity preparations and were restored with a hybrid composite (Filtek Z250), a packable composite (Filtek P60), an ormocer (Definite) and an amalgam (SDI Permite) with an amalgam bonding agent (Amalgam Bond Plus). All groups were stored in water at 37 degrees C for 15 days and thermocycled 1000 times between 5 degrees-55 degrees C. The specimens were preloaded five times in compression to 10 kg using two metal rods that contacted only the teeth on the cuspal inclines. The teeth were then loaded occlusally in an Instron Universal Testing Machine until fracture occurred. The means of force required to fracture the teeth in each of the five groups was analyzed using one-way ANOVA and Tukey Test. The difference between the mean cuspal fracture resistance of the unprepared control teeth and those restored with amalgam groups was found to be statistically significant (p < 0.05). No significant differences in resistance to cuspal fracture were found among the restoration groups, the unprepared control group and those teeth restored with hybrid composite, packable composite and ormocer groups (p > 0.05).     

The effect of proximal contour on marginal ridge fracture of Class II composite resin restorations

OBJECTIVES: To compare the marginal ridge fracture strength of Class II composite resin restorations placed with a straight or contoured matrix band using composite resins with different modulus of elasticity. METHODS: In 60 artificial first molars standardized MO-preparations were ground. Two matrix systems were used: (1) A straight matrix (Standard Tofflemire Matrix, KerrHawe) in Tofflemire retainer (Produits Dentaire). (2) A contoured matrix (Standard matrix, Palodent, Dentsply). In both groups, a wooden wedge and separation ring (Composi-Tight Gold, GDS) were placed and the matrix was burnished against the adjacent tooth. Three composite resins together were used (Filtek Supreme: e-modulus 13.3GPa (3M ESPE), Clearfil AP-X: 16.6GPa (Kuraray) and Clearfil Majesty Posterior: 22.0GPa (Kuraray)), resulting in six groups (n=10). Teeth were mounted into a MTS servo hydraulic testing machine (Mini Bionix II, MTS, USA) with stylus placed on the marginal ridge. Samples were loaded at a crosshead speed of 1.0mm/min until fracture occurred. Fracture resistance data were statistically analyzed using ANOVA and Scheffé's post hoc test for multiple comparison of groups (p<0.05). RESULTS: Contoured proximal surfaces (365.5+/-87.6N) resulted in significant stronger marginal ridges compared to straight surfaces (290.5+/-64.2N) (p<0.001). Clearfil AP-X (378.1+/-94.63N) provided a higher resistance to fracture than Filtek Supreme (301.4+/-67.3N) (p=0.001) and Clearfil Majesty Posterior (304.5+/-70.6N) (p=0.002). No differences were found between Filtek Supreme and Clearfil Majesty Posterior (p=0.890). CONCLUSION: Within the limitations of this in vitro study it was shown that use of a contoured matrix results in a stronger marginal ridge of a Class II composite resin restoration.     

银汞合金粘结修复后充填体边缘微漏的实验研究

目的 研究银汞合金粘结修复填体边缘的微漏情况,方法 将制备洞型后４０颗离体牙随机分二组,一组采用ＢＡＲ法充填银汞,另一组按常规充填银汞,所有标本均进行染料渗透试验,观测染料渗漏情况,并在ＳＥＭ下测量充填体与牙体间的微逢隙宽度,结果 ＢＡＲ组染料渗漏的例数少,程度轻,其微漏明显小于常规组（Ｐ〈０．０１）,扫描电镜观察发现,ＢＡＲ组充填体边缘缝隙宽度明显小于常规组（Ｐ〈０．０１）,结论 银汞合金粘结修     

Class II amalgam restorations, glass-ionomer tunnel restorations, and caries development on adjacent tooth surfaces: a 3-year clinical study.

Eighteen caries-active adolescents, each having both a class II conventional amalgam (Dispersalloy) and a glass-ionomer (Ketac Silver) tunnel restoration of the same age placed on a contralateral tooth, were part of a 3-year clinical study. At the 1- and 2-year examinations all test restorations were assessed as acceptable in all patients. At the 3-year assessment three amalgam restorations failed due to recurrent caries, and one glass-ionomer restoration failed due to marginal ridge fracture. During the entire study period, the requirement of restorative therapy because of primary proximal caries was significantly reduced (p < 0.05) on tooth surfaces adjacent to the glass-ionomer restorations as compared with that on tooth surfaces adjacent to the amalgam restorations.     

Effect of cavity varnish, amalgam liner or dentin bonding agents on the marginal leakage of amalgam restorations

The purpose of this in vitro study was to compare marginal leakage of Class II amalgam restorations lined with different agents (two new generation dentin bonding systems, a cavity varnish and an amalgam liner). Forty freshly extracted human molar teeth were divided into five groups. Class II preparations were prepared in the mesial and distal surfaces of each molar. While the cavities in two groups were lined with two new generation bonding systems, the other two groups were treated with an amalgam lining material and a cavity varnish. Fifth group was used as control, without any lining. Amalgam* was hand-condensed into each preparation. Specimens were thermocycled, stained and sectioned. Microleakage was graded using a stereomicroscope. Mean microleakage scores for occlusal and cervical margins were calculated and analysed. For the leakage values on occlusal margins, Kruskal-Wallis test indicated no significant difference in all groups. For the leakage values on cervical margins, Kruskal-Wallis test indicated significant difference in four groups when compared with controls (P < 0.001). On the other hand, there was no significant difference between the occlusal and cervical leakage values in each group.     

A two-year comparison of resin-based composite tunnel and Class II restorations in a randomized controlled trial

PURPOSE: To evaluate the performance of total tunnel restoration with resin-based composites compared to Class II resin-based composite restorations in a randomized controlled clinical study. METHODS: 63 approximal carious lesions were restored in 38 patients by two experienced operators. The carious dentin and approximal demineralized enamel were completely removed for the tunnel restoration leaving the marginal ridge intact. The occlusal opening was enlarged to the center of the tooth to make access easy. Conservative cavity preparation was performed for the Class II restorations. All cavities were restored with Scotchbond Multipurpose Plus and Z250. At baseline, 1- and 2-year recalls, the restorations were evaluated clinically by two examiners using a modified USPHS rating system and radiographically for recurrent, caries. RESULTS: Both types of restorations performed well clinically, and there was no significant difference (P> 0.05) by the chi square test in any category. Recurrent caries was not detected. Only one tunnel restoration had to be replaced with a Class II restoration because of falling of the restoration with the marginal ridge after 2 years. However, no significant difference in the survival rates (P> 0.05) could be demonstrated between the restorations by the log-rank test.     

Modified Class II tunnel preparation

Tunnel preparations for restoration of Class II carious lesions in primary molars preserve the marginal ridge and minimize sacrifice of healthy tooth substructure. Materials with improved bonding to tooth structure and increase potential for fluoride release allow Class II restorations without "extension for prevention".     

粘结技术对银汞合金充填体边缘微漏的影响

目的 研究粘结技术对银汞合金充填体边缘微漏的影响。方法 将制备洞型后的40颗离体牙随机分为二组,一组采用粘结技术法充填银汞。另一组按常规充填银汞,所有标本均进行染料渗透试验,观测染料渗漏情况,并在SEM下测量充填体与牙体间的微缝隙宽度。结果 粘结组染料渗漏的例数少、程度轻,其微漏明显小于对照组(P<0.01);扫描电镜观察发现,粘结组充填体边缘缝隙宽度明显小于对照组(P<0.01)。结论 采用粘结技术可以明显减少银汞合金充填体的边缘微漏。     

Marginal adaptation of amalgam and resin composite restorations in Class II conservative preparations.

OBJECTIVE: The purpose of this study was to compare and contrast the performance, in terms of marginal adaptation, of a non-gamma-2 amalgam alloy with a compact-filled light-cured composite in the restoration of Class II preparations of conservative design. METHOD AND MATERIALS: Fifty recently extracted teeth were selected for the study. The teeth were restored with either a non-gamma-2 amalgam alloy, Dispersalloy, or a compact-filled resin composite, Z100, using standard techniques. The marginal adaptation of the restorative materials to the proximal surface outline form of each preparation was assessed at magnification x30. RESULTS: Highly significant differences were demonstrated in the mean percentages of perfect margins in all 3 segments of the proximal boxes of the restorations with the resin composite performing significantly better than the amalgam. The percentages of marginal fissuring were significantly higher in the amalgam restorations, except at the cervical margin, where the incidence of fissuring was almost the same for the amalgam and resin composite restorations. The resin composite restorations had significantly fewer underfilled margins than the amalgam restorations. CONCLUSION: In the conservative Class II preparations, the amalgam restorations were of poor quality with respect to marginal adaptation, compared with the resin composite restorations. It is suggested that the use of amalgam as a control in a clinical evaluation of resin composite restorations in conservative preparations cannot be justified, because it is apparently not possible to compare restorations of equivalent initial quality.     

Effect of bonding amalgam on the reinforcement of teeth

STATEMENT OF PROBLEM: Extensively weakened maxillary premolars may be more prone to fracture due to their small size. The weakening may be due to excessive demineralization of supporting tooth structure caused by dental caries or nonconservative or traumatic tooth preparation. PURPOSE: The purpose of this study was to determine the effect of a bonded amalgam restoration on reinforcement of weakened tooth structure. MATERIAL AND METHODS: Forty extracted noncarious maxillary premolars were collected. The teeth were prepared individually with mesio-occluso-distal (MOD) cavities with specific dimensions (cavity width buccolingually, 1.8 to 2.1 mm; palatal cusp width, 1.7 to 2.2 mm; cusp height, 4.7 to 5.0 mm) and divided into 4 groups (n=10). The first group was prepared and not restored (control). The other 3 groups were restored with amalgam (Megalloy), bonding agent (Syntac) with amalgam, and amalgam with an adhesive resin luting agent (Resinomer), respectively. Fracture load (in kg) for specimens in all groups was determined by applying a vertical splitting load through a specially shaped steel rod at a crosshead speed of 1 mm/min. The data were analyzed by 1-way analysis of variance and least significant difference statistical tests (alpha=.01). RESULTS: The mean force and standard deviation values required to fracture the cusp of the control and amalgam groups were 25.2+/-3.27 kg and 26.1+/-3.07 kg , respectively, with no significant difference between the 2 groups (P>.01). Significant differences were found between control and Syntac groups (29.8+/-2.80 kg), as well as between control and Resinomer groups (37.9+/-3.55 kg). Significant difference was also noted between Syntac and Resinomer groups (P>.01) CONCLUSION: It was concluded that the use of resin cement increased the fracture resistance of the tooth with an MOD amalgam restoration.     

A six year follow-up of three dental alloy restorations with different copper contents.

Class II restorations of three amalgam alloys, with 6%, 12% and 23% copper content, respectively, were evaluated and compared intraindividually during a six year follow-up. In total 10.3% of the restorations were replaced during the test period. The reasons for replacement were bulk fracture (5.6%), tooth fracture (2.4%), marginal ridge fracture (0.8%), and secondary caries (1.6%). The intraindividual ranking of the three alloys, including evaluation of anatomical form, marginal adaptation and secondary caries, showed significantly better results for the two high copper alloys than for the conventional low copper alloy. No difference was seen between the two high copper containing alloys.     

Evaluation of the microleakage at the proximal walls of Class II cavities restored using resin composite and precured composite inserts.

OBJECTIVE: This in vitro study compared the microleakage of resin composite restorations placed in Class II cavity preparations using an incremental placement technique with and without the addition of precured resin composite inserts. METHOD AND MATERIALS: Sixty standardized mesio-occlusal and disto-occlusal cavities were prepared in 30 recently extracted molar teeth. Twenty cavities were restored by employing the incremental placement technique (group I), and 40 cavities were restored using the incremental placement in the presence of precured composite inserts of two sizes: 1 x 3 mm (group II) and 1.25 x 3 mm (group III). The restored teeth were thermocycled for 250 cycles in water baths set at temperatures of 5 degrees C and 50 degrees C using a 30-second dwell time, stained, and sectioned horizontally at the middle of the restoration. Following sectioning, each specimen was microscopically examined at x 4 magnification. The extent of dye penetration at the tooth/restoration interface was scored for each test group, and the scores obtained were subjected to one-way analysis of variance (ANOVA) and Tukey's pairwise comparison at a 95% significance level. RESULTS: The current investigation showed statistically significant differences in dye penetration between the three test groups. CONCLUSION: The use of precured resin composite inserts with the incremental placement technique in the restoration of Class II cavity preparations seems to improve the marginal seal of the proximal walls of finished restorations.     

Clinical behaviour of high-copper amalgams with time, site, size and class of cavity preparation

In this study 767 amalgam restorations placed in the posterior permanent teeth of 122 patients were evaluated at 6-monthly intervals up to 2 years. Six commercially available high-copper alloy amalgams were assessed for surface roughness, surface tarnish, marginal staining and marginal fracture and the results were related to product, restoration age, restoration cavity class type, restoration size (normal or large Class II preparations) and tooth type (premolar or permanent molar). Dispersalloy (Johnson and Johnson, East Windsor, USA) gave restorations which were overall superior for the clinical characteristics examined. Large restorations on the occlusal surfaces of molar teeth showed more signs of deterioration over the study than did other restoration types. However, all restorations remained clinically satisfactory throughout the study.