Silver Diamine Fluoride: A Successful Anticarious Solution with Limits.

Silver diamine fluoride (SDF) is a solution containing ionic silver, fluoride, and ammonia that arrests the progress of carious lesions and prevents the development of future caries. The silver particle extends into the dentin tubules and could create some bonding problems for subsequent composite resin restorations placed over SDF-treated darkened tooth structures. The fluoride penetrates deeper into the tooth with SDF as compared with other fluoride solutions, creating a fluoride reservoir in the tooth structure. The fluoride component of SDF contributes to remineralization and fluorapatite formation, producing harder, more caries-resistant tooth structures. The silver provides the antimicrobial activity for the material and inhibits biofilm formation. It has been evaluated in >20 clinical studies and reviewed in systemic reviews. The material was recently approved by the Food and Drug Administration for desensitizing cold-sensitive teeth and has been used off-label to treat carious lesions. SDF will produce a caries lesion darker (brown to black) than the original, which is the major criticism of the material. A nanoparticle-sized silver material was recently developed that may retain the antimicrobial properties of the larger-sized ion silver material without the discoloring effects. The application of SDF is easily adapted for field use. The lesion is isolated, and the solution is painted onto the clean caries lesion and dried. This simple application process requires little equipment, and its low cost per application makes the material ideal for large populations.

Effects of Particle Abrasion Media and Pressure on Flexural Strength and Bond Strength of Zirconia.

OBJECTIVES: To compare the effects of particle abrasion medium and pressure on shear bond strength and biaxial flexural strength of three generations of zirconia (Lava Frame, Lava Plus, and Lava Esthetic) with the goal of optimizing the bond to zirconia. METHODS: 280 discs (14 mm diameter; 1 mm thickness) of each zirconia were milled and sintered. Specimens of each material were randomly distributed into 14 groups (n=20); half were tested for shear bond strength and half were tested for biaxial flexural strength. The specimens were particle abraded on one surface by 2 different media (50 µm alumina particles or 50 µm glass beads) for 10 seconds at three different pressures (15, 30, and 45 psi or 0.1, 0.2, 0.3 MPa). Untreated specimens served as positive control. A tube (1.50 mm diameter) filled with dual cured resin cement (Panavia SA) was placed onto the surface and light cured. Specimens were stored in water (37°C for 24 hours) and shear bond strength was measured in a universal testing machine (Instron). Biaxial flexural strength of each specimen was measured according to ISO 6872. Shear bond strength and biaxial flexural strength were compared individually with a 2-way analysis of variance (ANOVA) for factors surface treatment and zirconia composition. RESULTS: Significant differences were seen between surface treatments (p<0.01), zirconia composition (p<0.01) and their interaction (p<0.01) for both bond strength and flexural strength. With alumina particle abrasion, higher pressure produced higher bonds for Lava Frame and Lava Plus zirconia while the bond of Lava Esthetic declined with increased pressure. Higher pressure (>0.2 MPa or 30 psi) with alumina decreased biaxial flexural strength with Lava Esthetic zirconia. CONCLUSIONS: Particle abrasion with alumina produced a significantly better combination of bond strength while maintaining biaxial strength of three zirconia materials than particle abrasion with glass beads. The bond strength also depended upon the pressure of particle abrasion and the generation of zirconia used.

Effect of light activation on resin-modified glass ionomer shear bond strength.

OBJECTIVE: Recent studies confirmed that resin-modified glass ionomers (RMGIs) set on the basis of two competing mechanisms, an acid-base reaction and a light-activated resin polymerization. This study evaluated the effect of the setting mechanism on bond strength by measuring the shear bond strength of three RMGIs to dentin with and without light activation. METHODS: Sixty human molars were ground to midcoronal dentin and randomly divided into six even groups: 1) Ketac Nano (KN), 2) KN without light cure (woLC), 3) Fuji Filling LC (FF), 4) FF woLC, 5) Fuji II LC (FII), and 6) FII woLC. The dentin surfaces of the specimens were conditioned/primed according to the manufacturers' instructions. A 1.54-mm diameter plastic tube was filled with RMGI material and affixed to the dentin surface. Groups 1, 3, and 5 were light cured for 20 seconds, and groups 2, 4, and 6 were immediately placed in a damp dark box with no light curing at 37°C for 24 hours. Shear bond strength testing was performed in an Instron device at 1 mm/min. Data were analyzed with a one-way analysis of variance (ANOVA) and Tukey/Kramer test (α=0.05). RESULTS: Mean ± standard deviation shear bond strength values (MPa) are: 7.1 ± 4.2 (KN), 11.7 ± 3.9 (FF), 10.2 ± 3.2 (FF woLC), 12.5 ± 5.1 (FII), and 0.3 ± 0.4 (FII woLC). Two KN, all KN woLC, and seven FII woLC specimens debonded before testing. Tukey/Kramer analysis revealed no significant differences in bond strength between the three light-cured RMGIs. KN and FII showed significantly lower bond strength without light cure, but no significant difference was observed between FF and FF woLC. CONCLUSIONS: The results of this study strongly suggest that light activation is necessary to obtain optimal bond strength between RMGI and dentin. FF may contain components that chemically activate resin polymerization. Clinically, KN and FII need to be light cured after placement of these RMGIs.

Demineralization Inhibition by Two Calcium-releasing Restorative Materials.

OBJECTIVE: To compare the ability of two calcium-releasing restorative materials to inhibit root dentin demineralization in an artificial caries model. METHODS AND MATERIALS: Preparations were made at the cementum-enamel junction of extracted human molars (40, n=10/material) and restored with two calcium-releasing materials (Experimental composite, Pulpdent Corporation and Cention N, Ivoclar Vivadent), a resin composite (Filtek Supreme Ultra, 3M Oral Care), and a resin-modified glass ionomer (RMGI) (Fuji II LC, GC). All materials (other than the RMGI) were used with an adhesive (Scotchbond Universal Adhesive, 3M Oral Care) in the self-etch mode, which was light cured for 10 seconds. All restorative materials were light cured in 2-mm increments for 20 seconds and then finished with a polishing disc. Teeth were incubated (37°C) for 24 hours in water. An acid-resistant varnish was painted onto the teeth around the restoration, leaving a 2-mm border of uncovered tooth. A demineralization solution composed of 0.1 M lactic acid, 3 mM Ca3(PO4)2, 0.1% thymol, and NaOH (to adjust pH=4.5), and a remineralization solution composed of 1.5 mM Ca, 0.9 mM P, and 20 mM Tris(hydroxymethyl)-aminomethane (pH=7.0) were prepared. Specimens were placed in the demineralization solution for 4 hours, followed by the remineralization solution for 20 hours and cycled daily for 30 days. The specimens were embedded, sectioned into 100-µm sections, and the interface between the restorative material and root dentin was viewed with polarized light microscopy. A line was drawn parallel with the zone of demineralization for each tooth. The area of "inhibition" (defined as the area external to the line) or "wall lesion" (defined as the area internal to the line) was measured with image evaluation software. Areas of inhibition were measured as positive values, and areas of wall lesions were measured as negative areas. RESULTS: A one-way analysis of variance (ANOVA) found significant differences between materials for "inhibition/wall lesion" areas in root dentin (p<0.001). Tukey post hoc analysis ranked materials (µm2, mean ±SD): Fuji II LC (5412±2754) > Cention N (2768±1576) and experimental composite (1484±1585) > Filtek Supreme Ultra (-1119±1029). CONCLUSION: The experimental composite and Cention N materials (used with an adhesive) showed net areas of inhibition greater than a reference resin composite, albeit at a lower level than a reference RMGI material (used with no adhesive).

Influence of Etching Protocol and Silane Treatment with a Universal Adhesive on Lithium Disilicate Bond Strength.

OBJECTIVES: To measure the effects of hydrofluoric acid (HF) etching and silane prior to the application of a universal adhesive on the bond strength between lithium disilicate and a resin. METHODS AND MATERIALS: Sixty blocks of lithium disilicate (e.max CAD, Ivoclar Vivadent) were sectioned into coupons and polished. Specimens were divided into six groups (n=10) based on surface pretreatments, as follows: 1) no treatment (control); 2) 5% HF etch for 20 seconds (5HF); 3) 9.5% HF etch for 60 seconds (9.5HF); 4) silane with no HF (S); 5) 5% HF for 20 seconds + silane (5HFS); and 6) 9.5% HF for 60 seconds + silane (9.5HFS). All etching was followed by rinsing, and all silane was applied in one coat for 20 seconds and then dried. The universal adhesive (Scotchbond Universal, 3M ESPE) was applied onto the pretreated ceramic surface, air thinned, and light cured for 10 seconds. A 1.5-mm-diameter plastic tube filled with Z100 composite (3M ESPE) was applied over the bonded ceramic surface and light cured for 20 seconds on all four sides. The specimens were thermocycled for 10,000 cycles (5°C-50°C/15 s dwell time). Specimens were loaded until failure using a universal testing machine at a crosshead speed of 1 mm/min. The peak failure load was used to calculate the shear bond strength. Scanning electron microscopy images were taken of representative e.max specimens from each group. RESULTS: A two-way analysis of variance (ANOVA) determined that there were significant differences between HF etching, silane treatment, and the interaction between HF and silane treatment (p<0.01). Silane treatment provided higher shear bond strength regardless of the use or concentration of the HF etchant. Individual one-way ANOVA and Tukey post hoc analyses were performed for each silane group. Shear bond strength values for each etch time were significantly different (p<0.01) and could be divided into significantly different groups based on silane treatment: no silane treatment: 0 HF < 5% HF < 9.5% HF; and RelyX silane treatment: 0 HF < 5% HF and 9.5% HF. CONCLUSIONS: Both HF and silane treatment significantly improved the bond strength between resin and lithium disilicate when used with a universal adhesive.

Two-year Randomized, Controlled Clinical Trial of a Flowable and Conventional Composite in Class I Restorations.

OBJECTIVES: This study evaluated the two-year clinical performance and volumetric wear of a flowable resin composite compared to a conventional highly filled composite resin in Class I restorations. METHODS AND MATERIALS: In this single-center, single-blinded, comparator-controlled clinical study (Institutional Review Board approved), 120 carious teeth distributed in 60 patients were randomly assigned to four calibrated practitioners who placed occlusal restorations (n=60 flowable and n=60 conventional composite). Direct and indirect assessment at baseline, six months, one year, and two years occurred during which the modified Cvar and Ryge criteria were evaluated. Volumetric wear was determined by superimposition of profilometer scans of baseline and two-year casts. RESULTS: At two years, there was no significant difference in anatomic form (p=0.80), color match (p=0.08), marginal adaptation (p=0.89), marginal discoloration (p=0.79), surface integrity (p=0.18), secondary caries (p=0.66), cold sensitivity (p=0.522), occlusal sensitivity (p=0.818), or volumetric wear (p=0.661) between materials. Both materials showed a decrease in all criteria except secondary caries (p=0.95) over time. Two-year mean volumetric wear was 3.16 ± 2.38 mm(3) for the flowable composite and 3.43 ± 2.50 mm(3) for the conventional composite. CONCLUSIONS: The flowable and conventional composites used in this study have similar clinical efficacy after two years of service when placed as Class I occlusal restorations having isthmus widths less than one-half the intercuspal distance.

The use of dentinal etching with endodontic bleaching procedures.

The removal of the smear layer from dentinal surfaces has been shown to increase significantly the permeability of dentin in both vital and endodontically treated teeth by opening the orifices of the dentinal tubules. This knowledge has led to the practice of acid etching the intracoronal dentin of endodontically treated teeth prior to nonvital bleaching procedures in order to increase the speed and effectiveness of the bleach. In this study extracted human teeth, which had been stained in vitro, were used to compare the effects of dentinal etching of the pulp chambers with no acid etching in conjunction with "walking bleach" procedures. In one experimental group, the pulp chambers were acid etched with 50% phosphoric acid for 1 min to remove the smear layer prior to insertion of the 30% hydrogen peroxide/sodium perborate bleaching agents. The second group had the same chamber preparation except the acid etching was deleted. Evaluators were unable to distinguish a significant difference between the effectiveness of the bleaching procedures in the two experimental groups.

Torsional testing of the Lightspeed nickel-titanium instrument system.

Revolutions to separation and maximum torque at failure of 216 Lightspeed instruments were determined in an instron using a clockwise rotation. After instruments failed, the distance the instrument separated from the tip was measured. Comparison of the results with existing ANSI/ADA specification no. 28 showed that the Lightspeed far exceeded the values of the specification for revolution to failure. On the other hand, torque to failure results showed that instrument sizes 20 and 25 exceeded the specification, whereas instrument sizes 30 through 50 were below the minimum values. Half-size instruments were not compared, because specifications for half-sizes do not exist. Comparison between mean torque values and instrument shaft diameters of the Lightspeed previously reported showed a near linear relationship up to and including instrument size 50, but overall torque to failure increased exponentially when related to shaft diameter (coefficient of determination = 0.9923). Lightspeed instruments separated 2.32 +/- 0.60 mm from the tip, generally within the land area or at the beginning of the shaft. Scanning electron microscopic observation of the Lightspeed instrument fracture site showed two distinct areas. There was a striated concentric area in the periphery of the fracture characteristic of a brittle or cleavage fracture and a corrugated area in the center of the fracture characteristic of a ductile fracture.

An in vivo and in vitro comparison of two dentin bonding agents.

The in vitro and in vivo shear bond strengths of two dentin bonding agents to dentin were measured by use of a goat model. The dentin was exposed in the mandibular incisors of 10 adult goats while they were maintained under general anesthesia. Separate gingival and incisal areas of dentin were isolated with Teflon tape, exposing an area 2.83 mm in diameter. GLUMA or Scotchbond II was applied to those dentin areas according to the manufacturers' directions. A column of resin was then applied over the bonding agent and light-cured. Two hours later, the animals were killed and the teeth removed. The teeth were then mounted in acrylic resin, and the resin composite tube was loaded in shear until failure on an Instron. Seven days later, the extracted teeth were re-prepared and the same bonding procedure re-applied. These teeth were placed in the Instron and loaded in shear until failure. Thirteen months later, the teeth bonded with GLUMA were re-prepared and bonded in the same manner as above. The resin composite was loaded in shear until failure. There was no significant difference between the two-hour in vivo bond strength and the seven-day or the 13-month in vitro bond strength with GLUMA. There was no significant difference between the two-hour in vivo or the seven-day in vitro bond strength for Scotchbond II. There was no significant difference between the shear bond strengths of the two dentin bonding agents.

Tensile bond strength of dental adhesives to dentin and enamel.

This study compared the tensile bond strengths of an unfilled resin bonding agent and four proprietary dentin bonding agents to dentin and acid-etched enamel. Forty-eight hours after bonding, 10 dentin-bonded teeth and 10 enamel-bonded teeth for each material were loaded in tension in an Instron Universal Testing Machine until bond failure. The remaining specimens were stored in a water bath for six months and then tested in a similar manner. At the end of six months, Universal Bond and Tenure (3-step) had bond strengths significantly greater than those of the other agents. All bonding agents, except Tenure (3-step), showed a significant decrease in tensile bond strength to both dentin and enamel after six months (p less than 0.0001).

Comparing the resistance of dentin bonding agents and pins in amalgam restorations.

This in vitro study involving 84 caries-free molar specimens examined the resistance of complex amalgam restorations retained by two dentin bonding agents--Amalgambond and Amalgambond Plus--four regular TMS pins, six regular TMS pins and four pins in conjunction with Amalgambond. Analysis indicated that the Amalgambond restorations were significantly weaker than the other types. Amalgambond Plus restorations were significantly stronger than the Amalgambond restorations but not different from the remaining groups. The authors concluded that complex amalgam restorations should be retained with a combination of adhesive and mechanical retention.

Retention and resistance features for complex amalgam restorations.

Although not absolute, there are indications for each of the retention and resistance features described. Amalgapins and circumferential slots have their greatest indication in teeth with short clinical crowns and in cusps that have been reduced 2-3 mm for coverage with amalgam. In these situations, slots provide more resistance than amalgapins and amalgam inserts. When amalgapins or slots are used as the only retention and resistance features, the restoration is susceptible to early fracture during matrix removal. When the technical requirements for placement of vertical pins can be met, they provide excellent retention and resistance form. Vertical pins should be placed at least 0.5 mm inside the dentinoenamel junction, at a depth of approximately 2 mm, and should protrude from the tooth approximately 2 mm. However, there are inherent risks involved with pin placement; these include crazing of tooth structure, perforation into the pulp or periodontium, and weakening of the amalgam restoration over the pins. The use of both vertical and horizontal pins may be limited by inadequate access; in these cases, alternate devices should be used. When a cusp has been reduced and increased resistance is needed, a ledge or peripheral step may be indicated. It must be remembered that this feature will result in a greater display of amalgam and may be esthetically unacceptable on a facial cusp. If esthetic appearance is a factor, horizontal pins may be used to reinforce a remaining facial cusp. Horizontal pins may also be used to splint or tie a remaining cusp to the restoration.(ABSTRACT TRUNCATED AT 250 WORDS)

The performance of bonded vs. pin-retained complex amalgam restorations: a five-year clinical evaluation.

BACKGROUND: The authors compared the clinical performance of complex amalgam restorations, replacing at least one cusp--retained either mechanically with self-threading pins or bonded--with a filled, 4-methacryloxyethyl trimellitate anhydride, or 4-META-based resin designed for amalgam bonding. METHODS: The authors placed 60 amalgam restorations (28 pin-retained and 32 bonded), each restoration replacing at least one cusp. They used self-threading stainless steel pins in the pin-retained group and a filled, 4-META-based bonding resin in the bonded group. For both groups, the authors left in place any retention form remaining after removal of an old restoration but did not enhance it. RESULTS: At four years, six restorations had failed. At five years, of the 40 restorations available for evaluation, three had failed, for a total of nine failed restorations; seven of those were pin-retained and two were bonded. Using the Fisher exact test to compare the groups at five years, the authors found no significant difference in failure rate, marginal adaptation, marginal discoloration, secondary caries, tooth sensitivity or tooth vitality. CONCLUSIONS: At five years, there was no difference in the performance of pin-retained amalgam restorations and bonded amalgam restorations. This study will be continued for at least a sixth year. CLINICAL IMPLICATIONS: Bonding with a filled, 4-META-based bonding resin appears to be a satisfactory method of retaining large amalgam restorations replacing cusps.

Retention and resistance provided by nine self-threading pins.

Extracted molar teeth, reduced to a flat surface approximately 3 mm coronal to the cementoenamel junction, were notched and embedded in acrylic. Nine types of pins were tested for retention in dentin and for resistance provided to complex amalgam restorations. Pins of each type were inserted into dentin and removed in tension with a constant load applied by an Instron Testing Machine (six pins per tooth). Minim and PPS pins provided significantly better retention in dentin than the other pins. Pins of each type were inserted into flattened teeth. Amalgam was condensed around the pins, allowed to set, and loaded in compression at 45 degrees. Pure titanium pins and heat-softened stainless steel pins provided significantly less resistance than titanium alloy or stainless steel pins.

Fracture resistance of complex amalgam restorations.

This study evaluated fracture resistance provided to complex amalgam restorations by adhesive and mechanical resistance features. The occlusal surfaces of 30 extracted molar teeth of similar size were ground flat to approximately 2 mm coronal to the CEJ. The teeth were divided into three groups. Roots were notched and embedded in acrylic resin. In two groups, four TMS Minim stainless steel pins were placed into dentin at the line angles. A copper band matrix was applied to each specimen and reinforced with compound. After applying either Copalite or Amalgambond Plus, Tytin amalgam was condensed into the matrix. The bands and excess amalgam were removed 10 minutes later, and each amalgam occlusal surface was ground flat to give the amalgam restoration a 4 mm occlusal height. Specimens were thermocycled for 2500 cycles at 6-60 degrees C with a 30-second dwell time. They were then stored in deionized water for 1 month at room temperature. A 1 mm 45 degrees bevel was placed on the facio-occlusal angle of the amalgam. Each specimen was loaded to failure in compression at 45 degrees in an Instron Testing Machine at a crosshead speed of 5 mm/min. The groups were: Group 1, four Minim pins and Copalite; Group 2, four Minim pins and Amalgambond Plus; and Group 3, Amalgambond Plus only. The data were analyzed using a one-factor ANOVA and a Tukey B post hoc test. There was no significant difference between Groups 1 and 3. The Amalgambond Plus combined with pins provided significantly greater resistance to fracture than pins or Amalgambond Plus alone (P < 0.05).

Selected mechanical properties of fluoride-releasing restorative materials.

Mechanical properties, diametral tensile strength (DTS) and flexural strength (FS) of six fluoride releasing materials were measured and compared. The samples were prepared and tested according to ISO specifications. The materials included a glass ionomer (Fuji IX), a resin-modified glass ionomer (Photac-Fil), two compomers (F 2000; Dyract AP) and two composites (Solitaire; Tetric Ceram). The tests were performed after the materials were stored in distilled water (DTS) and phosphate buffered saline solution (FS) at 37 degrees C for 24 hours and one week. Fluoride-releasing composite resin had the highest flexural and diametral tensile strengths and were statistically stronger than compomers, followed by resin-modified glass ionomer and conventional glass ionomer. However, a notable exception to this general trend was Solitaire, a fluoride-releasing composite resin.

Effect of delayed application on shear bond strength of four fifth-generation bonding systems.

This study compared the shear bond strength of four adhesives dispensed 10 minutes prior to use to immediate dispensing and use. For half (40) of the specimens (n = 10), four different dentin bonding agents (One Coat, Bisco One Step, Prime & Bond 2.1 and 3M Single Bond) were used to bond a column of composite resin (Z100 Restorative Resin) to the dentin surface following manufacturers' directions and using the dentin bonding agent immediately after dispensing. For the remaining specimens, the same procedure was followed except that the dentin-bonding agent was dispensed 10 minutes prior to use. All specimens were tested two weeks after bonding on a MTS machine. The data obtained was subjected to Two-factor ANOVA and Tukey-B post-hoc tests. The statistical analysis showed that there was no significant difference between the control groups and the experimental groups, although the dentin bonding agents containing acetone showed a trend toward lower bond strengths when not used immediately after dispensing.

Color stability of fluoride-containing restorative materials.

Six fluoride-releasing materials of shade A3 were tested: one glass ionomer (Fuji IX), one resin-modified glass ionomer (Photac-Fil), two compomers (F 2000 and Dyract AP) and two composites (Tetric Ceram and Solitaire). Disk-shaped specimens of each material were prepared according to manufacturer's instructions, polished and L*a*b* baseline measurements taken. Specimens were randomly divided into two groups and given four different treatments of UV light exposure and immersion in a staining solution. Chromo Meter color measurements were taken following each treatment. Two-way ANOVA and Duncan Multiple Range post-hoc tests were used to compare color changes as a function of the four treatment conditions and one-way ANOVA was used to compare materials for each treatment separately. The results showed significant difference in shade A3 between products. In general, the hydrophobic materials showed greater color stability and stain resistance than the hydrophilic materials. Tetric ceram had the best color stability and stain resistance, while Fuji IX had the least.

Effect of grooves on resistance/retention form of Class 2 approximal slot amalgam restorations.

This study evaluated in vitro the effectiveness of resistance/retention grooves in box-only (approximal slot) class 2 preparations. Forty-eight sound, caries-free maxillary premolars were distributed equally into four groups of 12 teeth based on faciolingual dimensions. Teeth were mounted vertically, and class 2 mesio-occlusal slot preparations were cut in each tooth. Resistance/retention grooves were placed in three of the four groups with a #1/4 round bur to a depth of 0.3-0.5 mm. Teeth were restored with amalgam and positioned 13.5 degrees from vertical; an area was flattened on each amalgam marginal ridge, and the flattened areas were loaded to failure using an Instron with a rectangular flat-ended rod at a cross-head speed of 1 mm/min. Mean load (SD) to failure of the group using "conventional" grooves extending in dentin from the gingival floor occlusally to near the occlusal DEJ was 196N (46N). For long grooves extending from the gingival floor to the occlusal surface, the mean failure load was 169N (58N). Slot restorations with short resistance/retention grooves or points (0.5-1.0 mm) just gingival to the occlusal DEJ had a mean failure load of 132N (44N). Slot restorations with no grooves had a mean failure load of 69N (46N). ANOVA and Student-Newman-Keuls tests were used for analysis. The no-groove group provided significantly less (P < 0.01) resistance than any group with grooves. Approximal slot restorations with "conventional" grooves were significantly more resistant (P < 0.01) than those with short grooves but were not significantly more resistant than those with long grooves.

Effect of distribution of resistance features in complex amalgam restorations.

This study measured fracture resistance of complex amalgam restorations when pins or amalgapins were either distributed around the preparation or concentrated in one area of the preparation. The occlusal surfaces of 80 extracted molars were ground flat to 2 mm occlusal to the cementoenamel junction (CEJ). Roots were notched and embedded. Teeth were sized and distributed equally into eight groups (n = 10). Resistance features, four TMS stainless steel Regular pins or four amalgapin channels, were inserted into each molar. Resistance features were either distributed at the four line angles of each molar or clustered at two line angles. Matrices were applied, and amalgam was mechanically condensed into the matrices. Restorations were adjusted to a 4 mm vertical height and flat occlusal surfaces. A load was applied to each restoration at either a 45 degrees or a 90 degrees angle to the long axis of the tooth. Distributed pins provided significantly more resistance than clustered pins in groups tested at 90 degrees. Resistance to fracture in all groups loaded at 45 degrees and in amalgapin groups was not significantly affected by distribution of resistance features. Pins provided significantly more resistance than amalgapins at both angles of testing.