Occlusal Wall Research Articles

Enamel hypoplasia in Northeast China: Evidence from Houtaomuga

The importance of the study of archaeological sites outside the Yangtze and Yellow River Valleys has been increasingly recognized as these peoples also played important roles in the formation of Chinese civilization. In Northeast China the boundary between sedentary agriculturists and nomadic pastoralists has fluctuated over the vast Dongbei Plain (Northeast Plain) providing opportunities to explore relationships between stress exposure, subsistence, and cultural complexity.The human remains for the present study were recovered from the upper level of the Houtaomuga site (2250–2050 BP) on the Dongbei plain, Northeast China, and categorized as Hanshu II cultural period. Inhabitants are believed to have practiced mixed hunting–gathering–fishing with limited millet cultivation.This study explores the dental expression of stress episodes in this period. Our results show overall 72.73% of the individuals examined (40/55) exhibited linear enamel hypoplasia (LEH). Additional data from labial/buccal casts from 105 teeth of 30 individuals from the upper level of the site reveal the duration of growth disruption, counted as numbers of perikymata in the occlusal wall of each hypoplastic defect, ranged from 2 to 14. Stress episodes, calculated as ranging from 17 to 28 days at the low end to 98 to 154 days for the longer duration events, are consistent with values reported from sites in other parts of the world. Examination of anterior permanent teeth for LEH also indicates that infants and children of Houtaomuga experienced extremely high levels of stress, sufficient to affect the developing teeth of almost all the inhabitants. In future examination of enamel hypoplasia of the pastoralists from the Neolithic levels of the site can provide time depth for this study of population stress, and facilitate our understanding of the changes in lifeways and adaptive strategies across subsistence transitions and climate change in Northeast China.

Comparing marginal microleakage of three Bulk Fill composites in Class II cavities using confocal microscope: An in vitro study.

Aim:This study aims to evaluate and compare microleakage at the occlusal wall and cervical wall in Class II cavities restored with one SonicFill Bulk Fill composite and two conventional Bulk Fill composites.Materials and Methods:Thirty freshly extracted teeth were divided into three groups of 10 teeth each. Standardized Class II cavities were made on the mesial and distal surfaces of each tooth and restored using SonicFill Bulk Fill composite and two conventional Bulk Fill composites, Tetric Evo Ceram, and X-tra fil. After storage, thermocycling and immersion in 0.6% rhodamine dye solution specimens were sectioned and evaluated for microleakage at the occlusal and cervical walls using confocal microscope.Statistical Analysis Used:Kruskal-Wallis test, Wilcoxon Signed-Rank test and Mann-Whitney U-test.Results:The results demonstrated that in the occlusal wall and cervical wall, SonicFill Bulk Fill composite, showed significantly less marginal microleakage than the other groups.Conclusion:Based on the results of this study, SonicFill Bulk Fill composite showed less microleakage than the other conventional Bulk Fill composites.

Effect of Three Light Curing Protocols and Load Cycling on Microleakage of Class V Composite Restorations

Objective: Different methods have been suggested to overcome the polymerization shrinkage of composite restorations. Changing the light curing protocol to improve polymerization by using new light curing units is among these methods. The new devices are more efficient, portable and durable and produce less heat. This study aimed to assess the marginal microleakage of class V composite restorations subjected to three different light curing protocols and mechanical cycles.Methods: This was an in-vitro experimental study. Class V cavities measuring 2x3x1.5 mm were prepared on the buccal and lingual surfaces of 90 extracted human premolar teeth 1.5 mm above and below the cement enamel junction (CEJ). The samples were selected using convenience sampling and divided into 9 experimental groups of 10 each by using the Table of Random Numbers to control for the bias. The cavities were restored with packable composite resin along with Tetric-N- Bond and cured using three light curing protocols of conventional (680 mW/cm2 for 30s), soft-start (380 mW/cm2 for 10s followed by 680 mW/cm2 for 20s) and pulse (680 mW/cm2 for 30s,1s interval and 1s of lighting). The teeth were then subjected to mechanical cycles of 0, 500,000 and 1,000,000 and immersed in 2% Fuchsin for 24h. The teeth were then sectioned in half from the middle of the restoration buccolingually and the degree of microleakage was evaluated under a stereomicroscope (Zeiss, Germany) with 40X magnification. Data were analyzed using the Kruskal Wallis and the Mann-Whitney tests.Results: Despite the structural differences between the enamel and dentin margins, no significant difference was found in the degree of microleakage between the enamel (occlusal wall, p>0.05) and dentin (gingival wall, p>0.05) margins among the understudy groups.Conclusion: The degree of marginal microleakage in soft-start (SS) polymerization was not significantly different from that in conventional and pulse polymerizations of class V composite restorations

In Vitro Comparison of the Effects of Two Different Acid Etchants on the Microleakage of Composite Restorations

Objective: Etching of enamel and dentin is an important step in restoration of teeth with composite resin ensuring the retention of restoration and decreasing microleakage. This in vitro study sought to compare the effects of Kimiya and Etch-Rite acid etchants on the microleakage of composite restorations.Methods: This experimental study was conducted on 30 sound human molar teeth. Class V cavities were prepared on the buccal surface of teeth and the teeth were randomly divided into 2 groups of15. Iranian acid etchant (Kimiya, Iran) was used in group 1 and Etch-Rite (Pulpdent, Watertown, MA, USA) in group 2. The teeth were restored with Valux Plus (3M, ESPE, St. Paul, MN, USA) composite resin and polished by disc. The canal apices were sealed with sticky wax and the entire tooth surface was coated with 2 layers of nail varnish except for 1 mm around the restoration margins. Specimens were immersed in 2% Fuchsin (Fuchsin Dye, Merck, Germany) for 24h and then buccolingually sectioned. Specimens were evaluated under a stereomicroscope (SF-100B, Lomo, Russia) at 40X magnification and the degree of microleakage was determined using a 0-4 scale. The degree of microleakage was statistically analyzed using Mann Whitney U test.Results: No significant difference was found between the two groups of Kimiya and Etch-Ritein the degree of microleakage at the occlusal wall (p=0.1). The degree of microleakage at the gingival wall was not significantly different between the two groups either (p=0.68).Conclusion: Based on the results, Kimiya Iranian acid etchant has an efficacy equal to that of Etch- rite.

A comparative study of stress episode prevalence and duration among jomon period foragers from hokkaido

This study reconstructs linear enamel hypoplasia (LEH) prevalence and stress episode duration among Jomon period foragers from Hokkaido, Japan (HKJ). Results are compared to Jomon period samples from coastal Honshu, Japan (HSJ) and Tigara Inupiat from Point Hope, Alaska (PHT) to provide a more comprehensive perspective on the manifestation of stress among circum-Pacific foragers. LEH were identified macro- and microscopically by enamel surface depressions and increased perikymata spacing within defects. Individuals with more than one anterior tooth affected by LEH were labeled as LEH positive. Stress episode durations were estimated by counting the number of perikymata within the occlusal wall of each LEH and multiplying that number by constants reflecting modal periodicities for modern human teeth. LEH prevalence and stress episode duration did not differ significantly between the two Jomon samples. Significantly greater frequencies of LEH were found in HKJ as compared to PHT foragers. However, HKJ foragers had significantly shorter stress episode durations as compared to PHT. This suggests that a greater proportion of HKJ individuals experienced stress episodes than did PHT individuals, but these stress events ended sooner. Similarity in stress experiences between the two Jomon samples and differences between the HKJ and PHT are found. These findings are important for two reasons. First, stress experiences of foraging populations differ markedly and cannot be generalized by subsistence strategy alone. Second, due to significant differences in episode duration, stress experiences cannot be understood using prevalence comparisons alone.

Detection of Marginal Leakage of Class V Restorations In Vitro by Micro–Computed Tomography

This in vitro study evaluated the efficacy of micro-computed tomography (CT) in marginal leakage detection of Class V restorations. Standardized Class V preparations with cervical margins in dentin and occlusal margins in enamel were made in 20 extracted human molars and restored with dental bonding agents and resin composite. All teeth were then immersed in 50% ammoniacal silver nitrate solution for 12 hours, followed by a developing solution for eight hours. Each restoration was scanned by micro-CT, the depth of marginal silver leakage in the central scanning section was measured, and the three-dimensional images of the silver leakage around each restoration were reconstructed. Afterward, all restorations were cut through the center and examined for leakage depth using a microscope. The silver leakage depth of each restoration obtained by the micro-CT and the microscope were compared for equivalency. The silver leakage depth in cervical walls observed by micro-CT and microscope showed no significant difference; however, in certain cases the judgment of leakage depth in the occlusal wall in micro-CT image was affected by adjacent enamel structure, providing less leakage depth than was observed with the microscope (p<0.01). Micro-CT displayed the three-dimensional image of the leakage around the Class V restorations with clear borders only in the dentin region. It can be concluded that micro-CT can detect nondestructively the leakage around a resin composite restoration in two and three dimensions, with accuracy comparable to that of the conventional microscope method in the dentin region but with inferior accuracy in the enamel region.

Detection of marginal leakage of Class V restorations in vitro by micro-CT

To evaluate the reliability and superiority of micro-CT in marginal leakage assessment of Class V restorations. Class V preparations with gingival margins in dentin and occlusal in enamel were made in sixteen extracted non-carious human molars and restored with dental bonding agents and composite resin. All teeth were then immersed in 50% ammonia-silver nitrate solution for 12 hours, followed by developing solution for 8 hours. Each restoration was scanned by a micro-CT and silver leakage was measured and three-dimensional image of the silver leakage alone cavity wall were reconstructed. Afterward, all restorations were sectioned and examined for leakage depth using a microscope. The silver leakage depth of each restoration obtained by micro-CT and microscope were compared for equivalency. The silver leakage depths in gingival wall obtained with micro-CT (0.78 mm) and microscope (0.74 mm) showed no significant difference (P > 0.05), while the judgment of leakage depths in occlusal wall in micro-CT image (0.40 mm) was affected by adjacent enamel structure, giving less leakage depths compared to microscope (0.72 mm)(P < 0.01). The three-dimensional shapes of the microleakages displayed clearly by micro-CT alone wall of Class V restorations were multiform and some leakages showed channels on their way to spreading. Micro-CT can detect precisely the silver leakage in the dentin wall of a restoration and display its three-dimensional shape fully. Enamel structure affects the detection of the silver leakage next to it.

Interfacial nanoleakage and internal cement thickness of three esthetic crown systems

ObjectivesTo evaluate interfacial nanoleakage expression of the combination of different cementation procedures and different crown systems. MethodsForty-five human premolars prepared to receive single crowns were randomly divided into three groups (n=15) based on the materials to be used for crown fabrication and cementation: group 1: Zirc (Ivoclar-Vivadent) cemented with Multilink Automix; group 2: Ivoclar disilicate IPS Empress 2 luted with Excite DSC in combination with Variolink II; group 3: AAdva Zirconia (GC) cemented with G-Cem Automix. The specimens were then assessed for interfacial nanoleakage expression and the amount of silver deposits along the interface was quantified. The thickness of the cement was assessed at 5 different levels: cervical margins, midway between the cervical margin and the occlusal wall along the axial walls and at the occlusal wall. The nanoleakage scores and the cement thickness were analyzed with Kruskall–Wallis non-parametric Analysis of Variance and Dunn's Multiple-range post hoc test. ResultsGroup 2 showed significantly less nanoleakage expression than group 1 (p<0.05). The groups can be ranked in the following order 3<1<2 with regard to the cement thickness. ConclusionsThere was no correlation among combination of different cementation procedures and different crown systems and interfacial nanoleakage. Also the cement thickness and the degree of nanoleakage cannot be related. The amount of cement found at the cervical margins of all groups showed discrepancies within a clinical acceptable range.

A comparative evaluation of dentinal hypersensitivity and microleakage associated with composite restorations in cavities preconditioned with air abrasion - An ex vivo study

Background and Objective:Enormous advances have been made in adhesives; however, the problem of post-operative sensitivity has dragged along. Enough literature exists on the effect of air abrasion over bond strength of composites. However, not much is reported on its relation with microleakage and post operative sensitivity. Therefore, the aim of the study was to compare and evaluate dentinal hypersensitivity and microleakage associated with composite restorations in cavities preconditioned with air abrasion.Study Design:Fifteen patients were selected for the study who had to undergo extractions of both maxillary first premolars. On each patient, occlusally placed Class V cavities were made using rotary burs on both the premolars. On the right side premolar, restoration was done using total etch technique. On the left side premolar, restoration was done in similar way after preconditioning of the cavity with air abrasion. Sensitivity levels were recorded on a modified visual analogue scale preoperatively and post operatively at 1 week and one month time period. Following extraction, dye penetration test was done and 1 sample each from one group was subjected to Scanning Electron Microscope for evaluation of tooth restoration interface.Results:Clinically significant difference was there in post operative sensitivity levels after one month between the two groups. Increase in sensitivity was less in teeth restored after preconditioning with air abrasion. Dye penetration was also less in teeth restored after preconditioning with air abrasion. However, penetration at the gingival wall was more than the occlusal wall in both the groups.Conclusion:The study consolidates the fact that microleakage and post operative sensitivity are linked directly. It also proves that air abrasion can help in reducing the post operative sensitivity to a level; however, a larger sample size would be needed to obtain more robust results with stronger validation.

Reconstructing patterns of systemic stress in a Jomon period subadult using incremental microstructures of enamel

This study reconstructs systemic stress patterning using incremental microstructures of enamel in a subadult from the Yoshigo cemetery (3200 through 2800 BP), Aichi Prefecture, Japan, with the goal of providing an improved methodological and theoretical framework for interpreting systemic stress among Jomon people. High resolution impressions and replicas were collected for each anterior maxillary tooth. Each replica was studied under 50, 100, or 200× magnification on a measuring microscope. Perikymata spacing and enamel surface profiles were recorded using specialized software. Linear enamel hypoplasia (LEH) defects were identified as accentuated spacing in perikymata combined with a depression in the enamel surface. Each defect was placed within a chronological sequence based on decile location. Stress duration was estimated by counting the perikymata in the occlusal wall of each defect and multiplying that value by the modal periodicity for striae formation. Percentage of enamel growth disruption was estimated by dividing the number of perikymata within the occlusal wall of each matched defect by the total number of perikymata within the imbricational enamel. Eight LEH defects were chronologically matched. Chronology of LEH defects ranged between 1.2 through 3.5 years. Number of perikymata located within the occlusal wall of each defect ranged from one through 20. Estimated durations of stress ranged from 12 through 129.6 days. These durations overlapped with Neandertals, though Point Hope foragers had greater durations of stress with no overlap in interquartile ranges. Disrupted enamel growth ranged from 8.1% in the maxillary left canine to 50.7% in the maxillary right central incisor.

Infiltração Marginal de Resinas Compostas Associadas a Sistemas Adesivos com e sem Carga

The objective of this research was to verify the degree of marginal infiltration in class-V, vestibular, and lingual cavities in 30 recently-extracted human premolar teeth, divided into four groups, which, after the thermal cycle at 5oC/55oC, and stained with 2% methylene blue, were assessed in two ways: 1 - types of dentin bonding: self-etching adhesive (no load) and restored with micro-hybrid composite resin, one-bottle adhesive (with load), on which acid attack was conducted, and which was restored with micro-hybrid composite resin, and 2 - location of the cavity wall ( enamel occlusal wall and cement gingival wall). The data were measured through scores of 0 to 4 and statistically analyzed by nonparametric Kruskal-Wallis test to demonstrate the most effective dentin adhesive and determine which cavity wall that allowed less dye leakage.

Influence of different bonding agents on marginal sealing quality of amalgam restorations

Although advanced adhesive systems are in use, marginal microleakage is one of the greatest problems of contemporary restorative dentistry. The aim of this in vitro study was to evaluate the influence of different bonding agents on the marginal sealing quality of class II amalgam restorations. Forty freshly extracted human premolar and molar teeth were divided into four groups with 10 teeth in each one. Class II preparations were prepared and different adhesives were applied as follows: group I--Amalgam Liner (Voco); group II--ONE-STEP PLUS (Bisco); group III--PQ 1 (Ultradent). Group IV was used as a control, without any bonding agent. Amalgam (Cavex Non Gamma 2, Cavex) was hand-condensed into each preparation. Specimens were thermocycled 200 times at the following temperatures: 5-7 degrees C, 37 degrees C and 57-59 degrees C, and were then immersed into 1% solution of gentian violet for 72 hours. The teeth were sectioned longitudinally and microleakage was graded in the area of the gingival and occlusal quantity rim using a binocular magnifying glass with 25 times magnification. The highest microleakage was recorded in the Amalgam Liner group; 1526.0 microm at the gingival wall and 694.5 microm at the occlusal cavity wall. The lowest dye penetration was observed in the PQ1 group; 589.5 microm at the gingival wall, and 599.9 microm at the occlusal wall of the restoration. ANOVA test showed that there was a statistically significant difference of dye penetration values at the gingival wall among all examination groups (p < 0.01). No statistically significant differences were found comparing microleakage values at the occlusal wall. Results of this study showed that the best marginal sealing was accomplished by using the PQ1 bonding agent.

Effect of different placement techniques on marginal microleakage of deep class-II cavities restored with two composite resin formulations

Aim:The study aims to evaluate and compare marginal microleakage in deep class II cavities restored with various techniques using different composites.Materials and Methods:Sixty freshly extracted teeth were divided into six groups of 10 teeth each. Standardized class II cavities were made and were restored using composites of different consistencies with different placement techniques. Group 1 with Microhybrid composite, Group 2 with Packable composite, Group 3 Microhybrid composite with a flowable composite liner, Group 4 Packable composite with a flowable composite liner, Group 5 Microhybrid composite with precured composite insert in second increment and Group 6 Packable composite with precured insert in second increment. Specimens then were stored in distilled water, thermocycled and immersed in 50% silver nitrate solution. These specimens were sectioned and evaluated for microleakage at the occlusal and cervical walls separately using stereomicroscope.Results:The results demonstrated that in the occlusal wall, packable composite, showed significantly more marginal microleakage than the other groups. In the cervical wall, teeth restored with a flowable composite liner showed less marginal microleakage when compared to all other groups.Conclusion:Based on the results of this study, the use of flowable composite as the first increment is recommended in deep class II cavities.

Effect of halogene light source on marginal microleakage of resin composite restorations

Introduction. Although the technology of production resin composite materials has been improved in the past years, polymerization shrinkage and microleakage still remain the main problem of the resin composite restorations. The most important issues are polymerization control, light source choice, quality and polymerization technique. The aim of this study was to evaluate the effect of the halogen light source on the marginal microleakage of the resin composite restorations class V. Material and Methods. The study included 40 extracted human teeth (20 intact and 20 with caries lesion). Class V cavity was prepared in each tooth. The light curing unit used in this study had irradiance 540 mW/cm2. Cavities were restored with the two resin composite materials, Filtek Supreme (3M ESPE) and Luksogal - Galenika. Microleakage was determined using colored solution of 50% silver-nitrate. Results were obtained using stereomicroscope with 6 times magnification. Color penetration was evaluated on the occlusal and gingival wall. Results. Linear color penetration was observed in all cavities restored using Luksogal. There was significant difference (p&lt;0.01) in color penetration between the occlusal (20.30 ?m) and gingival wall (34.00 ?m). Color penetration was shown in all cavities prepared on intact and caries teeth and restored using Filtek Supreme. Also, color penetration on the occlusal wall (13.80 ?m) was significantly lower (p&lt;0.01) than the penetration on the gingival wall (33.00 ?m). Conclusion. All the tested cavities showed marginal leakage, regardless the tooth or material used. Greater microleakage was noticed when Luksogal was used.

Effects of Different Light Curing Units/Modes on the Microleakage of Flowable Composite Resins

The aim of this in vitro study was to evaluate the influence of different light curing units and modes on microleakage of flowable composite resins. Eighty Class V cavities were prepared in buccal and lingual surfaces of 40 extracted human premolars with cervical wall located in dentin and the occlusal wall in enamel. These teeth were randomly assigned into two groups (n=20) and restored with different flowable composites; Group I: Esthet-X Flow, Group II: Grandio Flow. Each group was randomly divided into four subgroups; while the samples of the first subgroup were polymerized with conventional Halogen light, the rest of them were polymerized with different curing modes of Light Emitting Diode (LED). The second subgroup was polymerized with fast-curing; the third subgroup with pulse-curing and those of the fourth subgroup with step-curing modes of LED. After the samples were thermocycled and immersed in dye, they were longitudinally sectioned. Dye penetration was assessed under a stereomicroscope. Data were analyzed by Kruskal-Wallis and Mann-Whitney U tests. None of the restorations showed leakage on enamel margins. On dentin margins no significant differences were observed between flowable composite resins polymerized with halogen light (P>.05). While step curing mode of LED presented significant differences between the resins, the difference was insignificant when fast-curing and pulse-curing mode of LED were used. No statistically significant differences were observed between curing units for Esthet-X Flow samples. For Grandio Flow samples, only step-curing mode of LED caused statistically higher leakage scores than halogen and other curing modes of LED (P<.05). The effect of curing units' type and curing mode on flowable composite resin leakage might be material-dependent.

SEM and microleakage evaluation of the marginal integrity of two types of class V restorations with or without the use of a light-curable coating material and of polishing

Objectives To evaluate the marginal integrity of class V restorations through an SEM observation and a microleakage test. Methods Teeth with class V cavities were restored with either a flowable composite ( n = 20) or a glass ionomer cement (GIC) ( n = 20). Ten restorations in each group were immediately polished. A coating agent was applied on five polished and five non-polished restorations of each group. No coating was used on the remaining specimens. Epoxy resin replicas of the restorations were observed under a SEM and the percentage of marginal gaps was calculated. After immersion in a 2% methylene blue solution, three sections were obtained from each specimen and observed under a stereomicroscope. Occlusal and gingival microleakage were evaluated with a four-steps scoring system. The percentages of marginal gaps and the microleakage scores were analyzed with the Kruskal–Wallis ANOVA and the Mann–Whitney test with Bonferroni's correction. Occlusal and gingival microleakage were compared with the Wilcoxon test. Results No gaps were detected after coating. The restorative materials did not differ in interfacial gaps. Immediate polishing increased the gaps of uncoated restorations ( p < 0.05). The microleakage decreased with coating, except for occlusal wall of polished flowable composite restorations. After coating, the occlusal microleakage was higher than the gingival ( p < 0.05), except for non-polished flowable composite restorations. After polishing and coating, the flowable composite showed higher occlusal microleakage than the GIC. The polishing increased the occlusal microleakage of coated flowable composite restorations. Conclusions The coating procedure is advisable for restoring marginal integrity and reducing gingival microleakage in class V restorations.

Effect of the composite surface sealant application moment on marginal sealing of compactable composite resin restoration

An analysis was carried out to observe whether the application or not of a composite surface sealant (CSS), as well the moment for CSS application were able to reduce marginal microleakage in compactable composite resin restoration. All the preparations were restored with a compactable composite resin. The restored teeth were randomly assessed. G1 (control group): finished and polished; G2: finished, polished, etched and cover with CSS; G3: immediately after the restoration done the CSS was applied, then finished and polished; G4: CSS applied immediately after the restoration was done, the finished and polished, etched, and covered with CSS. The specimens were isolated with nail polish, thermocycled, immersed in aqueous solution of silver nitrate, and followed in a photo developing solution. The microleakage scores obtained from the occlusal and cervical walls were analyzed with the Kruskall-Wallis nonparametric test. No microleakage was found at the enamel margins. Comparing the microleakage scores at dentin/cementum margins (p < 0.05) it was found that G3 (p = 0.0162) and G4 (p = 0.0187) were able to reduce microleakage when compared with group G2. However the results were not statistically different from the control group. The application of CSS was not able to completely eliminate marginal microleakage at the dentin/cementum margins.

Influence of recasting palladium-silver alloy on the fit of crowns with different marginal configurations

Dental laboratories may occasionally recast previously cast dental alloy to produce a prosthesis, but this process may have a negative influence on marginal adaptation. The aim of this study was to evaluate the cervical and internal fit of complete metal crowns that were cast and recast using palladium-silver alloy and 3 different marginal configurations: straight shoulder, 20-degree bevel shoulder, and 45-degree chamfer. Thirty aluminum dies were made, 10 for each marginal configuration. Each group of 10 was further divided into 2 subgroups (n=5), according to the alloy (Pors-on 4) casting history. The dies were waxed using a cylindrical metal matrix to standardize the thickness of the walls. The wax patterns were invested in a phosphate-bonded investment (Deguvest) and cast after heating in an oven (EDG), according to the manufacturer's instruction. The alloy was melted with an oxygen-gas heat source and cooled to room temperature after casting. Afterwards, the specimens were seated on the dies with a static load of 9 kgf for 1 minute. The marginal discrepancy was measured with a metric microscope, using a digital micrometer. All the measurements were done by the same operator. Each crown-die interface was measured 3 times on each of the 4 diametrically opposite points, for a total of 12 measurements for each specimen. Specimens were longitudinally sectioned to obtain 2 hemi-sections for internal discrepancy measurements, measured at 3 points: 1 in the center of the occlusal wall and 2 at each center of each axial wall. Three measurements were made for each point, for a total of 9 measurements per specimen. The results were submitted to parametric statistical 3-way analysis of variance followed by Tukey-Kramer HSD post hoc analysis (alpha=.05). The new alloy provided significantly better adaptation (P<.001) than the recast alloy for both marginal and internal discrepancy measurements. Marginal designs did not shown any statistical differences when the new metal was used. For recast metal, the straight shoulder showed significantly better adaptation (P<.001) than the 20-degree bevel shoulder and the 45-degree chamfered configurations, which were statistically similar to each other. The results of this study suggest that recasting procedures for crown fabrication should not be used with the palladium-silver alloy tested.

Precision of a CAD/CAM technique for the production of zirconium dioxide copings

Purpose The precision of a computer-aided design/manufacturing (CAD/CAM) system to manufacture zirconium dioxide copings with a predetermined internal space was investigated. Materials and Methods Two master models were produced in acrylic resin. One was directly scanned by the Decim Reader. The Decim Producer then manufactured 10 copings from prefabricated zirconium dioxide blocks. Five copings were prepared, aiming for an internal space to the master of 45 μm. The other five copings were prepared for an internal space of 90 μm. The second test model was used to try in the copings produced. The obtained internal space of the ceramic copings was evaluated by separate measurements of the master models nd inner surfaces of the copings. The master models were measured at predetermined points with an optical instrument. The zirconium dioxide copings were measured with a contact instrument at the corresponding sites measured in the masters. Results The first group of copings had a mean internal space to the scanned master of 41 μm and of 53 μm to the try-in master. In general, the internal space along the axial walls of the masters was smaller than that along the occlusal walls. The second group had a mean internal space of 82 μm to the scanned master and of 90 μm to the try-in master. Conclusion The aimed-for internal space of the copings was achieved by the manufacturer. The CAD/CAM technique tested provided high precision in the manufacture of zirconium dioxide copings.— Reprinted with permission of Quintessence Publishing.

Prevalence and the duration of linear enamel hypoplasia: a comparative study of Neandertals and Inuit foragers

As a dental indicator of generalized physiological stress, enamel hypoplasia has been the subject of several Neandertal studies. While previous studies generally have found high frequencies of enamel hypoplasia in Neandertals, the significance of this finding varies with frequencies of enamel hypoplasia in comparative samples. The present investigation was undertaken to ascertain if the enamel hypoplasia evidence in Neandertals suggests a high level of physiological stress relative to a modern human foraging group, represented here by an archaeological sample of Inuit from Point Hope, Alaska. Unlike previous studies, this study focused specifically on linear enamel hypoplasia (LEH), emphasizing systemic over localized causes of this defect by considering LEH to be present in an individual only if LEH defects occur on two anterior teeth with overlapping crown formation periods. Moreover, this study is the first to evaluate the average growth disruption duration represented by these defects in Neandertals and a comparative foraging group. In the prevalence analysis, 7/18 Neandertal individuals (from Krapina and southern France) and 21/56 Neandertal anterior teeth were affected by LEH, or 38.9% and 37.5% respectively. These values do not differ significantly from those of the Inuit sample in which 8/21, or 38.1% of individuals, and 32/111, or 28.8% of anterior teeth were affected. For the growth disruption duration analysis, 22 defects representing separate episodes of growth disruption in Neandertals were compared with 22 defects in the Inuit group using three indicators of duration: the number of perikymata (growth increments) in the occlusal walls of LEH defects, the total number of perikymata within them, and defect width. Only one indicator, the total number of perikymata within defects, differed significantly between the Inuit and Neandertal groups (an average of 13.4 vs. 7.3 perikymata), suggesting that if there is any difference between them, the Inuit defects may actually represent longer growth disruptions than the Neandertal defects. Thus, while stress indicators other than linear enamel hypoplasia may eventually show that Neandertal populations were more stressed than those of modern foragers, the evidence from linear enamel hypoplasia does not lend support to this idea.