MOD Amalgam Research Articles

Determination of Mercury in Dental Hard Tissue: An in Vitro Study

The purpose of this study was to determine the levels of mercury in hard tissue from dental amalgam fillings under in vitro conditions. Methods and Results: The study included 30 human teeth that were extracted for various clinical reasons. The teeth were stored in a physiological solution until they were used. The teeth were divided into 3 experimental groups: Group 1 (n=10) – occlusal surface cavity preparation (class I according to Black); Group 2 (n=10) – proximal-occlusal surface cavity preparation (class II); and Group 3 (n=10) – mesio-occlusal-distal [MOD] surface cavity preparation. Each of these groups was divided into 2 subgroups: subgroup 1 (n=5) – amalgam fillings were not polished, and subgroup 2 (n=5) amalgam fillings were polished. The teeth were filled with amalgam, and those in subgroups 2 were polished after 24 hours. The amount of mercury released from the amalgam fillings was determined 9 months after the teeth were filled. Before chemical analysis, the teeth were irrigated 4 times over a period of 10 minutes in an ultrasonic bath. From each tooth, 250mg of the powder was mineralized with royal water (HCl+HNO3 in a ratio of 1:3) in a microwave oven, for 54 minutes. After mineralization, the samples were filtered and analyzed with inductively coupled plasma optical emission spectrometry. The average mercury level after polishing the amalgam filling was significantly smaller (P=0.032) only in Group 1. The average mercury levels in the 3 groups revealed significant differences between both the unpolished samples (one-way ANOVA F = 69.54, P < 0.001) and the polished samples (one-way ANOVA F = 110.54, P < 0.001). Group 3 with MOD surface cavity preparation was characterized by the highest mercury levels. Conclusion: The teeth with an MOD amalgam restoration are characterized by the highest mercury levels. The more mercury is released from unpolished amalgam fillings than from polished amalgam fillings in teeth with occlusal surface cavity preparation (class I according to Black).

Quantitative analysis of metallic artifacts caused by dental metallic restorations: Comparison between four CBCT scanners

PurposeThe objective of this study was to quantitatively evaluate the artifacts produced by different metallic restorations using four cone-beam computed tomography (CBCT) scanners. MethodsEight extracted teeth (four mandibular premolars and four mandibular molars) were randomly divided into four groups. Each group compromised one premolar and one molar. One group was prepared and restored with occluso-mesial amalgam restorations (MO), the second group with mesio-occluso-distal amalgam restorations (MOD), the third group with porcelain fused to metal full coverage restoration, and the fourth group with occluso-mesial indirect metallic restorations (inlays). The restored teeth were then placed in the sockets of dried mandible. Images were obtained using four different cone beam computed tomography (CBCT) scanners, with exposure parameters 85 kVp and 8 mA. Volumes of artifacts were then measured by segmentation using volumetric and8i thresholding methods. ResultsQuantitative evaluation of metallic artifacts using the volumetric method showed the greatest mean value obtained from J Morita for all types of restorations studied while when using the thresholding method Gallileos yielded the greatest mean value for crown, MO, and inlay restoration while scanora produced the greatest mean value for MOD restorations. ConclusionIn cases of scanning patients with multiple fixed restorations Scanora is recommended. In cases of patients with MO or inlay restorations Planmeca AINO™ is recommended. Gallileos and J Morita are acceptable for scanning patients with metallic restorations and recommended in cases of MOD amalgam restorations.

Restorative material and loading type influence on the biomechanical behavior of wedge shaped cervical lesions.

To evaluate the influence of restorative materials used on the rehabilitation of MOD cavities and loading type, on biomechanical behavior of wedge-shaped (WS) lesions in endodontically treated maxillary premolars. The investigation was conducted by 3D finite element analysis (FEA) and strain gauge test. Six models were generated, with MOD cavities and endodontic treatment: A (MOD amalgam restoration), R (MOD composite restoration), AL (A + cervical lesion (L)), RL, ALR (A + cervical lesion restored with composite (LR)), and RLR. Each model underwent two compressive loading (100N): axial and oblique-45° angle to the long axis on the buccal cusp. The models were analyzed by von Mises criteria. For strain gauge test, 14 standardized maxillary premolars were treated according to the groups described for FEA. Two strain gauges were bonded on each sample submitted to compressive loading in a mechanical testing machine. A presented higher stress concentration and strain values than R. Oblique loading promoted highest stress concentration and strain rates for all groups. ALR and RLR presented similar stress-strain distribution pattern when compared to A and R. The interaction between MOD cavity restored with amalgam and oblique loading propitiated the highest stress concentration and strain values on cervical region and WS lesion. The MOD cavity restored with composite resin is a better option than amalgam to improve the biomechanical behavior of wedge-shaped lesion, avoiding dental failure. In addition, the occlusal interferences must be removed, allowing homogeneous contact distribution and preventing WS lesion progression.

The influence of flowable composite liner on microleakageof class II packable composite resin restoration withdifferent application techniques (Comparative study)

Background: This in vitro study was conducted to evaluate and compare the influence of flowable composite and different application techniques of class II packable composite restoration on dentinal leakage. Materials and methods: Thirty human freshly-extracted Maxillary premolars were selected for this study. Conventional Class II MOD cavities were prepared in the sample teeth which were then divided into five groups .Each group consist of ten boxes either MO or DO according to the restorative procedure used except group A which consist of twenty boxes(ten teeth with MOD amalgam restoration). Group A: ten teeth where restored by amalgam- (SDI Australia) high strength admix amalgam type.Group B: ten teeth in which the mesio-occlusal (MO) sides were restored by {adhesive + flowable composite + one bulk packable composite (Filtek P60)}. Group C: ten teeth in which the disto-occlusal (DO) sides were restored by {adhesive +one bulk packable composite, (Filtek P60)}.Group D: ten teeth in which the mesio-occlusal (MO) sides were restored by {adhesive + flowable composite + successive build up technique for packable composite, (Filtek P60)}. Group E: ten teeth in which the disto-occlusal (DO) sides were restored by {adhesive+ successive build up technique for packable composite, (Filtek P60)}. After thermocycling and immersion in 2% methylene blue, the teeth were sectioned longitudinally mesio-occluso-distal and dye penetration was evaluated using a stereomicrscope, microleakage was recorded in mm. Results and Conclusions: ANOVA test and least significant difference (LSD) test were used to analyze the results, and the results showed that the use of flowable composite resin as a liner with packable composite resin decreases the amount of dentinal microleakage, and the restorative technique of packable composite whether it is bulk build up technique, or incremental successive build up technique has no difference on the improvement of microleakge value, and the packable resin composite restoration whatever applied with different application techniques or restored with or without flowable composite it still had or scored higher microleakage than amalgam restoration.

Re-Treatment Decisions for Failed Posterior Restorations among Dentists in Kuwait

To compare re-treatment choices for MOD amalgam or resin composite restorations with or without cusp fracture among dentists in Kuwait. A random sample of 158 dentists completed a questionnaire designed to obtain socio-demographic, educational and work-related information and their choices for re-treatment of four scenarios of failed restorations on lower first molars: 1. MOD amalgam restoration; 2. MOD composite restoration; 3. MOD amalgam restoration with cuspal fracture; 4. MOD composite restoration with cuspal fracture. Re-treatment options were: re-treating with amalgam; re-treating with composite; placing an onlay; or, placing a crown. For the purpose of analysis, responses were dichotomized into re-treatment with a direct or indirect restoration. For cases 1 and 2, most participants chose to re-treat with amalgam restoration and for cases 3 and 4, most chose to place an indirect restoration. In general, an increased tendency towards the indirect option was associated with increased age, being a male and being a specialist. Tendencies to place an indirect restoration did not differ between cases 1 and 2 (P=1.0) or cases 3 and 4 (P=0.317), although the tendency to do so was significantly greater in case 3 than 1 (P=0.000) and case 4 than 2 (P=0.000). The variation noted among dentists regarding their stated choices for re-treating failed posterior restorations appeared to be associated with gender, education and experience factors. A tendency towards indirect restorations was seen when the restoration is associated with a fractured cusp.

Finnish dentists’ perceptions of the longevity of direct dental restorations

Objectives. To evaluate Finnish dentists’ perceptions of the longevity of direct dental restorations; to assess the possible impacts of dentists’ characteristics on these perceptions; and to compare the present longevity estimates with those of recent European reports. Methods. A questionnaire to 592 general practitioners, systematically sampled from the Finnish Dental Association's membership list, was posted in April 2004 and data collection was finished by the end of June. The question “In general, what is your estimate for the mean age of restoration in permanent teeth?” pointed restorations: Class II and MOD composites and amalgam in a posterior tooth and Class III composites in an incisor. Dentists’ gender, main work, and year of graduation served as background information. Of the 339 (57%) respondents, only public and private dentists were included; 11 were excluded. Three studies fulfilled the inclusion criteria for recent reports on restoration longevity. Statistical evaluation was by one-way ANOVA, with p=0.05 as the level of significance. Results. The mean of the estimates for all types of composite was 9.0 years (SD 3.6; 95% CI 8.6–9.3) and 18.7 years for amalgam (SD 7.3; 95% CI 18.0–19.5). Male dentists gave longer estimates than female dentists for posterior composites, but shorter estimates for amalgam. Compared to public dentists, private dentists gave longer estimates for posterior composites. All estimates were longer than those reported in the recent literature. Conclusion. Dentists’ perceptions of posterior composite longevity are significantly longer among males than among females and among private than public sector dentists, and exceed the median longevity reported in recent studies.

A simple method to estimate restoration volume as a possible predictor for tooth fracture

Statement of problem Many dentists cite the fracture risk posed by a large existing restoration as a primary reason for their decision to place a full-coverage restoration. However, there is poor agreement among dentists as to when restoration placement is necessary because of the inability to make objective measurements of restoration size. Purpose The purpose of this study was to compare a new method to estimate restoration volumes in posterior teeth with analytically determined volumes. Material and methods True restoration volume proportion (RVP) was determined for 96 melamine typodont teeth: 24 each of maxillary second premolar, mandibular second premolar, maxillary first molar, and mandibular first molar. Each group of 24 was subdivided into 3 groups to receive an O, MO, or MOD amalgam preparation design. Each preparation design was further subdivided into 4 groups of increasingly larger size. The density of amalgam used was calculated according to ANSI/ADA Specification 1. The teeth were weighed before and after restoration with amalgam. Restoration weight was calculated, and the density of amalgam was used to calculate restoration volume. A liquid pycnometer was used to calculate coronal volume after sectioning the anatomic crown from the root horizontally at the cementoenamel junction. True RVP was calculated by dividing restoration volume by coronal volume. An occlusal photograph and a bitewing radiograph were made of each restored tooth to provide 2 perpendicular views. Each image was digitized, and software was used to measure the percentage of the anatomic crown restored with amalgam. Estimated RVP was calculated by multiplying the percentage of the anatomic crown restored from the 2 views together. Pearson correlation coefficients were used to compare estimated RVP with true RVP. Results The Pearson correlation coefficient of true RVP with estimated RVP was 0.97 overall ( P≤.0001). Coefficients for comparisons stratified by tooth type, restoration type, and restoration size groups were all greater than 0.90 ( P≤.0001). Conclusion Within the limitations of this study, the high correlation between estimated RVP and true RVP indicated that estimated RVP was an accurate method to quantify the relative volume of restorative material in coronal tooth structure. The fact that it can be done in a nondestructive manner makes it attractive for clinical situations.

Effect of Prolonged Water Storage and Repeated Thermocycling on the Reinforcing Ability of Refrigerated Amalgambond Plus/High Performance Additive in Third Molars with Large Mesio-occlusodistal Amalgam Restorations

This in vitro investigation examined what effect prolonged water immersion and repeated thermocycling had on the fracture strength of extracted third molars restored with refrigerated Amalgambond Plus with High Performance Additive (AB+/HPA) and Tytin amalgam. Mesio-occlusodistal (MOD) channels were prepared in one member from each of 19 contralateral pairs. After restoration, specimens were stored in water for 6 months, with thermocycling repeated every 2 months. Specimens were fractured in a universal testing machine, and the data were analyzed. Secondary effects of tooth location and tooth size were also examined. Fracture strengths of prepared/restored teeth were not statistically different from those of intact contralateral pairs (p > 0.05). Maxillary teeth had lower fracture strengths than mandibular teeth, and tooth size had no effect on fracture strength. Extracted molars with large MOD amalgam restorations bonded with refrigerated AB+/HPA had fracture strengths equivalent to those of intact contralateral pairs after 6 months of water storage and repeated thermocycling.

A comparison of the mechanical behavior of posterior teeth with amalgam and composite MOD restorations

Objective: To compare the mechanical behavior, and infer differences in fracture resistance, of mandibular molars with amalgam and composite MOD restorations to that of an unrestored molar. Method: Finite element models were developed for an unrestored molar and molars with MOD amalgam and composite restorations. The location and magnitude of maximum principal stress resulting from simultaneous mechanical and thermal loads were determined for each molar using a series of designed experiments. An analysis of variance was conducted with the components of stress to distinguish the relative influence of oral parameters and restoration on the stress distribution in each molar. Results: The maximum principal stress in the unrestored molar was the largest of all three molars examined and occurred within the dentin along the pulpal wall. Maximum principal stresses in the molars with amalgam and composite restorations both occurred along the cavosurface margin. Maximum principal stresses in the molar with amalgam restoration occurred at the pulpal floor and lingual wall junction and resulted from large occlusal loads. Although occlusal loading had minimal effects on the stress distribution within the molar with composite restoration, low oral temperatures were responsible for the maximum principal stresses, which were found at the lingual margin and occlusal surface junction. Conclusion: There was no significant difference in the magnitude of maximum stress that occurred in the molars with amalgam and light curing composite restorations. However, the location and orientation of maximum stress in the restored molars were largely dependent on the restorative material. Although clinical studies report that tooth fracture occurs predominately to restored molars, the unrestored molar experienced the highest stress in this investigation. Therefore, the reduction in fracture resistance of restored posterior teeth appears to result from changes in the location of maximum stress resulting from mastication and temperature changes.

In vitro fracture strength of endodontically treated premolars

The recent introduction of new bonding agents has led some authors to suggest that certain endodontically treated posterior teeth could be restored with a bonded restoration instead of a full-coverage crown or onlay. To test the fracture resistance of endodontically treated premolars restored with and without bonding agents, we randomly divided 56 intact and caries-free maxillary premolars into seven groups as follows: unaltered teeth; access only; MOD prep and RCT; MOD prep, RCT, and amalgam restoration; MOD prep, RCT, and amalgam with 4-META bonding agent; MOD prep, RCT, and composite resin restoration; and MOD prep, RCT, and composite resin with 4-META bonding agent. The teeth were subjected to compressive fracture tests in a Zwick 1435 Universal Testing Machine. Unaltered teeth and those with access only demonstrated similar fracture strengths. Under the conditions of this study, there was no significant difference in fracture strength between the experimental groups. The recent introduction of new bonding agents has led some authors to suggest that certain endodontically treated posterior teeth could be restored with a bonded restoration instead of a full-coverage crown or onlay. To test the fracture resistance of endodontically treated premolars restored with and without bonding agents, we randomly divided 56 intact and caries-free maxillary premolars into seven groups as follows: unaltered teeth; access only; MOD prep and RCT; MOD prep, RCT, and amalgam restoration; MOD prep, RCT, and amalgam with 4-META bonding agent; MOD prep, RCT, and composite resin restoration; and MOD prep, RCT, and composite resin with 4-META bonding agent. The teeth were subjected to compressive fracture tests in a Zwick 1435 Universal Testing Machine. Unaltered teeth and those with access only demonstrated similar fracture strengths. Under the conditions of this study, there was no significant difference in fracture strength between the experimental groups.

In vitro fracture strength of endodontically treated premolars

The recent introduction of new bonding agents has led some authors to suggest that certain endodontically treated posterior teeth could be restored with a bonded restoration instead of a full-coverage crown or onlay. To test the fracture resistance of endodontically treated premolars restored with and without bonding agents, we randomly divided 56 intact and caries-free maxillary premolars into seven groups as follows: unaltered teeth; access only; MOD prep and RCT; MOD prep, RCT, and amalgam restoration; MOD prep, RCT, and amalgam with 4-META bonding agent; MOD prep, RCT, and composite resin restoration; and MOD prep, RCT, and composite resin with 4-META bonding agent. The teeth were subjected to compressive fracture tests in a Zwick 1435 Universal Testing Machine. Unaltered teeth and those with access only demonstrated similar fracture strengths. Under the conditions of this study, there was no significant difference in fracture strength between the experimental groups.

In vivo cusp fracture of endodontically treated premolars restored with MOD amalgam or MOD resin fillings

The frequency of cusp fracture of endodontically treated premolars was investigated in a retrospective study. After endodontic therapy, the teeth were either restored with a MOD amalgam filling, or with an enamel-bonded MOD resin filling. A very high frequency of cusp fracture was found in premolars restored with amalgam: nearly one-third fractured within 3 years after endodontic treatment. The frequency of cusp fracture differed among the 4 amalgam-restored teeth; the lower first premolar had a 15-year survival rate of 74%, in contrast to an average of 32% for the other 3 premolars. No resinrestored premolar fractured during the first 3 years, and the difference between amalgam and resin-restored teeth was highly significant at the 0–3 year interval. However, fracture of resin-restored premolars did happen in the following 3–10 year interval. From a periodontal point of view, a low frequency of cusp fracture carries great weight, and it is therefore concluded that an enamelbonded resin filling may be a treatment option much preferred to amalgam in temporarily restoring endodontically treated premolars with MOD cavities.

Impact-fracture energy of human premolar teeth

The fracture strength of contralateral pairs of premolar teeth was determined by an in vitro method wherein impact loads of equal energy were applied to the medial aspects of the buccal cusps. Absorbed energy values quantified the fracture resistance of unprepared teeth and teeth restored with MOD amalgams, MOD amalgam overlays, MOD gold overlays, and full gold crowns. It was established that unprepared lower premolar teeth had a greater resistance to fracture than upper premolar teeth, and lower first premolar teeth were more resistant to fracture than the other premolar teeth; the fracture resistance of premolar teeth restored with MOD amalgams was significantly reduced compared with unprepared control teeth; MOD amalgam overlays in premolar teeth produced fracture resistances not significantly different from those for the unprepared controls; and restoration of premolar teeth with MOD gold overlays and full gold crowns enhanced fracture resistance to a level much greater than that of the unprepared control teeth.