Influence of Preparation Depth and Design on Stress Distribution in Maxillary Central Incisors Restored with Ceramic Veneers: A 3D Finite Element Analysis.

PURPOSE: To evaluate the influence of different preparation designs and depths on the stress field developed in maxillary central incisors restored with veneers made with different ceramic materials using finite element analysis (FEA). MATERIALS AND METHODS: A linear static three-dimensional finite element analysis model was used with the aid of reverse engineering to develop digital models of maxillary central incisors restored with ceramic veneers, according to two different preparation depths (thin vs deep) and two different preparation designs (feather edge vs butt joint). Three ceramic systems were tested: (i) feldspathic porcelain, (ii) heat pressed glass ceramic IPS Empress 2 (Ivoclar Vivadent AG), and (iii) heat pressed glass ceramic IPS e.max-Press (Ivoclar Vivadent AG). Each model was subjected to a compressive force of 200N applied to the palatal surface 2 mm below the incisal edge. The longitudinal axis of the restored tooth formed an angle of 130o with the direction of the force. The biomechanical behavior of the different models was examined according to the von Mises stress criterion. Statistical analysis was performed using nonparametric confidence interval estimation using bootstrapping. RESULTS: The maximum observed stress values were calculated and found to be similar between prepared and intact teeth. The cervical margin of the veneers displayed the highest von Mises stress values. Irrespectively of the depth and preparation design, the biggest von Mises stress values were observed at the veneer structures with the following order: (i) IPS Empress 2, (ii) IPS e.max-Press, (iii) feldspathic (p = 0.001). Preparation depth resulted in statistically significant differences (p = 0.001) in the stress distribution in the majority of tested structures. As the preparation depth was increased, the stresses within the veneer structure and the tooth structures were decreased. No statistically significant differences were detected in the stresses among the different restored models, when the preparation design was considered. CONCLUSIONS: This FEA study suggests that ceramic veneers could restore the biomechanical behavior of prepared central incisors and made it similar of that of an intact tooth. Regardless of the preparation depth and design and the ceramic system used, the cervical margin of ceramic veneers presents the highest von Mises stress values. When feldspathic porcelain was compared with lithium disilicate (IPS e.max Press), the latter displayed the lowest transfer of stresses to dental tissues. An increase in preparation depth resulted in a statistically significant stress decrease in both the veneer and the tooth.

Variables affecting the fit of zirconia fixed partial dentures: A systematic review.

STATEMENT OF PROBLEM: Different parameters affect the marginal and internal fit of zirconia fixed partial dentures (FPDs) on natural teeth. Determining a way to optimize these restorations is essential. PURPOSE: The purpose of this systematic review was to determine the variables affecting the marginal fit and internal accuracy of zirconia FPDs on natural teeth. MATERIAL AND METHODS: An electronic search was conducted by 2 independent reviewers by using the MEDLINE, Cochrane, Web of Science, and Scopus databases, as well as Google Scholar, for studies published up to July 2018, and a manual search was conducted from the reference lists of related articles. Eligibility criteria included articles in English published in peer-reviewed journals that assessed the marginal and/or internal adaptation of zirconia FPDs on teeth with 3 or more units, with at least 1 of the experimental groups being frameworks or FPDs fabricated from zirconia. Risk of bias was assessed with the aid of the Cochrane Handbook for Systematic Reviews of Interventions. RESULTS: The search provided 418 records, with 41 fulfilling the inclusion criteria. The selected studies showed considerable heterogeneity regarding materials, state of sintering, manufacturer and computer-aided design and computer-aided manufacturing (CAD-CAM) system, experimental methodology, sample size, and span length. Of the included articles, 36 were in vitro studies and 5 were clinical studies, most of which exhibited high-performance and detection biases. CAD-CAM systems provided more precise marginal and internal fit than CAM systems. An increase of framework span length to 6 or more units decreased both marginal and internal fit. The reported marginal gap tended to increase after the veneering process. The introduction of a conventional impression into an otherwise digital workflow seems to have a negative effect on the marginal fit. CONCLUSIONS: The accuracy of zirconia FPDs or frameworks is considerably influenced by the processing procedure used and the choice of CAD-CAM system.

The Effect of Clenching and Occlusal Instability on Body Weight Distribution, Assessed by a Postural Platform.

The purpose of this research project was to investigate whether or not clenching and occlusal instability of Angle's Class I malocclusion have an effect on body weight distribution in healthy adult subjects. Twenty adults (fourteen males and six females, ages 27-40, mean age 31.7 years, SD 3.32) were included in this study. The MatScan (Tekscan Inc., Boston, MA) system was used to measure the body weight distribution changes of the subjects. Four body weight distribution measurements were taken for each subject while (1) the mandible was in the rest position (no tooth contact) (RES), (2) subject was clenching (maximum intercuspation of the teeth with heavy occlusal forces) (CL), (3) subject was clenching on the right side (with 1 mm disocclusion on the left side) (CLR), and (4) subject was clenching on the left side (with 1 mm disocclusion on the right side) (CLL). The lateral and the anteroposterior body weight distribution changes during the different clenching conditions (both sides, right, and left) were compared to those at which the mandible was at the rest position. The statistical significance of these results was tested with a Chi-Squared test (p<0.05). Based on the findings of the present study it was concluded that clenching and occlusal instability are associated with lateral body weight distribution changes.

Association Between Increased Concavity of Maxillary Labial Alveolar Bone and Decreased Labial Cortical Bone Thickness: A Cone Beam Computed Tomography Aided Retrospective Cohort Study.

PURPOSE: To assess whether an increased concavity of maxillary labial alveolar bone is related to labial thickness of cortical bone in that area and to the presence of extraoral manifestations in the philtrum. MATERIALS AND METHODS: Cone beam computed tomography images along with intra- and extraoral photographic images of 50 Caucasian female patients, age range 18 to 65 years (mean: 37 years), previously evaluated for implant treatment were assessed by three experienced prosthodontists. Patients were divided into two groups (A and B), according to the presence or absence of a horizontal groove at the philtrum area. Mann-Whitney U test (α = 0.05) was performed to reveal any statistical differences regarding the angle of the maxillary labial concavity and the labial thickness of the alveolar cortical bone between the two groups. RESULTS: The mean angle of the maxillary concavity in group A was 127.76° while in group B it was 137.12°. The mean thickness of the labial cortical wall of the dental, interdental, and edentulous areas of the 8 anterior teeth for group A were: 0.41 mm, 0.61 mm, and 0.46 mm, respectively; and for group B were: 0.52 mm, 0.72 mm, and 0.56 mm, respectively. The Mann-Whitney U test (α = 0.05) revealed a statistically significant difference for both the angle (p = 0.008) but not for the thickness of the bone (p = 0.062). CONCLUSIONS: According to the results of this study an increased maxillary labial concavity was associated with reduced thickness of the labial cortical wall and the presence of a horizontal groove at the philtrum area.

Efficacy of two site-development procedures for implants in the maxillary esthetic region: a systematic review.

PURPOSE: The purpose of this systematic review was to identify studies in which either orthodontic extrusion or bone grafting was used prior to single implant placement in the maxillary esthetic zone and to compare the biologic, functional, and esthetic outcomes of these two approaches. MATERIALS AND METHODS: An electronic MEDLINE search was conducted by three independent reviewers to identify English-language articles, published in dental journals between January 1992 and August 2013, reporting on single-implant site development accomplished by orthodontic forced eruption of nonrestorable teeth or by bone grafting procedures. The search terms were categorized into four groups comprising a PICO (problem, intervention, comparison, outcome) question. Supplementary manual searches of published full-text articles and related reviews were also performed. RESULTS: The initial database search produced 301 relevant titles. After careful examination and discussion, 32 studies were selected for inclusion. No study directly comparing the two implant site-development methods was identified. The observation periods of the available studies were either short or not stated. CONCLUSION: There is a substantial lack of evidence to determine which method for implant site development is better. Definitive conclusions cannot be drawn, since no clinical trials have directly compared these two methods. All included studies reported separately on the two implant site-development methods and used different protocols. According to the literature reviewed, it seems that both methods of implant site development are effective and neither method is superior. Multicenter studies and randomized clinical trials should be performed to evaluate the efficacy of these two methods.

The effect of different implant-abutment connections on screw joint stability.

Dental implants with an internal connection have been designed to establish a better stress distribution when lateral external forces act on the prosthesis and minimize the forces transmitted to the fastening screw. In the present study, 10 externally and 10 internally hexed implants were tested with a compressive force applied with an Instron Universal machine. Four cycles of loading-unloading were applied to each specimen to achieve displacements of 0.5, 1, 2, and 2.5 mm. The mean loads for the first cycle were 256.70 N for the external connection and 256 N for the internal connection implants. The independent t test did not reveal any significant differences among the 2 tested groups (P = .780). For the second cycle, the mean loads needed for a displacement of 1 mm were 818.19 N and 780.20 N for the external connection and the internal connection implants, respectively. The independent t test revealed significant differences among the 2 tested groups (P < .001). In the third cycle, the mean load values for a 2-mm displacement were 1394.10 N and 1225.00 N. The independent t test revealed significant differences among the 2 tested groups (P < .001). The mean loads for the fourth cycle were 1488.00 N for the external connection and 1029.00 N for the internal connection implants. These loads were required for a displacement of 2.5 mm. The independent t test revealed significant differences among the 2 tested groups (P < .001). The results of this in vitro study suggest that the internal connection design of the examined implant system could not prevent screw loosening during overloading. No implant or prosthesis failure was noticed in either group.

Immediate provisionalization and nonfunctional loading of a single implant in the maxillary esthetic zone: a clinical presentation and parameters for consideration.

Restoration of single tooth loss with implant supported prosthesis is now considered a highly predictable treatment. However, the maxillary anterior region still presents a challenge for both the prosthodontist and the periodontist because of the inherent difficulties encountered in the provisionalization and harmonic incorporation of the definitive prosthesis into patient's dentogingival complex. This paper presents a clinical case of a single implant placed immediately after the extraction of a maxillary central incisor, followed by immediate provisionalization and nonfunctional loading. The surgical and the restorative techniques are described, and the parameters of consideration for this approach are presented.

Delayed linear dimensional changes of five high strength gypsum products used for the fabrication of definitive casts.

STATEMENT OF PROBLEM: Prolonged storage of definitive casts made from Type IV and Type V gypsum products, especially in an environment of increased temperature and low humidity, may result in contraction. PURPOSE: The purpose of this study was to evaluate the linear dimensional changes of 5 different high strength stones after exposing them to 2 different storage conditions over a period of 3 weeks. MATERIAL AND METHODS: Three Type IV dental stones (Fujirock, Vel-Mix, Suprastone) and 2 Type V dental stones (Hard Rock, Jade Stone) were tested in this study. A circular conical stainless steel die with a diameter of 66 mm and a height of 10 mm was made. Two V-shaped grooves, 38 mm apart, were scribed on the surface of the die for the purposes of measurement. A conical stainless steel ring with a bottom inner diameter of 68 mm and a top inner diameter of 65 mm was also fabricated to fit precisely around the stainless steel die. The dental stone was mixed with water under vacuum and poured under vibration onto the stainless steel die, which was surrounded by the ring. The specimens (n=20) were separated from the stainless steel die 1 hour after pouring. Half of these specimens (control) were stored in a room at 22 ±1°C with relative humidity of 50 ±5%, while the rest of the specimens were placed in a temperature regulating incubator at 40 ±1°C and relative humidity of <20%. The linear dimensional changes were recorded at designated time intervals with a traveling microscope over a 3 week period. Collected data were subjected to a 2-way repeated-measures analysis of variance (ANOVA) (α=.05). RESULTS: The highest expansion values for the specimens in the control group were recorded between 72 and 96 hours. A contraction was noticed thereafter for all specimens, in both groups. No difference in the measurements was registered between the second and third week. ANOVA revealed significant differences (P<.001) among different Type IV and V dental stone products, time, and storage conditions. CONCLUSIONS: The highest expansion values for all specimens in the control group were recorded between 72 and 96 hours. The highest expansion values for all specimens in the experimental group were recorded at 24 hours. For all specimens, contraction was noticed up to the 2-week measurements. All factors examined (dental stone, time, storage condition) significantly affected the linear dimensional changes.

Management of provisional restorations' deficiencies: a literature review.

UNLABELLED: Provisional restorations are designed in order to protect oral structures and promote function and esthetics for a limited period of time, after which they are to be replaced by a definite prosthesis. They play a particular role in diagnostic procedures and continued evaluation of the treatment plan, as they should resemble the form and function of the definite rehabilitation that they precede. Therefore, interim treatment should satisfy the criteria of marginal adaptation, strength, and longevity. In complicated treatment plans that intend to last for extended periods of time, the function of provisional prostheses involves the possibility of relining, modification, or repair. These adjustments raise considerations regarding the strength of the resultant bond. Chemical composition of the base and repair material, surface characteristics of fracture parts, and time elapsed since the initial set of the rehabilitation should be considered in the decision of the appropriate repair material and technique. Proper pretreatment of the provisional components' surfaces is essential to ensure bonding as well. The purpose of this article is to illustrate the management of provisional restorations' deficiencies. This article highlights possible failures of custom-fabricated provisional restorations, describes methods to prevent their occurrence, and discusses clinical techniques for their management. Finally, the proper combination of materials and surface preparation to achieve the optimum treatment outcomes are presented. CLINICAL SIGNIFICANCE: Provisional restorations' failures and other deficiencies are encountered by clinicians on a daily basis. Adequate laboratory techniques and material combinations presented herein may contribute to their efficient and predictable modifications and repairs.

Delayed setting and hygroscopic linear expansion of three gypsum products used for cast articulation.

STATEMENT OF PROBLEM: Wetting of the set gypsum product used for cast articulation may result in additional expansion. PURPOSE: The purpose of this study was to evaluate the linear expansion of 2 type II and 1 type III gypsum products with and without addition of water after setting, over a time period of 120 hours. MATERIAL AND METHODS: The gypsum products tested in this study were Model Plaster, Lab Plaster, and Mounting Stone. All materials were hand mixed for 5 seconds and mechanically mixed under vacuum for another 15 seconds. The mixes were poured into a linear expansion-measuring instrument (n=20). Half of the specimens were wet with 25 ml of water immediately after the setting time recommended by the manufacturer, and at all time intervals, immediately after data collection. No treatment was performed on the remainder of the specimens. The expansion values were recorded with an expansion-measuring device over a period of 120 hours. Collected data were subjected to a 2-way repeated-measures analysis of variance (ANOVA) (alpha=.05). RESULTS: The highest expansion values for all gypsum products were recorded at 96 and 120 hours. No significant difference in setting expansion values was recorded between these 2 time intervals for any of the materials and treatment conditions (dry vs. wet). Mean expansion values ranged between 0.08% +/-0.06% for dry Mounting Stone specimens at 15 minutes, to 0.57% +/- 0.02% for wet Lab Plaster specimens at 96 and 120 hours. Significant differences (P<.001) between different mounting gypsum products and time were identified. A significant difference between wet and dry specimens was not observed. CONCLUSIONS: The expansion of all gypsum products used for articulation purposes was complete at 96 hours. The type III gypsum product demonstrated lower mean expansion values than type II products. Time and material were more important factors than the dry/wet condition when measuring total expansion values. Type II gypsum products demonstrated 80% or more of the total expansion values in the first 45 minutes, while type III stone demonstrated the same expansion after 24 hours.

The effect of thermal cycling and air abrasion on cement failure loads of 4 provisional luting agents used for the cementation of implant-supported fixed partial dentures.

PURPOSE: To investigate the effects of thermal cycling and surface roughness of metal implant abutments and the intaglio surface of the copings on the retentive properties of 4 provisional luting agents commonly used in the cementation of implant-retained fixed partial dentures (FPDs). MATERIALS AND METHODS: A 2-unit implant-retained FPD and a 4-unit implant-retained FPD were fabricated using gold-palladium alloy. The abutments used were 5 mm in height. The FPDs were cemented with 4 commonly used provisional luting agents and thermocycled for 700 cycles from 5 degrees C to 36 degrees C to 55 degrees C and were then subjected to tensile strength testing. After thermal cycling, the intaglio surfaces of the same FPDs and the abutments were air-abraded with 50 microm Al2O3 particles. FPDs were cemented using the same provisional cements, and after 24 hours of storage in 100% humidity, tensile strength tests were performed. Descriptive statistics, 2-way analysis of variance, Friedman's 2-way ANOVA, and Tukey's HSD test (alpha = .05) were performed. RESULTS: Both thermal cycling and air abrasion had a significant effect (P < .001) on the retentive values of all cements tested. A noneugenol provisional cement (Nogenol) exhibited the lowest mean retentive value after both thermal cycling and air abrasion for both the 2- and 4-unit FPD models. The urethane resin provisional cement (Improv) exhibited the highest mean retentive strength for both the 2- and 4-unit FPDs after thermal cycling and air abrasion treatments. CONCLUSIONS: Thermal cycling had a detrimental effect on the retentive properties of all cements tested. Air abrasion significantly improved the cement failure loads of the provisional luting agents used in the study and seems to be an effective way of increasing the retention of implant-retained FPDs.

Comparison of temperature increase in the pulp chamber during the polymerization of materials used for the direct fabrication of provisional restorations.

STATEMENT OF PROBLEM: Polymerization of resin materials used for the fabrication of provisional restorations is associated with an exothermic reaction. This temperature rise may present a serious biological problem, since it can cause iatrogenic thermal trauma to the pulp. PURPOSE: This in vitro study compared the temperature increase in the pulp chamber of a molar placed in contact with different resins used for the direct fabrication of provisional restorations. MATERIAL AND METHODS: Polymethyl methacrylate (Jet), polyethyl methacrylate (Snap), polyvinylethyl methacrylate (Trim), Bis-acrylic composite (Protemp II), and a VLP urethane dimethacrylate (Revotec LC) were compared with respect to their exothermic reaction properties during polymerization. A mandibular molar prepared for a complete coverage restoration was placed in an acrylic resin block. A thermal probe connected to a digital thermometer was placed into the pulp chamber. Specimens were submerged in a water bath to simulate intraoral conditions. The provisional resin materials tested were measured and mixed according to manufacturer's instructions. The resin mixture was placed into a vacuum-formed acetate template and was then positioned on the prepared molar tooth. The temperature was recorded during polymerization at 30-second intervals until it was evident that the peak temperature had been reached. Temperature increase was measured ( degrees C) for both the initial crown fabrication and the reline procedures. Data were analyzed with descriptive statistics, 1-way analysis of variance, and Tukey Honestly Significant Difference tests (alpha=.05). RESULTS: One-way ANOVA revealed significant differences (F=57.010, P<.0001) in temperature rise for different provisional resin materials. Mean temperature increase for the provisional crown fabrication ranged from 37.76 degrees C for the polyvinylethyl methacrylate to 39.40 degrees C for the polymethyl methacrylate. Mean temperature rise for the reline procedures ranged from 36.80 degrees C for the polyvinylethyl methacrylate to 37.69 degrees C for the polymethyl methacrylate. All of the tested materials produced an exothermic chemical reaction. CONCLUSIONS: Polymethyl methacrylate produced the higher exothermic reaction in both initial crown fabrication and reline procedures. Polyethyl methacrylate, polyvinylethyl methacrylate, and Bis-acrylic resins tested were not significantly different from each other.

An experimental study on particular physical properties of several interocclusal recording media. Part III: resistance to compression after setting.

PURPOSE: The purpose of this study was to evaluate the resistance to compression after setting of several elastomeric interocclusal recording materials. MATERIALS AND METHODS: Testing of the resistance to compression after setting was performed following a modification of the method described in specification No. 19 (4.3.6) of the A.D.A., for the elastomeric impression materials-1 cylindrical stainless steel mold with an internal diameter of 20 mm and a height of 20 mm was constructed. Mixing of the interocclusal registration media was conducted according to manufacturers' instructions, and the materials were injected into the mold. Two subsequent loads, one of 100 g/cm2 and a second of 1000 g/cm2 were exerted on each sample. The deformation of each was calculated using a vertical traveling micrometer microscope with an accuracy of +/- 0.001 mm. RESULTS: One-way ANOVA revealed significant differences among the materials (F=331.58, p <0.0005). Tukey's HSD (p <0.05) test was used to determine the significant differences between the materials. CONCLUSIONS: Polyvinylsiloxane Blu Mousse displayed the greatest resistance to compression, as compared to other elastomeric interocclusal recording materials tested.

An experimental study on particular physical properties of several interocclusal recording media. Part II: Linear dimensional change and accompanying weight change.

PURPOSE: The purpose of this study was to evaluate the linear dimensional change and accompanying weight change of several elastomeric interocclusal recording media. MATERIALS AND METHODS: Ten 50 mm long, 8 mm wide, 3 mm deep Teflon molds and a stainless steel die were constructed for the purposes of this study. The die was made in order to produce standardized reference lines, which were used for the measurement of the linear change. After homogeneous mixing, each material was carried from the mixing pad or directly from the mixing tip to the Teflon mold. The mold was inverted onto the stainless steel die. The materials were allowed to set for the manufacturers' suggested setting time plus an additional 3 minutes to ensure polymerization of the material. An electronic scale (Galaxy 110, Ohaus, Pine Brook, NJ) was used for the measurement of the weight change of the specimens and a traveling micrometer microscope (Griffin Ltd., London, England) was used to measure the linear changes at 5 time intervals: 0, 1 hour, 24, 48, and 72 hours. RESULTS: Analysis of variance for a significance level of 5% revealed that there was a statistically significant effect of the "material" factor on the weight changes (F= 2,229.98, p < 0.0005). There was also a statistically significant effect of the "time" factor on the weight changes (F= 2,332.04, p < 0.0005). Descriptive statistics and Tukey's Honest Significant Difference Test revealed that the elastomeric material with the greatest weight changes is polyether (Ramitec). Analysis of variance for a significance level of 5% revealed that there is a statistically significant effect of the "material" factor on the linear changes (F= 215.54, p < 0.0005). There is also a statistically significant effect of the "time" factor on the linear changes (F= 1,996.01, p < 0.0005). Descriptive statistics and Tukey's Honest Significant Difference test revealed that the elastomeric material with the smallest linear changes is polyether (Ramitec). CONCLUSIONS: Of all materials tested, Ramitec (polyether) presented the smallest linear change at all time intervals. Addition reaction silicones presented statistically significant differences in recordings of linear changes among them only at the 1st and the 24th hour. Linear changes did not seem to be associated with weight changes.

A survey of the use of mandibular implant overdentures in 10 countries.

PURPOSE: This preliminary international survey compared provision of implant-retained overdentures to fixed implant-supported prostheses for edentulous mandibles. MATERIALS AND METHODS: Questionnaires based on a 2001 Swedish study were sent to prosthodontists and specialist clinics in nine additional countries. RESULTS: Response rate varied from 53% to 100% in 10 national surveys and should allow careful comparison of results. The relationship between implant overdentures and fixed implant-supported prostheses in treatment of edentulous mandibles varied much; in Sweden, the proportion of overdentures was 12%, whereas it was 93% in The Netherlands. In all countries, the most common reason for choice of the overdenture was reduced cost. In all but two countries, the majority of respondents thought that patients with implant overdentures were equally or more satisfied with overdentures as those with fixed implant-supported prostheses. CONCLUSION: There were great differences among the 10 countries in choice of implant treatment of the edentulous mandible. The relative proportion of mandibular overdentures to fixed prostheses was low in Sweden and Greece and varied from one to two thirds in the other countries, except The Netherlands.

An experimental study on particular physical properties of several interocclusal recording media. Part I: consistency prior to setting.

PURPOSE: To evaluate the consistency prior to the setting of 5 elastomeric interocclusal recording materials in comparison with a wax and a zinc oxide-eugenol paste. This property is related to the viscosity as well as to the working and setting times of these materials. MATERIALS AND METHODS: Testing of consistency was performed following a modification of the method described in ADA Specification No. 19, for elastomeric impression materials. Each one of the tested materials was mixed for 20 seconds and was then loaded into a 0.5 mL syringe. The material was syringed onto a 10 x 10 x 0.5 cm glass plate. A second 575 g glass plate was placed on top of the unset interocclusal registration material. A total of 10 samples were tested for each material. The surface area covered by the materials was measured with the help of a scanner and the use of appropriate computer software. RESULTS: One-way ANOVA revealed significant differences among the materials (F = 889.493, p < 0.0005). According to Tukey's honest significant difference test, all materials were significantly different (p < 0.05) from one another. All polyvinylsiloxanes occupied a smaller area than that of the polyether and of the zinc oxide-eugenol paste. CONCLUSIONS: Zinc oxide-eugenol paste was the most fluid of all materials tested. Polyvinylsiloxanes displayed less flow properties than polyether.