Retentive force variations in three polyamide and a polyetheretherketone denture attachments for implant-supported overdentures: An in vitro study.

STATEMENT OF PROBLEM: The loss in the retentive capability of implant-supported overdenture attachments has been related to the wear of the retentive inserts. Wear of the abutment coating material when following the replacement period for the retentive inserts requires investigation. PURPOSE: The purpose of this in vitro study was to compare the changes in retentive force of 3 polyamide and a polyetheretherketone denture attachments under repeated insertion and removal cycles in wet conditions while following their manufacturers' replacement time recommendations. MATERIAL AND METHODS: Four different denture attachments (LOCKiT, OT-Equator, Ball attachment, and Novaloc) with their retentive inserts were tested. Four implants were embedded into individual acrylic resin blocks, and 10 abutments for each attachment were used. Forty metal housings with their retentive inserts were attached to polyamide screws with autopolymerizing acrylic resin. A customized universal testing machine was used to simulate insertion and removal cycles. The specimens were mounted on a second universal testing machine at 0, 540, 2700, and 5400 cycles, and the maximum retentive force was recorded. The retentive inserts for LOCKiT (light retention), OT-Equator (soft retention), and Ball attachment (soft retention) were replaced every 540 cycles, while the Novaloc (medium retention) attachments were never replaced. All the abutments were weighed with a precision scale at 0, 2700, and 5400 cycles. The surface of every abutment was examined under a stereomicroscope at ×10 magnification. Data were analyzed with descriptive statistics. Two-way repeated measures ANOVA was used to compare the mean retentive force and mean abutment mass of all groups and time evaluation points. Bonferroni corrections were made to adjust for multiple tests (α=.05). RESULTS: The mean retention loss for LOCKiT was 12.6% after 6 months and 45.0% after 5 years of simulated use. The mean retention loss for OT-Equator was 16.0% after 6 months and 50.1% after 5 years of simulated use. The mean retention loss for Ball attachment was 15.3% after 6 months and 39.1% after 5 years of simulated use. The mean retention loss for Novaloc was 31.0% after 6 months and 59.1% after 5 years of simulated use. The mean abutment mass difference was statistically significant (P<.05) for LOCKiT and Ball attachment but not statistically significant (P>.05) for OT-Equator and Novaloc at baseline, 2.5 years, and 5 years. CONCLUSIONS: All tested attachments recorded retention loss under the experimental conditions, even when their manufacturers' recommendations for replacement time for the retentive inserts were followed. Patients should be aware that implant abutments should be replaced after a recommended period since their surfaces also change over time.

Integrating a complete denture digital workflow with polished surface registration: A single-procedure clinical protocol.

Intraoral digital scanning of edentulous arches has provided the dental profession with the ability to obtain genuinely mucostatic impressions. The drawback, because of the omission of border molding procedures, has been underextended flanges which might affect the retention and stability of the definitive prosthesis. A technique for combining the concept of registering the polished surfaces with a functional impression material and the intraoral digital mucostatic scanning workflow is described.

Exploring Adaptation and Satisfaction in Copied Complete Dentures Regarding Two Different Occlusal Schemes

PURPOSE: To compare patient adaptation to and satisfaction with new complete dentures fabricated with a duplication construction protocol (DCP) using two different occlusal schemes, bilateral balanced (BBO) and lingualized (LO). MATERIALS AND METHODS: Twenty complete denture wearers who received replacement DCP dentures participated in this study. Ten participants received complete dentures with a BBO scheme, and the other 10 received DCP dentures with an LO scheme. All of them evaluated their prostheses subjectively through the Oral Health Impact Profile-20 (OHIP-20) and the Complete Denture Satisfaction (CDS) questionnaires before treatment and at 3- and 6-month posttreatment intervals. The new prostheses were also normatively evaluated by recording the location and number of sore spots present at the scheduled early adjustment visits. Data were analyzed with nonparametric tests to identify differences in patient responses between groups and within each group at each evaluation interval point (α = .05). RESULTS: The within-group comparisons revealed statistically significant improvement for both denture groups (P < .05), while the between-group comparisons did not record statistically significant differences at the overall evaluation period (P > .05). Significant within-group differences were recorded in the pain, functional limitation, and psychologic disability domains of the OHIP-20 questionnaire and the comfort, esthetics, and stability domains of the CDS questionnaire. CONCLUSION: The patients' adaptation to and satisfaction with newly constructed DCP dentures improved significantly for both BBO and LO denture groups throughout the evaluation period. The mean number of early adjustment visits was equal for both the BBO and LO denture groups.

Evaluating temperature increase during the polymerization of dental acrylic resin materials used for the direct fabrication of anterior deprogramming devices.

STATEMENT OF PROBLEM: The polymerization of acrylic resin materials used for the direct fabrication of anterior deprogramming devices results in a temperature increase because of the exothermic reaction. This heat release might cause thermal trauma to the pulp, compromising the tooth's vitality. PURPOSE: The purpose of this in vitro study was to compare the temperature increase and the timing of the maximum temperature recording obtained inside the pulp chamber of a maxillary central incisor during the polymerization of different resins materials used for the direct fabrication of anterior deprogramming devices. MATERIAL AND METHODS: The exothermic reaction was examined during the polymerization of 4 different polymethyl methacrylate resin products: Pattern Resin LS; GC America, DuraLay inlay pattern resin; Reliance Dental, Kallocryl CPGM red; Speiko, and mega-Model Resin NF; Megadental. A polymeric matrix was fabricated to simulate the anterior deprogramming device. A freshly extracted intact maxillary central incisor was fixed in an acrylic resin mold, and a thermal probe was inserted into the pulp chamber to transmit the temperature recordings. The resin materials were mixed as per the manufacturer's instructions and an equal volume of each was inserted into the plastic matrix, which was then positioned on the tooth. The temperature increase and the time needed to obtain the maximum temperature were recorded. The temperature and time recordings were performed initially for the intact tooth and repeated after the tooth was prepared for a metal-ceramic restoration. The data were analyzed with descriptive statistics, 1-way analysis of variance, and the Tukey Honestly Significant Difference tests (α=.05). RESULTS: In accordance with the 1-way ANOVA, there was a statistically significant difference both in temperature increase (F [7,72] = 3.72, P=.002) and in the recorded time (F [7,72] = 160.80, P<.001). The mean temperature inside the pulp chamber ranged from 40.1 °C for the Pattern Resin LS to 41.4 °C for the DuraLay inlay pattern resin material. The mean time recordings ranged from 133 seconds for the Kallocryl CPGM red material to 266 seconds for the DuraLay inlay pattern resin material. CONCLUSIONS: The Pattern Resin LS revealed the lowest exothermic reaction (P<.05) when compared with the other materials tested in this study, whereas Kallocryl CPGM red had the shortest time increase without being statistically significantly different.

Comparative Study of Dimensional Stability and Detail Reproduction of Reformulated and Nonreformulated Elastomeric Impression Materials.

PURPOSE: To evaluate the dimensional stability and the detail reproduction of five current elastomeric impression materials in vitro. MATERIALS AND METHODS: The materials examined were: 3 different polyether impression materials, a vinyl polysiloxane impression material, and a vinyl polyether silicone impression material. All impression materials were of a medium viscosity. One stainless steel die was fabricated according to the ANSI/ADA specification no.19 criteria. Twenty impressions of this die were made for each material. Dimensional accuracy and surface detail were evaluated 24 hours after making the impressions using a measuring microscope. The data were analyzed using Welch's analysis of variance, Games-Howell Post-Hoc, and the Pearson's chi-square tests (α = 0.05). RESULTS: Statistical differences were observed in the mean percent dimensional stability (F [4,47] = 39, p < 0.001) of the tested impression materials. The highest dimensional change was recorded for the vinyl polysiloxane impression material, with a mean percent value of -0.09 ± 0.02% (p < 0.001). The lowest dimensional change was recorded for the Monophase polyether material with a mean percent value of -0.03 ± 0.01% (p < 0.038). The best surface detail reproduction results were obtained using the Monophase polyether material (90% acceptable impressions), with no significant differences (χ² [4] = 3.86, p = 0.483) observed between the Monophase and the rest impression materials. CONCLUSIONS: All materials exhibited acceptable dimensional stability, well below the ANSI/ADA specification no.19 standard of ≤0.5% dimensional change. All impression materials demonstrated acceptable surface detail reproduction with no significant differences between them.

In vitro investigation of the impact of remaining tooth structure on the tensile failure loads of overdenture copings.

BACKGROUND: The purpose of this in vitro study was to evaluate the impact of the remaining tooth structure on the retention of overdenture cast metal copings. MATERIAL AND METHODS: A freshly extracted intact mandibular human canine (length 25 mm) was selected and endodontically treated. An incisal reduction of 4 mm with no ferrule preparation was performed and a post space of 12 mm was created. By using polyvinyl siloxane duplication material and autopolymerizing polymethylmethacrylate resin, ten resin teeth analogs (control group) were obtained. A second set of ten resin teeth analogs (group 1) was created by preparing on the original natural tooth a 360o ferrule design of 1 mm in height and by using the same procedural technique. The canine was further reduced by an additional 1 mm, resulting in a ferrule of 2 mm in height, measured from the initial incisal reduction, thus a third set of ten resin teeth analogs (group 2) was created. For every tooth analog in all groups a dome-shaped metal coping was cast and luted with a glass ionomer cement. All specimens were subjected to tensile load testing until decementation occurred. RESULTS: The specimens in the control group exhibited a mean failure load of 87.21 ± 18.26 N, while the 1 mm ferrule group recorded a higher mean failure load of 125.43 ± 8.79 N and the 2 mm ferrule group recorded the highest mean failure load of 146.12 ± 23.38 N. One-way ANOVA revealed significant differences (F= 28.04, p<0.001) in the tensile failure loads between all of the groups being tested. CONCLUSIONS: The metal copings with a 2 mm ferrule design exhibited the highest retention values, followed by the 1 mm ferrule and the no ferrule design, with the differences among them being statistically significant. Key words:Ferrule effect, In vitro study, Metal copings, Overdenture, Tensile stress.

In vitro assessment of retention and resistance failure loads of complete coverage restorations made for anterior maxillary teeth restored with two different cast post and core designs.

BACKGROUND: The purpose of this in vitrostudy was to evaluate the retention and resistance form of complete coverage restorations supported by two different cast post and core designs. MATERIAL AND METHODS: Forty extracted maxillary central incisors were randomly divided into four groups of 10 specimens each (namely A, B, C and D). All specimens were endodontically treated and a uniform post space of 9mm was created. All prepared teeth had a 360o chamfer ferrule of 2mm in axial height measured 0.5mm coronally from the cementoenamel junction (CEJ) and an axial wall thickness of 1.5 mm. Specimens in groups A and C received cast post and cores with the standardized core design, where the core ended at the coronal part of the ferrule, while specimens in groups B and D received cores that were encircling the ferrule. Cemented complete coverage restorations in groups A and B underwent tensile load stress, while the restorations in groups C and D underwent compressive load stress until failure. RESULTS: Teeth in group A exhibited a mean failure load of 326.14±83.67 N under tension, while teeth in group B exhibited a mean failure load of 332.79±80.38 N (p=0.858). Teeth in group C recorded a mean failure load of 1042.81±205.07 N, and in group D a mean failure load of 875.15±167.64 N (p=0.061) under compression was registered. CONCLUSIONS: The standard cast post and core design with a 2 mm of ferrule height offers superior resistance, although not statistically significant (p=0.061), when compared to the core design encircling the axial wall ferrule. Both cast post and core designs offer equal retention. However, different failure modes of decementation were noted. Key words:Endodontically treated teeth, Post-and-core technique, Endodontic-post, Decementation, Root fracture, Ferrule effect.

Correction: Accuracy of fit of implant-supported bars fabricated on definitive casts made by different dental stones.

[This corrects the article on p. 252 in vol. 10, PMID: 29721227.].

In Vitro Assessment of Retention and Resistance Failure Loads of Teeth Restored with a Complete Coverage Restoration and Different Core Materials.

PURPOSE: To investigate in vitro the retention and the resistance form, as well as the failure modes of maxillary premolars restored with cast metal crowns and different core materials. MATERIALS AND METHODS: Sixty human extracted maxillary premolars were selected according to their size and were embedded in PMMA resin blocks. After removing a part of their clinical crowns, the teeth were randomly divided into 3 groups of 20 teeth and were either left unrestored, or they were restored with amalgam or composite resin. All teeth were prepared for a cast metal complete coverage restoration. The restorations were cemented on the prepared teeth with a resin-modified glass ionomer luting agent (GC Fuji Plus). All specimens were subjected to static loading at 1 mm/min by a universal testing machine, until failure. Half the specimens of each group were subjected to tensile loading along the long axis of the teeth. The other half were subjected to compressive loading at a 30° angle. Failure loads and failure modes for each tooth were recorded. The statistical analysis included descriptive statistics, one-way ANOVA, and Tukey's HSD test. RESULTS: One-way ANOVA revealed statistically significant differences among the 3 tested groups (p < 0.05) for both tests. The group of teeth with no core material presented the highest failure loads for both the tensile and the compressive loading tests, with mean loads of 381.02 Ν and 741.21 Ν, respectively. Mean tensile and compressive failure loads for the amalgam group were 277.34 Ν and 584.75 Ν, while the composite resin group presented the lowest tensile and compressive failure values, which were 250.77 Ν and 465.78 Ν, respectively. The compression loading test resulted in the same failure mode for all specimens, which included unfavorable fracture of the teeth in combination with detachment of the cast metal complete coverage restorations. The tensile loading test resulted in different failure modes between the groups that used a core material and the group with no core material. CONCLUSIONS: Teeth that lost more than half of their coronal structure presented better retention and resistance form if no core material was used, provided that a minimum of 2-mm axial wall height was present at the missing part. Teeth that have lost more than half of their coronal structure and were restored with amalgam core presented better retention and resistance form than those restored with composite resin. Catastrophic fractures, extending to the root, were associated with compression forces but not with tensile forces.

Accuracy of fit of implant-supported bars fabricated on definitive casts made by different dental stones.

BACKGROUND: The purpose of this study was to evaluate the accuracy of fitting of an implant supported screw-retained bar made on definitive casts produced by 4 different dental stone products. MATERIAL AND METHODS: The dental stones tested were QuickRock (Protechno), FujiRock (GC), Jade Stone (Whip Mix) and Moldasynt (Heraeus). Three external hexagon implants were placed in a polyoxymethylene block. Definitive impressions were made using monophase high viscosity polyvinylsiloxane in combination with custom trays. Then, definitive models from the different types of dental stones were fabricated. Three castable cylinders with a machined non-enganging base were cast and connected with a very small quantity of PMMA to a cast bar, which was used to verify the marginal discrepancies between the abutments and the prosthetic platforms of the implants. For that purpose special software and a camera mounted on an optical microscope were used. The gap was measured by taking 10 measurements on each abutment, after the Sheffield test was applied. Twelve definitive casts were fabricated for each gypsum product and 40 measurements were performed for each cast. Mean, minimum, and maximum values were calculated. The Shapiro-Wilk test of normality was performed. Mann-Whitney test (P<.06) was used for the statistical analysis of the measurements. RESULTS: The non-parametric Kruskal-Wallis test revealed a statistically significant effect of the stone factor on the marginal discrepancy for all Sheffield test combinations: 1. Abutment 2 when screw was fastened on abutment 1 (χ2=3, df=35.33, P<0.01), 2. Abutment 3 when the screw was fastened on abutment 1 (χ2=3, df=37.74, P<0.01), 3. Abutment 1 when the screw was fastened on abutment 3 (χ2=3, df=39.79, P<0.01), 4. Abutment 2 when the screw was fastened on abutment 3 (χ2=3, df=37.26, P<0.01). CONCLUSIONS: A significant correlation exists between marginal discrepancy and different dental gypsum products used for the fabrication of definitive casts for implant supported bars. The smallest marginal discrepancy was noted on implant supported bars fabricated on definitive casts made by Type III mounting stone. The biggest marginal discrepancy was noted on implant supported bars fabricated on definitive casts made by Type V dental stone. The marginal discrepancies presented on implant supported bars fabricated on definitive casts made by two types of Type IV dental stone were not significantly different. Key words:Dental implant, passive fit, dental stones, marginal discrepancy.

Marginal adaptation and CAD-CAM technology: A systematic review of restorative material and fabrication techniques.

STATEMENT OF PROBLEM: The comparative assessment of computer-aided design and computer-aided manufacturing (CAD-CAM) technology and other fabrication techniques pertaining to marginal adaptation should be documented. Limited evidence exists on the effect of restorative material on the performance of a CAD-CAM system relative to marginal adaptation. PURPOSE: The purpose of this systematic review was to investigate whether the marginal adaptation of CAD-CAM single crowns, fixed dental prostheses, and implant-retained fixed dental prostheses or their infrastructures differs from that obtained by other fabrication techniques using a similar restorative material and whether it depends on the type of restorative material. MATERIAL AND METHODS: An electronic search of English-language literature published between January 1, 2000, and June 30, 2016, was conducted of the Medline/PubMed database. RESULTS: Of the 55 included comparative studies, 28 compared CAD-CAM technology with conventional fabrication techniques, 12 contrasted CAD-CAM technology and copy milling, 4 compared CAD-CAM milling with direct metal laser sintering (DMLS), and 22 investigated the performance of a CAD-CAM system regarding marginal adaptation in restorations/infrastructures produced with different restorative materials. CONCLUSIONS: Most of the CAD-CAM restorations/infrastructures were within the clinically acceptable marginal discrepancy (MD) range. The performance of a CAD-CAM system relative to marginal adaptation is influenced by the restorative material. Compared with CAD-CAM, most of the heat-pressed lithium disilicate crowns displayed equal or smaller MD values. Slip-casting crowns exhibited similar or better marginal accuracy than those fabricated with CAD-CAM. Cobalt-chromium and titanium implant infrastructures produced using a CAD-CAM system elicited smaller MD values than zirconia. The majority of cobalt-chromium restorations/infrastructures produced by DMLS displayed better marginal accuracy than those fabricated with the casting technique. Compared with copy milling, the majority of zirconia restorations/infrastructures produced by CAD-CAM milling exhibited better marginal adaptation. No clear conclusions can be drawn about the superiority of CAD-CAM milling over the casting technique and DMLS regarding marginal adaptation.

Comparative Assessment of a New Holistic-Oriented and an Old Specialty-Specific Undergraduate Curriculum in Removable Prosthodontics: A Study Based on Senior Students' Perceptions.

PURPOSE: A survey was conducted in the Dental School, Aristotle University, Thessaloniki, Greece, (i) to assess the perceptions and experiences of senior dental students, Classes of 2014 and 2015, toward the old, specialty-specific (OC) and new, holistic-oriented (NC) undergraduate curriculum, respectively, in removable prosthodontics and (ii) to identify areas of improvement in prosthodontic training. MATERIALS AND METHODS: Structural components of both curricula were collected, including the total number of (i) laboratory/lecture/clinical training hours, (ii) written examinations, (iii) mandatory clinical cases, and (iv) European Credit Transfer and Accumulation System (ECTS) credits. A 20-item closed-type questionnaire using a five-point Likert scale was distributed in two consecutive groups of seniors, Classes of 2014 (n = 54) and 2015 (n = 57); 54 OC and 57 NC senior students filled out the questionnaire. RESULTS: A greater percentage of NC students stated that (i) they felt less confident to carry out jaw relation recording and removable partial denture metal framework design and (ii) the time allocated for clinical training was less sufficient. Students of both curricula reported that the laboratory courses and lectures contributed little to their clinical performance. Implant restorations and prosthetic management of patients with craniomandibular disorders were the most popular treatment options that the respondents felt that should be incorporated in the undergraduate curriculum. CONCLUSIONS: As a general trend, students completing the revised curriculum reported more difficulties during their training and felt more insecure about their clinical competences. To enhance students' self-confidence in prosthodontics, more effective preclinical training methods, introduction of additional treatment options, and alternative educational methods should be considered.

In vitro assessment of retention and resistance failure loads of two preparation designs for maxillary anterior teeth.

STATEMENT OF PROBLEM: Parallel labiolingual walls and the preservation of the cingulum in anterior tooth preparations have been advocated. However, their contribution to retention and resistance form has not been evaluated. PURPOSE: The purpose of this in vitro study was to evaluate the retention and resistance failure loads of 2 preparation designs for maxillary anterior teeth. MATERIAL AND METHODS: Forty metal restorations were fabricated and paired with 40 cobalt-chromium prepared tooth analogs. Twenty of the specimens had parallel buccolingual walls at the cervical part (group PBLW; the control group), whereas the remaining 20 had converging buccolingual walls (group CBLW; the experimental group). The restorations were cemented to the tooth analogs with a resin-modified glass ionomer luting agent. Ten specimens from each group were subjected to tensile loading with a universal testing machine; the rest were subjected to compression loading until failure. Descriptive statistics and the independent t test (α=.05) were used to determine the effect of failure loads in the tested groups. RESULTS: The independent t test revealed statistically significant differences between the tested groups in tensile loading (P<.001) and in compressive loading (P<.001). The PBLW group presented a higher tensile failure load than the CBLW. On the contrary, the PBLW group presented a smaller compression failure load than the CBLW. CONCLUSIONS: Parallelism of the buccolingual axial walls in anterior maxillary teeth increased the retention form but decreased the resistance form.

The Influence of Bone Quality on the Biomechanical Behavior of a Tooth-Implant Fixed Partial Denture: A Three-Dimensional Finite Element Analysis.

PURPOSE: The purpose of this study was to evaluate whether or not bone quality has an effect on the biomechanical behavior of a tooth connected to an implant, when a rigid and a nonrigid attachment are used. MATERIALS AND METHODS: Models of fixed partial dentures supported by a tooth and an implant were developed. These models were then imported into finite element analysis software to study the impact of forces on different types of attachments (rigid vs nonrigid) and bones (types 1 to 4). Each fixed partial denture was subjected to a vertical load of 200 N on the premolars and 230 N on the molar. The materials were considered linear, isotropic, and homogenous. Eight different scenarios were tested. The von Mises criterion was used to display the stress in five structures: fastening screw, implant, attachment, cortical, and trabecular bone. The displacements of the tooth and the implant were also examined. RESULTS: The calculated maximum observed stress values differed among the simulated scenarios. The biggest values of stress concentrations were observed at the lingual cervical areas, the implant-cortical bone interface, the implant-crown interface, the butt-joint contact of the implant-abutment screw, and the apical parts of the tooth and implant. The main difference between the rigid and nonrigid connection was observed between the natural tooth retainer and the pontic. In the rigid connection, the movement of the natural tooth retainer was smooth. In the nonrigid connection, the attachment exhibited a partial buccal displacement. Von Mises stresses among the different tested structures ranged between 24 and 840 MPa. CONCLUSION: The quality of the bone and the rigidity of the connection between a natural tooth and an implant influence both the generated stresses and the displacement of the tooth and the implant. The highest stresses for the implant-trabecular bone interface, the neck of the implant, and the fastening screw were observed in type 3 bone when a rigid connection was used. The lowest stresses for the implant-cortical bone interface, the neck of the implant, and the connector were registered in type 1 bone, when a rigid connection was used. The smallest tooth and implant displacement was observed in type 1 bone, when a rigid connection was used, while the biggest tooth and implant displacement was registered in type 4 bone when a nonrigid connection was used.

Theoretical Considerations and a Mathematical Model for the Analysis of the Biomechanical Response of Human Keratinized Oral Mucosa.

Removable complete and partial dentures are supported by the residual alveolar ridges consisting of mucosa, submucosa, periosteum, and bone. An understanding of the biomechanical behavior of the oral mucosa is essential in order to improve the denture-bearing foundations for complete and partially edentulous patients. The purpose of this paper was to examine the biomechanical behavior of the soft tissues supporting a removable denture and develop a model for that reason. Keratinized oral mucosa blocks with their underlying bone were harvested from the maxillary palatal area adjacent to the edentulous ridges of a cadaver. The compressive response of the oral mucosa was tested by using atomic force microscopy. The specimens were first scanned in order their topography to be obtained. The mechanical properties of the specimens were tested using a single crystal silicon pyramidal tip, which traversed toward the keratinized oral mucosa specimens. Loading-unloading cycles were registered and four mathematical models were tested using MATLAB to note which one approximates the force-displacement curve as close as possible: a. spherical, b. conical, c. third order polynomial, d. Murphy (fourth order polynomial, non-linear Hertzian based). The third order polynomial model showed the best accuracy in representing the force-displacement data of the tested specimens. A model was developed in order to analyze the biomechanical behavior of the human oral keratinized mucosa and obtain information about its mechanical properties.

Comparative Study of Acceptance and Adaptation to New Complete Dentures, Using Two Construction Protocols.

PURPOSE: To validate patients' acceptance and adaptation to new complete dentures, fabricated using two construction protocols. Evaluation was achieved by means of two psychometric questionnaires and registration of total number of sore spots. MATERIALS AND METHODS: Twenty complete denture wearers, who sought replacement dentures because of complaints (material degradation or unsatisfactory repaired fracture) associated with them, were selected according to specific inclusion criteria. The denture construction protocols were randomly assigned to the study participants. Ten participants received complete dentures using a duplication construction protocol with a bilateral balanced occlusal (BBO) scheme (duplicate complete denture group); ten participants received complete dentures using a traditional construction protocol with BBO (traditional complete denture group). All study participants completed the Complete Denture Satisfaction and the Oral Health Impact Profile-20 (OHIP-20) questionnaires before they received the new complete dentures (pretreatment) and at 3 and 6 months post-treatment. At the initial adaptation/adjustment visits, the location and number of sore spots were identified. Statistical analysis was performed to evaluate differences between groups and within each group pre- and post-treatment. RESULTS: Denture satisfaction and oral health related quality of life scores were independent of the complete denture construction protocol. Within the traditional complete denture group there was a statistically significant increase in denture satisfaction and equivalent decrease (improvement) in OHIP-20 scores between pre- and post-treatment (both at 3-month and 6-month visits). This finding was consistent for OHIP-20 scores within the duplicate complete denture group, but not for denture satisfaction, which was not statistically significant. The total number of recorded sore spots was approximately double for the traditional complete denture group compared to the duplicate complete denture group. CONCLUSIONS: According to the results of the study, patients' overall acceptance of their newly constructed complete dentures improved significantly for both groups (traditional and duplication construction protocols). Study participants adapted dissimilarly to their newly constructed complete dentures regarding comfort, as assessed by the total number of sore spots, although the recorded mean number of initial adaptation/adjustment visits was equal.

Influence of Alveolar Bone Loss and Different Alloys on the Biomechanical Behavior of Internal-and External-Connection Implants: A Three-Dimensional Finite Element Analysis.

PURPOSE: The purpose of this study was to evaluate the stress distribution during application of occlusal loads to maxillary anterior single external- and internal-connection implant-supported restorations with different amounts of bone loss and with the use of different metal alloys for restorations and fixation screws. MATERIALS AND METHODS: Models of external- and internal-connection implants, corresponding abutments/crowns, and fixation screws were developed. These models were then imported into finite element analysis software to study the impact of forces on different implant connections and materials. Each prosthesis was subjected to a 200-N compressive shear force applied at 130 degrees relative to the long axis of the implant. The materials were considered linear, isotropic, and homogenous. The parameters changed for each connection type included: bone resorption in relation to the prosthetic platform (no, 2 mm, or 4 mm of resorption); alloys of the restorations (nonprecious vs precious); and alloys of the abutment screws (titanium vs gold). Von Mises stresses were used to display the stress in five models: implant, restoration, screw, cancellous bone, and cortical bone. RESULTS: Statistically significant differences in the stresses of all involved structures occurred when the bone level decreased by 2 mm and by 4 mm. The connection type contributed to statistically significant differences in the stresses in both the restoration and the screw. The alloy type resulted in statistically significant differences in the implant, the superstructure, and the cortical bone stresses. CONCLUSION: As bone resorbed, the stresses generated within the internal-connection implant were greater than those generated in the external-connection implant. The same findings applied for the restoration and for cancellous and cortical bone. The stresses generated in the fixation screw were greater in the external-connection implant than in the internal-connection implant for all bone resorption scenarios.

Marginal adaptation of four inlay casting waxes on stone, titanium, and zirconia dies.

STATEMENT OF PROBLEM: Different inlay casting waxes do not produce copings with satisfactory marginal accuracy when used on different die materials. PURPOSE: The purpose of this study was to evaluate the marginal accuracy of 4 inlay casting waxes on stone dies and titanium and zirconia abutments and to correlate the findings with the degree of wetting between the die specimens and the inlay casting waxes. MATERIAL AND METHODS: The inlay casting waxes tested were Starwax (Dentaurum), Unterziehwachs (Bredent), SU Esthetic wax (Schuler), and Sculpturing wax (Renfert). The marginal opening of the waxes was measured with a stereomicroscope on high-strength stone dies and on titanium and zirconia abutments. Photographic images were obtained, and the mean marginal opening for each specimen was calculated. A total of 1440 measurements were made. Wetting between die materials and waxes was determined after fabricating stone, titanium, and zirconia rectangular specimens. A calibrated pipette was used to place a drop of molten wax onto each specimen. The contact angle was calculated with software after an image of each specimen had been made with a digital camera. Collected data were subjected to a 2-way analysis of variance (α=.05). Any association between marginal accuracy and wetting of different materials was found by using the Pearson correlation. RESULTS: The wax factor had a statistically significant effect both on the marginal discrepancy (F=158.31, P<.001) and contact angle values (F=68.09, P<.001). A statistically significant effect of the die material factor both on the marginal adaptation (F=503.47, P<.001) and contact angle values (F=585.02, P<.001) was detected. A significant correlation between the marginal accuracy and the contact angle values (Pearson=0.881, P=.01) was also found. CONCLUSIONS: Stone dies provided wax copings with the best marginal integrity, followed by titanium and zirconia abutments. Unterziehwachs (Bredent), wax produced the best marginal adaptation on different die materials. A significant correlation was found between the marginal accuracy and the contact angle values. As the contact angle value became smaller, the marginal accuracy improved. All combinations of waxes and stone and titanium dies presented a high wettability.

Association between functional tooth units and chewing ability in older adults: a systematic review.

OBJECTIVES: To systematically review the current evidence on the relationship between dentition status and chewing ability in older adults, as the latter was subjectively perceived by questionnaires. BACKGROUND: Tooth loss is associated with functional impairment regarding chewing ability, depending on the number and the location of the remaining teeth. METHODS: A search of the English literature was undertaken using the appropriate electronic databases and keywords in order to answer the question of this review. Independent extraction of the related articles was carried out by two authors using predefined eligibility criteria. RESULTS: Full-text analysis was performed for 51 articles of possible relevance. Finally, data were extracted from 18 studies, published in 20 articles that met the inclusion criteria. CONCLUSIONS: Although there was a conflict between the studies relevant to the number of functional tooth units needed to maintain adequate oral function, it was revealed that chewing ability was closely related to the number and distribution of teeth remaining. Treatment plan should focus on the preservation of the strategic parts of the dental arch that are critical for adequate oral function. Long-term prospective studies, comprising well-defined criteria, clinical variables, methods and utilising comprehensive questionnaires, should be preferred to obtain a clearer picture on the association between masticatory ability and functional tooth units.

Influence of thickness increase of intraoral autopolymerizing hard denture base liners on the temperature rise during the polymerization process.

STATEMENT OF PROBLEM: Increasing the thickness of intraoral autopolymerizing hard denture base liners may result in a temperature rise and a burning sensation for patients. PURPOSE: The purpose of the study was to determine whether increasing the thickness of hard autopolymerizing reline resin increases the temperature of the basal seat area of a denture during the polymerization process. MATERIAL AND METHODS: Four polyethyl methacrylate and 1 polymethyl methacrylate autopolymerizing reline resin products of 3 different thicknesses were tested. A cobalt-chromium edentulous maxillary cast was used to obtain 150 stone casts, 50 for each thickness of 1, 2, and 3 mm (n=10). Polystyrene record bases were filled with the autopolymerizing reline resin mixture and placed on the cobalt-chromium cast, which was mounted on a reline index, to serve as denture substitutes. Two thermal probes were used to monitor the temperature rise, which was recorded at 30-second intervals until no further increase was noted. Collected data were subjected to a 2-way ANOVA and the Tukey honestly significant difference test (α=.05). RESULTS: The mean temperature increase for the chairside denture reline procedure ranged from 39.45°C for the 1-mm thickness to 46.10°C for the 3-mm thickness. The 2-way ANOVA found significant differences (P<.001) among the different reline resin materials and thicknesses tested. All materials produced an exothermic chemical reaction. An increase in thickness was always accompanied by an increased temperature. The Tukey honestly significant difference test found that the highest temperature increase for all 3 thicknesses occurred in the polymethyl methacrylate resin. CONCLUSIONS: The polymethyl methacrylate autopolymerizing hard denture base liner produced a significantly higher (P<.001) exothermic reaction than the other materials included in this study. One of the polyethyl methacrylate resins presented a higher exothermic reaction than the polymethyl methacrylate product at a 3-mm thickness, but the difference was not statistically significant. The polymethyl methacrylate resin presented the highest mean time to reach the maximum temperature for all 3 thicknesses.