The International Journal of Prosthodontics, 06/2017

Purpose: To investigate the following three null hypotheses in patients rehabilitated with a mandibular overdenture supported by two unsplinted implants: (1) patient satisfaction is not related to the clinical quality of the dentures; (2) inter-implant distance (IID) has no effect on the clinical quality of the dentures; and (3) IID does not influence patient satisfaction. Materials and Methods: Forty edentulous patients who were rehabilitated with a two-implant-supported mandibular overdenture participated in the study. Independent investigators evaluated the dentures on the basis of five clinical criteria using the validated Denture Quality Evaluation Form, and the patients completed the validated Denture Satisfaction Scale. Irreversible hydrocolloid impressions of the mandible were made and poured immediately in die stone. The IID was measured by adapting an orthodontic wire to the mandibular alveolar ridge crest, extending from the center of one implant to the center of the other. Spearman correlation analyses were used to identify possible correlations, with a significance level set at P < .05. Results: The clinicians' overall mean rating of the clinical quality of the dentures was 91.5% (standard deviation 6.27%). The stability of the mandibular overdenture and of the maxillary conventional complete denture was significantly related to satisfaction (r = 0.389 and r = 0.44, respectively). Significant associations were found between the mandibular stability items and satisfaction with both maxillary and mandibular dentures. The stability of the maxillary denture was significantly associated with patient satisfaction with mandibular denture retention, stability, and comfort. None of the 12 denture satisfaction items were significantly associated with IID. Similarly, IID did not have an effect on the quality of either denture in terms of retention, stability, or occlusion. Conclusion: Denture stability was the feature that had the most influence on patient satisfaction with the mandibular overdenture and with the maxillary conventional denture. IID had no effect on the clinical quality of either denture and did not influence patient satisfaction.

Purpose: The purpose of this study was to assess the density of interforaminal bone using quantitative computed tomography (QCT) in simulated case histories to be prescribed an All-on-Five fixed implant treatment protocol. Materials and Methods: QCT scans from 30 edentulous patients (15 men and 15 women; mean age 63.33 ± 9.3 years) were analyzed using the Nobel Clinician software. Densities (in Hounsfield units [HU]) were recorded at the neck, middle part of the body, and apex of the lingual and buccal parts of proposed implant sites. Results: The highest bone densities were measured at the neck of the implant (1,187 ± 382 HU), with lower densities at the apex (774 ± 571 HU) (P < .01). Bone densities decreased on the lingual interforaminal portion of the implant, especially on the two intermediate implants. Bone density was lower in women (917 ± 510 HU) than in men (1,095 ± 601 HU) (P < .01). Conclusion: The interforaminal measured bone densities are lower on the paramedian region of the symphysis and in women. However, these levels are in accordance with immediate loading with a fixed partial denture.

Full-arch rehabilitation of patients with severe tooth wear due to parafunctional behavior is a challenge for dentists and dental technicians, especially when a highly esthetic outcome is desired. A variety of different treatment options and prosthetic materials are available for such a clinical undertaking. The ongoing progress of computer-aided design/computer-assisted manufacture technologies in combination with all-ceramic materials provides a predictable workflow for these complex cases. This case history report describes a comprehensive, stepby- step treatment protocol leading to an optimally predictable treatment outcome for an esthetically compromised patient.

Purpose: The aim of this study was to examine the ability of a poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butylmethacrylate-co-2-methacryloyloxyethyloxy-p-azidobenzoate) (PMBPAz) coating on polymethyl methacrylate (PMMA)-based dental resin to inhibit bacterial plaque formation, as well as the polymer's durability against water soaking and chemical exposure. Materials and Methods: Successful application of PMBPAz on PMMA surfaces was confirmed by x-ray photoelectron spectroscopy (XPS) and measuring the static air contact angle in water. The anti-adhesive effects to bacterial plaque were evaluated using Streptococcus mutans biofilm formation assay. The mechanical and chemical durabilities of the PMBPAz coating on the PMMA surfaces were examined using soaking and immersion tests, respectively. Results: XPS signals for phosphorus and nitrogen atoms and hydrophilic status on PMMA surfaces treated with PMBPAz were observed, indicating the presence of the polymer on the substrates. The treated PMMA surfaces showed significant inhibition of S mutans biofilm formation compared to untreated surfaces. The PMBPAz coating was preserved after water soaking and chemical exposure. In addition, water soaking did not decrease the ability of treated PMMA to inhibit biofilm formation compared to treated PMMA specimens not subjected to water soaking. Conclusion: This study suggests that PMBPAz coating may represent a useful modification to PMMA surfaces for inhibiting denture plaque accumulation.

Purpose: To examine the screw preload, coefficient of friction (COF), and tightening torque needed to overcome the thread friction of an implant-abutment-screw complex. Materials and Methods: In a customized load frame, 25 new implant-abutment-screw complexes including uncoated titanium alloy screws were torqued and untorqued 10 times each, applying 25 Ncm. Results: Mean preload values decreased significantly from 209.8 N to 129.5 N according to the number of repetitions. The overall COF increased correspondingly. There was no comparable trend for the thread friction component. Conclusion: These results suggest that the application of a used implant-abutment-screw complex may be unfavorable for obtaining optimal screw preload.

Purpose: To examine the in vitro effects of different cements, abutment surface preconditioning, and artificial aging on the maximum tensile force needed to detach cantilever fixed dental prostheses (FDPs) from dental implants with titanium abutments. Materials and Methods: A total of 32 tissue-level implants were combined with standardized titanium abutments. For each test group, eight cantilever FDPs were fabricated using selective laser melting (cobaltchromium [CoCr] alloy). The inner surfaces of the cantilever FDPs and half of the abutments were sandblasted and then joined by use of four different cements (two permanent and two semi-permanent) in two different amounts per cement. Subgroups were tested after either artificial aging (thermocycling and chewing simulation) or 3 days of water storage. Finally, axial pull off-tests were performed for each abutment separately. Results: Cement type and surface pretreatment significantly affected decementation behavior. The highest retention forces (approximately 1,200 N) were associated with sandblasted abutments and permanent cements. With unconditioned abutments, temporary cements (Fu < 100 N), as well as glassionomer cement (Fu ≈ 100 N), resulted in rather low retention forces. Zinc phosphate cement guaranteed high retention forces. After aging, retention was sufficient only for cementation with zinc phosphate cement and for the combination of sandblasted abutments and glass-ionomer cement. Conclusion: When glass-ionomer cement is used to fix cantilever FDPs on implants, sandblasting of standard titanium abutments may help prevent loss of retention. Retention forces were still high for FDPs fixed with zinc phosphate cement, even when the abutments were not pretreated. Use of permanent cements only, however, is recommended to prevent unwanted loosening of cantilever FDPs.

Purpose: This study evaluated the retention strength of welding caps for Ankylos standard abutments using a pull-out test. Materials and Methods: Each sample consisted of an implant abutment and its welding cap. The tests were performed with a Zwick Roell testing machine with a 1-kN load cell. Results: The retention strength of the welding caps increased with higher abutment diameters and higher head heights and was comparable or superior to the values reported in the literature for the temporary cements used in implant dentistry. Conclusion: Welding caps provide a reliable connection between an abutment and a fixed prosthesis without the use of cement.

Purpose: The objective of the present study was to analyze the clinical outcomes of 447 monoblock ceramic chairside computer-aided design/computer-aided manufacture (CAD/CAM) reconstructions over a 7-year functional period. Of these reconstructions, 212 were peripheral crowns and 235 were endocrowns. Materials and Methods: The restorations were placed between 2003 and 2008 in a total of 323 patients. They were created using a chairside CAD/CAM method and the same materials in all cases. All of the crowns were manufactured and glued during the same clinical session by the same practitioner. Data were descriptively analyzed and survival probabilities were calculated using Kaplan- Meier statistics. Results: Of the 447 restorations, only 6 failures occurred, resulting in a success rate of 98.66%. All of the failures were the result of a partial ceramic fracture. Of the six ceramic fractures, five appeared on peripheral crowns and one on an endocrown. All fractures appeared in the first 24 months, including two in the first month. Log-rank test comparing incidence rates between crowns and endocrowns showed no significant differences (P = .08). Conclusion: This survival rate study reinforced the use of CAD/CAM full ceramic crowns and endocrowns on molars, showing a much more favorable survival rate for endocrowns.

Purpose: This randomized clinical trial assessed how surface roughness (Ra) in resilient liners was affected by soft tissue health conditions and time-related aspects in patients with complete dentures. Methods: Specimens of acrylic resin (control) and denture liners (silicone-based or acrylic resin-based) were inserted into the dentures of patients with and without denture stomatitis (n = 30). Ra was evaluated before denture insertion and after 7, 14, and 21 days of prosthesis wearing. Data were analyzed using three-way analysis of variance and Student-Newman-Keuls test. Results: Patients with stomatitis showed a higher Ra (P < .001), while all liners presented rougher surfaces after 14 days of clinical service, irrespective of the soft tissue health condition. Conclusion: Ra of the tested denture liners was increased in patients with denture stomatitis. It is presumed that a longer wearing period will result in rougher surfaces.

Purpose: The aim of this cross-sectional study was to assess maximum restraining lip force (MLF), maximum voluntary bite force (MBF), and patient-related parameters to evaluate their influence on masticatory function in four groups of participants with different dental states. Methods: Participants were recruited and assigned to one of four different groups depending on dental status: complete removable dental prostheses (CRDP group); edentulous with two-implant overdentures (IOD group); Kennedy Class I partial removable dental prostheses (PRDP group); or fully dentate (control group). A dental examination was performed and history taken. MLF was measured as the maximum withstood pulling force with three sizes of oral screens, MBF was evaluated using a digital force gauge, and masticatory performance was assessed using a two-color mixing ability test. Linear regression was used to determine the predictive effects of covariates on masticatory performance. Global and pairwise comparisons were also carried out. Results: A total of 68 participants with an average age of 69.3 ± 7.7 years were recruited. MLF depended on the screen size (P = .0004; Kruskal-Wallis) and increased with CRDP use, especially in challenging tasks, such as restraining the smallest screen. The highest MBF was found in dentate participants (P < .0001; Mann-Whitney). Analysis of variance (ANOVA) showed a global significant difference in masticatory performance between groups, with PRDP patients chewing better than CRDP patients. Dental state, time lapse since last tooth loss, and MBF predicted masticatory function. Conclusion: Tooth loss significantly affects MBF and masticatory performance. Free-end saddles with a rotational axis in two-implant IODs and Kennedy Class I PRDPs may limit MBF and consequently masticatory performance. CRDP design should facilitate perioral muscular function.

Purpose: This study compared masticatory and swallowing functional outcomes in maxillectomy patients who underwent surgical and prosthetic rehabilitation or prosthetic rehabilitation only following surgical resection. Materials and Methods: This comparative cross-sectional study involved 20 maxillectomy patients and compared their masticatory and swallowing functions following combined surgical and prosthodontic management vs an exclusively prosthodontic approach. Masticatory performance was measured by an originally modified sieve method using hydrocolloid material, and video fluoroscopic examination was employed for swallowing assessments. Results: Masticatory performance was significantly better in the patient group treated with flaps and removable denture prostheses compared to patients treated with obturator prosthesis alone. Swallowing outcomes were comparable in both groups. Conclusion: Flap reconstruction followed by an obturator prosthesis seems to be a preferable option when planning for functional rehabilitation in maxillectomy patients. Further research is needed to substantiate the functional outcomes noted in this study.

Longevity of implant-supported fixed partial dentures (ISFPDs) may be associated with multiple clinical complications, irrespective of whether retention is achieved via screws or cement. While use of screws ensures ease of prosthesis retrievability and elimination of the inherently risky cementation process, more mechanical strains are induced in this design. A combined screw-retrievable and cement-retained ISFPD is designed to achieve the best passive fit and strain reduction while allowing complete excess cement removal and maintaining ease of retrievability. Moreover, this approach suggests better protection of the cement layer from oral environment degradation and offers scope for an alternative retention protocol. This paper outlines aspects of the clinical indications and fabrication of a screw-retrievable, cementretained ISFPD. A diagnostic assessment method that provides tactile resistance guidance for selection is also proposed.

Purpose: The purpose of this pilot study was to evaluate and compare polyetherketoneketone (PEKK) with different framework materials for implant-supported prostheses by means of a three-dimensional finite element analysis (3D-FEA) based on cone beam computed tomography (CBCT) and computer-aided design (CAD) data. Materials and Methods: A geometric model that consisted of four maxillary implants supporting a prosthesis framework was constructed from CBCT and CAD data of a treated patient. Three different materials (zirconia, titanium, and PEKK) were selected, and their material properties were simulated using FEA software in the generated geometric model. Results: In the PEKK framework (ie, low elastic modulus) group, the stress transferred to the implant and simulated adjacent tissue was reduced when compressive stress was dominant, but increased when tensile stress was dominant. Conclusion: This study suggests that the shock-absorbing effects of a resilient implant-supported framework are limited in some areas and that rigid framework material shows a favorable stress distribution and safety of overall components of the prosthesis.

Purpose: The purpose of this preliminary study was to examine the influence of overdenture attachment height and shape on lateral force on implants and denture displacement. Materials and Methods: A straight model was fabricated to simulate the edentulous ridge. Two strain gauges were attached to the mesial and distal surfaces of the implant in the canine area. Five types of ball attachments and three types of Locator attachments with three types of replacement male attachments were used. A vertical load of 49 N was applied. The lateral force on the implant and the denture displacement were measured. Statistical comparisons were performed using one-way analysis of variance, Tukey post hoc comparison test, and multivariate analysis. P < .05 was considered significant. Results: Ball attachments of 4-mm height exerted the highest lateral force on the implant, and the greatest displacement was also observed with attachments of 4-mm height. Different lateral forces were observed for different shapes of ball attachments, but there were no significant differences in denture displacement among the shapes. For Locator attachments, the highest lateral force was observed with the white male type, and the greatest denture displacement occurred with attachments of 4-mm height. There were no significant differences among male white, pink, and blue types. Conclusion: The height of the stud attachments in implant overdentures had a marked effect on the lateral force on implants and on denture displacement. To protect implants supporting an overdenture and to prevent bone resorption, the height of the attachment should be carefully considered.