The International Journal of Prosthodontics, 03/2016

Purpose: To compare the accuracy, reliability, and reproducibility of a structured light scanning system and a stereophotogrammetry scanning system on human faces. Materials and Methods: A total of 10 healthy volunteers were included in this study. After marking of facial anatomy points, their faces were scanned by a structured light scanning system and a stereophotogrammetry system, and three-dimensional (3D) images were reconstructed with corresponding software. For each volunteer, scanning was performed twice after calibration. Linear measurements were calculated and compared for the two scanning techniques with direct caliper measurements. Absolute errors (AE), absolute percentage errors (APE), and intraclass correlation coefficients (ICC) were chosen as indices to determine the accuracy, reliability, and reproducibility of the two systems. Results: There was no statistically significant difference among the three measuring techniques (.891 < P < .999). Both scanning systems demonstrated high accuracy (AE = 0.58 ± 0.37 mm and APE = 1.11 ± 0.73% for the structured light system; AE = 0.62 ± 0.39 mm and APE 1.17 ± 0.71% for the stereophotogrammetry system). The two systems demonstrated extremely high reliability compared to caliper measurement (0.982 < ICC < 0.998 for the structured light system; 0.984 < ICC < 0.999 for the stereophotogrammetry system). In addition, high reproducibility was observed with the two systems (0.981 < ICC < 0.999 for the structured light system; 0.984 < ICC < 1.000 for the stereophotogrammetry system). Conclusion: When applied in scanning and measuring human faces, the structured light scanning system and stereophotogrammetry scanning system both demonstrated high accuracy, reliability, and reproducibility.

Purpose: The aim of this study was to evaluate and compare the use of straight versus angulated abutments on tilted implants in the All-on-Four immediate function protocol. Materials and Methods: A total of 85 patients (36 men and 49 women; mean age 56.5 years) with edentulous mandibles were treated according to the All-on-Four concept using computer-guided implant placement. All patients received immediate interim prostheses screwed onto distal tilted implants by means of angulated (control group, n = 42) or straight abutments (test group, n = 43) and were followed for at least 3 years. Outcome considerations comprised implant and prosthetic survival and success rates, marginal bone level changes, patient satisfaction, and required clinical time. Student t test at a significance level of P < .05 was used to correlate the influence of the prosthetic protocol on marginal bone levels around the implants. Results: Overall implant survival rate was 98.21% for the control group and 98.83% for the test group. None of the 85 fixed prostheses were lost during the observation period (prosthetic survival rate of 100%). Statistically significant differences (P = .0068) in marginal bone loss were found between control and test groups. All patients were functionally and esthetically satisfied with their restorations. Required clinical time averaged 50 minutes for the control group and 30 minutes for the test group. Conclusion: The described simplified and shortened surgical-prosthodontic protocol that avoids use of angulated abutments may be considered a reliable alternative to the traditional All-on-Four protocol.

Free tissue transfers are used to restore maxillofacial resected tissues during tumor ablative surgery. The maxillofacial prosthodontist remains an integral member of the therapeutic team, since conventional retained facial prostheses are in certain cases the most practical, trouble-free, cost-efficient, and successful means of rehabilitation.

Purpose: To evaluate CAD/CAM conic crowns to obtain a reversible and predictable retention in implant-supported prostheses. Materials and Methods: Five 1- to 8-degree CAD/CAM abutments and their respective copings (n = 40) were designed and manufactured to measure the retention strength (in N) on a Zwick/Roell testing frame. Results: The mean retention strength values found, in descending order of cone angle, were as follows: 8 degrees, 21.02 N; 7 degrees, 23.16 N, 28 N, and 36.40 N; 6 degrees, 40.46 N; 5 degrees, 66.36 N; 4 degrees, 61.23 and 76.12 N; 3 degrees, 93.44 N, 103.21 N, and 112.04 N; 2 degrees, 154.20 N; and 1 degree, 204.74 N, 261 N, and 293.40 N. These data describe a high-intensity ratio with a curvilinear trend that can be used to develop predictive models. Conclusion: With the limits of this study, it can be concluded that retention strength increased as the cone angle decreased. The data described a curve from which two predictive models were developed to find retention strength from the cone angle used and the cone angle that would be needed to deliver a given retention strength. This study is the first step in searching for an alternative to cemented and screw-retained implant-supported prostheses and new retaining elements in implant-retained prostheses.

Purpose: This systematic review aimed to evaluate whether the survival rate and predictability of zirconia abutments are similar to those of titanium abutments for single implant crowns in the posterior area. Materials and Methods: A systematic search of two databases (Medline/ PubMed and Cochrane Library) was performed by two independent reviewers for articles published between January 2004 and July 2014. The electronic search was complemented by a hand search of the following journals from the same period: Journal of Periodontology, Clinical Oral Implants Research, International Journal of Prosthodontics, and International Journal of Oral and Maxillofacial Implants. Studies included were published in English, evaluated single implant crowns, and performed a mean observation ≥ 1 year. Any disagreement between the reviewers was solved by means of a discussion. Forest plot and funnel were used to compare zirconia and titanium abutments. Results: The search strategy identified 669 studies. Of these, 11 studies were included and only 6 studies were selected for meta-analysis. The pooled results for fixed implant single crowns in posterior areas showed a 5-year success rate of 99.3% for zirconia abutments and 99.57% for titanium abutments. There was no statistical difference regarding veneer failure (P = .26). The pooled results of these studies showed that the mean bone loss was 0.38 ± 0.87 mm for zirconia and 0.2 ± 0.13 mm for titanium abutments. Conclusion: The use of zirconia abutments for single implant-fixed crowns in posterior regions is questionable due to the absence of long-term data. The short-term results of zirconia abutments regarding mechanical and biologic responses are similar to titanium abutments. Caution when using zirconia abutments in posterior regions is necessary until further clinical evidence shows favorable long-term results.

Purpose: The aim of this in vitro study was to assess the increase in the polygonal area of implant-retained prosthesis supports in edentulous maxillae with the use of tilted distal implants compared with the use of straight distal implants, using a variety of implant lengths. Materials and Methods: A total of 25 DICOM datasets of atrophic edentulous maxillae were provided. Bone augmentations in the molar region had to be avoided. Two straight reference implants were virtually inserted in the anterior region. Two additional implants were placed far distally on both sides (4 groups: [1] straight, 12-mm length; [2] straight, 10 mm; [3] straight, 8 mm; [4] tilted, 12-16 mm). The resulting implant-supported polygon was measured for each of the 4 groups using three-dimensional planning software. Results: The mean sagittal depth of the supported polygon in Group 1 was 9.9 mm (standard deviation [SD] 4.4) on the right and 10.2 mm (SD 4.4) on the left, and it was 33.7 mm (SD 5.8) in width. For Group 2, the mean sagittal depth was 11.5 mm (SD 5.0) on the right and 11.9 mm (SD 4.7) on the left, and the width was 35.2 mm (SD 5.6). The measurements for Group 3 were 13.8 mm (SD 4.9) deep on the right, 13.8 mm (SD 5.1) deep on the left, and 37.0 mm (SD 5.4) in width. For Group 4, the depth was 15.8 mm (SD 4.9) on the right and 16.4 mm (SD 5.8) on the left, and the width was 39.0 mm (SD 5.1). Conclusion: The area of implant-retained prosthesis support can be enlarged by the use of tilted implants (12 to 16 mm in length, 42 to 45 degrees) compared to the use of straight 8-mm implants (resulting increase: about 15%).

Purpose: The aim of this study was to investigate the way intensive use and multiple cleanings of torque wrenches may interfere with accurary over time. Materials and Methods: Three different brands (one spring-style and two friction-style types) were tested at baseline and after enduring mechanical testing (1,000 cycles) and cleaning in a thermal disinfector (150 cycles). Torque wrenches were tested at a predetermined value of 30 Ncm at given intervals, and true values were registered by means of a digital torque gauge. Results: All measured values varied between 28.3 Ncm and 31.1 Ncm. Only the spring-style torque wrench revealed values that differed significantly from baseline after both mechanical testing (P < .001) and cleaning (P < .05). Conclusion: The spring-style torque wrench produced values that changed significantly after multiple mechanical and multiple cleaning cycles. However, the differences were small and the measured values from all tested specimens were close to the predetermined value of 30 Ncm.

Purpose: The aim of this study was to investigate and compare the marginal fit of posterior fixed dental prostheses (FDPs) made of monolithic and veneered computer-aided design/ computer-assisted manufacture (CAD/CAM) zirconia ceramic with metal-ceramic posterior FDPs. Materials and Methods: Thirty standardized steel dies were prepared to receive posterior three-unit FPDs. Specimens were randomly divided into three groups (n = 10): (1) metal-ceramic (control group), (2) veneered zirconia, and (3) monolithic zirconia. All FDPs were cemented using a glass-ionomer cement. The specimens were subjected to thermal cycling (5°C to 55°C). A scanning electron microscope (SEM) with a magnification of ×500 was used for measurements. The data were statistically analyzed using one-way analysis of variance and paired t test. Results: Both zirconia groups showed similar vertical marginal discrepancies, and no significant differences (P = .661) in marginal adaptation were observed among the groups. No differences were observed in either group in marginal discrepancies between surfaces or abutments. Conclusion: Monolithic zirconia posterior FDPs exhibit similar vertical marginal discrepancies to veneered zirconia posterior FDPs. No influence of localization measurements was observed.

Purpose: The aim of this randomized clinical study was to compare the 3-year clinical outcome of metal-ceramic fixed dental prostheses (MC-FDPs) and zirconia all-ceramic fixed dental prostheses (AC-FDPs) replacing a posterior tooth. Materials and Methods: A sample of 34 patients with a missing posterior tooth were randomly chosen to receive either a MC-FDP (n = 17) or an AC-FDP (n = 17). The FDPs were evaluated at baseline and yearly until 3 years after cementation. They were assessed using the California Dental Association assessment system. Periodontal parameters were measured at the abutment teeth, and the contralateral teeth served as control. The statistical unit was the FDP/patient. Results: The survival rates for MC-FDPs and AC-FDPs were 100%. The success rate was 76% and 71% for MC-FDPs and AC-FDPs, respectively. Three technical complications were observed in the MC-FDP group and five in the AC-FDP group, all chipping fractures of the ceramic veneer. Furthermore, one biologic complication in the MC-FDP group (an apical lesion) was observed. No framework fractures occurred. All patients had optimal oral hygiene and showed no bleeding on periodontal probing at any of the recalls. Only minor changes in the periodontal parameters were observed during the 3 years of observation. Conclusions: Three-unit posterior MC-FDPs and AC-FDPs showed similar high survival rates and acceptable success rates after 3 years of function, and ceramic veneer chipping fracture was the most frequent complication for both types of restorations.

Purpose: The aim of this in vitro study was to compare the accuracy of two different impression techniques for the All-on-Four implant therapy protocol. Materials and Methods: An acrylic resin analog for an edentulous maxilla with four internal connection implants (Replace Select, Nobel Biocare) was fabricated according to the All-on-Four protocol. A total of 40 impressions were made with different techniques (open and closed tray) at abutment and implant levels and poured in type IV dental stone. A coordinate measuring machine was used to record the x, y, and z coordinates and angular displacement. The measurements were compared with those obtained from the reference model. Data were analyzed with analysis of variance and t test at α = .05. Results: There was less linear and rotational displacement for the open-tray technique when compared with the closed-tray technique (P = .02 and P < .001, respectively). Impressions made at abutment level produced fewer linear and rotational displacements when compared with implantlevel impressions using the open-tray technique for straight and angulated implants (P = .04 and P < .001, respectively). However, less rotational dislocation was observed for impressions made with the closed-tray technique when compared with the open-tray technique at implant level (P < .001). Conclusion: Choice of impression technique affected the accuracy of impressions, and less displacement was observed with the open-tray method. Abutment-level impressions with an open-tray technique were more accurate, while implant-level impressions were more accurate when a closed-tray technique was used.

Purpose: This study determined the radiopacity of a group of computer-aided design/ computer-assisted manufacture blocks using digital radiography and pixel monitoring. Materials and Methods: Specimens 2.0 ± 0.05-mm thick were cut from nine different blocks. Longitudinal sections of the same thickness were obtained from molar and premolar. Specimens were assigned to one of two groups, and each group was placed on a digital radiograph sensor together with an aluminum step wedge. Following standardized technique, the sensor was exposed and two images were obtained from each group. Images were analyzed using ImageJ software to determine the number of pixels at five different locations for each specimen. Means and standard deviations were calculated and the data statistically analyzed. Radiopacity values were expressed as equivalent of aluminum thickness. Results: Analysis of variance revealed significant difference in mean pixels among the blocks (P < .001). Conclusion: The majority of blocks had radiopacity values that were higher than that of dentin.

Purpose: The aim of this study was to investigate the hamulus-incisive-papilla (HIP) plane as an alternative for transferring the three-dimensional position of a patient's maxilla to an articulator. Materials and Methods: Camper, Frankfurt horizontal, occlusal, and HIP planes were evaluated in 21 patients' computed tomography scans and compared to one another. Results: Analysis of variance showed significant differences between all planes, with the HIP plane being closest to the occlusal plane (HIP-OP: 0.6 ± 4.0 degrees). Frankfurt and Camper planes, being more peripheral, showed higher geometric asymmetries. Conclusion: The HIP plane, when used for articulator mounting, results in a closer and more technically reliable patient relationship in a clinical and laboratory context.

Purpose: The digitization of scanbodies on dental implants is required to use computer-aided design/computer-assisted manufacture processes for implant prosthetics. Little is known about the accuracy of scanbody digitization with intraoral scanners and dental lab scanners. This study aimed to examine the precision of different intraoral digital impression systems as well as a dental lab scanner using commercially available implant scanbodies. Materials and Methods: Two study models with a different number and distribution of dental implant scanbodies were produced from conventional implant impressions. The study models were scanned using three different intraoral scanners (iTero, Cadent; Trios, 3Shape; and True Definition, 3M ESPE) and a dental lab scanner (D250, 3Shape). For each study model, 10 scans were performed per scanner to produce repeated measurements for the calculation of precision. The distance and angulation between the respective scanbodies were measured. The results of each scanning system were compared using analysis of variance, and post hoc Tukey test was conducted for a pairwise comparison of scanning devices. Results: The precision values of the scanbodies varied according to the distance between the scanbodies and the scanning device. A distance of a single tooth space and a jaw-traversing distance between scanbodies produced significantly different results for distance and angle measurements between the scanning systems (P < .05). Conclusion: The precision of intraoral scanners and the dental lab scanner was significantly different. The precision of intraoral scanners decreased with an increasing distance between the scanbodies, whereas the precision of the dental lab scanner was independent of the distance between the scanbodies.

Purpose: A total of 24 zirconia-based single tooth-retained restorations inserted in 18 patients were followed up for 15 to 61 months (mean: 35 months). Materials and Methods: Recall consisted of dental and hygiene status as well as quality assessment and check for occlusal relationship. One patient was lost to follow-up. In the incuded patients, 15 central incisors, 3 canines, and 5 lateral incisors replaced 16 lateral incisors and 7 central incisors, mostly in the maxilla (n = 17). Results: One retainer debonded, two pontics experienced incisal chip-offs, and one patient showed an orthodontic relapse. The success rate was estimated at 82.4%, with 100% survival at 36 months. Conclusion: Technical protocol and occlusal protection are crucial.

Purpose: This study evaluated the pretreatment influence of occlusal splints and relines on mandibular movements (MM) and vertical dimension of occlusion (VDO) in longstanding complete denture wearers. Materials and Methods: A total of 30 volunteers were randomly assigned to three groups (n = 10): control (C), relining of old denture (RD), and occlusal splints (OS). Individual extent of MM was assessed via intraoral Gothic arch tracings and the VDO using posed frontal images taken at three time points. Results: The OS group showed statistically significant differences when compared with the other groups (P < .05). Conclusion: Both MM and VDO were significantly improved by use of occlusal splints pretreatment.

Purpose: The aim of this investigation was to measure the temperature increase due to heat transferred to the implant-bone interface when the abutment screw channel is accessed or a metal-ceramic crown is sectioned buccally with diamond or tungsten carbide bur using an air rotor, with or without irrigation. Materials and Methods: Cobalt-chromium copings were cemented onto straight titanium abutments. The temperature changes during removal of the copings were recorded over a period of 1 minute. Results: The sectioning of coping with diamond bur and without water irrigation generated the highest temperature change at the cervical part of the implant. Conclusion: Both crown removal methods resulted in an increase in temperature at the implant-bone interface. However, this temperature change did not exceed 47°C, the potentially damaging threshold for bone reported in the literature.

Purpose: This study aimed to compare the difference in mechanical behavior between two types of female-part clips of the Stress-Free Implant Bar (SFI-Bar) system during simulation of insertion-removal cycles. Materials and Methods: A total of 10 samples simulating SFI-Bar-attachment-retained implant overdentures were fabricated and randomly divided into two groups (n = 5). One group used E-clips (Elitor alloy) as the female part of the SFI-Bar, and the other used T-clips (all titanium grade IV with red nylon inserts). A total of 14,000 insertion- removal cycles were carried out on each sample. Retentive forces from each cycle were recorded for analysis. Results: Significant differences were found between the two groups (P < .05). Conclusion: The retentive force of E-clips increased as the number of dislodging cycles increased, suggesting that some adjustment may be needed to lower this part's retentive force. T-clips with changeable nylon inserts were deformed after about 4,200 insertion-removal cycles, which interfered with insertion. This indicated that T-clips may need replacement after 2 to 3 years of clinical use.

Purpose: Ceramic veneer fracture is a frequent complication in implant-borne fixed restorations. The retrospective clinical study assesses the effect of bruxism on this complication. Materials and Methods: A sample of 507 implant-borne fixed units inserted between 1995 and 2011 in 144 patients were examined. Any detected veneer fractures were assigned to one of four groups according to extent and position. A hypothetical correlation between bruxism and ceramic veneer fractures was examined. Results: Of 34 patients (23.6%) with at least one ceramic veneer fracture, 24 were bruxers (70%) and 10 were nonbruxers (30%) (P = .002). Conclusion: Bruxism may pose a risk for ceramic fractures.

Purpose: The objective of this study was to assess the stress distribution generated by a simulated loading (100 N) in the area of the cantilever in three different five-implant mandibular protocol prosthesis models. Materials and Methods: The finite element analysis was carried out in three-dimensional models simulating: (1) a temporary allacrylic resin mandibular protocol prosthesis; (2) a metal-acrylic mandibular protocol prosthesis; and (3) a metal-ceramic mandibular protocol prosthesis. Results: The allacrylic model promoted the highest stress values on the implant closest to the cantilever loading point. Conclusion: This study supports the need for a metallic bar reinforcement in the denture base.