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Background: Evaluation of a new vertical dimension of occlusion (VDO) in complex restorative treatments is considered a necessary step prior to placement of restorations. Objectives: This randomised controlled trial (RCT) aimed to assess the effects of using an evaluation of a VDO increase before restorative treatment in patients with moderate‐to‐severe tooth wear, on OHRQoL, freeway space (FWS) and interventions to restorations. Methods: Forty‐two patients with tooth wear were included and randomly allocated to either a test phase with a Removable Appliance (RA) or no test phase. Restorative treatment consisted of restoration of all teeth using composite restorations in an increased VDO. OHIP‐score, freeway space (FWS) and clinical acceptability of restorations were assessed at baseline and at recall appointments (1 month and 1 year). Intervention to restoration was scored in case of material chipping or when the abutment tooth had increased sensitivity that could be linked to occlusal overloading. ANCOVA analyses, Univariate Cox regression, t‐tests and descriptive analyses were performed (p <.05). Results: Clinical follow‐up after 1 year was completed for 41 patients. No significant effect of testing the VDO with a RA could be found on the OHIP‐score (p =.14). Reduction of FWS in the RA group, compared to the control group, was significantly lower at 1 year (p =.01, 95% CI −1.09 to −0.15). No effect on early interventions to restorations was found (p =.94). Conclusion: This RCT showed that a removable appliance is not indicated to functionally test the increased VDO prior to restorative treatment in patients with tooth wear. [ABSTRACT FROM AUTHOR]

Summary: Background: Root‐retained overdentures (OD) are one treatment option for partially edentulous patients. However, the available evidence regarding factors influencing abutment survival in root‐retained ODs is limited. Purpose: This retrospective study included clinical examinations and evaluated the survival rate of roots restored with precision attachments soldered to post‐and‐core (gold cap) retained ODs, analysed with respect to various patient‐ and prosthesis‐related factors. Methods: Patients receiving at least one OD with gold caps in the past were invited for comprehensive clinical examinations. The primary outcome parameter was the abutment survival rate over the observation period (2002‐2016). Possible contributing factors (eg closed vs open OD design) were analysed. Analyses included Kaplan‐Meier estimators, Cox regressions and hazard ratios (HR). Results: 114 patients with 128 ODs originally retained by 280 abutments, with a cumulative total exposure time of 2035.4 years, were examined. Twenty‐seven abutment teeth (9.6%) were lost after a mean observation period of 7.9 ± 3.4 years. Significant factors associated with abutment loss were a closed, compared to an open OD design (HR 8.38 (95% CI 1.11‐63.59), P =.040), which was independent of the number of abutments per OD. Furthermore, the loss rate was higher when the denture was not worn day‐and‐night (HR 3.52 (95% CI 1.32‐9.40), P =.012). Oral hygiene behaviour was associated with higher HRs. Conclusions: ODs remain a viable treatment option for patients with few teeth remaining in the dental arch. It is advisable to choose an open design for the OD, irrespective of the number of abutment teeth. Furthermore, gold cap‐retained ODs should not be removed overnight. [ABSTRACT FROM AUTHOR]

Osseointegrated implants have been widely used for decades with high survival and success rates. However, mechanical complications continue to be reported in the literature, and their clinical management can be often very challenging for the clinician while there is no consensus on the ideal management. The aim of this manuscript was to review the risk factors of abutment screw complications, to identify the most recent incidence of screw failure in the clinical setting and report on the methodology used and the outcome of intervention. Clinical studies and reports were reviewed that reported on abutment screw looseness and/or fracture. A search of the electronic database PUBMED was conducted in November 2018, including manuscripts published in English from 2004 to 2018. Study selection: animal studies, narrative reviews, expert opinions and communications/letters were excluded. Further exclusion criteria included reports on occlusal prosthetic screws and fracture of abutments, and reports that did not provide adequate data. A total of 12 manuscripts were finally included that reported on single implant crowns or 2‐unit implant fixed dental prosthesis. To conclude, the most current abutment screw loosening incidence ranges between 7% and 11%, while the abutment screw fracture incidence was found to be 0.6%. The majority reported on fracture of the screw body. Screw loosening or fracture was often located at the first molar restored area, while the maxillary central incisor area was also reported as an area that presented screw fracture. No single abutment screw failure management can be identified as the ideal treatment approach. [ABSTRACT FROM AUTHOR]

Summary: Background: Spherical shape and connecting bypass screw of the OT Equator abutment (Rhein83, Italy) provides several retentive possibilities, even in non‐parallel implants. Objective: This study assessed the long‐term survival of standard‐length and short implants receiving this multifunctional abutment. Methods: Partially, edentulous patients (44 males and 64 females) (mean age 58.2 ± 10.5 years) rehabilitated with a fixed implant‐supported prosthesis where the OT Equator abutments (Rhein83) were applied. Follow‐up evaluations were performed up to 5 years following prosthesis delivery. Kaplan‐Meier survival analysis and Cox regression analysis were used to determine whether the distribution of time to failure differed based on implant characteristics (length and region), adjusting for sex (α = 0.05). Results: In total, 216 implants (5 × 8 mm, n = 126; 5 × 6 mm, n = 90) (Betwice, Mech & Human, Italy) were installed. The average follow‐up period was 25.3 months (±19.3 months). Eight failures occurred, with most observed before loading (n = 6). Cumulative survival rates (CSR) at implant and abutment levels were 94.3% and 97.1%, respectively. Regarding implant length, CSRs were 97.8% and 90.6% for short and standard‐length implants, respectively, with no difference between subgroups (logrank: χ2 = 1.34, df = 1, P = 0.25). No significant difference was also found between implants of maxilla (CSR = 92.2%) and mandible (CSR = 95.5%; logrank: χ2 = 0.08, df = 1, P = 0.78). Conclusion: The OT Equator abutment (Rhein83) showed a stable clinical performance, with continuous and predictable survival. [ABSTRACT FROM AUTHOR]

Summary: Background: The potential of non‐invasive optical coherence tomography (OCT) as a tool for assessment of fit of indirect reconstructions is not fully explored. Objectives: The objectives were to investigate the feasibility and validity of OCT, and to measure the internal and marginal fit of acrylic bridges fabricated using direct and indirect digitalisation. Methods: The accuracy of the employed swept source OCT (wavelength: 1310 nm) was assessed by comparing with an object with known dimensions. Validity was assessed by measuring an OCT measurements on replica, mimicking the cement film thickness, with stereomicroscopic measurements. The reconstructions were placed on the abutments without cementation. The internal and marginal fit of acrylic bridges from direct and indirect digitalisation techniques were then assessed by obtaining 5 OCT B‐scans per abutment tooth at pre‐defined positions located 250 μm apart. The marginal and internal cement gaps were measured using image‐processing software (ImageJ). Mean and standard deviation were calculated for both groups and t test assuming unequal variances was carried out. The level of significance was defined at 0.05. Results: A strong linear correlation (r = 0.865) between OCT and stereomicroscopy was found. T test showed significantly (P < 0.01) better internal fit of bridges made from indirect digitalisation, but no difference in marginal fit. Conclusion: OCT is a feasible and valid tool for investigating internal and marginal fit of acrylic dental reconstructions. Better internal fit was observed in bridges fabricated using the direct digitalisation technique. No difference in marginal fit was found between the two fabrication methods. [ABSTRACT FROM AUTHOR]

Summary: The purpose of the systematic review and meta‐analysis was to compare the performance of 3‐unit bridges on teeth with 3‐unit bridges on implants, evaluating survival of the bridges, survival of the teeth or implants, condition of the hard and soft tissues surrounding the supports, complications and patient‐reported outcome measures (PROM) after a mean observation period of at least 1 year. A literature search was conducted using a combination of the search terms: fixed partial denture and fixed dental prostheses (FDPs). An electronic search for data published until January 2017 was undertaken using the MEDLINE, EMBASE and Cochrane Library databases. Eligibility criteria included clinical human studies, either randomised or not, interventional or observational, which evaluated the results of 3‐unit FDPs on either 2 implants or 2 abutment teeth. The search identified 1686 unique references. After applying eligibility criteria, 66 articles were included in the analysis. A total of 1973 3‐unit FDPs were supported by teeth, and 765 were implant‐supported. No significant differences were found either in the survival of the supporting abutments (P = .52; 99% vs 98.7% survival per year) or in the survival of the prostheses (P = .34; 96.4% vs 97.4% survival per year). Both treatments show an almost equally low complication rate, but there is a low level of reporting of hard and soft tissue conditions and PROM. It is concluded that implant‐supported 3‐unit FDPs seem to be a reliable treatment with survival rates not significantly different from the results of teeth‐supported 3‐unit FDPs. [ABSTRACT FROM AUTHOR]

To conduct a systematic review on the clinical outcome of single implant-supported two-unit cantilever FDP's and to conduct a 5-year prospective comparative pilot study of patients with a missing central and lateral upper incisor treated with either a single implant-supported two-unit cantilever FDP or two implants with solitary implant crowns in the aesthetic zone. Medline, Embase and the Cochrane Central Register of Controlled Trials were searched (last search 1 August 2016) for eligible studies. In the comparative pilot study, an implant-cantilever group of five patients with a single implant-supported two-unit cantilever FDP (NobelReplace Groovy Regular Platform) was compared with an implant-implant group of five patients with two adjacent single implant-supported crowns (NobelReplace Groovy Regular Platform) in the aesthetic zone. Implant survival, marginal bone level (MBL) changes, pocket probing depth, papilla index and patient satisfaction were assessed during a 5-year follow-up period. Five of 276 articles were considered eligible for data extraction. Implant survival ranged from 96·6% to 100%. Marginal bone level changes were higher in the anterior region than in the posterior region. Technical complications occurred more often in the posterior than anterior region. In the 5-year comparative pilot study, no clinically significant differences in hard and soft peri-implant tissue levels occurred between both groups. Single implant-supported two-unit cantilever FDP's can be a viable alternative to the placement of two adjacent single implant crowns in the aesthetic zone. Due to technical complications, placement of two-unit cantilever crowns in the posterior region can be considered unwise. [ABSTRACT FROM AUTHOR]

The purpose of this study is to measure and compare the retentive force of zirconia-based all-ceramic crowns cemented on zirconia abutments using five provisional luting agents. In addition, the effect of sandblasting and thermocycling on the retentive force was evaluated. Two hundred zirconia abutments and copings were fabricated (Procera system; Nobel Biocare) and divided into five groups. Hy bond temporary cement hard (Hard), Hy bond temporary cement soft (Soft), experimental temporary cement (New), Tempbond NE (Temp) and Freegenool temporary pack (Pack) were used according to the manufacturers’ instructions. Each group was divided into two groups, one with and one without sandblasting. Furthermore, thermocycling up to 2000 cycles was conducted on half of each group. After 24 h and thermocycling, the retentive force was measured using a universal testing machine. The data were subjected to analysis of variance, and comparisons of the means were performed with a Games–Howell test at a level of 95%. As a result, Hard showed the highest retentive force, sandblasting was effective for improving the durability, and no effect of sandblasting was detected in the others. New showed stability of the retentive force even after thermocycling. The retentive force of Temp and Pack decreased significantly after thermocycling even with sandblasting. The retentive forces were different from the provisional cement and sandblasting, and Temp and Pack may not be appropriate for the retention of single-tooth zirconia abutments and coping restorations. [ABSTRACT FROM AUTHOR]

The purpose of this prospective cohort study was to assess the performance of tooth-supported, extended zirconia, fixed dental prostheses (FDPs). Thirty FDPs with span-lengths between 36 and 46 mm (mean: 40·33 mm), four to seven units and with connector dimensions of ∼9 mm2 were inserted (19 in the posterior region, 11 including anterior teeth) using glass–ionomer cement and assessed (aesthetic evaluation, failures, hypersensitivity/tooth vitality, secondary caries, pocket depth, decementation and chipping) at baseline and after 2 years. Differences between baseline and 2-year recall were analysed using the Wilcoxon signed-rank test for matched pairs. There were five failures. One FDP revealed a core fracture at the base of the connector, probably caused by a damage induced during fabrication. Two FDPs had to be recemented, one abutment tooth had to be treated endodontically and one cohesive failure of the veneer was observed. There were no significant changes of pocket depth and hypersensitivity between baseline and 2-year recall. The aesthetics were rated as excellent by the patients at both baseline and recall. Two year clinical results of extended zirconia based FDPs with 9 mm2 connectors are promising. [ABSTRACT FROM AUTHOR]

The purpose of this study was to measure axial loading, generating bending moments on fibre reinforced composite (FRC) implant prostheses using strain-gauged customized abutment in vivo. Bending moments of conventional implant prosthetic material were also measured and the data were compared with those for FRC. Three unit fixed dental prostheses were made for two dental implant fixtures, which had been functioning properly for more than one year using TesceraTM ATLTM, porcelain fused to metal and gold as occlusal material. Three patients participated in this study; two patients had two implants on one side of the mandible and one had two implants on both sides of the mandible. Five sets of fixed dental prostheses were fabricated for each material and these were cemented with Temp-bond® on strain-gauged customized abutments, which were screwed into the underlying implant fixtures. Axial loadings and bending moments were measured when a patient bit the experimental fixed dental prosthesis.anova and the Tukey HSD test (α = 0·05) were used for statistical analysis. There were no significant differences in normalized bending moments among the three different implant prosthetic materials. Within the limitations of this study, TesceraTM ATLTM generated bending moments similar to conventional implant prosthetic materials such as gold and porcelain. [ABSTRACT FROM AUTHOR]

Designs of removable partial dentures are suggested to affect the mobility of abutment teeth and removable partial denture (RPD) during oral functions. This study aimed to examine the effect of direct retainer and major connector designs on RPD dynamics under simulated loading. Six different Kennedy class II maxillary RPDs were fabricated on a maxillary model. These dentures involved 3 different direct retainers (wrought-wire clasp, RPA clasp, and conical crown telescopic retainer) and 2 different major connectors (Co-Cr major connector and heat-cured acrylic resin with a metal strengthener). Using an experimental model with simulated periodontal ligaments and mucosa that were fabricated using silicone impression material, three-dimensional displacements of the RPDs were measured under a simulated 30-N loading with a displacement transducer type M-3. Significant effects of “direct retainer design” on bucco-palatal displacements and “major connector” on mesio-distal displacements were revealed by 2 × 3 two-way analysis of variance of abutment teeth movements ( P < 0·001 and P = 0·002, respectively). Additionally, analysis of variance of RPD displacements revealed significant effects of “direct retainer design” on corono-apical displacements and “major connector” on mesio-distal displacements ( P = 0·001 and P = 0·028, respectively). Rigid direct retainers and rigid major connectors decrease the movements of both abutment tooth and RPD. [ABSTRACT FROM AUTHOR]

Aims: The aim of this study was to evaluate the stress on the abutment teeth and framework in a unilateral maxillary defect which was restored by an obturator retained by resin-bonded extracoronal attachment. Methods: A three-dimensional finite element model of the human unilateral maxillary defect was constructed. Traditional obturator framework with four casting circumferential clasp was established (model 1). A continuous lingual guide plane of 0·5 mm thickness on all of the remaining teeth, with Mini-SG/F attachment on the mesial surface of the central incisor was also established (model 2). The modelling and analytical processes were performed using the ANSYS technologies. Results: Stress was transmitted to the anterior part of the palate, with stress values being lower on the anterior teeth compared with the posteriors. The highest stress value of model 1 and model 2 was 13·1 Mpa, 19·9 Mpa respectively. Stress concentrations were found at the junction of the attachment to the lingual guide plane and the anterior part of the lingual plane. Conclusion: The results of this study suggest that the application of a resin-bonded extracoronal attachment for obturator retention is in accordance with the design principles for the restorative treatment of maxillary defects. The design of the attachment framework needs to be further investigated. Benefit can be gained by splinting the abutment teeth. [ABSTRACT FROM AUTHOR]

The purpose of this study was to develop a technique to evaluate the implant–abutment gap of an external hexagon implant system as a function of radius. Six implants of 3·75 mm in diameter (Conexao Sistema de Protese Ltda, Sao Paulo, Brazil) and their respective abutments were screw connected and torqued to 20 N cm−1. The implants were mounted in epoxy assuring an implant long-axis position perpendicular to the vertical axis. Each implant was grounded through its thickness parallel to implant long-axis at six different distance interval. Implant–abutment gap distances were recorded along the implant–abutment region for each section. Individual measurements were related to their radial position through trigonometric inferences. A sixth degree polynomial line fit approach determined radial adaptation patterns for each implant. Micrographs along implant sections showed a approximately 300 μm length implant–abutment engagement region. All implants presented communication between external and internal regions through connection gaps and inaccurate implant–abutment alignment. Average gap distances were not significantly different between implants ( P > 0·086). Polynomial lines showed implant-abutment gap values below 10 μm from 0 μm to approximately 250 μm of the implant–abutment engagement region. Gap distances significantly increased from approximately 250 μm to the outer radius of the implant–abutment engagement region. The technique described provided a broader scenario of the implant–abutment gap adaptation compared with previous work concerning implant–abutment gap determination, and should be considered for better understanding mechanical aspects or biological effects of implant–abutment adaptation on peri-implant tissues. [ABSTRACT FROM AUTHOR]

The 3-D tensile and compressive forces exerted on a tooth were measured in vivo during function using a force-measuring device including a piezoelectric transducer. The device was mounted on the maxillary left second molar of a healthy male subject; the subject tooth had been endodontically treated and prepared for metal abutment and a crown. The 3-D forces were expressed as a vector of the coordinates based on the Frankfort horizontal ( x– y) and sagittal ( y– z) planes. The device captured the sequential changes in the forces. The directions of the forces changed during not only chewing a caramel or a peanut but also maximum voluntary clenching (MVC). As the magnitudes of the force increased during both MVC and caramel chewing (CaC), the force vector tended to correspond to the direction of the palatal root, medially and posteriorly. The compressive forces during MVC and caramel and peanut chewing were 173·29 ± 15·32, 146·3 ± 14·7 and 57·7 ± 35·7 N, respectively. The force vector during MVC was directed from the crown to the root medially at an angle of 10·27 ± 1·00° from the y– z plane and posteriorly at an angle of 3·18 ± 0·85° from the x– z plane to the perpendicular line of the F-H plane. There were significant differences in the behaviour of the compressive forces between clenching and chewing. The tensile force was recorded during CaC, not peanut chewing. [ABSTRACT FROM AUTHOR]

The purpose of this in vitro study was to evaluate the fracture resistance of single-tooth implant-supported all-ceramic restorations, composed of zirconium dioxide all ceramic restorations on different implant abutments, and to identify the weakest component of the restorative system. Forty-eight standardized maxillary central incisor zirconia crowns (Procera) were fabricated for two test groups and one control group (group Al: alumina abutments; group Zr: zirconia abutments; control group Ti: titanium abutments). All abutments were placed on the implants (Replace) using titanium screws. The crowns were adhesively luted using a resin luting agent (Panavia 21) and artificially aged through dynamic loading and thermal cycling. Afterwards, all specimens were tested for fracture resistance using compressive load on the palatal surfaces of the crowns. Pair-wise Wilcoxon rank tests were performed to test for differences in fracture resistance values with a global significance level of 0·05. All test specimens survived aging in the artificial mouth. No screw loosening was recorded. The median fracture resistance was 1251, 241 and 457 N for groups Ti, Al and Zr respectively. Statistically significant differences were found for the comparisons of group Ti with groups Al and Zr ( P < 0·00001), and for the comparison of group Al with Zr ( P < 0·00001). Results of this study showed that all tested implant-supported restorations have the potential to withstand physiological occlusal forces applied in the anterior region. Because of the low fracture resistance values of group Al, the combination of zirconia crowns and alumina abutments should carefully be considered before clinical application. [ABSTRACT FROM AUTHOR]

This paper describes the reconstruction of mandibular defects in four oral cancer patients using iliac crest bone grafts and osseointegrated implants. In three patients, reconstructive surgery using a reconstruction plate and free forearm skin flap was performed following tumour and segmental mandibular resection. After 7–9 months, mandibular reconstruction with a free iliac bone graft was carried out. In one patient, reconstructive surgery was performed with vascularized iliac bone grafting with an anterolateral thigh flap at the same time as the tumour resection. Fixtures were placed in the transplanted bone, and abutments were connected 6–9 months later together with vestibuloplasty. Gingival grafts were used to replace the skin flap around abutments. All implants survived throughout the approximately 4–6 years observation time. Marginal bone loss of the graft was originally several millimetres but less than 1·5 mm. Bone loss as well as management of peri-implant soft tissue was also discussed. [ABSTRACT FROM AUTHOR]

The purpose of this article is to report the clinical course and 6-year follow-up of a child with ectodermal dysplasia who was treated with implants surgery very early. This article reports placement of mandibular endosseous implants in a 4-year-old patient with hypohidrotic ectodermal dysplasia and oligodontia. This congenital anomaly does not appear to retard healing and the osseointegration remains after 6 years and 3 months of loading. Mandibular and maxillary skeletal growth and development was normal. However, because of lack of alveolar growth, in time, patient's vertical growth pattern changed to low angle. This could be corrected by changing the vertical heights of the abutment and prosthesis. As a result, in ectodermal dysplasias cases with anadontia, early implant placement and fixed prosthesis could be a good multidisciplinary treatment option for poor cooperative child. [ABSTRACT FROM AUTHOR]

The aim of this study was to clarify the difference in the stress distribution patterns between implants with external-hex or internal-hex connection systems using in vitro models. Three 13 mm fixtures with external-hex and internal-hex connections were installed into an acrylic bone analogue. One piece abutments of 7 mm height was connected. Strain gauges were attached to the abutment surface, and the cervical and fixture tip areas of the bone analogue surface. Vertical and horizontal load applied was 30 N. Data were normalized for each model by obtaining values relative to the sum of the three values. Almost the same force distribution pattern was found under vertical load in both systems. Fixtures with external-hex showed an increase in strain at the cervical area under horizontal load, while in internal-hex fixtures the strain was at the fixture tip area. Within limitations of our model study, it was suggested that fixtures with internal-hex showed widely spread force distribution down to the fixture tip compared with external hex ones. [ABSTRACT FROM AUTHOR]

The aim of this study was to compare titanium-reinforced ZrO2 and pure Al2O3 abutments regarding their outcome after chewing simulation and static loading. Forty-eight standard diameter implants with an external hexagon were divided into three groups of 16 implants each and restored with three different types of abutments (group A: ZrO2 abutments with titanium inserts; group B: Al2O3 abutments; group C: titanium abutments). All abutments were fixated on the implants with gold-alloy screws at 32 Ncm torque, and metal crowns were adhesively cemented onto the abutments. The specimens were exposed to 1·2 million cycles in a chewing simulator. Surviving specimens were subsequently loaded until fracture in a static testing device. Fracture loads (N) and fracture modes were recorded. A Wilcoxon Rank test to compare fracture loads among the three groups and a Fisher exact test to detect group differences in fracture modes were used for statistical evaluation ( P < 0·05). All specimens but one of group B survived chewing simulation. No screw loosening occurred. The median fracture loads (±s.d.) were as follows: group A, 294 N (±53); group B, 239 N (±83), and group C, 324 N (±85). The smaller fracture loads in group B were statistically significant. The use of pure Al2O3 abutments resulted in significantly more abutment fractures. It is proposed that titanium-reinforced ZrO2 abutments perform similar to metal abutments, and can therefore be recommended as an aesthetic alternative for the restoration of single implants in the anterior region. All-ceramic abutments made of Al2O3 possess less favourable properties. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the retention and marginal seating discrepancy of complete veneer crown cemented with zinc phosphate using various preparation convergence designs. The method employed was that of cementing cast metal crowns onto 46 metal dies fabricated as complete veneer crown preparations with various convergence angles ranging from 0° to 70° and a shoulder finish line. The marginal discrepancy was calculated by measuring the change in crown height before and after cementation using an optical measuring microscope. The force required to remove the crowns from the dies in a vertical direction was determined using an Instron universal testing machine and recorded as retention. The increase in preparation convergence exhibited a wide variation of seating discrepancy between specimens, ranging from 4.58 ± 1.13 to 73.13 ± 78.32 μm. Significant tilting of crown was observed as the convergence angle of preparation increased. The retention values ranged from 4.03 ± 0.61 to 12.12 ± 0.33 MPa. The Pearson analysis revealed statistically significant correlations between preparation convergence and marginal discrepancy (r = +0.62), and retention (r = −0.91). Complete veneer crown retention and marginal discrepancy were influenced by the preparation convergence design. [ABSTRACT FROM AUTHOR]

summary The purpose of this study is to clinically confirm the adhesive effect of a vinyl-thiol primer (V-Primer) for precious alloys. Further, we examined the failure of resin-bonded bridges (RBBs) in order to improve the clinical longevity of RBBs, and to analyse the causes of failure. Twenty-six RBBs were bonded with V-primer and Super Bond C & B between May 1987 and December 1997 in the Dental Clinic of the Health Sciences University of Hokkaido. The RBBs were made of silver–palladium–gold alloy or metal–ceramic gold alloys. V-primer was effective in bonding Super Bond C & B to the RBBs made of silver–palladium–gold alloys. Ten prostheses had functioned satisfactorily for 8–11 years. However, six of the 26 RBBs had become detached. In four of the six failed RBBs, the type of bond failure was a mixture fracture in the resin–enamel interface. Our results suggest that: (1) V-primer is effective on RBBs made of silver–palladium–gold alloys. (2) Mechanical retention is necessary for retainers to improve the longevity of RBBs when the V-primer is applied to RBBs made of precious alloys without copper. (3) The RBB should not be applied to abutment teeth that have differences in tooth mobility. [ABSTRACT FROM AUTHOR]

summary Bond strengths were evaluated for (1) metal primer systems when the metal was contaminated by a dentin conditioner and (2) a dentin adhesive system when dentin was contaminated by metal primers. Disc specimens were cast in a silver–palladium–copper–gold (Ag–Pd–Cu–Au) alloy and dentin specimens were prepared by grinding the labial surface of bovine teeth. Specimens were treated with (1) metal primer alone, (2) dentin conditioner alone, (3) metal primer followed by dentin conditioner and (4) dentin conditioner followed by metal primer. A resin cement was poured into a mould over a restricted bonding area and allowed to set. Metal specimens were shear stressed to failure after thermocycling (4–60 °C; 20 000 cycles). Dentin specimens were stressed in the same manner after 24 h of immersion in 37 °C water. The results were compiled and analysed by anova. Data for dentin specimens treated with dentin conditioner only or with the combination of dentin conditioner and metal primer were not significantly different, statistically. Post-thermocycled groups indicated that bond strengths to the alloy significantly decreased (P < 0·05) when the primed metal surface was contaminated with dentin conditioner regardless of the timing of its application. [ABSTRACT FROM AUTHOR]

summary New-generation composite materials have excellent strength and wear resistance, and thus can be used to make metal-free crowns. However, composite materials are translucent, and so when using them to make metal-free crowns, it is necessary to take the effect of the abutments into consideration. In this study, five types of materials including three types of new-generation composite materials, a conventional composite material, and a ceramic material were used to examine the translucency (contrast ratio) of the materials and the effects of the colour of the abutments on the final appearance of metal-free crowns. It was found that the materials varied slightly from one-another in translucency and that it was possible to reproduce the desired colour when gold alloy was used for the background. However, it was difficult to produce an adequate colour match when silver–palladium alloy was used for the background. When a tooth colour material that was darker than the target colour was used for the abutment teeth, some materials could not reproduce the target colour satisfactorily. [ABSTRACT FROM AUTHOR]

Summary All-ceramic crowns made of leucite-based heat-pressed ceramics are widely used to restore non-vital teeth in conjunction with various post and core materials. However, as some light passes through the ceramic, the colour of the abutment substrate can negatively affect the final aesthetic appearance of the all-ceramic crown. In this study, we made background specimens simulating gold-alloy cast posts and other simulating porcelain veneered cast posts, overlaid different thickness of heat-pressed ceramic on these background specimens, and measured the shifts in colour. We found that, when the background specimen was a gold alloy, the background colour had an effect on the apparent colour, unless the ceramic was more than 1·6 mm thick. When the background specimen was porcelain veneered, the background colour had no evident effect, even when the ceramic was not very thick. Therefore, when making a restoration using a leucite-based heat-pressed ceramic crown, it is advisable to use tooth-coloured materials such as a porcelain veneered cast post, if you will not be able to make the ceramic more than 1·6 mm thick. [ABSTRACT FROM AUTHOR]

The force transmission of tapered unthreaded posts along the root has been reported to be homogenous but their retentive strength was found to be lower compared with those of parallel unthreaded or other kinds of threaded posts. The purpose of this in vitro study was to investigate the effect of length and diameter on the retentive strength of sandblasted tapered prefabricated titanium posts (Erlangen post system®). Posts with constant taper angle but with three different lengths (9, 12, 15 mm) and apical diameters (0·5, 0·9, 1·1 mm) were cemented using zinc phosphate cement into the prepared and roughened post spaces of 90 intact anterior teeth. The post retention concerning length and diameter, being independent from each other, was measured by a tensile force test. The retentive strength was found to be proportional to the length as well as to the diameter of the posts. The mean minimum strength (181 ± 14 N) recorded for the thinnest and shortest post was significantly lower than that of mean maximum strength (612 ± 85 N) obtained from those of the thickest and longest post. Proportional bond strengths of the posts comprising their surface areas ranged between 6·8 and 7·9 N mm–2 which were not significantly different between any group. The retention was effected strongly with the increase in the length (approximately 100%) than with the increase in the diameter (approximately 60%). Concerning the posts tested in this study, it is concluded that some caution should be exercised in the choice of post with appropriate length rather than diameter for the tooth concerned. [ABSTRACT FROM AUTHOR]

A supplement to the Kennedy classification of partially edentulous arches for restoration with removable partial dentures has been suggested. Factors affecting denture design relating to the position of the abutment teeth, the symmetry of the edentulous distal extensions, the arch form and the cross-sectional shape of the residual ridges have been discussed and classified. An understanding of the movement of the denture bases in relation to the influence of these factors makes for a rational approach to removable partial denture design and the treatment of complications observed clinically in removable partial denture wearers. [ABSTRACT FROM AUTHOR]

The two-dimensional plane stress finite element stress analysis was used to evaluate the stress of mandibular posterior cantilevers for compromised periodontal involved distal terminal abutments. Some commonly practiced methods to alleviate the stress from mastication of the cantilever FPDs were also evaluated. From the analysis the following was concluded: (1) The most distal terminal abutment of a cantilever FPD generally experienced a high stress concentration. (2) The cantilever FPDs require at least two abutments. Optimum stress reduction occurred with a splinting of three abutments. To increase the number of abutments to more than three, would not result in a proportional and meaningful reduction of stress in the periodontium. (3) To alter the bridge material with more rigid material or to have a longer marginal preparation of the terminal abutment are ineffective for better stress distribution. [ABSTRACT FROM AUTHOR]

There is a methodological problem in analysis of data belonging to different hierarchical levels, e.g. patient, arch, and tooth. A method for multilevel modelling (MLM) that resolves this problem is available. This method which is presented in this article, was used to reanalyse previously published long-term treatment results concerning the longevity of fixed partial dentures, retainers and abutments. The main results were consistent, indicating that no great faults were committed when using the conventional logistic regression method. There were, however, differences when calculating the combined risks for various situations. The conventional method was found to over- and underestimate probabilities of survival in different cases, compared to the MLM method. Especially when the most negative factors were combined, the conventional method had a tendency to underestimate the risk. For example, if an abutment had the combination ‘endodontically treated’ ‘FPD placed by ‘another dentist’’; ‘distal abutment’; and ‘marginal bone loss >50%’; the probability of the tooth remaining after 18-23 years was only 20% according to the MLM method but 35% according to the conventional method. It was concluded that MLM is the method of choice for many situations in dental research where data belonging to different levels are to be analysed. [ABSTRACT FROM AUTHOR]

The aim of this retrospective study was to record patients' satisfaction with fixed metal ceramic bridges and crowns made by dental students and to evaluate the functioning and condition of the bridges and crowns clinically and radiologically. Out of the 60 patients treated at the Institute of Dentistry during 1984-85, 30 patients attended the follow-up examination (16 women, mean age 39, range 23-62 years and 14 men, mean age 44, range 26-65 years) The anamnestic data and data regarding treatment procedures were collected from the patient files. The patients had been supplied with 41 crowns and 24 bridges (mean 3.9 units, range 3-6 units), which included 61 abutments and 33 pontics or cantilever extensions (abutment/pontic ratio 1.85: 1). Marginal fidelity was unsatisfactory in 13% of the crowns and bridges and gingival bleeding and pockets of 4-6 mm were noted in 27% and 12% of cases, respectively. None of the subjects had caries in the abutments. [ABSTRACT FROM AUTHOR]

In a crossssectional study the fit of direct retainers was assessed after 8 years of use. A total of 101 metal frame removable partial dentures (RPD) were investigated, including 54 extension base prostheses without any tooth supported replacement and 47 tooth supported prostheses that replaced only premolars and molars. Of the frameworks studied, about 60% of the clasps showed a space between retainers and abutments. Logistic regression analyses demonstrated that the age of the RPD and the type of opposing dentition significantly influenced the fit of the clasps. The relative risks and a backward regression analysis revealed that the variable non rigid extension base RPD had the greatest influence on clasp fit. it was concluded that in extension base RPDs a rigid design should be preferred. [ABSTRACT FROM AUTHOR]

Loss of osseointegration of implant fixtures and mechanical failure of superstructures have been attributed to failure to achieve a passive fit between the superstructure and the transmucosal abutment (TMA). The fit of five mandibular superstructures, fabricated on Nobel Biocare implants, was investigated in vivo, using a polyvinyl siloxane impression material to record the discrepancies. Following sectioning of the impressions, the vertical and horizontal discrepancies were analysed at four locations using a travelling microscope. The discrepancies obtained were measured both when the gold cylinder screws were maximally tightened by hand and when tightened with a torque driver to the recommended value of 10 Ncm. The vertical discrepancies for the hand tightened abutments ranged from 0 μm to 63 μm with a mean of 14 μm. In the mechanically tightened group, the vertical discrepancies ranged from 0 μm to 130 μm with a mean of 21 μm. The horizontal discrepancies for the mechanically tightened abutments ranged from 0 μm to 140 μm with a mean of 31 μm, compared with a mean of 46 μm and range of 0 μm to 113 μm, for the hand-tightened abutments. A close fit was seldom achieved. It is concluded that considerable discrepancies existed around superstructures that had been judged to have a clinically acceptable fit. These were reduced in the vertical direction by hand tightening of the gold screws. [ABSTRACT FROM AUTHOR]

In this investigation 156 dental bridges, inserted for 132 individuals, were evaluated. Three- unit bridges accounted for the majority of fixed appliances surveyed. The results revealed that the mean longevity of the failed bridges was 6.1 years. There was no relation between the number of units in a bridge and its duration of service. The results also revealed that metal-ceramic retainers were the most commonly used in the series but exhibited the shortest duration of successful service. Of 325 abutments, 11.4% were endodontically treated and 10.8% of those were associated with periapical lesions. Periapical lesions were associated with 42% of the abutments presumed vital prior to the study. [ABSTRACT FROM AUTHOR]

The quasi-3D technique of photoelastic stress analysis was used to evaluate the stresses of mandibular posterior cantilevers for distal terminal abutments at various levels of periodontal support. The stress concentration index was selected to compare each model. The periodontal support of terminal abutment and the length of pontic must be considered, when a cantilever fixed partial denture is anticipated. [ABSTRACT FROM AUTHOR]

In dental clinics, composite resin and cement cores are routinely cut and polished during abutment tooth preparation. To identify their characteristics during cutting, weight-load cutting tests were performed on eight commercial core composites and two cements, using diamond points driven by an air-turbine handpiece. It became evident that the cutting effectiveness of the diamond points on nine workpieces exceeded that on natural tooth dentine, while that on one composite containing Si3N4 filler was analogous to that on dentine. With continued use, the cutting effectiveness of the diamond point on all workpieces gradually declined. SEM observations revealed that diamond particles of the diamond point wore out with repeated use. It is clinically advised to select the core material with material characteristics during cutting and mechanical strength similar to those of dentin. [ABSTRACT FROM AUTHOR]

The relationship between a removable partial denture (RPD) and damage caused to residual oral structures is the subject of on-going research. A group of patients wearing RPD, treated in the same way in the same department, were recalled to evaluate their oral hygiene and to compare the clinical condition of abutment teeth with that of non-abutment teeth. The study shows that most patients were unable to maintain high standards of oral hygiene. In the group of patients with non-optimal hygiene the clinical condition of abutment teeth was worse than that of non-abutment teeth. In the group of patients with optimal oral hygiene the condition of abutment teeth and non-abutment teeth was almost identical. To increase the standards of oral hygiene it is strongly advisable to recall and follow up patients on a regular basis. [ABSTRACT FROM AUTHOR]

The survival rate of 1674 bridges and the influence of several factors on the lifetime of bridges were analysed, based on data from patient records that belonged to a random sample of 40 Dutch general practices. It appears that the 12 year survival rate of the bridges is 87%. There is a significant difference in the survival rate between the bridges that meet and do not meet Ante's law, and only a weak significant difference between the bridges with vital vs. non-vital abutment teeth. Gender and age of the patient, length of the bridge, presence of a post and core build-up, or the construction of the bridge (conventional fixed vs. cantilever pontic) appear to have no influence on the survival rate of the bridges in this sample. [ABSTRACT FROM AUTHOR]

A knowledge-based system for designing removable partial dentures is described in which graphical representations of denture components are manipulated directly by the user to build the required denture design. The arch form of individual patients may be depicted by linear movement and rotation of the icons representing teeth. The size, shape and position of many denture components are determined dynamically to conform to the shape of abutment teeth and to the juxtaposition of other elements. Expert clinical knowledge is used to analyse the developing design and suggest alternate approaches. [ABSTRACT FROM AUTHOR]

Not only forces but also torque exerted on abutment teeth are important factors for planning the construction of distal extension removable partial dentures. The purpose of this study was to make longitudinal analysis of torque transmitted from denture base to a direct abutment tooth of these dentures with circumferential clasps. The results are summarized as follows: (i) Vertical Max MT (maximal mean value of torque) was decreased and became constant after one or one and half months of the insertion of new dentures. (ii) Lateral Max. MT in one subject was changed from the lingual direction to the buccal direction while in another subject it was constant. (iii) In the vertical direction, there were no remarkable differences of Max. MT and Ave. T (average value of torque) between subjects. Max. MT was 5-10 × 10-3 kgm-1 in the downward. Ave. T was 2-3 × 10-3 kgm ss-1 in the downward and 0.3 × 10-3 kgm ss-1 in the upward. (iv) In the lateral direction, there were considerable differences of Max. MT and Ave. T between subjects. Max. MT was less than 20 × 10-3 kgm. Ave. MT was 2-8 × 10-3 kgm ss-1. [ABSTRACT FROM AUTHOR]

The avoidance of lateral forces on overdenture retainers is essential to prevent pathological change in the supporting tissues of the root abutment. In this study, the influence of spacer thickness on the vertical and lateral forces exerted on overdenture abutments was examined clinically. Two subjects with an edentulous maxilla, two canines and a left first premolar remaining in the mandible were selected for the experiment. The anchor type attachment was embedded in the left canine portion of the denture base. The transducer used for the previous study (Ogata et al., 1990), was embedded in this left canine portion. The transducer could detect the magnitude and direction of lateral forces exerted on an abutment tooth parallel to the Camper's plane. The other transducer was embedded in the left first mandibular premolar area, and could detect vertical forces exerted on the abutment tooth perpendicular to the Camper's plane. Furthermore, the transducer could change the space between a denture base and an abutment tooth to 1.5 mm, 0.6 mm or 0.3 mm. Therefore measurements could be made in the same way as if three experimental dentures had been used with a different thickness spacer. Recordings of forces were taken during food chewing, using each spacer on the day of denture insertion and twice at intervals of 1-2 weeks thereafter. The results demonstrated that as spacer thickness decreased, the magnitude of the lateral forces decreased, while the magnitude of the vertical forces increased. These findings suggest that a large part of the lateral component of forces exerted on an abutment tooth could be converted into a vertical component by using a thinner spacer. [ABSTRACT FROM AUTHOR]

With increasing emphasis being placed on precision in the construction of prosthesis the importance of the visco-elastic characteristics of tooth support should be understood. Since the tooth returns to its resting position quite slowly, especially when repeated or sustained forces have been applied, an impression prepared prior to full recovery will convey erroneous relationships of the tooth with its neighbours to the working model and, eventually, to the prosthesis. Such an error has been identified in young human subjects when inter-dental wedges, gingival retraction cord, and rubber dam are placed. The preparation of conventional alginate impressions in special trays can displace abutment teeth to a clinically significant degree as was recorded for seven partially dentate patients. Simple precautions will circumvent these potential sources of error. [ABSTRACT FROM AUTHOR]

Using a laboratory model simulating a free-end saddle partial denture situation, the effect of variation of the angulation of the crest of the residual alveolar ridge to the horizontal on movement of the abutment tooth and saddle was observed. It was found that the inclination of the residual ridge affected the direction and magnitude of abutment tooth movement. The direction of abutment tooth movement was not related to the position of the occlusal rest. However, the magnitude of saddle and abutment tooth movement is affected by the design of the clasp used. [ABSTRACT FROM AUTHOR]

The aim of this study was to collect information about the mean working time needed to accomplish the clinical procedures in applying an adhesive bridge, and to gain an insight into the factors that influence the working time. The study was carried out as part of a clinical trial. One hundred and fifty-one patients needing one adhesive bridge were selected for this study and divided between five operators. Clinical procedures were carried out following a written protocol. The statistical method consisted of an ANOVA after log-transformation of the working times. The total mean working time needed to accomplish the clinical procedures for adhesive bridges was 60.7 min (s.d.±16.5 min). The mean working time increased by 30% where the abutment teeth were restored with class II or class III restorations. No influence was found related to: (1) type of bridge (i.e. macromechanical versus micromechanical), (2) type of luting resin and (3) location of the bridge. A significant effect on the working times was found for: (1) operator, (2) tooth preparation and (3) occlusal adjustments. With increasing experience of the operator the median working time decreased by up to 35%. The data from this study are considered as useful basic information for efficient planning in the dental practice and for a further cost-benefit analysis. [ABSTRACT FROM AUTHOR]

Studies on the adverse effects of partial dentures on the remaining tissues require both a yardstick of measurement to record the level of oral disease, and the use of controls, preferably within the same patient. A method was devised for pooling the individual values related to the level of periodontal disease on abutment and control teeth in partial dentitions. The difference in these combined values was expressed as the Biological Price. This value provided a useful means of evaluating partial denture designs and patient features, in attempting to assess the major contributing factors responsible for the Biological Price levied by the denture. Whilst wearing an acrylic partial denture at night adds to the price paid by the remaining tissues, the mechanical features of the partial denture, and the overall features of the patient and his remaining dentition appear to be insignificant in determining the Biological Price. [ABSTRACT FROM AUTHOR]

In this article the results are presented of an evaluation of crowns and bridges in a general practice. The study includes 601 solitary crowns, 213 crowns on bridge abutments and 103 crowns on RPD abutments. In total eighty-four bridges were examined. All these restorations were constructed during a period of 11.5 years. By means of the Kaplan-Meier method a prognosis is given of the life span of the different solitary crown-types over periods between 1 and 11 years. The total amount of failures and follow-up treatments on bridge and RPD abutments was very small. The authors also examined whether the bridges were constructed according Ante's law. A follow-up of this study in other Dutch general practices in combination with experimental clinical trials is under way. [ABSTRACT FROM AUTHOR]

A laboratory investigation designed to simulate the effect of loads applied to a free-end saddle partial denture was carried out. Abutment tooth and also saddle movement were monitored suing a photogrammetric method. Loads applied to the denture saddle were transmitted through the occlusal rest and also the clasp components causing movement of both denture saddle and the abutment tooth. The direction of abutment tooth movement was towards th mesial, whether the occlusal rest was situated on the mesial or distal aspect of the tooth crown. It was also evident that the design of the clasp unit used affects the magnitude and direction of abutment tooth movement. [ABSTRACT FROM AUTHOR]