Adhesive removable partial denture attachments made from zirconia ceramic: A finite element analysis and in vitro study.

STATEMENT OF PROBLEM: Whether adhesive zirconia ceramic removable partial denture attachments are feasible with current technology is unclear. PURPOSE: The purpose of this finite element analysis and in vitro study was to evaluate the effect of the lever arm, tooth preparation, and aging on the loading of the tooth-zirconia attachment interface. MATERIAL AND METHODS: Three different finite element analysis (FEA) models allowing for the loading of an adhesive attachment either directly or through a removable partial denture were used. Two models represented a human tooth with 2 different types of attachments, while the third model also included a removable partial denture. For the evaluation of bond strength, a combination of shear and hydrostatic stress was used. In addition, composite resin teeth were fabricated, and zirconia bars were bonded to them with varying tooth preparations and lever arm lengths. In 1 group the influence of aging was analyzed. Fracture load was determined by using a universal testing machine. Statistical analysis was based on the Shapiro-Wilk normality test, ANOVA, and Games-Howell test (α=.05). RESULTS: The maximum stress of 65 MPa occurring in the bonding area was reduced to 37 MPa by adding a retainer to the attachment. Loading of the denture resulted in a maximum stress of 9 MPa. Mean fracture loads ranged from 33.6 N to 209.1 N. Preparing a flat bonding surface showed a nonsignificant increase (P=.197), whereas aging led to a nonsignificant decrease in fracture load (P=.075). A lever arm extended by 2 mm significantly reduced fracture load (P=.002). The addition of an occlusal-distal (OD) cavity led to a nonsignificant increase (P=.186), which became significant when a mesial-occlusal-distal (MOD) preparation was applied (P=.001). CONCLUSIONS: Adhesive zirconia attachments should use a MOD cavity and have a cross section of at least 2.5×2.5 mm. The attachment should not extend more than 3 mm.

Evaluation of Insertion Energy as Novel Parameter for Dental Implant Stability.

Insertion energy has been advocated as a novel measure for primary implant stability, but the effect of implant length, diameter, or surgical protocol remains unclear. Twenty implants from one specific bone level implant system were placed in layered polyurethane foam measuring maximum insertion torque, torque-time curves, and primary stability using resonance frequency analysis (RFA). Insertion energy was calculated as area under torque-time curve applying the trapezoidal formula. Statistical analysis was based on analysis of variance, Tukey honest differences tests and Pearson's product moment correlation tests (α = 0.05). Implant stability (p = 0.01) and insertion energy (p < 0.01) differed significantly among groups, while maximum insertion torque did not (p = 0.17). Short implants showed a significant decrease in implant stability (p = 0.01), while reducing implant diameter did not cause any significant effect. Applying the drilling protocol for dense bone resulted in significantly increased insertion energy (p = 0.02) but a significant decrease in implant stability (p = 0.04). Insertion energy was not found to be a more reliable parameter for evaluating primary implant stability when compared to maximum insertion torque and resonance frequency analysis.

Peri-implant Bone Loss of Tissue-Level and Bone-Level Implants in the Esthetic Zone with Gingival Biotype Analysis.

PURPOSE: The esthetic outcome of dental implants can be compromised when some degree of bone loss occurs around the implant. This may particularly affect the tissue-level (TL) design. Therefore, bone-level (BL) design implants may be preferable if a natural emergence profile is important. Notwithstanding the implant design, the gingival biotype has been identified as a crucial factor in the stability of crestal bone. The objective of this study was to investigate bone loss in patients with different gingival biotypes at TL and BL implant sites in the esthetic zone. MATERIALS AND METHODS: In 41 patients, 20 TL and 22 BL implant procedures were carried out. Intraoral radiographs of all of the 42 sites were taken immediately after implant insertion as well as during the follow-up examination. The analysis of bone height was conducted using a computerized technique. The TRAN method was used to determine the gingival biotype. RESULTS: After a mean in situ period of 4.9 years in the TL group, 12 implants with a thick biotype had a mean bone loss of 0.21 mm (SD: 0.43 mm). The eight implants with a thin biotype had a loss of 0.05 mm (SD: 0.47 mm; P = .31). After a mean in situ period of 1.9 years, the 14 BL sites with a thick biotype showed a mean bone change of -0.03 mm (SD: 0.38 mm). In the eight implants with a thin biotype, a change of +0.09 mm (SD: 0.32 mm; P = .84) was noted. CONCLUSION: Analysis of the obtained results did not reveal a dependency of bone height on implant design or on gingival biotype. However, prior to choosing an implant design, it may nevertheless be beneficial to screen for transparent soft tissues, where the BL design offers a more natural emergence profile. For this purpose, the TRAN method is clearly the fastest and easiest.

Long-Term Esthetic Outcome of Tissue-Level and Bone-Level Implants in the Anterior Maxilla.

PURPOSE: The aim of this study was to assess and compare the esthetic outcome of tissue-level (TL) and bone-level (BL) implants that had been placed as single implants in the anterior maxilla. MATERIALS AND METHODS: Between 2001 and 2008, patients were treated using TL implants (Straumann). From 2008 until 2012, patients received the newly developed BL implant (Straumann). All patients with a single anterior maxillary implant who came to check-ups regularly were contacted and invited to take part in the study. Standardized photographs were taken to conduct the evaluation. Five observers analyzed the esthetic outcome using the pink esthetic score (PES). For the purpose of statistical analysis, the Wilcoxon rank sum test was applied. Interobserver reliability was evaluated with Krippendorff's alpha. RESULTS: Forty-six patients agreed to take part in the study. The study comprised 10 immediate (TL = 6, BL = 4), 21 early (TL = 6, BL = 15), and 15 delayed implantations (TL = 11, BL = 4). All implant sites were simultaneously augmented. The prosthetic restorations were delivered 6 to 24 weeks after implant placement in the TL group and 10 to 14 weeks after implant placement in the BL group. Esthetic evaluation was performed after a mean period of 9.5 years for TL implants (range: 5.5 to 12.0) and 3.7 years for BL implants (range: 2.6 to 7.1). The overall PES was 8.49 (SD: 2.35) for TL implants and 9.29 (SD: 1.90) for BL implants (P = .37). Comparison of single parameters was between P = .24 and P = .83, indicating no statistically significant difference between the two implant types. CONCLUSION: Within the limits of this study, it can be stated that both implant designs showed comparably satisfying esthetic results.

Alveolar Ridge Dimension 6 Months After Implant Placement with Simultaneous Hard Tissue Augmentation.

PURPOSE: When failing front teeth are replaced by implants, vestibular bone deficiencies frequently require augmentation, even though the amount of missing alveolar volume may vary. The objective of this study was to analyze the horizontal alveolar ridge dimension after implant placement and simultaneous augmentation, and to compare it to the condition at the contralateral natural site. MATERIALS AND METHODS: Forty-eight patients with a failing maxillary incisor received an immediate or early implant (Straumann Bone Level), according to a randomized study protocol. The vestibular wall of the implant site was reconstructed and moderately overcontoured with bovine hydroxyapatite and a collagen membrane (BioOss, BioGide, Geistlich). Provisional restoration followed either immediately, or after a 6-week healing period. To investigate the vestibular volume 6 months after surgery, a plaster model of the maxilla was scanned with cone beam computed tomography (CBCT; Morita 3D) and evaluated using coDiagnostiX software (Dental Wings). Statistical analysis comprised one- and two-sample t tests. RESULTS: The ridge volume was not significantly influenced by the treatment schedule. The vestibular segments had a mean ± SD volume of 207.9 ± 102.5 mm³ for the implant sites, and 202.1 ± 101.5 mm³ for the corresponding natural sites (P = .28). The difference in vestibular volume between implant sites and natural tooth sites was 10.4 ± 36.2 mm³ for immediate implantation, and 0.00 ± 31.1 mm³ for early implantation (P = .32). Comparing immediate and early restoration, a difference of 0.4 mm³ and 12.5 mm³ between the implant and contralateral site was found (P = .23). CONCLUSION: Six months after treatment, no significant differences between the alveolar volumes at augmented implant sites and natural sites were found. Moderate buccal overcontouring may have been beneficial to achieve a symmetrical contour. Long-term follow-up investigation will document if the restored volume remains stable over time.

Accuracy of impression scanning compared with stone casts of implant impressions.

STATEMENT OF PROBLEM: Accurate virtual implant models are a necessity for the fabrication of precisely fitting superstructures. PURPOSE: The purpose of this in vitro study was to evaluate different methods with which to build an accurate virtual model of a 3-dimensional implant in the oral cavity; this model would then be used for iterative computer-aided design and computer-aided manufacturing (CAD-CAM) procedures. MATERIAL AND METHODS: A titanium master model with 3 rigidly connected implants was manufactured and digitized with a noncontact industrial scanner to obtain a virtual master model. Impressions of the master model with the implant position locators (IPL) were made using vinyl siloxanether material. The impressions were scanned (Impression scanning technique group). For the transfer technique and pick-up technique groups (each group n=20), implant analogs were inserted into the impression copings, impressions were made using polyether, and casts were poured in Type 4 gypsum. The IPLs were screwed into the analogs and scanned. To compare the virtual master model with each virtual test model, a CAD interactive software, ATOS professional, was applied. The Kruskal-Wallis test was subsequently used to determine the overall difference between groups, with the Mann-Whitney U test used for pairwise comparisons. Through Bonferroni correction, the α-level was set to .017. RESULTS: The outcome revealed a significant difference among the 3 groups (P<.01) in terms of accuracy. With regard to total deviation, for all axes, the transfer technique generated the greatest divergence, 0.078 mm (±0.022), compared with the master model. Deviation with the pick-up technique was 0.041 mm (±0.009), with impression scanning generating the most accurate models with a deviation of 0.022 mm (±0.007). CONCLUSIONS: The impression scanning method improved the precision of CAD-CAM-fabricated superstructures.

Impact of placement and restoration timing on single-implant esthetic outcome - a randomized clinical trial.

AIM: The objective of this randomized clinical trial was to investigate the influence of the time of implant placement (immediate vs. early) and the time of restoration (immediate vs. early) on esthetic outcome in maxillary anterior single implants. MATERIAL AND METHODS: Forty-eight patients with a single failing incisor in the maxilla and a natural contralateral site were randomly distributed into four groups. Treatment variations affected the time of implant placement (immediate or early) as well as the time of restoration (immediate or early) - in detail, group 1a with immediate implant placement and immediate temporary restoration, group 1b with immediate implant placement and early restoration, group 2a with early implant placement and immediate temporary restoration, and group 2b with early implant placement and early restoration. All patients received the final prosthetic restoration 10-12 weeks after implant placement. Standardized photographs were taken eight months after tooth extraction. Five competent observers analyzed the esthetic outcome according to the PES after Fürhauser. For statistical analysis, the Kruskal-Wallis test and Dunn's post hoc test were applied. Interobserver reliability was evaluated by Krippendorff's alpha. RESULTS: The overall scores of the four treatment groups revealed PES values of 8.47 (SD 2.08, group 1a), 7.93 (SD 3.21, group 1b), 6.62 (SD 3.24, group 2a), and 8.10 (SD 3.25, group 2b). The differences between groups 2a and 1a and between groups 2a and 2b were statistically significant (P = 0.015 and P = 0.047). The single parameter analysis displayed a certain range of fluctuation and heterogeneity. CONCLUSIONS: Immediate implant placement and restoration appear to be a viable alternative to early implant placement if an experienced surgeon is entrusted with the implantation procedure.

Effect of various fixation parameters on strain development of screw- and cement-retained implant-supported restorations.

OBJECTIVE: The objective of this study was to quantify the potential effects of screw- and cement-retention on strain development of implant-supported fixed dental prostheses (FDPs). METHOD AND MATERIALS: A total of 20 single crowns and 70 three-unit FDPs were fabricated to fit an in vitro model situation with two implants. Using strain gauges attached to the model material adjacent to the implants, strain development of the restorations during fixation was recorded while the parameters cement type (provisional and definitive cement), cementation force (10 N and 100 N), and tightening torque (5 Ncm, 10 Ncm, and 15 Ncm) were varied. MANOVA with Pillai's trace was used for pairwise comparisons between groups (α = .05). RESULTS: Mean absolute strain development ranged from 5.11 µm/m for to 27.26 µm/m for single crowns and from 16.46 µm/m to 689.04 µm/m for multi-unit restorations. Screw-retained single crowns exhibited significantly smaller strain development as compared to cement-retained single crowns (P = .009). The type of cement used seemed to have no effect on strain development of an FDP regardless of the cementation force applied (P = .064 and P = .605). An increase in tightening torque for screw-retained FDPs also had no effect on resulting strain development (P values ranging from .692 to .807). Nonuniform results were found when comparing screw- and cementretention as the retention mechanism for FDPs. CONCLUSION: Strain development seems to depend predominantly on the accuracy achieved during the fabrication process whereas the retention mechanisms themselves as well as their potential parameters only have a minor effect.

A double-blind study on clonazepam in patients with burning mouth syndrome.

OBJECTIVES/HYPOTHESIS: In the treatment of burning mouth syndrome (BMS), various approaches have been tried with equivocal results. The aim of the present randomized clinical trial was to determine the efficacy of clonazepam, a GABA agonist designed as an antiepileptic drug that exerts the typical effects of benzodiazepines. STUDY DESIGN: Randomized clinical trial. METHODS: Twenty patients with idiopathic BMS were carefully selected. Clonazepam (0.5 mg/day, n = 10) or placebo (lactose, n = 10) were randomly assigned to the patients. RESULTS: Patients on clonazepam significantly improved in pain ratings (P < .001). These changes were less pronounced in the placebo group (P < .11). No significant changes were observed in a mood scale (P = .56) or for depression scores (P = .56). Taste test and salivary flow increased over sessions, but were not different between groups (P = .83 and P = .06, respectively). CONCLUSIONS: Clonazepam appears to have a positive effect on pain in BMS patients.

Long-term neuromuscular status in overdenture and complete denture patients with severe mandibular atrophy.

PURPOSE: The long-term neuromuscular status of edentulous patients with severe mandibular atrophy who wore complete dentures (CDs) or implant-supported overdentures (ISOs) was investigated in the present study. MATERIALS AND METHODS: Eleven CD patients and 11 patients with ISOs supported by two implants took part in the study. All patients had used their dentures for more than a decade. All patients (average age, 76 years) suffered from severe mandibular atrophy, which was to be quantified using panoramic radiographs and computer software. Kinesiographic parameters such as opening and extension movements as well as opening and closing velocities were recorded by means of a sirognathograph during test food chewing on the left and right sides. Simultaneously, electromyographic recording of masseter and temporalis activities was performed using surface electrodes. RESULTS: The kinesiographic values obtained from ISO patients were higher than those for CD patients: 12.65 mm for vertical opening (CD, 11.79 mm) and 5.66 mm for horizontal extension (CD, 5.11 mm). Opening velocity values were 100.93 mm/s and 91.74 mm/s, respectively. Closing velocity of 78.16 mm/s in ISO patients was significantly different from that measured in CD patients (58.45 mm/s). With regard to electromyographic activities, the increase was significant for the masseter during chewing on the working side (ISO: 189.79 µV, CD: 78.05 µV) and on the nonworking side (ISO: 130.53 µV, CD: 47.25 µV). For the temporalis, values of 194.11 µV and 119.02 µV in the ISO and CD patients, respectively, were observed for working side chewing. Nonworking side values reached 155.48 µV for ISO subjects and 78.35 µV for CD subjects, which was significantly different. The degree of atrophy in both groups did not differ statistically. CONCLUSIONS: The use of two interforaminal implants with an overdenture can provide long-term neuromuscular benefits for edentulous patients.

A methodology to study the effects of prosthesis misfit over time: an in vivo model.

PURPOSE: Passive fit of implant-supported superstructures cannot currently be achieved. The aim of this investigation was to create a methodology that can be used to study the effects of prosthesis misfit in humans. MATERIALS AND METHODS: An edentulous patient received two interforaminal implants and a screw-retained bar for the retention of the mandibular denture. A corresponding in vitro model with strain gauges placed mesially and distally, adjacent to the implants, was fabricated to serve as a standardizing control. Over a period of 6 months, a total of 10 measurements on both the in vitro model and in the patient's mouth were conducted with newly fixed strain gauges on the bar. RESULTS: The in vitro experiments showed that no component wear at the abutment-bar interface had occurred and that repositioning of the strain gauges on the bar caused deviations in strain measurements up to 10.55%. In vivo, a reduction in strain development, from 445 to 383 Mum/m, was observed in the initial phase up to 12 weeks after bar insertion. Subsequently, the measurement values increased, and after a period of 24 weeks, they nearly reached the initial strain level (443 microm/m). Only minor changes in strain development of the bar could be detected; these might be a result of limited dynamic loading and the cortical architecture of the surrounding bone. Deviations in measurement accuracy caused by repositioning of the bar strain gauge are a limitation of this technique and should be eliminated in future studies. CONCLUSIONS: The present methodology can be applied to study changes in static implant loading over time in humans.

Stability of screw-retained implant-supported fixed dental prostheses bonded to gold cylinders.

This study examined the adhesive stability of screw-retained implant-supported fixed dental prostheses (FDPs) bonded to prefabricated gold cylinders after a load cycling. Five FDP groups (n = 10 per group) that differed either in bonding or loading modality (no loading, loading, moment loading, humidity, silicoating) were compared based on the forces needed to separate the FDP frameworks from the gold cylinders. The mean separating forces for the different groups ranged from 311 N to 501 N. No statistically significant differences could be detected between the five groups (Welch t test, P = .447). Despite the limited transferability into clinical practice, it appears that sufficient bonding stability can be achieved for screw-retained implant-supported FDPs bonded to prefabricated gold cylinders.

Interforaminal implant therapy using a split skin graft--treatment outcome after 13 years.

In implant patients who have extended soft tissue deficiencies, split skin grafts have been performed for the prevention of peri-implant inflammation. The aim of this investigation was to assess a patient who received 2 interforaminal implants and a split skin graft 13 years prior. In addition to clinical, mycologic, and radiographic examinations, the condition of the split skin graft was evaluated using histologic analysis of 3 punch biopsies taken from the mucosa, grafted area, and border between both areas. The implants were found to have an overall good clinical condition. Fungal infection was not present. The histologic analysis revealed inflammation-free mucosal and submucosal tissue in all samples. In the area of the skin graft, the mucosa was not keratinized and showed an increased thickness of the submucosal connective tissue. For the patient under examination, an acceptable level of oral rehabilitation was achieved using a split skin graft. The follow-up investigation showed stable conditions for both the implants and the graft.

Strain development in 3-unit implant-supported CAD/CAM restorations.

PURPOSE: Passive fit is difficult to achieve in implant-supported restorations with existing superstructure fabrication techniques. The aim of the study presented was to investigate whether computer-generated fixed partial dentures (FPDs) based on optical impressions lead to less strain development than conventionally fabricated FPDs. MATERIALS AND METHODS: A measurement model with 2 implants was set up and strain gauges were attached to the model material mesially and distally adjacent to the implants. Two groups of conventional cementable restorations based on repositioning and pick-up impressions, respectively, and 1 group of CAD/CAM-generated FPDs based on optical impressions were fabricated (n = 10). Strain development during FPD fixation was recorded. In order to compare the different FPD groups with one another, a multivariate analysis of variance (MANOVA) was performed at a level of significance of alpha = .05. RESULTS: The mean strain development at the different strain gauge locations ranged from 80.38 microm/m to 437.11 microm/m. The 2 groups of conventionally fabricated FPDs showed no significant difference in terms of strain development (P = .07). The CAD/CAM-fabricated FPDs revealed a significantly lower strain development than those made from pick-up technique impressions (P = .01). No significant difference could be detected between the FPDs manufactured from repositioning technique impressions and the CAD/CAM-generated restorations (P = .19). CONCLUSION: Within the limitations of the study presented, it can be concluded that restorations fabricated on the basis of optical impressions demonstrate a level of fit which is at least as passive as that of conventional FPDs.

The effect of load cycling on metal ceramic screw-retained implant restorations with unrestored and restored screw access holes.

STATEMENT OF PROBLEM: It has been shown that under cyclic loading, more chipping fractures of the veneer ceramic occur on the occlusal surface of screw-retained implant-supported fixed partial dentures (FPDs) with unrestored screw access holes (SAHs) than in cemented restorations. This lack of stability may result in esthetic and functional problems. PURPOSE: The purpose of this study was to investigate whether, under dynamic loading, fewer chipping fractures occur on the occlusal surface of screw-retained ceramic veneered implant FPDs with restored SAHs than in those with unrestored SAHs. MATERIAL AND METHODS: Twenty screw-retained ceramic veneered 5-unit FPDs were manufactured for a 3-implant situation and divided into 2 groups of 10 unrestored and 10 SAHs restored with adhesive composite resin restorations (Tetric Evo Ceram). A masticatory simulator was used to load the FPDs occlusal to the implant positions for 20,000 cycles with a force of 100 N applied for 1 second, followed by 1 second of no loading. Three prosthodontists evaluated the FPDs using a light microscope and a dental probe. The number of chipping fractures found were analyzed using a generalized linear model with Poisson response and log link function (alpha =.05). RESULTS: Investigators found significantly more chipping fractures in the group of screw-retained FPDs with unrestored SAHs. The rate ratio of unrestored versus restored prostheses was 3.29 (P=.006). CONCLUSIONS: Adhesive composite resin restorations can significantly reduce the number of chipping fractures occurring around the SAHs of screw-retained implant-supported restorations.

Influence of fixation mode and superstructure span upon strain development of implant fixed partial dentures.

PURPOSE: Implant-borne fixed partial dentures (FPDs) should fit passively in order to avoid complications ranging from screw loosening to loss of osseointegration. The aim of this study was to measure the strain development of three-unit and five-unit screw- and cement-retained implant-supported FPDs. Additionally, the influence of the parameters retention mechanism and FPD span were evaluated. MATERIALS AND METHODS: Three Straumann implants were anchored in a measurement model based on a real-life patient situation and strain gauges (SGs) were fixed mesially and distally adjacent to the implants and on the pontics of the superstructures. During cement setting and screw fixation of 40 implant FPDs (10 samples from each group: three-unit cementable; five-unit cementable; three-unit screw-retained; five-unit screw-retained), strain development was recorded. For statistical analysis, multivariate two-sample tests were performed with the level of significance set at p= 0.1. RESULTS: The mean strain values for the four FPD groups at the different SG sites ranged from 26.0 to 637.6 microm/m. When comparing the four groups, no significant differences in strain magnitude could be detected. Similarly, a comparison of the two FPD spans revealed no significant difference (p= 0.18 for cementable FPDs; p= 0.22 for screw-retained FPDs). A comparison of the two fixation modes also revealed no significant difference (p= 0.67 for three-unit FPDs; p= 0.25 for five-unit FPDs). CONCLUSION: FPD span and retention mechanism appear to have only a minor influence on strain development in implant FPDs. As implant-supported restorations have proven to be successful over time, the question arises as to whether an "absolute" passive fit is a prerequisite for successful implant restorations.

Parameters of resonance frequency measurement values: a retrospective study of 385 ITI dental implants.

OBJECTIVES: There is no proven clinical tool to evaluate the amount of osseointegration and stability around dental implants. Therefore, the aim of this retrospective clinical study was to evaluate resonance frequency analysis values of 385 ITI solid screw implants. MATERIAL AND METHODS: Both at implant placement and after healing, implant stability quotients (ISQs) were determined. For statistical analysis, Pearson's correlation coefficients, Welch's two-sample t-tests and paired samples t-tests were computed at a level of significance of alpha=0.05. RESULTS: ISQ values ranged from 39 to 86 at implant placement and from 35 to 89 after healing, showing a significant increase. The highest ISQ values at both stages were obtained in the posterior mandible (P < or = 0.002). After healing, ISQ values in the anterior mandible were significantly higher than in the anterior maxilla (P=0.005). Implant length had a significant influence on ISQ in the anterior mandible (P=0) at insertion and in the anterior (P=0.005) and posterior mandible (P=0.036) after healing. Implant diameter and ISQ at insertion correlated in the anterior mandible (P=0.037). After healing, a significant influence was found for all regions, except the posterior maxilla (P=0.795). With the exception of the anterior maxilla (P=0.542), ISQ at placement had a significant influence on ISQ after healing. In the anterior maxilla (P=0.002) and in the posterior mandible (P=0.007), healing time significantly influenced ISQ after healing. CONCLUSIONS: It appears that only repeated ISQ measurements of a specific implant have some diagnostic benefit, although the parameters influencing the absolute values still remain unclear.

Structural changes in ceramic veneered three-unit implant-supported restorations as a consequence of static and dynamic loading.

OBJECTIVES: Static implant loading caused by non-passive restorations may cause technical complications. As metal-ceramic restorations are most common in implant prosthodontics, the objective of the study was to investigate the effect of static and dynamic loading upon the stability of the ceramic veneer of implant-supported fixed partial dentures (FPDs). METHODS: A total of 10 groups of three-unit implant FPDs with five samples each were investigated in the conditions after fabrication, static loading and dynamic loading (chewing simulator, 20,000 cycles, 100N). The fluorescent penetrant method (FPM) was applied to detect microcracks at the cervical and occlusal aspects of the FPD abutments. Statistical analysis was performed based on the number of microcracks (t-test) and the presence of chipping fractures (Exact Fisher test) with the level of significance set at alpha=0.05. RESULTS: Static and dynamic loading led to an increase both in number of microcracks and frequency of chipping fractures. After static loading, the screw-retained FPDs cast in one piece revealed significantly lower numbers of cervical microcracks than did the cementable restorations fabricated from repositioning technique impressions (p=0.003). The screw-retained FPDs which were fabricated using premachined gold cylinders showed the highest numbers of cracks and chipping fractures both after static and dynamic loading. SIGNIFICANCE: Static loading may damage the ceramic layer of implant-supported restorations. The use of prefabricated components may cause increased numbers of microcracks due to the lack of bonding oxides.

In vitro effect of load cycling on metal-ceramic cement- and screw-retained implant restorations.

STATEMENT OF PROBLEM: In implant prosthodontics, restorations can either be cement- or screw-retained. Aside from passivity of fit, esthetics, and retrievability, the occlusal opening of the screw-access hole (SAH) is a major difference between the 2 types of restorations. In veneered fixed partial dentures (FPDs), the SAH forms a discontinuity of the ceramic layer and may be an origin for chipping fractures. PURPOSE: The objective of this study was to investigate whether more chipping fractures occur during dynamic loading on the occlusal surface of screw-retained ceramic-veneered implant FPDs than in cement-retained restorations. MATERIAL AND METHODS: Ten cement-retained and 10 screw-retained ceramic veneered 5-unit FPDs were manufactured for a 3-implant situation. A masticatory simulator was used for loading the occlusal surface of the FPDs to the implant positions for 20,000 cycles with a force of 100 N applied for 1 second followed by 1 second of no loading. For analysis, 3 clinicians evaluated the FPDs using a light microscope and a dental probe. The numbers of chipping fractures found were analyzed by means of a generalized linear model with Poisson response (alpha=.05). RESULTS: The investigators found significantly more chipping fractures in the group of screw-retained FPDs, the rate ratio of screw-retained FPDs versus cement-retained FPDs being greater than 1 with a P value of .0023. CONCLUSION: The SAH of screw-retained implant FPDs forms a weak point of the ceramic layer.