Implant-supported Crowns Research Articles

Comparison of wear and fracture resistance of additively and subtractively manufactured screw-retained, implant-supported crowns

Statement of problemAdditively manufactured resins indicated for fixed definitive prostheses have been recently marketed. However, knowledge on their wear and fracture resistance when fabricated as screw-retained, implant-supported crowns and subjected to artificial aging is limited. PurposeThe purpose of this in vitro study was to evaluate the volume loss, maximum wear depth, and fracture resistance of screw-retained implant-supported crowns after thermomechanical aging when fabricated using additively and subtractively manufactured materials. Material and methodsTwo additively manufactured composite resins (Crowntec [CT] and VarseoSmile Crown Plus [VS]) and 2 subtractively manufactured materials (1 reinforced composite resin, Brilliant Crios [BC] and 1 polymer-infiltrated ceramic network, Vita Enamic [EN]) were used to fabricate standardized screw-retained, implant-supported crowns. After fabrication, the crowns were cemented on titanium base abutments and then tightened to implants embedded in acrylic resin. A laser scanner with a triangular displacement sensor (LAS-20) was used to digitize the pre-aging state of the crowns. Then, all crowns were subjected to thermomechanical aging (1.2 million cycles under 50 N) and rescanned. A metrology-grade analysis software program (Geomagic Control X 2020.1) was used to superimpose post-aging scans over pre-aging scans to calculate the volume loss (mm3) and maximum wear depth (mm). Finally, all crowns were subjected to a fracture resistance test. Fracture resistance and volume loss were evaluated by using 1-way analysis of variance and Tukey Honestly significant difference (HSD) tests, whereas the Kruskal-Wallis and Dunn tests were used to analyze maximum wear depth. Chi-squared tests were used to evaluate the Weibull modulus and characteristic strength data (α=.05). ResultsMaterial type affected the tested parameters (P<.001). CT and VS had higher volume loss and maximum wear depth than BC and EN (P<.001). EN had the highest fracture resistance among tested materials (P<.001), whereas BC had higher fracture resistance than CT (P=.011). The differences among tested materials were not significant when the Weibull modulus was considered (P=.199); however, VE had the highest characteristic strength (P<.001). ConclusionsAdditively manufactured screw-retained, implant-supported crowns had higher volume loss and maximum wear depth. All materials had fracture resistance values higher than the previously reported masticatory forces of the premolar region; however, the higher characteristic strength of the subtractively manufactured polymer-infiltrated ceramic network may indicate its resistance to mechanical complications.

The effect of different abutment and restorative crown materials on stress distribution in single-unit implant-supported restorations: A 3D finite element stress analysis.

To evaluate the effect of restorative materials with or without resin content, modeled on zirconia and titanium abutment materials, on the stress distribution on the alveolar bone, implant, and prosthetic crowns with a 3D finite element stress analysis. Titanium and zirconia abutments were combined with three implant-supported crown materials (polymer infiltrated hybrid ceramic (PICN), lithium disilicate (LD), and zirconia-reinforced lithium silicate (ZLS)) to create six experimental groups. The 40×30×20mm alveolar bone, 3.75× 10mm implant, esthetic abutment, and maxillary first premolar crown bonded over the abutment were the components of the finite element models. On the lingual cusp of the crown, the 150 N occlusal loading was applied in the buccolingual direction at a 30° angle. Equivalent von Mises stress and maximum and minimum principal stresses were used for both the qualitative and quantitative evaluation of the stress distribution of the created models. The von Mises stress in implant and abutment did not differ according to the crown materials. The use of a zirconia abutment resulted in higher von Mises stress values in the abutment but lower stress values in the implant. The highest stress values were obtained in ZLS (196.65MPa) and LD (194.05MPa) crowns. The use of titanium abutments, regardless of crown materials, resulted in higher von Mises stress values in restorative crowns than in zirconia abutments. The principal stress values in alveolar bone showed similar distribution and concentration in all models. Changes in crown material did not affect stress distribution in the implant and peripheral bone. However, the zirconia esthetic abutment resulted in a lower stress concentration on the implant.

Assessment of physiological posterior-tooth displacement under habitual occlusal force by intraoral scanning using implant-supported crowns as the reference

Statement of problemStudies that have used digital methods to quantitatively evaluate physiological tooth displacement under occlusal force are sparse. PurposeThe purpose of this clinical study was to measure physiological posterior tooth displacement under occlusal force by intraoral scanning and reverse engineering technology by using implants as the reference. Material and methodsA total of 14 participants received 15 implant-supported single mandibular first molar crowns. The surface data of maxillary and mandibular posterior teeth (U1 and L1) and the buccal occlusal data in the maximum intercuspal position (MIP) with habitual occlusal force were obtained by using an intraoral scanner (TRIOS 3, v20.1.2). The U1 and L1 data were segmented into single teeth, which were then aligned to the buccal occlusal data by using the “best-fit alignment” command to build the data under occlusal force (U2 and L2). U1 and L1 data were compared with U2 and L2 data to calculate the centroid and functional cusp vertex displacements and the long axis deflections of the second premolars and second molars, taking the first molar as the reference. The medians, and first quartile (Q1), third quartile (Q3) of the above data were reported, and the Shapiro-Wilk and Wilcoxon tests were used to analyze the differences (α=.05). ResultsUnder occlusal force, the median (Q1, Q3) centroid displacements of posterior teeth ranged from 61 (52, 101) μm to 146 (80, 186) μm; the functional cusp vertex displacements ranged from 82 (62, 117) μm to 146 (98, 189) μm, and the long axis deflections ranged from 0.45 (0.25, 0.87) degrees to 1.03 (0.52, 1.41) degrees. Mandibular second premolars displaced lingually, mesially, and apically; mandibular second molars displaced distally and apically; and maxillary second premolars and second molars displaced lingually and apically. ConclusionsA digital method taking implant-supported single crowns as the reference was used to demonstrate physiological posterior-tooth displacement under habitual occlusal force.

Influence of diameter in the stress distribution of extra-short dental implants under axial and oblique load

Aim: This study evaluated the influence of a wide diameter on extra-short dental implant stress distribution as a retainer for single implant-supported crowns in the atrophic mandible posterior region under axial and oblique load. Methods: Four 3D digital casts of an atrophic mandible, with a single implant-retained crown with a 3:1 crown-to-implant ratio, were created for finite element analysis. The implant diameter used was either 4 mm (regular) or 6 mm (wide), both with 5 mm length. A 200 N axial or 30º oblique load was applied to the mandibular right first molar occlusal surface. The equivalent von Mises stress was recorded for the abutment and implant, minimum principal stress, and maximum shear stress for cortical and cancellous bone. Results: Oblique load increased the stress in all components when compared to axial load. Wide diameter implants showed a decrease of von Mises stress around 40% in both load directions at the implant, and an increase of at least 3.6% at the abutment. Wide diameter implants exhibited better results for cancellous bone in both angulations. However, in the cortical bone, the minimum principal stress was at least 66% greater for wide than regular diameter implants, and the maximum shear stress was more than 100% greater. Conclusion: Extra-short dental implants with wide diameter result in better biomechanical behavior for the implant, but the implications of a potential risk of overloading the cortical bone and bone loss over time, mainly under oblique load, should be investigated.

Influence of anatomical changes in implant-supported crowns of maxillary central incisors on the functional state

BACKGROUND: Immediate implant placement and immediate loading after maxillary central incisor extraction are of great importance. Implant placement with immediate loading is the most preferred method of treatment in the long term. The anatomical constrictions of the maxilla make implant placement difficult. To achieve primary stability and make a screw-retained crown, dental surgeons are forced to fix the implant placing it toward the palatal wall. When the implant is placed this way, the crown will be bulkier than the one of the extracted tooth. This change in anatomy can lead to patient discomfort and some parafunctions (in speech, chewing, etc.).&#x0D; AIM: To assess the potential discomfort in patients with changes in the crown anatomy of maxillary central incisors after implant-supported prosthetics.&#x0D; METHODS: Fifty students (25 men and 25 women) underwent intraoral scanning with the 3Shape scanner. A possible increase in the crown volume was simulated in ExoCAD at a rate of an implant + titanium base + layer of structural material with zirconium dioxide as an example, on average equal to 34 mm. Onlays imitating the increased crown volume were milled and fixed in the oral cavity of the participants on tooth 1.1, and further examinations were conducted.&#x0D; RESULTS: The examination revealed that the crown anatomy change brought some discomforts in most of the respondents whose speech and eating were affected.&#x0D; CONCLUSION: The results reveal that a change in the anatomical shape of the crown during implant-supported prosthetics can affect vital functions and cause discomfort. More attention is needed to implant placement planning, taking into account further prosthetics in the esthetic area. Therefore, the use of angulated implants is encouraged.

Effects of crown contour on artificial biofilm removal efficacy with interdental cleaning aids: An in vitro study.

To evaluate the efficacy of various interdental cleaning aids for artificial biofilm removal on different implant-supported crown designs. Mandibular models with missing first molar were fabricated and installed with single implant analogs and loaded with crowns of different designs (concave, straight, and convex). Artificial biofilm was made with occlusion spray. Thirty volunteers (periodontists, dental hygienists, and laypersons) were asked to clean the interproximal areas. The crowns were unscrewed and photographed in a standardized setting. The outcome was measured by the cleaning ratio which represents the cleaned surfaces in relation to the area of the tested surface. A significant difference in favor of concave crown (p < .001) on the basal surface was cleaned by all tools, except the water flosser. There was evidence of an overall effect of "cleaning tool," "surface," and "crown design" (p < .0001) except for the "participant" factor. The mean cleaning ratio for each cleaning tool and overall combined surfaces were (in%): dental floss: 43.02 ± 23.93, superfloss: 42.51 ± 25.92, electric interspace brush: 36.21 ± 18.78, interdental brush: 29.10 ± 15.95, and electric water flosser: 9.72 ± 8.14. Dental floss and superfloss were significantly better (p < .05) than other tools in removing plaque. Concave crown contour had the greatest artificial biofilm removal, followed by straight and convex crowns at the basal surface. Dental floss and superfloss were the most effective interdental cleaning devices for artificial biofilm removal. None of the tested cleaning devices were able to completely remove the artificial biofilm from the interproximal/basal surfaces.

Influence of Mechanical Cycling on Torque Values of Tapped-In and Screw-In Implant-Supported Crowns.

This study investigated the influence of mechanical cycling on screwed-in and tappedin implants restored with screw-retained metallic crowns. Three implant-abutmentcrown systems were evaluated: T1 (multi abutment) and T2 (standard abutment) received tapped-in abutments and S received a screwed-in abutment. The specimens were subjected to two million cycles of 0-150 N load, at 2 Hz, 30° inclination in a dry medium, and torque evaluation. Survival and removal torque were analyzed using chisquare, ANOVA, followed by Tukey's test. Differences between installation and removal torque were determined using a T-test for dependent samples. Analyses were performed in SPSS, considering α = 0.05. All specimens survived mechanical cycling in S, 40% in T1, 80% in T2 (p=0.008). Failures occurred due to loosening of the crown screw. A significant decrease in torque (p=0.000) was found. Group T1 had the lowest removal torque (1.6 ± 0.84 N.Cm²), followed by T2 (3 ± 1.49 N.Cm²) and S (6.3 ± 1.16 N. Cm²), and a statistical difference was found between Groups T1 and S. Both types of implantabutment connections were stable and can be considered for rehabilitative treatment, but failure and removal torque were influenced by the design of prosthetic abutment. Crowns were more susceptible to becoming loose in tapped-in systems.

Comparative effect of rehabilitation with three different treatment modalities for single missing molar on the brain activity - A prospective clinical study.

The effect of single tooth replacement in brain activity is indistinct. Hence, to evaluate the changes in brain activity of individuals with a single missing mandibular molar replaced with removable, tooth-supported fixed, and implant prostheses in the static and post-masticatory phase. 24 patients with unilateral missing mandibular first molar were rehabilitated with a resin removable prosthesis (RPD) and then divided into two groups of 12 each; group A rehabilitated with implants and group B with 3-unit tooth-supported fixed partial dentures (FPD). EEG was taken during the three phases of assessment (i)before insertion of any prosthesis(N0), (ii)after insertion of an RPD(N1), and (iii)after cementation of an FPD or an implant crown(F2). The effect of the bite force with RPD(N1M) and FPD or implant prosthesis(F2M) on alpha waves was evaluated by recording EEG immediately after chewing gum for 30 seconds. The improvement of the amplitude of alpha waves before and after insertion of the prosthesis between group A and B showed a significant difference (P<.05) with the highest mean value of 158.3 μV, 147.9 μV, 182.1 μV in pair F2-N0, F2-N1, F2M-N1M respectively for Group A. Similarly, for the power of alpha waves between group A and B, a significant statistical difference (P<.05) with the highest mean value of 30.3 dB, 28.9 dB, 36.9 dB, 11.2 dB in pair F2-N0, F2-N1, F2M-N1M, F2M-F2 respectively were observed for Group A. There was no statistically significant increase in pair N0-N1(P<.05). Replacement of a single missing tooth enhanced brain activity and was highest with an implant-supported crown. Int J Prosthodont 2023. doi: 10.11607/ijp.7936.

Digital versus conventional prosthetic workflow for dental students providing implant-supported single crowns: A randomized crossover study

Statement of problemDigital scanning has become popular and has been reported to be more comfortable for patients and equally or more accurate than conventional impression techniques. However, clinical evidence to support the advantages of digital scanning is sparse. PurposeThe purpose of this randomized crossover study was to examine and compare the patient and provider perceptions of digital scanning and conventional impression making for implant-supported single crowns (ISSCs) provided by dental students under supervision. Furthermore, the quality and patient-reported outcome of the definitive restorations were compared. Material and methodsForty participants in need of a single tooth replacement were enrolled. Three months after initial implant placement, recordings were made for implant-supported crowns. The participants were randomized into a conventional or a digital group but underwent both procedures. Only the designated impression or scan was sent to the dental laboratory technician to be processed. All participants and students were asked questions concerning which technique they preferred. Furthermore, the participants filled out an oral health impact profile (OHIP-14) questionnaire before and after treatment. The restorations’ esthetic and technical quality was evaluated using the Copenhagen Index Score (CIS). ResultsThe participants preferred the digital technique (80%) over the conventional technique (2%), while 18% of the participants had no preference. The participants were bothered significantly more (P<.001), experienced significantly more shortness of breath (P<.001), and were significantly more anxious during the conventional impression than during the digital scan (P<.001). Most students also preferred the digital technique (65%) over the conventional technique (22%), and 13% had no preference. The students found that the conventional impression procedure was less time-consuming but more uncertain in comparison with the digital technique. The digital technique was perceived as significantly more impractical than the conventional technique (P<.05). The results from CIS showed no significant difference in the quality of the restorations. Following treatment, the OHIP-14 scores showed a significant drop, suggesting an increase in oral health-related quality of life (P<.001). ConclusionsThe perceptions of the participants and students of the digital intraoral scanning were significantly better than those of the conventional technique. No significant differences in the quality of the restorations or OHIP scores were observed using the two recording techniques.

In vitro fatigue and fracture testing of temporary materials from different manufacturing processes in implant-supported anterior crowns.

The aim of this study was to investigate the in vitro fatigue and fracture force of temporary implant-supported anterior crowns made of different materials with different abutment total occlusal convergence (TOC), with/without a screw channel, and with different types of fabrication. One hundred ninety-two implant-supported crowns were manufactured (4° or 8° TOC; with/without screw channel) form 6 materials (n = 8; 2 × additive, 3 × subtractive, 1 × automix; reference). Crowns were temporarily cemented, screw channels were closed (polytetrafluoroethylene, resin composite), and crowns were stored in water (37°C; 10days) before thermal cycling and mechanical loading (TCML). Fracture force was determined. Kolmogorov-Smirnov, ANOVA; Bonferroni; Kaplan-Meier; log-rank; α = 0.05. Failure during TCML varied between 0 failures and total failure. Mean survival was between 1.8 × 105 and 4.8 × 105 cycles. The highest impact on survival presented the material (η2 = 0.072, p < .001). Fracture forces varied between 265.7 and 628.6 N. The highest impact on force was found for the material (η2 = 0.084, p < .001). Additively and subtractively manufactured crowns provided similar or higher survival rates and fracture forces compared to automix crowns. The choice of material is decisive for the survival and fracture force. The fabrication is not crucial. A smaller TOC led to higher fracture force. Manually inserted screw channels had negative effects on fatigue testing. The highest stability has been shown for crowns with a low TOC, which are manufactured additively and subtractively. In automix-fabricated crowns, manually inserted screw channels have negative effects.

Using Distracting Capsule and Resin Bridge for Segmental Distraction Osteogenesis for an Implant-supported Ceramic Crown in the Esthetic Zone of the Anterior Maxilla: 10-year Clinical Report

Implant therapy for the esthetic zone of the anterior maxilla is a challenge when the support is deficient with the loss of alveolar bone. This article presents a 10-year clinical report of implant therapy for 23-year-old woman with a significant loss of alveolar bone following a loss of the maxillary right central incisor. The central incisor was restored with a screw-retained single implant ceramic crown where the implant site was augmented through sectional distraction osteogenesis involving a distracting capsule and a resin bridge to restore the missing span and serve as an anchorage for distraction. At the 10-year follow-up appointment, the implant-supported crown was stable with no signs or symptoms of biological and/or mechanical complications.

Amount of Residual Cement at the Margin of Implant-Supported Crowns Cemented Using the Polytetrafluoroethylene Tape, Replica Technique, and Conventional Cementation Technique

Background: This study compared the amount of residual cement at the margin of implant-supported crowns cemented using the polytetrafluoroethylene (PTFE) tape, replica technique, and conventional cementation technique. Methods: In this in vitro experimental study, a mandibular model underwent full-arch scanning. The right first molar tooth was eliminated on the scan using Exocad software, and a regular implant analog was modelled using the Exocad model creator. The designed abutment was then printed. The implant analog was fixed in place with acrylic resin and scanned using a scan body. A full-zirconia custom abutment was then designed by Exocad. Abutments were fabricated using zirconia and sintered. Twenty-seven resin crowns were fabricated for the abutments, and their fit was assessed. Nine crowns were conventionally cemented by filling half of the crown space with cement, 9 crowns were cemented using PTFE tape, and the remaining 9 were first placed on a resin replica and then cemented on the abutments. The residual cement was weighed using a digital scale, and the groups were compared by one-way ANOVA and LSD test (α=0.05). Results: The amount of residual cement was significantly different among the three groups, indicating that the amount of residual cement was the highest in conventional cementation, and the lowest in the replica group (P &lt; 0.05). Pairwise comparisons showed significant differences between all groups (P &lt; 0.05). Conclusions: The replica technique followed by the PTFE tape resulted in the minimum amount of residual cement at the margin of implant-supported cement-retained crowns and are preferred for use in the clinical setting.

Stress distribution on implant- supported zirconia crown of maxillary first molar: effect of oblique load on natural and antagonist tooth

This study evaluated the stress distribution on an implant-supported zirconia crown of a mandibular first molar subjected to oblique loading by occlusal contact with the natural maxillary first molar by using the 3D finite element method. Two virtual models were made to simulate the following situations: (1) occlusion between maxillary and mandibular natural first molars; (2) occlusion between zirconia implant-supported ceramic crown on a mandibular first molar and maxillary natural first molar. The models were designed virtually in a modeling program or CAD (Computer Aided Design) (Rhinoceros). An oblique load of 100 N was uniformly applied to the zirconia framework of the crown. The results were obtained by the Von Mises criterion of stress distribution. Replacement of the mandibular tooth by an implant caused a slight increase in stress on portions of the maxillary tooth roots. The crown of the maxillary model in occlusion with natural antagonist tooth showed 12% less stress when compared with the maxillary (model in occlusion with the) implant-supported crown. The mandibular crown of the implant show 35% more stress when compared with the mandibular antagonist crown on the natural tooth. The presence of the implant to replace the mandibular tooth increased the stresses on the maxillary tooth, especially in the region of the mesial and distal buccal roots.

Stress Distribution in Peri-implant Bone in the Replacement of Molars with One or Two Implants: A Finite Element Analysis.

In most cases, insertion of single implants with a standard diameter is used to replace a molar tooth but placing two implants with a narrow diameter seems to be a viable treatment modality to withstand functional and biomechanical forces. This study aimed to evaluate and compare stress distribution in the bone surrounding a single molar area rehabilitated by a single implant versus two implants with a narrow diameter. The study was conducted by computer-aided in vitro modeling. The initial model used a single implant, 4.8 mm wide in diameter, inserted with a 3.9-mm distance from both sides and 12.6-mm mesiodistal space. The second model used two 3.3-mm narrow-sized implants with a 3-mm distance from one another, 1.5 mm from both sides, and a 12.6-mm mesiodistal space. Following the completion of these models, a 100-N force was exerted obliquely, once in three locations and once in the mesial aspect of the implant-supported crown. Stress distribution was then measured using finite element analysis (FEA) with ANSYS Workbench software package in both models. The maximum stress in the bone around the single implant was less than that around double implants. The maximum stress of cortical bone in three-point loading was lower than mesial loading either in one (146.7 vs. 126.72 MPa) or two implants model (186.8 vs. 139.24). According to the results, because of more cortical bone contact area, the stress of surrounding bone in wide implant was decreased.

The Complete Digital Workflow in Fixed Prosthodontics Updated: A Systematic Review

Digital applications have changed therapy in prosthodontics. In 2017, a systematic review reported on complete digital workflows for treatment with tooth-borne or implant-supported fixed dental prostheses (FDPs). Here, we aim to update this work and summarize the recent scientific literature reporting complete digital workflows and to deduce clinical recommendations. A systematic search of PubMed/Embase using PICO criteria was performed. English-language literature consistent with the original review published between 16 September 2016 and 31 October 2022 was considered. Of the 394 titles retrieved by the search, 42 abstracts were identified, and subsequently, 16 studies were included for data extraction. A total of 440 patients with 658 restorations were analyzed. Almost two-thirds of the studies focused on implant therapy. Time efficiency was the most often defined outcome (n = 12/75%), followed by precision (n = 11/69%) and patient satisfaction (n = 5/31%). Though the amount of clinical research on digital workflows has increased within recent years, the absolute number of published trials remains low, particularly for multi-unit restorations. Current clinical evidence supports the use of complete digital workflows in implant therapy with monolithic crowns in posterior sites. Digitally fabricated implant-supported crowns can be considered at least comparable to conventional and hybrid workflows in terms of time efficiency, production costs, precision, and patient satisfaction.

Evaluation of debonding force of screw-retained lithium disilicate implant-supported crowns cemented to abutments of different designs and surface treatments

Statement of problemStraight preparable abutments provide an alternative to titanium bases (Ti-bases) for single-unit screw-retained implant-supported restorations. However, the debonding force between crowns with a screw access channel cemented to preparable abutments and Ti-bases of different designs and surface treatments is unclear. PurposeThe purpose of this in vitro study was to compare the debonding force of screw-retained lithium disilicate implant-supported crowns cemented to straight preparable abutments and Ti-bases of different designs and surface treatments. Material and methodsForty laboratory implant analogs (Straumann Bone Level) were embedded into epoxy resin blocks that were randomly divided into 4 groups (n=10 each) according to the abutment type used: CEREC group, Variobase group, airborne-particle abraded Variobase group, and airborne-particle abraded straight preparable abutment group. All specimens were restored with lithium disilicate crowns and cemented with resin cement to the corresponding abutments. They were thermocycled (from 5 to 55 °C for 2000 cycles) followed by cyclic loading (120 000 cycles). The tensile forces required to debond the crowns from the corresponding abutments were measured (N) by using a universal testing machine. The Shapiro–Wilk test of normality was used. Comparison between the study groups was done with 1-way ANOVA (α=.05). ResultsTensile debonding force values were significantly different according to the type of abutment used (P<.05). The highest retentive force value was recorded in the straight preparable abutment group (928.1 ±222.2 N) followed by the airborne-particle abraded Variobase group (852.6 ±164.6 N), and the CEREC group (498.8 ±136.6 N); the lowest value was reported in the Variobase group (158.6 ±85.2 N). ConclusionsThe retention of screw-retained lithium disilicate implant-supported crowns cemented to airborne-particle abraded straight preparable abutments is significantly higher than to non-surface treated Ti-bases and similar to airborne-particle abraded ones. Abrading abutments with 50-mm Al2O3 significantly increased the debonding force of the lithium disilicate crowns.

Evaluation of two different occlusal patterns on single posterior implant-supported crowns: A 12-month prospective study of occlusal analysis

Statement of problemAccording to the concept of implant-protected occlusion, light occlusion and late contact could prevent implants from occlusal overload. However, clinical data demonstrating how light occlusion differs from normal occlusion are lacking. PurposeThe purpose of this prospective clinical study was to characterize the occlusal variation of single posterior implant-supported crowns with or without light occlusion. Material and methodsParticipants with a single missing posterior maxillary or mandibular molar who were to receive implant-supported zirconia ceramic crowns were enrolled. The participants were divided into a light occlusion group, in which a 12-μm articulating film could be removed from the implant-supported crown and opposing natural teeth under the intercuspal position, and a normal occlusion group, in which the articulating film could not be removed. All participants underwent occlusal examinations using the T-scan III system, answered a satisfaction questionnaire using a visual analog scale (VAS), and received regular follow-ups. The participants were evaluated at 0.5, 3, 6, and 12 months after implant-supported crown delivery. The relative occlusal force of the implant-supported crowns, mesial teeth, control teeth (corresponding natural tooth on the dentition contralateral to each implant), and the occlusal contact time of implant-supported crowns were recorded. Moreover, the asymmetry index of the occlusal force and the VAS score were calculated. Two independent-sample tests were used to compare the 2 groups. The Wilcoxon rank sum and Mann‒Whitney tests were used to compare nonnormally distributed data (α=.001). ResultsFifty study participants with a mean ±standard deviation age of 36.97 ±7.34 years (23 men and 27 women aged 20 to 50 years) were followed for 0.5 to 12 months. No obvious complications of overloading were observed in either group. The mean ±standard deviation of the relative occlusal force of implant-supported crowns in the light occlusion group (from 4.91 ±3.52% to 10.34 ±4.35%) was always lower than that in the normal occlusion group (from 10.45 ±4.32% to 18.15 ±4.80%), while the mean ±standard deviation of the occlusal contact time in the light occlusion group (from 0.38 ±0.26 seconds to 0.10 ±0.07 seconds) was significantly later than that in the normal occlusion group (from 0.12 ±0.08 seconds to 0.04 ±0.02 seconds) (P<.001). The value of the asymmetry index of occlusal force remained within the normal range (10%). The VAS score in the normal occlusion group was significantly higher than that in the light occlusion group (P<.001). ConclusionsProviding light occlusion to reduce occlusal force and delay the contact time was not stable over time. The relative occlusal force and occlusal contact time showed a similar development trend in both groups, and no obvious signs of occlusal overloading were observed in this study. Long-term follow-up is necessary for implant-supported prostheses because of the continuous increase in occlusal force.

Tooth morphology fusion technique is more accurate than conventional technique in transferring morphology of provisional to definitive screw-retained, implant-supported crown: A preliminary intervention study.

To compare the accuracy of the tooth morphology fusion (TMF) digital technique and customized impression transfer coping (conventional) technique when transferring the morphology of a provisional crown to a definitive screw-retained implant-supported crown. Six cases of partial edentulism (one anterior and five posterior) treated with oral implant placement in our clinic for the loss of three or fewer teeth in the maxilla or mandible between April 2017 and September 2018 were included. After implant placement and re-entry surgery, provisional restorations were made and adjusted to obtain the ideal morphology. Two definitive restorations were constructed by transferring the complete morphology of the provisional restorations, including the subgingival contour, using the TMF digital and conventional techniques. Three sets of surface morphological data were obtained using a desktop scanner. The three-dimensional total discrepancy volume (TDV) between the provisional restoration (reference) and the two definitive restorations was digitally measured by overlapping the surface data of the stone cast using the Boolean operation. Each TDV ratio (%) was calculated by dividing the TDV by the volume of provisional restoration. The median TDV ratios for TMF and conventional techniques were compared using the Wilcoxon signed-rank test. The median TDV ratio between provisional and definitive restorations constructed using the TMF digital technique (8.05%) was significantly lower than that obtained using the conventional technique (13.56%, P < 0.05). In this preliminary intervention study, the TMF digital technique was more accurate than the conventional technique for the transfer of morphology from provisional to definitive prosthesis.

Stress distribution in resin-based CAD-CAM implant-supported crowns.

This study aimed to evaluate the influence of new resin-based CAD-CAM implant-supported materials on posterior crown restoration stress and strain concentrations. A previous 3D implant model was edited to receive a cement-retained posterior crown manufactured with different CAD/CAM materials (Estelite P Block, Estelite Block II or Estelite Layered Block). Each solid model was exported to the computer-aided engineering software and submitted to the finite element analysis of stress and strain. Material properties were assigned to each solid with isotropic and homogeneous behavior according to the manufacturer information. A vertical load of 600N was applied in the occlusal region of the crown, via a simulated food bolus, and stress was calculated in Von Misses (σVM) for the implant, abutment and screw, Maximum (σMAX) Principal Stresses for the crown and microstrain for the bone. All simulated materials showed acceptable stresses levels with a similar stress pattern among the models. At the crown intaglio region and cement layer, however, differences were observed: Estelite P Block showed a lower tensile and shear stresses magnitude when compared to other resin-based materials with lower elastic modulus. The stress effect of different resin-based CAD-CAM implant-supported crowns is predominant in the crown and cement layer, with Estelite P Block showing 7.4% versus 9.3% and 9.2% for Estelite Block II and Estelite Layered Block of crown failure risk.

Evaluation of the effect of oral health care product on the reverse torque value of the titanium prosthetic screw of an implant-supported crown following cyclic loading

Purpose of the study: To comparatively evaluate in vitro the effect of oral health care product on the reverse torque value of the titanium prosthetic screw of an implant-supported crown following cyclic loading. Materials and methods: Ten titanium screw-retained implant Co-Cr crowns without application of oral health care product (Group I) and ten titanium screw-retained implant Co-Cr crowns with the application of oral health care product (GC Tooth Mousse) (Group II) were connected to their respective analogs and prosthetic screws were torqued to 30 Ncm using a digital torque meter. Reverse Torque Values were measured before cycling loading and all the twenty samples were subjected to a cyclic loading simulating six months’ duration of the function. Reverse Torque Values were subsequently measured postcyclic loading. The results were analyzed using the Paired ‘t’ test and the Independent ‘t’ test. Results: The mean precyclic loading reverse torque values were 26.12 Ncm (Group I) and 26.57 Ncm (Group II) and the mean postcyclic loading reverse torque values were 22.49 Ncm (Group I) and 24.10 Ncm (Group II). There was no significant loss of preload for Group II test samples prior to cyclic loading compared to Group I test samples. Cyclic loading resulted in reduction of reverse torque values for both Group I and Group II test samples, indicating screw loosening. After cyclic loading, Group II test samples showed significantly higher detorque value than Group I test samples. Conclusion: Cyclic loading resulted in screw loosening in both test groups. Screw loosening was found to be significantly less for Co-Cr prosthetic screw-retained implant crown with the application of GC Tooth Mousse than Co-Cr prosthetic screw-retained implant crown without application of GC Tooth Mousse.