Experimental evaluation of stress distribution with narrow diameter implants: A finite element analysis.

STATEMENT OF PROBLEM: Narrow diameter implants were developed to allow placement in narrow alveolar ridges. Clinicians may have concerns about the durability and function of such implants. PURPOSE: The purpose of this finite element study was to compare the stress values occurring on the implant and at the implant bone interface after the application of the static and dynamic forces on narrow diameter, titanium and titanium-zirconia implants in the maxillary and mandibular second premolar region. MATERIAL AND METHODS: Titanium (Ti) and titanium-zirconium (Ti-Zr) narrow diameter implants (3.3 mm in diameter, 10 mm in length) were simulated in the maxillary and mandibular second premolar region, and metal-ceramic crown restorations were designed. Forces of 100 N were applied to crowns in a vertical and oblique (45-degree angle to the long axis) direction. Maximum and minimum principal stresses in the cortical and trabecular bone and the von Mises stresses and fatigue strength of the implants were evaluated with 3-dimensional finite element analysis. RESULTS: In vertical and oblique static loading, Ti and Ti-Zr implants showed similar stress distribution within the same jaw models. However, the von Mises stresses in Ti-Zr implants were slightly higher than for Ti implants in all models. In oblique static and dynamic loading, all stresses were found higher than vertical loading, and fatigue failure results were found to be more critical than vertical forces. CONCLUSIONS: Based on a numerical simulation, Ti and Ti-Zr alloys can be used successfully as narrow diameter implants in the second premolar area.

Influence of different surface treatments on bond strength of novel CAD/CAM restorative materials to resin cement.

PURPOSE: To evaluate the effects of different surface treatments on the bond strength of novel CAD/CAM restorative materials to resin cement by four point bending test. MATERIALS AND METHODS: The CAD/CAM materials under investigation were e.max CAD, Mark II, Lava Ultimate, and Enamic. A total of 400 bar specimens (4×1.2×12 mm) (n=10) milled from the CAD/CAM blocks underwent various pretreatments (no pretreatment (C), hydrofluoric acid (A), hydrofluoric acid + universal adhesive (Scotchbond) (AS), sandblasting (Sb), and sandblasting + universal adhesive (SbS)). The bars were luted end-to-end on the prepared surfaces with a dual curing adhesive resin cement (Variolink N, Ivoclar Vivadent) on the custom-made stainless steel mold. Ten test specimens for each treatment and material combination were performed with four point bending test method. Data were analyzed using ANOVA and Tukey's test. RESULTS: The surface treatment and type of CAD/CAM restorative material showed a significant effect on the four point bending strength (FPBS) (P<.001). For LDC, AS surface treatment showed the highest FPBS results (100.31 ± 10.7 MPa) and the lowest values were obtained in RNC (23.63 ± 9.0 MPa) for control group. SEM analyses showed that the surface topography of CAD/CAM restorative materials was modified after treatments. CONCLUSION: The surface treatment of sandblasting or HF acid etching in combination with a universal adhesive containing MDP can be suggested for the adhesive cementation of the novel CAD/CAM restorative materials.

Numerical assessment of bone remodeling around conventionally and early loaded titanium and titanium-zirconium alloy dental implants.

The aim of this study was to investigate conventionally and early loaded titanium and titanium-zirconium alloy implants by three-dimensional finite element stress analysis. Three-dimensional model of a dental implant was created and a thread area was established as a region of interest in trabecular bone to study a localized part of the global model with a refined mesh. The peri-implant tissues around conventionally loaded (model 1) and early loaded (model 2) implants were implemented and were used to explore principal stresses, displacement values, and equivalent strains in the peri-implant region of titanium and titanium-zirconium implants under static load of 300 N with or without 30° inclination applied on top of the abutment surface. Under axial loading, principal stresses in both models were comparable for both implants and models. Under oblique loading, principal stresses around titanium-zirconium implants were slightly higher in both models. Comparable stress magnitudes were observed in both models. The displacement values and equivalent strain amplitudes around both implants and models were similar. Peri-implant bone around titanium and titanium-zirconium implants experiences similar stress magnitudes coupled with intraosseous implant displacement values under conventional loading and early loading simulations. Titanium-zirconium implants have biomechanical outcome comparable to conventional titanium implants under conventional loading and early loading.

CAD/CAM glass ceramics for single-tooth implant crowns: a finite element analysis.

PURPOSE: To evaluate the load distribution of CAD/CAM mono-ceramic crowns supported with single-tooth implants in functional area. MATERIALS AND METHODS: A 3-dimensional numerical model of a soft tissue-level implant was constructed with cement-retained abutment to support glass ceramic machinable crown. Implant-abutment complex and the retained crown were embedded in a Ø 1.5 × 1.5 cm geometric matrix for evaluation of mechanical behavior of mono-ceramic CAD/CAM aluminosilicate and leucite glass crown materials. Laterally positioned axial load of 300 N was applied on the crowns. Resulting principal stresses in the mono-ceramic crowns were evaluated in relation to different glass ceramic materials. RESULTS: The highest compressive stresses were observed at the cervical region of the buccal aspect of the crowns and were 89.98 and 89.99 MPa, for aluminosilicate and leucite glass ceramics, respectively. The highest tensile stresses were observed at the collar of the lingual part of the crowns and were 24.54 and 25.39 MPa, respectively. CONCLUSION: Stresses induced upon 300 N static loading of CAD/CAM aluminosalicate and leucite glass ceramics are below the compressive strength of the materials. Impact loads may actuate the progress to end failure of mono-ceramic crowns supported by metallic implant abutments.

Comparative assessments, meta-analysis, and recommended guidelines for reporting studies on histomorphometric bone-implant contact in humans.

PURPOSE: To evaluate factors that have an influence on histomorphometric bone-to-implant contact (BIC) of dental implants in humans. MATERIALS AND METHODS: Using inclusion/exclusion criteria, eligible studies were searched in five databases and handsearched in 11 journals. A total of 351 articles were assigned to full text analysis. The extracted data were assigned to comparative statistical assessments and meta-analysis. RESULTS: A total of 55 articles were included in the analysis. The mean BIC found in comparative assessments and meta-analysis of implants in the mandible (70.97 and 69.744 ± 3.304, respectively) was higher than those in the maxilla (53.24 and 56.692 ± 3.598; P = .000 and P = .008, respectively). The mean BIC in the anterior mandible (79.42) and maxilla (74.19) were higher than the posterior mandible (69.14) and maxilla (36.68) (P < .05). Differences were detected in BIC of commercially available implants and experimental micro-implants (P < .05). Comparative assessments and meta-analysis showed that conventionally loaded implants (75.70 and 75.786 ± 4.889, respectively) had higher BIC than unloaded (54.07 and 53.24 ± 4.971, respectively) and immediately loaded implants (58.53 and 68.831 ± 4.972; P = .000 and P = .004, respectively). CONCLUSIONS: Based upon a meta-analysis of the literature the following conclusions can be made: The BIC in the mandible is higher than the maxilla. The BIC is higher in the anterior than the posterior regions. The implant design coupled with the anatomical region affects the amount of BIC. Placement of experimental micro-implants with different surfaces in the posterior region always result in low and almost comparable BIC. The loading state and healing period seems to have an influence on BIC. Specific reporting guidelines are required to improve reporting of studies on human BIC.

Early-loaded one-stage implants retaining mandibular overdentures by two different mechanisms: 5-year results.

PURPOSE: To compare the biologic and prosthetic outcomes of implants loaded early to retain mandibular overdentures by means of two different attachment systems. MATERIALS AND METHODS: Patients were screened according to specific inclusion/exclusion criteria and randomly allocated to treatment groups involving two-implant-supported early loaded mandibular overdentures retained by ball attachments or Locator attachments. Marginal bone loss, Plaque Index, peri-implant infection, Bleeding Index, prosthetic complications, and Kaplan-Meier survival estimates of the groups were assessed at the 5-year recall. RESULTS: Among the 29 patients (58 implants) who completed the study, one implant was lost during healing; all implants survived after prosthesis delivery. Bone loss in the ball attachment group (0.77 ± 0.05 mm) was significantly greater than that in the Locator group (0.59 ± 0.03 mm). The Plaque and Bleeding indices of both groups were comparable, and peri-implant inflammation scores in both groups were zero for all implants. The frequencies of activation of the matrix, replacement of the matrix, and denture reline in the ball attachment group were significantly higher than those observed in the Locator group. While assessments for the absence of any complication showed that the 1- and 3-year Kaplan-Meier survival probabilities of both groups were comparable, when activation of the retainer was excluded, survival probabilities of the ball attachment group were higher. CONCLUSIONS: The biologic outcomes of early loaded mandibular overdentures retained by ball attachments or Locators were comparable. Although the frequency of prosthetic complications with ball attachments was higher, this did not decrease the survival probability for the treatment.

Load distribution in fixed space maintainers: a strain-gauge analysis.

PURPOSE: The purpose of this study was to compare the biomechanics of space maintainers supported by primary and permanent teeth. METHODS: Photoelastic models of permanent and primary teeth with a single missing tooth space were cast, and band-and-loop, direct-bonded, and fiber-reinforced space maintainers were fabricated. Linear strain-gauges were bonded next to the teeth and in the middle of the missing tooth space. Strain gauge signals were quantified during 50 N and 100 N static axial load applications on the molar, maintainer, and anterior support at 10 KHz using a data acquisition device and associated computer software. RESULTS: Regardless of the tooth being restored, strains around the molar teeth and the maintainer region were comparable between the groups under molar and maintainer loading (P>.05). Under 100 N loading on the anterior support, the highest strains were observed in the direct-bonded group (P<.01). Direct-bonded design led to higher strains than the band-and-loop design under 100 N maintainer loading, whereas the strain output of other designs were comparable. CONCLUSION: Load distribution of band-and-loop, direct-bonded, and fiber-reinforced space maintainers seem comparable, although direct-bonded maintainers could lead to higher strain concentrations in the buccal side due to bending moments.

Two-year follow-up of early- and conventionally-placed two-stage implants supporting fixed prostheses.

PURPOSE: The objective of this study was to compare the biologic and prosthetic outcomes of early- and conventionally-placed implants supporting fixed prostheses. MATERIALS AND METHODS: Using inclusion/exclusion criteria, early- and conventionally-placed implant patient groups, rehabilitated with Branemark System implants supporting fixed prostheses for 2 years, were selected from the patient archives. Kaplan-Meier survival estimates, time-dependent marginal bone loss, Plaque Index, peri-implant infection, Bleeding Index scores, and prosthetic complications data of the groups were compared. RESULTS: A total of 212 implants were placed in early-placed (n=42, 101 implants) and conventionally-placed (n=45, 111 implants) patient groups and 5 implants failed during the 2-year follow-up. The 1- and 2-year Kaplan-Meier survival probabilities of early-placed (0.98) and conventionally-placed (0.973) groups were comparable (P=.735). The 6-month to 2-year marginal bone loss in the conventionally-placed group was higher than in the early-placed group (P<.05). There were differences between groups on soft tissue scores between the 2 years of function (P<.05). The frequency of prosthetic complications was very low and comparable in both groups (P=.476). CONCLUSIONS: Early- and conventionally-placed implants supporting fixed prostheses showed comparable clinical outcomes during the 2-year follow-up, although the marginal bone loss was higher in the latter group.

A randomized, prospective, open-ended clinical trial of zirconia fixed partial dentures on teeth and implants: interim results.

PURPOSE: The aim of this randomized controlled clinical trial was to compare the outcomes of zirconia crowns and fixed partial dentures (FPDs) supported by teeth or implants. MATERIALS AND METHODS: Patients were recruited based on inclusion/exclusion criteria, and 59 eligible subjects were assigned randomly to treatment by one of four zirconia systems (Cercon, ZirkonZahn, Lava, and Katana). One hundred seven single-tooth and 160 three- to six-unit FPDs were fabricated on teeth and implants and cemented using composite resin cement. Californian Dental Association (CDA) quality evaluation, Plaque Index, and Gingival Index scores were recorded, and radiographic assessment of the restorations was performed using periapical and panoramic radiographs at baseline and annually up to 4 years. RESULTS: Five failures (1.9%) were recorded. The 4-year Kaplan-Meier survival probabilities of FPDs were higher than those of single-tooth restorations (P = .046). The highest survival probability for crowns was observed for Katana and the lowest for Cercon (P < .05). For FPDs, the survival probabilities of Lava restorations were similar to those of Cercon but lower than those of ZirkonZahn and Katana (P < .05). The 4-year survival probabilities of implant- and tooth-supported crowns were comparable (P = .182). Regarding CDA ratings, the slight marginal discrepancy scores for the Cercon restorations were higher than for the other systems at 1 year (P < .05). In FPDs, 94.5% of Katana FPDs had slight or gross color mismatch scores, and the difference between color and surface ratings among zirconia systems was significant (P < .05). FPDs had better periodontal scores than crowns over the 4-year observation period (P < .05). CONCLUSION: The 4-year interim results of this study suggest that zirconia systems used to fabricate FPDs have predictably high survival rates on teeth and implants and may exhibit differences, particularly in terms of mechanical failures, marginal adaptation, and color matching.