Implant Angulation Effect on the Fracture Resistance of Monolithic Zirconia Custom Abutments: An In Vitro Study

Clinical Factors on Dental Implant Fractures: A Systematic Review

Dental implant fractures pose a significant challenge to long-term treatment success. This systematic review aims to comprehensively examine the clinical factors influencing dental implant fractures (IFs). Furthermore, strategies to choose the right type of implant and prevent this complication are addressed. A systematic search was conducted across PubMed, Scopus, and Web of Science databases. Eligible studies included retrospective case-control, prospective cohort studies, and clinical trials. The initial search yielded 361 articles, of which 312 were excluded being these reviews, case reports, irrelevant, or written in languages other than English. This left 49 articles, with only 6 meeting the eligibility criteria for an in-depth review. These studies, all retrospective case-control, examine implant characteristics, patient demographics, surgical and prosthetic variables, biomechanical and functional factors, clinical and procedural variables, complications and maintenance issues. The risk of bias was assessed as low using the ROBINS-I tool. Key findings suggest a correlation between implant diameter and structural resistance, with wider implants demonstrating reduced fracture risk. Additionally, posterior regions, especially molars and premolars, exhibit higher susceptibility to IFs due to increased masticatory forces. Implant design and material may considerably influence fracture risk, with conical implants and screw-retained prostheses showing higher vulnerability. Biomechanical overload, particularly in patients with bruxism, emerges as a primary contributing factor to IFs. Prosthesis type significantly influences fracture incidence, with cantilever prostheses posing a higher risk due to increased stress. Peri-implant bone loss is strongly associated with IFs, emphasizing the need for meticulous preoperative assessments and individualized management strategies. Future research should prioritize larger and heterogeneous populations with long-term follow-up and standardized methodologies to enhance the generalizability and comparability of findings. Randomized controlled trials and biomechanical studies under controlled conditions are also essential to elucidate the complex interactions contributing to IFs and developing effective prevention strategies. Additionally, integrating patient-reported outcomes may offer a comprehensive understanding of the impact of IFs on quality of life.

Influence of screw channel angulation on reverse torque value and fracture resistance in monolithic zirconia restorations after thermomechanical cycling: an in-vitro study

BACKGROUND

While the concept of angled screw channels has gained popularity, there remains a scarcity of research concerning the torque loss and fracture strength of monolithic zirconia restorations with various screw channel angulations when exposed to thermomechanical cycling. This in-vitro study aimed to evaluate the reverse torque value and fracture resistance of one-piece screw-retained hybrid monolithic zirconia restorations with angulated screw channels after thermomechanical cycling.

METHODS

One-piece monolithic zirconia restorations, with angulated screw channels set at 0°, 15°, and 25° (n = 6 per angulation) were fabricated and bonded to titanium inserts using a dual-cure adhesive resin cement. These assemblies were then screwed to implant fixtures embedded in acrylic resin using an omnigrip screwdriver, and reverse torque values were recorded before and after thermomechanical cycles. Additionally, fracture modes were assessed subsequent to the application of compressive load. One-way ANOVA and Bonferroni post hoc test were used to compare the groups (α = 0.05).

RESULTS

The study groups were significantly different regarding the fracture resistance (P = 0.0015), but only insignificantly different in the mean percentage torque loss (P = 0.4400). Specifically, the fracture resistance of the 15° group was insignificantly higher compared to the 0° group (P = 0.9037), but significantly higher compared to the 25° group (P = 0.0051). Furthermore, the fracture resistance of the 0° group was significantly higher than that of the 25° group (P = 0.0114).

CONCLUSIONS

One-piece hybrid monolithic zirconia restorations with angulated screw channels can be considered an acceptable choice for angulated implants in esthetic areas, providing satisfactory fracture strength and torque loss.

Load, unload and repeat: Understanding the mechanical characteristics of zirconia in dentistry

OBJECTIVES

Zirconia-based dental restorations and implants are gaining attention due to their bioactivity, corrosion resistance and mechanical stability. Further, surface modification of zirconia implants has been performed at the macro-, micro- and nanoscale to augment bioactivity. While zirconia's physical and chemical characteristics have been documented, its relation to mechanical performance still needs to be explored. This extensive review aims to address this knowledge gap.

METHODS

This review critically compares and contrasts the findings from articles published in the domain of 'mechanical stability of zirconia\ in dentistry' based on a literature survey (Web of Science, Medline/PubMed and Scopus databases) and a review of the relevant publications in international peer-reviewed journals. Reviewing the published data, the mechanical properties of zirconia, such as fracture resistance, stress/tension, flexural strength, fatigue, and wear are detailed and discussed to understand the biomechanical compatibility of zirconia with the mechanical performance of modified zirconia in dentistry also explored.

RESULTS

A comprehensive insight into dental zirconia's critical fundamental mechanical characteristics and performance is presented. Further, research challenges and future directions in this domain are recommended.

SIGNIFICANCE

This review extends existing knowledge of zirconia's biomechanical performance and it they can be modulated to design the next generation of zirconia dental restorations and implants to withstand long-term constant loading.

Implant angulation and fracture resistance of one-piece screw-retained hybrid monolithic zirconia ceramic restorations

OBJECTIVE

This study aimed to investigate the fracture resistance of one-piece screw-retained hybrid monolithic zirconia ceramic restorations in different implant angulations.

MATERIALS AND METHODS

Three implant fixtures were embedded in acrylic resin blocks with 0°, 15°, and 25° angulations. For each group of implant angulations, 11 screw-retained one-piece monolithic zirconia restorations were made and bonded to the titanium inserts with a dual-cure self-adhesive resin. The complexes were screwed to the implant fixtures with titanium screws. The samples were thermocycled, subjected to compressive load, and fracture modes were recorded. One-way ANOVA and post hoc Tukey's test were used for statistical analyses (α = 0.05).

RESULTS

One-way ANOVA showed the fracture resistance to be significanltly different among the study groups (P = 0.036). The 15° group was significantly more resistant than 0° (P = 0.031). However, the 25° group was not significantly different from the 15° (P = 0.203) and 0° groups (P = 0.624). Fractures occurred only on the restorations, not at the screw levels.

CONCLUSIONS

Tilting the implant up to 15° improves the fracture resistance of one-piece screw-retained hybrid monolithic zirconia restorations; however, increasing the tilt to 25° would not yield restorations with significantly better fracture strength than the straight implants. Accordingly, when angulated implants are indicated in the esthetic zones, one-piece screw-retained hybrid monolithic zirconia ceramic restorations can be used with acceptable fracture strength.

Mechanical stability of angulated zirconia abutments supporting maxillary anterior single crowns on narrow-diameter implants

OBJECTIVES

To investigate the fracture strength of angulated hybrid abutments supporting anterior single crowns on narrow-diameter implants (NDIs).

MATERIAL AND METHODS

Zirconia abutment with angulations of labial inclination 0° (TZ0Z), 15° (TZ15Z), 30° (TZ30Z) and palatal inclination 15° (TZ - 15Z) was designed on 3.3-mm titanium-zirconium (Ti-Zr) NDIs. Titanium abutment connected with Ti-Zr implant (TZ0T) and 0° zirconia abutment connected with pure titanium (Ti) implant (T0Z) were control groups. Thirty-six un-restored abutments and 36 abutments restored with highly translucent zirconia (HTZ) crowns were tested. Failure loads were compared among 6 groups, and bending moments were calculated for comparison between un-restored and restored abutments.

RESULTS

Failure loads of un-restored abutments were affected by the abutment angle. Sixty-seven percent samples in TZ30Z and 83% samples in TZ - 15Z group fractured at the thinnest part of the zirconia abutment and exhibited lower failure load (p < .05). Failure loads of restored abutments were close to or exceeded the maximum bite force of anterior teeth, and no differences were found among six groups (p > .05). Except TZ15Z and TZ0T group, the bending moment increased with the crown construction, especially for TZ30Z and TZ - 15Z groups (p < .001).

CONCLUSIONS

The fracture strength of hybrid abutments restored with HTZ crown on Ti-Zr NDIs exceeded the bite forces of anterior teeth for all the groups and were not affected by the abutment angle.

CLINICAL RELEVANCE

In terms of fracture strength, Ti-Zr NDIs combined with angulated hybrid abutments and HTZ crowns can be used in the anterior region.

Influence of Screw Channel Angulation on the Fracture Resistance of Zirconia Abutments: An In Vitro Study

PURPOSE

The aim of this study was to investigate the effect of implant screw channel angulation on the fracture resistance of zirconia abutments without artificial aging.

MATERIALS AND METHODS

Ten implant replicas were embedded in a jig of autopolymerizing acrylic resin. Using a surveyor and a metallic platform, the implant replicas were mounted centrally and with an angulation of 30°. A maxillary left central incisor crown was fabricated from pattern resin and scanned. The digital design of a monolithic zirconia implant abutment-crown was completed using a 3D imaging software. For all specimens of this group (ASC₂₅ ), the screw channel was positioned at 25° to the lingual. Following fabrication, the samples were attached onto the embedded implant replicas and manually torqued to 35 Ncm as recommended by the manufacturer. The monolithic zirconia implant abutment-crowns were mounted in a metallic platform, positioned perpendicular to the indenter, and subjected to loading until failure. Crosshead speed was set at 0.5 mm/min for the universal testing machine. Data from a similar in vitro study where straight zirconia custom abutments (ASC₀ ) were subjected to static load until failure was used as a control group. An unpaired Student's t-test was used to determine if fracture resistance based on load at failure and maximum load in each group were significantly different from each other (ASC₂₅ vs ASC₀ ). Statistical significance level was inferred at p ≤ 0.05 RESULTS: Group ASC₂₅ fractured at a mean (SD) load of 215.49 (47.10) N and a mean (SD) maximum load of 420.50 (17.18) N. Group ASC₀ fractured at a mean (SD) load of 534.04 (133.77) N and a mean (SD) maximum load of 762.69 (109.59) N. The difference was statistically significant for both mean load and mean maximum load at failure (p ≤ 0.05). The survival rate of 0° zirconia abutments was significantly higher than that of 25° ASC zirconia abutments.

CONCLUSIONS

Within the limitations of this in vitro study the mean fracture load was significantly higher in the group with a straight channel angulation.