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ORIGINAL RESEARCH
Year : 2021  |  Volume : 12  |  Issue : 3  |  Page : 128-131

Abutment Screw Loosening in Single Implant Restorations: Evaluation of Fracture Strength of Implant-Supported Cement-Retained Monolithic Zirconia Restorations Repaired with Porcelain and Composite Resin


1 Professor, Dental Sciences Research Center, Department of Prosthodontics, School of Dentistry, Guilan University of Medical Sciences, Rasht, Iran
2 Assistant Professor, Dental Sciences Research Center, Department of Prosthodontics, School of Dentistry, Guilan University of Medical Sciences, Rasht, Iran
3 Dental Sciences Research Center, School of Dentistry, Guilan University of Medical Sciences, Rasht, Iran
4 Assistant Professor, Dental Sciences Research Center, Department of Prosthodontics, School of Dentistry, Alborz University of Medical Sciences, Karaj, Iran

Date of Submission21-Apr-2021
Date of Decision16-May-2021
Date of Acceptance16-Sep-2021
Date of Web Publication2-Nov-2021

Correspondence Address:
Zoheir Mousavi Mehr
Department of Prosthodontics, Dental Sciences Research Center, School of Dentistry, Guilan University of Medical Sciences, Rasht-Fooman Road, Rasht, Postal Code 41938-33697
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/denthyp.denthyp_125_21

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  Abstract 


Aim: To assess the fracture strength of repaired implant-supported cement-retained monolithic zirconia restorations with porcelain and composite resin. Materials and methods: Nighty monolithic zirconia crowns were cemented over the implant abutments, and divided into three groups (n = 30): control, screw access hole preparation in the crown and its restoration with composite resin (HC), and screw access hole preparation in the crown and its restoration with feldspathic porcelain (HP). Fracture strength was measured by a universal testing machine. Data were analyzed (α < 0.05). Results: The maximum fracture strength was in the control group (764.23 ± 108.41 N), whereas the minimum was in HC group (686.25 ± 101.86 N). The mean fracture strength in HC group was significantly lower than that in the control group (P = 0.008). No significant difference was noted between other groups (P > 0.05). Conclusion: Repaired implant-supported monolithic zirconia crowns with feldspathic porcelain provided a fracture strength comparable to that in the control group.

Keywords: Implant supported dental prosthesis, single-tooth implants, Y-TZP ceramic


How to cite this article:
Asli HN, Falahchai M, Rahimabadi S, Arbab H, Mousavi Mehr Z. Abutment Screw Loosening in Single Implant Restorations: Evaluation of Fracture Strength of Implant-Supported Cement-Retained Monolithic Zirconia Restorations Repaired with Porcelain and Composite Resin. Dent Hypotheses 2021;12:128-31

How to cite this URL:
Asli HN, Falahchai M, Rahimabadi S, Arbab H, Mousavi Mehr Z. Abutment Screw Loosening in Single Implant Restorations: Evaluation of Fracture Strength of Implant-Supported Cement-Retained Monolithic Zirconia Restorations Repaired with Porcelain and Composite Resin. Dent Hypotheses [serial online] 2021 [cited 2021 Dec 3];12:128-31. Available from: http://www.dentalhypotheses.com/text.asp?2021/12/3/128/329757




  Introduction Top


Implant-supported fixed restoration is a predictable treatment option which has gained high popularity as a standard treatment.[1],[2] The abutment screw loosening is among the most common complications of implant treatment.[3],[4] Implant crowns may be cement retained or screw retained.[5] Cement-retained crowns have advantages such as the ability to compensate for the improper inclination of implant, passive fit, and allowing occlusal adjustment due to the presence of an intact occlusal surface.[5] However, in the case of abutment screw loosening, they are often damaged to access the abutment screw.[6] Krishnan et al.[7] and Patil[8] suggested reuse of crowns after repairing the screw access hole prepared due to abutment screw loosening, to save time and cost.

Several studies have evaluated the effect of screw access channel preparation on fracture strength of zirconia in screw–cement-retained restorations.[9],[10] Nonetheless, the fracture strength of cement-retained monolithic zirconia crowns after access hole preparation for tightening of a loose abutment has not been investigated. Furthermore, to the best of the authors’ knowledge, repair of screw access holes with porcelain in zirconia crowns has not been previously studied. Thus, this study aimed to assess the fracture strength of implant-supported cement-retained monolithic zirconia restorations repaired with porcelain and composite resin following abutment screw loosening and subsequent screw access hole preparation. The null hypothesis was that the fracture strength of crowns after repair with porcelain and composite resin would not be significantly different from each other and from the fracture strength of intact crowns.


  Materials and Methods Top


Nighty straight abutments (935729, SIC Standard Abutments, SIC Invent AG, Basel, Switzerland) were fixed on the analogs (5 × 11.5 mm; SIC Lab Implant, SIC Invent AG) according to the manufacturer’s instructions. The analog–abutment assembly was mounted in an acrylic resin mold (Palapress Vario, Heraeus Kulzer, Wehrheim, Germany) at 90° angle relative to the horizon using a surveyor such that the abutment–analog connection was 1 mm above the acrylic surface.

One abutment was scanned by a laboratory scanner (Ceramill Map 400; Amann Girrbach, Koblach, Austria). A full-contour crown was designed for the maxillary first premolar using a software program (Ceramill Mind; Amann Girrbach) and sent to Ceramill milling machine (Motion 2(5×); Amann Girrbach). Nighty monolithic zirconia crowns with 2 mm occlusal thickness were fabricated (Zolid FX multilayer; Amann Girrbach), and sintered according to the manufacturer’s instructions. Eventually, the crowns were cemented (Panavia F2.0; Kuraray Medical Inc, Tokyo, Japan). All specimens underwent 5000 thermal cycles between 5°C and 55°C with a dwell time of 60 seconds and a transfer time of 12 seconds.

A silicon index was obtained for standardization of the final repaired crowns. Thirty specimens were assigned to the control group and remained intact. In the remaining specimens, a taper round-end diamond bur (ZR Diamond, Komet Besigheim, Germany) was used to manually create a hole in the middle of the occlusal surface. A new bur was used for preparation of each specimen. To standardize the holes, a metal index was used. The specimens were then divided into two groups.

Holes restored with composite resin (HC group): The holes were sandblasted with an intraoral sandblaster (Dento-Prep, Ronvig, Daugaard, Denmark) by using 50 μm alumina particles with 40 psi pressure at 10 mm distance for 10 seconds, and then rinsed with water spray for 20 seconds, and dried with air spray for 5 seconds.[11] To create a 2-mm space for the restorative material, a piece of sterile polytetrafluoroethylene (PTFE) tape was placed in the prepared hole, and condensed with a plugger.[12] One layer of Z-Prime Plus primer (Bisco, Schaumburg, Illinois, USA) was applied in the hole and air-dried for 5 seconds.[13] The hole was then restored with composite resin (Filtek Z250; 3M ESPE, St Paul, Minnesota, USA), and cured for 20 seconds using a light-emitting diode device (Elipar Freelight 2; 3M ESPE).

Holes restored with porcelain (HP group): The abutment screw was completely unscrewed, and the crowns were removed along with the abutment and abutment screw. To separate the crowns from the abutment, the specimens were placed in a furnace and heated at 300°C to 400°C, and after 5 minutes of holding time, they were cooled at room temperature.[14] This led to cement degradation. The residual cement on the abutment was removed with acetone and water, and the abutment was dried.[9] The hole was sandblasted as explained earlier. The specimens were ultrasonicated in distilled water at room temperature for 1 minute. Eventually, the created holes were restored with incremental application of feldspathic porcelain (Vita Zahnfabrik, Bad Sackingen, Germany) and baked in two layer according to the manufacturer’s instructions.[15] The crown surface was then polished with diamond discs, and heated again in a furnace at 920°C for 1 minute.[15]

The crowns were cemented again by Panavia F2.0 resin cement (Kuraray Medical Inc) [Figure 1]. Eventually, all specimens were incubated at 37°C and 100% humidity for 24 hours and were then thermocycled again as explained earlier. Next, they underwent fracture strength test in a universal testing machine (DBBP-2t; Bongshin Loadcell Co., Ltd, Seoul, Korea). For this purpose, compressive load was applied by an applicator with 6 mm diameter at a crosshead speed of 1 mm/min with 0° angle relative to the abutment.[16]
Figure 1 Restoration of cavity with feldspathic porcelain

Click here to view


The Shapiro–Wilk test showed normal distribution of data in all groups. Thus, one-way analysis of variance (ANOVA) was applied to compare the fracture strength of the groups. Pairwise comparisons were performed by the Tukey post-hoc test at 0.05 level of significance. All statistical analyses were performed by using SPSS version 24 (SPSS Inc., Chicago, Illinois, USA).


  Results Top


The ANOVA revealed a significant difference in fracture strength of the groups (P = 0.009, F = 5.011). The mean fracture strength was 764.23 ± 108.41 N in the control group, 686.25 ± 101.86 N in HC group, and 709.61 ± 81.47 N in HP group. Pairwise comparisons by the Tukey test showed no significant difference between the HP and control (P = 0.100) or HP and HC (P > 0.999) groups. However, the fracture strength of HC group was significantly lower than that of the control group (P = 0.008) [Table 1].
Table 1 Comparison of fracture strength of the groups

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  Discussion Top


The current results revealed a significant difference in the mean fracture strength of the groups. Thus, the null hypothesis of the study was rejected.

In this study, preparation of access holes in implant-supported cement-retained monolithic zirconia crowns and their repair with composite resin significantly decreased their fracture strength. This result was in line with Wood et al.,[17] Scioscia et al.,[18] and Mokhtarpour et al.[9] It should be noted that preparation of sintered zirconia decreases its mechanical properties,[19] and the zirconia strength is directly affected by the size, number and location of cracks such that the superficial cracks directly serve as areas of stress accumulation, and can aggravate the stress depending on their size.[20]

According to the results of the present study, preparation of monolithic zirconia crowns and repair of the cavity with porcelain did not significantly decrease the fracture strength of implant-supported crowns. Although the bond strength between the veneering porcelain and zirconia has been previously studied,[21],[22],[23] to the best of the authors’ knowledge, repair of cavities prepared in monolithic zirconia with feldspathic porcelain has not been previously investigated. It is believed that the bonding of porcelain to zirconia restorations is influenced by formation of oxide layer, mechanical bonding by sandblasting, and compressive bonding due to the difference in the coefficients of thermal expansion. However, the details of these mechanisms have yet to be clearly elucidated.[24] The bond between the porcelain and zirconia may be influenced by residual thermal stresses in the cooling phase.[25] Thus, most manufacturers produce a feldspathic porcelain with a coefficient of thermal expansion compatible with that of zirconia.[26] It should be noted that the specimens in HP group were heated in the process of porcelain baking, whereas the specimens in HC group were not heated. Therefore, recovery of the primary bond strength in monolithic zirconia crowns after repair with porcelain may be attributed to the reversal of phase transformation caused by sandblasting in the process of feldspathic porcelain baking.[27],[28]In the present study, one type of load was applied along the longitudinal axis to cause fracture. However, dental ceramics are often degraded as the result of multiple loading cycles or accumulation of stress-related or water-related defects.[17],[27] Furthermore, storage of specimens in a wet environment for simulation of oral environment may accelerate ceramic fatigue.[17]


  Conclusion Top


Within the limitations of this in vitro study, it may be concluded that preparation of implant-supported cement-retained monolithic zirconia crowns following abutment screw loosening necessitating restoration retrieval, and subsequent repair of the cavity with composite resin significantly decreases the fracture strength. However, in case of repair with porcelain, the eventual fracture strength value would be comparable to that of the control group.

Financial support and sponsorship

This work was supported by Dental Research Center Dentistry Research Institute of Guilan University of Medical Sciences, Guilan, Iran (grant # IR.GUMS.REC.1398.093).

Conflicts of interest

There are no conflicts of interest.



 
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