Effects of pre-cooling and pre-heating procedures on cement polymerization and thermal osteonecrosis in cemented hip replacements

Bone Cement in Adult Hip and Knee Reconstruction: A Review of Commercially Available Options and Clinical Outcomes

Polymethyl-methacrylate (PMMA) bone cement is used extensively in hip and knee arthroplasty. A thorough understanding of the basic chemistry underlying PMMA is important for orthopaedic surgeons because this underscores the specific way bone cement is used during surgery. Recently, clinical research has shed light on the various types of PMMA regarding the viscosity of the mixture and the effect of cement additives. These variations in composition may alter the clinical efficacy of implanted bone cement in hip and knee arthroplasty. Understanding these key differences will allow the surgeon to tailor the PMMA composition as needed to maximize outcomes of hip and knee arthroplasty. This review will summarize the preclinical feature of PMMA, evaluate current and past commercially available bone cement options, analyze preclinical results and clinical outcomes of various bone cement types, and highlight future areas of research.

Effects of polymethyl methacrylate-based bone cement graft for treating excessive gingival display and its dimensional facial changes: 12-Month clinical study

Objective

to present a 12-month follow-up with photographic and tomographic analyses of the effect of polymethyl methacrylate-based bone cement graft (PMMA) in gingival exposure (GE) in patients with excessive gingival display (EGD).

Methods

Twelve patients with EGD were included. The PMMA was surgically placed. A frontal and lateral photograph protocol was performed at baseline (T0), 3 (T3), 6 (T6), and 12 months (T12) post-operatively. Soft tissue cone-beam computed tomography (ST-CBCT) was performed at T0 and T12. Measures included GE, length of the lip vermilion (LLV), lip shape (LS), nose width (NW), filter width (FW), nasolabial angle (NAS) while smiling, and nasolabial angle at rest (NAR). The height, thickness, and volume of the cement graft were also measured in the ST-CBCT. The comparisons were performed by Kruskal-Wallis test at 5 % of significance (p < 0.05).

Results

The height, thickness, and volume of the PMMA were respectively 12.84 ± 1.59 mm, 3.83 ± 0.53, and 1532.02 ± 532.52 mm3. PMMA significantly decreased GE from 8.33 ± 1.25 mm (T0) to 6.60 ± 0.93 mm (T12) (p < 0.01). NAR was 98.34 ± 9.28° at T0 and increased to 105.13 ± 7.33° at T12; however, the angle value was not statistically different (p = 0.08). LLV, LS, NW, FW, and NAS did not exhibit statistical differences between the baseline and follow-up periods.

Conclusions

PMMA significantly decreased GE in a 12-month follow-up without influencing adjacent soft tissue anatomical structures.

Polymethyl methacrylate cure time in simulated in vivo total knee arthroplasty versus in vitro conditions

Background

The present means of confirming the cure of intra-operative polymethyl methacrylate (PMMA) cement are to wait for the remainder cement to harden. To our knowledge, there is no available technique to determine the precise moment of cure for in-vivo cement beneath the tibial tray. This study uses a novel means to determine cement curing time in two environments. One environment represents the operating theater, and the other environment attempts to model cement conditions under the tibial tray during surgery.

Materials and methods

We determined the temperature-versus-time plot of cement curing using the following two temperature sensors: one in a simulated implanted tibial tray and another in the remainder cement. We performed 55 tests using dental methyl methacrylate cement mixed in the same ratio as the orthopedic cement. To simulate in vivo conditions, a simulated stainless-steel tibial tray was implanted on a cancellous bone substitute (Sawbones, Vashon Island, WA, USA) using standard cement technique and subsequently placed in a 90°F (32.2 °C) circulating water bath. We positioned a temperature sensor in the cement mantel and positioned a second sensor in a portion of the remaining cement. The temperature from both sensors was measured simultaneously, beginning at 5 min after mixing and continuing for 20 min. The first derivative of the temperature provided the precise curing time for each condition. We analyzed the results of 55 repeated experiments with an independent samples t-test.

Results

With the described technique, we were able to accurately determine the moment of cure of the cement beneath the simulated tray. There was a mean difference between cure time of 5 min and 26 s (p value < 0.001) between the two conditions.

Conclusions

We validated that our technique was successful in determining the precise time to cure in two different environments.

Level of evidence

This was not a clinical trial and did not involve patients as such the level of evidence was Grade A: Consistent 1 and 2.

Labial repositioning using polymethylmethracylate (PMMA)-based cement for esthetic smile rehabilitation-A case report

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PMMA-based bone cement proved effective in esthetic smile rehabilitation.

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The technique is operator-sensitive.

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The thickness of the PMMA implant is also paramount.

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PMMA is non-toxic, biocompatible with human tissues.

Introduction

One of the most common esthetic complaints among dental patients is a gingival smile, which may be of multifactorial etiology, e.g. gingival hyperplasia, skeletal deformities featuring overgrowth of the anterior maxilla, altered passive eruption, maxillary alveolar tooth extrusion, fine lip and hypermobility of lip elevator muscles, which must be diagnosed prior to treatment so that the appropriate management approach can be selected. Maxillary overgrowth may give rise to subnasal skeletal depression where the upper lip retracts to during smiling, causing gingival exposure. The objective of this case report was to describe a lip repositioning technique using polymethylmethacrylate (PMMA)-based bone cement for esthetic smile rehabilitation.

Case report

A 23-year-old female attended the Esthetic Dentistry Clinic of our institute, reporting dissatisfaction with her smile, due to the size of her teeth and the amount of gingiva exposed when smiling. A rehabilitation planning was designed, which was performed with periodontal surgical intervention to fill the subnasal depression with PMMA-based bone cement. After crown lengthening, the PMMA-based bone cement was prepared with gentamicin in a sterile surgical bowl. When the mixture stopped sticking to the surgical gloves, it was then positioned into the subnasal pit, under constant and copious saline irrigation. With the cement in place, the prosthesis was shaped in a maximum thickness of 7-mm. After complete polymerization and under abundant cooling, refinement and finishing of the PMMA prosthesis was performed. The prosthesis was fixed onto the bone with two titanium-based bone graft fixation screws. The smile aesthetic rehabilitation was complemented using 10 lithium disilicate-based ceramic veneers.

Discussion and conclusion

PMMA-based bone cement proved effective when combined to clinical crown lengthening for esthetic smile rehabilitation, acting as a filling material for subnasal depression, providing new lip support.

Towards the optimization of the preparation procedures of PMMA bone cement

The mechanical properties and thermal history of polymethyl-methacrylate bone cement vary significantly with the preparation procedure used. Because the polymerization reaction is exothermic, many researchers have attempted to minimize thermal osteonecrosis due to heat generation by altering procedures in the preparation of the cement. In most previous studies, only one or two aspects of the preparation procedure were controlled, and there has been little research that comprehensively examines the effects of preparation on the cure kinetics and resulting properties of bone cement. In this study, cement viscosity, cement layer thickness, initial cement temperature, initial metal component temperature, and mixing method were varied to assess the effects on the cement. Maximum temperature, polymerization time, necrosis index, bending strength, and porosity were chosen to evaluate the different preparation procedures, where an optimal procedure would minimize necrosis, reduce cement cure time, and maximize bending strength. Design of Experiments (DOE) was used to examine the main effects and interactions of preparation techniques. Among the most prominent results, it was found that the cure kinetics and the related quantities are primarily controlled by the initial metal component temperature and that the bending strength is most dependent on the mixing method. For the two formulations studied, the optimum preparation procedures should keep cement and metal components at room temperature prior to mixing with a vacuum mixing system. Reducing cement mantle thickness may also be advantageous, as it reduces the maximum temperature and the risk of tissue damage. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:915-923, 2016.

Effects of Cemented Hip Stem Pre-heating on Stem Push-out Strength

OBJECTIVE

To determine the effect on ultimate push-out load and cement-stem surface shear strength of thermally manipulating the cobalt-chromium-molybdenum (CoCrMo) alloy stems of bone cement-stem constructs.

METHODS

Satin-finished CoCrMo alloy stems were allocated to the following three groups with the predetermined temperatures: T24, ambient (24 °C); T37, body (37 °C); and T44, pre-heated stem (>44 °C). They were then inserted into hand-mixed high viscosity bone cement. Ultimate push-out load to failure was assessed with a servo hydraulic testing machine and the surface shear strength calculated. Data were compared among groups using the Kruskal-Wallis with Dunn's test. A P value of less than 0.05 was considered statistically significant.

RESULTS

According to Kruskal-Wallis analysis, ultimate push-out load and surface shear strength differed significantly between the groups (P = 0.001). The T37 and T44 groups had higher ultimate push-out loads and surface shear strengths than the T24 group (P = 0.04 and 0.001, respectively). However, there was no statistically significant difference in these two variables between the T37 and T44 groups (P = 0.08).

CONCLUSIONS

Pre-heating CoCrMo alloy stems enhance the ultimate push-out load and surface shear strength in vitro. The suggested temperature is 37 °C. This technique is recommended for hip arthroplasty procedures.

Thermal Isotherms in PMMA and Cell Necrosis during Total Hip Arthroplasty

Background

Polymethylmethacrylate (PMMA), also known as bone cement, is a commonly used adhesive material to fix implants in Total Hip Arthroplasty (THA). During implantation, bone cement undergoes a polymerization reaction which is an exothermic reaction and results in the release of heat to the surrounding bone tissue, which ultimately leads to thermal necrosis. Necrosis in the bony tissue results in early loosening of the implant, which causes pain and reduces the life of the implant.

Purpose

The main objective of the present study was to understand the thermal isotherms in PMMA and to determine the optimal cement mantle thickness to prevent cell necrosis during THA.

Methods

In this study, the environment in the bony tissue during implantation was simulated by constructing 3D solid models to observe the temperature distribution in the bony tissue at different cement mantle thicknesses (1 mm, 3 mm and 5 mm), by applying the temperature conditions that exist during the surgery. Stems made with Co-Cr-Mo, 316L stainless steel and Ti6Al4V were used, which acted as heat sinks, and a thermal damage equation was used to measure the bone damage. FEA was conducted based on temperature conditions and thermal isotherms at different cement mantle thicknesses were obtained.

Results

Thermal isotherms derived with respect to distance in the bony tissue from the center of the cement mantle, and cell necrosis was determined at different mantle thicknesses. Based on the deduced results, cement mantle thickness of 1-5 mm does not cause thermal damage in the bony tissue.

Conclusion

Considering the long term stability of the implant, cement mantle thickness range from 3 mm-5 mm was found to be optimal in THA to prevent cell necrosis.

A Device to Control Implant and Bone-Cement Temperatures in Cemented Arthroplasty

At present, most of the orthopaedic implants used in articular reconstruction are fixed to host bone using acrylic bone-cement. Bone-cement polymerization leads to an exothermic reaction with heat release and consequent temperature rise. The increase of temperature in the bone beyond the tolerated limits can develop osteocyte thermal necrosis and ultimately lead to bone resorption at the cement-bone interface, with subsequent loosening of the implant. Another issue that plays an important role in implant loosening is debonding of the cement from the implant initiated by crack formation at the interfacial voids. It is well established that low porosity enables better fatigue cement properties. Moderate preheating of the implant is expected to reverse the direction of polymerization, and has the ability to reduce interfacial void formation and improve interfacial shear strength. To increase the implant temperature at the initial cementing phase in order to reduce interfacial void formation, and subsequently, cool the implant in the latter cement polymerization phase to prevent the possibility of bone thermal necrosis, a new automated electronic device was designed to be use in cemented joint replacements. The developed device was specifically designed for the knee arthroplasty, namely for tibial-tray cementing. The device controls the heat flux direction between the tibial-tray and the atmosphere through the “Peltier effect,” using Peltier tablets. The device is placed on the tibial-tray during the cementing phase and starts to heat it in a first phase, promoting the polymerization that initiates at the warmer cement-implant interface. In a second phase, the heat flux in the Peltier tablets is inverted to extract the heat generated during cement polymerization. The device efficiency was evaluated by cementing several tibial-trays in bovine fresh bone and measuring the tray and cement temperatures. The temperature results in the implant and in the cement showed that the device increases and maintains the implant temperature above room temperature at the initial cementing phase, while in the subsequent phase it cools the tibial-tray and cement. Significant differences were found for peak cement temperatures between the tests performed with and without the device. The device showed its capacity to promote the beginning of cement polymerization at the implant interface contributing towards improving interfacial shear strength and in reducing the peak cement temperature in the subsequent polymerization process, thus contributing to the prevention of the bone thermal necrosis effect.

In Situ Tooth Replica Custom Implant: Rationale, Material, and Technique

This study introduced a new concept of an in situ, custom-made, tooth replica dental implant. It was obtained by injecting a self-set, nonresorbable polymer type bone graft substitute into the tooth socket after extraction. Based on its cited properties, new composite bone cement Cortoss was suggested. The properties were reviewed and evaluated. The technique of application was described with a simulation model presented that appeared simple. Apparently, immediate duplication of tooth anatomy was achieved; thus, the concept might have the potentials of spontaneous adaptation and stabilization, preservation of alveolar bone, increasing implant-bone surface area, better load distribution, and bone stimulation. Modifications were also described to manage cases of resorbed alveolar bone as well as long-standing extracted teeth. Investigations were still required to assess the performance of the material and if modifications would be needed.

Pore distribution and material properties of bone cement cured at different temperatures

Implant heating has been advocated as a means to alter the porosity of the bone cement/implant interface; however, little is known about the influence on cement properties. This study investigates the mechanical properties and pore distribution of 10 commercially available cements cured in molds at 20, 37, 40 and 50 degrees Celsius. Although each cement reacted differently to the curing environments, the most prevalent trend was increased mechanical properties when cured at 50 degrees Celsius vs. room temperature. Pores were shown to gather near the surface of cooler molds and near the center in warmer molds for all cement brands. Pore size was also influenced. Small pores were more often present in cements cured at cooler temperatures, with higher-temperature molds producing more large pores. The mechanical properties of all cements were above the minimum regulatory standards. This work shows the influence of curing temperature on cement properties and porosity characteristics, and supports the practice of heating cemented implants to influence interfacial porosity.

Temperature elevation during simulated polymethylmethacrylate (PMMA) cranioplasty in a cadaver model

The aims of this study were to: (i) obtain temperature measurements during in vitro polymerisation of polymethylmethacrylate (PMMA) disks of a range of thicknesses; and (ii) obtain tissue temperature measurements at various locations within a skull defect during a simulated PMMA cranioplasty procedure using a cadaver. In vitro, higher temperatures were recorded with increasing PMMA thickness. During the simulated cranioplasty, the maximum temperature was observed inside the PMMA sample, with nearby tissues being exposed to temperatures of greater than 50 degrees C over prolonged periods. There is conflicting information in the literature concerning the sensitivity of brain tissue and bone to elevated temperatures. Preoperatively fabricated PMMA cranioplasty prostheses are recommended.

Potential for thermal damage to articular cartilage by PMMA reconstruction of a bone cavity following tumor excision: A finite element study

Benign, giant cell tumors are often treated by intralesional excision and reconstruction with polymethylmethacrylate (PMMA) bone cement. The exothermic reaction of the in-situ polymerizing PMMA is believed to beneficially kill remaining tumor cells. However, at issue is the extent of this necrotic effect into the surrounding normal bone and the adjacent articular cartilage. Finite element analysis (ABAQUS 6.4-1) was used to determine the extent of possible thermal necrosis around prismatically shaped, PMMA implants (8-24cc in volume), placed into a peripheral, sagittally symmetric, metaphyseal defect in the proximal tibia. Temperature/exposure time conditions indicating necrotic potential during the exotherm of the polymerizing bone cement were found in regions of the cancellous bone within 3mm of the superior surface of the PMMA implant. If less than 3mm of cancellous bone existed between the PMMA implant and the subchondral bone layer, regions of the subchondral bone were also exposed to thermally necrotic conditions. However, as long as there were at least 2mm of uniform subchondral bone above the PMMA implant, the necrotic regions did not extend into the overlying articular cartilage. This was the case even when the PMMA was in direct contact with the subchondral bone. If the subchondral bone is not of sufficient thickness, or is not continuous, then care should be taken to protect the articular cartilage from thermal damage as a result of the reconstruction of the tumor cavity with PMMA bone cement.

Mechanical implications of interfacial defects between femoral hip implants and cement: A finite element analysis of interfacial gaps and interfacial porosity

Two types of defect between femoral hip implants and cement have been identified. Interfacial porosity arises from cement shrinkage during curing and presents as pores randomly located along the stem. Interfacial gaps are much larger stem—cement separations caused by air introduced during stem insertion. To investigate the mechanical consequences of both types of defect, a finite element analysis model was created on the basis of a computed tomography image of a Charnley—Kerboul stem, and alternating torsional and transverse loads were applied. The propagation of fatigue cracks within the cement and the rotational stability of the stem were assessed in models simulating increasing amounts of interfacial gaps and pores. Anterior gaps covering at least 30 per cent of the implant surface promoted cement cracks and destabilized the stem. Anterolateral gaps were less destabilizing, but had more potential to promote cracks. In both cases, cracks occurred mainly outside gap regions, in areas where the stem contacted the cement during cyclic loading. Although random interfacial pores did not destabilize the implant, they acted as crack initiators even at low fractions (10 per cent). In conclusion, random interfacial pores were more harmful for the cement mantle integrity than were larger regions of interfacial gaps, although gaps were more detrimental for the rotational stability of the stem.

Quantification of stem-cement interfacial gaps

Interfacial defects between the cement mantle and a hip implant may arise from constrained shrinkage of the cement or from air introduced during insertion of the stem. Shrinkage-induced interfacial porosity consists of small pores randomly located around the stem, whereas introduced interfacial gaps are large, individual and less uniformly distributed areas of stem-cement separation. Using a validated CT-based technique, we investigated the extent, morphology and distribution of interfacial gaps for two types of stem, the Charnley-Kerboul and the Lubinus SPII, and for two techniques of implantation, line-to-line and undersized.

The interfacial gaps were variable and involved a mean of 6.43% (sd 8.99) of the surface of the stem. Neither the type of implant nor the technique of implantation had a significant effect on the regions of the gaps, which occurred more often over the flat areas of the implant than along the corners of the stems, and were more common proximally than distally for Charnley-Kerboul stems cemented line-to-line. Interfacial defects could have a major effect on the stability and survival of the implant.

Preheating acrylic bone cement powder is not recommended for all brands

One strategy that has been suggested for reducing the operating room time for cemented total joint arthroplasties-and, hence, for reducing the total cost of these procedures-is to accelerate the polymerization of the acrylic bone cement by preheating the powder to 65 degrees C. We quantified the effect of preheating the cement powders on the fracture toughness and fatigue life of 3 cement brands that are widely used in clinical practice. The results suggest judicious selection of cements whose powders are to be preheated for use in cemented arthroplasties.

Complexity in modeling of residual stresses and strains during polymerization of bone cement: effects of conversion, constraint, heat transfer, and viscoelastic property changes

Aseptic loosening of cemented joint prostheses remains a significant concern in orthopedic biomaterials. One possible contributor to cement loosening is the development of porosity, residual stresses, and local fracture of the cement that may arise from the in-situ polymerization of the cement. In-situ polymerization of acrylic bone cement is a complex set of interacting processes that involve polymerization reactions, heat generation and transfer, full or partial mechanical constraint, evolution of conversion- and temperature-dependent viscoelastic material properties, and thermal and conversion-driven changes in the density of the cement. Interactions between heat transfer and polymerization can lead to polymerization fronts moving through the material. Density changes during polymerization can, in the presence of mechanical constraint, lead to the development of locally high residual strain energy and residual stresses. This study models the interactions during bone cement polymerization and determines how residual stresses develop in cement and incorporates temperature and conversion-dependent viscoelastic behavior. The results show that the presence of polymerization fronts in bone cement result in locally high residual strain energies. A novel heredity integral approach is presented to track residual stresses incorporating conversion and temperature dependent material property changes. Finally, the relative contribution of thermal- and conversion-dependent strains to residual stresses is evaluated and it is found that the conversion-based strains are the major contributor to the overall behavior. This framework provides the basis for understanding the complex development of residual stresses and can be used as the basis for developing more complex models of cement behavior.

Precooling of the femoral canal enhances shear strength at the cement-prosthesis interface and reduces the polymerization temperature

Preheating of the femoral stem in total hip arthroplasty improves the cement-prosthesis bond by decreasing the interfacial porosity. The main concern, however, is the potential thermal osteonecrosis because of an increased polymerization temperature. In this study, the effects of femoral canal precooling on the characteristics of the cement-stem interface were evaluated in an experimental model for three test conditions: precooling of the femoral canal, preheating of the stem (44 degrees C), and a control in which stems were inserted at room temperature without thermal manipulation of the implant, cement, or bone. Compared to the control group, precooling of the femoral canal and preheating of the stem had similar effects on the cement-stem interface, with greater interfacial shear strength and a reduced porosity. Femoral canal precooling also produced a lower temperature at the cement-bone interface. No difference was found in the ultimate compressive strength of bone cement for the three preparation conditions. Based on this laboratory model, precooling of the femoral canal could improve shear strength and porosity at the stem-cement interface, minimize thermal injury, and maintain the mechanical strength of the cement.

Numerical Predictions of the Thermal Behaviour and Resultant Effects of Grouting Cements While Setting Prosthetic Components in Bone

Acrylic cements are commonly used to attach prosthetic components in joint replacement surgery. The cements set in short periods of time by a complex polymerization of initially liquid monomer compounds into solid structures with accompanying significant heat release. Two main problems arise from this form of fixation: the first is the potential damage caused by the temperature excursion, and the second is incomplete reaction leaving active monomer compounds, which can potentially be slowly released into the patient. This paper presents a numerical model predicting the temperature-time history in an idealized prosthetic-cement-bone system. Using polymerization kinetics equations from the literature, the degree of polymerization is predicted, which is found to be very dependent on the thermal history of the setting process. Using medical literature, predictions for the degree of thermal bone necrosis are also made. The model is used to identify the critical parameters controlling thermal and unreacted monomer distributions.

Interfacial Strength of Resilon and Gutta-Percha to Intraradicular Dentin

Strengthening of Resilon-filled roots via an adhesive interface should be reflected by improvement in the interfacial strength and dislocation resistance between the root fillings and intraradicular dentin. This study compared the interfacial strengths of Resilon/Epiphany and gutta-percha/AH Plus using a thin-slice push-out test design. Failure modes of root slices after push-out testing were examined with environmental scanning electron microscopy. The gutta-percha group exhibited significantly higher interfacial strength than the Resilon group, when premature failures that occurred in Resilon root slices were included in the statistical analysis. The gutta-percha root slices failed exclusively along the gutta-percha/sealer interface. The Resilon root slices failed predominantly along the sealer/dentin interface with recognizable, fractured resin tags. Detachment of the Resilon from the Epiphany sealer was also surprisingly observed in some specimens. The similarly low interfacial strengths achieved with both types of root filling challenges the concept of strengthening root-filled teeth with the new endodontic material.

Thermal manipulation of bone cement

Many factors affect the rate of polymerization of polymethylmethacrylate (PMMA) and, therefore, the working time of bone cement. Surgeons may control some factors, but not all. A surgeon may change the temperature of the powder and the monomer, whereas the temperature and relative humidity of the operating room are more difficult to alter. The temperature of the mixing vessels may also be controlled. However, a surgeon has no control over the industrial mixture of the components of the bone cement, which can vary considerably from batch to batch. This article reviews the effect of temperature of cement mixtures on the working time of the cement, the interfacial strength of the cement-metal interface as well as the cement-bone interface, and tissue viability and cellular change at the bone-cement interface.

The effects of curing history on residual stresses in bone cement during hip arthroplasty

During cement curing in total hip arthroplasty, residual stresses are introduced in the cement mantle as a result of curing shrinkage, thermal shrinkage, and geometrical constraints. These high residual stresses are capable of initiating cracks in the mantle of cemented hip replacements. The purpose of this study was to determine the residual stresses in the cemented hip replacements. The finite element method was developed to predict the residual stresses built up in joint arthroplasties. Experimental tests were then performed to validate the numerical methodology. Then the effects of curing history on the residual stress distribution were investigated with finite element simulations. Results showed that the predictions of the thermal shrinkage residual stresses by the developed method agreed with the experimental tests very well. The residual stress buildup was shown to depend on the curing history. By preheating the prosthesis stem prior to implantation, a desired low-level residual stress at the critical prosthesis-cement interface was obtained. As a result, this article provides a numerical tool for the quantitative simulation of residual stress and for examining and refining new designs computationally.