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CERAMICS
INTERNATIONAL
Ceramics International 42 (2016) 3591–3597
www.elsevier.com/locate/ceramint
Effect of Al2O3 on leucite based bioactive glass ceramic composite
for dental veneering
Pattem Hemanth Kumara, Vinay Kumar Singha,n, Pradeep Kumarb, Gaurav Yadava,
R.K. Chaturvedia
a
Department of Ceramic Engineering, Indian Institute of Technology (BHU), Varanasi 221005, India
b
Department of Chemical Engineering and Technology, Indian Institute of Technology (BHU), Varanasi-221005, India.
Received 28 September 2015; received in revised form 28 October 2015; accepted 5 November 2015
Available online 12 November 2015
Abstract
A wide variety of dental ceramic composites have been introduced in the restorative dentistry in order to associate the desired aesthetics and
superior mechanical performance. Mechanochemically derived leucite based bioactive glass ceramic composites have been prepared and studied
by their thermal, crystal structure, microstructural, mechanical and biological behavior. In the prepared glass-ceramic composites, fine alumina
has been added to improve their mechanical properties because it has biocompatibility, high hardness and good mechanical strength. Flexural
strength and coefficient of thermal expansion (CTE) have been studied and the results are compared to the commercial dentine. Alumina added
glass ceramic composites show high flexural strength than that of the pure leucite based glass ceramic composite. A second phase nepheline has
been formed in the alumina added samples. Nepheline has high CTE. This causes a slight increase in the CTE of the whole matrix. Micrographs
show the complete attachment and proliferation of the SSC-25 cells on the surface of the samples. This confirms the bioactive behavior of the
prepared composites. Therefore, it is concluded that the addition of alumina to the glass ceramic composite is a successful approach to improve its
mechanical and biological properties.
& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: A. Milling; B. Composites; C. Thermal expansion; D. Glass ceramics; E. Alumina
1. Introduction accumulation in the marginal area between the fixed tooth
and restoration. This causes the bacterial attack leading to pulp
Ceramic materials used in restorative dentistry have specific irritation and the dissolution of the luting cement [13]. A
properties such as durability in the oral environment, similarity hypothetical tissue attachment on the margins of a restoration
with natural tooth structure, high wear resistance and mechan- would eliminate the marginal gap, cement dissolution and
ical strength [1–3]. Metal ceramic restorations (MCR) are subsequently the secondary caries. Cells no more adhere to the
commonly used due to their good fracture resistance [4]. These damaged tooth structure after preparation of a tooth for a
consist of metal substructure and several layers of dental restoration. The marginal gap is unavoidable in dentistry but it
porcelain [5]. Feldspathic porcelains consists of glassy alumi- could be decreased or filled by precipitation of hydroxyapatite
nosilicate and crystalline leucite is mostly used for MCR [6–8]. by using the developed ceramic composites in only marginal
Leucite is a precious phase in the dental ceramic restorations. It areas of restorations. As well as for different purposes in
increases the thermal expansion of dental ceramics and results implant custom ceramic abutments at collar or emerging
in a good bonding to the metal framework [9]. Problems occur profile regions.
with the patient is associated with the failure of fixed MCR due Dental ceramic materials are bio-inert and unable to interact
to secondary carries [10–12]. This resulted in a plaque with the surrounding tissues [1,14]. According to L. L. Hench,
a bioactive glass prompts a specific biological response at
n
Corresponding author. the interface of the hard tissue and the material [15,16].
http://dx.doi.org/10.1016/j.ceramint.2015.11.022
0272-8842/& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
3592 P.H. Kumar et al. / Ceramics International 42 (2016) 3591–3597
A hydroxyapatite (HAp) layer is formed which enhances the Table 1
cell proliferation and the cell attachment, thereby sealing the Chemical compositions of the composites.
marginal gap [17–21]. Over the last few years, research has Sample coding Leucite Bioglass LTF Alumina
been carried on the development of apatite layer on dental
ceramics by adding the bioactive glass. Chatzistavrou et al. has Al-0 40 40 20 0
been reported the growth of a hydroxyapatite layer on the Al-2 39 39 20 2
Al-4 38 38 20 4
surface of a bioactive glass coated dental ceramic substrate [3].
Al-8 36 36 20 8
Kontonasaki et al. has been reported that the bioactive dental
*
glass ceramic composite promotes a higher cell proliferation LTF: Low temperature frit.
than that of the unmodified porcelain [19]. Chatzistavrou et al.
has been studied the sol–gel derived bioactive glass ceramic was quenched in water and dried at 110 1C for 3 h subse-
composite material for dental application [14]. They found that quently milled to pass a 350 BSS mesh. A similar procedure
the prepared bioactive glass ceramic composite shows the was used for the preparation of LTF [8].
similar characteristics to that of a commercial dental ceramic
[14]. They also observed the cell attachment and proliferation
2.2. Formulation of composites
of the periodontal ligament and gingival fibroblasts cells on the
surface of the developed material [14].
Composites (referred as Al-0, Al-1 and Al-2) were prepared
Furthermore, the addition of fine alumina to bioactive glass
by mixing the different wt. % of mechanochemically derived
ceramic composite may increase the mechanical properties.
leucite, bioglass, LTF and fine alumina. Compositions are
Alumina has the biocompatibility, high hardness and good
given in Table 1. The mixture was ground in an agate mortar
mechanical properties [22–24]. The glass is toughened and
for 20 minutes to get a homogenous mixing. The milled
strengthened when a crystalline material such as alumina is
mixture was pelletized using a uniaxial hydraulic press by
added to it. This is because the crack cannot pass through the
applying a load of 200 MPa. The pressed pellets were heat
fine alumina particles as easily as it can pass through the glass
treated at 950 1C using a VITA VACUMAT 40 T furnace. The
matrix [25]. This technique has found the application in
heating schedule is given in Table 2.
dentistry in the development of aluminous porcelain particles
in a glassy porcelain matrix for porcelain jacket crowns [25].
Most dental ceramics that have a glassy matrix utilize 2.3. Characterizations
reinforcement of the glass by a dispersed crystalline substance
[24,25]. 2.3.1. Phase analysis, microstructure and CTE
Furthermore, mechanochemically derived leucite based X-ray diffraction (XRD) of the composite powders (before
bioactive glass ceramic composite have been previously and after firing) was carried out to confirm the phase formation
synthesized by us. A superior bioactivity and the moderate using a portable X-ray diffractometer (Rigaku, Japan) with Cu
mechanical properties have been investigated [1]. Subse- Kα radiation employing Ni filter and operating at 30 mA and
quently, the aim of present study is to enhance the mechanical 40 kV. Diffraction peaks were analyzed using standard JCPDS
properties without affecting the biological and thermal proper- file (PDF-2 database 2003). All the sintered specimens were
ties of the leucite based dental ceramic composite. The results polished using emery papers of grade 400–800 (Sia, Switzer-
have also been compared with a commercial product (VITA land) followed by polishing on a velvet cloth using diamond
VMK 95) to validate the feasibility of the prepared composite. paste of grade 1/4-OS-475 (HIFIN). These polished specimens
The composite material does not cause any significant apop- were chemically etched with 2% hydrofluoric acid for 10 s.
tosis of SCC-25 cells and allow the cells to grow over its Finally, they were dried and gold sputtered to make a smooth
surface indicating a high degree of biocompatibility. Further, conducting surface. Micrographs of the coated samples were
no work has been reported on the effect of addition of alumina recorded using scanning electron microscopy (SEM)
to the mechanochemically synthesized leucite based bioactive (INSPECT 50 FEI).
glass ceramic composite. The rectangular bars of dimension 50 10 10 mm3 were
made in a similar manner as discussed earlier for CTE
2. Materials and methods measurements. CTE and glass transition temperature (Tg) of
the composites were studied using a dilatometer (VB Ceramic
2.1. Preparation of leucite, bioglass and LTF Consultants, India).
AR grade potassium carbonate, aluminum oxide and silicon 2.3.2. Flexural strength, apparent porosity and bulk density
dioxide (Loba Chemie Pvt. Ltd., Mumbai, India) was weighed Flexural strength measurements were done according to
and mixed in a stoichiometric ratio of leucite. This mixture was ASTM C78 M using a universal testing machine; Instron 3344
ground for 6 h in a Fritsch Pulverisette high-energy ball mill (Germany). The specimens were fractured in three-point
and subsequently fired at 1100 1C as discussed in our previous crossways fit with the 20 mm span between the two supports
work [7]. Bioglasss 45S5 was prepared on a lab scale by (three point bending). The load and the corresponding deflec-
melting in a platinum crucible at 1400 1C. The molten glass tions were recorded. The standard deviation, S of the flexural
P.H. Kumar et al. / Ceramics International 42 (2016) 3591–3597 3593
Table 2
The firing schedule of composites at 950 1C using a VITA VACUMAT 40T furnace.
Samples Pre-Drying 1C Min. - Min. ↗ Min. 1C/min ↗ Temp. 1C Min. - VAC min
Al-0 500 2 5.62 80 950 1 5.62
Al-2 500 2 5.68 80 955 1 5.68
Al-4 500 2 5.68 80 955 1 5.68
Al-8 500 2 5.75 80 960 1 5.75
different culture periods. SCC-25 cells were cultured up to 10
days in order to assess the cell's response on the materials
surface subsequent increase interaction time. The composite
pellets with cells were fixed in 2.5% (v/v) glutaraldehyde in
0.14 M sodium cacodylate buffer (pH 7.3) (both Sigma-
Aldrich) at 4 1C, dehydrated in a graded series of alcohols
(50%, 70%, 90%, and two changes of 100% ethanol). The
pellets were treated with hexamethyldisilazane (Sigma-
Aldrich) for 1–2 min and kept in a desiccator to dry overnight.
After 24 h, the pellets were attached on aluminum stubs,
sputter-coated with gold and record using a scanning electron
microscopy (SEM) (INSPECT 50 FEI) at 10 to 12 kV.
Representative samples of the surfaces were used for observa-
tion and recording of images.
3. Results and discussion
Fig. 1. XRD pattern of the composite before firing. 3.1. Phase analysis
Fig. 1 exhibits the XRD pattern of the composites before
firing. In the composites, leucite has been found to be a major
crystalline phase along with alumina phase. Diffraction peaks
are (Fig. 1) well matched to JCPDS Card No. 87–1707 and
81–1667. It is seen that the intensity of the peak corresponding
to the Al2O3 phase increases with increasing the alumina
content in the matrix. Fig. 2 shows the XRD patterns of the
composite samples after firing. Diffraction peaks are well
matched to JCPDS Card No. 74-0387 and 81-1667. As can be
seen from Fig. 2 that a major crystalline phase nepheline has
formed after firing (at 950 1C) along with some alumina
crystalline phase subsequently decreasing the amorphous
phase. A second phase nepheline is formed due to reaction
of alumina with the free ions (K þ , Na þ and Si4 þ ) present in
the matrix during heat treatment. Nepheline has the highest
coefficient of thermal expansion and good mechanical strength
which may further increase the mechanical properties of the
Fig. 2. XRD pattern of the composite after heat treatment up to 960 1C with prepared composites [26].
heating rate 80 1C /min.
3.2. Microstructure
strength values was also calculated. Apparent porosity (AP)
and bulk density (BD) of all the composite samples were Figs. 3–5 show the surface morphology of Al–0%, Al–4%
determined according to ASTM C20-00. and Al–8% composites. It is seen that glassy surface reduces
slightly with increasing the content of fine alumina in the
2.4. SEM evaluation of cell morphology composites. It is due to the presence of crystalline alumina
particles which are distributed homogeneously along the glassy
Three sintered pellets of each leucite glass–ceramic compo- matrix. Micrographs show a very dense morphology with no
sites were used to consider cells morphology on their surface at visible micro-crack on the surface. SEM micrographs along
3594 P.H. Kumar et al. / Ceramics International 42 (2016) 3591–3597
Fig. 3. SEM image showing the surface morphology after heat treatment
of Al-0%.
Fig. 6. SEM micrographs and EDS analysis after heat treatment of Al-0%.
Fig. 4. SEM image showing the surface morphology after heat treatment
of Al-4%.
Fig. 5. SEM image showing the surface morphology after heat treatment
of Al-8%. Fig. 7. SEM micrographs and EDS analysis after heat treatment of Al-8%.
P.H. Kumar et al. / Ceramics International 42 (2016) 3591–3597 3595
Fig. 10. Flexural strength of composites and commercial dentine.
Fig. 8. CTE curves of composites along with commercial dentine (VITA
VMK 2 M2).
prepared composite materials are, therefore, suitable for PFM as
its CTE values are close to that of nickel–chrome alloy
(13.90 10 6 /1C).
3.4. Bulk density (BD) and apparent porosity (AP)
Fig. 9 shows the BD and AP of the bioactive glass ceramic
composites containing different wt% of alumina. It is seen from
Fig. 8 that BD increases (from 1.93 to 2.26 g/cc) with increasing
the alumina content followed by a continuous decrease in the
AP. Micro fine alumina particles homogeneously dispersed
throughout the glassy matrix, improves the packing density of
Fig. 9. BD and AP of the bioactive glass ceramic composites with different
wt% of alumina. the composites consequently reduces the apparent porosity.
with the EDX spectra of the compositions, Al–0% and Al–8%
3.5. Flexural strength
are shown in Figs. 6 and 7. EDX spectra confirms the presence
of all the constituent elements in an expected concentration.
Fig. 10 shows the flexural strength of the composite and the
commercial dentine VITA VMK 2 M2. Flexural strength
3.3. Coefficient of thermal expansion (CTE) increases with increasing the fine alumina in the matrix.
Homogenous dispersion of fine alumina particles within the
Fig. 8 shows the CTE curves of the composites along with glassy matrix leads to enhance the mechanical strength. This is
the commercial dentine (VITA VMK 2 M2). It has been because a crack cannot pass easily through the crystalline
observed that the compositions, Al–0, Al–4, Al–8% and VITA alumina particles whereas in the case of glassy matrix, it passes
dentine have a CTE 14.80 10 6 /1C, 15.00 10 6 /1C, easily and hence decreases the mechanical strength [24]. This
17.8 10 6 /1C and 13.60 10 6 /1C respectively. CTE of technique has also been used in the dentistry for the develop-
the composites, Al–0 and Al–4 is very similar to that of ment of aluminous porcelains [24,25]. Consequently the
commercial dentin. It is seen from Fig. 8 that thermal synthesized composites show the superior sinterability, low
expansion of the composition Al–8% increase linearly i.e. porosity and high flexural strength. The strength of all alumina
there is no glass transition. It may be due to high content of added composites are nearly similar to that of the commercial
alumina present in the matrix. It is found that the addition of dentine. One of the reasons for enhancement in the flexural
fine alumina to the composites increases the CTE values of the strength of the alumina added composites is the formation of
final mixture. This is due to the presence of nepheline crystalline nepheline phase. It was also reported in the
crystalline phase (as can be seen from XRD patterns in Fig. 2) literature that nepheline increases the mechanical strength of
which has the high CTE in the range 12.1–16.6 10 6 /K [27]. the glass–ceramics [26]. It is, therefore, concluded that fine
Khater et al. was also reported that the formation of nepheline in alumina particles act as ‘crack stoppers’ preventing the
the glass-ceramic increases the CTE of the matrix [28]. These propagation of a crack throughout the body of the porcelain.
3596 P.H. Kumar et al. / Ceramics International 42 (2016) 3591–3597
Fig. 11. SEM image of the surface of (a) Al–0%, (b) Al–2%, (c) Al–4%, and (d) Al–8% composites. Showing the proliferation and spreading of SCC-25 cells after
10 days of culture on composites (all images at same magnification and scale bars represent 30 mm (inset).
3.6. Culture of SCC-25 cells on glass–ceramic composites applications in the dental restorations. The addition of alumina
to the glass ceramic composites results in the formation of
Fig. 11(a)–(d) show SEM images of the surface of leucite nepheline crystalline phase. This leads to enhance the CTE and
glass–ceramic composite samples. SEM morphology reveals the flexural strength of the samples. Alumina added leucite glass
proliferation of SCC-25 cells after 10 days of culture and it ceramic composites show high flexural strength than that of the
covers the whole surface of the sample. The images also show leucite based glass ceramic composite and commercial dentine.
that the cells adhered to all composites with a flattened and A uniform attachment of SSC-25 cells after 10 days of culture
lengthened morphology. Higher numbers of cells are attached on the surface of the composites has been observed. It confirms
on the surface of composites Al-2 and Al-4. This is in consistent that the addition of alumina to the leucite glass ceramic
with our results as observed with reference to growth inhibition composite is a successful approach to improve its mechanical
and cytotoxicity [Fig. 11(b) and (c)]. These results also suggest and biological properties.
that the prepared composite materials allows the growth of the
cells efficiently over its surface (Fig. 11).
Acknowledgement
4. Conclusions The authors gratefully acknowledge the financial support of
DST [(TDT Division), Reference No. DST/SSTP/UP/197
This study has shown the successful investigation of (G) 2012], Ministry of Science & Technology, New Delhi,
alumina based leucite glass ceramic composite for possible India.
P.H. Kumar et al. / Ceramics International 42 (2016) 3591–3597 3597
References bioactive glass–ceramic composites for dental applications, J. Eur.
Ceram. Soc. 32 (2012) 3051–3061.
[1] P.H. Kumar, V.K. Singh, A. Srivastava, S.K. Hira, P.P. Pradeep Kumar, [15] L.L. Hench, H.A. Paschall, Direct chemical bond of bioactive glass
Manna, Mechanochemically synthesized leucite based bioactive glass ceramic materials to bone and muscle, J. Biomed. Mater. Res. Symp 4
ceramic composite for dental veneering, Ceram. Int. 41 (2015) (1973) 25–42.
11161–11168. [16] O.M. Goudouri, E. Kontonasaki, N. Kantiranis, X. Chatzistavrou,
[2] H. Milly, F. Festy, F.T. Watson, I. Thompson, A. Banerjee, Enamel white L. Papadopoulou, P. Koidis, K.M. Paraskevopoulos, A bioactive glass/
spot lesions can remineralise using bio-active glass and polyacrylic dental porcelain system by the sol gel route: fabrication and characteriza-
acidmodified bio-active glass powders, J. Dent. 42 (2014) 158–166. tion, Key Eng. Mater. 396–398 (2009) 95–98.
[3] X. Chatzistavrou, D. Esteve, E. Hatzistavrou, E. Kontonasaki, [17] A.C. Meijering, N.H. Creugers, F.J. Roeters, J. Mulder, Survival of three
K. Paraskevopoulos, A.R. Boccaccini, Sol–gel based fabrication of novel types of veneer restorations in a clinical trial a 2.5-year interim
glass-ceramics and composites for dental applications, Mater. Sci. Eng. C evaluation, J. Dent. 26 (1998) 563–568.
30 (2010) 730–739. [18] S. Pitaru, H. Tal, M. Soldinger, A. Grosskop, M. Noff, Partial regenera-
[4] Contemporary Fixed Prosthodontics, in: I.L. Denry, L.W. Laub, tion of periodontal tissues using collagen barriers. Initial observations in
S.F. Rosenstiel, M.F. Land, J. Fujimoto (Eds.), Mosby Inc., third ed., the canine, J. Periodont 59 (1988) 380–386.
St. Louis, 2001, pp. 614–617. [19] E. Kontonasaki, A. Sivropoulou, L. Papadopoulou, P. Garefis,
[5] M. Mrazova, A. Klouzkova, Leucite porcelain fused to metals for dental K. Paraskevopoulos, P. Koidis, Attachment and proliferation of human
restoration, Ceram. Silik. 53 (2009) 225–230. periodontal ligament fibroblasts on bioactive glass modified ceramics,
[6] J.R. Mackert, M.B. Butts, R. Morena, C.W. Fairhurst, The effect of the J. Oral Rehabil. 34 (2007) 57–67.
leucite transformation on dental porcelain expansion, Dent. Mater. 2 [20] R.G. Craig, R.Z. Legeros, Early events associated with periodontal
(1986) 32–36. connective tissue attachment formation on titanium and hydroxyapatite
[7] P.H. Kumar, A. Srivastava, V. Kumar, S. Sharma, H. Singh, P. Kumar, surfaces, J. Biomed. Mater. Res. 47 (1999) 585–594.
V.K. Singh, Role of CaF2 on mechanochemically synthesized leucite as [21] A. Noaman, S.C.F. Rawlinson, R.G. Hill, Bioactive glass-stoichiometric
dental veneering glass ceramics, Adv. Appl. Ceram. 114 (2015) 107–113. wollastonite glass alloys to reduce TEC of bioactive glass coatings for
[8] P.H. Kumar, A. Srivastava, V. Kumar, N. Jaiswal, P. Kumar, V.K. Singh, dental implants, Mater. Lett. 94 (2013) 69–71.
Role of MgF2 addition on high energy ball milled kalsilite: implementa- [22] F.A.A. Sanabani, A.A. Madfa, N.H. Al-Qudaimi, Alumina ceramic for
tion as dental porcelain with low temperature frit, J. Adv. Ceram. 3 dental applications: A review article, Am. J. Mater. Res. 1 (2014) 26–34.
(2014) 332–338. [23] Guazzato, M. Albakry, M. Ringer, S.P. Swain, M.V, Strength, fracture
[9] E.E. Meliegy, R.V. Noort, Glasses and Glass Ceramics for Medical toughness and microstructure of a selection of all-ceramic materials. Part
Applications, Springer science & business media, Berlin, Germany, 2012 I. pressable and alumina glass infiltrated ceramics, Dent. Mater. 20 (2004)
Chapter-10 Leucite Glass Ceramics, LLC. 441–448.
[10] R. Ravarian, F. Moztarzadeh, M.S. Hashjin, S.M. Rabiee, [24] J.Anusavice Kenneth, Phillips’ science of Dental materials, Dent. Ceram.
P. Khoshakhlagh, M. Tahriri, Synthesis characterization and bioactivity (2007).
investigation of bioglass hydroxyapatite composite, Ceram. Int. 36 (2010) [25] John F. McCabe, Angus W.G. Walls, Applied dental materials, Ceram.
291–297. Porcelain Fused Metal (PFM) (2008).
[11] D. Felton, B. Kanoy, S. Bayne, G. Wirthman, Effect of in vivo crown [26] E.M.A. Hamzawy, E.A.M. El-Meliegy, Preparation of nepheline glass–
margin discrepancies on periodontal health, J. Prosthet. Dent. 65 (1991) ceramics for dental applications, Mater. Chem. Phys. 112 (2008)
357–364. 432–435.
[12] J.N. Walton, F.M. Gardner, J.R. Agar, A survey of crown and fixed [27] M.C. Wang, N.C. Wu, M.H. Hon, Preparation of nepheline glass-
partial denture failures: length of service and reasons for replacement, ceramics dental porcelain, Mater. Chem. Phys. 37 (1994) 370–375.
J. Prosthet. Dent. 56 (1986) 416–421. [28] G.A. Khater, E.M.A. Hamzawy, H.I. Metwally, E. El-Meliegy, Spodu-
[13] J. Waerhaug, Tissue reaction around artificial crowns, J. Periodont. 24 mene nepheline- anorthite glass ceramics for dental applications, J. Appl.
(1953) 172–185. Sci. Res. 9 (2013) 821–825.
[14] X. Chatzistavrou, O. Tsigkou, H.D. Amin, K. Paraskevopoulos, V. Salih,
A.R. Boccaccini, Sol–gel based fabrication and characterization of new
