- Email: [email protected]
The use of visible light-cured resin system in maxillofacial prosthetics and neuro-orthopedic surgery
MANAGEMENT
OFORALMUCOSITIS
12. Arbuck SG. 5.FU/Leucnvorin: bioclemical modulation that works? Oncology 1987:1:61-‘70. 13. Arbuck SG, Ijouglass HO Jr, Travel F, Milliron S, Baroni M, Nava H, Emrich LJ, Rusturn YM. A phas: II trial of 5-Fluorouracil and high-dose intravenous 1e:lcovorin in gastric carcinoma. J Clin Onrol 1987;5:1150-6.
Reprint requests to: DR. WILLIAM CARL ROSWELLPARKMEMORIALINSTITIJTE ELMANDCARLTONSTS. BUFFALO,NY 14263
The use of visiblle light-cured resin system in maxillofacial prosthetics and neuro-orthopedic surgery M. M. Alsa-waf, DDS, MS,* R. Segal, MD,b A. Tabatabai, and R. E. McKinstry, IDMD, MDS,d University Health Center of Pittsburgh, Medical Center, Pittsburgh, Pa.
School of Dental Medicine,
MD,C
and Veterans Administration
The us’e of visible light-cured (VLC) resin was evaluated in contrast to more traditional chemical-cured resins for reconstruction of the spine in experimental rats. Such procedures are used to reconstruct vertebra in humans following corpectomy for neoplastic destruction of the spine. Numerous disadvantages exist in the use of chemical-cured resins, including excessive heat generated during the polymerizat:ion, cytotoxic effects of the nonpolymerized monomers on adjacent tissues, incrseased risk of infection due to impaired immunity, and distortion problems with the polymers. A new visible light-cured resin, Triad, was tested for use in lmaxillofacial prosthetics and for vertebral body replacement in neuroorthopedic surgery. This study evaluated the biocompatibility of the VLC resin system as a bone implant material. The results of this study have shown the VLC resins underwent polymerization without substantial exothermic reaction and the biologic testing indicated that they are nontoxic and biocompatible. Some of the advantages noticed by using VLC resin are accuracy of fit and ease of fabrication and manipulation. (J PROSTHET DENT 1991;66:369-76.)
METHYL
METHACRYLATE
SYSTEMS
The availability and ease of manipulation of autopolymerizing methyl methacrylate resin systems (chemicalcured acrylic resins) have led to their increased use for reconstruction of large cranial defects1-3 and for vertebral body replace.ment following corpectomy for neoplastic destruction of the spine. 4p5 In patients with neoplasms, the acrylic resin provides immedke stabilization that allows
Presentedat the American Academyof Maxillofacial Prosthetics meeting, Tucson, Ariz. *Clinical Fellow, Department
of Ma:uillofacial
Prosthodontics,
Eye
and Ear Hospital of Pittsburgh. bChief, Neurological Surgery, Center. CResearch Fellow, Neurological IMedical Center
Veterans
Administration
Medical
Surgery, Veterans Administration
dAssistantProfessor,andDirector, Regional Center for Maxillofacial ProstheGc burgh.
Rehabilitation,
Eye and Ear Hospital
Fig. 1. Anterior surgical appproach exposed first, second, and third cervical vertebral bodies (Cl, C2, and C3).
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2. Corpectomy of C3 vertebral body shows anterior spinal artery (A) through dura. 3. Vertebral body replacement using visible light-cured resin (VLC) was polymerized with hand-held ultraviolet light source. Fig. 4. Visible light-cured resin (VLC) bone substitute implant after setting. Fig. 5. Vertebral body replacement using methyl methacrylate resin (MM). Fig. Fig.
Fig.
6. Lateral cervical radiograph (flexion).
early ambulation and minimizes pulmonary and embolic complications. In view of the limited life expectancy of these cancer patients, chemically-cured resins as an immediate stabilizing agent offer major advantages over bone grafts. Although chemical cure acrylic resin systems have been used widely for various procedures in dentistry and as bone substitutes in neurosurgery and orthopedic surgery 370
Fig.
7. Lateral cervical radiograph (extension).
for four decades, they present the following significant disadvantages.a 1 1. There is an exothermic reaction from the heat of polymerization that may exceed the coagulation temperature of the tissue proteins (about 80’ to 100’ C) and may result in damage to bone, dura mater, and brain or spinal tissue.8 SEPTEMBER
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Fig. 11. At a higher power magnification in the micrograph, the implant-tissue interface is obliterated by dense exudate of leukocytes and histiocyte cells (H). B, Bone; im, implant.
Fig. 8. Histologic cross section before staining shows spine (S), vertebral body (‘J), esopl.agus (E), and trachea (T).
Fig. 12. This section shows example of vascular granulation tissue occupied by capillary network (C), lymphocytes (L), and a few macrophages CM). B. Bone: im, implant.
Fig. 9. Cervical radIograph shows defect after 2 momhs of implant insertion and splinting.
2. There is a cytotoxic and lipolytic effect of the nonpolymerized monomer to the surrounding tissue. Loss of excess free monomer by evaporation during late polymerization results in a weaker, more porous final product with a rough surface that could lead to possible bacterial adherence and potential late infection. 3. There is increased risk of infection9 due to decreased chemotaxis of leukocytes9 and impairment of the phagocytosis’” and killing of bacteria normally performed by polymorphonuclear leukocytes.” 4. There is a dimensional change, involving contraction and shrinkage when polymerization is complete, which results in less accuracy and adaptation to the defect. 5. There is decreasing mechanical stability with time under conditions of cyclical loading.”
VISIBLE SYSTEMS F’ig. 10. Histologic cross section (original magnification X251 shows implant rim), bone (B), spinal cord (S), dura mater M), a.?d gr.s.nulstion tissue (g) surrounding implant. THE
JOURNAL
OF PROSTHETIC
Dl:NTISTRY
LIGHT-CURED
RESIN
The introduction of Triad visible light-cured (VLC) urethane dimethacrylate resin systems (Dentsply International Inc., York, Pa.) in dental health sciences promises to 371
ALSAWAF
ET AL
Fig. 13. Histologic cross section shows implant (Grz), bone (B), spine (S), dura mater (d), anterior spine artery (A), and fibrous scar tissue (f) surrounding implant.
Fig. 16. Histologic cross section shows bone-implant (B, im) approximation. f, Fibrous scar tissue.
Fig. 14. At high power magnification in the micrograph, implant-tissue interface was filled with collagen and spindle-shaped fibroplasts (F). B, Bone; im, implant.
Fig. 17. At a higher magnification, thin fibrous tissue interface is less than 10 nm. Abbreviations as in Fig. 16.
Fig. 16. Bar graph of the number of specimens versus bone-implant interface distances. 272
further improve alloplastic implants in accuracy of fit, simplicity of construction, strength, and dimensional stability. The Triad system may also possess a lower inflammatory response and bacterial adherence when compared with the chemical-cured acrylic resin system.6 This VLC resin material is similar to light-cured composite resin filling material, which has been used for dental restorations. It differs from light-cured composite resin filling material in that it contains an organic filler rather than inorganic fillers. This filler is made of acrylic resin beads of different sizes that become part of the polymer network structure upon curing. The matrix is a urethane dimethacrylate with microfine silica that provides workable handling qualities and controls the flowability of the material. Triad resin also contains a camphoroquinone amine photoinitiator that is sensitive to 400 to 500 nm wave lengths of blue visible intense collimated light. This light activates polymerization of the resin in the matrix and results in deep curing of the material to a depth of 5 to 6 mm. There is no free methyl methacrylate monomer in the uncured or cured material.13 SEPTEMBER
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Table
RESII’;
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Table III. Percentages of inflammation findings in specimens with two different implant materials at 2 months after insertion
Animal model profile
I.
Time 2
months
Material
Visible light--cured resin Auto chemically cured resin Total
4 months
6 months
Inflammation
Total
12 Rats 12 Rats
6 Rats 6 Rats
4 Rats 4 Rats
22 Rats 22 Rats
24 Rats
12 Rats
8 Rats
44 Rats
-Moderate
Visible light-cured chemically
Auto
Table II. Average percentage of distances between two different implants and bone at 2 months after insertion
0-!iO Cc1n
51-100 w
Visible light- -cured rest n
42’~ n =- j
Auto chemically
33-c n= 4 ‘>
33 5 n=4 42’, n=5 9
cured resin
Total
resin cured resin
Total
Mild
0
17’ n = 2 i’
II
2
0
None -
Total
‘%1’~ rr = 10 100 ’ ,I= 1”
12
“”
24
12
x2 = 0.5454. p = 0.1602.
Distances
Material
+ *~
Material
rkgrees
101-200 m
Total
25 Cc n=:i 25’t n = :i 6
of frePdom
= 1.
IV. Percentages of granulation tissue findings in specimens with two different implant materials at 2 months after insertion
Table 1’1 _
Granulation
1% 24
Moderate
Mild
++
Material
-+
None -
Total
12
x:' = 0.2222. p = 0.8948.
Physical
Visible light-cured
properties
of ‘VLC resin material
VLC resin material has been subjected to numerous tests and has been found to exceed the American Dental Association (ADA) specification No. 12 for denture base resins.14 Some of the physical properties of the material
Auto chemically
resin cured resin
I;’ n-2 X3’,
75’< n=9
)I = :3
r1=1
n=5
4
Total k* =
8’, II = 1 251,
1;
421,
l-1
12
24
2.8095.
p = 0.2454.
Degrees of’ t’reedom = 2.
are:
1. The linear shrinkage of VLC resin is less when compared with heat-1:ured resin (HC) and autopolymerizing resin (AP). 2. The tensile strength of VLC resin is greater than that of HC and AP resins. 3. Data from the dimensional change tests indicate that VLC resin is superior in fit to HC and AP resins. 4. VLC resin is stiffer than HC and AP resins,6,19-15 making the VLC brittle by comparison with the other resin systems. Also, the Triad material showed greater staining than the acr,ylic resin material,16 and it formed voids on the tissue side upon adaptation.17 The Triad system is availakle in sheets of 2 mm thickness, in rope form, or in gel ointment form packed in lightshielded envelopes to prevent premature polymerization. The material is thermoplastic. At room temperature it has the consiste:ncy of glazing putty and can be readily shaped by finger pressure and with instruments. When lower viscosity is desired, it can be heated in its package in a water bath before opening. This procedure allows control of the material for various application procedures with good flowability to adapt to the tissues of various ranges of disp1acemen.t.l” The results of toxicity tests that were conducted on anirnals by several scientific laboratories to meet Food and Drug Administration (FDA) specifications showed the THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Table V. Percentages of fibrosis findings in specimens with two different implant materials at 2 months after insertion Fihrosis Moderate
Material Visible light-cured Auto
chemically
Total
resin cured resin
Mild
T+
r
50’r fl=6 75’ I n-9
ii?’ ;: = 8:
I,
9
5’ .>=/
None
-
Total
i:
I”
0 0
24
1”
y2 = 0.7111 p = 0.3991
cured VLC material to be nontoxic and the uncured material to be of low toxicity. l5 There were no mucous membrane or skin irritations and the VLC resin was nonmutagenie and was not cytotoxic to fibroblast cells.” This study evaluated the biocompatibility of the VLC resin Triad system as a bone implant material by using it for vertebral body replacement and immediate fixation following corpectomy. To date there has been no research on the biocompatibility of VLC resin as a dental implant material. 373
ALSAWAF
Fig. 18. Bar graph of the number of specimens versus the amount of inflammation in the tissue reaction. Inflammation was graded as: severe, moderate, mild, and none.
ET AL
Fig. 20. Bar graph of the number of specimens versus the amount of fibrosis in the tissue reaction.
different time intervals (2,4, and 6 months) searching for inflammatory or necrotic tissue changes, and the implantbone interface was investigated and asssessedby measuring the percentage of implant anchorage directly apposed to bone.i8 A pilot study on four rats who underwent craniotomy and cranioplasty using VLC resin was done to familiarize the surgeon with the new material and to standardize the operative technique. A stereotactic apparatus for positioning and immobilization of the animal’s head was used in this study.
Implant
Fig. 19. Bar graph of the number of specimens versus the amount of granulation tissue reaction. Granulation was graded as: severe, moderate, mild, or none.
MATERIAL
AND METHODS
This investigation was designed with a small animal model of cervical corpectomy and vertebral body replacement to evaluate the use of VLC resin compared with conventional chemical-cured resins. A total of 44 young adult Sprague-Dawley rats was used in this study. All animals weighed between 250 and 450 gm and were between 2 and 3 months of age.The population was divided into three sets of 24,12, and 8 rats that were to be put to death at 2,4, and 6 months, consecutively, after construction of the implant (Table I). The biocompatibility of the material was tested by chronic spinal implantation in rats. Spinal cord function was assessedby assigning a neurologic score and by checking spinal stability with dynamic radiographs. The spine, meninges, and spinal cord were studied histologically at
and surgical
technique
The rats underwent a microsurgical anterior cervical approach and corpectomy under aseptic conditions. During the surgical sessions, the animals were anesthetized with intraperitoneal injections of ketamine hydrochloride, 100 mg per kg, and acepromazine (Parke-Davis, Morris Plains, N.J.), 1 mg per kg. In the first group, the corpectomy defect was filled with VLC resin. A multiple layer technique and several visible light applications of 500 nm wavelength were used to ensure complete depth of polymerization.1g-22 The VLC resin was polymerized in situ with a hand-held visible light source (Efos, Fiber Optic Systems, Buffalo, N.Y.) for 60 seconds using the 8 mm diameter curved light guide (Figs. 1 through 4). In the second group, sterile chemically-cured autopolymerized methyl methacrylate (L.D. Caulk Co., Milford, Del.) was used (Fig. 5). Following surgery, neither antibiotics nor external orthosis was used, and unrestricted immediate activity was allowed. Clinical evaluation was performed throughout the duration of the experiment. Neurologic assessments for limb motor strength, gait, and feeding ability were graded 1 through 4. This allowed for quantitative, comparable measurements of neuromuscular coordination and work capacity of muscle groups. SEPTEMBER
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Preparation
of specimens
Cervical stability u as assessed in flexion and extension. L,ateral cervical radiographs were made before the animals were put to death, an.1 at 2,4, and 6 months after implant surgery (Figs. 6 and 7 s. The cervical spine was retrieved en bloc and axial sectiol s 5 mm in thickness were cut with a jeweler’s saw The specimens were dehydrated and were then embedded in acr,:lic resin Sections 20 pm in thickness were obtained with an Isomit Exact. sawing machine (IBuehler Ltd., Lake Bluff, Ill.) ander water irrigation*:’ and were stained with hernatoxylir and eosin for light microscopy to histol~ogically demonstrate the bone-to-implant interface and to investigate an;,1 inflammatory and/or necrotic change? (Fig. ? 6‘
RESULTS The measurements in this study were based on the neurophysical test scores and histopathologic test scores of a degree of tissue reaction to the mplants. Also the distances o:f the implant-bone iilterface xvere measured between the two groups. In both groups, no animal had radiographic signs of cervical instability (Fig. t) or a postoperative neurologic deficit, and all rats were graded i- in the neurologic function scales t,est. At death there was no evidence of implant fracture or extrusion nor any s,igns of biologic reaction on the adjacent meninges or spinal cord. The tissue reactions to the implants were described, graded, and categorized under histologic terms of inflammation, granulation, and fibrosis. The presence of intlammation was recognized by histologic observation of i he accumulation of histiocytes and leukocytes 1Figs. 10 and 11). The tissue reaction was attributed to contamination from the surgical procedure at the time of implantation. Granulation was characterized by the presence of lymphocytes, a highly vascular connective tissue, and capillaries (Fig. 12). These accumulations are associated with responses and reactions to the existence of foreign bodies in tht: system. The surgical injury was repaired by the formation of gmanulation tissue, which results in subsequent collagen scar formation. The avascular scar was recognized bv the presence of fibrocytes and collagen, and represents the fibrosis reaction (Figs. 13 and 14). Morphologically, the interface at 2 months after implant insertion consist,ed of fibrous tissue of the thickness of several cell layers, which ranged between 0 and 200 Frn in both groups. The measurements of the interface distances are summarized in Fig. 15 and in Table II. On average, 42’; of the specimens with VLC resin implants had surfaces with close approximatil>n to bone tissue (Figs. 16 and 17). The chi-square test was usec. to compare the variability between both materials and to analyze the preliminary data obtained from the 24 specimens of animals that were put to death at 2 months after construction of the implants. The p value!, for this test are shown in Tables II through V and in Fig;. 15 and 18 through 20. No significant differences (I-, = 0 24), ,I) = ie.39). and p = 0.46) in the measurement of the tissues’ reaction to the implants ~inflammaTHE
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HETIC
DENTISTRY
tion, granulation, and fibrosis) were found hetween the two groups. No significant differences !F = 0.89) in the measurement of implant-bone anchorage was observed between tht two groups.
DISCUSSION Methyl methacrylate resin has been used to provide immediate fixation and to eliminate the need for external bracing of a spine that must be stabilized because of destruction by a malignant tumor. However. there are some theoretical disadvantages related to the use of chemicalcured methyl methacryiai e resin dur to the Jaw release of free monomer. chemotaxis-exothermic reaction. and the risk of infection because of its porosity and possible bacterial adherence. The new light-cured resin Triad has been investigated for use in spinal surgery because of its advantages in acturaq’ of fit. superior strength, complete polymerization. and low bacterial adherence, -which has been reported previously in dentistry. Additionally, the visible blue light is capable of penetrating the Triad resin to provide a germicidal effect.” In this study, no significant differences in bone anchorage or tissue reaction to the implant materials between the two groups after 2 months of implant Insertion had been observed. However, forthcoming data show an increase in the amount of bone formed at the interface after 4 and 6 months rif implant insertion. The pxperlmental results sugggest 1hat VLC resin could be used safely for vertebral body replacement. An additional advant,ape of VLC resin over methy! methacrylate resin was the ease of manipulation. Preliminary studie;l of VLC resin:, have produced promising results. Biologic testing of’ Triad material indicates that it is nontoxic and biocompatibk. However. additional research is necessary. A sttlrly in the nonhuman primate f?XdXJOnj will be undertaken io evaluate the longterm maintenance of spinal stability in an animal model with upright posture in which resl:ltb c>)uld be better extrapolated to man.
CONCLUSION This new biocompatible implant material is easier to manipulate and less prone to failure or infections than chemically cured methyl methacrylate. Ir allows safe immediate stabilization and early ambulation in an animal model with surgically created destruction of the spine. Additional advantages may result from extending the use of this material for other surgical procedures
ALSAWAF
5. Siegal T, Siegal T. Vertebral body resection for epidural compression by malignant tumors. Results of forty-seven consecutive operative procedures. J Bone Joint Surg 1985;67:375-82. 6. Ogle RE, Sorensen SE, Lewis EA. A new visible light-cured resin system applied to removable prosthodontics. J PROSTHETDENT 1986; 56:497-506. 7. McAfee PC, Bohlman HH, Ducker T. Failure of stabilization of the spine with methyl methacrylate. J Bone Joint Surg 1986;68A:1145-57. 8. Tuckfield WJ. Acrylic resins in dentistry. Part II. Their use for denture construction. Aust J Dent 1943;47:1-26. 9. Petty W. The effect of methyl methacrylate on chemotaxis of polymorphonuclear leukocytes. J Bone Joint Surg 1978;606:492-8. 10. Green SA. The effect of methyl methacrylate on phagocytosis. In: Proceedings for the Orthopedic Research Society. J Bone Joint Surg 1975;57:583. 11. Petty W. The effect of methyl methacrylate on bacterial phagocytosis and killing by human polymorphonuclear leukocytes. J Bone Joint Surg 1918;60:752-7. 12. White AA, Panjabi MM. Biomechanical considerations in the surgical management of the spine. Part 3. Surgical constructs employing methyl methacrylate. In: Clinical biomechanics of the spine. Philadelphia: JB Lippincott, 1978:423-31. 13. Ortman HR. Refitting denture bases with a visible light-cured denture base resin. NY State Dent J 1986;52:29-32. 14. Council on Dental Materials and Devices. Revised American Dental Association Specification No. 12 for denture base polymers. J Am Dent Assoc 1975;90:451-8. 15. Lewis EA, Ogle RE, Sorensen SE. Orthodontic applications of a new visible light-curing (VLC) resin system. NY State Dent J 1986;52:32-4. 16. Khan Z, Von Fraunhofer JA, Razavi R. The staining characteristic, transverse strength, and microhardness of a visible light-cured denture base material. J PROSTHETDENT 1987;57:384-6. 17. Tan HK, Burdvik JS, Nicholls JI, Smith DE. Adaptation of a visible light-cured denture base material. J PROSTHETDENT 1988;61:326-33.
376
ET AL
18. Johnansson C, Albrektsson T. Integration of screw implants in the rabbit: a l-year follow-up of titanium implant. Int J Oral Maxillofac Implant 1987;2:69-75. 19. Leung R, Fan PL, Johnston WM. Exposure time and thickness of polymerization of visible light composite. J Dent Res 1982;61:248. 20. Baharav H, Abraham D, Cardash HS, Helft M. Effect of exposure time on the depth of polymerization of a visible light composite resin. J Oral Rehabil 1988;15:167-72. 21. Matsumoto H, Gres HE, Marker VA, et al. Depth of cure of visible light-cured resin: clinical simulation. J PROSTHETDENT 1986;55:574-8. 22. Eli I, Weiss E, Littner MM, Drutman M. Sequentially light-cured composites: strength of bond between layers. J PROSTHET DENT 1986;56:158-61. 23. Maniatoppulos C, Rodriguez A, Deporter DA, et al. An improved method for preparing histological sections of metallic implants. Int J Oral Maxillofac Implant 1988;1:31-7. 24. Harstad JB, Decker HM, Wedum AC. Use of ultraviolet irradiation in room air conditioner for removal of bacteria. Appl Microbial 1954;2:14851. Reprint requests to: DR. MOUFID ALSAWAF P.O. Box 607151 ORLANDO,FL 32860-7151
Contributing
authors
R. Saito, MD, Chief, Pathology Department, Veterans Administration Medical Center, Pittsburgh, Pa. J. M. Close, MS, Learning Resources Center, University of Pittsburgh, School of Dental Medicine, Pittsburgh, Pa.
SEPTEMBER
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VOLUME
66
NUMBER
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OFORALMUCOSITIS
12. Arbuck SG. 5.FU/Leucnvorin: bioclemical modulation that works? Oncology 1987:1:61-‘70. 13. Arbuck SG, Ijouglass HO Jr, Travel F, Milliron S, Baroni M, Nava H, Emrich LJ, Rusturn YM. A phas: II trial of 5-Fluorouracil and high-dose intravenous 1e:lcovorin in gastric carcinoma. J Clin Onrol 1987;5:1150-6.
Reprint requests to: DR. WILLIAM CARL ROSWELLPARKMEMORIALINSTITIJTE ELMANDCARLTONSTS. BUFFALO,NY 14263
The use of visiblle light-cured resin system in maxillofacial prosthetics and neuro-orthopedic surgery M. M. Alsa-waf, DDS, MS,* R. Segal, MD,b A. Tabatabai, and R. E. McKinstry, IDMD, MDS,d University Health Center of Pittsburgh, Medical Center, Pittsburgh, Pa.
School of Dental Medicine,
MD,C
and Veterans Administration
The us’e of visible light-cured (VLC) resin was evaluated in contrast to more traditional chemical-cured resins for reconstruction of the spine in experimental rats. Such procedures are used to reconstruct vertebra in humans following corpectomy for neoplastic destruction of the spine. Numerous disadvantages exist in the use of chemical-cured resins, including excessive heat generated during the polymerizat:ion, cytotoxic effects of the nonpolymerized monomers on adjacent tissues, incrseased risk of infection due to impaired immunity, and distortion problems with the polymers. A new visible light-cured resin, Triad, was tested for use in lmaxillofacial prosthetics and for vertebral body replacement in neuroorthopedic surgery. This study evaluated the biocompatibility of the VLC resin system as a bone implant material. The results of this study have shown the VLC resins underwent polymerization without substantial exothermic reaction and the biologic testing indicated that they are nontoxic and biocompatible. Some of the advantages noticed by using VLC resin are accuracy of fit and ease of fabrication and manipulation. (J PROSTHET DENT 1991;66:369-76.)
METHYL
METHACRYLATE
SYSTEMS
The availability and ease of manipulation of autopolymerizing methyl methacrylate resin systems (chemicalcured acrylic resins) have led to their increased use for reconstruction of large cranial defects1-3 and for vertebral body replace.ment following corpectomy for neoplastic destruction of the spine. 4p5 In patients with neoplasms, the acrylic resin provides immedke stabilization that allows
Presentedat the American Academyof Maxillofacial Prosthetics meeting, Tucson, Ariz. *Clinical Fellow, Department
of Ma:uillofacial
Prosthodontics,
Eye
and Ear Hospital of Pittsburgh. bChief, Neurological Surgery, Center. CResearch Fellow, Neurological IMedical Center
Veterans
Administration
Medical
Surgery, Veterans Administration
dAssistantProfessor,andDirector, Regional Center for Maxillofacial ProstheGc burgh.
Rehabilitation,
Eye and Ear Hospital
Fig. 1. Anterior surgical appproach exposed first, second, and third cervical vertebral bodies (Cl, C2, and C3).
101/l/21773
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of Pitts-
OF PROSTHETIC
DENTISTRY
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ALSAWAF
ET AL
2. Corpectomy of C3 vertebral body shows anterior spinal artery (A) through dura. 3. Vertebral body replacement using visible light-cured resin (VLC) was polymerized with hand-held ultraviolet light source. Fig. 4. Visible light-cured resin (VLC) bone substitute implant after setting. Fig. 5. Vertebral body replacement using methyl methacrylate resin (MM). Fig. Fig.
Fig.
6. Lateral cervical radiograph (flexion).
early ambulation and minimizes pulmonary and embolic complications. In view of the limited life expectancy of these cancer patients, chemically-cured resins as an immediate stabilizing agent offer major advantages over bone grafts. Although chemical cure acrylic resin systems have been used widely for various procedures in dentistry and as bone substitutes in neurosurgery and orthopedic surgery 370
Fig.
7. Lateral cervical radiograph (extension).
for four decades, they present the following significant disadvantages.a 1 1. There is an exothermic reaction from the heat of polymerization that may exceed the coagulation temperature of the tissue proteins (about 80’ to 100’ C) and may result in damage to bone, dura mater, and brain or spinal tissue.8 SEPTEMBER
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VOLUME
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NUMBER
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VLC
RESI
V SY :iTE\!
Fig. 11. At a higher power magnification in the micrograph, the implant-tissue interface is obliterated by dense exudate of leukocytes and histiocyte cells (H). B, Bone; im, implant.
Fig. 8. Histologic cross section before staining shows spine (S), vertebral body (‘J), esopl.agus (E), and trachea (T).
Fig. 12. This section shows example of vascular granulation tissue occupied by capillary network (C), lymphocytes (L), and a few macrophages CM). B. Bone: im, implant.
Fig. 9. Cervical radIograph shows defect after 2 momhs of implant insertion and splinting.
2. There is a cytotoxic and lipolytic effect of the nonpolymerized monomer to the surrounding tissue. Loss of excess free monomer by evaporation during late polymerization results in a weaker, more porous final product with a rough surface that could lead to possible bacterial adherence and potential late infection. 3. There is increased risk of infection9 due to decreased chemotaxis of leukocytes9 and impairment of the phagocytosis’” and killing of bacteria normally performed by polymorphonuclear leukocytes.” 4. There is a dimensional change, involving contraction and shrinkage when polymerization is complete, which results in less accuracy and adaptation to the defect. 5. There is decreasing mechanical stability with time under conditions of cyclical loading.”
VISIBLE SYSTEMS F’ig. 10. Histologic cross section (original magnification X251 shows implant rim), bone (B), spinal cord (S), dura mater M), a.?d gr.s.nulstion tissue (g) surrounding implant. THE
JOURNAL
OF PROSTHETIC
Dl:NTISTRY
LIGHT-CURED
RESIN
The introduction of Triad visible light-cured (VLC) urethane dimethacrylate resin systems (Dentsply International Inc., York, Pa.) in dental health sciences promises to 371
ALSAWAF
ET AL
Fig. 13. Histologic cross section shows implant (Grz), bone (B), spine (S), dura mater (d), anterior spine artery (A), and fibrous scar tissue (f) surrounding implant.
Fig. 16. Histologic cross section shows bone-implant (B, im) approximation. f, Fibrous scar tissue.
Fig. 14. At high power magnification in the micrograph, implant-tissue interface was filled with collagen and spindle-shaped fibroplasts (F). B, Bone; im, implant.
Fig. 17. At a higher magnification, thin fibrous tissue interface is less than 10 nm. Abbreviations as in Fig. 16.
Fig. 16. Bar graph of the number of specimens versus bone-implant interface distances. 272
further improve alloplastic implants in accuracy of fit, simplicity of construction, strength, and dimensional stability. The Triad system may also possess a lower inflammatory response and bacterial adherence when compared with the chemical-cured acrylic resin system.6 This VLC resin material is similar to light-cured composite resin filling material, which has been used for dental restorations. It differs from light-cured composite resin filling material in that it contains an organic filler rather than inorganic fillers. This filler is made of acrylic resin beads of different sizes that become part of the polymer network structure upon curing. The matrix is a urethane dimethacrylate with microfine silica that provides workable handling qualities and controls the flowability of the material. Triad resin also contains a camphoroquinone amine photoinitiator that is sensitive to 400 to 500 nm wave lengths of blue visible intense collimated light. This light activates polymerization of the resin in the matrix and results in deep curing of the material to a depth of 5 to 6 mm. There is no free methyl methacrylate monomer in the uncured or cured material.13 SEPTEMBER
1991
VOLUME
66
NUMBER
3
NIEW
VLC
Table
RESII’;
SYSTEM
Table III. Percentages of inflammation findings in specimens with two different implant materials at 2 months after insertion
Animal model profile
I.
Time 2
months
Material
Visible light--cured resin Auto chemically cured resin Total
4 months
6 months
Inflammation
Total
12 Rats 12 Rats
6 Rats 6 Rats
4 Rats 4 Rats
22 Rats 22 Rats
24 Rats
12 Rats
8 Rats
44 Rats
-Moderate
Visible light-cured chemically
Auto
Table II. Average percentage of distances between two different implants and bone at 2 months after insertion
0-!iO Cc1n
51-100 w
Visible light- -cured rest n
42’~ n =- j
Auto chemically
33-c n= 4 ‘>
33 5 n=4 42’, n=5 9
cured resin
Total
resin cured resin
Total
Mild
0
17’ n = 2 i’
II
2
0
None -
Total
‘%1’~ rr = 10 100 ’ ,I= 1”
12
“”
24
12
x2 = 0.5454. p = 0.1602.
Distances
Material
+ *~
Material
rkgrees
101-200 m
Total
25 Cc n=:i 25’t n = :i 6
of frePdom
= 1.
IV. Percentages of granulation tissue findings in specimens with two different implant materials at 2 months after insertion
Table 1’1 _
Granulation
1% 24
Moderate
Mild
++
Material
-+
None -
Total
12
x:' = 0.2222. p = 0.8948.
Physical
Visible light-cured
properties
of ‘VLC resin material
VLC resin material has been subjected to numerous tests and has been found to exceed the American Dental Association (ADA) specification No. 12 for denture base resins.14 Some of the physical properties of the material
Auto chemically
resin cured resin
I;’ n-2 X3’,
75’< n=9
)I = :3
r1=1
n=5
4
Total k* =
8’, II = 1 251,
1;
421,
l-1
12
24
2.8095.
p = 0.2454.
Degrees of’ t’reedom = 2.
are:
1. The linear shrinkage of VLC resin is less when compared with heat-1:ured resin (HC) and autopolymerizing resin (AP). 2. The tensile strength of VLC resin is greater than that of HC and AP resins. 3. Data from the dimensional change tests indicate that VLC resin is superior in fit to HC and AP resins. 4. VLC resin is stiffer than HC and AP resins,6,19-15 making the VLC brittle by comparison with the other resin systems. Also, the Triad material showed greater staining than the acr,ylic resin material,16 and it formed voids on the tissue side upon adaptation.17 The Triad system is availakle in sheets of 2 mm thickness, in rope form, or in gel ointment form packed in lightshielded envelopes to prevent premature polymerization. The material is thermoplastic. At room temperature it has the consiste:ncy of glazing putty and can be readily shaped by finger pressure and with instruments. When lower viscosity is desired, it can be heated in its package in a water bath before opening. This procedure allows control of the material for various application procedures with good flowability to adapt to the tissues of various ranges of disp1acemen.t.l” The results of toxicity tests that were conducted on anirnals by several scientific laboratories to meet Food and Drug Administration (FDA) specifications showed the THE
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Table V. Percentages of fibrosis findings in specimens with two different implant materials at 2 months after insertion Fihrosis Moderate
Material Visible light-cured Auto
chemically
Total
resin cured resin
Mild
T+
r
50’r fl=6 75’ I n-9
ii?’ ;: = 8:
I,
9
5’ .>=/
None
-
Total
i:
I”
0 0
24
1”
y2 = 0.7111 p = 0.3991
cured VLC material to be nontoxic and the uncured material to be of low toxicity. l5 There were no mucous membrane or skin irritations and the VLC resin was nonmutagenie and was not cytotoxic to fibroblast cells.” This study evaluated the biocompatibility of the VLC resin Triad system as a bone implant material by using it for vertebral body replacement and immediate fixation following corpectomy. To date there has been no research on the biocompatibility of VLC resin as a dental implant material. 373
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Fig. 18. Bar graph of the number of specimens versus the amount of inflammation in the tissue reaction. Inflammation was graded as: severe, moderate, mild, and none.
ET AL
Fig. 20. Bar graph of the number of specimens versus the amount of fibrosis in the tissue reaction.
different time intervals (2,4, and 6 months) searching for inflammatory or necrotic tissue changes, and the implantbone interface was investigated and asssessedby measuring the percentage of implant anchorage directly apposed to bone.i8 A pilot study on four rats who underwent craniotomy and cranioplasty using VLC resin was done to familiarize the surgeon with the new material and to standardize the operative technique. A stereotactic apparatus for positioning and immobilization of the animal’s head was used in this study.
Implant
Fig. 19. Bar graph of the number of specimens versus the amount of granulation tissue reaction. Granulation was graded as: severe, moderate, mild, or none.
MATERIAL
AND METHODS
This investigation was designed with a small animal model of cervical corpectomy and vertebral body replacement to evaluate the use of VLC resin compared with conventional chemical-cured resins. A total of 44 young adult Sprague-Dawley rats was used in this study. All animals weighed between 250 and 450 gm and were between 2 and 3 months of age.The population was divided into three sets of 24,12, and 8 rats that were to be put to death at 2,4, and 6 months, consecutively, after construction of the implant (Table I). The biocompatibility of the material was tested by chronic spinal implantation in rats. Spinal cord function was assessedby assigning a neurologic score and by checking spinal stability with dynamic radiographs. The spine, meninges, and spinal cord were studied histologically at
and surgical
technique
The rats underwent a microsurgical anterior cervical approach and corpectomy under aseptic conditions. During the surgical sessions, the animals were anesthetized with intraperitoneal injections of ketamine hydrochloride, 100 mg per kg, and acepromazine (Parke-Davis, Morris Plains, N.J.), 1 mg per kg. In the first group, the corpectomy defect was filled with VLC resin. A multiple layer technique and several visible light applications of 500 nm wavelength were used to ensure complete depth of polymerization.1g-22 The VLC resin was polymerized in situ with a hand-held visible light source (Efos, Fiber Optic Systems, Buffalo, N.Y.) for 60 seconds using the 8 mm diameter curved light guide (Figs. 1 through 4). In the second group, sterile chemically-cured autopolymerized methyl methacrylate (L.D. Caulk Co., Milford, Del.) was used (Fig. 5). Following surgery, neither antibiotics nor external orthosis was used, and unrestricted immediate activity was allowed. Clinical evaluation was performed throughout the duration of the experiment. Neurologic assessments for limb motor strength, gait, and feeding ability were graded 1 through 4. This allowed for quantitative, comparable measurements of neuromuscular coordination and work capacity of muscle groups. SEPTEMBER
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Preparation
of specimens
Cervical stability u as assessed in flexion and extension. L,ateral cervical radiographs were made before the animals were put to death, an.1 at 2,4, and 6 months after implant surgery (Figs. 6 and 7 s. The cervical spine was retrieved en bloc and axial sectiol s 5 mm in thickness were cut with a jeweler’s saw The specimens were dehydrated and were then embedded in acr,:lic resin Sections 20 pm in thickness were obtained with an Isomit Exact. sawing machine (IBuehler Ltd., Lake Bluff, Ill.) ander water irrigation*:’ and were stained with hernatoxylir and eosin for light microscopy to histol~ogically demonstrate the bone-to-implant interface and to investigate an;,1 inflammatory and/or necrotic change? (Fig. ? 6‘
RESULTS The measurements in this study were based on the neurophysical test scores and histopathologic test scores of a degree of tissue reaction to the mplants. Also the distances o:f the implant-bone iilterface xvere measured between the two groups. In both groups, no animal had radiographic signs of cervical instability (Fig. t) or a postoperative neurologic deficit, and all rats were graded i- in the neurologic function scales t,est. At death there was no evidence of implant fracture or extrusion nor any s,igns of biologic reaction on the adjacent meninges or spinal cord. The tissue reactions to the implants were described, graded, and categorized under histologic terms of inflammation, granulation, and fibrosis. The presence of intlammation was recognized by histologic observation of i he accumulation of histiocytes and leukocytes 1Figs. 10 and 11). The tissue reaction was attributed to contamination from the surgical procedure at the time of implantation. Granulation was characterized by the presence of lymphocytes, a highly vascular connective tissue, and capillaries (Fig. 12). These accumulations are associated with responses and reactions to the existence of foreign bodies in tht: system. The surgical injury was repaired by the formation of gmanulation tissue, which results in subsequent collagen scar formation. The avascular scar was recognized bv the presence of fibrocytes and collagen, and represents the fibrosis reaction (Figs. 13 and 14). Morphologically, the interface at 2 months after implant insertion consist,ed of fibrous tissue of the thickness of several cell layers, which ranged between 0 and 200 Frn in both groups. The measurements of the interface distances are summarized in Fig. 15 and in Table II. On average, 42’; of the specimens with VLC resin implants had surfaces with close approximatil>n to bone tissue (Figs. 16 and 17). The chi-square test was usec. to compare the variability between both materials and to analyze the preliminary data obtained from the 24 specimens of animals that were put to death at 2 months after construction of the implants. The p value!, for this test are shown in Tables II through V and in Fig;. 15 and 18 through 20. No significant differences (I-, = 0 24), ,I) = ie.39). and p = 0.46) in the measurement of the tissues’ reaction to the implants ~inflammaTHE
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HETIC
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tion, granulation, and fibrosis) were found hetween the two groups. No significant differences !F = 0.89) in the measurement of implant-bone anchorage was observed between tht two groups.
DISCUSSION Methyl methacrylate resin has been used to provide immediate fixation and to eliminate the need for external bracing of a spine that must be stabilized because of destruction by a malignant tumor. However. there are some theoretical disadvantages related to the use of chemicalcured methyl methacryiai e resin dur to the Jaw release of free monomer. chemotaxis-exothermic reaction. and the risk of infection because of its porosity and possible bacterial adherence. The new light-cured resin Triad has been investigated for use in spinal surgery because of its advantages in acturaq’ of fit. superior strength, complete polymerization. and low bacterial adherence, -which has been reported previously in dentistry. Additionally, the visible blue light is capable of penetrating the Triad resin to provide a germicidal effect.” In this study, no significant differences in bone anchorage or tissue reaction to the implant materials between the two groups after 2 months of implant Insertion had been observed. However, forthcoming data show an increase in the amount of bone formed at the interface after 4 and 6 months rif implant insertion. The pxperlmental results sugggest 1hat VLC resin could be used safely for vertebral body replacement. An additional advant,ape of VLC resin over methy! methacrylate resin was the ease of manipulation. Preliminary studie;l of VLC resin:, have produced promising results. Biologic testing of’ Triad material indicates that it is nontoxic and biocompatibk. However. additional research is necessary. A sttlrly in the nonhuman primate f?XdXJOnj will be undertaken io evaluate the longterm maintenance of spinal stability in an animal model with upright posture in which resl:ltb c>)uld be better extrapolated to man.
CONCLUSION This new biocompatible implant material is easier to manipulate and less prone to failure or infections than chemically cured methyl methacrylate. Ir allows safe immediate stabilization and early ambulation in an animal model with surgically created destruction of the spine. Additional advantages may result from extending the use of this material for other surgical procedures
ALSAWAF
5. Siegal T, Siegal T. Vertebral body resection for epidural compression by malignant tumors. Results of forty-seven consecutive operative procedures. J Bone Joint Surg 1985;67:375-82. 6. Ogle RE, Sorensen SE, Lewis EA. A new visible light-cured resin system applied to removable prosthodontics. J PROSTHETDENT 1986; 56:497-506. 7. McAfee PC, Bohlman HH, Ducker T. Failure of stabilization of the spine with methyl methacrylate. J Bone Joint Surg 1986;68A:1145-57. 8. Tuckfield WJ. Acrylic resins in dentistry. Part II. Their use for denture construction. Aust J Dent 1943;47:1-26. 9. Petty W. The effect of methyl methacrylate on chemotaxis of polymorphonuclear leukocytes. J Bone Joint Surg 1978;606:492-8. 10. Green SA. The effect of methyl methacrylate on phagocytosis. In: Proceedings for the Orthopedic Research Society. J Bone Joint Surg 1975;57:583. 11. Petty W. The effect of methyl methacrylate on bacterial phagocytosis and killing by human polymorphonuclear leukocytes. J Bone Joint Surg 1918;60:752-7. 12. White AA, Panjabi MM. Biomechanical considerations in the surgical management of the spine. Part 3. Surgical constructs employing methyl methacrylate. In: Clinical biomechanics of the spine. Philadelphia: JB Lippincott, 1978:423-31. 13. Ortman HR. Refitting denture bases with a visible light-cured denture base resin. NY State Dent J 1986;52:29-32. 14. Council on Dental Materials and Devices. Revised American Dental Association Specification No. 12 for denture base polymers. J Am Dent Assoc 1975;90:451-8. 15. Lewis EA, Ogle RE, Sorensen SE. Orthodontic applications of a new visible light-curing (VLC) resin system. NY State Dent J 1986;52:32-4. 16. Khan Z, Von Fraunhofer JA, Razavi R. The staining characteristic, transverse strength, and microhardness of a visible light-cured denture base material. J PROSTHETDENT 1987;57:384-6. 17. Tan HK, Burdvik JS, Nicholls JI, Smith DE. Adaptation of a visible light-cured denture base material. J PROSTHETDENT 1988;61:326-33.
376
ET AL
18. Johnansson C, Albrektsson T. Integration of screw implants in the rabbit: a l-year follow-up of titanium implant. Int J Oral Maxillofac Implant 1987;2:69-75. 19. Leung R, Fan PL, Johnston WM. Exposure time and thickness of polymerization of visible light composite. J Dent Res 1982;61:248. 20. Baharav H, Abraham D, Cardash HS, Helft M. Effect of exposure time on the depth of polymerization of a visible light composite resin. J Oral Rehabil 1988;15:167-72. 21. Matsumoto H, Gres HE, Marker VA, et al. Depth of cure of visible light-cured resin: clinical simulation. J PROSTHETDENT 1986;55:574-8. 22. Eli I, Weiss E, Littner MM, Drutman M. Sequentially light-cured composites: strength of bond between layers. J PROSTHET DENT 1986;56:158-61. 23. Maniatoppulos C, Rodriguez A, Deporter DA, et al. An improved method for preparing histological sections of metallic implants. Int J Oral Maxillofac Implant 1988;1:31-7. 24. Harstad JB, Decker HM, Wedum AC. Use of ultraviolet irradiation in room air conditioner for removal of bacteria. Appl Microbial 1954;2:14851. Reprint requests to: DR. MOUFID ALSAWAF P.O. Box 607151 ORLANDO,FL 32860-7151
Contributing
authors
R. Saito, MD, Chief, Pathology Department, Veterans Administration Medical Center, Pittsburgh, Pa. J. M. Close, MS, Learning Resources Center, University of Pittsburgh, School of Dental Medicine, Pittsburgh, Pa.
SEPTEMBER
1991
VOLUME
66
NUMBER
3