J . BIOMED. MATER. RES. SYMPOSIUM
No. 6, pp. 243 249 (1975)
Porous, Heat Cured Poly (methyl Methacrylate) for Dental Implants LAWRENCE GETTLEMAN, DAN NATHANSON, RICHARD L. M Y E R S O N , and M I L T O N H O D O S H , Harvard Tooth ZmplantTransplant Research Unit, Harvard School of Dental Medicine, 188 Longwood A venue, Boston, Massachusetts 021 15
Summary The use of polyl (methyl methacrylate) for tooth replica implants, as developed by Hodosh, is described as to indications, ingredients, and fabrication technique. Laboratory testing of this material for mechanical and thermal expansion properties, and porosity content were determined as a function of foaming agent and anorganic bone particle content.
INTRODUCTION
Of all the dental implant systems which are of current interest, the polymeric system which was developed by Hodosh, Povar, and Shklar [I], [2] is one of the most adaptable and promising. Poly (methyl methacrylate) (PMMA) has been used in dentistry since 1937 [3] for removable dentures, temporary and permanent crowns, filling materials, and as a veneering material for fixed prostheses. It has also been used for over 25 years as an orthopedic bone cement [4], [ 5 ] . Briefly, the tooth implant system consists of a methyl methacrylate polymer/monomer resin, mixed with anorganic bone particles and foaming agents which is then used to make a replica of an extracted tooth for reimplantation in the alveolus, or alternatively, to coat metallic implant devices or be premolded into a variety of shapes [6]. Some of the indications for replication of a tooth include: 1) root fractures; 2) endodontic impossibility or failures; 3) periodontal membrane disruption due to root canal or retention pin perforation; 4) unrestorable teeth due to extensive decay; 5 ) tooth avulsion; and 6) the financial burden of conventional restorative care. Virtually any tooth extracted for nonperiodontal reasons might be successfully replaced with polymer-replica tooth implants. The following technique has been developed by Hodosh and used to 243
0 1975 by John Wiley & Sons, Inc.
244
GETTLEMAN ET AL
produce consistent freestanding incisor replica implants in experimental animals: The tooth to be replicated is carefully extracted and debrided of soft tissue attachments. In the event that the crown or root is fractured, the pieces are reassembled or molded with repair resin and surface defects filled in. The tooth is then flasked in a small two-part brass crown and bridge processing flask in quick setting plaster (two parts water to three parts plaster: Snow White Impression Plaster No. 2, Kerr Manufacturing Company, Romulus, Michigan 48147). The first half is coated with an alginate separating medium (Separating Film, S. S . White, Dental Products Division, Philadelphia, Pennsylvania 19102) and after the second half of the plaster has set, the flask is opened and the tooth removed, then coated again with the alginate separating medium. The composition of one gram of the porous polymer mixture is shown in Table I. The powders are weighed out before each implant is to be fabricated, and the particles mixed thoroughly so as to incorporate some air in the “fluffed” powder. One gram of powder and associated liquid is usually sufficient to fabricate the root section of one large primate tooth. The liquid components are then pipetted and the mixture is again “fluffed” in order to incorporate air in the dough. The material will begin t o take on TABLE I
Powder
Implant Composition
Apparent Density
Poly(methy1 methacrylate) Beadsa (PMMA)
0.65 g
1.184 g/ml
N, N’-dinitrosopentamethylene tetramine ~ N P T )
0.15 g
1.51 g/ml
Anorganic Bone Chipsc ,7 (ABC)
0.20 g
2.247 g/ml
0.450 ml
0.943 g/ml
0.063 ml (3 drops)
0.966 g/ml
Liquid Methyl Methacrylate Monomer N-tributyl phosphatee (NTP)
d
(MMA)
a Hue-Lon Crystal Clear Polymer, L. D. Caulk Company, P. 0. Box 359, Milford, Delaware 19963 Opex 100, National Polychemicals, Inc., Wilmington, Massachusetts 01887 Kiel Bone (Cancellous bone pegs chopped in a Waring blender). Unilab, Incorporated, 27 Park Place, New York, New York 10007 Hue-Lon Noncrazing Monomer, L. D. Caulk Company, P. 0. Box 359, Milford, Delaware 19963) (C,H,), PO,. Baker & Adarnson, Allied Chemical, New York, New York
PMMA FOR DENTAL IMPLANTS
245
a foamy consistency and at that time the jar is covered for a few minutes in order to allow the dough to take on the proper packing consistency. If the material appears too wet initially, the jar may be left open for a few minutes in order for the monomer to evaporate slightly. One half of the mold is then packed with the porous polymer mixture in the root portion, with a clear or tooth-colored nonporous polymer/monomer mixture in the crown portion. The mold is then closed and compressed lightly in a flasking press, and this assembly placed in a preheated air oven at 220°C (428°F) for 30 min. The flask is then removed, cooled, and opened and the tooth recovered. Dental finishing burs may be used to remove any flash or surface defects, and the tooth is then dry sandblasted for 20-30 sec using quartz abrasive (Quartz Abrasive, J. F. Jelenko & Company, 170 Petersville Road, New Rochelle, New York 10801) at 100-120 psi air pressure to remove any surface film and to open up surface pores. Final ultrasonic cleaning for 2 min in distilled water is carried out prior to tooth implantation.
METHODS A N D RESULTS The following is a preliminary report on the laboratory properties of the polymer material and its ingredients. Initial tests were conducted on the particle sizes of the PMMA powder. It is known that one of the easiest ways to modify the packing properties as well as the final strength of acrylic denture resins is by adjusting the particle size distribution. This test was carried out on a RoTap Seive Shaker; finely ground feldspar was added t o the beads t o draw off static charges and allow passage of the beads through the brass screens. Results, shown in Figure 1, indicate that particles have a range of sizes with a mean of 62 p m and standard deviation of 23 pm. In order t o alter ingredients and still retain suitable packing properties of the resultant dough, apparent densities were determined and are also presented in Table I. A series of studies were conducted t o investigate compressive and thermal properties of this PMMA implant material upon alteration of the ingredient’s proportions. Specimens 6 mm in diameter and 12 mm in height were made by compression molding in plaster flasks and curing according t o the method of Hodosh. These specimens were then sandblasted and washed, mounted in polyester resin, sectioned and polished, and the pores stained with Sudan black and phloxine B in ethanol. (Figs. 2 and 3) Cylindrical specimens were then tested in compression at a constant load rate of 115 kgf/min (250 Ib/min), and yield strength was determined by the 0.1% offset method.
GETTLEMAN ET AL.
246
h i v e Opening in pm
Fig. I ,
Particle size of Hue-Lon P M M A beads as determined by sieving
Percent porosity was determined by microscopic measurement of stained pores observed on the prepared cross sections. Thermal expansion was determined from 0°C to 100°C on a ThermoPhysics dilatometer. It was found that a certain amount of shrinkage of the specimens took place, indicative of at least one of the following: 1) Sintering of the particles; 2) Pore collapse under the small but finite load of the dilatometer sensor device; 3 ) Volatilization of the unpolymerized monomer; or 4) Polymerization shrinkage. For these reasons, determination of a true giass transition temperature was impossible, but the temperature at which definite softening began was measured and is presented as the softening point in Figure 4. This chart shows volumetric compositional variations of foaming agents and anorganic bone, ranging from none of either t o double the amount determined by Hodosh t o be ideal (the second cell from the right and the bottom). Bars indicate the yield strength in compression, the softening point in "C, and the area percent of pores.
CONCLUSIONS A pattern is evident in the properties of these materials from which the following conclusions can be made: 1) Yield strength and softening point
PMMA I N EXPANSION DENTAL IMPLANTS
247
Fig. 2. Photomicrograph of nonporous, heat-cured, clear PMMA containing no foaming agents or anorganic bone chips. (62 x )
Fig. 3. Photomicrograph of porous, heat-cured PMMA containing 26.7 vol % foaming agents. (Composition = PMMA 1.250 g, DNPT 0.900 g. ABC 1.200 g, MMA 1.012 ml, NTP 0.376 ml). (62 x )
GETTLEMAN ET AL.
248
fooming Agents in Volume yo (DNPl/NTP Ratio Constant)
0 Anorganic Bone in Volume O h
6.67
13.3
26.7
0
8.91
W.!
O h Offset Yield Strength (OS1 in MN/m' (X145 3 psi)
Fig. 4.
@oft;n in
Point
Area % Porwity
Physical properties of the Hodosh P M M A implant material
both decrease as a function of anorganic bone and foaming agent additives, since these ingredients can be thought of (a) as fillers in the case of the bone, (b) as porosity producing ingredients in the case of the foaming agents, (c) as polymerization inhibition reactants, or (d) as plasticizing agents in the case of the N-tributyl phosphate. 2) Area percent porosity is promoted by both the foaming agents and the anorganic bone chips as a function of their'volume percent. 3) Two-thirds of the particles of the PMMA powder exist in the 39-85 pm range. Further studies are now in progress to determine the effects of each ingredient and the sequelae of altering processing variables. This work was supported by U S P H S Research Grant R23DE 03690 from the National Institute for Dental Research, National Institutes of Health, Bethesda, Maryland.
References [ I ] M. Hodosh, R.I. Med. J . , 47. 253 (1959). [2] M . Hodosh, M . Povar, and G. Shklar, Oral Surg., Oral Med., and Oral Path., 33(6), 1022 (1972). [3] S. D. Tylman and F. A . Peyton, Acrylic and Other Dental Resins Used in Dentistry, Lippincott, Philadelphia, 1946. [4] S. Kaier, Acta Orthop. Scand., 22, 126 (1952).
PMMA FOR DENTAL IMPLANTS
249
[5] E. J . Haboush, Bull. Hosp. J . Dis., 14, 242 (1953). [6] M . Hodosh, M . Povar, and G. Shk1ar.J. Prosrh. Denr., 22, 371 (1969). [7] Symposium o n Bone Grufiing Muteriuls. 1964. Armour Pharmaceutical Company, Ltd., Eastbourne, England.
No. 6, pp. 243 249 (1975)
Porous, Heat Cured Poly (methyl Methacrylate) for Dental Implants LAWRENCE GETTLEMAN, DAN NATHANSON, RICHARD L. M Y E R S O N , and M I L T O N H O D O S H , Harvard Tooth ZmplantTransplant Research Unit, Harvard School of Dental Medicine, 188 Longwood A venue, Boston, Massachusetts 021 15
Summary The use of polyl (methyl methacrylate) for tooth replica implants, as developed by Hodosh, is described as to indications, ingredients, and fabrication technique. Laboratory testing of this material for mechanical and thermal expansion properties, and porosity content were determined as a function of foaming agent and anorganic bone particle content.
INTRODUCTION
Of all the dental implant systems which are of current interest, the polymeric system which was developed by Hodosh, Povar, and Shklar [I], [2] is one of the most adaptable and promising. Poly (methyl methacrylate) (PMMA) has been used in dentistry since 1937 [3] for removable dentures, temporary and permanent crowns, filling materials, and as a veneering material for fixed prostheses. It has also been used for over 25 years as an orthopedic bone cement [4], [ 5 ] . Briefly, the tooth implant system consists of a methyl methacrylate polymer/monomer resin, mixed with anorganic bone particles and foaming agents which is then used to make a replica of an extracted tooth for reimplantation in the alveolus, or alternatively, to coat metallic implant devices or be premolded into a variety of shapes [6]. Some of the indications for replication of a tooth include: 1) root fractures; 2) endodontic impossibility or failures; 3) periodontal membrane disruption due to root canal or retention pin perforation; 4) unrestorable teeth due to extensive decay; 5 ) tooth avulsion; and 6) the financial burden of conventional restorative care. Virtually any tooth extracted for nonperiodontal reasons might be successfully replaced with polymer-replica tooth implants. The following technique has been developed by Hodosh and used to 243
0 1975 by John Wiley & Sons, Inc.
244
GETTLEMAN ET AL
produce consistent freestanding incisor replica implants in experimental animals: The tooth to be replicated is carefully extracted and debrided of soft tissue attachments. In the event that the crown or root is fractured, the pieces are reassembled or molded with repair resin and surface defects filled in. The tooth is then flasked in a small two-part brass crown and bridge processing flask in quick setting plaster (two parts water to three parts plaster: Snow White Impression Plaster No. 2, Kerr Manufacturing Company, Romulus, Michigan 48147). The first half is coated with an alginate separating medium (Separating Film, S. S . White, Dental Products Division, Philadelphia, Pennsylvania 19102) and after the second half of the plaster has set, the flask is opened and the tooth removed, then coated again with the alginate separating medium. The composition of one gram of the porous polymer mixture is shown in Table I. The powders are weighed out before each implant is to be fabricated, and the particles mixed thoroughly so as to incorporate some air in the “fluffed” powder. One gram of powder and associated liquid is usually sufficient to fabricate the root section of one large primate tooth. The liquid components are then pipetted and the mixture is again “fluffed” in order to incorporate air in the dough. The material will begin t o take on TABLE I
Powder
Implant Composition
Apparent Density
Poly(methy1 methacrylate) Beadsa (PMMA)
0.65 g
1.184 g/ml
N, N’-dinitrosopentamethylene tetramine ~ N P T )
0.15 g
1.51 g/ml
Anorganic Bone Chipsc ,7 (ABC)
0.20 g
2.247 g/ml
0.450 ml
0.943 g/ml
0.063 ml (3 drops)
0.966 g/ml
Liquid Methyl Methacrylate Monomer N-tributyl phosphatee (NTP)
d
(MMA)
a Hue-Lon Crystal Clear Polymer, L. D. Caulk Company, P. 0. Box 359, Milford, Delaware 19963 Opex 100, National Polychemicals, Inc., Wilmington, Massachusetts 01887 Kiel Bone (Cancellous bone pegs chopped in a Waring blender). Unilab, Incorporated, 27 Park Place, New York, New York 10007 Hue-Lon Noncrazing Monomer, L. D. Caulk Company, P. 0. Box 359, Milford, Delaware 19963) (C,H,), PO,. Baker & Adarnson, Allied Chemical, New York, New York
PMMA FOR DENTAL IMPLANTS
245
a foamy consistency and at that time the jar is covered for a few minutes in order to allow the dough to take on the proper packing consistency. If the material appears too wet initially, the jar may be left open for a few minutes in order for the monomer to evaporate slightly. One half of the mold is then packed with the porous polymer mixture in the root portion, with a clear or tooth-colored nonporous polymer/monomer mixture in the crown portion. The mold is then closed and compressed lightly in a flasking press, and this assembly placed in a preheated air oven at 220°C (428°F) for 30 min. The flask is then removed, cooled, and opened and the tooth recovered. Dental finishing burs may be used to remove any flash or surface defects, and the tooth is then dry sandblasted for 20-30 sec using quartz abrasive (Quartz Abrasive, J. F. Jelenko & Company, 170 Petersville Road, New Rochelle, New York 10801) at 100-120 psi air pressure to remove any surface film and to open up surface pores. Final ultrasonic cleaning for 2 min in distilled water is carried out prior to tooth implantation.
METHODS A N D RESULTS The following is a preliminary report on the laboratory properties of the polymer material and its ingredients. Initial tests were conducted on the particle sizes of the PMMA powder. It is known that one of the easiest ways to modify the packing properties as well as the final strength of acrylic denture resins is by adjusting the particle size distribution. This test was carried out on a RoTap Seive Shaker; finely ground feldspar was added t o the beads t o draw off static charges and allow passage of the beads through the brass screens. Results, shown in Figure 1, indicate that particles have a range of sizes with a mean of 62 p m and standard deviation of 23 pm. In order t o alter ingredients and still retain suitable packing properties of the resultant dough, apparent densities were determined and are also presented in Table I. A series of studies were conducted t o investigate compressive and thermal properties of this PMMA implant material upon alteration of the ingredient’s proportions. Specimens 6 mm in diameter and 12 mm in height were made by compression molding in plaster flasks and curing according t o the method of Hodosh. These specimens were then sandblasted and washed, mounted in polyester resin, sectioned and polished, and the pores stained with Sudan black and phloxine B in ethanol. (Figs. 2 and 3) Cylindrical specimens were then tested in compression at a constant load rate of 115 kgf/min (250 Ib/min), and yield strength was determined by the 0.1% offset method.
GETTLEMAN ET AL.
246
h i v e Opening in pm
Fig. I ,
Particle size of Hue-Lon P M M A beads as determined by sieving
Percent porosity was determined by microscopic measurement of stained pores observed on the prepared cross sections. Thermal expansion was determined from 0°C to 100°C on a ThermoPhysics dilatometer. It was found that a certain amount of shrinkage of the specimens took place, indicative of at least one of the following: 1) Sintering of the particles; 2) Pore collapse under the small but finite load of the dilatometer sensor device; 3 ) Volatilization of the unpolymerized monomer; or 4) Polymerization shrinkage. For these reasons, determination of a true giass transition temperature was impossible, but the temperature at which definite softening began was measured and is presented as the softening point in Figure 4. This chart shows volumetric compositional variations of foaming agents and anorganic bone, ranging from none of either t o double the amount determined by Hodosh t o be ideal (the second cell from the right and the bottom). Bars indicate the yield strength in compression, the softening point in "C, and the area percent of pores.
CONCLUSIONS A pattern is evident in the properties of these materials from which the following conclusions can be made: 1) Yield strength and softening point
PMMA I N EXPANSION DENTAL IMPLANTS
247
Fig. 2. Photomicrograph of nonporous, heat-cured, clear PMMA containing no foaming agents or anorganic bone chips. (62 x )
Fig. 3. Photomicrograph of porous, heat-cured PMMA containing 26.7 vol % foaming agents. (Composition = PMMA 1.250 g, DNPT 0.900 g. ABC 1.200 g, MMA 1.012 ml, NTP 0.376 ml). (62 x )
GETTLEMAN ET AL.
248
fooming Agents in Volume yo (DNPl/NTP Ratio Constant)
0 Anorganic Bone in Volume O h
6.67
13.3
26.7
0
8.91
W.!
O h Offset Yield Strength (OS1 in MN/m' (X145 3 psi)
Fig. 4.
@oft;n in
Point
Area % Porwity
Physical properties of the Hodosh P M M A implant material
both decrease as a function of anorganic bone and foaming agent additives, since these ingredients can be thought of (a) as fillers in the case of the bone, (b) as porosity producing ingredients in the case of the foaming agents, (c) as polymerization inhibition reactants, or (d) as plasticizing agents in the case of the N-tributyl phosphate. 2) Area percent porosity is promoted by both the foaming agents and the anorganic bone chips as a function of their'volume percent. 3) Two-thirds of the particles of the PMMA powder exist in the 39-85 pm range. Further studies are now in progress to determine the effects of each ingredient and the sequelae of altering processing variables. This work was supported by U S P H S Research Grant R23DE 03690 from the National Institute for Dental Research, National Institutes of Health, Bethesda, Maryland.
References [ I ] M. Hodosh, R.I. Med. J . , 47. 253 (1959). [2] M . Hodosh, M . Povar, and G. Shklar, Oral Surg., Oral Med., and Oral Path., 33(6), 1022 (1972). [3] S. D. Tylman and F. A . Peyton, Acrylic and Other Dental Resins Used in Dentistry, Lippincott, Philadelphia, 1946. [4] S. Kaier, Acta Orthop. Scand., 22, 126 (1952).
PMMA FOR DENTAL IMPLANTS
249
[5] E. J . Haboush, Bull. Hosp. J . Dis., 14, 242 (1953). [6] M . Hodosh, M . Povar, and G. Shk1ar.J. Prosrh. Denr., 22, 371 (1969). [7] Symposium o n Bone Grufiing Muteriuls. 1964. Armour Pharmaceutical Company, Ltd., Eastbourne, England.
