____Adjectives such as “smart”, “active”, “intelligent”, “trainable” or “adaptive” applied to inanimate objects are not a mere figure of style: some materials literally sense and act according to stimuli. In doing so, these duplicate up to a certain extent what living beings do. Known also as actuators, “smart” materials can respond by exhibiting shape-memory, piezoelectric, electro- or magnetostrictive effects. As their study lays at the cutting edge of science and technology, both books and journals are dedicated to the field¹.
____Orthodontists are already familiar with some smart materials, and others are in their way: the speed with which orthodontics catches new developments vouches for it. We feel that no clinician should be in the position of Moliere’s “Le burgeois Gentilhomme”, who was amazed to find out that he was making prose without knowing it. We are therefore attempting to help the reader to get a broader view on these uncommon materials providing him with simple explanations for knowledge at the cutting edge of science.
____The old story of the frog which due to a kiss (read: impulse), transforms itself instantly to a prince (read: changes structure) may well be already duplicated in your office. The most amazing feature of such a transformation is that it occurs from within, i.e. without anything to be added to, or removed from. While by far the most spectacular is the heat-sensitive NiTi shape-memory transformation (which we have already presented²), there are also other, no less interesting related phenomena worth knowing. Work on an austenitic stainless steel piece: it may change its structure, becoming suddenly magnetic. Hit a magnet: it may lose its magnetism. Subject a zirconia bracket to stress: it may exceed your strength expectations by self-healing at the crack-point, arresting the progress of the fissure.
____Such transformations from within, involve not only metals and ceramics, but also plastics and even... living creatures. Although the latter are not frogs, but T4-bacteriophages³, Fig. 1, such sudden changes leading to new structures is almost as amazing. The wonder resides not in the materials which transform (even transuranic elements do it), as much as in the process itself.
____The story of the transformations from within started in 1890 when Adolf Martens tried to find out why alloys that had an identical composition, behaved differently. Using a 300x microscope, he observed a variety of patterns, which he could associate with the properties of the steels examined. While incoherent patterns were common in inferior steels, bands having a distinct orientation were found on the hard ones. One of the patterns he described became later known as “martensite”, and the difussionless transition leading to it, “martensitic”. His finding seemed to be quite odd, as at that time, the only transformations known were those based upon atom migrations or displacements. Involving a transfer of matter (which is always slow), are nicknamed “civilian”. The new transformation, based only upon minor atom rearrangements, are both disciplined and fast: they were nicknamed “military”, or, more scientifically, “displacive” or “glissile”. Their “militarism” may be apparent in orthodontics: the expansion of nickel-titanium wires may be so violent that it can hurt the patient if suddenly heated above the transition temperature.
____Martens’s discovery led to a new discipline, “metallography”, and had a tremendous impact on many sciences. In time, difussionless phase transformations were found in other fields, and the term “martensitic” enlarged its meaning to cover all transformations which occur without a material exchange with the surrounding phases. While in most instances the phenomenon is irreversible, in few instances it is -leading to “shape memory”. However not all “shape memory” phenomena are, while still martensitic, due to minor atom displacements, as it will be shown below. In what follows, we will attempt to describe the materials, the phenomena involved and their application, in the hope that the clinician will broaden his views and -who knows- get new ideas.
PLASTICS
___ According to their behavior when heated, plastics are divided in two classes: thermoplastic and thermosets. Recently, an intermediate class has stirred an increasing interest: while still thermoplastic, some exhibit some of the advantages of hard thermosets.
Structure and mechanism. Certain polymers exhibit ”shape memory”, phenomenon that involves, as a difference from their metallic counterparts, the destruction of their crystalline structure. In the first step, these are heated, stretched and subjected to high-energy electron beam radiations, which randomly generate cross-links between the linear polymer chains. In a second step, these are allowed to cool while taking a second shape. When reheated, the polymer loses the crystalline structure corresponding to the cold shape, but maintains a controlled amount of cross-links. Generated in the first step, these allow stretching to a new form without the whole to collapse (melt). When cooled again, the plastic tends to return to its old shape, creating a tight, permanent covering over a substrate.
Applications. The transformation is martensitic4. Plastics, that shrink up to 4:1, are currently used to protect mechanical and electrical components against abrasion, temperature extremes and chemicals. Sold as films, these are used to generate an additional insulating air layer on windows or be wrapped around objects (pallets). Exposed to temperatures ranging from 95 to 175^oC, they shrink to their original size. Among the largest producers of shrink films are DuPont, the Cryovac Divivision of W. R. Grace, Reynolds Metals and 3M. As sleeves, these are applied in plumbing over difficult to assemble tube joints (plastic-metal) or to insulate electrical wire connections (Raychem). Applied cold and stretched, these plastics shrink when heated sealing the joint enough to stand high pressures. A similar product, a polymer matrix swollen with a solvent which can expand or contract up to five times when exposed to stimuli, has been developed at Sandia National Laboratories (Albuquerque, NM).
____While not yet used in orthodontics, it is foreseeable that some day, the remarkable properties of the plastics exhibiting "shape memory" will be used to make tooth positioners, guidance appliances or tighter mouth guards.
STEELS
___Most of the orthodontist’s armamentarium is made of stainless steel, and the instruments, which have to stand high forces. The hardness of many comes from a martensitic transformation.
Structure and mechanism. The introduction of iron was initially slow: improperly treated, it is too soft. Its carbon-added form, steel, was an immense improvement over bronze. The transformation of iron in steel is not simple, as it involves carburization and tempering, processes not understood until almost a century ago. In antiquity, quenching a Damascus sword in a Nubian slave, or choosing the right phase of the moon, were considered valuable recipes which had to be kept secret. In the first treatise on steelmaking, published two centuries and a half ago, the inventor of the third most-used thermometer scale, Reaumur5, made an interesting observation. Far from understanding the phenomena involved, he described the existence of substructural units which, properly preserved by rapid cooling, could determine the properties of the metal. The basic understanding of the process escaped metallurgists had to wait over a century, i.e. until Martens made his discovery and Roberts-Austen produced a constitution diagram for the Fe-C system. Their contribution cleared the path to understand the transformation we are discussing.
____At high temperatures, iron exhibits unit cells which are face centered cubic (f.c.c.). This homogeneous phase has been named "austenite", in honor of W.C. Roberts-Austen who first described it. In it, carbon is highly soluble (up to 2%). At lower temperatures, iron undergoes a transformation into body centered units (b.c.c.), structure known as ferrite. Its nine spheres structure, enlarged 165 billions of times, has been the symbol of Atomium at the 1958 World Fair in Brussels, Fig. 3. In fig. 4 are presented both structures.
____Although in the f.c.c. structure there is little empty space, small atoms such as carbon or nitrogen (known as interstitials and marked with a red sphere) can be accommodated in its center, Fig. 5. In contrast, the b.c.c. unit cell has more empty space, but the interstitials cannot be accommodated anymore due to the curvature of the atom occupying the center. Consequently, as a result of slow cooling, carbon separates from iron forming a precipitate -iron carbide. This transformation, which in this particular case is associated with carbon’s diffusion, is due to a rearrangement of the Fe atoms. Previously distributed in the diagonal plane of the cubes, these form faces (the McBain transformation, see our previous article²). If, however, the metal is rapidly quenched, the carbon atom cannot migrate and is trapped into the body centered unit cell which becomes tetragonal, as seen in Fig. 5. The higly stressed martensite resulted can be compared to an overstaffed, but otherwise soft suitcase: while it becomes hard, it easier to break.
____In the Fe-C system, austenite cannot be obtained at room temperature. By adding elements such as nickel or nitrogen, this solid solution becomes relatively stable. In stainless steel, the amount of such "austenitizing" elements has to be higher, to overcome the "ferritizing" action of chromium, the element which brings the sought after passivation, the resistance to chemical attack. Austenitic steels are corrosion resistant due to their homogeneous structure, while the martensitic ones are harder and tougher.
Applications. While the phases exhibited may differ, due to multiple constraints (cost, strength, corrosion susceptibility, ease in processing), the composition of most of the commercial stainless steels used today is quite near, bordering the austenite-martensite equilibrium line⁷, as seen in Fig. 6. This vicinity makes possible the phenomenon described earlier, the instantaneous switch from an austenitic structure (nonmagnetic) to a martensitic (magnetic one).
____Today, martensitic stainless steels are used to make both tools and “mini” brackets. For the last purpose, the most used is PH 17-4 (Precipitation Hardening, AISI 630). As shown, this may well be an advantage from the strength point of view, but is a set back from that of corrosion resistance due to their multi-phase structure (martensite in austenite, as well as other metals purposely selected to precipitate at lower temperatures). Indeed, the additional phases generate obstacles in the path of destructive atom dislocations but also lead to galvanism. Thus, the measurement of the volume of hydrogen released by the attack of a diluted solution of muriatic acid on an equal weight of brackets⁶ shows that the best austenitic steel is many times more corrosion resistant than the best martensitic one. Another difference is that while martensitic steels are hardenable by heat treatment (and up to some extent by cold work), the austenitic ones are not. As a result, martensitic steels are currently used to make hard knifes and tools.
MEMORY ALLOYS
___ As NiTi alloys have been amply examined in a former issue of our Newsletter², in what follows we will concentrate on their martensitic transformation and its applications.
Structure and mechanism. Metals have low ionization energy, that is form relatively weak bonds among them. The greatest stability (toward which each system tends) is reached when the valence electrons do not belong to only one atom but form a cloud of mobile electrons. Since there are no highly directional, localized forces, one plane of atoms may be moved over another with little expenditure of energy. As Ni and Ti have several valences, these can generate, in addition to TiNi, combinations such as Ti²Ni³ and Ti²Ni, phases which easily transform in each other by segregating in the process an excess of one metal or the other. This explains the mobility of the alloy to pass from one form into another and generate different structures. The maximum propensity for transformation, however, occurs only near the equiatomic Ni-Ti ratio: most shape-memory alloys are selected within the range 49.7 and 50.7 at. %. At less than 49.4 at. % Ti, the alloys become unstable and are seldom used. In the region between 50 to 52 at. % Ni, the alloys are too hard (an increase with just 1% Ni over the stoichiometric ratio is enough). This explains why several authors have reported different results seemingly using the same conditions⁸ showing that it is quite difficult to make reproducible memory alloys.
____The phenomenon called “shape-memory” was first found on a gold alloy⁹. The mechanic perturbation brought by this martensitic transformation was so significant, that even some sound could be heard. Ten years later, Buehler and his coworkers at the Naval Ordnance Laboratory found that an alloy of nickel and titanium exhibited the "shape memory effect" (SME). In addition, the new alloy was superelastic, less expensive and could be adjusted to have its transition within the convenient range, 0-100^oC¹⁰. In time, other alloys, referred to as SMA (“shape-memory alloys”) were found to display similar properties. Among these, the most promising to replace the expensive NiTi are the ones starting from Fe, Mn, and Si to which other elements are added. Their general characteristic is that all behave in a certain way below a certain range of temperatures (TTR) and in another above it. As a difference of melting points, which are always constant, no matter if approached from a higher temperature or a lower one, TTR can be quite large, and as a result efforts are constantly made to reduce the interval. Its consequence, hysteresis, is due to the fact that the new phase has to grow within the lattice of the old one.
____Most SMA exhibit a f.c.c. structure (austenite) which is stable at higher temperature, as in the case described above for steels. As at lower temperatures austenite is unstable, these alloys undergo a martensitic transformation into a b.c.c. structure of the McBain type. As a difference from steels, where martensite cannot revert to austenite without atom migration, SMA can return to their parent phase both when heated and cold worked, as represented in Fig 7. When slowly cooling austenite, the first martensite “embryos” (the name is common in the field) appear. Further lowering the temperature or increasing the stress, the conversion in martensite becomes greater, being translated into bumps on the previously smooth surface. When the conversion is total, the bumps take the shape of hill chains as shown in Fig. 8. Conversely, if the martensitic form is heated above TTR, these vanish as austenite forms.
____The difference between the martensitic transformations of steels and that of SMA resides in the fact that in steels, the parent and the transformed unit cells are not congruent, i.e. do not accommodate each other, and form therefore discrete zones. In SMA, the atoms in both the unchanged cubic unit cells and in the newly formed monoclinic ones remain connected, although at a slightly different distance. The last structure, made of parallelepipeds and equivalent to the hexagonal one, is self accommodating (lattice correspondence). In other words, if cooled or subjected to stress, the unit cells in the NiTi lattice take a zigzag shape (polysynthetic twins). If heated, the congruent cells respond by becoming cubic (straight) and stiffer. The twinned structure has been compared to a harmonica, being easily stretched or twisted: the cycle can be repeated indefinitely. Aside from the one-way shape memory effect, some alloys can remember not only the high temperature shape, but also the low temperature one. This behavior is dictated by martensite’s unit cells, which have their own preferences as more stable orientations concerns. While smaller than the one-way effect, it is equally reversible.
____Based upon the phenomena described, it is easy to understand why after becoming martensitic, steels are stronger, while NiTi alloys, softer. Understandably, in hard steels, the interstitial elements are desired, while in NiTi's manufacture, special care is taken to avoid its structure to be penetrated by elements such as O, N or C. If this happens, the alloy becomes stiffer and ceases to exhibit the shape memory effect. As oxygen considerably lowers elasticity, its levels are controlled to less than 500 parts per million (ppm). Even so, its influence is great: if at 150 parts per million (ppm) of oxygen, a stoichiometric alloy has its Ms at 45^oC, at 450 ppm its Ms is as low as -5^oC. While the phenomenon has not yet been documented, it is possible that orthodontic NiTi wires stored in hot and dry conditions may suffer changes in their properties.
Applications. Both “shape-memory” and the related superelasticity phenomena are increasingly being exploited in orthodontics. We would like to limit what follows only to some dental and medical applications which may inspire additional uses.
____In dentistry, shape memory implants are introduced in the alveols where they expand, allowing a good initial fixation in the jawbone. Easily installed through a simple operation, such implants can well stand the strong and continuous forces of mastication. In addition, due to their high elasticity, such implants exhibit good stress dispersion. The newly generated bone tissue, which surround NiTi implants after six months of wear demonstrate a good oral biocompatibility of the alloy. Approved by the Ministry of Health and Social Welfare of Japan in 1985, tens of thousands of such implants were successfully used within few years11. Following the same reasoning, it may be feasible to replace ceramic cavity fillers with properly shaped NiTi ones.
____Superelastic NiTi endodontic files are widely used as these allow a good adaptation along sharply curved root canals with a minimal risk for root perforation. For most of their uses in medicine, binary alloys are annealed and cold-worked to have the Ms at temperatures close to that of the human body. A correct match of the TTR seems, however, to be a goal seldom attained, as demonstrated by the study of seven commercial arch wires which has shown that the range varied from 25 to 82^oC (77-180^oF)¹² .
____In medicine, a slightly bent rod inserted into the back, close to the spine, is straighten when it is gentle heated, ensuring the alignment and support of the spine (intermedullary rods). The same alloy has been used for artificial limbs; assisting mobility impaired people, for bone plates¹³ and to close up bone fractures. In addition, it has been considered as a suitable material for artificial hearts. An electrically activated device where contractile NiTi wires actuate elastomeric parts can deliver water against a pressure similar to that of encountered by blood, but for the time being with only 15 cycles/minute. Other applications include devices, which prevent some types of miscarriage during pregnancy as well as others, which work as intrauterine contraceptives¹⁴, vascular, esophageal and biliary stents. Thus, EndoTex has developed a series of self-expanding stents, stent grafts and stent delivery systems, which use NiTi alloys. The warmth of the body activates all flexible catheters, implantable surgical guide-wires and expandable blood cloth filters. For the last application, the filter form is first “trained” through a thermal treatment at 800^oC, after which it is formed to take shape of a needle. After being introduced through a catheter in the vein, the filter recovers its original shape at the body temperature, preventing embolism. The same principle is used in pulmonary embolism filters (e.g. the Simon^R Nitinol filter).

____NiTi wires are currently used as staples in sutures drawing and holding together wounded tissues¹⁵, bones or to correct scoliosis¹⁶. The Anchor Exchange Device^R, developed by Advanced Cardiovascular Systems, uses a NiTi core wire for interventions such as atherectomy or stenting.
____In toolmaking, an advanced NiTi biopsy forceps allows taking multiple samples, with only one pass. The handles of some surgical tools can be custom shaped by the surgeon for each patient, and then brought back to their original shape by sterilization.
CERAMICS
Aluminum oxide, Al₂O₃ or leuco (white) sapphire, used for decades in orthopedics, has not met expectations in orthodontics. Today’s ceramic brackets have a poor mechanical resistance and are too hard. In dentistry, common ceramics easily crack under stress when it comes to be used in the most interesting application, porcelains-fused-to metal (PFM).
____The future may well be in zirconia and its composites, well as in leucite (KAlSi₂O₆), a preferred ingredient in cerramed glasses. Both have in common the phenomenon of transformation toughening, another name for the martensitic one.
Structure and mechanism. At room temperature, zirconia unit cells are monoclinic: upon heating, these become tetragonal (1175^oC) and then cubic (approx. 2000^oC). If pure, zirconia undergoes a martensitic transformation very rapidly. As in the previous cases examined, through additions and treatments it is possible to stabilize and put to use both these phases stable at high temperatures. There are, therefore, several types of zirconia: one is the common, monoclinic one, which is not too interesting. Another one is cubic and brittle (cubic zirconia), and a third is tetragonal. While the latter, known as TZP (Tetragonal Zirconia Polycrystals) is interesting, being both strong and dense (almost 100%)¹⁷, even more interesting are the ones designated as PSZ, “Partially Stabilized Zirconia”. In one of these, developed by Imperial Chemical Industries under the name Nicral and which is currently used to make zirconia brackets in Australia, the phases are 50% cubic, 10% monoclinic and 40% tetragonal. The key element in preferring the mixed structure reside in the fact that the monoclinic structure has a larger volume than the tetragonal one, and the last one reverts, when subjected to stimuli, into the monoclinic one. The procedure has led to a variety of mixtures of zirconia, which expand with some 3% and contain between 3-9% stabilizing oxide. To indicate the latter, it is usual to add the symbol of the corresponding element to the abbreviation. Commonly used in prosthetics are Mg-PSZ, Ca-PSZ and especially Y-PSZ (yttrium is a rare-earth element, or lanthanide).Under the stimuli mentioned, the tetragonal, unstable phase, undergoes a martensitic transformation, increasing thus the volume of the exposed part as shown in Fig. 8. Among the stimuli inducing the transformation are both time and the energy produced by the stress exerted upon the material. Indeed, being unstable, the tetragonal crystals will eventually become monoclinic without any exterior help, and therefore one of the problems to which the PSZ formulators have to answer is if the items they make will still able to exhibit this sought-after transformation when needed. In most conditions, however, the low temperature degradation of Y-TZP is very slow, at 37^oC being indefinite¹⁸. Energy input such as stress leads to a martensitic transformation (expansion) of the crystals found ahead of the crack. This puts them under compression, generating a resistance, which has to be overcome before the crack can extend any further.
____The phenomenon, known as transformation toughening, is based upon the fact that most failures start from surface cracks, and any increase in volume at their tip (notch root) blunts their progress. As a result, PSZ’s can exhibit a tensile strength similar to that of mild steel, and its bending strength is 2-3 times greater than that of alumina. Most important, its fracture toughness is twice the one of alumina (equal to that of cast iron), as shown in Table I. A high toughness, which is very desirable for all prostheses, indicates a material’s ability to withstand impact and chirping and an increased resistance to brittle fracture wear. In addition, PSZ are less hard than alumina (8.3 vs. 9 on the Mohs scale), offering thus fewer chances for tooth abrasion.
____Less interesting for orthodontists is leucite, which, like zirconia, exhibits a cubic structure at high temperatures. The structure stable at lower temperatures is tetragonal, and the TTR of its martensitic transformation is between 404-628^oC. As in stainless steels, it is possible to maintain the metastable cubic structure at room temperature by quenching; as in PSZ zirconia, this structure expands when subjected to stress¹⁹.
Applications. What determines the uses of zirconia and its compounds, as those of titanium or other expensive elements, is not their raw materials availability but the processing cost. Like pure alumina, which impure can be found in huge amounts as bauxite, pure zirconia requires a sophisticated manufacture, which involves the distillation of liquid zirconium chloride. Even so, its cost is by far lower than that of the gems it often replaces. Zirconia is also used in industrial cutting and slitting operations, in multilayer ceramic capacitors, fuel cells. In medicine, it is more and more used in implants or prostheses (especially as femoral ball heads). In orthodontics, the characteristics of the few zirconia brackets available have been analysed²⁰. It is very likely, however, that more and better are to come. Indeed, the ElipseR brackets (Australia’s Orthodontic Research Co.), are Mg-PSZ and cream, unlike alumina or Y-PSZ. In addition, no zirconia composites have been yet used. As in the case of leucite, which is used mostly in composite glasses to arrest cracks²¹, it is expected that tetragonal zirconia containing composites will significantly increase their strength²².
References.
1. Smart materials and structures, Chapman and Hall, London 1992; Journal of Smart Materials and Structures, Inst. of physics publications, Bristol, UK
2. Matasa C., NiTi alloys: Two metals in one, The orthodontic materials insider, 1997; 10(1); 2-9
3. Olson GB, Introduction: martensite in perspective, in: Martensite, Olson GB, Owen WS, ASM International, 1992, Materials Park OH.
4. Jackson CL, Barnes KA, Morrison FA, Mays JW, Nakatani AI, Han CC, Shear-induced martensitic -like transformation in a triblock copolymer melt, Macromolecules 1995; 28: 713-720
5. Reaumur RAF, L’art de convertir le fer forge en acier, Paris, 1722, from Smith CS, A history of martensite, early ideas on the structure of steel, in: Martensite, Olson GB, Owen WS, ASM International, 1992, Materials Park OH.
6. Matasa CG, Orthodontic attachment corrosion susceptibilities, J. Clin. Orthod. 1995; 29(1): 16-23
7. Matasa CG, Nicht rostende Edelstahle und Direkt - bonding- brackets (German) (Stainless steels and direct bonding brackets), Informationen aus Orthodontie und Kieferorthopadie", Heidelberg, Germany, 1992; 24(2): 237-249
8. Jackson CM, Wagner HJ, Wasilewski RJ, NASA SP 5110 Report, 1972)
9. Chang LC, The gold-cadmium beta phase, Trans AIME 1951; 191: 47
10. Buehler WJ, Gilfrich JV, Wiley RC, J. Effects of low temperature phase changes on the mechanical properties of alloys near composition TiNi, J. Appl. Phys. 1963; 34: 1475; US Patent 3,174,851’65; Buehler WJ, Cross WB, 55 Nitinol unique wire alloy with a memory, Wire J. 1969; 2: 41; Buehler WJ, Proceedings of the 7th Navy science (ONR-16 Office of Technical Services), US Dept. of Commerce, Washington DC, vol.1, 1963
11. Fukuyo S, Shape memory implants, International Journal of Oral and Maxillofacial Implants 1988; 2(3)
12. Hurst CL, Duncanson MG, Nanda RS, Angolkar PV, Shape-memory phenomenon of Ni-Ti wires, Am J Orthop. Dentofac Orthop. 1990; 90: 72-76
13. Johnson et al. USP 3,786,806’74
14. Fannon et al. USP 3,620,212 ’71
15.Krumme, US P 4,485,816’ 84; Pyka WR, Wuh HCK, Middleman LM, USP 5,002,563’91
16. Baumgart J, USP 4,170,990’79
17. Gupta TK, Lange FF, Bechtold JH, Properties of zirconia, J. Mater. Sci. 1978;13; 1464-70
18. Swab JJ, Stability of tetragonal zirconia, J. Mater. Sci. 1991;26: 6706
19. Bareiro MM, Vicente EE, Kinetics of isothermal phase transformations in a dental porcelain, J. Materials Sci., Mater. in Medicine 1993; 4: 431-436
20. Kittipibul P, Godfrey K In vitro shearing force testing of zirconia-based ceramic Begg bracket, Am J Orthop. Dentofac Orthop 1995; 108: 308-315; Keith O, Kusy RP, Whitley JQ, Zirconia brackets: An evaluation of morphology and coefficients of friction, Am J Orthop. Dentofac Orthop 1994;106:605-14
21. Mecholsky JJ, Toughening glass ceramics through microstructural design, Mechanics of Ceramics, E. Bradt, ed., Plenum Press, vol.6 1983; 165-179
22. Murase Y, Kato E, Daimon K, J. Amer. Ceram Soc. 1986; 69 : 3-10; Chang E, Chang WJ, Wang BC, Yang CY, Plasma spraying of zirconia-reinforced hydroxyapatite composite coatings on titanium, J. Materials Sci., Mater. in Medicine 1997; 8: 193-200.

NOTE
____In the last two issues, we have shown that in a court in Richmond, VA, an orthodontist, Dr. D.M. Fox, has sued a manufacturer, TP Orthodontics, for allegedly releasing faulty brackets. We also reported that during the trial, OMA's President, Dr. P.C. Kesling from TP Orthodontics has stated under oath in regard to slot tolerance: "I wouldn't know the difference if I had a .0025 or a .005" difference. Not significantly different". At the time, we didn't know that the jury has rendered a verdict in favor of TP Orthodontics nor that Dr. P.C. Kesling is not OMA's President, but his father.
We apologize for the incomplete information.