fig1 - 5 illustrate a prior art device , as described above . [ 0064 ] fig6 illustrates a first preferred embodiment of a dental impression tray or tray 10 . tray 10 includes a first side 14 and a second side 18 spaced apart therefrom . first and second sides 14 and 18 may be integrally joined at one end thereof . one or more strands 22 and 26 may extend between sides 14 and 18 . strands 22 and 26 may be made of a synthetic material . the synthetic material may selected for its affinity ( i . e ., propensity to bond with ) a dental impression material 30 disposed on strands 22 and 26 . strands 22 and 26 may be free of linking members ( other than first and second sides ) which extend between strand 22 and 26 . in that manner when a patient &# 39 ; s teeth bite down on impression material 30 and , hence , strands 22 and 26 disposed thereunder or therein , strands 22 and 26 will move toward or away from each other depending on the location of the portion of the patient &# 39 ; s tooth exerting pressure on a portion of the strand . unlike prior art devices , such as described in connection with fig1 - 5 above , the length , size , spacing , and material of strands 22 and 26 may be selected so that under pressure from a patent &# 39 ; s tooth , in use , there will be little or no tendency for first side 14 to move relative to second side 18 . in other words , sides 14 and 18 will not distort , thus causing the impression material 30 to distort . in known dental impression trays , there is a tendency for the opposing sides to move toward each other under pressure , and then “ spring back ” after the pressure is released , thereby distorting the impression of the patient &# 39 ; s tooth that was made in the impression material . a handle 34 for assisting in the manipulation of tray 10 may be provided . [ 0071 ] fig7 illustrates a further preferred embodiment of a portion of a dental impression tray 50 . tray 50 includes strands 52 and 56 which extend at a greater angle relative to the sides to which they are attached , as compared with the angle defined by strands 22 and 26 of tray 10 of fig6 . [ 0072 ] fig8 illustrates a further preferred embodiment of a tray 60 . tray 60 includes hook - like openings 66 in at least one of its side walls . hook like opening 66 are configured for receiving impression material 30 wherein when material 30 is in a softened and hardened state , to assist in retaining the impression material within the tray and relative to the side , for example . [ 0073 ] fig9 illustrates a further preferred embodiment of a tray 70 according to the invention . tray 70 includes one or more hook like elements 76 extending outwardly away from one or more of the sides of the tray . hook like elements 76 are configured for engaging impression material 30 . fig9 shows that , in use , extra impression material may be added in a region 78 outwardly of the free ends of the sides of tray 70 . in that manner , the rigidity and distortion - free properties of tray 70 , as well as other trays according to the invention described herein may be enhanced . [ 0074 ] fig1 illustrates yet another preferred embodiment of a portion of a tray 80 according to the invention . in tray 80 , only a single strand 82 of which is illustrated for clarity , strand 82 itself may be provided with one or more hooks 86 and 88 . hooks 86 and 88 may all extend outwardly away from the main body 84 of strand 82 at a common angle and orientation , or hooks 86 and 88 may be provided at various locations and extending at various angles and heights , relative to main body 84 , as shown . [ 0076 ] fig1 illustrates a premade thermoplastic insert 100 which may be used for converting a double arch triple tray into a rigid tray . by use of the novel premade insert 100 the dental impression tray can be completed on - site ( e . g ., in the dental practitioner &# 39 ; s office ) immediately prior to obtaining an impression of a patient &# 39 ; s teeth in a less expensive and a more accurate manner than by using the prior art devices . [ 0077 ] fig1 illustrates a prior art double arch triple tray such as a so - called neo tray ™. [ 0078 ] fig1 illustrates the inventive thermoplastic insert 100 in use with the tray of fig1 . one or more notches 104 provided in thermoplastic insert 100 may be selected to mate with respective prior art extensions on the prior art triple tray . after the dental practitioner places the insert 100 into an existing triple tray , for example , such would be placed in a water bath to heat up the insert 100 sufficiently , so that when the combination is removed from the water bath , the rehardening material provided by insert 100 will engage with the triple tray and be ready for use . the thermoplastic inserts 100 may be premade to fit into various known dental impression trays , such as neo trays ™ and multi trays . inserts 100 may be placed into the tray of fig1 so that the thermoplastic insert is on the opposing side of the tooth to be prepared , as shown in fig1 . the tray has then placed in a water bath to soften the thermoplastic as well as a known temp tab ™. the softened temp tab ™ is then adapted over the tooth to be prepared making an impression of the tooth after build - up prior to preparation , as in fig1 . before the temp tab hardens , the tray with the softened thermoplastic insert 100 is placed on the opposing arch pressing it against the opposing occlusal surfaces making an impression of these surfaces into the thermoplastic . the patient is then guided into maximum intercuspation and asked to hold the teeth together in occlusion until the thermoplastic completely hardens , fusing the temp tab ™ and the opposing thermoplastic together . this techniques converts a regular fig1 arch triple tray into a tray which is rigid and cannot flex and thereby preventing spring back distortion which is a common problem with conventional triple trays . further , the temp tab ™ on the prepared side over the tooth to be prepared acts as a vehicle to drive the wash impression material as well as a matrix to make a temporary . the advantages of the tray in conjunction with insert 100 over the known thermo trays is the cost - effectiveness of the insert 100 and the temp tabs ™. the current thermo tray is very small and only covers a small portion of the arch . the regular triple trays go around the arch making a larger impression making it easier to mount the cast , when one step mounting systems are not used . also , the temp tabs ™ incorporated into the tray will serve as a matrix to fabricate a temporary as well as a vehicle to drive the wash impression material assuring a good impression of the margins and prepared tooth without risking pulls or voids . fig1 - 17 illustrate several preferred embodiments of thermoplastic or thermal plastic dispensers according to the invention . [ 0087 ] fig1 illustrates a first preferred embodiment of a thermoplastic dispenser 200 . dispenser 200 may include a heating element 204 , a dispenser 208 and a water bath 220 . water bath 220 may be disposed substantially adjacent to 208 and provided on a common base 224 , as illustrated . a dispenser nozzle 228 may be provided and sized for general laboratory use or specifically sized for dispensing a thermoplastic material 230 onto a dental impression tray 10 of fig6 for example . thermoplastic material 230 may be dispensed in a molten or semi - molten state by pressing on an actuator portion or pressing device 240 operatively connected with dispensable material 230 . an integral or removable loading element 250 may be provided for ease of filling dispenser 200 with thermoplastic material to be dispensed . as shown , thermoplastic material may be provided in various degrees of softness or liquefaction in a region fluidly connecting dispenser 228 and actuator 240 . [ 0089 ] fig1 illustrates another preferred embodiment of a dispenser 300 according to the invention . dispenser 300 may include a nozzle 328 and a handle 334 . an actuator or trigger 342 may be configured for being pressed by the user &# 39 ; s finger or fingers . as in the embodiment of fig1 , a region 350 may be provided in which thermoplastic material is loaded for being softened or liquified . loading region 350 may be sized for receiving cartridges of thermoplastic material . [ 0090 ] fig1 illustrates a yet still further preferred embodiment of a thermoplastic dispenser 400 . dispenser 400 may be a free - standing device , in a manner analogous to dispenser 200 of fig1 . yet , dispenser 400 may be configured as a relatively tall dispenser , similar to the shape of known upright , free standing toothpaste dispensers . dispenser 400 may be provided with a heating element 404 including heating coils or thermally conductive elements 414 and a base 424 . one or more chambers 434 may be provided in which , for example , cartridges of thermoplastic material or thermoplastic stock may be provided . a dispenser nozzle 448 will be provided along the lines as discussed above , as well as an actuator for causing thermoplastic material to be dispensed . while this invention has been described as having a preferred design , it is understood that it is capable of further modifications , and uses and / or adaptations of the invention and following in general the principle of the invention and including such departures from the present disclosure as come within the known or customary practice in the art to which the invention pertains , and as may be applied to the central features hereinbefore set forth , and fall within the scope of the invention or limits of the claims appended hereto .