Intra-oral bony growths of all types, present a clinical challenge for the dental team attempting to capture accurate detail for final impressions of crown and bridge, removable prosthetics, oral appliances, accurate opposing models, study models, and whitening trays. Stock impression trays often can’t be seated to depth, because they get hung up on these bony anatomical variants, or the bony protuberances can cause pain during the impressioning procedure, as there is often only a thin membrane of covering tissue which is easily irritated1. For our medical confreres, mandibular tori can present significant challenges for endotracheal intubation2 and laryngoscopy3. Lingual tori may also limit the space for the tongue and can result in speech impediment. Even though these bony areas can create a clinical challenge with impressioning, these areas are prime sites for harvesting autogenous bone for bone grafting of dental implants4 and can be used for multiple reconstructive procedures such as nasal reconstruction5.
Bony exostosis is described as a benign localized overgrowth of bone of unknown6 or controversial etiology7, however the hypothesis is that there may be an interplay of genetic and environmental factors9 including severe occlusal stress. Buccal bony exostoses have been reported secondary to soft tissue graft procedures and free gingival grafts7,8 with periosteal trauma seemingly the main etiologic agent. In a study of 960 Thias, Jainkittivong found that 26.9% of the sample exhibited exostoses, which were more prevalent in the male maxilla, and most of the exostoses were located on the buccal of the jaws9. In a study by Horning buccal alveolar bone enlargements were found in 25% of all teeth examined; 18% were expressed as marginal bony lippings and 7% as buccal exostoses10. Small exostoses called palatal tubercles were present in 56% of all skulls examined by Sonnier which can require their removal for adequate flap adaptation after surgical procedures11. However, it is the presence of buccal exostoses that may require impression tray modification when they interfere with the path, insertion and final position of the tray.
The torus has been mentioned in the literature for about 180 years12 and has been described as a benign, anatomical, slowly growing bony prominence occurring in the hard palate and the lingual aspect of the mandible1 or an area of hyperostosis13. Although the etiology of Torus Palatinus and Torus Mandibularis is debated in the literature, tori seem to be a functional reaction to masticatory stresses14 and are due to genetic and environmental factors with suggestions of autosomal dominant transmission12,14,15. The reported literature on the occurrence of tori in the population varies with different ethnicity and sex. In most studies, ranges from 1.4 – 69.7 percent are reported12,16,17,18,19, while one publication states that tori occur 100% amongst Greenland Eskimos13. In some ethnic groups women are more likely to have larger torus palatinus, whereas men have larger torus mandibularis20 and there seems to be a strong link between the coexistence of palatal and mandibular tori21. There may also be a positive relation for postmenopausal Caucasian women between the bone mineral density and torus size22. In a study of 400 Japanese the reported risk factors for mandibular lingual torus were gender, number of sound teeth and bruxism, and for palatal torus the risk factors were gender and TMJ symptoms23. The number of remaining sound teeth also showed a positive correlation to tori prevalence in a Norwegian study24. The prevalence of torus mandibularis and parafunctional activity is higher in temporomandibular disorder than controls25. There seems to be a correlation between the presence of mandibular tori and the ability to maintain favourable bone height, with a suggestion that a genetic locus for this may shed some light on the genetic contribution and mechanisms that tend to make the marginal alveolar bone more resistant to destructive agents26.
Teeth that are mal-positioned in the dental arch often create a path of insertion problem when attempting to take final impressions. Often the maxillary canine is crowded and labially displaced. On the mandibular arch, the lower anteriors are often crowded, displaced, or rotated with lower first and second premolars often lingually displaced, making it impossible to seat a traditional impression tray. The creation of traditional custom impression trays for these clinical situations is often frustrating, time consuming, costly and the clinician wastes valuable operatory time. The availability of an instant “custom tray” allows for immediate treatment and impressioning.
The presence of tori ( Fig. 1) can complicate fixed prosthetic reconstruction13, the fabrication of dentures2, and any other oral appliance such as bruxism splints, mouth guards, and orthodontic appliances, with the clinical process of taking an accurate impression one of the most difficult tasks the clinician faces. Maxillary stock trays will often not seat deep enough in the buccal vestibule when there is a large torus palatinus, complicating the capture of detail, with resultant lack of control of the impression material towards the soft palate and throat, and loss of directional drive of the impression material which is critical in final crown and bridge impressions. Mandibular stock trays will sit on top of large mandibular tori (Fig. 2), or at best scrape the lingual tissue covering the tori during the impression, again resulting in complications during the impressioning phase for any application. In the past, solutions included cutting down the lingual flanges to make them end superior to the mandibular torus, or to take a preliminary impression which was not seated fully and then from the model fabricated, make a custom tray and re-impress. Clinicians have also attempted to use maxillary trays to impress lower arches, however it is difficult if not impossible to retract the tongue to accomplish this procedure27. Yung-tsung has suggested taking a maxillary tray, cutting out the palatal portion and adding utility wax to create a tray that will capture lingual tori28. Until now, there has not been an easy solution for satisfactorily modifying a stock tray to impress a maxillary tuberosity, unless one removes the centre of a plastic tray, and most often it required a first impression doing the best one could clinically, and then following with a final impression utilizing a custom tray fabricated from the initial model.
The clinical challenges that face the dental practitioner when attempting to impress these bony exostoses or dental mal-positions have now been solved. A new disposable heat mouldable tray (HeatWave, Clinician’s Choice/Clinical Research Dental) uses a biopearl modified polyactic acid-derived, extremely stiff, and inflexible plastic material. However when heated in water at 70 degrees Celsius for 60 seconds (Fig.3) the tray will soften allowing a moulding or reshaping of the tray to the desired contour. After heating the trays resume their normal rigidity after being heated, in approximately 20 seconds, or when placed briefly under cold running water. The tray becomes 100% rigid as soon as the tray reaches room temperature (23 degrees Celsius). Since these trays are mouldable, a smaller number and sizes of trays are needed than usual to address the many arch sizes and clinical challenges faced. Once the shape has been changed, even storing the thermoplastic trays for 2 hours at 40 degrees Celsius shows no further change in form29. For step 1 in this mandibular case, an intraoral caliper is used to judge the most appropriate size of the tray by measuring the arch width and angulation of the
dentition (Fig. 4 and Fig. 5).
This unique mouldable feature allows for softening of the palate to indent the tray to make room for maxillary torus (Fig. 6 and Fig.7) or to expand the buccal flanges of the upper tray to work around large tori, maxillary exostoses or labially displaced teeth (Fig. 8 and Fig. 9). For this mandibular case, the presence of a torus, (or lingually displaced tooth such as a second premolar) is no longer an obstacle to obtaining an exquisite mandibular impression. After heating the tray (Fig. 10) the lingual flanges can be moulded to any position (Fig. 11) so as to be positioned to accommodate the exostosis or mal-positioned tooth (Fig. 12). Figure 13 A and B shows the final impression of a mandibular arch complicated by a large mandibular torus, with an alginate substitute30 (CounterFIT Clinical Research Dental) and Figure 14 shows the detail of the mandibular cast produced with this Heatwave disposable heat mouldable technique. The use of this modified tray technique allows for the design of the tray to maintain the vertical drive necessary to achieve accurate detail when impressioning crown and bridge preparations (Fig. 15 and Fig.16) and as well minimizing the amount of PVS material used thus reducing the cost of the overall impression.
This article presents a new approach to taking impressions of exostosis, torus mandibularis, torus palatinus and mal-positioned teeth, which incorporates the use of a disposable heat mouldable, though rigid tray. This technique saves the clinician time, lowers costs, and eliminates the challenges faced by dentists with previous methods for difficult clinical cases of impressioning. oh
Dr. Len Boksman D.D.S., B.Sc., F.A.D.I., F.I.C.D. is Director of Clinical Affairs for Clinical Research Dental and Clinician’s Choice.
Dr. Carson is a graduate of the Schulich School of Medicine and Dentistry and practices at Sunningdale Dental Centre in London, Ontario.
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