Treating the Constricted Envelope of Function

Dental professionals see the detrimental effects of a constricted envelope of function every day. At an early stage in our dental career we learned about Posselt’s envelope of function. As long as the mandible functions within this envelope without interference of opposing teeth, and the occlusion is in harmony with the muscles of mastication, the teeth can be protected.¹ However, when the envelope is constricted and there is interference from opposing teeth or musculature in the neutral zone, the results can be very destructive. Anterior wear and chipping are the most noticed consequences. Other symptoms include tooth mobility, sensitivity from mobility and exposed dentin, myofascial pain, difficulty in chewing, cracked teeth, and often a patient embarrassed with their smile.

Often patients tend to develop this constriction in their late teenage years and into their early twenties when the mandible undergoes a late growth spurt.² Orthodontists treating children and adolescents build this growth into their treatment plans. When patients do not undergo early developmental orthodontics, fail to wear retainers after orthodontics, or have a malocclusion that causes the anterior teeth to interfere with one another when closing, the consequences can be destructive.

A 46-year-old male presented with existing porcelain veneers that were treated several years earlier (Figure 1 through Figure 3). The veneers were chipped, margins exposed, and the teeth were worn and chipped. He was unhappy with his smile. A comprehensive dental examination included full mouth radiographs, a complete periodontal exam, oral cancer screening, esthetic evaluation, and temporomandibular joint disorder (TMJ) evaluation. He had mild periodontal inflammation, no pocketing, and recession present on the maxillary cuspids. The veneers ended on some of the incisor teeth short of the gingival margin, with some root exposed. The temporomandibular joint was asymptomatic, accepted loading, and there were no posterior occlusal issues.

Evaluation for sleep apnea must be in the thought process when anterior tooth wear is present.³ The patient was negative for any sleep issues. Discussion centered on the final result looking more harmonious and natural, with a lighter color and, most importantly, long-term stability. He was diagnosed with a constricted chewing pattern, contributing to the wear on the lower anterior teeth, along with the upper anterior chipping and wear patterns. He just did not have enough room to function when chewing behind the maxillary anterior tooth without interferences. When humans swallow, the teeth still come in contact and anterior wear can continue to progress in a constricted bite.

A complete photographic series was taken with additional images. The photos allow for evaluation of the patient’s smile when not in the office; Figure 4 through Figure 6 show digital smile design work in the laboratory based on these photos. Video should be considered to capture all aspects of the patient’s lip movements that the still camera cannot visualize.⁴ This can be easily accomplished with a smartphone or other handheld video recorder. Initial diagnostic impressions for models were also taken, mounted in maximum intercuspation (MIP) on a Panadent articulator with a Kois Dento-Facial Analyzer (panadent.com).

Evaluation at this point involved the dental laboratory technician who would eventually be completing the laboratory phase of the treatment. Discussion centered on options to eliminate the anterior constriction. Either the vertical dimension of occlusion had to be opened, the lower anterior teeth moved lingually, or the upper anteriors moved forward facially. Restoring the maxillary anteriors to proper length without opening the vertical dimension of occlusion (VDO) would cause a more restricted envelope of function and put the restorations at severe risk of failure. Also, opening the vertical would have involved a significant amount of additional unnecessary dentistry in the posterior region and mandibular arch. Moving the anterior teeth facially or moving the lower anterior teeth lingually could not be done without orthodontics. In situations where the final treatment could not be visualized, an initial diagnostic wax-up would be prudent. In this case, orthodontics was the only option to gain the desired result. In the author’s opinion, failure of the patient to consider orthodontics would have rendered the case untreatable for long-term success.

The patient returned to the office for the consultation, options were presented, and he was referred to the orthodontist for comprehensive orthodontic treatment. Based on this author’s observations of tooth position, gingival margins, and occlusal issues, the discussion with the orthodontist concluded that brackets and wires were the best, most efficient treatment to accomplish the desired outcome. The patient consulted with the orthodontist, underwent a full orthodontic evaluation, and committed to treatment. Throughout the course of treatment, he was being evaluated during his routine hygiene appointments based on the treatment plan proposed. As orthodontic treatment neared completion, the patient was evaluated to ensure all the esthetic components were also in place. Gingival levels were determined and the orthodontist moved the maxillary anterior teeth through intrusion or extrusion to line up the gingival margins.⁵ The patient was given the option of porcelain restorations on the lower anteriors. If he preferred to proceed with the lower restorative treatment, the orthodontist would have intruded teeth Nos. 23 through 26 to level mandibular gingival levels and minimize the amount of incisal reduction that would have been necessary to properly treat these teeth. The patient declined lower anterior restorations, so the incisal edges were placed in line with the proper occlusal scheme and level with the mandibular posterior plane of occlusion. Treatment with porcelain restorations on the maxillary arch alone when hand polished compared to a fired porcelain glaze will not wear the opposing dentition significantly. In addition, this author keeps the centric stops on the anterior teeth lighter than those on the posterior teeth. From the cuspids posteriorly, the teeth should hold shimstock. On the anterior teeth, the shimstock will lightly pull through, though still maintaining a centric holding stop. In addition, by having the patient test chewing function on 200-μm articulating paper and removing all extraneous marks, except those in centric contact, there should be no harm to the opposing dentition through either wear or mobility of teeth. This is important to prevent a constricted chewing pattern patient from causing more destruction after treatment.

When the orthodontist was satisfied with the results, he sent the patient back to the office with a set of plaster models taken during a wire change (Figure 7). Photos were taken and shared with the laboratory technician along with the models. It is essential for the laboratory technician to identify and convey any necessary adjustments to the orthodontist for correction prior to bracket removal. In this case, the laboratory technician expressed concern about spacing and suggested minor changes prior to removal of the brackets (Figure 8). Aligning the teeth better and creating consistent spacing would make the final restorations look more realistic and create more ideal papillae height. The corrections were made, final approval given by all three dental professionals, and only then were the brackets removed (Figure 9 and Figure 10). The patient returned to this author’s dental practice for new diagnostic casts, photos, and a facebow.⁶ The casts were again mounted on the Panadent articulator, new photographs taken, and sent to the laboratory for a diagnostic wax-up on teeth Nos. 4 through 13.⁷ The laboratory technician sent back the diagnostic wax-up, a vacuform stent, and a putty matrix for chairside try-in of the esthetics.

When the patient returned to the office for the wax try-in appointment (Figure 11), a BIS-GMA resin (MirrorImage, Cosmedent, cosmedent.com) was placed inside the putty matrix. The matrix was inserted in the patient’s mouth, allowed to cure, and then removed. The resin remained in the mouth so the patient could also evaluate the proposed finished result (Figure 12). Photographs were taken and placed on a large computer monitor for proper visualization by the patient, dentist, and dental assistant. A critical esthetic analysis was done and no corrections were needed in the work sent from the laboratory. The incisal plane was level, position of cuspid teeth was excellent in relation to the lip at rest (Figure 13), which was equal to the lip edge, incisal embrasures were evaluated, and incisal edge position was acceptable. The patient was phonetically tested with a variety of words to ensure that “s,” “th,” “f,” and “v” sounds were all normal. The final shade of the restorations was discussed with the patient and Vita A1 was chosen. Overall, there were no corrections and the patient was appointed for the preparation phase.

In the treatment phase, the patient was anesthetized with local anesthetic. A double retraction cord technique was used (Ultrapak^®, Ultradent, ultradent.com). The authors prefer to start with the central incisor preparations and proceed laterally. Prior to starting the preparations and based on the diagnostic wax-up and position of the teeth for proper occlusion, a decision was made to prepare for crowns and not a traditional veneer prep. As discussed previously, the centric stops in the crowns were going to be designed to touch lighter, with no functional interferences within the envelope of function. The crown preparations would also allow for anterior contact on the lingual surfaces. This was not present after orthodontics because of the intrusion of several teeth to improve esthetics. Without centric holding stop contacts, there could be drifting of opposing teeth. This would minimize any abnormal wear on the lower incisors. All of the teeth were prepared. At that time, the putty matrix was again filled with the BIS-GMA resin, placed in the mouth, and allowed to cure. Removal of the putty revealed areas that were too thin.⁸ This could be readily visualized by tooth show-through, indicating that the tooth was not prepared enough for the final restoration position. The teeth were further prepared directly through the resin, and then refined prior to the final impression. Adequate reduction is essential so the final porcelain is a uniform thickness resulting in a uniform color without any show-through of the underlying dentin. A shade must also be taken of the tooth preparation to send to the laboratory to ensure the color does not show through the final porcelain restoration.

A PVS impression was taken using Imprint™ 4 Heavy Body (3M Oral Care, 3m.com) and Impressiv™ Light Body (Cosmedent) in a stock tray (Direct Flow Tray, 3M Oral Care). The second retraction cord was removed just prior to light body impression material placement. Opposing model impressions were taken, along with a PVS bite record (Blu-Mousse^®, Parkell, parkell.com) that does not distort. The provisional restorations were fabricated from the putty matrix of the diagnostic wax-up, utilizing Cosmedent MirrorImage shade A1. The restorations were trimmed, adjusted, and glazed (MirrorImage Adjust and Glaze, Cosmedent). They were seated with temporary cement (Cling2, Clinician’s Choice, clinicianschoice.com) and cleaned. An impression to make the model of the provisionals was taken along with a facebow recording of the provisionals with the Panadent Kois Facial Analyzer. Photographs were taken of the smile at rest and sent with the case to the laboratory (Figure 14).

Upon receiving the information from the doctor, the laboratory technician mounted the approved model of the maxillary provisionals using the Kois Analyzer on a Panadent articulator against the mandibular opposing model. Working impressions were poured and a working model fabricated and mounted to the already articulated mandibular model, allowing the laboratory to maintain the occlusal plane. This gave them an easy way to maintain occlusion, establish proper preparation of teeth, and accurate fabrication of final restorations.

Restoration Nos. 4 through 13 were waxed to full contour using the model of temps as a guide for incisal length and labial/incisal positon. The author requested a final shade of Vita A1 and reported the preparation shade as ND2 (Natural Shade Guide, Ivoclar Vivadent, ivoclarvivadent.com). The laboratory and doctor decided on an Ivoclar Vivadent e.max^® ingot color of medium translucency; A1 would be best choice for this case.⁹ The e.max lithium disilicate offers excellent strength and esthetics, and both attributes were required to meet the patient’s goals. After waxing, the crowns were invested, burned out, pressed, and divested. After seating the crowns, careful consideration was taken to adjust the interproximal contacts to allow maximum efficiency of try-in and seating of crowns intraorally. The interproximal contacts were adjusted on a solid working cast with Shimstock Strips (Almore International, almore.com). The crowns were then cut back on the facial surface maintaining the incisal edge. The lingual surfaces were left in monolithic e.max to support the patient’s function with increased strength. After internal staining, the crowns were layered, textured, and glazed.¹⁰ A final check of the occlusion and interproximal contacts was finished and the crowns were hand polished using fine Diashine^® Diamond paste (VH Technologies, vhtechnologies.com). The crowns were etched with 9.5% hydrofluoric acid for 10 seconds and sent to the author for final seating.

The patient returned a few weeks later for the final insertion of the restorations. The patient was anesthetized and the temporary crowns removed. The teeth were cleaned and retraction cord was placed, impregnated with aluminum chloride (Viscostat Clear, Ultradent). The teeth were further cleaned with 27-μm aluminum oxide in a PrepStart air abrasion unit (Danville Engineering, danvillematerials.com) to allow for the highest bond strength.^11,12 The restorations were tried in; all contacts, centric stops, and margins verified; and the patient had an opportunity to view the crowns for final approval. In order to hold the crowns in place during the try-in phase, TEMPLATE^® Ultra Quick Matrix Material (Clinician’s Choice), a PVS quick set material, was inserted in the crowns and they were seated on the preparations. The material is flexible when set and the clear color simulates the final clear cement that will be used. Also, this material can be easily removed after the try-in.

In order to remove blood and other contaminants from the restoration during the try-in phase, the crowns were cleaned internally, re-etched with hydrofluoric acid for 10 seconds, rinsed, and dried, followed by placement of silane for 30 seconds and dried. The crowns were seated two at a time using RelyX™ Unicem 2 self-etching resin cement (3M Oral Care). The crowns were seated firmly, held in place, then tack-cured for 1 second (Elipar™ curing light, 3M Oral Care). This allows for easier cleanup of the cement with a small scaler and floss. The cement was cured for 40 seconds on all surfaces. Unicem 2 is a dual-cure cement, and any areas not completely cured with the curing light will cure over the next several hours. This author prefers to have the centrals verified and seated first. At times, contacts can be too tight from model discrepancies. If adjustments need to be made it is best to avoid modifying the central incisors in order to keep the teeth the same size as mirror images of each other.

After all crowns were cemented, the retraction cords were removed and final clean-up of the gingival areas was completed. Occlusion was rechecked using an 8-μm-thin articulating paper, TrollFoil (Troll Dental, trolldental.com) for even centric contacts. This author prefers a very light contact on the incisor teeth compared with a tighter contact on the other teeth. This is verified with shim stock. The tooth occlusal contacts should hold the shim stock firmly on the cuspid and posterior teeth and just slide out on the anterior teeth. Further adjustments were made using 200-μm articulating paper with the patient in a fully upright position. The patient was instructed to chew around on the paper. Any markings except those made in MIP must be eliminated. These extraneous markings would indicate interference in the envelope of function and result in possible breakage of the restorations or mobility of the teeth. Therefore, all of these marks are removed. The porcelain was repolished with Dialite^® wheels (Brasseler USA, brasselerusadental.com) in all three grits followed by Diashine with a prophy cup.

The patient was instructed on proper care of his new restorations, including proper oral hygiene techniques and foods to avoid that may cause breakage. The patient was dismissed and reappointed several weeks later for follow-up (Figure 15 and Figure 16).

Predictability and success in the final esthetic result of any patient treatment starts with planning at the very beginning. When the entire dental team is involved early, communication is enhanced and minor issues eliminated before they become major disasters. A patient undergoing a major dental expense like this needs to be assured that the treatment is progressing well. Any chance for the patient to be involved in the decision process is critical and all patients appreciate seeing the final shape of their new smile preoperatively, both on the articulator and especially in the mouth. The diagnostic wax-up is an essential component, but having the vision of the final smile is the most critical. The orthodontist was again consulted for help in the final retention appliance. He needed to ensure the teeth did not move and the author wanted to ensure occlusal protection while the patient slept, which was accomplished.

1. Dawson, PJ. Evaluation, Diagnosis and Treatment of Occlusal Problems. 2nd ed. St. Louis, Mo: Mosby; 1989:369-370.

Fred H. Peck, DDS, AAACD
Private Practice
Cincinnati, Ohio

Dwight Rickert, CDT, FAACD
Owner, Preferred Dental Ceramics
Indianapolis, Indiana