Modified Occlusal Rim Design and Use of Phonetics to Determine Anterior Tooth Position and Vertical Dimension: A Clinical Report

A review of the prosthodontic literature by Ivanhoe et al¹ reveals that most “classic” articles regarding the clinical process for the construction of complete dentures have been empiric in nature. Authors of these articles have lacked agreement about topics such as occlusal design, selection of tooth mold, and facebow transfer systems. The literature contains many anecdotal references to esthetic aspects of complete denture construction. This is an imprecise area that combines “scientific” and “artistic” resolutions.²

Many techniques have been published to help clinicians establish incisal-edge position. Payne³ used phonetics to aid in determining the location of the maxillary anterior teeth using the sounds “S,” “Z,” and “C.” He reported that if the teeth were positioned too low, they would “click” together.⁴ Boucher⁵ noted that maxillary central and lateral incisors touched the lower lip during the pronunciation of the letters “V” and “F.” He also observed when the upper lip was at rest, the incisal edges of the maxillary teeth were usually visible.⁴

Several authors^6-9 have reported that, regardless of age or sex, the vertical position of the central incisors is mostly determined by their relationship to the lips in repose. As a general rule, these authors observed that the anterior aspect of the maxillary occlusal rim should extend approximately 1 mm to 2 mm below the lips in repose. Speech (the “F” sound, in particular) was then used to modify this vertical position.⁴

Frush and Fisher¹⁰ said the “smile line” helped the dental team gauge the proper vertical position of the maxillary teeth in complete dentures. They observed that the central incisors were longer than the other maxillary teeth and the curvature of the maxillary teeth followed the curve of the upper border of the lower lip during smiling. Following these guidelines, the incisal edges of the maxillary anterior teeth are noted to barely reach the lower lip during smiling. The clinician is challenged to match maxillary anterior teeth with the patient’s natural teeth, particularly when extensive tooth loss has occurred and the remaining natural teeth cannot provide guidance.¹¹

Clinical Report

A 75-year-old Hispanic man complaining of functional and esthetic problems presented to the Advanced Education General Dentistry clinic at Eastman Institute for Oral Health at the University of Rochester Medical Center in New York. The patient had no medical contraindications to dental treatment. Findings from the initial examination revealed that the maxillary arch was edentulous. Teeth Nos. 22 through 24 were periodontally compromised. The patient had no previous experience with any prosthesis. The lower teeth were determined to be hopeless and were extracted. The patient chose complete upper and lower dentures. The patient was not offered other options because he presented with Medicaid dental insurance and clearly stated that he could afford only what his insurance would cover.

After healing, preliminary impressions of the edentulous arches were made with irreversible hydrocolloid material (Jeltrate® Plus, DENTSPLY, www.dentsply.com). Preliminary casts were fabricated with type III dental stone (Dental Hydrocal, Kerr Corp., www.kerrdental.com), and custom trays were fabricated (Triad®, DENTSPLY). Border molding and final impressions were achieved using modeling compound (Kerr Impression Compound, Kerr Corp.) and vinylpolysiloxane impression material (Imprint™ 3 VPS, 3M ESPE, www.3mespe.com). The master casts were fabricated with type IV dental stone (Prima-Rock, Whip Mix Corp., www.whipmix.com). Maxillary and mandibular record bases were fabricated using heat-processed polymethylmethacrylate (PMMA) resin (Lucitone 199®, DENTSPLY). These bases would also serve as the base for each complete denture (Figure 1 and Figure 2).

Baseplate wax (Beauty Pink, Moyco) was warmed over a flame and folded along its shorter edge to create a strip approximately 12 mm wide and two (or three) layers thick. This 12-mm segment was cut off of a large piece of wax, and while it was warm, it was placed on the maxillary baseplate to mimic the anterior teeth. Because the maxillary ridge resorbs in an apical and palatal path, the facial/incisal edge of the wax rim was placed no further than the midpoint of the vestibule in the final impression. The thin rim was placed to approximate the position of the teeth. This was done empirically in the laboratory before the patient’s appointment. The model can be viewed from the occlusal, on the bench (Figure 3), and picked up so it can be viewed from the front and sides. While viewing the rim it is important to evaluate if the position looks “normal.” (When we say normal, we are referring to the anterior/posterior and the axial inclination of the wax rim. As you read further in this article, you will notice this position is modified once the base is in the patient’s mouth. However, the starting point should be as close as possible to ideal.) The rim was left slightly longer than the final length and was made parallel to the ridge, and the ends of the rim in the Nos. 6 and 11 positions were slightly curved upward to approximate the canine positions. The longer length gave the clinician the ability to adjust apically with a hot instrument when the patient was present.

The mandibular rim was fabricated in a similar fashion, except that the wax rim was placed directly over the remaining ridge. The lower ridge resorbs in a more apical path, so the rim was placed straight up from the ridge (Figure 4). It, too, was left longer than the final incisal height.

The maxillary baseplate was placed in the patient’s mouth, and the clinician viewed the patient from the front while the patient relaxed. At this point, the rim should be parallel to the pupillary line. If it is not, adjustment should be made to make it parallel. The clinician must check to see if it looks too long or too short. The patient was asked to count from 50 to 55 and to smile (Figure 5). The rim was adjusted so that the incisal edge of it touched just lingual to the wet-dry line of the lower lip when the patient said the “F” sound.

The lower base was then placed in the mouth. With a well-fitting, retentive upper base, the clinician could now place the patient in centric relation (CR). The clinician must determine where the rims are in relation to each other—are they touching in a class I, II, or III relationship? The upper rim was in the appropriate position based on phonetics and ridge anatomy. With class I occlusions, the lower rim will often fall just lingual to the upper rim. The patient was asked to remain with the rims touching (not biting hard), and the cheeks and lips were gently tugged to help them relax. If the patient’s vertical dimension looks too open at this point, the lower denture base gets removed and the rim shortened with a hot instrument. When vertical appears normal and relaxed in centric, the patient is asked to count quickly from 1 to 10 (Figure 6). If the counting sounds normal, especially the “6” and “7” sounds, the clinician can look away and ask a question to prompt the patient to speak freely without feeling pressured to please the clinician. All this time, the clinician listens to the patient’s speech. This method also helps reveal characteristics about the edentulous patient’s occlusion. Most people will be able to be constructed in a class I occlusion; however, some will need to be constructed as class II or III occlusions.

Once the patient’s speech sounds normal, the clinician stands in front of the patient and asks him or her to say the letter “M” repeatedly. It helps to say it with the patient. The clinician should be looking at the relationship of the incisal edges of the wax rims to each another. If the space between them is 4 mm to 7 mm, there is enough freeway space. Too little freeway space means one of the rims needs to be lowered. The upper rim is in the right position, so the lower rim can be adjusted apically. Too much freeway space means the lower rim could be lengthened. The proper position of the teeth has been determined based on function in speech. The midline can be marked and the distal of the canines marked on the upper rim. The next challenging task of obtaining a CR record can begin.

Baseplate wax was positioned in the posterior area of both denture bases, with retentive grooves placed on the occlusal surface. This will serve as a means of making a CR record using a bite-registration material (Blu-Mousse®, Parkell Inc., www.parkell.com). The patient was asked to close and swallow as the material was setting. The record was evaluated for no contact of the wax in the posterior region, with a thin ribbon of bite registration material between the rims (Figure 7).

Selection of teeth was simplified by measuring the distance between the canines and the height of the wax rim in the central incisor area (Figure 8). These two numbers made the selection process easier because mold guides contain these measurements. The clinician can communicate the mold to the laboratory and give specific instructions to place the anterior teeth on the wax rims for overbite and overjet.

At the time of esthetic try-in, the waxed dentures were tried in and evaluated for appearance and phonetics. The maxillary incisors contacted the lower lip just lingual to the wet-dry line during labiodental sounds (Figure 9). The posterior teeth were added. After conventional denture processing, the dentures were delivered (Figure 10). The patient did not require any post-delivery adjustment and was reevaluated at 3 and 6 months.

Discussion

The main objective of prosthodontics is to achieve restorations that are both functional and esthetic. Function is directly related to occlusion and phonetics. Esthetics involves proper vertical and horizontal positioning of teeth and selection of a tooth mold that fits well in the available space. This clinical report describes a practical technique to determine tooth position and vertical dimension using a modified occlusal rim that is thin and “feels” like teeth to the patient. With this technique, the clinician is able to determine where the teeth need to be before obtaining a bite registration. After the bite is recorded the clinician can make this determination. This avoids the all-too-common scenario where a bite is recorded, the case is sent to the laboratory where it is mounted, and once the mounting process is completed and vertical dimension is set on the articulator the technician removes all the bite material and sets the teeth where he or she thinks they belong.

This technique can be helpful in cases in which a CR record is difficult to capture. By measuring the upper rim, the clinician can easily select the proper tooth mold. The laboratory is given specific instructions to place the selected teeth in the identical position that the rims occupy. Teeth Nos. 6 through 11 can be placed on the upper base and Nos. 22 through 27 can be placed on the lower. The laboratory can then set Nos. 18 through 21 and Nos. 28 through 31 with an occlusal plane that extends halfway up the retromolar pad. The case can be returned to the clinician without any upper posterior teeth. It can be tried in, and patients can view the anterior set-up and decide if they like the esthetics. Speech can be checked with the same approach outlined above with the wax rims. Another attempt at a CR record can be made using any bite-registration material on the upper base, which will now imprint against the lower dentures. Patients who struggle with the CR record at the bite-registration appointment are often more relaxed at this try-in appointment. The CR record is often easier to attain with teeth on the bases.

Summary

A modified occlusal rim was used to assist in the determination of tooth position and vertical dimension. After preliminary impressions were taken and casts were made, custom trays were fabricated for final impression. PMMA-processed bases were constructed and used as baseplates and final denture bases. Thin anterior segment wax rims were used to phonetically determine the position of the anterior teeth. This method felt more natural to the patient during the bite-registration visit and provided information to the clinician, which was easily communicated to the laboratory.

About the Authors

Mario F. Romero, DDS
Assistant Professor
Department of Oral Rehabilitation
Georgia Regents University College of Dental Medicine
Augusta, Georgia

Thomas A. DeRosa
Assistant Professor
Department of General Dentistry
Eastman Institute for Oral Health
University of Rochester
Rochester, New York