Innovative Advanced Occlusion Planning with Superimposed CT and Optical Scans

By Gilbert Tremblay, BSc, DMD

In complex rehabilitation cases that involve the opening of the vertical dimension of occlusion, positioning the temporomandibular joints (TMJ) can be intuitively driven. However, with an unbalanced TMJ position, the discrepancy in the mandible position and the magnitude of prosthetic compensation can lead to an unsatisfactory prosthetic and functional outcome, complicating patient care. Positioning the mandible with a Kois deprogrammer followed by implementation of recent technological advances allows computerized measurement of the TMJ’s position bilaterally. Managing diagnostic and clinical information using computer software improves efficiency in treatment planning and accuracy in prosthetic execution, leading to a more precise and predictable outcome.

A 56-year-old woman initially presented in September 2008 in need of significant occlusion modification. The patient was looking to increase comfort, achieve improved esthetics, and restore function. This case, which employed an innovative scanning procedure, involved a three-phase plan that included implant treatment and increasing the patient’s occlusal vertical dimension. Active treatment was completed one year later, in September 2009.

Medical History

The patient had no contributory medical history or known allergies. No prior medication was taken by the patient.

Diagnostic Findings

Temporomandibular Joints: Loading and immobilization tests were completed without any positive findings. The maximum inter-incisal opening was within normal limits. Clinically, neither deviations nor pathological sounds were noted.

Extraoral: An upper lip asymmetry was found. In the smile position the upper left side of the patient’s lip was slightly lower than the contralateral side. A sagittal face view revealed a slightly retrognathic profile.

Intraoral: Soft tissue was scanned with fluoroscopy. No significant clinical findings were observed. The patient did not experience pain or discomfort when conducting digital palpation for intraoral and extraoral muscles (masseter, zygomatic, pterygoid, sternocleidomastoid, temporal, and occipital muscles were evaluated).

Occlusal Notes

The following occlusion issues were noted: dental angle classification of Class II Division ², along with a 90% deep bite; retroclined maxillary incisors for an overjet reduction compensation; hyper-eruption of the mandible incisors for dento-alveolar compensation; partial edentation of the posterior mandible segment with mesio-angulated molars, which resulted in an accentuated curve of Spee; and worn facets of the mandible incisors and canines but no posterior occlusal wear.

Radiographic Assessment

Bone levels were sound; no radiolucency was observed at any root apex. Panoramic radiography revealed normal contours for both mandible condyles, articular tubercle, and mandibular fossa. Maxillary and mandible morphology seemed to be within normal limits.

Diagnosis

Periodontal: Good. There was no bleeding on probing and no subgingival deposits, nor was there any bone loss or tooth mobility. Findings showed minor soft-tissue recession on posterior maxillary teeth. AAP Type I.

Biomechanical: Caries, defective restorations, questionable restorations, and structural compromises were observed on several teeth. Maxillary and mandible molars presented extensive defective restorations with secondary caries. Anterior maxillary incisors were compromised by extensive defective composite restorations.

Functional: Attrition was observed on all mandible incisors and canines incisally. A retroclined maxillary incisor reduced the overjet and constricted the anterior movement envelope. The maxillary incisors also exhibited wear facets on their lingual aspect. Generalized dental attrition was recorded on all mandible incisors and canines. Additionally, the patient complained of “having a hard time pressing my teeth together.” Fortunately, no premature excursion contacts were observed on the hyper-erupted maxillary molars. These findings led to a diagnosis of a constricted chewing pattern.

Dentofacial: The patient complained of unpleasant esthetic restorations and unappealing dental coloration. She also wished to replace her missing posterior molars with dental implants. Clinical findings revealed medium lip dynamics that were favorable, a normal scallop form, a thick biotype, and a non-harmonious gingival pre-maxillary contour. In the “E” position, incisal maxillary edges were 2 mm short of the occlusion line (Figure 1). Her mandible posterior teeth were short of the occlusion line in the repose position. A diastema was observed between teeth Nos. 32 and 33 (per the FDI tooth-numbering system) (Figure 2, Figure 3 and Figure 4). Finally, her right buccal corridor was much more apparent than the contralateral corridor.

Medical: Within normal limits.

Risk Assessment

Periodontal: Low risk. There was no evidence of or risk factors leading to bone loss.

Biomechanical: High risk. The patient presented with active caries. Structural compromises on the posterior teeth and anterior maxillary teeth were noted.

Functional: Moderate risk. Class II mechanics, severe overbite, mandible incisors attrition, accentuated curve of Spee, and constricted chewing pattern were observed.

Dentofacial: Moderate risk. The incisal edges needed to be leveled in the pre-maxilla, retroclined maxillary incisors; the vertical dimension of occlusion needed to be increased; and the diastema between teeth Nos. 32 and 33 needed correction. Gingival leveling in the esthetic zone needed improvement; fortunately, her lip dynamics did not expose the gingival contour. Cohesive restorations could be done to improve teeth color.

Prognosis

Periodontal: Good

Biomechanical: Poor

Functional: Poor

Dentofacial: Fair

Concerns

There were four main concerns to consider in this case:

1. The patient was a skeletal Class II. She expressively refused orthodontics with orthognathic surgery. Occlusion correction would be limited to dental improvement without having to revert the occlusion to a Class I. Would this be an acceptable compromise for the patient?
2. Biomechanical structural compromises would require cohesive restorations on all of the patient’s teeth. Would she be ready for these long-term restorations?
3. Would changing the vertical dimension of occlusion increase the patient’s comfort level?
4. As for changing the esthetics of the patient’s teeth and smile, would she accept the morphological change?

Treatment Goals

When formulating the treatment plan, the following goals were decided upon as being critical results to the case:

1. Reduce the biomechanical risk.
2. Increase the vertical dimension of occlusion.
3. Level the maxillary incisors by increasing the length of all four incisors.
4. Correct the crown length of the maxillary incisors.
5. Level the hyper-erupted first maxillary molars.
6. Level the gingival soft-tissue contour of the maxillary incisors.
7. Level the occlusion plane of the mandible molars.
8. Improve buccal corridor on the right side.
9. Whiten the teeth coloration.
10. Replace the missing teeth with dental implants.
11. Increase the length of the mandible incisors.
12. Reduce the incisors overbite.

Treatment Plan

This 56-year-old female patient expressed the need for a “more appealing smile and an improved chewing ability.” She also requested changing all amalgam restorations and replacing all missing teeth with dental implants. A diagnostic risk assessment was performed using the Kois protocol.¹

Phase I: Implant Treatment

Dental implants were inserted in position Nos. 36 and 46 (Figure 5). A one-stage approach was selected without requiring a bone graft.² Sufficient bone width was available because the patient had mandibular torus at the recipient bone site. Implant treatment was the first phase of the treatment sequence due to the long healing period required. During the healing period, all other treatment phases could be performed in order to synchronize both the teeth rehabilitation and the implant restoration. For implant No. 46, sufficient mesio–distal width allowed a platform-switching technique to maximize crestal bone stability.³ Unfortunately, contralateral side No. 36 mesio–distal width was restricted and only allowed for a regular prosthetic platform technique.

Phase II: Occlusal Vertical Dimension

In order to reduce the patient’s overbite, coronal elongations of her mandible incisor edges would require opening of the vertical dimension of occlusion. A Kois deprogrammer was prepared (Figure 6) and the protocol was applied to the patient. Vertical prosthetic requirements and comfort of the new acquired position of the patient’s mandible were all achieved. The deprogrammer enabled the patient to be positioned in centric relation (CR) by being bilaterally balanced in the TMJ.4 The patient was prescribed a CT scan and an evaluation of her TMJ with the deprogrammer in her mouth. A closed-jaw position during the CT scan was requested to allow an evaluation of her CR position to be confirmed by radiology.⁵ Evaluation by the radiologist described the condition as “TMJ non-pathological and within normal limits.”

The novelty of this treatment is the ability to visualize the contact point of the lower incisors on the deprogrammer using (with parametric software) a CT scan with an optical scan⁶ superimposition (Figure 7 and Figure 8). Once viewed, this will confirm whether the patient has reproduced the same clinical bite during the CT exposure versus when previously clinically observed. A precise evaluation of the TMJ in CR was measured off the orthogonal radiological frame.⁷ These measurements helped to confirm whether or not the condyles were well positioned in the mandibular fossa, bilaterally and vertically centered in the new CR as determined with the Kois deprogrammer. The vertical position of the condyle in relation to the mandibular fossa was symmetrical (Figure 9). This observation confirmed that the vertical position of the mandible was centered. As a result, this would increase the level of the patient’s comfort and also decrease the risk of building the patient’s occlusion on an unbalanced TMJ acquired position.

Cephalometric Analysis

A 3-D cephalometric analysis allowed the clinician to visualize and localize all anatomical landmarks of the patient’s skull (Simplant^®, Materialise Dental Inc, www.materialise.com). In 2-D cephalometric analysis, juxtaposition of all anatomical structures can introduce a component of guesswork into the anatomical structure landmark identification; canting of the patient’s head can distort these landmarks. Contrast of 2-D cephalometric can also be a challenging factor in anatomical identification. In a Class I relationship, ANB normal value is 3° + 2°; as for this clinical case ANB value was 6.47° (Figure 10 ). Clinically, this patient represented a skeletal Class II. Her gonial angle was within the normal range, which means she had a normal horizontal growing pattern. The patient was missing two teeth on her posterior right mandible and one tooth on the left posterior mandible. The difference in tooth mass created a more elevated posterior bite collapse on the right side compared to the left side. In 3-D cephalometric analysis, the left-side gonial angle was slightly different from the right side (135.94°), resulting in a more closed angle compared to the left side (137.14°). The difference between the two measures resulted in a non-harmonious bite collapse from right to left. Fortunately, right-to-left difference was clinically within the limits and did not need to be taken into consideration in the treatment plan.

Phase III: Prosthetics

According to the deprogrammer’s new CR position, and combined with dentofacial requirements, a prosthetic plan was prepared using a diagnostic wax set-up (Figure 11). A polyvinyl siloxane (PVS) was prepared from the diagnostic wax models and served the purpose of building temporary acrylic restorations, which were directly bonded on the patient’s teeth for esthetic and functional confirmation.⁸ In the esthetic zone, leveling of her gum line with gingivoplasty and clinical root lengthening was done using an 820-nm wavelength diode laser. Her acrylic temporary restorations were adjusted for occlusion equilibration in static and dynamic movements (Figure 12). One week later, assessment was done to confirm the patient’s comfort level, functionality, and esthetics. Permanent prosthetic restorations would start after two evaluations of the temporary restorations, the patient’s comfort level, and her esthetic satisfaction.

Two implants recently installed in position Nos. 36 and 47 (Biomet 3i Inc, ) would be restored only at the end of the treatment sequence (Figure 13 and Figure 14). Preparation for prosthetic restorations on the patient’s natural teeth was started during the healing period of the dental implants. A set of vacushells was prepared from the diagnostic wax cast, which served as a guide for teeth reduction. Records of Kois’ laser facial bow, CR registrations, and PVS final impressions were sent to the laboratory for core preparations of the zirconia restorations (NobelProcera^®, Nobel Biocare, www.nobelbiocare.com). Trial of the zirconia cores and radiographic evaluation of the seating of these cores were completed with one appointment and sent to the laboratory for final porcelain build-ups. Cementation of all the prosthetic components was synchronized at the end of the healing period of the implants (Figure 15). All teeth restorations were cemented with Panavia™ F (Kuraray Dental, www.kuraraydental.com). Occlusal equilibration and dynamic adjustments were executed on all restorations during the cementation appointment. An occlusal nightguard was provided at the end of treatment.

The patient was evaluated for function, phonetics, and dentofacial esthetics (Figure 16, Figure 17 and Figure 18), and the results exceeded her expectations (Figure 19).

Conclusion

This case report demonstrated that accuracy and precision in planning complex dental rehabilitation cases with significant modification of occlusion can be accomplished using an innovative scanning procedure that is an alternative to intuitively driven treatment planning. The use of an optical scan superimposed to a CT scan allowed the clinician to see the patient’s clinical bite on the Kois deprogrammer in a more precise manner than without using the optical scan. The key to this procedure is that when properly performed, one can measure with 3-D software the TMJ position in the alignment of the jaws. As a result, the treatment plan leads to a more predictable outcome, and in this particular case increased the patient’s comfort and provided successful esthetics and function restoration.

Optical scans are traditionally used for dental restorations; this new approach definitely has its merits and a promising future in dental rehabilitation application.

Acknowledgments

The author thanks John C. Kois, DMD, MSD, for his training, guidance, and support, and would also like to thank Therese Lanciault MSc, BSc, Director of the Quebec Dental Implant Institute, for her support and help with the manuscript; Anas Raffoul, Certified Technician, R&B Laboratories; and Tim Van Cleynenbreugel, Materialise Dental.

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