November 1, 2014
by Ming-Yi Chou BSc, DDS, MS, Cert. Prostho, FRCD(C)
There are many genetic conditions that may affect an individual and result in discoloured or malformed teeth. Gene changes that affect dentin and enamel formation are being defined scientifically and we now know more about these inherited disorders. Amelogenesis Imperfecta (AI) is one group of disorders that affects the formation of enamel covering the teeth.
Amelogenesis Imperfecta (AI) is a group of conditions that results in an inherited defect of enamel formation. AI affects the structure and clinical appearance of enamel, the enamel may be brown stained and porous. Individuals with AI may also be associated with morphologic of biochemical changes elsewhere in the body. The prevalence of AI varies from 1:700 to 1:14,000 depending on population studies. AI is genomic in origin. The disorder may be autosomal dominant, autosomal recessive, X-linked or sporadic in inheritance patterns.1
The etiology of AI involves the genetic mutation of any of the following proteins, all of which are crucial in enamel formation and maturation: enamelin, amelogenin, ameloblastin, tuftelin, amelotin, dentine sailophosphoprotein, enzymes such as kallikrein 4 and matrix metalloproteinase 20.
There are four major types of Amelogenesis Imperfecta: 1. Hypoplastic; 2. Hypomaturation; 3. Hypomineralizeation (Hypocalcification); 4. Any of the above with the addition of taurodontism.1,2 The enamel deficiencies can be quantitative (hypoplastic) or qualitative (hypomaturation/hypomineralized).
Hypoplastic AI defects appear as pits on the surface of enamel. The teeth can become severely worn, without mesial and distal contact points. Enamel has snow-like appearance and is very thin. Although patients with hypoplastic subtype of AI do not show increased risk of caries development in affected teeth, the absence of normal enamel morphology invariably results in diminished occlusal function and severely compromised aesthetics.
Hypomaturation AI display enamel that is opaque in appearance. Enamel layer is normal in thickness, but softer than normal enamel and can be easily detached from the underlying dentin.
Hypocalcification AI results in detachment of enamel from the underlying dentin soon after eruption, resulting in severely worn dentition. Teeth appear to be dark brown in colour and are extremely sensitive to thermal changes.
Patients with AI are often esthetically affected by tooth discolouration and often with accompanying tooth sensitivity. They may have been under the care of a pediatric dental specialist for many years and may later have concerns about their permanent teeth. The functional and aesthetic restoration of such compromised dentition is a major challenge and involves a multistep process of treatment by a Prosthodontist.
This is an example of Amelogenesis Imperfecta. The patient was a healthy 31-year-old female Caucasian. Her chief complaints were that her teeth were small, discoloured and sensitive. Patient was diagnosed with Amelogenesis Imperfecta five years ago. She was married with three children, one of which, her eight-year-old son, was also affected by the same condition. No other family members were reported to have AI. The patient expressed extreme dissatisfaction with her appearance, and had been socially affected by this problem.
Extraoral examination revealed no abnormality except for bilateral clicking of the temporomandibular joints. However, the patient reported no discomfort associated with the joints. Aesthetic evaluation revealed excessive gingival display when the patient smiled (Fig. 1). The enamel outer layer of the teeth was weak, porous and discoloured. The teeth appeared yellow due to the thin, irregular enamel overlying the dentin and were pitted and irregular in shape. In addition, there was wear of the weak enamel and a major change in the patient’s bite had occurred over time.
A close up of the teeth showed the deformed enamel (Fig. 2). The patient’s dentition displayed characteristics of hypoplastic AI, in which case, the lack of normal enamel morphology resulted in functional and aesthetic problems. Occlusal analysis revealed an overjet of ~3mm and 100 percent overbite. The maxillary dental midline was coincident with the facial midline; however, the mandibular dental midline was 1mm to the right of the maxillary dental midline. There were several composite resin restorations present. In general, the gingival tissue was healthy and the patient had taken the best possible care of the deformed teeth.
Due to the presence of abnormally thin enamel, the patient’s teeth had become severely worn, with very tight and broad mesial and distal contact points. Intraoral exam showed the presence of all maxillary and mandibular teeth, except for #38. There was complete wear of the enamel on the biting surfaces of the teeth. There was no enamel remaining on the incisal edges of the mandibular anterior teeth. It was uncomfortable for the patient to chew and the patient was dissatisfied with the unpleasant appearance. All of the teeth required restoration at this time (Fig. 3).
The patient’s panoramic x-ray (Fig. 4a) showed that all of the patient’s teeth were present and covered with very thin enamel. The roots of the teeth were able to support good function and replacement of enamel with full coverage restorations. Radiographic evaluation revealed that #38 was present, but unerupted. Tooth #41 had received root canal treatment. The layer of enamel was remarkably thin on all the teeth as seen in the FMS as opposed to the Panorex. The radiograph of quadrant one (Fig. 4b) revealed little to no enamel but the dentin and cementum appeared to be normal, both in structure and size. The roots and pulps of all teeth appeared to be normal in shape and size.
The patient’s diagnosis consisted of: Amelogenesis Imperfecta (hypoplastic); generalized severe attrition, carious and fractured #25 and soft tissue impaction of #38. Her problem list consisted of: aesthetic issues (gummy smile, small teeth), size of teeth (small in all dimensions); uneven occlusal plane and slight midline discrepancy.
The key to restorative success in the aesthetic zone depends largely on the interaction of dental and gingival beauty criteria. The golden standard values concerning the optimal length of maxillary central incisors is about 10-12mm, (as described by Chiche et al.3 and supported by anatomical averages from the population as described by Wolfart et al.4 and Magne et al.5,6) and the width-to-length ratio of the upper central incisors of approximately 75~85 percent.4 Gingival symmetry is also a key to esthetic success.
The goal in this patient’s case was to improve the appearance of the smile by correcting tooth length problems as they related to the upper lip line and to achieve left-to-right symmetry in the final result (Fig. 5).
The treatment options offered to the patient were: 1. Continued maintenance of existing dentition and management of sensitivity; 2. Extraction of selected teeth and fabrication of partial overdentures; or, 3. Full mouth rehabilitation with fixed dental prostheses/full coverage restorations. The patient chose to go ahead with the full mouth rehabilitation. Due to the complexity of her case and requirement for soft tissue management, a Periodontist was consulted and became involved in her treatment.
The final treatment plan included extraction of all erupted wisdom teeth (#18, 28 and 38) as well as #25, which was grossly decayed, fractured and unrestorable and crown lengthening of both maxillary and mandibular arches. This was followed by prosthodontic treatment involving placement of full coverage restorations on all existing teeth, including a fixed dental prosthesis for #24-x-26.
Prior to beginning any prosthodontic treatment, careful planning is indicated. For this patient, preliminary alginate impressions were made and diagnostic casts poured and mounted on a semi-adjustable articulator. Bone heights and resultant gingival heights were carefully planned to optimize clinical crown length for the definitive restoration without compromising osseous support that would result in an unfavourable crown-root ratio.
When planning to replace even a few teeth, a diagnostic wax-up must be performed. In this patient’s case, a plan for every tooth was considered and was represented by the diagnostic waxing. Just as an architect plans the appearance of a house that is constructed according to the plans; prosthodontists plan the appearance of the smile using many tools including this diagnostic wax-up. The patient was able to envision the result prior to beginning any irreversible procedures (Fig. 6). Diagnostic wax-up was completed as part of the preoperative planning, showing a desired maxillary central incisor length of approximately 10mm and width of 8mm. The desired overbite of ~40 percent was also achieved in the diagnostic wax-up. The waxup provided for even occlusal contacts of all teeth in maximum intercuspation and anterior disclusion of posterior teeth during excursive movements.
The surgical stents, showing the desired gingival contours marked with blue marker, were fabricated using a 2.5mm thick thermo-forming material (Fig. 7). The surgical guides, fabricated by the prosthodontist, were then used to aid the periodontist in performing the crown lengthening procedures. The stents were used as a guide for the final soft tissue position for the periodontist.
For this patient, full arch crown lengthening surgeries were planned in conjunction with preparation and provisionalization of all the teeth in the respective arch. This was necessary as the patient’s teeth were all positioned very close to each other. Mesio-distal and proximal reduction of the teeth allowed for proper osseous reduction and recontouring of the bone in the interproximal areas. Sutures were placed and the provisional restorations, fabricated the day of surgery, were cemented before the patient was dismissed.
Figure 8 shows the temporary crowns at six months following gingival surgery and provisionalization of both the maxillary and mandibular arches. The patient’s healing was uneventful. Compared to the pre-operative photo, the teeth are longer and more visible. The gingivae appeared pink and healthy around the provisional crowns and were similar on both the left and right side of the midline. Chlorhexidine mouthrinse was used throughout this important healing phase of the treatment. Unfortunately, the discolouration of the provisional crowns is not uncommon with the use of chlorhexidine. The patient was continuously evaluated for comfort and adaption to the new occlusal scheme of anterior disclusion during excursive movements, as well as the new vertical dimension of occlusion as established on the diagnostic wax-up.
For the final prostheses, full gold crowns were fabricated for #17, 27, 37 and 47 in order to sustain the occlusal load. Gold has many well-known features (strength, malleability) for function and since these last teeth were not visible without special effort, it was the restorative material of choice for the second molars. As well, a conventional porcelain-fused-to-metal (PFM) three-unit fixed partial denture was fabricated for #24-x-26. However, since 21 of the 28 crowns fabricated were all-ceramic crowns and these included posterior restorations, the all-ceramic system used was chosen with aesthetics, fracture resistance and strength as selection factors.
After an evaluation of current available studies and reports on the various all-ceramic systems (lithium disilicate, full-contour zirconia, zirconia core layered with veneering porcelain), lithium disilicate (IPS e.max) was chosen as the material of choice for the restorations for this patient. Lithium disilicate has been shown to be a reliable restorative material for single crowns in both the anterior and posterior region.7,8 The fatigue behaviour and reliability of monolithic lithium disilicate crowns have been shown to be superior to that of veneered zirconia crowns.8,9 As well, the superior aesthetics and more reliable tooth bonding potentia
l of lithium disilicate material compared to zirconia made it the restorative material of choice for this patient.
All the restorations were delivered in one single clinical session. The full gold and PFM restorations were cemented in place with GC FujiCEM™, a resin modified glass ionomer cement. The lithium disilicate crowns were bonded in place using RelyX™ Unicem 2 by 3M, a resin cement.
As one can appreciate from the picture taken at about one month after cementation (Figs. 9 and 10), the final result showed a marked improvement in aesthetics and function. The gingival tissue around the restoration margins had responded favourably to the all-ceramic margins and displayed characteristics of healthy gingiva. The close-up picture of the maxillary anterior teeth showcases the natural appearance of modern ceramic crowns. The relationship of the crowns with the roots and the adjacent gingival tissue was appropriately managed and contributed to the healthy pink natural appearance of the gingiva and a healthy smile.
The resting smile revealed the improvement in the esthetics provided by this comprehensive dental rehabilitation (Fig. 11). Without changing the bite and without changing the position of the gingival margin, this would not have been possible. The complexity of this treatment was envisioned and properly managed for the patient. The restoration of aesthetics and function had been achieved with an interdisciplinary team approach.
For this patient, meticulous attention to the details required for achievement of esthetics as determined by the maxillary anterior teeth, from diagnosis to fabrication of final restorations, allowed a controlled and logical treatment sequence. While many other prosthodontic management approaches have been reported, this case demonstrated one approach to comprehensive rehabilitation of a patient with Amelogenesis Imperfecta with successful results. OH
Dr. Ming-Yi Chou, BSc, DDS, MS, Cert. Prostho., FRCD(C) completed her DDS at the University of Western Ontario and the graduate program in Prosthodontics at the University of North Carolina at Chapel Hill. She returned to her home town of Toronto where she received her Board certification in Prosthodontics. In addition to her private practice in east Toronto, Dr. Chou is a Clinical Instructor in the Graduate Prosthodontic Clinic at the University of Toronto and an Adjunct Professor in the Graduate Prosthodontic Department at the University of North Carolina at Chapel Hill.
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