OHDE Articles

Oral Health and Dentistry
ISSN: 2573-4989

Case Report Volume 8 Issue 1
Modification of Unusual Crown Preparations - A Case Report
Omar El-Mowafy, BSD, PhD, FADM*
    Professor Emeritus, Faculty of Dentistry, University of Toronto, 124 Edward Street, Toronto, Ontario Mt5G 1G6
*Corresponding Author: Omar El-Mowafy, Professor Emeritus, Faculty of Dentistry, University of Toronto, 124 Edward Street, Toronto, Ontario Mt5G 1G6.
Received: August 04, 2026;   Published: August 11, 2026.
Abstract
Introduction: This case report is about two unsatisfactory porcelain-bonded-to-metal crowns placed on maxillary central incisors in a young female. The crowns had poor esthetics and caused gingival inflammation and edema due mainly to poor marginal fit. Upon removal of the crowns, it was revealed that the central incisors had preparations that did not meet the standard of care. They were short and lacked ideal taper. With careful reduction, the crown preparation were modified to create fundamental elements such as proper wall convergence, adequate length and well-defined finish lines. Glass-ceramic replacement crowns were made from a reliable lithium-disilicate glass-ceramic material. These were cemented in place using a dual-cure resin cement. The new crowns resulted in enhanced esthetics and resolved the gingival inflammation and edema issues.
Keywords: Anterior crowns; preparation design; lithium-disilicate glass-ceramic crowns; gingival response to crown margins and material
Introduction
Permanent maxillary incisors require crown coverage under a variety of conditions. These include extensive caries that resulted in significant loss of coronal tooth structure, accidental trauma resulting in fracture of a significant portion of the crown, developmental anomalies requiring esthetic intervention and discoloration caused by either severe fluorosis or the consumption of tetracycline antibiotics at a young age when the teeth were under development. The later two scenarios may be correctable through whitening, however, if it proved to be ineffective then crowns or veneers are always a viable option [1].
In the past the typical choice of a crown prescribed by the dentist for a maxillary incisor was the porcelain-bonded-to-metal (PBM) one. In such situations a coping is cast in a gold alloy and subsequently veneered with feldspathic porcelain by an experienced ceramist. However, other alternative metal-free crowns were made available over the past two decades. This resulted in a decline in the utilization of PBM crowns with zirconia-based and glass-ceramic crowns becoming the alternative choice. This shift can largely be attributed to the development of highly accurate computer-aided design and computer-aided manufacturing (CAD-CAM) technology, which enabled the fabrication of crowns from prefabricated zirconia or glass-ceramic blanks [2]. In addition, the introduction of zirconia and glass-ceramic materials with excellent mechanical properties and improved esthetics has further accelerated the transition away from conventional PBM crowns [3-5]. Several clinical studies have reported favorable outcomes for none-metallic crowns, even when provided by predoctoral dental students [6-11].
Although metal alloys used in fabrication of PBM crowns are generally biocompatible, irregular crown margins and some none-noble alloys may contribute to gingival inflammation, and some base-metal alloys have been associated with gingival discoloration [12, 13]. Moreover, the presence of a metal substructure blocks light transmission, resulting in reduced translucency and compromised esthetics.
When fabricated in the monolithic format, CAD-CAM crowns eliminate the interface between the coping and veneering porcelain, thereby virtually eliminating the risk of veneer chipping or delamination. Monolithic crowns also exhibit uniform translucency, while their final esthetic characterization is achieved through surface staining and glazing. Furthermore, some CAD-CAM systems permit chairside fabrication, thereby eliminating the need for provisional restorations thus rendering the process of providing a crown more efficient.
Methods
A 29-year-old female with a non-contributory medical history presented complaining of poor esthetic appearance of recently placed crowns on her maxillary central incisors. The crowns had been made by a dentist abroad and did not meet her esthetic expectations. Because she was unable to return to the treating dentist located abroad, she sought replacement treatment where she resides.
Clinical examination revealed two porcelain-bonded-to-metal (PBM) crowns on her maxillary central incisors that were esthetically unacceptable (Figure. 1). The underlying metal copings were visible through the thin veneering porcelain, producing a grayish appearance and reduced esthetics. The surrounding gingival tissues were inflamed, exhibiting gingivitis and edema consistent with a response to defective crown margins and plaque accumulation [12, 13] In addition, the crowns appeared disproportionately wide compared with the adjacent lateral incisors. The patient requested replacement of the crowns with more esthetic ones and also expressed interest in whitening her teeth.
Figure 1: Maxillary central incisors of a 29-year-old female presenting with suboptimal full metal–ceramic (PBM) crowns. The underlying metal copings are visible through the thin veneering porcelain, compromising esthetics. The surrounding gingival tissues exhibit signs of gingivitis and edema, likely associated with adverse tissue response to the crowns. Additionally, the dimensions of the central incisors appear disproportionate when compared with the adjacent laterals
Diagnostic casts were fabricated from alginate impressions (Jeltrate Plus, Dentsply/Sirona, USA). Periapical radiographs of the maxillary central incisors were made and revealed no abnormalities. A treatment plan was developed that included removal of the existing PBM crowns and replacement with well-fitted provisional crowns to allow healing of the inflamed gingival tissues to take place. To improve the mesiodistal proportions of the anterior teeth, composite resin was planned to be added to the mesial aspects of both lateral incisors. At-home bleaching with custom trays and whitening gel was also recommended and was planned to be performed before commencement of treatment. However, the patient elected to postpone tooth whitening until a later date and consented to proceed with the remaining treatment.
Following administration of local anesthesia, both crowns were removed simultaneously with relative ease using a manual crown remover. After removal, it was noted that the two incisors preparations exhibited an unusual rough semilunar configuration (Figure. 2). The preparations lacked essential retention features, including near-parallelism of the axial walls and adequate occlusogingival height. In addition, the lingual finish lines were irregular and required re-establishment. The removed crowns were found to be splinted together at the midline and had ragged margins (Figure. 4). The axial walls of the two crown preparations were judiciously modified using medium grit tapered diamond burs (Brasseler, USA) at high-speed with copious water cooling. As a result, the preparations were altered at the proximal aspects to establish proper length and angulation for optimum retention. The lingual surfaces of the teeth were refined with a medium-grit football diamond bur (Brasseler, USA) (Figure 5).
Figure 2: Appearance of the prepared maxillary central incisors after crown removal. The preparation design is suboptimal, with inadequate near-parallelism of the axial walls, compromising mechanical retention. The preparations are also short in height. The gingival inflammation affecting both central incisors appears to be directly related to the crown margins
Figure 3: The lingual aspects of the crown preparations on the maxillary centrals showing irregular finish line
Figure 4: Intaglio surfaces of the crowns following removal. The margins appear irregular and uneven. The two crowns were splinted together
Figure 5: Using a tapered diamond bur in a high-speed handpiece, the axial walls were redsigned and the finish line was redefined and repositioned slightly subgingivally. The axial walls were modified to achieve near-parallelism, thereby optimizing mechanical retention
Provisional crowns with improved marginal adaptation were fabricated chairside using a dual-polymerized material (Integrity, Dentsply/Sirona, USA). They were subsequently cemented with a eugenol -free clear temporary cement (Temp-Bond NE Clear, Kerr. USA). They remained in place for two weeks to permit initial healing of the gingival tissues.
At the subsequent appointment, the preparations were refined using a fine grit tapered diamond bur with flat end in a high-speed handpiece with copious water cooling. The finish lines were further defined with the flat bur tip. Furthermore, the preparations were smoothened with fine grit Soflex discs (3M/ESPE, USA) in preparation for impression taking.
In order to reduce the mesio-distal dimensions of the new crowns, composite resin was bonded to the mesial aspects of the lateral incisors. Following roughening of the mesial surfaces of the lateral incisors with a course grit diamond bur (Brasseler, USA) an acid etchant (Etch-rite, 38% phosphoric acid gel, Pulpdent, USA) was applied to condition the enamel surfaces for 30 seconds. After rinsing, a coat of bonding resin (Scotchbond Multipurpose, 3M/ESPE, USA) was then applied and light-polymerized. A layer of resin composite (Z250, 3M/ESPE, USA) was adapted free-hand to the mesial surfaces of the maxillary laterals following the anatomical features to increase their mesiodistal width. This was finished and polished with Soflex discs (3M/ESPE, USA). (Figure. 6).
Figure 6: The crown preparations were refined. In addition, the mesial aspects of the maxillary lateral incisors were augmented with resin composite to increase their apparent width and improve proportional harmony. Healing of the gingival tissues can be observed in this image, which was taken two weeks after removal of the original defective crowns and placement of properly fitted provisional crowns
A polyvinyl siloxane (PVS) impression material, putty and light-body (Express STD, 3M/ESPE, USA) was used in a stock tray according to standard clinical procedures to obtain an impression of the crown preparations. Jaw relation registration was performed using a PVS material (Blu-Mousse VPS, bite registration material, Parkell, USA).
Two monolithic fully-crystalized lithium disilicate glass-ceramic crowns (IPS e.Max, Ivoclar/Vivadent, USA) were subsequently fabricated at a commercial dental laboratory.
Figure 7: At a commercial dental laboratory, two lithium disilicate glass ceramic crowns were made. They were monolithic and milled out of IPS e.Max blocks (Ivoclar-Vivadent)
At the insertion appointment, the temporary crowns were removed and the tooth surfaces were cleaned first with a slurry of pumice in a rubber cup, then with Ivoclean (Ivoclar/Vivadent, USA). The crowns were then evaluated intraorally or fit and color (Figure. 8). Although the shade appeared slightly lighter than the adjacent teeth, this discrepancy was expected to diminish once the patient completed the planned tooth-whitening treatment. The crowns were then definitively cemented using a dual-polymerized resin cement (Panavia SA Cement Universal, Kuraray Noritake , Japan), a reliable resin cement (17) (Figure. 9).
Figure 8: The two fabricated crowns at try in stage. While they appear lighter in color than the rest of the teeth, the patient had planned to whiten her teeth at a later time
Figure 9: Two weeks after insertion, the gingival tissues at the crown margins appear to be healing well. Compared with the pretreatment image, a significant esthetic improvement can be observed
Results
As can be seen in Figures 5 through 9, the less than ideal crown preparations were transformed through carful reduction into proper configuration with adequate height and acceptable angle of convergence necessary for good mechanical retention of the crowns. The laboratory fabricated glass ceramic crowns provided superior esthetics and good marginal fit. Through elimination of the metal alloy of the previous PBM crowns and the superior marginal fit, the gingival inflammation and edema issuers were resolved.
Discussion
This case highlights several important clinical and technical considerations related to crown preparation, laboratory fabrication, and material selection. The original PBM crowns were esthetically unsatisfactory and were associated with gingival inflammation. The inflammatory response was most likely related to poorly adapted and rough crown margins that promoted plaque accumulation, although the contribution of the nonprecious alloy used cannot be completely excluded [12, 13]. Furthermore, less than optimal oral hygiene condition of the patient adversely contributed to the gingival inflammation. Following removal of the defective crowns and placement of well-adapted provisional restorations, the gingival tissues showed rapid clinical improvement.
The use of a clear temporary cement with the provisional crowns aided in optimizing their esthetics during the healing period as a traditional white cement would have contributed to increased opacity.
Removal of the original crowns revealed unusual tooth preparations that lacked adequate retention form (Figure. 2). Furthermore, the finish lines were poorly defined, particularly on the lingual surfaces (Figure 3). These findings indicate deficiencies in preparation design that compromised the mechanical retention of the crowns which were easily removed together without any drilling with a manual crown remover. Successful crown preparations require two essential features: near-parallel axial walls and adequate occlusogingival height [1, 18, 19]. Both features were deficient in the original preparations. Careful modification of the preparations without compromising the pulp established appropriate axial wall geometry and clearly defined finish lines, thereby improving retention and stability.
The original crowns had been splinted together, possibly to compensate for the inadequate retention of the preparations. In addition, the visibility of the metal copings through the veneering porcelain suggests inadequate porcelain thickness or insufficient support of the veneering ceramic during laboratory fabrication.
Monolithic lithium disilicate glass-ceramic crowns (IPS e.Max, Ivoclar/ Vivadent, USA ) were selected to replace the defective PBM crowns because they provide superior esthetics through their translucency and the absence of a metal substructure [17]. These were made at a commercial dental laboratory as the author did not have access to chairside scanning and milling. Resin cement was selected for definitive cementation to maximize bond strength, improve marginal sealing, and enhance the long-term performance of the restorations (18,19).
When the patient proceeds with the planned tooth-whitening treatment, the composite resin placed on the mesial surfaces of the maxillary lateral incisors is expected to maintain acceptable color harmony with the surrounding tooth structure [20].
Conclusion
  • Gingival inflammation associated with poorly-made crowns can resolve following replacement of the crowns with well-fitted ones.
  • Careful modification of inadequately prepared teeth can establish acceptable retention form for successful definitive crowns.
  • Monolithic lithium disilicate glass-ceramic crowns provide excellent esthetic outcomes for anterior restorations.
References
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Citation: Omar El-Mowafy. “Modification of Unusual Crown Preparations - A Case Report”. Oral Health and Dentistry 8.1 (2026): 22-28.
Copyright: © 2026 Dr. Omar El-Mowafy. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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