Clinical Case Study: Short Teeth, Gummy Smile and a Lack of Ferrule Effect.

By Dr Andrew See. Aesthetic Dentist and Educator, Founder of Dental Mastery Academy.

BDS Hons (Syd), FRACDS, MSc(Lond), PGDipDentImplantology, FCGDENT(UK), FICOI, MFDS RCSEng

In the world of aesthetic dentistry, achieving the perfect balance between form and function is an art. Short teeth, often accompanied by a gummy smile, present a unique set of challenges that demand a meticulous treatment strategy. This case study delves into the assessment, planning, and execution of crown lengthening surgery, offering a roadmap for practitioners seeking insights into managing similar cases.

Discover how a thoughtful treatment plan, tailored to the specific needs of the patient, not only addressed the cosmetic concerns associated with a gummy smile but also tackled the fundamental issue of insufficient tooth structure – a lack of ferrule effect. 

A patient-centered approach is paramount, ensuring transparent communication of all viable options. The case study presented herein evaluates the integration of gingival analysis into the treatment plan, showcasing how to address these often interrelated components. 

Read the full article below or download the article published in Australasian Dentist Magazine, March 2024 Edition.

Short Teeth

Recognising short anterior teeth is crucial in the practice of aesthetic dentistry. The average dimensions of an adult central incisor according to Magne 2003 has a width of 9.1mm and a length of 11.7mm. However, using general tooth dimensions does not take into account the differences in stature of the individual, the difference in size seen in male and female patients and the racial differences in dimensions.  What is more clinically useful is to use the crown width to length ratio. 

Analysis of this ratio shows that unworn central incisor teeth have an average ratio of 78%, in Caucasians and a ratio of 72% in Asians (Magne 2022). Where we can start to diagnose short teeth is when the length of the central incisor becomes similar to the width, resulting in a tooth that assumes a square-like appearance.

The literature is scarce in pinpointing the precise threshold, but Magne 2022 gives us a starting point. He defines worn teeth with a ratio of 87%, providing a basis for labelling a tooth as short.

See the image above which highlights the visual change where short teeth with a ratio over 100% was treated with crown lengthening surgery and restorative work, resulting in a more harmonious final ratio of 78%.

After establishing the diagnosis of a short central incisor, a crucial decision revolves around whether to enhance it’s length through incisal edge addition of surgical apical relocation of the gingival margin. This decision-making process is pivotal, as merely extending the length without a comprehensive understanding of underlying factors may yield aesthetically displeasing outcomes concerning the patient’s face and smile. Furthermore, it has the potential to negatively impact occlusion by modifying the jaw’s guidance pattern and restricting the envelope of function.

In addition, successful management of short teeth necessitates the identification of aetiological factors to prevent subsequent damage post-treatment. The common causes of short anterior teeth stem from attrition, erosion, a history of trauma and iatrogenic causes from adjustments made to the incisal edge.

Gummy Smile

A gummy smile can be considered as more than 2.0mm of gingival display during a high smile (Peck 1992). While this criterion may be subjective across various cultures, Kokich 1999 observed that an upper gingival display of  ≥ 4.0mm during a high smile line was considered as unattractive by clinicians and laypeople. A comprehensive understanding of the diagnosis of a gummy smile is required given that treatment options are aetiologically specific and incorrect treatment could result in undesirable and irreversible outcomes.

Case Study

A 33-year-old woman presented wanting an improvement of her existing crowns on her central incisors. Her main concerns were the short appearance of her central incisors, her gummy smile and the gingival margin discolouration. However, her main motivation for treatment was her crowns had become loose.

Medical and Dental History

Her medical history was unremarkable. The existing endodontic treatment and crowns were placed when she was 10-years-old after trauma. She felt that one of the crowns was mobile and would like a second opinion. She had been previously recommended extraction of the central incisors and placement of dental implants as there was limited tooth structure present. She was strongly against having orthodontics and implant treatment.

Clinical findings

The patient had an unremarkable extra-oral examination except minor asymptomatic clicking in her TMJ. During a normal smile and a high smile, she had 4.0mm and 6.0mm of gingival display respectively. At repose she had a central incisal display of 3mm. 21 had a periapical area had a slight swelling that was slightly tender to palpation. General periodontal condition was sound. She had bleeding on probing and gingival discolouration around 11 and 21. Neither 11 and 21 were tender to percussion. Both 11 and 21 crowns were mobile. The crowns were easily removed and 11 had an absence of ferrule and 21 preparation was extremely tapered.

Radiographic findings

11 and 21 was previously endodontically treated and had been restored with a post, core and crown. 21 had a periapical radiolucency present.

Clinical summary

From the findings it was concluded that she had a gummy smile. 21 had apical periodontitis and loss of retention of 11 and 21 post, core and crown restorations. The findings highlighted multiple issues such as compromised endodontic treatment, absence of ferrule effect and persistent inflammation likely due to invasion of biologic width and misfitting crowns. The width/length ratio of 11 and 21 was 94% and 98% respectively indicating short teeth.

Treatment Options

Simplifying the treatment plan for this case involved breaking it down into smaller objectives aligned with the patient’s expectations. Following a collaborative discussion, it was evident that the patient’s primary goal was to defer implant treatment and maintain her central incisors as long as possible. The ultimate objective was to achieve resolution to the aesthetic concerns linked with a gummy smile and ensure the stability of the final restorations.

A case could be made for extraction and implant therapy to replace the central incisors, particularly due to the insufficient coronal tooth structure for a sufficeint ferrule effect. The evidence strongly suggests that without adequate ferrule effect that a poor clinical outcome is very likely (Juloski et al 2012). 

Nevertheless, taking into account the patient’s age, the high smile line and high patient expectations, she opted to attempt to keep the central incisors acknowledging the risks, limitations and the potential for eventual failure.

Considering this, the treatment sequence becomes more apparent. This involves addressing the risk factors that may negatively impact on the desired outcome then aiming to improve function and aesthetics. The initial step in the treatment process involved assessing the potential resolution of the endodontic lesion associated with tooth 21. To address this, a referral was made to an Endodontist for potential retreatment of both 21 and 11.

Simultaneously, a crucial concern emerged regarding insufficient tooth structure, specifically the absence of a ferrule effect. As per Juloski et al.'s recommendations in 2012, the absence of coronal tooth structure suggests considering orthodontic extrusion as the primary option. However, given the patient's reluctance to undergo orthodontics, an alternative approach was pursued – functional crown lengthening surgery.

Functional crown lengthening not only facilitated the enhancement of the gummy smile but also addressed concerns related to the width/length ratio of the central incisors and encroachment on biologic width.

Upon conducting an aesthetic examination and analysing the ideal width/length ratio, it was determined that the optimal gingival margin should be positioned 2mm apical to the current location, considering the constraint that the width of teeth 11 and 21 cannot be altered. Botox treatment was also discussed to improve her overall gummy smile but was declined.

Treatment Sequence

Functional Crown Lengthening

Prior to the completion of retreatment by the endodontist, functional crown lengthening was necessary to provide additional coronal tooth structure for isolation. This involved ostectomy and osteoplasty. Bone was removed 3.0mm from the future crown margin position respecting biologic width. The healing process progressed uneventfully, and sutures were removed after a two-week period.

Endodontic Retreatment

After subsequent healing, the endodontist retreated both central incisors. A CBCT was taken after 6 months to confirm radiographic evidence that the periapical lesion had resolved. See the CBCT below at 6 month post endodontic retreatment showing the resolution of the periapical radiolucency on 21.

Restorative Phase 

Restorative treatment involved placement of a fibre post to enhance the retention of the core material. Special attention was given to avoid unnecessary enlargement of the existing canal, aiming to preserve as much tooth structure as possible to protect the teeth from fracture. The post space was cleaned and free of gutta percha. The post prep space was completed leaving 4.0mm of gutta percha in place. The post size selection was based on the largest post that would achieve passive fit in the canal and modified accordingly. A 1.9mm RelyX Fibre post (3M) was cemented with RelyX Universal cement (3M) in a self-adhesive mode.

The restorative phase began after there was radiographic evidence of resolution of the periapical radiolucent lesion. A fibre post was used to retain the core. Care taken to bond under rubber dam isolation and prepare the post space leaving the maximum amount of tooth structure.

A composite core was placed using Scotchbond Universal Plus (3M) and Filtek One Bulk Fill (3M) and the final crown preparations were carried out with a goal of achieving 1.5mm of circumferential ferrule.

The polyether (3M Impregum) impression was taken using a double cord technique and the preparations were provisionalised with 3M Protemp 4 and Tempbond Clear (Kerr).

Bonding

The provisionals were removed and the definitive crowns were issued under rubber dam isolation. The preparations were microetched with 50μm Aluminium Oxide and the crowns were adhesively bonded with Scotchbond Universal Plus (3M) and RelyX Universal cement (3M). The occlusion was adjusted and finalised.

Conclusion

The final outcome enhanced the harmony in the patient’s smile by improving the proportions of the central incisors. The integration of checklists and decision-making workflows, coupled with a patient-centered approach, plays a pivotal role in informed consent and meeting patient expectations. The article invites a holistic perspective in addressing short teeth and gummy smiles, offering a roadmap to navigate such scenarios.

For the full list of references, contact Australiasian Dentist on: [email protected]

Endodontist: Dr David Barnard.

Dental technician: Riccardo Borgonovo, Smile Art Lab.

"I’m forever grateful to Dr see and his team for the care, dedication, patience, integrity and professionalism they put into a complex and long dental procedure/treatment to replace 2 front teeth crowns. The results are more beautiful than I could have ever expected and life changing."

- V Sammut, Sydney Australia