Floating-harbour syndrome (FHS) was given its name from an amalgamation of the two hospitals where it was seen: Boston Floating Hospital and Harbor General Hospital.¹ FHS is a rare genetic syndrome that can affect many aspects of physical health, especially dental and oral health, but if affected, it can be ameliorated with specialist dental care or oral surgery. 

FHS is caused by a mutation on an autosome² (not a sex chromosome) and only one pathogenic copy needs to be inherited (from either parent) to cause FHS. The mutation occurs in the SCRAP gene which would normally create a protein to coactivate the CREBBP protein, needed for cell division³. However, in FHS, the gene mutation may stop the proteins from working together. This may cause physical deformities, from abnormal growth, which could affect multiple parts of the body. 

Complications listed below:

• Triangular face
• Reduced intellectual capability
• Sunken eyes
• Bone aging delay
• Overall delayed growth and calcification
• Broader mouth
• Thin lips
• Unusually long eye-lashes
• Speech, language and facial expression deficit
• Short stature
• Microcephaly
• Overhanging nasal columella 
• Low birth weight
• Bulbous nose
• Short philtrum

Dental and oral manifestations of FHS

Common dental problems

• Dental crowding and malocclusion

Malocclusion is the misalignment between the upper and lower teeth,⁴ which is very common in FHS. This is usually caused by typical facial abnormalities such as a smaller maxilla (upper jaw) that doesn't align well with the mandible (lower jaw), leading to the teeth having too little space.⁵ Malocclusion can affect chewing, speech and facial structure.⁴

• Retention of plaque and calculus with increased caries risk

Retention means that plaque and calculus (hardened plaque) can build up on supragingival (above the gum margin) and subgingival (below the gum margin, towards the teeth),⁶ which can lead to periodontal disease.⁷ Caries refer to any level of tooth decay, caused by bacteria (surviving off food build-up) which demineralise the tooth by producing acid.⁸ People with FHS are more at risk as they may find it harder to maintain good dental hygiene due to difficulty with mouth-opening, lack of understanding regarding dental hygiene and proclined⁶ teeth making it difficult to clean crevices.

• Delayed eruption of teeth

Delayed eruption of teeth means it takes longer for the adult teeth to replace baby teeth when compared to the average ages.⁹ People with FHS may be more likely to have delayed eruption, as many of their developmental growth processes are affected overall. Unerupted teeth can be problematic if intervention takes too long, leading to odontogenic cysts¹⁰ (cysts forming over the unerupted tooth), infection and sometimes ankylosis (fusing of the tooth to the bone).¹¹

 Oral cavity features

• High-arched palate

A high-arched palate means that the roof of the mouth is higher and more narrow than it should be, which can put someone at risk for malocclusion.¹² Moreover, it can lead to breathing difficulties, such as mouth breathing being favoured over nasal breathing, resulting in a nasal tone).¹ Additionally, it can cause speech problems and sleep apnoea and all the aforementioned problems may have psychological or mental health effects. 

• Potential for cleft lip or palate

A cleft lip is a congenital (from birth) deformity that can be seen in people with FHS, whereby there is an incomplete or complete separation between the lip and nasal sill.¹³ It is a genetic defect and is more common in those with a shortened philtrum (as seen in FHS patients).¹³ During the sixth and seventh weeks of pregnancy, the paired maxillary processes fuse with medial nasal processes¹⁴ in an unaffected embryo. However, it has been postulated that the mutated SCRAP gene could impede CREBBP’s role in embryogenesis, thus increasing the potential for a cleft lip or palate.¹⁵

• Ankyloglossia

Ankyloglossia is when the tongue is tied down by a lingual frenulum (a piece of tissue connecting the two), stopping it from moving (also known as a tongue-tie).¹⁶ This is a rare associated symptom with FHS,¹⁷ but is common with tooth agenesis which a proportion of FHS patients do have.¹ Ankyloglossia can increase the chance of malocclusion, speech and gum recession, which could worsen symptoms of FHS.¹⁶

Challenges in dental care for FHS patients

Overcoming behavioural and cooperation issues

• Enhancing communication:
  • To effectively communicate with patients who have Floating Harbor Syndrome (FHS), dental practitioners should consider utilizing visual aids such as videos and images.⁶ These tools can help bridge the communication gap by providing clear, visual explanations of oral hygiene techniques. For example, videos that demonstrate proper brushing methods and the effects of sugary foods on teeth can make it easier for patients to understand these concepts.⁶ It is crucial that FHS patients with malocclusion or overcrowding prevent the build-up of plaque and calculus

• Assessing and supporting capacity to consent:
  • Limited intellectual capacity in FHS patients¹ can affect their ability to consent to a well-informed decision. To address this, dental practitioners, upon every visit should perform a capacity assessment¹⁷ using simplified language and visual aids. This way if the level of treatment required is complex, it will be possible to intervene sooner with a care plan that the patient will actually be able to tolerate. It has been noted that some patients are unable to consider multiple options at once and evaluate the risks or benefits.⁶ Therefore, it may come down to the parent or carer making a decision on behalf of a child with FHS

• Adapting Anesthetic Techniques:
  • Anaesthetic techniques should be carefully tailored to the needs of FHS patients, who may have difficulty tolerating certain methods. Alternatives to the injection of local anaesthetic into the gingival margin may be possible. Firstly, nitrous oxide (NO) could be administered, which requires a mask with a nasal hood
  • However, it has been noted that the characteristic nose shape in FHS, may not fit well enough to allow NO inhalation.⁶ Secondly, the wand device could be used, whereby the local anaesthetic is applied topically around the gingival margin, which is a pain-free alternative.¹⁸ Moreover, the needle is hidden by a sheath which is helpful for patients who have needle phobia. Lastly, General anaesthetic may be considered whereby the patient is put to sleep. This is only if the aforementioned alternatives are not tolerated as GA for dental procedures is usually a last resort²⁰

Preventive dental care

• Importance of continuous dental visits:
  • It is important that children with FHS receive a diagnosis early on in their lives, as this allows for specialist dental care that can preempt what kind of dental challenges might be faced. This would allow for the expectation of supernumerary teeth (extra teeth), malocclusion (jaw and teeth misalignment), and caries (tooth decay).¹ Children with FHS, tend to be at higher risk for the aforementioned dental problems, as well as craniofacial problems which can affect the teeth too
  • In a few cases, it has been said that earlier diagnosis could have produced a more favourable outcome regarding the dental care plan, but as it is a rare syndrome, which has symptoms that overlap with other syndromes, early diagnosis may be difficult.²¹ Additionally, continuous visits allow for capacity reassessments regarding intellect but also tolerance of the dental environment and equipment which will affect what treatment can be done

Oral hygiene practices

• High fluoride toothpaste and fissure sealants 
  • For individuals with FHS, consistent oral hygiene practices are essential.⁶ However, if dental hygiene is problematic already, then a high fluoride toothpaste²² can be prescribed which will help to preserve the enamel of the teeth, prevent caries and reduce the possibility of a more invasive treatment such as a root canal
  • Secondly, fissure sealants²³ are a resin that can be applied to the central grooves of teeth (mesial aspect) which will then harden. It prevents food from getting stuck in the groove, which an FHS patient may struggle to brush away, which could lead to caries and a cavity.²⁴ Fissure sealants are often applied to children's teeth, as they may struggle to adjust to cleaning new adult teeth
• Recommendations for a tooth-friendly diet
  • A balanced diet containing micronutrients such as vitamin A, vitamin B1, vitamin B12, calcium, folate, zinc and iron are important for upkeep of strong teeth.²⁵ However, a diet high in sugar will negate this, therefore it is imperative that sugar attacks (any instance where the teeth touch sugar) are restricted to just main meal times.²⁶ This will help to reduce the food source that bacteria can metabolize to produce acid which can break down enamel, enabling decay⁸

 Specialized dental treatments

• Corrective Jaw Surgery
  • Corrective jaw surgery, also known as orthognathic surgery,²⁷ is often used to address significant jaw misalignments (skeletal malocclusion), causing such as overbite or overjet in patients with Floating Harbor Syndrome (FHS).¹⁵ This procedure involves fixing the maxilla or mandible (or both) to reposition their jaws to achieve proper alignment.²⁷ The repositioning is maintained by plates, (held in by screws) which the new bone will grow over. However, if an FHS patient has limited understanding then the recovery period for jaw surgery may be too uncomfortable due to it being quite invasive with the need for general anesthetic⁶

• Supernumerary Teeth Removal by Extraction:
  • It has been noted in some FHS patients that they have supernumerary teeth, alongside tooth agenesis. However, supernumerary teeth may need to be removed if they cause overcrowding or prevent unerupted teeth from having space and aligning properly.⁶ In FHS patients, it is usually important that this is addressed early, perhaps with a common extraction procedure, using one of the local anaesthetic alternatives mentioned earlier
• Braces for Overcrowding, Overbite and Overjet
  • Orthodontic braces are commonly used to correct dental overcrowding in FHS patients.¹⁰ Due to the smaller jaw size often associated with FHS, teeth may become crowded or misaligned. Braces gradually move the teeth into their correct positions, improving the overall alignment of the teeth. This treatment not only enhances the appearance of the teeth but also makes it easier for the patient to maintain proper oral hygiene, thus reducing the risk of cavities and gum disease.²⁸ However, prior to having braces dental hygiene must be excellent, as plaque and calculus accumulate more easily with braces²⁹

Collaboration with healthcare providers

• Role of Pediatricians, Geneticists, and ENT Specialists:
  • Effective dental care for patients with Floating Harbor Syndrome (FHS) often requires collaboration with a multidisciplinary team of healthcare providers.⁶ Paediatricians play a key role in monitoring the overall growth and development of the child, identifying early signs of dental issues, and referring patients to dental specialists.⁶ Geneticists are essential for confirming the diagnosis of FHS and providing insights into potential oral and craniofacial anomalies associated with the syndrome

 Summary of key points

• Floating Harbor Syndrome (FHS) is a rare genetic disorder that can have effects on dental and oral health, leading to issues like malocclusion, delayed tooth eruption, and a high-arched palate. Specialized care, including early diagnosis, preventive treatment, and sometimes corrective jaw surgery and orthodontics, is essential
• Collaboration with paediatricians, geneticists, and ENT specialists ensures comprehensive care tailored to the unique needs of FHS patients, enabling early intervention too for better patient outcomes