Mind the gap
space opening part 1

How much space is needed for an implant Vs bridge?

There are two aspects to space for a prosthetic tooth:

1. 1. Prosthodontic space: requirements for stability of the prosthesis
   2. Aesthetic space: determined by the size of adjacent dentition assessed through the golden proportion rule of 1.618:1 (Kalia, 2020).

Space requirements for the type of prosthesis should be considered

• Resin bonded bridge space requirements:
  • Minimum – no limit
  • Maximum – mesial distal width of abutment tooth
• Dental implant space requirements:
  • Minimum: 6.3mm between crowns (prosthodontic space / at gingival level), 5.5mm between roots (Olsen and Kokich Sr, 2010)
  • Maximum – no limit

Most clinical scenarios will permit both prosthetic options, however the differing minimum and maximum spaces should be considered where the planned space will be minimal or excessive.

How do I measure the space?

Seemingly simple yet a cause of colourful conversations between orthodontist and prosthodontist, space measurements relate to different aspects of the prosthesis:

Space measurement – at a crown level

• Aesthetic measurement – contact point to contact point
• Implant prosthodontic measurement – narrowest space at the gingival level.

Prosthodontic replacement with dental implants are usually positioned slightly palatal to the alveolar ridge, this does not corelate with the space measured between contact points either labio-lingually or incisal-gingivally.

Space measurement – at a root level

• Dental implants require a minimum of 5.5mm. This minimum size has been determined by the smallest dental implant diameter of 2.9mm, a minimum of 1.0mm space required between implant and tooth in order to allow stable osteointegration, and the final factor of 11% root relapse following orthodontics increases the total minimum size to 5.5mm.
• Periapicals and CBCT images can be used to assess inter-radicular spaces. Panoramic radiographs have been shown to have a distortion of 2mm resulting in unreliable space assessment and should not be used for the assessment of space (Al-Tamimi et al., 2016). CBCTs were shown to have the lowest level of distortion, clinically insignificant 0.57 mm.

What specific mechanics should be used when planning for a dental implant?

Root parallelism is a key determinate for optimal implant placement, the following can aid achieving this goal

• Bracket variation: Distal root tip of mesial tooth can be achieved by swapping the mesial bracket with the contralateral bracket, i.e. an upper right central incisor bracket exchanged with the upper left central incisor bracket = –4o tip
• Gable bend: a second order bend to upright the root tooth.

Bone considerations?

For implant placement the minimum bone height is 8mm or greater, measured from the crestal bone to the apical anatomical structure (6mm dental implants have been described but have reduced stability (Papaspyridakos et al., 2018)), with minimum 5.5mm length and 5.0mm width of bone (for 2.9mm implant diameter) (Liedke et al., 2017, Olsen and Kokich Sr, 2010). Bony deficiencies occur in hypodontia areas due to a lack of tooth eruption from the alveolus as well as the lack of mechanical stimulation to maintain bony architecture, resulting in a narrowing of the alveolar ridge, and / or a concavity in the alveolar process in the apical region, also known as an ‘hour glass ridge’(Durey et al., 2014).  Typically a bony deficiency of 25% occurs in areas of hypodontia following the loss of the primary tooth (Ostler and Kokich, 1994). It can be possible reduce the bony defect by allowing the canine to erupt into the lateral incisor space (usually through interceptive extraction of the primary canine and primary lateral incisor) followed by retraction of the permanent canine back into class 1. Through this process of canine eruption into the lateral incisor position the bony architecture is increased in height and width and maintained for implant placement (Scher, 1990).  Bony architecture can also be maintained through TAD supported prosthetic teeth, described later on.

At what age should the implant be placed?

Minimum 18 years, RCS England Guidelines 2019 (Cocchetto et al., 2019), with males later than females. This presents a challenge with the majority of orthodontic treatments being completed at the age of 14. The effects of early implant placement are of increasing infraocclusion of the implant (Thilander et al., 1999) as the remaining dento-alveolar structures continue to erupt throughout life Behrents 1985. Another common complication is root convergence which occurs while waiting for growth cessation, and another short course of orthodontics may be required (as pictured below). Some have advocated waiting until patients are 25 / 30 years of age as the rate of vertical dento-alveolar growth reduced from 1.02% per year to 0.27% per year  to avoid aesthetic consequences of infraocclusion (Schwartz‐Arad and Bichacho, 2015).

What temporary prosthesis can be used in treatment?

Prosthetic teeth can be added in a variety of ways:

1. Acrylic prosthetic tooth – bracket bonded with superglue or undercut and composite
2. Acrylic prosthetic tooth as above with a labial /lingual flange. The advantage this design gives is of a stable prosthetic tooth in lighter archwires, however it can be more challenging to maintain good hygiene
3. Composite bridge – Chairside prosthetic tooth made from composite and added to the palatal aspect of an adjacent tooth. The advantages of this design is that the prosthetic tooth is held securely, however there is a risk of debond and fracture
4. Mini-screw retained prosthesis – A relatively recent idea described by Roberto Ciarlantini in 2017 (Ciarlantini and Melsen, 2017), in which a horizontally inserted TAD has an acrylic tooth placed on it. This approach allows the medium term fixed prosthesis to be maintained until implant placement, and has shown minimal changes in bone volume after 5 years (Ciarlantini and Melsen, 2017).

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What is the best type of restoration?

Resin bonded bridges Vs dental implants

A much debated topic and without clear outcome, the debate lies in defining what outcome is defined as ‘best’, below are the key considerations which will vary depending on patients preferences.

• Longevity: bridge 82% Vs 94%  Implant (10 year survival) (Thoma et al., 2017) (Moraschini et al., 2015) = IMPLANT
• Patient satisfaction: overall no statistical difference p >0.05 (Lim and Ariff, 2020) = DRAW
• Aesthetics: NO CLEAR ANSWER (Abt et al., 2012) = DRAW
• Cost: Initial costs bridge more cost effective, no long term evaluation = BRIDGE

Outcome = draw

We hope you have enjoyed this first part in the new series of blogs, it came about through a conversation between us (Farooq Ahmed and James Andrews) about James’ instagram posts, which we have whisked into a blog, please do subscribe to James Andrew’s Instagram page, please do comment and subscribe for more blogs and podcasts

References

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CIARLANTINI, R. & MELSEN, B. 2017. Semipermanent replacement of missing maxillary lateral incisors by mini-implant retained pontics: A follow-up study. American Journal of Orthodontics and Dentofacial Orthopedics, 151, 989-994.

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