Infundibular Caries

Take Home Message—Infundibular cemental hypoplasia and caries are frequently diagnosed conditions in maxillary cheek teeth that predispose to sagittal dental fracture and endodontic infection. Endodontic-type intrainfundibular restoration techniques might be applied to stop dental decay and prevent these detrimental consequences. Additional studies are needed to further evaluate this technique.

I. Anatomy and physiology

The equine incisors and maxillary cheek teeth contain enamel invaginations called infundibula (infundibulum/-a: Latin, funnel). While all incisor teeth exhibit a single infundibulum, the maxillary cheek teeth feature a mesial and a distal infundibulum.¹ While incisor infundibula are comparatively short enamel infoldings, cheek teeth infundibula extend almost through the entire length of the reserve crown.¹

The infundibula contain a filling of cementum surrounded by the enamel wall of the infundibulum. Each maxillary cheek tooth infundibulum displays one or more small orifices in the center of the occlusal infundibular cementum. These canals extend through the infundibular cementum to the apical end of each infundibulum and represent the former location of blood vessels during dental development.^1,2 The differentiation of mesenchymal cells into cementoblasts and subsequent cementum formation depends on adequate blood supply which is provided by these blood vessels derived from the dental sac. The presence of apical blood supply to the infundibular cementum was detected histologically in the erupted cheek teeth of younger horses.³

Infundibular cementum formation during dental development starts at the coronal end of the tooth and proceeds in an apical direction. When the cheek teeth crowns erupt into the oral cavity, the blood vessels leading into the central infundibular canal are disrupted 2 and cementum formation ceases due to lack of blood supply.²

II. Pathological conditions of maxillary cheek teeth infundibula

Infundibular Cemental Hypoplasia

When cementum formation within the infundibula has not been completed at the time of dental eruption, some areas remain without cemental filling. This condition is termed cemental hypoplasia.^1,2 In a recently published study cemental hypoplasia was defined as “areas of developmental absence of infundibular cementum with the underlying infundibular enamel exposed” and found in 22.6 % of infundibula.³ In accordance with a study conducted at the reporting clinic, this condition was found mostly in apical infundibular areas and only occasionally at the occlusal surface.^3,4 In the study conducted by Aigner, 75% of teeth with low grade infundibular changes (cemental hypoplasia) at the occlusal surface displayed a significantly higher percentage of severe changes in the apical infundibular areas. Unchanged or grossly normal infundibula were only found in 11.7 % and 9.9 %of the examined infundibula respectively, suggesting that cemental hypoplasia is a normal finding in the horse.⁴

Premature removal of deciduous teeth (“caps”) may cause disruption of the central blood vessels of the underlying permanent tooth with resultant termination of cementum formation within the infundibula.⁵

Infundibular Caries, Infundibular Necrosis, Cemental Decay

These three terms are utilized synonymously in equine dental literature to address pathological conditions of the infundibulum. Cemental hypoplasiais diagnosed frequently and might even be considered a variation of normal.^2,6,7 However, these defects allow impaction of food material which undergoes bacterial colonization and fermentation. The acidic microenvironment within the infundibular cavity results in further demineralization of infundibular cementum, with extension of the cavity.^5,8 Thus cemental infundibular hypoplasia might predispose affected cheek teeth to infundibular caries.³ Eventually the infundibular enamel wall might be affected and dental decay might expand into the dentine. As a consequence coalescing of the two infundibula might occur, further weakening the center of the tooth and predisposing to sagittal dental fracture. The progression of infundibular caries into the surrounding dentine can also extend into the pulp canal, resulting in endodontic disease and apical abscessation.^5,9,10 Alternatively normal attrition can outpace the decay process. In this case no further dental pathologies will occur.

III. Diagnosis of infundibular pathology

During oral examination each maxillary cheek tooth should be examined for infundibular changes. This can be performed under direct visualization, with a dental mirror or an oral endoscope.¹¹ Care must be taken to differentiate between enlarged central infundibular canals and the dark brown stained columns of secondary dentine indicating pulp positions.⁵ Detection of patent pulp canals in conjunction with infundibular changes might indicate the progression of infundibular caries into the dentine and endodontic system of a tooth. Although infundibular carious lesions can be detected using radiography, computed tomography currently is the imaging technique of choice for precise diagnosis of the extent of infundibular pathology.^12-14

It might be difficult or impossible for the practitioner to correctly differentiate between cemental hypoplasia and infundibular caries based on visual findings at the occlusal surface, especially when the visible lesions are confined to the infundibular cementum. In a recently published studythis diagnostic predicament was avoided by addressing such lesions as infundibular hypoplasia/caries.¹⁰ However, advanced stages of infundibular caries can be diagnosed during oral examination without doubt when large cemental defects and discolorations of the infundibular enamel or adjacent dentine are observed.

The first grading system of infundibular caries based on clinical findings at the occlusal surface was published by Honma.¹⁵ The last modification was proposed by Pearce.¹⁰

Grading system for infundibular caries (Pearce)¹⁰

Grade 1: Caries of infundibular cementum only
Grade 2: Caries of infundibular cementum and enamel Grade 3: Caries of infundibular cementum, enamel and dentine
Grade 4: Grade 3 rostral and caudal infundibulum, coalescing lesion
Grade 5: Advanced caries resulting in apical abscessation, fracture or tooth loss

IV. Treatment of infundibular caries

Although critically discussed, prophylactic filling of infundibula might prevent longitudinal fracture of affected teeth.⁵ This therapy resembles an endodontic-type treatment of infundibular caries.^5,10,16 Thorough understanding of infundibular anatomy and adequate equipment are the essential prerequisites for performing infundibular restorations.³

Debridement and Sterilization of the Infundibular Cavity 

In a first step the majority of impacted food and other debris is removed from the infundibulum using dental picks.^5,10 Air abrasion and high-speed drills might help to speed up this time-consuming initial part of infundibular restoration. Repeated endoscopic control is recommended to evaluate the progress of work.¹⁰ 

A dental unit with air abrasion (150-200 psi) using sodium bicarbonate or aluminium oxide powder (25 μm) may be used for debridement of carious tissue inside the infundibula5,10 Alternatively a variety of surgical and dental burrs mounted on slow or high speed handpieces of the dental unit can be employed. Long endodontic files (70 mm) and sonic scalers might also be helpful during the later stages of debridement for removing decayed material from narrow infundibular enamel infoldings.^5,10 Following debridement and cleaning of the infundibulum, disinfectants like 4% sodium hypochlorite solution may be used.¹⁰ Finally repeated flushes with saline solutions are performed to remove the disinfectant.

Ample time is required for this first stage of infundibular preparation.⁵ Frequent use of an oral mirror or an endoscope might help to ensure thorough debridement of all aspects of the infundibulum and help to prevent inadvertent removal of the infundibular enamel wall or penetration into adjacent dentine or pulp canals.^5,10

Filling of the Infundibular Cavity

The next step involves acid etching and application of an unfilled composite resin bonding agent. Numerous products are available for accomplishing this initial step in composite restoration of the cavity.

When etching and bonding have been completed, restoration can commence. Dual cure, flowable composites, compactible self-cure composites, and light cure flowable composites may be used for infundibular restorations.¹⁰ It is advisable to apply light-cured composites in multiple layers to minimize shrinkage and the resulting marginal leakage. Glass ionomer restoratives can be used in lieu of composites for infundibular restoration. These products will bond directly to exposed dentin or enamel without the need for acid etching or bonding agents.

In a recently held presentation Pearce demonstrated that endodontic-type infundibular restoration techniques might be effective in stopping dental decay and preventing affected teeth from dental fracture and endodontic infection.¹⁰ However, additional studies including matched untreated controls are needed to further evaluate this technique.

References

1. Dixon PM, DuToit N. Equine dental pathology. In: Easley J, Dixon PM, Schumacher J, eds. Equine dentistry, 3^rd ed. Edinburgh: Saunders Elsevier 2011;129-147. [...]