The original and well-tested principles of implant placement in healed extraction sites (“delayed implant placement”) continue to be used, and certainly molar replacement with single implants using this approach has shown predictably successful long-term results, particularly in mandible and when natural teeth are present on either side of the implant.¹,²,³,⁴,⁵ More recently, however, the trend has been to place molar implants immediately after tooth extraction as this reduces treatment time and morbidity with increased patient acceptance.

The procedures needed for successful immediate molar implant (IMI) placement are definitely technique-sensitive and difficult to perform, especially by practitioners who attempt them infrequently.⁶ A detailed working knowledge of mandibular anatomy is crucial to avoid failures and serious complications such as inferior alveolar nerve injury or lingual bone plate perforation at sites with unrecognized mandibular undercuts. From a restorative perspective, the inter-radicular septum of bone (IRS) represents the ideal position for immediate mandibular molar implant placement,⁷,⁸ and its volume and height should be assessed preoperatively using cone-beam computed tomographic radiographic scan.⁹ These records will allow the practitioner to determine the suitability of the IRS, the locations of the inferior alveolar and mental nerves, the buccolingual alveolar ridge width at the site, the width and length of IRS to canal, the presence of apical pathology, and the vertical bone height available recognizing that a buffer zone of 2 mm from the planned implant apex to the mandibular canal must be maintained to avoid nerve damage.¹⁰,¹¹

Originally when IMIs were proposed, clinicians took the precautions of submerged initial healing and delayed loading. However, with time and experience the preferred approach became to allow nonsubmerged healing followed by delayed loading. More recently, however, it has been recognized that some early loading of a nonocclusal nature can be beneficial for IMIs and achieved by adding a stock or customized healing abutment immediately after implant placement. This limited loading was found to actually stimulate faster osseointegration.¹²,¹³ In general, however, true occlusal loading is still delayed for 3 or more months postimplantation. We were intrigued to know whether mandibular IMIs could be fully loaded earlier than this and report here our findings with early loading of mandibular premolar and molar immediate implants placed using one-step, trans-mucosal healing.

For conducting this retrospective case series study, protocols were prepared and performed according to the 1975 Declaration of Helsinki as renewed in 2013.

Patient selection

The data presented were collected from 18 patients (8 females and 10 males) with a mean age of 53.5 years who had received 27 (18 mandibular molars and 9 mandibular premolars) immediate implants. Criteria for selecting patients were as follows: (1) good general health; (2) recommendation of mandibular premolar and/or molar extractions due to root fracture, nontreatable caries, endodontic treatment failure or residual root retention; (3) for molar sites, a minimum of 5 mm width of IRS, as determined by means of periapical and cone beam computed tomographic (CBCT) radiographs; (4) and a minimum distance of 5 mm from the apices of the condemned tooth to mandibular canal to guarantee adequate primary stability of implants without violating the mandibular neurovascular canal. Criteria for excluding patients were history of (1) head and neck irradiation; (2) myocardial infarction in the previous year; (3) uncontrolled diabetes; (4) periodontitis, and (5) a smoking habit.

Surgical procedure

All surgeries were performed by a single surgeon (NA). On the day of surgery, a prophylactic antibiotic (amoxicillin, 1 g) was prescribed for all patients an hour before surgery. Adequate local anesthesia (4% Articaine, 1:100,000 epinephrine) to achieve an inferior alveolar nerve block was administered. Before molar extraction, teeth were decoronated and sectioned to allow mesial and distal roots to be removed atraumatically. After verifying adequate an (IRS) width (≥5 mm mesio-distally) at each molar site, osteotomies were initiated using either a small diameter round bur or a fine, sharp-pointed initial penetration bur positioned at the mesio-distal center of the IRS but slightly towards the lingual in order to compensate for any uncontrollable buccal drifting of subsequent burs.¹⁴ Implants placed were either Xive^®, (DENTSPLY International) or Axiom^® (Antogyr, France). All implants were placed 1–2 mm apical to the buccal and lingual bone crest. Afterwards, remaining mesial and distal socket gaps were grafted (Tutodent^® or Cerabon^®, Tutogen Medical Gmbh) and covered with acellular dermal matrix allograft membranes (SureDerm^®, Hans Biomed Co. Ltd). Implants were placed according to the one-stage approach with healing abutments of appropriate size used to secure the membranes. Flaps were secured utilizing 4-0 Vicryl. Sutures, and patients prescribed amoxicillin 500 mg to be taken three times daily (for 7 days), analgesics for use as required (ibuprofen, 200 mg; caffeine, 40 mg; and acetaminophen, 325 mg, Alhavi Pharmaceutical Co.) and 0.12% chlorhexidine mouth rinse for twice daily use.

All patients were evaluated 2 weeks after surgery and asked to continue using the chlorhexidine mouthwash and to avoid brushing over the implant area for another 3 weeks. After a healing period of 6–8 weeks, osseointegration was verified radiographically and with the Periotest^® Device as recommended by the manufacturer (Siemens AG). Periotest values (PTV) were recorded twice and mean values recorded. Implants were loaded if PTV was negative at 6–8 weeks.

Radiographic and clinical evaluation

The standard criteria of Albrektsson et al.¹⁵ were used to evaluate the success, i.e., absence of mobility, pain, radiolucency, and ≤1 mm at 1 year and ≤0.2 mm/year bone loss thereafter. Peri-implant probing depths at mesial, distal, buccal, and lingual surfaces were measured using a William's periodontal probe. An implant was considered as having failed if it displayed mobility or excessive marginal bone loss as seen in periapical radiographs obtained using a My Ray Digital Imaging X-ray sensor^™ and an X-Pod Wireless Digital System (Cefla SC Dental Group, Italy). The distances between the first bone-implant contact, which is the most coronal point of bone to implant contact and implant shoulder on the mesial and distal aspects of all implants were measured. The linear measurements were calibrated to the actual implant lengths using the X-Pod system. A molar sample case is shown in Figure 1a,Figure 1b,Figure 1c,Figure 1d,Figure 1e,Figure 1f,Figure 1g,Figure 1h,Figure 1i.Figure 1

(a) This first molar presented with buccal swelling indicative of furcal infection, (b) The preoperative radiograph showed a partial endodontic treatment with significant inter-radicular bone loss, (c) Following minimally invasive extraction a 4.5/10 mm Axiom implant immediately placed in the inter-radicular septum and gaps grafted with particulate allograft, (d) An acellular dermal collagen membrane was skewered with the threaded portion of an appropriately-sized healing abutment before connecting the latter to the implant, (e) The soft tissues were stabilized with vicryl sutures, (f) Excellent soft-tissue healing with minimal alveolar ridge remodeling was observed at 6 weeks at which time restoration was begun, (g) The implant was restored with its definite restoration 6 weeks postoperative, (h) This periapical radiograph shows the radiographic status of the restored implant after 6 months loading showing excellent bone preservation, (i) This periapical radiograph shows the radiographic status of the restored implant after 5 years loading showing excellent bone preservation.

Healing was uneventful for all patients except for one who had a buccal wound dehiscence in the 1 week. For that patient, topical chlorhexidine gel application was prescribed twice daily and the patient followed weekly until complete soft tissue healing occurred. Twenty-one implants were restored with single crowns, whereas nine implants placed in four patients were splinted.

The mean age of the patient was 53.5 years. The mean loading onset was 7.5 weeks after surgery. No implant has been lost to date yielding a cumulative survival rate of 100% 5 years postsurgical. Mean bone levels for each implant were calculated by summing up the bone gain and bone loss at the mesial and distal surfaces of each implant which gave an overall mean of-0.25 ± 0.54 mm. Individual mean bone levels for mesial and distal surfaces were − 0.24 ± 0.77 mm and − 0.26 ± 0.72 mm, respectively (P = 0.78) Table 1. A statistically significant difference in bone loss between genders was detected with less bone loss in females. Overall mean probing depth was 2.09 ± 0.57 mm Table 2.{Table 1}{Table 2}

Systematic literature reviews of outcomes following immediate mandibular molar implant (IMI) placement have suggested this treatment modality to be viable and predictable.¹⁶,¹⁷,¹⁸,¹⁹ Nevertheless, the approach is a challenging one requiring considerable skill and experience.⁶ When IMIs were first attempted, investigators cautiously loaded them only after a healing interval of 4 or more months,²⁰ but recently, more aggressive approaches have been attempted. The most recent has been to load IMIs immediately following placement seeing this as a way to dramatically reduce overall treatment times. However, this can come with significant risks of early implant failure.²¹

Implants placed in healed extraction sites have been tested for performance with early loading, i.e., after 4–8 weeks site healing. For example, Nicolau et al.²² recently reported 10-year results of a multicenter randomized controlled trial of implants placed in healed posterior jaw sites comparing immediate with early loading. Implant survival at 10 years was 98.2% and 97.1% for immediate and early loading. Mean crestal bone losses up to 10 years showed no significant difference (−1.25 ± 0.99 mm vs. −0.89 ± 1.11 mm for immediate/early loading. However, between implant placement and 10 years, there was a significant difference (−2.00 ± 1.19 mm vs. −1.37 ± 1.06 mm; P = 0.02) suggesting that early loading performed better. However, the immediately loaded implants had been placed significantly deeper than the those given early loading and when this was considered in the analyses, no significant difference between the two groups could be seen after 10 years. Most recently, Levine et al.²³ reported that moderately rough implants placed in healed sites with initial torque values of ≥35 Ncm could be loaded even as early as 3–4 weeks.

We have recently published 5-year results for immediate maxillary molar implants placed with simultaneous trans-crestal sinus floor elevation followed by early loading.²⁴ Mean crestal bone loss after 5 years in function was −0.054 ± 0.56 mm (range −0.86–+0.90 mm). Survival rates and success rates¹⁵ were 100% and 95.5%, respectively. Similar outcomes were seen in the present report using the same protocol of early loading with immediate implants placed into mandibular molar and premolar extraction sockets. Occlusal loading at 6–8 weeks resulted in 5-year survival and success rates both at 100%. The unusually small amounts of bone loss seen (‒0.24 ± 0.77 mm and ‒0.26 ± 0.72 mm for mesial/distal surfaces respectively) may be explained by several factors. First, all implants were placed using flap-less surgery, eliminating interruption of periosteal blood supply.²⁵ Second, ideal implant positioning was achieved with placement slightly toward the lingual, thereby ensuring remaining buccal gaps to minimize buccal bone loss.

Deporter et al.²⁶ recently presented a classification of gaps based on location about the implant periphery. Seven gap types were proposed and Type I (buccal gap) was considered favorable which, the implant has been placed slightly palatally leaving a horizontal buccal gap between the implant and its socket wall.

All implants were submerged sub-crestal compensating for the effects of early remodeling²⁷ and incorporated a platform switching feature helping to minimize later crestal loss.²⁸ Implants in the present study also were exposed to immediate nonocclusal loading through their exposed healing abutments. Regarding this last factor, in a recent literature review and meta-analysis,²⁹ investigators concluded that immediate nonocclusal loading led to less bone loss at 1 year compared to immediate occlusal loading or conventional delayed loading. This outcome might seem counter-intuitive except that some level of controlled implant loading during healing can be beneficial by stimulating bone formation.³⁰,³¹

Provided that flap-less surgery and atraumatic extraction has been accomplished, immediate implants placed at mandibular premolar and molar sites appear to be ready for early loading after shorter healing intervals than previously thought.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or non-financial in this article.